IGCSE
Computer Science
Index
Data Representation
Binary Systems
A binary digit is refered to as a BIT, 8 bits is a byte. Byte is used to measure memory size.
| Name of memory size | No. of Bits | Equivalent Denary Value |
|---|---|---|
| 1 kilobyte (1KB) | \(2^{10}\) | 1 024 bytes |
| 2 megabyte (1MB) | \(2^{20}\) | 1 048 576 bytes |
| 1 gigabyte (1GB) | \(2^{30}\) | 1 073 741 824 bytes |
| 1 terabyte (1TB) | \(2^{40}\) | 1 099 511 627 776 bytes |
| 1 petabyte (1PB) | \(2^{50}\) | 1 125 899 906 842 624 bytes |
A register is a group of bits, often depicted as:
- \(10010111\)
Example use of binary
Robotics
Digital instruments
Counting systems
Hexadecimal
Closely related to the binary system. Hexadecimal is a base 16 system. Numbers 0 to 9 and letters A to Fare used to represent each hexadecimal digit.
\(A =10, B = 11, C = 12, D = 13, E = 14, F = 15\)
| Hexadecimal Value | Denary Value |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| 4 | 4 |
| 5 | 5 |
| 6 | 6 |
| 7 | 7 |
| 8 | 8 |
| 9 | 9 |
| A | 10 |
| B | 11 |
| C | 12 |
| D | 13 |
| E | 14 |
| F | 15 |
Converting Binary to Hexadecimal
Q. Convert binary number 01100001 to hexadecimal
1. Separate into two nibbles (4 bits)
- \(0110\)
- \(0001\)
2. Convert nibbles to denary
| 8 | 4 | 2 | 1 |
|---|---|---|---|
| 0 | 1 | 1 | 0 |
6
| 8 | 4 | 2 | 1 |
|---|---|---|---|
| 0 | 0 | 0 | 1 |
1
\(= 61\)
4. Change denary numbers to hex if needed (e.g. 10 = A)
\(= 61\)
Converting Hexadecimal to Binary
Q. Convert hex value 6C to binary.
- Change hex value to denary numbers (e.g. 12 = C)
| 6 | C |
|---|---|
| 6 | 12 |
- Separate hex value and convert to 4 bit binary value
\(6 = 4 + 2\)
| 8 | 4 | 2 | 1 |
|---|---|---|---|
| 0 | 1 | 1 | 0 |
\(12 = 8 + 4\)
| 8 | 4 | 2 | 1 |
|---|---|---|---|
| 1 | 1 | 0 | 0 |
- Put the two nibbles together to form an 8 bit binary
\(0 1 1 0 1 1 0 0\)
Converting Hexadecimal to Denary
Q. To convert hex value \(2B\) to denary.
- Split the hex value into two
| 2 | b |
|---|---|
| 2 | 11 |
- Convert each number to binary
\(2 = 2\)
| 8 | 4 | 2 | 1 |
|---|---|---|---|
| 0 | 0 | 1 | 0 |
\(11 = 8 + 2 + 1\)
| 8 | 4 | 2 | 1 |
|---|---|---|---|
| 1 | 0 | 1 | 1 |
- Put the two binary numbers together
\(0 0 1 0 1 0 1 1\)
- Convert to denary
| 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
|---|---|---|---|---|---|---|---|
| 0 | 0 | 1 | 0 | 1 | 0 | 1 | 1 |
\(32 + 8 + 2 + 1 = 43\)
Use of the Hexadecimal System
Examples:
- Defining colours in Hypertext Markup Language (HTML).
- Media Access Control (MAC) addresses.
- Assembly languages and machine code.
- Debugging.
Memory Dumps:
- Hexadecimal is used when developing new software or when trying to trace errors.
- Memory dump is when the memory contents are output to a printer, monitor.
Assembly code and machine code (low level languages):
- Computer memory is machine code/ assembly code.
- Using hexadecimal makes it easier, faster, less error prone to write code compared to binary.
- Using machine code (binary) takes a long time to key in values and prone to errors.
Error Checking
Parity Checking:
Parity checking is used to check weather data has been changed or corrupted following transmission from one device to another.
A byte is an allocated parity bit:
- Systems that use even parity have an even number of 1-bits
- Systems that use odd parity have an even number of 1-bits
Automatic Repeat Request (ARQ):
- ARQ is another method to check if data has been transmitted correctly.
- It uses acknowledgement (message sent by the receiver indicating that data has been received correctly).
Checksum:
- Checksum is another way to see if data has been transmitted correctly.
- Data is sent in blocks and an additional value sent at the end of the block.
Echo check:
- When data is sent to another device, this data is sent back again to the sender.
- The sender compares the two sets to check if any errors occurred.
- Not reliable.
File types
Musical Instrument Digital Format (MIDI)
Used for storage of music files. It is a communications protocol that allows electronic musical instruments to interact with each other. It is stored as a series of demands but no actual music notes. It uses 8-bit serial transmission (asynchronous).
Each MIDI command has a sequence of bytes:
- First byte is the status byte – informs the MIDI device what function to preform
- Encoded in the status byte is the MIDI channel (operates on 16 different channels)
Examples of MIDI commands:
- Note on/off: indicates that a key has been pressed
- Key pressure: indicates how hard it has been pressed (loudness of music)
Its primary disadvantage is that it needs a lot of memory storage.
MP3
It uses technology known as Audio Compression to convert music and other sounds into an MP3 file format.
This compression reduces the normal file size by 90%:
- This is done using file compression algorithms which use Perceptual Music Shaping.
- It removes sounds that human ear cannot hear properly.
- Certain sounds are removed without affecting the quality too much.
CD files are converted using File Compression Software and use lossy format as the original file is lost following the compression algorithm.
MP4
This format allows the storage of multimedia files rather than just sound such as:
- Music, videos, photos and animations.
Videos, could be streamed without losing any real discernible quality.
Joint Photographic Experts Group (JPEG)
- JPEG is a file formats used to reduce photographic file sizes.
- Reducing picture resolution is changing the number of pixels per centimetre.
- When photographic file undergoes compression, file size is reduced.
- JPEG will reduce the raw bitmap image by a factor between 5 and 15.
Lossless and Lossy File Compression
Lossless File Compression
- All the data bits from the original file are reconstructed when the file again is uncompressed.
- Important for files where loss of data would be disastrous (spreadsheet).
Strong File Compression
- The file compression algorithm eliminates unnecessary bits of data like MP3 and JPEG formats.
- Impossible to get original file back once compressed.
Communication & Internet Technologies
Transmission of Data
Asynchronous data transmission refers to data being transmitted in an agreed bit pattern
- Data bits are grouped together & sent with control bits. This means the receiver of the data knows when the data starts and ends, prevents data getting mixed up
Synchronous data transmission is a continuous stream of data (not in discrete groups like asynchronous)
- Ensures that the sender and receiver are synchronized with each other. This is the faster method of the two.
Serial & Parallel Transmission
Serial data transmission is when data is sent one bit at a time over a single wire
- Works well over long distances
- But data transmitted at a slower rate (USB)
- Relatively cheap.
Parallel data transmission is when data several bits (1 byte) are sent down several wires at the same time
- Works well over short distance.
- Faster method (internal components use parallel for high speed).
- Expensive compared to serial.
Simplex, Half-duplex and Full-duplex
- Simplex data transmission is in one direction only (e.g. computer to printer).
- Half-duplex data transmission is in both directions but not at the same time (e.g. phone conversation where only one person speaks).
- Full-duplex data transmission is in both directions simultaneously (e.g. broadband connection on phone line).
Universal Serial Bus (USB)
USB is an asynchronous serial data transmission method.
It consists of:
- Four-wire shielded cable.
- Two wires used for power and earth.
- Two wires used in data transmission.
| Advantages | Disadvantages |
|---|---|
| Automatically detected | |
| Only fit one way, prevents incorrect connections | Maximum cable length is about 5 metres |
| Different data transmission rates | Transmission rate is less than 500 mb/sec |
Security Aspects
Hacking:
- The act of gaining illegal access to a computer system.
Effect:
- Leads to identity theft, gaining personal information.
- Data can be deleted, changed or corrupted.
To remove risk:
- Firewalls.
- Strong passwords/ user IDs.
- Use of anti-hacking software.
Difference between hacking and cracking:
- Hacking breaks into computer system to steal data.
- Cracking is where someone edits a program code, malicious.
Viruses:
- Program that can replicate itself with the intention of deleting or corrupting files, cause computer malfunction.
Effect:
- Can cause computer to crash.
- Can delete or corrupt files/data.
To remove risk:
- Install anti-virus software.
- Don’t use software from unknown sources.
- Be careful when opening emails from unknown.
Wardriving:
- The act of locating and using wireless internet connections illegally.
Effects:
- Possible to steal internet time.
- Possible to hack into wireless network and steal user’s password.
To remove risk:
- Use complex passwords.
- Firewalls.
Spyware:
- Software that gathers info by monitoring key presses on the user’s keyboard and info is sent back.
Effects:
- Access to all data entered.
- Software is able to install other spyware, read cookie data.
To remove risk:
- Use of anti-spyware software.
- Use a mouse to select characters from passwords rather than typing them.
Internet Principles of Operation
Internet Service Protocol:
- These are companies that provide user with access to the internet Internet Protocol (IP) Address. Each device on the internet is given a unique address known as the IP address. 32-bit number written in the form: <IP_ADDRESS> . IP address gives the location of a device on the internet whereas the MAC address identifies the device connected to the internet. IP address changes, MAC address remains unchanged.
HTML (HyperText Mark-up Language):
- Used when writing and developing pages. Mark-up language is used in the processing. Html use '\
' to bracket piece of codes. Different intensity of colours is determined by its hexadecimal value.
Media Access Control (MAC):
- MAC address refers to a number which uniquely identifies a device on the internet. Refers to the network interface card (NIC) which is part of the device. Usually made up of 48 bits shown as six groups of hexadecimal digits.
- NN:NN:NN:DD:DD:DD
- (NN:NN:NN) first half is the identity number of the manufacturer of the device.
- (DD:DD:DD) second half is the serial number of the device.
Types of MAC Address:
- Universally Administrated MAC Address (UAA). Locally Administrated MAC Address (LAA).
- UAA is the most common type set by the manufacturer.
- Reasons to change MAC address using LAA.
- To ensure they follow the correct formula.
- To bypass MAC address filter on a router or a firewall.
- To get past certain types of network restrictions.
Web addresses:
- Each character on the keyboard has its own ASCII code. Can be represented using hexadecimal or decimal values. Hexadecimal addresses are used in the address of files or webpages as a security figure. Takes longer to type in URL but advantage is that you are unlikely to fall into the trap of copying a fake website.
Cookies:
- A packet of information sent by a web server to a web browser.
- Generated each time the user visits the website.
- Every time a user visits a website, cookies will have collected some key information about the user.
- They are able to carry out user tracking and maintain user preferences.
- Cookies are pieces of data.
- Information gathered by cookies doesn’t contain personal information.
Hardware & Software
Logic Gates
Logic Gates: use one or more inputs and produces a single logical output.
AND gate: If both inputs high, output is high, \(A.B\) .
| A | B | Output |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
OR gate: If either inputs high, output is high, \(A + B\) .
| A | B | Output |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 1 |
NOT gate: an inverter, \(\overline{A}\) .
| A | Output |
|---|---|
| 1 | 0 |
| 0 | 1 |
NAND gate: \(\overline{\text{A.B}}\) .
| A | B | Output |
|---|---|---|
| 0 | 0 | 1 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
NOR gate: \(\overline{A + B}\) .
| A | B | Output |
|---|---|---|
| 0 | 0 | 1 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 0 |
XOR gate: \(\overline{A\ \bigoplus\ B}\) .
| A | B | Output |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
Computer Architecture & Fetch-Execute Cycle
Computer Architecture
- Address bus – unidirectional.
- Data bus – bi-directional.
- Control bus – unidirectional and bi-directional.
- Processor - The processor contains the Arithmetic and Logic Unit (ALU).
- Control Unit - The control unit controls the operation of the memory, processor and input/output devices.
The Fetch-Execute Cycle
- PC contains address of the next instruction to be fetched.
- This address is copied to the MAR via the address bus.
- The instruction of the address is copied into the MDR temporarily.
- The instruction in the MDR is then placed in the CIR.
- The value in the PC is incremented by 1, pointing the next instruction to be fetched.
- The instruction is finally decoded and then executed.
Input Devices
Two-dimensional Scanners: Used to input hard-copy documents. The image is converted into an electronic form which can be stored in the computer.
Process:
- Document is placed on a glass panel.
- A bright light illuminates the document.
- A scan head moves across the document until the whole page is scanned. And image of the document is produced and sent to a lens using a series of mirrors.
- The lens focuses the document image.
- The focused image now falls onto a charge couple device (CCD) which consists of a numbers of integrated circuits.
- Software produces a digital image from the electronic form.
Optical Character Recognition (OCR) is a software which converts scanned documents into a text file format.
Three-dimensional Scanners
- 3D scanners can scan solid objects and produce a three-dimensional image.
- Scanners take images at several points, x, y and z (lasers, magnetic, white light).
- The scanned images can be used in Computer Aided Design (CAD) or to a 3D printer to produce a working model.
Application of 2D Scanners at an Airport:
- Make use of (OCR) to produce digital images which represent the passport pages.
- Text can be stored in ASCII format.
- The 2D photograph in the passport is also scanned and stored as jpeg image.
- The passenger’s face is also photographed using a digital camera and compared using face recognition software.
- Key parts of the face are compared (distance between eyes, width of nose).
Barcode readers/scanners
- A barcode is a series of dark and light parallel lines of varying thicknesses.
- The numbers 0 -9 are each represented by a unique series of lines.
- The left and right hand sides of the barcode are separate using guard bars.
- Allows barcode to be scanned in any direction.
- Barcode is read by a red laser or red LED.
- Light is reflected back off the barcode; dark areas reflect little light which allows the bars to be read.
- Reflected light is read by sensors (photoelectric cells).
- Pattern is generated which is converted to digital.
Quick Response (QR) Codes
- Another type of barcode is the QR codes.
- Made up of a matrix of filled in dark squares on a light background.
- Can hold more storage (7000 digits).
- Advantages of QR codes:
- No need for the user to write down website address.
- QR codes can store website addresses.
Digital Cameras
- Controlled by microprocessor which automatically adjusts the shutter speed, focus the image, etc.
- Photo is captured when light passes through the lens onto a light sensitive cell.
- Cell is made up of pixels.
- Number of pixels determines size of the file.
Keyboards
- Connected to computer with a USB connection or by wireless connection.
- Each character has an ASCII value and is converted into a digital signal.
- Slow method.
- Prone to errors.
Pointing devices
- Mouse/trackball.
- Traditional; mechanical ball, connected by USB port.
- Modern type; red LEDs to detect movement.
Microphones
- Used to input sound to a computer.
- When a microphone picks up sound, a diaphragm vibrates producing an electric signal.
- The signal goes to a sound card and is converted into digital values and stored in computer.
- Voice recognition, voice is detected and converted into digital.
Touchscreens
- Capacitive (medium cost tech).
- Made up of many layers of glass.
- Creating electric fields between glass plates in layers.
- When top layer of glass is touched, electric current changes.
- Co-ordinates where the screen was touched is determined by an on-board microprocessor.
- Infra-red heat (expensive).
- Use glass as the screen material.
- Needs warm object to carry an input operation.
- Infra-red optical (expensive).
- Uses glass as screen material.
- Uses an array of sensors (grid form).
- Point of contact is based on which grid co-ordinate is touched.
- Resistive (inexpensive).
- Upper layer of polyester, bottom layer of glass.
- When the top polyester is touched, the top layer and bottom layer complete a circuit.
- Signals are then sent out which are interpreted by a microprocessor, determine where screen was touched.
Sensors
- Devices which read or measure physical properties.
- Data needs to be converted to digital.
- Analogue to Digital Converter (ADC) converts physical values into digital.
Control of Street Lighting
- Light sensor sends data to the ADC.
- Digitises data and sent to the microprocessor.
- Microprocessor samples data every minute.
- If data from sensor \< value stored in memory:
- Signal sent from microprocessor to street lamp.
- Lamp switched on.
Output Devices
- Inkjet Printers
- Used to print one-off pictures and documents.
- Data from document sent to printer driver.
- Printer driver ensures data is in correct format.
- Check made by printer driver that chosen printer is available.
- Data is sent to printer, stored in a temporary memory (printer buffer).
- Sheet of paper is fed; sensor detects if paper is available in paper tray.
- Print head moves across paper printing text/image, four ink colours sprayed in exact amount.
- Paper is advanced so next line is printed.
- Repeated until buffer is empty.
- Once it is done, printer send an interrupt to the processor (request for more data to be sent).
3D Printers
- Used for models of cars.
- Produce solid objects that work.
- Built up layer by layer, using powdered resin, ceramic powder.
- A design is made using Computer-aided Design (CAD).
2D and 3D Cutters
- 3D cutters can recognize objects in x, y, z direction.
- 3D laser cutters can cut; glass, crystal, metal, wood.
Actuators
- Used in many control applications involving sensors and devices (ADC and DAC).
Loudspeakers/Headphones
- Sound is produced by passing the digital data through a DAC then through amplifier and then emerges from loudspeaker.
- Produced by voltage differences vibrating a cone in the speaker at different frequencies.
LCD and LED Monitors
- Front layer of monitor is made up of Liquid Crystal Display (LCD), these tiny diodes are grouped together in threes as pixels (LCD doesn’t emit any light).
- LCD monitors are back lit using Light Emitting Diode (LED) because:
- LEDs reach their maximum brightness immediately.
- LEDs sharpens image (higher resolution), CCFL has yellow tint.
- LEDs improve colour image.
- Monitors using LED are much thinner than CCFL.
- LEDs consume very little power.
- Before LEDs, LCD monitors were backlit using CCFL.
- CCFL uses two fluorescent tubes behind the LCD screen which supplies the light source.
Light Projectors:
- Two common types of light projectors:
- Digital Light Projector (DLP).
- LCD Projector.
- Projectors are used to project computer output onto larger screens/interactive whiteboards.
Digital Light Projectors (DLP)
- Uses millions of micro mirrors.
- The number of micro mirrors and the way they are arranged on the DLP chip determines the resolution of the image.
- When the micro mirrors tilt towards the light source they are on.
- When the micro mirrors tilt away from the light source they are off.
- This creates a light or dark pixel on the projection screen.
- A bright white light source passes through a colour filter on its way to the DLP chip.
- White light splits into primary colours.
LCD Projectors
- Older technology than DLP.
- A powerful beam of white light is generated from a bulb.
- This beam of light is then sent to a group of chromatic-coated mirrors; these reflect the light back at different wavelengths.
- When the white light hits the mirrors, the reflected light has wavelengths corresponding to red, green and blue.
- These three different light pass through three LCD screens; these screens show the image to be projected as millions of pixels in grayscale.
- When the coloured light passes through the LCD screens, a red, green and blue version of the grey image emerges.
- Finally, the image passes through the projector lens onto the screen.
Memory, Storage Devices & Media
Primary Memory:
Random Access Memory (RAM)
- Features of RAM.
- Volatile/temporary memory (contents lost if RAM is turned off).
- Used to store; data, files.
- It can be written to or read from and the contents from the memory can be changed.
- Larger the size of the RAM, faster the computer will operate.
- RAM never runs out of memory, continues to run slow.
- As RAM becomes full, the processor has to continually access the hard drive to overwrite old data on RAM with new data.
Read Only Memory (ROM)
- Features of ROM.
- Non-volatile/permanent memories (contents remain even when ROM is turned off).
- Used to store start up instruction (basic input/output systems).
- Data/contents of a ROM chip can only be read, cannot be changed.
Secondary Storage:
Hard Disk Drives (HDD)
- Data is stored in a digital format on the magnetic surface of the disks (platter).
- Number of read/write heads can access all of the surfaces of the disk.
- Each platter will have two surfaces which can be used to store the data.
- Data is stored on the surfaces in sectors and tracks.
- HDD have very slow data access compared to RAM.
Solid-State Storage (SDD)
- No moving parts and all data is received at the same time (not like HDD).
- Store data by controlling the movement of electrons within NAND chips, as 1s and 0s.
- Non-volatile rewritable memory.
- Benefits of using SDD rather than HDD:
- More reliable (no moving parts).
- Considerably lighter (suitable for laptops).
- Lower power consumption.
- Run much cooler than HDDs.
- Very thin.
- Data access if faster than HDD.
- Drawback – questionable longevity (20GB per day).
Off-Line Storage:
CD/DVD Disks
- Laser (red) light is used to read and write data in the surface of the disk.
- Use a thin layer of metal alloy to store data.
- Both systems use a single, spiral track which runs from the centre of the disk to the edge.
- DVD uses Dual-Layering which increases the storage capacity (two individual recoding layers).
Blu-ray Disks
- Uses blue laser to carry out read and write operations.
- Wavelength of laser light is less than CD and DVD (stores up to five times more data than DVD).
- Automatically come with secure encryption (prevent piracy and copyright infringement).
- Used as back-up systems.
USB Flash Memories
- Very small, lightweight suitable from transferring files.
- Small back-up devices for photo, music.
- Solid state so need to be treated with care.
High- & Low-Level Languages
High-Level Languages
- Easier to read and understand as the language is closer to human language.
- Easier to write in shorter time.
- Easier to debug at the development stage.
- Easier to maintain once in use.
Low-Level Languages
- Refer to machine code.
- Binary instructions that computer understands.
Translators:
- A program must be translated into binary before a computer can use it.
- Types of translators; Compiler, Interpreter and Assembler.
Compiler
- Translates a program written in high-level language into machine code.
- Used without compiler.
- Executable file of machine code produced.
- One high-level language translated into several machine code instructions.
- Used for general use.
Interpreter
- Executes a high-language program a statement at a time.
- No executable file of machine code produced.
- One high-level language program statement may require several machine code instructions to be executed.
- Cannot be used without interpreter.
- Used when program is being developed.
Assembler
- Translates a low-level language program into machine code.
- Executable file of machine code produced.
- One low-level language translated into one machine code instructions.
- Can be used without assembler.
- Used for general use.
Syntax Errors:
- When program is being compiled, if any syntax errors are found no translated program is produced.
- Instead, a list of all errors in program is produced.
- Programmer corrects program and recompiles.
- When a program is being interpreted, the interpreter preforms the action until syntax error is found.
- The programmer is the alerted to the place in the program where error was found.
- The error is corrected and interpretation continues.
Security
Security
The need to keep data safe from accidental damage, including corruption and human errors and from malicious actions, including unauthorized viewing, deleting, copying and corruption.
Firewalls & Proxy Servers
A firewall sits between the user’s computer and an external network (internet) and filter information in and out of the computer.
Tasks carried out by firewall:
- Examining ‘traffic’.
- Checking weather incoming or outgoing data meets criteria.
- If data fails the criteria, the firewall blocks ‘traffic’.
- Firewall can keep a list of all undesirable IP addresses.
- Helping to prevent viruses or hackers entering the user’s computer.
Proxy servers act as an intermediary between the user and a web server.
Uses of proxy servers:
- Allowing the internet ‘traffic’ to be filtered.
- By using cache, they can speed up access to information from a website.
- Keeping the user’s IP address secret.
Security Protocols
Secure Sockets Layer (SSL)
- Type of protocol that allows data to be sent and received securely over the internet.
- When a user logs onto a website, SSL encrypts the data.
- https or padlock in the status bar.
- When user wants to access a secure website:
- User’s web browser sends a message so it can connect with required website which is secured by SSL.
- Web browser requests that the web server identifies itself.
- Web server responds by sending a copy of its SSL certificate.
- Web browser checks if certificate is authentic.
- Sends signal back to web browser.
- Starts to transmit data once connection is established.
- If not secure, browser will display an open padlock.
Transport Layer Security (TLS)
- Form of protocol that ensures the security and privacy of data between devices and users when communicating over the internet.
- Designed to provide encryption, authentication and data integrity in a more effective way than SSL.
- Possible to extend TLS by adding new authentication methods.
Encryption
Used to protect data in case it has been hacked but doesn’t prevent hacking, only making the data meaningless if unlawfully obtained.
Symmetric Encryption A secret key which can be a combination of characters. If this key is applied to a message, its contents is changed. One key is needed to encrypt a message and another key is needed to decrypt a message. Increasing the length of the key increases the strength of the encryption.
Plain text and Cypher Text Plain text is the normal representation of data before it goes through an encryption algorithm. Cypher text is the output from an encryption algorithm.
Authentication Authentication is used to verify that data come from a trusted source. Works with encryption to strengthen internet security.
- Passwords: usually a user id/name and password are used to log on to systems.
- Digital Signatures: public key encryption; ensure an electronic document is authentic.
- Biometrics: relies on the unique characteristics of human beings (fingerprint scans, retina scans).
Phishing, Pharming & DoS
Phishing: Creator sends out a legitimate-looking email; as soon as recipient clicks on link, user is sent to a fake website.
Effect:
- Creator of email can gain personal data; bank account.
- Can lead to fraud.
To remove risk:
- Many ISPs filter out phishing emails.
- User should be cautious.
Pharming Malicious code installed on a user’s hard drive or on the web server, code will redirect the user to a fake website.
Effect:
- Creator of malicious code can gain personal data; bank account.
- Can lead to fraud or identity theft.
To remove risk:
- Some anti-spyware can identify and remove pharming code from hard drive.
- User should be alert.
Denial of Service Attacks (DoS) An attempt at preventing users from accessing part of a network. Usually temporary but may be damaging.
Attacker may be able to prevent user from:
- Accessing their emails.
- Accessing websites.
- Accessing online services.
Applications
Ways bank protect their costumers from online fraud.
- Banks use 10/12-digit code unique to the costumer.
- May be asked to input three random numbers from a four-digit PIN.
- Some use a hand-held device into which a customer inserts their card. Device will generate an eight-digit code which the customer types into web page.
- Some ask to key in parts of their passwords using drop-down boxes (using a mouse).


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final
private
Since private methods cannot be meaningfully overridden because of their visibility, declaring them final is redundant.


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--- layout: docpage title: "Documentation" is_homepage: false is_sphinx_doc: true doc-parent: "Operating Cassandra" doc-title: "Compaction" doc-header-links: ' ' doc-search-path: "../search.html" extra-footer: ' ' ---
The concept of compaction is used for different kinds of operations in Cassandra, the common thing about these operations is that it takes one or more sstables and output new sstables. The types of compactions are;
nodetool compact -st x -et y
) will pick
all sstables containing the range between x and y and issue a compaction for those sstables. For STCS this will
most likely include all sstables but with LCS it can issue the compaction for a subset of the sstables. With LCS
the resulting sstable will end up in L0.# When an sstable is added to the node through flushing/streaming etc.
# When autocompaction is enabled after being disabled (nodetool enableautocompaction
)
# When compaction adds new sstables.
# A check for new minor compactions every 5 minutes.
Compaction is about merging sstables, since partitions in sstables are sorted based on the hash of the partition key it is possible to efficiently merge separate sstables. Content of each partition is also sorted so each partition can be merged efficiently.
When a delete request is received by Cassandra it does not actually remove the data from the underlying store. Instead it writes a special piece of data known as a tombstone. The Tombstone represents the delete and causes all values which occurred before the tombstone to not appear in queries to the database. This approach is used instead of removing values because of the distributed nature of Cassandra.
Imagine a three node cluster which has the value [A] replicated to every node.:
[A], [A], [A]
If one of the nodes fails and and our delete operation only removes existing values we can end up with a cluster that looks like:
[], [], [A]
Then a repair operation would replace the value of [A] back onto the two nodes which are missing the value.:
[A], [A], [A]
This would cause our data to be resurrected even though it had been deleted.
Starting again with a three node cluster which has the value [A] replicated to every node.:
[A], [A], [A]
If instead of removing data we add a tombstone record, our single node failure situation will look like this.:
[A, Tombstone[A]], [A, Tombstone[A]], [A]
Now when we issue a repair the Tombstone will be copied to the replica, rather than the deleted data being resurrected.:
[A, Tombstone[A]], [A, Tombstone[A]], [A, Tombstone[A]]
Our repair operation will correctly put the state of the system to what we expect with the record [A] marked as deleted
on all nodes. This does mean we will end up accruing Tombstones which will permanently accumulate disk space. To avoid
keeping tombstones forever we have a parameter known as gc_grace_seconds
for every table in Cassandra.
The table level gc_grace_seconds
parameter controls how long Cassandra will retain tombstones through compaction
events before finally removing them. This duration should directly reflect the amount of time a user expects to allow
before recovering a failed node. After gc_grace_seconds
has expired the tombstone may be removed (meaning there will
no longer be any record that a certain piece of data was deleted), but as a tombstone can live in one sstable and the
data it covers in another, a compaction must also include both sstable for a tombstone to be removed. More precisely, to
be able to drop an actual tombstone the following needs to be true;
gc_grace_seconds
only_purge_repaired_tombstones
is enabled, tombstones are only removed if the data has also been
repaired.If a node remains down or disconnected for longer than gc_grace_seconds
it’s deleted data will be repaired back to
the other nodes and re-appear in the cluster. This is basically the same as in the “Deletes without Tombstones” section.
Note that tombstones will not be removed until a compaction event even if gc_grace_seconds
has elapsed.
The default value for gc_grace_seconds
is 864000 which is equivalent to 10 days. This can be set when creating or
altering a table using WITH gc_grace_seconds
.
Data in Cassandra can have an additional property called time to live - this is used to automatically drop data that has
expired once the time is reached. Once the TTL has expired the data is converted to a tombstone which stays around for
at least gc_grace_seconds
. Note that if you mix data with TTL and data without TTL (or just different length of the
TTL) Cassandra will have a hard time dropping the tombstones created since the partition might span many sstables and
not all are compacted at once.
If an sstable contains only tombstones and it is guaranteed that that sstable is not shadowing data in any other sstable
compaction can drop that sstable. If you see sstables with only tombstones (note that TTL:ed data is considered
tombstones once the time to live has expired) but it is not being dropped by compaction, it is likely that other
sstables contain older data. There is a tool called sstableexpiredblockers
that will list which sstables are
droppable and which are blocking them from being dropped. This is especially useful for time series compaction with
TimeWindowCompactionStrategy
(and the deprecated DateTieredCompactionStrategy
).
With incremental repairs Cassandra must keep track of what data is repaired and what data is unrepaired. With anticompaction repaired data is split out into repaired and unrepaired sstables. To avoid mixing up the data again separate compaction strategy instances are run on the two sets of data, each instance only knowing about either the repaired or the unrepaired sstables. This means that if you only run incremental repair once and then never again, you might have very old data in the repaired sstables that block compaction from dropping tombstones in the unrepaired (probably newer) sstables.
Since tombstones and data can live in different sstables it is important to realize that losing an sstable might lead to data becoming live again - the most common way of losing sstables is to have a hard drive break down. To avoid making data live tombstones and actual data are always in the same data directory. This way, if a disk is lost, all versions of a partition are lost and no data can get undeleted. To achieve this a compaction strategy instance per data directory is run in addition to the compaction strategy instances containing repaired/unrepaired data, this means that if you have 4 data directories there will be 8 compaction strategy instances running. This has a few more benefits than just avoiding data getting undeleted:
When an sstable is written a histogram with the tombstone expiry times is created and this is used to try to find
sstables with very many tombstones and run single sstable compaction on that sstable in hope of being able to drop
tombstones in that sstable. Before starting this it is also checked how likely it is that any tombstones will actually
will be able to be dropped how much this sstable overlaps with other sstables. To avoid most of these checks the
compaction option unchecked_tombstone_compaction
can be enabled.
There is a number of common options for all the compaction strategies;
enabled
(default: true)tombstone_threshold
(default: 0.2)tombstone_compaction_interval
(default: 86400s (1 day))log_all
(default: false)unchecked_tombstone_compaction
(default: false)only_purge_repaired_tombstone
(default: false)min_threshold
(default: 4)LeveledCompactionStrategy
.max_threshold
(default: 32)LeveledCompactionStrategy
.Further, see the section on each strategy for specific additional options.
The nodetool utility provides a number of commands related to compaction:
enableautocompaction
disableautocompaction
setcompactionthroughput
compactionstats
compactionhistory
setcompactionthreshold
It is possible to switch compaction strategies and its options on just a single node using JMX, this is a great way to experiment with settings without affecting the whole cluster. The mbean is:
org.apache.cassandra.db:type=ColumnFamilies,keyspace=<keyspace_name>,columnfamily=<table_name>
and the attribute to change is CompactionParameters
or CompactionParametersJson
if you use jconsole or jmc. The
syntax for the json version is the same as you would use in an ALTER TABLE statement -
for example:
{ 'class': 'LeveledCompactionStrategy', 'sstable_size_in_mb': 123, 'fanout_size': 10}
The setting is kept until someone executes an ALTER TABLE that touches the compaction settings or restarts the node.
Enable with the compaction option log_all
and a more detailed compaction log file will be produced in your log
directory.
The basic idea of SizeTieredCompactionStrategy
(STCS) is to merge sstables of approximately the same size. All
sstables are put in different buckets depending on their size. An sstable is added to the bucket if size of the sstable
is within bucket_low
and bucket_high
of the current average size of the sstables already in the bucket. This
will create several buckets and the most interesting of those buckets will be compacted. The most interesting one is
decided by figuring out which bucket’s sstables takes the most reads.
When running a major compaction with STCS you will end up with two sstables per data directory (one for repaired data and one for unrepaired data). There is also an option (-s) to do a major compaction that splits the output into several sstables. The sizes of the sstables are approximately 50%, 25%, 12.5%… of the total size.
min_sstable_size
(default: 50MB)bucket_low
(default: 0.5)bucket_low * avg_bucket_size < sstable_size
(and the bucket_high
condition holds, see below), then
the sstable is added to the bucket.bucket_high
(default: 1.5)sstable_size < bucket_high * avg_bucket_size
(and the bucket_low
condition holds, see above), then
the sstable is added to the bucket.Defragmentation is done when many sstables are touched during a read. The result of the read is put in to the memtable so that the next read will not have to touch as many sstables. This can cause writes on a read-only-cluster.
The idea of LeveledCompactionStrategy
(LCS) is that all sstables are put into different levels where we guarantee
that no overlapping sstables are in the same level. By overlapping we mean that the first/last token of a single sstable
are never overlapping with other sstables. This means that for a SELECT we will only have to look for the partition key
in a single sstable per level. Each level is 10x the size of the previous one and each sstable is 160MB by default. L0
is where sstables are streamed/flushed - no overlap guarantees are given here.
When picking compaction candidates we have to make sure that the compaction does not create overlap in the target level. This is done by always including all overlapping sstables in the next level. For example if we select an sstable in L3, we need to guarantee that we pick all overlapping sstables in L4 and make sure that no currently ongoing compactions will create overlap if we start that compaction. We can start many parallel compactions in a level if we guarantee that we wont create overlap. For L0 -> L1 compactions we almost always need to include all L1 sstables since most L0 sstables cover the full range. We also can’t compact all L0 sstables with all L1 sstables in a single compaction since that can use too much memory.
When deciding which level to compact LCS checks the higher levels first (with LCS, a “higher” level is one with a higher number, L0 being the lowest one) and if the level is behind a compaction will be started in that level.
It is possible to do a major compaction with LCS - it will currently start by filling out L1 and then once L1 is full, it continues with L2 etc. This is sub optimal and will change to create all the sstables in a high level instead, CASSANDRA-11817.
During bootstrap sstables are streamed from other nodes. The level of the remote sstable is kept to avoid many compactions after the bootstrap is done. During bootstrap the new node also takes writes while it is streaming the data from a remote node - these writes are flushed to L0 like all other writes and to avoid those sstables blocking the remote sstables from going to the correct level, we only do STCS in L0 until the bootstrap is done.
If LCS gets very many L0 sstables reads are going to hit all (or most) of the L0 sstables since they are likely to be overlapping. To more quickly remedy this LCS does STCS compactions in L0 if there are more than 32 sstables there. This should improve read performance more quickly compared to letting LCS do its L0 -> L1 compactions. If you keep getting too many sstables in L0 it is likely that LCS is not the best fit for your workload and STCS could work out better.
If a node ends up with a leveling where there are a few very high level sstables that are not getting compacted they might make it impossible for lower levels to drop tombstones etc. For example, if there are sstables in L6 but there is only enough data to actually get a L4 on the node the left over sstables in L6 will get starved and not compacted. This can happen if a user changes sstable_size_in_mb from 5MB to 160MB for example. To avoid this LCS tries to include those starved high level sstables in other compactions if there has been 25 compaction rounds where the highest level has not been involved.
sstable_size_in_mb
(default: 160MB)fanout_size
(default: 10)LCS also support the cassandra.disable_stcs_in_l0
startup option (-Dcassandra.disable_stcs_in_l0=true
) to avoid
doing STCS in L0.
TimeWindowCompactionStrategy
(TWCS) is designed specifically for workloads where it’s beneficial to have data on
disk grouped by the timestamp of the data, a common goal when the workload is time-series in nature or when all data is
written with a TTL. In an expiring/TTL workload, the contents of an entire SSTable likely expire at approximately the
same time, allowing them to be dropped completely, and space reclaimed much more reliably than when using
SizeTieredCompactionStrategy
or LeveledCompactionStrategy
. The basic concept is that
TimeWindowCompactionStrategy
will create 1 sstable per file for a given window, where a window is simply calculated
as the combination of two primary options:
compaction_window_unit
(default: DAYS)compaction_window_size
(default: 1)Taken together, the operator can specify windows of virtually any size, and TimeWindowCompactionStrategy will work to create a single sstable for writes within that window. For efficiency during writing, the newest window will be compacted using SizeTieredCompactionStrategy.
Ideally, operators should select a compaction_window_unit
and compaction_window_size
pair that produces
approximately 20-30 windows - if writing with a 90 day TTL, for example, a 3 Day window would be a reasonable choice
('compaction_window_unit':'DAYS','compaction_window_size':3
).
The primary motivation for TWCS is to separate data on disk by timestamp and to allow fully expired SSTables to drop more efficiently. One potential way this optimal behavior can be subverted is if data is written to SSTables out of order, with new data and old data in the same SSTable. Out of order data can appear in two ways:
While TWCS tries to minimize the impact of comingled data, users should attempt to avoid this behavior. Specifically,
users should avoid queries that explicitly set the timestamp via CQL USING TIMESTAMP
. Additionally, users should run
frequent repairs (which streams data in such a way that it does not become comingled), and disable background read
repair by setting the table’s read_repair_chance
and dclocal_read_repair_chance
to 0.
Operators wishing to enable TimeWindowCompactionStrategy
on existing data should consider running a major compaction
first, placing all existing data into a single (old) window. Subsequent newer writes will then create typical SSTables
as expected.
Operators wishing to change compaction_window_unit
or compaction_window_size
can do so, but may trigger
additional compactions as adjacent windows are joined together. If the window size is decrease d (for example, from 24
hours to 12 hours), then the existing SSTables will not be modified - TWCS can not split existing SSTables into multiple
windows.


Colocar os Gráficos da visão Geral (Node, Coodenadas Paralelas, DRE Projetos)
Sistemas WEB
Aplicativos Android
>Descrição projeto 2
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A dark blue background with a colored pencil, a clip, and a tiny ice cream cone!

A yellow workspace with some scissors, pencils, and other objects.


Film - On the Line
Exhibition - Laurie Brown
Exhibition - Flash: Steve Rowell
Film - Los Sures
Film - 45 Years
Performance - Ian Dicke And Aron Kallay
Exhibition - Unruly Bodies
Exhibition - Instilled Life
Exhibition - Rotation 2015
Exhibition - Unposed: Street Photography from the CMP's Collection
Exhibition - For The Record...
Performance - Trauma, Loss and Transcendence


Index of exceptions
E
Error
[
Smt
]
U
Unsat
[
Smt
]
The exception raised by
Smt.Solver.check
and
Smt.Solver.assume
when the formula is unsatisfiable.


WITNESS LIST
Appropriations - S/C on Article III Committee
February 12, 2013 - 7:30 AM
General Academic Institutions Overview
For:
Moreno, Alejandro (Self; Texas Chapter of the American College of Physicians)
Moreno, Alejandro (Self; Texas Chapter of the American College of Physicians)
Midwestern State University
On:
Rogers, Jesse (Midwestern State University)
Registering, but not testifying:
On:
Fowle, Marilyn (Midwestern state university)
Stewart, Betty (Midwestern state university)
Texas Woman's University
On:
Stuart, Ann (Texas woman's university)
UH Clear Lake
On:
Staples, William (UH-Clear Lake)
UH Downtown
On:
Flores, William (University of Houston-Downtown)
UH System
On:
Khator, Renu (UH System)
UH Victoria
On:
Castille, Philip (University of Houston- Victoria)
University of Houston
On:
Khator, Renu (University of Houston)
UNT
On:
Rawlins, V. Lane (University of North Texas)
Registering, but not testifying:
On:
Bush, Jean (UNT)
Harris, Andrew (Unt)
1
WITNESS LIST
UNT Dallas
On:
Price, John (UNT Dallas)
UNT Health Science Center
On:
Williams, Michael (University of North Texas Health Science Center)
Registering, but not testifying:
On:
Harman, John (University of North Texas Health Science Center)
UNT System
On:
Jackson, Lee (University of North Texas System)
Registering, but not testifying:
On:
Mueller, Michael (University of North Texas System)
UT Arlington
On:
Spaniolo, James (University of texas at arlington)
UT Brownsville
On:
Garcia, Juliet V. (UT-Brownsville)
UT Dallas
On:
Daniel, David (Univ of Texas Dallas)
UT El Paso
On:
Natalicio, Diana (University of Texas at El Paso)
UT Pan American
On:
Nelsen, Robert (UT Pan American)
UT Permian Basin
On:
Watts, W David (University of texas of the permian basin)
UT San Antonio
On:
Romo, Ricardo (UTSA)
2
WITNESS LIST
UT System Administration
For:
Hanna, Deborah (Self; Texas Council on Alzheimers Disease and Related Disorders)
On:
Cigarroa, Francisco (The University of Texas System)
UT Tyler
On:
Mabry, Rodney (UT Tyler)
3


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Gold club becomes the first to use fully recyclable cups
It's the first one to stock the 'Frugal Cup'
by Lea NakacheStoke-on-Trent's Trentham Golf Club is the first to switch from cardboard cups to fully recyclable ones, called the Frugal Cup.
Paper cups are bonded on one side to a robust plastic film, making them impossible to join the recycling chains.
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In Britain, more than two and a half billion cups are used every year, but less than 0.25% of them are being recycled, the vast majority ending in landfills or the ocean.
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Specify the type of temporary database to create.
Credentials for each database server will be exposed as environment variables with a PREFIX_ based on the
type of server.
- TYPE_HOST
-
hostname or IP of database server.
Example: Redis would be
REDIS_HOST=i.mktmp.io
- TYPE_PORT
-
port the server is listening on.
Example: Postgres would be
POSTGRES_PORT=54321
- TYPE_USERNAME
-
root-level user to use when connecting to the server, if required.
Example: Postgres-9.5 would be
POSTGRES95_USERNAME=postgres
- TYPE_PASSWORD
-
password for server, if required.
Example: MySQL would be
MYSQL_PASSWORD=1a2c4f3d
- TYPE_ID
-
mktmpio instance id, which can be useful for debugging.
Example: MongoDB would be
MONGODB_ID=1a2c4f3d
- TYPE_TYPE
-
type of server that has been created
Example: PostgreSQL-9.5 would be
MONGODB_TYPE=postgres-9.5


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Soccer is a sport played between two teams of eleven players with a round ball and is known as football in most countries. It is played by 250 million players in over 200 countries, making it the world's most popular sport. See the soccer fact below for more information.
Like most other sports, table tennis had humble beginnings as a “parlor game,” open to anyone with access to a table, paddle, and ball. The game began in the 1880s, when lawn tennis players adapted their game to play indoors during the winter
Ping-Pong is a trademark name for table tennis and associated equipment. The name “Ping-Pong” was invented by the English firm J. Jaques and Son at the end of the 1800s and later trademarked in the United States by Parker Brothers, the board game company
The game quickly caught on, and as early as 1901, tournaments were being conducted with over 300 participants. The Ping-Pong Association was formed but was renamed The Table Tennis Association in 1922.
In 1902 a visiting Japanese university professor took the game back to Japan, where he introduced it to university students. Shortly after, a British salesman, Edward Shires, introduced it to the people of Vienna and Budapest, and the seeds were sown for a sport that now enjoys popularity all over the world. In Britain, table tennis had also begun to spread outside the distinctly middle-class confines of London, and leagues sprang up in provincial towns as far apart as Sunderland and Plymouth. In 1922, an All England Club was formed, which boasted such luminaries as Jack Hobbs the cricketer and other famous names of the time from the world of sport. The Daily Mirror organized and sponsored a nationwide tournament in which there were 40,000 competitors.
On this day in 1949, after a damaging three-year battle to win both players and fans, the rival Basketball Association of America (BAA) and National Basketball League (NBL) merge to form the National Basketball Association (NBA).
The BAA incorporated in 1946, challenging the hegemony of the nine-year old NBL. The BAA established itself in bigger cities than the NBL, which existed only in small Midwestern cities like Fort Wayne, Sheboygan and Akron. While the NBL held its games in small gymnasiums, the upstart BAA played its games in large major-market arenas such as the Boston Garden and New York City’s Madison Square Garden. By the 1948-49 season, the BAA had begun to attract some of the country’s best players, and four NBL franchises–Fort Wayne, Indianapolis, Minneapolis and Rochester–moved to the BAA, bringing their star players with them. George Mikan, the biggest attraction in either league who by himself could virtually assure a team’s success, defected to the new league with the Minneapolis Lakers.
On August 3, 1949, representatives from the two leagues met at the BAA offices in New York’s Empire State Building to finalize the merger. Maurice Podoloff, head of the BAA since its inception, was elected head of the new league. The new NBA was made up of 17 teams that represented both small towns and large cities across the country. Through the 1950s, though, the number of teams dwindled, along with fan support, and by the 1954-55 season, only eight teams remained. That year, the league transformed the game with the creation of the 24-second clock, making play faster-paced and more fun to watch. Fans returned, and the league, now financially solvent, expanded throughout the 1960s and 70s. Today, the NBA has 30 franchises and attracts players—and millions of fans—from countries around the world.
Many believe that rugby was born in 1823 when William Webb Ellis "with fine disregard for the rules of football (note that football was yet to split into the various codes) as played in his time at Rugby school, first took the ball in his arms and ran with it, thus originating the distinctive feature of the Rugby game". Although this is in fact apocryphal, since there is little in the way of evidence to substantiate this view, it is however the popular view. So much so in fact that the international committee named the Rugby world cup the "William Webb Ellis Trophy"
The towns first public commemoration of the game of Rugby was unveiled by Jeremy Guscott on 26th September 1997. The bronze statue, by Graham Ibbeson and modeled after his own son, cost £40,000 which was raised by a public appeal. The bronze statue of a boy running with a Rugby ball, cast using the lost wax technique, now stands at the junction of Lawrence Sheriff Street and Dunchurch Road, beside the school and opposite what is now called the Webb Ellis museum.
Swimming was initially one of the seven agilities of knights during the Middle Ages, including swimming with armor. However, as swimming was done in a state of undress, it became less popular as society became more conservative in the early Modern period. Leonardo da Vinci made early sketches of lifebelts. In 1539, Nikolaus Wynmann, a German professor of languages, wrote the first swimming book Colymbetes. His purpose was to reduce the dangers of drowning. The book contained a good methodical approach to learning breaststroke, and mentioned swimming aids such as air filled cow bladders, reed bundles, and cork belts.
In 1587, Everard Digby also wrote a swimming book, claiming that humans could swim better than fish. Digby was a Senior Fellow at St. John's College, Cambridge and was interested in the scientific method. His short treatise, De arte natandi, was written in Latin and contained over 40 woodcut illustrations depicting various methods of swimming, including the breaststroke, backstroke and crawl. Digby regarded the breaststroke as the most useful form of swimming. In 1603, Emperor Go-Yozei of Japan declared that schoolchildren should swim.
In 1696, the French author Melchisédech Thévenot wrote The Art of Swimming, describing a breaststroke very similar to the modern breaststroke. This book was translated into English and became the standard reference of swimming for many years to come. In 1739, Guts Muts (also spelled as Guts Muth) from Schnepfenthal, Germany, wrote Gymnastik für die Jugend (Exercise for youth), including a significant portion about swimming. In 1794, Kanonikus Oronzio de Bernardi of Italy wrote a two volume book about swimming, including floating practice as a prerequisite for swimming studies.
In 1798, Guts Muts wrote another book Kleines Lehrbuch der Schwimmkunst zum Selbstunterricht (Small study book of the art of swimming for self-study), recommending the use of a "fishing rod" device to aid in the learning of swimming. His books describe a three-step approach to learning to swim that is still used today. First, get the student used to the water; second, practice the swimming movements out of the water; and third, practice the swimming movements in the water. He believed that swimming is an essential part of every education. The Haloren, a group of salt makers in Halle, Germany, greatly advanced swimming through setting a good example to others by teaching their children to swim at a very early age.
Boxing originated when a person first lifted a fist against another in play. Different eras of the sport have been distinguished by the use or nonuse of fist coverings. The ancient Greeks believed fist fighting was one of the games played by the gods on Olympus; thus it became part of the Olympic Games in about 688 BC. Homer has a reference to boxing in the Iliad. During Roman times the sport began to thrive on a wide scale. Boxers fought with leather bands around their fists for protection and sometimes wore metal-filled, leather hand coverings called cesti, resulting in bloody, often duel-to-death, battles. Boxing diminished after the fall of Rome. It was revived in the 18th century in England and became especially popular during the championship reign of James Figg, who held the heavyweight title from 1719 through 1730. Boxing became a workingman's sport during the Industrial Revolution as prizefights attracted participants and spectators from the working class. Organization was minimal at first, and the bouts of those eras resembled street fights more than modern boxing.
The second heavyweight champion, Jack Broughton of England, drew his own set of rules for his own fights, and these were recognized in 1743. They outlawed some of the gorier aspects that the sport had acquired, such as hitting below the belt line. Instead of a ring of spectators--hence, the name ring--Broughton insisted upon a squared-off area. His rules governed what is known as the "bareknuckle era."


Pat's Salmon Cookies: Sales Data
Add a new store to the table:
Location Name
Minimum Customers per Hour
Maximum Customers per Hour
Average Cookies per Sale
Click here to add


20K
Members
12
Countries
3K
Hotels
72
Partners
Wisata Popular
Something that you never try
before in this World
Our Network
Companies that trusted us
more than just a trip
They are Loving Us
Moments were giving them
the best experience
Rizky Khairullah
"It was glorious and i could not stop to say whooo for every single moment
sankyuu"
Trip to Bromo
Hiro
"It was glorious and i could not stop to say whooo for every single moment
sankyuu"
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"It was amazing experience visiting many tourism destination with Nomads
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Telusko learnings is one of the largest tech educational youtube channel in India.Firstly I found this channel when I wanted to learn python programming then I check all the videos of this channel and it has best programming videos like Java,Node.js,Python,Git & Github basics videos.
Simple Snippets is an upcoming tech educational channel with more than 30k subsriber.I like this channel very much .It is one of my favourite channel. The way Tanmay Sakpal teaches seems very easy to understand.
This is Tanmay Sakpal favourite channel. But now I don't like this channel maybe in future might I like this channel.


Why Sharing?
Platforms
GitFAB
GitHub
mercurial
shapedo
Syncthing
Makeystreet
Instructables
Thingiverse
Open Design Contest


HtmlRenderer.HtmlContainer
Low level handling of Html Renderer logic, this class is used by HtmlPanel, HtmlLabel, HtmlToolTip and HtmlRender.
The class allows html layout and rendering without association to actual winforms control, thouse allowing to handle html rendering on any graphics object.
Using this class will require the client to handle all propogation of mouse\keyboard events, layout/paint calls, scrolling offset and location/size/rectangle handling and UI refresh requests.Properties
- CssData - the parsed stylesheet data used for handling the html.
- AvoidGeometryAntialias - Gets or sets a value indicating if antialiasing should be avoided for geometry like backgrounds and borders (default - false).
- IsSelectionEnabled - Is content selection is enabled for the rendered html (default - true).
- IsContextMenuEnabled - Is the build-in context menu enabled and will be shown on mouse right click (default - true).
- ScrollOffset - The scroll offset of the html.
- Location - the top-left most location of the rendered html.
- MaxSize - the max width and height of the rendered html, effects layout, actual size cannot exceed this values. Set zero for unlimited.
- ActualSize - The actual size of the rendered html (after layout).
Methods
- GetHtml(HtmlGenerationStyle styleGen = HtmlGenerationStyle.Inline) - Get html from the current DOM tree with style if requested.
- PerformLayout(Graphics) - Measures the bounds of box and children, recursively.
- PerformPaint(Graphics) - Render the html using the given device.
- HandleMouseDown(Control, MouseEventArgs) - Handle mouse down to handle selection.
- HandleMouseUp(Control, MouseEventArgs) - Handle mouse up to handle selection and link click.
- HandleMouseDoubleClick(Control, MouseEventArgs) - Handle mouse double click to select word under the mouse.
- HandleMouseMove(Control, MouseEventArgs) - Handle mouse move to handle hover cursor and text selection.
- HandleMouseLeave(Control, MouseEventArgs) - Handle mouse move to handle hover cursor.
- HandleKeyDown(parent, KeyEventArgs) - Handle key down event for selection and copy.
Events
- LinkClicked - Raised when the user clicks on a link in the html, Allows canceling the execution of the link.
- Refresh - Raised when html renderer requires refresh of the control hosting (invalidation and re-layout).
- RenderError - Raised when an error occured during html rendering.
- StylesheetLoad - Raised when aa stylesheet is about to be loaded by file path or URI by link element. This event allows to provide the stylesheet manually or provide new source (file or uri) to load from.
- ImageLoad - Raised when an image is about to be loaded by file path or URI. This event allows to provide the image manually, if not handled the image will be loaded from file or download from URI.
Remarks
MaxSize and ActualSize
The max width and height of the rendered html.
The max width will effect the html layout wrapping lines, resize images and tables where possible.
The max height does NOT effect layout, but will not render outside it (clip).
ActualSize can be exceed the max size by layout restrictions (unwrappable line, set image size, etc.).
Set zero for unlimited (width\height separately).
ScrollOffset
This will adjust the rendered html by the given offset so the content will be "scrolled".
Element that is rendered at location (50,100) with offset of (0,200) will not be rendered as it will be at -100 therefore outside the client rectangle of the control.
LinkClicked event
Raised when the user clicks on a link in the html.
Allows canceling the execution of the link.
StylesheetLoad event
Raised when aa stylesheet is about to be loaded by file path or URI by link element.
This event allows to provide the stylesheet manually or provide new source (file or uri) to load from.
If no alternative data is provided the original source will be used.
ImageLoad event
Raised when an image is about to be loaded by file path or URI.
This event allows to provide the image manually, if not handled the image will be loaded from file or download from URI.
Refresh event
Raised when html renderer requires refresh of the control hosting (invalidation and re-layout).
There is no garantie that the event will be raised on the main thread, it can be raised on threadpool thread.
RenderError event
Raised when an error occured during html rendering.


Shared Scope Directive
Isolate Scope Directive
Isolate Scope With String Directive
Isolate Scope With Object Directive
Isolate Scope With Event Directive


rotten
>
Library
> What's New
What's New
This describes the longer, more thoughtful additions.
Patton Oswalt
The Choking Game
tDCS
TGN1412
National Security Letter
Hollow Earth
Wonder Showzen
French Fries
Chess
Road Rage
Bongs
Stun Guns
Kid Marketing
Zombies
Date Rape
School Vandalism
Penis Cakes
Groping
Opium
Jamal al-Fadl
Eating Disorders
Vending Machines
Pope Clement V
Ali Mohammed
Methamphetamine
Dog Shit
Eugenics
Indian Call Centers
Card Cheats
Special Forces Underground
The Wow Signal
Flu Pandemic of 1918
Supervolcanoes
Jakob Bohme
Erich von Daniken
Krakatoa
Nazca Lines
Zodiac Killer
Cane Toads
Secret Societies
Siamese Twins
Fire Walking
Elephant Man
September 11
Douglas Adams
Doctor Who
Pope Benedict IX
Pope Sergius III
Pope Stephen VII
Racist Propaganda
Pope Pius II
Mermaids
Passions
Andre the Giant
Anne Catherine Emmerich
William Marston
Miracles
Project for a New American Century
Catholicism
Pope John XII
Shah of Iran
Pope Linus
Superbugs
Jesse Ventura
Eric Rudolph
Nick Berg
Joanie Laurer
Genghis Khan
Islam
Terrorist Videos
Truck Bombs
Lashkar-e-Jhangvi
Pentagram
Witchcraft
Numerology
Kabbalah
Mandeism
Pope John Paul I
Pope John Paul II
Port Chicago Disaster
Tunguska
Cult of the Supreme Being
al Qaeda and the Assassins
Abu Faraj al-Liby
Task Force 121
Bruce Lee
Rabbit's Foot
Flaming Carrot
Gas Chamber
Lobotomy
DNA
Hinduism
Taoism
September 11 Conspiracy Theories
Acupuncture
Chakras
Spells
Hexes
Lottery Winners
Moorish Science Temple of America
Suitcase Nukes
Unamerican Activities
Sugar
Montezuma
Dr. Rashid
The Prisoner
William Shakespeare
Leonardo da Vinci
Salvador Dali
Vincent van Gogh
Santo
Stone Cold Steve Austin
Buddha
Embalming
Cremation
Trepanation
Islamic Heresies
Catacombs
Antinomianism
Donatists
Circumcellions
Sexual Ethics in Psychology
Dirty Bomb
Ahmad Chalabi
Nostradamus
Tetris
Aliens
Satanism
Lashkar-e-Jhangvi
Mary Kay Letourneau
Al Takfir Wal Hijra
CACI International
Ansar al-Islam
Brazil
Abu Ghraib
Necrotizing Fasciitis
Soul
Astral Projection
Animal Homosexuality
Kamikaze Jet Hijacking
Paul Lynde
The Historical Construction of The Bible
Discrepancies Within The Bible
Hezbollah
Hamas
Muslim Brotherhood
Abu Musab al-Zarqawi
Kudzu
Dick Wolf
Human Sacrifice
Robert Tilton
Mark Roberts
Argyria
Jeffrey Skilling
Charles Nelson Reilly
Dippy Drinking Birds
Golem
Gang Bangs
Yeti
Elohim City
SpongeBob SquarePants
Corn
Mary Baker Eddy
Uri Geller
Madalyn Murray O'Hair
Gloryholes
Church of Christ, Scientist
James Bond
Faith Healing
George Tenet
Fred Rogers
Pope John VIII
Aryan Republican Army
Autism
Pentagon
Mohammed Atta
The Gunpowder Plot
i-Ching
Spinal Tap
Paris Hilton
Acupuncture
Astrology
Bob Ross
Rasputin
Press Your Luck
Richard Pryor
Palmistry
Area 51
George Carlin
Physiognomy
Mohammed Jamal Khalifa
Bermuda Triangle
Mickey Mouse Club
The Strange Case of the Shocker
Slobodan Milosevic
Inquisition
G. Gordon Liddy
Kami
Paula Poundstone
Vince Foster
The Simpsons
Ron Brown
Max Hardcore
Skull and Bones
Abu Nidal
Dr. Phil
Jerry Lewis
Ayatollah Khomeini
Atomic Bomb
Creationism
Cher
Iraqi WMDs
Jack Kevorkian
Eagle Scouts
Spiro T. Agnew
Siegfried and Roy
John Edward Robinson
Robert Noel and Marjorie Knoeller
Nuremberg Trials
Karl Rove
Information Awareness Office
Krampus
Patrick Naughton
War of the Worlds
Star Wars
My Lai Massacre
Kamikaze
Richard Scarry
Mary Carey
Fluoridation
King Arthur
Banned Cartoons
Secret Archives of the Vatican
Sacred Geometry
Gary Coleman
Marian Apparitions
Watersports
Bill O'Reilly
Gallagher
Judas Iscariot
Martyrdom
Walt Disney
Jesus Christ
Temp Agencies
Arnold Schwarzenegger
Shroud of Turin
Vince McMahon
Professional Wrestling
Pat Robertson
Prester John
Bumfights
Pissing
Drinking Pee
Practical Uses of Pee
Vampires
Cannibalism
Relics
Godzilla
Condoleezza Rice
Angels
Exorcism
Abortion
Cloning
Darlie Routier
The Matrix
Cathars
Crucifixion
Field Interrogation
Gnosticism
Kim Jong Il
Humanzee
Witchcraft
Jim Morrison
Ordo Templi Orientis
Hell
Scientology
Martha Stewart
Philip K Dick
Terence McKenna
Jack Chick
HAARP Project
L. Ron Hubbard
Mind Control
Talismans
The Invisibles
Jemaah Islamiah
George W Bush
Tarot
Star Trek
Armageddon
Apocalypse
Terry Nichols
Frank Costello
Joe Masseria
Salvatore Maranzano
Louis Buchalter
Carlo Gambino
Joe Adonis
Albert Anastasia
Pakistan
Dick Cheney
SARS
Carlos the Jackal
Lucky Luciano
Al Capone
Art Theft
Hermaphrodite
Majestic-12
Village People
Designer Vaginas
Bugs Moran
Central Intelligence Agency
Goat Suckling
Great Plague
Roswell
George HW Bush
Nerve Agents
Saudi Arabia
Watergate
Dune
Andrew Dice Clay
Gulf War
Brad Pitt
Elongated Labia
Joseph Smith
Jack Parsons
Plastic Shredder
Don Rickles
Houdini
Elvis Presley
Uday Hussein
Ramzi Yousef
John Walker Lindh
Suicide Notes
Sneezing
Knights Templar
Jose Padilla
Aleister Crowley
Kama Sutra
Ronald Reagan
Hambali
Dr. Gene Scott
Saddam Hussein
Bugsy Siegel
John Ashcroft
Ayman Al-Zawahiri
The Turner Diaries
Vagina Dentata
al Qaeda
Donald Rumsfeld
Larry Flynt
Emperor Norton
Osama bin Laden
Josef Stalin
Disneyland
Khalid Shaikh Mohammed
John Dillinger
Masturbation
Kelloggs Cornflakes
Bill Gates
Timothy McVeigh
ATF
David Koresh
Batman
Andy Kaufman
Charles Lindbergh
Doug Henning
Dildos
Chernobyl
Henri Landru
Eunuch
Microsoft
Marijuana
Geraldo Rivera
San Quentin
Alcatraz
Bill Clinton
Andy Warhol
William G Bonin
Castration
Timothy Leary
Absinthe
Graham Chapman
Female Circumcision
Sex Dolls
Eagle Scouts
Foot Binding
Hymen
Fecal Transplant
Freemasonry
Untouchables
Homeopathy
Mormonism
O.J. Simpson
Hybristophilia
Priapism
Cantor-Fitzgerald
DeBeers
Henry Ford
Eternal Flames
Wal-Mart
Jerkcity
Protocols of the Learned Elders of Zion
Goethe
Elmer Wayne Henley
Orgone Box
Sun Myung Moon
Wilhelm Reich
Heidi Fleiss
William S. Burroughs
Klaus Barbie
Torquemada
Superfund
Blood Diamonds
Assassins
Friedrich Nietzsche
Loch Ness Monster
Oscar Wilde
Phil Hartman
Steve Wozniak
Captain Crunch
Kevin Mitnick
David Letterman
Shawn "Napster" Fanning
Robert Morris
Jack Kerouac
Allen Ginsberg
Adolf Hitler
Lasse Braun
Michael Lookinland
Psychic Surgery
D.B. Cooper
Billy Tipton
Suicide Bombers
Stigmata
Piltdown Man
Incest
LSD Blotters
Self-Dentistry
Frederika "Ma" Mandelbaum
Jerry Falwell
Traci Lords
Cardiff Giant
Dowsing
Jumbo
Ponzi Schemes
Chris Farley
Swastika
Snipes
Hello Kitty
Dana Plato
Neal Cassady
Ted Bundy
Jeffrey Dahmer
Unabomber
Jim Bakker
Jimmy Swaggart
Lord Haw-Haw
Augusto Pinochet
Hirohito
Mother Teresa
Linda Lovelace
Adolf Eichmann
Kim Il Sung
Mao
Oliver North
Mumia Abu-Jamal
Pornopolis
|
Rotten
|
Faces of Death
|
Famous Nudes


The parser was configured to reject floats but the parsed value is not an integer.
An expected argument is missing.
When parsing a number if a range constraint is provided the parsed number may be out of range.
Can't parse the value according to the given pattern. If a number was expected and the parsed found something that isn't a number it's considered a syntax error too.
When parsing a string and a set of allowed value is provided this error is reported if the parsed value is not in the specified set.
Generated using TypeDoc
When parsing arguments one of the following error may occur.


{{mostRecentGame.date | smartDate}}
{{mostRecentGame.winnerScore}} - {{mostRecentGame.loserScore}}
{{game.date | smartDate}}
{{game.winnerName | shortFullName}} won against {{game.loserName | shortFullName}}
| Weekly Standings | Games | Wins | Losses | Win Rate |
|---|---|---|---|---|
| {{playerStats.name | shortFullName}} | {{playerStats.gameCount}} | {{playerStats.wins}} | {{playerStats.losses}} | {{playerStats.winRate | winRate}} |
{{winStreak.streak}} {{winStreak.name | shortFullName}}
{{losingStreak.streak}} {{losingStreak.name | shortFullName}}
{{sweepingScore.winnerScore}} - {{sweepingScore.loserScore}}
{{sweepingScore.winnerName | shortFullName}} vs. {{sweepingScore.loserName | shortFullName}}
{{totalGames.gameCount}}


Windows 10 Audio Setup
Open the Windows settings:
Navigate to the System settings:
Open the "audio" tab:
Check the following settings:
- The correct output should be set (your speakers / headphones)
- The volume should be high enough
- The correct input has to be set (your microphone / headset)
- You can run a microphone test here.
After adjusting these settings, you should rejoin the meeting by reloading the page.


A customizable search bar element.
This search bar uses mwc-textfield for the input element. More information about styling and the input element itself can be found on the link below: https://github.com/material-components/material-components-web-components/tree/master/packages/textfield
Import this element to your project with npm i @exmg/exmg-searchbar
.
Then add the snippet below into your code.
<exmg-searchbar></exmg-searchbar>
ExmgSearchBar has it's own filtering methods in it which you can also override. To achieve default filtering, take the example of html code below:
<exmg-searchbar .data="${dataArray}" .filterKeys="${filterKeys}" suggestion-label-key="url"> </exmg-searchbar>
When you pass the data array into data
property along with filterKeys
, exmg-search bar automatically filters
data and shows suggestions.
filterKeys
property has to contain specific key names from the type of each item in data
.
For example; if you have [{username:"exmachina",name: "Ex Machina"},{username:"livery",name:"Livery"}]
as the data array,
you can pass ['username']
to filter out username
values of data. Or pass ['username', 'name']
to filter out values of both keys.
To determine which value of items passed into data
should be shown as the label of each suggestion, use suggestion-label-key
just like filterKeys
but the only difference is, it accepts a single key as a simple string, not an array.
By extending ExmgSearchBar
, you can override any of
three functions of your selection.
These functions are:
filter(data: any[], filterKeys: string[], query: string): ExmgSearchSuggestion[]: TemplateResult
renderSuggestions(suggestions: ExmgSearchSuggestion[])
renderSuggestionsLoading(): TemplateResult
filter
expects array of ExmgSearchSuggestion
objects. By implementing your own filtering method,
you might not need suggestion-label-key
since you can place any string value into text
property of ExmgSearchSuggestion
.
Please check ExmgSearchBar
class in order to see how these three functions are working. After that you can extend
ExmgSearchBar
class and override those functions to create your fancy filtering methods or suggestions.
If you are handling filtering logic manually on the parent, you can follow this way to
show suggestions manually.
To show suggestons, pass the suggestion data to suggestions
property of exmg-searchbar
.
It accepts array of ExmgSearchSuggestion
type of elements into suggestions.
Follow this document for available properties, events, methods and styling.
| Variable | Default | Description |
|---|---|---|
| --exmg-searchbar-error-color | #b00020 | Error color of search bar |
| --exmg-searchbar-hint-color | rgba(0, 0, 0, 0.6) | Hint text color of search bar |
| --exmg-searchbar-primary-color | #0071dc | Primary theme color of search bar |
| --exmg-searchbar-text-color | rgba(0, 0, 0, 0.87) | Text color of search bar |
| --exmg-searchbar-suggestions-spinner-color | #0071dc | Suggestions loading indicator color |
| --exmg-searchbar-suggestions-spinner-width | 3px | Suggestions loading indicator spinner width |
| --exmg-searchbar-suggestions-max-visible-suggestions | 5 | Max visible suggestions before showing scrollbar |
| --exmg-searchbar-suggestions-min-height | 40px | Suggestion item row height |
| --exmg-searchbar-suggestions-text-color | rgba(0, 0, 0, 0.6) | Suggestion item text color |
| --exmg-searchbar-suggestions-background-color | #ffffff | Suggestions list background color |
| --exmg-searchbar-suggestions-z-index | 1 | z-index of suggestions list |
| --exmg-searchbar-width | 100% | Width of search bar |
| Name | Type | Default | Description |
|---|---|---|---|
| filterKeys | string[] | undefined |
Set of which keys of data should be checked to filter data by default. |
| data | any[] | undefined |
The data in search bar to filter. |
| keepFocus | boolean | false |
If true, keeps focus on search bar after query-submit is fired |
| keepSuggestionsOnSelect | boolean | false |
Option to whether keep suggestions visible or not on suggestion selection |
| submitKeys | string[] | ['ENTER'] |
Determines which keys should trigger submitting search query |
| notifyOnQueryChange | boolean | true |
If true, dispatches query-change event with the current query on every change of search input. |
| searchQuery | string | '' |
Current query of search bar |
| suggestionLabelKey | string | undefined |
Defines which property of each data item should be placed into suggestions' labels. |
| submitOnKeyPress | boolean | true |
If true, dispatches query-submit event with the current query upon receiving key press event with specific keys passed to keys string array |
| suggestions | ExmgSearchSuggestion[] | [] |
List of suggestions to be passed into and displayed |
| suggestionsLoading | boolean | false |
If true and there are no suggestions passed to element, a loading indicator should be shownbar |
Fired on query change.
Payload: {value: string}
Fired on query submit.
Payload: {value: string}
Fired on suggestion selection.
This event is also fired when there is only one suggestion and user submits query.
Payload: {value: any, index: number}
Clears suggestions.
Hides the loading indicator.
Fires query-submit
event with passed query into search bar.
Sets query.
Sets suggestions
.
Shows the loading indicator if there are no suggestions available.
Generated using TypeDoc


| Year-1 | Year-2 |
|---|---|
| 19 | 92 |
I) We want to split in years,So we have using array methodyears=["1990","1991"]
II) Our target for create a table format
III) Ok, first one we have concept with for looping method..
IV) Next, declare the initial value of i=0;
we want to dynamic value so put into "i<years.length"
,after add the value for i++
V) So years[i] is the array[0] and ok,but this is a string value for["1990"].we want to split,because one new function in substring(). used in split numbers.finally added to years[i].substring(0,2),this is parameter.starting point-0,ending point-2.2 is maximum value.next we got a one part of value in 19. then one more added for years[i].substring(2,4).
VI)2 part of added for +""+
this concatenation method ...add to values.
VII)Create id="a" for tbody
and fetching table body for document.getElementById("a").
and innerHTML
is tbody inside datalist.
VIII) same process concatenation for table data.


Tasks related to logging workflow activity, both in the internal log as well as using the notification mechanisms for external tools, such as Amazon SNS.
Create an event and submit it using notifiers.
The event is created according to the Event
message protocol (see task_config.proto
) and sent to all configured notifiers. The message optionally contains information about this task, such as id
and workspace
(see the TaskEvent
message).
@param event
a string describing the event. This will be set on the required event
field of the Event
message.
@param notifiers
the names of notifier
sections in lb-workflow-driver.config
that configure notification mechanisms to deliver the event.
@param details
optional details to add to the corresponding message field.
@param add_task_info
if true, include a TaskEvent
field in the Event
message that identifies this task.
task lb.log.Notify(
event,
notifiers*,
details?,
add_task_info = true,
driver_meta?
) extends AsyncTask(
driver_meta = $driver_meta,
task_implementation_class = "com.logicblox.workflow.task.log.Notify"
)


| Package | Description |
|---|---|
| com.gargoylesoftware.htmlunit |
Framework classes (contains the
WebClient
class which is the main entry point). |
| com.gargoylesoftware.htmlunit.activex.javascript.msxml |
Implementations of the MSXML's (ActiveX) JavaScript host objects - users of HtmlUnit shouldn't
need anything in this package.
|
| com.gargoylesoftware.htmlunit.attachment |
Attachment-related classes.
|
| com.gargoylesoftware.htmlunit.css |
Classes supporting Cascading Style Sheets.
|
| com.gargoylesoftware.htmlunit.html |
Classes specific to HTML pages, particularly the
HtmlPage which represents
an HTML document and provides access to its content. |
| com.gargoylesoftware.htmlunit.httpclient |
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Humidex
问题描述 :
Adapted from Wikipedia, the free encyclopedia
The humidex is a measurement used by Canadian meteorologists to reflect the combined effect of heat and humidity. It differs from the heat index used in the United States in using dew point rather than relative humidity.
When the temperature is 30°C (86°F) and the dew point is 15°C (59°F), the humidex is 34 (note that humidex is a dimensionless number, but that the number indicates an approximate temperature in C). If the temperature remains 30°C and the dew point rises to 25°C (77°F), the humidex rises to 42.3.
The humidex tends to be higher than the U.S. heat index at equal temperature and relative humidity.
The current formula for determining the humidex was developed by J.M. Masterton and F.A. Richardson of Canada’s Atmospheric Environment Service in 1979.
According to the Meteorological Service of Canada, a humidex of at least 40 causes "great discomfort" and above 45 is "dangerous." When the humidex hits 54, heat stroke is imminent.
The record humidex in Canada occurred on June 20, 1953, when Windsor, Ontario hit 52.1. (The residents of Windsor would not have known this at the time, since the humidex had yet to be invented.) More recently, the humidex reached 50 on July 14, 1995 in both Windsor and Toronto.
The humidex formula is as follows:
humidex = temperature + h
h = (0.5555)× (e - 10.0)
e = 6.11 × exp [5417.7530 × ((1/273.16) - (1/(dewpoint+273.16)))]
where exp(x) is 2.718281828 raised to the exponent x.
While humidex is just a number, radio announcers often announce it as if it were the temperature, e.g. "It’s 47 degrees out there … [pause] .. with the humidex,". Sometimes weather reports give the temperature and dewpoint, or the temperature and humidex, but rarely do they report all three measurements. Write a program that, given any two of the measurements, will calculate the third.
You may assume that for all inputs, the temperature, dewpoint, and humidex are all between -100°C and 100°C.
输入:
Input will consist of a number of lines. Each line except the last will consist of four items separated by spaces: a letter, a number, a second letter, and a second number. Each letter specifies the meaning of the number that follows it, and will be either T, indicating temperature, D, indicating dewpoint, or H, indicating humidex. The last line of input will consist of the single letter E.
输出:
T number D number H number
where the three numbers are replaced with the temperature, dewpoint, and humidex. Each value should be expressed rounded to the nearest tenth of a degree, with exactly one digit after the decimal point. All temperatures are in degrees celsius.
样例输入:
T 30 D 15 T 30.0 D 25.0 E
样例输出:
T 30.0 D 15.0 H 34.0 T 30.0 D 25.0 H 42.3
解题代码:
import java.util.Scanner; public class Main { public static void main(String[] args) { Scanner scan = new Scanner(System.in); while (scan.hasNext()) { double temperature = 0, dewpoint = 0, humidex = 0; String[] ss = scan.nextLine().split(" "); String sa = ss[0]; if (sa.equals("E")) { break; } double a = Double.parseDouble(ss[1]); String sb = ss[2]; double b = Double.parseDouble(ss[3]); if (sa.equals("T") && sb.equals("D")) { temperature = a; dewpoint = b; double e = 6.11 * Math.pow(2.718281828, 5417.7530 * ((1 / 273.16) - (1 / (dewpoint + 273.16)))); double h = (0.5555) * (e - 10.0); humidex = temperature + h; } if (sa.equals("D") && sb.equals("T")) { temperature = b; dewpoint = a; double e = 6.11 * Math.pow(2.718281828, 5417.7530 * ((1 / 273.16) - (1 / (dewpoint + 273.16)))); double h = (0.5555) * (e - 10.0); humidex = temperature + h; } if (sa.equals("D") && sb.equals("H")) { dewpoint = a; humidex = b; double e = 6.11 * Math.pow(2.718281828, 5417.7530 * ((1 / 273.16) - (1 / (dewpoint + 273.16)))); double h = (0.5555) * (e - 10.0); temperature = humidex - h; } if (sa.equals("H") && sb.equals("D")) { dewpoint = b; humidex = a; double e = 6.11 * Math.pow(2.718281828, 5417.7530 * ((1 / 273.16) - (1 / (dewpoint + 273.16)))); double h = (0.5555) * (e - 10.0); temperature = humidex - h; } if (sa.equals("T") && sb.equals("H")) { temperature = a; humidex = b; double h = humidex - temperature; double e = h / 0.5555 + 10.0; dewpoint = 1 / ((1 / 273.16) - Math.log(e / 6.11) / 5417.7530) - 273.16; } if (sa.equals("H") && sb.equals("T")) { temperature = b; humidex = a; double h = humidex - temperature; double e = h / 0.5555 + 10.0; dewpoint = 1 / ((1 / 273.16) - Math.log(e / 6.11) / 5417.7530) - 273.16; } System.out.print("T "); System.out.printf("%.1f", temperature); System.out.print(" D "); System.out.printf("%.1f", dewpoint); System.out.print(" H "); System.out.printf("%.1f", humidex); System.out.println(); } } }
great!
正确
写的好····· Pollard Rho快速因数分解
不好意思，写错了．应该是 path[0]=0, visited[V] = true;
这配图…..
问题3中，GetRightPosition()和GetLeftPosition()与STL中的upper_bound()和lower_boune()的代码实现一样吗？
厉害，支持
终于明白了递归和dp的关系，多谢分享！
正是我要找的，适合新手
remove没有实现
第二个方法挺不错。NewHead代表新的头节点，通过递归找到最后一个节点之后，就把这个节点赋给NewHead，然后一直返回返回，中途这个值是没有变化的，一边返回一边把相应的指针方向颠倒，最后结束时返回新的头节点到主函数。
有点意思
即为打印出的组合的个数C(n,r)，假设print函数复杂度为O(1)
加了星号 (*) 表示跳过此数据不读入. 因为scanf是不读取本行回车的