OpenLLM-France/wikimedia huggingface dataset:
# Communication Systems/Fading Channels

Over large distances, signal quality degrades even without the presence of large quantities of AWGN. This degradation is known as fading, and channels that exhibit these properties are known as fading channels.

## What Causes Fading

Fading can be caused due to natural weather disturbances, such as rainfall, snow, fog, hail and extremely cold air over a warm earth. Fading can also be created by man made disturbances, such as irrigation, or from multiple transmission paths, irregular earth surfaces, and varying terrains.

## Scales of Fading
### Large-Scale Fading

Fading generally is a signal loss either in amplitude or phase due to sudden changes in Channel response. Large scale fading " Shadowing" concerns about large distances effect so, its affect appears clearly in case of the a moving vehicle where the signal is influenced by Multipath phenomena where the transmitted signal is received from more than one path.

### Small-Scale Fading

Small scale fading is concerned about very small changes in the position of Transmitter or receiver in order of the wavelength as this affect greatly the received frequency due to doppler effect so as the speed of the vehicle increases as the frequency is more rapidly changing and it can be described as fast or slow fading AND flat or slow fading.

## Small-Scale Fading Types
### Flat Fading

In flat fading, the coherence bandwidth of the channel is larger than the bandwidth of the signal. Therefore, all frequency components of the signal will experience the same magnitude of fading. a signal undergoes flat fading if:

### Fast Fading

Fast fading occurs when coherent time of the channel is small relative to the delay constraint of the channel. Amplitude and phase changes imposed by the channel varies considerably over period of use.
# Communication Systems/Envelope Filters
## What is an Envelope Filter?

The envelope detector is a simple analog circuit that can be used to find the peaks in a quickly-changing waveform. Envelope detectors are used in a variety of devices, specifically because passing a sinusoid through an envelope detector will suppress the sinusoid.

## Circuit Diagram

In essence, an envelope filter has the following diagram:
Where (c) represents a capacitor, and R is a resistor. Under zero input voltage (vin = 0), the capacitor carries no charge, and the resistor carries no current. When vin is increased, the capacitor stores charge until it reaches capacity, and then the capacitor becomes an open circuit. At this point, all current in the circuit is flowing through the resistor, R. As voltage decreases, the capacitor begins to discharge it's stored energy, slowing down the state change in the circuit from high voltage to low voltage.

## Positive Voltages

By inserting a diode at the beginning of this circuit, we can negate the effect of a sinusoid, dipping into negative voltage, and forcing the capacitor to discharge faster:

## Purpose of Envelope Filters

Envelope filters help to find the outer bound of a signal that is changing in amplitude.
# Building and Flying Model Gliders and Rubber-powered Planes

This Wikibook will describe how to model gliders and rubber powered planes.
Contents
Introduction
Model gliders made out of paper and rubber powered planes fascinating toys. This book will describe how to build and fly these.
Part 1: Gliders from Paper
The first step is to build a simple paper glider such as the one shown. Cut the tabs at the back of the wing as shown in the diagram. These will be used to trim the paper plane, that is to adjust the wings so that the plane will fly level.
Why won't the paper plane fly straight without any adjustments? Just like its real life counterparts, the model plane may have inaccuracies in its construction- we call this the air frame, and will need to be trimmed, that is, adjusted in flight to make it fly correctly. For most single engined propeller planes, however, adjustments need to be made to counteract the effect of the slipstream from the propeller, different forces being felt at different speeds and power settings, as well as adjusting the plane so that it does not climb or dive.
Launch the paper plane holding it level. In the case of my paper plane...
Part 2 : Model Aircraft building
Durability issues
Engineering for impact resistance
Part 3 : Rubber Powered Free Flight Models
Rubber powered planes intro
Sheet balsa models
Alternatives to sheet Balsa
Built Up Balsa models
# Building a Beowulf Cluster/Profiling and Benchmarking/Temperature control

How to check the CPU temperature?
(you might have different THRM directories for your cores)
If this doesn't work or you want more information, install sensors (in fedora: yum install sensors). You install it by sensors-detect and sensors then prints you information.
# Building a House of Cards

This guide is about building a house of cards. It can be difficult, but persevere and you can do it!
The house of cards relies on nothing more than balance to stay upright. There's no glue, and no damage or alterations are made to the cards themselves. The larger your house, the more likely it is to fall.

## Construction

One of the most familiar form of a house of cards involves the creation of a triangular pyramid-style structure formed from a series of identical smaller structures that each emulate an inverted letter V.
1.) First, lean two cards against each other to form an A-frame, with the short ends resting upon a flat and stable surface:
2.) Next, place two more cards in a similar fashion immediately adjacent to the existing structure:
3.) Then bridge the space between the two structures with an additional card to form a level platform:
4.) On the developed platform, place two more cards (as described in step 1) completing the pyramid:
5.) This entire process can be repeated, each additional structure placed on the lowest level allowing for an increase in the overall height of the house of cards. The example above is two structures wide and two structures high, but with the addition of another eight cards it would become three structures wide and three structures high:

## World Records

A prominent house of cards builder is Bryan Berg. Berg broke the former world record in 1992 for "The Tallest House of Cards" with a tower that stood fourteen feet, six inches tall!
Another tower was built by Berg at the Department of Architecture at Iowa State University in 1998. It stood at approximately 25 feet tall and utilized over 1500 decks of standard playing cards that weighed over 250 pounds. It took two and a half weeks to build, with construction taking place in shifts that lasted anywhere from four to twelve hours each day. During construction, the tower was surrounded by scaffolding, which also formed the means of reaching the top of the tower to place additional cards.
On November 6 1999, Berg built an even taller tower in the lobby of the casino at Potsdamer Platz, Berlin. This time it stood at approximately 25.29 feet tall and utilized over 1700 decks to stack up to 131 stories high!
When he was asked whether it would be possible to build even taller (reaching for instance, about 100 feet), Berg just responded with a simple: "You bet!". Why don't you give it a go?

## See Also

* Bryan Berg's official webpage
* Image of one of Berg's record attempts
# Building the Root 2 CNC Multitool Router/Frequently Asked Questions
### What is the working area of this machine?

* 331x305x120mm (X,Y,Z)

### What Firmware or Software do you run on the Arduino Mega?

* Marlin the 3D printer firmware is a good choice. It has a strong community and most questions have been asked regarding it.
# Building the Root 2 CNC Multitool Router/Printing
## How Much Plastic

2x 1kg spools seem to be about the right amount of plastic. That that said if you are not already a 3D printer expert expect to see some failed prints that will need reprinted.

## ABS or PLA

ABS will have a strength advantage and provides the option to spray on acetone to perhaps help bond the layers together better.

## Settings
### Resolution

0.25-0.35

### Infill

50%

## Notes

* Print with 3-4 perimeters
* Print with ABS but PLA will be fine though your mileage may vary
# Built-In Rails Tools/Make a generator

rails generate model Person name:string age:integer
# C Sharp Programming/Keywords/null

The null keyword represents an empty value for a reference type variable, i.e. for a variable of any type derived from System.Object. In C# 2.0, null also represents the empty value for nullable value type variables.
C# Keywords :
| abstract | as | base | bool | break |
| byte | case | catch | char | checked |
| class | const | continue | decimal | default |
| delegate | do | double | else | enum |
| event | explicit | extern | false | finally |
| fixed | float | for | foreach | goto |
| if | implicit | in | int | interface |
| internal | is | lock | long | namespace |
| new | null | object | operator | out |
| override | params | private | protected | public |
| readonly | ref | return | sbyte | sealed |
| short | sizeof | stackalloc | static | string |
| struct | switch | this | throw | true |
| try | typeof | uint | ulong | unchecked |
| unsafe | ushort | using | var | virtual |
| void | volatile | while |
Special C# Identifiers (Contextual Keywords) :
| add | alias | async | await | dynamic |
| get | global | nameof | partial | remove |
| set | value | when | where | yield |
Contextual Keywords (Used in Queries) :
| ascending | by | descending | equals | from |
| group | in | into | join | let |
| on | orderby | select | where |
# C Sharp Programming/Keywords/new

The new keyword has two different meanings:
* It is an operator that requests a new instance of the class identified by its argument.
* It is a modifier that explicitly hides a member.
As an example, see the code below:
C# Keywords :
| abstract | as | base | bool | break |
| byte | case | catch | char | checked |
| class | const | continue | decimal | default |
| delegate | do | double | else | enum |
| event | explicit | extern | false | finally |
| fixed | float | for | foreach | goto |
| if | implicit | in | int | interface |
| internal | is | lock | long | namespace |
| new | null | object | operator | out |
| override | params | private | protected | public |
| readonly | ref | return | sbyte | sealed |
| short | sizeof | stackalloc | static | string |
| struct | switch | this | throw | true |
| try | typeof | uint | ulong | unchecked |
| unsafe | ushort | using | var | virtual |
| void | volatile | while |
Special C# Identifiers (Contextual Keywords) :
| add | alias | async | await | dynamic |
| get | global | nameof | partial | remove |
| set | value | when | where | yield |
Contextual Keywords (Used in Queries) :
| ascending | by | descending | equals | from |
| group | in | into | join | let |
| on | orderby | select | where |
# C Sharp Programming/Keywords/out

The out keyword explicitly specifies that a variable should be passed by reference to a method, and set in that method. A variable using this keyword must not be intialized before the method call to ensure the developer understand its intended effects. Using this keyword requires the called method to set the variable using this modifier before returning. Using out also requires the developer to specify the keyword even in the calling code, to ensure that it is easily visible to developers reading the code that the variable will have its value changed elsewhere, which is useful when analyzing the program flow.
An example of passing a variable with out follows:
C# Keywords :
| abstract | as | base | bool | break |
| byte | case | catch | char | checked |
| class | const | continue | decimal | default |
| delegate | do | double | else | enum |
| event | explicit | extern | false | finally |
| fixed | float | for | foreach | goto |
| if | implicit | in | int | interface |
| internal | is | lock | long | namespace |
| new | null | object | operator | out |
| override | params | private | protected | public |
| readonly | ref | return | sbyte | sealed |
| short | sizeof | stackalloc | static | string |
| struct | switch | this | throw | true |
| try | typeof | uint | ulong | unchecked |
| unsafe | ushort | using | var | virtual |
| void | volatile | while |
Special C# Identifiers (Contextual Keywords) :
| add | alias | async | await | dynamic |
| get | global | nameof | partial | remove |
| set | value | when | where | yield |
Contextual Keywords (Used in Queries) :
| ascending | by | descending | equals | from |
| group | in | into | join | let |
| on | orderby | select | where |
# C Sharp Programming/Keywords/override

The keyword override is use in declaring an overridden function, which extends a base class function of the same name.

## Further reading

C# Keywords :
| abstract | as | base | bool | break |
| byte | case | catch | char | checked |
| class | const | continue | decimal | default |
| delegate | do | double | else | enum |
| event | explicit | extern | false | finally |
| fixed | float | for | foreach | goto |
| if | implicit | in | int | interface |
| internal | is | lock | long | namespace |
| new | null | object | operator | out |
| override | params | private | protected | public |
| readonly | ref | return | sbyte | sealed |
| short | sizeof | stackalloc | static | string |
| struct | switch | this | throw | true |
| try | typeof | uint | ulong | unchecked |
| unsafe | ushort | using | var | virtual |
| void | volatile | while |
Special C# Identifiers (Contextual Keywords) :
| add | alias | async | await | dynamic |
| get | global | nameof | partial | remove |
| set | value | when | where | yield |
Contextual Keywords (Used in Queries) :
| ascending | by | descending | equals | from |
| group | in | into | join | let |
| on | orderby | select | where |
# C Sharp Programming/Keywords/params

The keyword params is used to describe when a grouping of parameters are passed to a method, but the number of parameters are not important, as they may vary. Since the number isn't important, the params keyword must be the last variable in a method signature so that the compiler can deal with the parameters which have been defined first, before dealing with the params.
Here are examples of where it will, and will not work:
A good example of this is the String.Format method. The String.Format method allows a user to pass in a string formatted to their requirements, and then many parameters for the values to insert into the string. Here is an example:
The String.Format method has taken a string, and replaced the {0}, {1}, {2} with the 1st, 2nd and 3rd parameters. If the params keyword did not exist, then the String.Format would need an infinite number of overloads to cater for each case.
C# Keywords :
| abstract | as | base | bool | break |
| byte | case | catch | char | checked |
| class | const | continue | decimal | default |
| delegate | do | double | else | enum |
| event | explicit | extern | false | finally |
| fixed | float | for | foreach | goto |
| if | implicit | in | int | interface |
| internal | is | lock | long | namespace |
| new | null | object | operator | out |
| override | params | private | protected | public |
| readonly | ref | return | sbyte | sealed |
| short | sizeof | stackalloc | static | string |
| struct | switch | this | throw | true |
| try | typeof | uint | ulong | unchecked |
| unsafe | ushort | using | var | virtual |
| void | volatile | while |
Special C# Identifiers (Contextual Keywords) :
| add | alias | async | await | dynamic |
| get | global | nameof | partial | remove |
| set | value | when | where | yield |
Contextual Keywords (Used in Queries) :
| ascending | by | descending | equals | from |
| group | in | into | join | let |
| on | orderby | select | where |
# C Sharp Programming/Keywords/object

The object keyword is used in field, method, property, and variable declarations and in cast and typeof operations as an alias for the .NET Framework structure System.Object. That is, it represents the base class from which all other reference types derive. On some platforms, the size of the reference is 32 bits, while on other platforms it is 64 bits.
C# Keywords :
| abstract | as | base | bool | break |
| byte | case | catch | char | checked |
| class | const | continue | decimal | default |
| delegate | do | double | else | enum |
| event | explicit | extern | false | finally |
| fixed | float | for | foreach | goto |
| if | implicit | in | int | interface |
| internal | is | lock | long | namespace |
| new | null | object | operator | out |
| override | params | private | protected | public |
| readonly | ref | return | sbyte | sealed |
| short | sizeof | stackalloc | static | string |
| struct | switch | this | throw | true |
| try | typeof | uint | ulong | unchecked |
| unsafe | ushort | using | var | virtual |
| void | volatile | while |
Special C# Identifiers (Contextual Keywords) :
| add | alias | async | await | dynamic |
| get | global | nameof | partial | remove |
| set | value | when | where | yield |
Contextual Keywords (Used in Queries) :
| ascending | by | descending | equals | from |
| group | in | into | join | let |
| on | orderby | select | where |
# C Sharp Programming/Keywords/orderby

The orderby contextual keyword is used to define the sort order of query results. Specifying orderby key1 ascending sorts from the smallest first to the largest at the end, while orderby key2 descending sorts from the largest first to the smallest at the end. The default sort order is ascending and if neither direction is specified, results will be sorted in ascending order. Multiple keys may be used to sort, with the first one specified being the primary sort and later entries providing secondary sorts when the first key matches, e.g., orderby lastName ascending, firstname ascending.
C# Keywords :
| abstract | as | base | bool | break |
| byte | case | catch | char | checked |
| class | const | continue | decimal | default |
| delegate | do | double | else | enum |
| event | explicit | extern | false | finally |
| fixed | float | for | foreach | goto |
| if | implicit | in | int | interface |
| internal | is | lock | long | namespace |
| new | null | object | operator | out |
| override | params | private | protected | public |
| readonly | ref | return | sbyte | sealed |
| short | sizeof | stackalloc | static | string |
| struct | switch | this | throw | true |
| try | typeof | uint | ulong | unchecked |
| unsafe | ushort | using | var | virtual |
| void | volatile | while |
Special C# Identifiers (Contextual Keywords) :
| add | alias | async | await | dynamic |
| get | global | nameof | partial | remove |
| set | value | when | where | yield |
Contextual Keywords (Used in Queries) :
| ascending | by | descending | equals | from |
| group | in | into | join | let |
| on | orderby | select | where |
# C Sharp Programming/Keywords/on

The join, in, on, equals, and sometimes into contextual keywords are used to relate items in two different data sources by a common attribute in a query. Specifically, the 'on this equals that' portion is used to identify the key from one data source that will be matched to the key in another data source.
C# Keywords :
| abstract | as | base | bool | break |
| byte | case | catch | char | checked |
| class | const | continue | decimal | default |
| delegate | do | double | else | enum |
| event | explicit | extern | false | finally |
| fixed | float | for | foreach | goto |
| if | implicit | in | int | interface |
| internal | is | lock | long | namespace |
| new | null | object | operator | out |
| override | params | private | protected | public |
| readonly | ref | return | sbyte | sealed |
| short | sizeof | stackalloc | static | string |
| struct | switch | this | throw | true |
| try | typeof | uint | ulong | unchecked |
| unsafe | ushort | using | var | virtual |
| void | volatile | while |
Special C# Identifiers (Contextual Keywords) :
| add | alias | async | await | dynamic |
| get | global | nameof | partial | remove |
| set | value | when | where | yield |
Contextual Keywords (Used in Queries) :
| ascending | by | descending | equals | from |
| group | in | into | join | let |
| on | orderby | select | where |
# C Sharp Programming/Keywords/operator

The operator keyword allows a class to overload arithmetic and cast operators:
C# Keywords :
| abstract | as | base | bool | break |
| byte | case | catch | char | checked |
| class | const | continue | decimal | default |
| delegate | do | double | else | enum |
| event | explicit | extern | false | finally |
| fixed | float | for | foreach | goto |
| if | implicit | in | int | interface |
| internal | is | lock | long | namespace |
| new | null | object | operator | out |
| override | params | private | protected | public |
| readonly | ref | return | sbyte | sealed |
| short | sizeof | stackalloc | static | string |
| struct | switch | this | throw | true |
| try | typeof | uint | ulong | unchecked |
| unsafe | ushort | using | var | virtual |
| void | volatile | while |
Special C# Identifiers (Contextual Keywords) :
| add | alias | async | await | dynamic |
| get | global | nameof | partial | remove |
| set | value | when | where | yield |
Contextual Keywords (Used in Queries) :
| ascending | by | descending | equals | from |
| group | in | into | join | let |
| on | orderby | select | where |
# C Sharp Programming/Keywords/partial

The special identifier partial is used to allow developers to build classes from different files and have the compiler generate one class, combining all the partial classes. This is mostly useful for separating classes into separate blocks. For example, Visual Studio 2005 separates the UI code for forms into a separate partial class that allows you to work on the business logic separately.
C# Keywords :
| abstract | as | base | bool | break |
| byte | case | catch | char | checked |
| class | const | continue | decimal | default |
| delegate | do | double | else | enum |
| event | explicit | extern | false | finally |
| fixed | float | for | foreach | goto |
| if | implicit | in | int | interface |
| internal | is | lock | long | namespace |
| new | null | object | operator | out |
| override | params | private | protected | public |
| readonly | ref | return | sbyte | sealed |
| short | sizeof | stackalloc | static | string |
| struct | switch | this | throw | true |
| try | typeof | uint | ulong | unchecked |
| unsafe | ushort | using | var | virtual |
| void | volatile | while |
Special C# Identifiers (Contextual Keywords) :
| add | alias | async | await | dynamic |
| get | global | nameof | partial | remove |
| set | value | when | where | yield |
Contextual Keywords (Used in Queries) :
| ascending | by | descending | equals | from |
| group | in | into | join | let |
| on | orderby | select | where |
# Cryptography/SHA-2

SHA-2 was designed and developed by the National Security Agency (NSA) and is today one of the hash algorithms where still no collisions have been found. SHA-2 was created because of the weakness of SHA-1 where a simple step was missing. SHA-2 takes the last bitgroup and after some bit operations the group will be placed at the beginning. It has been shown that this step makes SHA-2 very robust against attacks. SHA-2 can be used with different bit length: SHA-256, SHA-384 and SHA-512.