KBDA Science & technologie

Friday, September 30, 2005

Spectre Electromagnetique

The electromagnetic spectrum is the range of all possible electromagnetic radiation. Also, the "electromagnetic spectrum" (usually just spectrum) of an object is the range of electromagnetic radiation that it emits, reflects, or transmits.




γ = Gamma rays


HX = Hard X-rays [3 EHz to 30 EHz]

X-rays are a form of ionizing radiation and as such can be dangerous.

SX = Soft X-Rays

EUV = Extreme ultraviolet

Being very energetic, UV can break chemical bonds, make molecules unusually reactive or ionize them, in general changing their mutual behavior. Sunburn, for example, is caused by the disruptive effects of UV radiation on skin cells, which can even cause skin cancer, if the radiation damages the complex DNA molecules in the cells (UV radiation is a proven mutagen).

NUV = Near ultraviolet Visible light [480 THz to 700 THz]


red ~ 625 to 740 nm ~ 480 to 405 THz
orange ~ 590 to 625 nm ~ 510 to 480 THz
yellow ~ 565 to 590 nm ~ 530 to 510 THz
green ~ 520 to 565 nm ~ 580 to 530 THz
cyan ~ 500 to 520 nm ~ 600 to 580 THz
blue ~ 430 to 500 nm ~ 700 to 600 THz
violet ~ 380 to 430 nm ~ 790 to 700 THz

NIR = Near infrared [120 to 400 THz] (2,500 to 750 nm).

Optical telecommunication in the near infrared is technically often separated to different frequency bands because of availability of light sources, transmitting /absorbing materials (fibers) and detectors.
O-band 1260–1360 nm
E-band 1360–1460 nm
S-band 1460–1530 nm
C-band 1530–1565 nm
L-band 1565–1625 nm
U-band 1625–1675 nm

MIR = Moderate infrared [30 to 120 THz] (10 to 2.5 μm)

Mid-infrared, from 30 to 120 THz (10 to 2.5 μm). Hot objects (black-body radiators) can radiate strongly in this range. It is absorbed by molecular vibrations, that is, when the different atoms in a molecule vibrate around their equilibrium positions. This range is sometimes called the fingerprint region since the mid-infrared absorption spectrum of a compound is very specific for that compound.

FIR = Far infrared [300 GHz to 30 THz]

Far-infrared, from 300 GHz (1 mm) to 30 THz (10 μm). The lower part of this range may also be called microwaves. This radiation is typically absorbed by so-called rotational modes in gas-phase molecules, by molecular motions in liquids, and by phonons in solids. The water in the Earth's atmosphere absorbs so strongly in this range that it renders the atmosphere effectively opaque. However, there are certain wavelength ranges ("windows") within the opaque range which allow partial transmission, and can be used for astronomy. The wavelength range from approximately 200 μm up to a few mm is often referred to as "sub-millimeter" in astronomy, reserving far infrared for wavelengths below 200 μm.


Microwave frequency bands
Designation
Frequency range
L band 1 to 2 GHz
S band 2 to 4 GHz
C band 4 to 8 GHz
X band 8 to 12 GHz
Ku band 12 to 18 GHz
K band 18 to 26 GHz
Ka band 26 to 40 GHz
Q band 30 to 50 GHz
U band 40 to 60 GHz
V band 50 to 75 GHz
E band 60 to 90 GHz
W band 75 to 110 GHz
F band 90 to 140 GHz
D band 110 to 170 GHz
The above table reflects Radio Society of Great Britain (RSGB) usage. The term P band is sometimes used for UHF frequencies below L-band. For other definitions see Letter Designations of Microwave Bands


EHF = Extremely high frequency (Microwaves) [30 GHz to 300 GHz]

Extremely high frequency is the highest radio frequency band. EHF runs the range of frequencies from 30 to 300 gigahertz, above which electromagnetic radiation is considered to be low (or far) infrared light. This band has a wavelength of one to ten millimetres, giving it the name millimeter band.
Radio signals in this band are extremely prone to atmospheric attenuation, making them of very little use over long distances. Even over relatively short distances, rain fade is a serious problem, caused when absorption by rain reduces signal strength.
This band is commonly used in radio astronomy.

SHF = Super high frequency (Microwaves) [3 GHz to 30 GHz]

5 GHz Les protocoles de transmission sans fil pour réseaux locaux tels que Wi-Fi, bluetooth, DECT emploient également des micro-ondes dans la bande de 2,4 gigahertz, bien que quelques variantes emploient une bande de 5 gigahertz pour la communication

UHF = Ultrahigh frequency (Microwaves) [ 300 MHz to 3GHz ]

UHF and VHF are the most common frequency bands for television. Modern mobile phones also transmit and receive within the UHF spectrum, and UHF is widely used for two-way radio communication (usually using narrowband frequency modulation, but digital services are on the rise) by both public service agencies and the general public. Though television broadcasting is common on UHF, there has traditionally been very little radio broadcasting in this band until fairly recently; see digital audio broadcasting for details.

Characteristics
The transmission of radio waves from one point to another is affected by many variables such as atmospheric moisture, the stream of particles from the sun called solar wind, and time of day.
All radio waves are somewhat absorbed by atmospheric moisture. This reduces, or attenuates, the strength of radio signals over long distances. However, this effect increases according to the frequency: UHF signals are generally more degraded by moisture than lower bands such as VHF.
As well, the layer of the Earth's atmosphere called the ionosphere is filled with charged particles that can reflect radio waves. This can be helpful in transmitting a radio signal, since the wave bounces from the sky to the ground over and over, convering long distances. However, UHF benefits less from this effect than lower (VHF, etc.) frequencies.
As the atmosphere warms and cools throughout the day, UHF transmissions may be enhanced by tropospheric ducting.

Advantages
The main advantage of UHF transmission is that its high frequency means it has a physically short wave. Since the size of transmission and reception equipment (particularly antennas) is related to the size of the wave, smaller, less conspicuous antennas can be used than with VHF or lower bands.

Frequency Allocation - United States
A brief summary of some UHF frequency usage:
300–420 MHz: government use, including meteorology
420–450 MHz: radiolocation and Amateur "70 cm" band
450–470 MHz: UHF business band, GMRS, and FRS 2-way "walkie-talkies"
470–512 MHz: TV channels 14–20, public safety
512–698 MHz: TV channels 21–51
698–806 MHz: TV channels 52–69 (to be auctioned for other uses once conversion to digital TV has been accomplished)
806–824 MHz: pocket pagers and Nextel SMR band
824–849 MHz: Cellular phones, A & B franchises, mobile phone (USA GSM network)
849–869 MHz: public safety 2-way (fire, police, ambulance)
869–894 MHz: cellular phones, A & B franchises, base station

900 MHz GSM network (rest of the world)
902–928 MHz: ISM band: cordless phones and stereo, RFID, datalinks, Amateur radio 33cm band
928–960 MHz: mixed Studio-Transmitter Links, mobile 2-way, other
1240–1300 MHz: Amateur radio
1850–1910 MHz: PCS mobile phone—note below and GSM (1800 MHz)
1930–1990 MHz: PCS base stations—note below
note: order is A, D, B, E, F, C blocks. A, B, C = 15 MHz; D, E, F = 5 MHz
2310–2360 MHz: Satellite radio (Sirius and XM)
2390–2450 MHz: Amateur radio, shared with below:
2400–2483.5 MHz: ISM, IEEE 802.11, 802.11b, 802.11g Wireless LAN
2400 MHz 802.11b and 802.11g standards use the unlicensed 2.4 gigahertz (GHz)

around 2450 MHz: Microwave oven

VHF = Very high frequency [30 MHz to 300 MHz]

Very high frequency (VHF) is the radio frequency range from 30 MHz (wavelength 10 m) to 300 MHz (wavelength 1 m).

United States
The general services in the VHF band are:
30–46 MHz: Licensed 2-way land mobile communication
30–88 MHz: Military VHF-FM, including SINCGARS
43–50 MHz: Cordless telephones, "49 MHz" FM walkie-talkies, and mixed 2-way mobile communication
50–54 MHz: Amateur radio "6-meter" band
54–72 MHz: TV channels 2, 3, and 4
72–76 MHz: Remote Control devices
76–88 MHz: TV channels 5 and 6
88–108 MHz: FM radio broadcasting (88–92 non-commercial, 92–108 commercial)
108–118 MHz: Air navigation beacons VOR
118–132 MHz: Airband for Air Traffic Control, AM, 121.5 MHz is emergency frequency
132–144 MHz: Auxiliary civil services,satellite, space research, and other miscellaneous services
144–148 MHz: Amateur band 2 Meters
148–174 MHz: "VHF Business Band," the new unlicensed Multi-Use Radio Service (MURS), and other 2-way land mobile, FM
156–174 MHz VHF Marine Radio; narrow band FM, 156.8 MHz (Channel 16) is the maritime emergency and contact frequency
162.40–162.55: NOAA Weather Stations, FM
174–216 MHz: TV channels 7 through 13, and professional wireless microphones (low power, certain exact frequencies only)
216–222 MHz: mixed services
222–225 MHz: Amateur "1-1/4-meter" band
above 225 MHz: Federal services, notably military aircraft radio (225–400 MHz) AM, including HAVE QUICK

HF = High frequency [3 MHz to 30 Mhz]

High frequency (HF) radio frequencies are between 3 and 30 MHz. This range is often called shortwave.
Since the ionosphere often reflects HF radio waves quite well, this range is extensively used for medium and long range terrestrial radio communication. However, suitability of this portion of the spectrum for such communication varies greatly with a complex combination of factors:
Sunlight/darkness at site of transmission and reception
Transmitter/receiver proximity to terminator

MF = Medium frequency [300 kHz to 3 MHz]

Longwave radio frequencies are those below 500 kHz, which correspond to wavelengths longer than 600 meters. They have the property of following the curvature of the earth, making them ideal for continuous, continental communications. Unlike shortwave radio, longwave signals do not reflect or refract using the ionosphere, so there are fewer phase-caused fadeouts. Instead, the D-layer of the ionosphere and the surface of the earth serve as a waveguide directing the signal.

LF = Low frequency [30 kHz to 300 kHz]

Low Frequency or LF (sometimes called longwave) refers to Radio Frequencies (RF) in the range of 30–300 kHz. In Europe, part of the LF spectrum is used for AM broadcast service. In the western hemisphere, its main use is for aircraft beacon, navigation (LORAN), information, and weather systems. Time signal stations MSF, DCF77, JJY and WWVB are found in this band.

1.- AM radio is broadcast in on several frequency bands:
Long wave is 153–279 kHz
Medium wave is 530–1,710 kHz.
Short wave is 2,300–26,100 kHz, divided into 15 broadcast bands

Medium wave and short wave radio signals act differently during daytime and nighttime. During the day, AM signals travel by groundwave, refracting around the curve of the earth over a distance up to a few hundred kilometres (or miles) from the signal transmitter. However, after sunset, changes in the ionosphere cause AM signals to travel by skywave, enabling AM radio stations to be heard much farther from their point of origin than is normal during the day.

2.- LORAN (LOng RAnge Navigation) is a terrestrial navigation system using low frequency radio transmitters that use the time interval between radio signals received from two or more stations to determine the position of a ship or aircraft. Before the popularity of the satellite-based GPS system, it was primarily used in marine applications. The current version of LORAN in common use is LORAN-C, which operates in the low frequency 90 to 110 kHz band.

VLF = Very low frequency [3 kHz to 30 kHz]

Very low frequency or VLF refers to radio frequencies (RF) in the range of 3 to 30 kHz. Since there is not much bandwidth in this band of the radio spectrum, only the very simplest signals are used, such as for radionavigation. Because VLF waves can penetrate water only to a depth of roughly 10 to 40 metres (30 to 130 feet), depending on the frequency and the salinity of the water, they are used to communicate with submarines near the surface. (ELF is used for fully submerged vessels.)

VF = Voice frequency or ULF Ultra low Frequency [300 Hz to 3400 Hz]
A voice frequency (VF) or voice band is one of the frequencies, within part of the audio range, that is used for the transmission of speech.
In telephony, the usable voice frequency band ranges from approximately 300 Hz to 3400 Hz. The bandwidth allocated for a single voice-frequency transmission channel is usually 4 kHz, including guard bands, allowing a sample rate of 8 kHz to be used as the basis of the pulse code modulation system used for the digital PSTN

SLF Super Low Frequency [30 Hz to 300Hz]

Super Low Frequency (SLF) is the frequency range between 30 hertz and 300 hertz. This frequency range includes the frequencies of AC power grids (50 hertz and 60 hertz).

ELF = Extremely low frequency [3 to 300 Hz]
ELF was used by the US Navy to communicate with submerged submarines. Because of the electrical conductivity of salt water, submarines are shielded from most electromagnetic communications

Reference

[1] http://en.wikipedia.org/wiki/Very_low_frequency

Code Barre



Code Barre Lineaire:

Il existe une variete importante de standart de code barre.



Code Barre bidimensionel : Datamatrix




Datamatrix (or Data Matrix) is a two-dimensional matrix barcode consisting of black and white square modules arranged in either a square or rectangular pattern. The information to be encoded can be text or raw data. Usual data size is from a few bytes up to 2 kilobytes. The length of the encoded data depends on the symbol dimension is used. Error correction codes are added to increase symbol strength: even if they are partially damaged, they can still be read. A Datamatrix symbol can store upto 2,335 alphanumeric characters.

Universal Product Code (UPC)

The UPC (Universal Product Code) was the original barcode widely used in the United States and Canada for items in stores. The first item to be placed under a UPC scanner in a retail store was a 10-pack of Wrigley's Juicy Fruit chewing gum at Marsh's supermarket in Troy, Ohio, on June 24, 1974.
In the UPC-A barcode, each digit is represented by a seven-bit sequence, encoded by a series of alternating bars and spaces. Guard bars, shown in green, separate the two groups of six digits.The UPC (now officially EAN.UCC-12) encodes twelve digits as



SLLLLLLMRRRRRRE


  • where S (start) and E (end) are the bit pattern 101,

  • M (middle) is the bit pattern 01010 (called guard bars),

  • and each L (left) and R (right) are digits, seven bits long each.


This is a total of 95 bits. The bit pattern for each numeral is designed to be as little like the others as possible, and to have no more than four 1s or 0s in order. Both are for reliability in scanning. [2]

Reference:

[1] http://en.wikipedia.org/wiki/Datamatrix
[2] http://en.wikipedia.org/wiki/Universal_Product_Code
[3]

Saturday, September 24, 2005

GPS - (Garmin)

GPS: GLOBAL POSITIONING SYSTEM

Le système GPS comprend au moins 24 satellites artificiels orbitant à 20 200 km d'altitude. Ces satellites émettent en permanence un signal d'heure précis (grâce à leur horloge atomique), ainsi que leurs coordonnées exactes.
Ainsi un récepteur GPS qui capte les signaux d'au moins quatre satellites peut, en mesurant les écarts relatifs des horloges, connaître son éloignement par rapport aux quatre satellites et, par triangulation, situer précisément en trois dimensions n'importe quel point placé en dessous des satellites GPS (avec une précision de 15 à 100 mètres pour le système standard). Le GPS est ainsi utilisé pour localiser des véhicules roulants, des navires, des avions, des missiles et même des satellites évoluant en orbite basse.
Concernant la précision, le GPS étant un système développé pour les militaires américains, une disponibilité sélective (selective availability) a été prévue. Certaines informations peuvent ainsi être cryptées et priver les personnes qui ne disposent pas des codes de la précision maximale. Pendant de nombreuses années, les civils n'avaient accès qu'à une précision faible (environ 100m). Le 1er mai 2000, le président Bill Clinton a annoncé qu'il mettait fin à cette dégradation volontaire du service. Depuis, il est courant d'avoir une position précise à 20 mètres ou moins.
Certains systèmes GPS conçus pour des usages très particuliers peuvent fournir une localisation à quelques millimètres près. Le GPS différenciel (DGPS), corrige ainsi la position obtenue par GPS conventionnel par les données envoyées par une station terrestre de référence localisée très précisément. D'autres systèmes autonomes, affinant leur localisation au cours de 8 heures d'exposition parviennent à des résultats équivalents.
Il est à noter que dans certains cas, seuls 3 satellites peuvent suffire. La localisation en altitude (axe des Z) n'est pas correcte alors que la longitude et la latitude (axe des X et des Y) sont encore bonnes. On peut donc se contenter de trois satellites lorsque l'on évolue au-dessus d'une surface « plane » (océan, mer). Ce type d'exception est surtout utile au positionnement d'engins volants (avions, etc.) qui ne peuvent de toute façon pas se reposer sur le seul GPS, trop imprécis pour leur donner leur altitude. [2]

Several frequencies make up the GPS electromagnetic spectrum:
L1 (1575.42MHz):Carries a publicly usable coarse-acquisition (C/A) code as well as an encrypted precision P(Y) code.
L2 (1227.60MHz):Usually carries only the P(Y) code. The encryption keys required to directly use the P(Y) code are tightly controlled by the U.S. government and are generally provided only for military use. The keys are changed on a daily basis. In spite of not having the P(Y) code encryption key, several high-end GPS receiver manufacturers have developed techniques for utilizing this signal (in a round-about manner) to increase accuracy and remove error caused by the ionosphere.
L3 (1381.05MHz):Carries the signal for the GPS constellation's alternative role of detecting missile/rocket launches (supplementing Defense Support Program satellites), nuclear detonations, and other high-energy infrared events.
L4 (1841.40MHz):Being studied for additional ionospheric correction.
L5 (1176.45MHz):Proposed for use as a civilian safety-of-life signal.



Reference
[1] http://www.gpsworld.com/gpsworld/
[2] http://fr.wikipedia.org/wiki/Global_positioning_system
[3] http://en.wikipedia.org/wiki/Global_Positioning_System

GPX
GPX (the GPS Exchange Format) is a light-weight XML data format for the interchange of GPS data (waypoints, routes, and tracks) between applications and Web services on the Internet.

Reference
[1] http://www.topografix.com/gpx.asp


GARMIN TECHNOLOGY


Reference:
[1] http://www.garmin.com/

Friday, September 23, 2005

le savon - pourquoi ca netoye

Propriétés
Le savon est un tensioactif. Les propriétés détergentes des molécules de carboxylates R-CO2-Na sont dues à leur amphiphilie : elles se présentent sous la forme d'une longue chaîne dont
  • une extrémité, polarisée négativement, est hydrophile
  • tandis que l'autre extrémité est lipophile.
Cette dernière se fixe donc facilement sur les graisses, l'autre restant en contact avec l'eau de rinçage.

Le savon et la peau
Lors de la toilette, le savon dissout la graisse constituant le film hydrolipidique qui recouvre la peau. La graisse est entraînée dans l'eau avec les saletés qu'elle contient. L'inconvénient est que le film hydrolipidique sert à protéger la peau et à retenir son eau. Le savonnage — ou tout lavage à l'aide de produits comportant des tensio-actifs, par exemple les gels pour la douche ou les lessives — fragilise donc la peau, jusqu'à ce que le film hydrolipidique se reconstitue, au bout de plusieurs heures.
Le savon est basique. Son pH est proche de 10. Lors de la toilette, il perturbe l'acidité de la peau (dont le pH est proche de 5).

Dans une eau dure, les molécules du savon réagissent avec les ions calcium et forment des dépôts de sels de calcium. De plus, on a besoin d'une plus grande quantité de savon pour nettoyer. Pour éviter ces inconvénients, on ajoute aujourd'hui aux savons des agents anticalcaire comme l'EDTA.


Reference
[1] http://fr.wikipedia.org/wiki/Savon