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1 – Notions d’alphabets, mots & langages

\chapter{Langages et automates} \section{Alphabets, Mots et Langages} \section{Notion pr\'{e}liminaires} \subsection{D\'{e}finitions et notations} \begin{definition} Un alphabet est un ensemble fini quelconque non vide. Les \'{e}l\'{e}ments d'un alphabet sont appel\'{e}s des \textbf{lettres }ou\textbf{\ Symbols}. \end{definition} \begin{notation} Un alphabet sera not\'{e} en g\'{e}n\'{e}ral par la lettre grec $\ \sum $ \end{notation} \begin{definition} Un mot est une suite finie de lettres \end{definition} \begin{example} $\sum =\{a,b,c,\ldots ,z\}$ est un alphabet , $a,b,c,$ \ldots\ sont des lettres, \textbf{math,cpr, oujda},\ldots\ sont des mots \end{example} \begin{notation} L'ensemble des mots sur $\sum $ \ sera not\'{e} $\sum^{\ast }$ \end{notation} \begin{example} $\sum =\{0,1,2,...\}=% %TCIMACRO{\U{2115} }% %BeginExpansion \mathbb{N} %EndExpansion $ \ est un alphabet , $484,275,107,...$ \ sont des mots \end{example} \begin{notation} Le mot qui ne contient aucune lettre est appel\'{e} le mot vide not\'{e} $% \Lambda $ \end{notation} \begin{remark} On s'interesse seulement \`{a} la forme d'un mot qui peut \^{e}tre qq et on omet le sens du mot exemple : avhbrtys, jorbqhegd,... sont des mots. \end{remark} \begin{definition} La longueur d'un mot $x$ not\'{e} $|x|$ est le nombre de symbols qui le compose exemple si $x=arbre$ alors $|x|=5$ \end{definition} \begin{notation} Soit $x$ un mot de $\sum^{\ast }$ et $\sigma $ une lettre de $\sum $ le nombre d'apparition de \ $\sigma $\ dans $x$\ est not\'{e} $|x|_{\sigma }$ \end{notation} \begin{example} $|arbre|_{r}=2,$ \ $|arbre|_{a}=1$ ,\ $|abbcb|_{b}=3$ \end{example}

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iPod is a digital mp3 / mp4 player developed and marketed by Apple Inc., an American consumer electronics multinational corporation. During their research, Apple found that in comparison to available camcorders, digital cameras, and organizers; digital music players recorded poor sales, primarily due to their awful user interfaces. Apple wanted to do something about it and so Jon Rubinstein, Apple’s hardware engineering chief brought together a team comprising of Tony Fadell (who dreamed of a hard disk based music player), Michael Dhuey (hardware engineer), Jonathan Ive (design engineer), and Stan Ng (marketing manager). In less than a year, they designed a hard disk based music player, that had a 5 GB hard drive and capable of storing 1000 songs.

Apple’s iTunes software is utilized to operate the iPod (m3 / mp4 player). The software is compatible with all Mac systems. The operating system is stored on its hard disk. A boot loader program is contained in a NOR flash ROM chip (either 1 MB or 512 KB) which instructs the device to load the operating system from the hard disk. The iPod has a 32 MB of RAM, a portion of which is used to hold the operating system from firmware, and the rest is used to cache songs from the hard disk. Apple also invented a technology whereby the hard disk of iPod could spin up once and about 30 MB of upcoming songs could be cached into the RAM. This did not require the hard disk to spin up for every song and thereby saved battery power. Apple also introduced a Windows version of iPod, at a later stage.

The audio files that iPod (mp3 / mp4 player) supports are MP3, AAC/M4A, Protected AAC, AIFF, WAV, Audible audiobook, and Apple Lossless audio file formats. MIDI and WMA files can be played only after a convertor accomplishes conversion, for non-Digital Rights Management (DRM). Ogg Vorbis, FLAC, and other open-source audio formats are not supported at all.

Apple wanted an extremely user friendly interface and thus adopted the minimalist interface, which features only five essential buttons, namely, Menu (to access functions and to toggle the backlight); Center (for menu item selection); Play/ Pause (this also works as an off switch when held for few seconds); Skip Forward/ Fast Forward; and Skip Backwards/ Fast Reverse. An additional Hold button is provided for accidental button pressing prevention, and it can reset the iPod if it has frozen or crashed. Functions such as volume control, scrolling are handled by the usage of the rotational click wheel. Later models have some minor changes in the functions of the buttons but overall the number of buttons has remained at five.

To market this path-breaking mp3 / mp4 player, they needed a suitable futuristic name and so they hired a freelance copywriter, Vinnie Chieco, and other writers to give a name. Inspired by the movie 2001: A Space Odyssey and the dialogue « Open the pod bay door, Hal! » with reference to the context of the Discovery One spaceship and its white EVA Pods, Vinnie Chieco proposed the name of the product as iPod. The management of Apple accepted the proposed name and on 23 October 2001, the iPod was officially launched. The rest they say is history.

To enable customers to access songs of their choice, Apple opened up an online media store The iTunes Store on 29 April 2003, where individual songs could be downloaded at prices less than a U.S. dollar per song. The purchased songs can be played only on iPods. Subsequent versions of this iPod (mp3 / mp4 player) also featured video capabilities, and thus iTunes Store started selling short videos from 12 October 2005. From 12 September 2006, full-length movies were also available at the iTunes Store.

iPods have come a long way from their inception, and now the latest fifth generation iPods possess multimedia capabilities and are available in both Mac OS and Windows OS versions. Usually, if a new iPod is plugged into a Mac OS computer, then the hard disk of this mp3 / mp4 player is formatted as per the HFS+ file format, and if it plugged into a Windows OS computer, it is formatted as per the FAT32 file format. From being a digital music player, the iPod has now transformed into a digital media player.


Author Bio

This article can also be accessed in portuguese language from the News Article section of page www.polomercantil.com.br/mp3-mp4-audio-portatil.php – Roberto Sedycias works as IT consultant for PoloMercantil


Article Source: http://www.ArticleGeek.com – Free Website Content


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©2006 ArticleGeek.com: Free Website Content – All Rights Reserved




For the past ten years there has been a tremendous growth in the usage of notebook or laptop computers. The impact is that the notebooks are slowly replacing the traditional desktop computers from home as well as from office. There are so many varieties, technologies and brands of notebooks available in the market that it has become very difficult for a regular user to identify the best fit for his or her needs. This article will help you in getting a few tips on how to select the right notebook and make the most out of your investment.

A notebook offers several advantages. The most important being the trouble-free mobility. This is enhanced by the easily available wireless internet connections all over the world. It is very convenient to carry all your work with you anywhere you go. Advancement in technology has brought down the weight and size of the notebooks significantly, making it even more comfortable for a regular user.

What are the things that you should consider before purchasing your notebook? Start with doing an analysis of your needs. Ask questions like: For what purpose will I use this notebook? The answers could include — for internet browsing, chatting, high-end graphic designing, gaming, business or official work, programming, application development, etc. The type of notebook you choose will depend on what you need it for.

When you do your research, make notes on the prices, technical features, configuration, guarantees, and performance that each notebook has to offer. You would need to decide whether you want a notebook from an Original Equipment Manufacturer (OEM) or from a brand. It is believed that brand notebooks offer better post-sales service, and guarantee, while OEM notebooks are cheaper and offer the same hardware quality as the brand ones.

If you need a notebook that is small and light and should be carried around easily while you are traveling, go for the ultra-portable range models. These notebooks have screens smaller than 12 inches and weigh up to 5 pounds. Some models of such notebooks include Sony Vaio PCG-U3, Fujitsu Lifebook P1510, Toshiba Libretto U100, Panasonic R4, Dell Latitude X1 and many more.

If you are a business professional looking for a thin and light notebook that offers durability, security and all important features necessary for your office, then you can select from a wide range of business notebooks. These include Apple MacBook, Dell XPS M1210, Sony VAIO FJ, and Dell Latitude and etc.

If you are addicted to gaming you would need a notebook that has the capability to present high-end graphics performance. These would include notebooks with the latest processors, increased RAM and hard disk storage space, faster CPUs, top-of-the line graphic display capability, great wireless connectivity and a host of other compatibility features. Some of the best gaming notebooks include Alienware Aurora, Dell XPS M170, and Rock Xtreme CTX PRO and etc.

If you are looking for just an economic replacement for your desktop and you do not want to spend on a high-end notebook, then you can select from a variety of models offered by Acer, Apple, Dell, Fujitsu, HP, Samsung, Sony and Toshiba. These notebooks are fashioned to be used at a fixed location and weigh up to 13 pounds, so they are not very convenient if you have to travel a lot. They generally have bigger screen sizes and lower battery life.

Apart from the notebooks mentioned above you can also pick tablet PCs, transportables, high-end personal digital assistants (PDAs), handheld computers, or smart phones. These are mobile devices that you can carry with you wherever you go, if mobility is all you are looking for.


Author Bio

Roberto Sedycias works as IT consultant for polomercantil. This article can also be accessed in portuguese language from the News Article section of page PoloMercantil


Article Source: http://www.ArticleGeek.com – Free Website Content


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Before you make a choice about any webcam equipment, it helps to decide exactly how you want to use the technology.Is Notebook A Better Choice Than Desktop?
This article makes a comparison between notebooks and desktop computers. It also describes the advantages and benefits of using notebooks.

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©2006 ArticleGeek.com: Free Website Content – All Rights Reserved




The single most important reason anyone buys a notebook is for portability. This is something that you can take anywhere. If you frequently travel in your work, you need a notebook. If you are a student going back and forth to the university, you need a notebook. If you are journalist traveling the world and submitting articles, you need a notebook. And today’s notebooks can be as powerful as most desktops with dual processors, large capacity internal drives, and other attractive features. But which one is right for you? How do you determine what type of notebook will fit your current needs plus allow you to expand for the future?

And the first part of the answer to the question of which one is right for you leads to a half-answer: « It depends. » It depends on what you are going to do with the computer. Are you going to use it for work or recreation? Is it something needed for your profession or are you a hobbyist? Do you play a lot of games? What level of internet access do you need? It is also important to remember that unlike desktop models, notebook computers cannot be upgraded easily. In fact, they usually have no upgrade path so you should take the time to get exactly what you need in terms of features and performance.

One characteristic of a notebook computer one should consider is the screen size. If you need to be able to have a lot of landscape for projects you are working on then consider a wider screen. Screen sizes usually can range from 10.4 inches to 17.1 inches. If you do a lot of work on an airliner in economy class, you are probably better off with a smaller screen size (because of the reclining seatbacks in front of you). Also a smaller notebook is just easier and lighter to carry around. Some who do presentations with their notebook computers will benefit from larger screen sizes such as those that use the newer WXGA technology. WXGA notebook screens can achieve resolutions up to 1366 by 768 pixels.

Battery life in your notebook computer is very important too. If you move around quite a bit, you might want to consider buying a notebook with not only a long lasting battery (most go 2-3 hours), but also one where buying a spare battery is not very expensive. One very inexpensive solution for the battery problem is to buy an external universal battery that can last up to 3-4 hours.

Another feature you need to consider when buying a notebook is internet connectivity. You will find that a popular way for people to work these days is with a wifi-enabled notebook at a wireless hotspot (such as in coffee shops, restaurants, libraries and airports). If you are buying an older used notebook, you may have to get an additional wifi-card if you want to have the mobile connectivity provided by this technology. Also, you will find that most hotels nowadays offer high-speed internet access but it is usually through a wifi connection.

And lastly, you need to consider what other options you want for your notebook computer. Do you want a CD writer or will you need to record DVDs? Do you need premium sound? How large of a disk drive do you need? When it comes to disk space, CD/DVD writers, sound cards, memory, and processor speed, it’s best to get it now as opposed to get it later. Here’s why: The upgrade path for most laptops and notebooks is not very long. This is because notebooks are probably replaced every 2-3 years. They are quick becoming just as expendable as a set of tires for your car. And if you do not maximize on memory and processor speed, your notebook may not able run efficiently the new application and game software. The more your notebook is adaptable to software upgrades, the longer it will be an effective tool for you.


Author Bio

This article can also be accessed in portuguese language from the News Article section of page www.polomercantil.com.br/notebook.php – Roberto Sedycias works as IT consultant for PoloMercantil


Article Source: http://www.ArticleGeek.com – Free Website Content


Related Computer Hardware Articles


©2006 ArticleGeek.com: Free Website Content – All Rights Reserved

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