Low vitamin D risks death

Low vitamin D risks death

Thursday, 12 May 2011

The University of Waikato "The best source of vitamin D is sunlight." Image: io_nia/iStockphoto A New Zealand study looking at vitamin D levels in patients admitted to hospital with pneumonia has shown that patients with severe vitamin D deficiency are more likely to die from the disease. Researchers at Waikato University collaborated with doctors at Waikato Hospital to study the blood samples of 112 patients all admitted to Waikato hospital with community acquired pneumonia during the winter. They found that those with severe deficiency - 15 per cent of patients – were more likely to die within a month, when compared to the group of patients with normal or slightly low vitamin D levels. The research findings are published in the journal Respirology this month. Vitamin D is known to be involved in the innate immune response to infection and Dr Ray Cursons from Biological Sciences at Waikato University says this research enhances our understanding of the apparent importance of vitamin D in combating respiratory infections. Patient age, sex, additional health conditions, other prognostic factors did not affect the research outcome. “However as an observational study we were not able to establish causal associations between vitamin D deficiency and mortality in these patients.” At Waikato Hospital Dr Leong Leow did the clinical work with consultant and respiratory specialist Dr Noel Karalus. Dr Karalus says as yet they don’t know whether supplementing patients admitted to hospital with respiratory tract infections with vitamin D will alter outcome. “It may transpire that vitamin D helps us avoid infection rather than cure it once established.” Co-author Dr Bob Hancox from Otago University, who also works at the Department of Respiratory Medicine at Waikato Hospital says the improved understanding of vitamin D and its role in immunity may eventually lead to better ways to prevent and treat pneumonia. “We now need to investigate whether vitamin D supplements could be a useful addition to pneumonia treatment and whether using supplements could help to prevent or reduce the severity of pneumonia among high-risk populations.” Dr Cursons says the best source of vitamin D is sunlight as dietary sources such as fatty fish and cod liver oil do not include enough vitamin D. “There is still some controversy regarding the optimal daily allowance of vitamin D. How much we absorb through the skin depends on sun exposure, skin type and geographical latitude. Māori and Pacific Islanders absorb less because of their darker skin, and people in colder climates also have lower levels of vitamin D.”

Plant 'smoke detector' gene

Plant 'smoke detector' gene

Wednesday, 11 May 2011

The University of Western Australia Smoke from bushfires provide the stimulus for new plant growth. Image: robcruse/iStockphoto   Researchers at The University of Western Australia have discovered a gene that allows dormant seeds buried in the soil to detect germination stimulants in bushfire smoke called karrikins. The same gene has also been found to provide the means for plants to respond to a growth hormone called strigolactone, which controls shoot branching, the formation of beneficial fungal associations, and germination of parasitic weeds. The findings reinforce the view that smoke from bushfires not only signals destruction but also provides the stimulus for new vigorous plant growth with the following rains. UWA plant biologist Dr David Nelson, who led the research, selected plants that had lost the ability to respond to karrikins and then searched for the defective gene in those plants. "It was a ‘eureka moment' when I looked at the DNA sequence of the defective gene and realised what we had discovered," he said.   "That one gene has two very different functions, one in fire ecology and the other in plant development." The findings reflect the fact that the karrikins and the strigolactone hormone have very similar chemical structures.  Their slight differences allow them to perform different roles but their similarities mean they are detected by one plant chemical detection system.  Ultimately the detector system allows the plant to distinguish between these signals and respond appropriately. Winthrop Professor Steven Smith said the findings will give us a new perspective on how to adapt plant and fire management and response.   "It will help us to understand how plant communities will respond in future to the increasing incidents of fire, how we should use fire to manage plants, and to investigate new methods for controlling weeds," Professor Smith said.

"தாயே உன்னை.....!"

 ஆறாவது நாளாய், இரவு பகல் பாராமல் கடவுள் தாயைப் படைத்துக் கொண்டிருந்தார்.

by Keyem Dharmalingam on Wednesday, 11 May 2011 at 22:44

 "தாயே உன்னை.....!"  by Magendran Natarajan on Saturday, May 7, 2011 at 9:43pm

ஆறாவது நாளாய், இரவு பகல் பாராமல் கடவுள் தாயைப் படைத்துக் கொண்டிருந்தார்.  அவர் படுகின்ற பாட்டைக் கவனித்துக் கொண்டிருந்த ஒரு தேவதை, சற்று தைரியத்தை வரவழைத்துக்கொண்டு, அவரை அணுகி, "எதற்காக இவ்வளவு சிரமப்பட்டு இதனை உருவாக்குறீங்க?" எனக் கேட்டது.

"இதற்காக நான் தயாரித்து வைத்திருக்கும் படிவத்தைப் படிக்கலியா நீ?

முழுவதுமாக தூய்மைப்படுத்திக் கொள்பவளாக, அதே சமயம் பிளாஸ்டிக்கால் செய்யப்படாதவளாக இருக்கணும். கிட்டத்தட்ட 200 அசையும் உறுப்புகளைக் கொண்டவளாக இருக்கணும். வெறும் காப்பித்தண்ணியையும், மீதமான உணவையும் மட்டுமே சாப்பிட்டு உயிர் வாழணும். ஒரே நேரத்தில் குறைந்தது மூன்று குழந்தைகளையாவது தன் மடியில் வைத்துக் கொள்ளும்படி இருக்கணும். எழுந்திருக்கும்போது அந்த மடி[அடிவயிறு] மறைந்து அழகாகத் தெரியணும். அவள் கொடுக்கும் ஒரு முத்தத்திலேயே ஒரு சின்ன சிராய்ப்பிலிருந்து, நொறுங்கிப்போன இதயம் வரை அனைத்தையும் குணமாக்கணும். இவையெல்லாம் தவிர, இவளுக்கு ஆறு ஜோடிக் கைகளும் இருக்கணும். அதான் இவ்ளோ கவனமா வேலை செய்யறேன்." என்றார் கடவுள்.

"என்னது? ஆறு ஜோடிக் கைகளா? நடக்கவே நடக்காது!" என்றது தேவதை.

"அட, அதெல்லாம் கூட சமாளிச்சிரலாம். இந்த மூணு ஜோடிக் கண்ணுங்களை வைக்கணுமே, அதுக்குத்தான் நேரம் பிடிக்குது" எனச் சிரித்தார் கடவுள்.

"அது வேறயா? ஆமா, இதெல்லாம் ஒரு சாதாரண வடிவான தாயிடமா?" என்றது தேவதை.

ஆம் என்னும் விதமாகத் தலையை ஆட்டியபடியே, " ஆமாம். மூடிய கதவுக்கு வெளியே நின்றுகொண்டே, உள்ளே என்ன நடக்குது எனத் தெரிந்துகொண்டே, 'உள்ளே என்ன பண்றீங்க?'ன்னு கேக்கறதுக்கு ஒரு ஜோடி. இவளுக்கு என்ன தெரியும்னு மத்தவங்கல்லாம் நினைச்சாலும், அடுத்து என்ன பண்ணணும்ன்றதைப் பாக்கறதுக்கு தலைக்குப் பின்னாடி ஒரு ஜோடி. ஒண்ணுமே தெரியாத அப்பாவி மாதிரி பாக்கறதுக்கு முகத்துல ஒரு ஜோடி. தப்பு பண்ற பிள்ளையைப் பார்த்து, 'எல்லாம் எனக்குத் தெரியுண்டா/[டீ]; இருந்தாலும் நான் உன்னை ரொம்பவே நேசிக்கறேன்னு சொல்லாம சொல்றதுக்கு அது! இப்பிடி மூணு ஜோடி தயார் பண்ணணும். அதான் சிரமம்" என்றார் கடவுள்.

"இது ரொம்பவே கஷ்டமான வேலை. கொஞ்சம் ஓய்வு எடுத்துகிட்டு நாளைக்கு மிச்சம் வேலையைப் பண்ணுங்க" என்றது பரிவுடன் தேவதை.

"முடியலியே! நான் படைச்சதுலியே எனக்கு மிகவும் பிடிச்ச படைப்பு இதான்.தனக்கு ஒரு நோய் வந்தாலும் யார்கிட்டயும் சொல்லாம, தானே தன்னை குணப்படுத்திக்குவா இவள். ஒரு ஆழாக்கு அரிசியுல ஒன்பது பேருக்கு உணவு சமைச்சு வக்கணையாப் பரிமாறிட்டு, தான் பட்டினி கிடப்பா. வம்பு பண்ற ஒன்பது வயதுக் குழந்தையை குளிப்பாட்டிவிடுவாள்" எனக் கடவுள் பதிலிறுத்தார். 

ஆச்சரியத்துடன் அந்த வடிவத்தை நெருங்கி லேசாகத் தொட்டுப் பார்த்தது அந்தத் தேவதை. " ஆனா, இவளை இவ்வளவு மென்மையாப் படைச்சிருக்கீங்களே. வேலைக்காவுமா?' எனக் கூவியது.  "பாக்கறதுக்குத்தான் மென்மை. ஆனால் இவளைப் போல கடினமான படைப்பே கிடையாதுன்னு சொல்லுவேன். எந்த அளவுக்கு தாங்குவா, எவ்ளோ சாதனை செஞ்சு காட்டுவான்னு உனக்குத் தெரியாது' எனப் பெருமையுடன் சொன்னார் கடவுள்.  "அது சரி, இவளுக்கு சிந்திக்கத் தெரியுமா?" எனச் சந்தேகத்துடன் கேட்டது தேவதை.

"ஹஹ்ஹா! சிந்திக்கத் தெரியுமாவா? சிந்திக்கறது மட்டுமில்லை; சரியான யோசனையும், தீர்வையும் கூடச் சொல்லமுடியும் இவளால" எனச் சிலாகித்தார் கடவுள். திடீரென எதையோ பார்த்துவிட்டு, அவளது கன்னத்தைத் தொட்டது தேவதை. "அடடா! இப்படி அருமையாப் படைச்சிட்டு, இப்படி ஒரு ஓட்டையை வைச்சுட்டீங்களே! பாருங்க இங்கே! என்னமோ வழியுது. அளுவுக்கதிகமா எதையோ திணிச்சுட்டீங்களோ?" எனச் சற்றுக் கேலியுடன் கேட்டது தேவதை. "அது ஓட்டையல்ல, கண்ணீர்த் துளி!' என்றார் கடவுள்.  "அது எதுக்கு?" என்றது.

"தனது சந்தோஷம், வேதனை, சோகம், ஏமாற்றம், வலி, தனிமை, பெருமை அனைத்தையும் அவள் வெளிப்படுத்தும் ஒரே வழி இந்தக் கண்ணீர்த்துளியால் மட்டுமே! இதான் இதோட தனிச் சிறப்பு" என அளவிட முடியாத பெருமையுடன் கடவுள் ஆனந்தித்தார்.

"என்ன சொல்றதுன்னே தெரியலைங்க! உங்களைப் போல ஒரு திறமைசாலியை நான் பார்த்ததே இல்லை. எல்லா விஷயத்தையும் எவ்ளோ கச்சிதமா நினைச்சுப் பார்த்து இதைப் படைச்சிருக்கீங்க! தாய் தான் உங்க படைப்புகளிலேயே மிகச் சிறந்த ஒன்றுன்னு நிச்சயமா சொல்லுவேன்" என கடவுளை வணங்கியது தேவதை!

[அனைத்துத் தாய்மார்களுக்கும் சமர்ப்பணம்!]

['எர்மா பொம்பெக்' [Erma Bombeck] என்பவர் ஆங்கிலத்தில் எழுதிய ஒரு மடலை தமிழாக்கித் தந்திருக்கிறேன்.

நன்றி:நண்பர் (by Magendran Natarajan on Saturday, May 7, 2011 at 9:௪௩ப்ம)

Introduction to Computer Networks and Data Communications

Introduction to Computer Networks and
Data Communications
Learning Objectives
· Define the basic terminology of computer networks
· Recognize the individual components of the big picture of computer networks
· Outline the basic network configurations
· Cite the reasons for using a network model and how those reasons apply to current
network systems
· List the layers of the OSI model and describe the duties of each layer
· List the layers of the Internet model and describe the duties of each layer
· Compare the OSI and Internet models and list their differences and similarities
Lecture Notes
The Language of Computer Networks
To better understand the area of computer networks, you should understand the basic
broad categories of computer networks and data communications.  For example, you
should be able to define each of the following terms:
• computer network
• local area network
• metropolitan area network
• wide area network
• personal area network
• data communications
• voice network
• data network
• telecommunications
• network management
Chapter 11Data Comm. & Computer Networks, Second Edition
2
Computer Networks - Basic Configurations
Understand each of the following configurations.  Examine the figure from the text or
create your own example for each configuration.  Describe how this configuration works
in simple terms.  Describe one or more applications that use each configuration:
• terminal-to-mainframe
• microcomputer-to-mainframe
• microcomputer-to-local area network
• microcomputer-to-Internet
• local area network-to- local area network
• personal area network-to-workstation
• local area network-to-metropolitan area network
• local area network-to-wide area network
• sensor-to-local area network
• satellite and microwave
• wireless telephone
Network Architecture Models.
Know the OSI Model and its 7 layers including the basic functions performed at each
layer: Physical, Data Link, Network, Transport, Session, Presentation, and Application.
Even though the OSI model is not the actual model used to support the Internet, its
understanding is necessary as many networks and products often refer to the OSI model
for definition.
It is also important to learn the Internet Model (or DoD model or TCP/IP model) and its 4
layers: (Network) Interface, Network, Transport, and Application.  The Internet model is
the model used to support all activities on  the Internet.
Logical and Physical Connections
To avoid future confusion, you must know the difference between a logical connection
and a physical connection.  Note that the only physical connection in a network is at the
physical or interface layer.  Data Comm. & Computer Networks, Second Edition
3
Fundamentals of Data and Signals
Learning Objectives
• Distinguish between data and signals
• Cite the advantages of digital data and signals over analog data and signals
• Identify the three basic components of a signal
• Discuss the bandwidth of a signal and how it relates to data transfer speed
• Identify signal strength and attenuation and how they are related
• Outline the basic characteristics of transmitting digital data with digital signals,
analog data with digital signals, digital data with analog signals, and analog data
with analog signals
• List and draw diagrams of the basic digital encoding techniques, including the
advantages and disadvantages of each Identify the different modulation
techniques and describe their advantages, disadvantages, and uses
• Identify the different modulation techniques and describe their advantages,
disadvantages, and uses
• Identify the two most common digitization techniques and describe their
advantages and disadvantages
• Discuss the characteristics and importance of spread spectrum encoding
techniques
• Identify the different data codes and how they are used in communication systems
Chapter Outline
1. Basics of transmission
2. Data and Signals
a. Analog versus digital
b. Fundamentals of signals
c. Loss of signal strength
3. Converting Data into Signals
a. Transmitting digital data with digital signals: digital encoding schemes
· Non-return to zero digital encoding schemes
· Manchester digital encoding schemes
· 4B/5B digital encoding scheme
b. Transmitting digital data with analog signals
Chapter 21Data Comm. & Computer Networks, Second Edition
4
· Amplitude modulation
· Frequency modulation
· Phase modulation
c. Transmitting analog data with digital signals
· Pulse code modulation
· Delta modulation
d. Transmitting analog data with analog signals
4. Spread Spectrum Technology
5. Data Codes
a. EBCDIC
b. ASCII
Lecture Notes
Data and Signals
Information that is stored within computer systems and transferred over a computer
network can be divided into two categories: data and signals.  Data are entities that
convey meaning within a computer or computer system. If you want to transfer this data
from one point to another, either by using a physical wire or by using radio waves, the
data has to be converted into a signal.  Signals are the electric or electromagnetic
encoding of data and are used to transmit data.
Converting Data into Signals
Like data, signals can be analog or digital.  Typically, digital signals convey digital data,
and analog signals convey analog data.  However, you can use analog signals to convey
digital data and digital signals to convey analog data.  The choice of using either analog
or digital signals often depends on the transmission equipment that is used and the
environment in which the signals must travel. There are four combinations of data and
signals: digital data transmitted using digital signals, digital data transmitted using analog
signals, analog data transmitted using analog signals, and analog data transmitted using
digital signals.Data Comm. & Computer Networks, Second Edition
5
Spread Spectrum Technology
Using a spread spectrum transmission system, it is possible to transmit either analog or
digital data using an analog signal.  However, unlike other encoding and modulation
techniques, only an intended receiver with the same type of transmission system can
accept and decode the transmissions.  The idea behind spread spectrum transmission is to
bounce the signal around on seemingly random frequencies rather than transmit the signal
on one fixed frequency.  Anyone trying to eavesdrop will not be able to listen because the
transmission frequencies are constantly changing.
Data Codes
One of the most common forms of data transmitted between a sender and a receiver is
textual data.  This textual information is transmitted as a sequence of characters.  To
distinguish one character from another, each character is represented by a unique binary
pattern of 1s and 0s.  The set of all textual characters or symbols and their corresponding
binary patterns is called a data code.  Two important data codes are EBCDIC and ASCII.Data Comm. & Computer Networks, Second Edition
6
The Media: Conducted and Wireless
Learning Objectives
· Outline the differences between Category 1, 2, 3, 4, 5, 5e, 6, and 7 twisted pair wire.
· Outline the characteristics of coaxial cable including the advantages and
disadvantages.
· Outline the characteristics of fiber optic cable including the advantages and
disadvantages.
· Outline the characteristics of terrestrial microwave systems including the advantages
and disadvantages.
· Outline the characteristics of satellite microwave systems including the advantages
and disadvantages as well as the differences between low earth orbit, middle earth
orbit, geosynchronous earth orbit, and highly elliptical earth orbit satellites.
· Describe the basics of wireless radio, including AMPS, D-AMPS, PCS systems, and
third generation wireless systems.
· Outline the characteristics of pager systems including the advantages and
disadvantages.
· Outline the characteristics of short-range transmissions, including Bluetooth
· Describe the characteristics, advantages, and disadvantages of wireless application
protocol
· Outline the characteristics of broadband wireless systems including the advantages
and disadvantages.
· Apply the media selection criteria of cost, speed, distance and expandability,
environment, and security to various media in a particular application.
Chapter Outline
1. What is a transmission media
2. Conducted Media
a. Twisted pair wire
b. Coaxial cable
c. Fiber optic cable
3. Wireless Media
a. Terrestrial microwave transmission
b. Satellite microwave transmission
Chapter 31Data Comm. & Computer Networks, Second Edition
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c. Mobile telephones
d. Cellular digital packet data
e. Pagers
f. Infrared transmissions
g. Bluetooth
h. Wireless application protocol
i. Broadband wireless systems
4. Media Selection Criteria
a. Cost
b. Speed
c. Distance and expandability
d. Environment
e. Security
Lecture Notes
Introduction
All communications media can be divided into two categories: physical or conducted
media, such as wires, and radiated or wireless media, which use radio waves.  Conducted
media include twisted pair wire, coaxial cable, and fiber optic cable.  In wireless
transmission, various types of electromagnetic waves, such as radio waves, are used to
transmit signals. This chapter examines seven basic groups of wireless media used for the
transfer of data: terrestrial microwave transmissions, satellite transmissions, cellular radio
systems, personal communication systems, pagers, infrared transmissions, and
multichannel multipoint distribution service.
Twisted Pair Wire
The oldest, simplest, and most common type of conducted media is twisted pair wires.
Twisted pair is almost a misnomer, as one rarely encounters a single pair of wires. To
help simplify the numerous varieties, twisted pair can be specified as Category 1-5 and is
abbreviated as CAT 1-5.  While still a little away from being a published specification,
Category 6 twisted pair should support data transmission as high as 200 Mbps for 100
meters while Category 7 twisted pair will support even higher data rates.  If you
determine that the twisted pair wire needs to go through walls, rooms, or buildings where
there is sufficient electromagnetic interference to cause substantial noise problems,
shielded twisted pair can provide a higher level of isolation from that interference than
unshielded twisted pair wire, and thus a lower level of errors.Data Comm. & Computer Networks, Second Edition
8
Coaxial Cable
Coaxial cable, in its simplest form, is a single wire wrapped in a foam insulation,
surrounded by a braided metal shield, then covered in a plastic jacket.  The braided metal
shield is very good at blocking electromagnetic signals from entering the cable and
producing noise. Because of its good shielding properties, coaxial cable is very good at
carrying analog signals with a wide range of frequencies. There are two major coaxial
cable technologies, depending on the type of signal each carries: baseband or broadband.
Coaxial cable also comes in two primary physical types: thin coaxial cable and thick
coaxial cable.
Fiber Optic Cable
Fiber optic cable (or optical fiber) is a thin glass cable approximately a little thicker than
a human hair surrounded by a plastic coating. A light source, called a photo diode, is
placed at the transmitting end and quickly switched on and off.  The light pulses travel
down the glass cable and are detected by an optic sensor called a photo receptor on the
receiving end. Fiber optic cable is capable of transmitting data at over 100 Gbps (that’s
100 billion bits per second!) over several kilometers. In addition to having almost errorfree high data transmission rates, fiber optic cable has a number of other advantages over
twisted pair and coaxial cable.  Since fiber optic cable passes electrically nonconducting
photons through a glass medium, it is immune to electromagnetic interference and
virtually impossible to wiretap.
Wireless Media
All wireless systems employ radio waves at differing frequencies.  The FCC strictly
controls which frequencies are used for each particular type of service.  The services
covered in this section will include terrestrial microwave transmissions, satellite
transmissions, cellular radio systems, personal communication systems, pagers, infrared
transmissions, and multichannel multipoint distribution service Terrestrial microwave
transmission systems transmit tightly focused beams of radio signals from one groundbased microwave transmission antenna to another. Satellite microwave transmission
systems are similar to terrestrial microwave systems except that the signal travels from a
ground station on earth to a satellite and back to another ground station on earth, thus
achieving much greater distances than line-o f-sight transmission. Satellites orbit the earth
from four possible ranges: low earth orbit (LEO), middle earth orbit (MEO),
geosynchronous earth orbit (GEO), and highly elliptical earth orbit (HEO). Two basic
categories of mobile telephone systems currently exist: cellular telephone and personal
communication systems (PCS). Cellular digital packet data (CDPD) technology supports
a wireless connection for the transfer of computer data from a mobile location to the
public telephone network and the Internet. Another wireless communication technology
that has grown immensely in popularity within the last decade is the pager. Infrared
transmission is a special form of radio transmission that uses a focused ray of light in the
infrared frequency range. A broadband wireless system is one of the latest techniques for Data Comm. & Computer Networks, Second Edition
9
delivering Internet services into homes and businesses.  Bluetooth transmissions will
support the new short-range personal area networks, and wireless application protocol
will support cellular telephone to Internet connections.
Media Selection Criteria
When designing or updating a computer network, the selection of one type of media over
another is an important issue. The principal factors yo u should consider in your decision
include cost, speed, expandability, distance, environment, and security.Data Comm. & Computer Networks, Second Edition
10
Making Connections
Learning Objectives
· Identify a standard modem and cite its basic operating characteristics
· Discuss the advantages of the newer digital modems and recognize why they do not
achieve the high transfer speeds as advertised
· List the alternatives to traditional modems, including T1 modems, cable modems,
IDSN modems, and DSL modems.
· Recognize the uses of a modem pool and its advantages and disadvantages
· List the four components of all interface standards
· Discuss the basic operations of the EIA-232F interface standard
· Cite the advantages of FireWire and Universal Serial Bus interface standards
· Outline the characteristics of asynchronous and synchronous data link interfaces
· Recognize the difference between half duplex, full duplex, and simplex connections
· Identify the operating characteristics of terminal- to-mainframe connections and why
they are unique from other types of computer connections
Chapter Outline
1. Modems
a. Basic modem operating principles
b. Data transmission rate
c. Standard telephone operations
d. Connection negotiation
e. Compression and error correction
f. Facsimile
g. Security
h. Self- testing (loop back)
i. Internal versus external models
j. Modems for laptops
3. The 56K Digital Modem
4. Alternatives to Traditional Modems
a. Channel Service Unit / Data Service Unit (CSU/DSU)
b. Cable modems
c. ISDN modems
Chapter 41Data Comm. & Computer Networks, Second Edition
11
d. DSL modems
7. High-speed Interface Protocols
a. FireWire
b. Universal Serial Bus (USB)
8. Data Link Connections
a. Asynchronous connections
b. Synchronous connections
c. Half duplex, full duplex, and simplex connections
Lecture Notes
Introduction
To better understand the interconnection between a computer and a device such as a
modem requires you to understand the concept of interfacing.  Interfacing a device to a
computer is considered a physical layer activity since it deals directly with analog signals,
digital signals, and hardware components.  We will examine the four basic components
of an interface¾electrical, mechanical, functional and procedural¾and then introduce
several of the more common interface standards.
Modems
Today’s modems are complex and offer so many functions and features that the user
manuals accompanying them are sometimes hundreds of pages long.  For example, most
contemporary modems include functions such as support for multiple transmission rates,
standard telephone operations, connection negotiation, compression, error correction,
facsimile transmission, security, and loop-back testing.  Modems can also be physically
characterized by whether they are internal or external models and whether they are
suitable for use with a laptop computer.
The 56k Digital Modem
Approximately two years after the 33,600 bps modem was announced, the 56,000 bps
modem was announced.  Did something change to allow the faster transmission speed, or
were the industry experts wrong?  The experts were correct¾two important facts
changed with the 56,000 bps modems: digital signaling was introduced, and the signal
power level was increased.Data Comm. & Computer Networks, Second Edition
12
Alternatives to Traditional Modems
There are four alternative transmission technologies available, other than the traditional
telephone line, that can be used to connect a computer into a remote network system: T-1
digital telephone lines, cable television networks, Integrated Services Digital Network
(ISDN), and Digital Subscriber Line (DSL).  Each of these transmission technologies
requires a particular kind of device that converts the digital data of a computer to the
proper form for transmission.
Modem Pools
A modem pool is a relatively inexpensive technique that allows multiple workstations to
access a modem without placing a separate modem on each workstation. Modem pools
are also used to allow multiple outside users to dial into a computer system.
Interfacing a Computer to Modems and Other Devices
Interfacing is a complex area of study.  It is a relatively technical process and varies
greatly depending upon the type of device, the computer, and the desired connection
between the device and computer. Various organizations set about creating a standard
interface between devices such as computers and modems.  An interface standard
consists of four parts or components: the electrical component, the mechanical
component, the functional component, and the procedural component.
High-speed Interface Protocols
Interface standards such as EIA-232F, X.21, and Hayes have existed for many years and,
by current standards, are relatively complex to create and difficult to support.  They were
designed primarily to support modems.  Computer designers have been working for many
years trying to create a new interface that is flexible and fast and supports not only
modems but the growing array of peripheral devices such as document scanners and
video cameras.  Two new interface standards that have great potential are FireWire and
Universal Serial Bus.
Data Link Connections
Assuming that the physical layer connections are already defined by some protocol such
as EIA-232F, what is the basic form of the data that is passed between sender and
receiver?  Is the data transmitted in single-byte blocks, or does the connection create a
larger, multiple-byte block?  The former connection is an example of an asynchronous
connection, while the latter is a synchronous connection.Data Comm. & Computer Networks, Second Edition
13
Multiplexing: Sharing a Medium
Learning Objectives
· Describe frequency division multiplexing and list its applications, advantages, and
disadvantages
· Describe synchronous time division multiplexing and list its applications, advantages,
and disadvantages
· Outline the basic multiplexing characteristics of both T1 and ISDN telephone systems
· Describe statistical time division multiplexing and list its applications, advantages,
and disadvantages
· Cite the main characteristics of dense wavelength division multiplexing and its
advantages and disadvantages
· Cite the main characteristics of code division multiplexing and its advantages and
disadvantages
Chapter Outline
1. What is multiplexing
2. Frequency Division Multiplexing
3. Time Division Multiplexing
a. Synchronous time division multiplexing
b. T-1 multiplexing
c. ISDN multiplexing
d. SONET multiplexing
e. Statistical time division multiplexing
4. Dense Wavelength Division Multiplexing
5. Code Division Multiplexing
6. Comparison of Multiplexing Techniques
Chapter 51Data Comm. & Computer Networks, Second Edition
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Lecture Notes
Introduction
Under the simplest conditions, a medium can carry only one signal at any moment in
time. Many times, however, we want a medium to carry multiple signals at the same
time. This technique of transmitting multiple signals over a single medium is
multiplexing.  Multiplexing is a technique performed at the physical layer of the OSI
model or the interface layer of the Internet model.
Frequency Division Multiplexing
Frequency division multiplexing is the assignment of non-overlapping frequency ranges
to each “user” of a medium. So that multiple users can share a single medium, each user
is assigned a channel.  A channel is an assigned set of frequencies that is used to transmit
the user’s signal.
Time Division Multiplexing
Time division multiplexing directly supports digital signals.  In time division
multiplexing, sharing of the signal is accomplished by dividing available transmission
time on a medium among users. Since time division multiplexing was introduced in
1960s, it has split into two roughly parallel but separate technologies: synchronous time
division multiplexing and statistical time division multiplexing.
Dense Wavelength Division Multiplexing
Dense wavelength division multiplexing is a fairly new technology that multiplexes
multiple data streams onto a single fiber optic line.  Unlike frequency division
multiplexing, which assigns input sources to separate sets of frequencies, and time
division multiplexing, which divides input sources by time, wave division multiplexing
uses different wavelength lasers to transmit multiple signals.Data Comm. & Computer Networks, Second Edition
15
Code Division Multiplexing
This multiplexing technique assigns a multiple-bit sequence to each transmitter’s binary 1
and binary 0.  When all transmitters transmit at the same time, the receiver sums all
received values and performs a mathematical computation on the sums to separate one
code from another.
Comparison of Multiplexing Techniques
Frequency division multiplexing relies on analog signaling and is the simplest and most
noisy of all the multiplexing techniques.  Synchronous time division multiplexing is also
relatively straight forward, and like frequency division multiplexing, input devices that
have nothing to transmit can waste transmission space.  The big advantage of
synchronous TDM is the lower noise during transmission.  Statistical TDM is one step
above synchronous TDM because it transmits data only from those input devices that
have data to transmit.  Thus, statistical TDM wastes less bandwidth on the transmission
link.  Dense wavelength division multiplexing is a very good, albeit expensive, technique
for transmitting multiple concurrent signals over a fiber optic line.Data Comm. & Computer Networks, Second Edition
16
Errors, Error Detection, and Error
Control
Learning Objectives
· Identify the different types of noise commonly found in computer networks
· Specify the different error prevention techniques and be able to apply an error
prevention technique to a type of noise
· Compare the different error detection techniques in terms of efficiency and efficacy
· Perform simple parity calculations, and enumerate their strengths and weaknesses
· Cite the advantages of cyclic redundancy checksum, and specify what types of errors
cyclic redundancy checksum will detect
· Differentiate the three basic forms of error control, and describe under what
circumstances each may be used
Chapter Outline
1. Noise, errors, error prevention, detection and control
2. Noise and Errors
a. White noise
b. Impulse noise
c. Crosstalk
d. Echo
e. Jitter
f. Delay distortion
g. Attenuation
3. Error Prevention
4. Error Detection Techniques
a. Parity checks
· Simple parity
· Longitudinal parity
b. Cyclic redundancy checksum
Chapter 61Data Comm. & Computer Networks, Second Edition
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5. Error Control
a. Do nothing
b. Return a message
· Stop and wait ARQ
· Sliding window protocol
· Go-back-N ARQ
· Selective-reject ARQ
c. Correct the error
Lecture Notes
Introduction
Given that noise is inevitable and errors happen, something needs to be done to detect
error conditions. This chapter examines some of the more common error detection
methods and compares them in terms of efficiency and efficacy. Once an error has been
detected, what action should a receiver take?  There are three options:  ignore the error,
return an error message to the transmitter, or correct the error without help from the
transmitter.
Noise and Errors
Transmitted data—both analog and digital—are susceptible to many types of noise and
errors. Copper-based media have traditionally been plagued with many types of
interference and noise.  Satellite, microwave, and radio networks are also prone to
interference and crosstalk.  Even near-perfect fiber optic cables can introduce errors into
a transmission system, though the probability of this happening is less than with the other
types of media.
Error Prevention
Since there are so many forms of noise and errors, and since one form of noise or another
is virtually a given, every data transmission system must include precautions to reduce
noise and the possibility of errors. If you can reduce the possibility of noise before it
happens, the transmitting station may not have to slow down its transmission stream.
With proper error prevention techniques, many types of errors can be reduced.
Error Detection Techniques
Despite the best attempts at prevention, errors still occur. If an error is detected, it is
typical to perform some type of request for retransmission. Error detection techniques Data Comm. & Computer Networks, Second Edition
18
themselves can be relatively simple or relatively elaborate.  Generally, simple techniques
do not provide the same degree of error checking as more elaborate schemes.  For
example, the simplest error detection technique is simple parity.  It adds a single bit to a
character of data, but catches the fewest number of errors.  At the other end of the
spectrum is the most elaborate and most effective technique available today: cyclic
redundancy checksum.  Although it is more complex and typically adds 16 bits of error
detection code to a block of data, it is the most effective error detection technique ever
devised.
Error Control
Once an error is detected in the received data transmission stream, what is the receiver
going to do about it? The receiver can do one of three things: nothing, return a message to
the transmitter asking it to resend the data packet that was in error, or correct the error.Data Comm. & Computer Networks, Second Edition
19
Local Area Networks: The Basics
Learning Objectives
· State the definition of a local area network.
· List the primary function, activities, and application areas of a local area network.
· Cite the advantages and disadvantages of local area networks.
· Identify the physical and logical local area network topologies.
· Cite the characteristics of wireless local area networks and their medium access
control protocols.
· Specify the different medium access control techniques.
· Recognize the different IEEE 802 frame formats
· Describe the common local area network systems
Chapter Outline
1. Parts of the OSI
2. Primary Function of Local Area Networks
3. Advantages and Disadvantages of Local Area Networks
4. Basic Local Area Network Topologies
a. Bus/tree topology
b. Star-wired bus topology
c. Star-wired ring topology
d. Wireless LANs
e. Comparison of bus, star-wired bus, star-wired ring and wireless topolo gies
5. Medium Access Control Protocols
a. Contention-based protocols
b. Round robin protocol
c.   Reservation protocols
6. Medium Access Control Sublayer
a. IEEE 802 Frame Formats
Chapter 71Data Comm. & Computer Networks, Second Edition
20
7. Local Area Network Systems
a. Ethernet
b. IBM token ring
c. Fiber data distributed interface (FDDI)
d. 100VG-AnyLAN
Lecture Notes
Introduction
A local area network (LAN) is a communication network that interconnects a variety of
data communicating devices within a small geographic area, and broadcasts data at high
data transfer rates with very low error rates. Since the local area network first appeared in
the 1970s, its use has become widespread in commercial and academic environments.  It
would be very difficult to imagine a collection of personal computers within a comp uting
environment that does not employ some form of local area network. This chapter begins
by discussing the basic layouts or topologies of the most commonly found local area
networks, followed by the medium access control protocols that allow a workstation to
transmit data on the network.  We will then examine most of the common local area
network products such as Ethernet and token ring.
Primary Function of a Local Area Network
The majority of users expect a local area network to perform the primary function of
sharing resources.  This often includes the following applications: file serving, database
and application serving, print serving, electronic mail, remote links, video transfers,
process control and monitoring, and distributed processing.Data Comm. & Computer Networks, Second Edition
21
Advantages and Disadvantages of Local Area Networks
Local area networks have several advantages, including: hardware and software sharing,
workstation survival during network failure, component and system evolution,
heterogeneous mix of hardware and software, and access to other LANs, WANs, and
mainframe computers.  Disadvantages include complexity, maintenance costs, and the
network is only as strong as the weakest link.
Basic Network Topologies
Local area networks are interconnected using one of four basic configurations, or
topologies: bus/tree, star-wired bus, star-wired ring, and wireless.  The choice of topology
is occasionally dictated by the physical environment in which the local area network is to
be placed.  More than likely, the choice of a topology is determined by other factors such
as a preferred access method, data transfer speeds, and brand loyalty.  Let’s examine each
of the four topologies, paying special attention to advantages and disadvantages.
Medium Access Control Protocols
A medium access control protocol is part of the software that allows a workstation to
place data onto a local area network.  Depending on the network’s topology, several types
of protocols may be applicable.  The bottom line with all medium access control
protocols is this: since a local area network is a broadcast network, it is imperative that
only one workstation at a time be allowed to transmit its data onto the network.  In the
case of a broadband local area network, which can support multiple channels at the same
time, it is imperative that only one workstation at a time be allowed to transmit its data
onto a channel on the network. There are three basic categories of medium access control
protocols for local area networks: contention-based protocols, such as carrier sense
multiple access with collision detection; round robin protocols, such as token passing;
and reservation protocols, such as demand priority.
Medium Access Control Sublayer
Although the seven- layer OSI model was designed to support most typ es of
communication systems, it fell short in several areas. One of these areas was the data link
layer.  Thus, the data link layer has been split into two sublayers: the medium access
control sublayer and the logical link control sublayer.  The medium access control
(MAC) sublayer works more closely with the physical layer and contains a header,
computer (physical) addresses, error detection codes, and control information. The
logical link control (LLC) sublayer is primarily responsible for logical addressing and
providing error control and flow control information.  Data Comm. & Computer Networks, Second Edition
22
IEEE 802 Frame Formats
To standardize many of the local area network protocols, IEEE created a series of
protocols called the IEEE 802 suite of protocols.  With the IEEE 802 standards, the frame
formats for data at the medium access control (MAC) sublayer were also created.  Thus,
as data comes down from the application layer through the lower layers of the
communications model and arrives at the MAC sublayer, MAC software places the data
into a unique frame format, ready for transmission across the medium (the physical
layer).
Local Area Network Systems
The discussion of local area networks started by examining the main types of network
topologies: bus, star-wired bus, ring, and wireless. Then the three major categories of
medium access control protocols that can operate on these different topologies were
introduced: CSMA/CD, token passing, and demand priority.  Actual products or local
area network systems that are found in a typical computer environment.  Four of the most
popular local area network systems are Ethernet, IBM token ring, fiber data distributed
interface, and 100VG-AnyLAN.
Wireless Networks
Learning Objectives
· What are wireless networks
· How are they used
· Types of wireless systems
Fixed Wireless Access (last mile)
Wide Area Wireless Data Services (WWANs)
Cellular Systems
Satellite Systems & Paging Systems
HomeRF (SWAP)
Bluetooth
Wireless LANs , also know as or WLANs
WiFi
WiFi5
From LectureData Comm. & Computer Networks, Second Edition
23
· HomeRF vs Bluetooth vs WiFi
· Bluetooth – piconets and scattenets
· Bluetooth issues:
Cost
Limited support
Shortcomings in protocol itself
Positioning in marketplace
Conflicts with other devices in radio spectrum
· 802.11b WiFI (wireless Ethernet)
· Wireless NICs
· Access points APs
· Base station
· Bridge to wired LANs
· Ad Hoc modes
· Infrastructure Mode, also called Basic Service Set (BSS), has wireless clients and an
access point
· More access points can be added to create an Extended Service Set (ESS)
· Wireless Gateway
· All WLAN functions in physical and data link areas of OSI
· 802.11b uses Distributed Coordination Function (DCF) with modified procedure
known as Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)

Graphite paper beats steel

Graphite paper beats steel

Thursday, 28 April 2011

University of Technology Sydney A graphene paper sample. Image: Lisa Aloisio/UTS UTS Scientists have reported remarkable results in developing a composite material based on graphite that is a thin as paper and ten times stronger than steel. In work recently published in theJournal of Applied Physics, a UTS research team supervised by Professor Guoxiu Wang has developed reproducible test results and nanostructural samples of graphene paper, a material with the potential to revolutionise the automotive, aviation, electrical and optical industries. Graphene paper (GP) is a material that can be processed, reshaped and reformed from its original raw material state - graphite. Researchers at UTS have successfully milled the raw graphite by purifying and filtering it with chemicals to reshape and reform it into nano-structured configurations which are then processed into sheets as thin as paper. These graphene nanosheet stacks consist of monolayer hexagonal carbon lattices and are placed in perfectly arranged laminar structures which give them exceptional thermal, electrical and mechanical properties. Using a synthesised method and heat treatment, the UTS research team has produced material with extraordinary bending, rigidity and hardness mechanical properties. Compared to steel, the prepared GP is six times lighter, five to six times lower density, two times harder with 10 times higher tensile strength and 13 times higher bending rigidity. Lead researcher Ali Reza Ranjbartoreh said, "No one else has used a similar production and heat testing method to find and carry out such exceptional mechanical properties for graphene paper. We are definitely well ahead of other research societies." "The exceptional mechanical properties of synthesised GP render it a promising material for commercial and engineering applications. "Not only is it lighter, stronger, harder and more flexible than steel it is also a recyclable and sustainable manufacturable product that is eco-friendly and cost effective in its use." Mr Ranjbartoreh said the results promise great benefits for the use of graphene paper in the automotive and aviation industries, allowing the development of lighter and stronger cars and planes that use less fuel, generate less pollution, are cheaper to run and ecologically sustainable. He said large aerospace companies such as Boeing have already started to replace metals with carbon fibres and carbon-based materials, and graphene paper with its incomparable mechanical properties would be the next material for them to explore. The production of GP from graphite also provides a remarkable amount of added value for the mining, material processing and manufacturing industries in Australia. In the last decade, metals have increasingly and rapidly been replaced with carbon-based materials. Australian mines have immense graphite resources making the new material a favourable option to industry as an economical, home-grown and world-class technological advancement for mass production and industrial application. The findings of the UTS research group have been published in the article "Advanced mechanical properties of graphene paper" in the current edition of the Journal of Applied Physics.

New hope for lung cancer

New hope for lung cancer

Wednesday, 11 May 2011

The University of New South Wales Gene-silencing looks very promising as the next wave of therapeutics. Image: chemicalbilly/iStockphoto Scientists at the Lowy Cancer Research Centre fighting childhood cancer say a new treatment approach may also offer hope to adults with lung cancer. The experimental therapy – developed to combat solid tumour cancers in children – is also effective in targeting one of the most lethal lung cancers in adults, according to the team led by UNSW Professor Maria Kavallaris at Children’s Cancer Institute Australia (CCIA). More than 9,000 Australians are diagnosed with non-small lung cancer each year. Currently, the prognosis for patients with an advanced form of the disease is poor, because tumours often become resistant to conventional drug therapy. The Lowy Cancer Research Centre at UNSW is the first facility in Australia to bring together childhood and adult cancer researchers. The rationale for combining the research under the one roof was the potential for significant breakthroughs. “The most common childhood cancers – those of the nervous system and leukaemia – are rare in adults however, researchers are increasingly finding common pathways,” says the head of the Centre’s childhood cancer program and Executive Director of CCIA, Professor Michelle Haber. By targeting a structural protein in drug resistant lung cancer cells, the Lowy Cancer Research Centre’s novel therapy aims to increase the sensitivity of the tumour to standard chemotherapy drugs. It uses a gene-silencing approach, the next wave of cancer therapeutics, to suppress this structural protein. The promising results were presented this month at the Australasian Gene Therapy Society meeting in Melbourne. “This therapy could advance new ways of approaching treatment of non-small lung cancer, which accounts for 80 percent of all lung cancers,” said Professor Kavallaris, who is head of the Pharmacoproteomics Program at CCIA. It is hoped that the therapy will also have significance for solid tumour cancers in children, such as neuroblastoma, one of the most aggressive childhood cancers. CCIA scientists based at the Lowy Cancer Research Centre have been working closely with Benitec Ltd, an Australian biotechnology company with a dominant technology for silencing genes, to bring this new therapy from the laboratory to the clinic.   “Gene-silencing is looking very promising as the next wave of therapeutics,” said Dr Peter French, Chief Executive Officer of Benitec Ltd. “We have used this approach successfully in early stage HIV clinical trials in the US and believe that this same approach can be used for cancer and many other diseases.”

China shows a world lead in clean nuclear energy

Friday, 29 April 2011

By Gerry Grove-White Earlier this year the Chinese Academy of Science announced plans to finance the development of a programme to develop Thorium Fuelled Molten Salt Reactors (TFMSR). This is the first of four “strategic leader in science and technology projects” that the Chinese Academy of Science will be supporting. The Head of the Chinese TFMSR programme is Dr Jiang Mianheng, Graduate of Drexel University, with a PhD in electrical engineering. His father Jiang Zemin, was the former President of the People's Republic of China from 1993 to 2003. This gives an indication of the importance the Chinese Leadership attach to the thorium reactor programme. This is a clear and important endorsement of the benefits of the TFMSR namely:- Excellent nuclear and passive safety features, Greatly improved  proliferation resistance, Significantly reduced high active waste production, Excellent  resource utilisation as a result of the very high burn-up achieved, Overall economics that offer the prospect of being competitive with coal.   The decision clearly demonstrates China’s commitment to developing the TFMSR as a major energy source for the future. One can only applaud this far sighted decision by the Chinese Academy of Science. The Academy stated that -“The scientific goal is to develop a new generation of nuclear energy systems [and to achieve commercial] use [in] 20 years or so. We intend to complete the technological research needed for this system and to assert intellectual property rights to this technology”. Whist the announcement refers to a 20 year programme, rapid progress can be expected in the next 5 years towards a demonstration plant. This programme will place China at the forefront of development of truly competitive nuclear power suitable for large scale power production as well as supporting desalination, hydrogen production, and other high temperature chemical processing, due to the safe, clean and cost-efficient characteristics of thorium energy.  The TFMSR programme will see China leading the world in the development and application of high temperature materials, and quite probably the use of the Brayton power generating cycle. It is tempting to speculate about how other countries may react to what many observers see as “a Sputnik moment”, to borrow President Obama’s phrase. President Obama in his recent State of the Union speech pursued the Sputnik analogy when he stated that “We're telling America's scientists and engineers that if they assemble teams of the best minds in their fields, and focus on the hardest problems in clean energy, we'll fund the Apollo projects of our time”. He goes on to say “Some folks want wind and solar. Others want nuclear, clean coal and natural gas. To meet this goal, we will need them all”. So can we expect to see the Chinese announcement catalyse the countries and researchers who have been working on TFMSR’s for years to put together a team to deliver a second TFMSR programme? Given the intellectual capital  developed 50 years ago by the talented Team at Oak Ridge National Laboratory, under the leadership of the visionary Dr Alvin M Weinberg , it would be surprising if a Team were not assembled and funded to deliver a second TFMSR programme. This represents a “golden opportunity” for Australia to join an international consortium to develop what, in the opinion of many scientists and nuclear engineers, represents the most promising of the Generation 4 reactor systems. If Australia were to do this, then it would have available a nuclear reactor technology that has high enough temperatures to power hydrogen production and a host of other high temperature chemical processes with no resultant carbon emissions. In addition it would develop a world leading position in high temperature material and metallurgy. Competition is good for the overall development and deployment of TFMSR technology, given the various technological options that are available. The World requires TFMSR to meet the challenge of clean energy production in the coming years. The Chinese announcement is a great step forward, which many observers over the years have been arguing for.  The coming months may well see further similar announcements around the world. The question is will Australia be able to grasp the opportunity that the development of a TFMSR represents, or will we be buying our reactors and other high temperature technologies from China in 15 to 20 years time? Gerry Grove-White is a former mechanical engineer who worked as a technical operations engineer on MAGNOX, CANDU reactors and the Prototype Fast Reactor (PFR) at Dounreay in the UK. He is also the Australian representative for IThEO, a not-for profit organisation seeking to promote the adoption of Thorium Fuelled Molten Salt Reactors worldwide. This article is published with the permission of IThEO. www.itheo.org