Assistant Sub-Inspector (Telecom) posts in SSB

Applications are invited from male Indian citizens fulfilling the eligibility criteria for recruitment to the following posts in SSB :

• Assistant Sub-Inspector (Telecom) :  76 posts (UR-48, Sc-07, ST-04, OBC-10, Ex.SM-07), Pay Scale :  Rs. 5200-20200 grade pay Rs. 2800, Age : 18-25 years
• Head Constable (Telecom) : 250 posts (UR-99, SC-66, ST-27, OBC-33, Ex.SM-25), Pay Scale : Rs. 5200-20200 grade pay Rs.2400, Age : 18-23 years

Application Fee : Application fee will be Rs. 50/-  for candidates belonging to General and OBC categories in favour  of “Accounts Officer, SSB, FTR HQ, Ranikhet,”. No fee will be charged from SC/ST/Ex-Servicemen.

How to Apply : Eligible and desirous candidates should send their applications in the prescribed proforma with attested passport size photographs duly affixed on the application form and admit card and duly completed in all respect on or before 31/07/2012 to Inspector General, Sashatra Seem Bal, Frontier Hq.  Ranikhet, Sewa Bhawan (Ganiyadeoli), PO Sadar Bazar, District Almora, Uttarakhand. (Last date is 07/08/2012 for the candidates from far-flung areas)

Please see the document  

 

http://www.ssbrectt.gov.in/docs/Adv%20tech%2012.pdf 

 

for detailed information and application form.

 

Ph.D. Admissions:RGUKT Notification for Ph.D. Admissions 2012-13

RGUKT Notification for Ph.D. Admissions 2012-13

Rajiv Gandhi University of Knowledge Technologies, Gachibowli, Hyderabad is inviting applications for admission to Ph.D. Programme for the academic year 2012-13. Candidates should be from among the faculty of RGUKT who are eligible lecturers and academic consultants cadre and above. Candidates should apply in the prescribed format available on the GRUKT website at www.rgukt.in. RGUKT has campuses in Basar, RK Valley and Nuzvid. Here are details of disciplines and eligibility requirements:

Eligibility Criteria: Applicants for Ph.D. in engineering discipline should posses an M.Tech/ ME or MS (Masters degree by Research in Engineering/ Technology) degree with CGPA of preferably above 7.5 (CGPA 7.0 for SC and ST category). They also need first class performance all through their studies. Candidates for Ph.D. in Sciences and Arts should have a first class PG degree in relevant discipline / specialisation. Candidates with distinction with above 70 percent marks are preferred. Candidates should have qualified in UGC/ CSIR -NET/ SLET / NBHM or equivalent examinations.

Disciplines offered in Ph.D: 1. Chemical Engineering 2. Electrical Engineering 3. Civil Engineering 4. Material Science and Engineering 5. Computer Science and Engineering 6. Electronics and Communications Engineering 7. Mechanical Engineering 8. Mathematics and Statistics 9. English 10. Economics 11. Physics 12. Biological Sciences (Botany and Zoology) 13. Business Management 14. Chemistry and 15. Telugu . Interested candidates can apply through on-line mode at the website http://rguktphdadmissions.appspot.com/index.html . Hard copy of the application along with relevant enclosures should be sent to Registrar. Last date for the receipt of the same is 10-04-2012.

Read more: http://www.apcollegeadmissions.com/2012/04/rgukt-notification-for-phd-admissions.html#ixzz1rRE8DkQG

Intermediate(AP) Results 2012 available sites

Results may be declared in second week of April 2012.

మార్కులతో ఫలితాలు అందుబాటులో ఉండే వెబ్‌సైట్లు:

http://examresults.ap.nic.in

www.aponline.gov.in

http://results.egg.gov.in

www.esevaonline.com 

Inter Ist year Marks and grades will be available on – 
http://examresults.ap.nic.in,
http://results.cgg.gov.in

గ్రేడులతో పాటు ఫలితాలు అందుబాటులో ఉండే వెబ్‌సైట్లు:
www.indiaresults.com, www.exametic.com, www.rediff.com/exams, www.educationplus.net.in,www.examresults.net, www.nettlinxresults.net, www.manabadi.com, www.manabadi.co.in,www.results.educationandhra.com, www.results.manabadi.co.in, www.schools9.com,www.pratibhaplus.com, www.bharatstudent.com, www.deccanpost.in, www.searhandhra.com,www.vidyadata.com, www.bharatiresults.com, www.AndhraEducation.net, www.saagam.com

Inter 2012 Results: Inter 2nd year results 2012 :Inter Marks available websitesInter 2012 Results: Inter 2nd year results 2012 :Inter Marks available websitesInter 2012 Results: Inter 2nd year results 2012 :Inter Marks available websitesInter 2012 Results: Inter 2nd year results 2012 :Inter Marks available websitesInter 2012 Results: Inter 2nd year results 2012 :Inter Marks available websitesInter 2012 Results: Inter 2nd year results 2012 :Inter Marks available websites

Osmania University Mecharena 12 Technical Fest

Osmania University Mecharena 12 Technical Fest

University College of Engineering, Osmania University, Hyderabad is conducting Mecharena 2012, a Mechanical Fest for Engineering Graduates. The fest will be conducted during 9th - 10th March 2012. The Department of Mechanical Engineering, Osmania University is organising Mecharena 12. There will be number of competitions, events and innovative programmes to be shared by students across the country. This is a wonderful platform to show your talents in the subject and other creative activities. Here are other details of the fest: 

Events to be conducted in the Mecharena: Robotix, Papers and Presentations, Workshops, Spot Events , Quiz, Guest Lectures, Treasure Hunt, Business World etc. For any more information, you can contact at convener : Sampath Kumar (9866566491) OR co-convener: K. Vishwas Reddy (9493402636) OR C.Mrudula (9491213213). You can also send a main to 
mecharena2k12@gmail.com 

College Address: University College of Engineering, Osmania University, Hyderabad- 500 007, Andhra Pradesh, Contact: +914027098254, +914027682384. webmaster@uceou.edu . Website: http://mecharena2k12.org/ .

Read more: http://www.apcollegeadmissions.com/2012/03/osmania-university-mecharena-12.html#ixzz1oXywg6Gk

What is digital TV?

Digital TV, often abbreviated as DTV, is the broadcasting of television via digital signals – the pictures and sound are converted into digital signals and compressed before being broadcast, while the analog signals cannot be compressed.

What is a digital TV transition?

Digital TV transition, also known as digital TV switchover in some countries, is the process of rendering the older, analog television broadcasting obsolete and replacing it with digital TV broadcasting. The process was completed in the United States by June 12th 2009 after several delays, and other industrial countries have passed legislation taking steps in the same direction.

In Germany, the digital TV transition began in the Berlin area and the terrestrial digital TV transition was completed in 2009 in the rest of the country, while the existing analog cable and analog satellite broadcasting will be switched off in 2012. In the United Kingdom the process has started in 2008 and should be completed by the end of 2010, while all of the Scandinavian countries have already successfully completed the transition from analog to digital TV.

Digital TV vs. analog TV

Digital TV vs. analog TV: what are the advantages of digital TV broadcasting?

As already mentioned, the main advantage of the digital TV transmitting is that the television signal can be compressed, much like the files on a computer's hard drive. This enables the transmitting of as much as five times more information, using the same amount of bandwidth and this automatically results in the ability to broadcast more channels, without having to expand the frequency bandwidth.

The digital TV also offers new features like interactivity, on-screen listings, and wide screen pictures, and new services and packages like telephony, high-speed broadband Internet, and premium channels; subtitling and audio descriptions are also possible and likely to benefit older and disabled viewers.

The video signal in digital TV is encoded by using the MPEG-2 standard, which although has its disadvantages, still provides much better image quality than the standard NTSC analog image. Some digital TV programs are available with Dolby Digital AC-3 sound, which is the same audio encoding system that has been used in movie theaters and offers superb quality sound.

Another great characteristic of the digital TV broadcasting is that it keeps the quality of its signal – the analog TV signal weakens as the signal is transmitted farther away from the broadcasting station and this results in poorer picture and sound quality in the remote areas. The digital signal retains its quality, no matter how far the receiver is from the broadcasting station, as long as he is capable of receiving that signal.

Are there any drawbacks to switching to digital TV?

Although the digital TV is seen as a step in the right direction, it has its disadvantages with the two main concerns being the cost of the digital TV transition and the fact that many households had to either buy new, digitally enabled TV sets, or purchase analog-to-digital converters for each existing TV set in order to be able to watch digital TV.

Another concern was raised by the fact that the transition dramatically increased the disposal of old TV sets and their recycling is not always easy and is very costly. You don't even need to buy a digital tv antenna.

Overall, the digital TV advantages far outweigh its disadvantages and in the near future we are likely to see even more new and exciting features and services that will dramatically change the way we are informed and entertained!

What does a frequency of "X" Hz mean in LCD or Plasma TV or LED TV?

Introduction to 50Hz televisions

A regular PAL television changes the picture at a frequency of 50 Frames Per Second (FPS) or 50Hz. The illusion of movement in the picture is produced by the successive frame changes of the picture 50 times per Second. A 50 FPS (50Hz) Cathode Ray Television (CRT) creates the picture with an electron scan and there is a visible flicker that is sensed by the human eye.

The Human eye is at occasionally sensitive to this frequency depending on the intensity of darkness, the speed of the image, and the degree of brightness thus you will occasionally notice the picture flicker on a 50Hz TV. The flicker becomes more apparent on larger screen.

Early 100 hertz technology

A 100 Hz TV operates at twice the Frames Per Second (100FPS) by producing a replica of every frame and inserting it after the previous one. The result of this doubling of the scan frequency to 100Hz and inserting a copy frame is that this problem was eliminated as far as the eye perceived it. The result of this is to significantly lower the flicker.

How does 100Hz work on LCD and Plasma TV?

LCD and Plasma televisions don't produce flickering because they don't produce the picture with an electron scan. However LCD TV's still benefit from 100Hz because advanced digital circuitry creates an extra frame or middle image. This is done by the TV inventing an extra frame using complex interpolation and motion compensation calculations to work out what the extra fields and frames look like rather than inserting a replica frame. (e.g. the second frame is not the same as the first frame).

However even at 100 FPS the picture still does not deliver a entirely smooth picture particularly with fast motion images. Some television manufactures attempt to reduce this further by employing digital picture processing. Typically there is still a little blurring on quick moving images but the benefits are clearer and better-defined surfaces, sharper pictures, and smoother movement than is possible from 50 Frames Per Second Plasma and LCD televisions.

i.e. if a football moves ten pixels from right to left between frames one, two and three, the 100 Frames Per Second television will digitally create two added frames between one and two, along with two and three, in which the ball will travel five pixels. This therefore results in a total of five frames in which the ball moves a total of ten pixels i.e. the original frames one, two and three plus the digitally created frames that are inserted in between one and two, and between two and three. The eye thus sees a picture that moves more fluidly than before.

The benefits of 100 Hz

The benefit is that 100Hz televisions have a clear benefit of ending a lot of the ghosting effects sometimes seen in LCD TV's. The ghosting effect caused by the new image being displayed before the previous has faded away. The created middle frame also benefits the Plasma television picture by make the picture more fluid and natural.

Most top manufacturers have now got 100Hz LCD and Plasma televisions including Panasonic, JVC, Samsung, Toshiba, LG, Sony, Philips, Pioneer and Hitachi.

200Hz, 400Hz, 600Hz and now 1200Hz

Once Sony launched a 200Hz range which digitally inserts three additional frames between the original 50Hz frames we have seen the market go into overdrive with manufacturers aiming to give the maximum amount of Hertz possible. Overall though the effect of this is that we are seeing fast moving sequences being delivered with a amazingly smooth, more fluid and sharper images than ever before.

Backlight Blinking

XR200, XR400 and XR800 plus Panasonic`s backlight blinking technology has seen a slightly different slant to the traditional refreshing of the image. Whilst the image is cycling at 100Hz or 200Hz, out of phase or in between each frame the LED back light is actually turned off momentarily. This essentially introduces a blank, black frame in between the coloured image frames. This has the effect of creating a black back drop to the coloured image and when cycled very quickly it has the result of further emphasising the colour, whilst also improving the motion handling.

The added benefit for people with photosensitive epilepsy

Scientific studies have proven that for patients with photosensitive epilepsies 100Hz and 200Hz televisions can help prevent seizures when playing video games or watching TV.

PECET: Schedule Released by ANU for 2012

PECET 2012 Schedule Released by ANU
Acharya Nagarjuna University has announced PECET 2012 schedule. PECET
(Physical Education Common Entrance Test) is an entrance examination
for admission to Bachelor of Physical Education and Master of Physical
Education for the academic year 2012-13. ANU has been entrusted with
the responsibility of conducting PECET 2012 by APSCHE. Prof. K.
Viyanna Rao, Vice Chancellor of ANU will be serving as Convener of
PECET 2012.

Applications for PECET 2012 will be issued from 12th March 2012.
Filled in applications should be submitted along with all the
necessary copies of certificates to the Convener, PECET 2012, Acharya
Nagarjune University, Guntur, Andhra Pradesh. Last date for the
receipt of completed applications is 26th April 2012.

PECET is an objective type entrance examination to be conducted across
Andhra Pradesh. Notification will be issued soon by APSCHE on behalf
of ANU. Details of notification along with application procedure,
scheme of examination, download of hall tickets, declaration of
results and counseling will be available on ANU website at
www.anu.ac.in or www.apsche.org.

Read more: http://www.apcollegeadmissions.com/2012/02/pecet-2012-schedule-released-by-anu.html#ixzz1n28IunwF

JNU Online Application Process for Admissions 2012-13

JNU Online Application Process for Admissions 2012-13
Jawaharlal Nehru University, more popular as JNU is going online from
the academic year 2012-13. The prestigious university has decided to
receive applications for various PG, M.Phil and Ph.D. programmes
through online. As this is the first experiment by JNU, it is also
accepting offline applications. Online application facility will be
available on the newly developed website of JNU at www.jnuonline.in .
JNU admit candidates under various categories as described below:

1) Category A (Admission through Entrance Exam): BA (Hons), MA, M.Sc.,
M.Phil, Ph.D., MCA, M.Tech, MPH, Pre Ph.D.

2) Category B: Direction admission to Ph.D. programmes will be offered
in all schools and disciplines based on written test or viva - voce or
both.

3) Category C: M.Phil, Pre Ph.D. and Ph.D. admissions in Science
Schools except Molecular Biology.

JNU, New Delhi will conduct entrance exams between 22nd and 25th May
2012. Candidates can apply either online or offline. Offline
application forms can be obtained from Section Officer, Admissions,
Room No. 28, Administrative Block, Jawaharlal Nehru University, New
Delhi -67. More details are also available at www.jnu.ac.in or
employment news dated 4th February 2012.

Dates to remember:

1) Start of Online application Process: 6th February 2012
2) Close of online submission of applications: 21st March 2012
3) Start of issue of offline applications by post: 6th February 2012
4) Last date for issue of offline applications: 5th March 2012
5) Last date for the submission of completed offline applications:
21st March 2012
6) Last date for the submission of confirmation page of online
application form: 28th March 2012.

Read more: http://www.apcollegeadmissions.com/2012/02/jnu-online-application-process-for.html#ixzz1n288eY4R

deprived - definition of deprived

Adjective:	Suffering a severe and damaging lack of basic material and cultural benefits. (of a person) Suffering a lack of a specified benefit that is considered important.
Synonyms:	devoid

TEN THINGS THAT AN INTERVIEWER LOOKS IN YOU!

TEN THINGS THAT AN INTERVIEWER LOOKS IN YOU!

TEN THINGS THAT AN INTERVIEWER LOOKS IN YOU!

1. Family Background

2. Education

3. Experience

4. Stability

5. Initiative

6. General Ability

7. Interpersonal Skills

8. Confidence

9. Aptitude

10. Pleasant Looks

How one wished that an interview were a simple meeting of minds and hearts. Just one casual meeting where an employee's future gets sealed. Unfortunately, it's not something as pre-ordained as you would like it to be; it's a pre-meditated exercise which fetches you dividends only if your homework is done right.

Install Picasa 3.8 over the original Picasa 3.0 for Linux.

Install Picasa 3.8 over the original Picasa 3.0 for Linux.

Step 1 (optional): install the latest Wine via PPA:

sudo add-apt-repository ppa:ubuntu-wine/ppa sudo apt-get update && sudo apt-get install wine

Step 2: Add the Google Testing PPA

sudo sh -c "echo 'deb http://dl.google.com/linux/deb/ testing non-free' >> /etc/apt/sources.list.d/google.list" sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 7FAC5991

Step 3: Install Picasa 3.0

Yes, Picasa 3.0, but we'll update it in the next step:

sudo apt-get update && sudo apt-get install picasa

Step 4: Download and install Picasa 3.8 for Windows:

cd && wget http://dl.google.com/picasa/picasa38-setup.exe wine picasa38-setup.exe

Step 5: Now all we have to do is copy the Picasa 3.8 files over 3.0 using the following command:

sudo cp -r ~/.wine/drive_c/Program\ Files/Google/Picasa3/* /opt/google/picasa/3.0/wine/drive_c/Program\ Files/Google/Picasa3/

Now run Picasa 3.8 from Applications > Graphics > Picasa > Picasa.


Important note: Don't click the "Places" button as it will freeze Picasa 3.8 and it will fail to start again!


read more http://www.webupd8.org/2010/04/how-to-install-picasa-36-in-ubuntu.html

VLSI Terminology: Definition of process technology

Definition of: process technology 

With regard to digital integrated circuits, process technology refers to the particular method used to make silicon chips. The driving force behind the manufacture of integrated circuits is miniaturization, and process technology boils down to the size of the finished transistor and other components. The smaller the transistors, the more transistors in the same area, the faster they switch, the less energy they require and the cooler the chip runs (given equal numbers of transistors).

Measured in Nanometers
The size of the features (the elements that make up the structures on a chip) used to be measured in micrometers. A 3 µm process technology, also called a "technology node" and "process node," referred to a silicon chip with features three micrometers in size. Today, features are measured in nanometers. A 45 nm process technology refers to features 45 nm or 0.45 µm in size.

Elements Measured
Historically, the process technology referred to the length of the silicon channel between the source and drain terminals in field effect transistors (see FET). The sizes of other features are generally derived as a ratio of the channel length, where some may be larger than the channel size and some smaller. For example, in a 90 nm process, the length of the channel may be 90 nm, but the width of the gate terminal may be only 50 nm.

An Example of Progress
Consider that the process technology of the first 486 chip in 1989 was one micron (1,000 nanometers). By 2003, the state-of-the-art decreased to 90 nm ("90 nano"). In 15 years, feature sizes were reduced by slightly less than one millionth of a meter. What may seem like a minuscule, microscopic change to the casual observer took thousands of man years and billions of dollars worth of research and development. Note the huge variance in semiconductor feature sizes starting in the 1950s (see chart below).

Chips Are Nanotechnology
Intel introduced 45 nm processors in 2008. To understand how tiny 45 nanometers is, it would take two thousand 45 nm objects laid side-by-side to equal the thickness of one human hair.

In 2010, 32 nm chips were introduced, and feature sizes as low as 11 nm are expected in the future. For some time, chips have been in the realm of nanotechnology, which refers to elements 100 nanometers and smaller.

read more at http://www.pcmag.com/encyclopedia_term/0,2542,t=process+technology&i=49759,00.asp

Definition of: feature size

Definition of: feature size 

The size of the elements on a chip, which is designated by the "DRAM half pitch." The smallest feature size is generally smaller than the feature size for a technology generation (technology node). For example, the 180 nm technology generation will have gate lengths smaller than 180 nm.

Definition of: DRAM half pitch 

The common measure of the technology generation of a chip. It is half the distance between cells in a dynamic RAM memory chip. For example, in 2002, the DRAM half pitch had been reduced to 130 nm (.13 micron). By 2006, it had shrunk to 65 nm (.065 micron).

source :http://www.pcmag.com/encyclopedia_term/0,2542,t=feature+size&i=43075,00.asp

Integrated circuits: Generations

SSI, MSI and LSI

The first integrated circuits contained only a few transistors. Called "small-scale integration" (SSI), digital circuits containing transistors numbering in the tens provided a few logic gates for example, while early linear ICs such as the Plessey SL201 or the Philips TAA320 had as few as two transistors. The term Large Scale Integration was first used by IBM scientist Rolf Landauer when describing the theoretical concept[citation needed], from there came the terms for SSI, MSI, VLSI, and ULSI.

VLSI

The final step in the development process, starting in the 1980s and continuing through the present, was "very large-scale integration" (VLSI). The development started with hundreds of thousands of transistors in the early 1980s, and continues beyond several billion transistors as of 2009.

Multiple developments were required to achieve this increased density. Manufacturers moved to smaller design rules and cleaner fabrication facilities, so that they could make chips with more transistors and maintain adequate yield. The path of process improvements was summarized by the International Technology Roadmap for Semiconductors (ITRS). Design tools improved enough to make it practical to finish these designs in a reasonable time. The more energy efficient CMOS replaced NMOS and PMOS, avoiding a prohibitive increase in power consumption. Better texts such as the landmark textbook by Mead and Conway helped schools educate more designers, among other factors.

In 1986 the first one megabit RAM chips were introduced, which contained more than one million transistors. Microprocessor chips passed the million transistor mark in 1989 and the billion transistor mark in 2005

ULSI, WSI, SOC and 3D-IC

To reflect further growth of the complexity, the term ULSI that stands for "ultra-large-scale integration" was proposed for chips of complexity of more than 1 million transistors.

Wafer-scale integration (WSI) is a system of building very-large integrated circuits that uses an entire silicon wafer to produce a single "super-chip". Through a combination of large size and reduced packaging, WSI could lead to dramatically reduced costs for some systems, notably massively parallel supercomputers. The name is taken from the term Very-Large-Scale Integration, the current state of the art when WSI was being developed.

A system-on-a-chip (SoC or SOC) is an integrated circuit in which all the components needed for a computer or other system are included on a single chip. The design of such a device can be complex and costly, and building disparate components on a single piece of silicon may compromise the efficiency of some elements. However, these drawbacks are offset by lower manufacturing and assembly costs and by a greatly reduced power budget: because signals among the components are kept on-die, much less power is required (see Packaging).

A three-dimensional integrated circuit (3D-IC) has two or more layers of active electronic components that are integrated both vertically and horizontally into a single circuit. Communication between layers uses on-die signaling, so power consumption is much lower than in equivalent separate circuits. Judicious use of short vertical wires can substantially reduce overall wire length for faster operation.

GATE PREVIOUS PAPERS of EEE

GATE PREVIOUS PAPERS

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RRB-AJMER Assistant Station Master (ASM) Result 2011

RRB Ajmer 2011 Result: ASM 2011 Result

click here for the list of selected Candidates  

http://rrbajmer.org/results/2012/Result_cat_01_ASM_of_3_10_aft_APT.pdf

Download the admit card of UPSC CDS(Combined Defence Services Examination) 2012 (I)

Unlike past, from 2012 onwards  candidates will be able to download their exam admit card at UPSC website. Yes, you heard it. From now on even UPSC admit card will be available online.

Though little late but it seems that even UPSC is learning that it is much better to upload admit card on Internet, rather than sending it by post or asking the candidates to visit UPSC office physically for duplicate hall ticket. A press note which has appeared in The Times of India, main paper and not in Ascent has confirmed the same.

To Download Combined Defence Services Examination admit card  Click  here 

http://upsc.nic.in/onlineadmitcard/main.aspx for 12.02.2012 exam.

tags: upsc admit cards,CDS Hall Tickets ,CDS Admit cards, download   admit card  of UPSC CDS,

Setup and hold times of an flip-flop

Setup and hold times

Setup time is the minimum amount of time the data signal should be held steady before the clock event so that the data are reliably sampled by the clock. This applies to synchronous circuits such as the flip-flop.

Hold time is the minimum amount of time the data signal should be held steady after the clock event so that the data are reliably sampled. This applies to synchronous circuits such as the flip-flop.

To summarize: Setup time -> Clock flank -> Hold time.

The metastability in flip-flops can be avoided by ensuring that the data and control inputs are held valid and constant for specified periods before and after the clock pulse, called the setup time (t_su) and the hold time (t_h) respectively. These times are specified in the data sheet for the device, and are typically between a few nanoseconds and a few hundred picoseconds for modern devices.

Unfortunately, it is not always possible to meet the setup and hold criteria, because the flip-flop may be connected to a real-time signal that could change at any time, outside the control of the designer. In this case, the best the designer can do is to reduce the probability of error to a certain level, depending on the required reliability of the circuit. One technique for suppressing metastability is to connect two or more flip-flops in a chain, so that the output of each one feeds the data input of the next, and all devices share a common clock. With this method, the probability of a metastable event can be reduced to a negligible value, but never to zero. The probability of metastability gets closer and closer to zero as the number of flip-flops connected in series is increased.

So-called metastable-hardened flip-flops are available, which work by reducing the setup and hold times as much as possible, but even these cannot eliminate the problem entirely. This is because metastability is more than simply a matter of circuit design. When the transitions in the clock and the data are close together in time, the flip-flop is forced to decide which event happened first. However fast we make the device, there is always the possibility that the input events will be so close together that it cannot detect which one happened first. It is therefore logically impossible to build a perfectly metastable-proof flip-flop.

Propagation delay

Another important timing value for a flip-flop (F/F) is the clock-to-output delay (common symbol in data sheets: t_CO) or propagation delay (t_P), which is the time the flip-flop takes to change its output after the clock edge. The time for a high-to-low transition (t_PHL) is sometimes different from the time for a low-to-high transition (t_PLH).

When cascading F/Fs which share the same clock (as in a shift register), it is important to ensure that the t_CO of a preceding F/F is longer than the hold time (t_h) of the following flip-flop, so data present at the input of the succeeding F/F is properly "shifted in" following the active edge of the clock. This relationship between t_CO and t_h is normally guaranteed if the F/Fs are physically identical. Furthermore, for correct operation, it is easy to verify that the clock period has to be greater than the sum t_su + t_h.

source:http://en.wikipedia.org/wiki/Flip-flop_(electronics)