Showing posts with label are. Show all posts
Showing posts with label are. Show all posts
Tuesday, March 28, 2017
Gaming Websites Are at Risk
Gaming Websites Are at Risk
Online games are increasing in popularity with various groups of the population. Many people who start playing these very catchy games have no idea how exposed they can be to hacking. Hackers are looking for gaming websites that don’t have adequate security in place. They look for ways to take control of these websites using DDoS attacks. Once a website is hijacked it takes just a matter of minutes for the attackers to take over. If a website goes down, the damage could be irreversible. And, with over 145 million gamers online each day in over five different continents, having a gaming website that isnt reliable means you could lose your gamers, reputation and any associated gaming revenues in just a single day.
Gaming websites are big targets for DDoS attackers, but a website doesnt have to make it easy. With the right protection they can keep their gamers, reputation and keep revenue up.
Gaming websites are big targets for DDoS attackers, but a website doesnt have to make it easy. With the right protection they can keep their gamers, reputation and keep revenue up.
Created by the marketing team at Prolexic Technologies.
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Tuesday, February 14, 2017
Why are DC high voltage transmission lines replacing AC high voltage transmission lines at some places
Why are DC high voltage transmission lines replacing AC high voltage transmission lines at some places
With AC systems the peak voltage is 2^0.5 (1.4142) times the RMS (nominal) voltage. At transmission voltages that additional .4142 x voltage makes the insulation systems much more critical, lengthening the insulator strings and so increasing the cost of the insulators and poles required to separate the lines.
With DC systems the peak voltage is the nominal voltage, so the insulator strings need only deal with the nominal voltage reducing capital and maintenance costs (washing from helicopters etc.).
With very high voltage transmission where maximum voltage is limited by available technology, this fact is used to increase the nominal voltage on a given insulation type, resulting in a system which would be operated at 750,000 volts nominal (RMS) AC being used for 1,000,000 volts actual DC with 25% additional capacity for the same amperage (cable) design.
The other factors are
With DC systems the peak voltage is the nominal voltage, so the insulator strings need only deal with the nominal voltage reducing capital and maintenance costs (washing from helicopters etc.).
With very high voltage transmission where maximum voltage is limited by available technology, this fact is used to increase the nominal voltage on a given insulation type, resulting in a system which would be operated at 750,000 volts nominal (RMS) AC being used for 1,000,000 volts actual DC with 25% additional capacity for the same amperage (cable) design.
The other factors are
- In HVDC no corona loss is there as incase of HVAC.
- For longer distance,HVDC system is very economical as compared to the HVAC system.
- Allowing power transmission between unsynchronized AC distribution systems.
- HVDC increases the capacity of an existing power grid in situations where additional wires are difficult or expensive to install.
- For DC frequency is 0.Therefor there is no inductive reactance drop, result of it is improve voltage regulation.
- There is no problem of stability as in AC.
- There is no skin effect in DC.
- AC require 3 wire for transmission but DC require only 2 .
- There is no ferranti effect in DC{it doesnt mean that capacitance is absent in DC,capacitance act as open CKT for DC}
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Tuesday, January 17, 2017
Whether Tantalum capacitors are safe for use in new designs
Whether Tantalum capacitors are safe for use in new designs
The answer is "When you used properly". Tantalum capacitors are highly reliable.
They have the advantage of high capacitance per volume and good decoupling characteristics due to relatively low internal resistance and low inductance compared to traditional alternatives such as aluminum wet electrolytic capacitors.
They have the advantage of high capacitance per volume and good decoupling characteristics due to relatively low internal resistance and low inductance compared to traditional alternatives such as aluminum wet electrolytic capacitors.
The catch is in the qualifier "when used properly".Tantalum capacitors have a failure mode which can be triggered by voltage spikes only slightly more than their rated value. When used in circuits that can provide substantial energy to the capacitor failure can lead to thermal run-away with flame and explosion of the capacitor and low resistance short-circuiting of the capacitor terminals.
To be "safe" the circuits they are used in need to be guaranteed to have been rigorously designed and the design assumptions need to be met.This does not always happen.Tantalum capacitors are safe enough in the hands of genuine experts, or in undemanding circuits, and their advantages make them attractive. Alternatives such as "solid aluminum" capacitors have similar advantages and lack the catastrophic failure mode.
Many modern tantalum capacitors have built in protection mechanisms which implement fusing of various sorts, which is designed to disconnect the capacitor from its terminals when it fails and to limit pcb charring in most cases.
If when, limit and most are acceptable design criteria and/or you are a design expert and your factory always gets everything right and your application environment is always well understood, then tantalum capacitors may be a good choice for you.
If when, limit and most are acceptable design criteria and/or you are a design expert and your factory always gets everything right and your application environment is always well understood, then tantalum capacitors may be a good choice for you.
Source : electronics.stackexchange.com
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Wednesday, January 11, 2017
What are the different Classes of Amplifier
What are the different Classes of Amplifier
Amplifier Classes Explained...
Not all amplifiers are the same and there is a clear distinction made between the way their output stages operate. The main operating characteristics of an ideal amplifier are linearity, signal gain, efficiency and power output but in real world amplifiers there is always a trade off between these different characteristics.
Generally, large signal or Power Amplifiers are used in the output stages of audio amplifier systems to drive a loudspeaker load. A typical loudspeaker has an impedance of between 4? and 8?, thus a power amplifier must be able to supply the high peak currents required to drive the low impedance speaker.
One method used to distinguish the electrical characteristics of different types of amplifiers is by “class”, and as such amplifiers are classified according to their circuit configuration and method of operation. Then Amplifier Classes is the term used to differentiate between the different amplifier types.
Amplifier Classes represent the amount of the output signal which varies within the amplifier circuit over one cycle of operation when excited by a sinusoidal input signal. The classification of amplifiers range from entirely linear operation (for use in high-fidelity signal amplification) with very low efficiency, to entirely non-linear (where a faithful signal reproduction is not so important) operation but with a much higher efficiency, while others are a compromise between the two.
Amplifier classes are mainly lumped into two basic groups. The first are the classically controlled conduction angle amplifiers forming the more common amplifier classes of A, B, AB and C, which are defined by the length of their conduction state over some portion of the output waveform, such that the output stage transistor operation lies somewhere between being “fully-ON” and “fully-OFF”.
The second set of amplifiers are the newer so-called “switching” amplifier classes of D, E, F, G, S, Tetc, which use digital circuits and pulse width modulation (PWM) to constantly switch the signal between “fully-ON” and “fully-OFF” driving the output hard into the transistors saturation and cut-off regions.
The most commonly constructed amplifier classes are those that are used as audio amplifiers, mainly class A, B, AB and C and to keep things simple, it is these types of amplifier classes we will look at here in more detail.
Class A Amplifier
Class A Amplifiers are the most common type of amplifier class due mainly to their simple design. Class A, literally means “the best class” of amplifier due mainly to their low signal distortion levels and are probably the best sounding of all the amplifier classes mentioned here. The class A amplifier has the highest linearity over the other amplifier classes and as such operates in the linear portion of the characteristics curve.
Generally class A amplifiers use the same single transistor (Bipolar, FET, IGBT, etc) connected in a common emitter configuration for both halves of the waveform with the transistor always having current flowing through it, even if it has no base signal. This means that the output stage whether using a Bipolar, MOSFET or IGBT device, is never driven fully into its cut-off or saturation regions but instead has a base biasing Q-point in the middle of its load line. Then the transistor never turns “OFF” which is one of its main disadvantages.
Class A Amplifier
To achieve high linearity and gain, the output stage of a class A amplifier is biased “ON” (conducting) all the time. Then for an amplifier to be classified as “Class A” the zero signal idle current in the output stage must be equal to or greater than the maximum load current (usually a loudspeaker) required to produce the largest output signal.
As a class A amplifier operates in the linear portion of its characteristic curves, the single output device conducts through a full 360 degrees of the output waveform. Then the class A amplifier is equivalent to a current source.
Since a class A amplifier operates in the linear region, the transistors base (or gate) DC biasing voltage should by chosen properly to ensure correct operation and low distortion. However, as the output device is “ON” at all times, it is constantly carrying current, which represents a continuous loss of power in the amplifier.
Due to this continuous loss of power class A amplifiers create tremendous amounts of heat adding to their very low efficiency at around 30%, making them impractical for high-power amplifications. Also due to the high idling current of the amplifier, the power supply must be sized accordingly and be well filtered to avoid any amplifier hum and noise. Therefore, due to the low efficiency and over heating problems of Class A amplifiers, more efficient amplifier classes have been developed.
Class B Amplifier
Class B amplifiers were invented as a solution to the efficiency and heating problems associated with the previous class A amplifier. The basic class B amplifier uses two complimentary transistors either bipolar of FET for each half of the waveform with its output stage configured in a “push-pull” type arrangement, so that each transistor device amplifies only half of the output waveform.
In the class B amplifier, there is no DC base bias current as its quiescent current is zero, so that the dc power is small and therefore its efficiency is much higher than that of the class A amplifier. However, the price paid for the improvement in the efficiency is in the linearity of the switching device.
Class B Amplifier
When the input signal goes positive, the positive biased transistor conducts while the negative transistor is switched “OFF”. Likewise, when the input signal goes negative, the positive transistor switches “OFF” while the negative biased transistor turns “ON” and conducts the negative portion of the signal. Thus the transistor conducts only half of the time, either on positive or negative half cycle of the input signal.
Then we can see that each transistor device of the class B amplifier only conducts through one half or 180 degrees of the output waveform in strict time alternation, but as the output stage has devices for both halves of the signal waveform the two halves are combined together to produce the full linear output waveform.
This push-pull design of amplifier is obviously more efficient than Class A, at about 50%, but the problem with the class B amplifier design is that it can create distortion at the zero-crossing point of the waveform due to the transistors dead band of input base voltages from -0.7V to +0.7.
We remember from the Transistor tutorial that it takes a base-emitter voltage of about 0.7 volts to get a bipolar transistor to start conducting. Then in a class B amplifier, the output transistor is not “biased” to an “ON” state of operation until this voltage is exceeded.
This means that the the part of the waveform which falls within this 0.7 volt window will not be reproduced accurately making the class B amplifier unsuitable for precision audio amplifier applications.
To overcome this zero-crossing distortion (also known as Crossover Distortion) class AB amplifiers were developed.
Class AB Amplifier
As its name suggests, the Class AB Amplifier is a combination of the “Class A” and the “Class B” type amplifiers we have looked at above. The AB classification of amplifier is currently one of the most common used types of audio power amplifier design. The class AB amplifier is a variation of a class B amplifier as described above, except that both devices are allowed to conduct at the same time around the waveforms crossover point eliminating the crossover distortion problems of the previous class B amplifier.
The two transistors have a very small bias voltage, typically at 5 to 10% of the quiescent current to bias the transistors just above its cut-off point. Then the conducting device, either bipolar of FET, will be “ON” for more than one half cycle, but much less than one full cycle of the input signal. Therefore, in a class AB amplifier design each of the push-pull transistors is conducting for slightly more than the half cycle of conduction in class B, but much less than the full cycle of conduction of class A.
In other words, the conduction angle of a class AB amplifier is somewhere between 180o and 360odepending upon the chosen bias point as shown.
Class AB Amplifier
The advantage of this small bias voltage, provided by series diodes or resistors, is that the crossover distortion created by the class B amplifier characteristics is overcome, without the inefficiencies of the class A amplifier design. So the class AB amplifier is a good compromise between class A and class B in terms of efficiency and linearity, with conversion efficiencies reaching about 50% to 60%.
Class C Amplifier
The Class C Amplifier design has the greatest efficiency but the poorest linearity of the classes of amplifiers mentioned here. The previous classes, A, B and AB are considered linear amplifiers, as the output signals amplitude and phase are linearly related to the input signals amplitude and phase.
However, the class C amplifier is heavily biased so that the output current is zero for more than one half of an input sinusoidal signal cycle with the transistor idling at its cut-off point. In other words, the conduction angle for the transistor is significantly less than 180 degrees, and is generally around the 90 degrees area.
While this form of transistor biasing gives a much improved efficiency of a
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Tuesday, January 3, 2017
AVG PC TuneUp 2016 16 13 1 47453 FINAL Serial Keys are Here ! Full Version
AVG PC TuneUp 2016 16 13 1 47453 FINAL Serial Keys are Here ! Full Version
AVG PC TuneUp 2016 16.13.1.47453 FINAL Serial Keys are Here ! [Full Version]
New improved AVG PC TuneUp keeps your computer as good as new. It comprises range of 30 tools offer more speed, less crashing and longer battery life for both novice and experienced users.New features such as Live Optimization and Program Deactivator keep your PC at top speed.
Read more »New improved AVG PC TuneUp keeps your computer as good as new. It comprises range of 30 tools offer more speed, less crashing and longer battery life for both novice and experienced users.New features such as Live Optimization and Program Deactivator keep your PC at top speed.
Available link for download
Monday, January 2, 2017
Why 95 P C B s are of green colour
Why 95 P C B s are of green colour
Why 95% P.C.B.s are of green colour?
Answer: If the PCB itself is green, that indicates, that its made from glass-epoxy which is naturally green. Also your PCB could be made in every single color that exist. The finishing color is usually a solder mask. This mask is applied for safety reasons, for preventing eventual short circuits and etc. It could be every color, depends on the clients specifications.
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Tuesday, November 22, 2016
Are You Textually Active What Are You Really Saying on Text Message
Are You Textually Active What Are You Really Saying on Text Message
Text messaging has greatly grown in popularity even within the last ten years. Today, over 90% of people who have smartphones use text messaging via SMS, or short message service. However, there is a surprising divide between male and female messengers.
Although most people believe that females always have more to say than males do, this is not necessarily the case with texts. In fact, males generally send more texts each day with an average of 17 regular contacts with whom they stay in touch. On the other hand, women tend to stay in touch with about 13 contacts. There is a difference in the style of men’s and women’s text messages though. Men usually send shorter messages that are to the point; women are more likely to send longer messages and to express feelings of love and affection via SMS. Although women realize that texts alone do not keep a relationship alive, many men believe that texts are a valid form of daily communication.
There is also a gap between age groups. Those who are younger tend to send more texts than those who are older. This infographic shows more surprising data about this texting phenomenon.
There is also a gap between age groups. Those who are younger tend to send more texts than those who are older. This infographic shows more surprising data about this texting phenomenon.
This infographic was produced by Scratch Wireless. You can find unlimited data plans from Scratch Wireless.
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Sunday, October 23, 2016
Saturday, October 8, 2016
In Unix what are the sudo and su commands
In Unix what are the sudo and su commands
In Unix, what are the sudo and su commands?
The Unix commandssudo and suallow access to other commands as a different user.The sudo command
The sudo command stands for "superuser do". It prompts you for your personal password and confirms your request to execute a command by checking a file, called sudoers, which the system administrator configures. Using the sudoers file, system administrators can give certain users or groups access to some or all commands without those users having to know the root password. It also logs all commands and arguments so there is a record of who used it for what, and when.To use the
sudo command, at the command prompt, enter:sudo commandReplace
command with the command for which you want to use sudo.The
sudo command also makes it easier to practice the principle of least privilege (PoLP), which is a computer security concept that helps control system access and potential system exploits and compromises. For more information about the sudo command, visit A. P. Lawrences Using sudo page.The su command
The su command stands for "switch user", and allows you to become another user. To use the su command on a per-command basis, enter:su user -c commandReplace
user with the name of the account which youd like to run the command as, and command with the command you need to run as another user. To switch users before running many commands, enter:su userReplace
user with the name of the account which youd like to run the commands as.The
user feature is optional; if you dont provide a user, the su command defaults to the rootaccount, which in Unix is the system administrator account. In either case, youll be prompted for the password associated with the account for which youre trying to run the command. If you supply a user, you will be logged in as that account until you exit it. To do so, press Ctrl-d or type exit at the command prompt.Using
su creates security hazards, is potentially dangerous, and requires more administrative maintenance. Its not good practice to have numerous people knowing and using the root password because when logged in as root, you can do anything to the system. This could provide too much power for inexperienced users, who could unintentionally damage the system. Additionally, each time a user should no longer use the root account (e.g., an employee leaves), the system administrator will have to change the root password.Source : https://kb.iu.edu/d/amyi
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