Computer virus

Computer virus

 

 computer virus is a type of malicious software program ("malware") that, when executed, replicates by reproducing itself (copying its own source code) by infecting other computer programs by modifying them.^[1] Infecting computer programs can include as well, data files, or the "boot" sector of the hard drive. When this replication succeeds, the affected areas are then said to be "infected" with a computer virusr virus

 

 Computer viruses currently cause billions of dollars' worth of economic damage each year

Once a virus has successfully attached to a program, file, or document, the virus will lie dormant until circumstances cause the computer or device to execute its code. In order for a virus to infect your computer, you have to run the infected program, which in turn causes the virus code to be executed. This means that a virus can remain dormant on your computer, without showing major sings or symptoms. However, once the virus infects your computer, the virus can infect other computers on the same network. Stealing passwords or data, logging keystrokes, corrupting files, spamming your email contacts, and even taking over your machine are just some of the devastating and irritating things a virus can do.

 TYPE OF  Computer virus

Most Common Types of Viruses and Other Malicious Programs

1. Resident Viruses

This type of virus is a permanent which dwells in the RAM memory. From there it can overcome and interrupt all of the operations executed by the system: corrupting files and programs that are opened, closed, copied, renamed etc.

Examples include: Randex, CMJ, Meve, and MrKlunky.

2. Multipartite Viruses

Multipartite viruses are distributed through infected media and usually hide in the memory. Gradually, the virus moves to the boot sector of the hard drive and infects executable files on the hard drive and later across the computer system.

3. Direct Action Viruses

The main purpose of this virus is to replicate and take action when it is executed. When a specific condition is met, the virus will go into action and infect files in the directory or folder that it is in and in directories that are specified in the AUTOEXEC.BAT file PATH. This batch file is always located in the root directory of the hard disk and carries out certain operations when the computer is booted.

4. Overwrite Viruses

Virus of this kind is characterized by the fact that it deletes the information contained in the files that it infects, rendering them partially or totally useless once they have been infected.

The only way to clean a file infected by an overwrite virus is to delete the file completely, thus losing the original content.

Examples of this virus include: Way, Trj.Reboot, Trivial.88.D.

5. Boot Virus

This type of virus affects the boot sector of a floppy or hard disk. This is a crucial part of a disk, in which information on the disk itself is stored together with a program that makes it possible to boot (start) the computer from the disk.

The best way of avoiding boot viruses is to ensure that floppy disks are write-protected and never start your computer with an unknown floppy disk in the disk drive.

Examples of boot viruses include: Polyboot.B, AntiEXE.

6. Macro Virus

Macro viruses infect files that are created using certain applications or programs that contain macros. These mini-programs make it possible to automate series of operations so that they are performed as a single action, thereby saving the user from having to carry them out one by one.

Examples of macro viruses: Relax, Melissa.A, Bablas, O97M/Y2K.

7. Directory Virus

Directory viruses change the paths that indicate the location of a file. By executing a program (file with the extension .EXE or .COM) which has been infected by a virus, you are unknowingly running the virus program, while the original file and program have been previously moved by the virus.

Once infected it becomes impossible to locate the original files.

8. Polymorphic Virus

Polymorphic viruses encrypt or encode themselves in a different way (using different algorithms and encryption keys) every time they infect a system.

This makes it impossible for anti-viruses to find them using string or signature searches (because they are different in each encryption) and also enables them to create a large number of copies of themselves.

Examples include: Elkern, Marburg, Satan Bug, and Tuareg.

9. File Infectors

This type of virus infects programs or executable files (files with an .EXE or .COM extension). When one of these programs is run, directly or indirectly, the virus is activated, producing the damaging effects it is programmed to carry out. The majority of existing viruses belongs to this category, and can be classified depending on the actions that they carry out.

10. Encrypted Viruses

This type of viruses consists of encrypted malicious code, decrypted module. The viruses use encrypted code technique which make antivirus software hardly to detect them. The antivirus program usually can detect this type of viruses when they try spread by decrypted themselves.

11. Companion Viruses

Companion viruses can be considered file infector viruses like resident or direct action types. They are known as companion viruses because once they get into the system they "accompany" the other files that already exist. In other words, in order to carry out their infection routines, companion viruses can wait in memory until a program is run (resident viruses) or act immediately by making copies of themselves (direct action viruses).

Some examples include: Stator, Asimov.1539, and Terrax.1069

12. Network Virus

Network viruses rapidly spread through a Local Network Area (LAN), and sometimes throughout the internet. Generally, network viruses multiply through shared resources, i.e., shared drives and folders. When the virus infects a computer, it searches through the network to attack its new potential prey. When the virus finishes infecting that computer, it moves on to the next and the cycle repeats itself.

The most dangerous network viruses are Nimda and SQLSlammer.

13. Nonresident Viruses

This type of viruses is similar to Resident Viruses by using replication of module. Besides that, Nonresident Viruses role as finder module which can infect to files when it found one (it will select one or more files to infect each time the module is executed).

14. Stealth Viruses

Stealth Viruses is some sort of viruses which try to trick anti-virus software by intercepting its requests to the operating system. It has ability to hide itself from some antivirus software programs. Therefore, some antivirus program cannot detect them.

15. Sparse Infectors

In order to spread widely, a virus must attempt to avoid detection. To minimize the probability of its being discovered a virus could use any number of different techniques. It might, for example, only infect every 20th time a file is executed; it might only infect files whose lengths are within narrowly defined ranges or whose names begin with letters in a certain range of the alphabet. There are many other possibilities.

16. Spacefiller (Cavity) Viruses

Many viruses take the easy way out when infecting files; they simply attach themselves to the end of the file and then change the start of the program so that it first points to the virus and then to the actual program code. Many viruses that do this also implement some stealth techniques so you don't see the increase in file length when the virus is active in memory.

A spacefiller (cavity) virus, on the other hand, attempts to be clever. Some program files, for a variety of reasons, have empty space inside of them. This empty space can be used to house virus code. A spacefiller virus attempts to install itself in this empty space while not damaging the actual program itself. An advantage of this is that the virus then does not increase the length of the program and can avoid the need for some stealth techniques. The Lehigh virus was an early example of a spacefiller virus.

17. FAT Virus

The file allocation table or FAT is the part of a disk used to connect information and is a vital part of the normal functioning of the computer. 

This type of virus attack can be especially dangerous, by preventing access to certain sections of the disk where important files are stored. Damage caused can result in information losses from individual files or even entire directories.

18. Worms

A worm is technically not a virus, but a program very similar to a virus; it has the ability to self-replicate, and can lead to negative effects on your system and most importantly they are detected and eliminated by antiviruses.

Examples of worms include: PSWBugbear.B, Lovgate.F, Trile.C, Sobig.D, Mapson.

19. Trojans or Trojan Horses

Another unsavory breed of malicious code (not a virus as well) are Trojans or Trojan horses, which unlike viruses do not reproduce by infecting other files, nor do they self-replicate like worms.

20. Logic Bombs

They are not considered viruses because they do not replicate. They are not even programs in their own right but rather camouflaged segments of other programs.

Their objective is to destroy data on the computer once certain conditions have been met. Logic bombs go undetected until launched, and the results can be destructive.

 

 

How to protect against computer viruses?

As you can see, just like a vicious flu virus, a computer virus is something that you want to avoid. The terms virus and malware are often used interchangeably; however, a virus is one of many types of malware, and only one aspect of the overall threat landscape. As a result, traditional antivirus software alone will not fully protect you from all threats.
Instead, look into comprehensive security software like Norton Security.

International Court of Justice

International Court of Justice

 

The International Court of Justice (ICJ) is the principal judicial organ of the United Nations (UN). It was established in June 1945 by the Charter of the United Nations and began work in April 1946.
The seat of the Court is at the Peace Palace in The Hague (Netherlands). Of the six principal organs of the United Nations, it is the only one not located in New York (United States of America).
The Court’s role is to settle, in accordance with international law, legal disputes submitted to it by States and to give advisory opinions on legal questions referred to it by authorized United Nations organs and specialized agencies.
The Court is composed of 15 judges, who are elected for terms of office of nine years by the United Nations General Assembly and the Security Council. It is assisted by a Registry, its administrative organ. Its official languages are English and French.

Rensonware

 Rensonware

a type of malicious software designed to block access to a computer system until a sum of money is paid.

Ransomware is a type of malicious software that carries out the cryptoviral extortion attack from cryptovirology that blocks access to data until a ransom is paid and displays a message requesting payment to unlock it.

History

Encrypting ransomware

The first known malware extortion attack, the "AIDS Trojan" written by Joseph Popp in 1989, had a design failure so severe it was not necessary to pay the extortionist at all. Its payload hid the files on the hard drive and encrypted only their names, and displayed a message claiming that the user's license to use a certain piece of software had expired. The user was asked to pay US$189 to "PC Cyborg Corporation" in order to obtain a repair tool even though the decryption key could be extracted from the code of the Trojan. The Trojan was also known as "PC Cyborg". Popp was declared mentally unfit to stand trial for his actions, but he promised to donate the profits from the malware to fund AIDS research.^[27]
The notion of using public key cryptography for ransom attacks was introduced in 1996 by Adam L. Young and Moti Yung. Young and Yung critiqued the failed AIDS Information Trojan that relied on symmetric cryptography alone, the fatal flaw being that the decryption key could be extracted from the Trojan, and implemented an experimental proof-of-concept cryptovirus on a Macintosh SE/30 that used RSA and the Tiny Encryption Algorithm (TEA) to hybrid encrypt the victim's data. Since public key crypto is used, the cryptovirus only contains the encryption key. The attacker keeps the corresponding private decryption key private. Young and Yung's original experimental cryptovirus had the victim send the asymmetric ciphertext to the attacker who deciphers it and returns the symmetric decryption key it contains to the victim for a fee. Long before electronic money existed Young and Yung proposed that electronic money could be extorted through encryption as well, stating that "the virus writer can effectively hold all of the money ransom until half of it is given to him. Even if the e-money was previously encrypted by the user, it is of no use to the user if it gets encrypted by a cryptovirus".^[12] They referred to these attacks as being "cryptoviral extortion", an overt attack that is part of a larger class of attacks in a field called cryptovirology, which encompasses both overt and covert attacks.^[12]
Examples of extortionate ransomware became prominent in May 2005.^[28] By mid-2006, Trojans such as Gpcode, TROJ.RANSOM.A, Archiveus, Krotten, Cryzip, and MayArchive began utilizing more sophisticated RSA encryption schemes, with ever-increasing key-sizes. Gpcode.AG, which was detected in June 2006, was encrypted with a 660-bit RSA public key.^[29] In June 2008, a variant known as Gpcode.AK was detected. Using a 1024-bit RSA key, it was believed large enough to be computationally infeasible to break without a concerted distributed effort.^{[30][31][32][33]}
Encrypting ransomware returned to prominence in late 2013 with the propagation of CryptoLocker—using the Bitcoin digital currency platform to collect ransom money. In December 2013, ZDNet estimated based on Bitcoin transaction information that between 15 October and 18 December, the operators of CryptoLocker had procured about US$27 million from infected users.^[34] The CryptoLocker technique was widely copied in the months following, including CryptoLocker 2.0 (though not to be related to CryptoLocker), CryptoDefense (which initially contained a major design flaw that stored the private key on the infected system in a user-retrievable location, due to its use of Windows' built-in encryption APIs),^{[24][35][36][37]} and the August 2014 discovery of a Trojan specifically targeting network-attached storage devices produced by Synology.^[38] In January 2015, it was reported that ransomware-styled attacks have occurred against individual websites via hacking, and through ransomware designed to target Linux-based web servers.^[39][40][41]
Some ransomware strains have used proxies tied to Tor hidden services to connect to their command and control servers, increasing the difficulty of tracing the exact location of the criminals.^[42][43] Furthermore, dark web vendors have increasingly started to offer the technology as a service.^[43][44][45]
Symantec has classified ransomware to be the most dangerous cyber threat.^[46]

Non-encrypting ransomware

In August 2010, Russian authorities arrested nine individuals connected to a ransomware Trojan known as WinLock. Unlike the previous Gpcode Trojan, WinLock did not use encryption. Instead, WinLock trivially restricted access to the system by displaying pornographic images, and asked users to send a premium-rate SMS (costing around US$10) to receive a code that could be used to unlock their machines. The scam hit numerous users across Russia and neighboring countries—reportedly earning the group over US$16 million.^[15][47]
In 2011, a ransomware Trojan surfaced that imitated the Windows Product Activation notice, and informed users that a system's Windows installation had to be re-activated due to "[being a] victim of fraud". An online activation option was offered (like the actual Windows activation process), but was unavailable, requiring the user to call one of six international numbers to input a 6-digit code. While the malware claimed that this call would be free, it was routed through a rogue operator in a country with high international phone rates, who placed the call on hold, causing the user to incur large international long distance charges.^[13]
In February 2013, a ransomware Trojan based on the Stamp.EK exploit kit surfaced; the malware was distributed via sites hosted on the project hosting services SourceForge and GitHub that claimed to offer "fake nude pics" of celebrities.^[48] In July 2013, an OS X-specific ransomware Trojan surfaced, which displays a web page that accuses the user of downloading pornography. Unlike its Windows-based counterparts, it does not block the entire computer, but simply exploits the behavior of the web browser itself to frustrate attempts to close the page through normal means.^[49]
In July 2013, a 21-year-old man from Virginia, whose computer coincidentally did contain pornographic photographs of underaged girls with whom he had conducted sexualized communications, turned himself in to police after receiving and being deceived by ransomware purporting to be an FBI message accusing him of possessing child pornography. An investigation discovered the incriminating files, and the man was charged with child sexual abuse and possession of child pornography.^[50]

Leakware (also called Doxware)

The converse of ransomware is a cryptovirology attack that threatens to publish stolen information from the victim's computer system rather than deny the victim access to it.^[51] In a leakware attack, malware exfiltrates sensitive host data either to the attacker or alternatively, to remote instances of the malware, and the attacker threatens to publish the victim's data unless a ransom is paid. The attack was presented at West Point in 2003 and was summarized in the book Malicious Cryptography as follows, "The attack differs from the extortion attack in the following way. In the extortion attack, the victim is denied access to its own valuable information and has to pay to get it back, where in the attack that is presented here the victim retains access to the information but its disclosure is at the discretion of the computer virus".^[52] The attack is rooted in game theory and was originally dubbed "non-zero sum games and survivable malware". The attack can yield monetary gain in cases where the malware acquires access to information that may damage the victim user or organization, e.g., reputational damage that could result from publishing proof that the attack itself was a success.

Mobile ransomware

With the increased popularity of ransomware on PC platforms, ransomware targeting mobile operating systems have also proliferated. Typically, mobile ransomware payloads are blockers, as there is little incentive to encrypt data since it can be easily restored via online synchronization.^[53] Mobile ransomware typically targets the Android platform, as it allows applications to be installed from third-party sources.^[53][54] The payload is typically distributed as an APK file installed by an unsuspecting user; it may attempt to display a blocking message over top of all other applications,^[54] while another used a form of clickjacking to cause the user to give it "device administrator" privileges to achieve deeper access to the system.^[55]
Different tactics have been used on iOS devices, such as exploiting iCloud accounts and using the Find My iPhone system to lock access to the device.^[56] On iOS 10.3, Apple patched a bug in the handling of JavaScript pop-up windows in Safari that had been exploited by ransomware websites

Transformer

 

A transformer is an electrical device that transfers electrical energy between two or more circuits through electromagnetic induction.

 

    Ideal transformer equations (eq.)

By Faraday's law of induction:
${\displaystyle V_{\text{S}}=-N_{\text{S}}{\frac {\mathrm {d} \Phi }{\mathrm {d} t}}}$ . . . (1)^[a]
${\displaystyle V_{\text{P}}=-N_{\text{P}}{\frac {\mathrm {d} \Phi }{\mathrm {d} t}}}$ . . . (2)
Combining ratio of (1) & (2)
Turns ratio ${\displaystyle ={\frac {V_{\text{P}}}{V_{\text{S}}}}={\frac {-N_{\text{P}}}{-N_{\text{S}}}}=a}$ . . . (3) where

for step-down transformers, a > 1

for step-up transformers, a < 1

By law of conservation of energy, apparent, real and reactive power are each conserved in the input and output
${\displaystyle S=I_{\text{P}}V_{\text{P}}=I_{\text{S}}V_{\text{S}}}$ . . . (4)
Combining (3) & (4) with this endnote^[b][4] yields the ideal transformer identity
${\displaystyle {\frac {V_{\text{P}}}{V_{\text{S}}}}={\frac {I_{\text{S}}}{I_{\text{P}}}}={\frac {N_{\text{P}}}{N_{\text{S}}}}={\sqrt {\frac {L_{\text{P}}}{L_{\text{S}}}}}=a}$ . (5)
By Ohm's law and ideal transformer identity
${\displaystyle Z_{\text{L}}={\frac {V_{\text{S}}}{I_{\text{S}}}}}$ . . . (6)
Apparent load impedance Z'_L (Z_L referred to the primary)
${\displaystyle Z'_{\text{L}}={\frac {V_{\text{P}}}{I_{\text{P}}}}={\frac {aV_{\text{S}}}{I_{\text{S}}/a}}=a^{2}{\frac {V_{\text{S}}}{I_{\text{S}}}}=a^{2}{Z_{\text{L}}}}$ . (7)

color coding of resistance

color coding of resistance

The electronic color code is used to indicate the values or ratings of electronic components, usually for resistors, but also for capacitors, inductors, diodes and others.

Calculating Resistor Values

The Resistor Colour Code system is all well and good but we need to understand how to apply it in order to get the correct value of the resistor. The “left-hand” or the most significant coloured band is the band which is nearest to a connecting lead with the colour coded bands being read from left-to-right as follows;

Digit, Digit, Multiplier = Colour, Colour x 10 ^colour  in Ohm’s (Ω’s)

For example, a resistor has the following coloured markings;

Yellow Violet Red = 4 7 2 = 4 7 x 10² = 4700Ω or 4k7.

The fourth and fifth bands are used to determine the percentage tolerance of the resistor. Resistor tolerance is a measure of the resistors variation from the specified resistive value and is a consequence of the manufacturing process and is expressed as a percentage of its “nominal” or preferred value.
Related Products: Resistor Fixed Single-Other Mounting
Typical resistor tolerances for film resistors range from 1% to 10% while carbon resistors have tolerances up to 20%. Resistors with tolerances lower than 2% are called precision resistors with the or lower tolerance resistors being more expensive.
Most five band resistors are precision resistors with tolerances of either 1% or 2% while most of the four band resistors have tolerances of 5%, 10% and 20%. The colour code used to denote the tolerance rating of a resistor is given as;

Brown = 1%, Red = 2%, Gold = 5%, Silver = 10 %

If resistor has no fourth tolerance band then the default tolerance would be at 20%.

It is sometimes easier to remember the resistor colour code by using mnemonics or phrases that have a separate word in the phrase to represent each of the Ten + Two colours in the code. However, these sayings are often very crude but never the less effective for remembering the resistor colours. Here are just a few of the more “cleaner” versions but many more exist:

• Bad Booze Rots Our Young Guts But Vodka Goes Well
• Bad Boys Ring Our Young Girls But Vicky Goes Without
• Bad Boys Ring Our Young Girls But Vicky Gives Willingly — Get Some Now (This one is only slightly better because it includes the tolerance bands of Gold, Silver, and None).

As an added bonus, why not download and make our handy DIY Resistor Colour Code Wheel as a free and handy reference guide to help work out those resistor colour codes.
Related Products: Resistor Fixed Single-Surface Mount

Thermodynamics

Thermodynamics

                      
  is a branch of physics concerned with heat and temperature and their relation to energy and work.
Thermodynamics is the study of heat, "thermo," and work, "dynamics."
Thermodynamics is a branch of physics which deals with the energy and work of a system. It was born in the 19th century as scientists were first discovering how to build and operate steam engines. Thermodynamics deals only with the large scale response of a system which we can observe and measure in experiments. Small scale gas interactions are described by the kinetic theory of gases. The methods complement each other; some principles are more easily understood in terms of thermodynamics and some principles are more easily explained by kinetic theory. 

 

 

Thermodynamics

The 4 Laws

• Zeroth law of thermodynamics – If two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other.
• First law of thermodynamics – Energy can neither be created nor destroyed. It can only change forms. In any process, the total energy of the universe remains the same. For a thermodynamic cycle the net heat supplied to the system equals the net work done by the system.
• Second law of thermodynamics – The entropy of an isolated system not in equilibrium will tend to increase over time, approaching a maximum value at equilibrium.
• Third law of thermodynamics – As temperature approaches absolute zero, the entropy of a system approaches a constant minimum.

 

 

 

working principle of alternator

working principle of alternator

The working principle of alternator is very simple. It is just like basic principle of DC generator. It also depends upon Faraday's law of electromagnetic induction which says the current is induced in the conductor inside a magnetic field when there is a relative motion between that conductor and the magnetic field.
For understanding working of alternator let's think about a single rectangular turn placed in between two opposite magnetic pole as shown above.

What do you mean by armature reaction?

What do you mean by armature reaction?

Armature reaction in a DC machine. In a DC machine, the main field is produced by field coils. In both the generating and motoring modes, the armature carries current and a magnetic field is established, which is called the armature flux. The effect of armature flux on the main field is called the armature reaction.

 

WHO IS Stephen Hawking

WHO IS Stephen Hawking?

 Stephen William Hawking was born on 8 January 1942 (300 years after the death of Galileo) in Oxford, England. His parents' house was in north London, but during the second world war, Oxford was considered a safer place to have babies. When he was eight, his family moved to St. Albans, a town about 20 miles north of London. At the age of eleven, Stephen went to St. Albans School and then on to University College, Oxford; his father's old college. Stephen wanted to study Mathematics, although his father would have preferred medicine. Mathematics was not available at University College, so he pursued Physics instead. After three years and not very much work, he was awarded a first class honours degree in Natural Science. 

Stephen Hawking has worked on the basic laws which govern the universe. With Roger Penrose he showed that Einstein's General Theory of Relativity implied space and time would have a beginning in the Big Bang and an end in black holes.

 He is a fellow of the Royal Society and a member of the US National Academy of Science. Stephen Hawking is regarded as one of the most brilliant theoretical physicists since Einstein.

 Stephen was diagnosed with ALS, a form of Motor Neurone Disease, shortly after his 21st birthday. In spite of being wheelchair bound and dependent on a computerised voice system for communication Stephen Hawking continues to combine family life (he has three children and three grandchildren), and his research into theoretical physics together with an extensive programme of travel and public lectures. He still hopes to make it into space one day.Stephen was diagnosed with ALS, a form of Motor Neurone Disease, shortly after his 21st birthday. In spite of being wheelchair bound and dependent on a computerised voice system for communication Stephen Hawking continues to combine family life (he has three children and three grandchildren), and his research into theoretical physics together with an extensive programme of travel and public lectures. He still hopes to make it into space one day.

Black hole

 

Black hole

 

A black hole is a region of spacetime exhibiting such strong gravitational effects that nothing—not even particles and electromagnetic radiation such as light—can escape from inside it

A black hole is a region in space where the pulling force of gravity is so strong that light is not able to escape. The strong gravity occurs because matter has been pressed into a tiny space. This compression can take place at the end of a star's life. Some black holes are a result of dying stars. Because no light can escape, black holes are invisible. However, space telescopes with special instruments can help find black holes. They can observe the behavior of material and stars that are very close to black holes.

How Big Are Black Holes?
Black holes can come in a range of sizes, but there are three main types of black holes. The black hole's mass and size determine what kind it is.
The smallest ones are known as primordial black holes. Scientists believe this type of black hole is as small as a single atom but with the mass of a large mountain.
The most common type of medium-sized black holes is called "stellar." The mass of a stellar black hole can be up to 20 times greater than the mass of the sun and can fit inside a ball with a diameter of about 10 miles. Dozens of stellar mass black holes may exist within the Milky Way galaxy.
The largest black holes are called "supermassive." These black holes have masses greater than 1 million suns combined and would fit inside a ball with a diameter about the size of the solar system. Scientific evidence suggests that every large galaxy contains a supermassive black hole at its center. The supermassive black hole at the center of the Milky Way galaxy is called Sagittarius A. It has a mass equal to about 4 million suns and would fit inside a ball with a diameter about the size of the sun.

How Do Black Holes Form?
Primordial black holes are thought to have formed in the early universe, soon after the big bang.
Stellar black holes form when the center of a very massive star collapses in upon itself. This collapse also causes a supernova, or an exploding star, that blasts part of the star into space.
Scientists think supermassive black holes formed at the same time as the galaxy they are in. The size of the supermassive black hole is related to the size and mass of the galaxy it is in.

If Black Holes Are "Black," How Do Scientists Know They Are There?
A black hole can not be seen because of the strong gravity that is pulling all of the light into the black hole's center. However, scientists can see the effects of its strong gravity on the stars and gases around it. If a star is orbiting a certain point in space, scientists can study the star's motion to find out if it is orbiting a black hole.
When a black hole and a star are orbiting close together, high-energy light is produced. Scientific instruments can see this high-energy light.
A black hole's gravity can sometimes be strong enough to pull off the outer gases of the star and grow a disk around itself called the accretion disk. As gas from the accretion disk spirals into the black hole, the gas heats to very high temperatures and releases X-ray light in all directions. NASA telescopes measure the X-ray light. Astronomers use this information to learn more about the properties of a black hole.

Could a Black Hole Destroy Earth?
Black holes do not wander around the universe, randomly swallowing worlds. They follow the laws of gravity just like other objects in space. The orbit of a black hole would have to be very close to the solar system to affect Earth, which is not likely.
If a black hole with the same mass as the sun were to replace the sun, Earth would not fall in. The black hole with the same mass as the sun would keep the same gravity as the sun. The planets would still orbit the black hole as they orbit the sun now.

Will the Sun Ever Turn Into a Black Hole?
The sun does not have enough mass to collapse into a black hole. In billions of years, when the sun is at the end of its life, it will become a red giant star. Then, when it has used the last of its fuel, it will throw off its outer layers and turn into a glowing ring of gas called a planetary nebula. Finally, all that will be left of the sun is a cooling white dwarf star.

How Is NASA Studying Black Holes?
NASA is learning about black holes using spacecraft like the Chandra X-ray Observatory, the Swift satellite and the Fermi Gamma-ray Space Telescope. Fermi launched in 2008 and is observing gamma rays - the most energetic form of light - in search of supermassive black holes and other astronomical phenomena. Spacecraft like these help scientists answer questions about the origin, evolution and destiny of the universe.

SSC CGL 2017 Age Limit:

• SSC CGL 2017 Age Limit:

Post	Age Limit
Statistical Investigator Grade II	Maxi. 32 years
Assistant in CSS	20 – 30 years
Assistant in IB	21 – 30 years
Assistant Enforcement Officer / SI in CBI / SI in NIA	30 years
SI in Central Bureau of Narcotics	20 – 30 years
All Other posts	18 – 27 years

Highlights of SSC CGL 2017 Recruitment

Highlights of SSC CGL 2017 Recruitment

Events

	Dates
Starting Date of Online Application	16th May 2017
Last Date of Online Application	16th June 2017
Tier 1 Exam	1st August 2017 to 20th August 2017
Tier 2 Exam (Tentative Dates)	10th, 11th November 2017
Tier 3 Exam (Tentative Dates)	21st January 2018
Tier 4 Exam (Tentative Dates)	February 2018

 

WHAT COLOUR OF DG SET SMOKE AND WHAT THE REGION

WHAT COLOR OF DG SET SMOKE AND WHAT THE REGION

   

Blue/Gray Smoke: Blue/gray exhaust smoke is an indication of oil burning in the combustion chamber. These are possible symptoms and causes:

Valve Seals: Leaking valve seals will cause blue/gray exhaust smoke.

Valve Guides: Excessive clearance between the valve stem and the valve guide allows oil to leak past the gap into the cylinder.

Piston Rings: Worn or damaged piston rings will cause blow-by, resulting in blue/gray smoke.

Worn Cylinder Walls: Worn cylinder walls cause blow-by, resulting in blue/gray smoke.

PCV System: A stuck closed PCV valve causes excessive crankcase pressure, resulting in blue/gray smoke.

Black Smoke: Black exhaust smoke is an indication of a rich fuel condition. These are possible causes:

Fuel Injectors: A leaking or dripping fuel injector will cause a rich fuel condition.

Fuel Pressure Regulator: A stuck closed fuel pressure regulator will cause a rich fuel condition.

Fuel Return: A restricted fuel return line will cause a rich fuel condition.

White/Gray Smoke: White exhaust smoke is an indication that coolant is burning in the combustion chamber. These are possible causes:

Cylinder Head: A crack in the cylinder head (around the coolant jacket) will cause coolant to enter the combustion chamber.

Engine Block: A crack in the deck of an engine block near the coolant jacket will cause coolant to enter the combustion chamber.

Head Gasket: A damaged or blown head gasket will cause coolant to enter the combustion chamber resulting in white/gray smoke coming from the tailpipe.

What is the difference between a 'rocket' and a 'missile'?

 

Missile An object which is forcibly propelled at a target, either by hand or from a mechanical weapon

Rocket a cylindrical projectile that can be propelled to a great height or distance by the combustion of its contents...

 

JEE Advanced Pattern

JEE Advanced Pattern

 

1. The Joint Entrance Examination (Advanced) 2017 [JEE (Advanced) 2017] will be conducted by the seven Zonal Coordinating (ZC) IITs under the guidance of the Joint Admission Board (JAB) 2017.

2. Subjects include :- Physics, Chemistry, Maths

3. The question papers will consist of objective type (multiple choice and numerical answer type) questions designed to test comprehension, reasoning and analytical ability of candidates. Negative marks will be awarded for incorrect answers to some of the questions.

 

The examination consists of two papers, Paper 1 and Paper 2, each of 3 hours duration and will be held as per the following schedule:

 

Time -
Paper 1 09:00 to 12:00 IST
Paper 2 14:00 to 17:00 IST
Both the papers are compulsory.

 

Eligibility:-
Eligibility Criteria for Appearing In JEE (Advanced) 2017: A candidate, including a foreign national, must fulfil each and every one of the following five criteria to appear in JEE (Advanced) 2017.

Criterion 1 –
Performance in JEE (Main) 2017:
The candidate should be among the top 2, 20,000 (all categories included) in JEE (Main) 2017.

Criterion 2 –
Age limit: Candidates should have been born on or after October 1, 1992. Five years relaxation is given to SC, ST and PwD candidates, i.e., these candidates should have been born on or after October 1, 1987.

Criterion 3 –
Number of attempts: A candidate can attempt JEE (Advanced) a maximum of two times in consecutive years. Therefore, candidates who appeared in JEE (Advanced) 2016 for the first time are also eligible.

Criterion 4–
Appearance in Class XII(or equivalent) examination: A candidate should have appeared for the Class XII (or equivalent) examination for the first time in either 2016 or 2017. However, candidates whose Class XII (or equivalent) examination Board results for the academic year 2014-15 were declared after June 2015 are eligible to appear in JEE (Advanced) 2017.

Criterion 5–
Earlier admission at IITs:
A candidate should NOT have been admitted in an IIT irrespective of whether or not he/she continued in the program) OR accepted the IIT seat by reporting at a reporting centre in the past. The candidates whose admission at IITs was cancelled are also NOT eligible to appear in JEE (Advanced) 2017.
Candidates who have been admitted to a preparatory course in any of the IITs for the first time in 2016 can appear in JEE (Advanced) 2017. The candidates who have paid seat acceptance fee but not accepted the seat (by not reporting at any reporting centre during joint seat allocation in 2016) are eligible to appear in JEE (Advanced) 2017.
 

Scholarships: Motion gives opportunities to talented students for scholarships up to 80%. Scholarships are decided on various factors like academics and performance.