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Lubricants:-                         Those substance which is applied between two moving or sliding surface in order to reduce the frictional resistance called lubricant. Function of Lubricant:-        I.             It reduce the frictional forces between two rubbing surfaces.     II.             It reduces the cost of maintenance of the machines and tools.   III.             It acts as a cleaning agent to wash off the solid carbon.   IV.             It acts as a seal and prevents the entry of moisture i.e leakage of gases under high pressure.     V.    ...

Law Of Friction: (i)                 Anonton’s First Law:-     According to this Law, the friction between two solids is independent of the area of contact.   For example   a Bricks slides over a flat surface than the friction will be same whether it is sliding on its end or its side or its base, because the actual area of contact is always smaller than the apparent area. (ii)              Anonton’s Second Law:-   According to this Law, the friction force is proportional to the load exerted by one surface over the another . For example- If a brick is placed on the Top of the another brick the friction will be doubled and the another brick is placed on the second brick, than the friction will get trebled and so on.                 ...

Einstein’s Coefficients:                                             Possibility of laser action:   Consider an atomic medium like a monoatomic gas, sealed in an enclosure. Let the e closure be maintained at a constant temperature, T. Let us define two energy states of Energies E 1 and E 2 , such that E 2 >E 1 . Let N 1 and N 2 = number of atoms in lower and upper energy states i.e. E 1 and E 2 respectively. When an atom is in the lower energy state E 1 , it would be in a position to absorb a photon of energy, E 2 -E 1 =hv. Let the enclosure be irradiated with an isotropic radiation of frequency, v or angular frequency w . Where, w =2 π v.                          [where h =h/2 π; h= Plank’s constant] Let U(w)= Radiation density such that, U( w ) d w is radiation density in...

Mechanism of Lubrication: (i)                 Fluid-film or thick-film or Hydrodynamic Lubrication (ii)              Boundary Lubrication or thin-film lubrication (iii)            Extreme Pressure Lubrication All parts are described below one by one. (i)                 Fluid-film or thick-film or Hydrodynamic Lubrication:                                                                   ...

Inode and Ist Structure:                                                    Inode stands for index node. As soon as the file is created, the kernel allocates a unique inode number to that file. An inode number is a positive number whose maximum value depends on the total inode numbers of the file system. The total number of inode, a file system can have is decided by the person who create the file system. The inode for the file system are kept together in inode table or inode structure. An inode describes which blocks of data a file occupies as will as the access rights of the file, file modification times and type of the file. This is the file system, inode is the basic building block, every file and dilatory in the file system is described by one and only one inode. The inode structures are housed is a separate block called the inode block on secondary s...

Shell As A Command Processor:                   Whenever we log on to a Unix machine, we see a prompt. This prompt can be either $ and %. Infect a program is running every time we make a login to the system. This program is called as shell. Whenever we issue a command the shell acquires that information. Parses and rebuilds the command line and finally leaves the execution work to the kernel. The kernel handles all the hardware on behalf of these commands and all processes is the system. Every thing happens in the background keeping user ignorant of happening behind the scenes. The shell is generally in one of the three states namely waiting, sleeping and waking. The shell wakes up and perform the following. (1)    It parse the command line and identifies each and every word in it and removes additional spaces if present. (2)    Looks for special variables is the comma...

Types of Attacks:-     We shall classify attacks with respect to two views: the common person’s view and a technologist’s vies. 1      Attacks: A General View                                             From a common person’s point of view, we can classify attacks into three categories, as shown below. Criminal Attacks    criminal attacks are the simplest to understand. Here, the sole aim of the attackers is to maximize financial gain by attacking computer systems. The lists some forms of criminal attacks. Attack Description Fraud     Scams             Destruction           Identity thef...