Locks

Locks are advisory locks, where each thread cooperates by acquiring the lock before accessing the equivalent data. Some systems also implement mandatory locks, where attempting unauthorized access to a locked resource will force exclusion in the entity attempting to make the access.

In terms of access to the data, no difference is made between shared or exclusive modes. Other schemes provide for a shared mode, where several threads can obtain a shared lock for read-only access to the data. Other modes such as exclusive, intend-to-exclude and intend-to-upgrade are also widely implemented.

Independent of the type of lock chosen above, locks can be confidential by what happens when the lock strategy prevents progress of a thread. Most locking designs block the finishing of the process requesting the lock until it is allowed to access the locked resource. A spin lock is a lock where the thread simply waits until the lock becomes accessible. It is very efficient if threads are only likely to be uncreative for a short period of time, as it avoids the overhead of operating system process re-scheduling. It is wasteful if the padlock is held for a long period of time.

Color

Color is the visual perceptual possessions corresponding in humans to the categories called red, yellow, white, etc. Color derives from spectrum of light distribution of light energy versus wavelength interacting in the eye with the spectral sensitivities of the light receptors. Color categories and physical condition of color are also associated with objects, materials, light sources, etc., based on their physical properties such as light absorption, reflection, or emission spectra.

Typically, only features of the composition of light that are visible by humans wavelength spectrum from 400 nm to 700 nm, roughly are included, thereby objectively relating the psychological phenomenon of color to its physical specification. Because perception of color stems from the varying sensitivity of different types of cone cells in the retina to different parts of the spectrum, colors may be defined and quantify by the degree to which they stimulate these cells. These physical or physiological quantifications of color, however, do not fully clarify the psychophysical perception of color appearance.

The science of color is sometimes called chromatics. It includes the perception of color by the human eye and brain, the origin of color in materials, color theory in art, and the physics of electromagnetic emission in the visible range that is, what we commonly refer to simply as light.

Populations

Populations are studied, in particular, in a branch of ecology known as population biology, and in population inheritance. In population dynamics, size, age and sex structure, mortality, reproductive behaviour, and growth of a population are studied. In biology, an isolated population denotes a breeding group whose members breed mostly or solely among themselves, usually as a result of physical isolation, although biologically they could breed with any member of the species. If there are several completely or nearly completely secluded populations in the global population of a taxon, these are called subpopulations. The metapopulation is a network of subpopulations in a given area ,where the individuals of the various subpopulations are able to cross ramshackle areas of the region. Biological dispersal is one of the key elements disturbing such populations; if dispersal is sufficiently low for a prolonged period of time, speciation is likely to be a significance.

Demography is the learning of human populations. Its three central foci are the processes of fertility, mortality, and migration, though the field encompasses many extent of population change including the family , public health, work and the labor force, and family planning. Various aspects of human activities in populations are also studied in sociology, economics, and geography. Study of populations is almost always governed by the laws of probability, and the conclusions of the studies may thus not always be relevant to some individuals. This odd factor may be reduced by statistical means, but such a generalization may be too vague to imply anything. Demography is used extensively in marketing, which relates to economic units, such as retailers, to potential customers.