Rayleigh scattering is the elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the light. This effect in our atmosphere causes diffuse sky radiation, which is the reason for the blue color of the sky and the yellow tone of the sun itself.

A portion of the light coming from the sun scatters off molecules and other small particles in the atmosphere. It is this scattered light that gives the sky its brightness and its color. The resulting color, which appears like a pale blue, is actually a weighted average of all the scattered colors, mainly blue and green.

The color of sunlight is intensified when the sun is near the horizon because the volume of air through which sunlight must pass is significantly greater. The Rayleigh scattering effect is therefore increased, removing virtually all blue light from the direct path to the observer. The remaining unscattered light is of a longer wavelength and therefore appears to be orange.

In locations with minimal light pollution, the moonlit night sky is also blue for the same reasons that the sky is blue during the day, as moonlight is reflected sunlight with a slightly lower color temperature due to the brownish color of the moon. The moonlit sky is usually not perceived as blue because at low light levels human vision occurs mainly from rod cells in the eye that do not produce any color perception.


The Kappa effect is a term relating to the human perception of time. A demonstration of this effect can be displayed when considering a journey made in two parts that take an equal amount of time. Between these two parts, the journey that covers more distance will appear to take longer than the journey covering less distance, even though they take an equal amount of time.

Practically speaking, a faster journey over more distance will still appear more time-consuming than a slower journey over less distance. Another phenomenon in human psychology, the Tau effect, describes a related effect also dealing with two equidistant parts in a journey. The part of the journey that takes more time to complete will appear to have covered more distance.

In essence, a slower journey will appear to cover more ground than a faster one, since it takes more time to do so. This effect is noted in the study of psychology.

It has also been found that long periods of time appear to pass faster as people grow older. The time from a child’s eighth birthday to the ninth seems an eternity, while the time from the sixty-eighth to the sixty-ninth seems to pass in a flash.


Ochre is a term for a golden yellow or red color. Ochres are among the earliest pigments used by mankind, derived from naturally tinted clay containing mineral oxides. Chemically, it is hydrated iron oxide. Modern artists’ pigments continue to use the terms yellow ochre and red ochre for specific hues.

It was the most commonly used material for painting walls in the ancient Mediterranean world. In Athens, when assembly was called, a contingent of public slaves would sweep the open space with ropes dipped in ochre. Those citizens that loitered instead of moving to the assembly area would risk having their clothes stained with the paint. This prevented them from wearing these clothes in public again, as failure to attend the assembly incurred a fine.

A popular coloring during the time of the French Empire, many French citizens living in foreign colonies would import a great deal of ochre clay from France to make their new lands feel like home. After the period of French colonization ended, ochre became associated with repression and fell out of favor. Recently, however, natural ochre paint has seen something of a comeback as an upscale house paint option.

In Newfoundland, red ochre was the pigment of choice for use in vernacular outbuildings and work buildings associated with the cod fishery. Deposits of ochre are found throughout Newfoundland, notably near Fortune Harbor and at Ocher Pit Cove. While earliest settlers may have used locally collected ochre, people were later able to purchase pre-ground ochre through local merchants, largely imported from England.


In photography, Bokeh is an aesthetic quality of blur. It occurs in parts of a scene that lie outside the depth of field. Photographers sometimes deliberately use a shallow focus technique to create images with prominent out-of-focus regions.

The term Bokeh has appeared in photography books since at least 1998. The term comes from the Japanese word boke, which means “blur” or “haze”, or boke-aji (the “blur quality”).

The shape of the camera aperture has an influence on the subjective quality of Bokeh. When a lens is stopped down to something other than its maximum aperture size, out-of-focus points are blurred into the polygonal shape of the aperture rather than perfect circles. Some lenses have aperture blades with curved edges to make the aperture more closely approximate a circle rather than a polygon.

An alternative mechanical mechanism has been proposed for generating Bokeh in small aperture cameras such as compacts or cellphone cameras, called image destabilisation, in which both the lens and sensor are moved in order to maintain focus at one focal plane, while defocusing nearby ones. This effect currently generates blur in only one axis.



Automatic parallelization refers to converting sequential code into multi-threaded or vectorized code in order to utilize multiple processors simultaneously in a shared multiprocessor environment.

Though the quality of automatic parallelization has improved in the past few decades, fully automatic parallelization of sequential programs by compilers remains a grand challenge due to its need for complex program analysis and unknown factors such as input data range during compilation.

Gustafson’s Law is a law in computer science which states that any sufficiently large problem can be efficiently parallelized. Gustafson’s law addresses the shortcomings of Amdahl’s law, which does not scale the availability of computing power as the number of machines increase. It removes the fixed problem size or fixed computation load on the parallel processors.

Amdahl’s law, also known as Amdahl’s argument, is named after computer architect Gene Amdahl, and is used to find the maximum expected improvement to an overall system when only part of the system is improved. It is often used in parallel computing to predict the theoretical maximum speedup using multiple processors.


A perspective is the choice of a context or a reference, or the result of the choice, from which to sense, categorize, measure or codify experience, cohesively forming a coherent belief, typically for comparing with another. One may further recognize a number of subtly distinctive meanings, close to those of paradigm, point of view, reality tunnel, or worl view.

To choose a perspective is to choose a value system and, unavoidably, an associated belief system. When we look at a business perspective, we are looking at a monetary based value system and belief. When we look at a human perspective, it is a more social value system and its associated beliefs.

In social psychology one would talk in terms of the other person’s point of view when soliciting or motivating the other person to do something for you. Being able to see the other person’s point of view is one of Henry Ford’s advice towards being successful in business. “If there is any one secret of success, it lies in the ability to get the other person’s point of view and see things from that person’s angle as well as from your own”.

Perspection, a related concept, signifies the ability to inspect one’s own perception, or the perceive another individual’s inspection.


Olfaction is the sense of smell. This sense is mediated by specialized sensory cells of the nasal cavity of vertebrates, and by sensory cells of the antennae of invertebrates.

The importance and sensitivity of smell varies among different organisms. Most mammals have a good sense of smell, whereas most birds do not. Among mammals, it is well-developed in the carnivores and ungulates, who must always be aware of each other, and in those that smell for their food, like moles.

It is estimated that dogs have an olfactory sense approximately a hundred thousand to a million times more acute than a human’s. This does not mean they are overwhelmed by smells our noses can detect, rather, it means they can discern a molecular presence when it is in much greater dilution in the air.

Bears, such as the Silvertip Grizzly found in parts of North America, have a sense of smell seven times stronger than a dog, essential for locating food underground. Using their elongated claws, bears dig deep trenches in search of burrowing animals and nests as well as roots, bulbs, and insects. Bears can detect the scent of food from up to 18 miles away.

Fish also have a well-developed sense of smell, even though they inhabit an aquatic environment. Salmon utilize their sense of smell to identify and return to their home stream waters. Catfish use their sense of smell to identify other individual catfish and to maintain a social hierarchy.

Insects use their antennae for olfaction. Sensory neurons in the antenna generate electrical signals called spikes in response to odor. The antennae have sensory neurons in the sensilla with axons terminating in the antennal lobes where they synapse with other neurons in semidelineations called glomeruli.


The cocktail party effect describes the ability to focus one’s listening attention on a single talker among a mixture of conversations and background noises, ignoring other conversations. This effect reveals one of the surprising abilities of our auditory system, which enables us to talk in a noisy place.

The effect can occur both when we are paying attention to one of the sounds around us and when it is invoked by a stimulus which grabs our attention suddenly. For example, when we are talking with our friend in a crowded party, we still can listen and understand what our friend says even if the place is very noisy, and can simultaneously ignore what another nearby person is saying. Then if someone over the other side of the party room calls out our name suddenly, we also notice that sound and respond to it immediately.

It was first described and named by Colin Cherry in 1953. Much of the early work in this area can be traced to problems faced by air traffic controllers in the early 1950s. At that time, controllers received messages from pilots over loudspeakers in the control tower. Hearing the intermixed voices of many pilots over a single loudspeaker made the controller’s task very difficult.

Cherry conducted attention experiments in which subjects were asked to listen to two different messages from a single loudspeaker at the same time and try to separate them. His work reveals that our ability to separate sounds from background noise is based on the characteristics of the sounds, such as the gender of the speaker, the direction from which the sound is coming, the pitch, or the speaking speed.

This phenomenon is still very much a subject of research, in humans as well as in computer implementations, where it is typically referred to as source separation or blind source separation. The neural mechanism in human brains is not yet fully clear.


Rubin’s vase is a famous set of cognitive optical illusions developed around 1915 by the Danish psychologist Edgar Rubin. The illusion generally presents the viewer with a mental choice of two interpretations, each of which is valid. Often, the viewer sees only one of them, and only realizes the second valid interpretation after some time or prompting. When the viewer attempts to simultaneously see the interpretations together, they suddenly cannot see the first interpretation anymore, and no matter how they try they simply cannot encompass both interpretations simultaneously; one occludes the other.

The illusions are useful because they are an intuitive demonstration of the figure-ground distinction the brain makes during visual perception. Rubin’s figure-ground distinction influenced the Gestalt psychologists, who discovered many similar illusions themselves. It involves higher-level cognitive pattern matching in which the overall picture determines its mental interpretation, rather than the net effect of the individual pieces.

Normally the brain classifies images by what surrounds what, establishing depth and relationships. If something surrounds another thing, the surrounded object is seen as figure, and the presumably further away (and hence background) object is the ground, and vice versa. This makes sense, since if a piece of fruit is lying on the ground, one would want to pay attention to the “figure” and not the “ground”.

However, when the contours are not so unequal, ambiguity starts to creep into the previously simple inequality and the brain must begin “shaping” what it sees. It can be shown that this shaping overrides and is at a higher level than feature recognition processes that pull together the face and the vase images. One can think of the lower levels putting together distinct regions of the picture (each region of which makes sense in isolation), but when the brain tries to make sense of it as a whole, contradictions ensue, and patterns must be discarded.



The Ganzfeld effect is a phenomenon of visual perception caused by staring at an undifferentiated and uniform field of color. The effect is described as the loss of vision as the brain cuts off the unchanging signal from the eyes. The result is “seeing black” or apparent blindness. The word is from German for “complete field”.

The effect is the result of the brain amplifying neural noise in order to look for the missing visual signals. The noise is interpreted in the higher visual cortex, and gives rise to hallucinations. This is similar to dream production because of the brain’s state of sensory deprivation during sleep.

The Ganzfeld effect has been reported since ancient times. The adepts of Pythagoras retreated to pitch black caves to receive wisdom through their visions. Miners trapped by accidents in mines frequently reported hallucinations, visions and seeing ghosts when they were in the pitch dark for days. Arctic explorers seeing nothing but featureless landscape of white snow for a long time also reported hallucinations and an altered state of mind.

In Tibetan Buddhism a dark retreat refers to advanced practices of isolation in darkness. The time period dedicated to dark retreat varies from a few hours to decades. Dark retreat in the Himalayan tradition is a restricted practice only to be engaged by the senior spiritual practitioner under appropriate spiritual guidance. This practice is considered conducive for navigating the bardo at the time of death and for realising the rainbow body. The traditional dark retreat requires stability in the natural state and is only suitable for advanced practitioners.

Ancient Egyptians and Mayans practiced a form of the dark retreat as well, traditionally lasting 10 days. Holy men would enter into the center of their respective pyramids, completely removed from light and sound, and have visions of the workings of the universe. Today, scientists have hypothesized that when the human body is deprived of visual stimulation, the brain produces a substance called Dimethyltryptamine (DMT), a tryptamine, which results in intense visions.