Reverse learning is a neurobiological theory of dreams. It is like a computer that is off-line during dreaming or the REM phase of sleep. During this phase, the brain supposedly sifts through information gathered throughout the day and throws out all unwanted material. According to the theory, we dream in order to forget and this involves a process of unlearning.

The cortex cannot cope with the vast amount of information received throughout the day without developing parasitic thoughts that would disrupt the efficient organisation of memory. During REM sleep, these unwanted connections in cortical networks are supposedly wiped out or damped down by the process making use of impulses bombarding the cortex from sub-cortical areas.

Reverse learning eliminates unwanted modes of neural network interaction acquired in the adult mammal’s learning and also in the process of fetal brain growth. Therefore, there is a possibility that abnormalities of reverse learning in the fetal brain might explain some aspects of the autistic syndromes or other neurodevelopmental disorders.

The theory is a variant upon the activation-synthesis hypothesis that a brain stem neuronal mechanism sends pontine-geniculo-occipital (or PGO) waves that automatically activate the mammalian forebrain. By comparing information generated in specific brain areas with information stored in memory, the forebrain synthesizes dreams during REM sleep.

One problem for reverse-learning theory is that dreams are often organized into clear narratives or stories. It is unclear why dreams would be organized in a systematic way if they consisted only of disposable parasitic thoughts. It is also unclear why babies sleep so much, because it seems they would have less to forget.


Earworm is a term for a portion of a song or other musical material that repeats compulsively within one’s mind, known colloquially as “music being stuck in one’s head”. The Germans use the word Ohrwurm (rhymes with “door worm,” where the “w” is pronounced like a “v”) to denote these cognitively infectious musical agents. Use of the English translation was popularized by James Kellaris and Daniel Levitin.

Kellaris’ studies demonstrated that different people have varying susceptibilities to earworms, but that almost everybody has been afflicted with one at some time or another. The psychoanalyst Theodor Reik used the term “haunting melody” to describe the psychodynamic features of the phenomenon. Another scientific term for the phenomenon, involuntary musical imagery, was suggested by the neurologist Oliver Sacks in 2007.

People with obsessive-compulsive disorder are more likely to report being troubled by ear worms. In some cases medications can minimize the effects. Earworms should not be confused with endomusia, which is a serious affliction in which someone actually hears music that is not playing externally.


The Odic force is the name given in the mid-19th century to a hypothetical vital energy or life force by Baron Carl von Reichenbach. Von Reichenbach coined the name from that of the Norse god Odin in 1845.

As von Reichenbach was investigating the manner in which the human nervous system could be affected by various substances, he conceived the existence of a new force allied to electricity, magnetism, and heat, a force which he thought was radiated by most substances, and to the influence of which different persons are variously sensitive. He named this vitalist concept Odic force. Proponents say that Odic force permeates all plants, animals, and humans.

Believers in Odic force said that it is visible in total darkness as colored auras surrounding living things, crystals, and magnets, but that viewing it requires time first spent in total darkness, and that not everyone has the ability to see it. They also said that it resembles the eastern concepts prana and qi. However, they regarded the Odic force, not as associated with breath, like India’s prana and the qi of Eastern martial arts, but rather mainly with biological electromagnetic fields.

Von Reichenbach hoped to develop a scientific proof for a universal life force, however his experiments relied not on scientific instruments but on perceptions reported by individuals claimed to be psychically sensitive or psycho-kinetically adept. The “sensitives”, young women recruited from the poorer social classes, worked in total or near-total darkness, and were forerunners of the Spirit Mediums who appeared all over Europe 10 years later, in the 1850s.

The Odic force found no favor among mainstream scientists, and belief in it survives today as one among many concepts of spiritual energies associated with living things. The Odic force has been mentioned frequently in European books on dowsing, such as Reveal the Power of the Pendulum, by Karl Spiesberger.


Meditation has been defined as self regulation of attention, in the service of self-inquiry, in the here and now. The various techniques of meditation can be classified according to their focus. Some focus on the field or background perception and experience, often referred to as mindfulness. Others focus on a preselected specific object, and are called concentrative meditation. There are also techniques that shift between the field and the object.

In mindfulness meditation, the meditator sits comfortably and silently, centering attention by focusing awareness on an object or process such as the breath, a sound such as a mantra, or a koan or riddle-like question. The meditator is usually encouraged to maintain an open focus.

Concentration meditation is used in many religions and spiritual practices. Whereas in mindfulness meditation there is an open focus, in concentration meditation the meditator holds attention on a particular object such as a repetitive prayer, while minimizing distractions and bringing the mind back to concentrate on the chosen object.

Meditation can be practiced while walking or doing simple repetitive tasks. Walking meditation helps break down habitual automatic mental categories, thus regaining the primary nature of perceptions and events, focusing attention on the process while disregarding its purpose or final outcome. In a form of meditation using visualization, such as Chinese Qi Gong, the practitioner concentrates on flows of energy in the body, starting in the abdomen and then circulating through the body, until dispersed. Some meditative traditions, such as yoga or tantra, are common to several religions.


Manzanita is an evergreen shrub in the chaparral biome of western North America. It is characterized by smooth, orange or red bark and stiff, twisting branches. There are about 60 species of manzanita, ranging from ground-hugging coastal and mountain species to small trees up to 20 feet tall. Manzanitas bloom in the winter to early spring and carry berries in spring and summer. The berries and flowers of most species are edible.

Traditional uses of the plant include collecting the berries, drying them, and grinding them up into a coarse meal. Fresh berries and branch tips were also soaked in water and drunk as a refreshing cider. When the bark curls off, it can be used as a tea for nausea and upset stomach. The younger leaves are sometimes plucked and chewed by hikers to deter thirst. Original Americans used Manzanita leaves as toothbrushes.

The wood is notoriously hard to cure, mostly due to cracking against the grain, giving it few uses as timber. The slow growth rate and many branchings further decrease the sizes available. Some furniture and art employ whole round branches, which reduces cracking and preserves the deep red color.

The dead wood decays slowly and can last for many years. Sunlight smooths and bleaches manzanita to light grey or white, rendering it superficially akin to animal bones. Because of this and the stunted growth of many species, manzanita is often collected in its more unusual shapes, giving it the nickname mountain driftwood.

Manzanita wood is also used as perches for parrots and other large pet birds. The branches of the larger species are extremely long-lasting for this purpose.

Some aquarium keepers use sandblasted manzanita as driftwood in planted aquaria because of its attractive forked growth and its chemical neutrality. If properly cleaned and cured, it holds up well over extended periods of submersion.

Dry manzanita wood is excellent for burning in a campfire, barbecue, fireplace, or stove. It is dense and burns at a high temperature for long periods.

Some manzanita species are among the rarest plants in the world. Arctostaphylos hookeri subspecies ravenii (also known as Presidio manzanita) is the most endangered and restricted plant in the mainland United States. In 1987 only one specimen remained, at a secret location in the Presidio of San Francisco National Historic Landmark District in San Francisco, California. This plant has since been successfully cloned.



Indian summer is an informal expression given to a period of sunny, warm weather in autumn in the northern hemisphere, typically in late October or early November, after the leaves have turned but before the first snowfall.

The origins of the term Indian Summer are most commonly thought to have derived from the timing of Summer in India to correlate with good weather in Autumn in the Western world.

In former times in Europe, Indian summer was called Saint Martin’s Summer, referring to St. Martin’s day, November 11, when it was supposed to end.

In Bulgaria, the phenomenon is sometimes called Gypsy Summer and in some places Gypsy Christmas and refers to unseasonably warm weather in late fall, or a warm spell in between cold periods.

In Sweden it is called brittsommar, which is derived from Birgitta and Britta, who have their name day in the Swedish calendar on October 7. That is when Britt Mass, an official fall open-air market, was held.

In Germany and Austria it is called Altweibersommer (Old Ladies Summer) because the many white spider silks seen at this time of the year have been associated with the norns of Norse folklore or medieval witches.

There are around 43 different theories concerning the origin of the term.


Sunyata is a characteristic of phenomena arising from the fact, as observed and taught by the Buddha, that the impermanent nature of form means that nothing possesses essential, enduring identity. In the Buddha’s spiritual teaching, insight into the emptiness of phenomena is an aspect of the cultivation of insight that leads to wisdom and inner peace. The importance of this insight is especially emphasised in Mahayana Buddhism.

The teaching on the emptiness of all phenomena is a core basis of Buddhist philosophy and has implications for epistemology and phenomenology. It also constitutes a metaphysical critique of Greek philosophical realism, Abrahamic monotheism and Hindu concept of atman. Moreover, contrary to widely misconceived equation to the doctrine of nihilism, grasping the doctrine of sunyata is seen as a step to liberation.

Sunyata signifies that everything one encounters in life is empty of absolute identity, permanence, or an in-dwelling self. This is because everything is inter-related and mutually dependent – never wholly self-sufficient or independent. All things are in a state of constant flux where energy and information are forever flowing throughout the natural world giving rise to and themselves undergoing major transformations with the passage of time.

This teaching does not connote nihilism. In the English language the word emptiness suggests the absence of spiritual meaning or a personal feeling of alienation, but in Buddhism the realization of the emptiness of phenomena, at basic level, enables one to realise that the things which ultimately have no substance are trivial and not worthy of worry, conflict or antagonism. Ultimately, true realisation of the doctrine can bring liberation from the limitations of form in the cycle of uncontrolled rebirth.

One potent metaphor for Sunyata, often used in Tibetan art, is the sky. As the sky is the emptiness that offers clouds to our perception, so Sunyata is the space in which objects appear to us in response to our attachments and longings. The Japanese use of the Chinese character signifying Shunyata is also used to connote sky or air.


Multiobjective optimization or programming, also known as multi-criteria or multi-attribute optimization, is the process of simultaneously optimizing two or more conflicting objectives subject to certain constraints.

Multiobjective optimization problems can be found in various fields: product and process design, finance, aircraft design, the oil and gas industry, automobile design, or wherever optimal decisions need to be taken in the presence of trade-offs between two or more conflicting objectives. Maximizing profit and minimizing the cost of a product; maximizing performance and minimizing fuel consumption of a vehicle; and minimizing weight while maximizing the strength of a particular component are examples of multi-objective optimization problems.

If a multiobjective problem is well formed, there should not be a single solution that simultaneously minimizes each objective to its fullest. In each case we are looking for a solution for which each objective has been optimized to the extent that if we try to optimize it any further, then the other objectives will suffer as a result. Finding such a solution, and quantifying how much better this solution is compared to other such solutions (there will generally be many) is the goal when setting up and solving a multiobjective optimization problem.


The endless knot or eternal knot is a symbolic knot found in Tibet and Mongolia. The motif is used in Tibetan Buddhism, and may also be found in Chinese art as one of the Eight Auspicious Symbols.

The endless knot has been described as an ancient symbol representing the interweaving of the spiritual path and the flowing of time and movement within that which is eternal. All existence, it says, is bound by time and change, yet ultimately rests serenely within the divine and the eternal.

Various interpretations of the symbol are the inter-twining of wisdom and compassion, and the interplay and interaction of the opposing forces in the dualistic world of manifestation, leading to their union, and ultimately to harmony in the universe. The Endless knot iconography also symbolises Samsara, or the endless cycle of suffering or birth, death and rebirth within Tibetan Buddhism.

Endless knots as mystic and mythological symbols have developed independently in various cultures. A well-known example is the various Celtic knots. Since the knot has no beginning or end it symbolizes infinite wisdom.



Tree houses are buildings constructed among the branches, around or next to the trunk of one or more mature trees, and are raised above the ground. Tree houses can be used for recreation, work space, habitation or as temporary retreats. In some areas the wildlife, climate and illumination on ground level in areas of dense close-canopy forest is not well suited for human habitation, and tree houses are constructed to create improved conditions.

Because they do not require a clearing of a certain area of forest, tree houses are an option for building eco-friendly facilities in remote forest areas. In some parts of the tropics, ordinary houses are built in trees or elevated on stilts to keep the living quarters above hazards at ground level, and to keep the occupants and any stored food out of reach of scavenging animals. The Korowai, a Papuan tribe in the southeast of Irian Jaya, live in tree houses, some nearly 40 metres (130 ft) high, as protection against a tribe of neighbouring head-hunters, the Citak.

The tree house has been central to various environmental protest communities around the world, in a technique known as tree sitting. This method may be used in protests against proposed road building or old growth forestry operations. Tree houses are used as a method of defense from which it is difficult and costly to safely evict the protesters and begin work. Julia Butterfly Hill is a particularly well known tree sitter who occupied a Californian Redwood for 738 days, saving the tree and others in the immediate area. Her accommodation consisted of two 29 square foot platforms 200ft above the ground.

A very small number of planning departments have specific regulations for tree houses, which set out clearly what may be built and where. In some cases tree houses are given exemption from normal building regulations, as they are not considered to be a building in the normal sense of the word. There may be restrictions on height, distance from boundaries and privacy for nearby properties.