Unusual Twinnings

There are some patterns of twinning that are exceedingly rare: while they have been reported to happen, they are so unusual that most obstetricians or midwives may go their entire careers without encountering a single case.Among fraternal twins, in rare cases, the eggs are fertilized at different times with two or more acts of sexual intercourse, either within one menstrual cycle or, even more rarely, later on in the pregnancy . This can lead to the possibility of a woman carrying fraternal twins with different fathers . This phenomenon is known as heteropaternal superfecundation. One 1992 study estimates that the frequency of heteropaternal superfecundation among dizygotic twins whose parents were involved in paternity suits was approximately 2.4%; see the references section, below, for more details.

Among monozygotic twins, in extremely rare cases, twins have been born with opposite sexes . The probability of this is so vanishingly small that multiples having different genders is universally accepted as a sound basis for a clinical determination that in utero multiples are not monozygotic. When monozygotic twins are born with different genders it is because of chromosomal birth defects. In this case, although the twins did come from the same egg, it is incorrect to refer to them as genetically identical, since they have different karyotypes.

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Alternative education

Alternative education, also known as non-traditional education or educational alternative, describes a number of approaches to teaching and learning other than traditional publicly- or privately-run schools. These approaches can be applied to all students of all ages, from infancy to adulthood, and all levels of education.

Educational alternatives often are the result of education reform and are rooted in various philosophies that are fundamentally different from those of mainstream compulsory education. While some have strong political, scholarly, or philosophical orientations, others are more informal associations of teachers and students somehow dissatisfied with certain aspects of mainstream education.

Educational alternatives, which include charter schools, alternative schools, independent schools, and home-based learning vary widely, but often emphasize the value of small class size, close relationships between students and teachers, and a sense of community.

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Conjoined twins

Conjoined twins, are monozygotic twins, whose bodies are joined together at birth. This occurs where the single zygote of identical twins fails to separate completely, and the zygote starts to split after day 13 following fertilization. This condition occurs in about 1 in 50,000 human pregnancies. Most conjoined twins are now evaluated for surgery to attempt to separate them into separate functional bodies. The degree of difficulty rises if a vital organ or structure is shared between twins, such as brain, heart or liver.

A chimera is an ordinary person or animal except that some of his or her parts actually came from his or her twin. A chimera may arise either from identical twin fetuses,or from dizygotic fetuses, which can be identified by chromosomal comparisons from various parts of the body. The number of cells derived from each fetus can vary from one part of the body to another, and often leads to characteristic mosaicism skin colouration in human chimeras. A chimera may be a hermaphrodite, composed of cells from a male twin and a female twin.

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Tourism

Tourism is the act of travel for the purpose of recreation and business, and the provision of services for this act. Tourists are people who are "travelling to and staying in places outside their usual environment for not more than one consecutive year for leisure, business and other purposes not related to the exercise of an activity remunerated from within the place visited . The distance between these two places is of no significance.

A more comprehensive definition would be that tourism is a service industry, comprising a number of tangible and intangible components. The tangible elements include transport systems — air, rail, road, water and now, space; hospitality services — accommodation, foods and beverages, tours, souvenirs; and related services such as banking, insurance and safety and security. The intangible elements include: rest and relaxation, culture, escape, adventure, new and different experiences.
Many countries depend heavily upon travel expenditures by foreigners as a source of taxation and as a source of income for the enterprises that sell export services to these travellers. Consequently the development of tourism is often a strategy employed either by a Non-governmental organization NGO or a governmental agency to promote a particular region for the purpose of increasing commerce through exporting goods and services to non-locals.

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Immunology

Immunology is a broad branch of biomedical science that covers the study of all aspects of the immune system in all organisms. It deals with, among other things, the physiological functioning of the immune system in states of both health and disease; malfunctions of the immune system in immunological disorders autoimmune diseases, hypersensitivities, immune deficiency, allograft rejection; the physical, chemical and physiological characteristics of the components of the immune system in vitro, in situ, and in vivo. Immunology has various applications in several disciplines of science, and as such is further divided.

Classical immunology ties in with the fields of epidemiology and medicine. It studies the relationship between the body systems, pathogens, and immunity. The earliest written mention of immunity can be traced back to the plague of Athens in 430 BCE. Thucydides noted that people who had recovered from a previous bout of the disease could nurse the sick without contracting the illness a second time. Many other ancient societies have references to this phenomenon, but it was not until the 19th and 20th centuries before the concept developed into scientific theory.

The study of the molecular and cellular components that comprise the immune system, including their function and interaction, is the central science of immunology. The immune system has been divided into a more primitive innate immune system, and acquired or adaptive immune system of vertebrates, the latter of which is further divided into humoral and cellular components.

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Music

Music is an art, entertainment, or other human activity that involves organized and audible sounds and silence. It is expressed in terms of pitch, rhythm, harmony, and timbre. Music involves complex generative forms in time through the construction of patterns and combinations of natural stimuli, principally sound. As a human activity, music may be used for artistic or aesthetic, communicative, entertainment, or ceremonial purposes. The definition of what constitutes music varies according to culture and social context.

The broadest definition of music is organized sound. There are observable patterns to what is broadly labeled music, and while there are understandable cultural variations, the properties of music are the properties of sound as perceived and processed by humans.A more conservative definition would be: Music is harmonious sound created by the playing of instruments as a whole or individually. It is a direct expression of human emotions designed to manipulate and transform the emotion of the listener/listeners. Music is designed to be felt unlike sound which is heard.



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Naturism

The meanings of naturism and nudism are very similar, and refer to a cultural and political movement practicing,advocating and defending social nudity in private and public spaces. Several other terms have been proposed as a replacement of these terms, but none has yet found the same wide-spread acceptance as the older terms naturism and nudism.The movement includes a large range of variants including naturism, nudism, Freikörperkultur (FKK), the free beach movement as well as generalized public lands/public nudity advocacy. While there is a large amount of shared history and common themes, issues and philosophy, differences between these separate movements are sometimes contentious.

The usage of these terms varies geographically; people in the US often prefer the term nudism, while people in Europe more often than not refer to themselves as naturists. The predominant movement centers on established, family-friendly, non-sexualized variations. The inclusion of the topfree equality movement within this movement is under debate. Use of the word "clothes free" has also been used when preceding other words as a descriptive term, some arguing that it allows more inclusion of both the naturist and nudist philosophy, which are arguably similar in many regards.The movement also works in parallel to and sometimes influences and is influenced by popular culture as well as individuals and activists as well as organizations .

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Microphone
A microphone, sometimes referred to as a mike or mic both IPA pronunciation is an acoustic to electric transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, tape recorders, hearing aids, motion picture production, live and recorded audio engineering, in radio and television broadcasting and in computers for recording voice, VoIP and numerous other computer applications.

All microphones capture sound waves with a thin, flexible diaphragm or ribbon in the case of ribbon microphones. The vibrations of this element are then converted by various methods into an electrical signal that is an analog of the original sound. Most microphones in use today use electromagnetic generation dynamic microphones, capacitance change condenser microphones or piezoelectric generation to produce the signal from mechanical vibration.

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Coal

Coal is primarily used as a solid fuel to produce heat through combustion.
World coal consumption is about 5,800 million short tons annually, of which about 75% is used for electricity production. The region including China and India uses about 1,700 million short tons annually, forecast to exceed 3,000 million short tons in 2025. The USA consumes about 1,100 million short tons of coal each year, using 90% of it for generation of electricity. Coal is the fastest growing energy source in the world, with coal use increasing by 25% for the three-year period ending in December 2004.
When coal is used for electricity generation, it is usually pulverized and then burned in a furnace with a boiler. The furnace heat converts boiler water to steam, which is then used to spin turbines which turn generators and create electricity, with about 35–40% thermodynamic efficiency for the entire process. Approximately 40% of the world electricity production uses coal, and the total known deposits recoverable by current technologies are sufficient for 300 years' use at current rates.
A promising, more energy-efficient way of using coal for electricity production would be via solid-oxide fuel cells or molten-carbonate fuel cells, which would be able to get 60%–85% combined efficiency, compared to 35–40% normally obtained with steam-only turbines.Currently these fuel cell technologies can only process gaseous fuels, and they are also sensitive to sulfur poisoning, issues which would first have to be worked out before large scale commercial success is possible with coal. As far as gaseous fuels go, one idea is pulverized coal in a gas carrier, especially if the resulting carbon dioxide is sequestered, and has to be separated anyway from the carrier. A better idea is coal gasification with water,and then the water recycled.

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Coal

Coal is primarily used as a solid fuel to produce heat through combustion.
World coal consumption is about 5,800 million short tons annually, of which about 75% is used for electricity production. The region including China and India uses about 1,700 million short tons annually, forecast to exceed 3,000 million short tons in 2025. The USA consumes about 1,100 million short tons of coal each year, using 90% of it for generation of electricity. Coal is the fastest growing energy source in the world, with coal use increasing by 25% for the three-year period ending in December 2004.
When coal is used for electricity generation, it is usually pulverized and then burned in a furnace with a boiler. The furnace heat converts boiler water to steam, which is then used to spin turbines which turn generators and create electricity, with about 35–40% thermodynamic efficiency for the entire process. Approximately 40% of the world electricity production uses coal, and the total known deposits recoverable by current technologies are sufficient for 300 years' use at current rates.
A promising, more energy-efficient way of using coal for electricity production would be via solid-oxide fuel cells or molten-carbonate fuel cells, which would be able to get 60%–85% combined efficiency, compared to 35–40% normally obtained with steam-only turbines.Currently these fuel cell technologies can only process gaseous fuels, and they are also sensitive to sulfur poisoning, issues which would first have to be worked out before large scale commercial success is possible with coal. As far as gaseous fuels go, one idea is pulverized coal in a gas carrier, especially if the resulting carbon dioxide is sequestered, and has to be separated anyway from the carrier. A better idea is coal gasification with water,and then the water recycled.

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