Summary

HandWiki is the world's largest wiki-style encyclopedia dedicated to science, technology and computing. It allows you to create and edit articles as long as you have external citations and login account. In addition, this is a content management environment that can be used for collaborative editing of original scholarly content, such as books, manuals, monographs and tutorials.

Expand All
Entries
Topic Review
List of Countries by Wealth Equality
This is a list of countries by distribution of wealth, including Gini coefficients. Wealth distribution can vary greatly from income distribution in a country (see List of countries by income equality). Higher Gini coefficients signify greater inequality in wealth distribution, with 0 being complete equality, whereas a value near 1 can arise in a situation where everybody has zero wealth except a very small minority. It is a common misconception that Scandinavian countries have low wealth inequality. This is not true. These countries have low income inequality, meaning that the income is relatively equal for everyone. However, their wealth inequality is very high, meaning that a small minority of the people owns the vast majority of wealth.
  • 1.6K
  • 14 Oct 2022
Topic Review
Secular Humanism
Secular humanism, often simply called humanism, is a philosophy or life stance that embraces human reason, secular ethics, and philosophical naturalism while specifically rejecting religious dogma, supernaturalism, and superstition as the basis of morality and decision making. Secular humanism posits that human beings are capable of being ethical and moral without religion or belief in a deity. It does not, however, assume that humans are either inherently good or evil, nor does it present humans as being superior to nature. Rather, the humanist life stance emphasizes the unique responsibility facing humanity and the ethical consequences of human decisions. Fundamental to the concept of secular humanism is the strongly held viewpoint that ideology—be it religious or political—must be thoroughly examined by each individual and not simply accepted or rejected on faith. Along with this, an essential part of secular humanism is a continually adapting search for truth, primarily through science and philosophy. Many secular humanists derive their moral codes from a philosophy of utilitarianism, ethical naturalism, or evolutionary ethics, and some advocate a science of morality. Humanists International is the world union of more than one hundred humanist, rationalist, irreligious, atheist, Bright, secular, Ethical Culture, and freethought organizations in more than 40 countries. The "Happy Human" is recognized as the official symbol of humanism internationally, used by secular humanist organizations in every part of the world. Those who call themselves humanists are estimated to number between four and five million people worldwide.
  • 9.8K
  • 14 Oct 2022
Topic Review
Dyscalculia
Dyscalculia (/ˌdɪskælˈkjuːliə/) is a disability resulting in difficulty learning or comprehending arithmetic, such as difficulty in understanding numbers, learning how to manipulate numbers, performing mathematical calculations and learning facts in mathematics. It is sometimes informally known as "math dyslexia", though this can be misleading as dyslexia is a different condition from dyscalculia. Dyscalculia is associated with dysfunction in the region around the intraparietal sulcus and potentially also the frontal lobe. Dyscalculia does not reflect a general deficit in cognitive abilities or difficulties with time, measurement, and spatial reasoning. Estimates of the prevalence of dyscalculia range between 3 and 6% of the population. In 2015 it was established that 11% of children with dyscalculia also have ADHD. Dyscalculia has also been associated with Turner syndrome and people who have spina bifida. Mathematical disabilities can occur as the result of some types of brain injury, in which case the term acalculia is used instead of dyscalculia which is of innate, genetic or developmental origin.
  • 3.1K
  • 14 Oct 2022
Topic Review
Death of Sammy Yatim
The death of Sammy Yatim occurred early in the morning of July 27, 2013, in Toronto, Ontario, Canada. Yatim, an 18-year-old Toronto male armed with a switchblade knife, was shot at nine times, and was hit by eight of the shots fired by 30-year-old Toronto Police Service (TPS) officer James Forcillo. He later died from the injuries. The incident occurred after Yatim, brandishing a 12 cm (4.7 in) switchblade knife in a Toronto streetcar, advanced on a passenger, threatened other passengers, and exposed himself. The confrontation between Yatim and the police was recorded and footage of it was released publicly, prompting strong reactions across Canada. On August 19, 2013, Forcillo was charged with second-degree murder. On July 30, 2014, he was also charged with attempted murder. On January 25, 2016, he was found not guilty of second-degree murder and manslaughter, but guilty of attempted murder. On July 28, he was sentenced to six years in prison. The next day, he was granted bail pending an appeal of the court's sentence. This incident was the only time an on-duty Ontario officer was charged and convicted in the death of a person since the inception of the Special Investigations Unit (SIU) in 1990.
  • 2.6K
  • 14 Oct 2022
Topic Review
CHICKEN (Scheme Implementation)
CHICKEN is a compiler and interpreter for the Scheme programming language that compiles Scheme code to standard C. It is mostly R5RS compliant and offers many extensions to the standard. The newer R7RS standard is supported through an extension library. CHICKEN is free software available under the BSD license. It is implemented mostly in Scheme, with some parts in C for performance or to make embedding into C programs easier.
  • 1.4K
  • 14 Oct 2022
Topic Review
Seudat Mitzvah
A seudat mitzvah (Hebrew: סעודת מצוה, "commanded meal"), in Judaism, is an obligatory festive meal, usually referring to the celebratory meal following the fulfillment of a mitzvah (commandment), such as a bar mitzvah, a wedding, a brit milah (ritual circumcision), or a siyum (completing a tractate of Talmud or Mishnah). Seudot fixed in the calendar (i.e., for holidays and fasts) are also considered seudot mitzvah, but many have their own, more commonly used names.
  • 1.2K
  • 14 Oct 2022
Topic Review
Thiruvempavai
The Thiruvempavai (Tamil: திருவெம்பாவை, IAST: Tiruvempāvai) are a collection of songs composed by the poet and saint, Manikkavacakar. It consists of 20 stanzas devoted to the Hindu God Shiva. It forms part of the collection called Thiruvasagam, and the 8th book of the Thirumurai, a canonical text of the Tamil Shaiva Siddhanta. The songs form part of the Pavai ritual for unmarried young girls during the Tamil month of Margazhi.
  • 2.6K
  • 14 Oct 2022
Topic Review
Hadrosaurid
Hadrosaurids (Greek: ἁδρός, hadrós, "stout, thick"), or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The family, which includes ornithopods such as Edmontosaurus and Parasaurolophus, was a common herbivore in the Upper Cretaceous Period of what is now Asia, Europe, Antarctica, South America, and North America. Hadrosaurids are descendants of the Upper Jurassic/Lower Cretaceous iguanodontian dinosaurs and had a similar body layout. Like the rest of the ornithischians, these animals had a predentary bone and a pubic bone which was positioned backwards in the pelvis. Hadrosaurids are divided into two principal subfamilies: the lambeosaurines (Lambeosaurinae), which had hollow cranial crests or tubes, and the saurolophines, identified as hadrosaurines in most pre-2010 works (Saurolophinae or Hadrosaurinae), which lacked hollow cranial crests (solid crests were present in some forms). Saurolophines tended to be bulkier than lambeosaurines. Lambeosaurines included the aralosaurins, tsintaosaurins, lambeosaurins and parasaurolophins, while saurolophines included the brachylophosaurins, kritosaurins, saurolophins and edmontosaurins. Hadrosaurids were facultative bipeds, with the young of some species walking mostly on two legs and the adults walking mostly on four. Their jaws were evolved for grinding plants, with multiple rows of teeth replacing each other as the teeth wore down.
  • 2.0K
  • 14 Oct 2022
Topic Review
Classical Plant Breeding
Classical plant breeding uses deliberate interbreeding (crossing) of closely or distantly related species to produce new crops with desirable properties. Plants are crossed to introduce traits/genes from a particular variety into a new genetic background. For example, a mildew resistant pea may be crossed with a high-yielding but susceptible pea, the goal of the cross being to introduce mildew resistance without losing the high-yield characteristics. Progeny from the cross would then be crossed with the high-yielding parent to ensure that the progeny were most like the high-yielding parent, (backcrossing), the progeny from that cross would be tested for yield and mildew resistance and high-yielding resistant plants would be further developed. Plants may also be crossed with themselves to produce inbred varieties for breeding. Germplasm resources from genebanks have invaluable for classical breeding. Classical breeding relies heavily on the naturally occuring plant life-cycle and homologous recombination to generate genetic diversity and to eliminate undesirable traits. It may also makes use of a variety of artificial laboratory procedures to overcome obstacles to introduction of useful traits from wild species that do not usually exchange genes with the domesticated line. These approaches include in vitro techniques such as protoplast fusion, embryo rescue or mutagenisis (see below) to generate genetic alterations and produce transgenic plants that would not exist in nature. Traits that breeders' have tried to incorporate into crop plants in the last 100 years include: Intraspecific hybridization within a plant species was demonstrated by Charles Darwin and Gregor Mendel, and was further developed by geneticists and plant breeders. In the early 20th century, plant breeders realized that Mendel's findings on the non-random nature of inheritance could be applied to seedling populations produced through deliberate pollinations to predict the frequencies of different types. In 1908, George Harrison Shull described heterosis, also known as hybrid vigor. Heterosis describes the tendency of the progeny of a specific cross to outperform both parents. The detection of the usefulness of heterosis for plant breeding has lead to the development of inbred lines that reveal a heterotic yield advantage when they are crossed. Maize was the first species where heterosis was widely used to produce hybrids. Heterosis made breeders aware of the broad practical value of many genes carried in plant chromosomes even when the identity and trait specified by the paticular genes is unknown - that is that diverse plant Germplasm is generally valuable to the breeder. By the 1920s, statistical methods were developed to analyze gene action and distinguish heritable variation from variation caused by environment. In 1933, another important breeding technique, cytoplasmic male sterility (CMS), developed in maize, was described by Marcus Morton Rhoades. CMS is a maternally inherited trait that makes the plant produce sterile pollen, enabling the production of hybrids and removing the need for detasseling maize plants. The scientific use of Transgenic plants in farming gained impetus in the 1930s when a transgenic wheat variety named Hope bred by E. S. McFadden with a transgene originating in a wild grass saved American wheat growers from devastating stem rust outbreaks. These early breeding techniques resulted in large yield increase in the United States in the early 20th century. Similar yield increases were not produced elsewhere until after World War II, the Green Revolution increased crop production in the developing world in the 1960s. Success stories like Hope and hybrid-vigor made it clear that genetic divesity present in wild-species was of great potential value to plant breeders, and eventially lead to the establisment of Germplasm collections consisting of seed-banks devoted to preservation of potentially useful uncharacterised traits for posterity. Following World War II a number of techniques were developed that allowed plant breeders to hybridize distantly related species, and artificially induce genetic diversity. When distantly related species are crossed, plant breeders make use of a number of plant tissue culture techniques to produce progeny from other wise fruitless mating. Interspecific and intergeneric hybrids are produced from a cross of related species or genera that do not normally sexually reproduce with each other. These crosses are referred to as Wide crosses. The cereal triticale is a wheat and rye hybrid. The first generation created from the cross was sterile, so the cell division inhibitor colchicine was used to double the number of chromosomes in the cell. Cells with an uneven number of chromosomes are sterile. Failure to produce a hybrid may be due to pre- or post-fertilization incompatibility. If fertilization is possible between two species or genera, the hybrid embryo may abort before maturation. If this does occur the embryo resulting from an interspecific or intergeneric cross can sometimes be rescued and cultured to produce a whole plant. Such a method is referred to as Embryo Rescue. This technique has been used to produce new rice for Africa, an interspecific cross of Asian rice (Oryza sativa) and African rice (Oryza glaberrima). Hybrids may also be produced by a technique called protoplast fusion. In this case protoplasts are fused, usually in an electric field. Viable recombinants can be regenerated in culture. Chemical mutagens like EMS and DMSO, radiation and transposons are used to generate mutants with desirable traits to be bred with other cultivars. Classical plant breeders also generate genetic diversity within a species by exploiting a process called somaclonal variation, which occurs in plants produced from tissue culture, particularly plants derived from callus. Induced polyploidy, and the addition or removal of chromosomes using a technique called chromosome engineering also found uses. When a desirable trait has been bred into a species, a number of crosses to the favoured parent are made to make the new plant as similar as the parent as possible. Returning to the example of the mildew resistant pea being crossed with a high-yielding but susceptible pea, to make the mildew resistant progeny of the cross most like the high-yielding parent, the progeny will be crossed back to that parent for several generations (See backcrossing ). This process removes most of the genetic contribution of the mildew resistant parent. Classical breeding is therefore a cyclical process. It should be noted that with classical breeding techniques, the breeder does not know exactly what genes have been introduced to the new cultivars. Some scientists therefore argue that plants produced by classical breeding methods should undergo the same safety testing regime as genetically modified plants. There have been instances where plants bred using classical techniques have been unsuitable for human consumption, for example the poison solanine was accidentally re-introduced into varieties of potato through plant breeding.
  • 3.4K
  • 14 Oct 2022
Topic Review
Enteroaggregative Escherichia Coli
Enteroaggregative Escherichia coli (EAEC or EAggEC) are a pathotype of Escherichia coli which cause acute and chronic diarrhea in both the developed and developing world. They may also cause urinary tract infections. EAEC are defined by their "stacked-brick" pattern of adhesion to the human laryngeal epithelial cell line HEp-2. The pathogenesis of EAEC involves the aggregation of and adherence of the bacteria to the intestinal mucosa, where they elaborate enterotoxins and cytotoxins that damage host cells and induce inflammation that results in diarrhea. EAEC is now recognized as an emerging enteric pathogen. In particular, EAEC are reported as the second most common cause of traveler's diarrhea, second only to Enterotoxigenic E. coli, and a common cause of diarrhea amongst pediatric populations. It has also been associated with chronic infections in the latter, as well as in immunocompromised hosts, such as HIV-infected individuals. Awareness of EAEC was increased by a serious outbreak in Germany during 2011, causing over 5000 cases and at least 50 fatalities. The pathogen responsible was found to be an EAEC O104:H4 strain which was lysogenized by a Shiga toxin encoding phage (typically associated with Shiga toxin-producing Escherichia coli, which often encode the adhesin intimin). The putative cause of the outbreak were sprouted fenugreek seeds. Strains of EAEC are highly genetically heterogeneous, and the identification of virulence factors important for pathogenesis has proven difficult. Many EAEC encode a transcriptional factor named aggR (aggregative regulator), part of the AraC family of transcription activators. AggR regulates many plasmid, as well chromosomally encoded, virulence factors, that include genes implicated in aggregative adherence fimbriae biogenesis and toxin production. Several toxins have been linked to EAEC virulence, including ShET1 (Shigella enterotoxin 1), Pet (plasmid‐encoded toxin), and EAST-1. However, further studies of these factors have failed to elucidate their role in pathogenesis.
  • 789
  • 14 Oct 2022
  • Page
  • of
  • 863

Other Entry Collections

>>