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9671_34 | Further reading
Keppel, Robert. The Riverman: Ted Bundy and I Hunt for the Green River Killer. New York, Pocket Books, 2004 (revised and updated). Contains a chapter on the Atlanta Child Murders and Keppel's participation as a consultant with the investigation.
Jones, Tayari. Leaving Atlanta. New York, Warner Books, 2002. A novel that focuses on children during the time of the murders.
Bambara, Toni Cade. Those Bones Are Not My Child. New York, Pantheon Books, 1999. A novel about a mother who lost a child as part of the murders.
Reid, Kim. No Place Safe, New York: Kensington Publishing Corp., 2007. A memoir by the daughter of one of the police investigators.
James Baldwin, The Evidence of Things Not Seen 1985. Holt, Rinehart and Winston
Chet Dettlinger, Jeff Prugh, The List 1983. Philmay Enterprises, Inc. The most comprehensive account in print written by the private detective once considered a suspect because of his thorough knowledge of the case. |
9671_35 | John E. Douglas and Mark Olshaker, Mind Hunter: Inside the FBI's Elite Serial Crime Unit, Scribner, 1995, See: Chapter 11, Atlanta, paqes 199–224.
Mallard, Jack. "The Atlanta Child Murders: the Night Stalker" (Jack Mallard, 392pgs) released 2010-12-02. Jack Mallard was one of the Fulton County Assistant District Attorneys who prosecuted Wayne Williams for two murders. Includes footnotes and charts of testimony, physical evidence, trial strategy that led to the guilty verdicts. |
9671_36 | External links
FBI file on the Atlanta Child Murders
Crime Library: The Atlanta Child Murders
Atlanta's Missing and Murdered
- The Atlanta Child Murders subseries in the Maynard Jackson Mayoral Administrative Records chronicles the time period between 1979-1981 when multiple young black children and adults were murdered in the city of Atlanta. |
9671_37 | Child murders
1979 in Georgia (U.S. state)
1979 murders in the United States
Child murders
1980 in Georgia (U.S. state)
1980 murders in the United States
1981 in Georgia (U.S. state)
1981 murders in the United States
Child murders
American serial killers
Child murders
Crimes in Georgia (U.S. state)
Fugitives wanted by the United States
Incidents of violence against boys
Male serial killers
Murdered African-American people
Murdered American children
Murder in Georgia (U.S. state)
People murdered in Georgia (U.S. state)
Post–civil rights era in African-American history
Serial murders in the United States
Unidentified serial killers
Violence against children
Violence against men in North America |
9672_0 | Congenital adrenal hyperplasia (CAH) is a group of autosomal recessive disorders characterized by impaired cortisol synthesis. It results from the deficiency of one of the five enzymes required for the synthesis of cortisol in the adrenal cortex. Most of these disorders involve excessive or deficient production of hormones such as glucocorticoids, mineralocorticoids, or sex steroids, and can alter development of primary or secondary sex characteristics in some affected infants, children, or adults. It is one of the most common autosomal recessive disorders in humans. |
9672_1 | Types
CAH can occur in various forms. The clinical presentation of each form is different and depends to a large extent on the underlying enzyme defect, its precursor retention, and deficient products. Classical forms appear in infancy, and nonclassical forms appear in late childhood. The presentation in patients with classic CAH can be further subdivided into two forms: salt-wasting and simple-virilizing, depending on whether mineralocorticoid deficiency presents or absents, respectively. This subtyping is often not clinically meaningful, though, because all patients lose salt to some degree, and clinical presentations may overlap.
Classic
Salt-wasting
In 75% of cases of severe enzyme deficiency, insufficient aldosterone production can lead to salt wasting, failure to thrive, and potentially fatal hypovolemia and shock. A missed diagnosis of salt-loss CAH is related to the increased risk of early neonatal morbidity and death. |
9672_2 | Simple-virilizing
The main feature of CAH in newborn females is the abnormal development of the external genitalia, which has varying degrees of virilization. According to clinical practice guidelines, for newborns found to have bilateral inaccessible gonads, CAH evaluation should be considered. If virilizing CAH cannot be identified and treated, both boys and girls may undergo rapid postnatal growth and virilization. |
9672_3 | Nonclassic
In addition to the salt-wasting and simple-virilizing forms of CAH diagnosed in infancy, a mild or "nonclassic" form exists, which is characterized by varying degrees of postnatal androgen excess, but is sometimes asymptomatic. The nonclassic form may be noticed in late childhood and may lead to accelerated growth, premature sexual maturation, acne, and secondary polycystic ovary syndrome. In adult males, early balding and infertility may suggest the diagnosis. The nonclassic form is characterized by mild subclinical impairment of cortisol synthesis; serum cortisol concentration is usually normal.
Signs and symptoms
The symptoms of CAH vary depending upon the form of CAH and the sex of the patient. Symptoms can include:
Due to inadequate mineralocorticoids:
Vomiting due to salt-wasting, leading to dehydration and death |
9672_4 | Due to excess androgens:
In extreme virilization, an elongated clitoris with a phallic-like structure is seen.
Ambiguous genitalia, in some infants, occurs such that initially identifying external genitalia as "male" or "female" is difficult.
Early pubic hair and rapid growth occurs in childhood.
Precocious puberty or failure of puberty to occur (sexual infantilism: absent or delayed puberty)
Excessive facial hair, virilization, and/or menstrual irregularity in adolescence
Infertility due to anovulation
Clitoromegaly, enlarged clitoris and shallow vagina
Due to insufficient androgens and estrogens:
Undervirilization in XY males can result in apparently female external genitalia.
In females, hypogonadism can cause sexual infantilism or abnormal pubertal development, infertility, and other reproductive system abnormalities. |
9672_5 | Genetics
CAH results from mutations of genes for enzymes mediating the biochemical steps of production of mineralocorticoids, glucocorticoids, or sex steroids from cholesterol by the adrenal glands (steroidogenesis). |
9672_6 | Each form of CAH is associated with a specific defective gene. The most common type (95% of cases) involves the gene for 21-hydroxylase, which is found on 6p21.3 as part of the HLA complex; 21-hydroxylase deficiency results from a unique mutation with two highly homologous near-copies in series consisting of an active gene (CYP21A2) and an inactive pseudogene (CYP21A1P). Mutant alleles result from recombination between the active and pseudogenes (gene conversion). About 5% of cases of CAH are due to defects in the gene encoding 11β-hydroxylase and consequent 11β-hydroxylase deficiency. Other, more rare forms of CAH are caused by mutations in genes, including HSD3B2 (3β-hydroxysteroid dehydrogenase 2), CYP17A1 (17α-hydroxylase/17,20-lyase), CYP11A1 (P450scc; cholesterol side-chain cleavage enzyme), STAR (steroidogenic acute regulatory protein; StAR), CYB5A (cytochrome b5), and CYPOR (cytochrome P450 oxidoreductase; POR). |
9672_7 | Expressivity
Further variability is introduced by the degree of enzyme inefficiency produced by the specific alleles each patient has. Some alleles result in more severe degrees of enzyme inefficiency. In general, severe degrees of inefficiency produce changes in the fetus and problems in prenatal or perinatal life. Milder degrees of inefficiency are usually associated with excessive or deficient sex hormone effects in childhood or adolescence, while the mildest forms of CAH interfere with ovulation and fertility in adults.
Diagnosis
Clinical evaluation
Female infants with classic CAH have ambiguous genitalia due to exposure to high concentrations of androgens in utero. CAH due to 21-hydroxylase deficiency is the most common cause of ambiguous genitalia in genotypically normal female infants (46XX). Less severely affected females may present with early pubarche. Young women may present with symptoms of polycystic ovarian syndrome (oligomenorrhea, polycystic ovaries, hirsutism). |
9672_8 | Males with classic CAH generally have no signs of CAH at birth. Some may present with hyperpigmentation, due to co-secretion with melanocyte-stimulating hormone, and possible penile enlargement. Age of diagnosis of males with CAH varies and depends on the severity of aldosterone deficiency. Boys with salt-wasting disease present early with symptoms of hyponatremia and hypovolemia. Boys with non-salt-wasting disease present later with signs of virilization.
In rarer forms of CAH, males are undermasculinized and females generally have no signs or symptoms at birth.
Laboratory studies
Genetic analysis can be helpful to confirm a diagnosis of CAH, but it is not necessary if classic clinical and laboratory findings are present.
In classic 21-hydroxylase deficiency, laboratory studies will show: |
9672_9 | Hypoglycemia (due to hypocortisolism) - One of cortisol's many functions is to increase blood glucose levels. This occurs via a combination of several mechanisms, including (a) the stimulation of gluconeogesis (i.e. the creation of new glucose) in the liver, (b) the promotion of glycogenolysis (i.e. the breakdown of glycogen into glucose), and (c) the prevention of glucose leaving the bloodstream via the downregulation of GLUT-4 receptors (which normally promote movement of glucose from the bloodstream into adipose and muscle tissues). Therefore, when cortisol is deficient, these processes (effectively) occur in the reverse direction. Although there are compensatory mechanisms that mitigate the impact of hypocortisolism, they are limited in their extent and the net effect is still hypoglycemia. |
9672_10 | Hyponatremia (due to hypoaldosteronism) - Aldosterone is the end product of the renin-angiotensin-aldosterone system that regulates blood pressure via blood pressure surveillance in the Kidney Juxtaglomerular apparatus. Aldosterone normally functions to increase sodium retention (which brings water as well) in exchange for potassium. Thus, lack of aldosterone causes hyperkalemia and hyponatremia. In fact, this is a distinguishing point from 11-hydroxylase deficiency, in which one of the increased products is 11-deoxycorticosterone that has weak mineralocorticoid activity. In 11-hydroxylase deficiency, 11-deoxycorticosterone is produced in such excess that it acts to retain sodium at the expense of potassium. It is this reason that patients with 11-hydroxylase deficiency do not show salt wasting (although sometimes they do in infancy), and instead have hypertension/water retention and sometimes hypokalemia.
Hyperkalemia (due to hypoaldosteronism)
Elevated 17α-hydroxyprogesterone |
9672_11 | Classic 21-hydroxylase deficiency typically causes 17α-hydroxyprogesterone blood levels >242 nmol/L. (For comparison, a full-term infant at three days of age should have <3 nmol/L. Many neonatal screening programs have specific reference ranges by weight and gestational age because high levels may be seen in premature infants without CAH.) Salt-wasting patients tend to have higher 17α-hydroxyprogesterone levels than non-salt-wasting patients. In mild cases, 17α-hydroxyprogesterone may not be elevated in a particular random blood sample, but it will rise during a corticotropin stimulation test. |
9672_12 | Classification
Cortisol is an adrenal steroid hormone required for normal endocrine function. Production begins in the second month of fetal life. Poor cortisol production is a hallmark of most forms of CAH. Inefficient cortisol production results in rising levels of ACTH, because cortisol feeds back to inhibit ACTH production, so loss of cortisol results in increased ACTH. This increased ACTH stimulation induces overgrowth (hyperplasia) and overactivity of the steroid-producing cells of the adrenal cortex. The defects causing adrenal hyperplasia are congenital (i.e. present at birth). |
9672_13 | Cortisol deficiency in CAH is usually partial, and not the most serious problem for an affected person. Synthesis of cortisol shares steps with synthesis of mineralocorticoids such as aldosterone, androgens such as testosterone, and estrogens such as estradiol. The resulting excessive or deficient production of these three classes of hormones produce the most important problems for people with CAH. Specific enzyme inefficiencies are associated with characteristic patterns of over- or underproduction of mineralocorticoids or sex steroids. |
9672_14 | Since the 1960s, most endocrinologists have referred to the forms of CAH by the traditional names in the left column, which generally correspond to the deficient enzyme activity. As exact structures and genes for the enzymes were identified in the 1980s, most of the enzymes were found to be cytochrome P450 oxidases and were renamed to reflect this. In some cases, more than one enzyme was found to participate in a reaction, and in other cases, a single enzyme mediated in more than one reaction. Variation in different tissues and mammalian species also was found. |
9672_15 | In all its forms, congenital adrenal hyperplasia due to 21-hydroxylase deficiency accounts for about 95% of diagnosed cases of CAH. Unless another specific enzyme is mentioned, "CAH" in nearly all contexts refers to 21-hydroxylase deficiency. (The terms "salt-wasting CAH", and "simple virilizing CAH" usually refer to subtypes of this condition.) CAH due to deficiencies of enzymes other than 21-hydroxylase present many of the same management challenges, as 21-hydroxylase deficiency, but some involve mineralocorticoid excess or sex steroid deficiency.
Screening
Currently, in the United States and over 40 other countries, every child born is screened for 21-hydroxylase CAH at birth. This test detects elevated levels of 17α-hydroxyprogesterone (17-OHP). Detecting high levels of 17-OHP enables early detection of CAH. Newborns detected early enough can be placed on medication and live relatively normal lives. |
9672_16 | The screening process, however, is characterized by a high false-positive rate. In one study, CAH screening had the lowest positive predictive value (111 true-positive cases among 20,647 abnormal screening results in a 2-year period, or 0.53%, compared with 6.36% for biotinidase deficiency, 1.84% for congenital hypo-thyroidism, 0.56% for classic galactosemia, and 2.9% for phenylketonuria). According to this estimate, 200 unaffected newborns required clinical and laboratory follow-up for every true case of CAH.
Treatment
Since the clinical manifestations of each form of CAH are unique and depend to a large extent on the underlying enzyme defects, their precursor retention and defective products, the therapeutic goal of CAH is to replenish insufficient adrenal hormones and suppress excess of precursors.
Treatment of all forms of CAH may include any of: |
9672_17 | Supplying enough glucocorticoid to reduce hyperplasia and overproduction of androgens or mineralocorticoids
Providing replacement mineralocorticoid and extra salt if the person is deficient
Providing replacement testosterone or estrogens at puberty if the person is deficient
Additional treatments to optimize growth by delaying puberty or delaying bone maturation
If CAH is caused by the deficiency of the 21-hydroxylase enzyme, then treatment aims to normalize levels of main substrate of the enzyme - 17α-hydroxyprogesterone.
Epidemiology
The incidence varies ethnically. In the United States, congenital adrenal hyperplasia in its classic form is particularly common in Native Americans and Yupik Inuit (incidence ). Among American Caucasians, the incidence of the classic form is about ).
Continued treatment and wellness are enhanced by education and follow up.
History |
9672_18 | Before 20th century
An Italian anatomist, Luigi De Crecchio (1832-1894) provided the earliest known description of a case of probable CAH. |
9672_19 | I propose in this narrative that it is sometimes extremely difficult and even impossible to determine sex during life. In one of the anatomical theaters of the hospital..., there arrived toward the end of January a cadaver which in life was the body of a certain Joseph Marzo... The general physiognomy was decidedly male in all respects. There were no feminine curves to the body. There was a heavy beard. There was some delicacy of structure with muscles that were not very well developed... The distribution of pubic hair was typical of the male. Perhaps the lower extremities were somewhat delicate, resembling the female, and were covered with hair... The penis was curved posteriorly and measured 6 cm, or with stretching, 10 cm. The corona was 3 cm long and 8 cm in circumference. There was an ample prepuce. There was a first grade hypospadias... There were two folds of skin coming from the top of the penis and encircling it on either side. These were somewhat loose and resembled labia |
9672_20 | majora. |
9672_21 | De Crecchio then described the internal organs, which included a normal vagina, uterus, fallopian tubes, and ovaries.
It was of the greatest importance to determine the habits, tendencies, passions, and general character of this individual... I was determined to get as complete a story as possible, determined to get at the base of the facts and to avoid undue exaggeration which was rampant in the conversation of many of the people present at the time of the dissection.
He interviewed many people and satisfied himself that Joseph Marzo "conducted himself within the sexual area exclusively as a male", even to the point of contracting the "French disease" on two occasions. The cause of death was another in a series of episodes of vomiting and diarrhea.
This account was translated by Alfred Bongiovanni from De Crecchio ("Sopra un caso di apparenzi virili in una donna. Morgagni 7:154–188, 1865) in 1963 for an article in The New England Journal of Medicine. |
9672_22 | 20th and 21st centuries
The association of excessive sex steroid effects with diseases of the adrenal cortex have been recognized for over a century. The term "adrenogenital syndrome" was applied to both sex-steroid producing tumors and severe forms of CAH for much of the 20th century, before some of the forms of CAH were understood. Congenital adrenal hyperplasia, which also dates to the first half of the century, has become the preferred term to reduce ambiguity and to emphasize the underlying pathophysiology of the disorders. |
9672_23 | Much modern understanding and treatment of CAH comes from research conducted at Johns Hopkins Medical School in Baltimore in the middle of the 20th century. Lawson Wilkins, "founder" of pediatric endocrinology, worked out the apparently paradoxical pathophysiology: that hyperplasia and overproduction of adrenal androgens resulted from impaired capacity for making cortisol. He reported use of adrenal cortical extracts to treat children with CAH in 1950. Genital reconstructive surgery was also pioneered at Hopkins. After application of karyotyping to CAH and other intersex disorders in the 1950s, John Money, JL Hampson, and JG Hampson persuaded both the scientific community and the public that sex assignment should not be based on any single biological criterion, and gender identity was largely learned and has no simple relationship with chromosomes or hormones. See Intersex for a fuller history, including recent controversies over reconstructive surgery. |
9672_24 | Hydrocortisone, fludrocortisone, and prednisone were available by the late 1950s. By 1980, all of the relevant steroids could be measured in blood by reference laboratories for patient care. By 1990, nearly all specific genes and enzymes had been identified. The last decade, though, has seen a number of new developments, discussed more extensively in congenital adrenal hyperplasia due to 21-hydroxylase deficiency:
Debate over the value of genital reconstructive surgery and changing standards
Debate over sex assignment of severely virilized XX infants
New treatments to improve height outcomes
Newborn screening programs to detect CAH at birth
Increasing attempts to treat CAH before birth
Society and culture
People with CAH
Notable people with CAH include:
Jeff Cagandahan is a Filipino who successful appealed for a change of name and gender on his birth certificate.
Lisa Lee Dark
Betsy Driver
Casimir Pulaski, hypothesized based on examination of remains
See also |
9672_25 | Disorders of sex development
Inborn errors of steroid metabolism
Intersex
List of vaginal anomalies
5α-Reductase 2 deficiency
Androgen insensitivity syndrome
References
Further reading
External links
Autosomal recessive disorders
Congenital disorders of endocrine system
Endocrine-related cutaneous conditions
Intersex variations |
9673_0 | Agriculture in Mongolia constitutes over 10% of Mongolia's annual Gross domestic product and employs one-third of the labor force. However, the high altitude, extreme fluctuation in temperature, long winters, and low precipitation provides limited potential for agricultural development. The growing season is only 95 – 110 days. Because of Mongolia's harsh climate, it is unsuited to most cultivation.
The agriculture sector therefore remains heavily focused on nomadic animal husbandry with 75% of the land allocated to pasture, and cropping only employing 3% of the population. In 2002, about 30% of all households in Mongolia lived from breeding livestock. Most herders in Mongolia follow a pattern of nomadic or semi-nomadic pastoralism. |
9673_1 | Crops produced in Mongolia include corn, wheat, barley, and potatoes. Animals raised commercially in Mongolia include sheep, goats, cattle, horses, camels, and pigs. They are raised primarily for their meat, although goats are valued for their hair which can be used to produce cashmere. Due to the severe 2009–2010 winter, Mongolia lost 9.7 million animals, or 22% of total livestock. This immediately affected meat prices, which increased twofold; the GDP dropped 1.6% in 2009. |
9673_2 | History and growth of production
In the late 1980s, agriculture was a small but critical sector of the Mongolian economy. In 1985 agriculture accounted for only 18.3 percent of national income and 33.8 percent of the labor force. Nevertheless, agriculture remained economically important because much of Mongolia's industry processed agricultural products, foodstuffs, timber, and animal products, such as skins and hides for domestic consumption and for export. In 1986 agriculture supplied nearly 60 percent of Mongolia's exports. |
9673_3 | Mongolian agriculture developed slowly. An abortive attempt to collectivize all arads occurred in the early 1930s; efforts to encourage voluntary cooperatives and arad producers' associations followed. In the 1930s, the government also began developing state farms, and by 1940 there were ten state farms and ninety-one agricultural cooperatives. In 1937 the Soviet Union provided ten hay-making machine stations to prepare fodder for livestock. In 1940 agriculture represented 61 percent of national income, and it employed approximately 90 percent of the labor force. |
9673_4 | In the 1950s, agriculture began to adopt its present structure and modern techniques, based in part on material and technical assistance from the Soviet Union and East European countries. In the 1950s, the hay-making machine stations were reorganized as livestock machine stations. In 1955 negdels replaced the arad producers' associations. By 1959 the state had accomplished the collectivization of agriculture. In ten years, agricultural cooperatives had more than doubled, from 139 in 1950 to 354 by 1960. Ownership of livestock and sown areas changed dramatically as a result of collectivization. In 1950, according to Mongolian government statistics, state farms and other state organizations owned approximately 0.9 percent of livestock and 37.8 percent of sown areas; negdels had about 0.5 percent of livestock and no sown lands; and private owners some held 98.3 percent of livestock and 62.2 percent of sown areas. In 1960 state farms and other state organizations owned 2.7 percent of |
9673_5 | livestock; negdels, 73.8 percent; and individual negdel members, 23.5 percent. The state sector owned 77.5 percent of sown lands, and the cooperative sector the remainder. |
9673_6 | By 1960 agriculture's share of national income had fallen to 22.9 percent, but agriculture still employed 60.8 percent of the work force. After 1960 the number of state farms increased, state fodder supply farms were established, the number of negdels decreased through consolidation, and interagricultural cooperative associations were organized to facilitate negdel specialization and cooperation. Mongolia also began receiving large-scale agricultural assistance from the Soviet Union and other East European countries after Mongolia's 1962 entry into Comecon. The Soviet Union, for example, assisted in establishing and equipping several new state farms, and Hungary helped with irrigation. In 1967 the Third Congress of Agricultural Association Members founded the Union of Agricultural Associations to supervise negdels and to represent their interests to the government and to other cooperative and social organizations. The union elected a central council, the chairman of which was, ex |
9673_7 | officio, the minister of agriculture; it also adopted a Model Charter to govern members' rights and obligations. In 1969 the state handed over the livestock machine stations to the negdels. |
9673_8 | Negdels, which concentrated on livestock production, were organized into brigad (brigades) and then into suuri (bases), composed of several households. Each suuri had its own equipment and production tasks. Negdels adopted the Soviet system of herding, in which arad households lived in permanent settlements rather than traveling with their herds, as in the pastoral tradition. In 1985 the average negdel had 61,500 head of livestock, 438,500 hectares of land, of which 1,200 hectares was plowable land, 43 tractors, 2 grain harvesters, and 18 motor vehicles; it harvested 500 tons of grain. Individual negdel members were permitted to own livestock. In mountain steppe pasture areas, ten head of livestock per person, up to fifty head per household, were allowed. In desert regions, fifteen head per person, up to seventy-five head per household, were permitted. Private plots also were allowed for negdel farmers. |
9673_9 | State farms, compared with negdels, had more capital invested, were more highly mechanized, and generally were located in the most productive regions, or close to major mining and industrial complexes. State farms engaged primarily in crop production. In 1985 there were 52 state farms, 17 fodder supply farms, and 255 negdels. In 1985 the average state farm employed 500 workers; owned 26,200 head of livestock, 178,600 hectares of land, of which 15,400 hectares was plowable land, 265 tractors, 36 grain harvesters, and 40 motor vehicles; it harvested 12,100 tons of grain. |
9673_10 | In the late 1980s, several changes in governmental organization occurred to facilitate agricultural development. In October 1986, the Ministry of Agriculture absorbed the Ministry of Water Economy, which had controlled irrigation. In December 1987, the Ministry of Agriculture, the Ministry of Forestry and Woodworking, and the Ministry of Food and Light Industries were abolished and two new ministries, the Ministry of Agriculture and Food Industry, and the Ministry of Environmental Protection were established. Among the functions of the Ministry of Agriculture and Food Industry were the further coordination of agriculture and of industrial food processing to boost the food supply, and the development on state farms of agro-industrial complexes, which had processing plants for foodstuffs. The Sharin Gol state farm, for example, grew fruits and vegetables, which then were processed in the state farm's factories to produce dried fruit, fruit juices, fruit and vegetable preserves, and |
9673_11 | pickled vegetables. The Ministry of Environmental Protection incorporated the Forestry and Hunting Economy Section of the former Ministry of Forestry and Woodworking and the State Land and Water Utilization and Protection Service of the former Ministry of Agriculture. |
9673_12 | Crop production
Since its inception, the Mongolian People's Republic has devoted considerable resources to developing crop production in what was a predominantly nomadic, pastoral economy. Mongols traditionally disdained the raising of crops, which was conducted for the most part by Chinese farmers. Early efforts to force arads to become farmers failed, and the government turned to the creation of state farms to promote crop production. By 1941 when the state had established ten state farms, Mongolia had 26,600 hectares of sown land. State farms, however, accounted for only 29.6 percent of the planted areas. |
9673_13 | After World War II, Mongolia intensified efforts to expand crop production by establishing more state farms, by reclaiming virgin lands for crop raising, by mechanizing farm operations, and by developing irrigation systems for farmlands. When Mongolia began to report statistics on arable land in 1960, there were 532,000 hectares of arable land, and sown crops covered 265,000 hectares of the 477,000 hectares of plow land. Mongolia's 25 state farms accounted for 77.5 percent of sown areas, and cooperatives, for 22.5 percent. In 1985 when 52 state farms and 17 fodder supply farms existed, there were about 1.2 million hectares of arable land, and sown crops covered 789,600 hectares of the approximately 1 million hectares of plow land. The state sector accounted for 80.6 percent of sown areas, and cooperatives, for 19.4 percent. Development of virgin lands by state farms was responsible for most of the expansion of arable land and sown areas. Land reclamation started in the late 1950s and |
9673_14 | the early 1960s, when 530,000 hectares were developed, and it continued throughout each five-year plan. During the Seventh Plan, 250,000 hectares were assimilated, and the Eighth Plan called for an additional 120,000 to 130,000 hectares to be reclaimed. |
9673_15 | Mechanization of farm operations commenced on a large scale in the 1950s with Soviet assistance. The Soviet Union provided most agricultural machines, as well as advice and expertise in mechanization. State farms were more highly mechanized than cooperatives. For example, in 1985, 100 percent of potato planting and 84 percent of potato harvesting were mechanized on state farms, compared with 85 percent and 35 percent, respectively, in negdels. Beginning in the 1960s, state farms also pioneered the development of irrigation systems for crops. By 1985 Mongolia had 85,200 hectares of available irrigated land, of which 81,600 hectares actually were irrigated. |
9673_16 | Crop production initially concentrated on raising cereals; in 1941 cereals covered 95.1 percent of sown areas, while 3.4 percent was devoted to potatoes and 1.5 percent to vegetables. In 1960, Mongolia became self-sufficient as far as cereals were concerned. Cultivation of fodder crops began in the 1950s. In 1985 cereals covered 80.6 percent of sown areas, fodder crops 17.7 percent, potatoes 1.3 percent, and vegetables 0.4 percent. Mongolia's staple crops were wheat, barley, oats, potatoes, vegetables, hay, and silage crops. Since 1960 agricultural performance as measured by gross output, per capita output, and crop yields was uneven. Although sown acreage expanded dramatically between 1960 and 1980, output and crop yields remained stagnant and, in some cases, fell because of natural disasters and poor management. In addition to the staple crops mentioned, Mongolia also produced small quantities of oil-yielding crops, such as sunflower and grape, and fruits and vegetables, such as sea |
9673_17 | buckthorn, apples, European black currants, watermelons, muskmelons, onions, and garlic. Small amounts of alfalfa, soybean, millet, and peas also were grown to provide protein fodder. |
9673_18 | The Eighth Plan called for increasing the average annual gross harvest of cereals to between 780,000 and 800,000 tons; potatoes to between 150,000 and 160,000 tons; vegetables to between 50,000 and 80,000 tons; silage crops to between 280,000 and 300,000 tons; and annual and perennial fodder crops to between 330,000 and 360,000 tons. Emphasis was placed on raising crop production and quality by increasing mechanization, improving and expanding acreage, raising crop yields, expanding irrigation, selecting cereal varieties better adapted to natural climatic conditions and better locations for cereal cultivation. It also meant applying greater volumes of organic and mineral fertilizers; building more storage facilities; reducing losses because of pests, weeds, and plant diseases; and preventing soil erosion. Emphasis also was put on improving management of crop production on state farms and negdels as well as of procurement, transport, processing, and storage of agricultural products. |
9673_19 | In 2009, 388,122 tonnes of wheat (area harvested: 248,908 ha), 1,844 tonnes of barley (area harvested: 1,460 ha) and 1,512 tonnes of oat (area harvested: 1,416 ha) were produced. Vegetables like tomatoes, carrots, peas, beans, onions and cucumbers are grown in several oases in the South of Mongolia, e.g. in Dal in Ömnögovi Province.
Animal husbandry |
9673_20 | From prerevolutionary times until well into the 1970s, animal husbandry was the mainstay of the Mongolian economy. In the traditional economy, livestock provided foodstuffs and clothing; after the 1921 revolution, livestock supplied foodstuffs and raw materials for industries and for export. Mongolia had 9.6 million head of livestock in 1918 and 13.8 million head in 1924; arad ownership was estimated to be 50 to 80 percent of all livestock, and monastic and aristocratic ownership to be 50 to 20 percent. Policies designed to force collectivization in the early 1930s met with arad resistance, including the slaughter of their own animals. Reversal of these policies led to a growth in livestock numbers, which peaked in 1941 at 27.5 million head. World War II brought new commitments to provide food and raw materials for the Soviet war effort. With the levy of taxes in kind, livestock numbers fell to about 20 million in 1945, and they have hovered between 20 million and 24 million head |
9673_21 | since then. Collectivization and advances in veterinary science have failed to boost livestock production significantly since the late 1940s. In 1940 animal husbandry produced 99.6 percent of gross agricultural output. The share of animal husbandry in gross agricultural output declined after World War II, to 71.8 percent in 1960, 81.6 percent in 1970, 79.5 percent in 1980, and 70 percent in 1985. The rise in crop production since 1940 has accounted for animal husbandry's decline in gross agricultural output. |
9673_22 | Nevertheless, in the late 1980s, animal husbandry continued to be an important component of the national economy, supplying foodstuffs and raw materials for domestic consumption, for processing by industry, and for export. In 1985 there were 22,485,500 head of livestock, of which 58.9 percent were sheep; 19.1 percent, goats; 10.7 percent, cattle; 8.8 percent, horses; and 2.5 percent, camels. In addition, pigs, poultry, and bees were raised. In 1985 there were 56,100 pigs and 271,300 head of poultry; no figures were available on apiculture. Livestock products included meat and fat from camels, cattle, chickens, horses, goats, pigs and sheep; eggs; honey; milk; wool from camels, cattle, goats, and sheep; and hides and skins from camels, cattle, goats, horses, and sheep. In 1986 exports of livestock products included 15,500 tons of wool, 121,000 large hides, 1,256,000 small hides, and 44,100 tons of meat and meat products. |
9673_23 | In the late 1980s, differences existed in ownership and productivity of livestock among state farms, agricultural cooperatives, and individual cooperative members. For example, in 1985 agricultural cooperatives owned 70.1 percent of the "five animals", camels, cattle, goats, horses, and sheep; state farms, 6 percent, other state organizations, 1.7 percent; and individual cooperative members, 22.2 percent. State farms raised 81.4 percent of all poultry; other state organizations, 3.3 percent; cooperatives, 12.9 percent; and individual cooperative members, 2.4 percent. State farms accounted for 19.1 percent of pig raising; other state organizations, for 34.2 percent; agricultural cooperatives, for 12.5 percent; and individual cooperative members, for 34.2 percent. Survival rates of young livestock were higher in the cooperatives than on state farms; however, state farms produced higher yields of milk and wool. Fodder for livestock in the agricultural cooperatives was supplemented by |
9673_24 | production on state fodder supply farms and on state farms, which had higher output and yields. |
9673_25 | Despite its economic importance, in the late 1980s animal husbandry faced many problems: labor shortages, stagnant production and yields, inclement weather, poor management, diseases, and the necessity to use breeding stock to meet high export quotas. The Eighth Plan attempted to address some of these problems. To alleviate labor shortages, the plan called for higher income, increased mechanization, and improved working and cultural conditions in rural areas to retain animal husbandry workers, particularly those with technical training. Measures to raise productivity included increased mechanization; improved breeding techniques to boost meat, milk, and wool yields and to cut losses from barrenness and miscarriages; and strengthened veterinary services to reduce illness. Additional livestock facilities were to be built to provide shelter from harsh winter weather and to fatten livestock. More efficient use of fodder was sought through expanding production; improving varieties; and |
9673_26 | decreasing losses in procurement, shipping, processing, and storage. Pastureland was to be improved by expanding irrigation and by combating pests. |
9673_27 | Overcoming poor management was more difficult. Local party, state, and cooperative organizations were admonished to manage animal husbandry more efficiently, and cooperative members were requested to care for collectively owned livestock as if it were their own. In addition, more concrete measures to improve the management and the productivity of animal husbandry were adopted in the late 1980s. The individual livestock holdings of workers, employees, and citizens were increased to eight head per household in major towns, sixteen head in smaller towns, and twenty-five head in rural areas; households were allowed to dispose of surplus produce through the cooperative trade network and through the state procurement system. Auxiliary farms run by factories, offices, and schools were established to raise additional pigs, poultry, and rabbits, as well as to grow some vegetables. Family contracts concluded on a voluntary basis with cooperatives or with state farms were reported by the |
9673_28 | government to increase high-quality output, to lower production expenses, and to enhance production efficiency. |
9673_29 | As of 2006, livestock still constituted 80% of Mongolian agricultural output. 97% of Mongolian livestock remained privately owned. Meat exports of Mongolia is constrained by low technological and production capacity, logistics limitations, few meat plants, quotas, and phytosanitary barriers.
Forestry |
9673_30 | Mongolia's vast forests (15 million hectares) are utilized for timber, hunting, and fur-bearing animals. In 1984 a Mongolian source stated that the forestry sector accounted for about one-sixth of gross national product (GNP). Until December 1987, exploitation of these resources was supervised by the Forestry and Hunting Economy Section of the Ministry of Forestry and Woodworking. In that month this section was integrated into the new Ministry of Environmental. The Ministry of Environmental Protection's assumption of control of forest resources reflected the government's concern over environmental degradation resulting from indiscriminate deforestation. Forestry enterprises reafforested only 5,000 hectares of the 20,000 hectares felled annually. In addition, fires engulfed 1 million hectares of forest between 1980 and 1986. Mongolia's shrinking forests lowered water levels in many tributaries of the Selenge and Orhon rivers, hurting soil conservation and creating water shortages in |
9673_31 | Ulaanbaatar. |
9673_32 | Timber enterprises and their downstream industries made a sizable contribution to the Mongolian economy, accounting for 10 percent of gross industrial output in 1985. Approximately 2.5 million cubic meters of timber were cut annually. Fuel wood accounted for about 55 percent of the timber cut, and the remainder was processed by the woodworking industry. In 1986 Mongolia produced 627,000 cubic meters of sawn timber, of which 121,000 cubic meters was exported. Lumber also was exported; lumber exports declined dramatically from 104,000 cubic meters in 1984 to 85,700 cubic meters in 1985 and to 39,000 cubic meters in 1986. |
9673_33 | Mongolia's forests and steppes abounded with animals that were hunted for their fur, meat, and other products in the late 1980s. Fur-bearing animals included marmots, muskrats, squirrels, foxes, korsak (steppe foxes), and wolves, which were hunted, and such animals as deer, sable, and ermine, which were raised on state animal farms. Animal pelts were exported in large numbers. In 1985 Mongolia exported more than 1 million small hides, which included some of the 763,400 marmot pelts, 23,800 squirrel skins, 3,700 wolf skins, and other furs. Marmot also was hunted for its fat, which was processed industrially. Mongolian gazelles were hunted for their meat, and red deer, for their antler velvet. Organized hunting of wild sheep was a foreign tourist attraction.
Fishing |
9673_34 | Mongolia's lakes and rivers teem with freshwater fish. Mongolia has developed a small-scale fishing industry, to export canned fish. Little information was available on the types and the quantities of fish processed for export, but in 1986, the total fish catch was 400 metric tons in live weight.
See also
Agriculture in Central Asia
References
External links
Ministry of Food, Agriculture and Light Industry
Water Agency of Mongolia |
9674_0 | Bernard Morton Kopell (born June 21, 1933) is an American character actor known for his roles as Siegfried in Get Smart from 1966 to 1969 and as Dr. Adam Bricker ("Doc") on The Love Boat from 1977 to 1986.
Early beginnings
Kopell was born in Brooklyn, New York, the son of Pauline (née Taran) and Al Bernard Kopell of Jewish extraction. Kopell attended Erasmus Hall High School in Brooklyn before enrolling at New York University, majoring in dramatic arts and graduating with a bachelor of fine arts in 1955.
While fulfilling his military service, he served as a librarian at Naval Air Station, Norfolk, Virginia and then between 1956 and 1957 on board the , a World War II and Korean war battleship, stationed at Guantanamo Bay in Cuba. |
9674_1 | During his time on the USS Iowa, he travelled extensively to Europe in Italy, Spain, Greece, the Middle East in Turkey as well as to South America. He also taught the GED to other military personnel. After completing active duty, Kopell returned to New York before being lured to Los Angeles with the promise of an agent by fellow graduate James Drury.
Career
In Los Angeles, Kopell initially drove a taxi and tried to sell Kirby vacuum cleaners to make ends meet before being cast in a minor role in The Brighter Day, a daytime soap aired on CBS. From there, he moved on to star in My Favorite Martian and The Jack Benny Program impersonating Latino characters, eventually managing to branch out and do other accents. |
9674_2 | During the 1960s and early 1970s, Kopell appeared in many television series, often sitcoms, including Ripcord, That Girl, The Jack Benny Program, Our Man Higgins, Green Acres, Ben Casey, The Flying Nun, Needles And Pins, McHale's Navy, Lancelot Link-Secret Chimp, Petticoat Junction, The Streets of San Francisco, Room 222, The Mary Tyler Moore Show, The Dick Van Dyke Show, Bewitched, and Kojak.
However, Kopell's longest-running role was as Dr. Adam Bricker on The Love Boat, an Aaron Spelling production. He remained on the series during its entire run, appearing in 250 episodes. |
9674_3 | Siegfried and other roles
Kopell made memorable recurring appearances as KAOS agent Siegfried in Get Smart, Alan-a-Dale in When Things Were Rotten, Jerry Bauman in That Girl and Louie Pallucci in The Doris Day Show. He played several characters on Bewitched, including the witches' apothecary and the hippie warlock Alonzo in the episode "The Warlock in the Gray Flannel Suit". He played Charlie Miller as a member of the cast of the situation comedy Needles and Pins, which ran for 14 episodes in the autumn of 1973. He portrayed a plastic surgeon who gave Ed Brown a facelift on Chico and the Man. Earlier in his career, he played a director in an episode of Alfred Hitchcock Presents ("Good-Bye George"). About this same time, he guest starred on the short-lived The New Phil Silvers Show. |
9674_4 | Doc on The Love Boat and other roles |
9674_5 | Kopell's role as Doc on The Love Boat was parodied in a humorous appearance on Late Show with David Letterman in 1995. Two entries in that night's Top Ten List poked fun at The Love Boat, and at the Doc character specifically. The camera cut to Kopell, who was sitting in the audience, and he stormed out of the theater. A few moments later, he was shown having been re-seated in the mezzanine when the second parody was made at his expense, and again stood up, raised his fists and stormed out, playing along with the host. In a dream sequence of Fresh Prince of Bel Air, Kopell made a parody cameo as an actor who played a ship's doctor so many times he offers to perform an operation for real, while in a 1994 episode of Saturday Night Live he appeared as Doc during a Love Boat-themed spoof of Star Trek: The Next Generation. In the 1990s, Kopell traded on his Doc Bricker persona when he appeared in a commercial for an anti-snoring product named D-Snore, in which he noted that loud snoring |
9674_6 | "can even ruin a romantic cruise." |
9674_7 | After The Love Boat, Kopell was so recognizable that he was not in roles often without a nod to his most famous role. He appears as a coroner in "Which Prue Is It Anyway", an episode of Charmed. Kopell appears in the Monk episode "Mr. Monk and the Critic", playing Mr. Gilson, the ill-fated restroom attendant, whom Monk referred to as the Michelangelo of lavatories. He guest starred in "Pinky", a 2009 episode of My Name Is Earl. He made a cameo as a patient in the Scrubs episode "My Friend the Doctor", as well as an episode of The Suite Life of Zack & Cody.
Personal life
Kopell has been married three times, first to actress Celia Whitney, then actress Yolanda Veloz, before marrying Catrina Honadle in 1997. Kopell and Honadle have two children together, Adam (born 1998) and Josh (born 2003).
Filmography
Film
Television
Writer
References
External links |
9674_8 | 1933 births
Living people
20th-century American Jews
American male television actors
American male stage actors
Male actors from New York City
Male actors from Los Angeles
Military personnel from New York City
People from Brooklyn
20th-century American male actors
21st-century American male actors
Erasmus Hall High School alumni
United States Navy sailors
21st-century American Jews |
9675_0 | Orbit modeling is the process of creating mathematical models to simulate motion of a massive body as it moves in orbit around another massive body due to gravity. Other forces such as gravitational attraction from tertiary bodies, air resistance, solar pressure, or thrust from a propulsion system are typically modeled as secondary effects. Directly modeling an orbit can push the limits of machine precision due to the need to model small perturbations to very large orbits. Because of this, perturbation methods are often used to model the orbit in order to achieve better accuracy. |
9675_1 | Background
The study of orbital motion and mathematical modeling of orbits began with the first attempts to predict planetary motions in the sky, although in ancient times the causes remained a mystery. Newton, at the time he formulated his laws of motion and of gravitation, applied them to the first analysis of perturbations, recognizing the complex difficulties of their calculation.
Many of the great mathematicians since then have given attention to the various problems involved; throughout the 18th and 19th centuries there was demand for accurate tables of the position of the Moon and planets for purposes of navigation at sea. |
9675_2 | The complex motions of orbits can be broken down. The hypothetical motion that the body follows under the gravitational effect of one other body only is typically a conic section, and can be readily modeled with the methods of geometry. This is called a two-body problem, or an unperturbed Keplerian orbit. The differences between the Keplerian orbit and the actual motion of the body are caused by perturbations. These perturbations are caused by forces other than the gravitational effect between the primary and secondary body and must be modeled to create an accurate orbit simulation. Most orbit modeling approaches model the two-body problem and then add models of these perturbing forces and simulate these models over time. Perturbing forces may include gravitational attraction from other bodies besides the primary, solar wind, drag, magnetic fields, and propulsive forces. |
9675_3 | Analytical solutions (mathematical expressions to predict the positions and motions at any future time) for simple two-body and three-body problems exist; none have been found for the n-body problem except for certain special cases. Even the two-body problem becomes insoluble if one of the bodies is irregular in shape.
Due to the difficulty in finding analytic solutions to most problems of interest, computer modeling and simulation is typically used to analyze orbital motion. A wide variety of software is available to simulate orbits and trajectories of spacecraft.
Keplerian orbit model
In its simplest form, an orbit model can be created by assuming that only two bodies are involved, both behave as spherical point-masses, and that no other forces act on the bodies. For this case the model is simplified to a Kepler orbit. |
9675_4 | Keplerian orbits follow conic sections. The mathematical model of the orbit which gives the distance between a central body and an orbiting body can be expressed as:
Where:
is the distance
is the semi-major axis, which defines the size of the orbit
is the eccentricity, which defines the shape of the orbit
is the true anomaly, which is the angle between the current position of the orbiting object and the location in the orbit at it is closest to the central body (called the periapsis)
Alternately, the equation can be expressed as:
Where is called the semi-latus rectum of the curve. This form of the equation is particularly useful when dealing with parabolic trajectories, for which the semi-major axis is infinite.
An alternate approach uses Isaac Newton's law of universal gravitation as defined below:
where: |
9675_5 | is the magnitude of the gravitational force between the two point masses
is the gravitational constant
is the mass of the first point mass
is the mass of the second point mass
is the distance between the two point masses
Making an additional assumption that the mass of the primary body is much greater than the mass of the secondary body and substituting in Newton's second law of motion, results in the following differential equation
Solving this differential equation results in Keplerian motion for an orbit.
In practice, Keplerian orbits are typically only useful for first-order approximations, special cases, or as the base model for a perturbed orbit.
Orbit simulation methods |
9675_6 | Orbit models are typically propagated in time and space using special perturbation methods. This is performed by first modeling the orbit as a Keplerian orbit. Then perturbations are added to the model to account for the various perturbations that affect the orbit.
Special perturbations can be applied to any problem in celestial mechanics, as it is not limited to cases where the perturbing forces are small. Special perturbation methods are the basis of the most accurate machine-generated planetary ephemerides.
see, for instance, Jet Propulsion Laboratory Development Ephemeris
Cowell's method
Cowell's method is perhaps the simplest of the special perturbation methods;
mathematically, for mutually interacting bodies, Newtonian forces on body from the other bodies are simply summed thus, |
9675_7 | where
is the acceleration vector of body
is the gravitational constant
is the mass of body
and are the position vectors of objects and
is the distance from object to object
with all vectors being referred to the barycenter of the system. This equation is resolved into components in , , and these are integrated numerically to form the new velocity and position vectors as the simulation moves forward in time. The advantage of Cowell's method is ease of application and programming. A disadvantage is that when perturbations become large in magnitude (as when an object makes a close approach to another) the errors of the method also become large.
Another disadvantage is that in systems with a dominant central body, such as the Sun, it is necessary to carry many significant digits in the arithmetic because of the large difference in the forces of the central body and the perturbing bodies.
Encke's method |
9675_8 | Encke's method begins with the osculating orbit as a reference and integrates numerically to solve for the variation from the reference as a function of time.
Its advantages are that perturbations are generally small in magnitude, so the integration can proceed in larger steps (with resulting lesser errors), and the method is much less affected by extreme perturbations than Cowell's method. Its disadvantage is complexity; it cannot be used indefinitely without occasionally updating the osculating orbit and continuing from there, a process known as rectification.
Letting be the radius vector of the osculating orbit, the radius vector of the perturbed orbit, and the variation from the osculating orbit,
and are just the equations of motion of and ,
where is the gravitational parameter with and the masses of the central body and the perturbed body, is the perturbing acceleration, and and are the magnitudes of and .
Substituting from equations () and () into equation (), |
9675_9 | which, in theory, could be integrated twice to find . Since the osculating orbit is easily calculated by two-body methods, and are accounted for and can be solved. In practice, the quantity in the brackets, , is the difference of two nearly equal vectors, and further manipulation is necessary to avoid the need for extra significant digits. |
9675_10 | Sperling–Burdet method |
9675_11 | In 1991 Victor R. Bond and Michael F. Fraietta created an efficient and highly accurate method for solving the two-body perturbed problem. This method uses the linearized and regularized differential equations of motion derived by Hans Sperling and a perturbation theory based on these equations developed by C.A. Burdet in the year 1864. In 1973, Bond and Hanssen improved Burdet's set of differential equations by using the total energy of the perturbed system as a parameter instead of the two-body energy and by reducing the number of elements to 13. In 1989 Bond and Gottlieb embedded the Jacobian integral, which is a constant when the potential function is explicitly dependent upon time as well as position in the Newtonian equations. The Jacobian constant was used as an element to replace the total energy in a reformulation of the differential equations of motion. In this process, another element which is proportional to a component of the angular momentum is introduced. This brought |
9675_12 | the total number of elements back to 14. In 1991, Bond and Fraietta made further revisions by replacing the Laplace vector with another vector integral as well as another scalar integral which removed small secular terms which appeared in the differential equations for some of the elements. |
9675_13 | The Sperling–Burdet method is executed in a 5 step process as follows:
Step 1: Initialization
Given an initial position, , an initial velocity, , and an initial time, , the following variables are initialized:
Perturbations due to perturbing masses, defined as and , are evaluated
Perturbations due to other accelerations, defined as , are evaluated
Step 2: Transform elements to coordinates
where are Stumpff functions
Step 3: Evaluate differential equations for the elements
Step 4: Integration
Here the differential equations are integrated over a period to obtain the element value at
Step 5: Advance
Set and return to step 2 until simulation stopping conditions are met.
Models of perturbing forces
Perturbing forces cause orbits to become perturbed from a perfect Keplerian orbit. Models for each of these forces are created and executed during the orbit simulation so their effects on the orbit can be determined. |
9675_14 | Non-spherical gravity
The Earth is not a perfect sphere nor is mass evenly distributed within the Earth. This results in the point-mass gravity model being inaccurate for orbits around the Earth, particularly Low Earth orbits. To account for variations in gravitational potential around the surface of the Earth, the gravitational field of the Earth is modeled with spherical harmonics which are expressed through the equation:
where
is the gravitational parameter defined as the product of G, the universal gravitational constant, and the mass of the primary body.
is the unit vector defining the distance between the primary and secondary bodies, with being the magnitude of the distance.
represents the contribution to of the spherical harmonic of degree n and order m, which is defined as: |
9675_15 | where:
is the mean equatorial radius of the primary body.
is the magnitude of the position vector from the center of the primary body to the center of the secondary body.
and are gravitational coefficients of degree n and order m. These are typically found through gravimetry measurements.
The unit vectors define a coordinate system fixed on the primary body. For the Earth, lies in the equatorial plane parallel to a line intersecting Earth's geometric center and the Greenwich meridian, points in the direction of the North polar axis, and
is referred to as a derived Legendre polynomial of degree n and order m. They are solved through the recurrence relation:
is sine of the geographic latitude of the secondary body, which is .
are defined with the following recurrence relation and initial conditions: |
9675_16 | When modeling perturbations of an orbit around a primary body only the sum of the terms need to be included in the perturbation since the point-mass gravity model is accounted for in the term |
9675_17 | Third-body perturbations
Gravitational forces from third bodies can cause perturbations to an orbit. For example, the Sun and Moon cause perturbations to Orbits around the Earth. These forces are modeled in the same way that gravity is modeled for the primary body by means of Direct gravitational N-body simulations. Typically, only a spherical point-mass gravity model is used for modeling effects from these third bodies.
Some special cases of third-body perturbations have approximate analytic solutions. For example, perturbations for the right ascension of the ascending node and argument of perigee for a circular Earth orbit are:
where:
is the change to the right ascension of the ascending node in degrees per day.
is the change to the argument of perigee in degrees per day.
is the orbital inclination.
is the number of orbital revolutions per day.
Solar radiation |
9675_18 | Solar radiation pressure causes perturbations to orbits. The magnitude of acceleration it imparts to a spacecraft in Earth orbit is modeled using the equation below:
where:
is the magnitude of acceleration in meters per second-squared.
is the cross-sectional area exposed to the Sun in meters-squared.
is the spacecraft mass in kilograms.
is the reflection factor which depends on material properties. for absorption, for specular reflection, and for diffuse reflection.
For orbits around the Earth, solar radiation pressure becomes a stronger force than drag above 800 km altitude.
Propulsion
There are many different types of spacecraft propulsion. Rocket engines are one of the most widely used. The force of a rocket engine is modeled by the equation: |
9675_19 | {| border="0" cellpadding="2"
|-
|align=right|where:
|
|-
!align=right|
|align=left|= exhaust gas mass flow
|-
!align=right|
|align=left|= effective exhaust velocity
|-
!align=right|
|align=left|= actual jet velocity at nozzle exit plane
|-
!align=right|
|align=left|= flow area at nozzle exit plane (or the plane where the jet leaves the nozzle if separated flow)
|-
!align=right|
|align=left|= static pressure at nozzle exit plane
|-
!align=right|
|align=left|= ambient (or atmospheric) pressure
|}
Another possible method is a solar sail. Solar sails use radiation pressure in a way to achieve a desired propulsive force. The perturbation model due to the solar wind can be used as a model of propulsive force from a solar sail.
Drag
The primary non-gravitational force acting on satellites in low Earth orbit is atmospheric drag. Drag will act in opposition to the direction of velocity and remove energy from an orbit. The force due to drag is modeled by the following equation: |
9675_20 | where
is the force of drag,
is the density of the fluid,
is the velocity of the object relative to the fluid,
is the drag coefficient (a dimensionless parameter, e.g. 2 to 4 for most satellites)
is the reference area.
Orbits with an altitude below 120 km generally have such high drag that the orbits decay too rapidly to give a satellite a sufficient lifetime to accomplish any practical mission. On the other hand, orbits with an altitude above 600 km have relatively small drag so that the orbit decays slow enough that it has no real impact on the satellite over its useful life. Density of air can vary significantly in the thermosphere where most low Earth orbiting satellites reside. The variation is primarily due to solar activity, and thus solar activity can greatly influence the force of drag on a spacecraft and complicate long-term orbit simulation. |
9675_21 | Magnetic fields
Magnetic fields can play a significant role as a source of orbit perturbation as was seen in the Long Duration Exposure Facility. Like gravity, the magnetic field of the Earth can be expressed through spherical harmonics as shown below:
where
is the magnetic field vector at a point above the Earth's surface.
represents the contribution to of the spherical harmonic of degree n and order m, defined as: |
9675_22 | where:
is the mean equatorial radius of the primary body.
is the magnitude of the position vector from the center of the primary body to the center of the secondary body.
is a unit vector in the direction of the secondary body with its origin at the center of the primary body.
and are Gauss coefficients of degree n and order m. These are typically found through magnetic field measurements.
The unit vectors define a coordinate system fixed on the primary body. For the Earth, lies in the equatorial plane parallel to a line intersecting Earth's geometric center and the Greenwich meridian, points in the direction of the North polar axis, and
is referred to as a derived Legendre polynomial of degree n and order m. They are solved through the recurrence relation:
is defined as: 1 if m = 0, for and , and for and
is sine of the geographic latitude of the secondary body, which is .
are defined with the following recurrence relation and initial conditions: |
9675_23 | See also
n-body problem
Orbital resonance
Osculating orbit
Perturbation (astronomy)
Sphere of influence (astrodynamics)
Two-body problem
Notes and references
External links
Gravity maps of the Earth
Orbital perturbations
Dynamical systems
Dynamics of the Solar System |
9676_0 | The Magic School Bus is an animated children's television series, based on the book series of the same name by Joanna Cole and Bruce Degen. Running originally from 1994 to 1997, the series received critical acclaim for its use of celebrity voice talent and combining entertainment with an educational series.
Plot
Miss Frizzle embarks on adventures with her class on the eponymous school bus. As they journey on their exciting field trips, they discover locations, creatures, time periods and more to learn about the wonders of science along the way.
Voice cast
Lily Tomlin as Miss Frizzle
Amos Crawley (Season 1) and Danny Tamberelli (Season 2-4) as Arnold Perlstein
Daniel DeSanto as Carlos Ramon
Tara Meyer as Dorothy Ann Hudson
Erica Luttrell as Keesha Franklin
Maia Filar as Phoebe Terese
Stuart Stone as Ralphie Tennelli
Max Beckford (Season 1) and Andre Ottley-Lorant (Season 2-4) as Tim Wright
Lisa Yamanaka as Wanda Li
Episodes |
9676_1 | Production and broadcast
In early 1994, The Magic School Bus concept was made into an animated series of the same name by Scholastic Entertainment and it premiered on September 10, 1994. The idea for the TV series was developed by former Scholastic Entertainment Vice President and Senior Editorial Director Craig Walker. Scholastic Entertainment president Deborah Forte explained that adapting the books into an animated series was an opportunity to help kids "learn about science in a fun way". During this time, Forte had been hearing concerns from parents and teachers about how to improve science education for kids and minorities across the globe. Hanho Heung-Up Co., Ltd. contributed some of the animation for this series. The theme song, called "Ride on the Magic School Bus", was written by Peter Lurye and performed by Little Richard. The voice director was Susan Blu; two of the writers for the series were Brian Meehl and Jocelyn Stevenson. |
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