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PubMed2002

The astrophysics of crowded places.

Today the Sun is in a relatively uncrowded place. The distance between it and the nearest other star is relatively large (about 200,000 times the Earth-Sun distance!). This is beneficial to life on Earth; a close encounter with another star is extremely unlikely. Such encounters would either remove the Earth from its orbit around the Sun or leave it on an eccentric orbit similar to a comet's. But the Sun was not formed in isolation. It was born within a more-crowded cluster of perhaps a few hundred stars. As the surrounding gas evaporated away, the cluster itself evaporated too, dispersing its stars into the Galaxy. Virtually all stars in the Galaxy share this history, and here I will describe the role of 'clusterness' in a star's life. Stars are often formed in larger stellar clusters (known as open and globular clusters), some of which are still around today. I will focus on stars in globular clusters and describe how the interactions between stars in these clusters may explain the zoo of stellar exotica which have recently been observed with instruments such as the Hubble Space Telescope and the X-ray telescopes XMM-Newton and Chandra. In recent years, myriad planets orbiting stars other than the Sun--the so-called 'extrasolar' planets--have been discovered. I will describe how a crowded environment will affect such planetary systems and may in fact explain some of their mysterious properties.

Journal Article↗
PubMed2002

Effects of molecular crowding by saccharides on alpha-chymotrypsin dimerization.

Given the importance of protein complexes as therapeutic targets, it is necessary to understand the physical chemistry of these interactions under the crowded conditions that exist in cells. We have used sedimentation equilibrium to quantify the enhancement of the reversible homodimerization of alpha-chymotrypsin by high concentrations of the osmolytes glucose, sucrose, and raffinose. In an attempt to rationalize the osmolyte-mediated stabilization of the alpha-chymotrypsin homodimer, we have used models based on binding interactions (transfer-free energy analysis) and steric interactions (excluded volume theory) to predict the stabilization. Although transfer-free energy analysis predicts reasonably well the relatively small stabilization observed for complex formation between cytochrome c and cytochrome c peroxidase, as well as that between bobtail quail lysozyme and a monoclonal Fab fragment, it underestimates the sugar-mediated stabilization of the alpha-chymotrypsin dimer. Although predictions based on excluded volume theory overestimate the stabilization, it would seem that a major determinant in the observed stabilization of the alpha-chymotrypsin homodimer is the thermodynamic nonideality arising from molecular crowding by the three small sugars.

Chymotrypsin↗
PubMed1975

Mandibular anterior crowding in relation to tooth size and craniofacial morphology.

In the present study the problem of mandibular anterior crowding was investigated by comparing a group of adults having approximately ideal occlusion (n = 27) with a group with corresponding occlusion except for a slight crowding in the mandibular anterior segment (n = 39). Both sexes were represented. A statistical evaluation revealed that in the latter group the mesiodistal diameter of the four mandibular incisor teeth was significantly greater, whereas the intercanine width and the frequency of third molars were the same in both groups. A comparison of the craniofacial morphology of the two groups displayed limited differences, and only the basal sagittal jaw relationship and the mandibular inclination differed significantly. No significant correlations were observed between the space conditions and any of the variables studied.

Adult↗
PubMed2004

Lessons learned from public health mass media campaigns: marketing health in a crowded media world.

Every year, new public health mass media campaigns are launched attempting to change health behavior and improve health outcomes. These campaigns enter a crowded media environment filled with messages from competing sources. Public health practitioners have to capture not only the attention of the public amid such competition, but also motivate them to change health behaviors that are often entrenched or to initiate habits that may be new or difficult. In what ways are public health mass media campaigns now attempting to succeed in a world crowded with media messages from a myriad of sources? What are the conditions that are necessary for a media campaign to successfully alter health behaviors and alter outcomes in the long term? To what extent can the successes and failures of previous campaigns be useful in teaching important lessons to those planning campaigns in the future? In this chapter we attempt to answer these questions, drawing from recent literature on public health mass media campaigns.

Health Promotion↗
PubMed2005

Unfocused spatial attention underlies the crowding effect in indirect form vision.

We studied mechanisms underlying the crowding effect in indirect form vision by measuring recognition contrast sensitivity of a character with flankers to the left and right. Attentional and featural contributions to the effect can be separated by a new paradigm that distinguishes pattern location errors from pattern recognition errors and further by manipulating the focusing of spatial attention through a positional cue, appearing 150 ms before the target. Measurements were on the horizontal meridian, at 1, 2, and 4 deg eccentricity, and a range of flankers' distances were used. Our results show that in normal indirect viewing, the impairment of character recognition by crowding is--in particular at intermediate flanker distances--caused to a large part by spatially imprecise focusing of attention. In contrast, the enhancement of performance by a transient positional cue seems mediated through a separate attentional mechanism such that attentional locus and focus are controlled independently. Our results furthermore lend psychophysical support to a separate coding of the what and where in pattern recognition.

Attention↗
PubMed1992

Second molar extraction in the treatment of lower premolar crowding.

Thirty-four children with lower premolar crowding were treated by extraction of second molars. Thirteen cases had mechanical lower arch treatment started not less than 6 months after extractions. The remainder had no treatment in the lower arch. The change in premolar crowding was measured, and the reasons why spontaneous alignment occurred in some cases and not in others were examined.

Adolescent↗
PubMed1994

Late lower arch crowding: the role of differential horizontal growth.

Eighty-five subjects, recorded soon after eruption of second permanent molars, were followed longitudinally for 3 or 4 years. Correlation and multiple regression analyses were used to examine the relationship between the change in lower arch space condition and (1) the horizontal component of the change in position of various points on or near the anterior borders of the maxilla and mandible, (2) the differential horizontal-vertical change in these points and (3) differences in horizontal change between maxillary and mandibular, and between intramandibular points. No significant differences in amount or direction of growth were found between the maxillary and mandibular teeth or jaws. Pogonion changed more in a horizontal direction than B point. Increased lower arch crowding was weakly associated with differential horizontal growth of the teeth and jaws. Reduced horizontal growth and greater vertical as opposed to horizontal growth of the maxilla and teeth, and increased growth of the mandibular base were to some extent related to the crowding increase.

Adolescent↗
PubMed2005

Molecular crowding effects on protein stability.

The volume fraction occupied by the dry matter of the cell can be as large as 40%, of which more than half (approximately 60%) are proteins. Thus, cellular proteins and protein assemblies occupy a large volume that can have a profound effect on their own native-state stabilities and on their unfolding/refolding rates. In addition, macromolecular crowding can change the properties of a significant fraction of the water in the cell. We review features of the molecular crowding effect which are relevant for describing the microscopic mechanism of thermal injuries.

Mathematics↗
PubMed1996

Has Medicaid growth crowded out state educational spending?

Researchers have argued that the dramatic increase in Medicaid spending during the late 1980s and early 1990s "crowded out" state spending on other activities, particularly education. Medicaid growth has, at least in part, been driven by increased federal eligibility and service mandates, federal court decisions on hospital and nursing home rates, and health care inflation; and the need to respond to these outside forces has placed increasing pressure on state finances. Other evidence, however, suggests that the adverse effect of Medicaid growth on state finances has been overstated. During the late 1980s and early 1990s, states shifted many human service programs from general fund to Medicaid financing and took advantage of Medicaid rules governing the use of provider donations and assessments, such as state matching and claiming payments to disproportionate-share hospitals to increase federal reimbursement without increasing the claims on their own revenues. But the increased burden of Medicaid growth on state finances may be more apparent than real. In this article, we test the crowding-out hypothesis using a two-stage, least-squares fixed-effects model of Medicaid's impact on educational spending from 1980 to 1990. Our results indicate that Medicaid growth has had no significant effect on educational spending. Rather, educational spending has responded more to changes in states' own-source revenues than to growth in Medicaid spending.

Education↗
PubMed1992

Third molars and incisor crowding: when removal is unwarranted.

Recent evidence indicates that extracting unerupted mandibular third molars neither decreases interdental force measurably nor prevents mandibular incisor crowding. There are valid reasons for extracting third molars. But extraction for the exclusive purpose of relieving interdental pressure and thereby preventing incisor crowding is unwarranted.

Adult↗
PubMed2006

Protein aggregation in crowded environments.

The generic tendency of proteins to aggregate into non-functional, and sometimes cytotoxic, structures poses a universal problem for all types of cell. This tendency is greatly exacerbated by the high total concentration of macromolecules found within most intracellular compartments, a phenomenon referred to as macromolecular crowding. This review discusses the quantitative effects of crowding on protein aggregation and the role of molecular chaperones in combating this problem.

Algorithms↗
PubMed1999

Crowd out: evidence from the Florida Healthy Kids Program.

OBJECTIVE: To determine the percentage of children who had insurance coverage in the 12 months preceding enrollment in a state-subsidized program; the percentage of parents who had access to employer-based family coverage; and the cost of the families' share of the premium per month. METHODS: We randomly selected 930 families whose children were enrolled in the Florida Healthy Kids Program for a period of between 1 and 3 months and conducted telephone interviews with them in 1998 about their children's insurance coverage before program entry and their access to employer-based family coverage. There were 653 families in the final sample. RESULTS: Only 5% of the children had employer-based coverage before program enrollment. However, 26% had access to family coverage through their employers with the family share of the premiums representing on average 13% of their incomes. Access to employer-based coverage varied significantly by family income. CONCLUSIONS: Throughout the development of the State Children's Health Insurance Program legislation, policy analysts expressed concern that families may crowd out or substitute a subsidized state plan for employer-based coverage. This substitution could result in fewer improvements in access to care and health status than were anticipated, because families are simply moving to a different form of health insurance. There is some degree of crowd out in the Healthy Kids Program. The economic burden to near-poor families to purchase employer-based coverage is significant. Some degree of substitution may need to be tolerated to ensure that children receive needed health insurance.

Child↗
PubMed2004

Burning a hole in the budget: tobacco spending and its crowd-out of other goods.

Smoking is an expensive habit. Smoking households spend, on average, more than $US1000 annually on cigarettes. When a family member quits, in addition to the former smoker's improved long-term health, families benefit because savings from reduced cigarette expenditures can be allocated to other goods. For households in which some members continue to smoke, smoking expenditures crowd-out other purchases, which may affect other household members, as well as the smoker. We empirically analyse how expenditures on tobacco crowd-out consumption of other goods, estimating the patterns of substitution and complementarity between tobacco products and other categories of household expenditure. We use the Consumer Expenditure Survey data for the years 1995-2001, which we complement with regional price data and state cigarette prices. We estimate a consumer demand system that includes several main expenditure categories (cigarettes, food, alcohol, housing, apparel, transportation, medical care) and controls for socioeconomic variables and other sources of observable heterogeneity. Descriptive data indicate that, comparing smokers to nonsmokers, smokers spend less on housing. Results from the demand system indicate that as the price of cigarettes rises, households increase the quantity of food purchased, and, in some samples, reduce the quantity of apparel and housing purchased.

Adult↗
PubMed1989

The morphogenesis of hindbrain crowding associated with lumbosacral myeloschisis.

The teratogenicity of ethylenethiourea (ETU) was investigated in Sprague-Dawley rats and Landrace pigs. Pregnant rats each received a single intragastric dose of ETU on a given day from day 8 to day 19 of gestation, and pregnant pigs were given a single dose of ETU from day 15 to day 19. Control animals received an ETU-free vehicle. The newborn pigs were all normal, whereas there were high incidences of specific types of congenital malformation of the central nervous and other systems in the rats. A high incidence of lumbosacral myeloschisis associated with hindbrain crowding was observed in rat fetuses exposed to ETU on day 11 of gestation. This abnormality is considered comparable to Chiari type II malformation associated with spinal dysraphism (Arnold-Chiari malformation) in humans. Morphogenetic fetuses were examined by light and scanning electron microscopy and interactive image analysis. At gestational days 12 and 13, the volume of the caudal end of the neural tube from the anterior border of the hindlimb bud to the most caudal portion of the fetus was significantly greater in ETU-exposed than in control rat embryos. Experimental rat embryos also exhibited disturbance in closure of the posterior neuropore, with extrusion of neural tissue through the opening. An apparently unrelated abnormality in ETU-exposed rat fetuses was underdevelopment of the cranium, leading to hindbrain crowding.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1996

Medicaid eligibility policy and the crowding-out effect: did women and children drop private health insurance to enroll in Medicaid.

In the late 1980s and early 1990s, the federal government expanded Medicaid eligibility for children and pregnant women. By 1992, nearly a third of all children in the United States were eligible for Medicaid, and between 40 and 50 percent of women of childbearing age were eligible for Medicaid coverage for pregnancy-related services. During this period, the number of persons with employment-based insurance coverage declined, leading researchers to investigate whether Medicaid expansions have contributed to this decline--a so-called crowding-out effect. This Issue Brief discusses research findings and the health policy implications of the crowding-out effect.

Child↗
PubMed2000

Medicaid expansions and the crowding out of private health insurance among children.

This paper re-examines the magnitude of crowd out among children. We use longitudinal data that allow us to identify and differentiate groups of children based on whether their eligibility for Medicaid was affected by the program's eligibility expansions. We investigate whether changes in insurance coverage of children affected by the expansions differed from changes in insurance coverage of children unaffected by the expansions. For example, we directly measure whether there was a greater decrease in private insurance coverage among children who became eligible for Medicaid than among children whose eligibility was unaffected. Our results suggest that there was relatively little crowd out among children. We estimate that 18.9% of the recent increase in Medicaid enrollment came from private insurance.

Adolescent↗
PubMed2003

Crowding and winter emergency feeding as predisposing factors for kerato-conjunctivitis in semi-domesticated reindeer in Norway.

Due to the hard environmental and climatic situation in late winter 1999, a herd of about 200 free-ranging, semi-domesticated reindeer was gathered in a paddock in northern Norway for emergency feeding. About the same number of reindeer was not corralled but supplementary fed on their winter pastures. The fodder was of relatively good quality but very dusty and fed in a very dry environment. Six weeks later, an outbreak of eye-infection was diagnosed in one third of the corralled reindeer; mild symptoms were observed in most of them, but 11 animals showed severe signs of disease. No signs of disease were found in the non-corralled animals. Ten reindeer died through emaciation, the eleventh was sacrificed. Histopathological diagnosis of two severely affected eyes revealed a severe purulent kerato-conjunctivitis with bacteria and plant particles embedded in purulent exudates on the cornea and conjunctiva. In one eye from the two most affected animals Actinomyces pyogenes, coagulase-negative Staphylococci and Escherichia coli and in the other one Staphylococcus aureus and Escherichia coli were found. The bacteria encountered in this study are not considered the primary cause of disease. They seem rather to be opportunistic infectious agents of eyes that have been irritated mechanically through exposure to dusty fodder in a dry environment. The stress through unfamiliar corralling of the reindeer, that followed an insufficient fodder supply, could be considered as an additional infection supporting factor. This case-report emphasises on the importance of different factors involved in favouring outbreaks of disease in reindeer, under intensified husbandry conditions. Even though crowding and emergency feeding may be, at certain circumstances, the only means of survival for reindeer, a negative impact of implied crowding diseases on their productivity, must be considered, as well.

Animal Feed↗