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We measured with unprecedented precision the induced polarization P(y) in (4)He(e,e'p)(3)H at Q(2)=0.8 and 1.3 (GeV/c)(2). The induced polarization is indicative of reaction-mechanism effects beyond the impulse approximation. Our results are in agreement with a relativistic distorted-wave impulse approximation calculation but are overestimated by a calculation with strong charge-exchange effects. Our data are used to constrain the strength of the spin-independent charge-exchange term in the latter calculation.
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Proton recoil polarization was measured in the quasielastic 4He(e,e'p)3H reaction at Q{2}=0.8 and 1.3 (GeV/c){2} with unprecedented precision. The polarization-transfer coefficients are found to differ from those of the 1H(e,e'p) reaction, contradicting a relativistic distorted-wave approximation and favoring either the inclusion of medium-modified proton form factors predicted by the quark-meson coupling model or a spin-dependent charge-exchange final-state interaction. For the first time, the polarization-transfer ratio is studied as a function of the virtuality of the proton.
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We measured the angular dependence of the three recoil-proton polarization components in two-body photodisintegration of the deuteron at a photon energy of 2 GeV. These new data provide a benchmark for calculations based on quantum chromodynamics. Two of the five existing models have made predictions of polarization observables. Both explain the longitudinal polarization transfer satisfactorily. Transverse polarizations are not well described, but suggest isovector dominance.
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We report the results of a new Rosenbluth measurement of the proton electromagnetic form factors at Q2 values of 2.64, 3.20, and 4.10 GeV2. Cross sections were determined by detecting the recoiling proton, in contrast to previous measurements which detected the scattered electron. Cross sections were determined to 3%, with relative uncertainties below 1%. The ratio mu(p)G(E)/G(M) was determined to 4%-8% and showed mu(p)G(E)/G(M) approximately 1. These results are consistent with, and much more precise than, previous Rosenbluth extractions. They are inconsistent with recent polarization transfer measurements of similar precision, implying a systematic difference between the techniques.
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We have measured the differential cross section for the gamman-->pi(-)p and gammap-->pi(+)n reactions at theta(c.m.)=90 degrees in the photon energy range from 1.1 to 5.5 GeV at Jefferson Lab (JLab). The data at E(gamma) greater, similar 3.3 GeV exhibit a global scaling behavior for both pi(-) and pi(+) photoproduction, consistent with the constituent counting rule and the existing pi(+) photoproduction data. Possible oscillations around the scaling value are suggested by these new data. The data show enhancement in the scaled cross section at a center-of-mass energy near 2.2 GeV. The cross section ratio of exclusive pi(-) to pi(+) photoproduction at high energy is consistent with the prediction based on one-hard-gluon-exchange diagrams.
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The factors influencing the survival of greater horseshoe bat (Rhinolophus ferrumequinum) offspring born over seven years at a maternity colony in south-west Britain were studied. The effects of a range of phenotypic and maternal variables were analysed using a historical data set. In addition, the influence of two genetic measures on mortality, individual heterozygosity and a new measure of outbreeding, termed mean d(2), was assessed. Logistic regressions were undertaken with survival modelled as a binary response variable. Survival to two life stages was studied for each variable and all models were developed for both sexes separately and together. Only one variable, mean d(2), was significantly associated with survival. Male offspring with high mean d(2) scores were more likely to survive to their first and second summers. The influence of mean d(2) was not due to a single locus under selection but a wider multilocus effect and probably represents heterosis as opposed to solely inbreeding depression. Therefore, the extent to which an individual is outbred may determine survival more than widely used phenotypic characteristics such as size and mass. Mean d(2) may reflect immunocompetence, which influences mortality. Protection of mating sites in order to facilitate gene flow and, therefore, outbreeding may help to promote population stability and growth.
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Animales no Consanguíneos , Quirópteros , Animales , Animales Salvajes , Cruzamiento , Quirópteros/genética , Femenino , Variación Genética , Masculino , Modelos GenéticosRESUMEN
The recoil proton polarization has been measured in the p(e-->,e'p-->)pi(0) reaction in parallel kinematics around W = 1232 MeV, Q2 = 0.121 (GeV/c)2, and epsilon = 0.718 using the polarized cw electron beam of the Mainz Microtron. All three proton polarization components, Px/P(e) = (-11.4+/-1.3+/-1.4)%, P(y) = (-43.1+/-1.3+/-2.2)%, and P(z)/P(e) = (56.2+/-1.5+/-2.6)%, could be measured simultaneously. The Coulomb quadrupole to magnetic dipole ratio, CMR = (-6.4+/-0.7(stat)+/-0.8(syst))%, was determined from Px in the framework of the Mainz Unitary Isobar Model. The consistency among the reduced polarizations and the extraction of the ratio of longitudinal-to-transverse response is discussed.
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Esophageal cancer ranks among the 10 most common cancers worldwide and is almost invariably fatal. The detailed genetic repertoire involved in esophageal carcinogenesis has not been defined. We have shown previously that the esophageal squamous cell carcinoma genome exhibits a frequent loss of heterozygosity (LOH) in the pericentromeric region of chromosome 18. To construct a fine deletion map, we screened 76 new samples composed of microdissected esophageal squamous cell carcinoma and matched morphologically normal epithelial cells using closely spaced markers. Maximal LOH frequency (54%) was displayed by D18S542 on 18p11.2. The pattern of LOH in selected patients indicated that the short region of overlap extends 3 cM on either side of D18S542. On the long arm of chromosome 18, the highest frequency of allelic loss (42%) was detected by D18S978 on 18q12.2-q21.1. This analysis revealed a short region of overlap of approximately 0.8 cM. These findings further implicate unreported tumor suppressor genes encoded by 18p11.2 and 18q12.2 in esophageal squamous cell carcinogenesis and they indicate a refinement of their map location.
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Alelos , Carcinoma de Células Escamosas/genética , Cromosomas Humanos Par 18/genética , Neoplasias Esofágicas/genética , Pérdida de Heterocigocidad , Adulto , Anciano , Anciano de 80 o más Años , Mapeo Cromosómico , Femenino , Eliminación de Gen , Humanos , Masculino , Repeticiones de Microsatélite/genética , Persona de Mediana Edad , Reacción en Cadena de la Polimerasa , Polimorfismo GenéticoRESUMEN
Following a dramatic decline last century, the British population of the endangered greater horseshoe bat Rhinolophus ferrumequinum is highly fragmented. To examine the consequences of fragmentation and limited dispersal on patterns of genetic structure and variation, we used microsatellite markers to screen bats from around 50% of the known maternity colonies in Britain, and two areas from continental Europe. Analyses revealed that Welsh and English colonies were genetically isolated. This, and lower variability in Britain than north France, may result from either genetic drift, or the species' colonization history. Gene flow among most neighbouring colonies was not generally restricted, with one exception. These findings have important implications for the ongoing conservation management of this species.
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Quirópteros/genética , Variación Genética , Animales , Conservación de los Recursos Naturales , Inglaterra , Francia , Heterocigoto , Italia , Repeticiones de Microsatélite , Polimorfismo Genético , GalesRESUMEN
Female greater horseshoe bats form maternity colonies each summer in order to give birth and raise young. During the mating period, females visit males occupying territorial sites, copulation takes place and sperm are stored until ovulation occurs, normally in April. Using microsatellite markers and a likelihood method of parentage analysis, we studied breeding behaviour and male reproductive success over a five-year period in a population of bats in south-west Britain. Paternity was assigned with 80% confidence to 44% of young born in five successive cohorts. While a small annual skew in male reproductive success was detected, the variance increased over five years due to the repeated success of a few individuals. Mating was polygynous, although some females gave birth to offspring sired by the same male in separate years. Such repeated partnerships probably result from fidelity for either mating sites or individuals or from sperm competition. Females mated with males born both within and outside their own natal colony; however, relatedness between parents was no less than the average recorded for male female pairs. Gene flow between colonies is likely to be primarily mediated by both female and male dispersal during the mating period rather than more permanent movements.
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Quirópteros/genética , Conducta Sexual Animal , Animales , Femenino , MasculinoRESUMEN
The greater horseshoe bat, Rhinolophus ferrumequinum, is a model species in echolocation studies, and emits calls containing long constant-frequency (CF) components. The bats have auditory systems tuned sharply to frequencies close to the resting CF (RF) values. Call frequency and neural processing are both flexible within individual bats which use this mode of echolocation. The simple structure of the calls makes them ideal for sonographic analysis. Here, in a large-scale and long-term analysis of changes in the vocalizations of bats we show that: (i) the calls of R. ferrumequinum aged 1-28 years vary seasonally and over a lifetime in a predictable manner; and (ii) an infant's RF is at least partly determined by the RF of its mother. We consider the relative importance of genetic and learning factors upon the correlation between RFS of mothers and offspring.
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Quirópteros/fisiología , Ecolocación , Conducta Materna , Envejecimiento/fisiología , Análisis de Varianza , Animales , Femenino , Masculino , Estaciones del Año , Vocalización AnimalRESUMEN
In the period from January 1, 1976 to December 31, 1988, we reviewed the charts of 33 patients treated for carcinoma of the thyroid at Howard University Hospital. The three non-black patients (two Whites and one Pakistani) were excluded from the study. There were 19 females and 11 males. Of the 30 cases elevated, 10 were papillary, 7 were follicular variant of papillary, 8 were follicular, 3 were undifferentiated (anaplastic), and 2 were medullary. Ten patients had either distant metastasis (Hoffman, South Med J 80:741, 1987) or locally advanced disease in the neck (Woolner et al., Am J Surg 102:354, 1961.) at the time of diagnosis. The treatment of these lesions depended on, among other variables, the cell type, the extent of the lesion, and the personal preference of the attending surgeon. Carcinoma of the thyroid remains an uncommon lesion in Black patients. Because of its rarity, the diagnosis may often be delayed and, as a result, patients may first come to attention with a more advanced stage of this disease. To prevent this occurrence, a high index of suspicion must be maintained for all thyroid nodules, and appropriate diagnostic steps taken. Diagnostic and treatment options are discussed.