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571.
Harold F. Levison Katherine A. Kretke Kevin J. Walsh William F. Bottke 《Proceedings of the National Academy of Sciences of the United States of America》2015,112(46):14180-14185
Building the terrestrial planets has been a challenge for planet formation models. In particular, classical theories have been unable to reproduce the small mass of Mars and instead predict that a planet near 1.5 astronomical units (AU) should roughly be the same mass as Earth. Recently, a new model called Viscously Stirred Pebble Accretion (VSPA) has been developed that can explain the formation of the gas giants. This model envisions that the cores of the giant planets formed from 100- to 1,000-km bodies that directly accreted a population of pebbles—submeter-sized objects that slowly grew in the protoplanetary disk. Here we apply this model to the terrestrial planet region and find that it can reproduce the basic structure of the inner solar system, including a small Mars and a low-mass asteroid belt. Our models show that for an initial population of planetesimals with sizes similar to those of the main belt asteroids, VSPA becomes inefficient beyond ∼ 1.5 AU. As a result, Mars’s growth is stunted, and nothing large in the asteroid belt can accumulate.Classical models of terrestrial planet formation have a problem: The same models that produce reasonable Earth and Venus analogs tend to produce Mars analogs that are far too large (1). The only existing proposed explanations for the small mass of Mars based on classical modes of growth require a severe depletion of solids beyond 1 astronomical unit (AU) (2), involving either not-well-understood nebular processes (3) or a complicated and dramatic migration of the giant planets (4) to solve this problem. Recently, however, it has been shown that a new mode of planet formation known as Viscously Stirred Pebble Accretion (VSPA) can successfully explain the formation of the giant planets (5, 6). Here it is our hypothesis that Mars’s mass may simply be another manifestation of VSPA. To understand how, we need to describe the process. 相似文献
572.
Cardiorespiratory status in long-term survivors of prematurity, with and without hyaline membrane disease 总被引:2,自引:0,他引:2
Forty-eight children, born at less than 33 weeks' gestation and without bronchopulmonary dysplasia (BPD) or Wilson-Mikity syndrome (WM) were studied at a mean age of 9.1 years, to identify the incidence and possible factors contributing to the development of long-term abnormalities in pulmonary function. As neonates, 30 children had hyaline membrane disease (HMD) of whom 21 required ventilation. Eighteen did not have HMD, of whom 9 required ventilation for nonrespiratory reasons. All patients had grown normally. Four of the 48 (8.3%) had clinical asthma, 5 had persisting chest x-ray abnormalities (10.6% of 47 chest x-rays performed), each having been ventilated for HMD. There was a close association between duration of ventilation, oxygen administration, and subsequent abnormal chest x-ray. Electrocardiogram and M-mode echocardiograms were normal in all but 2 patients. Only 3 patients had significant restrictive lung disease, 3 had evidence of significant airways obstruction, and 13 (27.7%) had signs of air trapping. Methacholine challenge was positive in 30 of 46 patients (65.2%). The incidence of a positive methacholine challenge did not correlate with history of HMD, duration of ventilation, or high oxygen administration. There is an increased incidence of airway hyperreactivity in survivors of prematurity, not associated with any identified therapeutic maneuver during the neonatal period. 相似文献
573.
Epidemiology of bacteriuria in an elderly ambulatory population 总被引:5,自引:0,他引:5
J A Boscia W D Kobasa R A Knight E Abrutyn M E Levison D Kaye 《The American journal of medicine》1986,80(2):208-214
This study of bacteriuria in elderly (mean age 85 years, range 68 to 103) Jewish subjects of mostly middle and upper class attempted to determine disease prevalence, define the turnover in infected subjects, and assess the relation between functional status and infection. The prevalence of bacteriuria (midstream clean-catch method) was assessed in 373 women and 150 men. It was higher in women (18.2 percent) than in men (6.0 percent) (p less than 0.001) and was more common in functionally impaired nursing home residents (23.5 percent) than in apartment house dwellers (12.1 percent) (p less than 0.01). In longitudinal studies, 260 subjects (184 women and 76 men) had three urine culture surveys at six-month intervals. The cumulative percent infected on at least one survey was high (women 30.4 percent, men 10.5 percent). However, persistence of the same organism on all three surveys was surprisingly infrequent (women 6.0 percent, men 1.3 percent), and the turnover of infected and noninfected subjects was considerable. Persistence of bacteriuria on all three surveys was significantly more common in nursing home residents (13.9 percent) than in apartment house dwellers (3.1 percent) (p less than 0.01). Thus, bacteriuria is common in the elderly and appears related to functional status. However, the turnover of infected and noninfected subjects was high, and surprisingly, persistence was not found in most. The transient nature of bacteriuria in most provides support against the treatment of asymptomatic bacteriuria in the elderly. 相似文献
574.
J A Boscia W D Kobasa E Abrutyn M E Levison A M Kaplan D Kaye 《The American journal of medicine》1986,81(6):979-982
In a study of bacteriuria in elderly (mean age 85 years, range 69 to 101), mostly middle- and upper-class Jewish subjects, attempts were made to determine if bacteriuria without dysuria is otherwise asymptomatic. Seventy-two subjects (59 women and 13 men) without dysuria were questioned about other urinary symptoms (incontinence, frequency, urgency, suprapubic pain, flank pain, fever) and symptoms indicating a lack of well-being (anorexia, difficulty in falling asleep, difficulty in staying asleep, fatigue, malaise, weakness) when they were with and without bacteriuria. Twenty-two subjects had bacteriuria that resolved spontaneously; bacteriuria subsequently developed in 24 nonbacteriuric subjects; and 26 subjects had bacteriuria that resolved with antimicrobial therapy. Subjects occasionally reported urinary symptoms (especially incontinence) and commonly reported symptoms indicating a lack of well-being when they were with and/or without bacteriuria. However, no differences in symptoms were found when bacteriuric subjects were compared with themselves when they were nonbacteriuric. Thus, bacteriuria without dysuria in the elderly appears to be asymptomatic. 相似文献
575.
Antiretroviral therapy for treatment of HIV infection has become increasingly effective. Persistent poor HIV outcomes in racial and ethnic minority populations in the US call for a closer examination into why Latinos are at significant risk for acquiring and dying from HIV. To improve clinical outcomes and achieve an AIDS-free generation, HIV research must address disparities in HIV outcomes in Latinos, the largest ethnic/racial minority population in the US. Immigrant status as well as cultural factors influence HIV care utilization and are essential to highlight for effective intervention development in Latinos. A better understanding of these individual and contextual factors is critical to developing tailored approaches to engaging Latinos in HIV care. Based on a comprehensive literature review, we offer a framework for understanding what is needed from clinical practice and research to improve engagement in HIV care for US-based Latinos. These findings may have implications for other minority populations. 相似文献
576.
Lotte S. Levison Reimar W. Thomsen Henning Andersen 《European journal of neurology》2023,30(10):3277-3285