77,460 research outputs found

    Haze in the Mars atmosphere as revealed by the Mariner 4 television data

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    Photometric investigation of haze in Mars atmosphere revealed by Mariner 4 television dat

    Millipeds (Arthropoda: Diplopoda) of the Ark - La - Tex. VI. New Geographic Distributional Records from Select Counties of Arkansas

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    We continue to report, in the sixth of a series of papers, new geographic records for millipeds of the state, including noteworthy records for some taxa collected from Crowley’s Ridge in eastern Arkansas. This contribution documents 47 new co. records and includes records for 19 species within 9 families and 5 orders. More uncommon millipeds found included Okliulus carpenteri (Parajulidae), Eurymerodesmus newtonus (Eurymerodesmidae), Pseudopolydesmus minor (Polydesmidae) and undescribed species of Ethojulus (Parajulidae) and Nannaria (Xystodesmidae). Undoubtedly, additional records will be reported in the future as several gaps in the distribution of Arkansas millipeds remain

    Spectral Line Broadening and Angular Blurring due to Spacetime Geometry Fluctuations

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    We treat two possible phenomenological effects of quantum fluctuations of spacetime geometry: spectral line broadening and angular blurring of the image of a distance source. A geometrical construction will be used to express both effects in terms of the Riemann tensor correlation function. We apply the resulting expressions to study some explicit examples in which the fluctuations arise from a bath of gravitons in either a squeezed state or a thermal state. In the case of a squeezed state, one has two limits of interest: a coherent state which exhibits classical time variation but no fluctuations, and a squeezed vacuum state, in which the fluctuations are maximized.Comment: 21 pages, 2 figures. Dedicated to Raphael Sorkin on the occasion of his 60th birthday. (v2: several references added and some minor errors corrected

    Slip boundary conditions for shear flow of polymer melts past atomically flat surfaces

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    Molecular dynamics simulations are carried out to investigate the dynamic behavior of the slip length in thin polymer films confined between atomically smooth thermal surfaces. For weak wall-fluid interactions, the shear rate dependence of the slip length acquires a distinct local minimum followed by a rapid growth at higher shear rates. With increasing fluid density, the position of the local minimum is shifted to lower shear rates. We found that the ratio of the shear viscosity to the slip length, which defines the friction coefficient at the liquid/solid interface, undergoes a transition from a nearly constant value to the power law decay as a function of the slip velocity. In a wide range of shear rates and fluid densities, the friction coefficient is determined by the product of the value of surface induced peak in the structure factor and the contact density of the first fluid layer near the solid wall.Comment: 27 pages, 11 figure

    Magnetars and pulsars: a missing link

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    There is growing evidence that soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs) are isolated neutron stars with superstrong magnetic fields, i.e., magnetars, marking them a distinguished species from the conventional species of spindown-powered isolated neutron stars, i.e., radio pulsars. The current arguments in favor of the magnetar interpretation of SGR/AXP phenomenology will be outlined, and the two energy sources in magnetars, i.e. a magnetic dissipation energy and a spindown energy, will be reviewed. I will then discuss a missing link between magnetars and pulsars, i.e., lack of the observational evidence of the spindown-powered behaviors in known magnetars. Some recent theoretical efforts in studying such behaviors will be reviewed along with some predictions testable in the near future.Comment: Invited talk at the Sixth Pacific Rim Conference on Stellar Astrophysics, a tribute to Helmut A. Abt, July 11-17, 2002, Xi'an. To appear in the proceedings (eds. K. S. Cheng, K. C. Leung & T. P. Li

    Objectively measured physical activity and sedentary time in south Asian women: a cross-sectional study

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    BACKGROUND: South Asian (SA) women in the United Kingdom (UK) are known to be at high risk for developing chronic diseases, and to have low levels of physical activity (PA). Increasing levels of PA and reducing sedentary time (ST) are recognized as factors to target in an effort to curb chronic disease morbidity and mortality. There is limited evidence documenting objectively measured PA/ST and their correlates in SA women. Therefore the purpose of this cross-sectional study was to objectively measure and report patterns of PA/ST among SA women in the UK and examine potential socio-demographic correlates of PA/ST. METHODS: 140 UK SA women (Pakistani and Bangladeshi) wore an accelerometer for 7 consecutive days. Anthropometric measurements and self-reported socio-demographic information were taken. RESULTS: Mean daily moderate-to-vigorous PA (MVPA) was 34.66 ± 21.52 minutes and mean daily ST was 530.20 ± 81.76 minutes, with an inverse correlation (r = -.270, N = 140, p < .001) showing that higher ST was associated with lower MVPA. The same was seen for light intensity PA (LPA) (r = -.610, N = 140, p < .001). MVPA was significantly higher for younger women (18–64.5 yrs), with 64.7% of older women (≥65 yrs) failing to meet PA guidelines (t = 3.101, p < 0.05). Overweight/obese women had lower levels of LPA, MVPA and higher ST (p < .001). Multiple linear regression analyses indicated 14.9% of the variance in MVPA was explained by age and waist circumference (F(2,138) = 6.41, p < 0.002). LPA and ST were significantly higher on weekend days than weekdays (p < .001), and MVPA was significantly higher on weekdays than weekend days. CONCLUSIONS: Results indicate higher levels of PA in this sample than previously assumed. High levels of LPA in this sample indicate the need for health promotion interventions to target not only duration, but also intensity of activity in this population to achieve PA recommendations

    Probing of RNA structures in a positive sense RNA virus reveals selection pressures for structural elements.

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    In single stranded (+)-sense RNA viruses, RNA structural elements (SEs) play essential roles in the infection process from replication to encapsidation. Using selective 2'-hydroxyl acylation analyzed by primer extension sequencing (SHAPE-Seq) and covariation analysis, we explore the structural features of the third genome segment of cucumber mosaic virus (CMV), RNA3 (2216 nt), both in vitro and in plant cell lysates. Comparing SHAPE-Seq and covariation analysis results revealed multiple SEs in the coat protein open reading frame and 3' untranslated region. Four of these SEs were mutated and serially passaged in Nicotiana tabacum plants to identify biologically selected changes to the original mutated sequences. After passaging, loop mutants showed partial reversion to their wild-type sequence and SEs that were structurally disrupted by mutations were restored to wild-type-like structures via synonymous mutations in planta. These results support the existence and selection of virus open reading frame SEs in the host organism and provide a framework for further studies on the role of RNA structure in viral infection. Additionally, this work demonstrates the applicability of high-throughput chemical probing in plant cell lysates and presents a new method for calculating SHAPE reactivities from overlapping reverse transcriptase priming sites
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