4,049 research outputs found
Subject Acquisition for Web-Based Surveys
This article provides a basic report about subject recruitment processes for Web-based surveys. Using data from our ongoing Internet Survey of American Opinion project, two different recruitment techniques (banner advertisement and subscription campaigns) are compared. This comparison, together with a typology of Web-based surveys, provides insight into the validity and generalizability of Internet survey data. The results from this analysis show that, although Internet survey respondents differ demographically from the American population, the relationships among variables are similar across recruitment methods and match those implied by substantive theory. Thus, our research documents the basic methodology of subject acquisition for Web-based surveys, which, as we argue in our conclusion, may soon become the survey interview mode of choice for social scientists
The \u3cem\u3elet-7\u3c/em\u3e MicroRNA Family Members \u3cem\u3emir\u3c/em\u3e-48, \u3cem\u3emir\u3c/em\u3e-84, and mir-241 Function Together to Regulate Developmental Timing in \u3cem\u3eCaenorhabditis elegans\u3c/em\u3e
The microRNA let-7 is a critical regulator of developmental timing events at the larval-to-adult transition in C. elegans. Recently, microRNAs with sequence similarity to let-7 have been identified. We find that doubly mutant animals lacking the let-7 family microRNA genes mir-48 and mir-84 exhibit retarded molting behavior and retarded adult gene expression in the hypodermis. Triply mutant animals lacking mir-48, mir-84, and mir-241 exhibit repetition of L2-stage events in addition to retarded adult-stage events. mir-48, mir-84, and mir-241 function together to control the L2-to-L3 transition, likely by base pairing to complementary sites in the hbl-1 3′ UTR and downregulating hbl-1 activity. Genetic analysis indicates that mir-48, mir-84, and mir-241 specify the timing of the L2-to-L3 transition in parallel to the heterochronic genes lin-28 and lin-46. These results indicate that let-7 family microRNAs function in combination to affect both early and late developmental timing decisions
Most \u3cem\u3eCaenorhabditis elegans\u3c/em\u3e MicroRNAs are Individually Not Essential for Development or Viability
MicroRNAs (miRNAs), a large class of short noncoding RNAs found in many plants and animals, often act to post-transcriptionally inhibit gene expression. We report the generation of deletion mutations in 87 miRNA genes in Caenorhabditis elegans, expanding the number of mutated miRNA genes to 95, or 83% of known C. elegans miRNAs. We find that the majority of miRNAs are not essential for the viability or development of C. elegans, and mutations in most miRNA genes do not result in grossly abnormal phenotypes. These observations are consistent with the hypothesis that there is significant functional redundancy among miRNAs or among gene pathways regulated by miRNAs. This study represents the first comprehensive genetic analysis of miRNA function in any organism and provides a unique, permanent resource for the systematic study of miRNAs
Semiclassical Unimodular Gravity
Classically, unimodular gravity is known to be equivalent to General
Relativity (GR), except for the fact that the effective cosmological constant
has the status of an integration constant. Here, we explore various
formulations of unimodular gravity beyond the classical limit. We first
consider the non-generally covariant action formulation in which the
determinant of the metric is held fixed to unity. We argue that the
corresponding quantum theory is also equivalent to General Relativity for
localized perturbative processes which take place in generic backgrounds of
infinite volume (such as asymptotically flat spacetimes). Next, using the same
action, we calculate semiclassical non-perturbative quantities, which we expect
will be dominated by Euclidean instanton solutions. We derive the entropy/area
ratio for cosmological and black hole horizons, finding agreement with GR for
solutions in backgrounds of infinite volume, but disagreement for backgrounds
with finite volume. In deriving the above results, the path integral is taken
over histories with fixed 4-volume. We point out that the results are different
if we allow the 4-volume of the different histories to vary over a continuum
range. In this "generalized" version of unimodular gravity, one recovers the
full set of Einstein's equations in the classical limit, including the trace,
so is no longer an integration constant. Finally, we consider the
generally covariant theory due to Henneaux and Teitelboim, which is classically
equivalent to unimodular gravity. In this case, the standard semiclassical GR
results are recovered provided that the boundary term in the Euclidean action
is chosen appropriately.Comment: Substantially revised version, with new results and added discussio
Quantization of Superstrings in Ramond-Ramond Backgrounds
We present a perturbative study of Ramond-Ramond backgrounds in the NSR
formalism. We show how to perform sigma-model computations and discuss in
detail the structure of the BRST charge and picture-changing operators. Contact
terms play a vital role in the analysis. We also give evidence for a two loop
non-renormalization theorem for the background beta functions.Comment: 29 pages, 1 figure; uses LaTeX, epsf, hyperref packages; references
adde
Relationship Between Jump Capacity and Performance in BMX Cycling
The objective of this study is to assess the relationship between the results obtained on different vertical jump tests and the top score recorded during a BMX (Bicycle Moto-Cross) test and the rider''s performance. To do so, 10 BMX pilots participated in this study; 5 regarded as the elite group (EG) (age: 18.8 +/- 3.7, weight: 68.4 +/- 8.5 kg, height: 174 +/- 9 cm and previous BMX experience: 8 +/- 3.8 years) and 5 regarded as the recreational group (RG) (age: 19.8 +/- 4.8, weight: 69.2 +/- 11.7 kg, height: 170 +/- 9 cm, previous BMX experience: 4.2 +/- 1.3 years). Vertical jump capacity was obtained using the Bosco protocol, i.e. vertical squat jump (SJ), vertical countermovement jump (CMJ), drop jump (DJ) and repetitive jump (RJ), and time in race in a BMX circuit was determined. The results indicate a direct relationship between the time used to complete the circuit and the height of the jump reached in SJ (r: -.801; p:.017), CMJ (r : -.798; p :.018) and DJ (r : -.782; p:.022). This all suggests that assessing jump capacity using the Bosco test may be a useful tool for assessing BMX performance
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Gut microbiome composition in the Hispanic Community Health Study/Study of Latinos is shaped by geographic relocation, environmental factors, and obesity.
Background: Hispanics living in the USA may have unrecognized potential birthplace and lifestyle influences on the gut microbiome. We report a cross-sectional analysis of 1674 participants from four centers of the Hispanic Community Health Study/Study of Latinos (HCHS/SOL), aged 18 to 74 years old at recruitment.Results: Amplicon sequencing of 16S rRNA gene V4 and fungal ITS1 fragments from self-collected stool samples indicate that the host microbiome is determined by sociodemographic and migration-related variables. Those who relocate from Latin America to the USA at an early age have reductions in Prevotella to Bacteroides ratios that persist across the life course. Shannon index of alpha diversity in fungi and bacteria is low in those who relocate to the USA in early life. In contrast, those who relocate to the USA during adulthood, over 45 years old, have high bacterial and fungal diversity and high Prevotella to Bacteroides ratios, compared to USA-born and childhood arrivals. Low bacterial diversity is associated in turn with obesity. Contrasting with prior studies, our study of the Latino population shows increasing Prevotella to Bacteroides ratio with greater obesity. Taxa within Acidaminococcus, Megasphaera, Ruminococcaceae, Coriobacteriaceae, Clostridiales, Christensenellaceae, YS2 (Cyanobacteria), and Victivallaceae are significantly associated with both obesity and earlier exposure to the USA, while Oscillospira and Anaerotruncus show paradoxical associations with both obesity and late-life introduction to the USA.Conclusions: Our analysis of the gut microbiome of Latinos demonstrates unique features that might be responsible for health disparities affecting Hispanics living in the USA
Nonperturbative Superpotentials and Compactification to Three Dimensions
We consider four-dimensional N=2 supersymmetric gauge theories with gauge
group U(N) on R^3 x S^1, in the presence of a classical superpotential. The
low-energy quantum superpotential is obtained by simply replacing the adjoint
scalar superfield in the classical superpotential by the Lax matrix of the
integrable system that underlies the 4d field theory. We verify in a number of
examples that the vacuum structure obtained in this way matches precisely that
in 4d, although the degrees of freedom that appear are quite distinct. Several
features of 4d field theories, such as the possibility of lifting vacua from
U(N) to U(tN), become particularly simple in this framework. It turns out that
supersymmetric vacua give rise to a reduction of the integrable system which
contains information about the field theory but also about the Dijkgraaf-Vafa
matrix model. The relation between the matrix model and the quantum
superpotential on R^3 x S^1 appears to involve a novel kind of mirror symmetry.Comment: LaTeX, 45 pages, uses AmsMath, minor correction, reference adde
Vitamin D intake is associated with insulin sensitivity in African American, but not European American, women
<p>Abstract</p> <p>Background</p> <p>The prevalence of type 2 diabetes is higher among African Americans (AA) vs European Americans (EA), independent of obesity and other known confounders. Although the reason for this disparity is not known, it is possible that relatively low levels of vitamin D among AA may contribute, as vitamin D has been positively associated with insulin sensitivity in some studies. The objective of this study was to test the hypothesis that dietary vitamin D would be associated with a robust measure of insulin sensitivity in AA and EA women.</p> <p>Methods</p> <p>Subjects were 115 African American (AA) and 137 European American (EA) healthy, premenopausal women. Dietary intake was determined with 4-day food records; the insulin sensitivity index (S<sub>I</sub>) with a frequently-sampled intravenous glucose tolerance test and minimal modeling; the Homeostasis Model Assessment of Insulin Resistance (HOMA-IR) with fasting insulin and glucose; and body composition with dual-energy X-ray absorptiometry.</p> <p>Results</p> <p>Vitamin D intake was positively associated with S<sub>I </sub>(standardized β = 0.18, <it>P </it>= 0.05) and inversely associated with HOMA-IR (standardized β = -0.26, <it>P </it>= 0.007) in AA, and the relationships were independent of age, total body fat, energy intake, and % kcal from fat. Vitamin D intake was not significantly associated with indices of insulin sensitivity/resistance in EA (standardized β = 0.03, <it>P </it>= 0.74 and standardized β = 0.02, <it>P </it>= 0.85 for S<sub>I </sub>and HOMA-IR, respectively). Similar to vitamin D, dietary calcium was associated with S<sub>I </sub>and HOMA-IR among AA but not EA.</p> <p>Conclusions</p> <p>This study provides novel findings that dietary vitamin D and calcium were independently associated with insulin sensitivity in AA, but not EA. Promotion of these nutrients in the diet may reduce health disparities in type 2 diabetes risk among AA, although longitudinal and intervention studies are required.</p
FORTE satellite constraints on ultra-high energy cosmic particle fluxes
The FORTE (Fast On-orbit Recording of Transient Events) satellite records
bursts of electromagnetic waves arising from near the Earth's surface in the
radio frequency (RF) range of 30 to 300 MHz with a dual polarization antenna.
We investigate the possible RF signature of ultra-high energy cosmic-ray
particles in the form of coherent Cherenkov radiation from cascades in ice. We
calculate the sensitivity of the FORTE satellite to ultra-high energy (UHE)
neutrino fluxes at different energies beyond the Greisen-Zatsepin-Kuzmin (GZK)
cutoff. Some constraints on supersymmetry model parameters are also estimated
due to the limits that FORTE sets on the UHE neutralino flux. The FORTE
database consists of over 4 million recorded events to date, including in
principle some events associated with UHE neutrinos. We search for candidate
FORTE events in the period from September 1997 to December 1999. The candidate
production mechanism is via coherent VHF radiation from a UHE neutrino shower
in the Greenland ice sheet. We demonstrate a high efficiency for selection
against lightning and anthropogenic backgrounds. A single candidate out of
several thousand raw triggers survives all cuts, and we set limits on the
corresponding particle fluxes assuming this event represents our background
level.Comment: added a table, updated references and Figure 8, this version is
submitted to Phys. Rev.
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