274 research outputs found
The Hispanic Paradox: Race/Ethnicity and Nativity, Immigrant Enclave Residence and Cognitive Impairment Among Older US Adults
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137472/1/jgs14806.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137472/2/jgs14806_am.pd
Cuts and flows of cell complexes
We study the vector spaces and integer lattices of cuts and flows associated
with an arbitrary finite CW complex, and their relationships to group
invariants including the critical group of a complex. Our results extend to
higher dimension the theory of cuts and flows in graphs, most notably the work
of Bacher, de la Harpe and Nagnibeda. We construct explicit bases for the cut
and flow spaces, interpret their coefficients topologically, and give
sufficient conditions for them to be integral bases of the cut and flow
lattices. Second, we determine the precise relationships between the
discriminant groups of the cut and flow lattices and the higher critical and
cocritical groups with error terms corresponding to torsion (co)homology. As an
application, we generalize a result of Kotani and Sunada to give bounds for the
complexity, girth, and connectivity of a complex in terms of Hermite's
constant.Comment: 30 pages. Final version, to appear in Journal of Algebraic
Combinatoric
A Brownian particle in a microscopic periodic potential
We study a model for a massive test particle in a microscopic periodic
potential and interacting with a reservoir of light particles. In the regime
considered, the fluctuations in the test particle's momentum resulting from
collisions typically outweigh the shifts in momentum generated by the periodic
force, and so the force is effectively a perturbative contribution. The
mathematical starting point is an idealized reduced dynamics for the test
particle given by a linear Boltzmann equation. In the limit that the mass ratio
of a single reservoir particle to the test particle tends to zero, we show that
there is convergence to the Ornstein-Uhlenbeck process under the standard
normalizations for the test particle variables. Our analysis is primarily
directed towards bounding the perturbative effect of the periodic potential on
the particle's momentum.Comment: 60 pages. We reorganized the article and made a few simplifications
of the conten
A ballistic motion disrupted by quantum reflections
I study a Lindblad dynamics modeling a quantum test particle in a Dirac comb
that collides with particles from a background gas. The main result is a
homogenization theorem in an adiabatic limiting regime involving large initial
momentum for the test particle. Over the time interval considered, the particle
would exhibit essentially ballistic motion if either the singular periodic
potential or the kicks from the gas were removed. However, the particle behaves
diffusively when both sources of forcing are present. The conversion of the
motion from ballistic to diffusive is generated by occasional quantum
reflections that result when the test particle's momentum is driven through a
collision near to an element of the half-spaced reciprocal lattice of the Dirac
comb.Comment: 54 pages. I rewrote the introduction and simplified some of the
presentatio
The Liquidity Trap, the Real Balance Effect, and the Friedman Rule
This paper studies the behavior of the economy and the efficacy of monetary policy under zero nominal interest rates, using a model with population growth that nests, as a special case, a more conventional specification in which there is a single infinitely lived representative agent. The paper shows that with a growing population, monetary policy has distributional effects that give rise to a real balance effect, thereby eliminating the liquidity trap. These same distributional effects, however, can also work to make many agents much worse off under zero nominal interest rates than they are when the nominal interest rate is positive
Number Counts of GALEX Sources in FUV (1530A) and NUV (2310A) Bands
Number Counts of galaxies in two GALEX bands (FUV: 1530A and NUV: 2310A, both
in AB magnitudes) are reported. They provide for the first time in the
literature homogeneously calibrated number counts of UV galaxies covering
continuously a very wide range of UV magnitude (14 -- 23.8). Both the FUV and
NUV counts are inconsistent with a non-evolution model, while they are in good
agreement with evolution models (essentially luminosity evolution) derived from
the high-z UV luminosity functions of Arnouts et al. (2004). It is found that
the contribution from galaxies detected by GALEX to the UV background is
0.68+-0.10 nW m-2 sr-1 at 1530A and 0.99+-0.15 nW m-2 sr-1 at 2310A. These are
66+-9% and 44+-6% of the total contributions of galaxies to the the UV
background at 1530A, respectively, as estimated using the evolution models. ...Comment: This paper will be published as part of the Galaxy Evolution Explorer
(GALEX) Astrophysical Journal Letters Special Issue. Links to the full set of
papers will be available at http:/www.galex.caltech.edu/PUBLICATIONS/ after
November 22, 200
Effect of wearing a face mask on hand-to-face contact by children in a simulated school environment: the Back-to-School COVID-19 Simulation Randomized Clinical Trial
Importance Wearing a face mask in school can reduce SARS-CoV-2 transmission but it may also lead to increased hand-to-face contact, which in turn could increase infection risk through self-inoculation.
Objective To evaluate the effect of wearing a face mask on hand-to-face contact by children while at school.
Design, Setting, and Participants This prospective randomized clinical trial randomized students from junior kindergarten to grade 12 at 2 schools in Toronto, Ontario, Canada, during August 2020 in a 1:1 ratio to either a mask or control class during a 2-day school simulation. Classes were video recorded from 4 angles to accurately capture outcomes.
Interventions Participants in the mask arm were instructed to bring their own mask and wear it at all times. Students assigned to control classes were not required to mask at any time (grade 4 and lower) or in the classroom where physical distancing could be maintained (grade 5 and up).
Main Outcomes and Measures The primary outcome was the number of hand-to-face contacts per student per hour on day 2 of the simulation. Secondary outcomes included hand-to-mucosa contacts and hand-to-nonmucosa contacts. A mixed Poisson regression model was used to derive rate ratios (RRs), adjusted for age and sex with a random intercept for class with bootstrapped 95% CIs.
Results A total of 174 students underwent randomization and 171 students (mask group, 50.6% male; control group, 52.4% male) attended school on day 2. The rate of hand-to-face contacts did not differ significantly between the mask and the control groups (88.2 vs 88.7 events per student per hour; RR, 1.00; 95% CI, 0.78-1.28; P = >.99). When compared with the control group, the rate of hand-to-mucosa contacts was significantly lower in the mask group (RR, 0.12; 95% CI, 0.07-0.21), while the rate of hand-to-nonmucosa contacts was higher (RR, 1.40; 95% CI, 1.08-1.82).
Conclusions and Relevance In this clinical trial of simulated school attendance, hand-to-face contacts did not differ among students required to wear face masks vs students not required to wear face masks; however, hand-to-mucosa contracts were lower in the face mask group. This suggests that mask wearing is unlikely to increase infection risk through self-inoculation.
Trial Registration ClinicalTrials.gov Identifier: NCT0453125
Searching for DNA Lesions: Structural Evidence for Lower- and Higher-Affinity DNA Binding Conformations of Human Alkyladenine DNA Glycosylase
To efficiently repair DNA, human alkyladenine DNA glycosylase (AAG) must search the million-fold excess of unmodified DNA bases to find a handful of DNA lesions. Such a search can be facilitated by the ability of glycosylases, like AAG, to interact with DNA using two affinities: a lower-affinity interaction in a searching process and a higher-affinity interaction for catalytic repair. Here, we present crystal structures of AAG trapped in two DNA-bound states. The lower-affinity depiction allows us to investigate, for the first time, the conformation of this protein in the absence of a tightly bound DNA adduct. We find that active site residues of AAG involved in binding lesion bases are in a disordered state. Furthermore, two loops that contribute significantly to the positive electrostatic surface of AAG are disordered. Additionally, a higher-affinity state of AAG captured here provides a fortuitous snapshot of how this enzyme interacts with a DNA adduct that resembles a one-base loop.National Institutes of Health (U.S.) (grant no. P30-ES002109)National Institutes of Health (U.S.) (grant no. GM65337)National Institutes of Health (U.S.) (grant no. GM65337-03S2)National Institutes of Health (U.S.) (grant no. CA055042)National Institutes of Health (U.S.) (grant no. CA092584)Repligen Corporation (KIICR Graduate Fellowship
Does clinical equipoise apply to cluster randomized trials in health research?
This article is part of a series of papers examining ethical issues in cluster randomized trials (CRTs) in health research. In the introductory paper in this series, Weijer and colleagues set out six areas of inquiry that must be addressed if the cluster trial is to be set on a firm ethical foundation. This paper addresses the third of the questions posed, namely, does clinical equipoise apply to CRTs in health research? The ethical principle of beneficence is the moral obligation not to harm needlessly and, when possible, to promote the welfare of research subjects. Two related ethical problems have been discussed in the CRT literature. First, are control groups that receive only usual care unduly disadvantaged? Second, when accumulating data suggests the superiority of one intervention in a trial, is there an ethical obligation to act
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