9,065 research outputs found
Quantitative Determination of the Adiabatic Condition Using Force-Detected Nuclear Magnetic Resonance
The adiabatic condition governing cyclic adiabatic inversion of proton spins
in a micron-sized ammonium chloride crystal was studied using room temperature
nuclear magnetic resonance force microscopy. A systematic degradation of
signal-to-noise was observed as the adiabatic condition became violated. A
theory of adiabatic following applicable to cyclic adiabatic inversion is
reviewed and implemented to quantitatively determine an adiabaticity threshold
from our experimental results.Comment: 5 pages, 3 fig
Duality in the Th17-Treg developmental decision
Each of the effector CD4 T-cell lineages - Th1, Th2, and the more recently identified Th17 - arises from pluripotent naïve precursors whose developmental fate is largely controlled by cytokines that act in concert with antigenic signals. Remarkably, development of the Th17 lineage has been linked to that of regulatory T cells, which obviate or downregulate Th17 responses to preserve immune homeostasis, through a shared requirement for the cytokine transforming growth factor-beta. Several new studies offer insights into the mechanism whereby the precursors of these subsets are directed into distinct lineages
Spin-Echo Measurements for an Anomalous Quantum Phase of 2D Helium-3
Previous heat-capacity measurements of our group had shown the possible
existence of an anomalous quantum phase containing the zero-point vacancies
(ZPVs) in 2D He. The system is monolayer He adsorbed on graphite
preplated with monolayer He at densities () just below the 4/7
commensurate phase (). We carried out
pulsed-NMR measurements in order to examine the microscopic and dynamical
nature of this phase. The measured decay of spin echo signals shows the
non-exponential behaviour. The decay curve can be fitted with the double
exponential function, but the relative intensity of the component with a longer
time constant is small (5%) and does not depend on density and temperature,
which contradicts the macroscopic fluid and 4/7 phase coexistence model. This
slowdown is likely due to the mosaic angle spread of Grafoil substrate and the
anisotropic spin-spin relaxation time in 2D systems with respect to the
magnetic field direction. The inverse value deduced from the major echo
signal with a shorter time constant, which obeys the single exponential
function, decreases linearly with decreasing density from , supporting the
ZPV model.Comment: 4 pages, 6 figure
A longitudinal study of self-assessment accuracy
Although studies have examined medical students' ability to self-assess their performance, there are few longitudinal studies that document the stability of self-assessment accuracy over time. This study compares actual and estimated examination performance for three classes during their first 3 years of medical school. Methods Students assessed their performance on classroom examinations and objective structured clinical examination (OSCE) stations. Each self-assessment was then contrasted with their actual performance using idiographic (within-subject) methods to define three measures of self-assessment accuracy: bias (arithmetic differences of actual and estimated scores), deviation (absolute differences of actual and estimated scores), and covariation (correlation of actual and estimated scores). These measures were computed for four intervals over the course of 3 years. Multivariate analyses of variance and correlational analyses were used to evaluate the stability of these measures. Results Self-assessment accuracy measures were relatively stable over the first 2 years of medical school with a decease occurring in the third year. However, the correlational analyses indicated that the stability of self-assessment accuracy was comparable to the stability of actual performance over this same period. Conclusion The apparent decline in accuracy in the third year may reflect the transition from familiar classroom-based examinations to the substantially different clinical examination tasks of the third year OSCE. However, the stability of self-assessment accuracy compares favorably with the stability of actual performance over this period. These results suggest that self-assessment accuracy is a relatively stable individual characteristic that may be influenced by task familiarity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75505/1/j.1365-2923.2003.01567.x.pd
Interaction of an expanding plasma cloud with a simple antenna: Application to anomalous voltage signals observed by Voyager 1, Voyager 2, ICE, and Vega spacecraft
High‐velocity impacts of interplanetary dust grains with spacecraft can give rise to transient plasma clouds from the spacecraft bodies. It is believed these plasma clouds can affect spacecraft instruments. Laboratory results are presented demonstrating the interaction of small expanding plasma clouds with a simple antenna. Results corroborate the hypothesized origin of anomalous impulsive voltage signals recorded by Voyager 1 and 2 spacecraft during flybys of Saturn, Uranus, and Neptune, the International Cometary Explorer (ICE) during its flyby of comet Giacobini‐Zinner, and Vega during its flyby of comet Halley. Results suggest that preflight calibration of antenna‐plasma interactions may extend the range of spacecraft diagnostics
A MMT/Hectospec Redshift Survey of 24 Micron Sources in the Spitzer First Look Survey
We present a spectroscopic survey using the MMT/Hectospec fiber spectrograph
of 24 micron sources selected with the Spitzer Space Telescope in the Spitzer
First Look Survey. We report 1296 new redshifts for 24 micron sources,
including 599 with f(24micron) > 1 mJy. Combined with 291 additional redshifts
for sources from the Sloan Digital Sky Survey (SDSS), our observing program was
highly efficient and is ~90% complete for i' 1 mJy,
and is 35% complete for i' < 20.5 mag and 0.3 mJy < f(24micron) < 1 mJy. Our
Hectospec survey includes 1078 and 168 objects spectroscopically classified as
galaxies and QSOs, respectively. Combining the Hectospec and SDSS samples, we
find 24 micron-selected galaxies to z < 0.98 and QSOs to z < 3.6, with mean
redshifts of = 0.27 and =1.1. As part of this publication, we
include the redshift catalogs and the reduced spectra; these are also available
online (http://mips.as.arizona.edu/~papovich/fls) and through the NASA/IPAC
Infrared Science Archive (http://irsa.ipac.caltech.edu).Comment: Accepted for publication in the Astronomical Journal, AASTEX format,
23 pages, 7 figures (some in color). This replacement is the accepted
version, and includes minor changes from previous version. Data tables and
spectra available at http://mips.as.arizona.edu/~papovich/fls or at
http://irsa.ipac.caltech.ed
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