2,396 research outputs found
Neutron Beam Effects on Spin Exchange Polarized He-3
We have observed depolarization effects when high intensity cold neutron
beams are incident on alkali-metal-spin-exchange polarized He-3 cells used as
neutron spin filters. This was first observed as a reduction of the maximum
attainable He-3 polarization and was attributed to a decrease of alkali-metal
polarization, which led us to directly measure alkali-metal polarization and
spin relaxation over a range of neutron fluxes at LANSCE and ILL. The data
reveal a new alkali-metal spin-relaxation mechanism that approximately scales
as the square root of the neutron capture-flux density incident on the cell.
This is consistent with an effect proportional to the recombination-limited ion
concentration, but is much larger than expected from earlier work.Comment: submitted to Physical Review Letter
Direct observation of cycloidal spin modulation and field-induced transition in N\'eel-type skyrmion-hosting VOSeO
We investigate the spin rotational structure of magnetic skyrmions in a
tetragonal polar magnet VOSe2O5 via polarized small-angle neutron scattering
(SANS). Spin polarization analysis of the scattered neutrons provides
consistent evidence for the cycloidal spin modulation in all the incommensurate
phases at zero and non-zero magnetic field along the c axis, including the
triangular skyrmion-lattice phase. In the vicinity of the skyrmion phase, we
performed extensive SANS measurements to unravel a field-induced incommensurate
phase (IC-2 state). We discuss the possibility of anisotropic double-q state as
an alternative spin structure to provisional square skyrmion-lattice state.Comment: 27 pages, 5 figure
One ventilator for two patients: Feasibility and considerations of a last resort solution in case of equipment shortage
Quark Orbital Angular Momentum in the Baryon
Analytical and numerical results, for the orbital and spin content carried by
different quark flavors in the baryons, are given in the chiral quark model
with symmetry breaking. The reduction of the quark spin, due to the spin
dilution in the chiral splitting processes, is transferred into the orbital
motion of quarks and antiquarks. The orbital angular momentum for each quark
flavor in the proton as a function of the partition factor and the
chiral splitting probability is shown. The cancellation between the spin
and orbital contributions in the spin sum rule and in the baryon magnetic
moments is discussed.Comment: 26 pages, 3 figures, revised version with minor eq. no and ref. no.
corrections. Discussion on the spin and a new ref. are adde
Spectrometric method to detect exoplanets as another test to verify the invariance of the velocity of light
Hypothetical influences of variability of light velocity due to the
parameters of the source of radiation, for the results of spectral measurements
of stars to search for exoplanets are considered. Accounting accelerations of
stars relative to the barycenter of the star - a planet (the planets) was
carried out. The dependence of the velocity of light from the barycentric
radial velocity and barycentric radial acceleration component of the star
should lead to a substantial increase (up to degree of magnitude) semi-major
axes of orbits detected candidate to extrasolar planets. Consequently, the
correct comparison of the results of spectral method with results of other
well-known modern methods of detecting extrasolar planets can regard the
results obtained in this paper as a reliable test for testing the invariance of
the velocity of light.Comment: 11 pages, 5 figure
Recommended from our members
Working memory in older adults declines with age, but is modulated by sex and education
Working memory (WM), which underlies the temporary storage and manipulation of information, is critical for multiple aspects of cognition and everyday life. Nevertheless, research examining WM specifically in older adults remains limited, despite the global rapid increase in human life expectancy. We examined WM in a large sample (N=754) of healthy older adults (aged 58-89) in a non-Western population (Chinese speakers) in Taiwan, on a digit n-back task. We tested the influence not only of age itself and of load (1-back vs. 2-back), but also effects of both sex and education, which have been shown to modulate WM abilities. Mixed-effects regression revealed that, within older adulthood, age negatively impacted WM abilities (with linear, not nonlinear, effects), as did load (worse performance at 2-back). In contrast, education level was positively associated with WM. Moreover, both age and education interacted with sex. With increasing age, males showed a steeper WM decline than females; with increasing education, females showed greater WM gains than males. Together with other findings, the evidence suggests that age, sex, and education all impact WM in older adults, but interact in particular ways. The results have both basic research and translational implications, and are consistent with particular benefits from increased education for women
The HgMn Binary Star Phi Herculis: Detection and Properties of the Secondary and Revision of the Elemental Abundances of the Primary
Observations of the Mercury-Manganese star Phi Herculis with the Navy
Prototype Optical Interferometer (NPOI) conclusively reveal the previously
unseen companion in this single-lined binary system. The NPOI data were used to
predict a spectral type of A8V for the secondary star Phi Her B. This
prediction was subsequently confirmed by spectroscopic observations obtained at
the Dominion Astrophysical Observatory. Phi Her B is rotating at 50 +/-3
km/sec, in contrast to the 8 km/sec lines of Phi Her A. Recognizing the lines
from the secondary permits one to separate them from those of the primary. The
abundance analysis of Phi Her A shows an abundance pattern similar to those of
other HgMn stars with Al being very underabundant and Sc, Cr, Mn, Zn, Ga, Sr,
Y, Zr, Ba, Ce, and Hg being very overabundant.Comment: Accepted to ApJ, 45 pages, 11 figure
Effects of high-flux neutron beams on He-3 cells polarized in situ with spin-exchange optical pumping
Polarized He-3 produced by spin-exchange optical pumping (SEOP) has potential as a neutron spin filter for polarization and polarization analysis in many neutron-scattering and neutron particle physics applications. The advantage of the SEOP method is its suitability for providing continuous stable polarization over the course of long experiments. However, we have discovered that exposure to high neutron flux leads to additional strong relaxation mechanisms in the optically polarized alkali-metal vapor used to polarize the He-3. At a neutron flux density of 4.7 x 10(9) cm(-2) s(-1), the alkali-metal relaxation rate increased from 100 to 1000 s(-1) leading to reduced alkali-metal polarization. Other effects such as time dependence and gas composition dependence were explored to help understand the processes. In this paper we discuss our observations and present possible solutions for practical use of SEOP as a neutron spin filter for high-flux density applications
Transforming Post-Secondary Education in Mathematics
In this manuscript, I introduce and describe the work of mathematicians and
mathematics educators in the group Transforming Post-Secondary Education in
Mathematics (TPSE Math or TPSE, pronounced "tipsy", for short). TPSE aims to
coordinate and drive constructive change in education in the mathematical
sciences at two-year colleges, four-year colleges, and universities across the
nation. It seeks to build on the successes of the entire mathematical sciences
community.
This manuscript reviews the events that led to the founding of TPSE Math and
articulates its vision and mission. In its first phase with national events,
TPSE found broad consensus with the mathematical sciences community on the
challenges facing the community. Learning from educational transformations
experiences in other scientific fields, and with the support of the
Mathematical Advisory Group of 34 mathematical sciences department chairs and
leaders, TPSE moves into a second phase focused on action. This is a snapshot
in time, and TPSE's ongoing activities will continue to be documented and
disseminated. The piece concludes with a reflection of the impact that my
involvement in this work has had on my career.Comment: 17 page
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