687 research outputs found
In vivo nuclear magnetic resonance imaging
A number of physiological changes have been demonstrated in bone, muscle and blood after exposure of humans and animals to microgravity. Determining mechanisms and the development of effective countermeasures for long duration space missions is an important NASA goal. The advent of tomographic nuclear magnetic resonance imaging (NMR or MRI) gives NASA a way to greatly extend early studies of this phenomena in ways not previously possible; NMR is also noninvasive and safe. NMR provides both superb anatomical images for volume assessments of individual organs and quantification of chemical/physical changes induced in the examined tissues. The feasibility of NMR as a tool for human physiological research as it is affected by microgravity is demonstrated. The animal studies employed the rear limb suspended rat as a model of mucle atrophy that results from microgravity. And bedrest of normal male subjects was used to simulate the effects of microgravity on bone and muscle
Testing the assumption of measurement invariance in the SAMHSA mental health and alcohol abuse stigma assessment in older adults
Fermionic One-Loop Corrections to Soliton Energies in 1+1 Dimensions
We demonstrate an unambiguous and robust method for computing fermionic
corrections to the energies of classical background field configurations. We
consider the particular case of a sequence of background field configurations
that interpolates continuously between the trivial vacuum and a widely
separated soliton/antisoliton pair in 1+1 dimensions. Working in the continuum,
we use phase shifts, the Born approximation, and Levinson's theorem to avoid
ambiguities of renormalization procedure and boundary conditions. We carry out
the calculation analytically at both ends of the interpolation and numerically
in between, and show how the relevant physical quantities vary continuously. In
the process, we elucidate properties of the fermionic phase shifts and zero
modes.Comment: 12 pages, 4 figures, uses BoxedEPS;v2: fixed numerical error in
figure dat
Energy, Central Charge, and the BPS Bound for 1+1 Dimensional Supersymmetric Solitons
We consider one-loop quantum corrections to soliton energies and central
charges in the supersymmetric and sine-Gordon models in 1+1
dimensions. In both models, we unambiguously calculate the correction to the
energy in a simple renormalization scheme and obtain ,
in agreement with previous results. Furthermore, we show that there is an
identical correction to the central charge, so that the BPS bound remains
saturated in the one-loop approximation. We extend these results to arbitrary
1+1 dimensional supersymmetric theories.Comment: 15 pages, RevTeX; v2: generalized energy result, added minor
clarifications, and fixed typos; v3: more minor clarifications and
corrections; v4: fixed factor of 2 in eq. (25); v5: fixed minor error in eq.
(55
On the Quantization of the Abelian Chern-Simons Coefficient at Finite Temperature
We show that when the Abelian \CS\ theory coupled to matter fields is
quantized in a vacuum with non vanishing magnetic flux (or electric charge),
the requirement of gauge invariance at finite temperature leads to the
quantization of the \CS\ coefficient and its quantum corrections, in a manner
similar to the non-Abelian case.Comment: 11 pages, LaTeX, no figures, no special macros. Some discussion and
references added. A minor error corrected. Final version to appear in Phys.
Lett.
Fatty liver in familial hypobetalipoproteinemia: Triglyceride assembly into VLDL particles is affected by the extent of hepatic steatosis
Familial hypobetalipoproteinemia (FHBL) subjects may develop fatty liver. Liver fat was assessed in 21 FHBL with six different apolipoprotein B (apoB) truncations (apoB-4 to apoB-89) and 14 controls by magnetic resonance spectroscopy (MRS). Liver fat percentages were 16.7 ± 11.5 and 3.3 ± 2.9 (mean ± SD) (P = 0.001). Liver fat percentage was positively correlated with body mass index, waist circumference, and areas under the insulin curves of 2 h glucose tolerance tests, suggesting that obesity may affect the severity of liver fat accumulation in both groups. Despite 5-fold differences in liver fat percentage, mean values for obesity and insulin indexes were similar. Thus, for similar degrees of obesity, FHBL subjects have more hepatic fat. VLDL-triglyceride (TG)-fatty acids arise from plasma and nonplasma sources (liver and splanchnic tissues). To assess the relative contributions of each, [2H2] palmitate was infused over 12 h in 13 FHBL subjects and 11 controls. Isotopic enrichment of plasma free palmitate and VLDL-TG-palmitate was determined by mass spectrometry. Nonplasma sources contributed 51 ± 15% in FHBL and 37 ± 13% in controls (P = 0.02). Correlations of liver fat percentage and percent VLDL-TG-palmitate from liver were r = 0.89 (P = 0.0001) for FHBL subjects and r = 0.69 (P = 0.01) for controls. Thus, apoB truncation-producing mutations result in fatty liver and in altered assembly of VLDL-TG
Mode regularization of the susy sphaleron and kink: zero modes and discrete gauge symmetry
To obtain the one-loop corrections to the mass of a kink by mode
regularization, one may take one-half the result for the mass of a widely
separated kink-antikink (or sphaleron) system, where the two bosonic zero modes
count as two degrees of freedom, but the two fermionic zero modes as only one
degree of freedom in the sums over modes. For a single kink, there is one
bosonic zero mode degree of freedom, but it is necessary to average over four
sets of fermionic boundary conditions in order (i) to preserve the fermionic
Z gauge invariance , (ii) to satisfy the basic principle of
mode regularization that the boundary conditions in the trivial and the kink
sector should be the same, (iii) in order that the energy stored at the
boundaries cancels and (iv) to avoid obtaining a finite, uniformly distributed
energy which would violate cluster decomposition. The average number of
fermionic zero-energy degrees of freedom in the presence of the kink is then
indeed 1/2. For boundary conditions leading to only one fermionic zero-energy
solution, the Z gauge invariance identifies two seemingly distinct `vacua'
as the same physical ground state, and the single fermionic zero-energy
solution does not correspond to a degree of freedom. Other boundary conditions
lead to two spatially separated solutions, corresponding to
one (spatially delocalized) degree of freedom. This nonlocality is consistent
with the principle of cluster decomposition for correlators of observables.Comment: 32 pages, 5 figure
Chern-simon type photon mass from fermion electric dipole moments at finite temperature in 3+1 dimensions
We study the low energy effective field theory of fermions with electric and
magnetic dipole moments at finite temperature. We find that at one loop there
is an interaction term of the Chern-Simon form . The four vector is interpreted as a Chern- Simon type mass of photons,
which is determined by the electric (magnetic) dipole moments ()
of the fermions in the vacuum polarisation loop diagram. The physical
consequence of such a photon mass is that, photons of opposite circular
polarisations, propagating through a hot medium, have different group
velocities. We estimate that the time lag between the arrival times of the left
and right circularly polarised light signals from pulsars. If the light
propagates through a hot plasma (where the temperature in some regions is ) then the time lag between the two circularly polarised signals
of frequency will be . It may
be possible to observe this effect in pulsar signals which propagate through
nebula at high temperatures.Comment: plain TeX, 9 page
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