6,056 research outputs found
Large QCD at non-zero chemical potential
The general issue of large QCD at nonzero chemical potential is
considered with a focus on understanding the difference between large QCD
with an isospin chemical potential and large QCD with a baryon chemical
potential. A simple diagrammatic analysis analogous to `t Hooft's analysis at
implies that the free energy with a given baryon chemical potential is
equal to the free energy with an isospin chemical potential of the same value
plus corrections. Phenomenologically, these two systems behave quite
differently. A scenario to explain this difference in light of the diagrammatic
analysis is explored. This scenario is based on a phase transition associated
with pion condensation when the isospin chemical potential exceeds ;
associated with this transition there is breakdown of the expansion--in
the pion condensed phase there is a distinct expansion including a
larger set of diagrams. While this scenario is natural, there are a number of
theoretical issues which at least superficially challenge it. Most of these can
be accommodated. However, the behavior of quenched QCD which raises a number of
apparently analogous issues cannot be easily understood completely in terms of
an analogous scenario. Thus, the overall issue remains open
Primary Xanthoma of the Mandible: Report of a Rare Case
Xanthoma is a lesion most commonly seen in soft tissues such as the skin, subcutis, or tendon sheaths. Xanthoma formation is often associated with primary or secondary hyperlipidemia. Primary bone xanthomas are extremely rare benign bone lesions not associated with hyperlipidemia, histopathologically characterized by histiocytes, abundant lipid containing macrophages (foam cells), and multinucleated giant cells. Cholesterol clefts can be found in the medullary bone. Less than ten cases of xanthoma in the mandible have been reported. We present a rare primary intrabony xanthoma in a normolipidemic patient
VINCI / VLTI observations of Main Sequence stars
Main Sequence (MS) stars are by far the most numerous class in the Universe.
They are often somewhat neglected as they are relatively quiet objects (but
exceptions exist), though they bear testimony of the past and future of our
Sun. An important characteristic of the MS stars, particularly the solar-type
ones, is that they host the large majority of the known extrasolar planets.
Moreover, at the bottom of the MS, the red M dwarfs pave the way to
understanding the physics of brown dwarfs and giant planets. We have measured
very precise angular diameters from recent VINCI/VLTI interferometric
observations of a number of MS stars in the K band, with spectral types between
A1V and M5.5V. They already cover a wide range of effective temperatures and
radii. Combined with precise Hipparcos parallaxes, photometry, spectroscopy as
well as the asteroseismic information available for some of these stars, the
angular diameters put strong constraints on the detailed models of these stars,
and therefore on the physical processes at play.Comment: 5 pages, 3 figures. To appear in the Proceedings of IAU Symposium
219, "Stars as Suns", Editors A. Benz & A. Dupree, Astronomical Society of
the Pacifi
Disentangling discrepancies between stellar evolution theory and sub-solar mass stars. The influence of the mixing length parameter for the UV Psc binary
Serious discrepancies have recently been observed between predictions of
stellar evolution models in the 0.7-1.1 M_sun mass range and accurately
measured properties of binary stars with components in this mass range. We
study one of these objects, the eclipsing binary UV Piscium, which is
particularly interesting because Popper (1997) derived age estimates for each
component which differed by more than a factor of two. In an attempt to solve
this significant discrepancy (a difference in age of 11 Gyr), we compute a
large grid of stellar evolution models with the CESAM code for each component.
By fixing the masses to their accurately determined values (relative error
smaller than 1% for both stars), we consider a wide range of possible
metallicities Z (0.01 to 0.05), and Helium content Y (0.25 to 0.34)
uncorrelated to Z. In addition, the mixing length parameter alpha_MLT is left
as another free parameter. We obtain a best fit in the T_eff-radius diagram for
a common chemical composition (Z, Y)=(0.012, 0.31), but a different MLT
parameter alpha_MLT_A = 0.95+-0.12(statistical)+0.30(systematic) and
alpha_MLT_B = 0.65+-0.07(stat)+0.10(syst). The apparent age discrepancy found
by Popper (1997) disappears with this solution, the components being coeval to
within 1%. This suggests that fixing alpha_MLT to its solar value (~1.6), a
common hypothesis assumed in most stellar evolutionary models, may not be
correct. Secondly, since alpha_MLT is smaller for the less massive component,
this suggests that the MLT parameter may decrease with stellar mass, showing
yet another shortcoming of the mixing length theory to explain stellar
convection. This trend needs further confirmation with other binary stars with
accurate data.Comment: 8 pages, accepted for publication in Astronomy & Astrophysic
Current status of cardiac MRI in small animals
Cardiac magnetic resonance imaging (MRI) on small animals is possible but remains challenging and not well standardized. This publication aims to provide an overview of the current techniques, applications and challenges of cardiac MRI in small animals for researchers interested in moving into this field. Solutions have been developed to obtain a reliable cardiac trigger in both the rat and the mouse. Techniques to measure ventricular function and mass have been well validated and are used by several research groups. More advanced techniques like perfusion imaging, delayed enhancement or tag imaging are emerging. Regarding cardiac applications, not only coronary ischemic disease but several other pathologies or conditions including cardiopathies in transgenic animals have already benefited from these new developments. Therefore, cardiac MRI has a bright future for research in small animal
Power calculation for gravitational radiation: oversimplification and the importance of time scale
A simplified formula for gravitational-radiation power is examined. It is
shown to give completely erroneous answers in three situations, making it
useless even for rough estimates. It is emphasized that short timescales, as
well as fast speeds, make classical approximations to relativistic calculations
untenable.Comment: Three pages, no figures, accepted for publication in Astronomische
Nachrichte
Optimization of cardiac cine in the rat on a clinical 1.5-T MR system
Object: the overall goal was to study cardiovascular function in small animals using a clinical 1.5-T MR scanner optimizing a fast gradient-echo cine sequence to obtain high spatial and temporal resolution. Materials and methods: normal rat hearts (n = 9) were imaged using a 1.5-T MR scanner with a spiral fast gradient-echo (fast field echo for Philips scanners) sequence, three Cartesian fast gradient-echo (turbo field echo for Philips scanners) sequences with different in-plane resolution, and with and without flow compensation and half-Fourier acquisition. The hearts of four rats were then excised and left-ventricle mass was weighed. Inter- and intra-observer variability analysis was performed for magnetic resonance imaging (MRI) measurements. Results: half-Fourier acquisition with flow compensation gave the best sequence in terms of image quality, spatial as well as temporal resolution, and suppression of flow artifact. Ejection fraction was 71 ± 4% with less than 5% inter- and intra-observer variability. A good correlation was found between MRI-calculated left-ventricular mass and wet weight. Conclusions: using optimized sequences on a clinical 1.5-T MR scanner can provide accurate quantification of cardiac function in small animals and can promote cardiovascular research on small animals at 1.5-
Nonanalytic behavior of the spin susceptibility in clean Fermi systems
The wavevector and temperature dependent static spin susceptibility,
\chi_s(Q,T), of clean interacting Fermi systems is considered in dimensions
1\leq d \leq 3. We show that at zero temperature \chi_s is a nonanalytic
function of |Q|, with the leading nonanalyticity being |Q|^{d-1} for 1<d<3, and
Q^2\ln|Q| for d=3. For the homogeneous spin susceptibility we find a
nonanalytic temperature dependence T^{d-1} for 1<d<3. We give qualitative
mode-mode coupling arguments to that effect, and corroborate these arguments by
a perturbative calculation to second order in the electron-electron interaction
amplitude. The implications of this, in particular for itinerant
ferromagnetism, are discussed. We also point out the relation between our
findings and established perturbative results for 1-d systems, as well as for
the temperature dependence of \chi_s(Q=0) in d=3.Comment: 12pp., REVTeX, 5 eps figures, final version as publishe
Early major maxillary deformation after cerebral anoxia in an adult: Case report and literature review
WR 110: A Single Wolf-Rayet Star With Corotating Interaction Regions In Its Wind?
A 30-day contiguous photometric run with the MOST satellite on the WN5-6b
star WR 110 (HD 165688) reveals a fundamental periodicity of P = 4.08 +/- 0.55
days along with a number of harmonics at periods P/n, with n ~ 2,3,4,5 and 6,
and a few other possible stray periodicities and/or stochastic variability on
timescales longer than about a day. Spectroscopic RV studies fail to reveal any
plausible companion with a period in this range. Therefore, we conjecture that
the observed light-curve cusps of amplitude ~ 0.01 mag that recur at a 4.08 day
timescale may arise in the inner parts, or at the base of, a corotating
interaction region (CIR) seen in emission as it rotates around with the star at
constant angular velocity. The hard X-ray component seen in WR 110 could then
be a result of a high velocity component of the CIR shock interacting with the
ambient wind at several stellar radii. Given that most hot, luminous stars
showing CIRs have two CIR arms, it is possible that either the fundamental
period is 8.2 days or, more likely in the case of WR 110, there is indeed a
second weaker CIR arm for P = 4.08 days, that occurs ~ two thirds of a rotation
period after the main CIR. If this interpretation is correct, WR 110 therefore
joins the ranks with three other single WR stars, all WN, with confirmed CIR
rotation periods (WR 1, WR 6, and WR 134), albeit with WR 110 having by far the
lowest amplitude photometric modulation. This illustrates the power of being
able to secure intense, continuous high-precision photometry from space-based
platforms such as MOST. It also opens the door to revealing low-amplitude
photometric variations in other WN stars, where previous attempts have failed.
If all WN stars have CIRs at some level, this could be important for revealing
sources of magnetism or pulsation in addition to rotation periods.Comment: 25 pages, 8 figures, 2 tables, accepted in Ap
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