1,776 research outputs found
Physical Conditoins in Orion's Veil II: A Multi-Component Study of the Line of Sight Toward the Trapezium
Orion's Veil is an absorbing screen that lies along the line of sight to the
Orion H II region. It consists of two or more layers of gas that must lie
within a few parsecs of the Trapezium cluster. Our previous work considered the
Veil as a whole and found that the magnetic field dominates the energetics of
the gas in at least one component. Here we use high-resolution STIS UV spectra
that resolve the two velocity components in absorption and determine the
conditions in each. We derive a volume hydrogen density, 21 cm spin
temperature, turbulent velocity, and kinetic temperature, for each. We combine
these estimates with magnetic field measurements to find that magnetic energy
significantly dominates turbulent and thermal energies in one component, while
the other component is close to equipartition between turbulent and magnetic
energies. We observe molecular hydrogen absorption for highly excited v, J
levels that are photoexcited by the stellar continuum, and detect blueshifted S
III and P III. These ions must arise from ionized gas between the mostly
neutral portions of the Veil and the Trapezium and shields the Veil from
ionizing radiation. We find that this layer of ionized gas is also responsible
for He I absorption in the Veil, which resolves a 40-year-old debate on the
origin of He I absorption towards the Trapezium. Finally, we determine that the
ionized and mostly atomic layers of the Veil will collide in less than 85,000
years.Comment: 43 pages, 15 figures, to be published in Ap
Self-Binding Transition in Bose Condensates with Laser-Induced ``Gravitation''
In our recent publication (D. O'Dell, et al, Phys. Rev. Lett. 84, 5687
(2000)) we proposed a scheme for electromagnetically generating a self-bound
Bose-Einstein condensate with 1/r attractive interactions: the analog of a Bose
star. Here we focus upon the conditions neccessary to observe the transition
from external trapping to self-binding. This transition becomes manifest in a
sharp reduction of the condensate radius and its dependence on the laser
intensity rather that the trap potential.Comment: 5 pages, 2 figures: slightly enhanced text: more explanatio
Macroscopic Quantum Tunneling of Ferromagnetic Domain Walls
Quantum tunneling of domain walls out of an impurity potential in a
mesoscopic ferromagnetic sample is investigated. Using improved expressions for
the domain wall mass and for the pinning potential, we find that the cross-over
temperature between thermal activation and quantum tunneling is of a different
functional form than found previously. In materials like Ni or YIG, the
crossover temperatures are around 5 mK. We also find that the WKB exponent is
typically two orders of magnitude larger than current estimates. The sources
for these discrepancies are discussed, and precise estimates for the transition
from three-dimensional to one-dimensional magnetic behavior of a wire are
given. The cross-over temperatures from thermal to quantum transitions and
tunneling rates are calculated for various materials and sample sizes.Comment: 10 pages, 2 postscript figures, REVTe
Extended axion electrodynamics: Optical activity induced by nonstationary dark matter
We establish a new self-consistent Einstein-Maxwell-axion model based on the
Lagrangian, which is linear in the pseudoscalar (axion) field and its
four-gradient and includes the four-vector of macroscopic velocity of the axion
system as a whole. We consider extended equations of the axion electrodynamics,
modified gravity field equations, and discuss nonstationary effects in the
phenomenon of optical activity induced by axions.Comment: 6 pages, 0 figures, accepted for publication in the Journal
Gravitation and Cosmology, reported at the 14th Russian Gravitational
Conference (Ulyanovsk, 2011
The influence of transition metal solutes on dislocation core structure and values of Peierls stress and barrier in tungsten
Several transition metals were examined to evaluate their potential for
improving the ductility of tungsten. The dislocation core structure and Peierls
stress and barrier of screw dislocations in binary
tungsten-transition metal alloys (WTM) were investigated using
first principles electronic structure calculations. The periodic quadrupole
approach was applied to model the structure of dislocation. Alloying
with transition metals was modeled using the virtual crystal approximation and
the applicability of this approach was assessed by calculating the equilibrium
lattice parameter and elastic constants of the tungsten alloys. Reasonable
agreement was obtained with experimental data and with results obtained from
the conventional supercell approach. Increasing the concentration of a
transition metal from the VIIIA group, i.e. the elements in columns headed by
Fe, Co and Ni, leads to reduction of the elastic constant and
increase of elastic anisotropy A=. Alloying W with a group
VIIIA transition metal changes the structure of the dislocation core from
symmetric to asymmetric, similar to results obtained for WRe
alloys in the earlier work of Romaner {\it et al} (Phys. Rev. Lett. 104, 195503
(2010))\comments{\cite{WRECORE}}. In addition to a change in the core symmetry,
the values of the Peierls stress and barrier are reduced. The latter effect
could lead to increased ductility in a tungsten-based
alloy\comments{\cite{WRECORE}}. Our results demonstrate that alloying with any
of the transition metals from the VIIIA group should have similar effect as
alloying with Re.Comment: 12 pages, 8 figures, 3 table
Quantum Vacuum Contribution to the Momentum of the Dielectric Media
Momentum transfer between matter and electromagnetic field is analyzed. The
related equations of motion and conservation laws are derived using
relativistic formalism. Their correspondence to various, at first sight
self-contradicting, experimental data (the so called Abraham-Minkowski
controversy) is demonstrated. A new, Casimir like, quantum phenomenon is
predicted: contribution of vacuum fluctuations to the motion of dielectric
liquids in crossed electric and magnetic fields. Velocities about can
be expected due to the contribution of high frequency vacuum modes
Rotons in gaseous Bose-Einstein condensates irradiated by a laser
A gaseous Bose-Einstein condensate (BEC) irradiated by a far off-resonance
laser has long-range interatomic correlations caused by laser-induced
dipole-dipole interactions. These correlations, which are tunable via the laser
intensity and frequency, can produce a `roton' minimum in the excitation
spectrum--behavior reminiscent of the strongly correlated superfluid liquid
helium II.Comment: 6 pages, includes 3 figure
Relativistic nature of a magnetoelectric modulus of Cr_2O_3-crystals: a new 4-dimensional pseudoscalar and its measurement
Earlier, the magnetoelectric effect of chromium sesquioxide Cr_2O_3 has been
determined experimentally as a function of temperature. One measures the
electric field-induced magnetization on Cr_2O_3 crystals or the magnetic
field-induced polarization. From the magnetoelectric moduli of Cr_2O_3 we
extract a 4-dimensional relativistic invariant pseudoscalar
. It is temperature dependent and of the order of
10^{-4}/Z_0, with Z_0 as vacuum impedance. We show that the new pseudoscalar is
odd under parity transformation and odd under time inversion. Moreover,
is for Cr_2O_3 what Tellegen's gyrator is for two port
theory, the axion field for axion electrodynamics, and the PEMC (perfect
electromagnetic conductor) for electrical engineering.Comment: Revtex, 36 pages, 9 figures (submitted in low resolution, better
quality figures are available from the authors
Bivariate genetic modelling of the response to an oral glucose tolerance challenge: A gene x environment interaction approach
AIMS/HYPOTHESIS: Twin and family studies have shown the importance of genetic factors influencing fasting and 2 h glucose and insulin levels. However, the genetics of the physiological response to a glucose load has not been thoroughly investigated. METHODS: We studied 580 monozygotic and 1,937 dizygotic British female twins from the Twins UK Registry. The effects of genetic and environmental factors on fasting and 2 h glucose and insulin levels were estimated using univariate genetic modelling. Bivariate model fitting was used to investigate the glucose and insulin responses to a glucose load, i.e. an OGTT. RESULTS: The genetic effect on fasting and 2 h glucose and insulin levels ranged between 40% and 56% after adjustment for age and BMI. Exposure to a glucose load resulted in the emergence of novel genetic effects on 2 h glucose independent of the fasting level, accounting for about 55% of its heritability. For 2 h insulin, the effect of the same genes that already influenced fasting insulin was amplified by about 30%. CONCLUSIONS/INTERPRETATION: Exposure to a glucose challenge uncovers new genetic variance for glucose and amplifies the effects of genes that already influence the fasting insulin level. Finding the genes acting on 2 h glucose independently of fasting glucose may offer new aetiological insight into the risk of cardiovascular events and death from all causes
Search for the K(L) --> PI0 PI0 E+ E- Decay in the KTeV Experiment
The recent discovery of a large CP violating asymmetry in K(L) --> PI+ PI- E+
E- mode has prompted us to seach for the associated K(L) --> PI0 PI0 E+ E-
decay mode in the KTeV-E799 experiment at Fermilab. In 2.7E+11 K(L) decays, one
candidate event has been observed with an expected background of 0.3 event,
resulting in an upper limit for the K(L) --> PI0 PI0 E+ E- branching ratio of
6.6E-09 at the 90% confidence level.Comment: To be published in Phys. Rev. Let
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