1,454 research outputs found
An Apparatus to Control and Monitor the Para-D2 Concentration in a Solid Deuterium, Superthermal Source of Ultra-cold Neutrons
Controlling and measuring the concentration of para-D2 is an essential step
toward realizing solid deuterium as an intense ultra-cold neutron (UCN) source.
To this end, we implemented an experimental technique to convert para- to
ortho-deuterium molecules by flowing D2 gas through a cryogenic cell filled
with paramagnetic hydrous ferric oxide granules. This process efficiently
reduced the para-D2 concentration from 33.3% to 1.5%. Rotational Raman
spectroscopy was applied to measure the residual para-D2 contamination to
better than 2 parts in 10^3, and the hydrogen contamination to 1 part in 10^3.
We also contrast our optical technique to conventional thermal conductivity
measurements of the para-D2 concentration, reporting some of the relevant
strengths and weaknesses of our implementation of each technique.Comment: accepted for publication in NIM
Dipolar Bose-Einstein condensate soliton on a two-dimensional optical lattice
Using a three-dimensional mean-field model we study one-dimensional dipolar
Bose-Einstein condensate (BEC) solitons on a weak two-dimensional (2D) square
and triangular optical lattice (OL) potentials placed perpendicular to the
polarization direction. The stabilization against collapse and expansion of
these solitons for a fixed dipolar interaction and a fixed number of atoms is
possible for short-range atomic interaction lying between two critical limits.
The solitons collapse below the lower limit and escapes to infinity above the
upper limit. One can also stabilize identical tiny BEC solitons arranged on the
2D square OL sites forming a stable 2D array of interacting droplets when the
OL sites are filled with a filling factor of 1/2 or less. Such an array is
unstable when the filling factor is made more than 1/2 by occupying two
adjacent sites of OL. These stable 2D arrays of dipolar superfluid BEC solitons
are quite similar to the recently studied dipolar Mott insulator states on 2D
lattice in the Bose-Hubbard model by Capogrosso-Sansone et al. [B.
Capogrosso-Sansone, C. Trefzger, M. Lewenstein, P. Zoller, G. Pupillo, Phys.
Rev. Lett. 104 (2010) 125301].Comment: 8 pages, 5 figures and 2 table
Dust extinction and X-ray emission from the star burst galaxy NGC 1482
We present the results based on multiwavelength imaging observations of the
prominent dust lane starburst galaxy NGC 1482 aimed to investigate the
extinction properties of dust existing in the extreme environment. (B-V)
colour-index map derived for the starburst galaxy NGC 1482 confirms two
prominent dust lanes running along its optical major axis and are found to
extend up to \sim 11 kpc. In addition to the main lanes, several filamentary
structures of dust originating from the central starburst are also evident.
Though, the dust is surrounded by exotic environment, the average extinction
curve derived for this target galaxy is compatible with the Galactic curve,
with RV =3.05, and imply that the dust grains responsible for the optical
extinction in the target galaxy are not really different than the canonical
grains in the Milky Way. Our estimate of total dust content of NGC 1482
assuming screening effect of dust is \sim 2.7 \times 10^5 Msun, and provide
lower limit due to the fact that our method is not sensitive to the intermix
component of dust. Comparison of the observed dust in the galaxy with that
supplied by the SNe to the ISM, imply that this supply is not sufficient to
account for the observed dust and hence point towards the origin of dust in
this galaxy through a merger like event. Our multiband imaging analysis reveals
a qualitative physical correspondence between the morphologies of the dust and
H{\alpha} emission lines as well as diffuse X-ray emission in this galaxy.
continue.... for more detail please see in pdf file.Comment: 22 pages, 11 Figures. Accepted for publication in New Astronom
Percolation in random environment
We consider bond percolation on the square lattice with perfectly correlated
random probabilities. According to scaling considerations, mapping to a random
walk problem and the results of Monte Carlo simulations the critical behavior
of the system with varying degree of disorder is governed by new, random fixed
points with anisotropic scaling properties. For weaker disorder both the
magnetization and the anisotropy exponents are non-universal, whereas for
strong enough disorder the system scales into an {\it infinite randomness fixed
point} in which the critical exponents are exactly known.Comment: 8 pages, 7 figure
Measuring geometric phases of scattering states in nanoscale electronic devices
We show how a new quantum property, a geometric phase, associated with
scattering states can be exhibited in nanoscale electronic devices. We propose
an experiment to use interference to directly measure the effect of the new
geometric phase. The setup involves a double path interferometer, adapted from
that used to measure the phase evolution of electrons as they traverse a
quantum dot (QD). Gate voltages on the QD could be varied cyclically and
adiabatically, in a manner similar to that used to observe quantum adiabatic
charge pumping. The interference due to the geometric phase results in
oscillations in the current collected in the drain when a small bias across the
device is applied. We illustrate the effect with examples of geometric phases
resulting from both Abelian and non-Abelian gauge potentials.Comment: Six pages two figure
On non-local variational problems with lack of compactness related to non-linear optics
We give a simple proof of existence of solutions of the dispersion manage-
ment and diffraction management equations for zero average dispersion,
respectively diffraction. These solutions are found as maximizers of non-linear
and non-local vari- ational problems which are invariant under a large
non-compact group. Our proof of existence of maximizer is rather direct and
avoids the use of Lions' concentration compactness argument or Ekeland's
variational principle.Comment: 30 page
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Leucine-rich repeat containing 8A (LRRC8A) is essential for T lymphocyte development and function
Lrrc8a is a ubiquitously expressed gene that encodes a leucine-rich repeat (LRR)–containing protein detected at higher levels on the surface of thymocytes than on other immune cells. We generated Lrrc8a−/− mice to investigate the role of LRRC8A in lymphocyte development and function. Lrrc8a−/− mice had increased prenatal and postnatal mortality, growth retardation, and multiple tissue abnormalities. Lrrc8a−/− mice displayed a modest block in B cell development but intact intrinsic B cell function. In contrast, both Lrrc8a−/− mice and Lrrc8a−/−→Rag2−/− bone marrow chimeras exhibited a severe cell-intrinsic block in early thymic development, with decreased proliferation and increased apoptosis of thymocytes, and impaired peripheral T cell function. Thymic epithelial cells expressed an LRRC8A ligand that was critical for double-negative to double-positive thymocyte differentiation and survival in vitro. LRRC8A constitutively associated with the GRB2–GAB2 complex and lymphocyte-specific protein tyrosine kinase (LCK) in thymocytes. LRRC8A ligation activated AKT via the LCK–ZAP–70–GAB2–PI3K pathway, and AKT phosphorylation was markedly reduced in the thymus of Lrrc8a−/− mice. These findings reveal an essential role for LRRC8A in T cell development, survival, and function
Smeared phase transition in a three-dimensional Ising model with planar defects: Monte-Carlo simulations
We present results of large-scale Monte Carlo simulations for a
three-dimensional Ising model with short range interactions and planar defects,
i.e., disorder perfectly correlated in two dimensions. We show that the phase
transition in this system is smeared, i.e., there is no single critical
temperature, but different parts of the system order at different temperatures.
This is caused by effects similar to but stronger than Griffiths phenomena. In
an infinite-size sample there is an exponentially small but finite probability
to find an arbitrary large region devoid of impurities. Such a rare region can
develop true long-range order while the bulk system is still in the disordered
phase. We compute the thermodynamic magnetization and its finite-size effects,
the local magnetization, and the probability distribution of the ordering
temperatures for different samples. Our Monte-Carlo results are in good
agreement with a recent theory based on extremal statistics.Comment: 9 pages, 6 eps figures, final version as publishe
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