9,447 research outputs found
Clustering of vacancy defects in high-purity semi-insulating SiC
Positron lifetime spectroscopy was used to study native vacancy defects in
semi-insulating silicon carbide. The material is shown to contain (i) vacancy
clusters consisting of 4--5 missing atoms and (ii) Si vacancy related
negatively charged defects. The total open volume bound to the clusters
anticorrelates with the electrical resistivity both in as-grown and annealed
material. Our results suggest that Si vacancy related complexes compensate
electrically the as-grown material, but migrate to increase the size of the
clusters during annealing, leading to loss of resistivity.Comment: 8 pages, 5 figure
Vanishing discount problems for Hamilton--Jacobi equations on changing domains
We study the asymptotic behavior, as , of the
Hamilton-Jacobi equation
in with state-constraint boundary condition. Here,
is a bounded domain of , are continuous functions such that
is nonnegative and . Surprisingly, we are able to
obtain both convergence results and non-convergence results in this convex
setting. Moreover, we provide a very first result on the asymptotic expansion
of the additive eigenvalue of in as
. The main tool we use is a duality representation of
solution with viscosity Mather measures.Comment: 31 pages, 3 figures. AMSart style, errors fixe
Universal Properties of Two-Dimensional Boson Droplets
We consider a system of N nonrelativistic bosons in two dimensions,
interacting weakly via a short-range attractive potential. We show that for N
large, but below some critical value, the properties of the N-boson bound state
are universal. In particular, the ratio of the binding energies of (N+1)- and
N-boson systems, B_{N+1}/B_N, approaches a finite limit, approximately 8.567,
at large N. We also confirm previous results that the three-body system has
exactly two bound states. We find for the ground state B_3^(0) = 16.522688(1)
B_2 and for the excited state B_3^(1) = 1.2704091(1) B_2.Comment: 4 pages, 2 figures, final versio
Spontaneous Symmetry Breaking with Abnormal Number of Nambu-Goldstone Bosons and Kaon Condensate
We describe a class of relativistic models incorporating finite density of
matter in which spontaneous breakdown of continuous symmetries leads to a
lesser number of Nambu-Goldstone bosons than that required by the Goldstone
theorem. This class, in particular, describes the dynamics of the kaon
condensate in the color-flavor locked phase of high density QCD. We describe
the spectrum of low energy excitations in this dynamics and show that, despite
the presence of a condensate and gapless excitations, this system is not a
superfluid.Comment: 5 pages, 1 figure, REVTeX. Minor revisions made and 2 new references
added. To appear in Phys. Rev. Let
Characterization of the nitrogen split interstitial defect in wurtzite aluminum nitride using density functional theory
We carried out Heyd-Scuseria-Ernzerhof hybrid density functional theory plane
wave supercell calculations in wurtzite aluminum nitride in order to
characterize the geometry, formation energies, transition levels and hyperfine
tensors of the nitrogen split interstitial defect. The calculated hyperfine
tensors may provide useful fingerprint of this defect for electron paramagnetic
resonance measurement.Comment: 5 pages, 3 figure
Practical use of reactor anti-neutrinos for nuclear safeguard in Vietnam
One of the most abundant man-made sources of low energy (few~MeVs) neutrinos,
reactor neutrino, is not only useful for studying neutrino properties, but it
is also used in practical applications. In this study, we investigate the
practical use of reactor neutrino detectors for nuclear safeguard in Vietnam,
specifically at the Dalat Nuclear Reactor, a future research facility, and
presumably commercial reactors with 500~kW, 10~MW, and 1000~MW thermal powers,
respectively. We compute the rate of observed inverted beta decay events, as
well as the statistical significance of extracting isotope composition under
the practical assumptions of detector mass, detection efficiency, and
background level. We find that a 1-ton detector mass can allow us to detect the
reactor's on-off transition state from a few hours to a few days, depending on
the standoff distance and reactor thermal power. We investigate how background
and energy resolution affect the precision of the extracted weapon-usable
isotope. We conclude that in order to distinguish the 10\%
variation of the in the 10~MW thermal power reactor, a
1-ton detector placed 50~m away must achieve 1\% background level. Increasing
the statistics by using a 10x larger detector or placing it times
closer to the reactor alleviates the requirement of the background level to
10\%
Color Superconductivity from Supersymmetry
A supersymmetric composite model of color superconductivity is proposed.
Quarks and diquarks are dynamically generated as composite fields by a newly
introduced strong gauge dynamics. It is shown that the condensation of the
scalar component of the diquark supermultiplet occurs when the chemical
potential becomes larger than some critical value. We believe that the model
well captures aspects of the diquark condensate behavior and helps our
understanding of the diquark dynamics in real QCD. The results obtained here
might be useful when we consider a theory composed of quarks and diquarks.Comment: 4 pages, 2 figures, An error in Eq.(10) correcte
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