2,786,826 research outputs found
Relativistic N-boson systems bound by pair potentials V(r_{ij}) = g(r_{ij}^2)
We study the lowest energy E of a relativistic system of N identical bosons
bound by pair potentials of the form V(r_{ij}) = g(r_{ij}^2) in three spatial
dimensions. In natural units hbar = c = 1 the system has the semirelativistic
`spinless-Salpeter' Hamiltonian H = \sum_{i=1}^N \sqrt{m^2 + p_i^2} +
\sum_{j>i=1}^N g(|r_i - r_j|^2), where g is monotone increasing and has
convexity g'' >= 0. We use `envelope theory' to derive formulas for general
lower energy bounds and we use a variational method to find complementary upper
bounds valid for all N >= 2. In particular, we determine the energy of the
N-body oscillator g(r^2) = c r^2 with error less than 0.15% for all m >= 0, N
>= 2, and c > 0.Comment: 15 pages, 4 figure
An assessment of J/Psi formation in the light of initial RHIC data
Predictions of J/Psi formation at RHIC via "off-diagonal" combinations of
charm and anticharm quarks in a region of color deconfinement are confronted
with initial data from the PHENIX collaboration. We find that the measured
centrality behavior places significant constraints on the various parameters
which control model calculations of J/Psi formation. Within present statistical
and systematic uncertainties, one can map out a region of parameter space
within which the contribution of formation in a deconfined phase is allowed. As
these uncertainties decrease and new data from d-Au interactions becomes
available, it is expected that definitive tests for the presence of this
formation mechanism will be possible. We anticipate that the rapidity and
transverse momentum spectra will prove decisive for a final determination.Comment: 6 pages, 5 figures, presented at SQM2003, March 12-17, 2003. To be
published in J. Phys.
The Effect of Weak Gravitational Lensing on the Angular Distribution of Gamma-Ray Bursts
If Gamma-Ray Bursts (GRBs) are cosmologically distributed standard candles
and are associated with the luminous galaxies, then the observed angular
distribution of all GRBs is altered due to weak gravitational lensing of bursts
by density inhomogeneities. The amplitude of the effect is generally small. For
example, if the current catalogs extend to and we live in a
flat Universe, the angular auto-correlation function of GRBs will be
enhanced by due to lensing, on all angular scales. For an extreme
case of and (, )=(0.2, 0.8), an enhancement of
is predicted. If the observed distribution of GRBs is used in the
future to derive power spectra of mass density fluctuations on large angular
scales, the effect of weak lensing should probably be taken into account.Comment: 16 pages, 2 figures, uses AASTEX macros, aasms4.sty included,
accepted to Ap
Spectroscopic Confirmation of the Cl 1604 Supercluster at z~0.9
We present spectroscopic confirmation of the Cl 1604 supercluster at z~0.9.
Originally detected as two individual clusters, Cl 1604+4304 at z = 0.90 and Cl
1604+4321 at z = 0.92, which are closely separated in both redshift and sky
position, subsequent imaging revealed a complex of red galaxies bridging the
two clusters, suggesting that the region contained a large scale structure. We
have carried out extensive multi-object spectroscopy, which, combined with
previous measurements, provides ~600 redshifts in this area, including 230
confirmed supercluster members. We detect two additional clusters that are part
of this structure, Cl 1604+4314 at z = 0.87 and Cl 1604+4316 at z = 0.94. All
four have properties typical of local clusters, with line-of-sight velocity
dispersions between 489 and 962 km/s. The structure is significantly extended
in redshift space, which, if interpreted as a true elongation in real space,
implies a depth of 93 Mpc. We examine the spatial and redshift distribution of
the supercluster members.Comment: Accepted to ApJ Letters. 4 pages with 3 figure
Fluorinated esters of polycarboxylic acids
Fluorine containing esters of polycarboxylic acids are discussed. The use of these esters as extreme temperature lubricants and base fluids for greases is investigated
Wigner-Poisson and nonlocal drift-diffusion model equations for semiconductor superlattices
A Wigner-Poisson kinetic equation describing charge transport in doped
semiconductor superlattices is proposed. Electrons are supposed to occupy the
lowest miniband, exchange of lateral momentum is ignored and the
electron-electron interaction is treated in the Hartree approximation. There
are elastic collisions with impurities and inelastic collisions with phonons,
imperfections, etc. The latter are described by a modified BGK
(Bhatnagar-Gross-Krook) collision model that allows for energy dissipation
while yielding charge continuity. In the hyperbolic limit, nonlocal
drift-diffusion equations are derived systematically from the kinetic
Wigner-Poisson-BGK system by means of the Chapman-Enskog method. The
nonlocality of the original quantum kinetic model equations implies that the
derived drift-diffusion equations contain spatial averages over one or more
superlattice periods. Numerical solutions of the latter equations show
self-sustained oscillations of the current through a voltage biased
superlattice, in agreement with known experiments.Comment: 20 pages, 1 figure, published as M3AS 15, 1253 (2005) with
correction
Space Shuttle Lightning Protection
The technology for lightning protection of even the most advanced spacecraft is available and can be applied through cost-effective hardware designs and design-verification techniques. In this paper, the evolution of the Space Shuttle Lightning Protection Program is discussed, including the general types of protection, testing, and anlayses being performed to assess the lightning-transient-damage susceptibility of solid-state electronics
Bidirectional step torque filter with zero backlash characteristic Patent
Gearing system for eliminating backlash and filtering input torque fluctuations from high inertia loa
Emergence of skyrmion lattices and bimerons in chiral magnetic thin films with nonmagnetic impurities
Skyrmions are topologically protected field structures with particlelike characteristics that play important roles in several areas of science. Recently, skyrmions have been directly observed in chiral magnets. Here, we investigate the effects of pointlike nonmagnetic impurities on the distinct initial states (random or helical ones) and on the formation of the skyrmion crystal in a discrete lattice. Using Monte Carlo techniques, we have found that even a small percentage of spin vacancies present in the chiral magnetic thin film considerably affects the skyrmion order. The main effects of impurities are somewhat similar to thermal effects. The presence of these spin vacancies also induces the formation of bimerons in both the helical and skyrmion states. We also investigate how adjacent impurities forming a hole affect the skyrmion crystal
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