7,252 research outputs found
Ion engine thrust vector study, phase 2 Quarterly report
Performance prediction for expected thrust misalignment in electron bombardment ion thruste
Ion engine thrust vector study
Probability of thrust vector misalignment in ion thrustor arra
Muon-spin-rotation measurements of the penetration depth in Li_2Pd_3B
Measurements of the magnetic field penetration depth in the ternary
boride superconductor LiPdB ( K) have been carried out by
means of muon-spin rotation (SR). The absolute values of , the
Ginzburg-Landau parameter , and the first and the second
critical fields at T=0 obtained from SR were found to be
nm, , mT, and
T, respectively. The zero-temperature value of the
superconducting gap 1.31(3) meV was found, corresponding to the
ratio . At low temperatures saturates and
becomes constant below , in agreement with what is expected for
s-wave BCS superconductors. Our results suggest that LiPdB is a s-wave
BCS superconductor with the only one isotropic energy gap.Comment: 6 pages, 7 figure
Global Phase Diagram of the High Tc Cuprates
The high Tc cuprates have a complex phase diagram with many competing phases.
We propose a bosonic effective quantum Hamiltonian based on the projected SO(5)
model with extended interactions, which can be derived from the microscopic
models of the cuprates. The global phase diagram of this model is obtained
using mean-field theory and the Quantum Monte Carlo simulation, which is
possible because of the absence of the minus sign problem. We show that this
single quantum model can account for most salient features observed in the high
Tc cuprates, with different families of the cuprates attributed to different
traces in the global phase diagram. Experimental consequences are discussed and
new theoretical predictions are presented.Comment: 19 pages, 20 figures, with updated references, final versio
WIMP astronomy and particle physics with liquid-noble and cryogenic direct-detection experiments
Once weakly-interacting massive particles (WIMPs) are unambiguously detected
in direct-detection experiments, the challenge will be to determine what one
may infer from the data. Here, I examine the prospects for reconstructing the
local speed distribution of WIMPs in addition to WIMP particle-physics
properties (mass, cross sections) from next-generation cryogenic and
liquid-noble direct-detection experiments. I find that the common method of
fixing the form of the velocity distribution when estimating constraints on
WIMP mass and cross sections means losing out on the information on the speed
distribution contained in the data and may lead to biases in the inferred
values of the particle-physics parameters. I show that using a more general,
empirical form of the speed distribution can lead to good constraints on the
speed distribution. Moreover, one can use Bayesian model-selection criteria to
determine if a theoretically-inspired functional form for the speed
distribution (such as a Maxwell-Boltzmann distribution) fits better than an
empirical model. The shape of the degeneracy between WIMP mass and cross
sections and their offset from the true values of those parameters depends on
the hypothesis for the speed distribution, which has significant implications
for consistency checks between direct-detection and collider data. In addition,
I find that the uncertainties on theoretical parameters depends sensitively on
the upper end of the energy range used for WIMP searches. Better constraints on
the WIMP particle-physics parameters and speed distribution are obtained if the
WIMP search is extended to higher energy (~ 1 MeV).Comment: 25 pages, 27 figures, matches published versio
Hidden magnetic transitions in thermoelectric layered cobaltite, [CaCoO][CoO]
A positive muon spin rotation and relaxation (SR) experiment on
[CaCoO][CoO], ({\sl i.e.}, CaCoO, a layered
thermoelectric cobaltite) indicates the existence of two magnetic transitions
at 100 K and 400 - 600 K; the former is a transition from a paramagnetic
state to an incommensurate ({\sf IC}) spin density wave ({\sf SDW}) state. The
anisotropic behavior of zero-field SR spectra at 5 K suggests that the
{\sf IC-SDW} propagates in the - plane, with oscillating moments directed
along the c-axis; also the {\sf IC-SDW} is found to exist not in the
[CaCoO] subsystem but in the [CoO] subsystem. In addition, it is
found that the long-range {\sf IC-SDW} order completes below 30 K,
whereas the short-range order appears below 100 K. The latter transition is
interpreted as a gradual change in the spin state of Co ions %% at temperatures
above 400 K. These two magnetic transitions detected by SR are found to
correlate closely with the transport properties of
[CaCoO][CoO].Comment: 7 pages, 8 figures. to be appeared in Phys. Rev.
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