3,052 research outputs found
Inelastic neutron scattering in random binary alloys : an augmented space approach
Combining the augmented space representation for phonons with a generalized
version of Yonezawa-Matsubara diagrammatic technique, we have set up a
formalism to seperate the coherent and incoherent part of the total intensity
of thermal neutron scattering from disordered alloys. This is done exacly
without taking any recourse to mean-field like approximation (as done
previously). The formalism includes disorder in masses, force constants and
scattering lengths. Implementation of the formalism to realistic situations is
performed by an augmented space Block recursion which calculates entire Green
matrix and self energy matrix which in turn is needed to evaluate the coherent
and incoherent intensities. we apply the formalism to NiPd and NiPt alloys.
Numerical results on coherent and incoherent scattering cross sections are
presented along the highest symmetry directions. Finally the incoherent
intensities are compared with the CPA and also with experiments.Comment: 18 pages, 13 figure
The Structure of Barium in the hcp Phase Under High Pressure
Recent experimental results on two hcp phases of barium under high pressure
show interesting variation of the lattice parameters. They are here interpreted
in terms of electronic structure calculation by using the LMTO method and
generalized pseudopotential theory (GPT) with a NFE-TBB approach. In phase II
the dramatic drop in c/a is an instability analogous to that in the group II
metals but with the transfer of s to d electrons playing a crucial role in Ba.
Meanwhile in phase V, the instability decrease a lot due to the core repulsion
at very high pressure. PACS numbers: 62.50+p, 61.66Bi, 71.15.Ap, 71.15Hx,
71.15LaComment: 29 pages, 8 figure
Vibration Isolation Design for the Micro-X Rocket Payload
Micro-X is a NASA-funded, sounding rocket-borne X-ray imaging spectrometer
that will allow high precision measurements of velocity structure, ionization
state and elemental composition of extended astrophysical systems. One of the
biggest challenges in payload design is to maintain the temperature of the
detectors during launch. There are several vibration damping stages to prevent
energy transmission from the rocket skin to the detector stage, which causes
heating during launch. Each stage should be more rigid than the outer stages to
achieve vibrational isolation. We describe a major design effort to tune the
resonance frequencies of these vibration isolation stages to reduce heating
problems prior to the projected launch in the summer of 2014.Comment: 6 pages, 7 figures, LTD15 Conference Proceeding
Inclusion of additional studies yields different conclusions: Comment on Sedikides, Gaertner, & Vevea (2005), Journal of Personality and Social Psychology
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75100/1/j.1467-839X.2007.00211.x.pd
Metal-to-insulator crossover and pseudogap in single-layer compound BiSrCuO single crystals in high magnetic fields
The in-plane and the out-of-plane
magneto-transport in magnetic fields up to 28 T has been investigated in a
series of high quality, single crystal, hole-doped La-free Bi2201 cuprates for
a wide doping range and over a wide range of temperatures down to 40 mK. With
decreasing hole concentration going from the overdoped (p=0.2) to the
underdoped (p=0.12) regimes, a crossover from a metallic to and insulating
behavior of is observed in the low temperature normal state,
resulting in a disorder induced metal insulator transition. In the zero
temperature limit, the normal state ratio of the
heavily underdoped samples in pure Bi2201 shows an anisotropic 3D behavior, in
striking contrast with that observed in La-doped Bi2201 and LSCO systems. Our
data strongly support that that the negative out-of-plane magnetoresistance is
largely governed by interlayer conduction of quasiparticles in the
superconducting state, accompanied by a small contribution of normal state
transport associated with the field dependent pseudogap. Both in the optimal
and overdoped regimes, the semiconducting behavior of persists even
for magnetic fields above the pseudogap closing field . The method
suggested by Shibauchi \textit{et al.} (Phys. Rev. Lett. \textbf{86}, 5763,
(2001)) for evaluating is unsuccessful for both under- and overdoped
Bi2201 samples. Our findings suggest that the normal state pseudogap is not
always a precursor of superconductivity.Comment: 11 pages, 8 figures, published in PRB Nov 200
Overconfidence is universal? Elicitation of genuine overconfidence (EGO) procedure reveals systematic differences across domain, task knowledge, and incentives in four populations
Overconfidence is sometimes assumed to be a human universal, but there remains a dearth of data systematically measuring overconfidence across populations and contexts. Moreover, cross-cultural experiments often fail to distinguish between placement and precision and worse still, often compare population-mean placement estimates rather than individual performance subtracted from placement. Here we introduce a procedure for concurrently capturing both placement and precision at an individual level based on individual performance: The Elicitation of Genuine Overconfidence (EGO) procedure. We conducted experiments using the EGO procedure, manipulating domain, task knowledge, and incentives across four populations—Japanese, Hong Kong Chinese, Euro Canadians, and East Asian Canadians. We find that previous measures of population-level overconfidence may have been misleading; rather than universal, overconfidence is highly context dependent. Our results reveal cross-cultural differences in sensitivity to incentives and differences in overconfidence strategies, with underconfidence, accuracy, and overconfidence. Comparing sexes, we find inconsistent results for overplacement, but that males are consistently more confident in their placement. These findings have implications for our understanding of the adaptive value of overconfidence and its role in explaining population-level and individual-level differences in economic and psychological behavior
A single atom detector integrated on an atom chip: fabrication, characterization and application
We describe a robust and reliable fluorescence detector for single atoms that
is fully integrated into an atom chip. The detector allows spectrally and
spatially selective detection of atoms, reaching a single atom detection
efficiency of 66%. It consists of a tapered lensed single-mode fiber for
precise delivery of excitation light and a multi-mode fiber to collect the
fluorescence. The fibers are mounted in lithographically defined holding
structures on the atom chip. Neutral 87Rb atoms propagating freely in a
magnetic guide are detected and the noise of their fluorescence emission is
analyzed. The variance of the photon distribution allows to determine the
number of detected photons / atom and from there the atom detection efficiency.
The second order intensity correlation function of the fluorescence shows
near-perfect photon anti-bunching and signs of damped Rabi-oscillations. With
simple improvements one can boost the detection efficiency to > 95%.Comment: 24 pages, 11 figure
Effect of Electron Correlation on the Bragg Reflection
We study the effect of correlation on the Bragg reflection in the 3D electron
gas, the 1D Luttinger liquid, and the 1D Hubbard model in an alternating
periodic potential at half-filling. In the last system, we suggest a
Luttinger-liquid-type quasi-metallic state in the crossover region from the
band insulator to the Mott insulator. We explain the appearance of this state
in terms of the incompatibility of the Bragg reflection with the concept of
Luttinger liquids.Comment: 4 pages, 3 figure
Study of Phase Stability in NiPt Systems
We have studied the problem of phase stability in NiPt alloy system. We have
used the augmented space recursion based on the TB-LMTO as the method for
studying the electronic structure of the alloys. In particular, we have used
the relativistic generalization of our earlier technique. We note that, in
order to predict the proper ground state structures and energetics, in addition
to relativistic effects, we have to take into account charge transfer effects
with precision.Comment: 22 pages, 7 figures. Accepted for publication in JPC
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