4,047 research outputs found
Why do gallium clusters have a higher melting point than the bulk?
Density functional molecular dynamical simulations have been performed on
Ga and Ga clusters to understand the recently observed
higher-than-bulk melting temperatures in small gallium clusters [Breaux {\em et
al.}, Phys. Rev. Lett. {\bf 91}, 215508 (2003)]. The specific-heat curve,
calculated with the multiple-histogram technique, shows the melting temperature
to be well above the bulk melting point of 303 K, viz. around 650 K and 1400 K
for Ga and Ga, respectively. The higher-than-bulk melting
temperatures are attributed mainly to the covalent bonding in these clusters,
in contrast with the covalent-metallic bonding in the bulk.Comment: 4 pages, including 6 figures. accepted for publication in Phys. Rev.
Let
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
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
Phase Estimation from Atom Position Measurements
We study the measurement of the position of atoms as a means to estimate the
relative phase between two Bose-Einstein condensates. First, we consider
atoms released from a double-well trap, forming an interference pattern, and
show that a simple least-squares fit to the density gives a shot-noise limited
sensitivity. The shot-noise limit can instead be overcome by using correlation
functions of order or larger. The measurement of the
-order correlation function allows to estimate the relative phase
at the Heisenberg limit. Phase estimation through the measurement of the
center-of-mass of the interference pattern can also provide sub-shot-noise
sensitivity. Finally, we study the effect of the overlap between the two clouds
on the phase estimation, when Mach-Zehnder interferometry is performed in a
double-well.Comment: 20 pages, 6 figure
ΠΡΠΈΠΌΠ΅Π½Π΅Π½ΠΈΠ΅ ΠΌΠ΅ΡΠΎΠ΄Π° ΠΏΠΎΠ΄Π²ΠΈΠΆΠ½ΡΡ ΠΊΠ»Π΅ΡΠΎΡΠ½ΡΡ Π°Π²ΡΠΎΠΌΠ°ΡΠΎΠ² Π΄Π»Ρ ΠΎΠΏΡΠΈΠΌΠΈΠ·Π°ΡΠΈΠΈ Π²Π½ΡΡΡΠ΅Π½Π½Π΅ΠΉ ΡΡΡΡΠΊΡΡΡΡ ΡΠ½Π΄ΠΎΠΏΡΠΎΡΠ΅Π·Π° ΡΠ°Π·ΠΎΠ±Π΅Π΄ΡΠ΅Π½Π½ΠΎΠ³ΠΎ ΡΡΡΡΠ°Π²Π° ΡΠ΅Π»ΠΎΠ²Π΅ΠΊΠ°
ΠΠ° ΠΎΡΠ½ΠΎΠ²Π΅ ΠΌΠ΅ΡΠΎΠ΄Π° ΠΏΠΎΠ΄Π²ΠΈΠΆΠ½ΡΡ
ΠΊΠ»Π΅ΡΠΎΡΠ½ΡΡ
Π°Π²ΡΠΎΠΌΠ°ΡΠΎΠ² ΠΏΡΠΎΠ²Π΅Π΄Π΅Π½ΠΎ ΠΈΠ·ΡΡΠ΅Π½ΠΈΠ΅ Π²Π»ΠΈΡΠ½ΠΈΡ ΠΊΠΎΠ½ΡΡΡΡΠΊΡΠΈΠΎΠ½Π½ΡΡ
ΠΈΠ·ΠΌΠ΅Π½Π΅Π½ΠΈΠΉ ΡΠ½Π΄ΠΎΠΏΡΠΎΡΠ΅Π·Π° ΡΠ°Π·ΠΎΠ±Π΅Π΄ΡΠ΅Π½Π½ΠΎΠ³ΠΎ ΡΡΡΡΠ°Π²Π° ΡΠ΅Π»ΠΎΠ²Π΅ΠΊΠ° Π½Π° Π΄Π΅ΡΠΎΡΠΌΠ°ΡΠΈΠΎΠ½Π½ΡΠ΅ ΠΈ ΠΏΡΠΎΡΠ½ΠΎΡΡΠ½ΡΠ΅ ΡΠ²ΠΎΠΉΡΡΠ²Π°, Π° ΡΠ°ΠΊΠΆΠ΅ Π΄ΠΈΠ½Π°ΠΌΠΈΠΊΡ Π³Π΅Π½Π΅ΡΠ°ΡΠΈΠΈ ΠΈ ΡΠ°Π·Π²ΠΈΡΠΈΡ ΠΏΠΎΠ²ΡΠ΅ΠΆΠ΄Π΅Π½ΠΈΠΉ Π² ΡΠΈΡΡΠ΅ΠΌΠ΅ "ΡΡΡΡΠ°Π²-ΡΠ½Π΄ΠΎΠΏΡΠΎΡΠ΅Π·-Π±Π΅Π΄ΡΠ΅Π½Π½Π°Ρ ΠΊΠΎΡΡΡ". Π‘ΡΡΡΠΊΡΡΡΠ° ΠΏΡΠΎΡΠ΅Π·Π° ΠΌΠΎΠ΄ΠΈΡΠΈΡΠΈΡΠΎΠ²Π°Π»Π°ΡΡ Π²Π²Π΅Π΄Π΅Π½ΠΈΠ΅ΠΌ Π² ΡΠ΅ΠΉΠΊΡ Π΄Π΅ΠΌΠΏΡΠΈΡΡΡΡΠΈΡ
Π²ΠΊΠ»ΡΡΠ΅Π½ΠΈΠΉ ΠΈ Π½Π°Π½Π΅ΡΠ΅Π½ΠΈΠ΅ΠΌ ΠΏΠΎΠΊΡΡΡΠΈΡ Π½Π° Π½ΠΎΠΆΠΊΡ ΠΈΠΌΠΏΠ»Π°Π½ΡΠ°ΡΠ°. ΠΠΎΠΊΠ°Π·Π°Π½ΠΎ, ΡΡΠΎ Π½Π°Π»ΠΈΡΠΈΠ΅ ΡΠ°ΠΊΠΈΡ
Π²ΠΊΠ»ΡΡΠ΅Π½ΠΈΠΉ ΠΏΡΠ°ΠΊΡΠΈΡΠ΅ΡΠΊΠΈ Π½Π΅ ΠΈΠ·ΠΌΠ΅Π½ΡΠ΅Ρ ΠΏΡΠΎΡΠ½ΠΎΡΡΡ ΡΠΈΡΡΠ΅ΠΌΡ, Π½ΠΎ ΠΏΡΠΈ ΡΡΠΎΠΌ Π²Π΅Π΄Π΅Ρ ΠΊ Π·Π°ΠΌΠ΅ΡΠ½ΠΎΠΌΡ ΡΠ²Π΅Π»ΠΈΡΠ΅Π½ΠΈΡ ΠΏΡΠ΅Π΄Π΅Π»ΡΠ½ΠΎΠΉ Π΄Π΅ΡΠΎΡΠΌΠ°ΡΠΈΠΈ ΡΡΡΡΠΊΡΡΡΡ "ΠΊΠΎΡΡΡ - ΠΏΡΠΎΡΠ΅Π·", Π° ΡΠ°ΠΊΠΆΠ΅ ΠΎΠΊΠ°Π·ΡΠ²Π°Π΅Ρ Π²Π»ΠΈΡΠ½ΠΈΠ΅ Π½Π° Π΄ΠΈΠ½Π°ΠΌΠΈΠΊΡ Π·Π°ΡΠΎΠΆΠ΄Π΅Π½ΠΈΡ ΠΈ ΡΠ°Π·Π²ΠΈΡΠΈΡ ΠΏΠΎΠ²ΡΠ΅ΠΆΠ΄Π΅Π½ΠΈΠΉ Π² ΠΊΠΎΡΡΠ½ΠΎΠΉ ΡΠΊΠ°Π½ΠΈ
Total energy differences between SiC polytypes revisited
The total energy differences between various SiC polytypes (3C, 6H, 4H, 2H,
15R and 9R) were calculated using the full-potential linear muffin-tin orbital
method using the Perdew-Wang-(91) generalized gradient approximation to the
exchange-correlation functional in the density functional method. Numerical
convergence versus k-point sampling and basis set completeness are demonstrated
to be better than 1 meV/atom. The parameters of several generalized anisotropic
next-nearest-neighbor Ising models are extracted and their significance and
consequences for epitaxial growth are discussed.Comment: 8 pages, 3 figures, Latex, uses epsfig and revte
Exponential behavior of the interlayer exchange coupling across non-magnetic metallic superlattices
It is shown that the coupling between magnetic layers separated by
non-magnetic metallic superlattices can decay exponentially as a function of
the spacer thickness , as opposed to the usual decay. This effect
is due to the lack of constructive contributions to the coupling from extended
states across the spacer. The exponential behavior is obtained by properly
choosing the distinct metals and the superlattice unit cell composition.Comment: To appear in Phys. Rev.
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 populationsβJapanese, 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
Bundle Theory of Improper Spin Transformations
{\it We first give a geometrical description of the action of the parity
operator () on non relativistic spin Pauli spinors in
terms of bundle theory. The relevant bundle, , is a
non trivial extension of the universal covering group .
is the non relativistic limit of the corresponding Dirac matrix
operator and obeys . Then, from the direct
product of O(3) by , naturally induced by the structure of the galilean
group, we identify, in its double cover, the time reversal operator ()
acting on spinors, and its product with . Both, and
, generate the group . As in the case of parity,
is the non relativistic limit of the corresponding Dirac matrix
operator , and obeys .}Comment: 8 pages, Plaintex; titled changed, minor text modifications, one
reference complete
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