7,882 research outputs found
Spin interference in silicon three-terminal one-dimensional rings
We present the first findings of the spin transistor effect in the Rashba
gate-controlled ring embedded in the p-type self-assembled silicon quantum well
that is prepared on the n-type Si (100) surface. The coherence and phase
sensitivity of the spin-dependent transport of holes are studied by varying the
value of the external magnetic field and the bias voltage that are applied
perpendicularly to the plane of the double-slit ring. Firstly, the amplitude
and phase sensitivity of the 0.7(2e^2/h) feature of the hole quantum
conductance staircase revealed by the quantum point contact inserted in the one
of the arms of the double-slit ring are found to result from the interplay of
the spontaneous spin polarization and the Rashba spin-orbit interaction.
Secondly, the quantum scatterers connected to two one-dimensional leads and the
quantum point contact inserted are shown to define the amplitude and the phase
of the Aharonov-Bohm and the Aharonov-Casher conductance oscillations.Comment: 8 pages, 5 figure
Glacial cycles promote greater dispersal, which can help explain larger clutch sizes, in north temperate birds
Earth’s glacial history and patterns in the life history traits of the planet’s avifauna suggest the following interpretations of how recent geological history has affected these key characteristics of the biota: 1) Increased colonizing ability has been an important advantage of increased dispersal, and life history strategies are better categorized by dispersive colonizing ability than by their intrinsic growth rates; 2) Birds of the North Temperate Zone show a greater tendency to disperse, and they disperse farther, than tropical or south temperate birds; 3) Habitat changes associated with glacial advance and retreat selected for high dispersal ability, particularly in the North; and 4) Selection for greater dispersal throughout the unstable Pleistocene has also resulted in other well-recognized life history contrasts, especially larger clutch sizes in birds of North Temperate areas
Lateral spin-orbit interaction and spin polarization in quantum point contacts
We study ballistic transport through semiconductor quantum point contact
systems under different confinement geometries and applied fields. In
particular, we investigate how the {\em lateral} spin-orbit coupling,
introduced by asymmetric lateral confinement potentials, affects the spin
polarization of the current. We find that even in the absence of external
magnetic fields, a variable {\em non-zero spin polarization} can be obtained by
controlling the asymmetric shape of the confinement potential. These results
suggest a new approach to produce spin polarized electron sources and we study
the dependence of this phenomenon on structural parameters and applied magnetic
fields. This asymmetry-induced polarization provides also a plausible
explanation of our recent observations of a 0.5 conductance plateau (in units
of ) in quantum point contacts made on InAs quantum-well structures.
Although our estimates of the required spin-orbit interaction strength in these
systems do not support this explanation, they likely play a role in the effects
enhanced by electron-electron interactions.Comment: Summited to PRB (2009
Results of an investigation of the 0.003-scale space shuttle external tank MSFC model 460 in the NASA/MSFC 14 x 14-inch Trisonic Wind Tunnel to determine static pressure distributions during reentry (TA2F), volume 5
For abstract, see N76-16132
Results of an investigation of the 0.003-scale space shuttle external tank MSFC model 460 in the NASA/MSFC 14 x 14 inch Trisonic Wind Tunnel to determine static pressure distributions during reentry (TA2F), volume 3
Static pressure distributions for the external tank (ET) at reentry conditions are presented. Basic configuration of the model was the MCR 0200 ET modified to include a rectangular crossbar at the aft ET/orbiter attach point. Mach numbers were 1.96, 3.48, and 4.96. Reynolds number per foot at these Mach numbers were 6.95 million, 6.42 million, and 4.95 million, respectively. Angle of attack range was -8 to 100 degrees and roll angle was 0 to 315 degrees
Power dependence of pure spin current injection by quantum interference
We investigate the power dependence of pure spin current injection in GaAs
bulk and quantum-well samples by a quantum interference and control technique.
Spin separation is measured as a function of the relative strength of the two
transition pathways driven by two laser pulses. By keeping the relaxation time
of the current unchanged, we are able to relate the spin separation to the
injected average velocity. We find that the average velocity is determined by
the relative strength of the two transitions in the same way as in classical
interference. Based on this, we conclude that the density of injected pure spin
current increases monotonically with the excitation laser intensities. The
experimental results are consistent with theoretical calculations based on
Fermi's golden rule.Comment: 6 pages, 4 figure
Identification and Analysis of Young Star Cluster Candidates in M31
We present a method for finding clusters of young stars in M31 using
broadband WFPC2 data from the HST data archive. Applying our identification
method to 13 WFPC2 fields, covering an area of ~60 arcmin^2, has revealed 79
new candidate young star clusters in these portions of the M31 disk. Most of
these clusters are small (~<5 pc) young (~10-200 Myr) star groups located
within large OB associations. We have estimated the reddening values and the
ages of each candidate individually by fitting isochrones to the stellar
photometry. We provide a catalog of the candidates including rough
approximations of their reddenings and ages. We also look for patterns of
cluster formation with galactocentric distance, but our rough estimates are not
precise enough to reveal any clear patterns.Comment: 32 pages, 9 figures, 5 tables, accepted to Ap
Results of an investigation of the 0.003-scale space shuttle external tank MSFC model 460 in NASA/MSFC 14 x 14-inch trisonic wind tunnel to determine static pressure distributions during reentry (TA2F), volume 4
For abstract, see N76-16132
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