11,940 research outputs found
Resonant Tunneling Spin Pump
The resonant tunneling spin pump is a proposed semiconductor device that would generate spin-polarized electron currents. The resonant tunneling spin pump would be a purely electrical device in the sense that it would not contain any magnetic material and would not rely on an applied magnetic field. Also, unlike prior sources of spin-polarized electron currents, the proposed device would not depend on a source of circularly polarized light. The proposed semiconductor electron-spin filters would exploit the Rashba effect, which can induce energy splitting in what would otherwise be degenerate quantum states, caused by a spin-orbit interaction in conjunction with a structural-inversion asymmetry in the presence of interfacial electric fields in a semiconductor heterostructure. The magnitude of the energy split is proportional to the electron wave number. Theoretical studies have suggested the possibility of devices in which electron energy states would be split by the Rashba effect and spin-polarized currents would be extracted by resonant quantum-mechanical tunneling
Electron-Spin Filters Would Offer Spin Polarization Greater than 1
A proposal has been made to develop devices that would generate spin-polarized electron currents characterized by polarization ratios having magnitudes in excess of 1. Heretofore, such devices (denoted, variously, as spin injectors, spin polarizers, and spin filters) have typically offered polarization ratios having magnitudes in the approximate range of 0.01 to 0.1. The proposed devices could be useful as efficient sources of spin-polarized electron currents for research on spintronics and development of practical spintronic devices
The smallest sets of points not determined by their X-rays
Let be an -point set in with
and . A (discrete) X-ray of
in direction gives the number of points of on each line parallel to
. We define as the minimum number for which
there exist directions (pairwise linearly independent and
spanning ) such that two -point sets in exist
that have the same X-rays in these directions. The bound
has been observed many times in the
literature. In this note we show
for . For the
cases and , , this
represents the first upper bound on that is polynomial
in . As a corollary we derive bounds on the sizes of solutions to both the
classical and two-dimensional Prouhet-Tarry-Escott problem. Additionally, we
establish lower bounds on that enable us to prove a
strengthened version of R\'enyi's theorem for points in
HST/COS Observations of the Quasar Q0302-003: Probing the He II Reionization Epoch and QSO Proximity Effects
Q0302-003 () was the first quasar discovered that showed
a He II Gunn-Peterson trough, a sign of incomplete helium reionization at . We present its HST/Cosmic Origins Spectrograph far-UV medium-resolution
spectrum, which resolves many spectral features for the first time, allowing
study of the quasar itself, the intergalactic medium, and quasar proximity
effects. Q0302-003 has a harder intrinsic extreme-UV spectral index than
previously claimed, as determined from both a direct fit to the spectrum
(yielding ) and the helium-to-hydrogen ion ratio in the
quasar's line-of-sight proximity zone. Intergalactic absorption along this
sightline shows that the helium Gunn-Peterson trough is largely black in the
range , apart from ionization due to local sources, indicating
that helium reionization has not completed at these redshifts. However, we
tentatively report a detection of nonzero flux in the high-redshift trough when
looking at low-density regions, but zero flux in higher-density regions. This
constrains the He II fraction to be a few percent, suggesting helium
reionization has progressed substantially by . The Gunn-Peterson
trough recovers to a He II Ly forest at . We confirm a
transmission feature due to the ionization zone around a quasar just
off the sightline, and resolve the feature for the first time. We discover a
similar such feature possibly caused by a luminous quasar further
from the sightline, which suggests that this quasar has been luminous for >34
Myr.Comment: ApJ accepted version; 20 pages, 16 figure
Histopathological correlation of 11C-choline PET scans for target volume definition in radical prostate radiotherapy
Abstract not availableJoe H. Chang, Daryl Lim Joon, Sze Ting Lee, Sylvia J. Gong, Andrew M. Scott, Ian D. Davis, David Clouston, Damien Bolton, Christopher S. Hamilton, Vincent Kho
Why are wasteyutes a ting?
This paper examines lexical enregisterment through TH/DH-stopping in Multicultural Toronto English (MTE), a multiethnolect emergent in the Greater Toronto Area. Sociolinguistic interview data from young MTE speakers reveals an overall ~10% rate of stopping, with teenage males being the primary stoppers. However, despite the presence of stopping in the vernacular of most speakers, certain terms referring to character archetypes - e.g. wasteyutes, mandem - have become sites of enregisterment of TH/DH-stopping in MTE rather than enregisterment of stopping in more frequent words or of stopping itself. We argue that this is because these lexical items implement reflexive tropes, as speakers thought to be stoppers are those who might be labeled wasteyutes or mandem: young, male, suburban, typically non-white, and typically low status. As such, performance of these stereotypical personae fosters indexical linking between sound (TH/DH-stopping) and culturally salient identities (wasteyutes, mandem), cementing enregisterment of these terms in MTE
Nerve commitment in Hydra. I. Role of morphogenetic signals
The kinetics of nerve commitment during head regeneration in Hydra were investigated using a newly developed assay for committed cells. Committed nerve precursors were assayed by their ability to continue nerve differentiation following explanation of small pieces of tissue. Committed nerve precursors appear at the site of regeneration within 6 hr after cutting and increase rapidly. The increase is localized to the site of regeneration and does not occur at proximal sites in the body column of the regenerate. The increase is delayed about 8–12 hr when regeneration occurs at sites lower in the body column. The results show, furthermore, that redistribution of committed precursors does not play a major role in the pattern of nerve differentiation during regeneration. Since the increase in committed nerves coincides with the increase in morphogenetic potential of the regenerating tissue, the results strengthen the idea that morphogenetic signals are involved directly in the control of nerve commitment in Hydra
AGN Driven Weather and Multiphase Gas in the Core of the NGC 5044 Galaxy Group
A deep Chandra observation of the X-ray bright group, NGC 5044, shows that
the central region of this group has been strongly perturbed by repeated AGN
outbursts. These recent AGN outbursts have produced many small X-ray cavities,
cool filaments and cold fronts. We find a correlation between the coolest X-ray
emitting gas and the morphology of the Ha filaments. The Ha filaments are
oriented in the direction of the X-ray cavities, suggesting that the warm gas
responsible for the Halpha emission originated near the center of NGC 5044 and
was dredged up behind the buoyant, AGN-inflated X-ray cavities. A detailed
spectroscopic analysis shows that the central region of NGC 5044 contains
spatially varying amounts of multiphase gas. The regions with the most
inhomogeneous gas temperature distribution tend to correlate with the extended
235 MHz and 610 MHz radio emission detected by the GMRT. This may result from
gas entrainment within the radio emitting plasma or mixing of different
temperature gas in the regions surrounding the radio emitting plasma by AGN
induced turbulence. Accounting for the effects of multiphase gas, we find that
the abundance of heavy elements is fairly uniform within the central 100 kpc,
with abundances of 60-80% solar for all elements except oxygen, which has a
significantly sub-solar abundance. In the absence of continued AGN outbursts,
the gas in the center of NGC 5044 should attain a more homogeneous distribution
of gas temperature through the dissipation of turbulent kinetic energy and heat
conduction in approximately 10e8 yr. The presence of multiphase gas in NGC 5044
indicates that the time between recent AGN outbursts has been less than
approximately 10e8 yr
The WARPS survey - IV: The X-ray luminosity-temperature relation of high redshift galaxy clusters
We present a measurement of the cluster X-ray luminosity-temperature relation
out to high redshift (z~0.8). Combined ROSAT PSPC spectra of 91 galaxy clusters
detected in the Wide Angle ROSAT Pointed Survey (WARPS) are simultaneously fit
in redshift and luminosity bins. The resulting temperature and luminosity
measurements of these bins, which occupy a region of the high redshift L-T
relation not previously sampled, are compared to existing measurements at low
redshift in order to constrain the evolution of the L-T relation. We find a
best fit to low redshift (z1 keV, to be L proportional
to T^(3.15\pm0.06). Our data are consistent with no evolution in the
normalisation of the L-T relation up to z~0.8. Combining our results with ASCA
measurements taken from the literature, we find eta=0.19\pm0.38 (for Omega_0=1,
with 1 sigma errors) where L_Bol is proportional to (1 + z)^eta T^3.15, or
eta=0.60\pm0.38 for Omega_0=0.3. This lack of evolution is considered in terms
of the entropy-driven evolution of clusters. Further implications for
cosmological constraints are also discussed.Comment: 11 pages, 7 figures, accepted for publication in MNRA
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