11,736 research outputs found
Optical imaging of resonant electrical carrier injection into individual quantum dots
We image the micro-electroluminescence (EL) spectra of self-assembled InAs
quantum dots (QDs) embedded in the intrinsic region of a GaAs p-i-n diode and
demonstrate optical detection of resonant carrier injection into a single QD.
Resonant tunneling of electrons and holes into the QDs at bias voltages below
the flat-band condition leads to sharp EL lines characteristic of individual
QDs, accompanied by a spatial fragmentation of the surface EL emission into
small and discrete light- emitting areas, each with its own spectral
fingerprint and Stark shift. We explain this behavior in terms of Coulomb
interaction effects and the selective excitation of a small number of QDs
within the ensemble due to preferential resonant tunneling paths for carriers.Comment: 4 page
Glial and axonal body fluid biomarkers are related to infarct volume, severity, and outcome.
Body fluid biomarkers of central nervous system damage may help improve the prognostic and diagnostic accuracy in ischemic stroke. We studied 53 patients. Stroke severity and outcome was rated using the National Institutes of Health Stroke Scale and modified Rankin scale. Ferritin, S100B, and NfH were measured in cerebrospinal fluid (CSF) and serum. Infarct volume was calculated from T2W images. CSF S100B (median 1.00 ng/mL) and CSF ferritin (10.0 ng/mL) levels were elevated in patients with stroke compared with control subjects (0.62 ng/mL, P < .0001; 2.34 ng/mL, P < .0001). Serum S100B (0.09 ng/mL) was higher in patients with stroke compared with control subjects (0.01 ng/mL). CSF S100B levels were higher in patients with a cardioembolic stroke (2.88 ng/mL) than in those with small-vessel disease (0.89 ng/mL, P < .05). CSF S100B levels correlated with the National Institutes of Health Stroke Scale score on admission (R = 0.56, P < .01) and the stroke volume (R = 0.44, P = .01). CSF S100B and NfH-SMI35 levels correlated with outcome on the modified Rankin scale. CSF S100B levels were related to stroke severity and infarct volume and highest in cardioembolic stroke
Spin fluctuations and superconductivity in powders of Fe_1+xTe_0.7Se_0.3 as a function of interstitial iron concentration
Using neutron inelastic scattering, we investigate the role of interstitial
iron on the low-energy spin fluctuations in powder samples of
Fe_{1+x}Te_{0.7}Se_{0.3}. We demonstrate how combining the principle of
detailed balance along with measurements at several temperatures allows us to
subtract both temperature-independent and phonon backgrounds from S(Q,\omega)
to obtain purely magnetic scattering. For small values of interstitial iron
(x=0.009(3)), the sample is superconducting (T_{c}=14 K) and displays a spin
gap of 7 meV peaked in momentum at wave vector q_{0}=(\pi,\pi) consistent with
single crystal results. On populating the interstitial iron sites, the
superconducting volume fraction decreases and we observe a filling in of the
low-energy magnetic fluctuations and a decrease of the characteristic wave
vector of the magnetic fluctuations. For large concentrations of interstitial
iron (x=0.048(2)) where the superconducting volume fraction is minimal, we
observe the presence of gapless spin fluctuations at a wave vector of
q_{0}=(\pi,0). We estimate the absolute total moment for the various samples
and find that the amount of interstitial iron does not change the total
magnetic spectral weight significantly, but rather has the effect of shifting
the spectral weight in Q and energy. These results show that the
superconducting and magnetic properties can be tuned by doping small amounts of
iron and are suggestive that interstitial iron concentration is also a
controlling dopant in the Fe_{1+x}Te_{1-y}Se_{y} phase diagram in addition to
the Te/Se ratio.Comment: (10 pages, 8 figures, to be published in Phys. Rev. B
Chemical equilibrium study in nucleus-nucleus collisions at relativistic energies
We present a detailed study of chemical freeze-out in nucleus-nucleus
collisions at beam energies of 11.6, 30, 40, 80 and 158A GeV. By analyzing
hadronic multiplicities within the statistical hadronization approach, we have
studied the strangeness production as a function of centre of mass energy and
of the parameters of the source. We have tested and compared different versions
of the statistical model, with special emphasis on possible explanations of the
observed strangeness hadronic phase space under-saturation. We show that, in
this energy range, the use of hadron yields at midrapidity instead of in full
phase space artificially enhances strangeness production and could lead to
incorrect conclusions as far as the occurrence of full chemical equilibrium is
concerned. In addition to the basic model with an extra strange quark
non-equilibrium parameter, we have tested three more schemes: a two-component
model superimposing hadrons coming out of single nucleon-nucleon interactions
to those emerging from large fireballs at equilibrium, a model with local
strangeness neutrality and a model with strange and light quark non-equilibrium
parameters. The behaviour of the source parameters as a function of colliding
system and collision energy is studied. The description of strangeness
production entails a non-monotonic energy dependence of strangeness saturation
parameter gamma_S with a maximum around 30A GeV. We also present predictions of
the production rates of still unmeasured hadrons including the newly discovered
Theta^+(1540) pentaquark baryon.Comment: 36 pages, 14 figures. Revised version published in Phys. Rev. C:
title changed, one paragraph added in section 2, other typos correcte
PAHs and star formation in the HII regions of nearby galaxies M83 and M33
We present mid-infrared (MIR) spectra of HII regions within star-forming
galaxies M83 and M33. Their emission features are compared with Galactic and
extragalactic HII regions, HII-type galaxies, starburst galaxies, and
Seyfert/LINER type galaxies. Our main results are as follows: (i) the M33 and
M83 HII regions lie in between Seyfert/LINER galaxies and HII-type galaxies in
the 7.7/11.3 - 6.2/11.3 plane, while the different sub-samples exhibiting
different 7.7/6.2 ratios; (ii) Using the NASA Ames PAH IR Spectroscopic
database, we demonstrate that the 6.2/7.7 ratio does not effectively track PAH
size, but the 11.3/3.3 PAH ratio does; (iii) variations on the 17 m PAH
band depends on object type; however, there is no dependence on metallicity for
both extragalactic HII regions and galaxies; (iv) the PAH/VSG intensity ratio
decreases with the hardness of the radiation field and galactocentric radius
(Rg), yet the ionization alone cannot account for the variation seen in all of
our sources; (v) the relative strength of PAH features does not change
significantly with increasing radiation hardness, as measured through the
[NeIII]/[NeII] ratio and the ionization index; (vi) We present PAH SFR
calibrations based on the tight correlation between the 6.2, 7.7, and 11.3
m PAH luminosities with the 24 m luminosity and the combination of
the 24 m and H luminosity; (vii) Based on the total luminosity
from PAH and FIR emission, we argue that extragalactic HII regions are more
suitable templates in modeling and interpreting the large scale properties of
galaxies compared to Galactic HII regions.Comment: 26 pages, 24 figures, 6 tables. Accepted for publication in MNRA
A scalable, high-speed measurement-based quantum computer using trapped ions
We describe a scalable, high-speed, and robust architecture for
measurement-based quantum-computing with trapped ions. Measurement-based
architectures offer a way to speed-up operation of a quantum computer
significantly by parallelizing the slow entangling operations and transferring
the speed requirement to fast measurement of qubits. We show that a 3D cluster
state suitable for fault-tolerant measurement-based quantum computing can be
implemented on a 2D array of ion traps. We propose the projective measurement
of ions via multi-photon photoionization for nanosecond operation and discuss
the viability of such a scheme for Ca ions.Comment: 4 pages, 3 figure
Herschel PACS and SPIRE spectroscopy of the Photodissociation Regions associated with S 106 and IRAS 23133+6050
Photodissociation regions (PDRs) contain a large fraction of all of the
interstellar matter in galaxies. Classical examples include the boundaries
between ionized regions and molecular clouds in regions of massive star
formation, marking the point where all of the photons energetic enough to
ionize hydrogen have been absorbed. In this paper we determine the physical
properties of the PDRs associated with the star forming regions IRAS 23133+6050
and S 106 and present them in the context of other Galactic PDRs associated
with massive star forming regions. We employ Herschel PACS and SPIRE
spectroscopic observations to construct a full 55-650 {\mu}m spectrum of each
object from which we measure the PDR cooling lines, other fine- structure
lines, CO lines and the total far-infrared flux. These measurements are then
compared to standard PDR models. Subsequently detailed numerical PDR models are
compared to these predictions, yielding additional insights into the dominant
thermal processes in the PDRs and their structures. We find that the PDRs of
each object are very similar, and can be characterized by a two-phase PDR model
with a very dense, highly UV irradiated phase (n 10^6 cm^(-3), G
10^5) interspersed within a lower density, weaker radiation field phase
(n 10^4 cm^(-3), G 10^4). We employed two different numerical
models to investigate the data, firstly we used RADEX models to fit the peak of
the CO ladder, which in conjunction with the properties derived yielded
a temperature of around 300 K. Subsequent numerical modeling with a full PDR
model revealed that the dense phase has a filling factor of around 0.6 in both
objects. The shape of the CO ladder was consistent with these components
with heating dominated by grain photoelectric heating. An extra excitation
component for the highest J lines (J > 20) is required for S 106.Comment: 20 pages, 10 figures, A&A Accepte
Different environmental variables predict body and brain size evolution in Homo
Increasing body and brain size constitutes a key macro-evolutionary pattern in the hominin lineage, yet the mechanisms behind these changes remain debated. Hypothesized drivers include environmental, demographic, social, dietary, and technological factors. Here we test the influence of environmental factors on the evolution of body and brain size in the genus Homo over the last one million years using a large fossil dataset combined with global paleoclimatic reconstructions and formalized hypotheses tested in a quantitative statistical framework. We identify temperature as a major predictor of body size variation within Homo, in accordance with Bergmann’s rule. In contrast, net primary productivity of environments and long-term variability in precipitation correlate with brain size but explain low amounts of the observed variation. These associations are likely due to an indirect environmental influence on cognitive abilities and extinction probabilities. Most environmental factors that we test do not correspond with body and brain size evolution, pointing towards complex scenarios which underlie the evolution of key biological characteristics in later Homo.Introduction Results - Approach of power analysis and linear regressions - Power analysis of synthetic data - Analysis of fossil data Discussion Methods - Body and brain size database - Climate reconstructions - Synthetic datasets and power analysi
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