1,038 research outputs found
Quantum well behavior of single stacking fault 3C inclusions in 4H-SiC p-i-n diodes studied by ballistic electron emission microscopy
We show that "single" stacking fault 3C inclusions formed in 4H-SiC p-i-n diodes behave as electron quantum wells (QWs) with the QW energy depth of ???0.25 eV below 4H-SiC conduction band minimum, by measuring the Schottky barriers on and away from inclusions with ballistic electron emission microscopy (BEEM). The Schottky barrier on the 4H area ([11-20] oriented) is measured to be essentially the same as (0001) plane studied previously, indicating that the interface pinning effects on both crystal faces are almost identical. Additionally, BEEM current amplitude is observed to be very sensitive to subsurface damage induced by polishing.open91
The evolutionary causes of egg rejection in European thrushes (Turdusspp.): a reply to M. Soler
Neutron time-of-flight measurements of charged-particle energy loss in inertial confinement fusion plasmas
Neutron spectra from secondary ^{3}H(d,n)α reactions produced by an implosion of a deuterium-gas capsule at the National Ignition Facility have been measured with order-of-magnitude improvements in statistics and resolution over past experiments. These new data and their sensitivity to the energy loss of fast tritons emitted from thermal ^{2}H(d,p)^{3}H reactions enable the first statistically significant investigation of charged-particle stopping via the emitted neutron spectrum. Radiation-hydrodynamic simulations, constrained to match a number of observables from the implosion, were used to predict the neutron spectra while employing two different energy loss models. This analysis represents the first test of stopping models under inertial confinement fusion conditions, covering plasma temperatures of k_{B}T≈1-4 keV and particle densities of n≈(12-2)×10^{24} cm^{-3}. Under these conditions, we find significant deviations of our data from a theory employing classical collisions whereas the theory including quantum diffraction agrees with our data
Uncovering Dangerous Cheats: How Do Avian Hosts Recognize Adult Brood Parasites?
BACKGROUND: Co-evolutionary struggles between dangerous enemies (e.g., brood parasites) and their victims (hosts) lead to the emergence of sophisticated adaptations and counter-adaptations. Salient host tricks to reduce parasitism costs include, as front line defence, adult enemy discrimination. In contrast to the well studied egg stage, investigations addressing the specific cues for adult enemy recognition are rare. Previous studies have suggested barred underparts and yellow eyes may provide cues for the recognition of cuckoos Cuculus canorus by their hosts; however, no study to date has examined the role of the two cues simultaneously under a consistent experimental paradigm. METHODOLOGY/PRINCIPAL FINDINGS: We modify and extend previous work using a novel experimental approach--custom-made dummies with various combinations of hypothesized recognition cues. The salient recognition cue turned out to be the yellow eye. Barred underparts, the only trait examined previously, had a statistically significant but small effect on host aggression highlighting the importance of effect size vs. statistical significance. CONCLUSION: Relative importance of eye vs. underpart phenotypes may reflect ecological context of host-parasite interaction: yellow eyes are conspicuous from the typical direction of host arrival (from above), whereas barred underparts are poorly visible (being visually blocked by the upper part of the cuckoo's body). This visual constraint may reduce usefulness of barred underparts as a reliable recognition cue under a typical situation near host nests. We propose a novel hypothesis that recognition cues for enemy detection can vary in a context-dependent manner (e.g., depending on whether the enemy is approached from below or from above). Further we suggest a particular cue can trigger fear reactions (escape) in some hosts/populations whereas the same cue can trigger aggression (attack) in other hosts/populations depending on presence/absence of dangerous enemies that are phenotypically similar to brood parasites and costs and benefits associated with particular host responses
Measurement of the Strong Coupling Constant from Inclusive Jet Production at the Tevatron Collider
We report a measurement of the strong coupling constant, ,
extracted from inclusive jet production in collisions at
1800 GeV. The QCD prediction for the evolution of with
jet transverse energy is tested over the range 40<<450 GeV using
for the renormalization scale. The data show good agreement with QCD in
the region below 250 GeV. In the text we discuss the data-theory comparison in
the region from 250 to 450 GeV. The value of at the mass of the
boson averaged over the range 40<<250 GeV is found to be
. The associated theoretical uncertainties are mainly due to the choice
of renormalization scale (^{+6%}_{-4%}) and input parton distribution
functions (5%).Comment: 7 pages, 3 figures, using RevTeX. Submitted to Physical Review
Letter
Search for Narrow Diphoton Resonances and for gamma-gamma+W/Z Signatures in p\bar p Collisions at sqrt(s)=1.8 TeV
We present results of searches for diphoton resonances produced both
inclusively and also in association with a vector boson (W or Z) using 100
pb^{-1} of p\bar p collisions using the CDF detector. We set upper limits on
the product of cross section times branching ratio for both p\bar
p\to\gamma\gamma + X and p\bar p\to\gamma\gamma + W/Z. Comparing the inclusive
production to the expectations from heavy sgoldstinos we derive limits on the
supersymmetry-breaking scale sqrt{F} in the TeV range, depending on the
sgoldstino mass and the choice of other parameters. Also, using a NLO
prediction for the associated production of a Higgs boson with a W or Z boson,
we set an upper limit on the branching ratio for H\to\gamma\gamma. Finally, we
set a lower limit on the mass of a `bosophilic' Higgs boson (e.g. one which
couples only to \gamma, W, and Z$ bosons with standard model couplings) of 82
GeV/c^2 at 95% confidence level.Comment: 30 pages, 11 figure
Measurement of the p\bar{p}\sqrt{s}$ = 1.8 TeV
We update the measurement of the top production cross section using the CDF
detector at the Fermilab Tevatron. This measurement uses decays to
the final states +jets and +jets. We search for quarks from
decays via secondary-vertex identification or the identification of
semileptonic decays of the and cascade quarks. The background to the
production is determined primarily through a Monte Carlo simulation.
However, we calibrate the simulation and evaluate its uncertainty using several
independent data samples. For a top mass of 175 , we measure
pb and pb using
the secondary vertex and the lepton tagging algorithms, respectively. Finally,
we combine these results with those from other decay channels and
obtain pb.Comment: The manuscript consists of 130 pages, 35 figures and 42 tables in
RevTex. The manuscript is submitted to Physical Review D. Fixed typo in
author lis
Search for the Supersymmetric Partner of the Top-Quark in Collisions at
We report on a search for the supersymmetric partner of the top quark (stop)
produced in events using of
collisions at recorded with the Collider Detector at
Fermilab. In the case of a light stop squark, the decay of the top quark into
stop plus the lightest supersymmetric particle (LSP) could have a significant
branching ratio. The observed events are consistent with Standard Model production and decay. Hence, we set limits on the branching ratio of
the top quark decaying into stop plus LSP, excluding branching ratios above 45%
for a LSP mass up to 40 {\rm GeV/c}.Comment: 11 pages, 4 figure
The c2d Spitzer spectroscopic survey of ices around low-mass young stellar objects II: CO2
This paper presents Spitzer-IRS spectroscopy of the CO2 15.2 micron bending
mode toward a sample of 50 embedded low-mass stars in nearby star-forming
clouds, taken mostly from the ``Cores to Disks (c2d)'' Legacy program. The
average abundance of solid CO2 relative to water in low-mass protostellar
envelopes is 0.32 +/- 0.02, significantly higher than that found in quiescent
molecular clouds and in massive star forming regions. It is found that a
decomposition of all the observed CO2 bending mode profiles requires a minimum
of five unique components. Roughly 2/3 of the CO2 ice is found in a water-rich
environment, while most of the remaining 1/3 is found in a CO environment.
Ground-based observations of solid CO toward a large subset of the c2d sample
are used to further constrain the CO2:CO component and suggest a model in which
low-density clouds form the CO2:H2O component and higher density clouds form
the CO2:CO ice during and after the freeze-out of gas-phase CO. It is suggested
that the subsequent evolution of the CO2 and CO profiles toward low-mass
protostars, in particular the appearance of the splitting of the CO2 bending
mode due to pure, crystalline CO2, is first caused by distillation of the
CO2:CO component through evaporation of CO due to thermal processing to ~20-30
K in the inner regions of infalling envelopes. The formation of pure CO2 via
segregation from the H2O rich mantle may contribute to the band splitting at
higher levels of thermal processing (>50 K), but is harder to reconcile with
the physical structure of protostellar envelopes around low-luminosity objects.Comment: Accepted for Ap
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