4,200 research outputs found
Development of an intelligent hypertext manual for the space shuttle hazardous gas detection system
A computer-based Integrated Knowledge System (IKS), the Intelligent Hypertext Manual (IHM), is being developed for the Space Shuttle Hazardous Gas Detection System (HGDS) at the Huntsville Operations Support Center (HOSC). The IHM stores all HGDS related knowledge and presents them in an interactive and intuitive manner. The IHM's purpose is to provide HGDS personnel with the capabilities of: enhancing the interpretation of real time data; recognizing and identifying possible faults in the Space Shuttle sub-system related to hazardous gas detections; locating applicable documentation related to procedures, constraints, and previous fault histories; and assisting in the training of personnel
Neutrino-Mixing-Generated Lepton Asymmetry and the Primordial He Abundance
It has been proposed that an asymmetry in the electron neutrino sector may be
generated by resonant active-sterile neutrino transformations during Big Bang
Nucleosynthesis (BBN). We calculate the change in the primordial He yield
resulting from this asymmetry, taking into account both the time evolution
of the and distribution function and the spectral
distortions in these. We calculate this change in two schemes: (1) a lepton
asymmetry directly generated by mixing with a lighter right-handed
sterile neutrino ; and (2) a lepton asymmetry generated by a
or transformation
which is subsequently partially converted to an asymmetry in the
sector by a matter-enhanced active-active neutrino
transformation. In the first scheme, we find that the percentage change in
is between -1% and 9% (with the sign depending on the sign of the asymmetry),
bounded by the Majorana mass limit m_{\nu_e}\la 1 eV. In the second scheme,
the maximal percentage reduction in is 2%, if the lepton number asymmetry
in neutrinos is positive; Otherwise, the percentage increase in is \la 5%
for m^2_{\nu_\mu,\nu_\tau}-m^2_{\nu_s}\la 10^4 eV. We conclude that the
change in the primordial He yield induced by a neutrino-mixing-generated
lepton number asymmetry can be substantial in the upward direction, but limited
in the downward direction.Comment: 15 pages, 7 figures, submitted to PR
Evidence That Inhibition of p44/42 Mitogen-activated Protein Kinase Signaling Is a Factor in Proteasome Inhibitor-mediated Apoptosis
The proteasome is emerging as a target for cancer therapy because small molecule inhibitors of its catalytic activity induce apoptosis in both in vitro and in vivo models of human malignancies and are proving to have efficacy in early clinical trials. To further elucidate the mechanism of action of these inhibitors, their impact on signaling through the p44/42 mitogen-activated protein kinase (MAPK) pathway was studied. Proteasome inhibition with either carbobenzoxy-leucyl-leucyl-phenylalaninal or lactacystin led to a loss of dually phosphorylated, activated p44/42 MAPK in A1N4-myc human mammary and MDA-MB-231 breast carcinoma cells in a dose- and time-dependent fashion. This correlated with an induction of the dual specificity MAPK phosphatases (MKP)-1 and -2, and blockade of MKP induction using either actinomycin D or Ro-31-8220 significantly decreased loss of activated p44/42 MAPK. Inhibition of p44/42 MAPK signaling by use of the MAPK kinase inhibitors PD 98059 or U0126, or by use of a dominant negative MAPK construct, enhanced proteasome inhibitor-mediated apoptosis. Conversely, activation of MAPK by epidermal growth factor, or use of a mutant MAPK resistant to MKP-mediated dephosphorylation, inhibited apoptosis. These studies support a role for inactivation of signaling through the p44/42 MAPK pathway in proteasome inhibitor-mediated apoptosis
Field effect two-dimensional electron gases in modulation-doped InSb surface quantum wells
We report on transport characteristics of field effect two-dimensional
electron gases in surface indium antimonide quantum wells. A 5 nm thin -InSb
capping layer is shown to promote the formation of reliable, low resistance
Ohmic contacts to surface InSb quantum wells. High quality single-subband
magnetotransport with clear quantized integer quantum Hall plateaus are
observed to filling factor =1 in magnetic fields of up to B=18 T. We show
that the electron density is gate-tunable, reproducible, and stable from
pinch-off to 410 cm, and peak mobilities exceed 24,000
cm/Vs. Rashba spin-orbit coupling strengths up to 130 meV\r{A} are
obtained through weak anti-localization measurements. An effective mass of
0.019 is determined from temperature-dependent magnetoresistance
measurements, and a g-factor of 41 at a density of 3.610
cm is obtained from coincidence measurements in tilted magnetic fields.
By comparing two heterostructures with and without a doping layer beneath the
quantum well, we find that the carrier density is stable with time when doping
in the ternary AlInSb barrier is not present. Finally, the effect of modulation
doping on structural asymmetry between the two heterostructures is
characterized
The Increase in the Primordial He-4 Yield in the Two-Doublet Four-Neutrino Mixing Scheme
We assess the effects on Big Bang Nucleosynthesis (BBN) of lepton number
generation in the early universe resulting from the two-doublet four-neutrino
mass/mixing scheme. It has been argued that this neutrino mass/mixing
arrangement gives the most viable fit to the existing data. We study full 4 x 4
mixing matrices and show how possible symmetries in these can affect the BBN
He-4 abundance yields. Though there is as yet no consensus on the reliability
of BBN calculations with neutrino flavor mixing, we show that, in the case
where the sign of the lepton number asymmetry is unpredictable, BBN
considerations may pick out specific relationships between mixing angles. In
particular, reconciling the observed light element abundances with a
\bar\nu_\mu \bar\nu_e oscillation interpretation of LSND would allow unique
new constraints on the neutrino mixing angles in this model.Comment: 12 pages, including 4 figures, to appear in Phys. Rev.
Sterile neutrinos and supernova nucleosynthesis
A light sterile neutrino species has been introduced to explain
simultaneously the solar and atmospheric neutrino puzzles and the results of
the LSND experiment, while providing for a hot component of dark matter.
Employing this scheme of neutrino masses and mixings, we show how
matter-enhanced active-sterile neutrino transformation followed by
active-active neutrino transformation can solve robustly the neutron deficit
problem encountered by models of r-process nucleosynthesis associated with
neutrino-heated supernova ejecta.Comment: 29 pages, 3 postscript figures, submitted to Phys. Rev.
Sex differences in release of cardiac troponin T after endurance exercise.
CONTEXT: Post-exercise cardiac troponin release has been extensively described in athletic groups but little attention has been given to any role of sex in mediating this phenomenon. OBJECTIVE: We compared the release of cardiac troponin T (cTnT) after endurance running in training-experience, biological-age and maturity-matched young male and female runners. MATERIALS AND METHODS: Nineteen male (training history: 2.3 ± 1.0 years; mean age: 16.1 ± 1.2 years; Tanner stage: 3.7 ± 0.6) and 19 female (training history: 2.2 ± 1.0 years; mean age: 15.9 ± 1.4 years; Tanner stage: 4.0 ± 0.4) runners performed a 21 km run with "all-out" effort. Serum cTnT levels were assessed at pre-exercise (Pre-ex) and at 4 h post-exercise (Post-ex). RESULTS: At Pre-ex, cTnT concentrations were below the 99th percentile value (10 ng.l(-1)) in 32/38 runners. Post-ex cTnT increased in all subjects but the response was substantially higher (p < 0.05) in males [median (range): 210 (20-1360) ng.l(-1)] than females [median (range): 80 (10-550) ng.l(-1)]. At Post-ex, 95% (95% confidence interval: 75-99%) of males and 63% (95% confidence interval: 41-81%) of females (p < 0.05) had cTnT concentrations above the cut-off for acute myocardial infarction. CONCLUSIONS: The present data suggest that post-exercise cTnT elevation occurs in all runners but is augmented in young male compared to female athletes
Impact of high-intensity interval training and moderate-intensity continuous training on resting and post-exercise cardiac troponin T concentration.
We evaluated the influence of 12 weeks high-intensity interval training (HIIT, repeated 4-min cycling at 90% V̇O2max interspersed with 3-min rest, 200-300 KJ/session, 3-4 days wk-1 ) and work-equivalent moderate-intensity continuous training (MICT, continuous cycling at 60% V̇O2max ) on resting cardiac troponin T (cTnT) as well as exercise-induced cTnT appearance. Forty-eight sedentary obese young women were randomly assigned to HIIT, MICT, or a control group. V̇O2max and body composition were measured before and after training. At baseline, cTnT was assessed using a high-sensitivity assay at rest and immediately, 2 h and 4 h after 45-min cycling at 60% V̇O2max . After a 12-wk training period, cTnT was assessed before and after 45-min cycling at the same relative and absolute intensities as before training. Training led to higher V̇O2max and lower fat mass in both HIIT and MICT (all P < 0.05). Before training, cTnT was significantly elevated in all three groups (35 to 118%, all P < 0.05) with acute exercise. After training both resting and post-exercise cTnT levels (same relative intensity) were similar to pre-training values. In contrast, post-exercise cTnT (same absolute intensity, which represented a smaller exercise stimulus) was not elevated from rest in both HIIT and MICT groups. In conclusion, 12 weeks of either HIIT or MICT largely abolished the elevation of post-exercise cTnT concentration when exercise was performed at the same absolute intensity. There was, however, no impact of training on resting cTnT or post-exercise cTnT appearance for exercise performed at the same relative intensity. This article is protected by copyright. All rights reserved
Competing Ultrafast Energy Relaxation Pathways in Photoexcited Graphene
For most optoelectronic applications of graphene a thorough understanding of
the processes that govern energy relaxation of photoexcited carriers is
essential. The ultrafast energy relaxation in graphene occurs through two
competing pathways: carrier-carrier scattering -- creating an elevated carrier
temperature -- and optical phonon emission. At present, it is not clear what
determines the dominating relaxation pathway. Here we reach a unifying picture
of the ultrafast energy relaxation by investigating the terahertz
photoconductivity, while varying the Fermi energy, photon energy, and fluence
over a wide range. We find that sufficiently low fluence ( 4
J/cm) in conjunction with sufficiently high Fermi energy (
0.1 eV) gives rise to energy relaxation that is dominated by carrier-carrier
scattering, which leads to efficient carrier heating. Upon increasing the
fluence or decreasing the Fermi energy, the carrier heating efficiency
decreases, presumably due to energy relaxation that becomes increasingly
dominated by phonon emission. Carrier heating through carrier-carrier
scattering accounts for the negative photoconductivity for doped graphene
observed at terahertz frequencies. We present a simple model that reproduces
the data for a wide range of Fermi levels and excitation energies, and allows
us to qualitatively assess how the branching ratio between the two distinct
relaxation pathways depends on excitation fluence and Fermi energy.Comment: Nano Letters 201
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