3,994 research outputs found
Radiative, actively cooled panel tests results
The radiative, actively cooled panel designed to withstand a uniform incident heat flux of 136 kW/sq m to a 444 K surface temperature was evaluated. The test program consisted of preliminary static thermal mechanical loading and aerothermal flow tests. Test results are briefly discussed
Extension of the Morris-Shore transformation to multilevel ladders
We describe situations in which chains of N degenerate quantum energy levels,
coupled by time-dependent external fields, can be replaced by independent sets
of chains of length N, N-1,...,2 and sets of uncoupled single states. The
transformation is a generalization of the two-level Morris-Shore transformation
[J.R. Morris and B.W. Shore, Phys. Rev. A 27, 906 (1983)]. We illustrate the
procedure with examples of three-level chains
A Dynamical Study of the Non-Star Forming Translucent Molecular Cloud MBM16: Evidence for Shear Driven Turbulence in the Interstellar Medium
We present the results of a velocity correlation study of the high latitude
cloud MBM16 using a fully sampled CO map, supplemented by new CO
data. We find a correlation length of 0.4 pc. This is similar in size to the
formaldehyde clumps described in our previous study. We associate this
correlated motion with coherent structures within the turbulent flow. Such
structures are generated by free shear flows. Their presence in this non-star
forming cloud indicates that kinetic energy is being supplied to the internal
turbulence by an external shear flow. Such large scale driving over long times
is a possible solution to the dissipation problem for molecular cloud
turbulence.Comment: Uses AAS aasms4.sty macros. Accepted for publication in Ap
Time Minimal Trajectories for a Spin 1/2 Particle in a Magnetic Field
In this paper we consider the minimum time population transfer problem for
the -component of the spin of a (spin 1/2) particle driven by a magnetic
field, controlled along the x axis, with bounded amplitude. On the Bloch sphere
(i.e. after a suitable Hopf projection), this problem can be attacked with
techniques of optimal syntheses on 2-D manifolds. Let be the two
energy levels, and the bound on the field amplitude. For
each couple of values and , we determine the time optimal synthesis
starting from the level and we provide the explicit expression of the time
optimal trajectories steering the state one to the state two, in terms of a
parameter that can be computed solving numerically a suitable equation. For
, every time optimal trajectory is bang-bang and in particular the
corresponding control is periodic with frequency of the order of the resonance
frequency . On the other side, for , the time optimal
trajectory steering the state one to the state two is bang-bang with exactly
one switching. Fixed we also prove that for the time needed to
reach the state two tends to zero. In the case there are time optimal
trajectories containing a singular arc. Finally we compare these results with
some known results of Khaneja, Brockett and Glaser and with those obtained by
controlling the magnetic field both on the and directions (or with one
external field, but in the rotating wave approximation). As byproduct we prove
that the qualitative shape of the time optimal synthesis presents different
patterns, that cyclically alternate as , giving a partial proof of a
conjecture formulated in a previous paper.Comment: 31 pages, 10 figures, typos correcte
Time Averaged Quantum Dynamics and the Validity of the Effective Hamiltonian Model
We develop a technique for finding the dynamical evolution in time of an
averaged density matrix. The result is an equation of evolution that includes
an Effective Hamiltonian, as well as decoherence terms in Lindblad form.
Applying the general equation to harmonic Hamiltonians, we confirm a previous
formula for the Effective Hamiltonian together with a new decoherence term
which should in general be included, and whose vanishing provides the criteria
for validity of the Effective Hamiltonian approach. Finally, we apply the
theory to examples of the AC Stark Shift and Three- Level Raman Transitions,
recovering a new decoherence effect in the latter.Comment: 7 pages, 2 figure
Anticoagulation Management and Heparin Resistance During Cardiopulmonary Bypass: A Survey of Society of Cardiovascular Anesthesiologists Members
We surveyed Society of Cardiovascular Anesthesiologists members regarding anticoagulation practices for cardiopulmonary bypass and attitudes on heparin resistance. Of 550 respondents (18.5% response rate), 74.9% (95% CI, 71.3%-78.5%) used empiric weight-based dosing of heparin, and 70.7% (95% CI, 66.9%-74.5%) targeted an activated clotting time of either 400 or 480 seconds to initiate cardiopulmonary bypass. Of note, 17.1% (95% CI, 13.9%-20.2%) of respondents reported activated clotting time targets lower than those recommended by recent 2018 Society of Thoracic Surgeons/Society of Cardiovascular Anesthesiologists/American Society of Extracorporeal Technology guidelines or failed to monitor heparin effects at all. When heparin resistance was encountered, 54.2% of respondents (95% CI, 50.0%-58.4%) administered antithrombin concentrates as a first-line therapy
Pulse-driven near-resonant quantum adiabatic dynamics: lifting of quasi-degeneracy
We study the quantum dynamics of a two-level system driven by a pulse that
starts near-resonant for small amplitudes, yielding nonadiabatic evolution, and
induces an adiabatic evolution for larger amplitudes. This problem is analyzed
in terms of lifting of degeneracy for rising amplitudes. It is solved exactly
for the case of linear and exponential rising. Approximate solutions are given
in the case of power law rising. This allows us to determine approximative
formulas for the lineshape of resonant excitation by various forms of pulses
such as truncated trig-pulses. We also analyze and explain the various
superpositions of states that can be obtained by the Half Stark Chirped Rapid
Adiabatic Passage (Half-SCRAP) process.Comment: 21 pages, 12 figure
Fermi LAT Gamma-ray Detections of Classical Novae V1369 Centauri 2013 and V5668 Sagittarii 2015
We report the Fermi Large Area Telescope (LAT) detections of high-energy
(>100 MeV) gamma-ray emission from two recent optically bright classical novae,
V1369 Centauri 2013 and V5668 Sagittarii 2015. At early times, Fermi
target-of-opportunity observations prompted by their optical discoveries
provided enhanced LAT exposure that enabled the detections of gamma-ray onsets
beginning ~2 days after their first optical peaks. Significant gamma-ray
emission was found extending to 39-55 days after their initial LAT detections,
with systematically fainter and longer duration emission compared to previous
gamma-ray detected classical novae. These novae were distinguished by multiple
bright optical peaks that encompassed the timespans of the observed gamma rays.
The gamma-ray light curves and spectra of the two novae are presented along
with representative hadronic and leptonic models, and comparisons to other
novae detected by the LAT are discussed.Comment: 13 pages, 6 figures, 4 tables, ApJ accepte
Electrophysiology Practice During COVID-19 Pandemic: A New York Tertiary Hospital Experience
© 2020 Elsevier Inc. As hospitals became overwhelmed during the Covid-19 pandemic in March-May in New York, Cardiology and Electrophysiology (EP) departments rapidly developed protocols for case selection as well modifying the practice of managing the cases. Recommendations by the AHA/HRS as well as American Society of Anesthesiology (ASA) were considered in the multidisciplinary collaborative approach to patient care and personnel safety and the anesthesiology team had an integral role in developing protocols for workflow, care, recovery and transport during these challenging times
The Neon Abundance in the Ejecta of QU Vul From Late-Epoch IR Spectra
We present ground-based SpectroCam-10 mid-infrared, MMT optical, and Spitzer
Space Telescope IRS mid-infrared spectra taken 7.62, 18.75, and 19.38 years
respectively after the outburst of the old classical nova QU Vulpeculae (Nova
Vul 1984 #2). The spectra of the ejecta are dominated by forbidden line
emission from neon and oxygen. Our analysis shows that neon was, at the first
and last epochs respectively, more than 76 and 168 times overabundant by number
with respect to hydrogen compared to the solar value. These high lower limits
to the neon abundance confirm that QU Vul involved a thermonuclear runaway on
an ONeMg white dwarf and approach the yields predicted by models of the
nucleosynthesis in such events.Comment: ApJ 2007 accepted, 18 pages, including 5 figures, 1 tabl
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