62,762 research outputs found
Top-Antitop-Quark Production and Decay Properties at the Tevatron
At the Tevatron, the collider experiments CDF and DO have data sets at their
disposal that comprise a few thousand reconstructed top-antitop-quark pairs and
allow for precision measurements of the cross section as well as production and
decay properties. Besides comparing the measurements to standard model
predictions, these data sets open a window to physics beyond the standard
model. Dedicated analyses look for new heavy gauge bosons, fourth generation
quarks, and flavor-changing neutral currents. In this mini-review the current
status of these measurements is summarized.Comment: Mini-review to be submitted to Mod. Phys. Lett. A, was derived from
the proceedings of the 21st Rencontres de Blois: Windows on the Universe,
Blois, France, 21. - 27. June 2009. 19 pages. 2nd revision: correct a few
minor mistakes, update references
Numerical Investigation of Second Mode Attenuation over Carbon/Carbon Surfaces on a Sharp Slender Cone
We have carried out axisymmetric numerical simulations of a spatially
developing hypersonic boundary layer over a sharp 7-half-angle cone
at inspired by the experimental investigations by Wagner (2015).
Simulations are first performed with impermeable (or solid) walls with a
one-time broadband pulse excitation applied upstream to determine the most
convectively-amplified frequencies resulting in the range 260kHz -- 400kHz,
consistent with experimental observations of second-mode instability waves.
Subsequently, we introduce harmonic disturbances via continuous periodic
suction and blowing at 270kHz and 350kHz. For each of these forcing frequencies
complex impedance boundary conditions (IBC), modeling the acoustic response of
two different carbon/carbon (C/C) ultrasonically absorptive porous surfaces,
are applied at the wall. The IBCs are derived as an output of a pore-scale
aeroacoustic analysis -- the inverse Helmholtz Solver (iHS) -- which is able to
return the broadband real and imaginary components of the surface-averaged
impedance. The introduction of the IBCs in all cases leads to a significant
attenuation of the harmonically-forced second-mode wave. In particular, we
observe a higher attenuation rate of the introduced waves with frequency of
350kHz in comparison with 270kHz, and, along with the iHS impedance results, we
establish that the C/C surfaces absorb acoustic energy more effectively at
higher frequencies.Comment: AIAA-SciTech 201
Hot-wire anemometry in hypersonic helium flow
Hot-wire anemometry techniques are described that have been developed and used for hypersonic-helium-flow studies. The short run time available dictated certain innovations in applying conventional hot-wire techniques. Some examples are given to show the application of the techniques used. Modifications to conventional equipment are described, including probe modifications and probe heating controls
Abdominopelvic SplenosisāAn Unusual Cause of Tenesmus
Splenosis is a rare condition defined as seeding and autotransplantation of splenic tissue, typically after blunt
abdominal trauma (e.g. from road traffic collision). Sites of splenosis ranging from intrathoracic to intrapelvic have
been reported, and symptoms vary greatly depending on the site and size of lesions. We present the use of Tc-99m
sulphur colloid SPECT/CT in diagnosing a case of multiple abdominopelvic splenosis as the cause of new-onset
tenesmus and constipation, which was initially thought to be due to colorectal malignancy, 47 years following the
initial abdominal trauma
Probing Pauli Blocking Factors in Quantum Pumps with Broken Time-Reversal Symmetry
A recently demonstrated quantum electron pump is discussed within the
framework of photon-assisted tunneling. Due to lack of time-reversal symmetry,
different results are obtained for the pump current depending on whether or not
final-state Pauli blocking factors are used when describing the tunneling
process. Whilst in both cases the current depends quadratically on the driving
amplitude for moderate pumping, a marked difference is predicted for the
temperature dependence. With blocking factors the pump current decreases
roughly linearly with temperature until k_B T ~ \hbar\omega is reached, whereas
without them it is unaffected by temperature, indicating that the entire Fermi
sea participates in the electronic transport.Comment: 4 pages in RevTex4 (beta4), 6 figures; status: to appear in PR
(WP 2017-02) The Great Recession and Public Education
We examine the impact of the Great Recession on K-12 education finance and employment and generate five key results. First, nearly 300,000 school employees lost their jobs. Second, schools that were heavily dependent financially on state governments were particularly vulnerable to the recession. Third local revenues from the property tax actually increased during the recession, primarily because millage rates rose in response to declining property values. Fourth, inequality in school spending rose sharply during the Great Recession. Fifth, the federal governmentās efforts to shield education from some of the worst effects of the recession achieved their major goal
Dynamics of a two-level system coupled with a quantum oscillator in the very strong coupling limit
The time-dependent behavior of a two-level system interacting with a quantum
oscillator system is analyzed in the case of a coupling larger than both the
energy separation between the two levels and the energy of quantum oscillator
(, where is the frequency of the
transition between the two levels, is the frequency of the
oscillator, and is the coupling between the two-level system and the
oscillator). Our calculations show that the amplitude of the expectation value
of the oscillator coordinate decreases as the two-level system undergoes the
transition from one level to the other, while the transfer probability between
the levels is staircase-like. This behavior is explained by the interplay
between the adiabatic and the non-adiabatic regimes encountered during the
dynamics with the system acting as a quantum counterpart of the Landau-Zener
model. The transition between the two levels occurs as long as the expectation
value of the oscillator coordinate is driven close to zero. On the contrary, if
the initial conditions are set such that the expectation values of the
oscillator coordinate are far from zero, the system will remain locked on one
level.Comment: 4 pages, 4 figures, to be published in Physical Review
Impact for Agents
Impact for agents. Most of the agent research community has been predicting greater impact for years and many of us have been working to help the process along. Yet the tremendous growth on the research front has not been met with
Superstructure high efficiency photovoltaics
A novel class of photovoltaic cascade structures is introduced which features multijunction upper subcells. These superstructure high efficiency photovoltaics (SHEP's) exhibit enhanced upper subcell spectral response because of the additional junctions which serve to reduce bulk recombination losses by decreasing the mean collection distance for photogenerated minority carriers. Two possible electrical configurations were studied and compared: a three-terminal scheme that allows both subcells to be operated at their individual maximum power points and a two-terminal configuration with an intercell ohmic contact for series interconnection. The three-terminal devices were found to be superior both in terms of beginning-of-life expectancy and radiation tolerance. Realistic simulations of three-terminal AlGaAs/GaAs SHEP's show that one sun AMO efficiencies in excess of 26 percent are possible
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