393 research outputs found
Approximation of the acoustic radiation impedance of a cylindrical pipe
Useful approximation formulae for radiation impedance are given for the
reflection coefficients of both infinitely flanged and unflanged rigid-walled
cylindrical ducts. The expressions guarantee that simple but necessary physical
and mathematical principles are met, like hermitian symmetry for the reflection
coefficient (identical behaviour of positive and negative frequencies) and
causality for the impulse response. A non causal but more accurate expression
is also proposed that is suitable for frequency-domain applications. The
formulae are obtained by analytical and numerical fitting to reference results
from Levine & Schwinger for the unflanged case and extracted from the radiation
impedance matrix given by Zorumski for the infinite flanged case.Comment: Journal of Sound and Vibration (2008) accepte
BeppoSAX observations of the X-ray binary pulsar 4U1626-67
We report on observations of the low-mass X-ray binary 4U1626-67 performed
during the BeppoSAX Science Verification Phase. We present the broad-band
0.1-100 keV pulse averaged spectrum, that is well fit by a two-component
function: a 0.27 +/- 0.02 keV blackbody and an absorbed power law with a photon
index of 0.89 +/- 0.02. A very deep and narrow absorption feature at 38 keV,
attributable to electron cyclotron resonance, is clearly visible in the
broad-band spectrum. It corresponds to a neutron star magnetic field strength
of 3.3 x 10^{12} G. The 4U1626-67 pulse profiles show a dramatic dependance on
energy: the transition between the low energy (E<10 keV) "bi-horned" shape to
the high-energy (E>10 keV) sinusoidal profile is clearly visible in our data.
The modulation index shows a monotonic increase with energy.Comment: 4 pages, 2 figures. Uses espcrc2.sty (included). To appear in
Proceedings of "The Active X-ray Sky: Results from BeppoSAX and Rossi-XTE
Instanton propagator and instanton induced processes in scalar model
The propagator in the instanton background in the
scalar model in four dimensions is studied.Leading and sub-leading terms of its
asymptotics for large momenta and its on-shell double residue are calculated
analytically. These results are applied to the analysis of the initial-state
and initial-final-state corrections and the calculation of the next-to-leading
(propagator) correction to the exponent of the cross section of instanton
induced multiparticle scattering processes.Comment: 44 pages, 7 postscript figures, LaTe
Resonant Photonic Quasicrystalline and Aperiodic Structures
We have theoretically studied propagation of exciton-polaritons in
deterministic aperiodic multiple-quantum-well structures, particularly, in the
Fibonacci and Thue-Morse chains. The attention is concentrated on the
structures tuned to the resonant Bragg condition with two-dimensional
quantum-well exciton. The superradiant or photonic-quasicrystal regimes are
realized in these structures depending on the number of the wells. The
developed theory based on the two-wave approximation allows one to describe
analytically the exact transfer-matrix computations for transmittance and
reflectance spectra in the whole frequency range except for a narrow region
near the exciton resonance. In this region the optical spectra and the
exciton-polariton dispersion demonstrate scaling invariance and self-similarity
which can be interpreted in terms of the ``band-edge'' cycle of the trace map,
in the case of Fibonacci structures, and in terms of zero reflection
frequencies, in the case of Thue-Morse structures.Comment: 13 pages, 9 figures, submitted to Phys. Rev.
Mental health and substance use screening in HIV primary care before and during the early COVID-19 pandemic
Background: Mental health and substance use disorders disproportionately affect people with HIV (PWH), and may have been exacerbated during COVID-19. The Promoting Access to Care Engagement (PACE) trial was designed to assess the effectiveness of electronic screening for mental health and substance use in HIV primary care and enrolled PWH from October 2018 to July 2020. Our objective here was to compare screening rates and results for PWH before (October 2018 – February 2020) and early in the COVID-19 pandemic (March-July 2020). Methods: Adult (≥ 18 years) PWH from 3 large HIV primary care clinics in a US-based integrated healthcare system were offered electronic screening online or via in-clinic tablet computer every 6 months. Screening completion and results (for depression, suicidal ideation, anxiety, and substance use) were analyzed using logistic regression with generalized estimating equations to estimate prevalence ratios (PR) before and after the start of the regional COVID-19 shelter-in-place orders on March 17, 2020. Models adjusted for demographics (age, sex, race/ethnicity), HIV risk factors (men who have sex with men, injection drug use, heterosexual, other), medical center, and modality of screening completion (online or tablet). We conducted qualitative interviews with providers participating in the intervention to evaluate how the pandemic impacted patient care. Results: Of 8,954 eligible visits, 3,904 completed screenings (420 during COVID, 3,484 pre-COVID), with lower overall completion rates during COVID (38% vs. 44%). Patients completing screening during COVID were more likely to be White (63% vs. 55%), male (94% vs. 90%), and MSM (80% vs., 75%). Adjusted PRs comparing COVID and pre-COVID (reference) were 0.70 (95% CI), 0.92 (95% CI), and 0.54 (95% CI) for tobacco use, any substance use, and suicidal ideation, respectively. No significant differences were found by era for depression, anxiety, alcohol, or cannabis use. These results were in contrast to provider-reported impressions of increases in substance use and mental health symptoms. Conclusion: Findings suggest PWH had modest declines in screening rates early in the COVID-19 pandemic which may have been affected by the shift to telemedicine. There was no evidence that mental health problems and substance use increased for PWH in primary care. Trial registration: NCT03217058 (First registration date: 7/13/2017); https://clinicaltrials.gov/ct2/show/NCT03217058
A Framework for Organizational Compliance Management Tactics
Abstract. Organizational compliance with laws, industrial standards, procedures and enterprise architectures has become a highly relevant topic for both practitio-ners and academics. However, both the fundamental insights into compliance as a concept and the tactics for bringing an organization into a compliant state have been described in a fragmented manner. Using literature from various disciplines, this paper presents two contributions. First, it describes the fundamental concepts regarding compliance. Second, it presents a framework in which the various tactics for achieving organizational compliance can be positioned
Pion, kaon, proton and anti-proton transverse momentum distributions from p+p and d+Au collisions at GeV
Identified mid-rapidity particle spectra of , , and
from 200 GeV p+p and d+Au collisions are reported. A
time-of-flight detector based on multi-gap resistive plate chamber technology
is used for particle identification. The particle-species dependence of the
Cronin effect is observed to be significantly smaller than that at lower
energies. The ratio of the nuclear modification factor () between
protons and charged hadrons () in the transverse momentum
range GeV/c is measured to be
(stat)(syst) in minimum-bias collisions and shows little
centrality dependence. The yield ratio of in minimum-bias d+Au
collisions is found to be a factor of 2 lower than that in Au+Au collisions,
indicating that the Cronin effect alone is not enough to account for the
relative baryon enhancement observed in heavy ion collisions at RHIC.Comment: 6 pages, 4 figures, 1 table. We extended the pion spectra from
transverse momentum 1.8 GeV/c to 3. GeV/
Origins of the Ambient Solar Wind: Implications for Space Weather
The Sun's outer atmosphere is heated to temperatures of millions of degrees,
and solar plasma flows out into interplanetary space at supersonic speeds. This
paper reviews our current understanding of these interrelated problems: coronal
heating and the acceleration of the ambient solar wind. We also discuss where
the community stands in its ability to forecast how variations in the solar
wind (i.e., fast and slow wind streams) impact the Earth. Although the last few
decades have seen significant progress in observations and modeling, we still
do not have a complete understanding of the relevant physical processes, nor do
we have a quantitatively precise census of which coronal structures contribute
to specific types of solar wind. Fast streams are known to be connected to the
central regions of large coronal holes. Slow streams, however, appear to come
from a wide range of sources, including streamers, pseudostreamers, coronal
loops, active regions, and coronal hole boundaries. Complicating our
understanding even more is the fact that processes such as turbulence,
stream-stream interactions, and Coulomb collisions can make it difficult to
unambiguously map a parcel measured at 1 AU back down to its coronal source. We
also review recent progress -- in theoretical modeling, observational data
analysis, and forecasting techniques that sit at the interface between data and
theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue
connected with a 2016 ISSI workshop on "The Scientific Foundations of Space
Weather." 44 pages, 9 figure
Demonstration of the temporal matter-wave Talbot effect for trapped matter waves
We demonstrate the temporal Talbot effect for trapped matter waves using
ultracold atoms in an optical lattice. We investigate the phase evolution of an
array of essentially non-interacting matter waves and observe matter-wave
collapse and revival in the form of a Talbot interference pattern. By using
long expansion times, we image momentum space with sub-recoil resolution,
allowing us to observe fractional Talbot fringes up to 10th order.Comment: 17 pages, 7 figure
Kaon Production and Kaon to Pion Ratio in Au+Au Collisions at \snn=130 GeV
Mid-rapidity transverse mass spectra and multiplicity densities of charged
and neutral kaons are reported for Au+Au collisions at \snn=130 GeV at RHIC.
The spectra are exponential in transverse mass, with an inverse slope of about
280 MeV in central collisions. The multiplicity densities for these particles
scale with the negative hadron pseudo-rapidity density. The charged kaon to
pion ratios are and
for the most central collisions. The ratio is lower than the same
ratio observed at the SPS while the is higher than the SPS result.
Both ratios are enhanced by about 50% relative to p+p and +p
collision data at similar energies.Comment: 6 pages, 3 figures, 1 tabl
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