164 research outputs found
Derivatives of spin dynamics simulations
We report analytical equations for the derivatives of spin dynamics
simulations with respect to pulse sequence and spin system parameters. The
methods described are significantly faster, more accurate and more reliable
than the finite difference approximations typically employed. The resulting
derivatives may be used in fitting, optimization, performance evaluation and
stability analysis of spin dynamics simulations and experiments.
Keywords: NMR, EPR, simulation, analytical derivatives, optimal control, spin
chemistry, radical pair.Comment: Accepted by The Journal of Chemical Physic
Utilization of care among drug resistant epilepsy patients with symptoms of anxiety and depression
AbstractPurposeEpilepsy patients have a significantly higher rate of anxiety and depression than the general population, and psychiatric disease is particularly prevalent among drug resistant epilepsy patients. Symptoms of anxiety and depression might serve as a barrier to appropriate epilepsy care.The aim of this study was to determine if drug resistant epilepsy patients with symptoms of anxiety and/or depression receive different epilepsy management than controls.MethodWe identified 83 patients with drug resistant focal epilepsy seen at the Penn Epilepsy Center. Upon enrollment, all patients completed 3 self-report scales and a neuropsychiatric inventory and were grouped into those with symptoms of anxiety and/or depression and controls. Each patient's medical records were retrospectively reviewed for 1â2 years, and objective measures of outpatient and inpatient epilepsy management were assessed.ResultsAt baseline, 53% (n=43) of patients screened positive for symptoms of anxiety and/or depression. The remaining 47% (n=38) served as controls. Patients with anxiety and/or depression symptoms had more missed outpatient visits per year compared to controls (median 0.84 vs. 0.48, p=0.02). Patients with symptoms of both anxiety and depression were more likely to undergo an inpatient admission or procedure (56% vs. 24%, p=0.02).ConclusionFor most measures of epilepsy management, symptoms of anxiety and/or depression do not alter epilepsy care; however, drug resistant epilepsy patients with anxiety and/or depression symptoms may be more likely to miss outpatient appointments, and those with the highest burden of psychiatric symptoms may be admitted more frequently for inpatient services compared to controls
HST Observations of Heavy Elements in Metal-Poor Galactic Halo Stars
We present new abundance determinations of neutron-capture elements Ge, Zr,
Os, Ir, and Pt in a sample of 11 metal-poor (-3.1 <= [Fe/H] <= -1.6) Galactic
halo giant stars, based on Hubble Space Telescope UV and Keck I optical
high-resolution spectroscopy. The stellar sample is dominated by r-process-rich
stars such as the well-studied CS 22892-052 and bd+173248, but also includes
the r-process-poor, bright giant HD 122563. Our results demonstrate that
abundances of the 3rd r-process peak elements Os, Ir and Pt in these metal-poor
halo stars are very well-correlated among themselves, and with the abundances
of the canonical r-process element Eu (determined in other studies), thus
arguing for a common origin or site for r-process nucleosynthesis of heavier
(Z>56) elements. However, the large (and correlated) scatters of
[Eu,Os,Ir,Pt/Fe] suggests that the heaviest neutron-capture r-process elements
are not formed in all supernovae. In contrast, the Ge abundances of all program
stars track their Fe abundances, very well. An explosive process on iron-peak
nuclei (e.g., the alpha-rich freeze-out in supernovae), rather than neutron
capture, appears to have been the dominant synthesis mechanism for this element
at low metallicities -- Ge abundances seem completely uncorrelated with Eu.Comment: 35 pages, 5 tables, 7 figures; To appear in the Astrophysical Journa
The Rise of the s-Process in the Galaxy
From newly-obtained high-resolution, high signal-to-noise ratio spectra the
abundances of the elements La and Eu have been determined over the stellar
metallicity range -3<[Fe/H]<+0.3 in 159 giant and dwarf stars. Lanthanum is
predominantly made by the s-process in the solar system, while Eu owes most of
its solar system abundance to the r-process. The changing ratio of these
elements in stars over a wide metallicity range traces the changing
contributions of these two processes to the Galactic abundance mix. Large
s-process abundances can be the result of mass transfer from very evolved
stars, so to identify these cases, we also report carbon abundances in our
metal-poor stars. Results indicate that the s-process may be active as early as
[Fe/H]=-2.6, alalthough we also find that some stars as metal-rich as [Fe/H]=-1
show no strong indication of s-process enrichment. There is a significant
spread in the level of s-process enrichment even at solar metallicity.Comment: 64 pages, 15 figures; ApJ 2004 in pres
The Chemical Composition and Age of the Metal-Poor Halo Star BD +17^\circ 3248
We have combined new high-resolution spectra obtained with the Hubble Space
Telescope (HST) and ground-based facilities to make a comprehensive new
abundance analysis of the metal-poor, halo star BD +17^\circ 3248. We have
detected the third r-process peak elements osmium, platinum, and (for the first
time in a metal-poor star) gold, elements whose abundances can only be reliably
determined using HST. Our observations illustrate a pattern seen in other
similar halo stars with the abundances of the heavier neutron-capture elements,
including the third r-process peak elements, consistent with a scaled solar
system r-process distribution. The abundances of the lighter neutron-capture
elements, including germanium and silver, fall below that same scaled solar
r-process curve, a result similar to that seen in the ultra-metal-poor star CS
22892--052. A single site with two regimes or sets of conditions, or perhaps
two different sites for the lighter and heavier neutron-capture elements, might
explain the abundance pattern seen in this star. In addition we have derived a
reliable abundance for the radioactive element thorium. We tentatively identify
U II at 3859 A in the spectrum of BD +17^\circ 3248, which makes this the
second detection of uranium in a very metal-poor halo star. Our combined
observations cover the widest range in proton number (from germanium to
uranium) thus far of neutron-capture elements in metal-poor Galactic halo
stars. Employing the thorium and uranium abundances in comparison with each
other and with several stable elements, we determine an average
cosmochronological age for BD +17^\circ 3248 of 13.8 +/- 4 Gyr, consistent with
that found for other similar metal-poor halo stars.Comment: 58 pages, 4 tables, 11 figures; To appear in ApJ Typo correcte
Long-Term Assessment of the Effects of COVID-19 and Isolation Care on Survivor Disability and Anxiety
We conducted an assessment of disability, anxiety, and other life impacts of COVID-19 and isolation care in a unique cohort of individuals. These included both community admissions to a university hospital as well as some of the earliest international aeromedical evacuees. Among an initial 16 COVID-19 survivors that were interviewed 6-12 months following their admission into isolation care, perception of their isolation care experience was related to their reporting of long-term consequences. However, anxiety and disability assessed with standard scores had no relationship with each other. Both capture of the isolation care experience and caution relying on single scoring systems for assessing long-term consequences in survivors are important considerations for on-going and future COVID-19 and other pandemic survivor research
Improved Laboratory Transition Probabilities for Neutral Chromium and Re-determination of the Chromium Abundance for the Sun and Three Stars
Branching fraction measurements from Fourier transform spectra in conjunction
with published radiative lifetimes are used to determine transition
probabilities for 263 lines of neutral chromium. These laboratory values are
employed to derive a new photospheric abundance for the Sun: log (Cr
I) = 5.640.01 (). These Cr I solar abundances do
not exhibit any trends with line strength nor with excitation energy and there
were no obvious indications of departures from LTE. In addition, oscillator
strengths for singly-ionized chromium recently reported by the FERRUM Project
are used to determine: log (Cr II) = 5.770.03 (). Transition probability data are also applied to the spectra of three
stars: HD 75732 (metal-rich dwarf), HD 140283 (metal-poor subgiant), and CS
22892-052 (metal-poor giant). In all of the selected stars, Cr I is found to be
underabundant with respect to Cr II. The possible causes for this abundance
discrepancy and apparent ionization imbalance are discussed.Comment: 44 pages, 6 figure
The Extremely Metal-Poor, Neutron-Capture-Rich Star CS 22892-052: A Comprehensive Abundance Analysis
High-resolution spectra obtained with three ground-based facilities and the
Hubble Space Telescope (HST) have been combined to produce a new abundance
analysis of CS 22892-052, an extremely metal-poor giant with large relative
enhancements of neutron-capture elements. A revised model stellar atmosphere
has been derived with the aid of a large number of Fe-peak transitions,
including both neutral and ionized species of six elements.Several elements,
including Mo, Lu, Au, Pt and Pb, have been detected for the first time in CS
22892-052, and significant upper limits have been placed on the abundances of
Ga, Ge, Cd, Sn, and U in this star. In total, abundance measurements or upper
limits have been determined for 57 elements, far more than previously possible.
New Be and Li detections in CS 22892-052 indicate that the abundances of both
these elements are significantly depleted compared to unevolved main-sequence
turnoff stars of similar metallicity. Abundance comparisons show an excellent
agreement between the heaviest n-capture elements (Z >= 56) and scaled solar
system r-process abundances, confirming earlier results for CS 22892-052 and
other metal-poor stars. New theoretical r-process calculations also show good
agreement with CS 22892-052 abundances as well as the solar r-process abundance
components.The abundances of lighter elements (40<= Z <= 50), however, deviate
from the same scaled abundance curves that match the heavier elements,
suggesting different synthesis conditions or sites for the low-mass and
high-mass ends of the abundance distribution. The detection of Th and the upper
limit on the U abundance together imply a lower limit of 10.4 Gyr on the age of
CS 22892-052, quite consistent with the Th/Eu age estimate of 12.8 +/- ~= 3
Gyr. An average of several chronometric ratios yields an age 14.2 +/- ~= 3 Gyr.Comment: 65 pages, 8 figures, 10 tables; To appear in the Astrophysical
Journa
Spatial heterogeneity of habitat suitability for Rift Valley fever occurrence in Tanzania: an ecological niche modelling approach
Despite the long history of Rift Valley fever (RVF) in Tanzania, extent of its suitable habitat in the country remains unclear. In this study we investigated potential effects of temperature, precipitation, elevation, soil type, livestock density, rainfall pattern, proximity to wild animals, protected areas and forest on the habitat suitability for RVF occurrence in Tanzania. Presence-only records of 193 RVF outbreak locations from 1930 to 2007 together with potential predictor variables were used to model and map the suitable habitats for RVF occurrence using ecological niche modelling. Ground-truthing of the model outputs was conducted by comparing the levels of RVF virus specific antibodies in cattle, sheep and goats sampled from locations in Tanzania that presented different predicted habitat suitability values. Habitat suitability values for RVF occurrence were higher in the northern and central-eastern regions of Tanzania than the rest of the regions in the country. Soil type and precipitation of the wettest quarter contributed equally to habitat suitability (32.4% each), followed by livestock density (25.9%) and rainfall pattern (9.3%). Ground-truthing of model outputs revealed that the odds of an animal being seropositive for RVFV when sampled from areas predicted to be most suitable for RVF occurrence were twice the odds of an animal sampled from areas least suitable for RVF occurrence (95% CI: 1.43, 2.76, p < 0.001). The regions in the northern and central-eastern Tanzania were more suitable for RVF occurrence than the rest of the regions in the country. The modelled suitable habitat is characterised by impermeable soils, moderate precipitation in the wettest quarter, high livestock density and a bimodal rainfall pattern. The findings of this study should provide guidance for the design of appropriate RVF surveillance, prevention and control strategies which target areas with these characteristics
- âŠ