1,427 research outputs found
Relativistic fine structure oscillator strengths for Li-like ions: C IV - Si XII, S XIV, Ar XVI, Ca XVIII, Ti XX, Cr XXII, and Ni XXVI
Ab initio calculations including relativistic effects employing the
Breit-Pauli R-matrix (BPRM) method are reported for fine structure energy
levels and oscillator strengths upto n = 10 and 0.leq. l .leq.9 for 15 Li-like
ions: C IV, N V, O VI, F VII, Ne VIII, Na IX, Mg X, Al XI, Si XII, S XIV, Ar
XVI, Ca XIII, Ti XX, Cr XXII, and Ni XXVI. About one hundred bound fine
structure energy levels of total angular momenta, 1/2 .leq. J .leq. 17/2 of
even and odd parities, total orbital angular momentum, 0 .leq L .leq. 9 and
spin multiplicity (2S+1) = 2, 4 are considered for each ion. The levels provide
almost 900 dipole allowed and intercombination bound-bound transitions. The
BPRM method enables consideration of large set of transitions with uniform
accuracy compared to the best available theoretical methods. The CC
eigenfunction expansion for each ion includes the lowest 17 fine structure
energy levels of the core configurations 1s^2, 1s2s, 1s2p, 1s3s, 1s3p, and
1s3d. The calculated energies of the ions agree with the measured values to
within 1% for most levels. The transition probabilities show good agreement
with the best available calculated values. The results provide the largest sets
of energy levels and transition rates for the ions and are expected to be
useful in the analysis of X-ray and EUV spectra from astrophysical sources.Comment: 16 pgs., to appear in Astronomy and Astrophysic
Recombination Rate Coefficients for KLL Di-electronic Satellite Lines of Fe XXV and Ni XXVII
The unified method for total electron-ion recombination is extended to study
the dielectronic satellite (DES) lines. These lines, formed from radiative
decay of autoionizing states, are highly sensitive temperature diagnostics of
astrophysical and laboratory plasma sources. The computation of the unified
recombination rates is based on the relativistic Breit-Pauli R-matrix method
and close coupling approximation. Extending the theoretical formulation
developed earlier we present recombination rate coefficients for the 22
satellite lines of KLL complexes of helium-like Fe XXV and Ni XXVII. The
isolated resonance approximation, commonly used throughout plasma modeling,
treats these resonances essentially as bound features except for dielectronic
capture into, and autoionization out of, these levels. A line profile or cross
section shape is often assumed. On the other hand, by including the coupling
between the autoionizing and continuum channels, the unified method gives the
intrinsic spectrum of DES lines which includes not only the energies and
strengths, but also the natural line or cross section shapes. A formulation is
presented to derive autoionization rates from unified resonance strengths and
enable correspondence with the isolated resonance approximation. While the
rates compare very well with existing rates for the strong lines to <20%, the
differences for weaker DES lines are larger. We also illustrate the application
of the present results to the analysis of K ALPHA complexes observed in
high-temperature X-ray emission spectra of Fe XXV and Ni XXVII. There are
considerable differences with previous results in the total KLL intensity for
Fe XXV at temperatures below the temperature of maximum abundance in coronal
equilibrium. (Abbreviated Abstract)Comment: 21 pages, 5 figures, to appear in Physica Script
Electron impact ionization of metastable 2P-state hydrogen atoms in the coplanar geometry
AbstractTriple differential cross sections (TDCS) for the ionization of metastable 2P-state hydrogen atoms by electrons are calculated for various kinematic conditions in the asymmetric coplanar geometry. In this calculation, the final state is described by a multiple-scattering theory for ionization of hydrogen atoms by electrons. Results show qualitative agreement with the available experimental data and those of other theoretical computational results for ionization of hydrogen atoms from ground state, and our first Born results. There is no available other theoretical results and experimental data for ionization of hydrogen atoms from the 2P state. The present study offers a wide scope for the experimental study for ionization of hydrogen atoms from the metastable 2P state
K-shell dielectronic resonances in photoabsorption: differential oscillator strengths for Li-like C IV, O VI, and Fe XXIV
Recently X-ray photoabsorption in KLL resonances of O VI was predicted
[Pradhan, Astrophys.J. Lett. 545, L165 (2000)], and detected by the Chandra
X-ray Observatory [Lee et al, Astrophys. J. {\it Lett.}, submitted].
The required resonance oscillator strengths f_r, are evaluated in terms of
the differential oscillator strength df/de that relates bound and continuum
absorption. We present the f_r values from radiatively damped and undamped
photoionization cross sections for Li-like C,O, and Fe calculated using
relativistic close coupling Breit-Pauli R-matrix method. The KLL resonances of
interest here are: 1s2p (^3P^o) 2s [^4P^o_{1/2,3/2}, ^2P^o_{1/2,3/2}] and 1s2p
(^1P^o) 2s [^2P^o_{1/2,3/2}]. The KLL photoabsorption resonances in Fe XXIV are
fully resolved up to natural autoionization profiles for the first time. It is
demonstrated that the undamped f_r independently yield the resonance radiative
decay rates, and thereby provide a precise check on the resolution of
photoionization calculations in general. The predicted photoabsorption features
should be detectable by the X-ray space observatories and enable column
densities in highly ionized astrophysical plasmas to be determined from the
calculated f_r. The dielectronic satellites may appear as redward broadening of
resonances lines in emission and absorption.Comment: 9 pages, 2 figurs, Phys. Rev. A, Rapid Communication (submitted
GABA-B receptor function in healthy volunteers, a pharmacokinetic and pharmacodynamic study of two doses of baclofen compared to placebo
AIMS AND HYPOTHESIS To assess the subjective and objective effects of baclofen on brain function in healthy volunteers. BACKGROUND Recent evidence suggests baclofen, a γ-aminobutyric acid type B (GABA-B) receptor agonist, reduces alcohol consumption and craving and promotes abstinence in alcoholics. However, characterisation of the GABA-B receptor system in clinical addiction is limited, and it is unclear why some patients require, or tolerate, higher doses to treat alcoholism. This study assesses the effects of baclofen on brain function in healthy volunteers to inform future studies investigating the sensitivity of GABA-B receptors in alcohol addiction. METHODS Eight healthy male volunteers completed a double blind randomised 3-way cross over study, receiving oral placebo (vitamin C 100mg), 10mg and 60mg baclofen. Subjective and objective measurements were taken at baseline (before medication) and at +30mins, 1, 2, 3, 4 and 6 hours after dosing. Objective measures included blood plasma samples, heart rate and blood pressure. Subjective measures included; the Subjective High Assessment Questionnaire (SHAS), visual analogue scales for sleepy, relaxed, tense and alert and a motor coordination task (zig-zag task). Pharmacokinetic data was obtained using liquid chromatography mass-spectrometry (LC-MS) to measure plasma baclofen concentrations. RESULTS 60mg Baclofen showed changes in subjective measures peaking at 2 hours post dosing compared with placebo, including a significant increase (p<0.05) in total SHAS scores with individual items, including feeling ‘drunk or intoxicated’, effects of alcohol and ‘muddled or confused’ particular affected.. Systolic blood pressure was significantly increased (p<0.05) at the 2 hours post 60mg dose. For both 10mg and 60mg baclofen, peak plasma concentration was achieved 60 minutes post dose. Pharmacokinetic data will be presented. There were no significant changes in these measures between 10mg Baclofen and placebo. CONCLUSIONS The objective and subjective measures used in this study are able to differentiate between placebo and 60mg baclofen. These findings will inform further research investigating the sensitivity of GABA-B receptors in alcohol addiction
Electron-Ion Recombination Rate Coefficients and Photoionization Cross Sections for Astrophysically Abundant Elements. IX. Ni XXVI and Ni XXVII for UV and X-ray modeling
The inverse processes of photoionization and electron-ion recombination of
(hnu + Ni XXVI --> Ni XXVII + e and (hnu + Ni XXVII --> Ni XXVIII + e) are
studied using the unified method for the total recombination. The method
subsumes both the radiative and di-electronic recombination processes and
enables self-consistent sets of results for photoionization and electron-ion
recombination by using the same wavefunction expansion. Photoionization cross
sections (sigma_PI), recombination cross sections (sigma_{RC}), recombination
collision strengths (Omega_{RC}), and recombination rate coefficients
(alpha_{RC}) are obtained for ionization balance and spectral analysis of UV
and X-ray lines. Level-specific photoionization cross sections and
recombination rates are presented to enable accurate computation of
recombination-cascade matrices for all fine structure levels n(SLJ) up to n <=
10: 98 bound fine structure levels of Ni XXVI with 0 <= l <= 9, 0 <= L <= 11,
1/2 <= J <= 17/2, and 198 levels of Ni XXVII with 0 <= l <= 9, 0 <= L <= 14, 0
<= J <= 10. Total alpha_{RC} for Ni XXVI and Ni XXVII are compared with the
existing values with very good agreement. Total recombination rate coefficients
for the hydrogen-like recombined ion, Ni XXVIII, are also presented. The
calculations are carried out in relativistic Breit-Pauli R-matrix (BPRM)
approximation with inclusion of radiation damping of resonances. With
consideration of all details of the processes, the results, which include the
level specific sigma_{PI} and alpha_{R} calculated for the first time, should
be the most accurate for these ions.Comment: 27 pages, 10 figures, to appear in Astrophys. J. Supplement
Photoionization cross sections of O II, O III, O IV, and O V: benchmarking R-matrix theory and experiments
For crucial tests between theory and experiment, ab initio close coupling
calculations are carried out for photoionization of O II, O III, O IV, O V. The
relativistic fine structure and resonance effects are studied using the
R-matrix and its relativistic variant the Breit Pauli R-matrix (BPRM)
approximation. Detailed comparison is made with high resolution experimental
measurements carried out in three different set-ups: Advanced Light Source at
Berkeley, and synchrotron radiation experiments at University of Aarhus and
University of Paris-Sud. The comparisons illustrate physical effects in
photoionization such as (i) fine structure, (ii) resolution, and (iii)
metastable components. Photoionization cross sections sigma{PI} of the ground
and a few low lying excited states of these ions obtained in the experimental
spectrum include combined features of these states. Theoretically calculated
resonances need to be resolved with extremely fine energy mesh for precise
comparison. In addition, prominent resonant features are observed in the
measured spectra from transitions allowed with relativistic fine structure, but
not in LS coupling. The sigma_{PI} are obtained for ground and metastable (i)
2s^22p^3(^4S^o, ^2D^o, ^2P^o) states of O II, (ii) 2s^22p^2(^3P,^1D,^1S) and
2s2p^3(^5S^o) states of O III, (iii) 2s^22p(^2P^o_J) and 2s2p^2(^4P_J) levels
of O IV, and (iv) 2s^2(^1S) and 2s2p(^3P^o,^1P^o) states of O V. It is found
that resonances in ground and metastable cross sections can be a diagnostic of
experimental beam composition, with potential ap plications to astrophysical
and laboratory plasma environments.Comment: 27 pages, 7 figs., submitted to Phys. Rev. A., text with high
resolution figures at http://www.astronomy.ohio-state.edu/~pradhan/Oions.p
Validated method for the quantification of buprenorphine in postmortem blood using solid-phase extraction and two-dimensional gas chromatography–mass spectrometry
A highly sensitive and fully validated method was developed for the quantification of buprenorphine in postmortem blood. After a two-step protein precipitation process using acetonitrile, buprenorphine was purified using mixed-mode (C8/cation exchange) solid-phase extraction cartridges. Endogenous water-soluble compounds and lipids were removed from the cartridges before the samples were eluted, concentrated and derivatized using N-methyl-N-trimethylsilyltrifluoroacetamide. The samples were analyzed using two-dimensional gas chromatography–mass spectrometry (2D GC–MS) in selective ion-monitoring mode. A low polarity Rxi®-5MS (30 m × 0.25 mm I.D. × 0.25 µm) was used as the primary column and the secondary column was a mid-polarity Rxi® -17Sil MS (15 m × 0.32 mm I.D. × 0.25 µm). The assay was linear from 1.0 to 50.0 ng/mL (r2 > 0.99; n = 6). Intraday (n = 6) and interday (n = 9) imprecisions (percentage relative standard deviation, % RSD) were <5% and the average recovery was 60%. The limit of detection (LOD) of the method was 0.5 ng/mL and limit of quantification was 1.0 ng/mL. 2D GC–MS improved the LOD of buprenorphine by 20-fold compared with analysis on a conventional GC–MS. The method was highly selective with no interference from endogenous compounds or from 62 commonly encountered drugs. To prove method applicability to forensic postmortem cases, 14 authentic postmortem blood samples were analyzed
Misuse and mortality related to gabapentin and pregabalin are being under-estimated: a two-year post-mortem population
Due to the rise in their misuse and associated mortality, the UK government is reclassifying gabapentin (GBP) and pregabalin (PGL) to Class C controlled drugs from April 2019. However, it is impossible to gauge the extent of their use with current post-mortem toxicological screening, where GBP and PGL are only screened for if they are mentioned in the case documents. This study determines the prevalence of GBP and PGL, the potential extent of their under-reporting and poly-drug use in a post-mortem population. Between 1 January 2016 and 31 December 2017, 3,750 deceased from Coroners’ cases in London and South East England underwent a routine drugs screen and a specific screen for GBP and PGL. The prevalence of both drugs was determined in the cohort and the subcategories of heroin users and non-heroin-users. The prevalence of both drugs was compared to tramadol (Class C drug). Case documents were reviewed to investigate the under-reporting of GBP and PGL and poly-drug use. Of 3,750 samples analyzed, 118 (3.1%) were positive for GBP, 229 (6.1%) for PGL and 120 (3.2%) were positive for tramadol. If routine analysis without additional screening of GBP and PGL had been performed in this cohort, GBP would have been under-reported by 57.6% (P < 0.0001) and PGL by 53.7% (P < 0.0001) in deaths. The most common drug group observed with GBP and PGL was non-heroin-related opioids at 60.2% and 64.6%, respectively. In total 354 deceased (9.4%) were heroin users. GBP was positive in 23 (6.5%) of these cases and PGL was positive in 69 (19.5%). The prevalence of PGL in heroin users (19.5%) was 4.1 times greater than in non-heroin users (4.7%) (P < 0.0001). GBP and PGL are being significantly under reported in fatalities. Both drugs are extensively used with opioids. The prevalence of PGL in heroin users is highly significant
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