888 research outputs found
Modal test of the Viking orbiter
A modal test of the Orbiter Development Test Modal (ODTM) has been conducted to verify, or update, the mathematical model used for load analysis. The approach used to assure the quality and validity of the experimental data is defined, the modal test is described, and test results are presented and compared with analysis results. Good correlation between the analyses and the test data assures an acceptable model for incorporation into the mathematical model of the launch system
Chemical Mapping of Excitons in Halide Double Perovskites
Halide double perovskites are an emerging class of semiconductors with
tremendous chemical and electronic diversity. While their bandstructure
features can be understood from frontier-orbital models, chemical intuition for
optical excitations remains incomplete. Here, we use \textit{ab initio}
many-body perturbation theory within the and the Bethe-Salpeter Equation
approach to calculate excited-state properties of a representative range of
CsBBCl double perovskites. Our calculations reveal that double
perovskites with different combinations of B and B cations display a broad
variety of electronic bandstructures and dielectric properties, and form
excitons with binding energies ranging over several orders of magnitude. We
correlate these properties with the orbital-induced anisotropy of
charge-carrier effective masses and the long-range behavior of the dielectric
function, by comparing with the canonical conditions of the Wannier-Mott model.
Furthermore, we derive chemically intuitive rules for predicting the nature of
excitons in halide double perovskites using electronic structure information
obtained from computationally inexpensive DFT calculations
Mapping Charge-Transfer Excitations in Bacteriochlorophyll Dimers from First Principles
Photoinduced charge-transfer excitations are key to understand the primary
processes of natural photosynthesis and for designing photovoltaic and
photocatalytic devices. In this paper, we use Bacteriochlorophyll dimers
extracted from the light harvesting apparatus and reaction center of a
photosynthetic purple bacterium as model systems to study such excitations
using first-principles numerical simulation methods. We distinguish four
different regimes of intermolecular coupling, ranging from very weakly coupled
to strongly coupled, and identify the factors that determine the energy and
character of charge-transfer excitations in each case. We also construct an
artificial dimer to systematically study the effects of intermolecular distance
and orientation on charge-transfer excitations, as well as the impact of
molecular vibrations on these excitations. Our results provide design rules for
tailoring charge-transfer excitations in Bacteriochloropylls and related
photoactive molecules, and highlight the importance of including
charge-transfer excitations in accurate models of the excited-state structure
and dynamics of Bacteriochlorophyll aggregates
Coordination-driven magnetic-to-nonmagnetic transition in manganese doped silicon clusters
The interaction of a single manganese impurity with silicon is analyzed in a
combined experimental and theoretical study of the electronic, magnetic, and
structural properties of manganese-doped silicon clusters. The structural
transition from exohedral to endohedral doping coincides with a quenching of
high-spin states. For all geometric structures investigated, we find a similar
dependence of the magnetic moment on the manganese coordination number and
nearest neighbor distance. This observation can be generalized to manganese
point defects in bulk silicon, whose magnetic moments fall within the observed
magnetic-to-nonmagnetic transition, and which therefore react very sensitively
to changes in the local geometry. The results indicate that high spin states in
manganese-doped silicon could be stabilized by an appropriate lattice
expansion
Pain Management in Patients with Cancer: Focus on Opioid Analgesics
Cancer pain is generally treated with pharmacological measures, relying on using opioids alone or in combination with adjuvant analgesics. Weak opioids are used for mild-to-moderate pain as monotherapy or in a combination with nonopioids. For patients with moderate-to-severe pain, strong opioids are recommended as initial therapy rather than beginning treatment with weak opioids. Adjunctive therapy plays an important role in the treatment of cancer pain not fully responsive to opioids administered alone (ie, neuropathic, bone, and visceral colicky pain). Supportive drugs should be used wisely to prevent and treat opioids’ adverse effects. Understanding the pharmacokinetics, pharmacodynamics, interactions, and cautions with commonly used opioids can help determine appropriate opioid selection for individual cancer patients
Interferon beta 1b following natalizumab discontinuation: one year, randomized, prospective, pilot trial
Background: Natalizumab (NTZ) discontinuation leads to multiple sclerosis reactivation. The objective of this study is to compare disease activity in MS patients who continued on NTZ treatment to those who were switched to subcutaneous interferon 1b (IFNB) treatment. Methods: 1-year randomized, rater-blinded, parallel-group, pilot study (ClinicalTrial.gov ID: NCT01144052). Relapsing remitting MS patients on NTZ for ≥12 months who had been free of disease activity on this therapy (no relapses and disability progression for ≥6 months, no gadolinium-enhancing lesions on baseline MRI) were randomized to NTZ or IFNB. Primary endpoint was time to first on-study relapse. Additional clinical, MRI and safety parameters were assessed. Analysis was based on intention to treat. Results: 19 patients (NTZ n=10; IFNB n=9) with similar baseline characteristics were included. 78% of IFNB treated patients remained relapse free (NTZ group: 100%), and 25% remained free of new T2 lesions (NTZ group: 62.5%). While time to first on-study relapse was not significantly different between groups (p=0.125), many secondary clinical and radiological endpoints (number of relapses, proportion of relapse free patients, number of new T2 lesions) showed a trend, or were significant (new T2 lesions at month 6) in favoring NTZ. Conclusions: De-escalation therapy from NTZ to IFNB over 1 year was associated with some clinical and radiological disease recurrence. Overall no major safety concerns were observed
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Beyond Crossing Fibers: Bootstrap Probabilistic Tractography Using Complex Subvoxel Fiber Geometries
Diffusion magnetic resonance imaging fiber tractography is a powerful tool for investigating human white matter connectivity in vivo. However, it is prone to false positive and false negative results, making interpretation of the tractography result difficult. Optimal tractography must begin with an accurate description of the subvoxel white matter fiber structure, includes quantification of the uncertainty in the fiber directions obtained, and quantifies the confidence in each reconstructed fiber tract. This paper presents a novel and comprehensive pipeline for fiber tractography that meets the above requirements. The subvoxel fiber geometry is described in detail using a technique that allows not only for straight crossing fibers but for fibers that curve and splay. This technique is repeatedly performed within a residual bootstrap statistical process in order to efficiently quantify the uncertainty in the subvoxel geometries obtained. A robust connectivity index is defined to quantify the confidence in the reconstructed connections. The tractography pipeline is demonstrated in the human brain
Neurofilament results for the phase II neuroprotection study of phenytoin in optic neuritis
Background:
A randomized trial of phenytoin in acute optic neuritis (ON) demonstrated a 30% reduction in retinal nerve fiber layer (RNFL) loss with phenytoin versus placebo. Here we present the corresponding serum neurofilament analyses.
Methods:
Eighty-six acute ON cases were randomized to receive phenytoin (4–6 mg/kg/day) or placebo for 3 months, and followed up for 6 months. Serum was collected at baseline, 3 and 6 months for analysis of neurofilament heavy chain (NfH) and neurofilament light chain (NfL).
Results:
Sixty-four patients had blood sampling. Of these, 58 and 56 were available at 3 months, and 55 and 54 were available at 6 months for NfH and NfL, respectively. There was no significant correlation between serum NfH and NfL at the time points tested. For NfH, the difference in mean placebo – phenytoin was −44 pg/ml at 3 months (P = 0.019) and −27 pg/ml at 6 months (P = 0.234). For NfL, the difference was 1.4 pg/ml at 3 months (P = 0.726) and −1.6 pg/ml at 6 months (P = 0.766).
Conclusions:
At 3 months, there was a reduction in NfH, but not NFL, in the phenytoin versus placebo group, while differences at 6 months were not statistically significant. This suggests a potential neuroprotective role for phenytoin in acute ON, with the lower NfH at 3 months, when levels secondary to degeneration of the anterior visual pathway are still elevated, but not at 6 months, when levels have normalized
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