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

Halogen vacancy migration at surfaces of CsPbBr₃perovskites:Insights from density functional theory

Migration of halogen vacancies is one of the primary sources of phase segregation and material degradation in lead-halide perovskites. Here we use first principles density functional theory to compare migration energy barriers and paths of bromine vacancies in the bulk and at a (001) surface of cubic CsPbBr3. Our calculations indicate that surfaces might facilitate bromine vacancy migration in these perovskites, due to their soft structure that allows for bond lengths variations larger than in the bulk. We calculate the migration energy for axial-to-axial bromine vacancy migration at the surface to be only half of the value in the bulk. Furthermore, we study the effect of modifying the surface with four different alkali halide monolayers, finding an increase of the migration barrier to almost the bulk value for the NaCl-passivated system. Migration energies are found to be correlated to the lattice mismatch between the CsPbBr3 surface and the alkali halide monolayer. Our calculations suggest that surfaces might play a significant role in mediating vacancy migration in halide perovskites, a result with relevance for perovskite nanocrystals with large surface-to-volume ratios. Moreover, we propose viable ways for suppressing this undesirable process through passivation with alkali halide salts.</p

Workshop on computer applications in water management: proceedings of the 1995 workshop

Compiled and edited by L. Ahuja, J. Leppert, K. Rojas, E. Seely.Also published as: Great Plains Agricultural Council publication, no. 154.Includes bibliographical references.Presented at the Workshop on computer applications in water management: proceedings of the 1995 workshop held on May 23-25, 1995 at Colorado State University in Fort Collins, Colorado

Effects of Small Increases in Corticosterone Levels on Morphology, Immune Function, and Feather Development

Stressors encountered during avian development may affect an individual’s phenotype, including immunocompetence, growth, and feather quality. We examined effects of simulated chronic low-level stress on American kestrel (Falco sparverius) nestlings. Continuous release of corticosterone, a hormone involved in the stress response, can model chronic stress in birds. We implanted 13-d-old males with either corticosterone-filled implants or shams and measured their growth, immune function, and feather coloration.We found no significant differences between groups at the end of the weeklong exposure period in morphometrics (mass, tarsus, wing length, and asymmetry), immunocompetence (cutaneous immunity, heterophil/lymphocyte ratio, and humoral immunity), or feather coloration. One week subsequent to implant removal, however, differences were detected. Sham-implanted birds had significantly longer wings and a reduced level of cutaneous immune function compared with those of birds given corticosterone-filled implants. Therefore, increases of only 2 ng/mL in basal corticosterone titer can have small but measurable effects on subsequent avian development

Effects of Clinically Used Antioxidants in Experimental Pneumococcal Meningitis

Reactive oxygen intermediates mediate brain injury in bacterial meningitis. Several anti-oxidant drugs are clinically available, including N-acetylcysteine (NAC), deferoxamine (DFO), and trylizad-mesylate (TLM). The present study evaluated whether these antioxidants are beneficial in a model of pneumococcal meningitis. Eleven-day-old rats were infected intracisternally with Streptococcus pneumoniae and randomized to intraperitoneal treatment every 8 h with NAC (200 mg/kg), DFO (100 mg/kg), TLM (10 mg/kg), or saline (250 μL). TLM-treated animals showed a significantly reduced mortality compared with controls (P < .03). Meningitis led to extensive cortical injury at 22 ± 2.2 h after infection (median, 14.6% of cortex; range, 0-61.1%). Injury was significantly (P < .01) reduced to 1.1% (range, 0-34.6%) by NAC, to 2.3% (range, 0-19.6%) by DFO, and to 0.2% (range, 0-36.9%) by TLM (the difference was not significant among the 3 groups). None of the drugs reduced hippocampal injury. Thus, several clinically used antioxidants reduced cortical injury in experimental pneumococcal meningiti

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

Matrix Metalloproteinase (MMP)-8 and MMP-9 in Cerebrospinal Fluid during Bacterial Meningitis: Association with Blood-Brain Barrier Damage and Neurological Sequelae

To evaluate the spectrum and regulation of matrix metalloproteinases (MMPs) in bacterial meningitis (BM), concentrations of MMP-2, MMP-3, MMP-8, and MMP-9 and endogenous inhibitors of metalloproteinases (TIMP-1 and TIMP-2) were measured in the cerebrospinal fluid (CSF) of 27 children with BM. MMP-8 and MMP-9 were detected in 91% and 97%, respectively, of CSF speci-mens from patients but were not detected in control patients. CSF levels of MMP-9 were higher (P <.05) in 5 patients who developed hearing impairment or secondary epilepsy than in those who recovered without neurological deficits. Levels of MMP-9 correlated with concentrations of TIMP-1 (P <.001) and tumor necrosis factor-α (P =.03). Repeated lumbar punctures showed that levels of MMP-8 and MMP-9 were regulated independently and did not correlate with the CSF cell count. Therefore, MMPs may derive not only from granulocytes infiltrating the CSF space but also from parenchymal cells of the meninges and brain. High concentrations of MMP-9 are a risk factor for the development of postmeningitidal neurological sequela

The CCR5 antagonist maraviroc exerts limited neuroprotection without improving neurofunctional outcome in experimental pneumococcal meningitis.

One-third of pneumococcal meningitis (PM) survivors suffer from neurological sequelae including learning disabilities and hearing loss due to excessive neuroinflammation. There is a lack of efficacious compounds for adjuvant therapy to control this long-term consequence of PM. One hallmark is the recruitment of leukocytes to the brain to combat the bacterial spread. However, this process induces excessive inflammation, causing neuronal injury. Maraviroc (MVC)-a CCR5 antagonist-was demonstrated to inhibit leukocyte recruitment and attenuate neuroinflammation in several inflammatory diseases. Here, we show that in vitro, MVC decreased nitric oxide production in astroglial cells upon pneumococcal stimulation. In vivo, infant Wistar rats were infected with 1 × 104 CFU/ml S. pneumoniae and randomized for treatment with ceftriaxone plus MVC (100 mg/kg) or ceftriaxone monotherapy. During the acute phase, neuroinflammation in the CSF was measured and histopathological analyses were performed to determine neuronal injury. Long-term neurofunctional outcome (learning/memory and hearing capacity) after PM was assessed. MVC treatment reduced hippocampal cell apoptosis but did not affect CSF neuroinflammation and the neurofunctional outcome after PM. We conclude that MVC treatment only exerted limited effect on the pathophysiology of PM and is, therefore, not sufficiently beneficial in this experimental paradigm of PM

PIB is a non-specific imaging marker of amyloid-beta (Aβ) peptide-related cerebral amyloidosis

The in vivo imaging probe [11C]-PIB (Pittsburgh Compound B, N-methyl[11C]2-(4′-methylaminophenyl-6-hydroxybenzathiazole) is under evaluation as a key imaging tool in Alzheimer's disease (AD) and to date has been assumed to bind with high affinity and specificity to the amyloid structures associated with classical plaques (CPs), one of the pathological hallmarks of the disease. However, no studies have systematically investigated PIB binding to human neuropathological brain specimens at the tracer concentrations achieved during in vivo imaging scans. Using a combination of autoradiography and histochemical techniques, we demonstrate that PIB, in addition to binding CPs clearly delineates diffuse plaques and cerebrovascular amyloid angiopathy (CAA). The interaction of PIB with CAA was not fully displaceable and this may be linked to the apolipoprotein E-ε4 allele. PIB was also found to label neurofibrillary tangles, although the overall intensity of this binding was markedly lower than that associated with the amyloid-beta (Aβ) pathology. The data provide a molecular explanation for PIB's limited specificity in diagnosing and monitoring disease progression in AD and instead indicate that the ligand is primarily a non-specific marker of Aβ-peptide related cerebral amyloidosi

Levels of Matrix Metalloproteinase-9 within Cerebrospinal Fluid in a Rabbit Model of Coccidioidal Meningitis and Vasculitis

Matrix metalloproteinase (MMP)-9 is produced by the central nervous system and inflammatory cells in a variety of inflammatory conditions in both animals and humans. MMP-9 promotes inflammation, breakdown of the blood-brain barrier, and vasculitis. Because vasculitis is seen frequently in patients with coccidioidal meningitis (CM), this study evaluated the presence of MMP-9 within the cerebrospinal fluid (CSF) of rabbits infected intracisternally with Coccidioides immitis arthroconidia. Infected rabbits demonstrated systemic and neurological sequelae to infection, including CSF pleocytosis. Levels of MMP-9 within CSF were assayed by use of zymography and compared with MMP-2 levels, which served as an internal control. Elevated levels of MMP-9 were detectable by day 3, continued to increase through day 10, and declined by day 15 after infection. MMP-9 may contribute to inflammation and vasculitis in this animal model. Future work can focus on evaluation of MMP inhibitors, to gain a better perspective of the role of this MMP in C