Energy Spectrum Evolution of a Diffuse Field in Elastic Body Caused by Weak Nonlinearity

We study the evolution of diffuse elastodynamic spectral energy density under the influence of weak nonlinearity. It is shown that the rate of change of this quantity is given by a convolution of the linear energy at two frequencies. Quantitative estimates are given for sample aluminum and fused silica blocks of experimental interest.Comment: 9 pages, 3 figures; revised for better presentatio

Generalized Berry Conjecture and mode correlations in chaotic plates

We consider a modification of the Berry Conjecture for eigenmode statistics in wave-bearing systems. The eigenmode correlator is conjectured to be proportional to the imaginary part of the Green's function. The generalization is applicable not only to scalar waves in the interior of homogeneous isotropic systems where the correlator is a Bessel function, but to arbitrary points of heterogeneous systems as well. In view of recent experimental measurements, expressions for the intensity correlator in chaotic plates are derived.Comment: 5 pages, 1 figur

Probing the mechanical properties of graphene using a corrugated elastic substrate

The exceptional mechanical properties of graphene have made it attractive for nano-mechanical devices and functional composite materials. Two key aspects of graphene's mechanical behavior are its elastic and adhesive properties. These are generally determined in separate experiments, and it is moreover typically difficult to extract parameters for adhesion. In addition, the mechanical interplay between graphene and other elastic materials has not been well studied. Here, we demonstrate a technique for studying both the elastic and adhesive properties of few-layer graphene (FLG) by placing it on deformable, micro-corrugated substrates. By measuring deformations of the composite graphene-substrate structures, and developing a related linear elasticity theory, we are able to extract information about graphene's bending rigidity, adhesion, critical stress for interlayer sliding, and sample-dependent tension. The results are relevant to graphene-based mechanical and electronic devices, and to the use of graphene in composite, flexible, and strain-engineered materials.Comment: 5 pages, 4 figure

ASCA Observations of the Starburst-Driven Superwind Galaxy NGC 2146: Broad Band (0.6 - 9 keV) Spectral Properties

We report ASCA GIS and SIS observations of the nearby (D = 11.6 Mpc), nearly edge-on, starburst galaxy NGC 2146. These X-ray spectral data complement ROSAT PSPC and HRI imaging discussed by Armus et al., 1995. The broad band (0.6-9 keV) X-ray spectrum of NGC 2146 is best described by a two component model: the soft X-ray emission with a Raymond-Smith thermal plasma model having a temperature of kT $\sim 0.8$ keV; the hard X-ray emission with a thermal plasma model having kT $\sim 8$ keV or a power-law model having a photon index of $\sim 1.7$. We do not find compelling evidence of substantial excess absorption above the Galactic value. The soft (hard) thermal component provides about 30% (70%) of the total luminosity in the 0.5 - 2.0 keV energy band, while in the 2-10 keV energy range only the hard component plays a major role. The spectral results allow us to set tighter constraints on the starburst-driven superwind model, which we show can satisfactorily account for the luminosity, mass, and energy content represented by the soft X-ray spectral component. We estimate that the mass outflow rate ($\sim$ 9 M$_{\odot}$ per year) is about an order of magnitude greater than the predicted rate at which supernovae and stellar winds return mass into the interstellar medium and, therefore, argue that the flow is strongly "mass-loaded" with material in and around the starburst. The estimated outflow velocity of the hot gas is close to the escape velocity from the galaxy, so the fate of the gas is not clear. We suggest that the hard X-ray spectral component is due to the combined emission of X-ray binaries and/or young supernovae remnants associated with the starburst.Comment: 26 pages plus 4 figures, LaTex manuscript, Accepted for publication in the Astrophysical Journa

Identifying Optimal Equivalent Area Changes to Reduce Sonic Boom Loudness

This work explores the design space created from modeling the effect of localized geometric changes on a supersonic aircraft’s near-field pressure signature. These geometric changes are used to alter the aircraft’s near-field pressure signature in a way that reduces its sonic boom loudness at the ground. The aircraft used in this work is the NASA 25D concept and its near-field pressure signature is modeled using two separate methods. The first method uses the PANAIR panel code to obtain a near-field pressure signature for an axisymmetric representation of the 25D. This near-field signature is propagated to the ground using the NASA sBOOM propagation code and the perceived level in decibels is calculated using an in-house loudness code called PyLdB. The second method uses the equivalent area distribution of the 25D which is passed directly to sBOOM and the perceived level is again found using PyLdB. To model the geometric changes, the axisymmetric geometry and the equivalent area distributions are independently modified with a parameterized Gaussian deformation. These methods are fast enough to quickly explore the design space and find the change in loudness for different deformation parameters. This design space exploration is used to study loudness changes for both on-design conditions and the effects of deviations from on-design angle of attack, Mach number, and azimuth angle. A genetic algorithm is used in subsequent studies to explore the effects of different atmospheric conditions. These results can be used to inform higher fidelity CFD studies and structural adaptation design on the aircraft

Serum 25-Hydroxyvitamin D and Intact Parathyroid Hormone Influence Muscle Outcomes in Children and Adolescents

Increases in 25-hydroxyvitamin D concentrations are shown to improve strength in adults; however, data in pediatric populations are scant and equivocal. In this ancillary study of a larger-scale, multi-sited, double-blind, randomized, placebo-controlled vitamin D intervention in US children and adolescents, we examined the associations between changes in vitamin D metabolites and changes in muscle mass, strength, and composition after 12 weeks of vitamin D3 supplementation. Healthy male and female, black and white children and adolescents between the ages of 9 and 13 years from two US states (Georgia 34°N and Indiana 40°N) were enrolled in the study and randomly assigned to receive an oral vitamin D3 dose of 0, 400, 1000, 2000, or 4000 IU/d for 12 weeks between the winter months of 2009 to 2011 (N = 324). Analyses of covariance, partial correlations, and regression analyses of baseline and 12-week changes (post-baseline) in vitamin D metabolites (serum 25(OH)D, 1,25(OH)2 D, intact parathyroid hormone [iPTH]), and outcomes of muscle mass, strength, and composition (total body fat-free soft tissue [FFST], handgrip strength, forearm and calf muscle cross-sectional area [MCSA], muscle density, and intermuscular adipose tissue [IMAT]) were assessed. Serum 25(OH)D and 1,25(OH)2 D, but not iPTH, increased over time, as did fat mass, FFST, forearm and calf MCSA, forearm IMAT, and handgrip strength (p < 0.05). Vitamin D metabolites were not associated with muscle strength at baseline nor after the 12-week intervention. Changes in serum 25(OH)D correlated with decreases in forearm IMAT, whereas changes in serum iPTH predicted increases in forearm and calf MCSA and IMAT (p < 0.05). Overall, increases in 25(OH)D did not influence muscle mass or strength in vitamin D-sufficient children and adolescents; however, the role of iPTH on muscle composition in this population is unknown and warrants further investigation

Expanding Mouse-Adapted Yamagata-like Influenza B Viruses in Eggs Enhances In Vivo Lethality in BALB/c Mice

Despite the yearly global impact of influenza B viruses (IBVs), limited host range has been a hurdle to developing a readily accessible small animal disease model for vaccine studies. Mouseadapting IBV can produce highly pathogenic viruses through serial lung passaging in mice. Previous studies have highlighted amino acid changes throughout the viral genome correlating with increased pathogenicity, but no consensus mutations have been determined. We aimed to show that growth system can play a role in mouse-adapted IBV lethality. Two Yamagata-lineage IBVs were serially passaged 10 times in mouse lungs before expansion in embryonated eggs or Madin–Darby canine kidney cells (London line) for use in challenge studies. We observed that virus grown in embryonated eggs was significantly more lethal in mice than the same virus grown in cell culture. Ten additional serial lung passages of one strain again showed virus grown in eggs was more lethal than virus grown in cells. Additionally, no mutations in the surface glycoprotein amino acid sequences correlated to differences in lethality. Our results suggest growth system can influence lethality of mouse-adapted IBVs after serial lung passaging. Further research can highlight improved mechanisms for developing animal disease models for IBV vaccine research

Space Propulsion Research Facility (B-2): An Innovative, Multi-Purpose Test Facility

The Space Propulsion Research Facility, commonly referred to as B-2, is designed to hot fire rocket engines or upper stage launch vehicles with up to 890,000 N force (200,000 lb force), after environmental conditioning of the test article in simulated thermal vacuum space environment. As NASA s third largest thermal vacuum facility, and the largest designed to store and transfer large quantities of propellant, it is uniquely suited to support developmental testing associated with large lightweight structures and Cryogenic Fluid Management (CFM) systems, as well as non-traditional propulsion test programs such as Electric and In-Space propulsion. B-2 has undergone refurbishment of key subsystems to support the NASA s future test needs, including data acquisition and controls, vacuum, and propellant systems. This paper details the modernization efforts at B-2 to support the Nation s thermal vacuum/propellant test capabilities, the unique design considerations implemented for efficient operations and maintenance, and ultimately to reduce test costs

Racial Differences in Cortical Bone Mass, Size and Estimated Strength at the Tibial Diaphysis in Early Pubertal Children

poster abstractOsteoporotic fracture rates differ according to race, with blacks having up to half the rate of whites. The reduced fracture rate in blacks has been suggested to be due to their superior bone mass; however, mass is not the sole determinant of bone strength. Bone strength, and consequent fracture risk, is also influenced by how bone material is distributed or structured. It is likely bone structure also contributes to the lower incidence of fractures in blacks and that racial differences in bone structure have roots in childhood. The aim of this study was to assess the influence of race on pQCT-derived cortical bone mass, size and estimated strength at the tibial diaphysis in early pubertal children. 160 children were recruited, with equal subjects according to race (black, n=80; white, n=80) and sex (female, n=80; male, n=80). Subjects were at sexual maturation stages 2 or 3. Tomographic slices of the tibial diaphysis at 66% proximal from the medial malleolus were acquired using pQCT. Slices were assessed for cortical volumetric BMD (Ct.vBMD), cortical BMC (Ct.BMC), total (Tt.Ar) and cortical (Ct.Ar) area, density weighted maximum (IMAX) and minimum (IMIN) second moments of area, density-weighted polar strength-strain index (SSIP), and muscle cross-sectional area (mCSA). Group differences were assessed by two-way analysis of covariance, with race (black vs. white) and sex (female vs. male) as independent variables. Covariates included predicted years from peak height velocity (maturity offset), tibial length and mCSA. There were no interactions between race and sex (all P=0.50-0.98) or main effect for sex (all P=0.08-0.45). Blacks had 15.7% more Ct.BMC, and 10.8-11.8% larger Tt.Ar and Ct.Ar than whites (all P<0.001). The greater enhancement of Ct.BMC relative to Ct.Ar resulted in blacks having 3.6% greater Ct.vBMD than whites (P<0.001). The combination of increased cortical bone mass, size and density in blacks contributed to enhanced estimated bone strength, with IMAX, IMIN and SSIP being 20.0%, 34.5% and 25.2% greater in blacks than whites, respectively (all P<0.001). These data indicate that early pubertal black children have enhanced bone mass, size and estimated bone strength at the tibial diaphysis versus whites, independent of tibial length and mCSA. They suggest bone structural differences may contribute to observed racial differences in fracture rates and that structural divergence between races develops during childhood