5,622 research outputs found
NASTRAN general purpose interface requirements document
This NASTRAN (NASA STRuctural ANalysis) General Purpose Interface Requirements Document (IRD) defines standards for deliverables required of New Capability Contractors (NCCs) and relates these deliverables to the software development cycle. It also defines standards to be followed by NCCs for adding to and modifying the code in the NASTRAN software system and for adding to and modifying the four official NASTRAN manuals: The NASTRAN Theoretical Manual, the NASTRAN User's Manual, The NASTRAN Programmer's Manual, and The NASTRAN Demonstration Problem Manual. It is intended that this General Purpose IRD shall be incorporated by reference in all contracts for a new NASTRAN capability
Shear thickening in densely packed suspensions of spheres and rods confined to few layers
We investigate confined shear thickening suspensions for which the sample
thickness is comparable to the particle dimensions. Rheometry measurements are
presented for densely packed suspensions of spheres and rods with aspect ratios
6 and 9. By varying the suspension thickness in the direction of the shear
gradient at constant shear rate, we find pronounced oscillations in the stress.
These oscillations become stronger as the gap size is decreased, and the stress
is minimized when the sample thickness becomes commensurate with an integer
number of particle layers. Despite this confinement-induced effect, viscosity
curves show shear thickening that retains bulk behavior down to samples as thin
as two particle diameters for spheres, below which the suspension is jammed.
Rods exhibit similar behavior commensurate with the particle width, but they
show additional effects when the thickness is reduced below about a particle
length as they are forced to align; the stress increases for decreasing gap
size at fixed shear rate while the shear thickening regime gradually
transitions to a Newtonian scaling regime. This weakening of shear thickening
as an ordered configuration is approached contrasts with the strengthening of
shear thickening when the packing fraction is increased in the disordered bulk
limit, despite the fact that both types of confinement eventually lead to
jamming.Comment: 21 pages, 14 figures. submitted to the Journal of Rheolog
Blocking a wave: Frequency band gaps in ice shelves with periodic crevasses
We assess how the propagation of high-frequency elastic-flexural waves
through an ice shelf is modified by the presence of spatially periodic
crevasses. Analysis of the normal modes supported by the ice shelf with and
without crevasses reveals that a periodic crevasse distribution qualitatively
changes the mechanical response. The normal modes of an ice shelf free of
crevasses are evenly distributed as a function of frequency. In contrast, the
normal modes of a crevasse-ridden ice shelf are distributed unevenly. There are
"band gaps", frequency ranges over which no eigenmodes exist. A model ice shelf
that is 50 km in lateral extent and 300 m thick with crevasses spaced 500 m
apart has a band gap from 0.2 to 0.38 Hz. This is a frequency range relevant
for ocean wave/ice-shelf interactions. When the outermost edge of the crevassed
ice shelf is oscillated at a frequency within the band gap, the ice shelf
responds very differently from a crevasse-free ice shelf. The flexural motion
of the crevassed ice shelf is confined to a small region near the outermost
edge of the ice shelf and effectively "blocked" from reaching the interior.Comment: 6 pages, 4 figures, accepted to Annals of Glaciolog
Approximation Model Building for Reliability & Maintainability Characteristics of Reusable Launch Vehicles
This paper describes the development of parametric models for estimating operational reliability and maintainability characteristics for reusable launch vehicle concepts, based on vehicle size and technology support level. A reliability and maintainability analysis tool (RMAT) and response surface methods are utilized to build parametric approximation models for rapidly estimating operational reliability and maintainability characteristics such as mission completion reliability. These models that approximate RMAT, can then be utilized for fast analysis of operational requirements, for lifecycle cost estimating and for multidisciplinary design optimization
Study of aluminoborane compound AlB_4H_(11) for hydrogen storage
Aluminoborane compounds AlB_4H_(11), AlB_5H_(12), and AlB_6H_(13) were reported by Himpsl and Bond in 1981, but they have eluded the attention of the worldwide hydrogen storage research community for more than a quarter of a century. These aluminoborane compounds have very attractive properties for hydrogen storage: high hydrogen capacity (i.e., 13.5, 12.9, and 12.4 wt % H, respectively) and attractive hydrogen desorption temperature (i.e., AlB_4H_(11) decomposes at ~125 °C). We have synthesized AlB_4H_(11) and studied its thermal desorption behavior using temperature-programmed desorption with mass spectrometry, gas volumetric (Sieverts) measurement, infrared (IR) spectroscopy, and solid state nuclear magnetic resonance (NMR). Rehydrogenation of hydrogen-desorbed products was performed and encouraging evidence of at least partial reversibility for hydrogenation at relatively mild conditions is observed. Our chemical analysis indicates that the formula for the compound is closer to AlB_4H_(12) than AlB_4H_(11)
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Identification of unique reciprocal and non reciprocal cross packaging relationships between HIV-1, HIV-2 and SIV reveals an efficient SIV/HIV-2 lentiviral vector system with highly favourable features for in vivo testing and clinical usage.
BACKGROUND: Lentiviral vectors have shown immense promise as vehicles for gene delivery to non-dividing cells particularly to cells of the central nervous system (CNS). Improvements in the biosafety of viral vectors are paramount as lentiviral vectors move into human clinical trials. This study investigates the packaging relationship between gene transfer (vector) and Gag-Pol expression constructs of HIV-1, HIV-2 and SIV. Cross-packaged vectors expressing GFP were assessed for RNA packaging, viral vector titre and their ability to transduce rat primary glial cell cultures and human neural stem cells. RESULTS: HIV-1 Gag-Pol demonstrated the ability to cross package both HIV-2 and SIV gene transfer vectors. However both HIV-2 and SIV Gag-Pol showed a reduced ability to package HIV-1 vector RNA with no significant gene transfer to target cells. An unexpected packaging relationship was found to exist between HIV-2 and SIV with SIV Gag-Pol able to package HIV-2 vector RNA and transduce dividing SV2T cells and CNS cell cultures with an efficiency equivalent to the homologous HIV-1 vector however HIV-2 was unable to deliver SIV based vectors. CONCLUSION: This new non-reciprocal cross packaging relationship between SIV and HIV-2 provides a novel way of significantly increasing bio-safety with a reduced sequence homology between the HIV-2 gene transfer vector and the SIV Gag-Pol construct thus ensuring that vector RNA packaging is unidirectional.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are
What Brown saw and you can too
A discussion is given of Robert Brown's original observations of particles
ejected by pollen of the plant \textit{Clarkia pulchella} undergoing what is
now called Brownian motion. We consider the nature of those particles, and how
he misinterpreted the Airy disc of the smallest particles to be universal
organic building blocks. Relevant qualitative and quantitative investigations
with a modern microscope and with a "homemade" single lens microscope similar
to Brown's, are presented.Comment: 14.1 pages, 11 figures, to be published in the American Journal of
Physics. This differs from the previous version only in the web site referred
to in reference 3. Today, this Brownian motion web site was launched, and
http://physerver.hamilton.edu/Research/Brownian/index.html, is now correc
The atmospheres of the hot-Jupiters Kepler-5b and Kepler-6b observed during occultations with Warm-Spitzer and Kepler
This paper reports the detection and the measurements of occultations of the
two transiting hot giant exoplanets Kepler-5b and Kepler-6b by their parent
stars. The observations are obtained in the near infrared with Spitzer Space
Telescope and at optical wavelengths by combining more than a year of Kepler
photometry. The investigation consists of constraining the eccentricities of
these systems and of obtaining broad band emergent spectra for individual
planets. For both targets, the occultations are detected at 3 sigma level at
each wavelength with mid-occultation times consistent with circular orbits. The
brightness temperatures of these planets are deduced from the infrared
observations and reach T=1930+/-100K and T=1660+/-120K for Kepler-5b and
Kepler-6b respectively. We measure optical geometric albedos A_g in the Kepler
bandpass and find A_g=0.12+/-0.04 for Kepler-5b and A_g=0.11+/-0.04 for
Kepler-6b leading to an upper limit for the Bond albedo of A_B < 0.17 in both
cases. The observations for both planets are best described by models for which
most of the incident energy is redistributed on the dayside, with only less
than 10% of the absorbed stellar flux redistributed to the night side of these
planets. The data for Kepler-5b favor a model without a temperature inversion,
whereas for Kepler-6b they do not allow distinguishing between models with and
without inversion.Comment: 26 pages, 18 figures, 3 tables, submitted to Ap
Generality of shear thickening in suspensions
Suspensions are of wide interest and form the basis for many smart fluids.
For most suspensions, the viscosity decreases with increasing shear rate, i.e.
they shear thin. Few are reported to do the opposite, i.e. shear thicken,
despite the longstanding expectation that shear thickening is a generic type of
suspension behavior. Here we resolve this apparent contradiction. We
demonstrate that shear thickening can be masked by a yield stress and can be
recovered when the yield stress is decreased below a threshold. We show the
generality of this argument and quantify the threshold in rheology experiments
where we control yield stresses arising from a variety of sources, such as
attractions from particle surface interactions, induced dipoles from applied
electric and magnetic fields, as well as confinement of hard particles at high
packing fractions. These findings open up possibilities for the design of smart
suspensions that combine shear thickening with electro- or magnetorheological
response.Comment: 11 pages, 9 figures, accepted for publication in Nature Material
Rad GTPase is essential for the regulation of bone density and bone marrow adipose tissue in mice
The small GTP-binding protein Rad (RRAD, Ras associated with diabetes) is the founding member of the RGK (Rad, Rem, Rem2, and Gem/Kir) family that regulates cardiac voltage-gated Ca2 + channel function. However, its cellular and physiological functions outside of the heart remain to be elucidated. Here we report that Rad GTPase function is required for normal bone homeostasis in mice, as Rad deletion results in significantly lower bone mass and higher bone marrow adipose tissue (BMAT) levels. Dynamic histomorphometry in vivo and primary calvarial osteoblast assays in vitro demonstrate that bone formation and osteoblast mineralization rates are depressed, while in vitro osteoclast differentiation is increased, in the absence of Rad. Microarray analysis revealed that canonical osteogenic gene expression (Runx2, osterix, etc.) is not altered in Rad−/− calvarial osteoblasts; instead robust up-regulation of matrix Gla protein (MGP, + 11-fold), an inhibitor of extracellular matrix mineralization and a protein secreted during adipocyte differentiation, was observed. Strikingly, Rad deficiency also resulted in significantly higher marrow adipose tissue levels in vivo and promoted spontaneous in vitro adipogenesis of primary calvarial osteoblasts. Adipogenic differentiation of wildtype calvarial osteoblasts resulted in the loss of endogenous Rad protein, further supporting a role for Rad in the control of BMAT levels. These findings reveal a novel in vivo function for Rad and establish a role for Rad signaling in the complex physiological control of skeletal homeostasis and bone marrow adiposity
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