1,950 research outputs found
Figure of merit studies of beam power concepts for advanced space exploration
Surface to surface, millimeter wavelength beam power systems for power transmission on the lunar base were investigated. Qualitative/quantitative analyses and technology assessment of 35, 110 and 140 GHz beam power systems were conducted. System characteristics including mass, stowage volume, cost and efficiency as a function of range and power level were calculated. A simple figure of merit analysis indicates that the 35 GHz system would be the preferred choice for lunar base applications, followed closely by the 110 GHz system. System parameters of a 35 GHz beam power system appropriate for power transmission on a recent lunar base concept studied by NASA-Johnson and the necessary deployment sequence are suggested
Cones of closed alternating walks and trails
Consider a graph whose edges have been colored red and blue. Assign a
nonnegative real weight to every edge so that at every vertex, the sum of the
weights of the incident red edges equals the sum of the weights of the incident
blue edges. The set of all such assignments forms a convex polyhedral cone in
the edge space, called the \emph{alternating cone}. The integral (respectively,
) vectors in the alternating cone are sums of characteristic vectors
of closed alternating walks (respectively, trails). We study the basic
properties of the alternating cone, determine its dimension and extreme rays,
and relate its dimension to the majorization order on degree sequences. We
consider whether the alternating cone has integral vectors in a given box, and
use residual graph techniques to reduce this problem to searching for a closed
alternating trail through a given edge. The latter problem, called alternating
reachability, is solved in a companion paper along with related results.Comment: Minor rephrasing, new pictures, 14 page
The growth of galaxies in cosmological simulations of structure formation
We use hydrodynamic simulations to examine how the baryonic components of
galaxies are assembled, focusing on the relative importance of mergers and
smooth accretion in the formation of ~L_* systems. In our primary simulation,
which models a (50\hmpc)^3 comoving volume of a Lambda-dominated cold dark
matter universe, the space density of objects at our (64-particle) baryon mass
resolution threshold, M_c=5.4e10 M_sun, corresponds to that of observed
galaxies with L~L_*/4. Galaxies above this threshold gain most of their mass by
accretion rather than by mergers. At the redshift of peak mass growth, z~2,
accretion dominates over merging by about 4:1. The mean accretion rate per
galaxy declines from ~40 M_sun/yr at z=2 to ~10 M_sun/yr at z=0, while the
merging rate peaks later (z~1) and declines more slowly, so by z=0 the ratio is
about 2:1. We cannot distinguish truly smooth accretion from merging with
objects below our mass resolution threshold, but extrapolating our measured
mass spectrum of merging objects, dP/dM ~ M^a with a ~ -1, implies that
sub-resolution mergers would add relatively little mass. The global star
formation history in these simulations tracks the mass accretion rate rather
than the merger rate. At low redshift, destruction of galaxies by mergers is
approximately balanced by the growth of new systems, so the comoving space
density of resolved galaxies stays nearly constant despite significant mass
evolution at the galaxy-by-galaxy level. The predicted merger rate at z<~1
agrees with recent estimates from close pairs in the CFRS and CNOC2 redshift
surveys.Comment: Submitted to ApJ, 35 pp including 15 fig
ANALYSIS OF THE ANTIOXIDANT ACTIVITY OF GERANIOL EMPLOYING VARIOUS IN-VITRO MODELS: RELEVANCE TO NEURODEGENERATION IN DIABETIC NEUROPATHY
Objective: The aim of this study was to analyze antioxidant effect of geraniol (GE) in different in vitro models.Methods: Initially, the antioxidant activity of GE was assessed by diphenyl picrylhydrazyl radical (DPPH) assay. The modulatory effect of GE against 2,2'-azobis(2-amidinopropane) dihydrochloride induced lipid peroxidation in rat brain regions (cortex and cerebellum) and sciatic nerve (SN) homogenates was determined. Further, the effect of GE was assessed against hyperglycemia-induced oxidative stress (OS) in SHSY5Y, a human neuroblastoma cell line.Results: GE proved to be a good scavenger of DPPH free radical (inhibitory concentration 50% [IC50] value = 663 nmol) and could lower the lipid peroxidation levels in rat brain tissue and SN homogenates (25-40%). Further, it rescue the SHSY5Y cells from hyperglycemia-induced death. Co-exposure of GE with the IC50 level of glucose (100 mM) lowered the levels of reactive oxygen species, hydrogen peroxides and 3-nitrotyrosine levels with concomitant elevation in the glutathione levels (about two folds).Conclusion: Collectively from these findings and other studies previously conducted (from our lab and others) emphasize the potential benefit of GE against OS, a progressive pathological feature of neurodegenerative disorders.Â
DNA-amine interactions: from monolayers to nanoparticles
DNA is a polyanionic molecule that can electrostatically interact with positively charged ligands. Interaction with surfactants such as CTAB leads to cooperative binding of detergent molecules through synergistic effects of electrostatic and hydrophobic forces. DNA can also form a monolayer at air-water interface with positively charged octylamine and nanoparticles with cationic lysine capped gold nanoparticles. Formation of such electrostatic composites of DNA has practical implications for developing DNA diagnostic systems and for lipidencapsulated DNA delivery systems
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