6,884 research outputs found
Study of tooling concepts for manufacturing operations in space Final report
Mechanical linkage device for manufacturing operations with orbital workshop
Directionally asymmetric self-assembly of cadmium sulfide nanotubes using porous alumina nanoreactors: Need for chemohydrodynamic instability at the nanoscale
We explore nanoscale hydrodynamical effects on synthesis and self-assembly of
cadmium sulfide nanotubes oriented along one direction. These nanotubes are
synthesized by horizontal capillary flow of two different chemical reagents
from opposite directions through nanochannels of porous anodic alumina which
are used primarily as nanoreactors. We show that uneven flow of different
chemical precursors is responsible for directionally asymmetric growth of these
nanotubes. On the basis of structural observations using scanning electron
microscopy, we argue that chemohydrodynamic convective interfacial instability
of multicomponent liquid-liquid reactive interface is necessary for sustained
nucleation of these CdS nanotubes at the edges of these porous nanochannels
over several hours. However, our estimates clearly suggest that classical
hydrodynamics cannot account for the occurrence of such instabilities at these
small length scales. Therefore, we present a case which necessitates further
investigation and understanding of chemohydrodynamic fluid flow through
nanoconfined channels in order to explain the occurrence of such interfacial
instabilities at nanometer length scales.Comment: 26 pages, 6 figures; http://www.iiserpune.ac.in/researchhighlight
Electro-Magnetic Waves within a Model for Charged Solitons
We analyze the model of topological fermions (MTF), where charged fermions
are treated as soliton solutions of the field equations. In the region far from
the sources we find plane waves solutions with the properties of
electro-magnetic waves.Comment: 4 pages, 2 figure
Some Insights into the Method of Center Projection
We present several new results which pertain to the successes of center
projection in maximal center gauge (MCG). In particular, we show why any center
vortex, inserted "by hand" into a thermalized lattice configuration, will be
among the set of vortices found by the center projection procedure. We show
that this "vortex-finding property" is lost when gauge-field configurations are
fixed to Landau gauge prior to the maximal center gauge fixing; this fact
accounts for the loss of center dominance in the corresponding projected
configurations. Variants of maximal center (adjoint Landau) gauge are proposed
which correctly identify relevant center vortices.Comment: LATTICE99(confine), 3 pages, 3 figure
Radius Dependent Luminosity Evolution of Blue Galaxies in GOODS-N
We examine the radius-luminosity (R-L) relation for blue galaxies in the Team
Keck Redshift Survey (TKRS) of GOODS-N. We compare with a volume-limited, Sloan
Digital Sky Survey sample and find that the R-L relation has evolved to lower
surface brightness since z=1. Based on the detection limits of GOODS this can
not be explained by incompleteness in low surface-brightness galaxies. Number
density arguments rule out a pure radius evolution. It can be explained by a
radius dependent decline in B-band luminosity with time. Assuming a linear
shift in M_B with z, we use a maximum likelihood method to quantify the
evolution. Under these assumptions, large (R_{1/2} > 5 kpc), and intermediate
sized (3 < R_{1/2} < 5 kpc) galaxies, have experienced Delta M_B =1.53
(-0.10,+0.13) and 1.65 (-0.18, +0.08) magnitudes of dimming since z=1. A simple
exponential decline in star formation with an e-folding time of 3 Gyr can
result in this amount of dimming. Meanwhile, small galaxies, or some subset
thereof, have experienced more evolution, 2.55 (+/- 0.38) magnitudes. This
factor of ten decline in luminosity can be explained by sub-samples of
starbursting dwarf systems that fade rapidly, coupled with a decline in burst
strength or frequency. Samples of bursting, luminous, blue, compact galaxies at
intermediate redshifts have been identified by various previous studies. If
there has been some growth in galaxy size with time, these measurements are
upper limits on luminosity fading.Comment: 34 Total pages, 15 Written pages, 19 pages of Data Table, 13 Figures,
accepted for publication in Ap
The M(BH)-Sigma Relation for Supermassive Black Holes
We investigate the differences in the M(BH)-sigma relation derived recently
by Ferrarese & Merritt (2000) and Gebhardt et al. (2000). The shallower slope
found by the latter authors (3.75 vs. 4.8) is due partly to the use of a
regression algorithm that ignores measurement errors, and partly to the value
of the velocity dispersion adopted for a single galaxy, the Milky Way. A
steeper relation is shown to provide a better fit to black hole masses derived
from reverberation mapping studies. Combining the stellar dynamical, gas
dynamical, and reverberation mapping mass estimates, we derive a best-fit
relation M(BH) = 1.30 (+/- 0.36) X 10^8 (sigma_c/200)^{4.72(+/- 0.36)}, where
M(BH) is in solar masses, and sigma in km/s.Comment: The Astrophysical Journal, in pres
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