140,527 research outputs found
Synthesis of elastomers for use with liquid fluorine Quarterly letter report, 1 Sep. - 30 Nov. 1968
Phosphines as initiators of polymerization of hexafluorobutyne-
Synthesis of elastomers for use with liquid fluorine Final report
Synthesis and chemical properties of elastomeric polymers resistant to effects of fluorine, oxygen difluoride, nitrogen tetroxide, and similar agent
Radial segregation induced by natural convection and melt/solid interface shape in vertical Bridgman growth
The roles of natural convection in the melt and the shape of the melt/solid interface on radial dopant segregation are analyzed for a prototype of vertical Bridgman crystal growth system by finite element methods that solve simultaneously for the velocity field in the melt, the shape of the solidification isotherm, and the temperature distribution in both phases. Results are presented for crystal and melt with thermophysical properties similar to those of gallium-doped germanium in Bridgman configurations with melt below (thermally destabilizing) and above (stabilizing) the crystal. Steady axisymmetric flow are classified according to Rayleigh number as either being nearly the growth velocity, having a weak cellular structure or having large amplitude cellular convention. The flows in the two Bridgman configurations are driven by different temperature gradients and are in opposite directions. Finite element calculations for the transport of a dilute dopant by these flow fields reveal radial segregation levels as large as sixty percent of the mean concentration. Segregation is found most severe at an intermediate value of Rayleigh number above which the dopant distribution along the interface levels as the intensity of the flow increases
Synthesis of elastomers for use with liquid fluorine Annual interim report
Elastomer synthesis for copolymerization with liquid fluorin
Permutation groups, simple groups and sieve methods
We show that the number of integers n ≤ x which occur as indices of subgroups of nonabelian finite simple groups, excluding that of An-1 in An, is ∼ hx/log x, for some given constant h. This might be regarded as a noncommutative analogue of the Prime Number Theorem (which counts indices n ≤ x of subgroups of abelian simple groups). We conclude that for most positive integers n, the only quasiprimitive permutation groups of degree n are Sn and An in their natural action. This extends a similar result for primitive permutation groups obtained by Cameron, Neumann and Teague in 1982. Our proof combines group-theoretic and number-theoretic methods. In particular, we use the classification of finite simple groups, and we also apply sieve methods to estimate the size of some interesting sets of primes
Multiple buoyancy driven flows in a vertical cylinder heated from below
The structure of axisymmetric buoyancy-driven convection in a vertical cylinder heated from below is probed by finite element solution of the Boussinesq equations coupled with computed-implemented perturbation techniques for detecting and tracking multiple flows and for determining flow stability. Results are reported for fluids with Prandtl number of one and for cylinders with aspect ratio (Lambda) (defined as the height to radius of the cylinder) between 0.5 and 2.25. Extensive calculations of the neutral stability curve for the static solution and of the nonlinear motions along the bifurcating flow families show a continuous evolution of the primary cellular motion from a single toroidal cell to two and three cells nested radially in the cylinder, instead of the sharp transitions found for a cylinder with shear-free sidewalls. The smooth transitions in flow structure with Rayleigh number and lambda are explained by nonlinear connectivity between the first two bifurcating flow families formed either by a secondary bifurcation point for Lambda or = Lambda * approximately 0.80 or by a limit point for Lambda Lambda *. The transition between these two modes may be described by the theory of multiple limit point bifurcation
Three-Dimensional Structure of the Magnetic Field in the Disk of the Milky Way
We present Rotation Measures (RM) of the diffuse Galactic synchrotron
emission from the Canadian Galactic Plane Survey (CGPS) and compare them to RMs
of extragalactic sources in order to study the large-scale reversal in the
Galactic magnetic field (GMF). Using Stokes Q, U and I measurements of the
Galactic disk collected with the Synthesis Telescope at the Dominion Radio
Astrophysical Observatory, we calculate RMs over an extended region of the sky,
focusing on the low longitude range of the CGPS (l=52deg to l=72deg). We note
the similarity in the structures traced by the compact sources and the extended
emission and highlight the presence of a gradient in the RM map across an
approximately diagonal line, which we identify with the well-known field
reversal of the Sagittarius-Carina arm. We suggest that the orientation of this
reversal is a geometric effect resulting from our location within a GMF
structure arising from current sheets that are not perpendicular to the
Galactic plane, as is required for a strictly radial field reversal, but that
have at least some component parallel to the disk. Examples of models that fit
this description are the three-dimensional dynamo-based model of Gressel et al.
(2013) and a Galactic scale Parker spiral (Akasofu & Hakamada 1982), although
the latter may be problematic in terms of Galactic dynamics. We emphasize the
importance of constructing three-dimensional models of the GMF to account for
structures like the diagonal RM gradient observed in this dataset.Comment: Published in Astronomy and Astrophysics, Accepted 23 April, 201
Importance of including small body spin effects in the modelling of intermediate mass-ratio inspirals. II Accurate parameter extraction of strong sources using higher-order spin effects
We improve the numerical kludge waveform model introduced in [1] in two ways.
We extend the equations of motion for spinning black hole binaries derived by
Saijo et al. [2] using spin-orbit and spin-spin couplings taken from
perturbative and post-Newtonian (PN) calculations at the highest order
available. We also include first-order conservative self-force corrections for
spin-orbit and spin-spin couplings, which are derived by comparison to PN
results. We generate the inspiral evolution using fluxes that include the most
recent calculations of small body spin corrections, spin-spin and spin-orbit
couplings and higher-order fits to solutions of the Teukolsky equation. Using a
simplified version of this model in [1], we found that small body spin effects
could be measured through gravitational wave observations from
intermediate-mass ratio inspirals (IMRIs) with mass ratio eta ~ 0.001, when
both binary components are rapidly rotating. In this paper we study in detail
how the spin of the small/big body affects parameter measurement using a
variety of mass and spin combinations for typical IMRIs sources. We find that
for IMRI events of a moderately rotating intermediate mass black hole (IMBH) of
ten thousand solar masses, and a rapidly rotating central supermassive black
hole (SMBH) of one million solar masses, gravitational wave observations made
with LISA at a fixed signal-to-noise ratio (SNR) of 1000 will be able to
determine the inspiralling IMBH mass, the central SMBH mass, the SMBH spin
magnitude, and the IMBH spin magnitude to within fractional errors of ~0.001,
0.001, 0.0001, and 9%, respectively. LISA can also determine the location of
the source in the sky and the SMBH spin orientation to within ~0.0001
steradians. We show that by including conservative corrections up to 2.5PN
order, systematic errors no longer dominate over statistical errors for IMRIs
with typical SNR ~1000.Comment: 21 pages, 7 figures. v2: three references added, edits in Sections
II-V, including additional results in Section V to address comments by the
referee. v3: mirrors version accepted to PR
Boundary States and Black Hole Entropy
Black hole entropy is derived from a sum over boundary states. The boundary
states are labeled by energy and momentum surface densities, and parametrized
by the boundary metric. The sum over state labels is expressed as a functional
integral with measure determined by the density of states. The sum over metrics
is expressed as a functional integral with measure determined by the universal
expression for the inverse temperature gradient at the horizon. The analysis
applies to any stationary, nonextreme black hole in any theory of gravitational
and matter fields.Comment: 4 pages, Revte
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