27,982 research outputs found
Powder and particulate production of metallic alloys
Developments of particulate metallurgy of alloyed materials where the final products is a fully dense body are discussed. Particulates are defined as powders, flakes, foils, silvers, ribbons and strip. Because rapid solidification is an important factor in particulate metallurgy, all of the particulates must have at least one dimension which is very fine, sometimes as fine as 10 to 50 microns, but move typically up to several hundred microns, provided that the dimension permits a minimum solidification rate of at least 100 K/s
Research on mechanisms of alloy strengthening Semiannual report
Alloy strengthening by fine oxide particle dispersions, and splat cooling process for alloy developmen
Research on mechanisms of alloy strengthening. I. Alloy strengthening by fine oxide particle dispersion. II. The splat cooling process for alloy development Semiannual report
Alloy strengthening by fine oxide particle dispersion and splat cooling process for alloy developmen
Rapid solidification of metallic particulates
In order to maximize the heat transfer coefficient the most important variable in rapid solidification is the powder particle size. The finer the particle size, the higher the solidification rate. Efforts to decrease the particle size diameter offer the greatest payoff in attained quench rate. The velocity of the liquid droplet in the atmosphere is the second most important variable. Unfortunately the choices of gas atmospheres are sharply limited both because of conductivity and cost. Nitrogen and argon stand out as the preferred gases, nitrogen where reactions are unimportant and argon where reaction with nitrogen may be important. In gas atomization, helium offers up to an order of magnitude increase in solidification rate over argon and nitrogen. By contrast, atomization in vacuum drops the quench rate several orders of magnitude
Research on mechanisms of alloy strengthening 1 - Alloy strengthening by fine oxide particle dispersion. 2 - The splat cooling process for alloy development Semiannual report
Iron alloy strengthening by fine beryllium oxide particle dispersion, and fracture and tensile deformation of dispersioned strengthened alloy
Hidden Simplicity of the Gravity Action
We derive new representations of the Einstein-Hilbert action in which
graviton perturbation theory is immensely simplified. To accomplish this, we
recast the Einstein-Hilbert action as a theory of purely cubic interactions
among gravitons and a single auxiliary field. The corresponding equations of
motion are the Einstein field equations rewritten as two coupled first-order
differential equations. Since all Feynman diagrams are cubic, we are able to
derive new off-shell recursion relations for tree-level graviton scattering
amplitudes. With a judicious choice of gauge fixing, we then construct an
especially compact form for the Einstein-Hilbert action in which all graviton
interactions are simply proportional to the graviton kinetic term. Our results
apply to graviton perturbations about an arbitrary curved background spacetime.Comment: 20 pages, 1 figur
Bulk Connectedness and Boundary Entanglement
We prove, for any state in a conformal field theory defined on a set of
boundary manifolds with corresponding classical holographic bulk geometry, that
for any bipartition of the boundary into two non-clopen sets, the density
matrix cannot be a tensor product of the reduced density matrices on each
region of the bipartition. In particular, there must be entanglement across the
bipartition surface. We extend this no-go theorem to general, arbitrary
partitions of the boundary manifolds into non-clopen parts, proving that the
density matrix cannot be a tensor product. This result gives a necessary
condition for states to potentially correspond to holographic duals.Comment: 12 pages, 2 figure
Infrared Consistency and the Weak Gravity Conjecture
The weak gravity conjecture (WGC) asserts that an Abelian gauge theory
coupled to gravity is inconsistent unless it contains a particle of charge
and mass such that . This criterion is obeyed by all
known ultraviolet completions and is needed to evade pathologies from stable
black hole remnants. In this paper, we explore the WGC from the perspective of
low-energy effective field theory. Below the charged particle threshold, the
effective action describes a photon and graviton interacting via
higher-dimension operators. We derive infrared consistency conditions on the
parameters of the effective action using i) analyticity of light-by-light
scattering, ii) unitarity of the dynamics of an arbitrary ultraviolet
completion, and iii) absence of superluminality and causality violation in
certain non-trivial backgrounds. For convenience, we begin our analysis in
three spacetime dimensions, where gravity is non-dynamical but has a physical
effect on photon-photon interactions. We then consider four dimensions, where
propagating gravity substantially complicates all of our arguments, but bounds
can still be derived. Operators in the effective action arise from two types of
diagrams: those that involve electromagnetic interactions (parameterized by a
charge-to-mass ratio ) and those that do not (parameterized by a
coefficient ). Infrared consistency implies that is bounded from
below for small .Comment: 37 pages, 5 figures. Minor typos fixed and equation numbers changed
to match journal. Published in JHE
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