4,794 research outputs found
Material Strength in Polymer Shape Deposition Manufacturing
Shape Deposition Manufacturing (SDM) is a layered manufacturing process involving an
iterative combination of material addition and material removal. Polymer SDM processes have
used castable thermoset resins to build a variety of parts. The strength of such parts is determined
by the bulk material properties of the part materials and by their interlayer adhesion. This paper
describes tensile testing of three thermoset resins used for SDM - two polyurethane resins and one
epoxy resin. Both monolithic specimens and specimens with two interlayer !nterfaces were tested.
Interlayer tensile strengths were found to vary greatly among the three matenals, from 5-40 MPa.Mechanical Engineerin
Nuclear spin pumping and electron spin susceptibilities
In this work we present a new formalism to evaluate the nuclear spin dynamics
driven by hyperfine interaction with non-equilibrium electron spins. To
describe the dynamics up to second order in the hyperfine coupling, it suffices
to evaluate the susceptibility and fluctuations of the electron spin. Our
approach does not rely on a separation of electronic energy scales or the
specific choice of electronic basis states, thereby overcoming practical
problems which may arise in certain limits when using a more traditional
formalism based on rate equations.Comment: 9 pages, 2 figure
Beyond Appearances: The Content of Sensation and Perception
There seems to be a large gulf between percepts and concepts. In particular, con-cepts seem to be capable of representing things that percepts cannot. We can conceive of things that would be impossible to perceive. (The converse may also seem true, but I will leave that to one side.) In one respect, this is trivially right. We can conceive of things that we cannot encounter, such as unicorns. We cannot literally perceive unicorns, even if we occasionally ‘‘see’ ’ them in our dreams and hallucinations. To avoid triviality, I want to focus on things that we can actually encounter. We perceive poodles, perfumes, pinpricks, and pounding drums. These are concrete things; they are closely wedded to appearances. But we also encounter things that are abstract.We encounter uncles and instances of injustice. These things have no characteristic looks. Percepts, it is said, cannot represent abstract things. Call this claim the Imperceptability Thesis. I think the Imperceptibility Thesis is false. Perception is not restricted to the concrete. We can perceive abstract entities. This may sound like an obvious claim. We often use perceptual terms widely to say things such as: ‘‘I perceive a lack of agreement’ ’ or ‘‘I see where you ar
Adsorption, Segregation and Magnetization of a Single Mn Adatom on the GaAs (110) Surface
Density functional calculations with a large unit cell have been conducted to
investigate adsorption, segregation and magnetization of Mn monomer on
GaAs(110). The Mn adatom is rather mobile along the trench on GaAs(110), with
an energy barrier of 0.56 eV. The energy barrier for segregation across the
trenches is nevertheless very high, 1.67 eV. The plots of density of states
display a wide gap in the majority spin channel, but show plenty of
metal-induced gap states in the minority spin channel. The Mn atoms might be
invisibl in scanning tunneling microscope (STM) images taken with small biases,
due to the directional p-d hybridization. For example, one will more likely see
two bright spots on Mn/GaAs(110), despite the fact that there is only one Mn
adatom in the system
Superlattice properties of carbon nanotubes in a transverse electric field
Electron motion in a (n,1) carbon nanotube is shown to correspond to a de
Broglie wave propagating along a helical line on the nanotube wall. This
helical motion leads to periodicity of the electron potential energy in the
presence of an electric field normal to the nanotube axis. The period of this
potential is proportional to the nanotube radius and is greater than the
interatomic distance in the nanotube. As a result, the behavior of an electron
in a (n,1) nanotube subject to a transverse electric field is similar to that
in a semiconductor superlattice. In particular, Bragg scattering of electrons
from the long-range periodic potential results in the opening of gaps in the
energy spectrum of the nanotube. Modification of the bandstructure is shown to
be significant for experimentally attainable electric fields, which raises the
possibility of applying this effect to novel nanoelectronic devices.Comment: 7 pages, 3 figure
Pension Systems and Social Security: Trends and National Characteristics
This brief survey paper on the main characteristics of pension systems and social security systems in twelve European countries and Canada belongs to a series of papers originating from the project "Family, Household, and Social Security in Aging Societies." It provides a basis for comparing past and probable future trends in the thirteen countries currently participating in the project
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