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

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

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

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

Kinetic stabilization of Fe film on (4 by 2)-GaAs(100)

We grow Fe film on (4 by 2)-GaAs(100) at low temperature, (~ 130 K) and study their chemical structure by photoelectron spectroscopy using synchrotron radiation. We observe the effective suppression of As segregation and remarkable reduction of alloy formation near the interface between Fe and substrate. Hence, this should be a way to grow virtually pristine Fe film on GaAs(100). Further, the Fe film is found stable against As segregation even after warmed up to room temperature. There only forms very thin, ~ 8 angstrom thick interface alloy. It is speculated that the interface alloy forms via surface diffusion mediated by interface defects formed during the low temperature growth of the Fe film. Further out-diffusion of both Ga and As are suppressed because it should then proceed via inefficient bulk diffusion.Comment: 4 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