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Fabrication of X-Graded H13 and Cu Powder Mix Using High Power Pulsed Nd:YAG Laser
The manufacturing of Functionally Graded Material (FGM) parts using Solid Free Form
manufacturing technologies has been carried out since early 1980. At present, most of the
powder manufacturing techniques are being focused on layering powder with different
powder blend compositions with Z gradients (graded in direction of layer build). Although,
there are a few researchers working on multi powder feeder and deposition system, the study
of laser fusion of the deposited powder (by a powder deposition system) is minimum or not
known to date. Consequently, the manufacturing of functionally graded structures is still
geometry limited. This work was focused on the manufacturing of X-graded (graded along the
powder bed plane) specimens with H13 tool steel and Cu mix. Five bimodal powder blends
were used with a multi-container feed hopper to spread powder layers for the selective laser
fusion of the powder. The powder was fused using a high power Nd:YAG pulsed laser using a
specific scanning strategy to reduce porosity. Specimens were produced with graded Cu
within the H13 matrix. The specimens were analysed for dimensional accuracy,
microstructure, porosity, cracks and micro hardness of the FGM.Mechanical Engineerin
Higher order forward spin polarizability
As a guideline for future experiments to extract the four (leading) spin
polarizabilities of the nucleon, we have constructed the forward amplitude for
polarized Compton scattering by dispersion integrals. These integrals have been
saturated by recently measured helicity-dependent photoabsorption cross
sections as well as predictions for pion photoproduction multipoles from
several phenomenological descriptions and chiral perturbation theory. The
comparison of these results corroborates the strategy to extract the spin
polarizabilities by fitting them to polarized Compton data and fixing all
higher order spin effects by dispersion relations based on pion photoproduction
multipoles.Comment: 21 pages, 6 figures, 3 Tables; version to appear in Phys. Lett.
Interpretation of neutrino flux limits from neutrino telescopes on the Hillas plot
We discuss the interplay between spectral shape and detector response beyond
a simple E^-2 neutrino flux at neutrino telescopes, at the example of
time-integrated point source searches using IceCube-40 data. We use a
self-consistent model for the neutrino production, in which protons interact
with synchrotron photons from co-accelerated electrons, and we fully take into
account the relevant pion and kaon production modes, the flavor composition at
the source, flavor mixing, and magnetic field effects on the secondaries
(pions, muon, and kaons). Since some of the model parameters can be related to
the Hillas parameters R (size of the acceleration region) and B (magnetic
field), we relate the detector response to the Hillas plane. In order to
compare the response to different spectral shapes, we use the energy flux
density as a measure for the pion production efficiency times luminosity of the
source. We demonstrate that IceCube has a very good reach in this quantity for
AGN nuclei and jets for all source declinations, while the spectra of sources
with strong magnetic fields are found outside the optimal reach. We also
demonstrate where neutrinos from kaon decays and muon tracks from tau decays
can be relevant for the detector response. Finally, we point out the
complementarity between IceCube and other experiments sensitive to high-energy
neutrinos, at the example of 2004-2008 Earth-skimming neutrino data from Auger.
We illustrate that Auger, in principle, is better sensitive to the parameter
region in the Hillas plane from which the highest-energetic cosmic rays may be
expected in this model.Comment: 28 pages, 10 figures. Substantial clarifications, such as on
definition of "sensitivity" and model descriptio
Orbiting dynamic compression laboratory
In order to examine the feasibility of carrying out dynamic compression experiments on a space station, the possibility of using explosive gun launchers is studied. The question of whether powders of a refractory metal (molybdenum) and a metallic glass could be well considered by dynamic compression is examined. In both cases extremely good bonds are obtained between grains of metal and metallic glass at 180 and 80 kb, respectively. When the oxide surface is reduced and the dynamic consolidation is carried out in vacuum, in the case of molybdenum, tensile tests of the recovered samples demonstrated beneficial ultimate tensile strengths
Homotopy Type Theory in Lean
We discuss the homotopy type theory library in the Lean proof assistant. The
library is especially geared toward synthetic homotopy theory. Of particular
interest is the use of just a few primitive notions of higher inductive types,
namely quotients and truncations, and the use of cubical methods.Comment: 17 pages, accepted for ITP 201
Exact dimer ground states for a continuous family of quantum spin chains
Using the matrix product formalism, we define a multi-parameter family of
spin models on one dimensional chains, with nearest and next-nearest neighbor
anti-ferromagnetic interaction for which exact analytical expressions can be
found for its doubly degenerate ground states. The family of Hamiltonians which
we define, depend on 5 continuous parameters and the Majumdar-Ghosh model is a
particular point in this parameter space. Like the Majumdar-Ghosh model, the
doubly degenerate ground states of our models have a very simple structure,
they are the product of entangled states on adjacent sites. In each of these
states there is a non-zero staggered magnetization, which vanishes when we take
their translation-invariant combination as the new ground states. At the
Majumdar-Ghosh point, these entangled states become the spin-singlets
pertaining to this model. We will also calculate in closed form the two point
correlation functions, both for finite size of the chain and in the
thermodynamic limit.Comment: 11 page
From AMANDA to IceCube
The first string of the neoteric high energy neutrino telescope IceCube
successfully began operating in January 2005. It is anticipated that upon
completion the new detector will vastly increase the sensitivity and extend the
reach of AMANDA to higher energies. A discussion of the IceCube's discovery
potential for extra-terrestrial neutrinos, together with the prospects of new
physics derived from the ongoing AMANDA research will be the focus of this
paper. Preliminary results of the first antarctic high energy neutrino
telescope AMANDA searching in the muon neutrino channel for localized and
diffuse excess of extra-terrestrial neutrinos will be reviewed using data
collected between 2000 and 2003. Neutrino flux limits obtained with the
all-flavor dedicated UHE and cascade analyses will be described. A first
neutrino spectrum above one TeV in agreement with atmospheric neutrino flux
expectations and no extra-terrestrial contribution will be presented, followed
by a discussion of a limit for neutralino CDM candidates annihilating in the
center of the Sun.Comment: 15 pages, 8 figures Invited talk contribution at 5th International
Conference on Non-accelerator New Physics (NANP 05), Dubna, Russia, 20-25 Jun
200
A Western Range Extension for Caprella scaura (Amphipoda: Caprellidae) in the Aransas Bay Ecosystem, Texas
During March 2009, the skeleton shrimp Caprella scaura and Paracaprella tenuis (Amphipoda: Caprellidae) were collected from several locations throughout the Aransas Bay, Texas ecosystem from Texas Parks and Wildlife fishery—independent trawl and oyster dredge samples. This is a western range expansion for C. scaura; P. tenuis has been reported from this area before. Both species were exclusively associated with a bryozoan, Bugula neritina. Densities of both species ranged between 0.1–3.4 individuals per gram of attached bryozoans. A reproductive population is likely established since several sizes, including adult males and gravid females, were observed. No caprellids were observed after early April, which coincided with a reduction in bryozoan occurrence in our routine monthly samples. These collections represent the first documented occurrence of C. scaura west of Florida
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