268 research outputs found
Deep drawing simulation of Tailored Blanks
Tailored blanks are increasingly used in the automotive industry. A tailored blank consists of different metal parts, which are joined by a welding process. These metal parts usually have different material properties. Hence, the main advantage of using a tailored blank is to provide the right material properties at specific parts of the blank. The movement of the weld during forming is extremely important. Unwanted weld displacement can cause damage to both the product and the tool. This depends mainly on the original weld position and the process parameters. However experimental determination of the optimum weld position is quite expensive. Therefore a numerical tool has been developed for simulations of tailored blank forming. The Finite Element Code Dieka is used for the deep drawing simulations of some geometrically simple products. The results have been validated by comparing them with experimental data and show a satisfactory correlation
Selective metallization of alumina by laser
Nickel has been selectively deposited on an alumina substrate without any pretreatment from a flow of a nickel acetate solution using the focused beam of an excimer laser. Nickel spots as well as nickel lines were drawn and subsequently plated with an electroless Ni-B coating. Excellent adhesion of the metallized layers was achieved, since with laser irradiation, both etching and deposition took place simultaneously
Dual Liquid Flyback Booster for the Space Shuttle
Liquid Flyback Boosters provide an opportunity to improve shuttle safety, increase performance, and reduce operating costs. The objective of the LFBB study is to establish the viability of a LFBB configuration to integrate into the shuffle vehicle and meet the goals of the Space Shuttle upgrades program. The design of a technically viable LFBB must integrate into the shuffle vehicle with acceptable impacts to the vehicle elements, i.e. orbiter and external tank and the shuttle operations infrastructure. The LFBB must also be capable of autonomous return to the launch site. The smooth integration of the LFBB into the space shuttle vehicle and the ability of the LFBB to fly back to the launch site are not mutually compatible capabilities. LFBB wing configurations optimized for ascent must also provide flight quality during the powered return back to the launch site. This paper will focus on the core booster design and ascent performance. A companion paper 'Conceptual Design for a Space Shuttle Liquid Flyback Booster' will focus on the flyback system design and performance. The LFBB study developed design and aerodynamic data to demonstrate the viability of a dual booster configuration to meet the shuttle upgrade goals, i.e. enhanced safety, improved performance and reduced operations costs
Charged excitons in doped extended Hubbard model systems
We show that the charge transfer excitons in a Hubbard model system including
nearest neighbor Coulomb interactions effectively attain some charge in doped
systems and become visible in photoelectron and inverse photoelectron
spectroscopies. This shows that the description of a doped system by an
extended Hubbard model differs substantially from that of a simple Hubbard
model. Longer range Coulomb interactions cause satellites in the one electron
removal and addition spectra and the appearance of spectral weight if the gap
of doped systems at energies corresponding to the excitons of the undoped
systems. The spectral weight of the satellites is proportional to the doping
times the coordination number and therefore is strongly dependent on the
dimension.Comment: 10 pages revtex, 5 figures ps figures adde
Strengthening our grip on food security by encoding physics into AI
Climate change will jeopardize food security. Food security involves the
robustness of the global agri-food system. This agri-food system is intricately
connected to systems centering around health, economy, social-cultural
diversity, and global political stability. A systematic way to determine
acceptable interventions in the global agri-food systems involves analyses at
different spatial and temporal scales. Such multi-scale analyses are common
within physics. Unfortunately, physics alone is not sufficient. Machine
learning techniques may aid. We focus on neural networks (NN) into which
physics-based information is encoded (PeNN) and apply it to a sub-problem
within the agri-food system. We show that the mean squared error of the PeNN is
always smaller than that of the NNs, in the order of a factor of thousand.
Furthermore, the PeNNs capture extra and interpolation very well, contrary to
the NNs. It is shown that PeNNs need a much smaller data set size than the NNs
to achieve a similar mse. Our results suggest that the incorporation of physics
into neural networks architectures yields promise for addressing food security
Switching Casimir forces with Phase Change Materials
We demonstrate here a controllable variation in the Casimir force. Changes in
the force of up to 20% at separations of ~100 nm between Au and AgInSbTe (AIST)
surfaces were achieved upon crystallization of an amorphous sample of AIST.
This material is well known for its structural transformation, which produces a
significant change in the optical properties and is exploited in optical data
storage systems. The finding paves the way to the control of forces in
nanosystems, such as micro- or nanoswitches by stimulating the phase change
transition via localized heat sources.Comment: 7 pages, 3 figures The AFM images for the inset in Fig.2 were
replaced with new ones as obtained with tips having high aspect rati
Inter-site Coulomb interaction and Heisenberg exchange
Based on exact diagonalization results for small clusters we discuss the
effect of inter-site Coulomb repulsion in Mott-Hubbard or charge transfer
insulators. Whereas the exchange constant J for direct exchange is
substantially enhanced by inter-site Coulomb interaction, that for
superexchange is suppressed. The enhancement of J in the single-band models
holds up to the critical value for the charge density wave (CDW) instability,
thus opening the way for large values of J. Single-band Hubbard models with
sufficiently strong inter-site repulsion to be near a CDW instability thus may
provide `physical' realizations of t-J like models with the `unphysical'
parameter ratio J/t=1.Comment: Revtex file, 4 PRB pages, with 5 embedded ps-files. To appear in PRB,
rapid communications. Hardcopies of figures or the entire manuscript may also
be obtained by e-mail request to: [email protected]
Adsorption of colloidal particles in the presence of external field
We present a new class of sequential adsorption models in which the adsorbing
particles reach the surface following an inclined direction (shadow models).
Capillary electrophoresis, adsorption in the presence of a shear or on an
inclined substrate are physical manifestations of these models. Numerical
simulations are carried out to show how the new adsorption mechanisms are
responsible for the formation of more ordered adsorbed layers and have
important implications in the kinetics, in particular modifying the jamming
limit.Comment: LaTex file, 3 figures available upon request, to appear in
Phys.Rev.Let
The spectral weight of the Hubbard model through cluster perturbation theory
We calculate the spectral weight of the one- and two-dimensional Hubbard
models, by performing exact diagonalizations of finite clusters and treating
inter-cluster hopping with perturbation theory. Even with relatively modest
clusters (e.g. 12 sites), the spectra thus obtained give an accurate
description of the exact results. Thus, spin-charge separation (i.e. an
extended spectral weight bounded by singularities) is clearly recognized in the
one-dimensional Hubbard model, and so is extended spectral weight in the
two-dimensional Hubbard model.Comment: 4 pages, 5 figure
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