46,956 research outputs found
Response of A356 to warm rotary forming and subsequent T6 heat treatment
The through-process microstructural effects in A356 subjected to rotary
forming at elevated temperatures have been investigated. Macro and
micro-hardness testing have been used extensively to track changes in the
material from the as-cast state to as-formed, and T6 heat treated. Targeted
thermal treatments have been used to isolate the effects of mechanical
deformation through comparative measurements. These measurements include macro
and micro hardness measurements, Energy-dispersive X-ray analysis and
examination of eutectic-Si particle size and morphology. The results indicate
that the as-cast material is stable up to approximately 144{\deg}C, with the
rotary formed material exhibiting decreased macrohardness in-line with the time
spent at elevated temperature. Post heat treatment, there was a significant
decrease in hardness with increased levels of deformation. Results indicate
that precipitation hardening is not appreciably affected by rotary forming, and
the principal cause for the drop in hardness with deformation is due to the
condition of Al-Si eutectic phase.Comment: 26 pages, 13 figure
Distribution Functions of the Nucleon and Pion in the Valence Region
We provide an experimental and theoretical perspective on the behavior of
unpolarized distribution functions for the nucleon and pion on the
valence-quark domain; namely, Bjorken-x \gtrsim 0.4. This domain is key to much
of hadron physics; e.g., a hadron is defined by its flavor content and that is
a valence-quark property. Furthermore, its accurate parametrization is crucial
to the provision of reliable input for large collider experiments. We focus on
experimental extractions of distribution functions via electron and muon
inelastic scattering, and from Drell-Yan interactions; and on theoretical
treatments that emphasize an explanation of the distribution functions,
providing an overview of major contemporary approaches and issues.
Valence-quark physics is a compelling subject, which probes at the heart of our
understanding of the Standard Model. There are numerous outstanding and
unresolved challenges, which experiment and theory must confront. In connection
with experiment, we explain that an upgraded Jefferson Lab facility is
well-suited to provide new data on the nucleon, while a future electron ion
collider could provide essential new data for the mesons. There is also great
potential in using Drell-Yan interactions, at FNAL, J-PARC and GSI, to push
into the large-x domain for both mesons and nucleons. We argue furthermore that
explanation, in contrast to modeling and parametrization, requires a widespread
acceptance of the need to adapt theory: to the lessons learnt already from the
methods of nonperturbative quantum field theory; and a fuller exploitation of
those methods.Comment: Review article: 133 double-spaced pages, 44 figures, 6 table
Analysis and modelling of a rotary forming process for cast aluminum alloy A356
Spinning of a common aluminum automotive casting alloy A356 (Al-7Si-0.3 Mg)
at elevated temperatures has been investigated experimentally with a novel
industrial-scale apparatus. This has permitted the implementation of a fully
coupled thermomechanical finite element model aimed at quantifying the
processing history (stress, strain, strain-rate and temperature) and predicting
the final geometry. The geometric predictions of this model have been compared
directly to the geometry of the workpieces obtained experimentally. This study
is novel in regards to both the size and shape of the component as well as the
constitutive material representation employed. The model predictions are in
reasonable agreement with experimental results for small deformations, but
errors increase for large deformation conditions. The model has also enabled
the characterization of the mechanical state which leads to a common spinning
defect. Suggestions for improving the accuracy and robustness of the model to
provide a predictive tool for industry are discussed
Permeability of a one-dimensional potential barrier
Permeability of one dimensional potential barrie
X-ray bursts from solar flares behind the limb
X-ray bursts are identified from the UCSD OSO-7 X-ray experiment data. X-ray spectroheliograms of OSO-5, H alpha activity at the limb, and the emergence and disappearance of sunspot groups at the limb were studied and 17 active centers were found as likely seats of the X-ray bursts beyond the limb. The analysis of 37 X-ray bursts and their physical parameters is presented. Results show that (1) the distributions of maximum temperature, maximum emission measure, and characteristic cooling time of the over-the-limb events do not significantly differ from those of disk events; (2) that radiation is the dominant cooling mechanism for the hot flare plasma; and (3) that the scale height for X-ray emission in the 5-10 keV range is large. Observations show that the fraction of soft X-ray bursts which have a nonthermal component is the same on and off of the disk. Hard X-ray emission over extended regions is indicated
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A modular hybrid simulation framework for complex manufacturing system design
For complex manufacturing systems, the current hybrid Agent-Based Modelling and Discrete Event Simulation (ABM–DES) frameworks are limited to component and system levels of representation and present a degree of static complexity to study optimal resource planning. To address these limitations, a modular hybrid simulation framework for complex manufacturing system design is presented. A manufacturing system with highly regulated and manual handling processes, composed of multiple repeating modules, is considered. In this framework, the concept of modular hybrid ABM–DES technique is introduced to demonstrate a novel simulation method using a dynamic system of parallel multi-agent discrete events. In this context, to create a modular model, the stochastic finite dynamical system is extended to allow the description of discrete event states inside the agent for manufacturing repeating modules (meso level). Moreover, dynamic complexity regarding uncertain processing time and resources is considered. This framework guides the user step-by-step through the system design and modular hybrid model. A real case study in the cell and gene therapy industry is conducted to test the validity of the framework. The simulation results are compared against the data from the studied case; excellent agreement with 1.038% error margin is found in terms of the company performance. The optimal resource planning and the uncertainty of the processing time for manufacturing phases (exo level), in the presence of dynamic complexity is calculated
Massive particle creation in a static 1+1 dimensional spacetime
We show explicitly that there is particle creation in a static spacetime.
This is done by studying the field in a coordinate system based on a physical
principle which has recently been proposed. There the field is quantized by
decomposing it into positive and negative frequency modes on a particular
spacelike surface. This decomposition depends explicitly on the surface where
the decomposition is performed, so that an observer who travels from one
surface to another will observe particle production due to the different vacuum
state.Comment: 17 pages, RevTeX, no figure
Nucleon spin structure at very high-x
Dyson-Schwinger equation treatments of the strong interaction show that the
presence and importance of nonpointlike diquark correlations within the nucleon
are a natural consequence of dynamical chiral symmetry breaking. Using this
foundation, we deduce a collection of simple formulae, expressed in terms of
diquark appearance and mixing probabilities, from which one may compute ratios
of longitudinal-spin-dependent u- and d-quark parton distribution functions on
the domain x =1. A comparison with predictions from other approaches plus a
consideration of extant and planned experiments shows that the measurement of
nucleon longitudinal spin asymmetries on x =1 can add considerably to our
capacity for discriminating between contemporary pictures of nucleon structure.Comment: 6 pages, 1 table, 3 figures. To appear in Phys. Lett.
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