67,309 research outputs found
Beam-beam observations in the RHIC
The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory
has been in operation since 2000. Over the past decade, the luminosity in the
polarized proton (p-p) operations has increased by more than one order of
magnitude. The maximum total beam-beam tune shift with two collisions has
reached 0.018. The beam-beam interaction leads to large tune spread, emittance
growth, and short beam and luminosity lifetimes. In this article, we review the
beam-beam observations during the previous RHIC p-p runs. The mechanism for
particle loss is presented. The intra-beam scattering (IBS) contributions to
emittance and bunch length growths are calculated and compared with the
measurements. Finally, we will discuss current limits in the RHIC p-p
operations and their solutions.Comment: 7 pages, contribution to the ICFA Mini-Workshop on Beam-Beam Effects
in Hadron Colliders, CERN, Geneva, Switzerland, 18-22 Mar 201
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Mapping the evolutionary stages of asymmetrical supplier-buyer relationships: evidence from the Turkish textile industry
The aim of this paper is to empirically investigate asymmetrical relationship development stages by examining four relationship constructs from small textile suppliers’ perspective and identifying areas for improvement. This study adopted a multiple case study method for investigating the research question. Prior studies into business-to-business marketing have explored asymmetry in dyadic relationships that resulted in limited understanding to our knowledge. The research findings contributed to the understanding of how small suppliers identify critical relationship characteristics that help them to develop symmetries through initial, development and sustainment stages in size asymmetry
On the Finite-Time Blowup of a 1D Model for the 3D Incompressible Euler Equations
We study a 1D model for the 3D incompressible Euler equations in axisymmetric
geometries, which can be viewed as a local approximation to the Euler equations
near the solid boundary of a cylindrical domain. We prove the local
well-posedness of the model in spaces of zero-mean functions, and study the
potential formation of a finite-time singularity under certain convexity
conditions for the velocity field. It is hoped that the results obtained on the
1D model will be useful in the analysis of the full 3D problem, whose loss of
regularity in finite time has been observed in a recent numerical study (Luo
and Hou, 2013).Comment: 23 page
An invariant-based damage model for human and animal skins
Constitutive modelling of skins that account for damage effects is important to provide insight for various clinical applications, such as skin trauma and injury, artificial skin design, skin aging, disease diagnosis, surgery, as well as comparative studies of skin biomechanics between species. In this study, a new damage model for human and animal skins is proposed for the first time. The model is nonlinear, anisotropic, invariant-based, and is based on the Gasser–Ogden–Holzapfel constitutive law initially developed for arteries. Taking account of the mean collagen fibre orientation and its dispersion, the new model can describe a wide range of skins with damage. The model is first tested on the uniaxial test data of human skin and then applied to nine groups of uniaxial test data for the human, swine, rabbit, bovine and rhino skins. The material parameters can be inversely estimated based on uniaxial tests using the optimization method in MATLAB with a root mean square error ranged between 2.15% and 12.18%. A sensitivity study confirms that the fibre orientation dispersion and the mean fibre angle are among the most important factors that influence the behaviour of the damage model. In addition, these two parameters can only be reliably estimated if some histological information is provided. We also found that depending on the location of skins, the tissue damage may be brittle controlled by the fibre breaking limit (i.e., when the fibre stretch is greater than 1.13–1.32, depending on the species), or ductile (due to both the fibre and the matrix damages). The brittle damages seem to occur mostly in the back, and the ductile damages are seen from samples taken from the belly. The proposed constitutive model may be applied to various clinical applications that require knowledge of the mechanical response of human and animal skins
Preconditioning Markov Chain Monte Carlo Simulations Using Coarse-Scale Models
We study the preconditioning of Markov chain Monte Carlo (MCMC) methods using coarse-scale models with applications to subsurface characterization. The purpose of preconditioning is to reduce the fine-scale computational cost and increase the acceptance rate in the MCMC sampling. This goal is achieved by generating Markov chains based on two-stage computations. In the first stage, a new proposal is first tested by the coarse-scale model based on multiscale finite volume methods. The full fine-scale computation will be conducted only if the proposal passes the coarse-scale screening. For more efficient simulations, an approximation of the full fine-scale computation using precomputed multiscale basis functions can also be used. Comparing with the regular MCMC method, the preconditioned MCMC method generates a modified Markov chain by incorporating the coarse-scale information of the problem. The conditions under which the modified Markov chain will converge to the correct posterior distribution are stated in the paper. The validity of these assumptions for our application and the conditions which would guarantee a high acceptance rate are also discussed. We would like to note that coarse-scale models used in the simulations need to be inexpensive but not necessarily very accurate, as our analysis and numerical simulations demonstrate. We present numerical examples for sampling permeability fields using two-point geostatistics. The Karhunen--Loève expansion is used to represent the realizations of the permeability field conditioned to the dynamic data, such as production data, as well as some static data. Our numerical examples show that the acceptance rate can be increased by more than 10 times if MCMC simulations are preconditioned using coarse-scale models
Tuning the magnetism of ordered and disordered strongly-correlated electron nanoclusters
Recently, there has been a resurgence of intense experimental and theoretical
interest on the Kondo physics of nanoscopic and mesoscopic systems due to the
possibility of making experiments in extremely small samples. We have carried
out exact diagonalization calculations to study the effect of energy spacing
in the conduction band states, hybridization, number of electrons, and
disorder on the ground-state and thermal properties of strongly-correlated
electron nanoclusters. For the ordered systems, the calculations reveal for the
first time that tunes the interplay between the {\it local} Kondo and
{\it non local} RKKY interactions, giving rise to a "Doniach phase diagram" for
the nanocluster with regions of prevailing Kondo or RKKY correlations. The
interplay of and disorder gives rise to a versus
concentration T=0 phase diagram very rich in structure. The parity of the total
number of electrons alters the competition between the Kondo and RKKY
correlations. The local Kondo temperatures, , and RKKY interactions depend
strongly on the local environment and are overall {\it enhanced} by disorder,
in contrast to the hypothesis of ``Kondo disorder'' single-impurity models.
This interplay may be relevant to experimental realizations of small rings or
quantum dots with tunable magnetic properties.Comment: 10 pages, 13 figures, to appear in Physics of Spin in Solids:
Materials, Methods, and Applications, (2004
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