999 research outputs found
Effective scraping in a scraped surface heat exchanger: some fluid flow analysis
An outline of mathematical models that have been used to understand the behaviour of scraped surface heat exchangers is presented. In particular the problem of the wear of the blades is considered. A simple model, exploiting known behaviour of viscous flow in corners and in wedges, and accounting for the forces on the blade is derived and solutions generated. The results shows initial rapid wear but that the wear rate goes to zero
Organizational Purchasing Theory: A Review and Assessment
Mark C. Hall is an Associate Professor in the Department of Marketing at Mankato State University. C.P. Rao is University Professor in the Department of Marketing at the University of Arkansas. Kevin M. Elliott is an Associate Professor in the Department of Marketing at Mankato State University
Proteus: A Hierarchical Portfolio of Solvers and Transformations
In recent years, portfolio approaches to solving SAT problems and CSPs have
become increasingly common. There are also a number of different encodings for
representing CSPs as SAT instances. In this paper, we leverage advances in both
SAT and CSP solving to present a novel hierarchical portfolio-based approach to
CSP solving, which we call Proteus, that does not rely purely on CSP solvers.
Instead, it may decide that it is best to encode a CSP problem instance into
SAT, selecting an appropriate encoding and a corresponding SAT solver. Our
experimental evaluation used an instance of Proteus that involved four CSP
solvers, three SAT encodings, and six SAT solvers, evaluated on the most
challenging problem instances from the CSP solver competitions, involving
global and intensional constraints. We show that significant performance
improvements can be achieved by Proteus obtained by exploiting alternative
view-points and solvers for combinatorial problem-solving.Comment: 11th International Conference on Integration of AI and OR Techniques
in Constraint Programming for Combinatorial Optimization Problems. The final
publication is available at link.springer.co
Universal property of the information entropy in fermionic and bosonic systems
It is shown that a similar functional form holds approximately
for the information entropy S as function of the number of particles N for
atoms, nuclei and atomic clusters (fermionic systems) and correlated
boson-atoms in a trap (bosonic systems). It is also seen that rigorous
inequalities previously found to hold between S and the kinetic energy T for
fermionic systems, hold for bosonic systems as well. It is found that
Landsberg's order parameter is an increasing function of N for the
above systems. It is conjectured that the above properties are universal i.e.
they do not depend on the kind of constituent particles (fermions or correlated
bosons) and the size of the system.Comment: 6 pages, 2 EPS figures, LaTe
Constraints on the SU(3) Electroweak Model
We consider a recent proposal by Dimopoulos and Kaplan to embed the
electroweak SU(2)_L X U(1)_Y into a larger group SU(3)_W X SU(2) X U(1) at a
scale above a TeV. This idea is motivated by the prediction for the weak mixing
angle sin^2 theta_W = 1/4, which naturally appears in these models so long as
the gauge couplings of the high energy SU(2) and U(1) groups are moderately
large. The extended gauge dynamics results in new effective operators that
contribute to four-fermion interactions and Z pole observables. We calculate
the corrections to these electroweak precision observables and carry out a
global fit of the new physics to the data. For SU(2) and U(1) gauge couplings
larger than 1, we find that the 95% C.L. lower bound on the matching (heavy
gauge boson mass) scale is 11 TeV. We comment on the fine-tuning of the high
energy gauge couplings needed to allow matching scales above our bounds. The
remnants of SU(3)_W breaking include multi-TeV SU(2)_L doublets with electric
charge (+-2,+-1). The lightest charged gauge boson is stable, leading to
cosmological difficulties.Comment: 17 pages, LaTeX, 4 figures embedded, uses JHEP.cl
Supersymmetric Large Extra Dimensions and the Cosmological Constant: An Update
This article critically reviews the proposal for addressing the cosmological
constant problem within the framework of supersymmetric large extra dimensions
(SLED), as recently proposed in hep-th/0304256. After a brief restatement of
the cosmological constant problem, a short summary of the proposed mechanism is
given. The emphasis is on the perspective of the low-energy effective theory in
order to see how it addresses the problem of why low-energy particles like the
electron do not contribute too large a vacuum energy. This is followed by a
discussion of the main objections, which are grouped into the following five
topics:
(1) Weinberg's No-Go Theorem.
(2) Are hidden tunings of the theory required, and a problem?
(3) Why should the mechanism not rule out earlier epochs of inflation?
(4) How big are quantum effects, and which are the most dangerous?
(5) Can the mechanism be consistent with cosmological constraints?
It is argued that there are plausible reasons why the mechanism can thread
the potential objections, but that a definitive proof that it does depends on
addressing well-defined technical points. These points include identifying what
fixes the size of the extra dimensions, checking how topological obstructions
renormalize and performing specific calculations of quantum corrections. More
detailed studies of these issues, which are well reach within our present
understanding of extra-dimensional theories, are currently underway. As such,
the jury remains out concerning the proposal, although the prospects for
acquittal still seem good.Comment: 21 pages; an extended version of the contribution to the proceedings
of SUSY 2003, University of Arizona, Tucson AZ, June 2003, which has also
been updated to include developments since the conference. (v2 includes some
updated references and corrects a minor error in the bulk loop section
Loop-Generated Bounds on Changes to the Graviton Dispersion Relation
We identify the effective theory appropriate to the propagation of massless
bulk fields in brane-world scenarios, to show that the dominant low-energy
effect of asymmetric warping in the bulk is to modify the dispersion relation
of the effective 4-dimensional modes. We show how such changes to the graviton
dispersion relation may be bounded through the effects they imply, through
loops, for the propagation of standard model particles. We compute these bounds
and show that they provide, in some cases, the strongest constraints on
nonstandard gravitational dispersions. The bounds obtained in this way are the
strongest for the fewest extra dimensions and when the extra-dimensional Planck
mass is the smallest. Although the best bounds come for warped 5-D scenarios,
for which the 5D Planck Mass is O(TeV), even in 4 dimensions the graviton loop
can lead to a bound on the graviton speed which is comparable with other
constraints.Comment: 18 pages, LaTeX, 4 figures, uses revte
A Planck-scale axion and SU(2) Yang-Mills dynamics: Present acceleration and the fate of the photon
From the time of CMB decoupling onwards we investigate cosmological evolution
subject to a strongly interacting SU(2) gauge theory of Yang-Mills scale
eV (masquerading as the factor of the SM at
present). The viability of this postulate is discussed in view of cosmological
and (astro)particle physics bounds. The gauge theory is coupled to a spatially
homogeneous and ultra-light (Planck-scale) axion field. As first pointed out by
Frieman et al., such an axion is a viable candidate for quintessence, i.e.
dynamical dark energy, being associated with today's cosmological acceleration.
A prediction of an upper limit for the duration of the
epoch stretching from the present to the point where the photon starts to be
Meissner massive is obtained: billion years.Comment: v3: consequences of an error in evolution equation for coupling
rectified, only a minimal change in physics results, two refs. adde
Landscape equivalent of the shoving model
It is shown that the shoving model expression for the average relaxation time
of viscous liquids follows largely from a classical "landscape" estimation of
barrier heights from curvature at energy minima. The activation energy involves
both instantaneous bulk and shear moduli, but the bulk modulus contributes less
than 8% to the temperature dependence of the activation energy. This reflects
the fact that the physics of the two models are closely related.Comment: 4 page
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