2,127 research outputs found
An Empirical Analysis of Search in GSAT
We describe an extensive study of search in GSAT, an approximation procedure
for propositional satisfiability. GSAT performs greedy hill-climbing on the
number of satisfied clauses in a truth assignment. Our experiments provide a
more complete picture of GSAT's search than previous accounts. We describe in
detail the two phases of search: rapid hill-climbing followed by a long plateau
search. We demonstrate that when applied to randomly generated 3SAT problems,
there is a very simple scaling with problem size for both the mean number of
satisfied clauses and the mean branching rate. Our results allow us to make
detailed numerical conjectures about the length of the hill-climbing phase, the
average gradient of this phase, and to conjecture that both the average score
and average branching rate decay exponentially during plateau search. We end by
showing how these results can be used to direct future theoretical analysis.
This work provides a case study of how computer experiments can be used to
improve understanding of the theoretical properties of algorithms.Comment: See http://www.jair.org/ for any accompanying file
Allocation in Practice
How do we allocate scarcere sources? How do we fairly allocate costs? These
are two pressing challenges facing society today. I discuss two recent projects
at NICTA concerning resource and cost allocation. In the first, we have been
working with FoodBank Local, a social startup working in collaboration with
food bank charities around the world to optimise the logistics of collecting
and distributing donated food. Before we can distribute this food, we must
decide how to allocate it to different charities and food kitchens. This gives
rise to a fair division problem with several new dimensions, rarely considered
in the literature. In the second, we have been looking at cost allocation
within the distribution network of a large multinational company. This also has
several new dimensions rarely considered in the literature.Comment: To appear in Proc. of 37th edition of the German Conference on
Artificial Intelligence (KI 2014), Springer LNC
Unfolding the Sulcus
Sulci are localized furrows on the surface of soft materials that form by a
compression-induced instability. We unfold this instability by breaking its
natural scale and translation invariance, and compute a limiting bifurcation
diagram for sulcfication showing that it is a scale-free, sub-critical {\em
nonlinear} instability. In contrast with classical nucleation, sulcification is
{\em continuous}, occurs in purely elastic continua and is structurally stable
in the limit of vanishing surface energy. During loading, a sulcus nucleates at
a point with an upper critical strain and an essential singularity in the
linearized spectrum. On unloading, it quasi-statically shrinks to a point with
a lower critical strain, explained by breaking of scale symmetry. At
intermediate strains the system is linearly stable but nonlinearly unstable
with {\em no} energy barrier. Simple experiments confirm the existence of these
two critical strains.Comment: Main text with supporting appendix. Revised to agree with published
version. New result in the Supplementary Informatio
Mean Curvature Flow of Spacelike Graphs
We prove the mean curvature flow of a spacelike graph in of a map from a closed Riemannian
manifold with to a complete Riemannian manifold
with bounded curvature tensor and derivatives, and with
sectional curvatures satisfying , remains a spacelike graph,
exists for all time, and converges to a slice at infinity. We also show, with
no need of the assumption , that if , or if and
, constant, any map is trivially
homotopic provided where
, in case , and
in case . This largely extends some known results for
constant and compact, obtained using the Riemannian structure
of , and also shows how regularity theory on the mean
curvature flow is simpler and more natural in pseudo-Riemannian setting then in
the Riemannian one.Comment: version 5: Math.Z (online first 30 July 2010). version 4: 30 pages:
we replace the condition by the the weaker one .
The proofs are essentially the same. We change the title to a shorter one. We
add an applicatio
The cholesterol-raising diterpenes from coffee beans increase serum lipid transfer protein activity levels in humans
Cafestol and kahweol–diterpenes present in unfiltered coffee— strongly raise serum VLDL and LDL cholesterol and slightly reduce HDL cholesterol in humans. The mechanism of action is unknown. We determined whether the coffee diterpenes may affect lipoprotein metabolism via effects on lipid transfer proteins and lecithin:cholesterol acyltransferase in a randomized, double-blind cross-over study with 10 healthy male volunteers. Either cafestol (61–64 mg/day) or a mixture of cafestol (60 mg/day) and kahweol (48–54 mg/day) was given for 28 days. Serum activity levels of cholesterylester transfer protein, phospholipid transfer protein and lecithin:cholesterol acyltransferase were measured using exogenous substrate assays. Relative to baseline values, cafestol raised the mean (±S.D.) activity of cholesterylester transfer protein by 18±12% and of phospholipid transfer protein by 21±14% (both P<0.001). Relative to cafestol alone, kahweol had no significant additional effects. Lecithin:cholesterol acyltransferase activity was reduced by 11±12% by cafestol plus kahweol (P=0.02). It is concluded that the effects of coffee diterpenes on plasma lipoproteins may be connected with changes in serum activity levels of lipid transfer proteins
Mental health problems in deaf and severely hard of hearing children and adolescents : findings on prevalence, pathogenesis and clinical complexities, and implications for prevention, diagnosis and intervention
The aim of this thesis is to expand the knowledge of mental health problems with deaf and severely hard of hearing children and adolescents in the following domains: 1. The prevalence of mental health problems; 2. Specific intra- and interpersonal aspects of pathogenesis; 3. characteristics of the hearing impaired population with severe mental health problems. The rate of mental health problems, especially of emotional problems, was increased in deaf adolescents of normal intelligence compared with the general population. However, findings from the studies described in this thesis support the view that it is not deafness in itself which contributes to mental health problems but rather deafness in conjunction with physical health problems, communication problems, and adverse living conditions. For example, stress-inducing deafness-related characteristics such as an acquired cause of deafness moderated the associati on between low self-esteem and emotional disorder in deaf adolescents. Comparing hearing and hearing impaired children referred to a mental health service over a period of 15 years, more disabling physical health conditions, more intellectual impairment and more environmental distress were found with hearing impaired children. The findings argue for the importance of early detection of problems and a multi-informant approach to the assessment of disorder.UBL - phd migration 201
On The Complexity and Completeness of Static Constraints for Breaking Row and Column Symmetry
We consider a common type of symmetry where we have a matrix of decision
variables with interchangeable rows and columns. A simple and efficient method
to deal with such row and column symmetry is to post symmetry breaking
constraints like DOUBLELEX and SNAKELEX. We provide a number of positive and
negative results on posting such symmetry breaking constraints. On the positive
side, we prove that we can compute in polynomial time a unique representative
of an equivalence class in a matrix model with row and column symmetry if the
number of rows (or of columns) is bounded and in a number of other special
cases. On the negative side, we show that whilst DOUBLELEX and SNAKELEX are
often effective in practice, they can leave a large number of symmetric
solutions in the worst case. In addition, we prove that propagating DOUBLELEX
completely is NP-hard. Finally we consider how to break row, column and value
symmetry, correcting a result in the literature about the safeness of combining
different symmetry breaking constraints. We end with the first experimental
study on how much symmetry is left by DOUBLELEX and SNAKELEX on some benchmark
problems.Comment: To appear in the Proceedings of the 16th International Conference on
Principles and Practice of Constraint Programming (CP 2010
Fracture of a biopolymer gel as a viscoplastic disentanglement process
We present an extensive experimental study of mode-I, steady, slow crack
dynamics in gelatin gels. Taking advantage of the sensitivity of the elastic
stiffness to gel composition and history we confirm and extend the model for
fracture of physical hydrogels which we proposed in a previous paper (Nature
Materials, doi:10.1038/nmat1666 (2006)), which attributes decohesion to the
viscoplastic pull-out of the network-constituting chains. So, we propose that,
in contrast with chemically cross-linked ones, reversible gels fracture without
chain scission
Characterization of human high-density lipoprotein subclasses LP A-I and LP A-I/A-II and binding to HepG2 cells
Abstract
Plasma HDL can be classified according to their apolipoprotein content into at least two types of lipoprotein particles: lipoproteins containing both apo A-I and apo A-II (LP A-I/A-II) and lipoproteins with apo A-I but without apo A-II (LP A-I). LP A-I and LP A-I/A-II were isolated by immuno-affinity chromatography. LP A-I has a higher cholesterol content and less protein compared to LP A-I/A-II. The average particle mass of LP A-I is higher (379 kDa) than the average particle weight of LP A-I/A-II (269 kDa). The binding of 125I-LP A-I to HepG2 cells at 4°C, as well as the uptake of [3H]cholesteryl ether-labelled LP A-I by HepG2 cells at 37° C, was significantly higher than the binding and uptake of LP A-I/A-II. It is likely that both binding and uptake are mediated by apo A-I. Our results do not provide evidence in favor of a specific role for apo A-II in the binding and uptake of HDL by HepG2 cells
Magic angles and cross-hatching instability in hydrogel fracture
The full 2D analysis of roughness profiles of fracture surfaces resulting
from quasi-static crack propagation in gelatin gels reveals an original
behavior characterized by (i) strong anisotropy with maximum roughness at
-independent symmetry-preserving angles, (ii) a sub-critical instability
leading, below a critical velocity, to a cross-hatched regime due to straight
macrosteps drifting at the same magic angles and nucleated on crack-pinning
network inhomogeneities. Step height values are determined by the width of the
strain-hardened zone, governed by the elastic crack blunting characteristic of
soft solids with breaking stresses much larger that low strain moduli
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