100 research outputs found
Improving the Efficiency of Inductive Logic Programming Through the Use of Query Packs
Inductive logic programming, or relational learning, is a powerful paradigm
for machine learning or data mining. However, in order for ILP to become
practically useful, the efficiency of ILP systems must improve substantially.
To this end, the notion of a query pack is introduced: it structures sets of
similar queries. Furthermore, a mechanism is described for executing such query
packs. A complexity analysis shows that considerable efficiency improvements
can be achieved through the use of this query pack execution mechanism. This
claim is supported by empirical results obtained by incorporating support for
query pack execution in two existing learning systems
On a Tabling Engine That Can Exploit Or-Parallelism
Abstract. Tabling is an implementation technique that improves the declarativeness and expressiveness of Prolog by reusing solutions to goals. Quite a few interesting applications of tabling have been developed in the last few years, and several are by nature non-deterministic. This raises the question of whether parallel search techniques can be used to improve the performance of tabled applications. In this work we demonstrate that the mechanisms proposed to parallelize search in the context of SLD resolution naturally generalize to parallel tabled computations, and that resulting systems can achieve good per-formance on multi-processors. To do so, we present the OPTYap par-allel engine. In our system individual SLG engines communicate data through stack copying. Completion is detected through a novel parallel completion algorithm that builds upon the data structures proposed for or-parallelism. Scheduling is simplified by building on previous research on or-parallelism. We show initial performance results for our implemen-tation. Our best result is for an actual application, model checking, where we obtain linear speedups
Distilling Gaussian states with Gaussian operations is impossible.
We show that no distillation protocol for Gaussian quantum states exists that
relies on (i) arbitrary local unitary operations that preserve the Gaussian
character of the state and (ii) homodyne detection together with classical
communication and postprocessing by means of local Gaussian unitary operations
on two symmetric identically prepared copies. This is in contrast to the
finite-dimensional case, where entanglement can be distilled in an iterative
protocol using two copies at a time. The ramifications for the distribution of
Gaussian states over large distances will be outlined. We also comment on the
generality of the approach and sketch the most general form of a Gaussian local
operation with classical communication in a bipartite setting.Comment: 4 pages, 1 colour figure. This paper is closely related to [J.
Fiurasek, PRL 89, 137904 (2002), quant-ph/0204069] and to [G. Giedke and J.I.
Cirac, PRA 66, 032316 (2002), quant-ph/0204085]. In particular, the latter
paper arrives with independent methods at the general result that
distillation is not possible for an arbitrary number of input copies and
general Gaussian operations. The title of our contribution in its printed
version has been changed by the editors of Physical Review Letter
Non-equilibrium states of a photon cavity pumped by an atomic beam
We consider a beam of two-level randomly excited atoms that pass one-by-one
through a one-mode cavity. We show that in the case of an ideal cavity, i.e. no
leaking of photons from the cavity, the pumping by the beam leads to an
unlimited increase in the photon number in the cavity. We derive an expression
for the mean photon number for all times. Taking into account leaking of the
cavity, we prove that the mean photon number in the cavity stabilizes in time.
The limiting state of the cavity in this case exists and it is independent of
the initial state. We calculate the characteristic functional of this
non-quasi-free non-equilibrium state. We also calculate the energy flux in both
the ideal and open cavity and the entropy production for the ideal cavity.Comment: Corrected energy production calculations and made some changes to
ease the readin
Entanglement concentration of continuous variable quantum states
We propose two probabilistic entanglement concentration schemes for a single
copy of two-mode squeezed vacuum state. The first scheme is based on the
off-resonant interaction of a Rydberg atom with the cavity field while the
second setup involves the cross Kerr interaction, auxiliary mode prepared in a
strong coherent state and a homodyne detection. We show that the
continuous-variable entanglement concentration allows us to improve the
fidelity of teleportation of coherent states.Comment: 7 pages, 7 figure
Cell Migration in the Immune System: the Evolving Inter-Related Roles of Adhesion Molecules and Proteinases
Leukocyte extravasation into perivascular tissue during inflammation and lymphocyte homing
to lymphoid organs involve transient adhesion to the vessel endothelium, followed by transmigration
through the endothelial cell (EC) layer and establishment of residency at the tissue site
for a period of time. In these processes, leukocytes undergo multiple attachments to, and detachments
from, the vessel-lining endothelial cells, prior to transendothelial cell migration. Transmigrating
leukocytes must traverse a subendothelial basement membrane en route to perivascular
tissues and utilize enzymes known as matrix metalloproteinases to make selective clips in the
extracellular matrix components of the basement membrane. This review will focus on the evidence
for a link between adhesion of leukocytes to endothelial cells, the induction of matrix
metalloproteinases mediated by engagement of adhesion receptors on leukocytes, and the ability
to utilize these matrix metalloproteinases to facilitate leukocyte invasion of tissues. Leukocytes
with invasive phenotypes express high levels of MMPs, and expression of MMPs
enhances the migratory and invasive properties of these cells. Furthermore, MMPs may be used
by lymphocytes to proteolytically cleave molecules such as adhesion receptors and membrane
bound cytokines, increasing their efficiency in the immune response. Engagement of leukocyte
adhesion receptors may modulate adhesive (modulation of integrin affinities and expression),
synthetic (proteinase induction and activation), and surface organization (clustering of proteolyric
complexes) behaviors of invasive leukocytes. Elucidation of these pathways will lead to
better understanding of controlling mechanisms in order to develop rational therapeutic
approaches in the areas of inflammation and autoimmunity
A segment-swapping approach for executing trapped computations
We consider the problem of supporting goal-level, independent andparallelism (IAP) in the presence of non-determinism. IAP is exploited when two or more goals which will not interfere at run time are scheduled for simultaneous execution. Backtracking over non-deterministic parallel goals runs into the wellknown trapped goal and garbage slot problems. The proposed solutions for these problems generally require complex low-level machinery which makes systems difficult to maintain and extend, and in some cases can even affect sequential execution performance. In this paper we propose a novel solution to the problem of trapped nondeterministic goals and garbage slots which is based on a single stack reordering operation and offers several advantages over previous proposals. While
the implementation of this operation itself is not simple, in return it does not impose constraints on the scheduler. As a result, the scheduler and the rest of the run-time machinery can safely ignore the trapped goal and garbage slot problems and their implementation is greatly simplified. Also, standard sequential execution remains unaffected. In addition to describing the solution we report on an implementation and provide performance results. We also suggest other possible applications of the proposed approach beyond parallel execution
Improving the compilation of prolog to C using moded types and determinism information
We describe the current status of and provide performance
results for a prototype compiler of Prolog to C, ciaocc. ciaocc is novel in that it is designed to accept different kinds of high-level information, typically obtained via an automatic analysis of the initial Prolog program and expressed in a standardized language of assertions. This information is used to optimize the resulting C code, which is then processed by an off-the-shelf C compiler. The basic translation process essentially mimics the unfolding of a bytecode emulator with respect to the particular bytecode corresponding to the Prolog program. This is facilitated by a flexible design of the instructions and their lower-level components. This approach allows reusing a sizable amount of the machinery of the bytecode emulator: predicates already written in C, data definitions, memory management routines and áreas, etc., as well as mixing emulated bytecode with native code in a relatively straightforward way. We report on the performance of programs compiled by the current versión of the system, both with and without analysis information
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