384,326 research outputs found
An Engineering Approach towards Action Refinement
In the abstract modelling of distributed systems we may need methods to replace abstract behaviours by more concrete behaviours which are closer to implementation mechanisms. Furthermore, we may want these methods to preserve the correctness of such a replacement. This paper introduces an approach towards action refinement in which an abstract action is replaced by a concrete activity. This approach is based on a careful consideration of the `action' and `causality relation' architectural concepts, which enable an abstract action to be replaced by many alternative concrete activities in a general way. This approach is based on the application of abstraction rules to determine whether a concrete activity conforms to an abstract action, considering the context in which the concrete activity and the abstract action are embedde
Maximum power operation of interacting molecular motors
We study the mechanical and thermodynamic properties of different traffic
models for kinesin which are relevant in biological and experimental contexts.
We find that motor-motor interactions play a fundamental role by enhancing the
thermodynamic efficiency at maximum power of the motors, as compared to the
non-interacting system, in a wide range of biologically compatible scenarios.
We furthermore consider the case where the motor-motor interaction directly
affects the internal chemical cycle and investigate the effect on the system
dynamics and thermodynamics.Comment: 19 pages, 22 figure
The exclusion of improperly obtained evidence in Greece: Putting constitutional rights first
Copyright @ 2007 Vathek PublishingIn contrast with England and Wales, where there is a discretion to exclude improperly obtained evidence, exclusion in Greece is automatic. Article 177 para. 2 of the Code of Penal Procedure mandates that evidence obtained by the commission of criminal offences is not taken into consideration. In addition, article 19 para. 3 of the Constitution prohibits the use of evidence obtained in violation of the right to privacy. Inspired by the rigidity of these exclusionary rules, the rights-centred approach that they reflect and the context of a constitutional criminal procedure within which they apply, this article sheds light on the protection of constitutional rights as a rationale for the exclusion of improperly obtained evidence. It does so against the background of the reliability-centred exclusionary doctrine in England
Quasipinning and its relevance for -Fermion quantum states
Fermionic natural occupation numbers (NON) do not only obey Pauli's famous
exclusion principle but are even further restricted to a polytope by the
generalized Pauli constraints, conditions which follow from the fermionic
exchange statistics. Whenever given NON are pinned to the polytope's boundary
the corresponding -fermion quantum state simplifies due to
a selection rule. We show analytically and numerically for the most relevant
settings that this rule is stable for NON close to the boundary, if the NON are
non-degenerate. In case of degeneracy a modified selection rule is conjectured
and its validity is supported. As a consequence the recently found effect of
quasipinning is physically relevant in the sense that its occurrence allows to
approximately reconstruct , its entanglement properties and
correlations from 1-particle information. Our finding also provides the basis
for a generalized Hartree-Fock method by a variational ansatz determined by the
selection rule
Self-stabilizing tree algorithms
Designers of distributed algorithms have to contend with the problem of making the algorithms tolerant to several forms of coordination loss, primarily faulty initialization. The processes in a distributed system do not share a global memory and can only get a partial view of the global state. Transient failures in one part of the system may go unnoticed in other parts and thus cause the system to go into an illegal state. If the system were self-stabilizing, however, it is guaranteed that it will return to a legal state after a finite number of state transitions. This thesis presents and proves self-stabilizing algorithms for calculating tree metrics and for achieving mutual exclusion on a tree structured distributed system
Exclusion statistics,operator algebras and Fock space representations
We study exclusion statistics within the second quantized approach. We
consider operator algebras with positive definite Fock space and restrict them
in a such a way that certain state vectors in Fock space are forbidden ab
initio.We describe three characteristic examples of such exclusion, namely
exclusion on the base space which is characterized by states with specific
constraint on quantum numbers belonging to base space M (e.g.
Calogero-Sutherland type of exclusion statistics), exclusion in the
single-oscillator Fock space, where some states in single oscillator Fock space
are forbidden (e.g. the Gentile realization of exclusion statistics) and a
combination of these two exclusions (e.g. Green's realization of para-Fermi
statistics). For these types of exclusions we discuss extended Haldane
statistics parameters g, recently introduced by two of us in Mod.Phys.Lett.A
11, 3081 (1996), and associated counting rules. Within these three types of
exclusions in Fock space the original Haldane exclusion statistics cannot be
realized.Comment: Latex,31 pages,no figures,to appear in J.Phys.A : Math.Ge
Rules for biological regulation based on error minimization
The control of gene expression involves complex mechanisms that show large
variation in design. For example, genes can be turned on either by the binding
of an activator (positive control) or the unbinding of a repressor (negative
control). What determines the choice of mode of control for each gene? This
study proposes rules for gene regulation based on the assumption that free
regulatory sites are exposed to nonspecific binding errors, whereas sites bound
to their cognate regulators are protected from errors. Hence, the selected
mechanisms keep the sites bound to their designated regulators for most of the
time, thus minimizing fitness-reducing errors. This offers an explanation of
the empirically demonstrated Savageau demand rule: Genes that are needed often
in the natural environment tend to be regulated by activators, and rarely
needed genes tend to be regulated by repressors; in both cases, sites are bound
for most of the time, and errors are minimized. The fitness advantage of error
minimization appears to be readily selectable. The present approach can also
generate rules for multi-regulator systems. The error-minimization framework
raises several experimentally testable hypotheses. It may also apply to other
biological regulation systems, such as those involving protein-protein
interactions.Comment: biological physics, complex networks, systems biology,
transcriptional regulation
http://www.weizmann.ac.il/complex/tlusty/papers/PNAS2006.pdf
http://www.pnas.org/content/103/11/3999.ful
Enforcement and Spectrum Sharing: Case Studies of Federal-Commercial Sharing
To promote economic growth and unleash the potential of wireless broadband, there is a need to introduce more spectrally efficient technologies and spectrum management regimes. That led to an environment where commercial wireless broadband need to share spectrum with the federal and non-federal operations. Implementing sharing regimes on a non-opportunistic basis means that sharing agreements must be implemented. To have meaning, those agreements must be enforceable.\ud
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With the significant exception of license-free wireless systems, commercial wireless services are based on exclusive use. With the policy change facilitating spectrum sharing, it becomes necessary to consider how sharing might take place in practice. Beyond the technical aspects of sharing, that must be resolved lie questions about how usage rights are appropriately determined and enforced. This paper is reasoning about enforcement in a particular spectrum bands (1695-1710 MHz and 3.5 GHz) that are currently being proposed for sharing between commercial services and incumbent spectrum users in the US. We examine three enforcement approaches, exclusion zones, protection zones and pure ex post and consider their implications in terms of cost elements, opportunity cost, and their adaptability
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