Top Quarks, Axigluons and Charge Asymmetries at Hadron Colliders

Axigluons are colored heavy neutral gauge boson that couple to quarks through an axial vector current and the same strong coupling as gluons. The most important model-independent manifestation of axigluons is the generation of a forward--backward asymmetry in top-antitop quark production at $p\bar{p}$ collisions which originates from the charge asymmetry. We update our previous analysis for the inclusive QCD induced forward--backward asymmetry and define a new observable which is more sensitive to the effect than the forward--backward asymmetry. Furthermore, we find a lower limit of 1.2 TeV at 90% C.L. on the axigluon mass from recent measurements of the asymmetry at Tevatron. Also at LHC, the charge asymmetry is sizable in suitably selected samples. We evaluate this asymmetry in the central region for different selection cuts and show that, like at Tevatron, the charge asymmetry can probe larger values of the axigluon mass than the dijet mass distribution.Comment: 13 pages, 9 figure

On the testability of SDL specifications

The problem of testing from an SDL specification is often complicated by the presence of infeasible paths. This paper introduces an approach for transforming a class of SDL specification in order to eliminate or reduce the infeasible path problem. This approach is divided into two phases in order to aid generality. First the SDL specification is rewritten to create a normal form extended finite state machine (NF-EFSM). This NF-EFSM is then expanded in order to produce a state machine in which the test criterion may be satisfied using paths that are known to be feasible. The expansion process is guaranteed to terminate. Where the expansion process may lead to an excessively large state machine, this process may be terminated early and feasible paths added. The approach is illustrated through being applied to the Initiator process of the Inres protocol

Reshaping Ability Grouping Through Big Data

This Article examines whether incorporating data mining technologies in education can promote equality. Following many other spheres in life, big data technologies that include creating, collecting, and analyzing vast amounts of data about individuals are increasingly being used in schools. This process has already elicited widespread interest among scholars, parents, and the public at large. However, this attention has largely focused on aspects of student privacy and data protection and has overlooked the profound effects data mining may have on educational equality. This Article analyzes the effects of data mining on education equality by focusing on one educational practice--ability grouping--that is already being transformed by educational data mining

The Generic Reasons for Strikes: An Interpretative Analysis of the Israëli Case

À cause de leur effet néfaste sur l'économie en Israël, les grèves sont devenues sujets d'enquêtes scientifiques de la part des spécialistes en relations professionnelles dans ce pays. Plusieurs études ont été publiées, mais elles paraissent déficientes dans leurs conclusions en ce qu'elles ne parviennent pas à découvrir les causes profondesqui les engendrent. Celles-ci, en effet, ne doivent pas être confondues avec les occasions immédiates des grèves prises individuellement.Une distinction s'impose. Si les occasions de grèves peuvent résulter de différends entre les parties tels les désaccords en matière de salaires et d'avantages sociaux, l'embauchage ou le congédiement des salariés, la reconnaissance des syndicats, la fermeture des entreprises, etc., les causes véritables ont un caractère plus profond et elles peuvent être extrinsèques ou intrinsèques.Parmi les causes extrinsèques, on peut citer les conditions de la vie sociale, comme le manque de canaux d'expression politique, les conditions d'ordre économique comme l'inflation galopante. Il s'agit de situations favorisant les conflits qui dégénèrent ensuite en grève, et d'un état général de la société considérée à une période donnée qui s'applique à toutes les grèves et qui aide à en déterminer le nombre.En Israël, on a trouvé, par exemple, que le facteur qui avait exercé le plus d'influence sur le nombre des grèves n'était pas le niveau de l'activité économique, mais le taux, surtout le taux d'accélération, des investissements. Les espoirs exprimés par les investisseurs créent des espoirs similaires parmi les salariés désireux d'obtenir leur part du gâteau, ce qui constitue un climat général favorable aux grèves. De même, les effets funestes d'une inflation rapide, qui affectent toutes les branches de la vie économique ont aussi un effet négatif sur les relations professionnelles, parce que les syndicats doivent s'efforcer de protéger leurs membres par des clauses d'indexation.D'autre part, il faut aussi considérer les causes intrinsèques des grèves.Celles-ci résultent d'abord en Israël de la démocratisation des syndicats, soit par la mise en place de structures qui permettent à la base de jouer un rôle plus important dans la prise des décisions, soit par la multiplication et la fragmentation des sections locales. C'est ainsi, par exemple, que l'établissement de plusieurs unités de représentation dans une entreprise favorise la concurrence, les intrigues et la méfiance entre les diverses sections. Au lieu de faire valoir ses besoins et ses revendications spécifiques, chaque unité de négociation concentre son attention sur les gains des autres pour en obtenir d'identiques ou d'analogues, ce qui crée un cercle vicieux forçant quelquefois les parties à conclure des accords secrets.Autre cause intrinsèque des grèves: les erreurs de jugement provenant des maladresses des parties, du défaut de connaissances des règles du jeu ou du fait que des négociateurs inexpérimentés manquent de flexibilité au cours des tractations.On peut aussi ranger parmi les causes intrinsèques des grèves les pratiques de négociations incorrectes. Il arrive fréquemment que les négociations ne sont qu'apparentes. Au fond, il ne se passe rien dans la réalité, chaque partie demeurant cramponnée à ses exigences. En certains cas, on va jusqu'à rejeter le mécanisme de négociation lui-même. On abuse aussi du recours aux comparaisons: cette tendance a rendu la négociation collective plus rigide, principalement dans le secteur public, mais on la retrouve aussi dans le secteur privé. Au lieu de concentrer leur attention sur les enjeux de la négociation, les parties discutent des groupes auxquels elles estiment devoir être comparées, ce qui rend lourd le processus des négociations et augmente d'autant les possibilités de conflit.Par ailleurs, une des sources majeures d'opposition dans tout système social porte sur les questions d'idéologie. Chacun veut faire sa « guerre sainte ». En matièrede relations professionnelles, la situation devient particulièrement grave quand les mécanismes de négociation bien établis sont modifiés ou quand certaines questions, jusque là négociables, sont délibérément exclues par l'une ou l'autre des parties.Enfin, beaucoup de spécialistes accordent une grande importance à la législation dont les déficiences peuvent être et sont effectivement une source de conflits entre les parties. En Israël, l'une d'entre elles est qu'il n'existe à peu près pas de lois touchant l'établissement, les fonctions, les responsabilités et les obligations des syndicats et des associations d'employeurs.Que conclure si ce n'est que les grèves ne sont pas un indicateur de l'état de santé d'un système de relations professionnelles mais que, si l'on veut limiter le nombre de grèves, il faut en connaître les causes véritables plutôt que d'en traiter les symptômes? En Israël, on catalogue cinquante pour cent des grèves sous la rubrique « salaire insuffisant ». Il est naïf de penser que toutes ces grèves ont leur origine dans le refus des employeurs de satisfaire aux exigences du syndicat ou le désir du syndicat d'écraser l'employeur. Il est vrai que les questions d'argent furent souvent l'occasion immédiate de la grève, mais cela ne doit pas conduire à la conclusion énoncée que celles-ci expliquent totalement le fait de la grève. C'est une méprise d'imaginer qu'un désaccord sur des problèmes d'argent peut inexorablement entraîner une interruption des contacts entre les parties. Pour empêcher de pareilles interruptions, il faut non seulement se préoccuper des salaires, mais aussi des causes plus profondes des arrêts de travail.The purpose of this paper is to reveal those universal socio-economic conditions which generally foster strikes, and the most general labor relations-related reasons for conflicts which eventually result in strikes

Matching Subsequences in Trees

Given two rooted, labeled trees $P$ and $T$ the tree path subsequence problem is to determine which paths in $P$ are subsequences of which paths in $T$. Here a path begins at the root and ends at a leaf. In this paper we propose this problem as a useful query primitive for XML data, and provide new algorithms improving the previously best known time and space bounds.Comment: Minor correction of typos, et

Privacy Protection and Aggregate Health Data: A Review of Tabular Cell Suppression Methods (Not) Employed in Public Health Data Systems

Public health research often relies on individuals’ confidential medical data. Therefore, data collecting entities, such as states, seek to disseminate this medical data as widely as possible while still maintaining the privacy of the individual for legal and ethical reasons. One common way in which this medical data is released is through the use of Web-based Data Query Systems (WDQS). In this article, we examined WDQS listed in the National Association for Public Health Statistics and Information Systems (NAPHSIS) specifically reviewing them for how they prevent statistical disclosure in queries that produce a tabular response. One of the most common methods to combat this type of disclosure is through the use of suppression, that is, if a cell count in a table is below a certain threshhold, the true value is suppressed. This technique does work to prevent the direct disclosure of small cell counts, however, primary suppression by itself is not always enough to preserve privacy in tabular data. Here, we present several real examples of tabular response queries that employ suppression, but we are able to infer the values of the suppressed cells, including cells with 1 counts, which could be linked to auxiliary data sources and thus has the possibility to create an identity disclosure. We seek to stimulate awareness of the potential for disclosure of information that individuals may wish to keep private through an online query system. This research is undertaken in the hope that privacy concerns can be dealt with preemptively rather than only after a major disclosure has taken place. In the wake of a such an event, a major concern is that state and local officials would react to this by permanently shutting down these sites and cutting off a valuable source of research data

Compact Drawings of 1-Planar Graphs with Right-Angle Crossings and Few Bends

We study the following classes of beyond-planar graphs: 1-planar, IC-planar, and NIC-planar graphs. These are the graphs that admit a 1-planar, IC-planar, and NIC-planar drawing, respectively. A drawing of a graph is 1-planar if every edge is crossed at most once. A 1-planar drawing is IC-planar if no two pairs of crossing edges share a vertex. A 1-planar drawing is NIC-planar if no two pairs of crossing edges share two vertices. We study the relations of these beyond-planar graph classes (beyond-planar graphs is a collective term for the primary attempts to generalize the planar graphs) to right-angle crossing (RAC) graphs that admit compact drawings on the grid with few bends. We present four drawing algorithms that preserve the given embeddings. First, we show that every $n$-vertex NIC-planar graph admits a NIC-planar RAC drawing with at most one bend per edge on a grid of size $O(n) \times O(n)$. Then, we show that every $n$-vertex 1-planar graph admits a 1-planar RAC drawing with at most two bends per edge on a grid of size $O(n^3) \times O(n^3)$. Finally, we make two known algorithms embedding-preserving; for drawing 1-planar RAC graphs with at most one bend per edge and for drawing IC-planar RAC graphs straight-line

Spike Timing Dependent Plasticity: A Consequence of More Fundamental Learning Rules

Spike timing dependent plasticity (STDP) is a phenomenon in which the precise timing of spikes affects the sign and magnitude of changes in synaptic strength. STDP is often interpreted as the comprehensive learning rule for a synapse – the “first law” of synaptic plasticity. This interpretation is made explicit in theoretical models in which the total plasticity produced by complex spike patterns results from a superposition of the effects of all spike pairs. Although such models are appealing for their simplicity, they can fail dramatically. For example, the measured single-spike learning rule between hippocampal CA3 and CA1 pyramidal neurons does not predict the existence of long-term potentiation one of the best-known forms of synaptic plasticity. Layers of complexity have been added to the basic STDP model to repair predictive failures, but they have been outstripped by experimental data. We propose an alternate first law: neural activity triggers changes in key biochemical intermediates, which act as a more direct trigger of plasticity mechanisms. One particularly successful model uses intracellular calcium as the intermediate and can account for many observed properties of bidirectional plasticity. In this formulation, STDP is not itself the basis for explaining other forms of plasticity, but is instead a consequence of changes in the biochemical intermediate, calcium. Eventually a mechanism-based framework for learning rules should include other messengers, discrete change at individual synapses, spread of plasticity among neighboring synapses, and priming of hidden processes that change a synapse's susceptibility to future change. Mechanism-based models provide a rich framework for the computational representation of synaptic plasticity

Further study of the Over-Barrier Model to compute charge exchange processes

In this paper we study theoretically the process of electron capture between one-optical-electron atoms (e.g. hydrogenlike or alkali atoms) and ions at low-to-medium impact velocities ($v/v_e \approx 1$) working on a modification of an already developed classical In this work we present an improvement over the Over Barrier Model (OBM) described in a recent paper [F. Sattin, Phys. Rev. A {\bf 62}, 042711 (2000)]. We show that: i) one of the two free parameters there introduced actually comes out consistently from the starting assumptions underlying the model; ii) the modified model thus obtained is as much accurate as the former one. Furthermore, we show that OBMs are able to accurately predict some recent results of state selective electron capture, at odds with what previously supposed.Comment: RevTeX, 7 pages, 4 eps figures. To appear in Physical Review A (2001-september issue

AToM3: A Tool for Multi-formalism and Meta-modelling

The final publication is available at Springer via http://dx.doi.org/10.1007/3-540-45923-5_12Proceedings of 5th International Conference, FASE 2002 Held as Part of the Joint European Conferences on Theory and Practice of Software, ETAPS 2002 Grenoble, France, April 8–12, 2002This article introduces the combined use of multi-formalism modelling and meta-modelling to facilitate computer assisted modelling of complex systems. The approach allows one to model different parts of a system using different formalisms. Models can be automatically converted between formalisms thanks to information found in a Formalism Transformation Graph (FTG), proposed by the authors. To aid in the automatic generation of multi-formalism modelling tools, formalisms are modelled in their own right (at a meta-level) within an appropriate formalism. This has been implemented in the interactive tool AToM3. This tool is used to describe formalisms commonly used in the simulation of dynamical systems, as well as to generate custom tools to process (create, edit, transform, simulate, optimise, ...) models expressed in the corresponding formalism. AToM3 relies on graph rewriting techniques and graph grammars to perform the transformations between formalisms as well as for other tasks, such as code generation and operational semantics specification.This paper has been partially sponsored by the Spanish Interdepartmental Commission of Science and Technology (CICYT), project number TEL1999-0181. Prof.Vangheluwe gratefully acknowledges partial support for this work by a National Sciences and Engineering Research Council of Canada (NSERC) Individual Research Grant