Suppression of collision-induced dephasing by periodic, erratic, or noisy driving

We compare different driving scenarios for controlling the loss of single particle coherence of an initially coherent preparation in the vicinity of the hyperbolic instability of the two-mode bose-Hubbard model. In particular we contrast the quantum Zeno suppression of decoherence by broad-band erratic or noisy driving, with the Kapitza effect obtained for high frequency periodic monochromatic driving.Comment: 6 pages, 3 figure

On Bounded Weight Codes

The maximum size of a binary code is studied as a function of its length N, minimum distance D, and minimum codeword weight W. This function B(N,D,W) is first characterized in terms of its exponential growth rate in the limit as N tends to infinity for fixed d=D/N and w=W/N. The exponential growth rate of B(N,D,W) is shown to be equal to the exponential growth rate of A(N,D) for w <= 1/2, and equal to the exponential growth rate of A(N,D,W) for 1/2< w <= 1. Second, analytic and numerical upper bounds on B(N,D,W) are derived using the semidefinite programming (SDP) method. These bounds yield a non-asymptotic improvement of the second Johnson bound and are tight for certain values of the parameters

La prescription de stimulants aux enfants « hyperactifs » : une étude pilote des incitatifs et des contraintes pour les parents, les médecins et les enseignants

Le consensus scientifique sur l'utilisation des stimulants pour traiter les enfants « hyperactifs » consiste à reconnaître leur effet calmant sur la conduite perturbatrice et une amélioration de la performance de tâches répétitives, à court terme. Les effets à long terme restent incertains. Pourtant, au Québec, la prescription de stimulants pour enfants dont les parents sont prestataires de sécurité du revenu a triplé de 1990 à 1994, atteignant la prévalence de 11,9 %. À l'aide d'un modèle systémique intégrant les approches de médicalisation de la déviance, d'économie politique et d'analyse stratégique, nous avons envisagé la décision de prescrire comme le résultat d'interactions impliquant divers acteurs au pouvoir inégal et intérêts divergents. Nous avons tenté d'établir la « défendabilité » de ce modèle au moyen d'entrevues auprès de cinq parents, quatre enseignants et trois médecins en contact prolongé avec un enfant hyperactif. Le matériel recueilli révèle l'omniprésence du modèle médical dans le système de traitement de l'hyperactivité mais les enseignants et non les médecins apparaissent comme le moteur de la médicalisation. Selon les parents et les médecins, les enseignants dépistent et « diagnostiquent » les enfants, proposent la médication aux parents et, dans certains cas, l'école exige du médecin une prescription. Les médecins admettent que l'évaluation médicale est souvent très sommaire. Pour leur part, les enseignants soulignent les difficultés de leur tâche et le manque d'encadrement psychosocial à l'école. Les commentaires de nos répondants font ressortir la perception de chacun qu'il voudrait agir différemment mais n'a pas d'autre choix que d'opter pour la médication. Ces observations limitées, qui devraient être validées, suggèrent que le système de traitement des enfants hyperactifs fonctionne de manière irrationnelle et qu'on ne peut raisonnablement s'attendre à le voir servir les intérêts des enfants.The scientific consensus on the use of stimulants to treat "hyperactive" or ADHD-diagnosed children amounts to recognizing a calming effect on children's disruptive behavior and better performance of repetitive tasks, both in the short-term. Long-term effects remain unknown. Still, in Québec, prescription of stimulants to children of welfare recipients nearly tripled between 1990 and 1994, reaching a prevalence of 11.9%. Using a systemic model integrating three approaches (medicalization of deviance, political economy, and strategic analysis), we conceptualized the decision to prescribe as the result of interactions involving different actors holding unequal power and seeking to further their interests. We attempted to establish the defendability of this model by means of in-depth interviews with five parents, four primary school teachers and three physicians in prolonged contact with a hyperactive child receiving stimulant medication. Data from the interviews reveal the omnipresence of the medical model in the hyperactivity treatment system, although teachers rather than physicians appear as the engine of this medicalization. According to parents and physicians, teachers identify and "diagnose" children, propose the use of medication to parents and, in some cases, the school requires that doctors write a prescription. Doctors admit that medical evaluation of referred children is often inadequate. For their part, teachers stress the growing difficulties of their task and the lack of psychosocial supports in the schools. Our respondants' comments highlight the divergent interests of the actors involved as well as each actor's own perception that he or she wishes to act differently but lacks any real choice other than opting for medication. These limited observations should be validated in further studies. They suggest that the current system functions irrationally and that we should not expect it to act in the best interests of children

School Victimization and Bullying Experiences: Cross-national Comparisons Between Canada and the United States

The victimization of children in school and its mental health consequences have become national problems in both Canada and the United States, with evidence that severe cases of peer victimization might precede and/or be related to posttraumatic stress disorder. This study examines the frequency of victimization in schools, perpetrated by both peers and educators, and the psychological outcomes. The cross-national study included 1007 college/university students from four universities in the US and 210 university students from mid-western Canada. The “Student Alienation and Trauma Scale–Revised” (SATS–R) measures students’ negative experiences in school and assesses whether an individual developed PTSD. Overall, Canadian students remembered more victimization in school than US students. For both country samples, the verbal/relational bullying factor was most often identified as a student’s very worst school experience (approximately 40% for both countries). Both samples had similar rates of PTSD after their very worst school experience with no real differences in the types of symptoms experienced by students after their very worst school experience

Squeezing in driven bimodal Bose-Einstein Condensates: Erratic driving versus noise

We study the interplay of squeezing and phase randomization near the hyperbolic instability of a two-site Bose-Hubbard model in the Josephson interaction regime. We obtain results for the quantum Zeno suppression of squeezing, far beyond the previously found short time behavior. More importantly, we contrast the expected outcome with the case where randomization is induced by erratic driving with the same fluctuations as the quantum noise source, finding significant differences. These are related to the distribution of the squeezing factor, which has log-normal characteristics: hence its average is significantly different from its median due to the occurrence of rare events.Comment: 5 pages, 4 figure