141 research outputs found
Circular polarization dependent study of the microwave photoconductivity in a two-dimensional electron system
The polarization dependence of the low field microwave photoconductivity and
absorption of a two-dimensional electron system has been investigated in a
quasi-optical setup in which linear and any circular polarization can be
produced in-situ. The microwave induced resistance oscillations and the zero
resistance regions are notedly immune to the sense of circular polarization.
This observation is discrepant with a number of proposed theories. Deviations
only occur near the cyclotron resonance absorption where an unprecedented large
resistance response is observed.Comment: 5 pages, 3 figure
Dynamical scaling of the quantum Hall plateau transition
Using different experimental techniques we examine the dynamical scaling of
the quantum Hall plateau transition in a frequency range f = 0.1-55 GHz. We
present a scheme that allows for a simultaneous scaling analysis of these
experiments and all other data in literature. We observe a universal scaling
function with an exponent kappa = 0.5 +/- 0.1, yielding a dynamical exponent z
= 0.9 +/- 0.2.Comment: v2: Length shortened to fulfil Journal criteri
A distributed optimization method for the geographically distributed data centres problem
The geographically distributed data centres problem (GDDC) is a naturally distributed resource allocation problem. The problem involves allocating a set of virtual machines (VM) amongst the data centres (DC) in each time period of an operating horizon. The goal is to optimize the allocation of workload across a set of DCs such that the energy cost is minimized, while respecting limitations on data centre capacities, migrations of VMs, etc. In this paper, we propose a distributed optimization method for GDDC using the distributed constraint optimization (DCOP) framework. First, we develop a new model of the GDDC as a DCOP where each DC operator is represented by an agent. Secondly, since traditional DCOP approaches are unsuited to these types of large-scale problem with multiple variables per agent and global constraints, we introduce a novel semi-asynchronous distributed algorithm for solving such DCOPs. Preliminary results illustrate the benefits of the new method
A time predefined variable depth search for nurse rostering
This paper presents a variable depth search for the nurse rostering problem. The algorithm works by chaining together single neighbourhood swaps into more effective compound moves. It achieves this by using heuristics to decide whether to continue extending a chain and which candidates to examine as the next potential link in the chain. Because end users vary in how long they are willing to wait for solutions, a particular goal of this research was to create an algorithm that accepts a user specified computational time limit and uses it effectively. When compared against previously published approaches the results show that the algorithm is very competitive
O momento da avaliação na intervenção precoce: o envolvimento da famĂlia estudo das qualidades psicomĂ©tricas do ASQ-2 dos 30 aos 60 meses
A relação entre pais e profissionais de saĂşde e de educação Ă© fundamental para o desenvolvimento da criança. Esta se torna ainda mais essencial em crianças que apresentam risco de desenvolvimento. Essa mesma relação Ă© valorizada numa abordagem centrada na famĂlia tendo implicações significativas nas práticas nos diferentes contextos e na sua aplicabilidade, exigindo que os profissionais assumam novos papĂ©is e que aprendam novas competĂŞncias no trabalho com as famĂlias. Estas competĂŞncias concretizam-se nos primeiros contactos com a famĂlia desde o momento da avaliação atĂ© Ă efetiva prestação de serviços. A realização deste estudo surgiu da necessidade constatada de envolver os pais desde o primeiro momento do processo em intervenção precoce atravĂ©s de um instrumento formal e de simples aplicação. O ASQ-2 Ă© constituĂdo por 19 questionários divididos por diferentes idades entre os quatro e os 60 meses. Cada questionário Ă© composto por 30 itens divididos pelas áreas de desenvolvimento comunicação, motricidade global, motricidade fina, resolução de problemas e pessoal-social. Este trabalho constitui a análise dos questionários dos 30 aos 60 meses para observar as qualidades psicomĂ©tricas do ASQ, tendo sido aplicados a uma amostra de conveniĂŞncia de 127 famĂlias do distrito de Braga. Foi possĂvel verificar que o ASQ-2 traduzido apresenta resultados atraentes o que significa que poderá vir a ser utilizado pela população portuguesa de pais e profissionais (de saĂşde e de educação) que pretendam concretizar as suas dĂşvidas atravĂ©s de um instrumento formal de rastreio e de monitorização do desenvolvimento da criança.The relationship between parents and health and education professionals is fundamental to the development of the child. This becomes even more important in children who are at risk. This relationship is valued in a family-centered approach and there are significant implications for practice in different contexts, requiring professionals to take on new roles and learn new skills in working with families. These skills come to the foreground during the first contacts with the family beginning at the time of assessment through to the effective provision of services. This study arose due to the perception that parents needed to be involved from the very beginning of the process in Early Intervention, by means of a formal instrument and simple application. The ASQ-2 is composed of 19 different questionnaires organized according to age intervals from 4 to 60 months. Each questionnaire comprises 30 items grouped according to the developmental areas of communication, gross motor, fine motor, problem solving and personal-social. This study presents the analysis of questionnaires from 30 to 60 months to observe the psychometric properties of the ASQ applied to a convenience sample of 127 households in the district of Braga. We concluded that the ASQ-2 presents attractive results suggesting that it could be used by the Portuguese population of parents and professionals (health and education) who wish to answer some questions using a formal screening and monitoring of child development instrument
Galaxy bulges and their massive black holes: a review
With references to both key and oft-forgotten pioneering works, this article
starts by presenting a review into how we came to believe in the existence of
massive black holes at the centres of galaxies. It then presents the historical
development of the near-linear (black hole)-(host spheroid) mass relation,
before explaining why this has recently been dramatically revised. Past
disagreement over the slope of the (black hole)-(velocity dispersion) relation
is also explained, and the discovery of sub-structure within the (black
hole)-(velocity dispersion) diagram is discussed. As the search for the
fundamental connection between massive black holes and their host galaxies
continues, the competing array of additional black hole mass scaling relations
for samples of predominantly inactive galaxies are presented.Comment: Invited (15 Feb. 2014) review article (submitted 16 Nov. 2014). 590
references, 9 figures, 25 pages in emulateApJ format. To appear in "Galactic
Bulges", E. Laurikainen, R.F. Peletier, and D.A. Gadotti (eds.), Springer
Publishin
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