Dynamic instabilities in resonant tunneling induced by a magnetic field

We show that the addition of a magnetic field parallel to the current induces self sustained intrinsic current oscillations in an asymmetric double barrier structure. The oscillations are attributed to the nonlinear dynamic coupling of the current to the charge trapped in the well, and the effect of the external field over the local density of states across the system. Our results show that the system bifurcates as the field is increased, and may transit to chaos at large enough fields.Comment: 4 pages, 3 figures, accepted in Phys. Rev. Letter

Análise comparativa dos ficocolóides produzidos por algas carragenófitas usadas industrialmente e algas carragenófitas portuguesas

As Carragenanas (E-407) constituem um dos principais aditivos usados pela indústria alimentar, como agentes gelificantes, emulsionantes, estabilizantes e espessantes. São ingredientes naturais, usados há várias décadas na área alimentar e são considerados como seguros, tendo obtido a classificação GRAS (Generally Recognised As Safe). Neste trabalho foram analisadas a percentagem de peso seco e a composição química (por FTIR e FT-Raman) das carragenanas produzidas pelas carragenófitas (Gigartinales, Rhodophyta) oriundas de diversos países: Kappaphycus alvarezzi (Tanzânia, Indonésia, Filipinas); Kappaphycus striatum (Madagáscar); Eucheuma denticulatum (Tanzânia, Filipinas e Madagáscar); Betaphycus gelatinum (Filipinas); e Sarcothalia crispata (Chile). Para comparação foram também analisadas algas carragenófitas da costa portuguesa (Gigartinales, Rhodophyta): Chondrus crispus, Mastocarpus stellatus; Gigartina pistillata; Chondracanthus teedei var. lusitanicus; Chondracanthus acicularis; Calliblepharis jubata; Gymnogongrus crenulatus; e Ahnfeltiopsis devoniensis. Os principais resultados a reter são: a maior percentagem de peso seco em carragenanas foi obtida a partir das algas carragenófitas Kappaphycus alvarezzi (Filipinas), com 84.4% e Gigartina pistillata (Praia do Norte, Viana do Castelo), com 65.4%. Relativamente à natureza dos ficocolóides produzidos pelas carragenófitas estudadas, as nossas análises espectroscópicas permitiram determinar a presença de um leque diversificado de carragenanas: carragenana iota pura; carragenana kappa quase pura; uma série de carragenanas híbridas kappa-iota, com diferentes rácios iota/kappa; carragenanas kappa-beta, xi-tetha e xi-lambda

Foraging at the Edge of Chaos: Internal Clock versus External Forcing

Activity rhythms in animal groups arise both from external changes in the environment, as well as from internal group dynamics. These cycles are reminiscent of physical and chemical systems with quasiperiodic and even chaotic behavior resulting from “autocatalytic” mechanisms. We use nonlinear differential equations to model how the coupling between the self-excitatory interactions of individuals and external forcing can produce four different types of activity rhythms: quasiperiodic, chaotic, phase locked, and displaying over or under shooting. At the transition between quasiperiodic and chaotic regimes, activity cycles are asymmetrical, with rapid activity increases and slower decreases and a phase shift between external forcing and activity. We find similar activity patterns in ant colonies in response to varying temperature during the day. Thus foraging ants operate in a region of quasiperiodicity close to a cascade of transitions leading to chaos. The model suggests that a wide range of temporal structures and irregularities seen in the activity of animal and human groups might be accounted for by the coupling between collectively generated internal clocks and external forcings

Long-term creep behavior of the intervertebral disk: comparison between bioreactor data and numerical results

The loaded disk culture system is an intervertebral disk (IVD)-oriented bioreactor developed by the VU Medical Center (VUmc, Amsterdam, The Netherlands), which has the capacity of maintaining up to 12 IVDs in culture, for approximately 3 weeks after extraction. Using this system, eight goat IVDs were provided with the essential nutrients and submitted to compression tests without losing their biomechanical and physiological properties, for 22 days. Based on previous reports (Paul et al., 2012, 2013; Detiger et al., 2013), four of these IVDs were kept in physiological condition (control) and the other four were previously injected with chondroitinase ABC (CABC), in order to promote degenerative disk disease (DDD). The loading profile intercalated 16 h of activity loading with 8 h of loading recovery to express the standard circadian variations. The displacement behavior of these eight IVDs along the first 2 days of the experiment was numerically reproduced,using an IVD osmo-poro-hyper-viscoelastic and fiber-reinforced finite element (FE) model. The simulations were run on a custom FE solver (Castro et al., 2014). The analysis of the experimental results allowed concluding that the effect of the CABC injection was only significant in two of the four IVDs. The four control IVDs showed no signs of degeneration, as expected. In what concerns to the numerical simulations, the IVD FE model was able to reproduce the generic behavior of the two groups of goat IVDs (control and injected). However, some discrepancies were still noticed on the comparison between the injected IVDs and the numerical simulations, namely on the recovery periods. This may be justified by the complexity of the pathways for DDD, associated with the multiplicity of physiological responses to each direct or indirect stimulus. Nevertheless, one could conclude that ligaments, muscles, and IVD covering membranes could be added to the FE model,in order to improve its accuracy and properly describe the recovery periods.FCT - Ph.D. grant SFRH/BD/63882/200

Understanding the UK hospital supply chain in an era of patient choice

Author Posting © Westburn Publishers Ltd, 2011. This is a post-peer-review, pre-copy-edit version of an article which has been published in its definitive form in the Journal of Marketing Management, and has been posted by permission of Westburn Publishers Ltd for personal use, not for redistribution. The article was published in Journal of Marketing Management, 27(3-4), 401 - 423, doi:10.1080/0267257X.2011.547084 http://dx.doi.org/10.1080/0267257X.2011.547084The purpose of this paper is to investigate the UK hospital supply chain in light of recent government policy reform where patients will have, inter alia, greater choice of hospital for elective surgery. Subsequently, the hospital system should become far more competitive with supply chains having to react to these changes as patient demand becomes less predictable. Using a qualitative case study methodology, hospital managers are interviewed on a range of issues. Views on the development of the hospital supply chain in different phases are derived, and are used to develop a map of the current hospital chain. The findings show hospital managers anticipating some significant changes to the hospital supply chain and its workings as Patient Choice expands. The research also maps the various aspects of the hospital supply chain as it moves through different operational phases and highlights underlying challenges and complexities. The hospital supply chain, as discussed and mapped in this research, is original work given there are no examples in the literature that provide holistic representations of hospital activity. At the end, specific recommendations are provided that will be of interest to service to managers, researchers, and policymakers

Landau levels in the case of two degenerate coupled bands: kagome lattice tight-binding spectrum

The spectrum of charged particles hopping on a kagome lattice in a uniform transverse magnetic field shows an unusual set of Landau levels at low field. They are unusual in two respects: the lowest Landau levels are paramagnetic so their energies decrease linearly with increasing field magnitude, and the spacings between the levels are not equal. These features are shown to follow from the degeneracy of the energy bands in zero magnetic field. We give a general discussion of Landau levels in the case of two degenerate bands, and show how the kagome lattice tight-binding model includes one special case of this more general problem. We also discuss the consequences of this for the behavior of the critical temperature of a kagome grid superconducting wire network, which is the experimental system that originally motivated this work.Comment: 18 pages, 8 figure

Azbel-Hofstadter model on triangular lattice revisited

In the present paper, the mean of Lyapunov exponents for the Azbel-Hofstadter model on the triangular lattice is calculated. It is recently proposed that [Phys. Rev. Lett. {\bf 85}, 4920 (2000)], for the case of the square lattice, this quantity can be related to the logarithm of the partition function of the two dimensional Ising model and has a connection to the asymptotic bandwidth. We find that the correspondence of this quantity to the logarithm of the partition function of the two dimensional Ising model is not complete for the triangular lattice. Moreover, the detailed connection between this quantity and the asymptotic bandwidth is not valid. Thus the conclusions for the mean of Lyapunov exponents suggested previously depend on the lattice geometry.Comment: RevTeX, 4 page, no figur

Plasmon oscillations in ellipsoid nanoparticles: beyond dipole approximation

The plasmon oscillations of a metallic triaxial ellipsoid nanoparticle have been studied within the framework of the quasistatic approximation. A general method has been proposed for finding the analytical expressions describing the potential and frequencies of the plasmon oscillations of an arbitrary multipolarity order. The analytical expressions have been derived for an electric potential and plasmon oscillation frequencies of the first 24 modes. Other higher orders plasmon modes are investigated numerically.Comment: 33 pages, 12 figure

Groundwater quality:Study of the Nitrate(NO3-) concentration in the Urban Area of the Brazil/Bolivia Border

Objective: To analyze the quality of groundwater potentially impacted by nitrate (NO3-), before and after the flooding of the Madeira River, in two urban areas of Rondônia on the Brazil / Bolivia border. Method: Data and water samples were collected according to Standard Methods for the Examination for Water and Wasterwater (APHA, 1998) together with the methodology proposed in the Water Sample Collection and Preservation Environmental Sanitation – CETESB. The place were georeferenced using the Global Positioning System (GPS). For nitrate measurement, the spectrophotometry method was used using the Spectrophotometer, brand Micronal B495, the chemical reagents used were made by Alfatecnoquímica and available in two vials called reagents 1 and 2 (nitrate reagent). Results: In the first large area of risk in 100% of samples, high levels of N nitrate (NO3-) were detected. > 10 mg / L. In the second area in 30% of the samples were detected NO3 content higher than 10mg / L. Conclusions: The population is consuming water with a high degree of nitrate contamination. It alerts itself to a public health issue

Qualidade em educação e atmosfera escolar: apontamentos gerais

It is necessary to define what is understood by quality in education to orientate the improvements in the educational system. In this article, it is proposed as the foundation to comprehend such quality a phenomenon is called: school climate. This phenomenon reveals some variables of the processes that influence significantly on the learning process of children. To sustain what is raised, it is first described a conception of the human being. Then, the concept of school climate is elaborated, considering what is found in the literature and including some useful distinctions to give better account of what happens in the school communities. The comprehension of the processes related to the education is completed bearing in mind two areas other than climate: the pedagogic-curricular and the administrative area. It is projected as a challenge to develop understandings about the quality in education where these three areas are integrated.  Es necesario definir qué se entiende por calidad en educación para orientar las mejoras en el sistema educativo. En este artículo se propone como fundamento de la comprensión de dicha calidad el concepto de clima escolar. Este fenómeno pone al descubierto cualidades de los procesos que influyen sustantivamente en los aprendizajes de niñas y niños. Para sustentar lo que se plantea, se parte describiendo una concepción acerca del ser humano. Luego, se desarrolla el concepto de clima escolar, considerando lo encontrado en la literatura e incluyendo algunas distinciones útiles para dar mejor cuenta de lo que sucede en las comunidades escolares. Se completa la comprensión de los procesos relativos a la educación considerando dos ámbitos, aparte del clima: lo pedagógico curricular y lo administrativo. Se proyecta como desafío desarrollar entendimientos acerca de la calidad en educación que integren estos tres ámbitos.  É necessário definir o que se entende por qualidade em educação para orientar as melhoras no sistema educativo. Assim, propõe-se um fenômeno chamado de atmosfera escolar como fundamento da compreensáo da dita qualidade. Este fenômeno põe ao descoberto qualidades dos processos que influenciam substantivamente nas aprendizagens de meninas e meninos. Para sustentar o que se propõe, parte-se da descrição de uma concepção de ser humano. Depois, desenvolve-se o conceito de atmosfera escolar, considerando a literatura existente e incluindo algumas distinções úteis para melhor dar conta do que sucede nas comunidades escolares. Complementa-se a compreensáo dos processos relativos â educação considerando dois âmbitos fora da atmosfera: o pedagógico curricular e o administrativo. Projeta-se como desafio desenvolver entendimientos a respeito da qualidade em educação que integrem estes três âmbitos. &nbsp