Generation and remote detection of THz sound using semiconductor superlattices

The authors introduce a novel approach to study the propagation of high frequency acoustic phonons in which the generation and detection involves two spatially separated superlattices $\sim 1 {\rm \mu m}$ apart. Propagating modes of frequencies up to $\sim 1 {\rm THz}$ escape from the superlattice where they are generated and reach the second superlattice where they are detected. The measured frequency spectrum reveals finite size effects, which can be accounted for by a continuum elastic model.Comment: Submitted to Applied Physics Letter

Contextos organizacionais do desenvolvimento das práticas de supervisão : que cooperação no processo formativo dos estudantes de enfermagem?

A questão central na formação de estudantes de Enfermagem advém da revalorização do potencial formativo das práticas nas organizações de saúde, devendo estas assegurar as condições de aprendizagem clínica para os cursos e garantir os respetivos padrões de qualidade. Isto obriga a que sejam potenciadas sinergias entre ambas as organizações. O Decreto-Lei n.º 206/2004 de 19 de Agosto, clarifica a relação entre as entidades prestadoras de cuidados de saúde e as instituições responsáveis pelo ensino, a educação e a investigação científica, nomeadamente com as escolas de enfermagem, como explicitamente determina o n.º 3, do artigo 1.º, conjugado com o que preconiza o artigo 13.º. Aqui, está também traçado o quadro geral de articulação entre as duas organizações, a qual é feita mediante o estabelecimento de protocolos para a realização de estágios e desenvolvimento da investigação. Este estudo, de carater exploratório e descritivo teve como objetivo compreender os processos de parceria em uso entre as Escolas Superiores de Enfermagem e as entidades prestadoras de cuidados onde se realizam as práticas cínicas. Metodologicamente foi suportado na análise de conteúdo de 66 protocolos firmados por sete Escolas de Enfermagem. Os achados do estudo revelaram fragilidades na formalização dos protocolos com as instituições de saúde, não surgindo claro, qual a natureza ou extensão da sua cooperação. Evidenciaram ausência de uma definição clara do papel a desempenhar no processo formativo dos estudantes e a falta da clarificação de indicadores necessários a uma forma integrada de agir em articulação. Apesar de no atual quadro legal, assente na celebração formal de protocolos, estarem reunidas as condições para a efetivação da articulação entre as duas entidades, os protocolos firmados não obedecem, com as devidas adaptações, aos princípios gerais definidos no n.º 2 do artigo 13.º do referido diploma, o que parece condicionar a corresponsabilização dos intervenientes no processo.The central issue in the training nursing students arises from the revaluation of the training potential of the practices in health organizations, which should ensure the conditions for clinical training of the courses guaranteeing the respective standards of quality. This requires being further enhanced synergies between both organizations. Decree-Law number 206/2004, August 19, clarifies the relationship between health institutions and institutions responsible by education and scientific research, particularly with nursing schools, as explicitly determines the number 3, Article 1, in conjunction with advocated in Article 13.º. Here is also outlined the general framework of coordination between both organizations, which is done by establishing protocols for the stages conduct and scientific research development. Aiming to understanding the processes in use of partnership between Nursing Schools and health institutions where they carry out the clinical practices, we developed a study of exploratory and descriptive nature. Methodologically was supported in content analysis of 66 protocols signed by seven Nursing Schools. The results of this study demonstrated flaws in the formalization of agreements with health institutions, not appearing clear what is the nature or extent of their cooperation. It was evidenced a lack of definition by the health institutions role in the students training and the dearth of clarification the indicators needed to an articulated working. In the current legal framework, although contemplated the conditions for effective coordination between both entities, based on formal protocols, these weren´t in accordance to the general principles defined in number 2, article 13.º of the referenced law, which can determine the co-responsibility the involved parts

Observation of Surface-Avoiding Waves: A New Class of Extended States in Periodic Media

Coherent time-domain optical experiments on GaAs-AlAs superlattices reveal the exis-tence of an unusually long-lived acoustic mode at ~ 0.6 THz, which couples weakly to the environment by evading the sample boundaries. Classical as well as quantum states that steer clear of surfaces are generally shown to occur in the spectrum of periodic struc-tures, for most boundary conditions. These surface-avoiding waves are associated with frequencies outside forbidden gaps and wavevectors in the vicinity of the center and edge of the Brillouin zone. Possible consequences for surface science and resonant cavity ap-plications are discussed.Comment: 16 pages, 3 figure

MAXI J1659-152: the shortest orbital period black-hole binary

Following the detection of a bright new X-ray source, MAXI J1659-152, a series of observations was triggered with almost all currently flying high-energy missions. We report here on XMM-Newton, INTEGRAL and RXTE observations during the early phase of the X-ray outburst of this transient black-hole candidate. We confirm the dipping nature in the X-ray light curves. We find that the dips recur on a period of 2.4139+/-0.0005 hrs, and interpret this as the orbital period of the system. It is thus the shortest period black-hole X-ray binary known to date. Using the various observables, we derive the properties of the source. The inclination of the accretion disk with respect to the line of sight is estimated to be 60-75 degrees. The companion star to the black hole is possibly a M5 dwarf star, with a mass and radius of about 0.15 M_sun and 0.23 R_sun, respectively. The system is rather compact (orbital separation is about 1.35 R_sun) and is located at a distance of roughly 7 kpc. In quiescence, MAXI J1659-152 is expected to be optically faint, about 28 mag in the V-band.Comment: 5 pages, 4 figures, to be published in the proceedings of the 4th International MAXI Workshop `The First Year of MAXI: Monitoring variable X-ray sources', 2010 Nov 30 - Dec 2, Tokyo, Japa

Photoinduced suppression of the ferroelectric instability in PbTe

The interactions between electrons and phonons drive a large array of technologically relevant material properties including ferroelectricity, thermoelectricity, and phase-change behaviour. In the case of many group IV-VI, V, and related materials, these interactions are strong and the materials exist near electronic and structural phase transitions. Their close proximity to phase instability produces a fragile balance among the various properties. The prototypical example is PbTe whose incipient ferroelectric behaviour has been associated with large phonon anharmonicity and thermoelectricity. Experimental measurements on PbTe reveal anomalous lattice dynamics, especially in the soft transverse optical phonon branch. This has been interpreted in terms of both giant anharmonicity and local symmetry breaking due to off-centering of the Pb ions. The observed anomalies have prompted renewed theoretical and computational interest, which has in turn revived focus on the extent that electron-phonon interactions drive lattice instabilities in PbTe and related materials. Here, we use Fourier-transform inelastic x-ray scattering (FT-IXS) to show that photo-injection of free carriers stabilizes the paraelectric state. With support from constrained density functional theory (CDFT) calculations, we find that photoexcitation weakens the long-range forces along the cubic direction tied to resonant bonding and incipient ferroelectricity. This demonstrates the importance of electronic states near the band edges in determining the equilibrium structure.Comment: 9 page, 3 figure