Optical precursors and Beer's law violations; non-exponential propagation losses in water

We develop a model for exponential decay of broadband pulses, and examine its implications for experiments on optical precursors. One of the signature features of Brillouin precursors is attenuation with a less rapid decay than that predicted by Beer's Law. Depending on the pulse parameters and the model that is adopted for the dielectric properties of the medium, the limiting z-dependence of the loss has been described as z(-1/2), z(-1/3), exponential, or, in more detailed descriptions, some combination of the above. Experimental results in the search for precursors are examined in light of the different models, and a stringent test for sub-exponential decay is applied to data on propagation of 500 femtosecond pulses through 1-5 meters of water. (C) 2005 Optical Society of America.

Hearing sensitivity and bone mineral density in older adults: the Health, Aging and Body Composition Study

Bone mineral density (BMD) may be associated with hearing loss in older adults. Demineralization of the cochlear capsule has been associated with hearing loss in those with Paget's disease of the bone and otosclerosis. Osteoporosis may also result in cochlear capsule demineralization. We hypothesized that lower hip BMD and lower heel ultrasound measurements would be associated with hearing loss in a population-based sample of 2,089 older black and white men and women. Bone parameters and hearing function were measured at the fourth clinical follow-up visit. Audiometric threshold testing was used to measure air- and bone-conduction hearing sensitivity. BMD of the hip and its subregions was measured using dual-energy X-ray absorptiometry. Calcaneal bone measurements [broadband ultrasound attenuation (BUA), speed of sound (SOS) and the quantitative ultrasound index (QUI)] were obtained using heel ultrasound. After adjusting for known hearing loss risk factors, no association was found between hearing and any of the bone measurements in whites and black women. In black men, however, lower hip BMD was associated with higher odds of hearing loss; for each standard deviation decrease in total hip BMD, the odds of hearing loss were 1.41 (95% confidence interval 1.08, 1.83), 1.39 (95% CI 1.07, 1.82) for femoral neck BMD and 1.65 (95% CI 1.26, 2.16) for trochanter BMD. Conductive hearing loss was associated with lower heel ultrasound measurements, though only among white men. The results of this study are mixed and inconclusive. Lower BMD of the hip and its subregions was associated with hearing loss among black men, but not among whites or black women. Lower measurements on heel ultrasound were associated with conductive hearing loss, though only among white men. These results suggest that axial and appendicular bone parameters may be modestly associated with hearing loss in older men, but not in women.

Adaptive phase measurements for narrowband squeezed beams

We have previously [Phys. Rev. A 65, 043803 (2002)] analyzed adaptive measurements for estimating the continuously varying phase of a coherent beam, and a broadband squeezed beam. A real squeezed beam must have finite photon flux N and hence can be significantly squeezed only over a limited frequency range. In this paper we analyze adaptive phase measurements of this type for a realistic model of a squeezed beam. We show that, provided it is possible to suitably choose the parameters of the beam, a mean-square phase uncertainty scaling as (N/kappa)(-5/8) is possible, where kappa is the linewidth of the beam resulting from the fluctuating phase. This is an improvement over the (N/kappa)(-1/2) scaling found previously for coherent beams. In the experimentally realistic case where there is a limit on the maximum squeezing possible, the variance will be reduced below that for coherent beams, though the scaling is unchanged.

Collective coherent population trapping in a thermal field

We analyze the efficiency of coherent population trapping (CPT) in a superposition of the ground states of three-level atoms under the influence of the decoherence process induced by a broadband thermal field. We show that in a single atom there is no perfect CPT when the atomic transitions are affected by the thermal field. The perfect CPT may occur when only one of the two atomic transitions is affected by the thermal field. In the case when both atomic transitions are affected by the thermal field, we demonstrate that regardless of the intensity of the thermal field the destructive effect on the CPT can be circumvented by the collective behavior of the atoms. An analytic expression was obtained for the populations of the upper atomic levels which can be considered as a measure of the level of thermal decoherence. The results show that the collective interaction between the atoms can significantly enhance the population trapping in that the population of the upper state decreases with an increased number of atoms. The physical origin of this feature is explained by the semiclassical dressed-atom model of the system. We introduce the concept of multiatom collective coherent population trapping by demonstrating the existence of collective (entangled) states whose storage capacity is larger than that of the equivalent states of independent atoms.

Design of compact directive ultra wideband antipodal antenna

In this paper, a novel design procedure for designing a compact UWB antipodal Vivaldi antenna is presented. The antenna operates over the UWB frequency, band from 3.1 to more than 10.6 GHz. Its measured far-field radiation is directive and its peak gain is 10.2 dBi in the specified band. The antenna pulse response shows negligible distortion, indicating that it can be useful in a precision ranging and imaging instrumentation. (c) 2006 Wiley Periodicals, Inc.

Fully spatial wide-band beamforming using a rectangular array of planar monopoles

This paper describes a spatial beamformer which by using a rectangular array antenna steers a beam in azimuth over a wide frequency band without frequency filters or tap-delay networks. The weighting coefficients are real numbers which can be realized by attenuators or amplifiers. A prototype including a 4 x 4 array of square planar monopoles and a feeding network composed of attenuators, power divider/combiners and a rat-race hybrid is developed to test the validity of this wide-band beamforming concept. The experimental results prove the validity of this wide-band spatial beamformer for small size arrays.

Government relations, government regulations: jumping through the hoops

Over the last decade, telehealth in Australia has been primarily facilitated and driven by government funding. The government now has a major policy initiative in online health. However, in pursuing the broad initiative there is a danger that some of the smaller components can get lost, and this is probably what has happened to telehealth. There appear to be a number of steps required if telehealth in Australia is to keep up the pace of development that occurred in the 1990s, as we move into what is now being called the era of e-health, involving broadband Internet health service delivery. This area is changing extremely rapidly and is increasingly migrating away from the public sector in Australia, where most of the developmental work has occurred, and into the private sector. Many of the issues that require consideration within the domain of e-health in Australia are also relevant to other countries. E-health will significantly change the way that health-care is practised in future, and it is clear that it is the human factors that are more difficult to overcome, rather than the technological ones.

Government relations, government regulations: Jumping through the hoops

Over the last decade, telehealth in Australia has been primarily facilitated and driven by government funding. The government now has a major policy initiative in online health. However, in pursuing the broad initiative there is a danger that some of the smaller components can get lost, and this is probably what has happened to telehealth. There appear to be a number of steps required if telehealth in Australia is to keep up the pace of development that occurred in the 1990s, as we move into what is now being called the era of e-health, involving broadband Internet health service delivery. This area is changing extremely rapidly and is increasingly migrating away from the public sector in Australia, where most of the developmental work has occurred, and into the private sector. Many of the issues that require consideration within the domain of e-health in Australia are also relevant to other countries. E-health will significantly change the way that health-care is practised in future, and it is clear that it is the human factors that are more difficult to overcome, rather than the technological ones.

Novel ultra-wideband pulse spectrum modulation scheme

Current ultra-wideband communication systems use short narrow timed pulse sequences to transmit information. Some disadvantages of UWB communication systems are its interference of other conventional wireless systems and its reliance on time hopping schemes for multiple access. This paper presents a novel UWB data modulation scheme based on pulse shaping. This modulation scheme adds more flexibility for data modulation in UWB communication systems. The modulation scheme encodes data in both the timing and frequency spectrum of the transmitted pulse. This has the potential to improve data throughput rates and to lower interference between UWB and narrowband systems.

TV DIGITAL INTERATIVA NO BRASIL: ESTUDO DOS APLICATIVOS INTERATIVOS STICKERCENTER E DO TELEJORNAL MGTV

Com o avanço da tecnologia e chegada da TV digital no Brasil, estudos apontam que a televisão aberta começa um novo estágio desde seu surgimento. Esta mídia disponibiliza ferramentas que permitem aos emissores de conteúdo uma dimensão interativa ainda não experimentada, sobretudo nos processos de comunicação massivos indicando que é possível novos caminhos de investimento na produção de conteúdo por parte das emissoras de TV. Com esta realidade de fundo, experiências começam a ser testadas no âmbito da televisão, como o StickerCenter, um software - desenvolvido pela TOTVS - que reúne elementos da internet na TV possibilitando ao receptor maior interação com o conteúdo televisivo, outra experiência é a realizada pela Rede Integração, afiliada à Rede Globo em Minas Gerais, com o software desenvolvido pela HXD Interactive Television, que testa um modelo brasileiro de interatividade no telejornal. Este trabalho mostra como estas duas empresas estão desenvolvendo aplicativos interativos para a TV utilizando o Middleware Ginga e os motivos pelos quais sua popularização não aconteceu. O StickerCenter não se popularizou e indica que o motivo seja erro de estratégia da empresa em desenvolver um produto que une broadband e broadcast TV sem atrativos ao consumidor, já o aplicativo interativo da Rede Integração não foi colocado no ar e apresenta inúmeros fatores que demonstram que não explorará a interatividade pela ausência de canal de retorno. Este estudo investigou o impacto da interatividade no mercado da radiodifusão e como a convergência tecnológica aponta para a construção de uma nova mídia baseada em displays interativos capazes de oferecer aos consumidores uma nova forma de recepção de conteúdo.

TV Digital aberta no Brasil

O presente trabalho analisa os importantes desafios que as novas tecnologias e as transformações na sociedade pós-industrial estão impondo à TV digital brasileira e ao seu modelo de negócios. Tem como principal objetivo realizar uma reflexão sobre a viabilidade financeira das emissoras abertas com a chegada da TV digital. Para tanto, analisa o modelo de negócios anterior, da TV analógica, baseado nos comerciais de trinta segundos e como esta forma poderá ser afetada inviabilizando a estrutura de produção e distribuição de conteúdo pelas emissoras abertas digitais. Ainda, busca evidenciar demais fatores que contribuem para a migração da audiência para outras plataformas de distribuição de conteúdo, refutando o senso comum de que o acesso à internet banda larga é a principal causa da queda dos índices de audiência. Este estudo se utiliza de uma ampla bibliografia que extrapola o campo específico da Comunicação e amplia o olhar sobre a indústria televisiva aberta no Brasil, enumerando fragilidades do setor e apontando possíveis estratégias para que a televisão brasileira possa se adaptar à nova estrutura da comunicação que está se formando em nosso país.

Psychophysical evidence for two routes to suppression before binocular summation of signals in human vision

Visual mechanisms in primary visual cortex are suppressed by the superposition of gratings perpendicular to their preferred orientations. A clear picture of this process is needed to (i) inform functional architecture of image-processing models, (ii) identify the pathways available to support binocular rivalry, and (iii) generally advance our understanding of early vision. Here we use monoptic sine-wave gratings and cross-orientation masking (XOM) to reveal two cross-oriented suppressive pathways in humans, both of which occur before full binocular summation of signals. One is a within-eye (ipsiocular) pathway that is spatially broadband, immune to contrast adaptation and has a suppressive weight that tends to decrease with stimulus duration. The other pathway operates between the eyes (interocular), is spatially tuned, desensitizes with contrast adaptation and has a suppressive weight that increases with stimulus duration. When cross-oriented masks are presented to both eyes, masking is enhanced or diminished for conditions in which either ipsiocular or interocular pathways dominate masking, respectively. We propose that ipsiocular suppression precedes the influence of interocular suppression and tentatively associate the two effects with the lateral geniculate nucleus (or retina) and the visual cortex respectively. The interocular route is a good candidate for the initial pathway involved in binocular rivalry and predicts that interocular cross-orientation suppression should be found in cortical cells with predominantly ipsiocular drive. © 2007 IBRO.