Ergodic Capacity of Cognitive TAS/GSC Relaying in Nakagami-m Fading Channels

We examine the impact of transmit antenna selection with receive generalized selection combining (TAS/GSC) for cognitive decode-and-forward (DF) relaying in Nakagami-m fading channels. We select a single transmit antenna at the secondary transmitter which maximizes the receive signal-to-noise ratio (SNR) and combine a subset of receive antennas with the largest SNRs at the secondary receiver. In an effort to assess the performance, we first derive the probability density function and cumulative distribution function of the end-to-end SNR using the moment generating function. We then derive new exact closed-form expression for the ergodic capacity. More importantly, by deriving the asymptotic expression for the high SNR approximation of the ergodic capacity, we gather deep insights into the high SNR slope and the power offset. Our results show that the high SNR slope is 1/2 under the proportional interference power constraint. Under the fixed interference power constraint, the high SNR slope is zero.

A statistical characterization of on���body fading using the shadowed k����� fading model

In this paper we investigate the received signal characteristics of on-body communications channels at 2.45 GHz. The hypothetical body area network configuration considered a transmitter node situated on the person���s left waist and receiving nodes positioned on the head, knee and wrist of the person���s right side. The on-body channel measurements were performed in both anechoic and reverberant environments while the person was moving. It was found that the recently proposed shadowed ������� fading model provided an excellent fit to the measured data.

Shadowed fading in body���to���body communications channels in an outdoor environment at 2.45 GHz

In this paper a number of outdoor body-to-body communications channels at 2.45 GHz which are deemed to be susceptible to shadowed fading are analyzed. The newlyproposed shadowed K-Il model is used to characterize thesechannels. Its probability density function is shown to provide an improved fit to the distribution of the signal fading compared to established models such as lognormal, Nakagamiand Rice.

Hyperglycemia and Diabetes Downregulate the Functional Expression of TRPV4 Channels in Retinal Microvascular Endothelium

<p>Retinal endothelial cell dysfunction is believed to play a key role in the etiology and pathogenesis of diabetic retinopathy. Numerous studies have shown that TRPV4 channels are critically involved in maintaining normal endothelial cell function. In the current paper, we demonstrate that TRPV4 is functionally expressed in the endothelium of the retinal microcirculation and that both channel expression and activity is downregulated by hyperglycaemia. Quantitative PCR and immunostaining demonstrated molecular expression of TRPV4 in cultured bovine retinal microvascular endothelial cells (RMECs). Functional TRPV4 activity was assessed in cultured RMECs from endothelial Ca2+-responses recorded using fura-2 microfluorimetry and electrophysiological recordings of membrane currents. The TRPV4 agonist 4��-phorbol 12,13-didecanoate (4-��PDD) increased [Ca2+]i in RMECs and this response was largely abolished using siRNA targeted against TRPV4. These Ca2+-signals were completely inhibited by removal of extracellular Ca2+, confirming their dependence on influx of extracellular Ca2+. The 4-��PDD Ca2+-response recorded in the presence of cyclopiazonic acid (CPA), which depletes the intracellular stores preventing any signal amplification through store release, was used as a measure of Ca2+-influx across the cell membrane. This response was blocked by HC067047, a TRPV4 antagonist. Under voltage clamp conditions, the TRPV4 agonist GSK1016790A stimulated a membrane current, which was again inhibited by HC067047. Following incubation with 25mM D-glucose TRPV4 expression was reduced in comparison with RMECs cultured under control conditions, as were 4��PDD-induced Ca2+-responses in the presence of CPA and ion currents evoked by GSK1016790A. Molecular expression of TRPV4 in the retinal vascular endothelium of 3 months' streptozotocin-induced diabetic rats was also reduced in comparison with that in age-matched controls. We conclude that hyperglycaemia and diabetes reduce the molecular and functional expression of TRPV4 channels in retinal microvascular endothelial cells. These changes may contribute to diabetes induced endothelial dysfunction and retinopathy.</p>

CaV3.1 T-Type Ca2+ Channels Contribute to Myogenic Signalling in Rat Retinal Arterioles

Purpose: Although L-type Ca2+ channels are known to play a key role in the myogenic reactivity of retinal arterial vessels, the involvement of other types of voltage-gated Ca2+ channels in this process remains unknown. In the present study we have investigated the contribution of T-type Ca2+ channels to myogenic signalling in arterioles of the rat retinal microcirculation. <br/><br/>Methods: Confocal immunolabelling of wholemount preparations was used to investigate the localisation of CaV3.1-3 channels in retinal arteriolar smooth muscle cells. T-type currents and the contribution of T-type channels to myogenic signalling were assessed by whole-cell patch-clamp recording and pressure myography of isolated retinal arteriole segments. <br/><br/>Results: Strong immunolabelling for CaV3.1 was observed on the plasma membrane of retinal arteriolar smooth muscle cells. In contrast, no expression of CaV3.2 or CaV3.3 could be detected in retinal arterioles, although these channels were present on glial cell end feet surrounding the vessels and retinal ganglion cells, respectively. TTA-A2 sensitive T-type currents were recorded in retinal arteriolar myocytes with biophysical properties distinct from those of the L-type currents present in these cells. Inhibition of T-type channels using TTA-A2 or ML-218 dilated isolated, myogenically active, retinal arterioles. <br/><br/>Conclusions: CaV3.1 T-type Ca2+ channels are functionally expressed on arteriolar smooth muscle cells of retinal arterioles and play an important role in myogenic signalling in these vessels. The work has important implications concerning our understanding of the mechanisms controlling blood flow autoregulation in the retina and its disruption during ocular disease.

Dual-Hop Cognitive Amplify-and-Forward Relaying Networks over ����� �� Fading Channels

This paper presents a thorough performance analysis of dual-hop cognitive amplify-and-forward (AF) relaying networks under spectrum-sharing mechanism over independent non-identically distributed (i.n.i.d.) &amp;#x100000; fading channels. In order to guarantee the quality-of-service (QoS) of primary networks, both maximum tolerable peak interference power Q at the primary users (PUs) and maximum allowable transmit power P at secondary users (SUs) are considered to constrain transmit power at the cognitive transmitters. For integer-valued fading parameters, a closed-form lower bound for the outage probability (OP) of the considered networks is obtained. Moreover, assuming arbitrary-valued fading parameters, the lower bound in integral form for the OP is derived. In order to obtain further insights on the OP performance, asymptotic expressions for the OP at high SNRs are derived, from which the diversity/coding gains and the diversity-multiplexing gain tradeoff (DMT) of the secondary network can be readily deduced. It is shown that the diversity gain and also the DMT are solely determined by the fading parameters of the secondary network whereas the primary network only affects the coding gain. The derived results include several others available in previously published works as special cases, such as those for Nakagami-m fading channels. In addition, performance evaluation results have been obtained by Monte Carlo computer simulations which have verified the accuracy of the theoretical analysis.

A Statistical Characterization of Shadowed Fading in Indoor Off-Body Communications Channels At 5.8 GHz

This paper investigates the characteristics of the shadowed fading observed in off-body communications channels at 5.8 GHz using the ��-�� / gamma composite fading model. Realistic measurements have been conducted considering four individual scenarios namely line of sight (LOS) and non-LOS (NLOS) walking, rotation and random movements within an indoor laboratory environment. It is shown that the ��-�� / gamma composite fading model provides a better fit to the fading observed in off-body communications channels compared to the conventional Nakagami-m and Rician fading models.

Fading Characteristics of Body���to���Body Channels Subject to Vehicular Traffic Conditions at 2.45 GHz

In this paper we investigate the small-scale fading characteristics of body-to-body communications channels in an urban environment at 2.45 GHz. The experiments considered body-to-body channels between devices positioned on two persons on either side of a busy road. The Ricean-K factors estimated from the measurements suggest that a significant dominant component existed in the majority of the channels.

Shadowed Fading in Indoor Off-Body Communications Channels: A Statistical Characterization using the <i>�� ��� ��</i> / Gamma Composite Fading Model

This paper investigates the characteristics of the shadowed fading observed in off-body communications channels at 5.8 GHz. This is realized with the aid of the $\kappa-\mu$ / gamma composite fading model which assumes that the transmitted signal undergoes $\kappa-\mu$ fading which is subject to \emph{multiplicative} shadowing. Based on this, the total power of the multipath components, including both the dominant and scattered components, is subject to non-negligible variations that follow the gamma distribution. For this model, we present an integral form of the probability density function (PDF) as well as important analytic expressions for the PDF, cumulative distribution function, moments and moment generating function. In the case of indoor off-body communications, the corresponding measurements were carried out in the context of four explicit individual scenarios namely: line of sight (LOS) and non-LOS (NLOS) walking, rotational and random movements. The measurements were repeated within three different indoor environments and considered three different hypothetical body worn node locations. With the aid of these results, the parameters for the $\kappa-\mu$ / gamma composite fading model were estimated and analyzed extensively. Interestingly, for the majority of the indoor environments and movement scenarios, the parameter estimates suggested that dominant signal components existed even when the direct signal path was obscured by the test subject's body. Additionally, it is shown that the $\kappa-\mu$ / gamma composite fading model provides an adequate fit to the fading effects involved in off-body communications channels. Using the Kullback-Leibler divergence, we have also compared our results with another recently proposed shadowed fading model, namely the $\kappa-\mu$ / lognormal LOS shadowed fading model. It was found that the $\kappa-\mu$ / gamma composite fading model provided a better fit for the majority of the scenarios considered in this study.

Switched Diversity Techniques for Indoor Off-body Communications Channels: An Experimental Analysis and Modeling

This paper investigates the potential improvement in signal reliability for indoor off-body communications channels operating at 5.8 GHz using switched diversity techniques. In particular we investigate the performance of switch-and-stay combining (SSC), switch-and-examine combining (SEC) and switch-and-examine combining with post-examining selection (SECps) schemes which utilize multiple spatially separated antennas at the base station. During the measurements a test subject, wearing an antenna on his chest, performed a number of walking movements towards and then away from a uniform linear array. It was found that all of the considered diversity schemes provided a worthwhile signal improvement. However, the performance of the diversity systems varied according to the switching threshold that was adopted. To model the fading envelope observed at the output of each of the combiners, we have applied diversity specific equations developed under the assumption of Nakagami-$m$ fading. As a measure of the goodness-of-fit, the Kullback-Leibler divergence between the empirical and theoretical probability density functions (PDFs) was calculated and found to be close to 0. To assist with the interpretation of the goodness-of-fit achieved in this study, the standard deviation, $\sigma$, of a zero-mean, $\sigma^2$ variance Gaussian PDF used to approximate a zero-mean, unit variance Gaussian PDF is also presented. These were generally quite close to 1 indicating that the theoretical models provided an adequate fit to the measured data. <br/>

High-resolution seismic reflection investigation of gas accumulation and seepage in the tidal channels of the Ria of Aveiro barrier lagoon (Portugal)

O metano �� um g��s de estufa potente e uma importante fonte de energia. A import��ncia global e impacto em zonas costeiras de acumula����es e escape de g��s metano s��o ainda pouco conhecidas. Esta tese investiga acumula����es e escape de g��s em canais de mar�� da Ria de Aveiro com dados de cinco campanhas de reflex��o s��smica de alta resolu����o realizadas em 1986, 1999, 2002 e 2003. Estas incluem tr��s campanhas de Chirp (RIAV99, RIAV02 e RIAV02A) e duas campanhas de Boomer (VOUGA86 e RIAV03). O processamento dos dados de navega����o inclu��ram filtros de erros, correc����es de sincroniza����o de rel��gios de sistemas de aquisi����o de dados, ajuste de ���layback��� e estimativa da posi����o de ���midpoint���. O processamento do sinal s��smico consistiu na correc����o das amplitudes, remo����o de ru��do do tipo ���burst���, correc����es est��ticas, correc����o do ���normal move-out���, filtragem passabanda, desconvolu����o da assinatura e migra����o Stolt F-K. A an��lise da regularidade do trajecto de navega����o, dos desfasamentos entre horizontes e dos modelos de superf��cies foi utilizada para controlo de qualidade, e permitiu a revis��o e melhoria dos par��metros de processamento. A heterogeneidade da cobertura s��smica, da qualidade do sinal, da penetra����o e da resolu����o, no seu conjunto constrangeram o uso dos dados a interpreta����es detalhadas, mas locais, de objectos geol��gicos da Ria. �� apresentado um procedimento para determinar a escolha de escalas adequadas para modelar os objectos geol��gicos, baseado na resolu����o s��smica, erros de posicionamento conhecidos e desfasamentos m��dios entre horizontes. As evid��ncias de acumula����o e escape de g��s na Ria de Aveiro incluem turbidez ac��stica, reflex��es refor��adas, cortinas ac��sticas, domas, ���pockmarks��� e alinhamentos de ���pockmarks��� enterradas, horizontes perturbados e plumas ac��sticas na coluna de ��gua (flares). A estratigrafia e a estrutura geol��gica controlam a distribui����o e extens��o das acumula����es e escape de g��s. Ainda assim, nestes sistemas de baixa profundidade de ��gua, as varia����es da altura de mar�� t��m um impacto significativo na detec����o de g��s com m��todos ac��sticos, atrav��s de altera����es nas amplitudes originais de reflex��es refor��adas, turbidez ac��stica e branqueamento ac��stico em zonas com g��s. Os padr��es encontrados confirmam que o escape de bolhas de g��s �� desencadeado pela descida da mar��. H�� acumula����es de g��s em sedimentos Holoc��nicos e no substrato de argilas e calc��rios do Mesoz��ico. Evid��ncias directas de escape de g��s em sondagens em zonas vizinhas, mostraram g��s essencialmente biog��nico. A maioria do g��s na ��rea deve ter sido gerado em sedimentos lagunares Holoc��nicos. No entanto, a localiza����o e geometria de estruturas de escape de fluidos em alguns canais de mar��, seguem o padr��o de fracturas do substrato Mesoz��ico, indicando uma poss��vel fonte mais profunda de g��s e que estas fracturas funcionam como condutas preferenciais de migra����o dos fluidos e exercem um controlo estrutural na ocorr��ncia de g��s na Ria.