Performance Evaluation of Packet Mobile Communications through Level Crossing Analysis

In this paper the performance of a packet mobile radio network is studied inthe presence of shadow fading outage intervals.Under quite general assumptions for the medium access protocol,the probability mass function of the sequence of packets that may be lostdue to an outage interval is derived. It is seen that long sequences of lostpackets are likely to occur for typical values of the mobile speed andshadowing correlation parameters.For delay constrained sources, e.g., voice, the analysis is mainly focused atderiving the probability function of the sequence of dropped packetsand the probability of dropping. For data sources, the delay statistic isalso derived. In the latter case, the effect of finite buffer length isaddressed. Simulation is used to verify the accuracy of approximations introduced in the analysis.     

An Exact Framework for Performance Analysis of IR?UWB Systems: The Need for Approximations

In this letter, we propose an exact analytical framework for analyzing the performance of impulse radio (IR) ultra wide band (UWB) receiver architectures. In particular, the framework can handle i. various multipath fading distributions, ii. correlated fading, iii. channel sparseness, iv. time overlap among multipath components (MPCs), i.e., intra-pulse interference and v. both all-rake and transmitted-reference (TR) receiver architectures. The proposed methodology is based on estimating the characteristic function (CF) of the signal-to- noise ratio at the receiver, which can be reduced to a quadratic form of a random vector.     

Power Allocation and Control in Multimedia CDMA Wireless Systems

This paper proposes an analysis of outage performance of a Direct Sequence-Code Division Multiple Access (DS-CDMA) wireless system with heterogeneous traffic. Imperfections in closed-loop power control and the activity characteristics of any traffic source in the system are taken into account. For given requirements of signal-to-(noise + interference) ratio and outage probability of every user in the system, the system capacity is derived in terms of the maximum number of users of each class that can be accomodated. The optimization problem is explicitly solved for a system consisting of a single cell and an approach is outlined for solving the optimization problem in a multi-cell system. The analysis is carried out by resorting to various approximations of Multiple Access Interference (MAI), that require different methods for solving the optimization problem and yield different degrees of accuracy. From numerical results it is seen that optimal power allocation is essential to limit the effects of power control imperfections, mainly in the case of non uniform amplitudes of residual power fluctuations. In the second part of the paper, a performance study of fixed step closed-loop power control algorithms is presented. A detailed simulation of the power control loop evidences that fast fading phenomena can not be easily tracked, even at moderate Doppler spread. Statistics of residual power fluctuations are estimated and can be used to support the assumptions in the first part of the paper. Furthermore, second order statistics of the controlled channel are estimated, and second order outage statistics (average rate and duration of outage events) are derived as a quantitative measure of residual channel burstiness.     

Accumulation of human immunodeficiency virus-specific cytotoxic T lymphocytes away from the predominant site of virus replication during primary infection

Down-regulation of the initial burst of viremia during primary human immunodeficiency virus (HIV) infection is thought to be mediated predominantly by HIV-specific CD8+ cytotoxic T lymphocytes (CTL). This response is associated with major perturbations in the T cell receptor (TCR) repertoire. To investigate the failure of the cellular immune response to adequately control viral spread and replication and to prevent establishment of HIV infection, changes in the TCR repertoire and in the distribution of virus-specific CTL between blood and lymph node were analyzed in three patients with primary infection. By the combined use of clonotype-specific polymerase chain reaction and analysis of the frequency of in vivo activated HIV-specific CTL, it was shown that HIV-specific CTL clones preferentially accumulated in blood as opposed to lymph node. Accumulation of HIV-specific CTL in blood occurred prior to effective down-regulation of virus replication in both blood and lymph node. These findings should provide new insights into how HIV, and possibly other viruses, elude the immune response of the host during primary infection.     

Analysis of virologic and immunologic events in HIV infection

A number of pathogenic events occurring immediately after the transmission of HIV lead to the establishment of chronic infection. In fact, despite the detection of vigorous virus-specific immune responses during primary infection, HIV is able to establish chronic infection in most of the cases. This is the result of several virologic and immunologic mechanisms that HIV has evolved to escape and/or to weaken virus-specific immune responses. Lymphoid organs represent the primary anatomic site for the establishment of chronic infection, and if highly active antiretroviral therapy is not initiated in early stage disease, there is a progressive destruction of lymphoid tissue that ultimately leads to the profound immunosuppression typical of AIDS. Therefore, analysis of lymphoid organs is crucial for the correct evaluation of the effectiveness of antiretroviral therapy in HIV infection.     

A Comprehensive Framework for Performance Analysis of Dual?Hop Cooperative Wireless Systems with Fixed?Gain Relays over Generalized Fading Channels

In the present contribution, we propose a comprehensive framework for the analysis of cooperative dual-hop wireless systems over generalized fading channels, which use an amplify and forward (AF) relaying mechanism with blind and semi-blind relays. In particular, the proposed framework provides either exact results or very accurate bounds for computing the moment generating function (MGF) of the end-to-end signal-to-noise ratio (SNR) for various fading channel models typically encountered in real propagation environments. Furthermore, with the help of the MGF-based approach for performance analysis of wireless systems over fading channels, we will show that important performance indexes can be easily derived from the MGF. With respect to previous published articles on the matter, the main contribution of the paper is twofold: i) by relying on the properties of the Meijer-G function, either exact expressions or accurate bounds for the MGF of the end-to-end SNR are provided, and ii) the analysis encompasses the vast majority of fading channel models. Numerical and simulation results will be compared to substantiate the analytical derivation.     

Tuning of a Vertical Spin Valve with a Monolayer of Single Molecule Magnets

The synthesis and the chemisorption from solution of a terbium bis‐phthalocyaninato complex suitable for the functionalization of lanthanum strontium manganite (LSMO) are reported. Two phosphonate groups are introduced in the double decker structure in order to allow the grafting to the ferromagnetic substrate actively used as injection electrode in organic spin valve devices. The covalent bonding of functionalized terbium bis‐phthalocyaninato system on LSMO surface preserves its molecular properties at the nanoscale. X‐ray photoelectron spectroscopy confirms the integrity of the molecules on the LSMO surface and a small magnetic hysteresis reminiscent of the typical single molecule magnet behavior of this system is detected on surface by X‐ray magnetic circular dichroism experiments. The effect of the hybrid magnetic electrode on spin polarized injection is investigated in vertical organic spin valve devices and compared to the behavior of similar spin valves embedding a single diamagnetic layer of alkyl phosphonate molecules analogously chemisorbed on LSMO. Magnetoresistance experiments have evidenced significant alterations of the magneto‐transport by the terbium bis‐phthalocyaninato complex characterized by two distinct temperature regimes, below and above 50 K, respectively.     

Outage Performance with Handover Triggering in Cellular Mobile Networks

An approach to performance evaluation of cellular mobile networksis proposed, which includes the behavior of handover algorithmsin the computation of outage probability.In a general system scenario, with a central cluster and interferingbase stations, the average outage probability is computed along a trip of themobile terminal that involves crossing the boundary between adjacent cells.The effects of correlated co-channel interferersare accounted for in the computationof outage probability, as well as in the dynamics of a relative signalstrengthhandover algorithm.Numerical results are provided and discussed as obtained over a wide rangeof values of system parameters, namely cluster size and channel parameters.Trade-off curves are shown in terms of outage probability and cross-overpoint versus the average number of handovers, and possible design criteriaare outlined.It is also seen that the local outage analysis (without handover triggering)can be referred to as a lower performance bound in cases of practicalinterest.     

A New Apparatus for the Determination of the Emitted Dose from Pressurized Metered Dose Inhalation Aerosols with Inhalation Devices

A new in vitro test apparatus is described in this report to test the emitted dose from the pressurized metered dose inhalation aerosols (MDI) with inhalation devices. Drug deposition from MDIs in conjunction with different inhalation chambers was studied using a new apparatus and compendial apparatuses. The new apparatus is simple and offers an alternate method to determine the small particle fraction delivered from MDI aerosols with inhalation devices.