4,960 research outputs found

    Efficient Beam Alignment in Millimeter Wave Systems Using Contextual Bandits

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    In this paper, we investigate the problem of beam alignment in millimeter wave (mmWave) systems, and design an optimal algorithm to reduce the overhead. Specifically, due to directional communications, the transmitter and receiver beams need to be aligned, which incurs high delay overhead since without a priori knowledge of the transmitter/receiver location, the search space spans the entire angular domain. This is further exacerbated under dynamic conditions (e.g., moving vehicles) where the access to the base station (access point) is highly dynamic with intermittent on-off periods, requiring more frequent beam alignment and signal training. To mitigate this issue, we consider an online stochastic optimization formulation where the goal is to maximize the directivity gain (i.e., received energy) of the beam alignment policy within a time period. We exploit the inherent correlation and unimodality properties of the model, and demonstrate that contextual information improves the performance. To this end, we propose an equivalent structured Multi-Armed Bandit model to optimally exploit the exploration-exploitation tradeoff. In contrast to the classical MAB models, the contextual information makes the lower bound on regret (i.e., performance loss compared with an oracle policy) independent of the number of beams. This is a crucial property since the number of all combinations of beam patterns can be large in transceiver antenna arrays, especially in massive MIMO systems. We further provide an asymptotically optimal beam alignment algorithm, and investigate its performance via simulations.Comment: To Appear in IEEE INFOCOM 2018. arXiv admin note: text overlap with arXiv:1611.05724 by other author

    Complications leading to hospitalization due to consumption of anti-TB drugs in patients with tuberculosis in Gorgan, Iran (2007-12)

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    Background and Objective: Anti tuberculosis drugs therapy is the most effective method for controling the tuberculosis (TB). Early detection and appropriate treatment can prevent the TB-drug resistance. This study was carried out to determine the complications leading to hospitalization due to consumption of anti-TB drugs in patients with tuberculosis. Methods: In this descriptive-analytic study, 1550 records of patients with TB in urban and rural health centers of Gorgan, north of Iran were assessed during 2007-12. Checklist consists of demographic and clinical data for each patient was recorded in a questionare. Results: 44 cases experienced the complications of anti-TB drugs. 27 (61.4%) of cases with complications were women. 77.3% and 22.7% of patients affected with pulmonary and extra pulmonary tuberculosis,respectively. 38.6% of patients were diabetic. The hepatic complication was seen in 37 cases (84.1%). Skin and other complications were seen in 5 and 2 cases, respectively. There was not any relationship between drug complications and other disases. Conclusion: Hepatic damage is the most common complication leading to hospitalization in tuberculosis patients using anti-TB drugs. Keywords: Tuberculosis, Anti-TB drug, Live

    Energy and low-income tropical housing in Tanzania

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    Low-income housing in Tanzania is traditionally made from mud and thatch. With thatch having a typical life span of 2-7 years and mangrove poles 5-15 years, low durability is identified as the key issue with the traditional low-income house design. This paper studies the financial and social implications, embodied energy (EE) and human energy (HE) of a variety of materials in a bid to identify both the positive and negative impacts of each material substitution on the overall design, the environment and the local community. Using primary data collected from houses in the Mbweni district of Dar es Salaam and The Inventory of Carbon and Energy to calculate EE, a qualitative and quantitative assessment of each material is made. 47% of residents questioned in Tanzania, identified low durability to be the key issue with their mud house, with design changes which address this issue therefore affecting the largest share of the population. Stabilised bricks are identified as the key material substitution that should be adopted by local people, they perform well in terms of improved durability, financial and environmental considerations, and have the potential to be socially beneficial as well. This research identifies the social considerations to be key to understanding how local people will respond to the suggested material substitutions and whether they are likely to be adopted in the future. Whilst the environmental considerations are important, this is not a concept local people can relate to and does not affect their day-to-day lives as much as financial and social implications. It is extremely difficult and ethically questionable, especially in communities with people living close to poverty, to expect someone to adopt a design which requires more effort/money on their part, just because it is better for the environment

    Optical properties of Born-Infeld-dilaton-Lifshitz holographic superconductors

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    In this paper, we first study the Lifshitz-dilaton holographic superconductors with nonlinear Born-Infeld (BI) gauge field and obtain the critical temperature of the system for different values of Lifshitz dynamical exponent, zz, and nonlinear parameter bb. We find that for fixed value of bb, the critical temperature decreases with increasing zz. This indicates that the increase of anisotropy between space and time prevents the phase transition. Also, for fixed value of zz, the critical temperature decrease with increasing bb. Then, we investigate the optical properties of (2+12+1) and (3+13+1)-dimensional BI-Lifshitz holographic superconductors in the the presence of dilaton field. We explore the refractive index of the system. For z=1z=1 and (2+1)(2+1)-dimensional holographic superconductor, we observe negative real part for permittivity Re[ϵ]\textrm{Re}[\epsilon] as frequency ω\omega decreases. Thus, in low frequency region our superconductor exhibit metamaterial property. This behaviour is independent of the nonlinear parameter and can be seen for either linear (b=0b=0) and nonlinear (b0b\neq 0) electrodynamics. Interestingly, for (3+13+1)-dimensional Lifshitz-dilaton holographic superconductors, we observe metamaterial behavior neither in the presence of linear nor nonlinear electrodynamics.Comment: 11 pages, 9 figures (including subfigures), some references added in V

    Multi-Objective Gust Load Alleviation Control Designs for an Aeroelastic Wind Tunnel Demonstration Wing

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    This paper presents several control and gust disturbance estimation techniques applied to a mathematical model of a physical flexible wing wind tunnel model used in ongoing tests at the University of Washington Aeronautical Laboratory's Kirsten Wind Tunnel. Three methods of gust disturbance estimation are presented, followed by three control methods: LQG, Basic Multi-Objective (BMO), and a novel Multi-Objective Prediction Correction (MOPC) controller. The latter of which augments a multi-objective controller, and attempts to correct for errors in the disturbance estimate. A simplified linear simulation of the three controllers is performed and a simple MIMO stability and robustness assessment is performed. Then, the same controllers are simulated in a higher fidelity Simulink environment that captures sampling, saturation and noise effects. This preliminary analysis indicates that the BMO controller provides the best performance and largest stability margins

    A novel vacuum ultra violet lamp for metastable rare gas experiments

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    We report on a new design of a vacuum ultra violet (VUV) lamp for direct optical excitation of high laying atomic states e.g. for excitation of metastable rare gas atoms. The lamp can be directly mounted to ultra high vacuum vessels (p <= 10^(-10) mbar). It is driven by a 2.45 GHz microwave source. For optimum operation it requires powers of approximately 20 W. The VUV light is transmitted through a magnesium fluoride window, which is known to have a decreasing transmittance for VUV photons with time. In our special setup, after a run-time of the VUV lamp of 550 h the detected signal continuously decreased to 25 % of its initial value. This corresponds to a lifetime increase of two orders of magnitude compared to previous setups or commercial lamps

    Analysis of masonry walls subjected to high strain rate out-of-plane loads with a rate dependent interface model

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    Masonry is a composite material composed of individual units laid in and bound together by mortar. Appropriate Understanding of masonry material properties results in secure and efficient protection and strengthening of historical structures. Due to high computation costs and difficulties deal with detailed modelling of masonry structures, few studies are available in open literature dedicated to micro numerical modelling of masonry structures subjected to blast loading. In present study, the objective is to propose a dynamic interface model obeying non-associated flow rule with high strain rate effects to apply as material model for interface elements. In order to introduce the strain rate effects of brick and mortar properties, a recent developed model is applied here. Verifying the capability of the model proposed, numerical simulations are carried out to investigate the behaviour of unreinforced brick masonry walls subjected to explosive blast loading by using the finite element (FE) code ABAQUS. The results obtained are compared with field test data to find good agreement. A comprehensive parametric analysis is finally accomplished with different main material properties to evaluate the effect of each parameter on high strain rate response of masonry walls

    A constitutive three-dimensional interface model for masonry walls subjected to high strain rates

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    Investigation of the dynamic properties of construction materials is critical for structural engineering. The strain rate effect influences the properties of most constructions materials and this effect on materials such as concrete or steel has been intensively investigated. However, such studies on masonry materials are scarce. Understanding the strain rate effect on masonry materials is important for proper modelling and design of masonry structures under high velocity impacts or blast loads. The work, described in this paper, aims to study the behaviour of masonry at different strain rates. First, a drop weight impact machine is used at different heights and weights introducing different levels of strain rate. Then, a dynamic constitutive material interface model that includes an non-associated flow rule and high strain rate effects is proposed. The model capability is validated with numerical simulations of unreinforced block work masonry walls subjected to impact.(undefined
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