In multiuser MIMO downlink communications, it is necessary to design precoding schemes that are able to suppress co-channel interference. This paper proposes designing precoders by maximizing the ...so-called signal-to-leakage-and-noise ratio (SLNR) for all users simultaneously. The presentation considers communications with both single- and multi-stream cases, as well as MIMO systems that employ Alamouti coding. The effect of channel estimation errors on system performance is also studied. Compared with zero-forcing solutions, the proposed method does not impose a condition on the relation between the number of transmit and receive antennas, and it also avoids noise enhancement. Simulations illustrate the performance of the scheme
Spectrum sensing is an essential functionality that enables cognitive radios to detect spectral holes and to opportunistically use under-utilized frequency bands without causing harmful interference ...to legacy (primary) networks. In this paper, a novel wideband spectrum sensing technique referred to as multiband joint detection is introduced, which jointly detects the primary signals over multiple frequency bands rather than over one band at a time. Specifically, the spectrum sensing problem is formulated as a class of optimization problems, which maximize the aggregated opportunistic throughput of a cognitive radio system under some constraints on the interference to the primary users. By exploiting the hidden convexity in the seemingly nonconvex problems, optimal solutions can be obtained for multiband joint detection under practical conditions. The situation in which individual cognitive radios might not be able to reliably detect weak primary signals due to channel fading/shadowing is also considered. To address this issue by exploiting the spatial diversity, a cooperative wideband spectrum sensing scheme refereed to as spatial-spectral joint detection is proposed, which is based on a linear combination of the local statistics from multiple spatially distributed cognitive radios. The cooperative sensing problem is also mapped into an optimization problem, for which suboptimal solutions can be obtained through mathematical transformation under conditions of practical interest. Simulation results show that the proposed spectrum sensing schemes can considerably improve system performance. This paper establishes useful principles for the design of distributed wideband spectrum sensing algorithms in cognitive radio networks.
An adaptive distributed strategy is developed based on incremental techniques. The proposed scheme addresses the problem of linear estimation in a cooperative fashion, in which nodes equipped with ...local computing abilities derive local estimates and share them with their predefined neighbors. The resulting algorithm is distributed, cooperative, and able to respond in real time to changes in the environment. Each node is allowed to communicate with its immediate neighbor in order to exploit the spatial dimension while limiting the communications burden at the same time. A spatial-temporal energy conservation argument is used to evaluate the steady-state performance of the individual nodes across the entire network. Computer simulations illustrate the results.
Cognitive radio technology has been proposed to improve spectrum efficiency by having the cognitive radios act as secondary users to opportunistically access under-utilized frequency bands. Spectrum ...sensing, as a key enabling functionality in cognitive radio networks, needs to reliably detect signals from licensed primary radios to avoid harmful interference. However, due to the effects of channel fading/shadowing, individual cognitive radios may not be able to reliably detect the existence of a primary radio. In this paper, we propose an optimal linear cooperation framework for spectrum sensing in order to accurately detect the weak primary signal. Within this framework, spectrum sensing is based on the linear combination of local statistics from individual cognitive radios. Our objective is to minimize the interference to the primary radio while meeting the requirement of opportunistic spectrum utilization. We formulate the sensing problem as a nonlinear optimization problem. By exploiting the inherent structures in the problem formulation, we develop efficient algorithms to solve for the optimal solutions. To further reduce the computational complexity and obtain solutions for more general cases, we finally propose a heuristic approach, where we instead optimize a modified deflection coefficient that characterizes the probability distribution function of the global test statistics at the fusion center. Simulation results illustrate significant cooperative gain achieved by the proposed strategies. The insights obtained in this paper are useful for the design of optimal spectrum sensing in cognitive radio networks.
Summary
The prevalence of multidrug‐resistant microbial pathogens due to the continued misuse and overuse of antibiotics in agriculture and medicine is raising the prospect of a return to the ...preantibiotic days of medicine at the time of diminishing numbers of drug leads. The good news is that an increased understanding of the nature and extent of microbial diversity in natural habitats coupled with the application of new technologies in microbiology and chemistry is opening up new strategies in the search for new specialized products with therapeutic properties. This review explores the premise that harsh environmental conditions in extreme biomes, notably in deserts, permafrost soils and deep‐sea sediments select for micro‐organisms, especially actinobacteria, cyanobacteria and fungi, with the potential to synthesize new druggable molecules. There is evidence over the past decade that micro‐organisms adapted to life in extreme habitats are a rich source of new specialized metabolites. Extreme habitats by their very nature tend to be fragile hence there is a need to conserve those known to be hot‐spots of novel gifted micro‐organisms needed to drive drug discovery campaigns and innovative biotechnology. This review also provides an overview of microbial‐derived molecules and their biological activities focusing on the period from 2010 until 2018, over this time 186 novel structures were isolated from 129 representatives of microbial taxa recovered from extreme habitats.
Summary
Alopecia areata (AA) is a recurrent, immune‐mediated, hair‐loss disorder. It is associated with other autoimmune disorders that carry a high risk of cardiovascular disease (CVD). However, ...there is a lack of reports on the association of cardiovascular comorbidities and AA. Cardiac troponin I is a biomarker of myocardial ischaemia and inflammation, while N‐terminal pro‐B‐type natriuretic peptide is used in the diagnosis of congestive heart failure. This study was conducted to assess the serum level of both markers by ELISA in 44 patients with AA compared with 44 healthy controls (HCs). None of the participants had CVD, CVD risk factors or other diseases associated with elevation of either marker. The study revealed that serum levels of both markers were significantly higher in patients with AA compared with HCs (P < 0.001). The inflammatory milieu encountered in AA may be associated with subtle myocardial inflammation that causes elevation of levels of both of these cardiac markers.
To examine the peristaltic motion of a Newtonian fluid through an axisymmetric tube, many writers assume that viscosity is either a constant or a radius exponential function in Stokes' equations. In ...this study, viscosity is predicated on both the radius and the axial coordinate. The peristaltic transport of a Newtonian nanofluid with radially varying viscosity and entropy generation has been studied. Under the long-wavelength assumption, fluid flows through a porous media between co-axial tubes, with heat transfer. The inner tube is uniform, while the outer tube is flexible and has a sinusoidal wave travelling down its wall. The momentum equation is solved exactly, and the energy and nanoparticle concentration equations are solved using the homotopy perturbation technique. Furthermore, entropy generation is obtained. The numerical results for the behaviours of velocity, temperature, and nanoparticle concentration, as well as the Nusselt number and Sherwood number with physical problem parameters, are obtained and graphically depicted. It is discovered that as the values of the viscosity parameter and the Prandtl number rise, so does the value of the axial velocity. Temperature values decrease as the wave amplitude and radiation parameter increase. Furthermore, at high values of the dependent viscosity parameter, the fluid nanoparticle gains more active energy and can move more freely, which is the main idea behind crude oil refinement. This physical modelling is essential for some physiological flows, such as the flow of stomach juice during the insertion of an endoscope.
A fundamental task in a wireless sensor network is to broadcast some measured data from an origin sensor to a destination sensor. Since the sensors are typically small, power limited, and low cost, ...they are only able to broadcast low-power signals. As a result, the propagation loss from the origin to the destination nodes can attenuate the signals beyond detection. One way to deal with this problem is to pass the transmitted signal through relay nodes. In this paper we propose and study two-hop multisensor relay strategies that achieve minimum mean-square-error (MSE) performance subject to either local or global power constraints. The capacity of the resulting relay link and its diversity order are studied. The effect of channel uncertainties on system performance is examined and a modified relay scheme is proposed.
Monitoring Health Related Quality of Life (HRQoL) in different stages of chronic kidney disease is advised by all nephrology societies. We aimed to study the relation between quality of life and ...dialysis adequacy.
One hundred patients (51% males), on regular hemodialysis 3/week for > 6 months in two hospitals were included. Single pool Kt/V was used to assess dialysis adequacy. Patients were grouped into 3 divisions according to Kt/v: Group A > 1.5 (n = 24), group B 1.2-1.5 (n = 54) and group C < 1.2 (n = 22). KDQOL-SF™ questionnaire was used to study quality of life in our groups. Group C was reassessed after 3 months of improving Kt/v.
Mean values were: Kt/V (1.48 ± 0.41), Cognitive Function (84.27 ± 9.96), Work status (30.00 ± 33.33), Energy (45.70 ± 13.89), Physical Function and Role limitations due to physical function (45.30 ± 12.39 and 31.25 ± 19.26, respectively). Group A had significantly higher scores of KDQOL-SF except Role limitations due to Physical Function. All subscales improved in group C after Kt/v improvement except 3 subscales, namely, work status, patient satisfaction and role limitation due to physical and emotional functions.
Inadequate HD badly affects quality of life and improving adequacy refines many components of quality of life.
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