Gibbs sampling detection for large MIMO and MTC uplinks with adaptive modulation

Wireless networks beyond 5G will mostly be serving myriads of sensors and other machine-type communications (MTC), with each device having different requirements in respect to latency, error rate, energy consumption, spectral efficiency or other specifications. Multiple-input multiple-output (MIMO) systems remain a central technology towards 6G, and in cases where massive antenna arrays or cell-free networks are not possible to deploy and only moderately large antenna arrays are allowed, the detection problem at the base-station cannot rely on zero-forcing or matched filters and more complex detection schemes have to be used. The main challenge is to find low complexity, hardware feasible methods that are able to attain near optimal performance. Randomized algorithms based on Gibbs sampling (GS) were proven to perform very close to the optimal detection, even for moderately large antenna arrays, while yielding an acceptable number of operations. However, their performance is highly dependent on the chosen “temperature” parameter (TP). In this paper, we propose and study an optimized variant of the GS method, denoted by triple mixed GS, and where three distinct values for the TP are considered. The method exhibits faster convergence rates than the existing ones in the literature, hence requiring fewer iterations to achieve a target bit error rate. The proposed detector is suitable for symmetric large MIMO systems, however the proposed fixed complexity detector is highly suitable to spectrally efficient adaptively modulated MIMO (AM-MIMO) systems where different types of devices upload information at different bit rates or have different requirements regarding spectral efficiency. The proposed receiver is shown to attain quasi-optimal performance in both scenarios.info:eu-repo/semantics/publishedVersio

Biofilm reactors

After presenting the concept of biofilms, reference is made to their importance in industry and health. Although biofilms are also well known for their deleterious effects (biofouling), emphasis is here given to the beneficial use of biofilms in wastewater treatment. The main types of biofilm reactors are briefly described and the role of support material in the adhesion and stability of biofilms is explained, taking into account the mechanisms involved in biofilm attachment. Practical procedures for the start-up of biofilm reactors are also mentioned. Biofilm growth processes are described together with their properties, structure and Performance. The advantages and disadvantages of biofilm reactors versus suspended biomass systems are discussed. The main equations of the diffusion-reaction model are developed from engineering science principles. Equations derived from the diffusion-reaction model to calculate the reactor volume are presented, together with experimental values of the kinetic parameters. Practical empirical expressions or rules-of-thumb used in the design of fixed biomass reactors are also given. An overall model to predict the growth rate of biofilms and their final thickness or mass is established. The main problems concerning biofilm reactor modelling are discussed and the "missing links" for an optimised design are identified

Fast matrix inversion updates for massive MIMO detection and precoding

In this letter, methods and corresponding complexities for fast matrix inversion updates in the context of massive multiple-input multiple-output (MIMO) are studied. In particular, we propose an on-the-fly method to recompute the zero forcing (ZF) filter when a user is added or removed from the system. Additionally, we evaluate the recalculation of the inverse matrix after a new channel estimation is obtained for a given user. Results are evaluated numerically in terms of bit error rate (BER) using the Neumann series approximation as the initial inverse matrix. It is concluded that, with fewer operations, the performance after an update remains close to the initial one.info:eu-repo/semantics/acceptedVersio

Pairs of matrices that preserve the value of a generalized matrix function on the set of the upper triangular matrices

AbstractLet H be a subgroup of the symmetric group of degree m and let χ be an irreducible character of H. In this paper we give conditions that characterize the pairs of matrices that leave invariant the value of a generalized matrix function associated with H and χ, on the set of the upper triangular matrices

Spatial approximation of nondivergent type parabolic PDEs with unbounded coefficients related to finance

We study the spatial discretisation of the Cauchy problem for a multidimensional linear parabolic PDE of second order, with nondivergent operator and unbounded time- and space-dependent coefficients. The equation free termand the initial data are also allowed to grow. Under a nondegeneracy assumption, we consider the PDE solvability in the framework of the variational approach and approximate in space the PDE problem’s generalised solution, with the use of finite-difference methods.Therate of convergence is estimated.info:eu-repo/semantics/publishedVersio

Synergy of farnesol and antibiotics against planktonic versus biofilm cells of Staphylococcus epidermidis

Staphylococcus epidermidis is the most frequent cause of nosocomial sepsis and catheter-related infections, in which biofilm formation is considered to be one of the main virulence mechanisms. Moreover, their increased resistance to conventional antibiotic therapy enhances the need to develop new therapeutical agents. Farnesol, a quorum-sensing molecule in Candida albicans, has been described as impairing bacterial growth. The goal of this study was to evaluate the synergistic effect of farnesol and antibiotics on planktonic and biofilm cells of S. epidermidis strains (1457 and 9142). To accomplish that, three antibiotics with different mechanisms of action were tested: vancomycin (cell wall synthesis inhibitor), tetracycline (Protein synthesis inhibitor) and rifampicin (RNA synthesis inhibitor). A 24 h kinetic study was performed using these antibiotics at the peak serum concentration along with farnesol at concentrations of 30, 100, 200 and 300 μM. To evaluate planktonic cells viability, it was used two tests: a rapid colorimetric method that is based on the reduction of tetrazolium salt (XTT) to measure mitochondrial cellular activity and standard colony forming units enumeration (CFU). The growth inhibition effect of farnesol and/or antibiotics on biofilm cells of S. epidermidis was assessed by XTT, CFU enumeration and Crystal Violet, which measures total biomass of biofilm. In planktonic as well as in biofilm cells, both strains of S. epidermidis studied were much less susceptible to farnesol than to all the antibiotics tested. All the antibiotics were highly effective against planktonic cells. Biofilm cells were much less susceptible than planktonic cultures to vancomycin, tetracycline and rifampicin. In planktonic cells it was not observed a synergistic effect of farnesol and any of the antibiotics used, except for the strain 9142 when treated with vancomycin. In biofilms, there was a synergistic effect of farnesol and all antibiotics, expressed by the reduction of biomass and mitochondrial cellular activity of biofilm cells. The susceptibility of biofilm cells to farnesol and antibiotics was higher when the antibiotic tested was rifampicin, followed by tetracycline and finally by vancomycin

Farnesol as a prospective antimicrobial agent against Staphylococcus epidermidis

Objectives: Staphylococcus epidermidis is now among the most important pathogenic agents responsible for bloodstream nosocomial infections and for biofilm formation on indwelling medical devices. Its increasing resistance to common antibiotics is a challenge for the development of new antimicrobial agents. Accordingly, the goal of this study was to evaluate the effect of farnesol, a natural sesquiterpenoid, on Staphylococcus epidermidis biofilm cells and compare this one with the effect of vancomycin, one of the most frequently used antibiotics to treat resistant nosocomial infections. Another aim of this work was to determine if subjecting S. epidermidis cells to farnesol they acquire resistance. Methods: A 24 h kinetic study was performed using vancomycin at the peak serum concentration (40mg/L) and farnesol at concentrations of 30, 100, 200 and 300 microM. The growth inhibition effect of farnesol and vancomycin on biofilm cells of S. epidermidis was assessed by XTT (the reduction of this tetrazolium salt is a measure of cellular activity and is easily assessed by colorimetry) and Crystal Violet, which measures total biomass of biofilm. The biofilm cells were analysed by confocal laser scanning microscopy after being stained with Live/Dead. Resistance to farnesol and vancomycin was tested growing S. epidermidis planktonic cells in sub-inhibitory concentrations of farnesol and vancomycin and then subjecting these cells to inhibitory concentrations of both antimicrobial agents during 24 hours. After that, cellular activity was assessed by XTT. This was repeated for 5 consecutive days. Results: Both tested agents act at the cell wall level, vancomycin inhibits the biosynthesis of bacterial cell wall, while farnesol is considered to disrupt the normal barrier function of the cell membrane. Interestingly, farnesol at a concentration higher than 200 microM displayed the same or higher effectiveness of vancomycin at peak serum concentration. In fact, the response of the strains tested was very similar for both farnesol (>200 microM) and vancomycin. Regarding cells resistance to farnesol, the results point out to a slight increase of tolerance but not to an acquired resistance, because the percentage of inhibition was steady along the time. Conclusions: Overall, the results indicate a potential antibacterial effect of farnesol against S. epidermidis, and therefore the possible action of this molecule on the prevention of S. epidermidis related infections