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Second order cone (SOC) restrictions have been widely employed in the design of wireless communication systems to recast precoding optimizations in convex form. This paper highlights the flexibility of this framework to handle various transmit power and interference limitations also in the multistream multiple-input multiple-output broadcast channel with imperfect channel state information at the transmitter. In particular, we propose an iterative solution for mean square error (MSE) balancing with such constraints via the Lagrangian dual formulation. The MSE balancing criteria, contrary to signal-to-interference plus-noise ratio and rate criteria, exhibit an interesting property when considering different targets for the receivers. Users with low target values are strictly prioritized in comparison to users with large MSE targets that can even be switched off. Therefore, only a subset of the receivers is served at the solution with stringent limitations for the precoders. An example of such stringent limitations are small power constraints and probabilistic interference temperature constraints that set a measurable threshold on the generated interference in a cognitive radio system. We provide four different approaches to approximate these probabilistic constraints with deterministic SOC constraints, and compare their accuracy. [ABSTRACT FROM PUBLISHER]

Abstract: A selective resin for linking trans-diequatorial-1,2-diols to solid support is described. This linking was carried out under mild and aprotic conditions involving the use of trimethylsilyl methyl ether in the presence of trimethylsilyl trifluoromethanesulfonate. Cleavage from the resin was also carried out under mild conditions by treatment with dichloromethane/trifluoroacetic acid/water (21:20:1). The usefulness of the described cyclohexane-1,2-diketone resin 7 in quinic acid chemistry was also studied. [Copyright &y& Elsevier]

Coupling nicotinoyl chloride with 3,4-dimetoxyphenethylamine under Bischler-Napieralski cyclization afforded the isoquinoline (4) in good yield. This latter was used as starting material to obtain with only hydrobromic acid a product with demethylation at the position 7 (5). In addition, treatment of (4) with NaBH4/MeOH gave 6,7-dimetoxy-1-(pyridin-3-yl)-1,2,3,4-tetrahydroisoquinoline (6) and unexpectedly, under mild reduction of the pyridine moiety with H2/PtO2/AcOH/, gave 6,7-dimetoxy-1-(piperidin-3-yl)-1,2,3,4-tetrahydroisoquinoline (7) as the title compound. The unusual chemical reactivity of 4 onto acidic conditions and catalytic hydrogenation allowed us to obtain anabaseine and anabasine derivatives under mild conditions. [ABSTRACT FROM AUTHOR]

Bio-inspired cyclopeptidic heterodimers built on β-sheet-like hydrogen-bonding networks and bearing photoactive and electroactive chromophores on the outer surface have been prepared. Different cross-strand pairwise relationships between the side chains of the cyclic α,γpeptides afford the heterodimers as three nonequivalent dimeric species. Steady-state and time-resolved spectroscopies clearly show an electron transfer process from Ꮐextended tetrathiafulvalene, covalently attached to one of the cyclopeptides, to photoexcited [60]fullerene, located on the complementary cyclopeptide. The charge-separated state was stabilized for up to 1 μs before recombining and repopulating the ground state. Our current example shows that cyclopeptidic templates can be successfully used to form light-harvesting/light-converting hybrid ensembles with a distinctive organization of donor and acceptor units able to act as efficient artificial photosystems. [ABSTRACT FROM AUTHOR]

A computational DFT examination (B3LYP/6-31G* and B3LYP/6-311+G**//B3LYP/6-31G*) of the thermal [5C + 2C] cycloaddditions of 6-acetoxy-3-pyranones and 3-silyloxy-4-pyrones with tethered alkenyl sulfoxides confirms that the high level of diastereofacial selectivity obtained is ultimately due to the preference of the alkenesulfinyl group to adopt a well-defined conformation in the transition state of the reaction. This conformation, which is different from that found in the ground state, is most probably dictated by dipolar interaction effects between the sulfoxide and the oxidopyrylium ylide intermediate. [ABSTRACT FROM AUTHOR]

This paper introduces an iterative space–time soft estimator (ISSE) that performs joint channel estimation and soft data detection in time-varying multiple-input multiple-output channels. The ISSE alternates channel estimation, taking explicitly into account the channel variability, and soft data detection. We suggest to implement the latter stage as a decision feedback (DF) structure consisting of two linear minimum mean square error (MMSE) matrix filters with an intercalated threshold detector. DF schemes are known to provide an appealing trade-off between performance and computational complexity. The main contribution of the paper is the channel estimation scheme. We derive a time-varying sequence of linear filters for channel estimation according to the MMSE principle. These filters depend both on the data and the second order statistics of the channel. Hence, we introduce a scalar approximation of the channel autocovariance function that relies on the statistical homogeneity of the multipath scattering. Under this assumption, we also design a globally convergent block-adaptive algorithm to estimate and track the second order statistics of a stationary channel. The robustness of the proposed approach when either the homogeneity or the stationarity hypotheses do not hold is shown through computer simulations. [Copyright &y& Elsevier]

In this paper we propose a new approach to blind separation of independent source signals that, while avoiding the imposition of an orthogonal mixing matrix, is robust with respect to the existence of additive Gaussian noise in the mixture. We demonstrate that, for the wide class of source distributions with certain non-null cumulants and a pre-specified scaling, separation is always a saddle point of a cumulant-based cost function. We propose a quasi-Newton approach for determining this saddle point. This enables us to obtain a family of separation algorithms which, based on higher order statistics, yields unbiased estimates even in the presence of large Gaussian noise and has the interesting property of local isotropic convergence. Another family of algorithms that incorporates second-order statistics loses the former desirable convergence properties but it provides more precise estimates in the absence of noise. Extensive computer simulations confirm robustness and the excellent performance of the resulting algorithms. [Copyright &y& Elsevier]

Presents a study that investigated the problem of channel estimation and symbol detection in wireless direct-sequence code-division multiple-access (CDMA) communication systems. Background on the performance of direct-sequence CDMA schemes used in third-generation mobile communication systems; Details on the multiuser demodulation scheme applied in the study; Results and implications.

It has been recently shown that deploying multiple transmitting and receiving antennae can substantially improve the capacity of multipath wireless channels if the rich time-scattering is properly exploited. Space–time coding (STC) is a novel proposal that combines channel coding techniques suitable for multiple transmitting elements with signal processing algorithms that exploit the spatial and temporal diversity at the receiver. In this paper, we focus on the signal processing perspective and propose a novel space–time semiblind decoding scheme that performs maximum likelihood (ML) based channel estimation and data detection. The multiple input multiple output (MIMO) time-scattering channel is estimated using a block iterative expectation-maximization (EM) algorithm that fully exploits the statistical features of the transmitted signal together with the knowledge of a small number of transmitted symbols, hence the term semiblind. Data detection is efficiently carried out using the Viterbi algorithm. In order to reduce the computational load of the receiver, a modification of the EM algorithm with a potentially lower complexity is also suggested. Computer simulations show that the proposed semiblind decoder clearly outperforms conventional receivers that estimate the channel parameters exclusively from the a priori known transmitted symbols. [Copyright &y& Elsevier]

Shows that the opening of the bridging ether of 8-oxabicyclo[3.2.1]oct-6-ene systems 1,7-fused to a five-membered carbocycle that bears a double bond conjugated to that of the oxabicycle can be induced at low temperature. Addition of an organolithium reagent; Occurrence of the opening via an anti-1,6-addition pathway if the double bond is unsubstituted.

Demonstrates the regioselective synthesis of isoquino[1,2-b][3]benzazepines (homoprotoberberines) through 11-membered-ring stilbene lactams obtained by radical macrocyclization. Preparation of silylated 11-membered-ring stilbene lactams by intramolecular addition of an aryl radical to a trimethylsilylacetylene.

Presents a study on the conversion of silylated stilbene lactams into protoberberines using dimethyldioxirane epoxidation and subsequent acid-catalyzed cyclization of the epoxysilane with hydrochloric acid. Formation of 13-hydroxytetrahydroprotoberberines and 13a-hydroxy-13ketotetrahydroprotoberberines as main products; Reaction of silylated and nonsilylated lactams.

Provides information on a study which presented a modified constant modulus algorithm (CMA) equalizer for the removal of length dependent local minima in autoregressive channels. Statement of the problem; Modification of CMA; Conclusions.

Presents a study on the total synthesis of (+,-)-clavizepine using the dibenzoxepinediol as main intermediate. Contraction of the oxepine ring as key step; Assembly of nitrogenated ring; Versatility of dibenzopyranazepines for the synthesis of both cularine alkaloids and the dibenzopyranazepine skeleton.

Proposes an approach based on the constant modulus (CM) criterion to separate instantaneous linear mixtures of signals using a linear memoryless multiple input multiple output (MIMO) system. Constant modulus analysis-based optimization criterion; Analysis of stationary points of the proposed cost function; Results of the computer simulations of the proposed method; Conclusions.

The design of zero-delay Joint Source-Channel Coding (JSCC) schemes for the transmission of correlated information over fading Multiple Access Channels (MACs) is an interesting problem for many communication scenarios like Wireless Sensor Networks (WSNs). Among the different JSCC schemes so far proposed for this scenario, Distributed Quantizer Linear Coding (DQLC) represents an appealing solution since it is able to outperform uncoded transmissions for any correlation level at high Signal-to-Noise Ratios (SNRs) with a low computational cost. In this paper, we extend the design of DQLC-based schemes for fading MACs considering sphere decoding to make the optimal Minimum Mean Squared Error (MMSE) estimation computationally affordable for an arbitrary number of transmit users. The use of sphere decoding also allows to formulate a practical algorithm for the optimization of DQLC-based systems. Finally, non-linear Kalman Filtering for the DQLC is considered to jointly exploit the temporal and spatial correlation of the source symbols. The results of computer experiments show that the proposed DQLC scheme with the Kalman Filter decoding approach clearly outperforms uncoded transmissions for medium and high SNRs. [ABSTRACT FROM AUTHOR]

In this correspondence, we reply to the comments in Gu ["Comments on `A blind signal separation method for multiuser communications'", IEEE Transactions on Signal Processing, vol. 55, no. 5, pp. 2355-2356, May 2007]. We explain that the global convergence analysis of the method in Castedo ["A blind signal separation method for multiuser communications", IEEE Transactions on Signal Processing, vol. 45, no. 5, pp. 1343-1348, May 1997] can be completed as an extension of the results that were already presented. Also, we recall that two of the authors put forward (Dapena and Castedo ["Stochastic gradient adaptive algorithms for blind source separation", Elsevier Signal Processing, vol. 75, pp. 11-27]) a similar method with more attractive properties whose convergence analysis is not affected by the counterexample provided in Gu et al [ABSTRACT FROM PUBLISHER]

Reports on the structural and thermodynamic basis of a class of cyclic peptide nanotubes with hydrophobic cavities. Validation of the possibility of expanding the self-assembling peptide nanotube class to other hybrid systems; Use of a hybrid of alpha-gamma-cyclic peptides subunits.

A new, efficient and mild method for the formation of 1,2-diacetals is described. [Copyright &y& Elsevier]

Examines the ruthenium-catalyzed alkyne-alkene coupling and a prins-type cyclization. Use of 1-trimethylsilyl-1-alkyn-3-ols and allyl ethers; Application of aromatic system as the nucleophilic partner; Assembly of a homologous oxygen-bridged system.

Analog transmission of correlated information over Gaussian broadcast channels (BCs) using analog joint source–channel coding (JSCC) is addressed. This communication strategy has attractive advantages, such as low complexity, minimal delay, graceful degradation, and adaptation to time-varying environments. In this paper, we focus on the optimization of parametric continuous mappings that satisfy individual quality of service requirements over Gaussian BCs. This optimization is based on the balancing of the user distortions to ensure the feasibility of the resulting optimization problems. An analysis of the overall distortion corresponding to the considered mappings is carried out to design algorithms that determine the optimal values for the mappings parameters. Results show that the proposed analog JSCC scheme provides near optimal performance and an adequate balancing of the individual distortions. [ABSTRACT FROM AUTHOR]

Examines the development of an efficient three- or four-step synthesis of heterocyclic phenanthrenoids. Description of a novel strategy; Pursuing of an application to the presentation of active compounds; Support for research.

Demonstrates that unreactive alkenes can be induced to participate in the thermal cycloaddition for the synthesis of carbocycles by their temporary attachment to the pyrone through a readily removable connector. Insurance of complete regio-and stereochemical control; Strategies developed for synthesis of the rings; Mixtures of stereoisomeric cycloadducts.

Joint source-channel coding for discrete-time analog sources is an appealing transmission approach because of its extremely low delay and complexity. When the users access the channel orthogonally, analog transmission of correlated information over fading multiple access channels (MACs) using modulo-like mappings provides better performance than uncoded transmission. In this paper, we propose a simplified decoder for modulo mappings in possibly non-orthogonal MAC scenarios with a single-antenna users and a multiple-antenna receiver. Sphere decoding is investigated to reduce the computational complexity when the number of users is large. In addition, affordable strategies are proposed to optimize the mapping parameters according to the channel conditions and the source correlation. The obtained results show that the use of modulo mappings is suitable when the number of antennas at the receiver is larger than the number of users and for high correlation between user data. [ABSTRACT FROM PUBLISHER]

Nowadays, the railway industry is in a position where it is able to exploit the opportunities created by the IIoT (Industrial Internet of Things) and enabling communication technologies under the paradigm of Internet of Trains. This review details the evolution of communication technologies since the deployment of GSM-R, describing the main alternatives and how railway requirements, specifications and recommendations have evolved over time. The advantages of the latest generation of broadband communication systems (e.g., LTE, 5G, IEEE 802.11ad) and the emergence ofWireless Sensor Networks (WSNs) for the railway environment are also explained together with the strategic roadmap to ensure a smooth migration from GSM-R. Furthermore, this survey focuses on providing a holistic approach, identifying scenarios and architectures where railways could leverage better commercial IIoT capabilities. After reviewing the main industrial developments, short and medium-term IIoT-enabled services for smart railways are evaluated. Then, it is analyzed the latest research on predictive maintenance, smart infrastructure, advanced monitoring of assets, video surveillance systems, railway operations, Passenger and Freight Information Systems (PIS/FIS), train control systems, safety assurance, signaling systems, cyber security and energy efficiency. Overall, it can be stated that the aim of this article is to provide a detailed examination of the state-of-the-art of different technologies and services that will revolutionize the railway industry and will allow for confronting today challenges. [ABSTRACT FROM AUTHOR]

Metal-directed supramolecular construction represents one of the most powerful tools to prepare a large variety of structures and functions. The ability of metals to organize different numbers and types of ligands with a variety of geometries (linear, trigonal, octahedral, etc.) expands the supramolecular synthetic architecture. We describe here the precise construction of homo- and heterodimeric cyclic peptide entities through coordination of a metal (Pd, Au) and to β-sheet-type hydrogen-bonding interactions. The selective coordination properties of the appropriate metal allow control over the cross-strand interaction between the two-peptide strands. [ABSTRACT FROM AUTHOR]

3-(Propa-1,2-dien-1-yl)oxazolidin-2-one works as an efficient two-carbon partner in a variety of intermolecular gold-catalyzed [2+2] cycloadditions to alkenes. The transformation represents a simple and practical entry to highly substituted cyclobutane derivatives and takes place with complete regio- and stereocontrol. [ABSTRACT FROM AUTHOR]

dimer-forming self-assembling cyclic hexapeptide with a control register and a large association constant in water is described. The self-assembly process is followed by pyrene-excimer emission and the main diastereomeric dimer present in solution is switched by controlled addition of divalent cations (e.g., Ca, Mg) or oxalic acid. [ABSTRACT FROM AUTHOR]

We consider the robust precoder design for multiuser multiple- input single-output (MU-MISO) systems where the channel state information (CSI) is fed back from the single antenna receivers to the centralized transmitter equipped with multiple antennas. We propose to compress the feedback data by projecting the channel estimates onto a vector basis, known at the receivers and the transmitter, and quantizing the resulting coefficients. The channel estimator and the basis for the rank reduction are jointly optimized by minimizing the mean-square error (MSE) between the true and the rank-reduced CSI. Expressions for the conditional mean and the conditional covariance of the channel are derived which are necessary for the robust precoder design. These expressions take into account the following sources of error: channel estimation, truncation for rank reduction, quantization, and feedback channel delay. As an example for the robust problem formulation, vector precoding (VP) is designed based on the expectation of the MSE conditioned on the fed-back CSI. Our results show that robust precoding based on fed-back CSI clearly outperforms conventional precoding designs which do not take into account the errors in the CSI. [ABSTRACT FROM AUTHOR]

Abstract: A new approach to carbazoles and benzannulated carbazoles by means of intramolecular dehydro Diels–Alder of ynamides is reported. N-(o-Ethynyl)aryl ynamides and N-(o-ethynyl) arylynamides were prepared in a few steps starting from o-iodoaniline. Thermal cycloaddition of N-(o-ethynyl)aryl ynamides and N-(o-ethynyl) arylynamides affords carbazoles and benzannulated and heteroannulated carbazoles in moderate-to-good yields. [Copyright &y& Elsevier]

"Formal" and standard Ru(II)-catalyzed [2 + 2 + 2] cycloaddition of 1,6-diynes 1 to alkenes gave bicyclic 1,3-cyclohexadienes in relatively good yields. The neutral Ru(II) catalyst was formed in situ by mixing equimolecular amounts of [Cp*Ru(CH3CN)3IPF6 and Et4NCI; Two isomeric bicyclic 1,3-cyclohexadienes 3 and 8 were obtained depending on the cyclic or acyclic nature of the alkene partner. Mechanistic studies on the Ru catalytic cycle revealed a clue for this difference: (a) when acyclic alkenes were used, linear coupling of 1,6-diynes with alkenes was observed giving 1,3,5-trienes 6 as the only initial reaction products, which after a thermal disrotatory 6e-π electrocyclization led to the final 1,3-cyclohexadienes 3 as probed by NMR studies. This cascade process behaved as a formal Ru-catalyzed [2 + 2 + 2] cycloaddition. (b) With cyclic alkenes, the standard Ru-catalyzed [2 + 2 + 21 cycloaddition occurred, giving the bicyclic 1,3-cyclohexadienes 8 as reaction-products. A complete catalytic cycle for the formal and standard Ru-catalyzed [2 + 2 + 2] cycloaddition of acetylene and cyclic and acyclic alkenes with the Cp*RuCl fragment has been proposed and discussed based on DFT/B3LYP calculations. The most likely mechanism for these processes would involve the formation of ruthenacycloheptadiene intermediates XXIII or XXVII depending on the alkene nature. From these complexes, two alternatives could be envisioned: (a) a reductive elimination in the case of cyclic alkenes 7 and (b) a β-elimination followed by reductive elimination to give 1,3,5-hexatrienes 6 in the case of acyclic alkenes. Final 6e-π electrocyclization of 6 gave 1,3-cyclohexadienes 3. [ABSTRACT FROM AUTHOR]

Mild conditions are described that allow the palladium-catalyzed cross-coupling of Cα-alkynylated glycine with a wide variety of electron-rich and electron-poor aryl and heteroaryl halides in aqueous media. [ABSTRACT FROM AUTHOR]

Abstract: N,N′-aryl- and N,N′-alkyl-buta-1,3-diyne-1,4-ditosylamides have been synthesized for the first time, in good to excellent yields, by copper-catalyzed dimerization of the corresponding N-aryl or N-alkyl tosylynamides. Negishi coupling of N-ethynylzinc tosylamides derivatives with (hetero)aryl iodides in the presence of Pd2dba3 and triphenylphosphine affords N-aryl and N-alkyl arylynamides in yields of up to 90%. Intramolecular [4+2] cycloaddition reactions of N-ethynylphenyl ynamides and arylynamides allow the synthesis of carbazoles and benzannulated and heteroannulated carbazoles in moderate-to-good yields. [Copyright &y& Elsevier]

This paper addresses the problem of interference suppression in direct sequence code division multiple access systems. We propose a novel semiblind decision feedback (DF) receiver based on the maximum likelihood principle that simultaneously exploits the transmission of training sequences and the statistical information of the unknown transmitted symbols. Both iterative and adaptive implementations of the proposed receiver, derived within the framework of the expectation maximization algorithm, are presented. Computer simulations show that the resulting multiuser detectors attain practically the same performance as the theoretical DF minimum mean square error receiver. [Copyright &y& Elsevier]

An efficient and versatile strategy for the synthesis of polyhydroxycyclohexanes and related compounds 3-6 is reported. The successful synthesis of these analogues has been achieved from a common intermediate, quinic acid derived lactone 2, rapidly accessible from cheap and commercially available (-)-quinic acid (1) as a chiral template. A practical route involving stereocontrolled epoxide formation and hydrolysis has been developed for the synthesis of 2,3-trans analogues 3 and 4. The preparation of the 2,3-cis analogues 5 and 6 has been realized by diasteroselective oxidation of a 5,6-double bond. [ABSTRACT FROM AUTHOR]

A comprehensive theoretical and experimental investigation of dehydro Diels-Alder reactions examining the evolution of the cyclic allene intermediates under conditions for intramolecular and ionic and radical intermolecular cycloaromatization processes is reported. Theoretical calculations showed that the most favored intramolecular path for cycloaromatization of 1,2,4-cyclohexatriene 4 and its benzoannulated derivative 14, strained cyclic allenes, consists of a pair of successive [1,2] H shifts rather than a [1,5] shift. Cycloaromatization of cyclic allenes may follow both inter- and intra-molecular pathways, depending on the experimental conditions (use of protic or aprotic solvents). For synthetic purposes, the best procedure is to use a protic solvent to promote the ionic intermolecular route, the fastest and highest yielding. When the reaction is carried out in CCl[sub 4], intermolecular radical addition of chlorine to the cyclic allene competes with intramolecular aromatization paths. Theoretical calculations predict a low barrier for the reaction of cyclic allenes with carbon tetrachloride, and that the cyclic allenes act as nucleophiles in this reaction. [ABSTRACT FROM AUTHOR]

In multicarrier code-division multiple access systems the linear distortion introduced by the channel causes a perturbation in the received user codes that produces multiple access interference. This paper introduces two new techniques to combat this distortion that are based on subspace decomposition. The first one consists of obtaining an approximation of the received desired user code to improve the output signal to interference noise ratio in blind linear receivers. This approximation is obtained by means of the projection of the known transmitted desired user code onto the signal subspace. The second one is a blind channel estimation method that uses the orthogonality property between the received user codes and the noise subspace. We demonstrate that the performance of channel estimation methods based on this property are severely limited by the number of simultaneous users. Nevertheless, it is shown how this limitation is overcome if user codes spanning several transmitted symbols (long codes) are used. [Copyright &y& Elsevier]

A new rearrangement of cyclic allenes giving benzo[c]fluorenones was observed when studying intramolecular dehydro Diels–Alder reactions of silyl-substituted alkynes with arenynes (aryldiacetylenes). [Copyright &y& Elsevier]

Presents information on a study which examined blind multiple access interference and inter-symbol interference suppression in direct sequence code division multiple access systems in signal processing. Methodology; Results and discussion.

Doubly-selective channels, such as those that occur when the transmitter and the receiver move relative to each other at high speeds, are a key scenario for fifth generation (5G) cellular systems, which are mostly based in the use of the orthogonal frequency-division multiplexing (OFDM) modulation. In this paper, we consider an OFDM system using quadrature amplitude modulation (QAM) symbols and we show that, when transmitting over deterministic doubly-selective channels, the inter-carrier-interference (ICI) affecting a symbol can be well approximated by a complex-valued normal distribution. Based on this, we derive a lower bound for the link capacity using the Shannon-Hartley theorem. Finally, we provide an approximation of the bit error probability (BEP) using the well-known BEP expressions for Gray-coded QAM constellations over additive white Gaussian noise (AWGN) channels, and show numerical results that confirm that the proposed BEP expression approximates accurately the bit error ratio (BER) of the OFDM system for standardized channel models. The proposed closed-form analytical expressions for the capacity and the BEP do not only allow for discarding the need of computationally-costly Monte-Carlo system simulations, but also provide a theoretical framework to optimize the system parameters directly impacting on the achievable performance. [ABSTRACT FROM AUTHOR]

Treatment of β,β-dichloroenamides with n-butyllithium, followed by addition of an electrophile, provides disubstituted yn�amides in far greater yield than direct functionalization of terminal ynamides. [ABSTRACT FROM AUTHOR]

Abstract: Our studies directed towards the preparation of novel steroid-like derivatives using RCM reactions are described. The strategy here described was applied to the construction of novel ring-inserted skeleton-expanded steroid analogs by combination of tandem ring-closing metathesis of lineal dienynes and Diels–Alder reaction. [Copyright &y& Elsevier]

Treatment of N-carbethoxy-1-benzylideneisoquinolines with LDA gives N-ethoxycarbonyl-1-amino-1-(2-vinylphenyl)-2-phenylethylenes, which can be transformed into 3-(2-vinylphenyl)-2-methyl-2H-isoquinolin-1-ones by Bischler–Napieralski reactions, and thence into benzo[c]phenanthridin-6-ones. The use of this route for a new total synthesis of fagaronine is described. [Copyright &y& Elsevier]

We describe a new total synthesis of 2-styrylbenzoic acids by Heck coupling of methyl o-iodobenzoates to styrenes. Additionally, in the first general synthesis of naphtho[2,1-f]isoquinolines, these acids were transformed into phenanthrenoic acids and thence into the target compounds by a six-step sequence including a Bischler–Napieralski cyclization. [Copyright &y& Elsevier]

Modern Internet of Things (IoT) systems have to be able to provide high-security levels, but it is difficult to accommodate computationally-intensive cryptographic algorithms on the resource-constrained hardware used to deploy IoT end nodes. Although this scenario brings the opportunity for using advanced security mechanisms such as Transport Layer Security (TLS), several configuration factors impact both the performance and the energy consumption of IoT systems. In this study, two of the most used TLS authentication algorithms (ECDSA and RSA) were compared when executed on a resource-constrained IoT node based on the ESP32 System-on-Chip (SoC), which was tested at different clock frequencies (80, 160 and 240 MHz) when providing different security levels (from 80 to 192 bits). With every tested configuration, energy consumption and average time per transaction were measured. The results show that ECDSA outperforms RSA in all performed tests and that certain software implementations may lead to scenarios where higher security-level alternatives outperform cryptosystems that are theoretically simpler and lighter in terms of energy consumption and data throughput. Moreover, the performed experiments allow for concluding that higher clock frequencies provide better performance in terms of throughput and, in contrast to what may be expected, less energy consumption. [ABSTRACT FROM AUTHOR]

This paper focuses on distributed linear precoding when users transmit correlated information over a fading multiple-input and multiple-output multiple access channel. The precoders are optimized in order to minimize the sum-mean square error (MSE) between the source and the estimated symbols. When sources are correlated, minimizing the sum-MSE results in a non-convex optimization problem. The precoders for an arbitrary number of users and transmit and receive antennas are thus obtained via a projected steepest-descent algorithm and a low-complexity heuristic approach. For the more restrictive case of two single-antenna users, a closed-form expression for the minimum sum-MSE precoders is derived. Moreover, for the scenario with a single receive antenna and any number of users, a solution is obtained by means of a semi-definite relaxation. Finally, we also consider precoding schemes where the precoders are decomposed into complex scalars and unit norm vectors. Simulation results show a significant improvement when source correlation is exploited at precoding, especially for low signal-to-noise ratios and when the number of receive antennas is lower than the number of transmitting nodes. [ABSTRACT FROM AUTHOR]

Radon is a noble gas originating from the radioactive decay chain of uranium or thorium. Most radon emanates naturally from the soil and from some building materials, so it can be found in many places around the world, in particular in regions with soils containing granite or slate. It is almost impossible for a person to detect radon gas without proper tools, since it is invisible, odorless, tasteless and colorless. The problem is that a correlation has been established between the presence of high radon gas concentrations and the incidence of lung cancer. In fact, the World Health Organization (WHO) has stated that the exposure to radon is the second most common cause of lung cancer after smoking, and it is the primary cause of lung cancer among people who have never smoked. Although there are commercial radon detectors, most of them are either expensive or provide very limited monitoring capabilities. To tackle such an issue, this article presents a cost-effective IoT radon gas remote monitoring system able to obtain accurate concentration measurements. It can also trigger events to prevent dangerous situations and to warn users about them. Moreover, the proposed solution can activate mitigation devices (e.g., forced ventilation) to decrease radon gas concentration. In order to show its performance, the system was evaluated in three different scenarios corresponding to representative buildings in Galicia (Spain), a region where high radon gas concentrations are common due to the composition of the soil. In addition, the influence of using external hardware (i.e., WiFi transceivers and an embedded System-on-Chip (SoC)) next to the radon gas sensor is studied, concluding that, in the tested scenarios, they do not interfere with the measurements. [ABSTRACT FROM AUTHOR]

This work addresses the design of optimal linear transmit filters for the Multiple Input-Multiple Output (MIMO) Broadcast Channel (BC) when several spatial streams are allocated to each user. We further consider that the Channel State Information (CSI) is perfect at the receivers but is only partial at the transmitter. A statistical model for the partial CSI is assumed and exploited for the filter design. The relationship between average rate and average Mean Square Error (MSE) is studied to determine the optimal way to distribute the per-user rates among the streams. Finally, the feasible average sum-MSE (sMSE) region is studied and the impact of the CSI uncertainty over the overall system performance is evaluated. [ABSTRACT FROM AUTHOR]

Nowadays telecommunication companies have shown a great interest in deploying broadband mobile wireless networks in high-speed trains (HSTs) with the aim of supporting both passenger services provisioning as well as automatic train control and signaling. The train carriage, as a confined steel structure, has specific propagation characteristics, which motivates the study of the indoor-to-indoor and outdoor-to-indoor radio propagation characteristics for broadband wireless communication systems in high-speed railways, constituting the main contribution of this work. This study has been performed by means of measurements considering an actual Long Term Evolution (LTE) network deployment, as well as a portable test transmitter and different configurations of antennas and receivers at 2.4, 2.6 and 5.7 GHz in a commercial high-speed rail line in Spain. The results show that radio waves incur obvious waveguiding effects inside the HST car. Moreover, for the propagation from the railway station to a mobile receiver inside the HST car, waves at higher frequencies experience less attenuation through the train carriage, by better propagating through windows. Although the railway station and train interior contain objects that induce a rich set of multipath components, the analysis of small-scale fading statistics shows that the channel still has a dominant path. Also, the LTE coverage tests for Base Transceiver Station (BTS)-Train and BTS-Mobile links were conducted and with internal and external antennas on board the train. We found that there was a strong signal penetration loss of approximately 26 dB caused by the train carriage structure. The final results constitute an initial model for the propagation incurred by a relay-based communications system for fourth generation (4G) network in railways. [ABSTRACT FROM AUTHOR]