Conductive Anodic Filament Formation Part II: Electrochemical Reactions Leading to CAF

Conductive anodic filament (CAF) formation has been studied for a number of years, but the mechanism of its formation has not previously been defined. In 2002, Ready identified CAF as atacamite, Cu₂(OH)₃Cl. Electrochemical studies have shown that both CuCl and CuCl ₂ ^? participate in the formation of Cu₂(OH)₃Cl, with the predominating species being CuCl. This paper proposes a mechanism for CAF formation based on x-ray photoelectron spectroscopy. The data show that CuCl is the precursor to the formation of Cu₂(OH)₃Cl in the presence of oxygen and water. Earlier, Meeker and Lu Valle had proposed that CAF failure is best represented by two competing reactions: the formation of a copper chloride corrosion compound (now identified as Cu₂(OH)₃Cl) and the formation of innocuous trapped chlorine compounds. Since no evidence of any trapped chloride compounds has been found, we propose that the formation of CAF is best represented by a single nonreversible reaction.     

Chemically Resistant,Shapeable, and Conducting Metal‐Organic Gels and Aerogels Built from Dithiooxamidato Ligand

Metal‐organic gels (MOGs) appear as a blooming alternative to well‐known metal‐organic frameworks (MOFs). Porosity of MOGs has a microstructural origin and not strictly crystalline like in MOFs; therefore, gelation may provide porosity to any metal‐organic system, including those with interesting properties but without a porous crystalline structure. The easy and straightforward shaping of MOGs contrasts with the need of binders for MOFs. In this contribution, a series of MOGs based on the assembly of 1D‐coordination polymer nanofibers of formula [M(DTA)]_n (M^II: Ni, Cu, Pd; DTA: dithiooxamidato) are reported, in which properties such as porosity, chemical inertness, mechanical robustness, and stimuli‐responsive electrical conductivity are brought together. The strength of the M? S bond confers an unusual chemical resistance, withstanding exposure to acids, alkalis, and mild oxidizing/reducing chemicals. Supercritical drying of MOGs provides ultralight metal‐organic aerogels (MOAs) with densities as low as 0.03 g cm^?3 and plastic/brittle behavior depending on the nanofiber aspect ratio. Conductivity measurements reveal a semiconducting behavior (10^?12 to 10^?7 S cm^?1 at 298 K) that can be improved by doping (10^?5 S cm^?1). Moreover, it must be stressed that conductivity of MOAs reversibly increases (up to 10^?5 S cm^?1) under the presence of acetic acid.     

On the Use of Asymmetric Windows for Robust Speech Recognition

This paper deals with the problem of searching for a suitable window for robust speech recognition in noisy conditions. A set of asymmetric windows, so-called DDR _c,w , are proposed which are controlled by two parameters, center c and width w. These windows are derived from the DDR window used in the higher-lag autocorrelation spectrum estimation (HASE) method and act over the OSA (One-Sided Autocorrelation) in order to perform spectral estimation. The two parameters, c and w, allow us to control the level of weight given to the first noisy autocorrelation coefficients and to emphasize the important ones. Finally, it is shown that the best window of the proposed set is the DDR _62,200. This window is centered around the average pitch of human speech and it provides a higher speech recognition performance over the Aurora-2 and Aurora-3 databases than those obtained by previously proposed windows.     

Fully digital BPSK demodulator for satellite supressed carrier telecommand system

In this paper, we present the design of a fully digital binary phase shift keying demodulator for application in satellite high‐rate suppressed carrier telecommand system. The proposed system digitalizes the received signal in the intermediate frequency stage using bandpass sampling technique, and the resulting baseband signal is used to synchronization of symbol and phase and to bit detection. The design of all functional modules is presented in details. Another innovation presented in this work is the inclusion of a non‐linearity in the phase synchronizer module to permit its operation independent from the signal amplitude. Moreover, aiming the characterization and performance evaluation of the system, we do some original mathematical analyses. Finally, test results show that the demodulator complies all the project requirements, and the prototype implementation loss, in terms of bit energy to noise power density ratio, is less than 0.3 dB. Copyright © 2016 John Wiley & Sons, Ltd.     

Nanostructured β‐Bi2O3 Fractals on Carbon Fibers for Highly Selective CO2 Electroreduction to Formate

3D Bi₂O₃ fractal nanostructures (f‐Bi₂O₃) are directly self‐assembled on carbon fiber papers (CFP) using a scalable hot‐aerosol synthesis strategy. This approach provides high versatility in modulating the physiochemical properties of the Bi₂O₃ catalyst by a tailorable control of its crystalline size, loading, electron density as well as providing exposed stacking of the nanomaterials on the porous CFP substrate. As a result, when tested for electrochemical CO₂ reduction reactions (CO₂RR), these f‐Bi₂O₃ electrodes demonstrate superior conversion of CO₂ to formate (HCOO^?) with low onset overpotential and a high mass‐specific formate partial current density of ?52.2 mA mg^?1, which is ≈3 times higher than that of the drop‐casted control Bi₂O₃ catalyst (?15.5 mA mg^?1), and a high Faradaic efficiency (FE_HCOO^?) of 87% at an applied potential of ?1.2 V versus reversible hydrogen electrode. The findings reveal that the high exposure of roughened β‐phase Bi₂O₃/Bi edges and the improved electron density of these fractal structures are key contributors in attainment of high CO₂RR activity.     

Complexity of gradient projection method for optimal routing indata networks

In this paper, we derive a time-complexity bound for the gradient projection method for optimal routing in data networks. This result shows that the gradient projection algorithm of Goldstein-Levitin-Poljak type formulated by Bertsekas (1982), Bertsekas and Gallager (1987) and Bertsekas et al. (1984) converges to within ε in relative accuracy in O(ε^-2h_minN_max) number of iterations, where N_max is the number of paths sharing the maximally shared link, and h_min is the diameter of the network. Based on this complexity result, we also show that the one-source-at-a-time update policy has a complexity bound which is O(n) times smaller than that of the all-at-a-time update policy, where n is the number of nodes in the network. The result of this paper argues for constructing networks with low diameter for the purpose of reducing complexity of the network control algorithms. The result also implies that parallelizing the optimal routing algorithm over the network nodes is beneficial     

Hierarchically Structured Magnetic Nanoconstructs with Enhanced Relaxivity and Cooperative Tumor Accumulation

Iron oxide nanoparticles are formidable multifunctional systems capable of contrast enhancement in magnetic resonance imaging, guidance under remote fields, heat generation, and biodegradation. Yet, this potential is underutilized in that each function manifests at different nanoparticle sizes. Here, sub‐micrometer discoidal magnetic nanoconstructs are realized by confining 5 nm ultra‐small super‐paramagnetic iron oxide nanoparticles (USPIOs) within two different mesoporous structures, made out of silicon and polymers. These nanoconstructs exhibit transversal relaxivities up to ≈10 times (r ₂ ≈ 835 mm ^?1 s^?1) higher than conventional USPIOs and, under external magnetic fields, collectively cooperate to amplify tumor accumulation. The boost in r ₂ relaxivity arises from the formation of mesoscopic USPIO clusters within the porous matrix, inducing a local reduction in water molecule mobility as demonstrated via molecular dynamics simulations. The cooperative accumulation under static magnetic field derives from the large amount of iron that can be loaded per nanoconstuct (up to ≈65 fg) and the consequential generation of significant inter‐particle magnetic dipole interactions. In tumor bearing mice, the silicon‐based nanoconstructs provide MRI contrast enhancement at much smaller doses of iron (≈0.5 mg of Fe kg^?1 animal) as compared to current practice.     

Solution‐Processed High‐Performance Tetrathienothiophene‐Based Small Molecular Blends for Ambipolar Charge Transport

Four soluble dialkylated tetrathienoacene ( TTAR) ‐based small molecular semiconductors featuring the combination of a TTAR central core, π‐conjugated spacers comprising bithiophene ( bT ) or thiophene ( T ), and with/without cyanoacrylate ( CA ) end‐capping moieties are synthesized and characterized. The molecule DbT‐TTAR exhibits a promising hole mobility up to 0.36 cm² V^?1 s^?1 due to the enhanced crystallinity of the microribbon‐like films. Binary blends of the p‐type DbT‐TTAR and the n‐type dicyanomethylene substituted dithienothiophene‐quinoid ( DTTQ‐11 ) are investigated in terms of film morphology, microstructure, and organic field‐effect transistor (OFET) performance. The data indicate that as the DbT‐TTAR content in the blend film increases, the charge transport characteristics vary from unipolar (electron‐only) to ambipolar and then back to unipolar (hole‐only). With a 1:1 weight ratio of DbT‐TTAR DTTQ‐11 in the blend, well‐defined pathways for both charge carriers are achieved and resulted in ambipolar transport with high hole and electron mobilities of 0.83 and 0.37 cm² V^?1 s^?1, respectively. This study provides a viable way for tuning microstructure and charge carrier transport in small molecules and their blends to achieve high‐performance solution‐processable OFETs.     

Design of a Web Based Underwater Acoustic Communication Testbed and Simulation Platform

Wireless Personal Communications - Underwater Wireless Sensor Networks (UWSNs) are playing a vital role in exploring the unseen underwater (UW) natural resources. However, performance evaluation of...