Ni Nanoparticles Stabilized by Hyperbranched Polymer: Does the Architecture of the Polymer Affect the Nanoparticle Characteristics and Their Performance in Catalysis?

Heat-up and hot-injection methods were employed to synthesize Ni nanoparticles (NPs) with narrow size distribution in the presence of hyperbranched pyridylphenylene polymer (PPP) as a stabilizing agent. It was shown that depending on the synthetic method, Ni NPs were formed either in a cross-linked polymer network or stabilized by a soluble hyperbranched polymer. Ni NPs were characterized by a combination of transmission electron microscopy (TEM), scanning TEM, thermogravimetric analysis, powder X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive X-ray analysis, and magnetic measurements. The architecture of polymer support was found to significantly effect Ni NPs characteristics and behavior. The Ni NPs demonstrated a high catalytic activity in a model Suzuki–Miyaura cross-coupling reaction. No significant drop in activity was observed upon repeated use after magnetic separation in five consecutive catalytic cycles. We believe that hyperbranched PPP can serve as universal platform for the controllable synthesis of Ni NPs, acting as highly active and stable catalysts.     

Carbon-coated silicon as anode material for lithium ion batteries: advantages and limitations

Carbon coating of silicon powder was studied as a means of preparation of silicon-based anode material for lithium ion batteries. Carbon-coated silicon has been investigated at various cycling modes vs. lithium metal. Ex situ X-ray data suggest that there is irreversible reduction of crystallinity of the silicon content. Since carbon layer preserving the integrity of the particle, the reversibility of the structural changes in the amorphous state Li-Si alloy provides the reversible capacity. The progressively decreased Coulomb efficiency with cycling indicates that more and more lithium ions are trapped in some form of Li-Si alloy and become unavailable for extraction. This is the main factor for the capacity fading during cycling. Qualitative studies of the impedance spectra of the electrode material at the first cycle for the fresh anode and at the last cycle after the anode capacity faded considerably and provide further support for this model of fading mechanism.     

Spatial and temporal patterns of remotely-sensed and field-measured rainfall in southern California

Quantification of spatial and temporal patterns of rainfall is an important step toward developing regional hydrological models. However, traditionally used rain gauge data are sparse and do not always provide adequate spatial representation of rainfall. In this study, we evaluated the daily 1-degree resolution remotely-sensed atmospheric precipitation data provided by Global Precipitation Climatology Project (GPCP) as an alternative to rain gauge-measured data. We analyzed data from the watersheds of southern California during the period of 1996-2003, focusing on the comparison of patterns of spatial, seasonal, and interannual rainfall dynamics. We used Empirical Orthogonal Functions to discern the patterns of precipitation and atmospheric circulation at different time scales, from synoptic to interannual. The correlation between the daily rain gauge-measured and remotely-sensed precipitation was poor and the resulting patterns of remotely-sensed precipitation are different than the temporal patterns of precipitation accumulated by rain gauges. These differences likely result from the fact that the precipitable water concentration measured by satellites is not always highly correlated to rainfall reaching the earth surface. Differences in the spatial resolution and coverage of the two methods and the differential influence of orographic effects and wind patterns on each also contribute to low correlations. We conclude that daily remotely-sensed precipitation produced at GPCP is not currently appropriate for use in assessing fine-scale hydrological processes in arid zones like southern California, and would not be a recommended surrogate for event-based hydrologic modeling. At the same time, the interannual variabilities of remotely-sensed and gauge-measured precipitation were highly correlated and the regional patterns of gauge-measured and remotely-sensed precipitation variability were similar; though the total precipitation estimated from satellite data was substantially lower than the gauge-measured data. Therefore, remotely-sensed precipitation data may be appropriate for use in long-term regional hydrologic or climate modeling focused on trends and patterns of rainfall in southern California. Both data sets showed that precipitation generally decreases from the northern to the southern watersheds. At interannual time-scale, the rainfall is related to the ENSO cycle. At synoptic time-scales, the rainfall patterns in southern California result from atmospheric moisture transport from the south-southwest.     

Coordination chemistry of a para-tert-octylcalix[4]arene fitted with phosphinoyl pendant arms towards 4f-elements: Extraction,synergism, separation

The solvent extraction of trivalent lanthanoids (Ln³⁺) by 5,11,17,23-tetra(para-tert-octyl)-25,26,27,28-tetrakis(dimethylphosphinoylmethoxy)calix[4]arene (S), bearing four phosphine oxide donor groups at the lower rim as synergistic agent in combination with a 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one (HP) in CHCl₃ from chloride medium at µ = 0.1 was quantitatively described in the form of LnP₃·S complexes. The role of the synergistic agent on the extraction process was discussed. The values of the separation factors have been evaluated. On the basis of the IR and NMR spectra the stoichiometry and the structure of the solid mixed complex of Eu(III) with HP and S were proposed.     

Dielectric and microwave properties of elastomer composites loaded with carbon–silica hybrid fillers

In this study, we investigated the influence of carbon–silica dual‐phase fillers on the dielectric and microwave properties of natural‐rubber‐based composites determined in the frequency range from 1 to 12 GHz. The fillers were prepared by the impregnation of two types of carbon black with various silicasol amounts. As the results show, the fillers affected both the dielectric and microwave properties of the obtained composites. The higher the quantity of the dielectric phase (silica) in the hybrid filler was, the lower the real part of the permittivity of the composites was. This caused changes in the total, reflective, and absorptive shielding effectivenesses of the latter and their reflection and attenuation coefficients. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42978.     

Nano-scale multi-layered coatings for improved efficiency of ceramic cutting tools

Electron beam welding, though considered a sophisticated welding process, still requires the operator to first carry out several trial welds to find the right combination of welding parameters based on intuition and experience. This archaic method is often unreliable, leading to unproductive manufacturing lead time, man hours, quality control tests, and material wastage. The current study eliminates this “trial and error” method by providing a reliable model which can predict the right combination of weld parameters to achieve a high-quality weld. Beads on plate welds were carried out on AISI 304 stainless steel plates using a low-kilovolt electron beam welding (EBW) machine. A model that can predict weld bead geometry and provide optimized output for minimum weld area condition without compromising on weld quality was developed. Experimental data were collected as per full factorial design of experiments, and the levels for each input parameter were established through pilot experiments. A multivariate regression analysis has been conducted to establish a relationship between four weld input parameters (three levels each) and four weld bead responses. Response surface methodology (RSM) has been used to study the interrelationship between input parameters and their effect on each response variable. Further, minimization of weld cross-sectional area was done using genetic algorithm for maximum penetration and minimum weld area condition. The optimized mathematical model convincingly establishes that the focusing current is a significant input parameter with very high influence over the weld bead geometry. Extensive material characterization and mechanical tests have been carried out to validate the regressed input-output relationship and the optimized mathematical model.     

Hydrothermal synthesis of improved ZnO crystals for epitaxial growth of GaN thin films

ZnO single crystals with thickness up to 12 mm, 2 inches in “diameter” and weight of about 150 g have been grown from KOH, NaOH, and K₂CO₃ based hydrothermal solutions on the seeds of (0001) orientation. The addition of LiOH up to 3.0–4.5 mol/L allowed to decrease the growth rate of ZnO crystals along the 〈0001〉 crystallographic direction. For positive and negative monohedra, it was achieved 0.12 and 0.01 mm/day, respectively, at temperature 340 °С and ΔТ = 10 °С. The best ZnO etching agent was found to be the solutions 25 mol% HCl + 3 mol% NH₄F at room temperature, and etching time 5 min. The dislocation density of ZnO crystals varied from 240 cm⁻² to 3,200 cm⁻² in the case of growth rates 0.04 mm/day to 0.11 mm/day, respectively. It was also found that ZnO crystals grown are stable in air, oxygen, nitrogen, and argon atmosphere as well as in vacuum at the temperatures up to 1,000 °C under thermal treatment during 4 h.     

Effect of Trace Addition of Sn on the Precipitation Hardening in Al-Si-Cu Eutectic Alloy

JOM - The work is devoted to studying the effect of a Sn trace addition on the precipitation hardening after aging of the eutectic Al-7 wt.% Si-7 wt.% Cu alloy. The addition of Sn and Si has a...     

Design,Synthesis, and Biological Evaluation of (+)-Camphor- and (−)-Fenchone-Based Derivatives as Potent Orthopoxvirus Inhibitors

In this work, a library of (+)-camphor and (−)-fenchone based N-acylhydrazones, amides, and esters, including para-substituted aromatic/hetaromatic/cyclohexane ring was synthesized, with potent orthopoxvirus inhibitors identified among them. Investigations of the structure-activity relationship revealed the significance of the substituent at the para-position of the aromatic ring. Also, the nature of the linker between a hydrophobic moiety and aromatic ring was clarified. Derivatives with p-Cl, p-Br, p-CF_3, and p-NO₂ substituted aromatic ring and derivatives with cyclohexane ring showed the highest antiviral activity against vaccinia virus, cowpox, and ectromelia virus. The hydrazone and the amide group were more favourable as a linker for antiviral activity than the ester group. Compounds 3 b and 7 e with high antiviral activity were examined using the time-of-addition assay and molecular docking study. The results revealed the tested compounds to inhibit the late processes of the orthopoxvirus replication cycle and the p37 viral protein to be a possible biological target.     

Boundary layer development and meteorological parameters impact on the ground level ozone concentration over an urban area in a mountain valley (Sofia,Bulgaria)

The ecological problems caused by the increasing ozone concentration are not easily solved because ozone is not directly emitted by certain sources Its concentration depends on numerous dynamical and chemical processes. Stratosphere–troposphere exchange and subsequent ozone penetration into the boundary layer determine the contribution of so-called ‘natural’ ozone to ozone pollution near the ground. However, the main contribution to the concentration of this pollution is that of the anthropogenic ozone, which is generated as a result of complex photochemical reactions. The purpose of this research is the ground level ozone concentration behaviour to be studied during the stable boundary layer (SBL) and the residual layer (RL) destruction and the convective boundary layer (CBL) formation, so the influence of the temperature, the relative humidity and the height of the mixing layer (ML) as well as that of the ML formation in different areas of Sofia (42° 39′ N, 23° 23′ E, 591 m above sea level), Bulgaria, have to be determined. The ground level ozone concentration in the area of the Institute of Electronics changes synchronously with the development of the ML. The maximum values of the ground level ozone concentration are reached when the height of the ML reached its maximum and afterwards. The maximum growth of the ground level ozone concentration is around 11:00–12:30 h LST when a fast growth of the ML begins and the complete destruction of the RL is observed, that is, the two processes of ML growth and entrainment of aerosol and ozone from the higher layers of the atmospheric boundary layer are observed. The values of the ground level ozone concentration during the summer months are higher than those during the fall.