Nanocrystalline CoSn2-carbon composite electrode prepared by using sonochemistry

A sonochemical method has been used to prepare negative electrode materials containing intermetallic nanoparticles and polyacrylonitrile (PAN). The ultrasound irradiation is applied to achieve small particle size. After annealing at 490 °C under Ar-flow, the polymer PAN is partially carbonized and the metallic nanoparticles are surrounded by a carbonaceous matrix. The main metallic phase is CoSn₂. The carbonaceous coating and the surface oxides have been explored by using XPS. The resulting CoSn₂-carbonaceous phase electrode (CoSn₂@C) shows improved electrochemical behavior (ca. 450 mAh/g after 50 cycles) in comparison with previous reports on pure crystalline CoSn₂. The reaction between CoSn₂@C and Li has been studied by using XRD and ¹¹⁹Sn Mössbauer spectroscopy. The formation of large grains of crystalline Li_xSn phases after the first discharge is discarded. The small particle size which is achieved by using ultrasonication and the carbonaceous matrix contribute to maintain the Co-Sn interactions during the electrochemical cycling. The aggregation of the nanosized metallic particles upon electrochemical cycling can be suppressed by the carbonaceous matrix (pyrolytic PAN).     

Differentiation of aminomethyl corrole isomers by mass spectrometry

Two new isomeric aminomethyl corrole derivatives of [5,10,15-tris(pentafluorophenyl)corrolato]gallium(III) were synthesized with pyridine (py) molecules as axial ligands. When investigated by electrospray ionization mass spectrometry, in the positive and the negative ion modes, these compounds showed an unusual gas-phase behavior that could be used for their differentiation. In the positive ion mode, the differentiation was achieved through the formation of diagnostic fragment ions formed from [M-py?+?H](+) precursors, by (CH(3) )(2) NH and HF losses. An unusual addition of water to the main fragment ions provides an alternative route for isomer identification. Semi-empirical calculations were performed to elucidate the structures and stabilities of the main ionic species formed in the positive ion mode. In the negative ion mode isomer discrimination is accomplished via the fragmentation of the methoxide adduct ions [M-py?+?CH(3) O](-) through (CH(3) )(2) N(.) and HF losses.     

Cohomology of the complement of a free divisor

We prove that if is a ``strongly quasihomogeneous" free divisor in the Stein manifold , and is its complement, then the de Rham cohomology of can be computed as the cohomology of the complex of meromorphic differential forms on with logarithmic poles along , with exterior derivative. The class of strongly quasihomogeneous free divisors, introduced here, includes free hyperplane arrangements and the discriminants of stable mappings in Mather's nice dimensions (and in particular the discriminants of Coxeter groups).

     

Propane absorption band intensities and band model parameters from 680 to 1580cm-1 at 296 and 200 K

Band intensities and profiles have been measured for the propane absorption bands from 680 to 1580cm^-1 at 296 and 200 K. This work was stimulated by the discovery of several propane bands in the spectrum of Titan by the Voyager 1 spacecraft. The low temperature laboratory data show that the bands become narrower and the Q branches of the bands somewhat stronger than they are at room temperature. Random band model parameters were determined over the entire region from the 42 spectra obtained at room temperature.     

A longitudinal study comparing the sensitivity of CSE and RARE sequences in detecting new multiple sclerosis lesions

In this longitudinal study, we evaluated the sensitivities of dual-echo, conventional spin-echo (CSE), and rapid-acquisition relaxation-enhanced (RARE) scans for detecting the appearance of new lesions in multiple sclerosis (MS). Dual echo, CSE, and RARE scans were obtained on four occasions each separated by 28 days from five patients with relapsing-remitting MS using a 1.5-Tesla machine. A total of 44 new lesions were detected by the two sequences. Thirty-five lesions were seen on both sequences, three only on CSE and six only on FSE. This study indicates that CSE may be substituted by RARE when monitoring short-term disease activity in MS.     

Finite element approximation of nematic liquid crystal flows using a saddle-point structure

In this work, we propose finite element schemes for the numerical approximation of nematic liquid crystal flows, based on a saddle-point formulation of the director vector sub-problem. It introduces a Lagrange multiplier that allows to enforce the sphere condition. In this setting, we can consider the limit problem (without penalty) and the penalized problem (using a Ginzburg–Landau penalty function) in a unified way. Further, the resulting schemes have a stable behavior with respect to the value of the penalty parameter, a key difference with respect to the existing schemes. Two different methods have been considered for the time integration. First, we have considered an implicit algorithm that is unconditionally stable and energy preserving. The linearization of the problem at every time step value can be performed using a quasi-Newton method that allows to decouple fluid velocity and director vector computations for every tangent problem. Then, we have designed a linear semi-implicit algorithm (i.e. it does not involve nonlinear iterations) and proved that it is unconditionally stable, verifying a discrete energy inequality. Finally, some numerical simulations are provided.     

A computational modeling approach of the jet-like acoustic streaming and heat generation induced by low frequency high power ultrasonic horn reactors

High power ultrasound reactors have gained a lot of interest in the food industry given the effects that can arise from ultrasonic-induced cavitation in liquid foods. However, most of the new food processing developments have been based on empirical approaches. Thus, there is a need for mathematical models which help to understand, optimize, and scale up ultrasonic reactors. In this work, a computational fluid dynamics (CFD) model was developed to predict the acoustic streaming and induced heat generated by an ultrasonic horn reactor. In the model it is assumed that the horn tip is a fluid inlet, where a turbulent jet flow is injected into the vessel. The hydrodynamic momentum rate of the incoming jet is assumed to be equal to the total acoustic momentum rate emitted by the acoustic power source. CFD velocity predictions show excellent agreement with the experimental data for power densities higher than W(0)/V ≥ 25kWm(-3). This model successfully describes hydrodynamic fields (streaming) generated by low-frequency-high-power ultrasound.     

DTI at 7 and 3 T: systematic comparison of SNR and its influence on quantitative metrics

Diffusion tensor imaging (DTI) and advanced related methods such as diffusion spectrum and kurtosis imaging are limited by low signal-to-noise ratio (SNR) at conventional field strengths. DTI at 7 T can provide increased SNR; however, B0 and B1 inhomogeneity and shorter T2? still pose formidable challenges. The purpose of this study was to quantify and compare SNR at 7 and 3 T for different parallel imaging reduction factors, R, and TE, and to evaluate SNRs influences on fractional anisotropy (FA) and apparent diffusion coefficient (ADC). We found that R>4 at 7 T and R≥2 at 3 T were needed to reduce geometric distortions due to B0 inhomogeneity. For these R at 7 T, SNR was 70-90 for b=0 s/mm² and 22-28 for b=1000s/mm² in central brain regions. SNR was lower at 3 T (40 for b=0 s/mm² and 15 for b=1000 s/mm²) and in lateral brain regions at 7 T due to B1 inhomogeneity. FA and ADC did not change with MRI field strength, SENSE factor or TE in the tested range. However, the coefficient of variation for FA increased for SNR <15 and for SNR <10 in ADC, consistent with published theoretical studies. Our study demonstrates that 7 T is advantageous for DTI and lays the groundwork for further development. Foremost, future work should further address challenges with B0 and B1 inhomogeneity to take full advantage for the increased SNR at 7 T.     

Investigation of the possible origins of sulfur in 19th century salted paper photographs by x‐ray fluorescence spectroscopy

An X‐ray fluorescence method to determine whether sulfur is present in 19th century photographs due to intentional toning or to environmental deterioration is proposed. In the 19th century salted paper print photographic process, AgCl formed on the surface of a sheet of paper was exposed to sunlight in contact with a negative, leading to the printing out of a Ag image that was fixed by immersing it in a sodium thiosulfate solution or hypo. The improper execution of the fixing in these photographs may result in the presence of sulfur, mostly manifested in image fading, irregular staining, and discoloration. Also, 19th century artists produced salted paper prints with a variety of image tonalities, for example, by using an artificially aged thiosulfate bath. The presence of sulfur in photographs may also be due to sulfur‐containing environmental pollutants. Therefore, knowledge about the location and amounts of sulfur is important to understand the artistic technique and/or the deterioration processes. In this study, the amounts of sulfur and the silver to sulfur signal ratios were determined for a salted paper print made in the laboratory following a 19th century procedure and for two artistic salted paper photographs using X‐ray fluorescence and standards prepared with different amounts of retained hypo and quantified by inductively coupled plasma atomic emission spectroscopy. The amounts of sulfur and the normalized silver to sulfur ratios for the artistic photographs were evaluated based on the results obtained in the samples prepared in the laboratory and in the context of the 19th century practices. Copyright © 2016 John Wiley & Sons, Ltd.