Novel rGO@Fe3O4 nanostructures: An active electrocatalyst for hydrogen evolution reaction in alkaline media

Because of energy crisis, the hydrogen evolution reaction (HER) limits the feasible utilization of water splitting. Herein, we report reduced graphene-oxide (rGO) with Iron-oxide (Fe₃O₄) nanostructures as highly active electrocatalyst for HER. As-prepared [email protected]₃O₄ shows superior electrochemical responses to those of corresponding its monometallic rGO and Fe₃O₄. The overpotential of [email protected]₃O₄ has been achieved as 300 mV at 10 mA/cm² current density with a Tafel slope of 80 mV/dec. The [email protected]₃O₄ nanostructure has its stability for 24 h to reveal long term electrochemical performance.     

Functionalization of surface‐grafted polymethylhydrosiloxane thin films with alkyl side chains

Thin films of crosslinked polymethylhydrosiloxane (PMHS) have been grafted on silica using the sol–gel process allowing further functionalization by effective quantitative hydrosilylation of SiH groups by olefins within the network. Postfunctionalization gives the polysiloxane network with n‐alkyl side chains. The PMHS coating was prepared by room temperature polycondensation of a mixture of methyldiethoxysilane HSiMe(OEt)₂ monomer and triethoxysilane HSi(OEt)₃ (TH) as crosslinker. The surface‐attached films are chemically stable and covalently bonded to the silica surface. Subsequently, films were functionalized without delamination. We showed by FTIR spectroscopy how the crosslinking ratio and the molecular size of the alkenes precursors influence the extent of the hydrosilylation reaction of SiH groups in the PMHS network. We have determined that quasi‐full olefin addition catalyzed by a platinum complex occurred within soft networks of less than 5% TH with 1‐alkenes CH₂?CH(CH₂)_n‐2CH₃ of various alkyl chain lengths (n = 5, 11, 17). Powders of PMHS gel were also modified with 1‐alkenes by hydrosilylation. The SiH groups within the soft gel (5% crosslinked) were fully functionalized as shown by ²⁹Si and ¹H solid‐state NMR. The structure of functionalized polysiloxane with n‐octadecyl and n‐dodecyl side chains was studied by FTIR, wide angle X‐ray diffraction, and DSC showing crystallization of the long n‐alkyl chains in the network. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3546–3562, 2008     

Uniformity study of wafer-scale InP-to-silicon hybrid integration

β-SiC nanowires were synthesized by a simple carbothermal reduction of carbonaceous silica xerogel. The morphology and structure of the nanowires were investigated by X-ray diffraction, scanning electron microscope and transmission electron microscopy. The results showed that the nanowires were hexagonal prism-shaped hierarchical nanostructures. The typical stacking faults and twin defects of SiC nanowires were also observed. Band-gap characterization and photoluminescence properties of SiC nanowires were investigated by UV-vis absorption spectroscopy and fluorescence photometry, respectively. The results showed the SiC nanowire was an indirect transition semiconductor and the band gap energy for the SiC nanowires was 2.85 eV. The photoluminescence peak value at 470 nm (2.64 eV) originating from the SiC nanowires was a little higher than the value of band-gap energy.     

An asymptotic expansion for the expected number of real zeros of real random polynomials spanned by OPUC

Let ${\{{\phi }_i\}}_{i=0}^{\infty }$ be a sequence of orthonormal polynomials on the unit circle with respect to a positive Borel measure μ that is symmetric with respect to conjugation. We study asymptotic behavior of the expected number of real zeros, say ${\mathbb{E}}_n(\mu )$, of random polynomials

$P_n(z):=\sum _{i=0}^n{\eta }_i{\phi }_i(z),$

where ${\eta }_0,\dots ,{\eta }_n$ are i.i.d. standard Gaussian random variables. When μ is the acrlength measure such polynomials are called Kac polynomials and it was shown by Wilkins that ${\mathbb{E}}_n(|\mathrm{d}\xi |)$ admits an asymptotic expansion of the form

${\mathbb{E}}_n(|\mathrm{d}\xi |)～\frac{2}{\pi }\log ?(n+1)+\sum _{p=0}^{\infty }{A}_p{(n+1)}^{?p}$

(Kac himself obtained the leading term of this expansion). In this work we generalize the result of Wilkins to the case where μ is absolutely continuous with respect to arclength measure and its Radon–Nikodym derivative extends to a holomorphic non-vanishing function in some neighborhood of the unit circle. In this case ${\mathbb{E}}_n(\mu )$ admits an analogous expansion with the coefficients $A_p$ depending on the measure μ for $p\ge 1$ (the leading order term and $A_0$ remain the same).     

A Model for Advanced Reservations for Large Scale Conferencing Services

This note describes a model for advanced reservations extended to systems which can serve many customers at the same time. The new model has been developed for a communication network which provides intercity visual conferencing services via a satellite capable of accommodating many conferences simultaneously. Each customer calls in advance to reserve time on a future date. A scheduler either satisfies the request, or offers available alternatives which may or may not be acceptable to the customer. The model is used to examine different measures of quality-of-service and system utilization.     

Inspection Policies When Duration of Checkings is Non-Negligible

Inspection policy models deal with stochastically failing systems, in which failure is detected by inspection only. Previous authors assume that the time required for checking is zero, while the current study deals with preparedness models when duration of checking is non-negligible. Costs are introduced for checking, unknown lost time and repairing (or replacing) the failed system. Furthermore, uncertainty probabilities associated with inspections are introduced. Optimal checking policies are calculated for three different objective functions: expected loss per cycle, per time unit and per unit of good time. The models are solved by differentiation and by dynamic programming. Numerical results indicate that the optimal policy for IFR distributions is characterized by decreasing checking time intervals, with a marked difference only between the first and second intervals.     

Densities and Viscosities of the Regular Quinary System: Benzene (1) + Toluene (2) + Ethylbenzene (3) + Heptane (4) + Cyclooctane (5) and Its Quaternary Sub-Systems at 293.15 and 298.15 K

The densities and viscosities of the regular quinary system: benzene (1) + toluene (2) + ethylbenzene (3) + heptane (4) + cyclooctane (5), and all its corresponding quaternary sub-systems were measured over the entire composition range at 293.15 and 298.15 K. Kinematic viscosity–composition data reported in the present study were utilized to test the predictive capability of some well-known viscosity models. The models subjected to testing were: the predictive version of the McAllister’s three-body model, a generalized corresponding states principle, the group contribution GC-UNIMOD method, and the Allan and Teja correlation. Results of testing these models led to an overall AAD (%) of 1.20 for the one quaternary system that did not contain cyclooctane, and an overall AAD (%) of 8.59 for the remaining cyclooctane-containing systems. For the quinary system, the overall AAD (%) was found to be 2.92; the last two values were calculated using the value of cyclooctane of 10.595.