Alkaline oxygen evolution: exploring synergy between fcc and hcp cobalt nanoparticles entrapped in N-doped graphene

Herein, we report a Mott-Schottky catalyst by entrapping cobalt nanoparticles inside the N-doped graphene shell (Co@NC). The Co@NC delivered excellent oxygen evolution activity with an overpotential of merely 248 mV at a current density of 10 mA cm^–2 with promising long-term stability. The importance of Co encapsulated in NC has further been demonstrated by synthesizing Co nanoparticles without NC shell. The synergy between the hexagonal close-packed (hcp) and face-centered cubic (fcc) Co plays a major role to improve the OER activity, whereas the NC shell optimizes the electronic structure, improves the electron conductivity, and offers a large number of active sites in Co@NC. The density functional theory calculations have revealed that the hcp Co has a dominant role in the surface reaction of electrocatalytic oxygen evolution, whereas the fcc phase induces the built-in electric field at the interfaces with N-doped graphene to accelerate the H⁺ ion transport.     

An efficient two-step synthesis of 3-allylindoles

A two-step synthetic sequence for an efficient synthesis of 3-allylindoles is described.     

On sequential procedures for the point estimation of the mean of a normal population

The sequential procedures developed by Starr (1966, Ann. Math. Statist., 37, 1173–1185) for estimating the mean of a normal population are further analyzed. Asymptotic properties of the regret and first two moments of the stopping rules are studied and second-order approximations are derived.     

X-Ray Absorption Spectroscopy of Strontium(II) Coordination

Detailed analyses of crystalline, hydrated, and precipitated strontium compounds and an aqueous strontium solution by synchrotron extended X-ray absorption fine structure (EXAFS) were used to quantify local thermal and static disorder and to characterize strontium coordination in a variety of oxygen-ligated bonding environments. Analysis of anharmonic vibrational disorder (i.e., significant contribution from a third cumulant term (C(3)) in the EXAFS phase-shift function) in compounds with low and high static disorder around strontium showed that first-shell anharmonic contributions were generally not significant above experimental error in the EXAFS fits (R+/-0.02 ? with and without C(3)). The only case in which a significant apparent decrease in Sr-O distance was observed with increasing temperature, and for which a third cumulant term was significant, was for dilute strontium in aqueous solution. Empirical parameterization of Debye-Waller factor (sigma(2)) for strontium compounds as a function of backscatterer atomic number (Z), interatomic Sr-Z distance, and temperature of spectral data collection showed systematic increases in sigma(2) as a function of increasing temperature and Sr-Z bond length. At values of sigma(2) greater than approximately 0.025 ?(2) (for N<12 and R(Sr)-Z>3 ?), backscattering was generally not significant above noise levels in spectra of compounds of known crystal structure. Comparison of the EXAFS spectra of freshly precipitated SrCO(3) (spectra collected wet) to that of dry, powdered strontianite (SrCO(3)(s)) indicated no significant differences in the local atomic structure around strontium. Analysis of partially hydrated strontium in natural Ca-zeolite (heulandite) showed that strontium is substituted only in the calcium (Ca2) site. Backscattering from aluminum and silicon atoms in the zeolite framework were apparent in the EXAFS spectra at low and room temperature at distances from central strontium of <4.2 ?. Comparison of strontium structural coordination determined in this and previous studies suggests that previous EXAFS determinations of hydrated strontium may have underestimated first-shell interatomic distances and coordination numbers because minor contributions to the EXAFS phase-shift and amplitude functions were not accounted for, either theoretically or empirically. Copyright 2000 Academic Press.     

Kinetic studies of nonaqueous polymerization of methyl methacrylate initiated by ferric laurate–n-hexyl amine system

The polymerization of methyl methacrylate was studied in carbon tetrachloride medium with ferric laurate, a metal soap, in combination with n-hexyl amine as the initiator system at 60°C. The rate of polymerization was found to be linear with the monomer concentration and proportional to the square root of both ferric ion and amine concentration. A reaction scheme involving initial complex formation between ferric ion and amine and subsequent reaction of the complex with the solvent molecule to produce free radicals responsible for initiation of polymerization has been postulated to account for the observed results.     

The coupled-cluster method with a multiconfiguration reference state

The coupled-cluster approach to obtaining the bond-state wave functions of many-electron systems is extended, with a set of physically reasonable approximations, to admit a multiconfiguration reference state. This extension permits electronic structure calculations to be performed on correlated closed- or open-shell systems with potentially uniform precision for all molecular geometries. Explicit coupled cluster working equations are derived using a multiconfiguration reference state for the case in which the so-called cluster operator is approximated by its one- and two-particle components. The evaluation of the requisite matrix elements is facilitated by use of the unitary group generators which have recently received wide attention and use in the quantum chemistry community.     

Divisibility of certain $$\ell $$ -regular partitions by 2

The Ramanujan Journal - For a positive integer $$\ell $$ , let $$b_{\ell }(n)$$ denote the number of $$\ell $$ -regular partitions of a nonnegative integer n. Motivated by some recent conjectures...     

An approximate max-flow min-cut relation for undirected multicommodity flow,with applications

In this paper, we prove the first approximate max-flow min-cut theorem for undirected multicommodity flow. We show that for a feasible flow to exist in a multicommodity problem, it is sufficient that every cut's capacity exceeds its demand by a factor ofO(logClogD), whereC is the sum of all finite capacities andD is the sum of demands. Moreover, our theorem yields an algorithm for finding a cut that is approximately minimumrelative to the flow that must cross it. We use this result to obtain an approximation algorithm for T. C. Hu's generalization of the multiway-cut problem. This algorithm can in turn be applied to obtain approximation algorithms for minimum deletion of clauses of a 2-CNF formula, via minimization, and other problems. We also generalize the theorem to hypergraph networks; using this generalization, we can handle CNF clauses with an arbitrary number of literals per clause.Most of the results in this paper were presented in preliminary form in Approximation through multicommodity flow,Proceedings, 31th Annual Symposium on Foundations of Computer Science (1990), pp. 726–737.Research supported by the National Science Foundation under NSF grant CDA 8722809, by the Office of Naval and the Defense Advanced Research Projects Agency under contract N00014-83-K-0146, and ARPA Order No. 6320, Amendament 1.Research supported by NSF grant CCR-9012357 and by an NSF Presidential Young Investigator Award.     

Polymerization of methyl methacrylate with cupric laurate–benzoin system as initiator

The polymerization of methyl methacrylate initiated by cupric laurate in combination with benzoin has been investigated in carbon tetrachloride medium at 60°C. The rate of polymerization was found to be proportional to the square root of both cupric ion and benzoin concentrations, and to the 1.5th power of the monomer concentration. Spectral studies indicated that there is a complex formation between cupric ion and the monomer methyl methacrylate. A reaction scheme, based on initial formation of the complex and its subsequent reaction with benzoin to produce the free radicals responsible for initiation has been postulated to explain the observed results.