Air‐stable and recoverable catalyst for copper‐catalyzed controlled/living radical polymerization of styrene; In situ generation of Cu(I) species via electron transfer reaction

Copper‐catalyzed controlled/living radical polymerization (LRP) of styrene (St) was conducted using the silica gel‐supported CuCl₂/N,N,N′,N′,N″‐pentamethyldiethylenetriamine (SG‐CuCl₂/PMDETA) complex as catalyst at 110 °C in the presence of a definite amount of air. This novel approach is based on in situ generation and regeneration of Cu(I) via electron transfer reaction between phenols and Cu(II). Sodium phenoxide or p‐methoxyphenol was used as a reducing agent of Cu(II) complexes in LRP. The number–average molecular weight, M_n,GPC, increases linearly with monomer conversion and agrees well with the theoretical values up to 85% conversion The molecular weight distribution, M_w/M_n, decreases as the conversion increases and reaches values below 1.2. The catalyst was recovered in aerobic condition and reused in copper‐catalyzed LRP of St. For the second run, the number–average molecular weights increased with monomer conversion and the polydispersities decreased as the polymerization proceeded and reached to the value <1.3 at 81% conversion. The recycled catalyst retained 90% of its original activity in the subsequent polymerization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 77–87, 2006     

Microencapsulated oleic–capric acid/hexadecane mixture as phase change material for thermal energy storage

Journal of Thermal Analysis and Calorimetry - Thermal energy storage systems provide efficiency in order to have better utilization of energy sources while protecting the environment. Thermal...     

Comparison of certain value-at-risk estimation methods for the two-parameter Weibull loss distribution

The Weibull distribution is one of the most important distributions that is utilized as a probability model for loss amounts in connection with actuarial and financial risk management problems. This paper considers the Weibull distribution and its quantiles in the context of estimation of a risk measure called Value-at-Risk (VaR). VaR is simply the maximum loss in a specified period with a pre-assigned probability level. We attempt to present certain estimation methods for VaR as a quantile of a distribution and compare these methods with respect to their deficiency (Def) values. Along this line, the results of some Monte Carlo simulations, that we have conducted for detailed investigations on the efficiency of the estimators as compared to MLE, are provided.     

Green's function study of a mixed spin-1 and spin-3/2 Heisenberg ferrimagnetic system

The magnetic properties of a mixed spin-1 and spin-3/2 Heisenberg ferrimagnetic system on a square lattice are investigated by using the double-time temperature-dependent Green's function technique. In order to decouple the higher order Green's functions, Anderson and Callen's decoupling and random phase approximations have been used. The nearest- and next-nearest-neighbor interactions and the single-ion anisotropies are considered and their effects on compensation and critical temperature are studied.     

Corrosion prevention of mild steel in acidic medium by 2-Pyrrolidin-1-yl-1,3-thiazole-5-carboxylic acid: Theoretical and experimental approach

The inhibition efficiency of 2-Pyrrolidin-1-yl-1,3-thiazole-5-carboxylic acid (PTCA) against mild steel (MS) corrosion was investigated in acidic solution by using quantum chemical calculations based on Density Functional Theory (DFT) method and electrochemical measurements. The electrochemical impedance spectroscopy (EIS), potentiodynamic, potential zero charge (pzc) analysis and electrochemical noise (EN) measurements at various concentrations (from 0.1 to 10 mM) and immersion times were utilized in experimental part. The surface analysis was achieved scanning electron microscope (SEM) and contact angle measurements in the absence and presence of 10 mM PTCA. According to DFT results, PTCA exhibited 3.737 eV band gap and 8.130 Debye dipole moment which were a signal of potentially convenient corrosion inhibitor properties. PTCA has a remarkable corrosion inhibition capability to mild steel, which inhibited both anodic and cathodic corrosion rates, relying on it's physically adsorption on the metal solution interface and protection ability was increased with increasing PTCA concentration. The obtained adsorption equilibrium constant was 11.11 × 10³ M^-1 and calculated standard free energy of adsorption was ?33.03 kJ mol^?1. The determined activation energy values were 55.58 kJ mol^?1 and 96.86 kJ mol^?1 in 0.5 M HCl in the absence and presence of 10 mM PTCA, respectively. PTCA demonstrated a strong inhibition efficiency of 98.3%, after 168 h immersion, according to the EIS results. As a consequently, we recommend that PTCA is a convenient inhibitor in 0.1 M HCl for mild steel protection against corrosion.     

Synthesis,spectroscopic (FT-IR and NMR), DFT and molecular docking studies of ethyl 1-(3-nitrophenyl)-5-phenyl-3-((4-(trifluoromethyl)phenyl)carbamoyl)-1H-pyrazole-4-carboxylate

Research on Chemical Intermediates - Trifluoromethyl group containing pyrazole-3-carboxamide derivative is synthesized and the structure of the molecule (E3N5PC) has been verified by using FT-IR,...     

Selfadjoint extensions of a singular differential operator

In this work, firstly in the Hilbert space of vector-functions all selfadjoint extensions of the minimal operator generated by linear singular symmetric differential expression with a selfadjoint operator coefficient A in any Hilbert space H, are described in terms of boundary values. Later structure of the spectrum of these extensions is investigated.     

A Stochastic Subgradient Method for Distributionally Robust Non-convex and Non-smooth Learning

Journal of Optimization Theory and Applications - We consider a distributionally robust formulation of stochastic optimization problems arising in statistical learning, where robustness is with...     

Tensor Approximation Approach to Calculation of Singular Values and Vectors for SVD Problem

A new method of calculation of singular values and left and right singular vectors of arbitrary nonsquare matrices is proposed. The method allows one to avoid solutions of high rank systems of linear equations of singular value decomposition problems, which makes it not sensitive to ill-conditioness of the decomposed matrix. On the base of the Eckart–Young theorem, it was shown that each second order r-rank tensor can be represented as a sum of the first rank r-order “coordinate” tensors. A new system of equations for “coordinate” tensor generator vectors was obtained. An iterative method of solution of the system was elaborated. Results of the method were compared with classical methods of solutions of singular value decomposition problems.