Dynamic compensation temperature in the mixed spin-1 and spin-2 Ising model in an oscillating field on alternate layers of a hexagonal lattice

The dynamic behavior of a mixed spin-1 and spin-2 Ising system with a crystal-field interaction in the presence of a time-dependent oscillating external magnetic field on a hexagonal lattice is studied by using the Glauber-type stochastic dynamics. The lattice is formed by alternate layers of spins σ=1$\sigma =1$ and S=2. The Hamiltonian model includes intersublattice, intrasublattice and crystal-field interactions. The set of mean-field dynamic equations is obtained by employing the Glauber transition rates. Firstly, we study time variations of the average sublattice magnetizations in order to find the phases in the system, and the thermal behavior of the average sublattice magnetizations in a period or the dynamic sublattice magnetizations to obtain the dynamic phase transition points as well as to characterize the nature (continuous and discontinuous) of transitions. Then, the behavior of the dynamic total magnetization as a function of the temperature is investigated to find the dynamic compensation points as well as determine the type of behavior. We also present the dynamic phase diagrams for both presence and absence of the dynamic compensation temperatures in the nine different planes. According to the values of Hamiltonian parameters, besides the paramagnetic (p), antiferromagnetic (af), ferrimagnetic (i) and non-magnetic (nm) fundamental phases, eight different mixed phases and the compensation temperature or L- and N-types behavior in the Néel classification nomenclature exist in the system.     

Deposition of MgF2 thin films for antireflection coating by using thermionic vacuum arc (TVA)

In this study, optical and surface properties of MgF₂ thin films produced by thermionic vacuum arc (TVA) technique have been investigated. By means of this technique the MgF₂ thin film produced by condensing the plasma of anode material generated by using TVA under high vacuum conditions on the glass. The optical properties have been investigated by using Filmetrics F20 and UV/VIS spectrometer. For surface properties of produced thin films EDS, SEM and AFM have been used. Our analysis shows that MgF₂ thin films produced by using TVA are proper single and multi layer anti-reflective (AR) coating and TVA technique brings very important advantages for ophthalmic glass coating and industrial applications' optical purposes.     

Hydrogen Bonded Supramolecular Network from a Mixed Valence Cobalt System: Synthesis and Crystal Structure of [Co(H2O)6][Co(pydc)2(en)]2·14H2O

Abstract  

The [Co(H₂O)₆][Co(pydc)₂(en)]₂·14H₂O (1) compound (H₂pydc = Pyridine-2,3-dicarboxylic acid and en = ethylenediamine) was synthesized and characterized by elemental analysis, magnetic and spectroscopic measurements (UV–Vis and IR spectra) and single crystal X-ray diffraction technique. There are two coordination spheres with different charges inside this aqueous compound of ionic character. The cationic part is composed of Co(II) encircled by six aqua ligand. Whereas the anionic part contains two anions complex unit each with −1 charge and have Co(III) ions in the centre. As a result different coordination spheres have cobalt ions with different states. The crystallographic analysis revealed that 1 consists of both discrete one-cationic and two-anionic entities, [Co(H₂O)₆]²⁺ and [Co(pydc)₂(en)]₂⁻ and fourteen crystal water molecules. Two water molecules within the water cluster act as hydrogen-bonding acceptors, whereas one water molecule acts as a hydrogen-bonding donor to form a discrete water trimer. These water molecules have stabilized the crystal structure by strong hydrogen bonding interactions.     

The mixed vertex packing problem

We study a generalization of the vertex packing problem having both binary and bounded continuous variables, called the mixed vertex packing problem (MVPP). The well-known vertex packing model arises as a subproblem or relaxation of many 0-1 integer problems, whereas the mixed vertex packing model arises as a natural counterpart of vertex packing in the context of mixed 0-1 integer programming. We describe strong valid inequalities for the convex hull of solutions to the MVPP and separation algorithms for these inequalities. We give a summary of computational results with a branch-and-cut algorithm for solving the MVPP and using it to solve general mixed-integer problems. Received: June 1998 / Accepted: February 2000?Published online September 20, 2000     

Investigation of the alterations induced in erythrocyte membrane physical characteristics of non-insulin-dependent type II diabetic Patients: an ESR study

The physical and dynamic properties of intact erythrocyte membranes of two groups, diabetic patients treated by diet alone (27 women and 41 men, 40–75 years old) and healthy subjects (controls) (25 women and 35 men, 35–75 years old) were investigated by electron spin resonance (ESR) spectroscopy. 5-doxyl stearic acid (5-DSA) and 4-maleimido-2,2,6,6-tetramethyl-piperidine-1-oxyl (MAL-6) are employed as spin labels throughout the experiments. While 5-DSA monitors the membrane surface region and gives information about the order of lipids in this region through the order parametersS′, MAL-6 binds thiol groups S-H to the membrane protein and gives information about possible protein conformational changes. Order parameters were calculated from room temperature spectra recorded for intact erythrocytes labeled with 5-DSA and the values of 0.682±0.004 and 0.666±0.004 were obtained for diabetic patients and controls, respectively. Variations of theh ₍₋₁₎,h ₍₀₎,h ₍₊₁₎ and 2A ₁₁ parameters in the temperature range of 10–50 °C were also studied and fairly different behaviors were observed for both groups, especially for theh ₍₋₁₎ parameter. Line intensitiesW andS characterizing the concentrations of weakly and strongly immobilized MAL-6 species bound to S-H groups of intact erythrocyte membrane proteins were used to calculate theW/S ratios. They were found to be 34.1±1.9 and 30.5±2.4 for diabetic patients and controls, respectively. While line intensitiesT, those of theM ₁=−1 high-field resonance line associated with the weakly immobilized S-H sites, of both groups exhibit a very similar microwave saturation behavior in the range of 0.5–20 mW, line intensitiesW of both groups saturated differently. Variations of line intensitiesS, W andT with temperature were also investigated in the temperature range of 10–50 °C and characteristic differences were observed to exist between two groups implying a less fluid erythrocyte membrane for diabetic patients. Increases in the order parameterS′ and in theW/S ratio are considered as major factors attributable to the alteration in the physical and dynamic properties of erythrocyte membrane in the diabetic state.     

Determination of the ESR parameters of Cu2+ doped in CdC4H4O6 · 5H2O single crystals using a statistical calculation technique

Electron spin resonance spectra of Cu²⁺-doped cadmium tartrate pentahydrate single crystals grown by the diffusion technique have been investigated at 77 K. Two magnetically inequivalent Cu²⁺ lattice sites were identified. For each site four hyperfine lines and some additional weak forbidden hyperfine lines due to the quadrupole interaction were observed. The spectra were analyzed by a perfect least-squares procedure based on an appropriate statistical model to determine the spin-Hamiltonian parameters.     

Rhodium(I) catalyzed carbonylation reactions of halides and ethers

Benzylic bromides and methyl iodide react with ethers, carbon monoxide, potassium iodide, and the dimer of chloro(1,5-hexadiene)rhodium($\text{I}$) to give esters in good yields.     

Preparation,Characterization and Thermal Energy Storage Properties of Micro/Nano Encapsulated Phase Change Material with Acrylic-Based Polymer

The eutectic mixture of octacosane (C28)–heptadecane (C17) as core material was successfully encapsulated with an acrylic-based polymer (polymethylmethacrylate; PMMA) as shell material through emulsion polymerization. The polymeric reaction occurred around the core material was characterized by FTIR spectroscopy analysis. The polarized optical microscopy, scanning electron microscopy and particle size distribution investigations showed that the most of the prepared capsules had almost spherical shape with non-unimodal size distribution in micro-nano range. The differential scanning calorimetry analysis results exhibited that the capsules including highest amount of the eutectic PCM had a melting temperature of about 21°C and a latent heat capacity of about 98 J/g. The high thermal durability of the prepared capsules was confirmed by thermogravimetric analysis. The thermal cycling test designated that the synthesized capsules had good long-term usage latent heat thermal energy storage (LHTES) performance and chemical stability. Furthermore; the fabricated capsules with (1: 2) shell/core ratio had a reasonable thermal conductivity. It can be drawn a conclusion from all results that the prepared capsules especially PMMA/(C28–C17) (1: 2) product is a hopeful PCM that can be evaluated for low-temperature LHTES applications.     

Photoinduced Rearrangement of Dienones and Santonin Rerouted by Amines

The photoinduced rearrangement pathways of simple 2,5‐dienones and the natural product santonin were found to be effectively rerouted by amines, giving rise to unprecedented products. Either cis olefins or cyclobutenes were obtained from 4,4‐disubstituted 2,5‐dienone upon irradiation (365 nm) in the presence of various amines depending on the solvent. Previously undescribed [4.4.0] and [5.3.0] fused‐ring‐containing products were obtained when santonin was irradiated (365 nm) in the presence of methylamine. The amines present in these reactions were incorporated into the products by means of amide‐group formation.     

An efficient synthesis of propargylamines via C-H activation catalyzed by copper(I) in ionic liquids

A readily available copper(I) catalyst, in an ionic liquid, can effect three-component coupling of aldehydes, amines and alkynes to generate propargylamines in high yields.