E.S.R. of a one-dimensional Heisenberg antiferromagnet which undergoes a crystalline to discotic phase transition

Abstract

Single crystals and polycrystalline samples of the compounds bis(1,3-di(p-n-octylphenyl)propane-l,3-dionato)copper(II) [I], and bis(l,3-di(p-n-octyloxy-phenyl)propane-l,3-dionato)copper(II) [II] have been studied by E.S.R. The E.S.R. spectra of single crystals of [I] at 298 K have the features associated with a spin 1/2 one-dimensional Heisenberg antiferromagnet while the spectra of single crystals of [II] do not. E.S.R. of single crystals of [I] and [II] provides a reliable means of detecting previously reported crystalline to discotic phase transitions. Single crystals of [I] heated beyond the temperature of the first discotic phase transition yield single line E.S.R. spectra which have an angular dependence and an asymmetric lineshape; these observations suggest that, in the discotic phase, exchange interactions are still significant and a degree of long range order is maintained.     

A hybrid neuro-fuzzy analytical approach to mode choice of global logistics management

This paper presents a hybrid neuro-fuzzy methodology to identify appropriate global logistics (GL) operational modes used for global supply chain management. The proposed methodological framework includes three main developmental phases: (1) establishment of a GL strategic hierarchy, (2) formulation of GL-mode identification rules, and (3) development of a GL-mode choice model. By integrating advanced multi-criteria decision-making (MCDM) techniques including fuzzy analytical hierarchy process (Fuzzy-AHP), Fuzzy-MCDM, and the technique for order preference by similarity to an ideal solution (TOPSIS), six types of global logistics and operational modes coupled with corresponding fuzzy-based multi-criteria decision-making rules are specified in the second phase. Using the specified fuzzy decision-making rules as the input database, an adaptive neuro-fuzzy inference system (ANFIS) is then developed in the third phase to identify proper GL modes for the implementation of global supply chain management. A numerical study with a questionnaire survey database aimed at the information technology (IT) industries of Taiwan is conducted to illustrate the applicability of the proposed method.     

Electrical-optical analysis of a GaN/sapphire LED chip by considering the resistivity of the current-spreading layer

The effects of current distribution in LED chips on the electrical potential and optical light extraction efficiency are investigated by a numerical simulation. The results show that when the resistivity of the current-spreading layer is decreased there is current-crowding near the n-contact. On the other hand, when the resistivity in the current-spreading layer increases, there is current-crowding near the p-contact. When the current is crowded near the n-contact due to less resistivity of the current-spreading layer, the input power is lower because of the smaller series resistance in the chip, and the light extraction efficiency is higher since the shadowing effect of the p-contact can be avoided. For L _p = 50 μm in this study, the light extraction efficiency at ρ _ITO = 0.1 × 10⁻³ Ω·cm is 1.4 times better than that when L _p = 100 μm, even though the driving voltage is raised 1.02 times.     

Briaexcavatins A and B, novel briaranes from the octocoral Briareum excavatum

Two novel briaranoidal derivatives, designated as briaexcavatins A (1) and B (2), along with two known metabolites, excavatolides B and C (3 and 4), were isolated from the octocoral Briareum excavatum. Both compounds 1 and 2 possess unprecedented 5,6-epoxy moiety in the 10-membered ring. Diterpenoid 1 possesses a novel pentacyclic skeleton with a ε-lactone. The structures of diterpenoids 1 and 2 were elucidated by interpretation of spectral data and the absolute stereochemistry was established by application of modified Mosher’s method on 3.     

Ionic liquid of choline chloride/malonic acid as a solvent in the synthesis of open-framework iron oxalatophosphates

Two new iron(III) oxalatophosphates, Cs2Fe(C2O4)(0.5)(HPO4)2 (1) and CsFe(C2O4)(0.5)(H2PO4)(HPO4) (2), have been synthesized by using a low melting point eutectic mixture of choline chloride and malonic acid as a solvent and characterized by single-crystal X-ray diffraction and magnetic susceptibility. Crystal data are as follows: compound 1, monoclinic, P2(1)/c (No. 14), a = 8.5085(4) A, b = 12.7251(6) A, c = 9.8961(4) A, beta = 107.117(1) degrees , V = 1024.01(8) A(3), Z = 4, and R(1) = 0.0264; compound 2, monoclinic, P2(1)/n (No. 14), a = 8.0038(3) A, b = 10.2923(3) A, c = 11.4755(4) A, beta = 100.507(1) degrees , V = 929.47(5) A(3), Z = 4, and R(1) = 0.0311. The structure of 1 comprises FeO6 octahedra connected by HPO4(2-) tetrahedra and bisbidentate oxalate anions to form a 3D framework containing intersecting 12-ring channels, with the charge-compensating Cs+ cations being located at the intersections of these channels. The structure of 2 consists of 2D layers of octahedral FeO6, tetrahedral H2PO4- and HPO4(2-) moieties, and bisbidentate oxalate ligands with the Cs+ cations between the layers. They are the first examples for the use of ionic liquid as a solvent in the synthesis of metal oxalatophosphates.     

Carbon dioxide fixation by an unprecedented hydroxo lead-chromium carbonyl complex: synthesis, reactivity, and theoretical calculations

The novel hydroxo-bridged dimeric lead-chromium carbonyl complex [Et4N]2[{PbCr2(CO)10}2(mu-OH)2] ([Et4N]2[1]) was synthesized from the reaction of PbCl2 and Cr(CO)6 followed by metathesis with [Et4N]Br in a KOH/MeOH solution. The X-ray crystallographic structure shows that dianion 1 consists of two Pb{Cr(CO)5}2 units bridged by two hydroxo fragments in which the Pb atoms are further coordinated with two Cr(CO)5 groups, resulting in a distorted tetrahedral geometry. A CO2 molecule can insert itself into dianion 1 to form two new carbonate complexes, [Et(4)N]2[{PbCr2(CO)10}(CO3)] ([Et4N]2[2]) and [Et4N]2[{PbCr2(CO)10}2(CO3)] ([Et4N]2[3]), depending on the reaction conditions. In addition, complex 2 can be transformed into 3 in CH2Cl2 solution at an elevated temperature. While the carbonate group in dianion 2 is bonded to one Pb atom, which is coordinated with two Cr(CO)5 fragments, the carbonate group in 3 bridges the two Pb centers in a mu-1kappa2OO':2kappa2OO' fashion in which each Pb atom is further bonded to two Cr(CO)5 moieties. Complexes 2 and 3 can be converted back the hydroxo complex 1 under appropriate conditions. All three unprecedented lead-chromium compounds, 1-3, were fully characterized by spectroscopic methods and single-crystal X-ray diffraction analyses. The nature and formation of complexes 1-3 were also examined by molecular orbital calculations using the B3LYP method of the density functional theory.     

Max-Plus Stochastic Control and Risk-Sensitivity

In the Maslov idempotent probability calculus, expectations of random variables are defined so as to be linear with respect to max-plus addition and scalar multiplication. This paper considers control problems in which the objective is to minimize the max-plus expectation of some max-plus additive running cost. Such problems arise naturally as limits of some types of risk sensitive stochastic control problems. The value function is a viscosity solution to a quasivariational inequality (QVI) of dynamic programming. Equivalence of this QVI to a nonlinear parabolic PDE with discontinuous Hamiltonian is used to prove a comparison theorem for viscosity sub- and super-solutions. An example from mathematical finance is given, and an application in nonlinear H-infinity control is sketched.     

Optimal age-replacement model with age-dependent type of failure and random lead time based on a cumulative repair-cost limit policy

In this paper, we consider an age-replacement model with minimal repair based on a cumulative repair cost limit and random lead time for replacement delivery. A cumulative repair cost limit policy uses information about a system’s entire repair cost history to decide whether the system is repaired or replaced; a random lead time models delay in delivery of a replacement once it is ordered. A general cost model is developed for the average cost per unit time based on the stochastic behavior of the assumed system, reflecting the costs of both storing a spare and of system downtime. The optimal age for preventive replacement minimizing that cost rate is derived, its existence and uniqueness is shown, and structural properties are presented. Various special cases are included, and a numerical example is given for illustration. Because the framework and analysis are general, the proposed model extends several existing results.