38 research outputs found
Algorithm for Linear Response Functions at Finite Temperatures: Application to ESR spectrum of s=1/2 Antiferromagnet Cu benzoate
We introduce an efficient and numerically stable method for calculating
linear response functions of quantum systems at finite
temperatures. The method is a combination of numerical solution of the
time-dependent Schroedinger equation, random vector representation of trace,
and Chebyshev polynomial expansion of Boltzmann operator. This method should be
very useful for a wide range of strongly correlated quantum systems at finite
temperatures. We present an application to the ESR spectrum of s=1/2
antiferromagnet Cu benzoate.Comment: 4 pages, 4 figure
Itinerant ferromagnetism in half-metallic CoS_2
We have investigated electronic and magnetic properties of the pyrite-type
CoS_2 using the linearized muffin-tin orbital (LMTO) band method. We have
obtained the ferromagnetic ground state with nearly half-metallic nature. The
half-metallic stability is studied by using the fixed spin moment method. The
non-negligible orbital magnetic moment of Co 3d electrons is obtained as in the local spin density approximation (LSDA). The calculated
ratio of the orbital to spin angular momenta / = 0.15 is
consistent with experiment. The effect of the Coulomb correlation between Co 3d
electrons is also explored with the LSDA + U method. The Coulomb correlation at
Co sites is not so large, eV, and so CoS_2 is possibly
categorized as an itinerant ferromagnet. It is found that the observed
electronic and magnetic behaviors of CoS_2 can be described better by the LSDA
than by the LSDA + U.Comment: 4 pages, 3 postscript figure
The Many Virtues of Second Nature : Habitus in Latin Medieval Philosophy
This chapter consists of a systematic introduction to the nature and function of habitus in Latin medieval philosophy. Over the course of this introduction, several topics are treated: the theoretical necessity to posit habitus; their nature; their causal contribution to the production of internal and external acts; how and why habitus can grow and decay; what makes their unity when they can have multiple objects and work in clusters. Finally we examine two specific questions: why intellectual habitus represent a special case that triggered considerable debate; how human beings can be said to be free if their actions are determined by moral habitus
Thermal behavior of covalently bonded phosphonate flame-retarded poly(methyl methacrylate) systems
Pyrolysis studies of reactively flame-retarded methyl methacrylate copolymers MMA/diethyl(acryloyloxymethyl)phosphonate (MMA/DEAMP) and MMA/diethyl(methacryloyloxymethyl)phosphonate (MMA/DEMMP) have been undertaken with a view to gaining information pertinent to the mechanisms of their flame-retardant behavior. The homopolymer with and without the additive diethylethylphosphonate was also investigated for comparison purposes. Each system contained 3.5 wt% of phosphorus. A range of techniques, namely TG with EGA, DSC, SEM, laser and microfurnace pyrolysis mass spectrometry, and isothermal pyrolysis-GC-MS, enabled the study to be carried out under a range of conditions. In the case of the additive system, the additive was evolved prior to the polymer decomposition. Little or no char residue remained at the end of the decomposition. Thus, the additive acted almost completely in the vapor phase. In the case of the MMA/DEMMP and MMA/DEAMP copolymers, substantial char residues were formed with 1.0 and 2.5 wt% phosphorus contents, respectively. This is evidence that predominantly condensed phase flame retardation occurs in these systems. SEM studies showed the chars from both copolymers to have flaky and smooth surfaces. Both copolymer samples showed slower decomposition rates compared to PMMA, the MMA/DEAMP being the slowest. Decomposition of MMA/DEMMP occurred mainly via end-chain scission with both MMA and DEMMP appearing concurrently, which would facilitate condensed-phase flame-retardant action. On the other hand, in the case of MMA/DEAMP, end-chain scission is to some extent is inhibited so that both end and the slower random-chain scission occur. As a result, the decomposition of the acrylate system was slower than that of the methacrylate copolymer. The former system yields more char which contains the higher percentage of phosphorus than does the methacrylate copolymer. Thus, MMA/DEAMP showed the greater condensed-phase flame-retardant action. This is consistent with the results of our previous flammability studies of these copolymers. The flame-retardant abilities of these two phosphonate copolymers are assessed with reference to previous studies of their equivalent phosphate copolymers. Copyright © 2008 John Wiley & Sons, Ltd