49 research outputs found
On a method to calculate conductance by means of the Wigner function: two critical tests
We have implemented the linear response approximation of a method proposed to
compute the electron transport through correlated molecules based on the
time-independent Wigner function [P. Delaney and J. C. Greer, \prl {\bf 93},
36805 (2004)]. The results thus obtained for the zero-bias conductance through
quantum dot both without and with correlations demonstrate that this method is
either quantitatively nor qualitatively able to provide a correct physical
escription of the electric transport through nanosystems. We present an
analysis indicating that the failure is due to the manner of imposing the
boundary conditions, and that it cannot be simply remedied.Comment: 22 pages, 7 figur
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