Biodegradable polycaprolactone–polyanhydrides blends

Biodegradable polymers based on a blend of polycaprolactone (PCL) and aliphatic polyanhydrides with various monomer lengths were prepared to obtain desired polymer blends for use as drug carriers. The physicochemical, mechanical, and drug‐release properties of these blends were investigated by various techniques to evaluate the uniformity degree of the polymer blends to establish their potential applications in drug delivery. The results demonstrated that the heat of fusion (ΔH) of the polyanhydride or the blend is increased in relation to the length of the aliphatic chain. However, the blends had different properties than pure polyanhydride, and the crystallization degree of the blends, as expressed by the ΔH, decreased in relation to the ΔH of the pure polyanhydride. Drug‐release studies from blends of PCL and aliphatic polyanhydrides demonstrated first‐order kinetics of the release rate. Polymer degradation was independent at the polyanhydride monomer length. On the basis of theoretical calculation of the interaction factor, a blend of PCL and poly(dodecanedeoic anhydride) was chosen for further elucidation of its thermal, mechanical, and degradation properties. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3781–3787, 2003     

Preparation and Electrochemical Properties of Tin–Iron–Carbon Nanocomposite as the Anode of Lithium‐Ion Batteries

Tin–iron–carbon nanocomposite is successfully prepared by a sol–gel method followed by a chemical vapor deposition (CVD) process with acetylene gas as the carbon source. The structural properties, morphology, and electrochemical performances of the nanocomposite are comprehensively studied in comparison with those properties of tin–carbon and iron–carbon nanocomposites. Sheet‐like carbon architecture and different carbon contents are induced thanks to the catalytic effect of iron during CVD. Among three nanocomposites, tin–iron–carbon demonstrates the highest reversible capacity of 800 mA h g^?1 with 96.9 % capacity retention after 50 cycles. It also exhibits the best rate capability with a discharge capacity of 420 mA h g^?1 at a current density of 1000 mA g^?1. This enhanced performance is strongly related to the carbon morphology and content, which can not only accommodate the large volume change, but also improve the electronic conductivity of the nanocomposite. Hence, the tin–iron–carbon nanocomposite is expected to be a promising anode for lithium‐ion batteries.     

Photocatalytic splitting of CS2 to S8 and a carbon-sulfur polymer catalyzed by a bimetallic ruthenium(II) compound with a tertiary amine binding site: toward photocatalytic splitting of CO2?

The catalytic photocleavage of CS(2) to S(8) and a (C(x)S(y))(n) polymer with visible light using a dinuclear ruthenium(II) compound with a bipyridine units for photoactivity and a vicinal tertiary amine binding site for CS(2) activation was studied. The catalyst was characterized by X-ray diffraction, (1)H NMR, and (13)C NMR, ESI-MS and elemental analysis. CS(2) photocleavage was significant (240 turnovers, 20 h) to yield isolable S(8) and a (C(x)S(y))(n) polymer. A mononuclear catalyst or one without an amine binding site showed significantly less activity. XPS of the (C(x)S(y))(n) polymer showed a carbon/sulfur ratio ～1.5-1.6 indicating that in part both C-S bonds of CS(2) had been cleaved. Catalyst was also included within the polymer. The absence of peaks in the (1)H NMR verified the (C(x)S(y))(n) nature of the polymer, while (13)C NMR and IR indicated that the polymer had multiple types of C-S and C-C bonds.     

Simulation of CPMAS Signals at High Spinning Speeds

The spin dynamics of anS( )I_Nsystem during the CP mixing time of continuous wave and variable amplitude cross-polarization magic angle spinning (CWCPMAS and VACPMAS) experiments is discussed. The signal enhancement of a low abundantSspin, coupled to a set ofN= 6 coupled spins withI= , is evaluated as a function of the length of the mixing time. For CWCPMAS this signal is first evaluated in the frequency domain and then transformed to the time domain. These calculations provide some additional insight into the CP spin dynamics and enable a practical approach toward the evaluation of CP signals of large spin systems. In addition the adiabatic character of the ramped VACPMAS experiments is discussed andS-spin signals of a spin system withN= 6 are simulated. Estimates of the upper bounds of the CP signals as a function of the number ofIspins in anS( )I_Nsystem are given and compared with the calculated values.     

Formation of argon fluoride molecules under interaction of an argon plasma flow with potassium fluoride and sulfur hexafluoride vapors

The formation of argon fluoride molecules in plasma-dynamic jets of argon-potassium fluoride vapor and argon-sulfur hexafluoride vapor mixtures is investigated. The intensity of the ArF* luminescence band at 193 nm versus the argon and sulfur hexafluoride flow rates, pump power, and distance from the nozzle is studied.     

Reformulation of general relativity as a gauge theory

The starting point is a spinor affine space-time. At each point, two-component spinors and a basis in spinor space, called “spin frame,” are introduced. Spinor affine connections are assumed to exist, but their values need not be known. A metric tensor is not introduced. Global and local gauge transformations of spin frames are defined with GL(2) as the gauge group. Gauge potentials B_μ are introduced and corresponding fields F_μν are defined in analogy with the Yang-Mills case. Gravitational field equations are derived from an action principle. Incases of physical interest SL(2, C) is taken as the gauge group, instead of GL(2). In the special case of metric space-times the theory is identical with general relativity in the Newman-Penrose formalism. Linear combinations of B_μ are generalized spin coefficients, and linear combinations of F_μν are generalized Weyl and Ricci tensors and Ricci scalar. The present approach is compared with other formulations of gravitation as a gauge field.     

A Whiteheadian approach to Bell's correlations

Certain properties of the Bell-type correlations and, in particular, the impossibility of using them to transmit signals faster than light, are investigated from the point of view of the conceptual structure of quantum mechanics and of Whitehead's process philosophy. The collapses of quantum states are shown to correspond to perspectives of different frames of reference on a Whiteheadian process of self-creation of actual entities. The analysis suggests a fundamental limitation on the capacity to describe the propagation of influences among the results of measurements at space-like separation. It is further shown that, if Whitehead's framework is modified in a specific way, it accounts very well for the apparent existence of superluminal influences, and for the impossibility of using them for superluminal communication.This work was supported in part by a grant from the Colgate Research Council.     

A note on the Stokes resistance tensors of multiparticle systems in shear fields

The Stokes resistance tensors (material tensors) of a multiparticle system subjected to a general shear flow depends on the spatial configuration of the particles, their shape, size and location of some arbitrarily fixed set of points locked to the particles by which their linear velocities are traced. The objective of this work is the determination of some symmetry properties of the material tensors and the transformation laws which govern them under translation of the set of points fixed to the particles.