In vivo degradation of semi-rigid polymeric films made of alginate and polyethylene glycol

Alginate-based biomaterials can form naturally derived polymeric hydrogels with sufficient structural integrity to readily be used in many clinical applications. However, ionically cross-linked alginate gels do not always possess structural properties suitable for application as erodable polymeric films for controlled release of drugs and growth factors. In this study, semi-rigid polymeric films were constructed of sodium alginate and polyethylene glycol (PEG) by means of a rehydration cross-linking technique. The films were assembled by dehydrating a solution of alginate and PEG and cross-linking the alginate during its rehydration with a solution of calcium chloride. The product is a highly dense polymeric network that prevents in vivo cellular infiltration and disassembles primarily by surface erosion. By implanting the PEG-alginate films into the subcutis of rats, the mechanism of polymer degradation was demonstrated to occur via inflammation-mediated erosion of the material rather than by means of cellular infiltration. There were extensive areas of foamy macrophages at the site of the implant, indicating a likely mechanism of removal and disposal of the disassembled PEG and alginate polymer. The eroded fragments of the film that remained after six weeks did not exhibit signs of a cellular infiltrate but rather stayed intact, appearing as small, dense fragments of polymer. Our observations that nearly all the PEG-alginate material was cleared from the implantation site by the sixth postoperative week highlight the potential exploitation of these films as bioresorbable wound dressings with prospective utilization as a drug delivery device. Moreover, the employment of polymeric films made of functionalized PEG, which enables covalent attachment of biological molecules, potentiates their use for growth factor delivery applications.     

Self-adjusting compensating thermal lens to balance the thermallyinduced lens in solid-state lasers

The thermal lens is a critical issue, particularly in high-power diode-pumped solid-state laser rods. A self-adjusting scheme for compensation of the thermally induced lens is presented. The requirements for such an element and its influence on the resonator are discussed. With an appropriate compensating element and a suitable resonator design, constant beam parameters are expected to be achieved over a pump range of several kilowatts     

Numerical simulation and analytical description of thermallyinduced birefringence in laser rods

The results of numerical simulations based on finite-element methods for thermally induced birefringence in Nd:YAG crystal rods are compared with measurements and analytical solutions. A novel analytical solution for inhomogeneous pumping is presented. It is shown that the behavior of thermally induced birefringence is very sensitive to the pump geometry     

Synthesis and X-ray crystal structure of a bis-cyclometalated phosphorescent red-emitting iridium(III) complex

The synthesis of the bis-cyclometalated complex [{Ir(μ-Cl)(ccpz)₂}₂] (1, cppz = 1-chloro-4-(4-chlorophenyl)-phthalazine) from hydrated iridium(III) chloride and the ligand ccpz in refluxing ethoxyethanol is described. Compound 1 was characterized by spectroscopic means and the crystal structure was determined by X-ray crystallography. The absorption and emission spectra exhibit the new compound as a red-emitting phosphorescent complex.     

Preparation of highly dispersed gold nanoparticles inside the porous support assisted by amphiphilic vinyl maleate copolymer

An amphiphilic copolymer composed of maleic acid and alkyl (C₁₈) vinyl monomer was encapsulated into the porous support. A series of colloidal gold nanoparticles of known size was substantially immobilized in the composite porous supports based on cross-linked polyacrylate ester and cross-linked polystyrene resin. Maleic acid moiety of the amphiphilic copolymer can act as a stabilizer for gold nanoparticles in analogy to citric acid, whereas alkyl chains play a role for the stable accommodation of the amphiphilic copolymer. Maleic acid stabilizes the gold nanoparticles by flexing the geometrical arrangement of the linear polymer. Presence of C₁₈ alkyl chain in the poly(C₁₈-vinyl maleate) is indispensable to act as spacing group that prevents mutual aggregation of gold nanoparticles. On the other hand, gold nanoparticles with average diameter of less than 8 nm were spontaneously formed by treatment of the composite resin beads with aqueous HAuCl₄ solution, subsequently dispersed inside the pores of resin beads as observed by TEM. We have also elucidated the catalytic activity of the material with the hydrogenation of cinnamaldehyde in supercritical carbon dioxide. Notably, apparent size effect of gold was observed in the selectivity of the reaction.     

Advanced three-dimensional two-phase flow simulation tools for application to reactor safety (ASTAR)

This paper summarizes the cumulative work undertaken in the frame of the EU shared-cost action “ASTAR Project”—the current status and future perspectives in the field of advanced numerical simulation of three-dimensional two-phase flow processes. This 3-year running project, which started in September 2000, involves seven partner institutes from around Europe. Specific emphasis is given to the further development of characteristic-based upwind differencing (also called “hyperbolic”) numerical methods and their application to transient two-phase flow. The paper summarizes the common basis adopted for the physical and mathematical modelling of two-phase flow in the form of a single-pressure “two-fluid” model and the various numerical solution techniques developed by the partners. Several benchmark exercises are presented which have been used as verification and assessment procedures for comparing the different modelling and numerical approaches. Comments on the suitability, accuracy, numerical stability, algorithmic robustness and computational efficiency serve as indicators for the possible extension of these methods to future code development activities. Two further tasks of the ASTAR project dealt with the production of high quality experimental field data in the LINX facility of PSI, for the validation of CFD models for two-phase bubbly flow, and the coupling of a two-phase CFD module with a system code. Details of these tasks have been published separately, and will not be recalled in this paper.     

An introduction to speech and speaker recognition

Five approaches that can be used to control and simplify the speech recognition task are examined. They entail the use of isolated words, speaker-dependent systems, limited vocabulary size, a tightly constrained grammar, and quiet and controlled environmental conditions. The five components of a speech recognition system are described: a speech capture device, a digital signal processing module, preprocessed signal storage, reference speech patterns, and a pattern-matching algorithm. Current speech recognition systems are reviewed and categorized. Speaker recognition approaches and systems are also discussed     

美洲华人博物馆

<正>美洲华人博物馆(简称MOCA),占地1161.25m2(12500平方英尺),位于曼哈顿下城区,连接着传统中国城与当代新Soho和Nolita艺术界之间的文化鸿沟。美洲华人博物馆的落成标志着国家制度的发展,从当地一个     

Investigation of the degree of homogeneity and hydrogen bonding in PEG/PVP blends prepared in supercritical CO2: Comparison with ethanol-cast blends and physical mixtures

The degree of homogeneity and H-bond interaction in blends of low-molecular-mass poly(ethylene glycols) (PEG, M_w = 400, 600, 1000) and poly(vinylpyrrolidone) (PVP, M_w = 9 × 10³) prepared in supercritical CO₂, ethanol and as physical mixtures were studied by differential scanning calorimetry (DSC), Fourier-transform infrared (FTIR) spectroscopy and dynamic mechanical analysis (DMA) techniques. Homogeneity of samples prepared in supercritical CO₂ were greater than physically mixed samples, but slightly less than ethanol-cast samples. PEG-PVP H-bond interaction was higher for ethanol-cast blends when compared to blends prepared in supercritical CO₂. This reduced interaction was attributed to a combination of: (1) shielding of PEG-PVP H-bond interactions when CO₂ is dissolved in the blend; (2) rapidly reduced PEG and PVP chain mobility upon CO₂ venting, delaying rearrangement for optimum PEG-PVP H-bond interaction.