Piezoelectric properties of PVDF-conjugated polymer nanofibers

This study presents the development and characterization of PVDF-conjugated polymer nanofiber-based systems. Five different conducting polymers (CPs) were synthesized successfully and used to create the nanofiber systems. The CPs used are polyaniline (PANI), polypyrrole (PPY), polyindole (PIN), polyanthranilic acid (PANA), and polycarbazole (PCZ). Nanofiber systems were produced utilizing the Forcespinning® technique. The nanofiber systems were developed by mechanical stretching. No electrical field or post-process poling was used in the nanofiber systems. The morphology, structure, electrochemical and piezoelectric performance was characterized. All of the nanofiber PVDF/CP systems displayed higher piezoelectric performance than the fine fiber PVDF systems. The PVDF/PPY nanofiber system displays the highest piezoelectric performance of 15.56 V. The piezoelectric performance of the PVDF/CP nanofiber systems favors potential for an attractive source of energy where highly flexible membranes could be used in power actuators, sensors and portable, and wireless devices to mention some.     

Influence of the dispersion of Nanoclays on the cellular structure of foams based on polystyrene

In the present work blends of polystyrene (PS) with sepiolites have been produced using a melt extrusion process. The dispersion degree of the sepiolites in the PS has been analyzed by dynamic shear rheology and X-ray micro-computed tomography. Sepiolites treated with quaternary ammonium salts (O-QASEP) are better dispersed in the PS matrix than natural sepiolites (N-SEP) or sepiolites organo-modified with silane groups (O-SGSEP). A percolated network is obtained when using 6.0 wt% of O-QASEP, 8.0 wt% of N-SEP and 10.0 wt% of O-SGSEP. It has been shown that multiple extrusion processes have a negative effect on the polymer architecture. They produce a reduction in the length of the polymeric chains, and they do not lead to a better dispersion of the particles in the polymer matrix. Foams have been produced using a gas dissolution foaming process, where a strong effect of the dispersion degree on the cellular structure of the different foams was found. The effects on the cellular structure obtained by using different types of sepiolites, different contents of sepiolites and different extrusion conditions have been analyzed. The foams produced with the formulations containing O-QASEP present the lowest cell size and the most homogeneous cellular structures.     

Microwave-Assisted Reaction Sintering of Bismuth Titanate-Based Ceramics

Bismuth titanate-based ceramics, pure and doped with 5 mol% WO₃, were prepared by reaction-sintering using a microwave oven. High densities, ≥96% of theoretical density were achieved with very short thermal treatments, with soaking time ranging from 5 to 15 min. Relatively small platelet-like grains were formed, and microstructure seemed not to be strongly affected by doping nor soaking time. Electrical measurements were performed and, as expected, a decrease of electrical conductivity was observed in WO₃-doped materials. The results of reaction-sintered samples, both conventional as well as microwave sintered, are compared with those of samples prepared with previously calcined powders and sintered using microwaves as well as a conventional electric furnace.     

Effect-Size Indices for Dichotomized Outcomes in Meta-Analysis.

It is very common to find meta-analyses in which some of the studies compare 2 groups on continuous dependent variables and others compare groups on dichotomized variables. Integrating all of them in a meta-analysis requires an effect-size index in the same metric that can be applied to both types of outcomes. In this article, the performance in terms of bias and sampling variance of 7 different effect-size indices for estimating the population standardized mean difference from a 2 × 2 table is examined by Monte Carlo simulation, assuming normal and nonnormal distributions. The results show good performance for 2 indices, one based on the probit transformation and the other based on the logistic distribution. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acute endocarditis of the native aortic valve caused by Propionibacterium acnes

Propionibacterium acnes is often considered to be a contaminant but it has also been found to be the principal pathogen in serious infections. P. acnes is a rare cause of infective endocarditis. It has been suggested that aortic root abscesses are caused by bacteria that are particularly virulent. The strongest risk factor for serious infections by this bacteria is the presence of foreign bodies. A case is presented in which endocarditis of a native aortic valve caused by P. acnes was associated with an aortic root abscess. Transesophageal echocardiography is particularly helpful in the diagnosis of this severe complication of infective endocarditis. The literature for P. acnes endocarditis is reviewed.     

Ornament and function

The architects and builders in the past lacked our knowledge concerning fluid dynamics, but they exhibited a deep rooted ability to observe and reflect - thus, different cultures have developed by trial and error. The authors have produced a stimulating analysis which couples the science of fluid dynamics and a sensitive understanding of past cultures. The paper is recommended reading.     

Scene Graph and Frame Update Algorithms for Smooth and Scalable 3D Visualization of Simulated Construction Operations

One of the prime reasons inhibiting the widespread use of discrete-event simulation in construction planning is the absence of appropriate visual communication tools. Visualizing modeled operations in 3D is arguably the best form of communicating the logic and the inner working of simulation models and can be of immense help in establishing the credibility of analyses. New software development technologies emerge at incredible rates that allow engineers and scientists to create novel, domain-specific applications. The authors capitalized on a computer graphics technology based on the concept of the scene graph to design and implement a general-purpose 3D visualization system that is simulation and CAD-software independent. This system, the Dynamic Construction Visualizer, enables realistic visualization of modeled construction operations and the resulting products and can be used in conjunction with a wide variety of simulation tools. This paper describes the scene graph architecture and the frame updating algorithms used in designing the Dynamic Construction Visualizer.     

Transplantectomy today: indications and complications

Analysis of the indications for transplantectomy and its complications over a 12-year period. Over a total of 159 failure grafts, we performed 53 transplantectomies (33.3%). The percentage of complications was 16.9%. Three patients died (5.6%) during the more or less immediate post-operative period. In our experience, consistent and prolonged maintenance of immunosuppression should avoid the need for transplantectomy in a high percentage of grafts. Only 15 transplantectomies were made on 104 failure grafts after 6 months (14.4%). Our short but successful experience with embolization of 2 rejected grafts confirms the validity of this conservative alternative versus conventional surgical transplantectomy in selected cases.