Miscibility and the specific interaction of polyhydroxybutyrate blended with polyvinylacetate and poly(vinyl acetate‐co‐vinyl alcohol) with some biological applications

Bacterially produced polyhydroxybutyrate (PHB) polymer has a lot of potential as an application for environmentally degradable plastics. We aimed in this study to blend PHB with the semicrystalline polymers poly(vinyl acetate) (PVAc) and poly(vinyl acetate‐co‐vinyl alcohol) (PACA) to obtain material with better physical properties. We investigated compatibility over a wide composition range using different techniques. Viscosity measurements were used to study polymer–polymer miscibility in dilute solutions with chloroform as cosolvent. The data is discussed according to the viscosity interaction parameters, which are treated as excess properties by similarity with those of real solutions. Dielectric investigations were carried out at different frequencies ranging from 100 Hz to 50 kHz. The obtained data indicated that more than one relaxation mechanism was present, which were ascribed to the rotation of the main chain and its related motions. A glass‐transition temperature composition diagram, IR spectroscopy, and a morphological investigation were also used to give more information about the compatibility of such blends. The results of this study indicate that PHB/PVAc is semicompatible, whereas PHB/PACA is compatible at least in the assayed composition range of hydrolysis. We also extended the study to carry out some biological activity investigations, which were tested against the representative number of pathogenic organisms with the disk diffusion method. The different compositions of the investigated blend were biologically active when compared with the individual polymers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2363–2374, 2002     

X-ray imaging with “edge-on” microchannel plate detector: first experimental results

A novel scanning slit X-ray imaging system based on an “edge-on” microchannel plate detector was developed and tested. Images were acquired at 50 kV(p) X-ray tube voltage with a limiting spatial resolution of 7 lp/mm. The pixel noise was measured to be 0.3 count/pixel/s for a 50×70 μm² pixel size. This photon counting detector can be considered to be virtually noise free.     

Effect of TiO2 nanotube parameters on field emission properties

The dependence of field emission properties of titanium dioxide (TiO(2)) nanotubes (NTs) has been studied as a function of NT diameter (D) and height (h), which varied in the ranges 18-500 nm and 500-12,000 nm, respectively. The studies showed a strong dependence of the field emission on these parameters. With an increase of NT diameter, the field enhancement factor increased monotonically from 120 to 3800; the current density also increased until D = 320 (current density ～ 3.8 mA cm( - 2)), with subsequent decrease for larger diameters. The field emission properties initially improved with NT height until h = 5 μm, and later remained unchanged with further increases in h.     

A numerical method for predicting intermetallic layer thickness developed during the formation of solder joints

A numerical, method has been developed for calculating the thickness of intermetallic layers formed in substrate-solder systems during the soldering process. As input, the method requires the temperature-time profile for the soldering process and the isothermal liquid state growth rate parameters for the growth of the intermetallic layer. These usually consist of a growth constant, k_o, and an activation energy, Q. The method allows one to predict the thickness of a layer at any time during the soldering process. As such, it can be used in industrial solder processing to enhance the reliability and lifetime of solder joints by allowing control of the thickness of intermetallic layers. The validity of the method is demonstrated for intermetallic growth between copper and 62Sn-36Pb-2Ag solder. The kinetic parameters for the chosen model system were experimentally determined and isothermal intermetallic layer growth between molten solder and copper was found to follow a t^0.25 dependence on time t. The growth rate increased with increasing temperature according to an Arrhenius dependence in the temperature range 187 to 258°C with Q = 7.04 kJ/mol and k_o = 7.75 μm/min^0.25.     

Some biophysical properties of castor oil esterified with some acid anhydrides

A series of castor oil adducts were synthesized by esterification of castor oil with acid anhydrides: phthalic, maleic and succinic anhydrides. The chemical structure of castor oil and the prepared adducts were characterized by means of IR and ¹H NMR spectroscopy. The number‐average and weight‐average molecular weights were measured by gel permeation chromatography. The electrical properties were studied through the permittivity, dielectric loss and conductivity measurements, which are considered to be in the range of electrical insulation. The electrical conductivity, which describes the ionic mobility of the systems, was found to be in the range of 10^–9 to 10^–12 S/cm. This indicates that castor oil and its esters could be used for antistatic applications. The viscosity η and the activation energy E_η, obtained from the dependency of viscosity on temperature using the Arrhenius equation, were found to increase with increasing molecular weight of the system. The effect of different concentrations of castor oil and its esters on the growth activities of the sugar beet pathogens R. solani and S. rolfsii was studied through the determination of percent germination, average length of hyphal extensions, dry mass yield and the production of sclerotia. The obtained data indicate that the esterification of castor oil with anhydrides improves the antifungal activity.     

CCD camera for dual-energy digital subtraction angiography

A motion immune dual-energy subtraction technique in which X-ray tube voltage and beam filtration were switched at 30 Hz between 60 kVp (2.0 mm Al filter) and 120 kVp (2.00 mm Al+2.5 mm Cu filter) was previously reported. In this study the effects of camera lag on the dual-energy iodine signal is investigated. The temporal lag of the lead oxide vidicon tested reduced the dual-energy iodine signal by a factor of 2.3, as compared to a mode that included 4 scrub frames between low- and high-energy images, for an iodine phantom with thicknesses of 0-86.0 mg/cm(2), imaged over a 15 cm thick Lucite phantom. On the other hand, the Charge-Coupled Device (CCD) camera has inherently no temporal lag and its versatile scanning characteristics make it near ideal for dual-energy DSA. The CCD camera eliminates the reduction of dual-energy iodine signal, since it does not mix low- and high-energy image data. Another benefit of the CCD camera is that the separation time between low and high-energy images is not limited to the frame period, as is the lead oxide vidicon; and as small as a 5-msec time difference is possible. The short time interval between low and high-energy images minimizes motion misregistration artifacts. Due to these advantages, the CCD camera significantly improves the utility of dual-energy DSA.     

A digital filtration technique for scatter-glare correction based on thickness estimation

In order to quantitate anatomical and physiological parameters such as vessel dimensions and volumetric blood flow, it is necessary to make corrections for scatter and veiling glare, which are the major sources of nonlinearities in videodensitometric digital subtraction angiography (DSA). A convolution filtering technique has been investigated to estimate scatter-glare distribution in DSA images without the need to sample the scatter-glare intensity for each patient. This technique utilizes exposure parameters and image gray levels to assign equivalent Lucite thickness for every pixel in the image. The thickness information is then used to estimate scatter-glare intensity on a pixel-by-pixel basis. To test its ability to estimate scatter-glare intensity, the correction technique was applied to images of a Lucite step phantom, anthropomorphic chest phantom, head phantom, and animal models at different thicknesses, projections, and beam energies. The root-mean-square (rms) percentage error of these estimates was obtained by comparison with direct scatter-glare measurements made behind a lead strip. The average rms percentage errors in the scatter-glare estimate for the 25 phantom studies and the 17 animal studies were 6.44% and 7.96%, respectively. These results indicate that the scatter-glare intensity can be estimated with adequate accuracy for a wide range of thicknesses, projections, and beam energies using exposure parameters and gray level information     

Scatter-glare estimation for digital radiographic systems: comparison of digital filtration and sampling techniques

The scatter and veiling glare distribution in images acquired with a digital subtraction angiography imaging system was estimated using a digital filtration and a beam-stop technique. The digital filtration technique utilizes exposure parameters and image gray levels to estimate scatter-glare intensity based on previous phantom measurements. The beam-stop technique uses an array of lead discs in order to sample scatter-glare intensity for each patient. To test the ability of digital filtration and beam-stop techniques to estimate the scatter-glare intensity, they were applied to images of postmortem swine animal models at different projections and beam energies. The systematic and root-mean-square (rms) percentage errors of these estimates were obtained by comparison to directly measured scatter-glare images using a scanning lead strip technique. The average rms percentage error for the digital filtration and beam-stop techniques were 8.07% and 6.67%, respectively. The changes in scatter-glare intensity due to contrast injection during coronary arteriography and ventriculography were also measured using the beam-stop technique. The maximum changes in scatter-glare intensities during coronary arteriography and ventriculography were 19 and 88%, respectively. The results indicate that the digital filtration technique is more suited for applications such as coronary arteriography and ventriculography where the iodinated contrast material significantly changes the scatter-glare intensity.