A Setup for Studying Electroluminescence in Gaseous Xenon

Instruments and Experimental Techniques - A laboratory experimental setup based on an electroluminescent chamber with gaseous xenon at room temperature and a pressure of 6 atm is described. It is...     

Stripline bandpass filters with step-impedance resonators

Research results for stripline bandpass filters with step-impedance resonators formed on Al₂O₃ (Alumina, polycor) and operating in the frequency band 1500–2500 MHz are presented in this article. Use of step-impedance resonators breaks repetition factor in frequency positioning of passbands in such filters. This allows suppressing harmonics of output signal in transmitters and widening stopband for parasitic signals in receivers.     

Preparation and Properties of Hydroxyapatite Strengthened with a Glass Phase

A method is described for preparing hydroxyapatite strengthened with a glass phase. The properties of the composites obtained containing both biological and synthetic hydroxyapatite are studied. Characteristics of the test materials such as pycnometric density, volumetric porosity, biological solubility, and mechanical strength are determined.     

Enhanced biosurfactant production by <Emphasis Type="Italic">Corynebacterium alkanolyticum</Emphasis> ATCC 21511 using self-cycling fermentation

Enhanced biosurfactant production by Corynebacterium alkanolyticum ATCC 21511 was accomplished in a self-cycling fermenter (SCF) on a hexadecane substrate. The phospholipid biosurfactant produced during each cycle could be monitored rapidly using fluorescence spectroscopy. By optimizing the cycling pattern of the SCF, significantly better yields of biosurfactant were obtained than previously reported for this microorganism. It was also possible to virtually eliminate the hydrocarbon residue in the product. Harvest concentrations of 1.9 g L⁻¹ were obtained by using a two-stage fermentation. The first step was the growth of C. alkanolyticum in an SCF to yield a harvest of synchronous cells. These cells were transferred to a second vessel for the production stage. The concentration of biosurfactant could be further increased to 2.7 g L⁻¹ by the addition of more hexadecane at the beginning of the second stage.     

Effects of low levels of methacrylic acid on the swelling behavior of poly(2-hydroxyethyl methacrylate)

The effects of low levels of methacrylic acid (MAA) (less than 4 mol %) and a crosslinker (less than 0.3 mol %) on the equilibrium swelling and water content of poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogels were investigated. Numerous pHEMA disks, some of which were doped with small amounts of MAA, were placed in swelling baths simulating possible urological as well as physiological conditions. Several interesting facts are reported, such as, in dilute urea (0.15M) or in alkali solution, gels containing 2% MAA are capable of swelling to 3600% their size in mild acid, saline, or distilled water, with associated water contents that range as high as 98%. Also, gels containing small amounts of MAA and finite crosslinker content can be made that are soluble in mild urea or alkali solution. The significance of this study is that gels or gel surfaces can be fabricated that are highly responsive to their environment. In addition, since the level of MAA that cause this shrink–swell behavior are well within the impurity levels of MAA found in unpurified commercial HEMA, it is conceivable that this shrink–swell behavior may have occurred in early studies of implanted pHEMA gels, thus confusing the subsequent evaluation of its performance as a biomaterial.     

Nature and thermal stability of radiation-induced defects in zirconium hydride

Atomic Energy - The authors wish to thank V. I. Shcherbak for great help in the electron-microscope investigations.     

Thermally Pretreated 46% Pt/Vulcan XC72: Characterisation by TGA/DSC/TEM and Cyclic Voltammetry

We report a study of thermal stability and impact of thermal pretreatment procedures for 46% Pt/Vulcan XC72 (Tanaka) fuel cell catalyst. Stability in air and in inert gas (nitrogen, argon, helium) has been investigated by thermal gravimetric analysis (TGA), TGA‐mass spectrometry (TGA‐MS) and differential scanning calorimetry (DSC). Two distinct low temperature mass loss processes (100–200 and 285–300 °C) were observed, each exhibiting unique pretreatment temperature dependencies. TGA‐MS data in helium show fragment ions that suggest the thermal degradation processes are associated with decomposition of materials such as processing aids. Transmission electron microscopy (TEM) reveals a modest increase in average Pt nanoparticle size upon thermal pretreatment. After a pretreatment protocol based on TEM and thermal characterisation (300 °C/15 min, N₂), the electrochemically active surface area did not increase. At the kinetically controlled potential region (E >0.8 V) there was a small drop in current density for treated 46% Pt/C in comparison with as‐received catalyst. The slowing in ORR kinetics is significant. Apparently, the removal of organic components, which would improve mass transport, is negated by increased nanoparticle size.