Controlling phosphonic acid substitution degree on proton conducting polyphosphazenes

This paper is to describe the development of a synthetic strategy for the preparation of phosphonic acid functionalized poly(aryloxyphosphazene) membranes with different substitution degree of phosphonic acid. Synthesized polymers have been characterized by standard spectroscopic techniques; FT-IR, ¹H, ³¹P and ¹⁹F NMR and element analysis. Proton conductivities of phosphonic acid substituted polymers have been investigated with impedance spectroscopy at different temperatures. Furthermore, the correlations of the proton conductivity and ion exchange capacity with the substitution degree of phosphonic acid have also been investigated. Thermal properties and water uptake properties of the polymers are also investigated. It is found that the proton conductivity and initial decomposition temperature of the polymers increases up to an appropriate amount of phosphonic acid substitution degree, which can be a useful PEM candidate for fuel cells.     

Isolation and identification of Treponema pedis and Treponema phagedenis-like organisms from bovine digital dermatitis lesions found in dairy cattle in Turkey

The isolation and identification of microorganisms associated with digital dermatitis (DD) in Turkish dairy cattle was investigated using punch skin biopsy samples from typical clinical lesions; they were collected from dairy farms and abattoirs in 5 different geographical locations in Turkey. Morphological characteristics and flagellation types were examined using a transmission electron microscope, and their enzyme profiles by enzyme activation kits; their catalase reaction characteristics were evaluated by the addition of 3% H₂O₂. Their phylogenies were identified using 16S rRNA and the results compared with known gene bank data. Bacterial cells were 5.0 to 18.2 µm long, 0.2 to 0.5 µm wide, and their minimum number of periplasmic flagellum was 4 (4:8:4) with a maximum of 8 (8:16:8). All isolates were catalase negative. Of the spirochetes isolated and identified, group I organisms showed close similarity with Treponema pedis (99% genetic homology), whereas those in group II were similar to Treponema phagedenis (98% homology). This is the first report of specific sub-groups of Treponema spp., isolated from Turkish dairy cattle presenting with DD lesions, being associated with this disease; these morphotypes were similar to those found globally in housed dairy cattle units and are probably significant microorganisms associated with the aetiopathogensis of this infectious disease causing acute bovine lameness. These results suggest that the distribution of DD-associated treponemes is not specific to particular geographic regions of Turkey.     

Modeling of Thermal Spalling During Electrical Discharge Machining of Titanium Diboride

Erosion in electrical discharge machining has been described as occurring by melting and flushing the liquid formed. Recently, however, thermal spalling was reported as the mechanism for machining refractory materials with low thermal conductivity and high thermal expansion. The process is described, here, by a model based on a ceramic surface exposed to a constant circular heating source which supplies a constant flux over the pulse duration. The calculations were based on TiB₂ mechanical properties along a and c directions. Theoretical predictions were verified by machining hexagonal TiB₂. Large flakes of TiB₂ with sizes close to grain size and maximum thickness close to the predicted values were collected, together with spherical particles of Cu and Zn eroded from cutting wire. The cutting surfaces consist of cleavage planes sometimes contaminated with Cu, Zn, and impurities from the dielectric fluid.     

Investigation of oxygen diffusion into contact lenses using electron spin resonance spectroscopy

Oxygen permeability is the most important parameter of contact lenses, as lack of oxygen causes corneal edema and threatens the vision of the patient. This study was unique in that it used an electron spin resonance (ESR) technique to determine the oxygen diffusion coefficient (D) of contact lenses. Although there are many methods and techniques for investigating oxygen diffusion into contact lenses, ESR was used for the first time in this study. The ESR technique is based on the scavenging of radicals produced in lenses by oxygen. As a contact lens is not a paramagnetic substance, it cannot give an ESR spectrum. But it does produce an ESR spectrum after γ irradiation. When a vacuum‐irradiated contact lens is exposed to air, the radicals trapped in the lens are transformed into peroxide radicals by the addition of molecular oxygen to the free radicals, and the ESR spectrum begins to change with time. This effect can be used as a tool to measure oxygen uptake in irradiated contact lenses. The oxygen diffusion coefficient of a contact lens was determined from changes in ESR signal intensity varying with time. The diffusion coefficients of oxygen for a contact lens were determined for rapid decay [(1.5 + 0.4) × 10^?8 cm²/s] and slow decay [(1.3 + 0.3) × 10^?9 cm²/s] in this study. These values are in agreement with the D values given in the literature for polymeric materials used for contact lenses. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2937–2941, 2006     

Avalanche breakdown in silicon devices for contactless logic testing and optical interconnect

A silicon p–n junction that is biased in avalanche breakdown mode emits visible light. Although the efficiency of such silicon emitters is poor, their ability to modulate at GHz frequencies make them a good choice for many applications including optical interconnect and optical contactless logic testing. Results demonstrate the feasibility of an all silicon optical interconnect system and an all silicon contactless testing methodology using the silicon light emitter and standard silicon detectors. The development of truly efficient silicon light emitting would enable many new applications.     

Comparison of effective doses from various monoenergetic particles based on the stylised and the VIP-Man tomographic models

This study compares the effective doses from a MIRD-type stylised model with those derived from the scaled-down version of the tomographic VIP-Man model for photon, electron, neutron and proton beams. The effective dose results from these two models show that they differ from each other within approximately 10% for common high-energy photon beams, within approximately 16% for neutrons, and within approximately 4% for high-energy proton beams. However, for low-energy protons and common electron beams, the effective doses can be different in >100%. It is concluded that the use of a single tomographic models will not improve the operational radiation protection dosimetry involving external beam exposures.     

Thermoluminescence properties of irradiated chickpea and corn

A study was carried out to establish a detection method for irradiated chickpea and corn by thermoluminescence (TL) method. The leguminous were packed in polyethylene bags and then the packets were irradiated at room temperature at different doses by ⁶⁰Co gamma source at 1, 4, 8 and 10 kGy. Minerals extracted from the leguminous were deposited onto a clean aluminum disc and TL intensities of the minerals were measured by TL. It was observed that the extracted samples from both leguminous exhibit good TL Intensity and the TL intensity of glow curves of them increased proportionally to irradiation doses. The TL glow curve of both irradiated leguminous presents a single broad peak below 400 °C. The TL trapping parameters glow peaks were estimated by the additive dose (AD), T_m(E_a)-T_stop and computerized glow curve deconvolution (CGCD) methods. The fading characteristics of glow curves were also recorded up to 6 months.     

Deep-collapse operation of capacitive micromachined ultrasonic transducers

Capacitive micromachined ultrasonic transducers (CMUTs) have been introduced as a promising technology for ultrasound imaging and therapeutic ultrasound applications which require high transmitted pressures for increased penetration, high signal-to-noise ratio, and fast heating. However, output power limitation of CMUTs compared with piezoelectrics has been a major drawback. In this work, we show that the output pressure of CMUTs can be significantly increased by deep-collapse operation, which utilizes an electrical pulse excitation much higher than the collapse voltage. We extend the analyses made for CMUTs working in the conventional (uncollapsed) region to the collapsed region and experimentally verify the findings. The static deflection profile of a collapsed membrane is calculated by an analytical approach within 0.6% error when compared with static, electromechanical finite element method (FEM) simulations. The electrical and mechanical restoring forces acting on a collapsed membrane are calculated. It is demonstrated that the stored mechanical energy and the electrical energy increase nonlinearly with increasing pulse amplitude if the membrane has a full-coverage top electrode. Utilizing higher restoring and electrical forces in the deep-collapsed region, we measure 3.5 MPa peak-to-peak pressure centered at 6.8 MHz with a 106% fractional bandwidth at the surface of the transducer with a collapse voltage of 35 V, when the pulse amplitude is 160 V. The experimental results are verified using transient FEM simulations.