Volume contraction on photoexcitation of the reaction center from Rhodobacter sphaeroides R-26: internal probe of dielectrics

Reaction centers of Rhodobacter sphaeroides undergo a approximately 20 A3/mole volume contraction in < 50 ns after excitation. The rapid volume change is tentatively assigned to electrostriction. From its magnitude, we infer that the effective dielectric coefficient is 10-15 if the compressibility of the reaction center is similar to that of globular proteins. The volume contraction is not sensitive to replacement of the natural ubiquinone at the QA site by other quinones or to the occupancy of the QB site. The quenching caused by pressure on the reaction centers most likely occurs on a faster time scale than that of electron transfer.     

Effects of Thermal Annealing and Pulsed Photon Processing on the Magnetomechanical Properties of the Amorphous Fe<Subscript>79.3</Subscript>P<Subscript>18.2</Subscript>V<Subscript>2.5</Subscript> Alloy

The effects of thermal annealing and pulsed photon processing on the structural transformations, ΔE effect, and internal friction in the amorphous Fe_79.3P_18.2V_2.5 alloy are studied. The results demonstrate that annealing and pulsed irradiation in a magnetic field have a significant influence on the magnetomechanical properties of the alloy, whereas pulsed irradiation in zero magnetic field has little effect on these properties. The irradiation effect is shown to depend on the structural transformations of the alloy at temperatures far below its crystallization temperature.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 7, 2005, pp. 823–827.Original Russian Text Copyright © 2005 by Braun, Vavilova, Ievlev, Kalinin, Kovneristyi, Palii, Perov, Serbin.     

Performance of thermal barrier coatings on γ‐TiAl

The current development of new generation gamma titanium aluminides is expected to result in alloy chemistries and microstructures capable of operating at temperatures in excess of 850 °C. Under these conditions, environmental and thermal protection becomes a concern since oxidation might eventually limit the maximum service temperatures achievable. Therefore protective coatings are necessary to exploit the full potential of gamma titanium aluminides at moderately elevated temperatures; however, as yet no coating system tested has proven sufficient performance for long‐term use in automotive and aerospace applications. Thermal barrier coatings (TBCs), typically applied to nickel‐based alloys, offer the potential to increase the service temperature of components by lowering the metal surface temperature in combination with cooling systems. The paper is focussed on development of thermal barrier coatings for gamma titanium aluminides. Different coatings were used for oxidation protection and bond coat application. Substrate specimens were either pre‐oxidized or coated with PVD‐Al₂O₃, TiAlCrYN, or diffusion aluminides. Yttria‐stabilized zirconia TBCs were deposited applying electron‐beam physical vapour deposition. Cyclic and quasi‐isothermal oxidation tests were carried out at 900 °C in air. Post‐oxidation analysis of the coating systems was performed using scanning electron microscopy with energy‐dispersive X‐ray spectroscopy. Zirconia top coats offer a promising thermal protection concept to be applied on γ‐TiAl components. However, high oxidation resistance has to be supplied by protective coatings. Diffusion layers of the TiAl₃ aluminide provided excellent environmental protection because of the formation of a continuous alumina scale. No spallation of the thermal barrier coatings was observed on aluminized specimens during 1000 1‐h cycles and 3000 h of cyclic and isothermal oxidation testing, respectively.     

Controlled free‐radical polymerization of vinyl chloride

Owing to the importance of poly(vinyl chloride) (PVC) as the second‐largest plastic in volume after the polyolefins and above styrene polymers, the control of the free‐radical polymerization of vinyl chloride (VC) is of high industrial and academic interest. But still the term “controlled” polymerization is not yet clearly defined. Often it is used for quasi‐living polymerizations with equilibrium reactions in the initiation and/or termination step or for the control of the molecular weight distribution (MWD), but it can also be applied to several structural aspects such as stereochemistry, branching, or special technical properties. In the present article, the control of chain growth and chain transfer is discussed. It has been well known for many years that the propagation step in the VC polymerization is terminated to a large degree by the rather frequent and temperature‐dependent chain transfer of the growing macromolecules to the monomer. Therefore, the degree of polymerization is strongly governed by the polymerization temperature. However, this transfer step does not result in a controlled or a narrow MWD. By means of free‐radical nitroxide‐mediated polymerization of VC in suspension, PVC with a narrower MWD can be obtained also at higher polymerization temperatures. The resulting PVC with nitroxide end groups can act as a macro‐initiator for various monomers, resulting in two‐block copolymers, which are, e.g., interesting compatibilizers in blends with PVC. J. VINYL ADDIT. TECHNOL., 11:86–90, 2005. © 2005 Society of Plastics Engineers     

Electrophysiologic changes in preterm neonates: auditory brain stem response and distortion product otoacoustic emissions

The purposes of this investigation were to determine 1) if auditory peripheral maturity is present in the newborn; 2) if not, at what age maturational changes occur in the peripheral auditory system from preterm to full-term; and 3) how results of tests used to identify auditory dysfunction in neonates, such as distortion product otoacoustic emissions (DPEs) and auditory brain stem responses (ABRs), change during this period. Longitudinal DPE amplitude and ABR wave I latency measurements were obtained from a single ear of 18 preterm neonates. The DPEs were evoked at f2s of 2, 3, 4, and 5 kHz. The longitudinal data revealed that in general, DPE amplitude increased and ABR wave I latency decreased as a function of postconceptional age. These findings suggest that 1) the peripheral auditory system has not reached maturity in the preterm neonate; 2) maturational changes continue from preterm to full-term; and 3) these changes are reflected in ABR and DPE measurements.     

Alternative medicine instruction in medical schools and family practice residency programs

Mutations in the gene encoding neural cell adhesion molecule L1 (L1CAM) are involved in X-linked hydrocephalus (HSAS, hydrocephalus due to stenosis of the aqueduct of Sylvius), MASA syndrome (mental retardation, aphasia, shuffling gait, and adducted thumbs), and spastic paraplegia type 1. We examined the L1CAM mutation in a Japanese family with HSAS for the purpose of DNA-based genetic counseling. The proband was a 9-year-old boy who had a 1-bp deletion in exon 22 of the L1CAM gene. This resulted in a shift of the reading frame, and introduction of a premature stop codon. Translation of this mRNA will create a truncated protein without the transmembrane domain, which cannot be expressed on the cell surface. Magnetic resonance images (MRI) revealed markedly enlarged lateral ventricles, hypoplastic white matter, thin cortical mantle, agenesis of the corpus callosum and septum pellucidum, and a fused thalamus. These findings represented impaired L1CAM function during development of the nervous system with resultant adhesion between neurons, neurites outgrowth and fasciculation, and neural cell migration. Screening by Apa I digestion of polymerase chain reaction (PCR) products identified the mother and the younger sister as heterozygous carriers. The carriers were asymptomatic. The father and the other sister did not have the mutation. The identification of L1CAM mutation in families with HSAS will give them the opportunity for DNA-based counseling and prenatal diagnosis.     

Identification of a steroidogenic neurohormone in female mosquitoes

In the female mosquito, Aedes aegypti, neurohormones are released from the brain in response to a blood meal and stimulate the ovaries to secrete ecdysteroid hormones, which modulate yolk protein synthesis in the fat body. Neuropeptides with this bioactivity were isolated from head extracts, and partial sequences from these peptides when aligned gave a 31-residue sequence at the amino terminus. Oligonucleotide primers for this sequence were used to amplify with the polymerase chain reaction a genomic DNA product that hybridized to a clone from a head cDNA library. The cDNA encodes a 149-residue preprohormone that is processed into an 86-residue peptide, as indicated by the mass value obtained from the native peptide, with the expected amino-terminal sequence. After modification, the cDNA for the putative neurohormone was expressed in a bacterial system, and the purified peptide had high specific activity in bioassays, thus confirming that it is a steroidogenic gonadotropin, the first to be identified for invertebrates.