Er doped waveguide amplifiers written with femtosecond laser in germanate glasses

The authors report the fabrication and characterization of active waveguides in GeO₂–PbO–Ga₂O₃ glass samples doped with Er³⁺, written with a femtosecond laser delivering pulses of 150 fs duration at 1 kHz repetition rate. Permanent refractive index change was obtained and waveguides were formed under different laser pulse energies and scan velocities. The passive and active optical properties of the waveguides were investigated. The minimum value of propagation loss was of 4.8 dB/cm. Optical amplification at 1.5 μm under 980 nm excitation was observed showing a maximal internal gain of 2.7 dB/cm.     

Pheomelanin Effect on UVB Radiation-Induced Oxidation/Nitration of l-Tyrosine

Pheomelanin is a natural yellow-reddish sulfur-containing pigment derived from tyrosinase-catalyzed oxidation of tyrosine in presence of cysteine. Generally, the formation of melanin pigments is a protective response against the damaging effects of UV radiation in skin. However, pheomelanin, like other photosensitizing substances, can trigger, following exposure to UV radiation, photochemical reactions capable of modifying and damaging cellular components. The photoproperties of this natural pigment have been studied by analyzing pheomelanin effect on oxidation/nitration of tyrosine induced by UVB radiation at different pH values and in presence of iron ions. Photoproperties of pheomelanin can be modulated by various experimental conditions, ranging from the photoprotection to the triggering of potentially damaging photochemical reactions. The study of the photomodification of l-Tyrosine in the presence of the natural pigment pheomelanin has a special relevance, since this tyrosine oxidation/nitration pathway can potentially occur in vivo in tissues exposed to sunlight and play a role in the mechanisms of tissue damage induced by UV radiation.     

Methylmercury Causes Neurodegeneration and Downregulation of Myelin Basic Protein in the Spinal Cord of Offspring Rats after Maternal Exposure

Methylmercury (MeHg) is one of the most dangerous toxic pollutants spread throughout the earth. Chronic MeHg intoxication by contaminated food ingestion is the most common threat to human health, including impairment to the developing fetus. The present study aims at investigating the effects of maternal exposure to MeHg during gestation and lactation on the spinal cord of offspring. Pregnant rats received oral doses of MeHg (40 μg/kg/day) over a period of 42 days (21 gestation and 21 lactation). Control animals received the vehicle only. Total mercury concentration was measured in blood samples from offspring collected at the 41st postnatal day. Counting of motor neurons and immunoreactivity for myelin basic protein (MBP) were assessed in the spinal cords in both control and MeHg-intoxicated animals. Our results showed that MeHg promoted an increase in blood Hg levels. In addition, it caused a reduction in the number of spinal cord motor neurons as well as decreased MBP immunoreactivity in the cervical, thoracic and lumbar segments. Our present findings suggest that MeHg intoxication during rat pregnancy and lactation is associated with a pattern of motor neuron degeneration and downregulation of myelin basic protein in different segments of a developing spinal cord. Further studies are needed to establish the effect of MeHg intoxication in both young and adult rats.     

HPLC separation and wavelength area ratios of more than 50 phenolic acids and flavonoids

Relative retention times and wavelength area ratios for over 50 standard compounds were calculated using reverse-phase HPLC. The standard compounds analyzed included benzoic acids, cinnamic acids, benzene carboxylic acids, acetic acids, coumarins, benzaldehydes and a variety of flavonoid compounds including flavanones, flavones, isoflavones, and their glycosides. Each standard compound was chromatographed by three different gradient elutions. Compounds were detected by UV absorption at 254 nm and 280 nm. Relative retention times with respect to two different internal references and the 254nm: 280nm wavelength area ratio was determined for each standard. Soybean root and seed extracts were analyzed for the presence of the standard compounds using the chromatographic conditions described.     

The source of degradation during extrusion of polystyrene

The nature and magnitude of mechanical reactions of polystyrene in capillary flow has been examined in a model extrusion process. Studies on polystyrene quantify the sensitive increase in shear degradation tendency with increasing polymer molecular weight. A molecular weight spectrum caused by the shear stress profile was measured across the extrudate radius by the new technique of solvent coring. It was further determined that an appreciable fraction of the mechanical reaction is shear induced in the capillary reservoir. This is confirmed by precision determinations of molecular weights and distributions by gel permeation chromatography on samples taken from concentric layers in the capillary reservoir after 50% sample extrusion. These results, involving traces of oxygen as a chemical probe, describe the stress profile in the reservoir and in the capillary during the pressure extrusion of high molecular weight polystyrene. Thus, changes in molecular weight and distribution may be attributable to changes in different portions of the shear geometry rather than the uniform changes generally considered. Clear evidence is also presented showing the dramatic effects of oxygen on these shear-induced changes in molecular weight and distribution.     

De novo fatty acid synthesis and fatty acid elongation catalyzed by subcellular fractions from hog and human aorta

De novo synthesis and mitochondrial elongation of fatty acids have been demonstrated in subcellular fractions from hog and human aorta. Microsomal fatty acid elongation has been shown in hog aorta. The activity catalyzing the formation of fatty acids from acetyl and malonyl CoA was associated with a high molecular weight complex in the 6×10⁶g×min supernatant fraction. The principal product was palmitic acid. Some myristic and stearic acids were also formed. One elongation system was associated with protein which sedimented between 4500 g×min and 150,000 g×min. It used acetyl CoA but not malonyl CoA, and NADH was the preferred reducing agent. Radioactivity from acetyl CoA was incorporated into many fatty acids. In hog aorta a second elongation system was found associated with protein which sedimented at 6×10⁶ g×min. It used malonyl CoA preferentially as substrate and either NADH or NADPH as reducing agent.     

Metallic fast reactor fuel fabrication for the global nuclear energy partnership

Fast reactors are once again being considered for nuclear power generation, in addition to transmutation of long-lived fission products resident in spent nuclear fuels. This re-consideration follows with intense developmental programs for both fuel and reactor design. One of the two leading candidates for next generation fast reactor fuel is metal alloys, resulting primarily from the successes achieved in the 1960s to early 1990s with both the experimental breeding reactor-II and the fast flux test facility. The goal of the current program is to develop and qualify a nuclear fuel system that performs all of the functions of a conventional, fast-spectrum nuclear fuel while destroying recycled actinides, thereby closing the nuclear fuel cycle. In order to meet this goal, the program must develop efficient and safe fuel fabrication processes designed for remote operation. This paper provides an overview of advanced casting processes investigated in the past, and the development of a gaseous diffusion calculation that demonstrates how straightforward process parameter modification can mitigate the loss of volatile minor actinides in the metal alloy melt.