Comparison of fatty acid α-oxidation by rat hepatocytes and by liver microsomes fortified with NADPH,Fe3+ and phosphate

Rat liver microsomes, when fortified with NADPH, Fe³⁺ and phosphate, can catalyze the oxidative decarboxylation (α-oxidation) of 3-methyl-substituted fatty acids (phytanic and 3-methylheptadecanoic acids) at rates that equal 60–70% of those observed in isolated hepatocytes (Huang, S., Van Veldhoven, P.P., Vanhoutte, F., Parmentier, G., Eyssen, H.J., and Mannaerts, G.P., 1992,Arch. Biochem. Biophys. 296, 214–223). In the present study we set out to identify and compare the products and possible intermediates of α-oxidation formed in rat hepatocytes and by rat liver microsomes. In the presence of NADPH, Fe³⁺ and phosphate, microsomes decarboxylated not only 3-methyl fatty acids but also 2-methyl fatty acids and even straight chain fatty acids. The decarboxylation products of 3-methylheptadecanoic and palmitic acids were purified by highperformance liquid chromatography and identified by gas chromatography/mass spectrometry as 2-methyl-hexadecanoic and pentadecanoic acids, respectively. Inclusion in the incubation mixtures of glutathione plus glutathione peroxidase inhibited decarboxylation by more than 90%, suggesting that a 2-hydroperoxy fatty acid is formed as a possible intermediate. However, we have not yet been able to unequivocally identify this intermediate. Instead, several possible rearrangement metabolites were identified. In isolated rat hepatocytes incubated with 3-methylheptadecanoic acid, the formation of the decarboxylation product, 2-methylhexadecanoic acid, was demonstrated, but no accumulation of putative intermediates or rearrangement products was observed. Our data do not allow us to draw conclusions on whether the reconstituted microsomal system is representative of the cellular α-oxidation system. However, the results we obtained with [3-³H]-labelled fatty acids indicate that during α-oxidation in intact cells the hydrogen at carbon-3, which carries the methyl branch, is not attacked.     

Deformation of graphite at high pressures

In high pressure experiments, it is shown that the compression stress-strain curve of a porous polycrystalline graphite depends markedly on the confining pressure in the range 1–8 kb and that considerable volume changes occur during the deformation as well as during application of the pressure. There is also an almost complete recovery of both length and volume during release of the pressure after strains of up to 20 per cent. After allowing for the interaction with the stress-strain behaviour of the work associated with volume changes, it is concluded that, in addition to basal slip, frictional sliding on internal surfaces is an important mechanism of deformation, especially at the lower pressures, and that the deformation is accompanied by some process such as flexure of platelets which introduces the internal stresses responsible for the recovery effects.     

The energetic NeUtral Atom Detector Unit (NUADU) for China''s Double Star Mission and its calibration

An account is provided of an advanced Energetic NeUtral Atom Detector Unit (NUADU) designed for China's Double Star Mission. Special emphasis is given to describing the detector head of the instrument and its calibration.     

Polyacrylonitrile-based carbonized fibers and metal-carbonized fiber nanocomposites for thermal transport

This work examines the fabrication and thermal analysis of metal-carbon composite fibers prepared via an electrospinning process. The metal-carbon composite fibers of silver, copper, gold, and nickel were prepared by electrospinning of a composite solution of polyacrylonitrile (PAN) and metal precursor followed by heat treatment in air, nitrogen to 1000 degrees C and in 6% H2, respectively. Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), Energy dispersive spectroscopy (EDS) and Scanning thermal microscopy (SThM) were applied to characterize the metal-carbon fibers. TEM analysis showed a relatively uniform, contact-free distribution of the nanoparticles on the surface of the carbon fibers with size range of 3 nm-10 nm. Thermal analysis data showed an enhancement in the thermal conductivity of the nanomaterials when compared with the model PAN-based carbonized fibers. This was attributed to the incorporation of metal nanoparticles in the fiber matrix and on the surface.     

Tumor-targeted polydiacetylene micelles for in vivo imaging and drug delivery

In vivo tumor targeting and drug delivery properties of small polymerized polydiacetylene (PDA) micelles (～10 nm) is investigated in a murine MDA-MB-231 xenograft model of breast cancer. Three micelles with different surface coatings are synthesized and tested for their ability to passively target tumor through the enhanced permeability and retention effect. After injection (24 h), fluorescence diffuse optical tomographic imaging indicates a tumor uptake of nearly 3% of the injected dose for the micelles with a 2 kDa poly(ethylene glycol) (PEG)-coating (PDA-PEG2000). The uptake of PDA micelles in tumors is confirmed by co-localization with [(18) F]-fluorodeoxyglucose (FDG) positron emission tomography. Although FDG has a higher diffusion rate in tumors, 40 ± 19% of the retained micelles is co-registered with the tumor volume visualized by FDG. Finally, PDA-PEG2000 micelles are loaded with the hydrophobic anticancer drug paclitaxel and used in vivo to inhibit tumor growth. These findings demonstrate the potential of PDA-PEG2000 micelles for both in vivo tumor imaging and drug delivery applications.     

Enhanced fluorescence emission from quantum dots on a photonic crystal surface

Colloidal quantum dots display a wide range of novel optical properties that could prove useful for many applications in photonics. Here, we report the enhancement of fluorescence emission from colloidal quantum dots on the surface of two-dimensional photonic crystal slabs. The enhancement is due to a combination of high-intensity near fields and strong coherent scattering effects, which we attribute to leaky eigenmodes of the photonic crystal. By fabricating two-dimensional photonic crystal slabs that operate at visible wavelengths and engineering their leaky modes so that they overlap with the absorption and emission wavelengths of the quantum dots, we demonstrate that the fluorescence intensity can be enhanced by a factor of up to 108 compared with quantum dots on an unpatterned surface.     

Thin film deposition and microelectronic and optoelectronic devicefabrication and characterization in monocrystalline alpha and betasilicon carbide

The deposition of silicon carbide thin films and the associated technologies of impurity incorporation, etching, surface chemistry, and electrical contacts for fabrication of solid-state devices capable of operation at temperatures to 925 K are addressed. The results of several research programs in the United States, Japan and the Soviet Union, and the remaining challenges related to the development of silicon carbide for microelectronics are presented and discussed. It is concluded that the combination of α-SiC on α-SiC appears especially viable for device fabrication. In addition, considerable progress in the understanding of the surface science, ohmic and Schottky contacts, and dry etching have recently been made. The combination of these advances has allowed continual improvement in Schottky diode p-n junction, MESFET, MOSFET, HBT, and LED devices     

Silicon carbide UV photodiodes

SiC photodiodes were fabricated using 6 H single-crystal wafers. These devices have excellent UV responsivity characteristics and very low dark current even at elevated temperatures. The reproducibility is excellent and the characteristics agree with theoretical calculations for different device designs. The advantages of these diodes are that they will operate at high temperatures and are responsive between 200 and 400 nm and not responsive to longer wavelengths because of the wide 3-eV bandgap. The responsivity at 270 nm is between 70% and 85%. Dark-current levels have been measured as a function of temperature that are orders of magnitude below those previously reported. Thus, these diodes can be expected to have excellent performance characteristics for detection of low light level UV even at elevated temperatures