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Hu, M.

Publications and source records attributed to Hu, M..

28 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Investigation of catalytic pathways and separations for lignin breakdown into monomers and fuels

An analysis of the energy and material consumption for three different lignin conversion pathways has been carried out in order to assess their relative promise. Recommendations to allow for improved performance based on the current state of the art have been made, with particular focus on the use of heterogeneous nanocatalysts. Lignin is currently burned for heat and power in industrial processes, but its aromaticity and high energy content make it a good source for fuels and chemical feedstocks. The conversion of lignin to value added products has been the subject of a number of excellent reviews, and it is upon this literature as well as recent publications that the processes were selected. The analysis includes consideration of the thermodynamics of conversion, the technical feasibility of each process, and the energy and material balance. For each of the processes, improvements to future research activities have been suggested to move the processes from the bench-scale to large-scale demonstrations. This analysis is not meant to be comprehensive, in terms of process, feedstock, or selected criteria. However, this work illustrates a path forward following pre-established goals of thermodynamic efficiency, selectivity, and feasibility.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Facile synthesis of air-stable Prussian white microcubes via a hydrothermal method

Research highlights: {yields} We have synthesized Prussian white microcubes in large quantities by a facile hydrothermal method for the first time. {yields} It is the first report about air-stable PW. {yields} The shape of crystals strongly depended on the concentration of K{sub 4}[Fe(CN){sub 6}], the hydrothermal temperature and the reaction duration. {yields} A layer-by-layer growth mechanism was proposed to explain the formation of PW microcubes. -- Abstract: Air-stable Prussian white (PW) microcubes were fabricated by the slow dissociation of K{sub 4}[Fe(CN){sub 6}] under hydrothermal condition without the protection of inert atmosphere. Moessbauer spectra and Fourier transform infrared (FT-IR) spectrum were used to characterize the composition of PW. X-ray diffraction (XRD) identified the obtained PW was monoclinic, and the purity was high. Scanning electron microscopy (SEM) images indicated the cubes were composed by solid cubes and hollow cubes. The shape of crystals strongly depended on the concentration of K{sub 4}[Fe(CN){sub 6}], the hydrothermal temperature as well as the reaction duration. The lower concentration and lower temperature resulted in perfect cubic crystals, while the higher concentration or the higher temperature resulted in irregular cubic crystals. After exposing in air for 2 months, no oxidation of PW occurred. To explain the formation of the PW microcubes, a layer-by-layer growth mechanism was put forward based on the low dissociation rate of K{sub 4}[Fe(CN){sub 6}]. The partially solubility of PW in water caused the formation of hollow cubes.

36 MATERIALS SCIENCE↗
NASA NTRS1992

V-band pseudomorphic HEMT MMIC phased array components for space communications

Recent advances in pseudomorphic high-electron-mobility transistor (PMHEMT) monolithic microwave integrated circuit (MMIC) technology have made it the preferred candidate for high performance millimeter-wave components for phased array applications. The development of V-band PMHEMT/MMIC components including power amplifiers and phase shifters is described. For the single-stage MMIC power amplifier employing a 200 micron PMHEMT, we achieved 151.4 mW output power (757.0 mW/mm) with 1.8 dB associated gain and 26.4 percent power-added efficiency at 60 GHz. A two-stage MMIC amplifier utilizing the same devices demonstrated small-signal gain as high as 15 dB at 58 GHz. And, for the phase shifter, a four-bit phase shifter with less than 8 dB insertion loss from 61 to 63 GHz was measured.

Lan, G. L.↗
NASA NTRS1992

Utilization of peptide carrier system to improve intestinal absorption: targeting prolidase as a prodrug-converting enzyme

The feasibility of targeting prolidase as a peptide prodrug-converting enzyme has been examined. The enzymatic hydrolysis by prolidase of substrates for the peptide transporter L-alpha-methyldopa-pro and several dipeptide analogues without an N-terminal alpha-amino group (phenylpropionylproline, phenylacetylproline, N-benzoylproline, and N-acetylproline) was investigated. The Michaelis-Menten parameters Km and Vmax for L-alpha-methyldopa-pro are 0.09 +/- 0.02 mM and 3.98 +/- 0.25 mumol/min/mg protein, respectively. However, no hydrolysis of the dipeptide analogues without an N-terminal alpha-amino group is observed, suggesting that an N-terminal alpha-amino group is required for prolidase activity. These results demonstrate that prolidase may serve as a prodrug-converting enzyme for the dipeptide-type prodrugs, utilizing the peptide carrier for transport of prodrugs into the mucosal cells and prolidase, a cytosolic enzyme, to release the drug. However, a free alpha-amino group appears to be necessary for prolidase hydrolysis.

NASA Discipline Regulatory Physiology↗
NASA NTRS1991

Millimeter-wave pseudomorphic HEMT MMIC phased array components for space communications

Recent advances in pseudomorphic HEMT MMIC (PMHEMT/MMIC) technology have made it the preferred candidate for high performance millimeter-wave components for phased array applications. This paper describes the development of PMHEMT/MMIC components at Ka-band and V-band. Specifically, the following PMHEMT/MMIC components will be described: power amplifiers at Ka-band; power amplifiers at V-band; and four-bit phase shifters at V-band. For the Ka-band amplifier, 125 mW output power with 5.5 dB gain and 21 percent power added efficiency at 2 dB compression point has been achieved. For the V-band amplifier, 112 mW output power with 6 dB gain and 26 percent power added efficiency has been achieved. And, for the V-band phase shifter, four-bit (45 deg steps) phase shifters with less than 8 dB insertion loss from 61 GHz to 63 GHz will be described.

Lan, G. L.↗
NASA NTRS1990

Low dark current photovoltaic multiquantum well long wavelength infrared detectors

The authors have, for the first time, demonstrated photovoltaic detection for an multiple quantum well (MQW) detector. With a blocking layer, the MQW detector exhibits Schottky I-V characteristics with extremely low dark current and excellent ideality factor. The dark current is 5 times 10(exp -14) A for an 100x100 square micron 10 micron detector at 40 K, 8 to 9 orders of magnitude lower than that of a similar 10 micron MQW detector without blocking layer. The ideality factor is about 1.01 to 1.05 at T = 40 to 80 K. The measured barrier height is consistent with the energy difference between first excited states and ground states, or the peak of spectral response. The authors also, for the first time, report the measured effective Richardson constant (A asterisk asterisk) for the GaAs/AlGaAs heterojunction using this blocking layer structure. The A asterisk asterisk is low approx. 2.3 A/sq cm/K(exp 2).

Wu, C. S.↗