Search Results - (Author, Cooperation:T. H. Chang)

2015-03-04

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Acylation ; Animals ; Binding Sites ; Carboxylesterase/chemistry/*metabolism ; Drosophila Proteins/chemistry/*metabolism ; Esterases/chemistry/genetics/*metabolism ; Fatty Acids, Monounsaturated/metabolism ; Glycosylphosphatidylinositols/metabolism ; Glypicans/metabolism ; Humans ; Kinetics ; Ligands ; Mass Spectrometry ; Models, Molecular ; Protein Binding ; Wnt Proteins/*chemistry/*metabolism ; *Wnt Signaling Pathway

2013-05-15

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Angiosperms/*genetics ; DNA, Intergenic/genetics ; *Evolution, Molecular ; Gene Duplication/genetics ; Genes, Plant/genetics ; Genome, Plant/*genetics ; Models, Genetic ; Solanum/genetics ; Synteny/genetics ; Vitis/genetics

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

Generation of a uniform density plasma has been a key consideration in the design of microwave/plasma processing systems. A circularly polarized wave can generate a plasma with good azimuthal uniformity as well as provide strong resonant interaction with the plasma electrons. In this article, we report the development of a three-port polarization converter which efficiently converts the TE10 wave of a standard rectangular waveguide into a circularly polarized TE11 wave of a cylindrical waveguide. Employing the same principle for mode conversion, the converter is also made to function as a protective device of the high power microwave source by providing a separate port for the return and damping of the reflected wave. Such a converter has been analyzed, constructed, and tested. At the operating frequency of 2.45 GHz, test results indicate a 25 dB return loss, 97% end-to-end polarization conversion efficiency, and better than 20 dB rejection of the reflected wave. The structural simplicity of the device allows high power operation as well as easy construction for system research and applications. © 1999 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The energy distributions of electron emission from a Schottky emitter have been studied at tip temperatures from 1450 to 1800 K and angular current densities from 0.1 to 240 μA/sr. We have observed broadening of the energy distribution, with increase of angular current density and decrease of tip temperature, from 0.4 to 1.32 eV resulting from electron tunneling and electron–electron interaction. Good agreement between the experimental results and predictions from Monte Carlo simulation of the emission process is observed. © 1997 American Institute of Physics.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

A scanning soft x-ray microscope has been built and operated at the National Synchrotron Light Source. It makes use of a mini-undulator as a bright source of 3.2-nm photons. An electron beam fabricated Fresnel zone plate focuses the beam onto the specimen, which is scanned under computer control. The scanning stage can be moved by both piezoelectric transducers and stepping motors, and the location is monitored by a high-speed laser interferometer. X rays transmitted through the specimen are detected using a flow proportional counter. Images of biological specimens and of artificial microstructures have been made with resolution in the 75–100-nm range. Acquisition time for 256×256-pixel images is about 5 min.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

We have designed and fabricated a cryogenic scanning tunneling microscope for probing lithography defined nanometer-scale devices. The piezoelectric double tube is capable of scanning an area up to 22 μm×22 μm, while maintaining atomic resolution. In addition, the sample mount has a 5 mm×4 mm traveling range. Most importantly, the system is compact and, as a result, it can be inserted into the bore of a superconducting magnet. In this work, we demonstrate a unique application of scanning tunneling system, i.e., the scanning tip is in direct contact with the sample. The spectroscopic information therefore reflects the true characteristics of the devices under test, unlike the typical case where the tunneling barrier through vacuum imposes a large series resistance, on the order of 109 Ω. The design as well as the operation of this compact scanning tunneling microscope is described. © 2001 American Institute of Physics.

Electronic Resource

1365-2958

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Medicine

Host parasitism by Trichomonas vaginalis is complex and in part mediated by adherence to vaginal epithelial cells (VECs). Four trichomonad surface proteins bind VECs as adhesins, and AP65 is a major adhesin with sequence identity to an enzyme of the hydrogenosome organelle that is involved in energy generation. In order to perform genetic analysis and assess the role of AP65 in T. vaginalis adherence, we silenced expression of ap65 using antisense RNA. The gene for ap65 was inserted into the vector pBS-neo in sense and antisense orientations to generate plasmids pBS-neoS (S) and pBS-neoAS (AS), respectively. Trichomonads were then transfected with S and AS plasmids for selection of stable transfectants using Geneticin, and the presence of plasmid in transfectants was confirmed by polymerase chain reaction of the neo gene. Reverse transcription polymerase chain reaction and Northern blot analysis showed decreased amounts of ap65 transcript in AS transfected parasites. Growth kinetics of the antisense-transfected and wild type organisms were similar, suggesting that silencing AP65 did not affect overall energy generation for growth. Immunoblot analysis using monoclonal antibody (mAb) to AP65 of AS transfectants showed decreased amounts of AP65 when compared to wild type or S transfectants. Not unexpectedly, this corresponded to decreased amounts of AP65 bound to VECs in a functional ligand assay. Reduction in parasite surface expression of AP65 was related to lower levels of adherence to VECs by AS-transfectants compared to control organisms. Antisense silencing of ap65 was not alleviated by growth of trichomonads in high iron, which up-regulates transcription of ap65. Our work reaffirms the role for AP65 as an adhesin, and in addition, we demonstrate antisense RNA gene silencing in T. vaginalis to study the contribution of specific genes in pathogenesis.

Electronic Resource

0014-4827

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Medicine

Electronic Resource

0014-4827

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Medicine

Electronic Resource

0027-5107

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Medicine

Electronic Resource

0277-5387

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Chemistry and Pharmacology

Electronic Resource

1574-6968

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Trichomonas vaginalis is a flagellated, parasitic protozoan that inhabits the urogenital tract of humans. Some isolates of T. vaginalis are infected with a double-stranded RNA (dsRNA) virus, which was described in the literature as homogeneous icosahedral viral particles with an isometric symmetry and 33 nm in diameter. This study examined in detail the viral particles in T. vaginalis isolate 347 and describes a heterogeneous population of viral particles. The different dsRNA viruses were only observed after a change in the technique. The sample was prepared by the negative staining carbon-film method directly onto freshly cleft mica. The detected viruses ranged in size from 33 to 200 nm. Among the shapes observed were filamentous, cylindrical, and spherical particles. These results show that T. vaginalis may be a reservoir for several different dsRNA viruses simultaneously.

Electronic Resource

1432-0800

Springer Online Journal Archives 1860-2000

Energy, Environment Protection, Nuclear Power Engineering

Medicine

Electronic Resource

1573-4978

Springer Online Journal Archives 1860-2000

Biology

Electronic Resource

1434-4726

Springer Online Journal Archives 1860-2000

Medicine

Summary The proliferation rate of tumor cells is analysed by the proportion of cells in the S-phase of the cell cycle expressed as the labeling index. During DNA synthesis, regions of single-stranded DNA are exposed. As antinucleosid antibodies react specifically with single-stranded or denatured DNA, only the nuclei of cells in S-phase are immunreactive. Pretreatment with RNase avoids interference of unspecific RNA immunreactivity. The labeling index was determined in different head and neck cancer specimen by a bridge technique for antinucleosid antibody immunperoxidase or with a direct immunfluorescent staining. The rapid assessment of this immuno-chemical method in comparison to the conventional autoradiography seems to open a future application for determining the labeling index in the routine diagnosis in correlation to morphological structures of solid tumors.

Electronic Resource

1040-0397

Propylene carbonate ; Gamma-butyrolactone ; Impurities ; Lithium batteries ; Potentiometric sensors ; Chemistry ; Polymer and Materials Science

Wiley InterScience Backfile Collection 1832-2000

Chemistry and Pharmacology

This article deals with an experimental protocol developed to characterize reactive impurities that seriously compromise the utility of relatively insert solvents such as those discussed here. It was found that potentiometric sensors for hydrogen, silver(I), and copper(II) ions give Nernstian response over a broad activity range in solutions of widely differing buffer capacity in γ-butyrolactone (GBL), a promising but inadequately explored solvent for a variety of applications. Advantage was taken of the proper response of these sensors in applying the “ion probe method” described before to characterize impurities in both unpurified and purified γ-butyrolactone on the basis of their reactivities rather than their concentrations alone. The same sensors were also used in conventional potentiometric titrations of impurities in propylene carbonate (PC), a solvent that has been extensively used in fundamental studies of solute-solvent interactions as well as in the construction of commercial lithium batteries. The results of the potentiometric studies served as a guide in the design of appropriate gas chromatographic measurements. Three impurities not reported before were found in a reagent grade propylene carbonate: triethylamine and chloride ion, both at concentrations above 10-4 M, as well as 1,2-dibromopropane. The effectiveness of different purification procedures was studied.

6 Ill.

Electronic Resource