Search Results - (Author, Cooperation:C. H. Chen)

2018-01-26

American Physical Society (APS)

0556-2821

1089-4918

Physics

General relativity, alternative theories of gravity

2018-06-23

BMJ Publishing

2044-6055

Medicine

Open access, Pathology

2018-05-18

Nature Publishing Group (NPG)

2045-2322

Natural Sciences in General

2012-03-31

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Brain Mapping ; Cerebral Cortex/*anatomy & histology/*metabolism ; Gene Expression ; *Genes ; Genetic Variation ; Humans ; Image Processing, Computer-Assisted ; Magnetic Resonance Imaging ; Male ; Middle Aged ; Phenotype ; Twins, Dizygotic/genetics ; Twins, Monozygotic/genetics

2015-07-16

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Alzheimer Disease/complications/prevention & control ; Animals ; Antibodies, Monoclonal/*immunology/*pharmacology/therapeutic use ; Antibody Affinity ; Axons/metabolism/pathology ; Brain/metabolism/pathology ; Brain Injuries/complications/metabolism/*pathology/*prevention & control ; Disease Models, Animal ; Epitopes/chemistry/immunology ; Female ; Humans ; Male ; Mice ; Phosphoproteins/antagonists & inhibitors/biosynthesis/immunology/toxicity ; Stress, Physiological ; Tauopathies/complications/metabolism/pathology/*prevention & control ; tau Proteins/*antagonists & ; inhibitors/biosynthesis/*chemistry/immunology/toxicity

2013-05-03

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Argonaute Proteins/*chemistry/*metabolism ; Breast Neoplasms/genetics/metabolism/mortality/pathology ; Cell Hypoxia/genetics/*physiology ; Cell Line, Tumor ; Cell Survival ; Female ; Gene Expression Regulation, Neoplastic ; Humans ; MicroRNAs/biosynthesis/chemistry/genetics/*metabolism ; Neoplasm Invasiveness ; Nucleic Acid Conformation ; Phosphorylation ; Phosphotyrosine/metabolism ; Prognosis ; Protein Binding ; RNA Precursors/chemistry/genetics/metabolism ; Receptor, Epidermal Growth Factor/*metabolism ; Ribonuclease III/metabolism ; Survival Analysis

2018-03-06

The American Association for Cancer Research (AACR)

1078-0432

1557-3265

Medicine

2018-03-06

The American Association for Cancer Research (AACR)

1078-0432

1557-3265

Medicine

2018-02-28

American Physical Society (APS)

1098-0121

1095-3795

Physics

Electronic structure and strongly correlated systems

1089-7550

AIP Digital Archive

Physics

Due to rapid progress in the development of high-power tunable visible lasers, it is expected that eye protection from tunable lasers in the open field will be needed in the near future. A nonlinear method is proposed that will transmit low-intensity light, but absorb light at high intensities. This high-intensity attenuator is based on the use of a liquid or solid made up of molecules having the property of undergoing two-photon photodissociation through most of the visible part of the spectrum. This material must also have the additional property that one of the products of the photodissociation is a one-photon absorber throughout the same wavelength region. It is suggested that the laser beam intensity can be attenuated by a large factor through these two-step absorption mechanisms, and that if the one-photon absorbing product is quenched by collisions with some component of the liquid in a time that is small compared with the laser pulse length, very large attenuation can be achieved from the built-up concentration of one-photon absorbers. Thus, the early part of a laser pulse is attenuated by two-photon absorption only, but the later parts of the pulse can be attenuated by factors as large as 105. Using a double-pass geometry, the leading edge of the pulse can be absorbed by linearly absorbing species formed on the first pass. The double-pass method, with an optical delay line, can even work well with picosecond pulses.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

InGaAs(P)/InP double heterojunction bipolar transistors have been successfully fabricated by inserting an n-type InGaAsP (Eg=0.95 eV) quaternary (0.1 μm, undoped) layer on either side of the base by liquid-phase epitaxy (LPE). As we know, it is the first time to grow this structure by LPE. These devices have been fabricated using a non-self-aligned technology. In this case it can improve the common-emitter current/voltage (IC /VCE) characteristics. Small signal current gain hfe about 100 and dc current gain hFE about 80 at IC=38 mA can be obtained. The ideality factor of emitter-base junction is 1.43.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Quantitative measurements of desorbed ions and neutral molecules by a quadruple mass spectrometer from laser ablation of Tl-Ca-Ba-Cu-O were obtained. The results indicate that more neutral atoms and molecules desorbed than the corresponding ions. More elementary ions desorbed than the corresponding oxide compounds.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Quantitative measurements of desorbed ions and neutral molecules by a mass spectrometer from laser ablation of Bi2Sr2CaCu2O8+x were obtained. The results indicate that more neutral atoms and molecules desorbed than the corresponding ions. The ratio of neutral atoms to ions decreases when the laser power density increases.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Partial substitution of light rare earths (LRE) for Sm in 2:17 magnets improves the remanence, maximum energy product and the loop squareness without affecting their Curie temperature and the temperature dependence of 4πMs. Uniform, single-phased microstructures were obtained for LRE substituted magnets after heat treatment. Heat treated metallographic specimens revealed striations on the etched surfaces parallel within each grain and perpendicular to the c axis of the magnet alloy.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

A newly developed Sb source, triisopropylantimony (TIPSb), has been successfully used to grow InSb and GaSb epilayers by atmospheric pressure organometallic vapor phase epitaxy (OMVPE). Both GaSb and InSb have been grown with excellent morphologies. Growth efficiencies indicate that there are no parasitic reactions between TIPSb and trimethylgallium (TMGa) or trimethylindium. For GaSb growth, the temperatures have been varied between 500 and 600 °C. V/III ratios close to unity are necessary to obtain the best morphologies at 600 °C. As the growth temperature is decreased, lower V/III ratios are required. This is because TMGa decomposition is incomplete and TIPSb decomposes completely at these temperatures. The GaSb layers grown at 500 °C have background hole concentrations of 2×1016 cm−3. Low-temperature photoluminescence (PL) measurements indicate that the acceptor is due to Sb vacancies rather than carbon acceptors. A major advantage of TIPSb is that it decomposes at temperatures much lower than that for trimethylantimony (TMSb). InSb with good morphologies can be grown using V/III ratios close to unity at temperatures as low as 430 °C. On the other hand, growth temperatures higher than 500 °C are necessary for the growth of InSb using TMSb with V/III ratios of close to 1. For temperatures lower than 430 °C, InSb can be grown using TIPSb, but higher V/III ratios are required due to incomplete TIPSb pyrolysis. The InSb epilayers have electron concentrations of about 5×1016 cm−3 at 77 K and low-temperature PL shows well-resolved exciton and acceptor-related peaks. These results indicate that TIPSb is a viable source for the OMVPE growth of Sb-containing III-V semiconductors.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

Two-photon cross sections of neat benzene and methyl substituted benzenes at various wavelengths for selective excitation were measured by two-photon induced fluorescence spectra for the first time. The results show that the two-photon rate increases rapidly with the frequency of the photon.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

In this article, we discuss parameters influencing (a) the properties of thin AlxGa1−xN layers grown by metalorganic chemical vapor deposition and (b) the electrical properties of the two-dimensional electron gas (2DEG) forming at the AlxGa1−xN/GaN heterojunction. For xAl〉0.3, the AlxGa1−xN layers showed a strong tendency towards defect formation and transition into an island growth mode. Atomically smooth, coherently strained AlxGa1−xN layers were obtained under conditions that ensured a high surface mobility of adsorbed metal species during growth. The electron mobility of the 2DEG formed at the AlxGa1−xN/GaN interface strongly decreased with increasing aluminum mole fraction in the AlxGa1−xN layer and increasing interface roughness, as evaluated by atomic force microscopy of the surfaces prior to AlxGa1−xN deposition. In the case of modulation doped structures (GaN/AlxGa1−xN/AlxGa1−xN:Si/AlxGa1−xN), the electron mobility decreased with decreasing thickness of the undoped spacer layer and increasing silicon doping. The electron mobility was only moderately affected by the dislocation density in the films and independent of the growth temperature of the AlxGa1−xN layers at xAl=0.3. For Al0.3Ga0.7N/GaN heterojunctions, electron mobility values up to 1650 and 4400 cm2/V s were measured at 300 and 15 K, respectively. © 1999 American Institute of Physics.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

Two-photon transitions have been examined in argon, krypton, xenon, and molecular hydrogen using a coherent vacuum ultraviolet (VUV) photon at a fixed wavelength of 118 nm and a tunable photon from a dye laser. The 118 nm VUV photon is produced by third harmonic generation in xenon using UV light at 355 nm from a frequency tripled Nd:YAG laser. Though the VUV intensity is very weak, (∼100 nJ per pulse) it was utilized very efficiently since most of VUV photons in the ionization region were absorbed. Spectra were obtained in the region of 12.5 to 13.5 eV and the corresponding two-photon rate constants were calculated. This is the first time that coherent VUV light has been employed with tunable visible light for the production of two-photon spectra and the measurement of two-photon rates. The two-photon ionization rate of xenon was measured using photons at fixed wavelengths of 118 and 355 nm. A new parameter is proposed for direct comparison of the data from various two-photon experiments.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We present studies of the compositional dependence of the optical properties of AlxGa1−xN(0〈x〈0.22) alloys by modulation spectroscopy and photoluminescence. The yellow luminescence, which is well known in GaN and is generally assigned to shallow donor–deep acceptor pair recombination has also been observed in AlxGa1−xN. As aluminum concentration increases, the color of the band changes from yellow (2.2 eV) to blue (2.6 eV). The shift was less than that of the band gap. Together with previously published studies, it implies that the deep acceptor level is pinned to a common reference level to both materials, thus the deep level responsible for the yellow emission is used as a common reference level to determine the band alignment in AlxGa1−xN/GaN heterojunctions. Combining with the near-band-edge modulation spectra, the estimated ratio of conduction-to-valence band discontinuity is 65:35. Our results are close to the values obtained from PL measurements on Al0.14Ga0.86N/GaN quantum wells and those calculated by linear muffin-tin orbital method and linearized augmented plane wave method. © 2001 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Optoelectronic properties of undoped ZnSe/ZnMgSSe multiple quantum wells (MQWs) grown by molecular beam epitaxy on (001) GaAs substrates have been investigated by photoluminescence, photoconductivity, and persistent photoconductivity (PPC) measurements. The features related to the band-to-band excitonic and impurity-related transitions of ZnSe/ZnMgSSe MQWs are observed and discussed. In addition, the parameters that describe the temperature dependence of the interband transition energy and broadening function of the excitonic feature are evaluated. PPC has been observed in undoped ZnSe/ZnMgSSe MQWs. The decay kinetics of the PPC effect can be described by a stretched-exponential function, Ippc(t)=Ippc(0)exp[−(t/τ)β], (0〈β〈1). Through the study of the PPC effect under various conditions, such as different temperature, different photon energy of photoexcitation, and different ZnSe well width, we identify that the carrier excitation from the defect level in ZnMgSSe barrier layer into the ZnSe well layer is the origin of the PPC effect in ZnSe/ZnMgSSe MQWs. © 2001 American Institute of Physics.

Electronic Resource