Search Results - (Author, Cooperation:G. Xiong)

2013-05-25

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2013-05-11

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Animals ; Communicable Diseases, Emerging/*transmission/*virology ; Humans ; Influenza A virus/*physiology ; Influenza in Birds/*transmission ; Influenza, Human/*virology

2013-01-26

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

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2012-11-03

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

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2014-12-24

Nature Publishing Group (NPG)

0028-0836

1476-4687

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Arabidopsis/*genetics/growth & development/*metabolism ; Arabidopsis Proteins/genetics/metabolism ; Cell Wall/*metabolism ; DNA, Plant/genetics/metabolism ; E2F Transcription Factors/metabolism ; Feedback ; Gene Expression Regulation, Developmental/genetics ; Gene Expression Regulation, Plant/*genetics ; Gene Regulatory Networks/*genetics ; Iron/deficiency ; Organ Specificity ; Promoter Regions, Genetic/genetics ; Reproducibility of Results ; Salinity ; Time Factors ; Transcription Factors/*metabolism ; Xylem/genetics/growth & development/metabolism

2013-12-18

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

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Cloning, Molecular ; Gene Expression Regulation, Plant ; Lactones/*antagonists & inhibitors/*metabolism ; Models, Biological ; Multiprotein Complexes/chemistry/metabolism ; Mutation/genetics ; Oryza/genetics/*metabolism ; Plant Growth Regulators/antagonists & inhibitors/*metabolism ; Plant Proteins/chemistry/genetics/*metabolism ; Proteasome Endopeptidase Complex/metabolism ; Protein Binding ; Proteolysis ; *Signal Transduction ; Ubiquitin/metabolism

1089-7550

AIP Digital Archive

Physics

Superconducting YBa2Cu3O7−δ thin films with Tc=89.5 K were deposited on MgLaAl11O19 (11¯0) substrates by pulsed laser deposition. X-ray diffraction patterns indicate that the YBa2Cu3O7−δ films were epitaxial films, with the c axis perpendicular to the substrate surfaces. Microstrip resonators of YBa2Cu3O7−δ thin films deposited on MgLaAl11O19 substrates were fabricated. The loaded quality factor of the resonator was 1007 at 77 K and 4.28 GHz. As a new substrate for high Tc oxide superconducting films, MgLaAl11O19 substrates are especially suitable for superconducting-microwave applications.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The effect of an electric field on GMR oxide films was studied in a MOSFET configuration where the gate dielectric was a layer of SrTiO3 epitaxially grown on an underlying layer of the manganate which served as the source/drain. The response of the manganate channel was studied for different gate voltages. The following significant features were observed. The peak resistance temperature shifted to lower temperature for both polarities of the field. The resistance change varied quadratically with the field indicating the dominance of strain or polarization effects. In dynamical studies of the system using the gate voltage as an excitation the system showed anomalous slowing down near the peak of the resistivity. These results are understood on the basis of a stress effect on the film due to electro-elastic effects in the SrTiO3 layer, which introduces a tensile stress in the manganate layer upon the application of a gate voltage. The anomalous slowing down of the system near the ferromagnetic phase transition suggests a strong coupling between the spins, transport and structural distortions in the system. © 1996 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

There are different models which to try to explain the transport properties of the manganese oxides in terms of magnetic polarons, Zener double exchange and Jahn-Teller distortions of the lattice which is temperature dependent. Using Rutherford backscattering techniques (2–3 MeV He ions) we are measuring the presence of lattice distortions by studying the angular scans in the channeling mode. The angular widths (FWHM) can be used to extract both dynamic and static displacements of the atoms from their equilibrium sites. The technique is extremely powerful in the sense that local uncorrected displacements as small as 0.01 A(ring) from the equilibrium position can be detected. The extraction of the physics from the data is relatively straight forward compared to other techniques such as XRD or neturon scattering. Using a variable temperature backscattering system at our center (one of three or four systems around the world) the angular width (FWHM) is found to exhibit a dramatic change with temperature increasing with decreasing temperature showing a possible correlation with both the transport and magnetic properties. The results suggest a decrease in the lattice disorder with reduced temperature far in excess of what one would predict on the basis of a simple Debye behavior. The reduction in the lattice disorder correlates very well with the resistance vs temperature dependence. A variety of manganese oxide epitaxial thin films grown by pulsed laser deposition have been studied and the data suggests a role for structural distortions in any mechanism to explain the transport properties of these materials. © 1996 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We have studied the magnetic and magnetotransport properties of oxygen deficient R0.67Sr0.33MnOz (R=Nd, Pr) films and have observed superparamagnetic behavior in these films. The superparamagnetism is indicated by (i) the increasing spread between zero field cooled (ZFC) and field cooled (FC) magnetization curves as temperature decreases, (ii) a sharp drop of the ZFC magnetization at low temperature, (iii) enhanced Curie–Weiss constant above the ferromagnetic temperature, and (iv) at low temperature a sharp drop of coercivity (Hc) with increasing temperature. These findings strongly suggest that all oxygen deficient manganites are magnetically inhomogeneous; i.e., ferromagnetic clusters exist. We estimate the spin cluster diameter to be 7–10 nm at low temperature (T〈30 K). We discuss a possible origin of the giant magnetoresistance effect based on the existence of spin clusters. © 1996 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Systematic magnetization and ferromagnetic resonance (FMR) measurements have been performed on thin-film samples of La0.67Ba0.33MnOz (TC∼340 K). It is found from the FMR data that as- grown films show broad lines whose width Γ increases to nearly 1 kOe as T reduced to 77 K. The increase roughly follows the increase in the magnetization suggesting magnetic inhomogeneity as the main cause for the rise in Γ. However, when films were properly annealed in O2, we obtained narrow lines (Γ∼200 Oe at 10 GHz). Γ was effectively independent of temperature and linearly dependent upon microwave frequency, both of which are strong signs that, we have succeeded in obtaining a uniform, homogeneous manganite sample. Having gotten a uniform material, we have measured the intrinsic properties of this system. © 1996 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

A novel giant magnetoresistance memory effect has been observed in epitaxial Nd0.7Sr0.3MnOz thin films which have previously been found to exhibit a linear increase in conductivity on first application of a magnetic field (B). Here we reported that the conductivity of the films depends not only on the applied field but also on the magnetic history. At T well below the temperature Tp where the zero-field resistivity has a peak, the film enters a high conductivity state [(ΔR/RB)(approximately-greater-than)103] upon application of a magnetic field which persists even when B is reduced to zero. The original "zero'' field state is not recovered until the sample is warmed to T∼Tp. Surprisingly, the dc magnetization exhibits only a weak irreversibility while the magnetoconductivity is markedly hysteretic. That is, while the remanent magnetization is small the remanent magnetic resistivity is 10−3 times the initial zero-field-cooled resistivity. A possible explanation based on a two-component model of semiconducting matrix with embedded shunting paths of ferromagnetic material will be presented. © 1996 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We report large-scale synthesis of silica nanowires (SiONWs) using an excimer laser ablation method. Silica was produced in the form of amorphous nanowires at a diameter of ∼15 nm and a length up to hundreds micrometers. The SiONWs emit stable and high brightness blue light at energies of 2.65 and 3.0 eV. The intensity of the emission is two orders of magnitude higher than that of porous silicon. The SiONWs may have potential applications in high-resolution optical heads of scanning near-field optical microscope or nanointerconnections in future integrated optical devices. © 1998 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Perfect epitaxial growth of superconducting YBa2Cu3O7−x thin films have been achieved on (100) SrTiO3, (110) SrTiO3, and (100) ZrO2 substrates using a modified planar dc magnetron sputtering system. The films exhibit zero resistances at 87–90 K with transition widths of about 2 K. The critical current density of 1.4×106 A/cm2 at 77 K so far has been measured on the (100) SrTiO3 substrate. The epitaxial orientation of the thin films was influenced by the substrate orientation, the substrate temperature, and the oxygen partial pressure. The quality of growth and the epitaxial orientation of the films were examined by electron channeling, x-ray diffraction, and reflection high-energy electron diffraction techniques. The preferential epitaxial orientation is discussed.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The magnetoresistance of epitaxial Nd0.7Sr0.3MnOδ thin films has been studied. A giant magnetoresistance, with more than 4 orders of magnitude change in resistance (−ΔR/RH(approximately-greater-than)106%), was obtained at ∼60 K and a magnetic field of 8 T. This giant magnetoresistance (GMR) ratio is about one order of magnitude larger than the highest value reported previously which was observed in La–Ca–Mn–O film. We have also obtained a large GMR ratio with −ΔR/RH(approximately-greater-than)3000% for H=5 T in an in situ Nd0.7Sr0.3MnOδ thin film, a much larger effect than the previous results in doped manganese oxide films in which a large GMR ratio was obtained only in postannealed samples. Our results also show that the GMR effect in these films can be strongly influenced by the thin-film preparation conditions. © 1995 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

In situ epitaxial growth of YBa2Cu3O7−x superconducting thin films on (100)BaF2 substrates has been successful by an off-axis dc planar magnetron sputtering method. The zero-resistance temperatures of these thin films are about 81–84 K with transition width of 1.5 K. The characteristics of the films were examined by x-ray diffraction, reflection high energy electron diffraction, Rutherford backscattering spectroscopy ion channeling techniques, and scanning electron microscopy. The experimental results suggest that BaF2 is a promising material as substrates or buffer layers for the epitaxial growth of high Tc superconducting thin films, especially in high frequency applications. Discussions on the heteroepitaxy of the YBCO/BaF2 system are propounded.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The influence of sample preparation on the resistivity and magnetoresistance (MR) behavior of doped manganese oxides has been studied. Two systems, Nd0.7Sr0.3MnO3−δ and La0.67Ba0.33MnO3−δ thin films, have been chosen for this study. The former has the largest reported MR ratio at 60 K and the latter has a large MR ratio at room temperature. Two processes, deposition at a high temperature and annealing at a high temperature, have opposite influences on the resistivity behavior of these films. The results suggest that oxygen stoichiometry and diffusion are important factors in causing the behavior observed in doped manganese oxide films. © 1995 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

A novel giant magnetoresistance memory effect has been observed in epitaxial Nd0.7Sr0.3MnOz thin films which have previously been found to exhibit a linear increase in conductivity on first application of magnetic field B. The resistivity of the films depends not only on the instantaneous applied field but also on the magnetic history of the sample. At T well below the temperature Tp, where the zero-field resistivity has a peak, the film enters a high-conductivity state (upon application of a magnetic field) which persists even when B is reduced to zero. The original "zero'' field state is not recovered until the sample is warmed to T∼Tp. Surprisingly, the dc magnetization exhibits only a weak irreversibility while the magnetoconductivity is markedly hysteretic. A possible explanation is proposed. © 1995 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We report measurements of 1/f electrical noise in two hole doped manganite perovskite oxides, La0.67Ca0.33MnO3 and Pr0.67Sr0.33MnO3, which exhibit colossal magnetoresistance. The noise magnitude represented by the Hooge parameter is nearly 8 orders of magnitude larger than that observed in ordinary metals (and semiconductors) and nearly 5–6 orders of magnitude larger than that observed in epitaxial films of the perovskite oxide YBa2Cu3O7 in the normal state. The normalized noise spectral density increases with decreasing temperature below the resistivity peak, suggestive of the presence of additional low energy noise processes in the ferromagnetic metallic state. © 1996 American Institute of Physics.

Electronic Resource