271 research outputs found
IPS Observation System for Miyun 50m Radio Telescope and Its Acceptance Observation
Ground-based observation of Interplanetary Scintillation(IPS) is an important
approach of monitoring solar wind. A ground-based IPS observation system is
newly implemented on 50m radio telescope, Miyun station, National Astronomical
Observatories, Chinese Academy of Sciences(NAOC). This observation system is
constructed for purpose of observing the solar wind speed and scintillation
index by using the normalized cross-spectrum of simultaneous dual-frequency IPS
measurement. The system consists of a universal dual-frequency front-end and a
dual-channel multi-function back-end specially designed for IPS. After careful
calibration and testing, IPS observations on source 3C273B and 3C279 are
successfully carried out. The preliminary observation results show that this
newly developed observation system is capable of doing IPS observation.The
system sensitivity for IPS observation can reach over 0.3Jy in terms of IPS
polarization correlator with 4MHz bandwidth and 2s integration time.Comment: 8 pages, 7 figure
The influence of structural defects on intra-granular critical currents of bulk MgB2
Bulk MgB2 samples were prepared under different synthesis conditions and
analyzed by scanning and transmission electron microscopy. The critical current
densities were determined from the magnetization versus magnetic field curves
of bulk and powder-dispersed-in-epoxy samples. Results show that through a slow
cooling process, the oxygen dissolved in bulk MgB2 at high synthesis
temperatures can segregate and form nanometer-sized coherent precipitates of
Mg(B,O)2 in the MgB2 matrix. Magnetization measurements indicate that these
precipitates act as effective flux pinning centers and therefore significantly
improve the intra-grain critical current density and its field dependence.Comment: 4 pages, 4 figures, to be published in IEE Transactions in Applied
Superconductivit
Influence of sintering temperature and pressure on crystallite size and lattice defect structure in nanocrystalline SiC
Microstructure of sintered nanocrystalline SiC is studied by x-ray line profile analysis and transmission electron microscopy. The lattice defect structure and the crystallite size are determined as a function of pressure between 2 and 5.5 GPa for different sintering temperatures in the range from 1400 to 1800 degrees C. At a constant sintering temperature, the increase of pressure promotes crystallite growth. At 1800 degrees C when the pressure reaches 8 GPa, the increase of the crystallite size is impeded. The grain growth during sintering is accompanied by a decrease in the population of planar faults and an increase in the density of dislocations. A critical crystallite size above which dislocations are more abundant than planar defects is suggested
Phonon-induced electron relaxation in weakly-confined single and coupled quantum dots
We investigate charge relaxation rates due to acoustic phonons in
weakly-confined quantum dot systems, including both deformation potential and
piezoelectric field interactions. Single-electron excited states lifetimes are
calculated for single and coupled quantum dot structures, both in homonuclear
and heteronuclear devices. Piezoelectric field scattering is shown to be the
dominant relaxation mechanism in many experimentally relevant situations. On
the other hand, we show that appropriate structure design allows to minimize
separately deformation potential and piezolectric field interactions, and may
bring electron lifetimes in the range of microseconds.Comment: 20 pages (preprint format), 7 figures, submitted to Physical Review
Effect of the Coulomb interaction on the electron relaxation of weakly-confined quantum dot systems
We study acoustic-phonon-induced relaxation of charge excitations in single
and tunnel-coupled quantum dots containing few confined interacting electrons.
The Full Configuration Interaction approach is used to account for the
electron-electron repulsion. Electron-phonon interaction is accounted for
through both deformation potential and piezoelectric field mechanisms. We show
that electronic correlations generally reduce intradot and interdot transition
rates with respect to corresponding single-electron transitions, but this
effect is lessened by external magnetic fields. On the other hand,
piezoelectric field scattering is found to become the dominant relaxation
mechanism as the number of confined electrons increases. Previous proposals to
strongly suppress electron-phonon coupling in properly designed single-electron
quantum dots are shown to hold also in multi-electron devices. Our results
indicate that few-electron orbital degrees of freedom are more stable than
single-electron ones.Comment: 20 pages (preprint format), 7 figures, submitted to Phys. Rev.
Twin-induced plasticity of an ECAP-processed TWIP steel
The TWIP steels show high strain hardening rates with high ductility which results in high ultimate tensile strength. This makes their processing by equal channel angular pressing very difficult. Up to now, this has only been achieved at warm temperatures (above 200 °C). In this paper, a FeMnCAl TWIP steel has been processed at room temperature and the resulted microstructure and mechanical properties were investigated. For comparison, the material has also been processed at 300 °C. The TWIP steel processed at room temperature shows a large increase in yield strength (from 590 in the annealed condition to 1295 MPa) and the ultimate tensile strength (1440 MPa) as a consequence of a sharp decrease in grain size and the presence within the grains of a high density of mechanical twins and subgrains. This dense microstructure results also in a loss of strain hardening and a reduction in ductility. The material processed at 300 °C is more able to accommodate deformation and has lower reduction in grain size although there is a significant presence of mechanical twins and subgrains produced by dislocation activity. This material reaches an ultimate tensile strength of 1400 MPa with better ductility than the room temperature material.Postprint (published version
Mediator-free interaction of glucose oxidase, as model enzyme for immobilization, with Al-doped and undoped ZnO thin films laser-deposited on polycarbonate supports
Al doped and undoped ZnO thin films were deposited by pulsed-laser deposition on polycarbonate sheets. The films were characterized by optical transmission, Hall effect measurement, XRD and SEM. Optical transmission and surface reflectometry studies showed good transparency with thicknesses ∼100 nm and surface roughness of 10 nm. Hall effect measurements showed that the sheet carrier concentration was −1.44 × 1015 cm−2 for AZO and −6 × 1014 cm−2 for ZnO. The films were then modified by drop-casting glucose oxidase (GOx) without the use of any mediators. Higher protein concentration was observed on ZnO as compared to AZO with higher specific activity for ZnO (0.042 U mg−1) compared to AZO (0.032 U mg−1), and was in agreement with cyclic voltemmetry (CV). X-ray photoelectron spectroscopy (XPS) suggested that the protein was bound by dipole interactions between AZO lattice oxygen and the amino group of the enzyme. Chronoamperometry showed sensitivity of 5.5 μA mM−1 cm−2 towards glucose for GOx/AZO and 2.2 μA mM−1 cm−2 for GOx/ZnO. The limit of detection (LoD) was 167 μM of glucose for GOx/AZO, as compared to 360 μM for GOx/ZnO. The linearity was 0.28–28 mM for GOx/AZO whereas it was 0.6–28 mM for GOx/ZnO with a response time of 10s. Possibly due to higher enzyme loading, the decrease of impedance in presence of glucose was larger for GOx/ZnO as compared to GOx/AZO in electrochemical impedance spectroscopy (EIS). Analyses with clinical blood serum samples showed that the systems had good reproducibility and accuracy. The characteristics of novel ZnO and AZO thin films with GOx as a model enzyme, should prove useful for the future fabrication of inexpensive, highly sensitive, disposable electrochemical biosensors for high throughput diagnostics
- …