[en] Nanometer-sized PbS particles in the size of about 3 nm produced by exposing a self-assembled monolayer of 11-mercaptoundecanoic acid salts on gold (111) substrate in a H₂S atmosphere were studied by scanning tunneling microscopy (STM) and high-resolution transmission electron microscopy at room temperature in air. The stability of thus-obtained PbS nanoparticles makes STM imaging possible and repeatable scans of the semiconductor nanoparticles were performed. The current-voltage (I--V) characteristics of a single PbS nanoparticle exhibited clearly Coulomb blockade and Coulomb staircase. Furthermore, by varying the gap between a STM tip and the PbS nanoparticle, we also verified the dependence of staircase width on the change of the gap in the local I--V characteristics on the same PbS nanoparticle. The phenomena can be well described by a semi-classical double-barrier tunneling model. copyright 2001 American Institute of Physics

[en] Image reconstruction of 3D cone-beam tomography using the FDK algorithm requires huge computational resource. The reconstruction of a high resolution 3D object would usually take a long time, which is intolerable in real applications. Parallel computing using cluster systems is one of the common approaches to solve this problem. The mixed model with both MPI and Pthreads is used to parallelize the FDK algorithm on a SMP cluster. The computation is parallelized in a two-level manner with both Message-passing among nodes and Shared-Memory within each node. Our simulation results on the SMP cluster system are reported. (authors)

[en] In this paper, we consider a non-equilibrium diffusion approximation model in thermally radiative magnetohydrodynamics (MHD) which describe the compressible viscous, heat-conducting fluid coupled with the Maxwell equations governing the behavior of the magnetic field with taking into account the radiation effect under the non-local thermal equilibrium case. The system consists of the radiative transfer equation coupled with the compressible MHD equations, and the magnetic diffusion coefficient, viscosity coefficient, heat-conducting coefficient are all allowed to be positive constants. We prove existence, uniqueness and regularity of global-in-time classical solutions to one-dimensional case of this model. Based on the fundamental local existence results and global-in-time a priori estimates, we can establish the global existence of a unique classical solutions with large initial data to the initial-boundary value problems.

[en] The operating parameters of plasma generator under various regimes were measured by a newly developed digital plasma measurement system,which can test the flowrate of working gas, temperature rise of cooling water, arc voltage and arc current. According to energy balance principle, plasma average enthalpy, plasma average temperature and its distribution at the plasma generator exit were calculated. The results show that at the plasma generator exit, the distribution of jet temperature is parabolic. Increasing gas flowrate, plasma jet enthalpy and temperature will decline, and while adding hydrogen as a supplementary gas, the enthalpy and temperature will increase significantly. (authors)

[en] Using two volume-limited main galaxy samples of the Sloan Digital Sky Survey Data Release 8 (SDSS DR8), we explore the environmental dependence of the star formation rate (SFR), specific star formation rate (SSFR), and the presence of active galactic nuclei (AGNs) for high stellar mass (HSM) and low stellar mass (LSM) galaxies. It is found that the environmental dependence of the SFR and SSFR for luminous HSM galaxies and faint LSM ones remains very strong: galaxies in the lowest density regime preferentially have higher SFR and SSFR than galaxies in the densest regime, while the environmental dependence of the SFR and SSFR for luminous LSM galaxies is substantially reduced. Our result also shows that the fraction of AGNs in HSM galaxies decreases as a function of density, while the one in LSM galaxies depends very little on local density. In the faint LSM galaxy sample, the SFR and SSFR of galaxies strongly decrease with increasing density, but the fraction of AGNs depends very little on local density. Such a result can rule out that AGNs are fueled by the cold gas in the disk component of galaxies that is also driving the star formation of those galaxies.

[en] Using the volume-limited Main galaxy sample of the Sloan Digital Sky Survey Data Release 6, we have explored the dependence of clustering properties of galaxies on the star formation activity. It is found that star-forming galaxies preferentially form isolated, close double and multiple systems, while passive galaxies preferentially inhabit the dense groups and clusters. We also construct the two samples with the same galaxy number and number density, and reach the same conclusion, which shows that our statistical conclusion is robust.

[en] The dc power supply can effectively improve the reliability of the output voltage and current through parallel connection, but at the same time, there will be an increase in the output current voltage harmonic compared to a single dc power supply. For this problem. In this paper, the dc step-down chopper circuit is taken as an example to analyze the output current under the double-pulse width modulation mode. Through calculation and experimental verification, it is shown that the modulation mode used in this paper can realize the suppression of specific subharmonics. (paper)

[en] Considering the complexity of the electromagnetic environment, a large number of electronic equipment and cable harnesses are concentrated. For different environments, this paper is prepared to consider the three problems of cable crosstalk, field-line coupling and cable radiation, which basically covers all cable electromagnetic interference problems. Considering the changes of cable length, cable height from the ground, cable distance, angle and grounding mode, this paper also takes these factors into account and explores the results by changing these parameters. According to this, the anti-interference measures between the cables of Electrical Multiple Unit can be obtained. (paper)

[en] Using two volume-limited Main galaxy samples of the Sloan Digital Sky Survey Data Release 8 above and below the value of M*_r, we have explored some properties of AGNs. In the luminous volume-limited sample, 9.5% is composite galaxies (C) and 5.0% AGNs, while in the faint volume-limited sample, these fractions are 7.2% and 2.9%, respectively. The C and AGN fractions increase with luminosity. We also note that the fraction of star-forming galaxies decreases with luminosity, but the fraction of low signal-to-noise star-forming galaxies slightly increases with luminosity. In two volume-limited samples, the fraction of star-forming galaxies decreases with density, while the AGN fraction is nearly insensitive to the local environment. If composite galaxies (C) are classified as AGNs, then the fraction of AGNs in the luminous volume-limited sample declines with increasing local density. When focusing on some properties of AGN host galaxies, we find that galaxies hosting AGNs are preferentially more massive and have high concentration indices. In the faint volume-limited sample, AGN host galaxies preferentially have low star formation rates (SFRs) and specific SFRs (SSFRs). However, in the luminous volume-limited sample, AGN host galaxies preferentially have moderate SFRs and SSFRs.

[en] In the actual production, when the structures are welded, the weld inevitably bears the constraint stress which changes the internal stress state of the weld, and the properties of welding in actual welding structure are different from those in welding sample, so the effect of constraint stress on the microstructure and properties of electron beam welded joint is revealed by the characterization of solidification microstructure of joint under constraint conditions. The results show that the constraint conditions have a great influence on the microstructure, microhardness and properties. The unevenness of the microstructure of the weld increases, the grain size difference increases, the martensite is smaller with a lot of dislocations, and the continuous grain boundary α phase appears. The fusion zone and the heat affected zone consist of fine acicular martensite and residual α with dislocation tangles. The microhardness distribution of the weld is saddle-shaped, and the microhardness of weld metal is the highest. The tensile strength of the constraint welds is 898 MPa, which is higher than conventional EBW joints, and the fracture position is located in the weld. Due to the existence of a large number of dislocations in the martensite under the constraint condition, the hardness and difficulty of slip deformation increase.