Results 1 - 10 of 834
Results 1 - 10 of 834. Search took: 0.025 seconds
|Sort by: date | relevance|
[en] The differential conductance of armchair and zigzag carbon nanotubes (CNTs) in a wide energy range has been numerically calculated by using the tight-binding model and the Green’s function method. The effects of the contact coupling between CNTs and electrodes on conductance have been explored. The ballistic conductance is proportional to the band numbers and has a ladder-like feature. As the increase of the contact coupling, the conductance oscillations appear and they are robust against the coupling. More importantly, on the first step of the conductance ladder, the armchair CNTs have two quasi-periodic conductance oscillations, i.e. a rapid conductance oscillation superimposed on a slow fluctuation background; while the zigzag CNTs have only one conductance oscillation. But on the second conductance step, all CNTs have two quasi-periodic conductance oscillations. The physical origin of the conductance oscillations has been revealed
[en] Based on first-principle calculations, we have studied the electronic and magnetic properties of AlP with aluminium vacancy and calcium doping. It was found that while Al vacancy and Ca impurity themselves are nonmagnetic, they generate holes residing in P 2p orbitals that lead to magnetic moments in AlP. The coupling between two Al vacancies in AlP are always antiferromagnetic because of half-filled t2 level. However, the coupling becomes ferromagnetic with large magnetic energy when vacancies are replaced by nonmagnetic Ca atoms. Moreover, the presence of Ca dopants reduces the formation energy of Al vacancy. These results suggest that Ca-doped AlP is a promising room temperature ferromagnetic semiconductor free of magnetic precipitates, and it may find applications in the field of spintronics. - Highlights: • “d0 ferromagnetism” has been found in Ca-doped AlP. • Unpaired t2 state of P atoms has an important impact on magnetic properties. • Room temperature TC may be expected in Ca-doped AlP
[en] A scheme to decouple neighboring qubits in quantum computers through pulse control is presented. We show that two similar sequences of bang-bang pulses with different time intervals not only suppress decoherence but entirely or selectively decouple two neighboring qubits
[en] An empirical pseudopotential method is demonstrated for realistically and accurately calculating the band structure of partially CuPt ordered GaxIn1-xP alloys. A sufficiently large supercell of ∼3500 atoms, with all atomic positions relaxed by applying a valence force field method, is used to simulate the (Ga,In) distribution in the partially ordered alloy with the order parameter η varying from 0 to 1. While agreeing very well with experimental data in the experimentally verifiable region η<0.5, our results illustrate that a commonly accepted interpolation scheme (i.e., the η2 rule) is grossly inaccurate for determining certain primary band structure parameters (e.g., the band gap) between η=0 and η=1
[en] We have investigated the statistical effects of spontaneous ordering on the electronic and structural properties of a semiconductor alloy as a function of order parameter using an empirical pseudopotential method in conjunction with a valence force field method in a supercell approach. The theoretical modeling yields valuable information on the statistical fluctuation of electronic properties, which includes the individual band edge as well as the band gap, for understanding the effects of ordering on various optical and transport measurements. The results on the average bond lengths and the statistical distributions of different types of bonds provide a guideline for the measurability of the effects of ordering in a partially ordered alloy in terms of the order parameter
[en] The long horizontal and vertical sampling pipelines are used in the gaseous radioactive effluent monitoring system in Qinshan Nuclear Power Plant, so there is design deficiency for the monitoring of gaseous effluent. The long sampling pipelines, especially horizontal pipe, will result in the losing of sampling particulate and iodine. By means of modification, the sampler for particulate and iodine is moved into the small corrective room at the bottom of the stack, therefore, 85.4 meters long horizontal sampling pipe is cancelled, only 70.6 meter long vertical sampling pipe is reserved. The test and assessment result indicated that the corrective factor of the radioactive iodine sampling is 1.65. For radioactive particulate, according to conservative estimate, the corrective factor is less than 1.65 under accident condition. During normal operation, the particulate is consisted of tiny particles, and the corrective factor is 1.1. (authors)
[en] The d"0 ferromagnetism in wurtzite GaN is investigated by the first-principle calculations. It is found that spontaneous magnetization occurs if sufficient holes are injected in GaN. Both Ga vacancy and Na doping can introduce holes into GaN. However, Ga vacancy has a high formation energy, and is thus unlikely to occur in a significant concentration. In contrast, Na doping has relatively low formation energy. Under N-rich growth condition, Na doping with a sufficient concentration can be achieved, which can induce half-metallic ferromagnetism in GaN. Moreover, the estimated Curie temperature of Na-doped GaN is well above the room temperature. - Highlights: • Hole-induced ferromagnetism in GaN is confirmed. • Both Ga Vacancy and Na-doping can introduce hole into GaN. • The concentration of Ga vacancy is too low to induce detectable ferromagnetism. • Na-doped GaN is a possible ferromagnet with a high curie-temperature.
[en] The effects of reducing radiation level with primary circuit oxygenation operation during cold shutdown were described in this paper. Based on the results of radiological analysis of primary coolant, radiation measurement on workplace during the 1st outage (without oxygenation operation) and the 2nd, 3rd and 4th (with oxygenation operation) in Qinshan NPP, the effects of oxygenation operation on reduction of radiation level in working area were analyzed. It shows that oxygenation operation during cold shutdown process can reduce radioactive source term, radiation level in working area and collective dose effectively. It is one of the ways to carry out the ALARA
[en] Geobacter sulfurreducens is a model exoelectrogen known for its capability to generate high current density. Microbes genetically related to G. sulfurreducens often dominate the anodic microbial consortia in the microbial electrochemical systems. Electroanalyses had revealed that G. sulfurreducens utilizes at least three electron transfer (ET) pathways. The ET pathway with a mid-point potential of − 0.22 V is responsible for the reduction of low-potential electron acceptors. Nonetheless, the identity of the corresponding ET proteins remained unknown. This study compared the voltammograms of wild type G. sulfurreducens to those of a strain deficient in the cytochrome OmcZ (strain ΔomcZ). In bioelectrochemical reactors equipped with Indium tin oxide glasses as the working electrodes, the ΔomcZ strain generated lower current density (28.1 ± 8.2 μA/cm2) compared to that of the wild strain (82.9 ± 16.7 μA/cm2). For ΔomcZ, the catalytic wave in the low-potential region disappeared from the biofilm voltammogram. Differential pulse voltammetries also demonstrated the loss of a low-potential redox couple. OmcZ is therefore likely to be part of the low-potential pathway. Nevertheless, pathways with higher mid-point potentials remained functional after the deletion of the omcZ gene. OmcZ is hence probably specifically required for the low-potential ET pathway. On the other hand, mutant strain deficient in the omcB gene, which was previously found to be up-regulated under current-generating conditions, exhibited similar voltammetric patterns to the wild strain.