Electronic states and magnetotransport in quantum waveguides with nonuniform magnetic fields

The electronic states and magnetotransport properties of quantum waveguides (QW’s) in the presence of nonuniform magnetic fields perpendicular to the QW plane are investigated theoretically. It is found that the magnetoconductance of those structures as a function of Fermi energy exhibits stepwise variation or square-wave-like oscillations, depending on the specific distributions (both in magnitude and direction) of nonuniform magnetic fields in QW’s. We have investigated the dual magnetic strip structures and three magnetic strip structures. The character of the magnetotransport is closely related to the effective magnetic potential and the energy-dispersion spectrum of electron in the structures. It is found that dispersion relations seem to be combined by different sets of dispersion curves that belong to different individual magnetic subwaveguides. The magnetic effective potential leads to the coupling of states and the substantial distortion of the original dispersion curves at the interfaces in which the abrupt change of magnetic fields appears. Magnetic scattering states are created. Only in some three magnetic strip structures, these scattering states produce the dispersion relations with oscillation structures superimposed on the bulk Landau levels. It is the oscillatory behavior in dispersions that leads to the occurrence of square-wave-like modulations in conductance.published_or_final_versio

Development and present status of the research on optimal control of chilled water systems in central air-conditioning

2002-2003 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Tunneling transmission in two quantum wires coupled by a magnetically defined barrier

A numerical analysis of an electron waveguide coupler based on two quantum wires coupled by a magnetically defined barrier is presented with the use of the scattering-matrix method. For different geometry parameters and magnetic fields, tunneling transmission spectrum is obtained as a function of the electron energy. Different from that of conventional electron waveguide couplers, the transmission spectrum of the magnetically coupled quantum wires does not have the symmetry with regard to those geometrically symmetrical ports. It was found that the magnetic field in the coupling region drastically enhances the coupling between the two quantum wires for one specific input port while it weakens the coupling for the other input port. The results can be well understood by the formation of the edge states in the magnetically defined barrier region. Thus, whether these edge states couple or decouple to the electronic propagation modes in the two quantum wires, strongly depend on the relative moving directions of electrons in the propagating mode in the input port and the edge states in the magnetic region. This leads to a big difference in transmission coefficients between two quantum wires when injecting electrons via different input ports. Two important coupler specifications, the directivity and uniformity, are calculated which show that the system we considered behaves as a good quantum directional coupler. ©1997 American Institute of Physics.published_or_final_versio

Dynamic and nonlinear magnetoconductance: Numerical analysis in two dimensions

We report theoretical investigations on the magnetoconductance of a two-probe two-dimensional mesoscopic conductor in the dynamic and weakly nonlinear transport regimes. Crucial to the investigation is the development of a viable numerical scheme for evaluating functional derivatives of a scattering matrix with respect to the scattering potential landscape in the presence of a magnetic field. The physical behavior of the local partial density of states, the sensitivity, the dynamic conductance, and the second order nonlinear dc conductance as functions of an external uniform magnetic field is revealed at two dimensions. Due to symmetry breaking the magnetic field adds very important effects to these physical quantities.published_or_final_versio

Superderivations for Modular Graded Lie Superalgebras of Cartan-type

Superderivations for the eight families of finite or infinite dimensional graded Lie superalgebras of Cartan-type over a field of characteristic $p>3$ are completely determined by a uniform approach: The infinite dimensional case is reduced to the finite dimensional case and the latter is further reduced to the restrictedness case, which proves to be far more manageable. In particular, the outer superderivation algebras of those Lie superalgebras are completely determined

Ubiquitination is indispensible for the insulin-sensitising activity of the adaptor protein APPL1

published_or_final_versio

Microbial community analysis of fresh and old microbial biofilms on Bayon Temple sandstone of Angkor Thom, Cambodia

The temples of Angkor monuments including Angkor Thom and Bayon in Cambodia and surrounding countries were exclusively constructed using sandstone. They are severely threatened by biodeterioration caused by active growth of different microorganisms on the sandstone surfaces, but knowledge on the microbial community and composition of the biofilms on the sandstone is not available from this region. This study investigated the microbial community diversity by examining the fresh and old biofilms of the biodeteriorated bas-relief wall surfaces of the Bayon Temple by analysis of 16S and 18S rRNA gene sequences. The results showed that the retrieved sequences were clustered in 11 bacterial, 11 eukaryotic and two archaeal divisions with disparate communities (Acidobacteria, Actinobacteria, Bacteroidetes, Cyanobacteria, Proteobacteria; Alveolata, Fungi, Metazoa, Viridiplantae; Crenarchaeote, and Euyarchaeota). A comparison of the microbial communities between the fresh and old biofilms revealed that the bacterial community of old biofilm was very similar to the newly formed fresh biofilm in terms of bacterial composition, but the eukaryotic communities were distinctly different between these two. This information has important implications for understanding the formation process and development of the microbial diversity on the sandstone surfaces, and furthermore to the relationship between the extent of biodeterioration and succession of microbial communities on sandstone in tropic region. © 2010 The Author(s).published_or_final_versionSpringer Open Choice, 01 Dec 201

Self-Organized Ni Nanocrystal Embedded in BaTiO3 Epitaxial Film

Ni nanocrystals (NCs) were embedded in BaTiO3 epitaxial films using the laser molecular beam epitaxy. The processes involving the self-organization of Ni NCs and the epitaxial growth of BaTiO3 were discussed. With the in situ monitoring of reflection high-energy electron diffraction, the nanocomposite films were engineered controllably by the fine alternation of the self-organization of Ni NCs and the epitaxial growth of BaTiO3. The transmission electron microscopy and the X-ray diffraction characterization confirmed that the composite film consists of the Ni NCs layers alternating with the (001)/(100)-oriented epitaxial BaTiO3 separation layers

Characterization of upstream sequences from the 8S globulin gene of Vigna radiata

Seeds rich in protein in nature, are ideal bioreactors for economic production and storage of valueadded recombinant proteins and enzymes for industries. The upstream region of the seed storage protein gene is able to provide an attractive promoter for seed-specific expression of heterologous genes. Our previous research showed that 8S globulin occupied the majority of total soluble protein stored in seeds of mung bean (Vigna radiata), a rich source of protein, indicating that the promoter of this gene could be a seed-specific promoter with high activity. To improve the expression of heterologous proteins in plants to act as a bioreactor, the putative seed-specific promoter of 8S globulin gene was characterized in this study. Hence, this potential promoter of beta subunit gene of 8S globulin (8SGb) was isolated by genome walking. Analysis with various promoter prediction softwares showed that the promoter sequence possessed many common motifs related to gene transcription in the seed (such as W-box, ABRE element, E-box, etc.). The putative promoter was subsequently cloned into the binary vector pBI121-GFP by replacing the CaMV 35S promoter. The resultant construct designated as pBI-8SGb-GFP was transformed to mung bean cotyledon mesophyll protoplasts. Reporter gene GFP was expressed high in cotyledon protoplasts, which was detected by confocal microscopy, demonstrating the specific activity of 8SGb promoter in driving gene expression. This study also proved that the 8SGb promoter is an efficient regulatory element for plant seeds to act as a bioreactor.Key words: Seed-specific, promoter, genome walking, Vigna radiata