Magnetotunnelling in resonant tunnelling structures with spin-orbit interaction

Magnetotunnelling spectroscopy of resonant tunnelling structures provides information on the nature of the two-dimensional electron gas in the well. We describe a model based on nonequilibrium Green's functions that allows for a comprehensive study of the density of states, tunnelling currents and current spin polarization. The investigated effects include the electron-phonon interaction, interface roughness scattering, Zeeman effect and the Rashba spin-orbit interaction. A qualitative agreement with experimental data is found regarding the satellite peaks. The spin polarization is predicted to be larger than ten percent for magnetic fields above 2 Tesla and having a structure even at the satellite peaks. The Rashba effect is confirmed to be observable as a beating pattern in the density of states but found to be too small to affect the tunnelling current.Comment: 31 pages, 11 figure

Helical structure motifs made searchable for functional peptide design

The systematic design of functional peptides has technological and therapeutic applications. However, there is a need for pattern-based search engines that help locate desired functional motifs in primary sequences regardless of their evolutionary conservation. Existing databases such as The Protein Secondary Structure database (PSS) no longer serves the community, while the Dictionary of Protein Secondary Structure (DSSP) annotates the secondary structures when tertiary structures of proteins are provided. Here, we extract 1.7 million helices from the PDB and compile them into a database (Therapeutic Peptide Design database; TP-DB) that allows queries of compounded patterns to facilitate the identification of sequence motifs of helical structures. We show how TP-DB helps us identify a known purification-tag-specific antibody that can be repurposed into a diagnostic kit for Helicobacter pylori. We also show how the database can be used to design a new antimicrobial peptide that shows better Candida albicans clearance and lower hemolysis than its template homologs. Finally, we demonstrate how TP-DB can suggest point mutations in helical peptide blockers to prevent a targeted tumorigenic protein-protein interaction. TP-DB is made available at http://dyn.life.nthu.edu.tw/design/

Consequences of local gauge symmetry in empirical tight-binding theory

A method for incorporating electromagnetic fields into empirical tight-binding theory is derived from the principle of local gauge symmetry. Gauge invariance is shown to be incompatible with empirical tight-binding theory unless a representation exists in which the coordinate operator is diagonal. The present approach takes this basis as fundamental and uses group theory to construct symmetrized linear combinations of discrete coordinate eigenkets. This produces orthogonal atomic-like "orbitals" that may be used as a tight-binding basis. The coordinate matrix in the latter basis includes intra-atomic matrix elements between different orbitals on the same atom. Lattice gauge theory is then used to define discrete electromagnetic fields and their interaction with electrons. Local gauge symmetry is shown to impose strong restrictions limiting the range of the Hamiltonian in the coordinate basis. The theory is applied to the semiconductors Ge and Si, for which it is shown that a basis of 15 orbitals per atom provides a satisfactory description of the valence bands and the lowest conduction bands. Calculations of the dielectric function demonstrate that this model yields an accurate joint density of states, but underestimates the oscillator strength by about 20% in comparison to a nonlocal empirical pseudopotential calculation.Comment: 23 pages, 7 figures, RevTeX4; submitted to Phys. Rev.

Group-IV graphene- and graphane-like nanosheets

We performed a first principles investigation on the structural and electronic properties of group-IV (C, SiC, Si, Ge, and Sn) graphene-like sheets in flat and buckled configurations and the respective hydrogenated or fluorinated graphane-like ones. The analysis on the energetics, associated with the formation of those structures, showed that fluorinated graphane-like sheets are very stable, and should be easily synthesized in laboratory. We also studied the changes on the properties of the graphene-like sheets, as result of hydrogenation or fluorination. The interatomic distances in those graphane-like sheets are consistent with the respective crystalline ones, a property that may facilitate integration of those sheets within three-dimensional nanodevices

Catalytic deoxygenation of triolein to green fuel over mesoporous TiO2 aided by in situ hydrogen production

The greenhouse gases contributed by combustion of fossil fuel has urged the need for sustainable green fuel production. Deoxygenation is the most reliable process to convert bio-oil into green fuel. In this study, the deoxygenation of triolein was investigated via mesoporous TiO2 calcined at different temperature in the absence of external H2. The high conversion of fuel-liked hydrocarbons showed the in situ H2 produced from the reaction. The mesoporous TiO2 calcined at 500 °C (M500) demonstrated the highest activity, around 76.9% conversion was achieved with 78.9% selectivity to hydrocarbon. The reaction proceed through second order kinetic with a rate constant of 0.0557 g−1trioleinh−1. The major product of the reaction were diesel range saturated and unsaturated hydrocarbon (60%) further the formation of in situ H2. It is interesting to observe that higher calcination temperature improve crystallinity and remove surface hydroxyls, meanwhile increase the acid density and medium strength acid site. The conversion of triolein increased linearly with the amount of medium strength acid sites. This result suggests that medium-strength acidity of catalyst is a critical factor in determining deoxygenation activities. In addition, the presence of mesopores allow the diffusion of triolein molecules and improve the selectivity. Hence, mesoporous TiO2 with Lewis acidity is a fascinating catalyst and hydrogen donor in high-value green fuel

Response theory for time-resolved second-harmonic generation and two-photon photoemission

A unified response theory for the time-resolved nonlinear light generation and two-photon photoemission (2PPE) from metal surfaces is presented. The theory allows to describe the dependence of the nonlinear optical response and the photoelectron yield, respectively, on the time dependence of the exciting light field. Quantum-mechanical interference effects affect the results significantly. Contributions to 2PPE due to the optical nonlinearity of the surface region are derived and shown to be relevant close to a plasmon resonance. The interplay between pulse shape, relaxation times of excited electrons, and band structure is analyzed directly in the time domain. While our theory works for arbitrary pulse shapes, we mainly focus on the case of two pulses of the same mean frequency. Difficulties in extracting relaxation rates from pump-probe experiments are discussed, for example due to the effect of detuning of intermediate states on the interference. The theory also allows to determine the range of validity of the optical Bloch equations and of semiclassical rate equations, respectively. Finally, we discuss how collective plasma excitations affect the nonlinear optical response and 2PPE.Comment: 27 pages, including 11 figures, version as publishe

Reading Your Counterpart: The Benefit of Emotion Recognition Accuracy for Effectiveness in Negotiation

10.1007/s10919-007-0033-7Journal of Nonverbal Behavior314205-22