Self-Aligned Ballistic Molecular Transistors and Electrically Parallel Nanotube Arrays

Carbon nanotube field-effect transistors with structures and properties near the scaling limit with short (down to 50 nm) channels, self aligned geometries, palladium electrodes with low contact resistance and high-k dielectric gate insulators are realized. Electrical transport in these miniature transistors is near ballistic up to high biases at both room and low temperatures. Atomic layer deposited (ALD) high-k films interact with nanotube sidewalls via van der Waals interactions without causing weak localization at 4 K. New fundamental understanding of ballistic transport, optical phonon scattering and potential interfacial scattering mechanisms in nanotubes are obtained.Comment: Nano Letters, in pres

Improved predictions by Pcons.net using multiple templates

Summary: Multiple templates can often be used to build more accurate homology models than models built from a single template. Here we introduce PconsM, an automated protocol that uses multiple templates to build protein models. PconsM has been among the top-performing methods in the recent CASP experiments and consistently perform better than the single template models used in Pcons.net. In particular for the easier targets with many alternative templates with a high degree of sequence identity, quality is readily improved with a few percentages over the highest ranked model built on a single template. PconsM is available as an additional pipeline within the Pcons.net protein structure prediction server

Decoherence due to contacts in ballistic nanostructures

The active region of a ballistic nanostructure is an open quantum-mechanical system, whose nonunitary evolution (decoherence) towards a nonequilibrium steady state is determined by carrier injection from the contacts. The purpose of this paper is to provide a simple theoretical description of the contact-induced decoherence in ballistic nanostructures, which is established within the framework of the open systems theory. The active region's evolution in the presence of contacts is generally non-Markovian. However, if the contacts' energy relaxation due to electron-electron scattering is sufficiently fast, then the contacts can be considered memoryless on timescales coarsened over their energy relaxation time, and the evolution of the current-limiting active region can be considered Markovian. Therefore, we first derive a general Markovian map in the presence of a memoryless environment, by coarse-graining the exact short-time non-Markovian dynamics of an abstract open system over the environment memory-loss time, and we give the requirements for the validity of this map. We then introduce a model contact-active region interaction that describes carrier injection from the contacts for a generic two-terminal ballistic nanostructure. Starting from this model interaction and using the Markovian dynamics derived by coarse-graining over the effective memory-loss time of the contacts, we derive the formulas for the nonequilibrium steady-state distribution functions of the forward and backward propagating states in the nanostructure's active region. On the example of a double-barrier tunneling structure, the present approach yields an I-V curve with all the prominent resonant features. The relationship to the Landauer-B\"{u}ttiker formalism is also discussed, as well as the inclusion of scattering.Comment: Published versio

The Smell of Age: Perception and Discrimination of Body Odors of Different Ages

Our natural body odor goes through several stages of age-dependent changes in chemical composition as we grow older. Similar changes have been reported for several animal species and are thought to facilitate age discrimination of an individual based on body odors, alone. We sought to determine whether humans are able to discriminate between body odor of humans of different ages. Body odors were sampled from three distinct age groups: Young (20–30 years old), Middle-age (45–55), and Old-age (75–95) individuals. Perceptual ratings and age discrimination performance were assessed in 41 young participants. There were significant differences in ratings of both intensity and pleasantness, where body odors from the Old-age group were rated as less intense and less unpleasant than body odors originating from Young and Middle-age donors. Participants were able to discriminate between age categories, with body odor from Old-age donors mediating the effect also after removing variance explained by intensity differences. Similarly, participants were able to correctly assign age labels to body odors originating from Old-age donors but not to body odors originating from other age groups. This experiment suggests that, akin to other animals, humans are able to discriminate age based on body odor alone and that this effect is mediated mainly by body odors emitted by individuals of old age

Orientation-dependent perimeter recombination in GaAs diodes

Perimeter recombination currents affect the performance of GaAs-based devices such as solar cells, heterojunction bipolar transistors, and injection lasers. We report that the n SEf 2 perimeter recombination current has a strong orientation dependence. More than a factor of five variation in the surface recombination current at mesa-etched edges has been observed. These results suggest that with proper device design, perimeter recombination currents could be substantially reduced

Thermoelectric properties of the bismuth telluride nanowires in the constant-relaxation-time approximation

Electronic structure of bismuth telluride nanowires with the growth directions [110] and [015] is studied in the framework of anisotropic effective mass method using the parabolic band approximation. The components of the electron and hole effective mass tensor for six valleys are calculated for both growth directions. For a square nanowire, in the temperature range from 77 K to 500 K, the dependence of the Seebeck coefficient, the electron thermal and electrical conductivity as well as the figure of merit ZT on the nanowire thickness and on the excess hole concentration are investigated in the constant-relaxation-time approximation. The carrier confinement is shown to play essential role for square nanowires with thickness less than 30 nm. The confinement decreases both the carrier concentration and the thermal conductivity but increases the maximum value of Seebeck coefficient in contrast to the excess holes (impurities). The confinement effect is stronger for the direction [015] than for the direction [110] due to the carrier mass difference for these directions. The carrier confinement increases maximum value of ZT and shifts it towards high temperatures. For the p-type bismuth telluride nanowires with growth direction [110], the maximum value of the figure of merit is equal to 1.3, 1.6, and 2.8, correspondingly, at temperatures 310 K, 390 K, 480 K and the nanowire thicknesses 30 nm, 15 nm, and 7 nm. At the room temperature, the figure of merit equals 1.2, 1.3, and 1.7, respectively.Comment: 13 pages, 7 figures, 2 tables, typos added, added references for sections 2-