Noise spectroscopy to study the 1D electron transport properties in InAs nanowires.

InAs nanowires (NWs) are recognized as a key material due to their unique transport properties. Despite remarkable progress in designing InAs NW device structures, there are still open questions on device variability. Here, we demonstrate that noise spectroscopy allows us to study not only the parameters of traps, but also to shed light on quantum transport in NW structures. This provides an important understanding of structural behavior as well as the background and strategy required to design NW structures with advanced properties.

MetaMap: an atlas of metatranscriptomic reads in human disease-related RNA-seq data.

Background: With the advent of the age of big data in bioinformatics, large volumes of data and high-performance computing power enable researchers to perform re-analyses of publicly available datasets at an unprecedented scale. Ever more studies imply the microbiome in both normal human physiology and a wide range of diseases. RNA sequencing technology (RNA-seq) is commonly used to infer global eukaryotic gene expression patterns under defined conditions, including human disease-related contexts; however, its generic nature also enables the detection of microbial and viral transcripts. Findings: We developed a bioinformatic pipeline to screen existing human RNA-seq datasets for the presence of microbial and viral reads by re-inspecting the non-human-mapping read fraction. We validated this approach by recapitulating outcomes from six independent, controlled infection experiments of cell line models and compared them with an alternative metatranscriptomic mapping strategy. We then applied the pipeline to close to 150 terabytes of publicly available raw RNA-seq data from more than 17,000 samples from more than 400 studies relevant to human disease using state-of-the-art high-performance computing systems. The resulting data from this large-scale re-analysis are made available in the presented MetaMap resource. Conclusions: Our results demonstrate that common human RNA-seq data, including those archived in public repositories, might contain valuable information to correlate microbial and viral detection patterns with diverse diseases. The presented MetaMap database thus provides a rich resource for hypothesis generation toward the role of the microbiome in human disease. Additionally, codes to process new datasets and perform statistical analyses are made available.

Full thermoelectric characterization of InAs nanowires using MEMS heater/sensors.

Precise measurements of a complete set of thermoelectric parameters on a single indium-arsenide nanowire (NW) have been performed using highly sensitive, micro-fabricated sensing devices based on the heater/sensor principle. The devices were fabricated as micro electro-mechanical systems consisting of silicon nitride membranes structured with resistive gold heaters/sensors. Preparation, operation and characterization of the devices are described in detail. Thermal decoupling of the heater/sensor platforms has been optimized reaching thermal conductances as low as 20 nW K(-1) with a measurements sensitivity below 20 nW K(-1). The InAs NWs were characterized in terms of thermal conductance, four-probe electrical conductance and thermopower (Seebeck coefficient), all measured on a single NW. The temperature dependence of the parameters determining the thermoelectric figure-of-merit of an InAs NW was acquired in the range 200-350 K featuring a minor decrease of the thermal conductivity from 2.7 W (m K)(-1) to 2.3 W (m K)(-1).

Inducing a direct-to-pseudodirect bandgap transition in wurtzite GaAs nanowires with uniaxial stress.

Many efficient light-emitting devices and photodetectors are based on semiconductors with, respectively, a direct or indirect bandgap configuration. The less known pseudodirect bandgap configuration can be found in wurtzite (WZ) semiconductors: here electron and hole wave-functions overlap strongly but optical transitions between these states are impaired by symmetry. Switching between bandgap configurations would enable novel photonic applications but large anisotropic strain is normally needed to induce such band structure transitions. Here we show that the luminescence of WZ GaAs nanowires can be switched on and off, by inducing a reversible direct-to-pseudodirect band structure transition, under the influence of a small uniaxial stress. For the first time, we clarify the band structure of WZ GaAs, providing a conclusive picture of the energy and symmetry of the electronic states. We envisage a new generation of devices that can simultaneously serve as efficient light emitters and photodetectors by leveraging the strain degree of freedom.

Temporal interaction in electrical hearing elucidates auditory nerve dynamics in humans.

In cochlear implants, severe limitations arise from electrical crosstalk between channels. Therefore, the current trend in cochlear implants is to increase stimulation rates to encode signals with higher temporal precision. However, the fundamental question: "What is the limit of temporal precision due to inherent neuronal dynamics of the stimulated neurons?" has not yet been resolved. In this study we have developed a double-pulse method and, for the first time, reversed stimulus polarity systematically between consecutive pulses to elucidate subthreshold-induced temporal interaction effects. This method allowed us to determine the time-course of subthreshold temporal interaction in human subjects which identifies the limits of encoded temporal precision. Our results show significant temporal interaction up to 600 µs inter-pulse interval. In all the cases tested we saw a facilitation effect on threshold. Interaction effects at a 20% below threshold pre-conditioning stimulation showed up to 38% ± 6% threshold reduction. These results imply that there is significant temporal interaction between two subsequent pulses. This interaction diminishes the precision of amplitude coding. We predict interaction effects on temporal precision and channel interaction. For (interleaved) stimulation with short inter-pulse intervals it is interesting to consider our interaction results; and it may become important to consider them for future coding strategies where high temporal precision is required. In an increasing group of binaural implanted patients this will be the case when interaural time differences are encoded with µs precision.

Solid-state diffusion as an efficient doping method for silicon nanowires and nanowire field effect transistors.

In this work we investigate doping by solid-state diffusion from a doped oxide layer, obtained by plasma-enhanced chemical vapor deposition (PECVD), as a means for selectively doping silicon nanowires (NWs). We demonstrate both n-type (phosphorous) and p-type (boron) doping up to concentrations of 10(20) cm(-3), and find that this doping mechanism is more efficient for NWs as opposed to planar substrates. We observe no diameter dependence in the range of 25 to 80 nm, which signifies that the NWs are uniformly doped. The drive-in temperature (800-950 °C) can be used to adjust the actual doping concentration in the range 2 × 10(18) to 10(20) cm(-3). Furthermore, we have fabricated NMOS and PMOS devices to show the versatility of this approach and the possibility of achieving segmented doping of NWs. The devices show high I(on)/I(off) ratios of around 10(7) and, especially for the PMOS, good saturation behavior and low hysteresis.

Comment on "30,000-year-old wild flax fibers".

Kvavadze et al. (Brevia, 11 September 2009, p. 1359) identified fiber samples as 30,000-year-old flax based on a comparison with modern flax fibers analyzed by compound microscope and on the presence of dislocations/nodes in the fibers. We argue that this evidence is not sufficient to identify the fibers as flax.