Efficient photogeneration of charge carriers in silicon nanowires with a radial doping gradient

by performing electrodeless time-resolved microwave conductivity measurements, the efficiency of charge carrier generation, their mobility, and the decay kinetics on photoexcitation were studied in arrays of Si nanowires grown by the vapor-liquid-solid mechanism. Large enhancements in the magnitude of the photoconductance and charge carrier lifetime are found depending on the incorporation of impurities during the growth. They are explained by the internal electric field that builds up, due to higher doped sidewalls, as revealed by detailed analysis of the nanowire morphology and chemical composition.     

Dynamic behavior of amplitude detection Kelvin force microscopy in ultrahigh vacuum

The acquisition rate of all scanning probe imaging techniques with feedback control is limited by the dynamic response of the control loops. Performance criteria are the control loop bandwidth and the output signal noise power spectral density. Depending on the acceptable noise level, it may be necessary to reduce the sampling frequency below the bandwidth of the control loop. In this work, the frequency response of a vacuum Kelvin force microscope with amplitude detection (AM-KFM) using a digital signal processing (DSP) controller is characterized and optimized. Then, the main noise source and its impact on the output signal is identified. A discussion follows on how the system design can be optimized with respect to output noise. Furthermore, the interaction between Kelvin and distance control loop is studied, confirming the beneficial effect of KFM on topography artefact reduction in the frequency domain. The experimental procedure described here can be generalized to other systems and allows to locate the performance limitations.     

Complex mental arithmetic: The contribution of the number sense.

Young adults were asked to solve two-digit addition problems and to say aloud the result of each calculation step to allow the identification of computation strategies. We manipulated the position of the largest addend (e.g., 25 + 48 vs. 48 + 25) to assess whether strategies are modulated by magnitude characteristics. With some strategies, participants demonstrated a clear preference to take the largest addend as the starting point for the calculation. Hence, rather than applying strategies in an inflexible manner, participants evaluated and compared the operands before proceeding to calculation. Further, mathematically skilled participants tended to use those magnitude-based strategies more often than less skilled ones. The findings demonstrate that magnitude information plays a role in complex arithmetic by guiding the process of strategy selection, and possibly more so for mathematically skilled participants. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of Crystal Properties on Powder Flow Behavior of an Aromatic Amine and L-Glutamic Acid

Polycrystalline particles with a roughly spherical shape (spherulites) have been identified in the industrial production of an aromatic amine derivative, where powder handling is one of the downstream processes following crystallization. This comparative study focuses on how uniaxial flow functions as measures of flowability of dry material of L-glutamic acid and an aromatic amine are affected by the crystal morphology and size, as analyzed by the chord length distribution measurements (FBRM) and scanning electron microscopy (SEM). L-glutamic acid was chosen as a model substance since it can be crystallized as spherulites as well as needle-shaped and polyhedral particles. Failure strength values were measured as a function of consolidation stress using the uniaxial tester. The failure strength values of L-glutamic acid were found to be lower for polyhedral particles than for needle-shaped particles with approximately the same mean chord length. Needle-shaped particles were found to have lower values for failure strength than L-glutamic acid spherulites with smaller chord lengths. It has been shown that spherulites are more unstable with respect to particle breakage than the other morphologies. Although the chord length distributions of the L-glutamic acid spherulites were shifted towards smaller values than those of the aromatic amine spherulites, the failure strength of the aromatic amine particles is more than four times as large. This can be explained by more extensive particle breakage during filtration, sample storage, and consolidation of the aromatic amine.     

Protocadherin 19 Clustering Epilepsy and Neurosteroids: Opportunities for Intervention

Steroids yield great influence on neurological development through nuclear hormone receptor (NHR)-mediated gene regulation. We recently reported that cell adhesion molecule protocadherin 19 (encoded by the PCDH19 gene) is involved in the coregulation of steroid receptor activity on gene expression. PCDH19 variants cause early-onset developmental epileptic encephalopathy clustering epilepsy (CE), with altered steroidogenesis and NHR-related gene expression being identified in these individuals. The implication of hormonal pathways in CE pathogenesis has led to the investigation of various steroid-based antiepileptic drugs in the treatment of this disorder, with mixed results so far. Therefore, there are many unmet challenges in assessing the antiseizure targets and efficiency of steroid-based therapeutics for CE. We review and assess the evidence for and against the implication of neurosteroids in the pathogenesis of CE and in view of their possible clinical benefit.     

A High Temperature Micropower Capacitive Pressure Sensor Interface Circuit

A pressure sensor interface circuit featuring micropower consumptionis presented. The sensitivity to leakage currents has been reduced, allowingoperation at high temperature. Special attention has been paid to minimisealiasing in the sampled interface. An optimal combination of contradictoryrequirements on power consumption, temperature range and sampling speed wasobtained by a very careful system design and optimisation. The circuitconverts a sensor capacitance variation of ±5pF into an 11 bit outputword at a 2Hz rate. This resolution is guaranteed in the –40°C to100°C temperature range. It may slowly decay above 100°C but ensuresat least 5 bit at 130°C. The power consumption at room temperature issmaller than 2µA from a 2.4V to 4V battery.     

Dynamics of Algal Secondary Metabolites in Two Species of Sea Hare

The function of acquired algal secondary metabolites in sea hares is the subject of debate, in part because the dynamics/processing of metabolites by sea hares is poorly understood. This study investigates the dynamics of red algal secondary metabolites in two sea hares, Aplysia parvula and Aplysia dactylomela. Secondary metabolite levels were quantified for the dietary red algae Laurencia obtusa and Delisea pulchra and for sea hares collected from these seaweeds in the field. The patterns and dynamics of algal secondary metabolites were further investigated in the laboratory by quantitative analysis of secondary metabolites in sea hares grown on diets of L. obtusa, D. pulchra, or the green alga Ulva sp. Sea hares accumulated the most abundant metabolites from each red alga, the terpene palisadin A from L. obtusa, and the halogenated furanone 3 from D. pulchra, and stored a greater proportion of these metabolites than other algal metabolites. A. parvula accumulated D. pulchra metabolites at much higher levels than L. obtusa metabolites. A. dactylomela accumulated similar concentrations of L. obtusa metabolites to A. parvula. The loss of L. obtusa metabolites by A. dactylomela matched that expected for dilution of metabolites via growth of the sea hares. However, the loss of L. obtusa metabolites by A. parvula was faster than predicted for growth alone, suggesting that metabolites were actively metabolized or excreted. Data for the loss of D. pulchra metabolites by A. parvula was equivocal. The secretions of A. parvula fed D. pulchra or L. obtusa were analyzed for the presence of algal secondary metabolites to investigate one possible path of excretion. L. obtusa secondary metabolites were detected in the mucous and opaline secretions of A. parvula, but D. pulchra metabolites were not detected in any secretions. The deployment of L. obtusa secondary metabolites in secretions by A. parvula may explain the more rapid rate of loss of these compounds and is consistent with a possible defensive role for acquired metabolites.     

Faceting, composition and crystal phase evolution in III-V antimonide nanowire heterostructures revealed by combining microscopy techniques

III-V antimonide nanowires are among the most interesting semiconductors for transport physics, nanoelectronics and long-wavelength optoelectronic devices due to their optimal material properties. In order to investigate their complex crystal structure evolution, faceting and composition, we report a combined scanning electron microscopy (SEM), transmission electron microscopy (TEM), and scanning tunneling microscopy (STM) study of gold-nucleated ternary InAs/InAs(1-x)Sb(x) nanowire heterostructures grown by molecular beam epitaxy. SEM showed the general morphology and faceting, TEM revealed the internal crystal structure and ternary compositions, while STM was successfully applied to characterize the oxide-free nanowire sidewalls, in terms of nanofaceting morphology, atomic structure and surface composition. The complementary use of these techniques allows for correlation of the morphological and structural properties of the nanowires with the amount of Sb incorporated during growth. The addition of even a minute amount of Sb to InAs changes the crystal structure from perfect wurtzite to perfect zinc blende, via intermediate stacking fault and pseudo-periodic twinning regimes. Moreover, the addition of Sb during the axial growth of InAs/InAs(1-x)Sb(x) heterostructure nanowires causes a significant conformal lateral overgrowth on both segments, leading to the spontaneous formation of a core-shell structure, with an Sb-rich shell.     

Spinodal decomposition in the Fe−Cr system

Fe?Cr binary alloys ranging from 20 to 50 pct Cr have been analyzed by Mössbauer spectroscopy, in the queached state and after aging respectively at 470° and 540°C. A clear distinction could be made in this way between the nucleation and growth, and the spinodal process of decomposition during aging. When the alloy lies inside of the miscibility gap but outside of the spinodal, a pramagnetic precipitate clearly appears right from the beginning of the aging process, while when the alloy lies inside of the spinodal, no paramagnetic phase appears even after 1050 hr of aging at 470°C. This certainly indicates that the spinodal decomposition is very slow. One more point is shown: aging outside of the miscibility gap shows clearly a clustering of the chromium atoms and a large departure from the concept of an ideal solid solution.