1,495 research outputs found
1-octadecene monolayers on Si(111) hydrogen-terminated surfaces: effects of substrate doping
We have studied the electronic properties, in relation to their structural
properties, of monolayers of 1-octadecene attached on a hydrogen-terminated
(111) silicon surface. The molecules are attached using the free-radical
reaction between C=C and Si-H activated by an ultraviolet illumination. We have
compared the structural and electrical properties of monolayers formed on
silicon substrate of different types (n-type and p-type) and different doping
concentrations from low-doped (~1E14 cm-3) to highly doped (~1E19 cm-3) silicon
substrates. We show that the monolayers on n-, p- and p+ silicon are densely
packed and that they act as very good insulating films at a nanometer thickness
with leakage currents as low as ~1E-7 A.cm-2 and high quality
capacitance-voltage characteristics. The monolayers formed on n+-type silicon
are more disordered and therefore exhibit larger leakage current densities
(>1E-4 A.cm-2) when embedded in a silicon/monolayer/metal junction. The
inferior structural and electronic properties obtained with n+-type silicon
pinpoint the important role of surface potential and of the position of the
surface Fermi level during the chemisorption of the organic monolayers.Comment: 33 pages, 8 figures, to be published J. Appl. Phy
Effects of impurities on radiation damage of silicon solar cells
Impurities effects on radiation damage of silicon solar cell
Cell Detection with Star-convex Polygons
Automatic detection and segmentation of cells and nuclei in microscopy images
is important for many biological applications. Recent successful learning-based
approaches include per-pixel cell segmentation with subsequent pixel grouping,
or localization of bounding boxes with subsequent shape refinement. In
situations of crowded cells, these can be prone to segmentation errors, such as
falsely merging bordering cells or suppressing valid cell instances due to the
poor approximation with bounding boxes. To overcome these issues, we propose to
localize cell nuclei via star-convex polygons, which are a much better shape
representation as compared to bounding boxes and thus do not need shape
refinement. To that end, we train a convolutional neural network that predicts
for every pixel a polygon for the cell instance at that position. We
demonstrate the merits of our approach on two synthetic datasets and one
challenging dataset of diverse fluorescence microscopy images.Comment: Conference paper at MICCAI 201
Nondestructive Inspection and Evaluation of Metal Matrix Composites
A review is presented of work performed in our laboratory on the nondestructive inspection of metal matrix composites. In order to obtain damage representative of that which occurs in service, the specimens were mechanically loaded to intermediate load levels below that which causes final, catastrophic failure. Various nondestructive techniques were used both during and after the applied loadings to follow damage initiation and progress.</p
Human Aging Magnifies Genetic Effects on Executive Functioning and Working Memory
We demonstrate that common genetic polymorphisms contribute to the increasing heterogeneity of cognitive functioning in old age. We assess two common Val/Met polymorphisms, one affecting the Catechol-O-Methyltransferase (COMT) enzyme, which degrades dopamine (DA) in prefrontal cortex (PFC), and the other influencing the brain-derived neurotrophic factor (BDNF) protein. In two tasks (Wisconsin Card Sorting and spatial working memory), we find that effects of COMT genotype on cognitive performance are magnified in old age and modulated by BDNF genotype. Older COMT Val homozygotes showed particularly low levels of performance if they were also BDNF Met carriers. The age-associated magnification of COMT gene effects provides novel information on the inverted U-shaped relation linking dopaminergic neuromodulation in PFC to cognitive performance. The modulation of COMT effects by BDNF extends recent evidence of close interactions between frontal and medial-temporal circuitries in executive functioning and working memory
Age-Related Decline in Brain Resources Modulates Genetic Effects on Cognitive Functioning
Individual differences in cognitive performance increase from early to late adulthood, likely reflecting influences of a multitude of factors. We hypothesize that losses in neurochemical and anatomical brain resources in normal aging modulate the effects of common genetic variations on cognitive functioning. Our hypothesis is based on the assumption that the function relating brain resources to cognition is nonlinear, so that genetic differences exert increasingly large effects on cognition as resources recede from high to medium levels in the course of aging. Direct empirical support for this hypothesis comes from a study by Nagel et al. (2008), who reported that the effects of the Catechol-O-Methyltransferase (COMT) gene on cognitive performance are magnified in old age and interacted with the Brain-Derived Neurotrophic Factor (BDNF) gene. We conclude that common genetic polymorphisms contribute to the increasing heterogeneity of cognitive functioning in old age. Extensions of the hypothesis to other polymorphisms are discussed. (150 of 150 words
Psychological principles of successful aging technologies: A mini-review
Based on resource-oriented conceptions of successful life-span development, we propose three principles for evaluating assistive technology: (a) net resource release; (b) person specificity, and (c) proximal versus distal frames of evaluation. We discuss how these general principles can aid the design and evaluation of assistive technology in adulthood and old age, and propose two technological strategies, one targeting sensorimotor and the other cognitive functioning. The sensorimotor strategy aims at releasing cognitive resources such as attention and working memory by reducing the cognitive demands of sensory or sensorimotor aspects of performance. The cognitive strategy attempts to provide adaptive and individualized cuing structures orienting the individual in time and space by providing prompts that connect properties of the environment to the individual's action goals. We argue that intelligent assistive technology continuously adjusts the balance between `environmental support' and `self-initiated processing' in person-specific and aging-sensitive ways, leading to enhanced allocation of cognitive resources. Furthermore, intelligent assistive technology may foster the generation of formerly latent cognitive resources by activating developmental reserves (plasticity). We conclude that `lifespan technology', if co-constructed by behavioral scientists, engineers, and aging individuals, offers great promise for improving both the transition from middle adulthood to old age and the degree of autonomy in old age in present and future generations. Copyright (C) 2008 S. Karger AG, Basel
Conductance statistics from a large array of sub-10 nm molecular junctions
Devices made of few molecules constitute the miniaturization limit that both
inorganic and organic-based electronics aspire to reach. However, integration
of millions of molecular junctions with less than 100 molecules each has been a
long technological challenge requiring well controlled nanometric electrodes.
Here we report molecular junctions fabricated on a large array of sub-10 nm
single crystal Au nanodots electrodes, a new approach that allows us to measure
the conductance of up to a million of junctions in a single conducting Atomic
Force Microscope (C-AFM) image. We observe two peaks of conductance for
alkylthiol molecules. Tunneling decay constant (beta) for alkanethiols, is in
the same range as previous studies. Energy position of molecular orbitals,
obtained by transient voltage spectroscopy, varies from peak to peak, in
correlation with conductance values.Comment: ACS Nano (in press
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