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901.
Thomas Hanauer Dr. Johann Rietzler Prof. Dr. Thomas R. Rüde Prof. Dr. Stefan Wohnlich Willibald Stichler 《Grundwasser》2006,11(3):194-206
The sharply confined pattern of arsenic groundwater contamination at the site of a historic dye factory suggests that natural attenuation processes are active and efficient. The supporting data included sequential soil extractions combined with analyses of other soil properties like carbonate content, the loss of ignition and cation exchange capacity and the extraction characteristics of the original dye pigment. The results point to iron oxides and iron hydroxides as the most important adsorbers for copper and arsenic. The attenuation of copper can be estimated to be very efficient mainly due to its pH-controlled low solubility. Besides the specific adsorption to iron oxides, however, arsenic exhibits a rather large, loosely bound and easily exchangeable fraction. The speciation of arsenic in groundwater is dominated by As(V). The oxidation state of the original pigment is As(III). In some parts of the aquifer where suboxic conditions prevail, this oxidation state is conserved. In oxic zones of the aquifer, oxidation to the pentavalent form As(V) takes place. 相似文献
902.
Stefan K. Zeisler Vinder Jaggi 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2008,590(1-3):18
The TRIUMF Applied Technology Group operates high-power industrial cyclotrons for commercial radioisotope production. Two of these cyclotrons, TR30-1 and TR30-2, are capable of accelerating H− ions to an energy of 30 MeV and beam currents in excess of 1000 μA. For many years, amorphous carbon foils of approximately 2.0 μm thickness have been utilized to extract proton beams from these accelerators.Novel multilayer foils consisting of layers of amorphous and diamond-like carbon (DLC) of 2.0±0.2 μm thickness were manufactured in-house by carbon arc and pulsed laser deposition, respectively. In the TR30 cyclotrons, the new composite foils with 25% DLC content show a three times longer lifetime than the purely amorphous foils, while maintaining their excellent physical and mechanical characteristics during irradiation. 相似文献
903.
Rupitsch SJ Kindermann S Zagar BG 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2008,55(1):225-235
This paper is concerned with the characterization of the true locally resolved surface normal velocity of an assumed piston-type ultrasonic transducer. Instead of involving a very complicated direct pointwise measurement of the velocity distribution, an inverse problem is solved which yields a spatially discretized weighting vector for the surface normal velocity of the transducer. The study deals with a spherically focused high frequency transducer, which is driven in pulse-echo mode. As a means of posing the inverse problem, the active transducer surface is divided into annuli of equal surface so that for each annulus the spatial impulse response can be calculated. An acrylic glass plate acts as a simple structured target. The resulting ill-posed nonlinear inverse problem is solved with an iterative regularized Gauss-Newton algorithm. The solution of the inverse problem yields an estimated weight for the surface normal velocity for each annulus. Experimental results for a thin copper wire target are compared to simulation results for both uniform and estimated surface normal velocities. 相似文献
904.
We analyzed seven years of pre‐program and post‐program survey data to evaluate the Clarkson University Research Experience for Undergraduates (REU) Site Program in Environmental Science and Engineering, and evaluated whether our program was successful at meeting the intended outcome of increasing participants' likelihood of attending graduate school and pursuing a career in science or engineering research or education. We also evaluated how participant satisfaction in the program changed with the addition of a weekly seminar on environmental sustainability that was intended to improve participants' understanding of the societal value of their research projects. Participant satisfaction in the Clarkson REU Program was high, and increased after the addition of the sustainability seminar. Participants' intention to attend graduate or professional school increased after participating in the program, but their intention to pursue a career in science or engineering research declined. Over 60 percent of participants eventually attended graduate or professional school. 相似文献
905.
Three-dimensional photonic metamaterials at optical frequencies 总被引:3,自引:0,他引:3
Metamaterials are artificially structured media with unit cells much smaller than the wavelength of light. They have proved to possess novel electromagnetic properties, such as negative magnetic permeability and negative refractive index. This enables applications such as negative refraction, superlensing and invisibility cloaking. Although the physical properties can already be demonstrated in two-dimensional (2D) metamaterials, the practical applications require 3D bulk-like structures. This prerequisite has been achieved in the gigahertz range for microwave applications owing to the ease of fabrication by simply stacking printed circuit boards. In the optical domain, such an elegant method has been the missing building block towards the realization of 3D metamaterials. Here, we present a general method to manufacture 3D optical (infrared) metamaterials using a layer-by-layer technique. Specifically, we introduce a fabrication process involving planarization, lateral alignment and stacking. We demonstrate stacked metamaterials, investigate the interaction between adjacent stacked layers and analyse the optical properties of stacked metamaterials with respect to an increasing number of layers. 相似文献
906.
Nanoparticle self-assembly on a DNA-scaffold written by single-molecule cut-and-paste 总被引:1,自引:0,他引:1
Self-assembly guided by molecular recognition has in the past been employed to assemble nanoparticle superstructures like hypercrystals or nanoparticle molecules. An alternative approach, the direct molecule-by-molecule assembly of nanoscale superstructures, was demonstrated recently. Here we present a hybrid approach where we first assemble a pattern of binding sites one-by-one at a surface and then allow different nanoparticles to attach by self-assembly. For this approach, biotin bearing DNA oligomers were picked up from a depot using a cDNA strand bound to an AFM tip. These units were deposited in the target area by hybridization, forming a recognition pattern on this surface. Fluorescent semiconductor nanoparticles conjugated with streptavidin were allowed to assemble on this scaffold and to form the final nanoparticle superstructures. 相似文献
907.
Tang Xiaohong Yin Zongyou Teng Jinghua Du Anyan Chin Mee Koy 《Nanotechnology, IEEE Transactions on》2008,7(4):422-426
908.
Loher S Schneider OD Maienfisch T Bokorny S Stark WJ 《Small (Weinheim an der Bergstrasse, Germany)》2008,4(6):824-832
The antimicrobial activity of silver has attracted significant research interest and contributes to an exponentially growing use of this noble metal in commodity products. In this investigation, we describe a general approach to increase the antimicrobial activity of a silver-containing surface by two to three orders of magnitude. The use of 1-2-nm silver particles decorating the surface of 20-50-nm carrier particles consisting of a phosphate-based, biodegradable ceramic allows the triggered release of silver in the presence of a growing microorganism. This effect is based on the organism's requirements for mineral uptake during growth creating a flux of calcium, phosphate, and other ions to the organism. The growing micro-organism dissolves the carrier containing these nutrients and thereby releases the silver nanoparticles. Further, we demonstrate the rapid self-sterilization of polymer surfaces containing silver on calcium phosphate nanoparticles using a series of human pathogens. Colony-forming units (viable bacteria or fungi counts) have been routinely reduced below detection limit and suggest application of these self-sterilizing surfaces in hospital environments, food and pharmaceutical processing, and personal care. 相似文献
909.
910.
Fölling J Polyakova S Belov V van Blaaderen A Bossi ML Hell SW 《Small (Weinheim an der Bergstrasse, Germany)》2008,4(1):134-142
We have designed and synthesized a new functional (amino reactive) highly efficient fluorescent molecular switch (FMS) with a photochromic diarylethene and a rhodamine fluorescent dye. The reactive group in this FMS -N-hydroxysuccinimide ester- allows selective labeling of amino containing molecules or other materials. In ethanolic solutions, the compound displays a large fluorescent quantum yield of 52 % and a large fluorescence modulation ratio (94 %) between two states that may be interconverted with red and near-UV light. Silica nanoparticles incorporating the new FMS were prepared and characterized, and their spectroscopic and switching properties were also studied. The dye retained its properties after the incorporation into the silica, thereby allowing light-induced reversible high modulation of the fluorescence signal of a single particle for up to 60 cycles, before undergoing irreversible photobleaching. Some applications of these particles in fluorescence microscopy are also demonstrated. In particular, subdiffraction images of nanoparticles were obtained, in the focal plane of a confocal microscope. 相似文献