A good heterogeneous catalyst for a given chemical reaction very often has only one specific type of surface site that is catalytically active. Widespread methodologies such as Sabatier-type activity ...plots determine optimal adsorption energies to maximize catalytic activity, but these are difficult to use as guidelines to devise new catalysts. We introduce "coordination-activity plots" that predict the geometric structure of optimal active sites. The method is illustrated on the oxygen reduction reaction catalyzed by platinum. Sites with the same number of first-nearest neighbors as (111) terraces but with an increased number of second-nearest neighbors are predicted to have superior catalytic activity. We used this rationale to create highly active sites on platinum (111), without alloying and using three different affordable experimental methods.
Resonant Optical Antennas Mühlschlegel, P.; H. -J. Eisler; Martin, O. J. F. ...
Science,
06/2005, Letnik:
308, Številka:
5728
Journal Article
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We have fabricated nanometer-scale gold dipole antennas designed to be resonant at optical frequencies. On resonance, strong field enhancement in the antenna feed gap leads to white-light ...supercontinuum generation. The antenna length at resonance is considerably shorter than one-half the wavelength of the incident light. This is in contradiction to classical antenna theory but in qualitative accordance with computer simulations that take into account the finite metallic conductivity at optical frequencies. Because optical antennas link propagating radiation and confined/enhanced optical fields, they should find applications in optical characterization, manipulation of nanostructures, and optical information processing.
Gastroparesis is a neuromuscular disorder of the upper gastrointestinal tract. Patients typically complain about early satiety, postprandial fullness, nausea and vomiting. Etiology is multifactorial. ...Treatment strategies include nutritional support, pharmacologic agents or surgery for refractory cases. Metoclopramide is the first and only FDA approved pharmacologic agent for (diabetic) Gastroparesis. A couple of compounds are currently in clinical testing. Some beacons of hope have failed recently, however. Here we present an update on possible future treatment options.
We report on the design, production, and performance of compact 40-cm3 Time Projection Chambers (TPCs) that detect fast neutrons by measuring the three-dimensional (3D) ionization distribution of ...nuclear recoils in 4He:CO2 gas at atmospheric pressure. We use these detectors to characterize the fast-neutron flux inside the Belle II detector at the SuperKEKB electron–positron collider in Tsukuba, Japan, where the primary design constraint is a small form factor. We find that the TPCs meet or exceed all design specifications, and are capable of measuring the 3D surface shape and charge density profile of ionization clouds from nuclear recoils and charged tracks in exquisite detail. Scaled-up detectors based on the detection principle demonstrated here may be suitable for directional dark matter searches, measurements of coherent neutrino–nucleus scattering, and other experiments requiring precise detection of neutrons or nuclear recoils.
The interaction of a single quantum dot with a bowtie antenna is demonstrated for visible light. The antenna is generated at the apex of a Si3N4 atomic force microscopy tip by focused ion beam ...milling. When scanned over the quantum dot, its photoluminescence is enhanced while its excited-state lifetime is decreased. Our observations demonstrate that the relaxation channels of a single quantum emitter can be controlled by coupling to an efficiently radiating metallic nanoantenna.
We present a method that allows for a quantitative measurement of the surface self-diffusion on nanostructures, such as nanoparticles, at the atomic scale using aberration-corrected high-resolution ...transmission electron microscopy (HRTEM). The diffusion coefficient can be estimated by measuring the fluctuation of the atom column occupation at the surface of Au nanoparticles, which is directly observable in temporal sequences of HRTEM images. Both a Au icosahedron and a truncated Au octahedron are investigated, and their diffusion coefficients are found to be in the same order of magnitude, D = 10–17 to 10–16 cm2/s. It is to be assumed that the measured surface diffusion is affected by the imaging electron beam. This assumption is supported by the observed instability of a (5 × 1) surface reconstruction on a {100} Au facet.
•Electrolyte composition affects the performance of catalytic centers.•Alkali metal cations as well as anions mainly influence the activity.•Ionic liquids often change selectivity of ...electrocatalysts.
The capability to efficiently design new electrocatalytic materials depends on a deeper understanding of all factors influencing the performance of active sites under reaction conditions. While the electrode surface structure and composition are primary, the role of electrolyte components in the activity and selectivity of catalytic centers is also significant, if not drastic. Interestingly, the performance of electrocatalysts is not only affected by the so-called specifically adsorbing ions. Many species, which are generally considered “inert”, can de facto change the key properties of the catalytic sites. However, the origin of such experimentally observed effects is often poorly understood. Despite the fact that certain trends are frequently observed, further investigation of model systems and development in the field of quantum chemistry calculations are necessary in order to gain deeper insight into the effects of the electrolyte composition. The goal of this review article is to summarize and analyze recent achievements in the elucidation of the non-trivial effects of electrolyte components and their contribution to the observed performance of catalytic centers. A particular focus is set on the influence of (i) alkali metal cations, (ii) commonly used anions, (iii) unexpected pH effects, as well as (iv) the impact of certain ionic liquids on the activity and selectivity of catalytic systems. Reactions which are essential for the prospective sustainable energy provision schemes are selected as illustrative examples.
BDAQ53 is a readout system and verification framework for hybrid pixel detector readout chips of the RD53 family. These chips are designed for the upgrade of the inner tracking detectors of the ATLAS ...and CMS experiments. BDAQ53 is used in applications where versatility and rapid customization are required, such as in laboratory testing environments, test beam campaigns, and permanent setups for quality control measurements. It consists of custom and commercial hardware, a Python-based software framework, and FPGA firmware. BDAQ53 is developed as open source software with both software and firmware being hosted in a public repository.
Depleted Monolithic Active Pixel Sensors (DMAPS) are monolithic pixel detectors with high-resistivity substrates designed for use in high-rate and high-radiation environments. They are produced in ...commercial CMOS processes, resulting in relatively low production costs and short turnaround times, and offer a low material budget. LF-Monopix1 and TJ-Monopix1 are large DMAPS prototypes produced in 150 nm LFoundry and 180 nm TowerJazz technology, respectively, that follow two different design concepts regarding the charge collection electrode. Prototypes of both development lines have been extensively tested and characterized over the last years. The second-generation Monopix prototypes, Monopix2, were recently produced. They were designed to address the shortcomings of their predecessors, in particular related to radiation hardness and cross talk, and further improve upon their performance. The latest measurements with LF-Monopix1 and TJ-Monopix1 concerning hit efficiency, depletion, and radiation hardness as well as the initial test results of the new Monopix2 prototypes are presented.
•Measurement of mass transfer coefficients in a helical pipe.•Locally resolved measurement through colour reaction with resazurin.•Comparison with straight horizontal tube shows the advantages of the ...helix.•First two to three turns have about one order of magnitude higher volumetric mass transfer coefficients.
The gas-liquid mass transfer of oxygen has been examined experimentally in a helically-coiled pipe using an optical colorimetric method. Two tracer redox-reactions have been used for this purpose: (i) methylene blue and (ii) resazurin. The gas hold-up has been varied from 0.1 to 0.6, and liquid flow rate from 0.37 to 0.68 l/min, both leading to plug-flow conditions in the helix for all parameter combinations. A progress variable has been defined to measure the advancement of the reaction and thus, oxygen transfer to the liquid. The resazurin reaction turned out to be more appropriate for mass transfer studies, due to the bigger time constant difference of oxidation and reduction. Therefore, it can be adapted more easily to the specific conditions of the set-up. It also possesses more intense colours and higher fluorescence intensity, which might be useful for other mass transfer studies. As expected, the oxygen mass transfer increases with gas hold up, but liquid flow rate has little influence. A comparison with a horizontal tube of the same diameter shows the drastically increased mass transfer in the helix, due to better radial mixing and different flow pattern. Depending on the experimental conditions, oxygen concentration in the helix was up to twice that of the horizontal tube. This can be explained by the much higher liquid side mass transfer velocity, which is determined in this study from the experimental kla-values and specific bubble surface per turn of the helix. For this purpose, bubble dimensions and gas-liquid cell volumes have been determined from the experimental images. The paper thus presents a locally resolved characterization of gas-liquid mass transfer in a helically coiled reactor. The high mass transfer especially during the first turns of the helix shows its advantages compared to a straight tube.
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