A light-field camera captures both the intensity and the direction of incoming light
. This enables a user to refocus pictures and afterwards reconstruct information on the depth of field. Research ...on light-field imaging can be divided into two components: acquisition and rendering. Microlens arrays have been used for acquisition, but obtaining broadband achromatic images with no spherical aberration remains challenging. Here, we describe a metalens array made of gallium nitride (GaN) nanoantennas
that can be used to capture light-field information and demonstrate a full-colour light-field camera devoid of chromatic aberration. The metalens array contains an array of 60 × 60 metalenses with diameters of 21.65 μm. The camera has a diffraction-limited resolution of 1.95 μm under white light illumination. The depth of every object in the scene can be reconstructed slice by slice from a series of rendered images with different depths of focus. Full-colour, achromatic light-field cameras could find applications in a variety of fields such as robotic vision, self-driving vehicles and virtual and augmented reality.
Magnetic nickel–ruthenium based catalysts on resin beads for hydrogen generation from alkaline NaBH
4 solutions were synthesized with combined methods of chemical reduction and electroless ...deposition. Factors, such as solution temperature, NaBH
4 loadings, and NaOH concentration, on performance of these catalysts on hydrogen production from alkaline NaBH
4 solutions were investigated. Furthermore, characteristics of these nickel–ruthenium based catalysts were carried out by using various instruments, such as SEM/EDS, XPS, SQUID VSM and BET. These catalysts can be easily recycled from spent NaBH
4 solution with permanent magnets owing to their intrinsic soft ferromagnetism and, therefore, reducing the operation cost of the hydrogen generation process. A rate of hydrogen evolution as high as
ca. 400
mL min
−1 g
−1 could be reached at 35
°C in 10
wt% NaBH
4 solution containing 5
wt% NaOH using Ni–Ru/50WX8 catalysts. Activation energy of hydrogen generation using such catalysts is estimated at 52.73
kJ mol
−1.
Dense bismuth telluride (Bi
2Te
3) bulk materials with randomly packed grains were prepared using attrition milling and spark plasma sintering (SPS). Experimental results indicate that the high ...energy ball milling produces donor-like carriers in Bi
2Te
3 samples and enhances thermoelectric transport properties such as carrier concentration, electrical conductivity and power factor. The maximum power factor of 1
mW
m
−1
K
−2 was obtained at 500
K for the 3
h-milled Bi
2Te
3 sample sintered at 573
K. Results of this study demonstrate that adequately controlling the milling time can enhance the thermoelectric performance of Bi
2Te
3 bulk materials without adding dopants.
A method for numerically calculating the rate distortion region for the central estimation officer (CEO) problem when the sources are independent is derived by generalizing the Blahut-Arimoto ...algorithm. Unlike the traditional rate distortion function computation problem, the Lagrangian for the CEO rate distortion region can be nonconvex. When the Lagrangian is convex, the presented algorithm is converged from every initialization to the global optimum under some additional uniqueness conditions. When the Lagrangian is nonconvex, the convergent value obtained by the algorithm can be initialization dependent. To handle these nonconvex cases, an explicit nonrandom initialization that is in the region of attraction of the global optimum for low distortions is provided. Some example problems motivated by remote lossy function computation in sensor networks and wireless resource controllers highlight that both the convex and nonconvex cases occur in practice and the utility of the algorithm in computing their rate distortion regions.
Ammonia borane (NH
3BH
3, AB), one kind of promising hydrogen storage materials, is hydrolyzed to produce hydrogen in presence of HCl, Co/IR-120 and Ru/IR-120 catalysts. The kinetics analysis of the ...AB hydrolysis shows that hydrogen production is of the first-order reaction in regard to both concentrations of ammonia borane and catalysts initially present, respectively. The hydrolyzate of ammonia borane after hydrogen evolution is also characterized with XRD, FT-IR and
11B NMR. Boric acid (H
3BO
3) is found to be the dominant product in the hydrolyzate. Besides, the produced gas is discovered to contain both hydrogen and ammonia according to the GC–MS analysis and the indophenol colorimetric analysis. A possible reaction pathway on hydrogen generation from hydrolysis of ammonia borane is, accordingly, proposed based on the existence of boric acid, hydrogen and ammonia in the products. The total life cycle of ammonia borane is also proposed to illustrate formation of different intermediates during the AB hydrolysis for hydrogen generation and a possible regeneration scheme of the spent ammonia borane.
► Hydrogen is produced from hydrolysis of ammonia borane in presence of light-weight Co or Ru catalysts. ► The hydrolysis reaction of ammonia borane is of the first-order in concentrations of ammonia borane and catalysts. ► Ammonia is conjointly produced with hydrogen from hydrolysis of ammonia borane, and can be reduced with proper management of exothermic reaction heat. ► Boric acid is the major hydrolyzate of ammonia borane for hydrogen evolution.
A key aspect of many resource allocation problems is the need for the resource controller to compute a function, such as the max or arg max, of the competing users' metrics. Information must be ...exchanged between the competing users and the resource controller in order for this function to be computed. In many practical resource controllers, the competing users' metrics are communicated to the resource controller, which then computes the desired extremization function. However, in this paper, it is shown that information rate savings can be obtained by recognizing that the controller only needs to determine the result of this extremization function. If the extremization function is to be computed losslessly, the rate savings are shown in most cases to be at most 2 b independent of the number of competing users. Motivated by the small savings in the lossless case, simple achievable schemes for both the lossy and interactive variants of this problem are considered. It is shown that both of these approaches have the potential to realize large rate savings, especially in the case where the number of competing users is large. For the lossy variant, it is shown that the proposed simple achievable schemes are in fact close to the fundamental limit given by the rate distortion function.
In this work, a ruthenium catalyst was prepared for hydrogen generation from the hydrolysis reaction of an alkaline sodium borohydride solution. The reactions were carried out in a batch reactor at ...temperatures of 10, 30, 40 and 60
°C for at least 70% conversion or 500
min, whichever came first. The experimental data was fitted to the following three kinetic models: zero-order, first-order, and Langmuir–Hinshelwood. The results indicate that the Langmuir–Hinshelwood model gives a reasonable description of the hydrogen generation rate over the entire temperature range studied as well as the time spans of the experiments. The zero-order model gives good behavior description only at relatively low temperature, i.e. 10
°C. The first-order model works fairly well for a temperature range up to 30
°C.
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