Liquid–Liquid Diffusion‐Assisted Crystallization: A Fast and Versatile Approach Toward High Quality Mixed Quantum Dot‐Salt Crystals

Here, a new, fast, and versatile method for the incorporation of colloidal quantum dots (QDs) into ionic matrices enabled by liquid–liquid diffusion is demonstrated. QDs bear a huge potential for numerous applications thanks to their unique chemical and physical properties. However, stability and processability are essential for their successful use in these applications. Incorporating QDs into a tight and chemically robust ionic matrix is one possible approach to increase both their stability and processability. With the proposed liquid–liquid diffusion‐assisted crystallization (LLDC), substantially accelerated ionic crystallization of the QDs is shown, reducing the crystallization time needed by one order of magnitude. This fast process allows to incorporate even the less stable colloids including initially oil‐based ligand‐exchanged QDs into salt matrices. Furthermore, in a modified two‐step approach, the seed‐mediated LLDC provides the ability to incorporate oil‐based QDs directly into ionic matrices without a prior phase transfer. Finally, making use of their processability, a proof‐of‐concept white light emitting diode with LLDC‐based mixed QD‐salt films as an excellent color‐conversion layer is demonstrated. These findings suggest that the LLDC offers a robust, adaptable, and rapid technique for obtaining high quality QD‐salts.     

Strain relief in epitaxial HgCdTe by growth on a reticulated substrate

In nearly all cases when an epitaxial layer of HgCdTe is grown on a CdZnTe substrate, there will be a finite lattice mismatch due to the lack of precise control over the ZnTe mole fraction. This leads to strains in the layer, which can be manifested in one or more ways: (1) as misfit dislocations near the interface, (2) as threading dislocations, (3) as surface topographical textures, and (4) as cross-hatch lines seen by x-ray topography. We have found that much of the strain can be relieved by growing on a reticulated substrate. Specifically, when the substrate has been etched to form mesas prior to growth of the layer, the resulting layer on the tops of the mesas shows evidence of significantly reduced strain. CdZnTe substrates oriented (111)A were prepared with two sets of mesas on 125 μm centers and 60 μm centers, and with other planar areas remaining for comparison. From a Hg melt, a layer of LWIR HgCdTe was grown about 16 μm thick on each substrate. Nomarski microscopy showed that the layers on the mesa tops were extremely flat, showing no sign of curvature or surface texture. X-ray topography showed no cross hatch on the mesa tops, while the usual cross hatch appeared in the planar regions. The LPE layer extended laterally beyond the edges of the original mesa because of faster growth in non-(111) directions. Samples were cleaved and examined in cross section. The linear density of etch pits seen in the cross section near the substrate, which represent misfit dislocations, was three times lower in the layer on the mesas than in the layer in the unpatterned region, although both regions have the same layer/substrate lattice mismatch. When an epilayer is grown on an unpatterned wafer (the conventional approach), the growth in any small region is confined laterally by the growing layer in the neighboring regions. However, when growth occurs on a reticulated surface, the lateral confinement is removed, providing strain relief and fewer defects.     

A substrate-dependent CAD model for ceramic multilayer capacitors

In this paper, a substrate-dependent lumped-element model for ceramic multilayer capacitors is presented. The height and dielectric constant of a substrate have a significant impact on the frequency response of a chip capacitor, and these effects cannot be treated independently from the capacitor model. Rather, the equivalent-circuit parameters in the model must be made to vary in accordance with changes in the substrate. The model presented in this paper is suitable for microstrip-mounted components, and has been applied up to 10 GHz for values from 0.5 pF to 0.47 μF, and for FR-4 substrates ranging in height from 5 to 62 mil. The modeling and extraction procedure is demonstrated for 0805- and 1206-style capacitors     

Unsupervised image-set clustering using an information theoretic framework.

In this paper, we combine discrete and continuous image models with information-theoretic-based criteria for unsupervised hierarchical image-set clustering. The continuous image modeling is based on mixture of Gaussian densities. The unsupervised image-set clustering is based on a generalized version of a recently introduced information-theoretic principle, the information bottleneck principle. Images are clustered such that the mutual information between the clusters and the image content is maximally preserved. Experimental results demonstrate the performance of the proposed framework for image clustering on a large image set. Information theoretic tools are used to evaluate cluster quality. Particular emphasis is placed on the application of the clustering for efficient image search and retrieval.     

Highly Conductive Carbon Nanotube‐Graphene Hybrid Yarn

An efficient procedure for the fabrication of highly conductive carbon nanotube/graphene hybrid yarns has been developed. To start, arrays of vertically aligned multi‐walled carbon nanotubes (MWNT) are converted into indefinitely long MWNT sheets by drawing. Graphene flakes are then deposited onto the MWNT sheets by electrospinning to form a composite structure that is transformed into yarn filaments by twisting. The process is scalable for yarn fabrication on an industrial scale. Prepared materials are characterized by electron microscopy, electrical, mechanical, and electrochemical measurements. It is found that the electrical conductivity of the composite MWNT‐graphene yarns is over 900 S/cm. This value is 400% and 1250% higher than electrical conductivity of pristine MWNT yarns or graphene paper, respectively. The increase in conductivity is asssociated with the increase of the density of states near the Fermi level by a factor of 100 and a decrease in the hopping distance by an order of magnitude induced by grapene flakes. It is found also that the MWNT‐graphene yarn has a strong electrochemical response with specific capacitance in excess of 111 Fg^?1. This value is 425% higher than the capacitance of pristine MWNT yarn. Such substantial improvements of key properties of the hybrid material can be associated with the synergy of MWNT and graphene layers in the yarn structure. Prepared hybrid yarns can benefit such applications as high‐performance supercapacitors, batteries, high current capable cables, and artificial muscles.     

Quantitative and Qualitative Evaluation of Geometric Deconvolution of Distortion in Limited-View Computed Tomography

Images reconstructed using a set of a few projections spanning a narrow angular range suffer from a systematic geometric distortion due to the point spread function of the reconstruction process. This distortion can be removed by deconvolving a complementary set of projections calculated from the initial reconstruction. Homomorphic deconvolution and inverse filtering techniques were used for this purpose. A second reconstruction is computed from the union of both sets of projections. Although the distortion is removed, the results are noisy due to problems associated with inverse filtering. Two-dimensional (2-D) filtering of the second reconstruction is performed to reduce the noise, while preserving the reduction in geometric distortion. Results obtained using several 2-D filters were compared visually and by point noise content, distortion, and projection error measures. Quantitative measures of geometric distortion removal for test images are also described.     

How to forge RSA key certificates

It is shown how certain types of key certificate suggested for preventing masquerade when using the RSA public key cryptosystem can be easily forged. A remedy is given, which is to use an alternative type of certificate, incorporating a one-way function.