Elastic properties of porous thermosetting polymers

A new equationE =E ₀ (1 –bp) ⁿ has been derived semi-empirically to describe the porosity dependence of elastic properties of thermosetting polymers. The material constantb is defined as a pore distribution geometry factor and the other material constantn is dependent on pore geometry. The equation shows good agreement with the data on porous polyester and epoxy resins.     

In situ synchrotron X-ray studies on copper-nickel 5 V Mn oxide spinel cathodes for Li-ion batteries

Partial substitution of Mn in lithium manganese oxide spinel materials by Cu and Ni greatly affects the electrochemistry and the cycle life characteristics of the cathode. Substitution with either metal or a combination of both metals in the spinel lattice structure reduces the 3.9-4.2 V potential plateaus associated with the conversion of Mn³⁺ to Mn⁴⁺. Higher potential plateau associated with oxidation of the substituted transition elements is also observed. These substituents also significantly alter the onset of Jahn-Teller distortions in the 3 V potential plateau. Synchrotron based in situ X-ray absorption (XAS) was used to determine the exact nature of the oxidation state changes in order to explain the overall observed capacities at different potential plateaus. The studies on LiCu_0.5Mn_1.5O₄ show single phase behavior in the 4-5 V potential region with a good cycle life. Lower cycle life characteristic observed in cycling LiNi_0.5Mn_1.5O₄ and LiNi_0.25Cu_0.25Mn_1.5O₄ versus Li metal are ascribed to coexistence of several phases in this potential region. However, LiCu_0.5Mn_1.5O₄ shows onset of Jahn-Teller distortions in the 3 V potential plateau, in contrast to LiNi_0.5Mn_1.5O₄ and LiNi_0.25Cu_0.25Mn_1.5O₄ cathode materials.     

Viscous flow past a porous sphere with an impermeable core : effect of stress jump condition

An arbitrary flow of a viscous, incompressible fluid past a porous sphere of radius `a' with an impermeable core of radius `b', using Brinkman's equation in the porous region is discussed. At the interface of the clear fluid and porous region, stress jump boundary condition for the tangential stresses along with the continuity of normal stresses and the velocity components are used. On the surface of the impermeable core no slip condition is used. The corresponding Faxen's laws are derived to compute the drag and torque acting on the surface r=a. It is found that the drag and torque not only change with the change of the permeability, but also a significant effect of the stress jump co-efficient is observed. The variation of drag and torque with permeability for different thickness (a-b) of the porous region as well as for different values of stress jump coefficient is discussed when the basic flow is due to uniform flow, two dimensional irrotational flow, doublet in a uniform flow, stokeslet, rotlet. In case of uniform flow the flow field has been plotted. In all the cases, a significant effect of the stress jump coefficient has been realized.     

Experimental realization of quantum cheque using a five-qubit quantum computer

Quantum cheques could be a forgery-free way to make transaction in a quantum networked banking system with perfect security against any no-signalling adversary. Here, we demonstrate the implementation of quantum cheque, proposed by Moulick and Panigrahi (Quantum Inf Process 15:2475–2486, 2016), using the five-qubit IBM quantum computer. Appropriate single qubit, CNOT and Fredkin gates are used in an optimized configuration. The accuracy of implementation is checked and verified through quantum state tomography by comparing results from the theoretical and experimental density matrices.     

Grounded discovery of symbols as concept–language pairs

In human designer usage, symbols have a rich semantics, grounded on experience, which permits flexible usage — e.g. design ideation is improved by meanings triggered by contrastive words. In computational usage however, symbols are syntactic tokens whose semantics is mostly left to the implementation, resulting in brittle failures in many knowledge-based systems. Here we ask if one may define symbols in computational design as {label,meaning} pairs, as opposed to merely the label. We consider three questions that must be answered to bootstrap a symbol learning process: (a) which concepts are most relevant in a given domain, (b) how to define the semantics of such symbols, and (c) how to learn labels for these so as to form a grounded symbol. We propose that relevant symbols may be discovered by learning patterns of functional viability. The stable patterns are information-conserving codes, also called chunks in cognitive science, which relate to the process of acquiring expertise in humans. Regions of a design space that contain functionally superior designs can be mapped to a lower-dimensional manifold; the inter-relations of the design variables discovered thus constitute the chunks. Using these as the initial semantics for symbols, we show how the system can acquire labels for them by communicating with human designers. We demonstrate the first steps in this process in our baby designer approach, by learning two early grounded symbols, tight and loose.     

On the approximate frequentist validity of the posterior quantiles of a parametric function: results based on empirical and related likelihoods

With reference to a wide class of empirical and related likelihoods, we study priors which ensure approximate frequentist validity of the posterior quantiles of a general parametric function. It is seen that no data-free prior entails such frequentist validity but, at least for the usual empirical likelihood, a data-dependent prior serves the purpose. Accounting for the nonlinearity of the parametric function of interest requires special attention in the derivation. A simulation study is seen to provide support, in finite samples, to our asymptotic results.     

Evaluation of high‐resolution and mobile display systems for digital radiology in dark and bright environments using human and computational observers

Abstract— As digital display systems replace film traditionally used for reading radiographic images, resource‐intensive acceptance testing must be performed to ensure that quality meets and maintains desired specifications. If machine observers can replace human readers, whose performances are highly variable, the results will be more consistent and less costly. To be effective, however, the automated observers must track human performance. An approach for a model observer, validated with human readers, for the evaluation of the visibility of low‐contrast small targets in high‐resolution and mobile displays under different ambient illumination, will be described. The displays were tested using CDMAM‐like digital phantoms containing disks of varying diameters and contrasts on a flat background. For this task, we find the best indicator of display performance to be the display's ability to represent small luminance contrast, not resolution or pixel size. The results confirm that high‐resolution systems perform better under low illumination while illuminance has a minor impact on the mobile‐display performance. Finally, the results show that the machine observer tracks the performance of human readers. Machine observers with proper validation can replace humans in the acceptance testing procedures, saving the testers both time and money.     

Electrochemical studies of ferrocene in a lithium ion conducting organic carbonate electrolyte

We carried out a detailed study of the kinetics of oxidation of ferrocene (Fc) to ferrocenium ion (Fc⁺) in the non-aqueous lithium ion conducting electrolyte composed of a solution of 1 M LiPF₆ in 1:1 EC:EMC solvent mixture. This study using cyclic (CV) and rotating disk electrode (RDE) voltammetry showed that the Fc⁰/Fc⁺ redox couple is reversible in this highly concentrated electrolyte. The ferrocene and ferrocenium ion diffusion coefficients (D) were calculated from these results. In addition, the electron transfer rate constant (k⁰) and the exchange current density for the oxidation of ferrocene were determined. A comparison of the kinetic data obtained from the two electrochemical techniques appears to show that the data from the RDE experiments are more reliable because they are collected under strict mass transport control. A Tafel slope of c.a. 79 mV/decade and a transfer coefficient α of 0.3 obtained from analysis of the RDE data for ferrocene oxidation suggest that the structure of the activated complex is closer to that of the oxidized specie due to strong interactions with the carbonate solvents. The experiments reported here are relevant to the study of redox reagents for the chemical overcharge protection of Li-ion batteries.