Mathematical modelling and numerical simulation of ordered porosity metal materials formation

Ordered porosity metal materials belong to a relatively new class of porous materials named gasars. This paper presents a mathematical model of the complex physical phenomena in the production of gasars. Analyses for heat transfer, solidification kinetics and gas diffusion were coupled to describe the formation of unique gasar structure. Several criterial functions were introduced to provide significant quantitative information about the relationship between the operating technological parameters and the final structure. The computational outcomes of the numerical simulation were compared with the characteristics of real gasar ingots. The model was applied to determine the boundary conditions that would provide approximately constant physical conditions on the solidification front. The structure sensitiveness of gasars with respect to the different technological parameters is discussed.     

利用精密仪表放大器实现负压电流检测

监测正电源的电流时，通常使用高边检流放大器。然而，对于ISDN、电信电源，通常需要一个工作在负电源的检流放大器。本文介绍了一种采用MAX4460单电源仪表放大器设计负压检流放大器的方法。     

Novel Ultrahigh-Energy Materials

This paper reviews the recent work carried out in the field of modern high-energy materials (HEMs) with the emphasis on homoleptic polynitrogen compounds. A large volume of quantum-chemical investigations have predicted the possibility of existence of polynitrogen compounds not only as short-lived transient species but also in the form of isolable discrete molecules. Despite the theoretical speculations, only a few polynitrogen ions are known today in addition to well-entrenched N _1– ³ discovered almost 100 year ago. Extraordinary potential of these green molecules to deliver high amounts of energy in comparison with todays and tomorrows most powerful HEMs, namely, hexanitrohexaazaisowurtzitane (CL-20) and octanitrocubane (ONC), has fuelled the imagination of propellant and explosive engineers and technologists. Research activities are in progress in many quantum-chemical schools to explore the possibility of other promising polynitrogen compounds. After the recent discovery of key synthons/building blocks Mg(N₅)₂, N ₁₊ ⁵ SbF _1– ⁶ , N ₁₊ ⁵ SbF₁₁, N ₁₊ ⁵ , N ₁₊ ⁵ SnF₆, and N ₁₊ ⁵ Sn(CF₃)₄, the wealth of polynitrogen compounds is just waiting to be harvested by the HEMs community. There are ambitious plans all over the globe to realize N₆₀, which only prove a eco-friendly dense powerhouse of energy.__________Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 3, pp. 29–45, May–June, 2005.     

A novel microfluidic switch for pH control using Chitosan based hydrogels

We report a novel pH-sensitive hydrogel based micro-valve for metered flow that has applications in a laboratory made “Intelligent valving system”. The hydrogel solution was prepared through Chitosan and poly vinyl alcohol in acetic acid and crystallized using gluteraldehyde as the crosslinking agent in the form of thin wafers and it was found to be very sensitive to pH changes. The pore structure of hydrogel was investigated through Field Emission Scanning Electron Microscopy and thin wafers of the gel were physically placed inside PDMS microchannels. Flow metering in these channels was observed by controlled expansion of the hydrogel plug till complete valving was realized. This valving device was further precisely characterized with micro Particle Image Velocimetry using a solution containing fluorescent polymeric micro beads. The principle advantage of this hydrogel device is the smaller range of pH (varying between pH 3 and 7) over which the valving response is observed.     

Targeting and design of energy allocation networks with carbon capture and storage

The mathematical formulation for targeting during energy allocation with carbon capture and storage (CCS) is formally developed. For operating-cost optimization with zero excess, it is shown that CCS sources may be regarded as resources with their cost taken as the increment over the non-CCS option. CCS sources along with clean-carbon resources may then be targeted by profile matching with the limiting composite to establish optimal primary cases. The limiting composite curve is itself sacrosanct and obtained by a single computation of the composite table algorithm (CTA) including only non-CCS sources. Carbon emission networks (CENs) are designed by the nearest neighbors algorithm (NNA). A cost criterion is established to determine cost-factor ranges for optimality of the primary cases, and results validated by solving linear programming (LP) and mixed integer linear programming (MILP) formulations. The methodology essentially comprises four distinct stages – targeting, network design, cost analysis, and optimization – with the first two stages not requiring any cost data.     

Direct optical-structure correlation in atomically thin dichalcogenides and heterostructures

Atomically thin transition metal dichalcogenides (TMDs) have distinct opto-electronic properties including enhanced luminescence and high on-off current ratios, which can be further modulated by making more complex TMD heterostructures. However, resolution limits of conventional optical methods do not allow for direct nanoscale optical-structural correlation measurements in these materials, particularly of buried interfaces in TMD heterostructures. Here we use, for the first time, electron beam induced cathodoluminescence in a scanning transmission electron microscope (CL-STEM) to measure optical properties of monolayer TMDs (WS₂, MoS₂ and WSSe alloy) encapsulated between layers of hBN. We observe dark areas resulting from localized (~ 100 nm) imperfect interfaces and monolayer folding, which shows that the intimate contact between layers in this application-relevant heterostructure is required for proper inter layer coupling. We also realize a suitable imaging method that minimizes electron-beam induced changes and provides measurement of intrinsic properties. To overcome the limitation of small electron interaction volume in TMD monolayer (and hence low photon yield), we find that encapsulation of TMD monolayers with hBN and subsequent annealing is important. CL-STEM offers to be a powerful method to directly measure structure-optical correspondence in lateral or vertical heterostructures and alloys.

     

Viscous Potential Flow Analysis of Kelvin–Helmholtz Instability of a Cylindrical Flow with Heat and Mass Transfer

A linear analysis of Kelvin–Helmholtz instability of a cylindrical interface has been carried out when there is heat and mass transfer across the interface, using viscous potential flow theory. Both fluids are considered as incompressible, viscous, and thermally conducting with different kinematic viscosities. Both axisymmetric as well as asymmetric disturbances are considered. Stability criterion is given by a critical value of relative velocity and stability is discussed theoretically as well as numerically. Various graphs with respect to physical parameters such as wave number, viscosity ratio, heat transfer coefficients, Reynolds number, etc., have been drawn and the effect of various parameters have been described. A comparison with the linear stability analysis of inviscid fluids (Lee [10]) has been made and it is observed that viscosity has a stabilizing effect on the stability of the system. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 43(6): 489–503, 2014; Published online 3 October 2013 in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21092     

An investigation of sound absorption coefficient on sisal fiber poly lactic acid bio‐composites

In this research, the mechanical, acoustical, thermal, morphological, and infrared spectral properties of untreated, heat and alkaline‐treated sisal fiber‐reinforced poly‐lactic‐acid bio‐composites were analyzed. The bio‐composite samples were fabricated using a hot press molding machine. The properties mentioned above were evaluated and compared with heat‐treated and alkaline‐treated sisal fibers. Composites with heat‐treated sisal fibers were found to exhibit the best mechanical properties. Thermo‐gravimetric analysis (TGA) was conducted to study the thermal degradation of the bio‐composite samples. It was discovered that the PLA‐sisal composites with optimal heat‐treated at 160°C and alkaline‐treated fibers possess good thermal stability as compared with untreated fiber. The results indicated that the composites prepared with 30wt % of sisal had the highest sound absorption as compared with other composites. Evidence of the successful reaction of sodium hydroxide and heat treatment of the sisal fibers was provided by the infrared spectrum and implied by decreased bands at certain wavenumbers. Observations based on scanning electron microscopy of the fracture surface of the composites showed the effect of alkaline and heat treatment on the fiber surface and improved fiber‐matrix adhesion. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42470.