Reliability of a cascade system with normal stress and exponential strength

In this paper we study the reliability of an N-cascade system whose stress and strength follow normal and exponential distributions, respectively. In this system we can observe that reliability increases for lower values of strength parameter (λ) and stress parameter (μ). Marginal reliability rate also increases at higher values of λ. Hence we conclude that the addition of components by a cascade system gives a significant improvement.     

Droplet dynamics passing through obstructions in confined microchannel flow

Motivated by the previous studies (Lee et al., Lab Chip 10:1160–1166, 2010; Link et al., Phys Rev Lett 92:054503-1–054503-4, 2004), the droplet dynamics passing through obstructions in confined microchannel was explored both numerically and experimentally. The effects of obstruction shape (cylinder and square), droplet size, and capillary number (Ca) on droplet dynamics were investigated. For the size control, due to an obstruction-induced droplet breakup, the cylinder obstruction was found to be advantageous over square type for practical purposes. The thread breakup was attributed to both normal and shear components of velocity gradients near the obstruction, in particular, near the corners of the square. As a result, the square obstruction was considered to generate more non-trivial satellite droplets. The droplet size showed little influence on the droplet dynamics. Considering the wetting process on the cylinder surface, we explored the droplet dynamics passing through two successive cylinder obstructions, where more complicated dynamics was observed depending on Ca (capillary number ~ viscous force / interface tension), cylinder interval, and droplet size. Here, we propose two requirements for independent wetting on each cylinder: (i) low Ca droplet should be manipulated, and (ii) cylinder interval should be larger than channel width. That is, low Ca droplet could intrude the region between two cylinders if the cylinder interval was far enough, while the droplet could not intrude due to geometric hindrance for close obstructions. In the numerical viewpoint, the proposed requirements were also valid for multi-cylinder obstructions up to 6. In addition, we propose a novel design of array structure of cylinders for a selective wetting, which might be useful to fabricate Janus particles. We hereby prove by both simulation and experiments that the wetting on the obstruction is controllable by changing Ca and cylinder design in the multilayer deposition process.     

Gelation behavior of PEO-PLGA-PEO triblock copolymers in water

Aqueous solutions of poly(ethylene oxide-b-(dl-lactic acid-co-glycolic acid)-b-ethylene oxide) with two different molecular weights (550-3.4K-550 and 750-3.5K-750) show the change in turbidity as a function of temperature. The variation in turbidity is also found to be independent of block copolymer concentration. By increasing the molecular weight of the hydrophilic PEO end block with the molecular weight of the hydrophobic PLGA middle block kept almost the same, it is found that the phase boundary is shifted to a higher temperature and only soft gels are observed. Large aggregates or clusters of micelles with sizes larger than 5000 nm are observed with dynamic light scattering at the temperatures of turbid region and the size distribution of the aggregates is also found to depend only on temperature, not on concentration. The storage moduli (G′) of aqueous solutions of the PEO-PLGA-PEO do not show the abrupt change at the sol-to-(hard) gel boundary, as normally seen in the case of PEO-PPO (poly(propylene oxide))-PEO block copolymers and the behavior of G′ as a function of temperature is qualitatively the same and independent of polymer concentration except the absolute values of G′, which are proportional to the copolymer concentration. This implies that micelle-micelle clusters are formed due to hydrophobic attraction between core phases.     

Maximum density effects on natural convection in a vertical annulus filled with a non-Darcy porous medium

Summary This article numerically studies the problem of natural convection in a porous medium saturated with cold water, under density inversion, within a vertical annulus. In modeling the flow in the porous medium the non-Darcy effects, which include the Forchheimer inertia and Brinkman viscous effects are taken into account. The governing equations are solved numerically by the finite difference method using the modified strongly implicit procedure. The effects of the inversion parameter _m , radius ratioR ^*, aspect ratioAR, Forchheimer inertia parameter Fc/Pr, and Darcy number parameter Da on the heat transfer and fluid flow characteristics are discussed in detail. Results show that both the inversion parameter and radius ratio have a significant influence on the flow structure and heat transfer rate in the annulus. It is also found that the mean Nusselt number decreases as the Forchheimer inertia parameter or the Darcy number increases. Moreover, the results obtained here are also compared and favorably agree with numerical results and with experimental data.Nomenclature AR aspect ratio,H/L - d particle diameter - Da Darcy number,K/(L ²) - Fc Forchheimer number,K/L - g gravitational acceleration - H annulus height - K permeability - K transport property defined in Eq. (5) - L gap width,r _o –r _i - Nu _i , Nu _o local Nusselt number of the inner and outer cylinders, respectively - mean Nusselt number of the inner and outer cylinders, respectively - p pressure - Pr Prandtl number, / - q constant in Eq. (9) - r radial coordinate - R dimensionless radial coordinate,(r–r _i )/L - r _i radius of inner cylinder - r _o radius of outer cylinder - R ^* radius ratio,(r _o –r _i )/r _i - Ra Rayleigh number,K _m gL(T _h –T _c ) ^q / - T dimensional temperature - T _c dimensional temperature of inner cylinder - T _h dimensional temperature of outer cylinder - T _m temperature corresponding to the density maximum, 4.029325°C - u, v Darcian velocity components inr andz directions, respectively     

A Pyrene–Poly(acrylic acid)–Polyrotaxane Supramolecular Binder Network for High‐Performance Silicon Negative Electrodes

Although being incorporated in commercial lithium‐ion batteries for a while, the weight portion of silicon monoxide (SiO_x, x ≈ 1) is only less than 10 wt% due to the insufficient cycle life. Along this line, polymeric binders that can assist in maintaining the mechanical integrity and interfacial stability of SiO_x electrodes are desired to realize higher contents of SiO_x. Herein, a pyrene–poly(acrylic acid) (PAA)–polyrotaxane (PR) supramolecular network is reported as a polymeric binder for SiO_x with 100 wt%. The noncovalent functionalization of a carbon coating layer on the SiO_x is achieved by using a hydroxylated pyrene derivative via the π–π stacking interaction, which simultaneously enables hydrogen bonding interactions with the PR–PAA network through its hydroxyl moiety. Moreover, the PR's ring sliding while being crosslinked to PAA endows a high elasticity to the entire polymer network, effectively buffering the volume expansion of SiO_x and largely mitigating the electrode swelling. Based on these extraordinary physicochemical properties of the pyrene–PAA–PR supramolecular binder, the robust cycling of SiO_x electrodes is demonstrated at commercial levels of areal loading in both half‐cell and full‐cell configurations.     

Optimisation of minimal processing variables to preserve the functional quality and colour of carrot juice by means of the response surface methodology

Combined processes based on acidification (pH: 4.5, 5.0, 5.5) and mild thermal treatments (T: 56, 58, 60°C) at different exposure times (t: 2, 4, 6 min) were optimised using the response surface methodology to improve the functional quality of carrot juice. The effects on α‐ and β‐carotenes, total antioxidant activity (TAA) and colour parameters were assessed. All combinations exhibited higher α‐ and β‐carotenes than untreated juice due to an increase on the extractability during processing. T was the most influential factor increasing carotenes as T increased. Conversely, TAA was more affected by pH. The maximum TAA was observed at pH 4.5 at 56°C. Moreover, samples with the lowest pH were the most luminous with highest a* and b*. The combination of pH 4.5 at 60°C, 4 min simultaneously showed high carotenes and TAA, resulting a good alternative to improve the functional quality and colour of carrot juice.     

An efficient access control scheme for files protection

Abstract

A dynamic access control mechanism suitable for hardware implementation is proposed. Each file is safeguarded by q lock values, where q is number of the possible access classes. The access right of a user to some file can be revealed very efficiently. In addition, dynamic operations such as changing a privilege value, insertion or deletion of a user, and insertion or deletion of a file can be done easily. Compared to Wu and Hwangs’ and Chang's methods, the computation of lock values is simple and the verification of an access request is quite efficient. The storage required is proportional to m?n which is less than that of the above‐mentioned methods, where m is the number of users and n is the number of files.     

An ablation problem in a finite medium with time‐dependent heat flux

Abstract

The objective of this work is to develop an approximate analytical solution for the transient ablation problem in a finite medium. The medium is subjected to time‐dependent boundary heat flux, i. e., q₀=at^P , and with this refined integral technique, the complicated nonlinear problem is reduced to an initial value problem, which is then solved by the Runge‐Kutta method. Results are more accurate than with the classical heat balance integral method and also indicate that the dependence of the solution on the assumed temperature profile is much weaker than is the case with the classical integral method.