Force and flow characteristics of an intruder immersed in 3D dense granular matter

The motion of a projectile impact onto a granular target results in both the resistance force exerted on the projectile and rheology of granular media. A horizontal arrangement of cylinder quasistatically and dynamically intruding into granular media under different velocities and angles is simulated using discrete element method. Three distinguished drag force regimes are exhibited, including hydrostatic-like force independent of velocity, viscous force related to velocity, and inertial drag force proportional to the square of velocity. Meanwhile, the influence of penetration angles on drag force is examined for these three regimes, and a force model, which is related to penetration depth and angle, is proposed for quasi-static penetration. Then, flow characteristics of the granular media, such as velocity field, pressure field, packing fraction etc., are traced, and a rheology model of packing fraction and inertial number is established.     

The minimum size instance of a Pallet Loading Problem equivalence class

The Pallet Loading Problem (PLP) maximizes the number of identical rectangular boxes placed within a rectangular pallet. Boxes may be rotated 90° so long as they are packed with edges parallel to the pallet’s edges, i.e., in an orthogonal packing. This paper defines the Minimum Size Instance (MSI) of an equivalence class of PLP, and shows that every class has one and only one MSI. We develop bounds on the dimensions of box and pallet for the MSI of any class. Applying our new bounds on MSI dimensions, we present an algorithm for MSI generation and use it to enumerate all 3,080,730 equivalence classes with an area ratio (pallet area divided by box area) smaller than 101 boxes. Previous work only provides bounds on the ratio of box dimensions and only considers a subset of all classes presented here.     

Computing the asymptotic worst-case of bin packing lower bounds

This paper addresses the issue of computing the asymptotic worst-case of lower bounds for the Bin Packing Problem. We introduce a general result that allows to bound the asymptotic worst-case performance of any lower bound for the problem and to derive for the first time the asymptotic worst-case of the well-known bound L₃ by Martello and Toth. We also show that the general result allows to easily derive the asymptotic worst-case of several lower bounds proposed in the literature.     

A space on which diameter-type packing measure is not Borel regular

We construct a separable metric space on which 1-dimensional diameter-type packing measure is not Borel regular.

     

Applying self-adaptive evolutionary algorithms to two-dimensional packing problems using a four corners’ heuristic

This paper proposes a four corners’ heuristic for application in evolutionary algorithms (EAs) applied to two-dimensional packing problems. The four corners’ (FC) heuristic is specifically designed to increase the search efficiency of EAs. Experiments with the FC heuristic are conducted on 31 problems from the literature both with rotations permitted and without rotations permitted, using two different EA algorithms: a self-adaptive parallel recombinative simulated annealing (PRSA) algorithm, and a self-adaptive genetic algorithm (GA). Results on bin packing problems yield the smallest trim losses we have seen in the published literature; with the FC heuristic, zero trim loss was achieved on problems of up to 97 rectangles. A comparison of the self-adaptive GA to fixed-parameter GAs is presented and the benefits of self-adaption are highlighted.     

Fast, accurate, and convenient analysis of bed densities for columns packed with fine reversed-phase particles

We determine the interparticle porosities of commercially available, analytical, reversed-phase HPLC columns by Donnan exclusion of a small, unretained, co-ionic tracer (nitrate ions). The columns contained packings of C(18)-modified, endcapped, silica particles, which differed in their nominal particle diameters (1.8-5 μm) and construction (fully porous or core-shell). Experiments were carried out by monitoring the elution volumes of nitrate samples in a mobile phase of acetonitrile/water 80:20 v/v at increasing concentrations of Tris-HCl buffer (pH 8.1) from 0.01 to 60 mM. At low buffer concentrations, nitrate ions are completely electrostatically excluded from the intraparticle mesopore space, which is reflected by a plateau region in the elution curves. The elution volume in the plateau region equals the interparticle void volume. Clearly defined plateau regions were observed for all columns, even those densely packed with core-shell and sub-2 μm particles, enabling the accurate determination of interparticle porosities to three decimal places in a fast and convenient way.     

Membranes of epitaxial-like packed, super aligned electrospun micron hollow poly(l-lactic acid) (PLLA) fibers

Novel epitaxial-like packed, super aligned, mono-layered hollow fibrous membranes were prepared by co-axial electrospinning technology. PLLA pellets were dissolved in solvent mixture of dichloromethane and dimethyl formamide (DCM/DMF = 9:1) to prepare sheath solution dope with various concentrations (from 8 to 19 wt.%). Aqueous solution of poly-ethylene glycol (PEG) was used as core solution dope. During the electrospinning process, dope concentrations and feed rate ratios were adjusted, separately, to evaluate the formation of resulting membranes. With lower shell solution concentration (from 8 to 15 wt.%), the collected, flattened film showed arrangement of lower order. A stood-up film was clearly seen when concentration increased to 17 wt.% and higher. As the collecting time went longer, these fibers piled up and eventually, stood up as a thin film from the surface of collector. Increasing flow rate ratio (FRR) also resulted similar outcomes and verify the cause of this phenomenon. After washing with water, scanning electron microscopy (SEM) revealed sheets of mono-layered, micron-sized hollow fiber arrays which were well aligned and tightly packed, just like the epitaxial growth of some semiconducting materials. These perfectly aligned and tightly packed hollow fiber arrays can be considered as highly anisotropic scaffolds that mimic tissue structures, such as nerve tissue, vascular structure as well as other application.     

Improving LTL truck load utilization on line

In this document we consider an optimization problem which origins from freight exchanges. The aim is to increase the utilization of already scheduled road transportation activities by accepting extra loads. Such utilization increase reduces costs for the freight sender, increases revenue for the transportation provider, and reduces congestion and pollution for the society at large.     

高效毛细管电泳-紫外检测法测定饮料等包装材料中的双酚A

建立了饮料等包装材料中双酚A的高效毛细管电泳-紫外检测法.以无水乙醇为提取溶剂,采用硼砂-十二烷基硫酸钠-乙腈溶液为运行缓冲液(pH 9.5);分离毛细管为50cm×50μm,有效长度41cm的熔融石英毛细管;电泳温度为20℃;检测波长为195n m;重力进样,进样时间为15s.以相对迁移时间定性,标准曲线法定量.方法...