Topology of Force Networks in Granular Media under Impact

We investigate the evolution of the force network in experimental systems of two-dimensional granular materials under impact. We use the first Betti number, $\beta_1$, and persistence diagrams, as measures of the topological properties of the force network. We show that the structure of the network has a complex, hysteretic dependence on both the intruder acceleration and the total force response of the granular material. $\beta_1$ can also distinguish between the nonlinear formation and relaxation of the force network. In addition, using the persistence diagram of the force network, we show that the size of the loops in the force network has a Poisson-like distribution, the characteristic size of which changes over the course of the impact

Force and Mass Dynamics in Non-Newtonian Suspensions

Above a certain solid fraction, dense granular suspensions in water exhibit non-Newtonian behavior, including impact-activated solidification. Although it has been suggested that solidification depends on boundary interactions, quantitative experiments on the boundary forces have not been reported. Using high-speed video, tracer particles, and photoelastic boundaries, we determine the impactor kinematics and the magnitude and timings of impactor-driven events in the body and at the boundaries of cornstarch suspensions. We observe mass shocks in the suspension during impact. The shockfront dynamics are strongly correlated to those of the intruder. However, the total momentum associated with this shock never approaches the initial impactor momentum. We also observe a faster second front, associated with the propagation of pressure to the boundaries of the suspension. The two fronts depend differently on the initial impactor speed, $v_0$, and the suspension packing fraction. The speed of the pressure wave is at least an order of magnitude smaller than (linear) ultrasound speeds obtained for much higher frequencies, pointing to complex amplitude and frequency response of cornstarch suspensions to compressive strains

Using transfer-resource graph for software-based verification of system-on-chip

Copyright © 2006 IEEEThe verification of system-on-chip is challenging due to its high level of integration. Multiple components in a system can behave concurrently and compete for resources. Hence, for simulation-based verification, we need a methodology that allows one to automatically generate test cases for testing concurrent and resource-competing behaviors.We introduce the use of a transferresource graph (TRG) as the model for test generation. From a high abstraction level, TRG is able to model the parallelism between heterogeneous interaction forms in a system. We show how TRG is used in generating test cases of resource competitions and how these test cases are structured in event-driven test programs. For coverage, TRG can be converted to a Petri net, allowing one to measure the completeness of concurrency in simulation.Xiaoxi Xu and Cheng-Chew Li

Measurement of Spin Polarization by Andreev Reflection in Ferromagnetic In1-xMnxSb Epilayers

We carried out Point Contact Andreev Reflection (PCAR) spin spectroscopy measurements on epitaxially-grown ferromagnetic In1-xMnxSb epilayers with a Curie temperature of ~9K. The spin sensitivity of PCAR in this material was demonstrated by parallel control studies on its non-magnetic analog, In1-yBeySb. We found the conductance curves of the Sn point contacts with In1-yBeySb to be fairly conventional, with the possible presence of proximity-induced superconductivity effects at the lowest temperatures. The experimental Z-values of interfacial scattering agreed well with the estimates based on the Fermi velocity mismatch between the semiconductor and the superconductor. These measurements provided control data for subsequent PCAR measurements on ferromagnetic In1-xMnxSb, which indicated spin polarization in In1-xMnxSb to be 52 +- 3%

Consumer-driven e-commerce: A literature review, design framework, and research agenda on last-mile logistics models

Purpose The purpose of this paper is to re-examine the extant research on last-mile logistics (LML) models and consider LML’s diverse roots in city logistics, home delivery and business-to-consumer distribution, and more recent developments within the e-commerce digital supply chain context. The review offers a structured approach to what is currently a disparate and fractured field in logistics. Design/methodology/approach The systematic literature review examines the interface between e-commerce and LML. Following a protocol-driven methodology, combined with a “snowballing” technique, a total of 47 articles form the basis of the review. Findings The literature analysis conceptualises the relationship between a broad set of contingency variables and operational characteristics of LML configuration (push-centric, pull-centric, and hybrid system) via a set of structural variables, which are captured in the form of a design framework. The authors propose four future research areas reflecting likely digital supply chain evolutions. Research limitations/implications To circumvent subjective selection of articles for inclusion, all papers were assessed independently by two researchers and counterchecked with two independent logistics experts. Resulting classifications inform the development of future LML models. Practical implications The design framework of this study provides practitioners insights on key contingency and structural variables and their interrelationships, as well as viable configuration options within given boundary conditions. The reformulated knowledge allows these prescriptive models to inform practitioners in their design of last-mile distribution. Social implications Improved LML performance would have positive societal impacts in terms of service and resource efficiency. Originality/value This paper provides the first comprehensive review on LML models in the modern e-commerce context. It synthesises knowledge of LML models and provides insights on current trends and future research directions. </jats:sec

Symplectic Elasticity: Theory and Applications

International audienceSymplectic Elasticity: Theory and Applications Many of the early works on symplectic elasticity were published in Chinese and as a result, the early works have been unavailable and unknown to researchers worldwide. It is the main objective of this paper to highlight the contributions of researchers from this part of the world and to disseminate the technical knowledge and innovation of the symplectic approach in analytic elasticity and applied engineering mechanics. This paper begins with the history and background of the symplectic approach in theoretical physics and classical mechanics and subsequently discusses the many numerical and analytical works and papers in symplectic elasticity. This paper ends with a brief introduction of the symplectic methodology. A total of more than 150 technical papers since the middle of 1980s have been collected and discussed according to various criteria. In general, the symplectic elasticity approach is a new concept and solution methodology in elasticity and applied mechanics based on the Hamiltonian principle with Legendre's transformation. The superiority of this symplectic approach with respect to the classical approach is at least threefold: (i) it alters the classical practice and solution technique using the semi-inverse approach with trial functions such as those of Navier, Lévy, and Timosh-enko; (ii) it consolidates the many seemingly scattered and unrelated solutions of rigid body movement and elastic deformation by mapping with a series of zero and nonzero eigenvalues and their associated eigenvectors; and (iii) the Saint–Venant problems for plane elasticity and elastic cylinders can be described in a new system of equations and solved. A unique feature of this method is that bending of plate becomes an eigenvalue problem and vibration becomes a multiple eigenvalue problem

Prophylactic non-steroidal anti-inflammatory drugs for the prevention of macular oedema after cataract surgery.

BACKGROUND: Macular oedema (MO) is the accumulation of extracellular fluid in the central retina (the macula). It may occur after cataract surgery and may give rise to poor visual outcome, with reduced visual acuity and distortion of the central vision. MO is often self-limiting with spontaneous resolution, but a small proportion of people with chronic persistent MO may be difficult to treat. Chronic oedema may lead to the formation of cystic spaces in the retina termed 'cystoid macular oedema' (CMO). Non-steroidal anti-inflammatory drugs (NSAIDs) are commonly used in cataract surgery and may reduce the chances of developing MO. OBJECTIVES: The aim of this review is to answer the question: is there evidence to support the prophylactic use of topical NSAIDs either in addition to, or instead of, topical steroids postoperatively to reduce the incidence of macular oedema (MO) and associated visual morbidity. SEARCH METHODS: We searched a number of electronic databases including CENTRAL, MEDLINE and Embase. Date last searched 2 September 2016. SELECTION CRITERIA: We included randomised controlled trials (RCTs) in which adult participants had undergone surgery for age-related cataract. We included participants irrespective of their baseline risk of MO, in particular we included people with diabetes and uveitis. We included trials of preoperative and/or postoperative topical NSAIDs in conjunction with postoperative topical steroids. The comparator was postoperative topical steroids alone. A secondary comparison was preoperative and/or postoperative topical NSAIDs alone versus postoperative topical steroids alone. DATA COLLECTION AND ANALYSIS: Two review authors independently selected studies for inclusion, assessed risk of bias and extracted data using standard methods expected by Cochrane. We pooled data using a random-effects model. We graded the certainty of the evidence using GRADE and considered the following: risk of bias of included studies, precision of the effect estimate, consistency of effects between studies, directness of the outcome measure and publication bias. MAIN RESULTS: We identified 34 studies that were conducted in the Americas, Europe, the Eastern Mediterranean region and South-East Asia. Over 5000 people were randomised in these trials. The majority of studies enrolled one eye per participant; a small subset (4 trials) enrolled a proportion of people with bilateral surgery. Twenty-eight studies compared NSAIDs plus steroids with steroids alone. Six studies compared NSAIDs with steroids. A variety of NSAIDs were used, including ketorolac, diclofenac, nepafenac, indomethacin, bromfenac, flurbiprofen and pranopfen. Follow-up ranged from one to 12 months. In general, the studies were poorly reported. We did not judge any of the studies at low risk of bias in all domains. Six studies were funded by industry, seven studies were funded from non-industry sources, and the rest of the studies did not report the source of funding.There was low-certainty evidence that people receiving topical NSAIDs in combination with steroids may have a lower risk of poor vision due to MO at three months after cataract surgery compared with people receiving steroids alone (risk ratio (RR) 0.41, 95% confidence interval (CI) 0.23 to 0.76; eyes = 1360; studies = 5; I2 = 5%). We judged this to be low-certainty evidence because of risk of bias in the included studies and indirectness, as the extent of visual loss was not always clear. Only one study reported poor vision due to MO at 12 months and we judged this to be very low-certainty evidence as there were only two events. Quality of life was only reported in one of the 34 studies comparing NSAIDs plus steroids versus steroids alone, and it was not fully reported, other than to comment on lack of differences between groups. There was evidence of a reduced risk of MO with NSAIDs at three months after surgery, but we judged this to be low-certainty due to risk of bias and publication bias (RR 0.40, 95% CI 0.32 to 0.49; eyes = 3638; studies = 21). There was inconsistent evidence on central retinal thickness at three months (I2 = 87%). Results ranged from -30.9 µm in favour of NSAIDs plus steroids to 7.44 µm in favour of steroids alone. Similarly, data on best corrected visual acuity (BCVA) were inconsistent, but nine out of 10 trials reporting this outcome found between-group differences in visual acuity of less than 0.1 logMAR.None of the six studies comparing NSAIDs alone with steroids reported on poor vision due to MO at three or 12 months. There was low-certainty evidence that central retinal thickness was lower in the NSAIDs group at three months (mean difference (MD) -22.64 µm, 95% CI -38.86 to -6.43; eyes = 121; studies = 2). Five studies reported on MO and showed a reduced risk with NSAIDs, but we judged this evidence to be of low-certainty (RR 0.27, 95% CI 0.18 to 0.41; eyes = 520). Three studies reported BCVA at three months and the results of these trials were inconsistent, but all three studies found differences of less than 0.1 logMAR between groups.We did not note any major adverse events - the main consistent observation was burning or stinging sensation with the use of NSAIDs. AUTHORS' CONCLUSIONS: Using topical NSAIDs may reduce the risk of developing macular oedema after cataract surgery, although it is possible that current estimates as to the size of this reduction are exaggerated. It is unclear the extent to which this reduction has an impact on the visual function and quality of life of patients. There is little evidence to suggest any important effect on vision after surgery. The value of adding topical NSAIDs to steroids, or using them as an alternative to topical steroids, with a view to reducing the risk of poor visual outcome after cataract surgery is therefore uncertain. Future trials should address the remaining clinical uncertainty of whether prophylactic topical NSAIDs are of benefit, particularly with respect to longer-term follow-up (at least to 12 months), and should be large enough to detect reduction in the risk of the outcome of most interest to patients, which is chronic macular oedema leading to visual loss