An Exact Algorithm for the Capacitated Vertex p-Center Problem

Cataloged from PDF version of article.We develop a simple and practical exact algorithm for the problem of locating p facilities and assigning clients to them within capacity restrictions in order to minimize the maximum distance between a client and the facility to which it is assigned (capacitated p-center). The algorithm iteratively sets a maximum distance value within which it tries to assign all clients, and thus solves bin-packing or capacitated concentrator location subproblems using off-the-shelf optimization software. Computational experiments yield promising results. 2004 Elsevier Ltd. All rights reserved

The contrasting oceanography of the Rhodes Gyre and the Central Black Sea

The Rhodes Gyre, a prominent feature of the oceanography of the eastern Mediterranean, is modelled as a vertical, continuous flow, cylindrical reactor illuminated during the day at its upper end. If the Gyre is supposed to be in a steady state whilst the concentrations, C, of a chemical are being measured, the nett rate of formation or consumption of the chemical is given by -w d C/d z + u d C/d r, where w is the upward velocity of the water in the vertical, z , direction and u is the velocity of the water in the radial, r, direction. The behaviour of w and u is analysed to show that the Gyre may be used as a field laboratory in which rates of chemical change may be derived from depth profiles together with values of the surface velocities of the Gyre waters. In contrast, the central Black Sea is modelled as an ideal, strongly stratified sea in which the nett rates of formation or consumption of chemicals under steady state conditions are given by Ds d2C/ds 2, where s is the water density and Ds is an eddy diffusion coefficient. Computations reveal that, given better knowledge of its eddy diffusion coefficients, the Black Sea can also be treated as a field laboratory where rates of reaction mediated by bacteria may be derived from depth profiles

A Liquid Extraction Column With Reciprocated Wire Mesh Packing

In a new type of pulsating, liquid extractor, pulsating energy is added to the counter currently flowing liquid streams by a stainless-steel wire mesh packing which is reciprocated vertically in a 3-inch i.d. extraction column. The mass transfer performance and flooding characteristics are studied as a function of the frequency and amplitude of reciprocation, the total solvent and feed throughputs, and choice of phase dispersion. The benzene-HAc-H2O and MIBK-HAcH2O systems were used. Extraction data for the benzene system were correlated in terms of a dimensionless pulse velocity group. Operating throughputs are significantly higher than those achieved with other designs of mechanically aided extractors, while maintaining high rates of extraction. © 1969, American Chemical Society. All rights reserved

Investigation of an actively controlled robot arm for vibration suppression in milling

In recent years, the use of robotic systems to enhance the productivity of machining operations has received significant attention from the research and manufacturing communities. Robots have the potential to further improve productivity, for example by providing automated workpiece fixturing, or by providing a flexible and reconfigurable platform from which a variety of subtractive or additive manufacturing operations could be performed. One possible approach is the use of a robotic arm to provide additional fixturing or support of the workpiece during the machining operation. This can increase the stiffness of the workpiece system during machining, which can improve productivity by limiting the onset of undesirable vibrations such as chatter. Chatter is a form of self-excited vibration which leads to low surface quality of the workpiece, shortens the cutting tool life and increases the cutting forces. In this paper, an actively controlled robot arm is simulated in order to suppress the chatter, in an effort to further improve the chatter stability. During the milling operation, preload can be applied through the robot to support the flexible structure, however, the robot cannot suppress high-frequency forces. Since the stiffness and damping ratio of the large flexible structure vary during the operation due to material removal, active vibration control is performed. A proof-mass actuator is proposed that can provide 45 N force up to 2000 Hz with 2 mm stroke. The dynamic properties of the device are identified experimentally as part of a model of a robot fixture prototype. The robotic arm is modelled as a three degree of freedom system; this is combined with a simplified representation of the workpiece dynamics, and the proof-mass actuator, within a Matlab environment. The effect of active control on the chatter stability is evaluated, focussing initially on the use of direct velocity feedback as a control strategy. Estimated chatter stability predictions, along with time, frequency domain simulation results, show that the application of active control method in robotic-assisted machining can suppress the chatter vibrations during machining and hence increase productivity

Spatial and temporal analysis of extreme sea level and storm surge events around the coastline of the UK

In this paper we analyse the spatial footprint and temporal clustering of extreme sea level and skew surge events around the UK coast over the last 100 years (1915-2014). The vast majority of the extreme sea level events are generated by moderate, rather than extreme skew surges, combined with spring astronomical high tides. We distinguish four broad categories of spatial footprints of events and the distinct storm tracks that generated them. There have been rare events when extreme levels have occurred along two unconnected coastal regions during the same storm. The events that occur in closest succession (< 4 days) typically impact different stretches of coastline. The spring/neap tidal cycle prevents successive extreme sea level events from happening within 4-8 days. Finally, the 2013/14 season was highly unusual in the context of the last 100 years from an extreme sea level perspective

Active chatter suppression through virtual inerter-based passive absorber control

The role of inerter-based devices has generated considerable interest in terms of suppressing the vibrations in machines and structures. The inerter is a mechanical device that generates force proportional to the relative acceleration between its terminals. Recently, it has been shown that inerter-based dynamic vibration absorbers (IDVAs, for the mass ratios between 0 and 0.2) can improve the chatter suppression performance compared to a traditional tuned mass damper (TMD) for the same mass ratios. This study proposes an IDVA applied to machining operations as a novel active control method to increase chatter suppression performance. Considering the TMD application as a virtual passive absorber (VPA) method in active control, IDVAs can be potentially employed in the same framework. A proof-mass actuator, which is mounted on a beam that is designed to support a flexible structure, is proposed. Once the IDVA parameters are optimised, a time-domain model is applied to explore the actuator saturation effects. The effect of an IDVA as a novel active control method on chatter stability is then evaluated. The simulated stability lobe diagram shows that the IDVA increases the absolute chatter stability by just above 20%. To validate the simulation results, an experimental setup is designed including a flexible workpiece to be machined and a proof-mass actuator assembled using a beam. In summary, it is shown that inerter-based dynamic vibration absorbers, as an active control method, can successfully be implemented to improve the chatter suppression performance and critical limiting depth of cut

Spontaneous splenic rupture in an active duty Marine upon return from Iraq: a case report

<p>Abstract</p> <p>Introduction</p> <p>Atraumatic splenic rupture is a rare event that has been associated with several infectious disease processes. In the active duty military population, potential exposure to these pathogens is significant. Here we discuss the case of an active duty Marine with spontaneous splenic rupture upon return from a six-month deployment in Iraq.</p> <p>Case presentation</p> <p>A previously healthy 30-year-old Caucasian male active duty Marine presented with abdominal pain, fever and diarrhea after deployment to Iraq in support of Operation Iraqi Freedom. Based on clinical and radiographic evidence, a diagnosis of spontaneous splenic rupture was ultimately suspected. After exploratory laparotomy with confirmation of rupture, splenectomy was performed, and the patient made a full, uneventful recovery. Histopathologic examination revealed mild splenomegaly with a ruptured capsule of undetermined cause.</p> <p>Conclusion</p> <p>Spontaneous splenic rupture is a rare event that may lead to life-threatening hemorrhage if not diagnosed and treated quickly. Although the cause of this patient's case was unknown, atraumatic splenic rupture has been associated with a variety of infectious diseases and demonstrates some risks the active duty military population may face while on deployment. Having an awareness of these pathogens and their role in splenic rupture, clinicians caring for military personnel must be prepared to recognize and treat this potentially fatal complication.</p