Aggregation and breakup of colloidal particle aggregates in shear flow: A combined Monte Carlo - Stokesian dynamics approach

A method for the simulation of aggregation and breakup processes in colloidal particle suspensions is presented. The method combines a Monte Carlo algorithm to determine, on the basis of probabilistic considerations, the sequence of aggregation and breakup events, and a Discrete Element Method, built in the framework of Stokesian dynamics and contact mechanics, to accurately reproduce them. Liquid-solid suspensions subject to a uniform shear stress are investigated. The model is seen to be able to reproduce the typical dynamic steady state which is observed in colloidal suspensions under severe shearing, in which the effects of aggregation and breakup balance each other. The structural properties of the aggregates and the dynamics of the aggregation and breakup phenomena are characterized in detail. Both fragmentation and erosion are seen to contribute to the breakup process, which is characterized by an exponent similar to the one reported in the literature for compact clusters

Effect of Poisson ratio on cellular structure formation

Mechanically active cells in soft media act as force dipoles. The resulting elastic interactions are long-ranged and favor the formation of strings. We show analytically that due to screening, the effective interaction between strings decays exponentially, with a decay length determined only by geometry. Both for disordered and ordered arrangements of cells, we predict novel phase transitions from paraelastic to ferroelastic and anti-ferroelastic phases as a function of Poisson ratio.Comment: 4 pages, Revtex, 4 Postscript figures include

Awake one stage bilateral thoracoscopic sympathectomy for palmar hyperhidrosis: a safe outpatient procedure

OBJECTIVE: To verify the feasibility and compare the results of thoracoscopic sympathectomy under local anaesthesia (LA) and spontaneous breathing vs. general anaesthesia (GA) with one-lung ventilation. METHODS: Two groups of consecutive patients underwent one stage bilateral T2-T3 thoracoscopic sympathectomy under LA (n=15) and GA (n=30) by the same surgical team for treatment of primary palmar hyperhidrosis. The groups were homogeneous for relevant demographic, physiological and clinical data, including pulmonary function. In both groups, patient's satisfaction was evaluated 24h after surgery by a simple interview and scored into five grades (1=very poor to 5=excellent), while quality of life (QOL) was evaluated by SF-36 and Nottingham's Health Profile questionnaires before and 6 months after surgery. A cost comparison between groups concerning devices, drugs, global in operating room time, medical personnel and hospital stay was also carried out. RESULTS: No operative mortality was recorded. The overall in operating room time for the whole bilateral procedure under LA was 63.55+/-10.58 vs. 86.05+/-5.75 under GA (P<0.01) and temperature increased in all patients from a baseline of 25.42+/-0.56 up to 32.15+/-0.84 degrees C. All patients undergone LA were discharged the same day after a chest roentgenogram and a short stay in the outpatient clinic. Among them three patients (20%) experienced a minimal (<30%) pneumothorax that required no treatment, while five (33.3%) had a trunk compensatory sweating that spontaneously resolved on the long run. Patients undergoing GA were discharged after a mean stay of 1.38+/-0.6 days. Among these, eight (26.6%) had prolonged trunk compensatory sweating that did not persist longer than 3 months. At a follow-up of 7.16+/-2.97 months, QOL was significantly improved with no difference between groups. The overall rate of satisfaction was greater in the LA group (P<0.05). CONCLUSIONS: In our study, awake one stage bilateral thoracoscopic sympathectomy for palmar hyperhidrosis could be safely and effectively performed as an outpatient procedure in patients refusing GA. Postoperative quality of life was equal to that in patients undergone the same procedure under GA, while patient satisfaction was better and cost were significantly reduced

CFD-DEM characterization and population balance modelling of a dispersive mixing process

This work investigates the breakup dynamics of solid agglomerates in a polymer compounding operation, by using computational fluid dynamics (CFD) simulations together with discrete element method (DEM) simulations. CFD simulations are used to compute the flow field and the shear stress distribution inside a 2D section of a typical internal mixer for polymer compounding. DEM simulations are instead used to predict the mechanical response of the agglomerates and to detect the critical viscous shear stress needed to induce breakup. DEM breakup data and viscous stress distributions are correlated by a first–time passage–statistics and used to calibrate a population balance model. The work returned detailed insights into the flow field characteristics and into the dispersive mixing kinetics. The simulation strategy herein reported can be adapted to study generic solid–liquid disperse flows in which the breakup of the solid phase is found at the core of the system behaviour

Exploring efficient imperative handover mechanisms for heterogeneous wireless networks

The Next Generation Internet will provide ubiquitous computing by the seamless operation of heterogeneous wireless networks. It will also provide support for quality-ofservice, QoS, fostering new classes of applications and will havea built-in multi-level security environment. A key requirement of this new infrastructure will be support for efficient vertical handover. Y-Comm is a new architecture that will meet the challenge of this new environment. This paper explores the design of efficient imperative handover mechanisms using the Y-Comm Framework. It first looks at different types of handovers, then examines the Y-Comm Framework and shows how Y-Comm maps unto current mobile infrastructure. It then explores support for different handover mechanisms using Y-Comm. Finally, it highlights the development of a new testbed to further investigate the proposed mechanisms

A QoS framework for heterogeneous networking

In order for next generation networks to support effective handover procedures, there is a need for defining QoS signaling mechanisms that guarantee the provision of point- to- point as well as network level QoS. This paper proposes a QoS signaling mechanism to be implemented by the Y-Comm architecture as a potential 4G framework. The proposed mechanism requires certain level of cooperation among network elements; therefore, it proposes some functional modules/ interfaces to be run on different network entities. As showed in the paper, the proposed mechanism could be implemented in different scenarios such as initial registration and connection, and also in the case of handover