3,449 research outputs found
Energy Efficient Ant Colony Algorithms for Data Aggregation in Wireless Sensor Networks
In this paper, a family of ant colony algorithms called DAACA for data
aggregation has been presented which contains three phases: the initialization,
packet transmission and operations on pheromones. After initialization, each
node estimates the remaining energy and the amount of pheromones to compute the
probabilities used for dynamically selecting the next hop. After certain rounds
of transmissions, the pheromones adjustment is performed periodically, which
combines the advantages of both global and local pheromones adjustment for
evaporating or depositing pheromones. Four different pheromones adjustment
strategies are designed to achieve the global optimal network lifetime, namely
Basic-DAACA, ES-DAACA, MM-DAACA and ACS-DAACA. Compared with some other data
aggregation algorithms, DAACA shows higher superiority on average degree of
nodes, energy efficiency, prolonging the network lifetime, computation
complexity and success ratio of one hop transmission. At last we analyze the
characteristic of DAACA in the aspects of robustness, fault tolerance and
scalability.Comment: To appear in Journal of Computer and System Science
High concentration Brownian coagulation in jet flow using two enhancement formulations
Ultra-fine particle coagulation by Brownian motion at high concentration in planar jet flow is simulated. A Taylor-Series Expansion Method of Moments is employed to solve the particle general dynamic equation. The volume fraction gets high value, very closes to that at the nozzle exit. As the vortex pairing develops, the high volume fraction region rolls out and mixes with the low value region. The enhancement factor given by Trzeciak et al. will be less than one at some specific outer positions, which seems to be less accurate than the one given by Heine et al
The Effect of Energy Service Companies on Energy Use in Selected Developing Countries: A Synthetic Control Approach
This study investigates the empirical effect of the service provided by the energy service companies (ESCOs) on the total energy use in thirteen developing countries by employing a transparent and data-driven statistical methodology, the synthetic control method (SCM). This methodology compares the post-treatment total energy use of a treated country, a country that has initiated ESCO activities, with the trajectory of total energy use for a synthetic control unit, a combination of economies being similar to the treated country with the exception of no ESCO activities initiated. The SCM can account for the potential heterogeneity regarding the effect of ESCO activities in various countries. In these thirteen countries, we find that the ESCOs exert a strong energy-saving effect in Colombia, Ghana, Kenya and South Africa; while a robust energy-using effect is found in Chile. No significant energy using or saving effects are found in the rest of treated countries. Â Â Â
Keywords: Energy service companies (ESCOs), Synthetic control method (SCM), Total energy use
JEL Classifications: O13, Q43, Q5
A giant hemolymphangioma of the pancreas in a 20-year-old girl: a report of one case and review of the literature
<p>Abstract</p> <p>Background</p> <p>Hemolymphangioma of the pancreas is a very rare benign tumor. There were only six reports of this disease until December 2008. Herein, we report a case of giant hemolymphangioma of the pancreas in a 20-year-old girl.</p> <p>Case presentation</p> <p>We describe a 20-year-old girl who presented with a mass in abdominal cavity and epigastric discomfort about a week. Physical examination showed a great abdominal mass. Abdominal computed tomography showed extrinsic duodenal compression due to a large retroperitoneal tumor possibly arising from pancreas. The tumor enucleation was performed and a diagnosis of hemolymphangioma of the pancreas was made. The patient had a complication of chylous leakage, which was successfully managed. The patient is alive and well, after 26 months of follow-up, with no complaints or recurrence.</p> <p>Conclusion</p> <p>From this case and literature, we can conclude that hemolymphangioma of the pancreas in adult is a rare benign tumor, and accurate diagnosis can not be preoperatively established. Tumor resection should be performed whenever possible. The risk of recurrence seems very low.</p
Biomechanical characterization of the periodontal ligament: Orthodontic tooth movement
To quantify the biomechanical properties of the bovine periodontal ligament (PDL) in postmortem sections and to apply these properties to study orthodontic tooth intrusion using finite element analysis (FEA). We hypothesized that PDL’s property inherited heterogeneous (anatomical dependency) and nonlinear stress-strain behavior that could aid FEA to delineate force vectors with various rectangular archwires
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