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COMPARATIVE STUDY OF TERTIARY WASTEWATER TREATMENT BY COMPUTER SIMULATION  [PDF]
Stefania Iordache,Nicolae Petrescu,Cornel Ianache
Annals : Food Science and Technology , 2010,
Abstract: The aim of this work is to asses conditions for implementation of a Biological Nutrient Removal (BNR) process in theWastewater Treatment Plant (WWTP) of Moreni city (Romania). In order to meet the more increased environmentalregulations, the wastewater treatment plant that was studied, must update the actual treatment process and have tomodernize it. A comparative study was undertaken of the quality of effluents that could be obtained by implementationof biological nutrient removal process like A2/O (Anaerobic/Anoxic/Oxic) and VIP (Virginia Plant Initiative) aswastewater tertiary treatments. In order to asses the efficiency of the proposed treatment schemata based on the datamonitored at the studied WWTP, it were realized computer models of biological nutrient removal configurations basedon A2/O and VIP process. Computer simulation was realized using a well-known simulator, BioWin by EnviroSimAssociates Ltd. The simulation process allowed to obtain some data that can be used in design of a tertiary treatmentstage at Moreni WWTP, in order to increase the efficiency in operation.
Study of Genetic Connectedness in Genetic Evaluation by Computer Simulation
K. Radjabalizadeh
Journal of Animal and Veterinary Advances , 2012, DOI: 10.3923/javaa.2010.1324.1327
Abstract: Connectedness is a statistical approach that could help breeder, under specific animal breeding situations in better deciding for animal selection from different environment. The accuracy of the comparison between EBVs from different herds depends upon the degree of connectedness between them. In this study, for considering effect of genetic connectedness effect on the genetic evaluation, comparisons of estimated evaluations and genetic parameters in two cases lack and un-lack (GC) and identification of (CR) between herd (s), Birth Weight (BW), Weaning Weight (WW) and Staple Length (SL) traits have been written in the C++ language program by simulation method in sheep herds with consideration of natural conditions (fertility percent, mortality percent). It is argued that connectedness increases as the proportion of offspring from common sires. It is very high if the 100% of the offspring in both herds are from common sires. Connectedness ratings were higher for highly heritable traits and lower for traits with low heritability.
Deposition of magnetic particles: A computer simulation study  [PDF]
F. de los Santos,M. Tasinkevych,J. M. Tavares,P. I. C. Teixeira
Physics , 2003, DOI: 10.1088/0953-8984/15/15/301
Abstract: We report a Monte Carlo simulation of deposition of magnetic particles on a one-dimensional substrate. Incoming particles interact with those that are already part of the deposit via a dipole-dipole potential. The strength of the dipolar interaction is controlled by an effective temperature $T^*$, the case of pure diffusion-limited deposition being recovered in the limit $T^*\to\infty$. Preliminary results suggest that the fractal dimension of the deposits does not change with temperature but that there is a (temperature-dependent) cross-over from regimes of temperature-dependent to universal behaviour. Furthermore, it was found that dipoles tend to align with the local direction of growth.
Computer Simulation Study of the Levy Flight Process  [PDF]
Mehrdad Ghaemi,Zahra Zabihinpour,Yazdan Asgari
Statistics , 2010, DOI: 10.1016/j.physa.2008.12.071
Abstract: Random walk simulation of the Levy flight shows a linear relation between the mean square displacement and time. We have analyzed different aspects of this linearity. It is shown that the restriction of jump length to a maximum value (lm) affects the diffusion coefficient, even though it remains constant for lm greater than 1464. So, this factor has no effect on the linearity. In addition, it is shown that the number of samples does not affect the results. We have demonstrated that the relation between the mean square displacement and time remains linear in a continuous space, while continuous variables just reduce the diffusion coefficient. The results are also implied that the movement of a levy flight particle is similar to the case the particle moves in each time step with an average length of jumping . Finally, it is shown that the non-linear relation of the Levy flight will be satisfied if we use time average instead of ensemble average. The difference between time average and ensemble average results points that the Levy distribution may be a non-ergodic distribution.
A computer simulation study of ionic conductivity in polymer electrolytes  [PDF]
Aninda Jiban Bhattacharyya,T. R. Middya,S. Tarafdar
Physics , 1997,
Abstract: In this paper we present a computer simulation study of ionic conductivity in solid polymeric electrolytes. The multiphase nature of the material is taken into account. The polymer is represented by a regular lattice whose sites represent either crystalline or amorphous regions with the charge carrier performing a random walk. Different waiting times are assigned to sites corresponding to the different phases. A random walk (RW) is used to calculate the conductivity through the Nernst-Einstein relation. Our walk algorithm takes into account the reorganisation of the different phases over time scales comparable to time scales for the conduction process. This is a characteristic feature of the polymer network. The qualitative nature of the variation of conductivity with salt concentration agrees with the experimental values for PEO-NH$_{4}$I and PEO-NH$_{4}$SCN. The average jump distance estimated from our work is consistent with the reported bond lengths for such polymers.
Electrophoretic mobility of a charged colloidal particle: A computer simulation study  [PDF]
Vladimir Lobaskin,Burkhard Duenweg,Christian Holm
Physics , 2004, DOI: 10.1088/0953-8984/16/38/021
Abstract: We study the mobility of a charged colloidal particle in a constant homogeneous electric field by means of computer simulations. The simulation method combines a lattice Boltzmann scheme for the fluid with standard Langevin dynamics for the colloidal particle, which is built up from a net of bonded particles forming the surface of the colloid. The coupling between the two subsystems is introduced via friction forces. In addition explicit counterions, also coupled to the fluid, are present. We observe a non-monotonous dependence of the electrophoretic mobility on the bare colloidal charge. At low surface charge density we observe a linear increase of the mobility with bare charge, whereas at higher charges, where more than half of the ions are co-moving with the colloid, the mobility decreases with increasing bare charge.
Minimum in the thermal conductivity of supercooled water: a computer simulation study  [PDF]
F. Bresme,J. W. Biddle,J. V. Sengers,M. A. Anisimov
Physics , 2014, DOI: 10.1063/1.4873167
Abstract: We report the results of a computer simulation study of the thermodynamic properties and the thermal conductivity of supercooled water as a function of pressure and temperature using the TIP4P-2005 water model. The thermodynamic properties can be represented by a two-structure equation of state consistent with the presence of a liquid-liquid critical point in the supercooled region. Our simulations confirm the presence of a minimum in the thermal conductivity, not only at atmospheric pressure, as previously found for the TIP5P water model, but also at elevated pressures. This anomalous behavior of the thermal conductivity of supercooled water appears to be related to the maximum of the isothermal compressibility or the minimum of the speed of sound. However, the magnitudes of the simulated thermal conductivities are sensitive to the water model adopted and appear to be significantly larger than the experimental thermal conductivities of real water at low temperatures.
Computer simulation study of surface wave dynamics at the crystal--melt interface  [PDF]
Jorge Benet,Luis G. MacDowell,Eduardo Sanz
Physics , 2014, DOI: 10.1063/1.4886806
Abstract: We study, by means of computer simulations, the crystal-melt interface of three different systems: hard-spheres, Lennard Jones and the TIP4P/2005 water model. In particular, we focus on the dynamics of surface waves. We observe that the processes involved in the relaxation of surface waves are characterized by distinct time scales: a slow one related to the continuous recrystallization and melting, that is governed by capillary forces; and a fast one which we suggest to be due to a combination of processes that quickly cause small perturbations to the shape of the interface (like e. g. Rayleigh waves, subdiffusion, or attachment/detachment of particles to/from the crystal). The relaxation of surface waves becomes dominated by the slow process as the wavelength increases. Moreover, we see that the slow relaxation is not influenced by the details of the microscopic dynamics. In a time scale characteristic for the diffusion of the liquid phase, the relaxation dynamics of the crystal-melt interface of water is around one order of magnitude slower than that of Lennard Jones or hard spheres, which we ascribe to the presence of orientational degrees of freedom in the water molecule. Finally, we estimate the rate of crystal growth from our analysis of the capillary wave dynamics and compare it with previous simulation studies and with experiments for the case of water.
Topological effects in ring polymers: A computer simulation study  [PDF]
M. Mueller,J. P. Wittmer,M. E. Cates
Physics , 1998, DOI: 10.1103/PhysRevE.53.5063
Abstract: Unconcatenated, unknotted polymer rings in the melt are subject to strong interactions with neighboring chains due to the presence of topological constraints. We study this by computer simulation using the bond-fluctuation algorithm for chains with up to N=512 statistical segments at a volume fraction \Phi=0.5 and show that rings in the melt are more compact than gaussian chains. A careful finite size analysis of the average ring size R \propto N^{\nu} yields an exponent \nu \approx 0.39 \pm 0.03 in agreement with a Flory-like argument for the topologica interactions. We show (using the same algorithm) that the dynamics of molten rings is similar to that of linear chains of the same mass, confirming recent experimental findings. The diffusion constant varies effectively as D_{N} \propto N^{-1.22(3) and is slightly higher than that of corresponding linear chains. For the ring sizes considered (up to 256 statistical segments) we find only one characteristic time scale \tau_{ee} \propto N^{2.0(2); this is shown by the collapse of several mean-square displacements and correlation functions onto corresponding master curves. Because of the shrunken state of the chain, this scaling is not compatible with simple Rouse motion. It applies for all sizes of ring studied and no sign of a crossover to any entangled regime is found.
Scheduling of a computer integrated manufacturing system: A simulation study  [cached]
Nadia Bhuiyan,Gerard Gouw,Daryoosh Yazdi
Journal of Industrial Engineering and Management , 2011, DOI: 10.3926/jiem.331
Abstract: Purpose: The purpose of this paper is to study the effect of selected scheduling dispatching rules on the performance of an actual CIM system using different performance measures and to compare the results with the literature. Design/methodology/approach: To achieve this objective, a computer simulation model of the existing CIM system is developed to test the performance of different scheduling rules with respect to mean flow time, machine efficiency and total run time as performance measures. Findings: Results suggest that the system performs much better considering the machine efficiency when the initial number of parts released is maximum and the buffer size is minimum. Furthermore, considering the average flow time, the system performs much better when the selected dispatching rule is either Earliest Due Date (EDD) or Shortest Process Time (SPT) with buffer size of five and the initial number of parts released of eight. Research limitations/implications: In this research, some limitations are: a limited number of factors and levels were considered for the experiment set-up; however the flexibility of the model allows experimenting with additional factors and levels. In the simulation experiments of this research, three scheduling dispatching rules (First In/First Out (FIFO), EDD, SPT) were used. In future research, the effect of other dispatching rules on the system performance can be compared. Some assumptions can be relaxed in future work. Practical implications: This research helps to identify the potential effect of a selected number of dispatching rules and two other factors, the number of buffers and initial number of parts released, on the performance of the existing CIM systems with different part types where the machines are the major resource constraints. Originality/value: This research is among the few to study the effect of the dispatching rules on the performance of the CIM systems with use of terminating simulation analysis. This is also significant given the nature of the CIM systems that are mostly used to produce different parts in varying quantities and thus do not produce parts on a continuing basis. This research is amongst the first to study the combined effect of dispatching rule and the buffer size in the CIM systems where the job arrivals are predetermined and depend on the completion of the existing parts in the system. A description of how buffer size and initial part release is related to the performance of the CIM system under study for the studied priority dispatching rule is also provided.
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