Beyond the Maxwell Limit: Thermal Conduction in Nanofluids with Percolating Fluid Structures

In a well-dispersed nanofluid with strong cluster-fluid attraction, thermal conduction paths can arise through percolating amorphous-like interfacial structures. This results in a thermal conductivity enhancement beyond the Maxwell limit of 3*phi, with phi being the nanoparticle volume fraction. Our findings from non-equilibrium molecular dynamics simulations, which are amenable to experimental verification, can provide a theoretical basis for the development of future nanofluids.Comment: 5 Pages, 3 Figures, In Review: APL, Accepted for presentation at "Nanofluids: Fundamentals and Applications", September 16-20, 2007, Copper Mountain, Colorad

Modeling Solute Thermokinetics in LiCI-KCI Molten Salt for Nuclear Waste Separation

Recovery of actinides is an integral part of a closed nuclear fuel cycle. Pyrometallurgical nuclear fuel recycling processes have been developed in the past for recovering actinides from spent metallic and nitride fuels. The process is essentially to dissolve the spent fuel in a molten salt and then extract just the actinides for reuse in a reactor. Extraction is typically done through electrorefining, which involves electrochemical reduction of the dissolved actinides and plating onto a cathode. Knowledge of a number of basic thermokinetic properties of salts and salt-fuel mixtures is necessary for optimizing present and developing new approaches for pyrometallurgical waste processing. The properties of salt-fuel mixtures are presently being studied, but there are so many solutes and varying concentrations that direct experimental investigation is prohibitively time consuming and expensive (particularly for radioactive elements like Pu). Therefore, there is a need to reduce the number of required experiments through modeling of salt and salt-fuel mixture properties. This project will develop first-principles-based molecular modeling and simulation approaches to predict fundamental thermokinetic properties of dissolved actinides and fission products in molten salts. The focus of the proposed work is on property changes with higher concentrations (up to 5 mol%) of dissolved fuel components, where there is still very limited experimental data. The properties predicted with the modeling will be density, which is used to assess the amount of dissolved material in the salt; diffusion coefficients, which can control rates of material transport during separation; and solute activity, which determines total solubility and reduction potentials used during electrorefining. The work will focus on La, Sr, and U, which are chosen to include the important distinct categories of lanthanides, alkali earths, and actinides, respectively. Studies will be performed using LiCl-KCl salt at the eutectic composition (58 mol% LiCl, 42 mol% KCl), which is used for treating spent EBR-II fuel. The same process being used for EBRII fuel is currently being studied for widespread international implementation. The methods will focus on first-principles and first- principles derived interatomic potential based simulations, primarily using molecular dynamics. Results will be validated against existing literature and parallel ongoing experimental efforts. The simulation results will be of value for interpreting experimental results, validating analytical models, and for optimizing waste separation by potentially developing new salt configurations and operating conditions

Transport modeling of simple fluids and nano-colloids : thermal conduction mechanisms and coarse projection

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2006.Includes bibliographical references (p. 159-166).In the first part of this thesis, the modes of microscopic energy fluctuations governing heat flow in nano-colloids are quantitatively assessed by combining linear response theory with molecular dynamics (MD) simulations. The intrinsic thermal conductivity is decomposed into self and cross correlations of the three modes that make up the microscopic heat flux vector, namely, the kinetic, the potential and the virial. By this decomposition analysis, the interplay between the molecular mechanisms that govern the variation of the thermal conductivity with volume fraction and solid-fluid interaction is examined. For a specific system of nanosized platinum clusters which interact strongly with host liquid xenon, a significant thermal conductivity enhancement is obtained as a result of self correlation in the potential energy flux. The effect saturates at higher volume fractions due to the cross-mode correlation between the potential and the virial flux. A strong solid-fluid coupling also introduces an amorphous-like structural transition and a pronounced cage effect that significantly reduces the self diffusion of the nano-clusters. These attendant structural and diffusive effects, unlike the self correlation of the potential flux, are amenable to experimental observations. The cluster-fluid interface is characterized by large fluctuations in the potential energy which is indicative of an unusual exchange of potential energy among the interfacial fluid atoms. For small nano-clusters, the interfacial layers interact with each other to form a percolating network. The research findings highlight the importance of surface interactions and show that the interfacial thermal resistance emanating from the self correlation of the collision flux is not the limiting mechanism for heat transfer in nano-colloids.(cont.) This thesis also addresses several theoretical concerns regarding the microscopic thermal transport in colloids by using non-equilibrium molecular dynamics simulations (NEMD). The time averaged microscopic heat flux which assumes spatial homogeneity is shown to be applicable to nano-colloidal systems. Further, it is demonstrated that the thermal conductivity from a NEMD simulation is statistically equivalent to that of an equilibrium linear response evaluation only under certain dynamic conditions at the cluster-fluid interface. The concept of interfacial dynamical similarity is developed to establish this equivalence. The proposed thermal conduction model is consistent with several experimental observations such as the anomalous enhancement at small volume fractions with very small nanoparticles (3-10nm), limiting behavior at higher volume fractions, and the lack of correlation of the enhancement to the intrinsic thermal conductivity of the nano-clusters. The model also suggests possible avenues for optimizing the colloids by developing nano-clusters that have functionalized surface layers to maximize the interactions with the fluid atoms. In the second part of this thesis, smooth field estimators based on statistical inference and smoothing kernels are developed to transfer molecular data to the continuum for hybrid and equation-free multiscale simulations. The field estimators are then employed to implement coarse projection, a multiscale integration scheme, for a shear driven flow in an enclosure. This thesis shows that the spatial continuity and smoothness of the microscopically generated coarse variables, geometrically similar initial conditions and the separation of timescales are essential for the correct coarse field evolution with coarse projection.by Jacob Eapen.Sc.D

Captive breeding, developmental biology and commercial production of Dravidia fasciata- An indigenous ornamental fish of the Western Ghats of India

Ornamental fishes of the Western Ghats of India have great demand in the export market. At present these fishes are collected from the wild and exported. Hence many times, the demand could not be met due to short supply. The only remedial measure for a sustainable supply is to produce the fish in captive conditions. Unfortunately, the breeding technology for the ornamental fishes of the Western Ghats of India has not been attempted seriously till date. The present paper is almost a pioneering attempt to develop captive breeding technology for 12 prioritized species of the indigenous ornamental fishes of the Western Ghats of India. Dravidia fasciata is one of them. It is popularly known as Melon barb. It is a beautiful barb, growing to a maximum size of 80 mm. In the present paper the methodology of captive breeding of this fish is provided with the economics of its production. Melon barbs were collected from the wild and brought to the hatchery of College of Fisheries in oxygen filled plastic bags and gradually acclimatized to the captive conditions. Its size at first maturity, sexual dimorphism, and developmental biology were studied and described with photographs. The total length (TL) at first maturity for males was 50 mm (50-55 mm) and 40 mm for females (40-45 mm). A sexually mature male developed beautiful pinkish red tinge all over the body. The black bands over the body also became deeper in colour during this time. The intensity of the colour reached its maximum during the courtship activities. Male also possessed nuptial tubercles on the operculum which could be identified only by keen observation. But a sexually mature female did not develop any colour change by the onset of sexual maturity. The results of the study clearly demonstrated that D. fasciata could be successfully produced in captivity through scientific management of brooders, eggs, larvae and hatchlings. The successful development of captive breeding technology is likely to pave way towards commercialization of the technology thus leading to the sustainable export of the species

The Classical Nature of Thermal Conduction in Nanofluids,

We show that a large set of nanofluid thermal conductivity data falls within the upper and lower Maxwell bounds for homogeneous systems. This indicates that the thermal conductivity of nanofluids is largely dependent on whether the nanoparticles stay dispersed in the base fluid, form large aggregates, or assume a percolating fractal configuration. The experimental data, which are strikingly analogous to those in most solid composites and liquid mixtures, provide strong evidence for the classical nature of thermal conduction in nanofluid

Computing the viscosity of supercooled liquids

We describe an atomistic method for computing the viscosity of highly viscous liquids based on activated state kinetics. A basin-filling algorithm allowing the system to climb out of deep energy minima through a series of activation and relaxation is proposed and first benchmarked on the problem of adatom diffusion on a metal surface. It is then used to generate transition state pathway trajectories in the potential energy landscape of a binary Lennard-Jones system. Analysis of a sampled trajectory shows the system moves from one deep minimum to another by a process that involves high activation energy and the crossing of many local minima and saddle points. To use the trajectory data to compute the viscosity we derive a Markov Network model within the Green-Kubo formalism and show that it is capable of producing the temperature dependence in the low-viscosity regime described by molecular dynamics simulation, and in the high-viscosity regime (10(2)-10(12) Pa s) shown by experiments on fragile glass-forming liquids. We also derive a mean-field-like description involving a coarse-grained temperature-dependent activation barrier, and show it can account qualitatively for the fragile behavior. From the standpoint of molecular studies of transport phenomena this work provides access to long relaxation time processes beyond the reach of current molecular dynamics capabilities. In a companion paper we report a similar study of silica, a representative strong liquid. A comparison of the two systems gives insight into the fundamental difference between strong and fragile temperature variations

Penetration and infectivity of entomopathogenic nematodes against Lema sp. (Chrysomelidae: Coleoptera) infesting turmeric (Curcuma longa L.) and their multiplication

Penetration and infectivity of eight native isolates of entomopathogenic nematodes (EPNs), Heterorhabditis sp. (IISR-EPN 01); Steinernema sp. (IISR-EPN 02); S. ramanai (IISR-EPN 03); S. carpocapsae (IISR-EPN 06), Oscheius gingeri (IISR-EPN 07) and Oscheius spp. (IISR-EPN 04, 05 and 08) were evaluated against larvae of leaf feeder (LF) Lema sp. infesting turmeric. Among the tested EPNs, Steinernema sp. (IISR-EPN 02) and O. gingeri (IISR-EPN 07) were more pathogenic to LF larva as they brought about 100% mortality to the insect within 48 h post exposure, followed by Heterorhabditis sp. (IISR-EPN 01) and Oscheius sp. (IISR-EPN 08) after 72 h of exposure. S. ramanai (IISR-EPN 03) and Oscheius spp. (IISR-EPN 04 and 05) took 96 and 120 h, respectively, to kill the test insect. Lema sp. larva was the most suitable host for multiplication of infective juveniles (IJs) of O. gingeri (IISR-EPN 07), which yielded 11, 480 IJs larva-1, followed by Steinernema sp. (IISREPN 02) (8, 658 IJs larva-1) and S. carpocapsae (IISR-EPN 06) (6, 810 IJs larva-1), however, Heterorhabditis sp. (IISR-EPN 01) less multiplied. The maximum number of Steinernema sp. (IISREPN 02) IJs penetrated into test larva (17.5 IJs larva-1), followed by S. carpocapsae (IISR-EPN 06) (10.2 IJs larva-1) and the fewest (2.8 IJs larva-1) were of Oscheius sp. (IISR-EPN 08). The infectivity of the above EPNs against LF is being reported for the first time which opens up a new hope of utilizing them in insect pest management in turmeric. &nbsp

Multicenter data acquisition made easy

<p>Abstract</p> <p>Background</p> <p>The process for data collection in multicenter trials may be troublesome and expensive. We report our experience with the spreadsheet function in Googledocs for this purpose.</p> <p>Methods</p> <p>In Googledocs the data manager creates a form similar to the paper case record form, which will function as a decentral data entry module. When the forms are submitted, they are presented in a spreadsheet in Googledocs, which can be exported to different standard spreadsheet formats.</p> <p>Results</p> <p>For a multicenter randomized clinical trial with five different participating hospitals we created a decentral data entry module using the spreadsheet function in Googledocs. The study comprised 332 patients (clinicaltrials.gov identifier: NCT00815698) with five visits per patient. One person at each study site entered data from the original paper based case report forms which were kept at the study sites as originals. We did not experience any technical problems using the system.</p> <p>Conclusions</p> <p>The system allowed for decentral data entry, and it was easy to use, safe, and free of charge. The spreadsheet function in Googledocs may potentially replace current expensive solutions for data acquisition in multicenter trials.</p> <p>Trial registration</p> <p>clinicaltrials.gov NCT00815698</p