2,576 research outputs found
Design of Integrated Nanostructured Wicks for High-Performance Vapor Chambers
No full textThe performance of passive phase-change cooling devices, such as vapor chambers or heat pipes, may be significantly enhanced by exploiting the superior thermal properties of carbon nanotube (CNT) arrays. The potential for large reductions in overall package resistance with the use of high-conductivity wick materials enhanced with CNT nanostructures is investigated. While such nanostructured wicks feature very small pore sizes that support high capillary pressures, it is shown that the high fluid flow resistance through these dense arrays prevents their use as the lone fluid transport mechanism. It is proposed that evaporator surfaces comprised of nanostructured wicks fed by interspersed conventional wick materials (such as sintered powders) can provide the required permeability for fluid flow while simultaneously decreasing the effective evaporator thermal resistance. Optimization of wicks with integrated sintered and nanostructured areas requires a study of the trade-offs between the greater permeability of the sintered materials and the greater capillary pressure and thin-film evaporation area offered by the nanostructures. A numerical model is developed to estimate the thermal resistance of the evaporator region compared to that of a homogeneous sintered powder wick. The inputs needed for this model include the permeability and the capillary pressure in the two regions. A parametric study is conducted as a function of the ratio of conduction and evaporative resistances for the nanostructured and sintered regions. For a given heat input, the optimal liquid-feeding geometry that minimizes thermal resistance is obtained. In the best cases, the thermal resistance is reduced by a factor of thirteen through the use of the integrated nanostructured wicks compared to the resistance of a homogeneous sintered powder wick
Modeling and Design Optimization of Ultra-Thin Vapor Chambers for High Heat Flux Applications
No full textPassive phase-change thermal spreaders, such as vapor chambers have been widely employed to spread the heat from small-scale high-flux heat sources to larger areas. In this paper, a numerical model for ultrathin vapor chambers has been developed, which is suitable for reliable prediction of the operation at high heat fluxes and small scales. The effects of boiling in the wick structure on the thermal performance are modeled, and the model predictions are compared with experiments on custom-fabricated vapor chamber devices. The working fluid for the vapor chamber is water and a condenser side temperature range of 293 K–333 K is considered. The model predictions agree reasonably well with experimental measurements and reveal the input parameters to which thermal resistance and vapor chamber capillary limit are most sensitive. The vapor space in the ultrathin devices offers significant thermal and flow resistances when the vapor core thickness is in the range of 0.2 mm–0.4 mm. The performance of a 1-mm-thick vapor chamber is optimized by studying the variation of thermal resistance and total flow pressure drop as functions of the wick and vapor core thicknesses. The wick thickness is varied from 0.05 to 0.25 mm. Based on the minimization of a performance cost function comprising the device thermal resistance and flow pressure drop, it is concluded that the thinnest wick structures (0.05 mm) are optimal for applications with heat fluxes below 50 W/cm2, while a moderate wick thickness of 0.1 mm performs best at higher heat flux inputs (\u3e50 W/cm2)
Associations of parental food-choice control and use of food to soothe with adiposity in childhood and adolescence
No full textAbstract not availableShiau Y. Chong, Catherine R. Chittleborough, Tess Gregory, John W. Lynch, Murthy N. Mittinty, Lisa G. Smither
Novel miniaturized ring resonator and metamaterial filters for UHF applications
No full textEmerging applications such as wireless communications continue to
challenge RF/microwave filters with ever more stringent requirements as:
smaller size, lighter weight, and lower cost. Ring resonators have been widely
studied in the literature of filter applications because they are cheap and of
easy fabrication. Due to the large size of these resonators, various techniques
have been suggested in the literature to achieve miniaturization. Two main
parameters which affect the frequency response of the ring resonators are the
differences in the substrate’s thickness and tolerances in the dielectric
constant of the substrate. A new miniaturization technique is introduced in this
thesis. This novel technique is based on the use of vias to ground and
interdigital capacitors. Vias to ground allow size reduction and eliminate
harmonics. The addition of the interdigital capacitor to the electromagnetic
structure greatly reduces the sensitivity to substrate thickness. The resulting
resonators are highly miniaturized, cheap, of easy fabrication, of low
sensibility to differences in the substrate’s thickness, and independent of the
excitation orientation. Ultra High Frequency filters based on these novel
electromagnetic ring resonant structures are presented.
The growth of interest in metamaterials has recently led to novel and
interesting theoretical possibilities for microwave, infrared and optical
applications. One advantage of metamaterial structures is the size reduction.
In this thesis, the design of a metamaterial (MTM) transmission line based on
the negative magnetic coupling using the planar technology is presented. A
spiral inductor and interdigital capacitor are used as basic elements to realize
the MTM transmission line. Simulations are done using the full-wave
simulator SONNET and measurements are perform using the Agilent PNA
series microwave vector network analyzer (E8361A).Las comunicaciones inalámbricas emergentes requieren que los filtros de
microondas sean cada vez más pequeños, más ligeros y más baratos. Ya
que son baratos y de fácil fabricación los resonadores de anillo han sido
ampliamente estudiados en la literatura para aplicaciones de filtrado. Debido
al gran tamaño de estos resonadores varias técnicas se han sugerido en la
literatura para obtener miniaturización. Dos parámetros importantes que
afectan la respuesta en frecuencia de los resonadores de anillo son las
diferencias en el espesor del dieléctrico y las tolerancias de la constante
dieléctrica del substrato. En esta tesis se propone una novedosa técnica de
miniaturización, la cual está basada en el uso de una vía a tierra y un
capacitor interdigital. La vía a tierra permite reducir el tamaño del resonador y
elimina su segundo armónico. El capacitor interdigital reduce grandemente la
sensibilidad que el resonador tiene con respecto al espesor del substrato.
Los resonadores resultantes son altamente miniaturizados, baratos, de fácil
fabricación, de baja sensibilidad a las variaciones del substrato y no
dependen de la orientación con la cual son excitados. Usando estos
novedosos resonadores se diseñan y fabrican filtros de ultra alta frecuencia.
El creciente interés en metamateriales ha llevado a novedosas e interesantes
posibilidades teóricas para posibles aplicaciones en los rangos de
microondas, infrarrojo y óptico. Una de las ventajas de los metamateriales es
la reducción de tamaño. En esta tesis, se presenta el diseño de una línea de
transmisión metamaterial (MTM) la cual está basada en acoplamiento
magnético negativo y hace uso de la tecnología planar. Los elementos
básicos para realizar la línea de transmisión metamaterial son un inductor de
espiral y un capacitor interdigital. Las simulaciones son hechas en el
simulador de onda completa SONNET y las mediciones realizadas con el
analizador de redes vectoriales Agilent PNA (E8361A)
Numerical Analysis Of Large Size Horizontal Strip Anchors
No full textStructures like transmission towers, tele-communication masts, dry-docks, tall chimneys, tunnels and burried pipelines under water etc are subjected to considerable uplift forces. The net effect of external loading on the foundations of these structures results in forces that try to pull the foundations out of the ground. Anchors are usually provided to resist such uplift forces.
Earlier theoretical research of anchor behavior has focused on elastic response and ultimate pullout capacity. Many investigators have proposed techniques for determining the collapse load of anchors. Essentially the approaches involve the use of limit equilibrium concepts, with some assumptions regarding the shape of the failure surface and/or the influence of the soil above the anchor. The possible effect of dilatency and initial stress state are not considered in these methods. A number of investigators have used the results of small size model anchors to understand the behavior and extrapolated the results for predicting the behavior of large sized anchors. This has lead to unsatisfactory results. It has been clearly shown by Dickin (1989) that the failure displacements and load displacement curve patterns are very different for small and large sized anchors, i.e. they are not just proportional to the size of the anchor. Critical pullout load and the load displacement behavior are required for the complete analysis of anchor foundations. Though, many theories have been proposed to predict the uplift capacity within the limits of accuracy required at engineering level, at present no simple rational method is available for computing deformations.
In the present investigation attempts have been made to analyze the load deformation behavior of large size strip anchors in sands, clays and layered soils using two-dimensional explicit finite difference program FLAG (Fast Lagrangian Analysis of Continua), well suited for geomaterials, by assuming soil to be a Mohr-Coulomb material in the case of sands and modified Cam-clay material in the case of clays.
It is now well understood that the shearing resistance of a granular soil mass is derived from two factors frictional resistance and the dilatency of the soil. So the peak friction angle can be divided in to two components critical friction angle Фcv and dilation angle Ψ. Critical friction angle is the true friction angle as a result of frictional resistance at interparticle level when the soil is shearing at constant volume. If Фcv for a given soil remains constant, the value of Ψ has to increase with the increase in initial density of soil packing. The dilatency of a soil mass gradually decreases with continued shearing from its initial high value to zero after very large shear strains, when the soil finally reaches a constant, steady volume at critical states. Correspondingly the observed friction angle Ф reduces from its peak value to Фcv at a very large strain.
In earlier days, clays used to be characterized by the strength parameters c and Ф. often, under undrained conditions, Ф would be even considered zero. But in the recent developments, it is understood that all the strength of clays is frictional. There is nothing like cohesion. The part of shear strength, which appears to be independent of normal stress, is shown to be the effect of over-consolidation and the resulting dilation. Thus although Cam-clay model uses zero cohesion for all clays, it reflects this component of strength through over-consolidation and in a more realistic way. Hence, it is appropriate to consider the pre-consolidation pressure as parameter in the analysis. More specifically, the various aspects covered in this investigation are as follows.
Chapter 1 provides the general introduction. In chapter 2, the existing literature for the analysis of anchors for both experimental and analytical investigations on the pullout capacity of anchors in homogeneous and layered soils and the load deformation behavior of anchors under pullout are briefly reviewed.
Chapter 3 deals with the features and the implementation of the two-dimensional explicit finite difference program, Fast Lagrangian Analysis of Continua (FLAC) and the constitutive modeling of soils. It discusses the background and implementation of Strain softening / hardening model. This model is based on the Mohr- Coulomb model with non-associated shear and associated tension flow rules. In this model the cohesion, friction, dilation and tensile strength may harden or soften after the onset of the plastic yield. Further the critical state concepts and implementation of the modified Cam-clay model have been discussed. Cam-clay model originally developed for clays reflects the hydrostatic pressure or density dependent hardening material response.
Chapter 4 focuses on the analysis of load deformation behavior of large size anchors in granular soils. Two-dimensional explicit finite difference program (FLAC) is used for the simulations and the soil is modeled as a Mohr-Coulomb strain softening/hardening material In this chapter a series of simulations have been carried out on large size anchor plates, with parametric variation. By analyzing these results, a generalized load deformation relationship for different sizes of anchors and different types of soil have been proposed. The results are presented in the form of influence/design charts which can be used in hand calculations to obtain an estimate of anchor capacity and deformation for a wide range of soil types and size of anchors.
Chapter 5 deals with the analysis of the drained and undrained behavior of large size horizontal strip anchors in clays using modified Cam-clay model. Earlier investigators have studied the undrained behavior of anchor plates in clays, but no studies are reported in literature for the drained behavior of anchors in clays. Further it is not clear whether, drained or undrained condition will be critical for an anchor. In this chapter the drained and undrained behavior of large size anchor plates in both normally consolidated and over-consolidated states have been made. It has been found that the undrained pullout capacity of an anchor in a soil of normally consolidated state will always be more than the drained capacity. This is contrast to the usual understanding that undrained behavior is more critical than the drained behavior.
In Chapter 6 an attempt has been made to analyze the behavior of large size anchors in two layered sands and in conditions where backfill material has a higher or lower strength than the native soil, for different shape of excavations. Soil is assumed to be a Mohr-coulomb strain softening/hardening material.
In Chapter 7 the entire investigation covered in earlier chapters has been synthesized and some specific conclusions have been highlighted
Data Fusion Based Physical Layer Protocols for Cognitive Radio Applications
No full textThis thesis proposes and analyzes data fusion algorithms that operate on the physical layer of a wireless sensor network, in the context of three applications of cognitive radios: 1. Cooperative spectrum sensing via binary consensus; 2. Multiple transmitter localization and communication footprint identification; 3.Target self-localization using beacon nodes.
For the first application, a co-phasing based data combining scheme is studied under imperfect channel knowledge. The evolution of network consensus state is modeled as a Markov chain, and the average transition probability matrix is derived. Using this, the average hitting time and average consensus duration are obtained, which are used to determine and optimize the performance of the consensus procedure.
Second, using the fact that a typical communication footprint map admits a sparse representation, two novel compressed sensing based schemes are proposed to construct the map using 1-bit decisions from sensors deployed in a geographical area. The number of transmitters is determined using the K-means algorithm and a circular fitting technique, and a design procedure is proposed to determine the power thresholds for signal detection at sensors.
Third, an algorithm is proposed for self-localization of a target node using power measurements from beacon nodes transmitting from known locations. The geographical area is overlaid with a virtual grid, and the problem is treated as one of testing overlapping subsets of grid cells for the presence of the target node. The column matching algorithm from group testing literature is considered for devising the target localization algorithm. The average probability of localizing the target within a grid cell is derived using the tools from Poisson point processes and order statistics. This quantity is used to determine the minimum required node density to localize the target within a grid cell with high probability.
The performance of all the proposed algorithms is illustrated through Monte Carlo simulations
In-vitro toxigenic activity of Zingiber zerumbet oil on A. ochraceus.
No full textThis Dissertation / Report is the outcome of investigation carried out by the creator(s) / author(s) at the department/division of Central Food Technological Research Institute (CFTRI), Mysore mentioned below in this page
In-vitro toxigenic activity of Zingiber zerumbet oil on A. ochraceus
No full textThis Dissertation / Report is the outcome of investigation carried out by the creator(s) / author(s) at the department/division of Central Food Technological Research Institute (CFTRI), Mysore mentioned below in this page
Demucilization of Coffee Beans using Enzymes
No full textThis Dissertation / Report is the outcome of investigation carried out by the creator(s) / author(s) at the department/division of Central Food Technological Research Institute (CFTRI), Mysore mentioned below in this page
Aplicación del aprendizaje en espiral para incorporar la informática al plan de estudios de la formación de pregrado en enfermería
No full textA lack of informatics proficiency among nursing students, working professionals, and academics hinders nurses' skills to use technologies to enhance sufferers' care globally. Programmed health is a field that requires investment, according to national nursing education initiatives and professional organizations' suggestions. In the United Kingdom, a Bachelor of Nursing degree incorporates health informatics, as shown in the following case study. International collaboration with a United States-United Kingdom Fulbright Expert Scholar allowed for the development and inclusion of unique training units matching crucial health informatics competencies in an educational structure focused on the spiral training approach. This method is suggested as a means of integrating information into nursing training so that students can develop into competent clinicians who can provide care in a healthcare system that is technologically enabled.La falta de dominio de la informática entre los estudiantes de enfermería, los profesionales en activo y los académicos dificulta las habilidades de las enfermeras para utilizar las tecnologías con el fin de mejorar la atención a los enfermos a nivel mundial. La salud programada es un campo que requiere inversión, según las iniciativas nacionales de educación en enfermería y las sugerencias de las organizaciones profesionales. En el Reino Unido, la licenciatura en enfermería incorpora la informática sanitaria, como se muestra en el siguiente estudio de caso. La colaboración internacional con un becario Fulbright experto de Estados Unidos y el Reino Unido permitió desarrollar e incluir unidades de formación únicas que corresponden a competencias informáticas sanitarias cruciales en una estructura educativa centrada en el enfoque de formación en espiral. Se sugiere este método como medio de integrar la informática en la formación de enfermería para que los estudiantes se conviertan en clínicos competentes capaces de prestar cuidados en un sistema sanitario tecnológicamente habilitado
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