Academic literature on the topic 'Density gradient technique'

The mechanical oscillator technique permits determining blood density continuously with high accuracy. Using this technique arteriovenous density gradients were recorded in the coronary vascular bed of anesthetized dogs. It was found that the coronary sinus blood has a higher density than arterial blood due to the loss of filtered fluid in the microcirculation. The amount of fluid loss corresponds to the lymph flow in the myocardium. Increase of venous pressure leads to an increase of the density gradient. Intermittent coronary sinus occlusion (ICSO) surprisingly leads to a reduction of the density gradient. Injection of osmotically hypertensive fluids influences the arteriovenous gradient by shifting extravascular fluid into the blood. The method permits the determination of filtration coefficients and to estimate the tissue volume available for fluid exchange.

This experimental study determines H2 transfer properties of High Density PolyEthylene (HDPE) or epoxy membranes. Two different techniques are compared. The pressure gradient technique is analyzed for permeability or diffusion. Results show that the main phenomenon involved is diffusion. The second technique involves a gas concentration gradient. Although implying significantly slower kinetics, this classical technique is consistent with results obtained with the faster pressure gradient technique.

Designing an efficient filtering technique is an ill-posed problem especially for image affected from high density of noise. The majority of existing techniques suffer from edge degradation and texture distortion issues. Therefore, in this paper, an efficient weighted nuclear norm minimization (NNM)-based filtering technique to preserve the edges and texture information of filtered images is proposed. The proposed technique significantly improves the quantitative improvements on the low rank approximation of nonlocal self-similarity matrices to deal with the overshrink problem. Extensive experiments reveal that the proposed technique preserves edges and texture details of filtered image with lesser number of visual artifacts on visual quality. The proposed technique outperforms the existing techniques over the competitive filtering techniques in terms of structural similarity index metric (SSIM), peak signal-to-noise ratio (PSNR) and edge preservation index (EPI).

ABSTRACT Considering the spatially separated polarization radiation and Faraday rotation regions to simulate complex interstellar media, we study synchrotron polarization gradient techniques’ measurement capabilities. We explore how to trace the direction of projected magnetic field of emitting-source region at the multifrequency bands, using the gradient technique compared with the traditional polarization vector method. Furthermore, we study how Faraday rotation density in the foreground region, i.e. a product of electron number density and parallel component of magnetic fields along the line of sight, affects the measurement of projected magnetic field. Numerical results show that synchrotron polarization gradient technique could successfully trace projected magnetic field within emitting-source region independent of radio frequency. Accordingly, the gradient technique can measure the magnetic field properties for a complex astrophysical environment.

La finalidad del presente estudio fue evaluar en 2 tiempos la calidad espermática de muestras de semen de ovino tratadas por la técnica de gradiente de densidad con respecto a muestras no tratadas. Se utilizó un total de 102 eyaculados de carnero que presentaron en promedio un volumen de 1.12 ± 0.34 ml, color blanquecino, aspecto cremoso, pH de 6.73 ± 0.25, concentración inicial de 3.54 x 109 ± 5.30 x 108 esp/ml y motilidad masal alrededor del grado 4. Posteriormente, cada eyaculado se dividió en un grupo control y experimental de volúmenes iguales. El semen del grupo control fue diluido con Triladyl® y el experimental, tratado con la técnica de gradiente de densidad. La tasa de recuperación espermática después del tratamiento fue del 31.50 ± 10.89%. Se encontró un aumento significativo (p<0.05) en la motilidad individual progresiva, el porcentaje de espermatozoides vivos y de espermatozoides con membrana intacta en las muestras tratadas con respecto al grupo control (92.07 ± 1.81% vs. 85.74 ± 1.75%, 78.42 ± 5.13% vs. 75.19 ± 4.59%, 78.55 ± 4.34% vs. 73.37 ± 4.48%, respectivamente); así como una disminución significativa (p<0.05) en el porcentaje de espermatozoides anormales en las muestras del grupo experimental con respecto al grupo control (8.41 ± 1.33% vs. 9.94 ± 1.73%). El resto de muestras de ambos grupos fue distribuido en pajillas de 0.25 ml y enfriadas hasta alcanzar los 5°C para su refrigeración por 24 horas. Las muestras tratadas con gradiente de densidad presentaron un aumento significativos (p<0.05), con respecto al grupo control, en motilidad individual progresiva, el porcentaje de espermatozoides vivos y el porcentaje de espermatozoides con membrana intacta (86.94 ± 3.14% vs. 82.44 ± 2.26%, 71.24 ± 4.11% vs. 68.82 ± 4.15%, 70.87 ± 3.11% vs. 67.98 ± 4.42%, respectivamente). En conclusión, la técnica de gradiente favoreció la obtención de un mayor número de espermatozoides vivos, de mejor motilidad y con membrana intacta, así como la disminución del número de espermatozoides anormales tanto en muestras frescas como refrigeradas. The purpose of the present study was to assess at 2 evaluation times the sperm quality from ram semen treated with the density gradient technique and to compare it against non-treated ram semen. A total of 102 ejaculates were evaluated. The mean macroscopic parameters were: volume of 1.12 ± 0.34 ml, creamy white color, creamy-dense appearance, pH of 6.73 ± 0.25, initial concentration of 3.54 x 109 ± 5.30 x 108 spz/ml and mass motility around grade 4. Then, each ejaculate was divided into two equal volume groups: the control and experimental group. For the control group, the sample was diluted in Triladyl®. The experimental group was treated with the density gradient technique. The recovery rate after treatment was 31.50 ± 10.89%.The results showed that, at zero hour, samples treated undergo a significant increase (p <0.05), compared with the control group, in individual progressive motility, percentage of living spermatozoa and the percentage of spermatozoa with intact membrane (92.07 ± 1.81% vs. 85.74 ± 1.75%, 78.42 ± 5.13% vs. 75.19 ± 4.59%, 78.55 ± 4.34% vs. 73.37 ± 4.48%, respectively). There was also a significant decrease (p <0.05) in the percentage of abnormal in samples from the experimental group compared to control group spermatozoa (8.41 ± 1.33% vs. 9.94 ± 1.73%). The remaining samples, from both the control and experimental group, were distributed in 0.25 ml straws and cooled to 5°C for 24 hours refrigeration. Then, the samples were evaluated. After 24 hours at 5°C, the samples treated with the density gradient technique showed significantly greater values (p <0.05), compared with the control group, in individual progressive motility, percentage of living spermatozoa and the percentage of spermatozoa with intact membrane (86.94 ± 3.14% vs. 82.44 ± 2.26%, 71.24 ± 4.11% vs. 68.82 ± 4.15%, 70.87 ± 3.11% vs. 67.98 ± 4.42%, respectively). In conclusion, in the present study, the density gradient technique allowed to obtain better a greater number of living spermatozoa with better motility, intact membrane and with lower abnormalities in fresh and refrigerated samples.

The trend towards more and all-electric apparatuses and more electrification will lead to higher electrical demand. Increases in electrical power demand can be provided by either higher currents or higher voltages. Due to "weight" and "voltage" drop, a raise in the current is not preferred; so, "higher voltages" are being considered. Another trend is to reduce the size and weight of apparatuses. Combined, these two trends result in the high voltage, high power density concept. It is expected that by 2030, 80% of all electric power will flow through "power electronics systems". In regards to the high voltage, high power density concept described above, "wide bandgap (WBG) power modules" made from materials such as "SiC and GaN (and, soon, Ga2O3 and diamond)", which can endure "higher voltages" and "currents" rather than "Si-based modules", are considered to be the most promising solution to reducing the size and weight of "power conversion systems". In addition to the trend towards higher "blocking voltage", volume reduction has been targeted for WBG devices. The blocking voltage is the breakdown voltage capability of the device, and volume reduction translates into power density increase. This leads to extremely high electric field stress, E, of extremely nonuniform type within the module, leading to a higher possibility of "partial discharge (PD)" and, in turn, insulation degradation and, eventually, breakdown of the module. Unless the discussed high E issue is satisfactorily addressed and solved, realizing next-generation high power density WBG power modules that can properly operate will not be possible. Contributions and innovations of this Ph.D. work are as follows. i) Novel electric field grading techniques including (a) various geometrical techniques, (b) applying "nonlinear field-dependent conductivity (FDC) materials" to high E regions, and (c) combination of (a) and (b), are developed; ii) A criterion for the electric stress intensity based upon accurate dimensions of a power device package and its "PD measurement" is presented; iii) Guidelines for the electrical insulation design of next-generation high voltage (up to 30 kV), high power density "WBG power modules" as both the "one-minute insulation" and PD tests according to the standard IEC 61287-1 are introduced; iv) Influence of temperature up to 250°C and frequency up to 1 MHz on E distribution and electric field grading methods mentioned in i) is studied; and v) A coupled thermal and electrical (electrothermal) model is developed to obtain thermal distribution within the module precisely. All models and simulations are developed and carried out in COMSOL Multiphysics.
Doctor of Philosophy
In power engineering, power conversion term means converting electric energy from one form to another such as converting between AC and DC, changing the magnitude or frequency of AC or DC voltage or current, or some combination of these. The main components of a power electronic conversion system are power semiconductor devices acted as switches. A power module provides the physical containment and package for several power semiconductor devices. There is a trend towards the manufacturing of electrification apparatuses with higher power density, which means handling higher power per unit volume, leading to less weight and size of apparatuses for a given power. This is the case for power modules as well. Conventional "silicon (Si)-based semiconductor technology" cannot handle the power levels and switching frequencies required by "next-generation" utility applications. In this regard, "wide bandgap (WBG) semiconductor materials", such as "silicon carbide (SiC)"," gallium nitride (GaN)", and, soon, "gallium oxide" and "diamond" are capable of higher switching frequencies and higher voltages, while providing for lower switching losses, better thermal conductivities, and the ability to withstand higher operating temperatures. Regarding the high power density concept mentioned above, the challenge here, now and in the future, is to design compact WBG-based modules. To this end, the extremely nonuniform high electric field stress within the power module caused by the aforementioned trend and emerging WBG semiconductor switches should be graded and mitigated to prevent partial discharges that can eventually lead to breakdown of the module. In this Ph.D. work, new electric field grading methods including various geometrical techniques combined with applying nonlinear field-dependent conductivity (FDC) materials to high field regions are introduced and developed through simulation results obtained from the models developed in this thesis.

[EN] This Thesis is focused on the development and implementation of efficient numerical methods for the acoustic modelling and design of noise control devices in the exhaust system of combustion engines. Special attention is paid to automotive perforated dissipative silencers, in which significant differences are likely to appear in their acoustic behaviour, depending on the temperature variations within the absorbent material. Also, material heterogeneities can alter the silencer attenuation performance. Therefore, numerical techniques considering all these features are required to guarantee the accuracy of the results. A literature review is carried out, mainly related to one-dimensional models, as well as to acoustic models for absorbent materials and perforated surfaces. However, plane wave model limitations make indispensable using alternative multidimensional methods. In addition, the possibility of using new acoustic elements is explored. These elements have as an objective being a potential alternative to the fibrous absorbent materials, which can have a negative impact on health. The Thesis considers the use of microperforated and sintered surfaces. The latter have, in some cases, a nearly constant acoustic impedance, whose value depends, among others, on the thickness and porosity of the plates. To avoid the limitations of plane wave models, a finite element (FE) approach is proposed for the acoustic analysis of dissipative silencers including a perforated duct with uniform axial mean flow and an outer chamber with a heterogeneous distribution of the absorbent material. On the other hand, property variations can be also produced by temperature gradients. In this case, a hybrid FE model has been derived for perforated dissipative silencers including: (1) Thermal gradients in the central duct and the chamber; (2) A perforated passage carrying non-uniform axial mean flow. A FE approach has been implemented to solve the pressure-based wave equation for a non-moving heterogeneous medium, associated with the chamber. Also, the governing equation in the central duct has been written and solved in terms of an acoustic velocity potential to allow the presence of an axially inhomogeneous flow. The coupling between both regions has been carried out by means of a perforated duct and its acoustic impedance, adapted here to include absorbent material heterogeneities and mean flow effects. It has been found that the presence of non-homogeneities can have a significant influence on the acoustic attenuation of a silencer and should be included in the theoretical models. Optimization techniques for industrial noise control devices are relevant, since they lead to the production of elements with better characteristics. Evolutionary algorithms are emergent techniques able to obtain a solution, even in those problems in which the traditional optimization have difficulties. Optimization techniques are combined with the FE method to achieve the maximum attenuation in the frequency range of interest. A multichamber silencer optimization problem is defined and several analyses are carried out to obtain the most suitable configuration for each application. Under certain assumptions of axial uniformity, several techniques have been considered to reduce the computational effort of a full 3D FE analysis for dissipative silencers with temperature gradients and mean flow. These are based on a decomposition of the acoustic field into transversal and axial modes within each silencer subdomain, and a matching procedure of the modal expansions at the silencer area changes through the continuity conditions of the acoustic fields. The relative computational efficiency and accuracy of predictions for the matching techniques are studied, including point collocation at nodes and Gauss points and also mode-matching with weighted integration. All of them provide accurate predictions of the attenuation and improve the computational cost of a FE calculation
[ES] Esta Tesis se centra en el desarrollo e implementación de métodos numéricos eficientes para el diseño y modelado de componentes de la línea de escape en motores de combustión interna. Merecen especial atención los silenciadores disipativos perforados de automóviles, ya que su comportamiento acústico puede sufrir variaciones importantes debidas a las variaciones de temperatura en el material absorbente, así como a las heterogeneidades de la fibra. Por tanto, se requieren técnicas numéricas que consideren estos casos para garantizar la precisión de los resultados. Se lleva a cabo una revisión bibliográfica que recoge los modelos de onda unidimensionales, así como modelos acústicos de materiales absorbentes y superficies perforadas. Sin embargo, las limitaciones de los primeros hacen indispensable el uso de modelos multidimensionales. Además se explora la posibilidad de usar nuevos elementos acústicos, cuyo objetivo es ser una alternativa potencial a los materiales absorbentes, que pueden tener un efecto negativo sobre la salud. La Tesis considera el uso de superficies microperforadas y sinterizadas. Estas últimas en algunos casos presentan una impedancia casi constante, cuyo valor depende, entre otras cosas, del espesor y la porosidad de las placas. Para evitar las limitaciones de los modelos de onda plana, se propone un enfoque en elementos finitos (EF) para el análisis acústico de silenciadores disipativos que incluyen un conducto con flujo medio axial uniforme y una cámara externa con una distribución heterogénea de material absorbente. Por otro lado, la variación de las propiedades también puede producirse por gradientes térmicos. En este caso, se propone una formulación híbrida de EF para silenciadores disipativos perforados que incluye: (1) Gradientes térmicos en el conducto central y la cámara; (2) Un conducto perforado que canaliza flujo medio axial no uniforme. Se ha implementado una formulación de EF para resolver la ecuación de ondas en términos de presión para el medio estacionario heterogéneo asociado a la cámara. Además, la ecuación asociada al conducto central, expresada en términos de potencial de velocidad acústica, permite la presencia de flujo axial no uniforme. El acoplamiento entre ambas regiones se ha realizado mediante un conducto perforado y su impedancia acústica y se ha adaptado para incluir la citada falta de homogeneidad. Se ha visto que las heterogeneidades pueden influir notablemente en la atenuación acústica de un silenciador, debiéndose incluir en los modelos teóricos. Las técnicas de optimización para componentes industriales de control de ruido son importantes, ya que producen elementos con mejores características. Los algoritmos evolutivos son técnicas emergentes capaces de obtener una solución, incluso cuando la optimización tradicional tiene dificultades. Las técnicas de optimización se combinan con el MEF para conseguir la máxima atenuación posible en el rango de frecuencias de interés. Se ha definido un problema de optimización de un silenciador multicámara y se han llevado a cabo varios análisis para obtener la configuración más adecuada para cada caso. Bajo ciertas hipótesis de uniformidad axial, se han considerado varias técnicas para reducir el coste computacional de un análisis 3D completo para silenciadores disipativos con gradientes de temperatura y flujo medio. Éstas se basan en la descomposición del campo acústico en modos axiales y transversales dentro de cada subdominio, y un procedimiento de acoplamiento de las expansiones modales en los cambios de sección del silenciador mediante las condiciones de continuidad de los campos acústicos. Se estudia la eficiencia computacional y precisión de las predicciones de las técnicas de acoplamiento, incluyendo colocación puntual en nodos y puntos de Gauss, así como ajuste modal. Todos ellos proporcionan predicciones precisas de la atenuación mejorando el coste
[CAT] Aquesta Tesi es centra en el desenvolupament i implementació de mètodes numèrics eficients per al disseny i modelatge de components de la línia d'escapament en motors de combustió interna. Mereixen especial atenció els silenciadors dissipatius perforats d'automòbils, ja que el seu comportament acústic pot patir variacions importants degudes a les variacions de temperatura en el material absorbent, així com a les heterogeneïtats de la fibra. Per tant, es requereixen tècniques numèriques que considerin aquests casos per garantir la precisió dels resultats. Es porta a terme una revisió bibliogràfica que recull els models d'ona unidimensionals, així com models acústics de materials absorbents i superfícies perforades. No obstant això, les limitacions dels primers fan indispensable l'ús de models multidimensionals. A més s'explora la possibilitat d'usar nous elements acústics amb l'objectiu que siguen una alternativa potencial als materials absorbents, que poden tenir un efecte negatiu sobre la salut. La Tesi considera l'ús de superfícies microperforades i sinteritzades. Aquestes últimes en alguns casos presenten una impedància gairebé constant. El seu valor depèn, entre altres coses, del gruix i la porositat de les plaques. Per evitar les limitacions dels models d'ona plana, es proposa un enfocament amb elements finits (EF) per a l'anàlisi acústic de silenciadors dissipatius que inclouen un conducte amb flux mig axial uniforme i una càmera externa amb una distribució heterogènia de material absorbent. D'altra banda, la variació de les propietats també es pot produir per gradients tèrmics. En aquest cas, es proposa una formulació híbrida d'EF per silenciadors dissipatius perforats que inclou: (1) Gradients tèrmics en el conducte central i la càmera; (2) Un conducte perforat que canalitza flux mig axial no uniforme. S'ha implementat una formulació d'EF per resoldre l'equació d'ones en termes de pressió per al medi estacionari heterogeni associat a la càmera. A més, l'equació associada al conducte central, expressada en termes de potencial de velocitat acústica, permet la presència de flux axial no uniforme. L'acoblament entre les dues regions s'ha realitzat mitjançant un conducte perforat i la seva impedància acústica i s'ha adaptat per incloure la esmentada falta d'homogeneïtat. S'ha vist que les heterogeneïtats poden influir notablement en l'atenuació acústica d'un silenciador i s'han d'incloure en els models teòrics. Les tècniques d'optimització per a components industrials de control de soroll són importants, ja que produeixen elements amb millors característiques. Els algoritmes evolutius són tècniques emergents capaces d'obtenir una solució, fins i tot quan l'optimització tradicional té dificultats. Les tècniques d'optimització es combinen amb el mètode d'elements finits (MEF) per aconseguir la màxima atenuació possible en el rang de freqüències d'interès. S'ha definit un problema d'optimització d'un silenciador multicàmera i s'han dut a terme diverses anàlisis per obtenir la configuració més adequada per a cada cas. Sota certes hipòtesis d'uniformitat axial, s'han considerat diverses tècniques per reduir el cost computacional d'una anàlisi 3D complet per silenciadors dissipatius amb gradients de temperatura i flux mig. Aquestes es basen en la descomposició del camp acústic en modes axials i transversals dins de cada subdomini, i un procediment d'acoblament de les expansions modals en els canvis de secció del silenciador mitjançant les condicions de continuïtat dels camps acústics. S'estudia l'eficiència computacional i precisió de les prediccions de les tècniques d'acoblament, incloent col·locació puntual en nodes i punts de Gauss, així com ajust modal. Tots ells proporcionen prediccions precises de l'atenuació millorant el cost computacional d'EF.
Sánchez Orgaz, EM. (2016). Advanced numerical techniques for the acoustic modelling of materials and noise control devices in the exhaust system of internal combustion engines [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/64090
TESIS

In order to achieve the maximum accuracy in characterizing the PES and the associated force fields for an MD investigation, careful preparation of the database is an essential step in the process. The points that must be addressed include the following: 1. The total volume of configuration space is extremely large, and its size increases as the internal energy of the system rises. For example, consider a four-atom system. For this system, at least six internal coordinates must be specified to determine the spatial configuration of the molecular system. At a given internal energy, each of these six coordinates can span a continuous range of values from some minimum to some maximum. If each variable range is divided into 100 equal increments and the potential energy of the system computed by some ab initio method for all possible configurations of the system, a total of 1006or 1012 electronic structure calculations would need to be executed. This is clearly beyond the computational capabilities of any computational system currently in existence. Grid sampling methods can and have been used effectively for three atom systems. However, for more complex systems, it is essential that procedures be developed that permit the regions of configuration space that are important in the reaction dynamics to be identified. 2. Sampling methods usually should be optimized to produce a reasonably uniform density of data points in those regions of configuration space that are important in the dynamics. If this is not done and there are regions of very high point density and others with low point density, no fitting technique will function well. The parameters of the method will adjust themselves to fit regions of high density preferentially over those with low density even when the low-density regions may be more important in the dynamics. An exception to the need to have an approximately uniform density of points in the database occurs in regions where the potential gradient is large. In such regions, the density of points in the database will need to be larger than in regions in which the gradient is small.

50–60% of infertility cases are as a result of male infertility and infertile men semen sample is characterize with poor motility, abnormal morphology, low sperm concentration, azoospermic and increased levels of sperm DNA damage. As a result of this heterogeneity of the ejaculate, sperm selection has become a necessary step to carry out prior to in vitro fertilization. Furthermore, the choice of sperm cell selection techniques depend on sperm concentration and sperm biology and the recovery of highly functional sperm cell population depend on the combination of more than one technique in some cases. The regular sperm cell selection methods in ART laboratory are swim up, density gradient, simple wash and other advanced and emerging sperm selection techniques which include hyaluronic acid mediated sperm binding, Zeta potential, hypoosmotic swelling test, magnetic activated cell sorting and microfluidic separation of sperm cells. The various methods have its own advantages and disadvantages which may be applicable to the individual need of infertile men and its effect on ART outcome.

Each crop has their own weed problems. Therefore, to understand each problem, agronomists and weed scientists must be able to determine the weed abundance with the most precise method. There are several techniques to scouting, including visual counting for density or estimations for coverage of weeds. However, this technique depends by the evaluator subjectivity, performance, and training, causing errors and bias when estimating weeds abundance. This chapter introduces a methodology to process multispectral images, based on histograms of oriented gradients and support vector machines to detect weeds in lettuce crops. The method was validated by experts on weed science, and the statistical differences were calculated. There were no significant differences between expert analysis and the proposed method. Therefore, this method offers a way to analyze large areas of crops in less time and with greater precision.

<em>Abstract</em>.—Community ecology increasingly seeks to integrate the influences of regional and historical processes with species interactions within local habitats. This broadened perspective is largely based on comparative approaches that employ “natural experiments” to identify factors shaping community structure. Because coastal rivers are separated from one another by insurmountable barriers (oceans or land), freshwater fishes are particularly well suited for comparative analyses of factors that influence fish community organization. In this chapter, we review how this comparative approach shed light on large-scale biodiversity gradients, community saturation, community convergence, density compensation, and the role of intrinsic and extrinsic factors in community dynamics. The main factors (e.g., river mouth discharge and history) empirically related to species richness of a river are well identified, and metacommunity ecology provides a fruitful conceptual framework for understanding how regional (river) species richness translates into local species richness. Much work remains to identify factors explaining differences among whole river basin assemblages with regard to ecological traits (e.g., trophic status and life history) composition and to assess whether trait-related environmental and biotic local filters act similarly over large spatial scales. One important conclusion that can be drawn from the studies reviewed here is that history cannot be neglected whatever the scale of investigation (global, river, or site). A second conclusion is that historical effects are not strong enough to blur the occurrence of qualitatively repeatable patterns of community structure over large spatial scale, which is encouraging because it suggests development of general predictive models of community structure is an attainable goal.

<em>Abstract</em>.—In regional survey studies of habitat and fish assemblages, potentially important biological interactions can be masked by strong gradients in habitat variables and associated collinearities among biological variables. We used structural equation modeling to compare the causal influences of local habitat and biotic factors on fish density in rivers and to determine the extent to which the set of sites chosen for analysis influenced their apparent importance. When all sites in our Michigan data set were used, spatial patterns in brook trout <em>Salvelinus fontinalis </em>biomass were 28 times more sensitive to habitat variables than brown trout <em>Salmo trutta </em>biomass. However, when the sample was restricted to trout streams, then brook trout biomass patterns were twice as sensitive to brown trout biomass as habitat variables. In a similar analysis for smallmouth bass <em>Micropterus dolomieu</em>, habitat factors had the strongest effects on fish densities when the analysis was based on all samples available. However, when the sample was limited to steams in which smallmouth bass actually occurred, direct effects of forage fish abundance and indirect effects of habitat via forage fish abundance were more prominent. In both the trout and smallmouth bass analyses, regional data sets (which included sites where the species of interest was absent) overemphasized the importance of habitat factors on fish abundance, but restricting the sample to sites having the species of interest elevated the importance of biotic factors. In reality, both habitat and biotic factors are important to these species, but the variance structure of the sample being analyzed had an overriding influence on the statistical importance of one versus the other. These findings help to resolve apparently conflicting results of previous studies assessing the relative influence of habitat and biotic factors on population abundance.

Lateral variations in the density and magnetization of the rocks within the crust give rise to "anomalies" in the Earth's gravity and magnetic fields. These anomalies can be measured and interpreted in terms of the geology both in a qualitative sense, by mapping out trends and changes in anomaly style, and quantitatively, by creating models of the subsurface which reproduce the observed fields. Such interpretations are generally less definitive in themselves than the results from seismic surveys (see chapter 12), but the data are widely available and can provide information in areas where other methods are ineffective or have not been applied. As the different geophysical techniques respond to specific rock properties such as density, magnetization, and acoustic velocity, the results are complementary, and a fully integrated approach to data collection and interpretation is generally more effective than the sum of its parts assessed on an individual basis. Gravity and magnetic data have been acquired, at least to a reconnaissance scale, over most of the world. In particular, the release into the public domain of satellite altimetry information (combined with improved methods of data processing) means that there is gravity coverage to a similar standard for most of the offshore region to within about 50 km of the coast. Magnetic anomalies recorded from satellites provide global coverage, but the high altitude of the observations means that only large-scale features extending over many 10s of kilometers are delineated. Reconnaissance aeromagnetic surveys with flight lines 10-20 km apart provide a lateral anomaly resolution similar to that of the satellite gravity data. Oceanographic surveys undertaken by a variety of academic and research institutions are another valuable source of data in remote regions offshore which supplement and extend the more detailed coverage obtained over the continental shelves, for example, by oil companies in areas of hydrocarbon interest. Surveys over land vary widely in terms of acquisition parameters and quality, but some form of national compilation is available from many countries. A number of possible applications of the potential field (i.e., gravity and magnetic) data follow from the terms set out by UNCLOS. Paragraph 4(b) of article 76 states, "In the absence of evidence to the contrary, the foot of the continental slope is to be determined as the point of maximum change in the gradient at its base" (italics added).

The development of efficient and reliable processes for bioseparations is dependent on the availability of suitable analytical methods. This means it is important that work on analytical methodology for the bioproduct of interest starts at the very beginning of process development. Analytical studies are important throughout the development and scale up of the process, as changes can occur either to the product or to its associated impurities from what may be thought of as minor changes in the process. This chapter gives access to the vocabulary and techniques used in quality control and analytical development activities, starting with a description of specifications typically set for a pharmaceutical and the rationale behind them. Then, before discussing the assays themselves, we describe assay attributes, which can be measured and used to help not only the assay developer but also the biochemist and engineer responsible for developing downstream processes determine the usefulness and meaning of the assay. Finally, we turn to assays that are commonly applied in biotechnology, as they apply to biological activity, identity, and purity. These assays are the ultimate yardsticks by which the process is measured. Purification methods are developed for their ability to remove a contaminant from the product of interest, whether it is a related molecule, a contaminant related to a host organism, such as DNA or endotoxin, or a process contaminant, such as a residual solvent or water. Critical to understanding process performance is an understanding of how the assays that measure these contaminants have been developed, what the assay strengths and limitations are, and what they indicate and why. Electrophoresis and magnetic separation are two methods that are now used for the bench scale preparative purification of bioproducts, including living cells. The electrophoresis systems with the highest capacity are free-flow electrophoresis, density gradient electrophoresis, recycling free-flow isoelectric focusing, and rotating isoelectric focusing, and the principles of operation of these are discussed. The physical principles of magnetic separations are presented, as well as magnetic reagents and applications of magnetic separators.

A systematic investigation of the influence of molecular Schmidt number on cooling film mass transfer coefficient has been conducted using a swollen polymer technique and laser holographic interferometry. A variation in Schmidt number by about 28% was accomplished by injection of a foreign gas and gas mixtures through a single normal hole at a blowing rate of one. The experiments were performed at a constant temperature in a subsonic, zero mainstream pressure gradient turbulent boundary layer on a flat plate. The experimental results indicate that Schmidt number has a negligible effect on cooling film mass transfer coefficient within the range examined. Consequently, measurement of cooling film mass transfer coefficients at non-unity density ratios using a mass transfer method with foreign gas injection is experimentally validated.

Abstract A spectrum filtering technique has been introduced to improve harmonic analysis in this study. The impact of site characterization and physical processes have been examined to justify the necessity of applying the spectrum filtering technique following classic harmonic analysis. Investigations show that the imperfection of the harmonic toolbox, e.g. T_Tide, could be attributed to significant contributions to the long period energy of density gradient and background currents, the greater variability of current amplitude energy, and the larger energy surrounding the clustering diurnal and semi-diurnal tidal constituents. From applications on hydrodynamic model data, this study supports the argument that harmonic analysis with the spectrum filtering technique could significantly improve the accuracy of tidal energy and residuals separation.

This paper studies several base substrate materials and interlayer dielectric materials for High Density Interconnect (HDI) boards, addressing reliability issues such as warpage, dielectric cracking and microvia cracking. Design of simulation models with an optimization technique is developed to study material interaction effects on the HDI reliability. A plastic strain gradient-based computational algorithm is developed to study the thermo-mechanical deformation of fine-feature microvia structures.

We address nonuniform coverage with networked multi-agent systems and a nonuniform, time varying risk density function throughout the spatial workspace. The proposed solution for the nonuniform coverage problem is different from existing ones in that the evolution of the density is described by a conservation law with time-varying boundary conditions. By adopting a first gradient constitutive relation between the flux and the density we obtain a simple diffusion equation. The diffused density is then employed by a platoon of autonomous agents for spatially configuring themselves in optimum locations so that the coverage metric is maximized or minimized. We exploit the generalized centroidal Voronoi tessellation technique for generating the motion control of autonomous agents. By assuming that the risk density evolves much faster than the boundary conditions, we prove that the generalized Voronoi centroids are equilibrium points for the coverage metric. A set of numerical simulations illustrate the theoretical results.

Quantitative image analysis and measurement of flow fields in convective heat transfer has great importance for the optimum energy consumption problems. In natural and forced convection phenomena of fluids, the complexity of flow field prevents us from detailed three dimensional (3D) experimental analyses of steady/unsteady dynamics in fluids. These flow fields have locally different density and temperature values and yet to be observed quantitatively. Recent development of the Particle Image Velocimetry (PIV) and Particle Tracking Velocimetry (PTV) techniques lead us to the quantitative investigation of flow fields in experimental researches. On the other hand, in image measurements density and temperature distributions have been grasped only in two-dimensions (2D). These qualitative image analyses of flow fields were obtained by using classical flow visualizing techniques, such as shadowgraph and color schlieren method. This paper describes the quantitative measurement of convective flow field using our originally proposed color striped background oriented schlieren (CSBOS) method. The obtained measured image data is used for CT reconstruction and 3D temperature gradient distributions.

Point of Interests (POI) identification using social media data (e.g. Flickr, Microblog) is one of the most popular research topics in recent years. However, there exist large amounts of noises (POI irrelevant data) in such crowd-contributed collections. Traditional solutions to this problem is to set a global density threshold and remove the data point as noise if its density is lower than the threshold. However, the density values vary significantly among POIs. As the result, some POIs with relatively lower density could not be identified. To solve the problem, we propose a technique based on the local drastic changes of the data density. First we define the local maxima of the density function as the Urban POIs, and the gradient ascent algorithm is exploited to assign data points into different clusters. To remove noises, we incorporate the Laplacian Zero-Crossing points along the gradient ascent process as the boundaries of the POI. Points located outside the POI region are regarded as noises. Then the technique is extended into the geographical and textual joint space so that it can make use of the heterogeneous features of social media. The experimental results show the significance of the proposed approach in removing noises.

The combined effects of a favorable, mainstream pressure gradient and coolant-to-mainstream density ratio have been investigated. Detailed film cooling effectiveness distributions have been obtained on a flat plate with either cylindrical (θ = 30°) or laidback, fan-shaped holes (θ = 30°, β = γ = 10°) using the pressure sensitive paint (PSP) technique. In a low speed wind tunnel, both non-accelerating and accelerating flows were considered while the density ratio varied from 1–4. In addition, the effect of blowing ratio was considered, with this ratio varying from 0.5 to 1.5. The film produced by the shaped hole outperformed the round hole under the presence of a favorable pressure gradient for all blowing and density ratios. At the lowest blowing ratio, in the absence of freestream acceleration, the round holes outperformed the shaped holes. However, as the blowing ratio increases, the shaped holes prevent lift-off of the coolant and offer enhanced protection. The effectiveness afforded by both the cylindrical and shaped holes, with and without freestream acceleration, increased with density ratio.

Semi-solid powder processing (SPP) is a promising technique in the fabrication of composite materials. Former work has experimentally shown that SPP was able to synthesize composite materials with reduced load and high efficiency. However, limited work was found in the modeling of the SPP. In this work, SPP was modeled with Shima-Oyane’s model and compared with experimental data in a closed die compaction setup. The evolution and distribution of the density and stress were analyzed. The model prediction agreed with the experimentally measured values. As the compaction pressure increased, the density gradient in the axial compaction direction decreased, while the stress gradient increased.

Despite the importance of near-wall flow, the well-known difficulties of applying PIV adjacent to walls have attracted little attention. In recent work, the authors have proposed and validated an extension of PIV, called “Interface Gradiometry” (PIV/IG), designed to directly measure the velocity gradient at a fixed wall. For a suitable choice of template height, combined with a sufficiently high density of flow tracers, the method was found to yield substantially more accurate results for wall velocity gradient than PIV/PID. This notwithstanding, the following restrictions and issues demand attention. For accurate measurements the template height must be sufficiently thin that the velocity increases only linearly therein; this is often a restrictive condition at practical Reynolds numbers. On the other hand, tracer concentration is often low adjacent to a wall, and it is often difficult to obtain enough tracers within templates satisfying the linearity condition. Finally, the method requires precise knowledge of the position of the wall. Accordingly, we present a technique that relies less critically on the choice of template height and on presumed wall position, while still exploiting most constraints that the wall imposes on the adjacent flow. Assuming the wall to be horizontal on the image, the basic method is, very simply, to perform 1D PIV on each horizontal line of pixels within the template. The principal “deliverable” at each point on the boundary is the wall-normal profile of horizontal velocity. In addition, our new work handles curved walls by transforming image segments into rectangles; this proposed enhancement should be significant in applications to real boundaries found industrially, or in biomedical imaging. The method is tested successfully on experimental images from a turbulent, locally recirculating flow over a sinusoidal wall.

The turbulent flow field of a film cooling flow is investigated using the particle-image velocimetry (PIV) technique. Cooling jets are injected from a multi-row hole configuration into a turbulent boundary layer flow of a flat plate in the presence of a zero and an adverse pressure gradient. The investigations focus on full-coverage film cooling. Therefore, the film cooling configuration consists of three staggered rows of holes with a lateral spacing of p/D = 3 and a streamwise row distance of l/D = 6. The inclined cooling holes feature a fan-shaped exit geometry with lateral and streamwise expansions. Jets of air and CO2 are injected separately at different blowing ratios into a boundary layer to examine the effects of the density ratio between coolant and mainstream on the mixing behavior and consequently, the cooling efficiency. For the zero pressure gradient case the measurement results indicate the different nature of the mixing process between the jets and the crossflow after the first, second, and third row. The mainstream velocity distributions evidence the growth of the boundary layer thickness at increasing row number. The interaction between the undisturbed boundary layer and first two rows leads to maximum values of turbulent kinetic energy. The presence of an adverse pressure gradient in the mainstream clearly intensifies the growth of the boundary layer thickness and increases the velocity fluctuations in the upper mixing zone. The measurements considering an increased density ratio show higher turbulence intensities in the shear zone between the jets and the main flow leading to a more pronounced mixing in this area. The results of the experimental measurements are used to validate numerical findings from a large-eddy simulation. This comparison shows a very good agreement for mean velocity distributions and velocity fluctuations.