• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 11
  • 7
  • 3
  • 1
  • 1
  • 1
  • Tagged with
  • 28
  • 28
  • 9
  • 7
  • 6
  • 6
  • 5
  • 4
  • 4
  • 4
  • 4
  • 4
  • 4
  • 4
  • 4
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Variation in tissue correction factors for LiF, Al2O3 and Silicon Dosimeters as a function of tissue depth with comparison between intensity weighted mono-energetic photon and the poly-energetic photons used in brachytherapy and diagnostic radiology.

Poudel, Sashi 14 October 2017 (has links)
"The MCNP6 radiation transport code was used to quantify changes in the absorbed dose tissue conversion factors for LiF, Al2O3, and silicon-based electronic dosimeters. While normally calibrated in-air and applied to all general geometric measurements, tissue conversion factors for each dosimeter were obtained at various depths in a simulated water phantom and compared against the standard in-air calibration method. In these experiments, a mono-energetic photon source was modeled at energies between 30 keV and 300 keV for a point-source placed at the center of a water phantom, a point-source placed at the surface of the phantom, and for a 10-cm radial field geometry. Again, mono-energetic photon source was modeled up to 1300 keV for a disk-source placed at the surface of the phantom and dosimetric calculations were obtained for water, LiF, Al2O3, and silicon at depths of 1 mm to 35 cm from the source. The dosimeter’s absorbed dose conversion factor was calculated as a ratio of the absorbed dose to water to that of the dosimeter measured at a specified phantom depth. The dosimeter’s calibration value also was obtained for both mono and polyenergetic source and the calibration value from poly-energetic source was compared with the intensity weighted average calibration value from mono-energetic photon. The calculated changes in the tissue conversion factors are significant because the American Association of Physicists in Medicine (AAPM) recommend that measurements of a brachytherapy or diagnostic source be made with an overall uncertainity of 5% or better. Yet, based on results, the absorbed dose tissue conversion factor for a LiF dosimeter was found to deviate from its calibration value by up to 9%, an Al2O3 dosimeter by 43%, and a silicon dosimeter by 61%. These uncertainties are in addition to the normal measurement uncertainties. By applying these tissue correction factors, these data may be used to meet the AAPM measurement requirements for mono-energetic and poly-energetic sources at measurement depths up to 35 cm under the irradiation geometries investigated herein. "
2

Monte Carlo calculations of correction factors for plastic phantoms in clinical photon and electron beam dosimetry

Oguchi, Hiroshi, Okumura, Masahiko, Matsumoto, Kenji, Fukuoka, Miyoko, Hanyu, Yuji, Araki, Fujio 07 1900 (has links)
No description available.
3

Operating correction factor of PV system : Effects of temperature, angle of incidence and invertor in PV system performance

Lopez Ramirez, Izar January 2017 (has links)
In this project, the correction factor of different solar panels of the laboratory of the University of Gävle, located in Sweden, is going to evaluated. The solar modules’working conditions are different from the ones used to test them in the laboratory. In the laboratory. the output energy of the modules is less than in working conditions,and therefore a correction factor is going to be calculated from the data collected, inorder to describe the factors that affect the performance of the solar modules.Also, the obtained correction factor validity for different PV systems it is going to be examined, determining which system has a better correction factor and the energy losses due to temperature, angle of incidence and micro invertor.
4

Operating performance of passive infrared counters under different seasons

Nytepchuk, Nini Johanna 14 April 2016 (has links)
This research analyzes the operating performance of two commercially available passive infrared counters (PICs) of pedestrians as a function of site, summer, fall and winter seasons in terms of counter sensitivity. Three sites were selected for field analysis in Winnipeg, Canada. Based on a sample of 24,690 people counted by the two PICs from July 2014 to February 2015, this research found that with a 95 percent confidence, Eco-Counter’s sensitivity ranged from 73 to 97 percent while TRAFCO’s ranged from 57 to 97 percent related to people occlusion. On weekdays, Eco-Counter’s absolute error was 16 percent and TRAFCO’s was 18 percent. On weekends, Eco-Counter’s absolute error was 18 percent and TRAFCO’s was 21 percent. In addition to people occlusion, site, seasons, and time of week (weekday and weekend) were found to affect the operating performance of the PICs. Correction factors were also calculated per counter, site, and seasons. / May 2016
5

The influence of the menstrual cycle on exercise performance and stable isotopic tracer measures of fat metabolism

Oosthuyse, Tanja 02 March 2007 (has links)
Student Number : 9404757K - PhD thesis - School of Physiology - Faculty of Science / Natural secretions of oestrogen and progesterone vary according to menstrual phase in eumenorrhoeic women and have an affect on physiological systems that could consequentially influence exercise performance. In a series of menstrual phase comparative investigations (considering mainly the early follicular (EF), late follicular (LF) and mid-luteal (ML) phase), I aimed to elucidate the physiological relation of oestrogen and progesterone to fat metabolism and ventilation during endurance exercise and exercise performance. I measured plasma free fatty acid (FFA) kinetics during prolonged exercise from an intravenous infusion of K+[1-13C]palmitate in eumenorrhoeic women and found the change in palmitate rate of appearance and disappearance between menstrual phases to be related to the oestrogen/progesterone (E/P) ratio. Overall the results from this study suggest that oestrogen promotes increases in FFA availability during exercise, while progesterone mitigates this response. Therefore, a high oestrogen concentration and E/P ratio in the ML phase is required in order to produce a favourable FFA metabolic response for endurance events. In order to estimate plasma FFA oxidation rate using carbon-FFA tracers, the acetate correction factor which accounts for carbon-label retention in secondary metabolic pools, must be applied. When I derived the acetate correction factor by measuring fractional recovery of carbon-13 in expired CO2 from a constant infusion of Na+[1- 13C]acetate during submaximal exercise we found the acetate correction factor to be significantly lower in the ML than EF phase (average change from EF phase -1.8± 0.5%, p<0.05). Failure to account for the lower correction factor in the ML phase will result in a 6% underestimation of plasma FFA oxidation rate. Furthermore, since human serum albumin (HSA) routinely used as a carrier for parenteral delivery of FFA tracers has various disadvantages, I tested the feasibility of using 2-hydroxypropyl-b- cyclodextrin (HP-b-CD) as a possible alternative carrier. A comparison of expired CO2 enrichment following HSA-FFA (7.4±2.0 %o) and HP-b-CD-FFA (8.6±2.1%o) infusion during exercise showed that the HP-b-CD does not compromise natural in vivo behaviour of the FFA tracer (p=0.4). Progesterone-induced hyperventilation is occasionally reported during exercise in the luteal phase. I found that the change in ventilatory parameters (minute ventilation and respiratory rate) during exercise from EF to ML phase is related to both the oestrogen and progesterone concentration in the ML phase. However, the associated increase in respiratory rate throughout prolonged exercise in the ML versus EF phase did not increase metabolic demand and therefore could not be expected to exacerbate fatigue. When exercise performance was evaluated by means of a cycling time trial, I found a trend for best performance in the LF phase versus the EF phase (8 of 11 subjects improved by 5.2±2.9%, p=0.027), while no differences occurred between other menstrual phases. Metabolic and performance benefits of oestrogen may be concealed in the ML phase by the coincident increase in progesterone in this phase and thus a significant effect is often only evident with a high E/P ratio in the ML phase. The transient LF phase, characterised by the pre-ovulatory surge in oestrogen, reveals the maximum benefits of oestrogen on metabolism and performance during submaximal exercise.
6

Efeito da deformação por cortante no cálculo de edifícios de andares múltiplos com núcleos estruturais / Effect of shear deformation in the analysis of multistory buildings with structural cores

Torres, Ivan Francisco Ruiz 07 May 1999 (has links)
O principal objetivo deste trabalho é realizar a análise estrutural de edifícios de andares múltiplos que apresentam núcleos resistentes, considerando a deformação pelo esforço cortante nos mesmos, bem como nos pilares. Para atingir esse objetivo, será preciso que o comportamento à flexão dos elementos verticais de contraventamento passe a ser regido pela teoria de barras de Timoshenko e não mais pela de Euler-Bernoulli. Foram então desenvolvidos algoritmos que, utilizando o Método dos Elementos Finitos (MEF), permitem calcular os fatores de forma de quaisquer seções transversais abertas de paredes delgadas pertencentes a núcleos estruturais, bem como a distribuição da tensão de cisalhamento na seção transversa em função do esforço cortante atuante. As alterações acima descritas foram feitas em um programa de análise de edifícios denominado CEASO 01, de autoria de MATIAS JR (1997). Embora esse programa realize análise não-linear geométrica, a consideração da deformação por cortante só foi implementada na análise linear. Apresentam-se, ao final, exemplos numéricos que permitem avaliar a influência da deformação pelo esforço cortante sobre os deslocamentos e esforços de núcleos resistentes e pilares. / The main aim of this work is to perform structural analysis of multistory buildings with resistant cores, taking into account shear deformation in those elements, as well as in columns. To achieve this objective, the flexural behaviour of vertical elements must be governed by Timoshenko beam theory, rather than the Euler-Bernoulli theory. Procedures using the finite element method (FEM) were developped, which enable to evaluate shear correction factors of generic thin-walled open sections and shear stress distribution as a function of the shear resultant. Changes described above were made in a structural analysis program named CEASO 01, whose author is MATIAS JR (1997). Even though this program is able to perform nonlinear analysis, only in linear analysis the effect of shear deformation is taken into account. Numerical examples are provided, which enable to evaluate the influence of taking into account shear deformation on displacements and stress resultants of resistant cores and columns.
7

Effect Of Skew On Live Load Distribution In Integral Bridges

Erol, Mehmet Ali 01 January 2010 (has links) (PDF)
Structural analysis of highway bridges using complicated 3-D FEMs to determine live load effects in bridge components is possible due to the readily available computational tools in design offices. However, building such complicated 3-D FEMs is tedious and time consuming. Accordingly, most design engineers prefer using simplified 2-D structural models of the bridge and live load distribution equations (LLDEs) available in current bridge design codes to determine live load effects in bridge components. Basically, the live load effect obtained from a 2-D model is multiplied by a factor obtained from the LLDE to calculate the actual live load effect in a 3-D structure. The LLDE available in current bridge design codes for jointed bridges were also used for the design of straight and skewed integral bridges by bridge engineers. As a result, these bridges are either designed conservatively leading to additional construction cost or unconservatively leading to unsafe bridge designs. Recently, LLDEs for integral bridges (IBs) with no skew are developed. To use these equations for skewed integral bridges (SIBs) a correction factor is needed to multiply these equations to include the effect of skew. Consequently, in this research study, skew correction factors for SIBs are developed. For this purpose, finite element models of 231 different three dimensional and corresponding two dimensional structural models of SIBs are built and analyzed under live load. The analyses results reveal that the effect of skew on the distribution of live load moment and shear is significant. It is also observed that skew generally tends to decrease live load effects in girders and substructure components of SIBs. Using the analyses results, analytical equations are developed via nonlinear regression techniques to include skew effects in the LLDEs developed for straight IBs. The developed skew correction factors are compared with FEAs results. This comparison revealed that the developed skew correction factors yield a reasonably good estimate of the reduction in live load effects due to the effect of skew.
8

Nozzle Design for Vacuum Aerosol Deposition of Nanostructured Coatings

January 2017 (has links)
abstract: Nanomaterials exhibit unique properties that are substantially different from their bulk counterparts. These unique properties have gained recognition and application for various fields and products including sensors, displays, photovoltaics, and energy storage devices. Aerosol Deposition (AD) is a relatively new method for depositing nanomaterials. AD utilizes a nozzle to accelerate the nanomaterial into a deposition chamber under near-vacuum conditions towards a substrate with which the nanomaterial collides and adheres. Traditional methods for designing nozzles at atmospheric conditions are not well suited for nozzle design for AD methods. Computational Fluid Dynamics (CFD) software, ANSYS Fluent, is utilized to simulate two-phase flows consisting of a carrier gas (Helium) and silicon nanoparticles. The Cunningham Correction Factor is used to account for non-continuous effects at the relatively low pressures utilized in AD. The nozzle, referred to herein as a boundary layer compensation (BLC) nozzle, comprises an area-ratio which is larger than traditionally designed nozzles to compensate for the thick boundary layer which forms within the viscosity-affected carrier gas flow. As a result, nanoparticles impact the substrate at velocities up to 300 times faster than the baseline nozzle. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2017
9

Efeito da deformação por cortante no cálculo de edifícios de andares múltiplos com núcleos estruturais / Effect of shear deformation in the analysis of multistory buildings with structural cores

Ivan Francisco Ruiz Torres 07 May 1999 (has links)
O principal objetivo deste trabalho é realizar a análise estrutural de edifícios de andares múltiplos que apresentam núcleos resistentes, considerando a deformação pelo esforço cortante nos mesmos, bem como nos pilares. Para atingir esse objetivo, será preciso que o comportamento à flexão dos elementos verticais de contraventamento passe a ser regido pela teoria de barras de Timoshenko e não mais pela de Euler-Bernoulli. Foram então desenvolvidos algoritmos que, utilizando o Método dos Elementos Finitos (MEF), permitem calcular os fatores de forma de quaisquer seções transversais abertas de paredes delgadas pertencentes a núcleos estruturais, bem como a distribuição da tensão de cisalhamento na seção transversa em função do esforço cortante atuante. As alterações acima descritas foram feitas em um programa de análise de edifícios denominado CEASO 01, de autoria de MATIAS JR (1997). Embora esse programa realize análise não-linear geométrica, a consideração da deformação por cortante só foi implementada na análise linear. Apresentam-se, ao final, exemplos numéricos que permitem avaliar a influência da deformação pelo esforço cortante sobre os deslocamentos e esforços de núcleos resistentes e pilares. / The main aim of this work is to perform structural analysis of multistory buildings with resistant cores, taking into account shear deformation in those elements, as well as in columns. To achieve this objective, the flexural behaviour of vertical elements must be governed by Timoshenko beam theory, rather than the Euler-Bernoulli theory. Procedures using the finite element method (FEM) were developped, which enable to evaluate shear correction factors of generic thin-walled open sections and shear stress distribution as a function of the shear resultant. Changes described above were made in a structural analysis program named CEASO 01, whose author is MATIAS JR (1997). Even though this program is able to perform nonlinear analysis, only in linear analysis the effect of shear deformation is taken into account. Numerical examples are provided, which enable to evaluate the influence of taking into account shear deformation on displacements and stress resultants of resistant cores and columns.
10

Prey preferences of the Persian leopard and trophic competition with human hunters in Iran

Ghoddousi, Arash 24 August 2016 (has links)
No description available.

Page generated in 0.1156 seconds