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  • 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.

Reversibilidade e atractores simétricos

Mendes, Miguel Ângelo de Sousa January 1999 (has links)
Dissertação apresentada para obtenção do grau de Mestre em Matemática Aplicada, na Faculdade de Ciências da Universidade do Porto

De la nanopoudre aux matériaux denses nanostructurés à base de l’alliage métastable Ni-P : microstructure et comportements magnétiques et mécaniques / Nanopowder with dense nanostructured materials based on the metastable Ni-P : magnetic and mechanical behavior and microstructure

Bousnina, Mohamed Ali 20 December 2013 (has links)
Des matériaux denses nanostructurés à base de l’alliage métastable Ni-P ont été élaborés par une stratégie "bottom-up" qui combine deux étapes. La première consiste en la préparation de nanoparticules de l’alliage grâce au procédé polyol modifié par l’ajout d’hypophosphite, un agent réducteur fort. Les nanoparticules obtenues sont de morphologie sphérique et de taille variant de 39 à 220 nm. La deuxième étape consiste en la consolidation de ces nanopoudres par le procédé SPS. Les massifs denses obtenus sont constitués de grains polygonaux de nickel (taille variant de 154 à 650 nm) et de nanoparticules sphériques de Ni₃P localisées aux points de jonction triple et aux joints des grains de nickel. Ces nanoparticules de taille ne dépassant pas 250 nm sont formées par un mécanisme de diffusion du phosphore à travers les grains de nickel. Les matériaux denses élaborés présentent les caractéristiques magnétiques d’un ferromagnétisme doux (faible champ coercitif) mais une aimantation à saturation élevée proche de celle du nickel massif. Les propriétés mécaniques sont fonction de la taille des grains. Quand cette taille est faible, les matériaux manifestent une résistance mécanique et une limite élastique élevées accompagnées d’une faible ductilité. Une augmentation de la taille des grains entraine des évolutions inverses conformément à la loi de Hall-Petch. / Dense nanostructured materials based on the metastable Ni- P alloy were prepared by "bottom- up" strategy. This synthesis pathway is the combination of two steps. The first is to prepare the powder by soft chemistry (reduction in polyol medium modified by the addition of hypophosphite a strong reducing agent). The nanoparticles produced have spherical morphology and size ranging from 39 to 220 nm. These powders are metastable solid solutions Ni- P. The second step is to consolidate these powders by SPS process; it results in dense nanostructured material consisting of polygonal grains of nickel (size ranging from 254 to 650 nm) along with spherical nanoparticles Ni3P located at triple junction points and grain boundaries. These nanoparticles of size no greater than 250 nm are formed by a diffusion mechanism through the phosphorous nickel grains. The as-obtained dense materials have magnetic characteristics of a soft ferromagnetism (low coercivity) but a good saturation magnetization close to that of bulk nickel. These materials also exhibit very interesting mechanical properties depending on the grain size. When the grain size is small, the materials exhibit mechanical strength and high elastic limit accompanied by low ductility. An increase in grain size leads to inverse changes in line with the Hall-Petch law.

Mashup-Werkzeuge zur Ad-hoc-Datenintegration im Web

Aumüller, David, Thor, Andreas 05 November 2018 (has links)
No description available.


林修竹 Unknown Date (has links)
在這一篇論文中我們討論的是下列這個非線性初值問題: u''(t)=u'(t)^q(c_1+c_2u(t)^p) u(0) = u_0; u'(0) = u_1: 我們關注於上述問題正解的一些性質。我們發現了一些爆破(Blow-up)現象,並獲得一些結果,有關爆破率(Blow-up rate)、爆破常數(Blow-up constant)以及爆破時間(Blow-up time)。 / In this paper we study the following initial value problem for the nonlinear equation, u''(t)=u'(t)^q(c_1+c_2u(t)^p) u(0) = u_0; u'(0) = u_1: We are interested in properties of positive solutions of the above problem.We have found blow-up phenomena and obtained some results on blowup rates, blow-up constants and life-spans.

Development of the Yugoslav military industry 1918-1991

Watkins, Amadeo January 2002 (has links)
No description available.

Conformance testing issues with application to the CANopen protocol

Barbosa, Manuel January 2000 (has links)
No description available.

The use of biological methods for the assessment of oil contamination and bioremediation

Bundy, J. G. January 1999 (has links)
There is a concern that concentration-based targets for soil clean-up are arbitrary, and do not necessarily relate to the environmental threat posed by the residual contamination. The development of sensitive, reliable, and ecologically relevant biological tests for oil-polluted soils would address these problems, and form a valuable complement to chemical analysis. Three biological test systems were chosen for examining the impact of oil contamination on soil microbes: (1) lux-marked bacterial biosensors, (2) Biological carbon source utilization profiles, and (3) phospholipid fatty acid (PLFA) community profiles. This allowed the testing of effects at three different levels of ecological complexity: respectively, single species; culturable bacteria; and eubacteria and eukaryotes. The use of specific bioluminescent biosensors (i.e. with lux genes fused to promoters from hydrocarbon degradation pathways) allowed the rapid detection of different hydrocarbon classes. The bacterial biosensors were optimized for the assessment of hydrocarbon compounds. Development of quantitative structure-activity relationships (QSARs) increased understanding of their responses to hydrocarbons and other petroleum-derived compounds. The three biological methods were then used to monitor the nutrient-assisted bioremediation of oil-spiked soils in two separate microcosm experiments: (1) remediation of four crude oils and one refined oil compared using bacterial biosensors, and (2) effects of diesel on three different soil types, and effects of three refined oils on one soil type, assessed using Biolog and PLFA profiling. All three biological test methods were sensitive to the oil contamination levels applied in the microcosm experiments. Individual species (biosensor tests) gave different responses to different oils; however, the community-level responses showed no differences. The microbial communities of the three different soil types could still be distinguished after 14-15 weeks of hydrocarbon contamination. The community response of the contaminated soils had changed from that of the control soils after four weeks of bioremediation, and did not return in similarity to the control over the course of the experiment.

The effects of a dryland activation protocol during the transition phase on elite swimming performance

Bagshaw, Jeremy 26 April 2019 (has links)
The purpose of the present study was to determine the effect of including a dryland activation during a 30-minute transition phase time between pool warm-up and competition on elite swimming performance. Previous research has shown the benefits of shorter transition times, or transition times that include dryland activation, improve swimming performance. Nine elite swimmers from the High-Performance Centre Victoria, 2 males and 7 females (18.7 ± 4.3 yrs), completed two testing sessions separated by one week, consisting of a 30-minute traditional (TRAD) or dryland (DL) transition phase followed by a 200-metre time-trial (TT). The swimmers swam the TT in their primary 200m event. Both transition phases were identical through the first 20-minutes but for the next 10 minutes, swimmers either sat quietly for 10 minutes (TRAD) or completed a 5-minute dryland activation 5 minutes pre-TT (DL). The dryland activation consisted of 2 sets of 40 seconds of jumping jacks and 6 explosive burpees completed self-paced but within a 5 minute time limit. Core temperature (Tcore) and Heart Rate (HR) were measured throughout the entire testing sessions. TT performance was significantly faster (p < .010) following DL (130.61 ± 10.46 secs) compared to TRAD (131.71 ± 11.08secs), an improvement of 0.84%. The third 50m split was also significantly faster (p < 0.18) following DL (34.83 ± 4.28secs) compared to TRAD (35.47 ± 4.47secs). Heart rate was significantly elevated following the dryland activation compared to the same time in TRAD (134 ± 22 vs. 84 ± 13bpm, p < 0.001). There were no significant differences in Tcore between the two transition phase conditions. The results from this research support the inclusion of a dryland activation during the transition phase of elite swimming competitions. As the smallest of differences can influence final placing at international level swimming competitions, the small gains found in the present study may have considerable implications for optimal swimming performance. / Graduate

Um estudo de técnicas enumerativas e bilineares para programas lineares complementares

Ribeiro, Isabel Cristina da Silva Martins January 1996 (has links)
Dissertação de Mestrado, na especialidade de Optimização e Controle, na Faculdade de Ciências da Universidade do Porto

Études asymptotiques en filtrage non lineaire avec petit bruit d'observation

Oliveira, P. Milheiro de January 1990 (has links)
Dissertation pour obtenir le grade de Docteur de l'Université de Provence, spécialité: Mathématiques Appliquées

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