Página 4 dos resultados de 9995 itens digitais encontrados em 0.254 segundos

‣ Unmasking the functions of the chromaffin cell α7 nicotinic receptor by using short pulses of acetylcholine and selective blockers

López, Manuela G.; Montiel, Carmen; Herrero, Carlos J.; García-Palomero, Esther; Mayorgas, Inés; Hernández-Guijo, Jesús M.; Villarroya, M.; Olivares, Román; Gandía, Luis; McIntosh, J. Michael; Olivera, Baldomero M.; García, Antonio G.
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
Publicado em 24/11/1998 Português
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Methyllycaconitine (MLA), α-conotoxin ImI, and α-bungarotoxin inhibited the release of catecholamines triggered by brief pulses of acetylcholine (ACh) (100 μM, 5 s) applied to fast-superfused bovine adrenal chromaffin cells, with IC50s of 100 nM for MLA and 300 nM for α-conotoxin ImI and α-bungarotoxin. MLA (100 nM), α-conotoxin ImI (1 μM), and α-bungarotoxin (1 μM) halved the entry of 45Ca2+ stimulated by 5-s pulses of 300 μM ACh applied to incubated cells. These supramaximal concentrations of α7 nicotinic receptor blockers depressed by 30% (MLA), 25% (α-bungarotoxin), and 50% (α-conotoxin ImI) the inward current generated by 1-s pulses of 100 μM ACh, applied to voltage-clamped chromaffin cells. In Xenopus oocytes expressing rat brain α7 neuronal nicotinic receptor for acetylcholine nAChR, the current generated by 1-s pulses of ACh was blocked by MLA, α-conotoxin ImI, and α-bungarotoxin with IC50s of 0.1 nM, 100 nM, and 1.6 nM, respectively; the current through α3β4 nAChR was unaffected by α-conotoxin ImI and α-bungarotoxin, and weakly blocked by MLA (IC50 = 1 μM). The functions of controlling the electrical activity, the entry of Ca2+, and the ensuing exocytotic response of chromaffin cells were until now exclusively attributed to α3β4 nAChR; the present results constitute the first evidence to support a prominent role of α7 nAChR in controlling such functions...

‣ Dynamical principles in biological processes: A model of charge migration in proteins and DNA

Schlag, E. W.; Yang, D.-Y.; Sheu, S.-Y.; Selzle, H. L.; Lin, S. H.; Rentzepis, P. M.
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
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The generalized master equations (GMEs) that contain multiple time scales have been derived quantum mechanically. The GME method has then been applied to a model of charge migration in proteins that invokes the hole hopping between local amino acid sites driven by the torsional motions of the floppy backbones. This model is then applied to analyze the experimental results for sequence-dependent long-range hole transport in DNA reported by Meggers et al. [Meggers, E., Michel-Beyerle, M. E., & Giese, B. (1998) J. Am. Chem. Soc. 120, 12950–12955]. The model has also been applied to analyze the experimental results of femtosecond dynamics of DNA-mediated electron transfer reported by Zewail and co-workers [Wan, C., Fiebig, T., Kelley, S. O., Treadway, C. R., Barton, J. K. & Zewail, A. H. (1999) Proc. Natl. Acad. Sci. USA 96, 6014–6019]. The initial events in the dynamics of protein folding have begun to attract attention. The GME obtained in this paper will be applicable to this problem.

‣ Monarch larvae sensitivity to Bacillus thuringiensis- purified proteins and pollen

Hellmich, Richard L.; Siegfried, Blair D.; Sears, Mark K.; Stanley-Horn, Diane E.; Daniels, Michael J.; Mattila, Heather R.; Spencer, Terrence; Bidne, Keith G.; Lewis, Leslie C.
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
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Laboratory tests were conducted to establish the relative toxicity of Bacillus thuringiensis (Bt) toxins and pollen from Bt corn to monarch larvae. Toxins tested included Cry1Ab, Cry1Ac, Cry9C, and Cry1F. Three methods were used: (i) purified toxins incorporated into artificial diet, (ii) pollen collected from Bt corn hybrids applied directly to milkweed leaf discs, and (iii) Bt pollen contaminated with corn tassel material applied directly to milkweed leaf discs. Bioassays of purified Bt toxins indicate that Cry9C and Cry1F proteins are relatively nontoxic to monarch first instars, whereas first instars are sensitive to Cry1Ab and Cry1Ac proteins. Older instars were 12 to 23 times less susceptible to Cry1Ab toxin compared with first instars. Pollen bioassays suggest that pollen contaminants, an artifact of pollen processing, can dramatically influence larval survival and weight gains and produce spurious results. The only transgenic corn pollen that consistently affected monarch larvae was from Cry1Ab event 176 hybrids, currently <2% corn planted and for which re-registration has not been applied. Results from the other types of Bt corn suggest that pollen from the Cry1Ab (events Bt11 and Mon810) and Cry1F, and experimental Cry9C hybrids...

‣ Magnetic microposts as an approach to apply forces to living cells

Sniadecki, Nathan J.; Anguelouch, Alexandre; Yang, Michael T.; Lamb, Corinne M.; Liu, Zhijun; Kirschner, Stuart B.; Liu, Yaohua; Reich, Daniel H.; Chen, Christopher S.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Cells respond to mechanical forces whether applied externally or generated internally via the cytoskeleton. To study the cellular response to forces separately, we applied external forces to cells via microfabricated magnetic posts containing cobalt nanowires interspersed among an array of elastomeric posts, which acted as independent sensors to cellular traction forces. A magnetic field induced torque in the nanowires, which deflected the magnetic posts and imparted force to individual adhesions of cells attached to the array. Using this system, we examined the cellular reaction to applied forces and found that applying a step force led to an increase in local focal adhesion size at the site of application but not at nearby nonmagnetic posts. Focal adhesion recruitment was enhanced further when cells were subjected to multiple force actuations within the same time interval. Recording the traction forces in response to such force stimulation revealed two responses: a sudden loss in contractility that occurred within the first minute of stimulation or a gradual decay in contractility over several minutes. For both types of responses, the subcellular distribution of loss in traction forces was not confined to locations near the actuated micropost...

‣ Sustainable and efficient biohydrogen production via electrohydrogenesis

Cheng, Shaoan; Logan, Bruce E.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Hydrogen gas has tremendous potential as an environmentally acceptable energy carrier for vehicles, but most hydrogen is generated from nonrenewable fossil fuels such as natural gas. Here, we show that efficient and sustainable hydrogen production is possible from any type of biodegradable organic matter by electrohydrogenesis. In this process, protons and electrons released by exoelectrogenic bacteria in specially designed reactors (based on modifying microbial fuel cells) are catalyzed to form hydrogen gas through the addition of a small voltage to the circuit. By improving the materials and reactor architecture, hydrogen gas was produced at yields of 2.01–3.95 mol/mol (50–99% of the theoretical maximum) at applied voltages of 0.2 to 0.8 V using acetic acid, a typical dead-end product of glucose or cellulose fermentation. At an applied voltage of 0.6 V, the overall energy efficiency of the process was 288% based solely on electricity applied, and 82% when the heat of combustion of acetic acid was included in the energy balance, at a gas production rate of 1.1 m3 of H2 per cubic meter of reactor per day. Direct high-yield hydrogen gas production was further demonstrated by using glucose, several volatile acids (acetic, butyric...

‣ Dendritic processes of osteocytes are mechanotransducers that induce the opening of hemichannels

Burra, Sirisha; Nicolella, Daniel P.; Francis, W. Loren; Freitas, Christopher J.; Mueschke, Nicholas J.; Poole, Kristin; Jiang, Jean X.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Osteocytes with long dendritic processes are known to sense mechanical loading, which is essential for bone remodeling. There has been a long-standing debate with regard to which part(s) of osteocyte, the cell body versus the dendritic process, acts as a mechanical sensor. To address this question experimentally, we used a transwell filter system that differentiates the cell body from the dendritic processes. Mechanical loading was applied to either the cell body or the dendrites, and the osteocyte’s response was observed through connexin 43 hemichannel opening. The hemichannels located on the cell body were induced to open when mechanical loading was applied to either the dendritic processes or the cell body. However, no significant hemichannel activity in the dendrites was detected when either part of the cell was mechanically stimulated. Disruption of the glycocalyx by hyaluronidase on the dendrite side alone is sufficient to diminish a dendrite’s ability to induce the opening of hemichannels on the cell body, while hyaluronidase has no such effect when applied to the cell body. Importantly, hyaluronidase treatment to the dendrite side resulted in formation of poor integrin attachments with the reduced ability of the dendrites to form integrin attachments on the underside of the transwell filter. Together...

‣ Hypothesis-driven structural connectivity analysis supports network over hierarchical model of brain architecture

Thompson, Richard H.; Swanson, Larry W.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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The brain is usually described as hierarchically organized, although an alternative network model has been proposed. To help distinguish between these two fundamentally different structure-function hypotheses, we developed an experimental circuit-tracing strategy that can be applied to any starting point in the nervous system and then systematically expanded, and applied it to a previously obscure dorsomedial corner of the nucleus accumbens identified functionally as a “hedonic hot spot.” A highly topographically organized set of connections involving expected and unexpected gray matter regions was identified that prominently features regions associated with appetite, stress, and clinical depression. These connections are arranged as a longitudinal series of circuits (closed loops). Thus, the results do not support a rigidly hierarchical model of nervous system organization but instead indicate a network model of organization. In principle, the double-coinjection circuit tracing strategy can be applied systematically to the rest of the nervous system to establish the architecture of the global structural wiring diagram, and its abstraction, the connectome.

‣ Transcranial direct-current stimulation modulates synaptic mechanisms involved in associative learning in behaving rabbits

Márquez-Ruiz, Javier; Leal-Campanario, Rocío; Sánchez-Campusano, Raudel; Molaee-Ardekani, Behnam; Wendling, Fabrice; Miranda, Pedro C.; Ruffini, Giulio; Gruart, Agnès; Delgado-García, José María
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Transcranial direct-current stimulation (tDCS) is a noninvasive brain stimulation technique that has been successfully applied for modulation of cortical excitability. tDCS is capable of inducing changes in neuronal membrane potentials in a polarity-dependent manner. When tDCS is of sufficient length, synaptically driven after-effects are induced. The mechanisms underlying these after-effects are largely unknown, and there is a compelling need for animal models to test the immediate effects and after-effects induced by tDCS in different cortical areas and evaluate the implications in complex cerebral processes. Here we show in behaving rabbits that tDCS applied over the somatosensory cortex modulates cortical processes consequent to localized stimulation of the whisker pad or of the corresponding area of the ventroposterior medial (VPM) thalamic nucleus. With longer stimulation periods, poststimulation effects were observed in the somatosensory cortex only after cathodal tDCS. Consistent with the polarity-specific effects, the acquisition of classical eyeblink conditioning was potentiated or depressed by the simultaneous application of anodal or cathodal tDCS, respectively, when stimulation of the whisker pad was used as conditioned stimulus...

‣ Mechanical impulses can control metaphase progression in a mammalian cell

Itabashi, Takeshi; Terada, Yasuhiko; Kuwana, Kenta; Kan, Tetsuo; Shimoyama, Isao; Ishiwata, Shin’ichi
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Chromosome segregation machinery is controlled by mechanochemical regulation. Tension in a mitotic spindle, which is balanced by molecular motors and polymerization-depolymerization dynamics of microtubules, is thought to be essential for determining the timing of chromosome segregation after the establishment of the kinetochore-microtubule attachments. It is not known, however, whether and how applied mechanical forces modulate the tension balance and chemically affect the molecular processes involved in chromosome segregation. Here we found that a mechanical impulse externally applied to mitotic HeLa cells alters the balance of forces within the mitotic spindle. We identified two distinct mitotic responses to the applied mechanical force that either facilitate or delay anaphase onset, depending on the direction of force and the extent of cell compression. An external mechanical impulse that physically increases tension within the mitotic spindle accelerates anaphase onset, and this is attributed to the facilitation of physical cleavage of sister chromatid cohesion. On the other hand, a decrease in tension activates the spindle assembly checkpoint, which impedes the degradation of mitotic proteins and delays the timing of chromosome segregation. Thus...

‣ High-throughput screen using a single-cell tyrosine phosphatase assay reveals biologically active inhibitors of tyrosine phosphatase CD45

Stanford, Stephanie M.; Panchal, Rekha G.; Walker, Logan M.; Wu, Dennis J.; Falk, Matthew D.; Mitra, Sayantan; Damle, Sagar S.; Ruble, David; Kaltcheva, Teodora; Zhang, Sheng; Zhang, Zhong-Yin; Bavari, Sina; Barrios, Amy M.; Bottini, Nunzio
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Many cellular signaling events are regulated by tyrosine phosphorylation and mediated by the opposing actions of protein tyrosine kinases and phosphatases. Protein tyrosine phosphatases are emerging as drug targets, but poor cell permeability of inhibitors has limited the development of drugs targeting these enzymes [Tautz L, et al. (2006) Expert Opin Ther Targets 10:157–177]. Here we developed a method to monitor tyrosine phosphatase activity at the single-cell level and applied it to the identification of cell-permeable inhibitors. The method takes advantage of the fluorogenic properties of phosphorylated coumaryl amino propionic acid (pCAP), an analog of phosphotyrosine, which can be incorporated into peptides. Once delivered into cells, pCAP peptides were dephosphorylated by protein tyrosine phosphatases, and the resulting cell fluorescence could be monitored by flow cytometry and high-content imaging. The robustness and sensitivity of the assay was validated using peptides preferentially dephosphorylated by CD45 and T-cell tyrosine phosphatase and available inhibitors of these two enzymes. The assay was applied to high-throughput screening for inhibitors of CD45, an important target for autoimmunity and infectious diseases [Hermiston ML...

‣ Extracellular transmission of a DNA mycovirus and its use as a natural fungicide

Yu, Xiao; Li, Bo; Fu, Yanping; Xie, Jiatao; Cheng, Jiasen; Ghabrial, Said A.; Li, Guoqing; Yi, Xianhong; Jiang, Daohong
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Mycoviruses are thought not to be infectious as free particles and to lack an extracellular phase in their life cycles, limiting the broad use of hypovirulence-associated mycoviruses in controlling fungal disease. Here, we demonstrate that purified particles of a DNA mycovirus, Sclerotinia sclerotiorum hypovirulence-associated DNA virus 1 (SsHADV-1), are infectious when applied extracellularly to its host Sclerotinia sclerotiorum. Virus particles isolated from an infected host can infect the hyphae of virus-free S. sclerotiorum directly when applied to hyphae grown on potato dextrose agar or sprayed on leaves of Arabidopsis thaliana and Brassica napus, regardless of vegetative compatibility affiliation. When applied to leaves, the virus can suppress the development of lesions. SsHADV-1 can also reduce disease severity and enhance rapeseed yield significantly under field conditions. SsHADV-1 has a narrow host range; it can infect Sclerotinia minor and Sclerotinia nivalis, sister species of S. sclerotiorum, and cause debilitation of these two fungi, but cannot infect or transfect other tested fungi, such as Botrytis cinerea, which shares the same family with S. sclerotiorum. Virus particles are likely to be very stable on the leaves of A. thaliana plants because viral DNA could be detected at 15 d postinoculation on unwounded leaves and at 10 d postinoculation on wounded leaves...

‣ Impact of Climate Change on Fine Particulate Matter ((PM_{2.5})) Air Quality

Tai, Pui Kuen Amos P. K.
Fonte: Harvard University Publicador: Harvard University
Tipo: Thesis or Dissertation
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This dissertation investigates the impact of 2000-2050 climate change on fine particulate matter ((PM_{2.5})) air quality. We first applied a multiple linear regression model to study the correlations of total (PM_{2.5}) and its components with meteorological variables using the past decadal (PM_{2.5}) observations over the contiguous US. We find that daily variation in meteorology can explain up to 50% of (PM_{2.5}) variability. Temperature is positively correlated with sulfate and organic carbon (OC) almost everywhere. The correlation of nitrate with temperature is negative in the Southeast but positive in California and the Great Plains. Relative humidity (RH) is positively correlated with sulfate and nitrate, but negatively with OC. Precipitation is strongly negatively correlated with all (PM_{2.5}) components. We then compared the observed correlations of (PM_{2.5}) with meteorological variables with results from the GEOS-Chem chemical transport model. The results indicate that most of the correlations of (PM_{2.5}) with temperature and RH do not arise from direct dependence but from covariation with synoptic transport. We applied principal component analysis and regression to identify the dominant meteorological modes controlling (PM_{2.5}) variability...

‣ Observations and modeling of wave-acceleration-induced sediment transport in the surfzone

Hoefel, Fernanda Gemael, 1973-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 61 leaves; 3012035 bytes; 3017570 bytes; application/pdf; application/pdf
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Onshore sediment transport and sandbar migration are important to the morphological evolution of beaches, but are not understood well. Here, a new model that accounts for accelerations of wave-orbital velocities predicts onshore sandbar migration observed on an ocean beach. In both the observations and the model, the location of the maximum acceleration-induced transport moves shoreward with the sandbar, resulting in feedback between waves and morphology that drives the bar shoreward until conditions change. A model that combines the effects of transport by waves and mean currents simulates both onshore and offshore bar migration observed over a 45-day period. A stochastic nonlinear Boussinesq model for the evolution of waves in shallow water is coupled with the wave-acceleration-driven sediment transport model to predict observed onshore sediment transport and sandbar migration given observations of the offshore wave field and initial bathymetry. The Boussinesq-wave model has skill in predicting wave spectra, as well as velocity and acceleration statistics across the surfzone, but it underpredicts acceleration skewness on top of the sandbar. As a result, the coupled wave-sediment transport model underpredicts sediment transport, and thus fails to move the sandbar onshore. Although the coupled wave and sediment model can be tuned to yield skillful predictions of onshore sandbar migration...

‣ Monaural perception under dichotic conditions

Shub, Daniel E. (Daniel Eric), 1974-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 195 p.
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Most people have two ears, but we can hear with only one ear. The ability to use two ears can substantially improve performance in many circumstances. There are times, however, when the addition of a second ear results in poorer performance (i.e., contra-aural interference). Contra-aural interference is of interest because it is not explained by current auditory models, it has theoretical ramifications, and its understanding could lead to improvements in the quality of life of the hearing-impaired. More generally, the techniques and results can be applied to fields in which information is combined across an array of sensors (e.g., vision with two eyes and radar arrays). This thesis includes both psychophysical measurements and black-box modeling of level discrimination. Level discrimination was chosen to study contra-aural interference since it has traditionally been considered a monaural task (dependent on only a single ear) even though the loudness of a sound depends on both ears (i.e., binaural). This thesis demonstrates that the ability to discriminate small changes in the level of a low-frequency target stimulus presented at one ear can be adversely affected by a distractor stimulus presented simultaneously and contra-aurally to the target.; (cont.) The thesis focuses on conditions in which the target and distractor perceptually fuse; the dominant perception of the stimulus is a compact auditory image with a salient loudness and position and a secondary image referred to as the "time-image". Contra-aural interference was greatest when the introduction of the distractor decreased the reliability of both the perceived loudness and position of the dominant-image. Although the tasks used in this thesis are artificial...

‣ Grain size evolution and strain localization in deformed marbles

Austin, Nicholas James
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 226 p.
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In the lithosphere, strain is frequently accommodated along localized shear zones, the rheology of which are inextricably linked to their microstructural characteristics. Shear zones in orogenic belts frequently form in calcite-rich lithologies due to the relatively low strength of these rocks, especially when compared to quartz- and feldspar-rich lithologies. This dissertation addresses the kinetics of microstructural evolution during deformation of calcite-rich rocks, and the coupling between the rheological properties of deforming rocks and such microstructural characteristics as grain size and crystallographic preferred orientation (CPO) by combining laboratory studies with field based observations. In Chapter 2, a scaling relationship for recrystallized grain size is derived based on a balance between the rate that mechanical work is done during deformation and the rate that this energy can be dissipated. This suggests that recrystallized grain size reflects the product of stress and strain rate rather than stress alone. When this scaling relationship is applied to measured calcite grain sizes from the Morcles nappe, in the Swiss Helveitc Alps, where the microstructure is unaffected by second phases, the geologically estimated regional strain rates are successfully reproduced...

‣ Mechanical loading impacts intramuscular drug transport : impact on local drug delivery

Wu, Peter I-Kung
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 214 leaves
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Controlled-release drug-delivery systems enable efficient and defined administration of therapeutic agents to target tissues. However, ultimate drug distribution and pharmacologic effect are determined by target tissue pharmacokinetics. In muscular tissues, complex architecture that is further augmented by dynamic motion and contraction can alter the pharmacokinetics and deposition of locally delivered macromolecules. We developed a system and applied a quantitative schema to investigate the impact of controlled mechanical loads applied to skeletal and cardiac muscle tissue on intramuscular transport of locally delivered drug. In a series of studies, we examined how the interaction between architectural configuration and functional mechanics alters the transport of drugs across both physicochemical and binding properties. We correlated these pharmacokinetic effects with characteristic parameters in the physiologic range of the tissue to derive mechanistic insight into the fundamental structural and dynamic elements that underlie these effects. While previous studies have revealed the unilateral scaling of substrate uptake with mechanical influences, we elucidated an architecturally defined pharmacokinetic setpoint whereby maximal drug penetration corresponds with optimal muscle function. Our findings elucidate basic biologic design in muscle that optimizes the interface between tissue and its physical environment. The unique insights from our investigations have broad impact on current understanding of the pharmacokinetic influences of biologic form and function...

‣ Models and algorithms for the capacitated location-routing problem

Contardo, Claudio
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Thèse ou Mémoire numérique / Electronic Thesis or Dissertation
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Le problème de localisation-routage avec capacités (PLRC) apparaît comme un problème clé dans la conception de réseaux de distribution de marchandises. Il généralisele problème de localisation avec capacités (PLC) ainsi que le problème de tournées de véhicules à multiples dépôts (PTVMD), le premier en ajoutant des décisions liées au routage et le deuxième en ajoutant des décisions liées à la localisation des dépôts. Dans cette thèse on dévelope des outils pour résoudre le PLRC à l’aide de la programmation mathématique. Dans le chapitre 3, on introduit trois nouveaux modèles pour le PLRC basés sur des flots de véhicules et des flots de commodités, et on montre comment ceux-ci dominent, en termes de la qualité de la borne inférieure, la formulation originale à deux indices [19]. Des nouvelles inégalités valides ont été dévelopées et ajoutées aux modèles, de même que des inégalités connues. De nouveaux algorithmes de séparation ont aussi été dévelopés qui dans la plupart de cas généralisent ceux trouvés dans la litterature. Les résultats numériques montrent que ces modèles de flot sont en fait utiles pour résoudre des instances de petite à moyenne taille. Dans le chapitre 4...

‣ Impacts and Detection of Design Smells

Maiga, Abdou
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Thèse ou Mémoire numérique / Electronic Thesis or Dissertation
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Les changements sont faits de façon continue dans le code source des logiciels pour prendre en compte les besoins des clients et corriger les fautes. Les changements continus peuvent conduire aux défauts de code et de conception. Les défauts de conception sont des mauvaises solutions à des problèmes récurrents de conception ou d’implémentation, généralement dans le développement orienté objet. Au cours des activités de compréhension et de changement et en raison du temps d’accès au marché, du manque de compréhension, et de leur expérience, les développeurs ne peuvent pas toujours suivre les normes de conception et les techniques de codage comme les patrons de conception. Par conséquent, ils introduisent des défauts de conception dans leurs systèmes. Dans la littérature, plusieurs auteurs ont fait valoir que les défauts de conception rendent les systèmes orientés objet plus difficile à comprendre, plus sujets aux fautes, et plus difficiles à changer que les systèmes sans les défauts de conception. Pourtant, seulement quelques-uns de ces auteurs ont fait une étude empirique sur l’impact des défauts de conception sur la compréhension et aucun d’entre eux n’a étudié l’impact des défauts de conception sur l’effort des développeurs pour corriger les fautes. Dans cette thèse...

‣ A flexible modelling framework leading to a pobabilistic multiaxial Kitagawa-Takahashi diagram : applied to cast Al-Si alloys

LE, Viet-Duc; BELLETT, Daniel; MOREL, Franck; SAINTIER, Nicolas; PALIN-LUC, Thierry; PESSARD, Etienne; OSMOND, Pierre
Fonte: MATEC Web of Conferences Publicador: MATEC Web of Conferences
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The aim of this work is to propose simple analytical tools to predict the fatigue strength of cast aluminium components as a function of the casting process and post-cast treatment. The proposed methodology is based on the Murakami approach to predict the maximum defect size and a flexible modelling framework which leads to the construction of a probabilistic, multiaxial Kitagawa-Takahashi diagram. This framework is capable of modelling two independent co-existing fatigue damage mechanisms. This methodology will be applied to fatigue data taken from the literature as well as tests conducted on AlSi7 cast specimens manufactured via three different processes.

‣ Adaptive Wavelets Applied to the Analysis of Nonlinear Systems with Chaotic Dynamics

Gusev, V. A.; Hramov, A. E.; Koronovskii, A. A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 28/01/2006 Português
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We consider an approach to the analysis of nonstationary processes based on the application of wavelet basis sets constructed using segments of the analyzed time series. The proposed method is applied to the analysis of time series generated by a nonlinear system with and without noise; Comment: 4 pages, 2 figures