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Sistema de instrumentação mecanizada reciprocante

Grilo, Tiago José Monteiro Carreirinha
Fonte: [s.n.] Publicador: [s.n.]
Tipo: Dissertação de Mestrado
Publicado em //2014 POR
Relevância na Pesquisa
35.72%
Projeto de Pós-Graduação/Dissertação apresentado à Universidade Fernando Pessoa como parte dos requisitos para obtenção do grau de Mestre em Medicina Dentária; Introdução Nos últimos anos, a Endodontia tem sofrido inúmeros avanços e melhorias clínicas que ajudaram a tornar o tratamento Endodôntico cada vez mais viável e eficaz. Uma das áreas onde se tem verificado maior investigação e consequente aparecimento e disponibilização de avanços tecnológicos é a instrumentação dos canais radiculares, tais como instrumentação mecanizada com movimentos reciprocantes e sistemas de lima única. Propomo-nos então com a execução deste trabalho, realizar um levantamento relativo ao sistema Reciproc®, acerca de vários factores, tais como a resistência à fadiga cíclica, resistência à fratura dos instrumentos, extrusão de detritos a nível apical, erros de instrumentação, capacidade de remoção de detritos dos canais e tempo de trabalho do sistema Reciproc, bem como à sua comparação com os sistemas ProTaper e WaveOne. Metodologia Elaboração de uma pesquisa bibliográfica recorrendo às bases de dados: Pubmed, B-On e RCAAP, Scielo, Mesh Database e Science Direct com as seguintes palavras-chave: “Continuous Rotation”...

Problems of maximal mean resistance on the plane

Plakhov, Alexander; Gouveia, Paulo D.F.
Fonte: IOP Publicador: IOP
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
35.68%
A two-dimensional body moves through a rarefied medium; the collisions of the medium particles with the body are absolutely elastic.The body performs both translational and slow rotational motion. It is required to select the body, from a given class of bodies, such that the average force of resistance of the medium to its motion is maximal. There are presented numerical and analytical results concerning this problem. In particular, the maximum resistance in the class of bodies contained in a convex body K is proved to be 1.5 times resistance of K. The maximum is attained on a sequence of bodies with very complicated boundary. The numerical study was made for somewhat more restricted classes of bodies. The obtained values of resistance are slightly lower, but the boundary of obtained bodies is much simpler, as compared to the analytical solutions.

Bodies of maximal aerodynamic resistance on the plane

Plakhov, Alexander; Gouveia, Paulo D.F.
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Relatório
ENG
Relevância na Pesquisa
35.68%
A two-dimensional body moves through a rarefied medium; the collisions of the medium particles with the body are absolutely elastic. The body performs both translational and slow rotational motion. It is required to select the body, from a given class of bodies, such that the average force of resistance of the medium to its motion is maximal. There are presented numerical and analytical results concerning this problem. In particular, the maximum resistance in the class of bodies contained in a convex body K is proved to be 1.5 times resistance of K. The maximum is attained on a sequence of bodies with very complicated boundary. The numerical study was made for somewhat more restricted classes of bodies. The obtained values of resistance are slightly lower, but the boundary of obtained bodies is much simpler, as compared to the analytical solutions.

Estimativa do fator de forma e da resistência ao avanço de embarcações através da dinâmica dos fluidos computacional.; Estimate of the form factor and the resistance of ships through the computational fluid dynamics.

Araujo, Marcos Felipe Bettini Pereira de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 12/12/2013 PT
Relevância na Pesquisa
35.61%
Este trabalho discute o efeito da escala na obtenção do fator de forma de embarcações e avalia a estimativa de resistência ao avanço e o padrão de ondas gerado pelo movimento relativo entre o fluido e o casco, através de análises computacionais. A estimativa adequada do fator de forma é importante para a determinação da resistência do casco na escala real, possibilitando o dimensionamento do sistema propulsivo, isto é, motor e hélice. Tradicionalmente o valor do fator de forma é obtido experimentalmente através de ensaios de reboque de modelos em escala reduzida. Observa-se na maioria dos laboratórios, que durante os testes o valor do fator de forma é adotado como constante, independentemente de Froude e Reynolds, conforme proposto de ITTC. É apresentada uma alternativa computacional para a determinação do fator de forma. Para tal, utiliza-se a metodologia double-model nas simulações relativas ao casco adotado, em que se obtém os coeficientes de resistência viscosa, enquanto que as linhas de correlação da ITTC'57, Grigson e Schoenherr, além das simulações de arrasto de placas planas, calculam os coeficientes de resistência friccional. Da relação entre os coeficientes viscosos e friccionais encontra-se a tendência do fator de forma em função do número de Reynolds...

Utilização de dinamômetro de rolo de baixa potência em veículo supereconômico; Utilization of a low-power roll dynamometer in a low fuel consumption vehicle

Dornelles, Renato Tonin
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Trabalho de Conclusão de Curso Formato: application/pdf
POR
Relevância na Pesquisa
45.43%
O presente trabalho visa auxiliar o desenvolvimento de um veículo supereconômico pelo Departamento de Engenharia Mecânica. Buscando tecnologias para a redução do consumo de combustível, procurou-se a melhoria da eficiência através da redução de perdas. Foram realizados testes em um protótipo produzido pela ULBRA em um dinamômetro de rolo de baixa potência, tendo como principal parâmetro de referência a potência do motor. Foram feitas seis medições com diferentes parâmetros de lubrificação, peso e pressão de pneus, com o objetivo de analisar as diferenças presentes na potência. Avaliando as incertezas de medição presentes nos resultados finais, pode-se afirmar que a maior pressão nos pneus traseiros (50 PSI), a lubrificação das correntes e rolamentos e o menor peso possível no chassi representam um aumento na potência na roda para uma mesma posição do pedal do acelerador.; This work seeks to support the development of a low fuel consumption vehicle for the Department of Mechanical Engineering. Searching for technologies to reduce fuel consumption, it was looked to improve the efficiency by reducing losses. Tests were conducted on a prototype produced by ULBRA on a low-power roll dynamometer, having the engine power as the main benchmark parameter. Six measurements were made with different parameters of lubrication...

Toxicological effects and resistance to pyrethroids in Boophilus microplus from Goiás, Brazil

Fernandes,F.F.
Fonte: Universidade Federal de Minas Gerais, Escola de Veterinária Publicador: Universidade Federal de Minas Gerais, Escola de Veterinária
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2001 EN
Relevância na Pesquisa
45.5%
In order to monitor the susceptibility of Boophilus microplus to acaricides and improve control measures, the effects of cypermethrin, deltamethrin and permethrin on larvae obtained in the city of Goiânia in the Brazilian state of Goiás were studied. Although these pyrethroids are already sold as acaricides, their cost-benefit efficiency has been questioned. Fasting 14-21 day-old larvae were immersed in solutions of the acaricides under test, maintained at 27±1° C, and relative humidity over 80%, and observed under the stereoscope within an apparatus originally designed for studying the non-parasitic phase of the tick life cycle. The observed toxicological effects were: excitability, repetitive motion, decreased motor ability, detachment, paralysis, knock-down and cuticular proliferation of liquids and gases. The materials used in the manufacture of this apparatus consisted of disposable Petri dishes, "organza" cloth and paraffin, none of which are toxic to tick larvae. Mean death rates after 24h were 76.3%, 87.5%, 77.6%, 91.2%, 86.2% and 100% for 25 and 50ppm deltamethrin, 150 and 300ppm cypermethrin and 1250 and 2500ppm permethrin, respectively. The ticks were resistant to commercial concentrations of deltamethrin and cypermethrin. Only 2500ppm permethrin produced the mortality recommended by the Brazilian Ministry of Agriculture.

Analysis of red blood cell motion through cylindrical micropores: effects of cell properties.

Secomb, T W; Hsu, R
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1996 EN
Relevância na Pesquisa
35.67%
Filtration through micropores is frequently used to assess red blood cell deformability, but the dependence of pore transit time on cell properties is not well understood. A theoretical model is used to simulate red cell motion through cylindrical micropores with diameters of 3.6, 5, and 6.3 microns, and 11-microns length, at driving pressures of 100-1000 dyn/cm2. Cells are assumed to have axial symmetry and to conserve surface area during deformation. Effects of membrane shear viscosity and elasticity are included, but bending resistance is neglected. A time-dependent lubrication equation describing the motion of the suspending fluid is solved, together with the equations for membrane equilibrium, using a finite difference method. Predicted transit times are consistent with previous experimental observations. Time taken for cells to enter pores represents more than one-half of the transit time. Predicted transit time increases with increasing membrane viscosity and with increasing cell volume. It is relatively insensitive to changes in internal viscosity and to changes in membrane elasticity except in the narrowest pores at low driving pressures. Elevating suspending medium viscosity does not increase sensitivity of transit time to membrane properties. Thus filterability of red cells is sensitively dependent on their resistance to transient deformations...

The Physics of Blood Flow in Capillaires: II. The Capillary Resistance to Flow

Prothero, J. W.; Burton, A. C.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /03/1962 EN
Relevância na Pesquisa
45.67%
A previous communication described the peculiar motion of the plasma trapped between erythrocytes in a capillary (bolus flow). In this paper the effect of this motion on capillary resistance to flow, as well as on dissipative effects associated directly with the cells, are described. The resistance that would be associated with plasma in bolus flow at high Reynolds numbers (relative to a capillary value of 0.01) was studied in a model, in which air bubbles, separated by short segments of water, passed along a glass tube. The resistance to flow, especially with short boluses, was at least ten times greater than that associated with Poiseuille flow. In a second series of experiments at lower Reynolds numbers, a single bolus of liquid was forced by air pressure along a glass tube. In these latter experiments, which more closely simulate biological conditions, the mean resistance to flow was only 30 per cent greater than that associated with Poiseuille flow. In the final series of experiments human blood and plasma, diluted in acid-citrate dextrose (A.C.D.) in varying degrees, were forced through glass micropipettes of capillary dimensions. The mean apparent viscosity of whole blood was found to exceed that of plasma by only about 5 per cent...

Mechanism of Amphotericin B Resistance in Clinical Isolates of Leishmania donovani

Purkait, Bidyut; Kumar, Ashish; Nandi, Nilay; Sardar, Abul Hasan; Das, Sushmita; Kumar, Sudeep; Pandey, Krishna; Ravidas, Vidyananda; Kumar, Manish; De, Tripti; Singh, Dharmendra; Das, Pradeep
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /02/2012 EN
Relevância na Pesquisa
45.59%
The clinical value of amphotericin B, the mainstay therapy for visceral leishmaniasis in sodium antimony gluconate-nonresponsive zones of Bihar, India, is now threatened by the emergence of acquired drug resistance, and a comprehensive understanding of the underlying mechanisms is the need of the hour. We have selected an amphotericin B-resistant clinical isolate which demonstrated 8-fold-higher 50% lethal doses (LD50) than an amphotericin B-sensitive strain to explore the mechanism of amphotericin B resistance. Fluorimetric analysis demonstrated lower anisotropy in the motion of the diphenylhexatriene fluorescent probe in the resistant strain, which indicated a higher fluidity of the membrane for the resistant strain than for the sensitive strain. The expression patterns of the two transcripts of S-adenosyl-l-methionine:C-24-Δ-sterol methyltransferase and the absence of ergosterol, replaced by cholesta-5,7,24-trien-3β-ol in the membrane of the resistant parasite, indicate a decreased amphotericin B affinity, which is evidenced by decreased amphotericin B uptake. The expression level of MDR1 is found to be higher in the resistant strain, suggesting a higher rate of efflux of amphotericin B. The resistant parasite also possesses an upregulated tryparedoxin cascade and a more-reduced intracellular thiol level...

Elastic resistance of the spine: Why does motion preservation surgery almost fail?

Landi, Alessandro
Fonte: Baishideng Publishing Group Co., Limited Publicador: Baishideng Publishing Group Co., Limited
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
35.59%
Single metamere motility should not be interpreted merely as a movement on the 3 planes but also, and above all, as elastic resistance to dynamic stress on these 3 planes. In the light of this consideration, the aim of motion preservation is to neutralize excessive movements while preserving the physiological biomechanical properties of the metamere involved to interrupt the progression of degenerative processes and to prevent adjacent segment disease. Despite the fact that a myriad of devices have been developed with the purpose of achieving dynamic neutralization of the spine, there are now some doubts regarding the true efficacy of these devices.

Motion sickness: more than nausea and vomiting

Lackner, James R.
Fonte: Springer Berlin Heidelberg Publicador: Springer Berlin Heidelberg
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
45.67%
Motion sickness is a complex syndrome that includes many features besides nausea and vomiting. This review describes some of these factors and points out that under normal circumstances, many cases of motion sickness go unrecognized. Motion sickness can occur during exposure to physical motion, visual motion, and virtual motion, and only those without a functioning vestibular system are fully immune. The range of vulnerability in the normal population varies about 10,000 to 1. Sleep deprivation can also enhance susceptibility. Systematic studies conducted in parabolic flight have identified velocity storage of semicircular canal signals—velocity integration—as being a key factor in both space motion sickness and terrestrial motion sickness. Adaptation procedures that have been developed to increase resistance to motion sickness reduce this time constant. A fully adequate theory of motion sickness is not presently available. Limitations of two popular theories, the evolutionary and the ecological, are described. A sensory conflict theory can explain many but not all aspects of motion sickness elicitation. However, extending the theory to include conflicts related to visceral afferent feedback elicited by voluntary and passive body motion greatly expands its explanatory range. Future goals should include determining why some conflicts are provocative and others are not but instead lead to perceptual reinterpretations of ongoing body motion. The contribution of visceral afferents in relation to vestibular and cerebellar signals in evoking sickness also deserves further exploration. Substantial progress is being made in identifying the physiological mechanisms underlying the evocation of nausea...

Avaliação da composição corporal e qualidade de vida em pacientes submetidos ao esvaziamento cervical supraomohióideo; Evaluation of body composition and quality of life in patients sunmitted to supraomohyoid neck dissection

PAULA JÚNIOR, Célio Antônio de
Fonte: Universidade Federal de Goiás; BR; UFG; Mestrado em Ciências da Saúde; Ciências da Saúde - Medicina Publicador: Universidade Federal de Goiás; BR; UFG; Mestrado em Ciências da Saúde; Ciências da Saúde - Medicina
Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
35.66%
Supraomohyoid neck dissection is an important procedure in the treatment of patients with malignancy in the oral cavity and oropharynx, however there are common side effects in the post operative period. Results of an elaborate review of literature in electronic databases to investigate the effect of a resistance exercise protocol in this population showed significant improvement in the quality of life of patients trained, however studies which deal with the issue are limited. To quantify the damage caused by post-operative supraomohyoid neck dissection, and thus develop a secure protocol of exercises for this population, this study evaluated changes in body composition, body mass index, range of motion and quality of life in patients undergoing unilateral or bilateral supraomohyoid neck dissection pre and post-operatively (30 and 90 days). In the post-operative period, the 28 patients observed showed a significant reduction in body weight, muscle weight, and fat percentage. In terms of range of motion, a reduction of flexion, extension, abduction, medial rotation and lateral rotation was detected in the post-operative period (30 and 90 days). Decreased range of motion of flexion and abduction post-operatively had a negative correlation with quality of life...

Mutagénèse semi-aléatoire au site actif de la DHFR humaine : création et caractérisation de variantes hautement résistantes au MTX.

Volpato, Jordan
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Thèse ou Mémoire numérique / Electronic Thesis or Dissertation
FR
Relevância na Pesquisa
35.63%
La dihydrofolate réductase humaine (DHFRh) est une enzyme essentielle à la prolifération cellulaire. Elle réduit le dihydrofolate en tétrahydrofolate, un co-facteur impliqué dans la biosynthèse des purines et du thymidylate. La DHFRh est une cible de choix pour des agents de chimiothérapie comme le méthotrexate (MTX), inhibant spécifiquement l’enzyme ce qui mène à un arrêt de la prolifération et ultimement à la mort cellulaire. Le MTX est utilisé pour le traitement de plusieurs maladies prolifératives, incluant le cancer. La grande utilisation du MTX dans le milieu clinique a mené au développement de mécanismes de résistance, qui réduisent l’efficacité de traitement. La présente étude se penche sur l’un des mécanismes de résistance, soit des mutations dans la DHFRh qui réduisent son affinité pour le MTX, dans le but de mieux comprendre les éléments moléculaires requis pour la reconnaissance de l’inhibiteur au site actif de l’enzyme. En parallèle, nous visons à identifier des variantes plus résistantes au MTX pour leur utilisation en tant que marqueurs de sélection en culture cellulaire pour des systèmes particuliers, tel que la culture de cellules hématopoïétiques souches (CHS), qui offrent des possibilités intéressantes dans le domaine de la thérapie cellulaire. Pour étudier le rôle des différentes régions du site actif...

Resistance to mantle flow inferred from the electromagnetic strike of the Australian upper mantle

Simpson, Fiona
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em //2001 EN
Relevância na Pesquisa
45.68%
Seismic anisotropy is thought to result from the strain-induced lattice-preferred orientation of mantle minerals, especially olivine, owing to shear waves propagating faster along the a-axis of olivine crystals than along the other axes. This anisotropy results in birefringence, or 'shear-wave splitting', which has been investigated in numerous studies. Although olivine is also anisotropic with respect to electrical conductivity (with the a-axis being most conductive), few studies of the electrical anisotropy of the upper mantle have been undertaken, and these have been limited to relatively shallow depths in the lithospheric upper mantle. Theoretical models of mantle flow have been used to infer that, for progressive simple shear imparted by the motion of an overriding tectonic plate, the a-axes of olivine crystals should align themselves parallel to the direction of plate motion. Here, however, we show that a significant discrepancy exists between the electromagnetic strike of the mantle below Australia and the direction of present-day absolute plate motion. We infer from this discrepancy that the a-axes of olivine crystals are not aligned with the direction of the present-day plate motion of Australia, indicating resistance to deformation of the mantle by plate motion.

Resistance to Flexural Fatigue of Reciproc R25 Files under Continuous Rotation and Reciprocating Movement

Gavini, Giulio; Caldeira, Celso Luiz; Akisue, Eduardo; Candeiro, George Táccio de Miranda; Kawakami, Dirce Akemi Sacaguti
Fonte: ELSEVIER SCIENCE INC; NEW YORK Publicador: ELSEVIER SCIENCE INC; NEW YORK
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
45.72%
Introduction: The aim of the present work was to evaluate the resistance to flexural fatigue of Reciproc R25 nickel-titanium files, 25 mm, used in continuous rotation motion or reciprocation motion, in dynamic assays device. Methods: Thirty-six Reciproc R25 files were divided into 2 groups (n = 18) according to kinematics applied, continuous rotary (group CR) and reciprocation motion (group RM). The files were submitted to dynamic assays device moved by an electric engine with 300 rpm of speed that permitted the reproduction of pecking motion. The files run on a ring's groove of temperate steel, simulating instrumentation of a curved root canal with 400 and 5 mm of curvature radius. The fracture of file was detected by sensor of device, and the time was marked. The data were analyzed statistically by Student's t test, with level of significance of 95%. Results: The instruments moved by reciprocating movement reached significantly higher numbers of cycles before fracture (mean, 1787.78 cycles) when compared with instruments moved by continuous rotary (mean, 816.39 cycles). Conclusions: The results showed that the reciprocation motion improves flexural fatigue resistance in nickel-titanium instrument Reciproc R25 when compared with continuous rotation movement. (J Endod 2012;38:684-687)

Problems of minimal and maximal aerodynamic resistance

Plakhov, Alexander
Fonte: Springer Publicador: Springer
Tipo: Parte de Livro
ENG
Relevância na Pesquisa
35.63%
This is a review of results recently obtained by the author, related to problems of the body of minimal and maximal resistance. The cases of purely translational motion, as well as (rotational & translational) motion are considered. The notions of rough body and law of scattering on a body are discussed. Connections with the Monge-Kantorovich problem of optimal mass transportation are revealed, and applications to the Magnus effect and retroreflectors are discussed.

Toward the modeling of mucus draining from human lung: role of airways deformation on air-mucus interaction

Mauroy, Benjamin; Flaud, Patrice; Pelca, Dominique; Fausser, Christian; Merckx, Jacques; Mitchell, Barrett R.
Fonte: Frontiers Media S.A. Publicador: Frontiers Media S.A.
Tipo: Artigo de Revista Científica
Publicado em 05/08/2015 EN
Relevância na Pesquisa
35.59%
Chest physiotherapy is an empirical technique used to help secretions to get out of the lung whenever stagnation occurs. Although commonly used, little is known about the inner mechanisms of chest physiotherapy and controversies about its use are coming out regularly. Thus, a scientific validation of chest physiotherapy is needed to evaluate its effects on secretions. We setup a quasi-static numerical model of chest physiotherapy based on thorax and lung physiology and on their respective biophysics. We modeled the lung with an idealized deformable symmetric bifurcating tree. Bronchi and their inner fluids mechanics are assumed axisymmetric. Static data from the literature is used to build a model for the lung's mechanics. Secretions motion is the consequence of the shear constraints apply by the air flow. The input of the model is the pressure on the chest wall at each time, and the output is the bronchi geometry and air and secretions properties. In the limit of our model, we mimicked manual and mechanical chest physiotherapy techniques. We show that for secretions to move, air flow has to be high enough to overcome secretion resistance to motion. Moreover, the higher the pressure or the quicker it is applied, the higher is the air flow and thus the mobilization of secretions. However...

Development of motion resistant instrumentation for ambulatory near-infrared spectroscopy

Zhang, Quan; Yan, Xiangguo; Strangman, Gary E.
Fonte: Society of Photo-Optical Instrumentation Engineers (SPIE) Publicador: Society of Photo-Optical Instrumentation Engineers (SPIE)
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
45.59%
Ambulatory near-infrared spectroscopy (aNIRS) enables recording of systemic or tissue-specific hemodynamics and oxygenation during a person's normal activities. It has particular potential for the diagnosis and management of health problems with unpredictable and transient hemodynamic symptoms, or medical conditions requiring continuous, long-duration monitoring. aNIRS is also needed in conditions where regular monitoring or imaging cannot be applied, including remote environments such as during spaceflight or at high altitude. One key to the successful application of aNIRS is reducing the impact of motion artifacts in aNIRS recordings. In this paper, we describe the development of a novel prototype aNIRS monitor, called NINscan, and our efforts to reduce motion artifacts in aNIRS monitoring. Powered by 2 AA size batteries and weighting 350 g, NINscan records NIRS, ECG, respiration, and acceleration for up to 14 h at a 250 Hz sampling rate. The system's performance and resistance to motion is demonstrated by long term quantitative phantom tests, Valsalva maneuver tests, and multiparameter monitoring during parabolic flight and high altitude hiking. To the best of our knowledge, this is the first report of multiparameter aNIRS monitoring and its application in parabolic flight.

Large amplitude oscillatory microrheology

Swan, James W.; Zia, Roseanna N.; Brady, John F.
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /01/2014
Relevância na Pesquisa
35.69%
We study the motion of a colloidal particle as it is driven by an oscillating external force of arbitrary amplitude and frequency through a colloidal dispersion. Large amplitude oscillatory flows (LAOFs) are examined predominantly from a phenomenological perspective in which experimental measurements inform constitutive models. Here, we investigate a LAOF from a microstructural perspective by connecting motion of the probe particle to the material response while making no assumptions a priori about how stress relaxes in the material. The suspension exerts nonconservative, hydrodynamic forces on the probe, while distortions in the particle configuration exert conservative forces: Brownian and interparticle forces, for example. The relative importance of each of these contributions to particle motion evolves with the degree of displacement from equilibrium. When the force on the probe is weak, the linear microviscoelasticity of the suspension is probed [see, e.g., Khair and Brady, J. Rheol. 49, 1449–1481 (2005)]. When oscillation rate is slow, the steady microrheology is probed [see, e.g., Squires and Brady, Phys. Fluids 17, 073101 (2005); Khair and Brady, J. Fluid Mech. 557, 73–117 (2006)]. This article develops a micromechanical model that recovers these limiting cases and then uses the same model to reveal the microrheology of colloidal dispersions deformed by a probe driven with arbitrary force amplitude and frequency. A chief result of this work is the discovery of a regime in which the resistance to motion of the probe particle is on average weaker than the resistance the probe experiences when deformed by high frequency oscillation. This hypoviscous effect arises when the reciprocating motion of the probe particle opens a channel free of other particles which is thus less resistive to probe motion. This effect is most apparent under the conditions of strong forces...

A prediction equation for the estimation of cardiorespiratory fitness using an elliptical motion trainer

Brown,GA; Krueger,RD; Cook,CM; Heelan,KA; Shaw,BS; Shaw,I
Fonte: West Indian Medical Journal Publicador: West Indian Medical Journal
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/02/2013 EN
Relevância na Pesquisa
35.74%
OBJECTIVE: In the United States of America, 6.2 million individuals are using elliptical motion trainers in fitness centres. However, graded exercise test protocols to estimate peak oxygen consumption (VO2peak) using elliptical motion trainers have not been developed for the general population. METHODS: Fifty-nine subjects (mean age: 23.5 ± 4.1 years) were randomly divided into a validation (VAL: n = 39) or cross-validation (XVAL: n = 20) group. Peak oxygen consumption (ml×kg-1×min-1) was measured via indirect calorimetry on an elliptical motion trainer for both groups. Subjects exercised at 150 strides×min-1 against a resistance of four and a crossramp of 8%. The resistance was increased every two minutes by two units until exhaustion. For the VAL group, a stepwise regression analysis was used to predict VO2peak from resistance, maximal heart rate (HRmax), body mass index (BMI), height and gender (female = 0, male = 1). RESULTS: The prediction equation derived from this study was VO2peak (ml·kg-1·min-1) = 187.39403 + 12.97271 (gender) - 1.45311 (height) - 1.21604 (BMI) - 0.19613 (HRmax) + 1.57093 (resistance) (R² = 0.76, SEE = 4.47, p < 0.05). Using this equation, the predicted VO2peak of the XVAL group was 45.18 ± 6.42 ml·kg-1×min-1...