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Relationship between installation torque and uplift capacity of deep helical piles in sand

TSUHA, Cristina de Hollanda Cavalcanti; AOKI, Nelson
Fonte: CANADIAN SCIENCE PUBLISHING, NRC RESEARCH PRESS Publicador: CANADIAN SCIENCE PUBLISHING, NRC RESEARCH PRESS
Tipo: Artigo de Revista Científica
ENG
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26.88%
Le facteur empirique de correlation du torque K(T), qui represente la capacite de soulevement du torque d`installation de pieux helicoidaux, est generalement utilise comme instrument de controle de la qualite sur le terrain pour ce type de fondations. Dans cet article, une relation theorique entre la capacite de soulevement et le torque d`installation de pieux helicoidaux places profondement dans du sable est presentee. Un programme experimental, qui comprend des essais centrifuge et de cisaillement direct a l`interface, a ete effectue dans le but de valider cette relation theorique. Les resultats experimentaux ont ete compares aux resultats predits par l`approche suggeree, et les resultats montrent une bonne concordance. Puisque le modele developpe depend de l`angle de friction residuel a l`interface delta(r) entre la surface de l`helice du pieu et le sable, les resultats de delta(r) obtenus a partir de differents echantillons de sable sont presentes afin d`etre utilises lors de l`application sur le terrain de la relation theorique proposee. De plus, les valeurs de K(T) obtenues dans ces travaux ont ete comparees a celles reportees dans la litterature; celles-ci ayant ete obtenues lors d`essais sur le terrain et en laboratoire sur des pieux helicoidaux dans le sable. Cette analyse a permis de demontrer que les valeurs mesurees de K(T) diminuent lorsque la dimension des pieux augmente...

Estudo probabilístico do comportamento de ancoragens helicoidais baseado em dados de campo e de modelos testados em centrífuga; Probabilistic study of the behaviour of helical anchors based on field data and centrifuge model tests

Zapata Mosquera, Zorany Suley
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 13/04/2015 PT
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Na prática de fundações por estacas helicoidais submetidas a esforços de tração (também conhecidas como ancoragens helicoidais) frequentemente são observadas discrepâncias entre valores de capacidade de carga previstos por métodos teóricos e medidos em provas de carga. Entre outros fatores, estas diferenças ocorrem pelo fato de nenhum dos métodos teóricos existentes considerarem adequadamente o efeito da instalação no comportamento deste tipo de ancoragem. Durante a penetração por rotação das hélices da estaca/ancoragem no terreno, os parâmetros de resistência e de rigidez do solo penetrado, e as tensões radiais em torno da estaca são modificados. O nível de degradação do solo que suportará as cargas aplicadas na ancoragem é dependente do tipo e características do solo, e do número e geometria das hélices. Diante deste cenário de incertezas provenientes do efeito da instalação, duas distintas abordagens probabilísticas são apresentadas nesta dissertação. A primeira abordagem tem o intuito de verificar o efeito da variabilidade de distintas variáveis influentes no comportamento de ancoragens helicoidais. Para este fim, foi utilizado o método de expansão em Polinômio de Caos, baseado na modelagem numérica de ancoragens helicoidais em areia...

Influence of variables on centrifuge-flotation technique for recovery of Toxocara canis eggs from soil

Santarém,Vamilton Alvares; Magoti,Luciana Puga; Sichieri,Tathiana Dias
Fonte: Instituto de Medicina Tropical Publicador: Instituto de Medicina Tropical
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2009 EN
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26.88%
The purpose of this study was to evaluate the influence of variables in a flotation technique for the recovery of Toxocara canis eggs from soil. The trials were done under standardized conditions on one gram of previously sterilized soil samples contaminated with 200 eggs of T. canis. The following variables were evaluated in serial steps: sieving; type of wash; time of stirring; resuspension of sediment; solution flotation. Centrifuge-flotation in sodium nitrate (d = 1.20 g/cm³) was adopted as an initial technique, using Tween 80 (0.2%) and decinormal sodium hydroxide as solutions for washing the samples. Ten tests were done to compare the variables, using counting in triplicate. The sieving of the material reduced significantly the recovery of eggs (p < 0.001) and the number of eggs recovered was higher when the sediment was resuspended (p < 0.05). After standardization, flotation solutions sodium chloride, zinc sulfate, sodium dichromate, magnesium sulfate, and sodium nitrate (d = 1.20g/cm³) were compared. The best results were obtained by using zinc sulfate solution. In conclusion, the chances of recovering T. canis eggs from samples using flotation solutions can be increased by washing of soil twice using distilled water, and resuspension of sediment. On the other hand...

Influence of removal time and particle size on the particle substrate adhesion force

Felicetti,M. A.; Piantino,F.; Coury,J. R.; Aguiar,M. L.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2008 EN
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26.88%
An investigation was conducted on influence of removal time on the particle substrate adhesive force. The centrifuge technique was used to determine the adhesion force at different compression and removal rates. A microcentrifuge with a maximum rotation of 14000 rpm was used to both compress upon particles and remove them from the surface of the substrate. An image analysis program (Image-Pro Plus 4.5) was employed to monitor the number of particles adhering to and removed from the surface of the substrate after each increase in angular speed. The influence of removal time on the adhesion force was investigated, using removal times of 1, 3 and 5 minutes, which indicated that removal time does not interfere with the adhesion force within the diameter range analyzed here.

Size-Separation of Yeast Mitochondria in the Zonal Centrifuge

Avers, Charlotte J.; Szabo, Arlene; Price, Carl A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1969 EN
Relevância na Pesquisa
26.88%
Mitochondria, released from yeast spheroplasts and subjected to rate separation through sorbitol gradients in the zonal centrifuge, migrated in a wide symmetrical zone. Electron micrographs showed that the mitochondria had been resolved within the zone according to size. The mean mitochondrial diameter at the leading edge was approximately twice that at the trailing edge of the particle zone. Activities of the enzymes cytochrome oxidase, malate dehydrogenase, and reduced nicotinamide adenine dinucleotide- and d-lactate cytochrome c reductases were essentially uniform throughout the mitochondrial zone. Mitochondria from a vegetative-petite mutant had almost the same size distribution as the isogenic wild type, but with somewhat larger mean diameter and either absent or markedly reduced enzyme activities. Mixtures of wild-type and petite mitochondria produced sedimentation profiles showing overlap of particle populations with respect to mean sedimentation rates and mitochondrial diameters, as well as intermediate levels of enzyme activities. Both cristate and noncristate organelles were present throughout the mitochondrial zone from these mixtures. Mitochondria centrifuged in sorbitol density gradients were well-preserved and yielded consistent sedimentation profiles...

Mass Purification of Nucleopolyhedrosis Virus Inclusion Bodies in the K-Series Centrifuge

Breillatt, J. P.; Brantley, J. N.; Mazzone, H. M.; Martignoni, M. E.; Franklin, J. E.; Anderson, N. G.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/1972 EN
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26.88%
Nucleopolyhedrosis virus inclusion bodies specific for Hemerocampa pseudotsugata, Neodiprion sertifer, Porthetria dispar, and Heliothis zea have been purified by using a continuous-sample-flow-with-isopycnic-banding centrifuge in quantities up to 6 × 1013 polyhedral inclusion bodies per day. Continuous-flow methods for S-ρ type purification have been evolved to deal with mass isolation of bioparticles.

Centrifuge modeling of rocking-isolated inelastic RC bridge piers

Loli, Marianna; Knappett, Jonathan A; Brown, Michael J; Anastasopoulos, Ioannis; Gazetas, George
Fonte: BlackWell Publishing Ltd Publicador: BlackWell Publishing Ltd
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.15%
Experimental proof is provided of an unconventional seismic design concept, which is based on deliberately underdesigning shallow foundations to promote intense rocking oscillations and thereby to dramatically improve the seismic resilience of structures. Termed rocking isolation, this new seismic design philosophy is investigated through a series of dynamic centrifuge experiments on properly scaled models of a modern reinforced concrete (RC) bridge pier. The experimental method reproduces the nonlinear and inelastic response of both the soil-footing interface and the structure. To this end, a novel scale model RC (1:50 scale) that simulates reasonably well the elastic response and the failure of prototype RC elements is utilized, along with realistic representation of the soil behavior in a geotechnical centrifuge. A variety of seismic ground motions are considered as excitations. They result in consistent demonstrably beneficial performance of the rocking-isolated pier in comparison with the one designed conventionally. Seismic demand is reduced in terms of both inertial load and deck drift. Furthermore, foundation uplifting has a self-centering potential, whereas soil yielding is shown to provide a particularly effective energy dissipation mechanism...

Robust constrained optimization approach to control design for International Space Station centrifuge rotor auto balancing control system

Postma, Barry Dirk
Fonte: Universidade Rice Publicador: Universidade Rice
ENG
Relevância na Pesquisa
27.15%
This thesis discusses application of a robust constrained optimization approach to control design to develop an Auto Balancing Controller (ABC) for a centrifuge rotor to be implemented on the International Space Station. The design goal is to minimize a performance objective of the system, while guaranteeing stability and proper performance for a range of uncertain plants. The performance objective is to minimize the translational response of the centrifuge rotor due to a fixed worst-case rotor imbalance. The robustness constraints are posed with respect to parametric uncertainty in the plant. The proposed approach to control design allows for both of these objectives to be handled within the framework of constrained optimization. The resulting controller achieves acceptable performance and robustness characteristics.

Physical modelling of Flowslide Mobility

Davoodi Bilesavar, ROYA
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 4752993 bytes; application/pdf
EN; EN
Relevância na Pesquisa
27.15%
Static liquefaction is a sudden decrease of soil shear strength due to the rapid development of pore pressures generated during the collapse of loose, saturated soil deposits. If this type of failure occurs in sloping soils, a flowslide can result. Viscous debris moving down a slope with high velocity could cover a vast area and cause significant loss of life and property. The primary objective of this study was to investigate the triggering factors of liquefaction in shallow slopes through the physical modeling technique of centrifuge testing. A flowslide simulator was developed to investigate the factors that lead to the liquefaction of soil slopes. This simulator was capable of replicating groundwater regimes and intense rainfalls with pore pressure transducers to monitor the pore pressure changes in the model slope and digital cameras to calculate the resultant slope deformation, velocity, and acceleration using the Particle Image Velocimetry method (PIV) of digital image correlation. In the course of this research, four centrifuge tests have been performed to evaluate the triggering mechanisms of fast landslides in shallow slopes. A seepage induced failure was simulated in the first test. The second and third tests were conducted applying different groundwater regimes in combination with intense rainfall to bring the slope to failure. The last test was a rainfall induced failure in the absence of a pre-existing groundwater table. The results from these experiments illustrate that the initial groundwater level has a considerable effect on the mobility of flowslides.; Thesis (Master...

Role of reactivated basement faults in localizing deformation in the upper crust: Insights from centrifuge analogue modelling

Waffle, Lindsay
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
27.15%
Dynamically scaled centrifuge analogue models are used to investigate recent interpretation of enhanced gravity data, which highlights northeast-striking inherited faults in the crust of northern India. The reactivation of these faults in the subducting Indian crust during the collision of India and Asia in the Paleogene (ca. 45–40 Ma) and early Neogene (ca. 20–15 Ma) is investigated to elucidate their potential role in localizing deformation in the upper crust. Models consist from bottom to top of a rigid basement material, a ductile middle, a layered package representing the upper crust, and a near-surface brittle layer. Viscoelastic materials used as analogues for the mid- and lower crust demonstrate complex dynamic behaviour; effective viscosity alone is not sufficient to determine if a material will be an effective analogue. Two series of rheological experiments are conducted using an oscillating parallel-plate rheometer to measure the storage and loss moduli and effective viscosities of potential materials. Inherently cohesive synthetic sands are suggested as suitable analogues for the brittle upper crust, historically not reproduced in centrifuge models. In models simulating early stage collision (ca. 10 Myr after onset)...

Physical Modelling of the Mobility of Dry Granular Landslides

Bryant, SARAH
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
27.15%
In geotechnical engineering, granular flows are often studied as a means to further the understanding of the mechanisms that drive landslide motion. High quality experimental data is essential in providing evidence for the development and verification of new theoretical methods that link complex grain interactions to the extended mobility of some landslide events. At present, limited experimental data is available that captures the full range of landslide mobility. In an attempt to add to the present data sources, high quality experimental data was obtained through the use of high speed cameras and physical modelling using a geotechnical centrifuge and a large scale landslide flume. These modelling techniques allow for landslide motion, representative of field scale events, to be observed in a well-defined and controlled setting. A series of nine tests were performed in a geotechnical centrifuge under varying slope inclinations and Coriolis conditions. The effects of Coriolis on landslide mobility were evident when comparing final deposit shapes and total runout. The effects of Coriolis were more pronounced for higher velocity situations and when material was travelling on the horizontal base section opposed to the sloped section of the physical model. A series of thirty tests were performed using a large scale flume under varying source volumes and basal friction conditions...

Processing Sputum Specimens in a Refrigerated Centrifuge Does Not Increase the Rate of Isolation of Mycobacterium tuberculosis

Selvakumar, N.; Govindan, Dakshayani; Chandu, Naik Ashok; Frieden, Thomas R.; Narayanan, P. R.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /01/2003 EN
Relevância na Pesquisa
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A total of 1,047 sputum samples from pulmonary tuberculosis patients was collected in cetyl pyridinium chloride-sodium chloride solution. Each sample was divided into two parts and randomly allocated for the isolation of Mycobacterium tuberculosis, with one part to be processed by the standard method and the other by a modified method. In the standard method, the samples were processed by using nonrefrigerated centrifuges, while in the modified method, they were processed by using a refrigerated centrifuge. Fifty-seven samples that yielded contaminants were excluded, and the remaining 990 samples were taken up for analysis. The rates of isolation of M. tuberculosis with the standard and modified methods were 48.6 and 48.1%, respectively, and the difference was not statistically significant (McNemar's test; P > 0.5). However, 51% of the positive cultures were isolated within 2 weeks with the modified method compared to 37% with the standard method (chi-square test; P < 0.001). The results of the study reveal that processing of sputum samples in a refrigerated centrifuge does not improve the rate of isolation but will result in rapid isolation of M. tuberculosis.

Quick Detection of Contaminants Leaching from Polypropylene Centrifuge Tube with Surface Enhanced Raman Spectroscopy and Ultra Violet Absorption Spectroscopy

Xu, Zhida; Liu, Logan
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/02/2014
Relevância na Pesquisa
27.15%
Anomalous surface enhanced Raman scattering (SERS) peaks are identified for liquid sample stored in polypropylene centrifuge tubes (PP tube) for months. We observed the unexpected Raman peaks during experiments for Thiamine Hydrochloride aqueous solution stored in PP tube for two months. In order to identify the contaminants we have performed SERS experiments for de-ionized water (DI water) stored in polypropylene centrifuge tube for two months and compared them with fresh DI water sample. We have also carried out Ultra Violet (UV) absorption spectra for both fresh and contaminated water. We believe that the water is contaminated because of chemicals leaching from the PP tube. From the GC-MS data the main contaminant was found to be Phthalic acid and its derivatives. Further SERS and UV absorption experiment for Phthalic acid correlates well with the anomalous peaks identified earlier. We qualitatively confirmed the identification and quantitatively estimated the concentration of suspect contaminants as between 1uM and 10uM with both SERS and UV absorption spectroscopy. With UV absorption spectroscopy, we precisely estimate the concentration as 2.1uM. We have shown that sample in PP tube can be contaminated due to leaching chemicals upon long term storage and suggested SERS and UV-absorption spectroscopy as two quick and simple techniques to detect the contamination

Rotating Atomic Traps for Bosons and the Centrifuge Effect

Majmudar, T.; Widom, A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/02/2000
Relevância na Pesquisa
27.15%
A rigorous time independent Hamiltonian for rotating atomic traps is discussed. The steady states carry a mass current and thereby an angular momentum. It is shown that the rotation positions the atoms away from the rotation axis (after taking both the time and quantum mechanical averages) as in a conventional centrifuge. Some assert that the rotation for Bose condensates cause the atoms to move towards the rotation axis; i.e. act oppositely to fluids in a centrifuge. The opposing physical pictures are reminiscent of the difference between the rotational motion views of Newton and Cassini.; Comment: 4 pages, 2 figures, RevTeX format

Adiabatic field-free alignment of asymmetric top molecules with an optical centrifuge

Korobenko, A.; Milner, V.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/10/2015
Relevância na Pesquisa
27.15%
We use an optical centrifuge to align asymmetric top $\mathrm{SO_2}$ molecules by adiabatically spinning their most polarizable O-O axis. The effective centrifugal potential in the rotating frame confines sulfur atoms to the plane of the laser-induced rotation, leading to the planar molecular alignment which persists after the molecules are released from the centrifuge. Periodic appearance of the full three-dimensional alignment, typically observed only with linear and symmetric top molecules, is also detected. Together with strong in-plane centrifugal forces, which bend the molecules by up to 10 degrees, permanent field-free alignment offers new ways of controlling molecules with laser light.

On preparation of viscous pore fluids for dynamic centrifuge modelling

Adamidis, O.; Madabhushi, S. P. G.
Fonte: ICE Publicador: ICE
Tipo: Article; accepted version
EN
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This is the accepted manuscript currently embargoed pending publication. Permission is granted by ICE Publishing to print one copy for personal use. Any other use of these PDF files is subject to reprint fees.; The scaling laws that arise from dynamic centrifuge modelling contain an inconsistency between the scaling of time for dynamic events and diffusion events. This problem can be resolved by reducing the permeability of the soil, with the help of high viscosity pore fluids. Hydroxypropyl methylcellulose is a water soluble cellulose ether that is widely used to create such fluids. In this paper, the effects that concentration, temperature, ageing, and shearing rate have on the viscosity of hydroxypropyl methylcellulose solutions are examined and equations that quantify them are presented. This information is meant to act as a guideline in preparing high viscosity pore fluids for dynamic centrifuge tests.

Soil Liquefaction?Induced Uplift of Underground Structures: Physical and Numerical Modeling

Chian, Siau Chen; Tokimatsu, Kohji; M.ASCE; Madabhushi, Santana Phani Gopal
Fonte: ASCE Publicador: ASCE
Tipo: Article; published version
EN
Relevância na Pesquisa
27.15%
This is the final published version. It first appeared at http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0001159.; Underground structures located in liquefiable soil deposits are susceptible to floatation following a major earthquake event. Such failure phenomenon generally occurs when the soil liquefies and loses its shear resistance against the uplift force from the buoyancy of the underground structure. Numerical modeling accompanied with centrifuge experiments with shallow circular structures has been carried out to investigate the floatation failure at different buried depths of the structure. The influence of the magnitude of input sinusoidal earthquake shaking was also studied. Both numerical and experimental results showed matching uplift response of the structures and acceleration and pore-pressure measurements in the liquefied soil deposit. A higher uplift displacement of the structure was observed for shallower buried depth, thereby indicating the influence of overlying soil weight against floatation. Results also showed that the structures commenced floatation in the presence of high excess pore pressure, but they ceased when the earthquake shaking stopped. The higher rate of uplift in stronger earthquake shaking further substantiates the dependency of the uplift to the shaking amplitude. A constant rate of uplift of the structure was attained after the soil liquefied...

Centrifuge modeling of earthquakes

Liu, Hsi-Ping; Hagman, Ronald L.; Scott, Ronald F.
Fonte: American Geophysical Union Publicador: American Geophysical Union
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /05/1978
Relevância na Pesquisa
27.15%
The major problem in scale modeling of crustal tectonic processes, namely, the requirement for a brittle modeling material of extremely low strength (∼0.1 bar) can be overcome by doing model tests under artificial gravity in a centrifuge. When conditions of dynamic similarity are observed, scale modeling, because of its controlled nature, can be an important tool supplementing field investigation, theoretical study, and numerical simulation of crustal tectonic processes. Fracture events by simulated tectonic stress loading in a model thrust fault (model dimensions: 20 cm depth × 25 cm × 27 cm) have been generated when the model is subject to 50 g in a centrifuge of 1.53 m radius. Measurements obtained are: the total loading force, the stress change at one location inside the fault zone, and model seismic signals recorded on the model top surface. With use of a scaled brittle model material, the model scales up to a prototype approximately 2.2 km depth × 2.8 km × 3.0 km in dimensions.

Cyclic Lateral Loading of Piles; Analysis of Centrifuge Tests

Scott, Ronald F.
Fonte: California Institute of Technology Publicador: California Institute of Technology
Tipo: Report or Paper; PeerReviewed Formato: application/pdf
Publicado em 04/06/1979
Relevância na Pesquisa
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In two previous reports (6,7) results were given of a number of cyclic lateral load tests on model piles loaded in a centrifuge. The tests results were obtained in the form of loads and deflections at the top of the pile and readings from strain gauges distributed down the pile; the latter are interpreted in the form of moments. In contrast to field tests, the centrifuge pile experiments are carried out in an extremely uniform medium consisting, in the tests discussed, of dry and wet sand in two test series. The result of this soil uniformity is that moment readings can be represented by a smooth and continuous curve. Erratic data due to alternately dense and loose soil layers are avoided. In the second report (7) the fitting of curves to this data was discussed briefly with reference to the use of a fifth-order spline function. The advantage of the technique is that the curve passes through all the data points in contrast with least squares or linear regression fits. In the latter, general curves are obtained representative of the pile deflections in some way which pass near but not necessarily through the data points. Errors in the data are inherently accepted in this method.

Dynamic centrifuge testing of cantilever retaining walls

Ortiz, L. Alexander
Fonte: California Institute of Technology Publicador: California Institute of Technology
Tipo: Report or Paper; PeerReviewed Formato: application/pdf
Publicado em 01/01/1982
Relevância na Pesquisa
27.15%
An investigation was made into the behavior of flexible cantilever walls retaining a cohesionless soil backfill and subjected to earthquake-type dynamic excitations using the centrifuge modelling technique. The study was motivated by the abundant observations of earth retaining structure damage and failures documented in earthquake damage reports. The "prototype" typical walls were designed using the traditional Mononobe-Okabe dynamic lateral earth pressure theory, were properly scaled for use in the centrifuge at 50 g's, and were subjected to lateral earthquake-like motions which were considered to be of realistic levels. The walls were amply instrumented with pressure and displacement transducers, accelerometers, and strain gages. Moment, pressure, shear, and displacement distributions (static, dynamic, and residual) were obtained. From the test data, some empirical curves for relating the upper bound responses of the retaining walls to the strong motion characteristics of the applied earthquakes were obtained.