641 research outputs found
Experimental characterisation of fatigue crack growth based on the CTOD measured from crack tip displacement fields using DIC
The current work presents an experimental study on the use of the crack tip opening displacement (CTOD) to evaluate its ability to characterise fatigue crack growth. A methodology is developed to measure and to analyse the CTOD from experimental data. The vertical displacements obtained by implementing digital image correlation (DIC) on growing fatigue cracks are used to measure the CTOD. Two fatigue tests at stress ratios of 0.1 and 0.6 were conducted on compact tension (CT) specimens manufactured from a 1 mm thick sheet of commercially pure titanium. A sensitivity analysis to explore the effect of the position selected behind the crack tip for the CTOD measurement was performed. The analysis of a full loading cycle allowed identifying the elastic and plastic components of the CTOD. The plastic CTOD was found to be directly related to the nonlinear zone (i.e., plastic deformation) generated at the crack tip during fatigue propagation. Moreover, a linear relationship between da/dN and ÎCTODp independent of the stress ratio was found. Results show that the CTOD can be used as a viable alternative to the stress intensity factor range (ÎK) in characterising fatigue crack propagation since the parameter considers the fatigue threshold and crack shielding in an intrinsic way
Relevância da Infecção VHC em Coagulopatias CongÊnitas
Introdução: A infecção pelo vĂrus da hepatite C (VHC) em doentes com coagulopatias congĂŠnitas (CC), como consequĂŞncia da terapĂŞutica empregue entre os anos 70 e 80 com transfusĂŁo de derivados de plasma humano, constitui um problema de saĂşde substancial e relevante.
Objectivos: Anålise e avaliação da relevância representada pela infecção VHC e suas complicaçþes no tratamento duma população de doentes com CC.
MĂŠtodos: AnĂĄlise retrospectiva duma sĂŠrie de 161 doentes com CC tratados no Serviço de Imunohemoterapia do Centro Hospitalar de Lisboa Central (Lisboa, Portugal). RevisĂŁo sistemĂĄtica de processos clĂnicos. Elaboração duma base de dados compreendendo a informação reunida e estudo estatĂstico das suas variĂĄveis: idade, gĂŠnero, tipo e gravidade da coagulopatia e modalidade de tratamento. Relativamente Ă infecção por VHC: genotipo, tipo e duração do tratamento, frequĂŞncia de resposta mantida ao tratamento e recidiva, co-infecçþes e complicaçþes major e minor.
Resultados: Dos 161 doentes 65 (40%) estão infectados pelo VHC. Dos doentes com hemofilia A: 36% são grave e 62% dos quais estão infectados pelo VHC; 9% moderada com 57%; 25% ligeira com 20%. No grupo da hemofilia B: 8% são grave com 23% infectados e 6% moderada ou ligeira com 10%. Relativamente ao grupo com doença de von Willebrand: 12% são tipo 2 com 16% infectados e 4% tipo 3 com 86%. Uma coorte de 26 doentes foi submetida a terapêutica para a infecção pelo VHC, com o primeiro doente a receber tratamento em 1993. Destes, 5 eram seropositivos para o VIH. O tratamento variou de monoterapia com interferão a terapêutica combinada de interferão ou interferão-peguilado com ribavirina.
ConclusĂľes: A infecção pelo VHC representa uma complicação significativa do tratamento empregue no passado na população em estudo. Considerando que a maioria destes doentes foi infectada nos finais dos anos 70 e inĂcio dos anos 80 assim como a evolução natural da infecção pelo VHC em doentes sem CC, prevĂŞ-se que a prevalĂŞncia de complicaçþes major deverĂĄ aumentar significativamente nos prĂłximos anos. Ă de suma importância a implementação de medidas profilĂĄcticas na revisĂŁo e adaptação dos protocolos de seguimento de forma a prevenir a progressĂŁo da patologia hepĂĄtica nestes doentes
Experimental evaluation of CTOD in constant amplitude fatigue crack growth from crack tip displacement fields
Š 2017, Gruppo Italiano Frattura. All rights reserved. In the current work an experimental study of the crack tip opening displacement (CTOD) is performed to evaluate the ability of this parameter to characterise fatigue crack growth. A methodology is developed to measure and to analyse the CTOD from experimental data. The vertical displacements measured by implementing Digital Image Correlation on growing fatigue cracks are used to measure the CTOD. Fatigue tests at R ratios of 0.1 and 0.6 were conducted on compact-tension specimens manufactured from commercially pure titanium. A sensitivity analysis was performed to explore the effect of the position selected behind the crack tip for the CTOD measurement. The analysis of a full loading cycle allowed identifying the elastic and plastic components of the CTOD. The plastic CTOD was found to be directly related to the plastic deformation at the crack tip. Moreover, a linear relationship between da/dN and the plastic CTOD for both tests was observed. Results show that the CTOD can be used as a viable alternative to ÎK in characterising fatigue crack propagation because the parameter considers fatigue threshold and crack shielding in an intrinsic way. This work is intended to contribute to a better understanding of the different mechanisms driving fatigue crack growth and the address the outstanding controversy associated with plasticity-induced fatigue crack closure
Characterisation of fatigue crack growth using the CJP model of crack tip fields or plastic CTOD
This paper provides an update on the current status of work that has been done to validate the CJP model of crack tip stresses and also summarises some findings from linked work that has used DIC to determine the range of plastic crack tip opening displacement as a correlator of fatigue crack growth rate. The paper considers several ways of calculating an effective range of stress intensity factor that have been proposed in various papers, as the preferred option is not yet fully clear. It further highlights the potential value, in terms of elucidating the mechanisms involved in plasticity-induced crack tip shielding, arising from data obtained from using two different DIC techniques on the same specimens
Evaluation of small-scale yielding boundary using digital image correlation results
In this work, the boundaries of small-scale yielding (SSY) and large-scale yielding (LSY) have been experimentally evaluated from the analysis of crack tip opening displacement (CTOD) measured by digital image correlation (DIC). According to a previous numerical work, the ratio between the elastic CTOD range and the total CTOD range (Îδe/Îδt) defines the boundaries of SSY conditions and LSY. Three materials have been studied, commercially pure titanium and 2024-T3 and 7050-T6 aluminum alloys, tested at different stress ratio values. SSY conditions are shown to dominate when Îδe/Îδt ⼠79% and âĽ78% for titanium and the two aluminum alloys, respectively. In addition, LSY can be established when Îδe/Îδt ⤠66.3% and â¤67.2% for titanium and for 2024-T3 and 7050-T6 aluminum alloys, respectively. Transition or LSY conditions are more probable in fatigue tests conducted at low R ratio and for crack lengths above 40% with respect to the width of the specimen
Chilling requirement for seed germination and phenological observations on peach cultivars
Performance of CMS muon reconstruction in pp collision events at sqrt(s) = 7 TeV
The performance of muon reconstruction, identification, and triggering in CMS
has been studied using 40 inverse picobarns of data collected in pp collisions
at sqrt(s) = 7 TeV at the LHC in 2010. A few benchmark sets of selection
criteria covering a wide range of physics analysis needs have been examined.
For all considered selections, the efficiency to reconstruct and identify a
muon with a transverse momentum pT larger than a few GeV is above 95% over the
whole region of pseudorapidity covered by the CMS muon system, abs(eta) < 2.4,
while the probability to misidentify a hadron as a muon is well below 1%. The
efficiency to trigger on single muons with pT above a few GeV is higher than
90% over the full eta range, and typically substantially better. The overall
momentum scale is measured to a precision of 0.2% with muons from Z decays. The
transverse momentum resolution varies from 1% to 6% depending on pseudorapidity
for muons with pT below 100 GeV and, using cosmic rays, it is shown to be
better than 10% in the central region up to pT = 1 TeV. Observed distributions
of all quantities are well reproduced by the Monte Carlo simulation.Comment: Replaced with published version. Added journal reference and DO
The novel object recognition memory: neurobiology, test procedure, and its modifications
Animal models of memory have been considered as the subject of many scientific publications at least since the beginning of the twentieth century. In humans, memory is often accessed through spoken or written language, while in animals, cognitive functions must be accessed through different kind of behaviors in many specific, experimental models of memory and learning. Among them, the novel object recognition test can be evaluated by the differences in the exploration time of novel and familiar objects. Its application is not limited to a field of research and enables that various issues can be studied, such as the memory and learning, the preference for novelty, the influence of different brain regions in the process of recognition, and even the study of different drugs and their effects. This paper describes the novel object recognition paradigms in animals, as a valuable measure of cognition. The purpose of this work was to review the neurobiology and methodological modifications of the test commonly used in behavioral pharmacology
Performance of CMS muon reconstruction in pp collision events at sqrt(s) = 7 TeV
The performance of muon reconstruction, identification, and triggering in CMS
has been studied using 40 inverse picobarns of data collected in pp collisions
at sqrt(s) = 7 TeV at the LHC in 2010. A few benchmark sets of selection
criteria covering a wide range of physics analysis needs have been examined.
For all considered selections, the efficiency to reconstruct and identify a
muon with a transverse momentum pT larger than a few GeV is above 95% over the
whole region of pseudorapidity covered by the CMS muon system, abs(eta) < 2.4,
while the probability to misidentify a hadron as a muon is well below 1%. The
efficiency to trigger on single muons with pT above a few GeV is higher than
90% over the full eta range, and typically substantially better. The overall
momentum scale is measured to a precision of 0.2% with muons from Z decays. The
transverse momentum resolution varies from 1% to 6% depending on pseudorapidity
for muons with pT below 100 GeV and, using cosmic rays, it is shown to be
better than 10% in the central region up to pT = 1 TeV. Observed distributions
of all quantities are well reproduced by the Monte Carlo simulation.Comment: Replaced with published version. Added journal reference and DO
X-ray emission from the Sombrero galaxy: discrete sources
We present a study of discrete X-ray sources in and around the
bulge-dominated, massive Sa galaxy, Sombrero (M104), based on new and archival
Chandra observations with a total exposure of ~200 ks. With a detection limit
of L_X = 1E37 erg/s and a field of view covering a galactocentric radius of ~30
kpc (11.5 arcminute), 383 sources are detected. Cross-correlation with Spitler
et al.'s catalogue of Sombrero globular clusters (GCs) identified from HST/ACS
observations reveals 41 X-rays sources in GCs, presumably low-mass X-ray
binaries (LMXBs). We quantify the differential luminosity functions (LFs) for
both the detected GC and field LMXBs, whose power-low indices (~1.1 for the
GC-LF and ~1.6 for field-LF) are consistent with previous studies for
elliptical galaxies. With precise sky positions of the GCs without a detected
X-ray source, we further quantify, through a fluctuation analysis, the GC LF at
fainter luminosities down to 1E35 erg/s. The derived index rules out a
faint-end slope flatter than 1.1 at a 2 sigma significance, contrary to recent
findings in several elliptical galaxies and the bulge of M31. On the other
hand, the 2-6 keV unresolved emission places a tight constraint on the field
LF, implying a flattened index of ~1.0 below 1E37 erg/s. We also detect 101
sources in the halo of Sombrero. The presence of these sources cannot be
interpreted as galactic LMXBs whose spatial distribution empirically follows
the starlight. Their number is also higher than the expected number of cosmic
AGNs (52+/-11 [1 sigma]) whose surface density is constrained by deep X-ray
surveys. We suggest that either the cosmic X-ray background is unusually high
in the direction of Sombrero, or a distinct population of X-ray sources is
present in the halo of Sombrero.Comment: 11 figures, 5 tables, ApJ in pres
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