This paper deals with the identification of material parameters in a constitutive model for sheet metals using the bending moment versus curvature diagrams obtained by cyclic bending tests. The model ...can describe the cyclic strain hardening by the isotropic hardening and the Bauschinger effect by the kinematic hardening. An optimization technique based on the iterative multipoint approximation concept was used for the identification of the material parameters. This paper describes the experimentation, the fundamentals and the technique of the identification problem, and the verification of this approach.
This paper addresses a constitutive model of cyclic plasticity with special emphasis on the yield-point phenomena. In order to point out the deformation characteristics of a mild steel, four types of ...experiments were conducted, i.e. uniaxial tension at several crosshead speeds, cyclic straining, and stress- and strain-controlled ratchetting. A viscoplastic constitutive model of cyclic plasticity is proposed on the premise that the phenomena of sharp yield point and the subsequent abrupt yield drop result from rapid dislocation multiplication and the stress-dependence of dislocation velocity. Besides, cyclic plasticity behavior, such as the Bauschinger effect, cyclic hardening/softening characteristics and ratchet-strain accumulation, is described by some kinematic and isotropic hardening rules. The cyclic stress–strain responses predicted by this model agree well with the corresponding experimental results.
Elastic–plastic behavior of two types of steel sheets for press-forming (an aluminum-killed mild steel and a dual-phase high strength steel of 590
MPa ultimate tensile strength) under in-plane cyclic ...tension–compression at large strain (up to 25% strain for mild steel and 13% for high strength steel) have been investigated. From the experiments, it was found that the cyclic hardening is strongly influenced by cyclic strain range and mean strain. Transient softening and workhardening stagnation due to the Bauschinger effect, as well as the decrease in Young's moduli with increasing prestrain, were also observed during stress reversals. Some important points in constitutive modeling for such large-strain cyclic elasto-plasticity are discussed by comparing the stress–strain responses calculated by typical constitutive models of mixed isotropic–kinematic hardening with the corresponding experimental observations.
Finite element method (FEM), using a viscoplastic constitutive model proposed by Yoshida Int. J. Plasticity 16 (2000) 359, has been applied to simulate the propagation of Lüders band for an annealed ...low-carbon steel strip under uniaxial tension test. By reducing the thickness of corresponding element, additional stress concentration is introduced into the FEM model. Calculated results show that the formation and propagation of Lüders band are affected by the level of stress concentration existing at the ends of the specimen.
Origin of Planetary Impactors in the Inner Solar System Strom, Robert G; Malhotra, Renu; Ito, Takashi ...
Science (American Association for the Advancement of Science),
09/2005, Letnik:
309, Številka:
5742
Journal Article
Recenzirano
Odprti dostop
Insights into the history of the inner solar system can be derived from the impact cratering record of the Moon, Mars, Venus, and Mercury and from the size distributions of asteroid populations. Old ...craters from a unique period of heavy bombardment that ended approximately3.8 billion years ago were made by asteroids that were dynamically ejected from the main asteroid belt, possibly due to the orbital migration of the giant planets. The impactors of the past approximately3.8 billion years have a size distribution quite different from that of the main belt asteroids but very similar to that of near-Earth asteroids.
Context. In the past decade, more than one hundred asteroid models were derived using the lightcurve inversion method. Measured by the number of derived models, lightcurve inversion has become the ...leading method for asteroid shape determination. Aims. Tens of thousands of sparse-in-time lightcurves from astrometric projects are publicly available. We investigate these data and use them in the lightcurve inversion method to derive new asteroid models. By having a greater number of models with known physical properties, we can gain a better insight into the nature of individual objects and into the whole asteroid population. Methods. We use sparse photometry from selected observatories from the AstDyS database (Asteroids – Dynamic Site), either alone or in combination with dense lightcurves, to determine new asteroid models by the lightcurve inversion method. We investigate various correlations between several asteroid parameters and characteristics such as the rotational state and diameter or family membership. We focus on the distribution of ecliptic latitudes of pole directions. We create a synthetic uniform distribution of latitudes, compute the method bias, and compare the results with the distribution of known models. We also construct a model for the long-term evolution of spins. Results. We present 80 new asteroid models derived from combined data sets where sparse photometry is taken from the AstDyS database and dense lightcurves are from the Uppsala Asteroid Photometric Catalogue (UAPC) and from several individual observers. For 18 asteroids, we present updated shape solutions based on new photometric data. For another 30 asteroids we present their partial models, i.e., an accurate period value and an estimate of the ecliptic latitude of the pole. The addition of new models increases the total number of models derived by the lightcurve inversion method to ~200. We also present a simple statistical analysis of physical properties of asteroids where we look for possible correlations between various physical parameters with an emphasis on the spin vector. We present the observed and de-biased distributions of ecliptic latitudes with respect to different size ranges of asteroids as well as a simple theoretical model of the latitude distribution and then compare its predictions with the observed distributions. From this analysis we find that the latitude distribution of small asteroids (D < 30 km) is clustered towards ecliptic poles and can be explained by the YORP thermal effect while the latitude distribution of larger asteroids (D > 60 km) exhibits an evident excess of prograde rotators, probably of primordial origin.
The near-Earth Asteroid 25143 Itokawa, the target of the Japanese space mission Hayabusa, was observed in June, 2004 with the Torino photopolarimeter attached at the 2.15 m telescope of the El ...Leoncito Observatory (Argentina). The degree of linear polarization in five colors was measured over a wide range of phase angles, between 40° and 80°. The data obtained are sufficient to derive an estimate of the asteroid's albedo of
0.24
±
0.01
, which is in good agreement with the
S-type taxonomic classification of this object. The phase-polarization curve has been sampled in
UBVRI colors, covering a wide range of phase angles that cannot be reached by Earth-based observations of Main Belt asteroids.
An investigation was conducted involving 255 renal transplant
recipients in the state of Goiás, Central Brazil, to determine the
prevalence of hepatitis C virus (HCV), its risk factors, the genotypes
...involved, and the level of alanine aminotransferase (ALT) present in
the patients. All serum samples were tested for anti-HCV antibodies and
HCV RNA. Forty-one patients were anti-HCV and/or HCV RNA positive,
resulting in an overall HCV infection prevalence of 16.1% (95% CI:
11.9-21.3). A multivariate analysis of risk factors showed that a
history of blood transfusions without anti-HCV screening, the length of
time spent on hemodialysis, and renal transplantation before 1994 are
all associated with HCV positivity. In HCV-positive patients, only
12.2% had ALT levels above normal. Twenty-eight samples were genotyped
as genotype 1, subtypes 1a (62.5%) and 1b (31.3%), and two samples
(6.2%) were genotype 3, subtype 3a. These data show a high prevalence
of HCV infection and low ALT levels in the studied population. The risk
factor analysis findings emphasize the importance of public health
strategies such as anti-HCV screening of candidate blood and organ
donors, in addition to the stricter adoption of hemodialysis-specific
infection control measures. The present study also demonstrates that
HCV genotype 1 (subtype 1a) is predominant in this population
Orexins are hypothalamic neuropeptides involved in the regulation of sleep, appetite and arousal. An altered orexin system has been implicated in the pathophysiology of psychiatric disorders. This ...study aimed to examine whether plasma orexin-A levels differ in patients with schizophrenia, major depressive disorder (MDD), or bipolar disorder (BD) compared to in healthy controls. We also examined the possible correlations between plasma orexin-A levels and clinical variables.
All participants were Japanese. The sample consisted of 80 patients with schizophrenia (42 women, 52.5%; mean age 36.8 years), 80 patients with MDD (43 women, 53.8%; 43.7 years), and 40 patients with BD (24 women, 60%; 41.1 years), as well as 80 healthy controls (48 women, 60%; 47.0 years). Plasma orexin-A levels were quantified by an enzyme-linked immunosorbent assay.
Mean orexin-A levels were significantly different across the four diagnostic groups (F=4.09; df=3;
=0.007,
=0.06). In particular, the patients with BD showed significantly lower orexin-A levels than did the controls. When the median value of the control group (109.8 pg/ml) was set as a cut-off value, subjects whose orexin-A levels were below the cut-off were more common in all psychiatric groups (schizophrenia: 73.8%,
=9.56, df=1,
=0.003, OR=2.81, 95% CI: 1.45 to 5.45,
=0.57; MDD: 78.5%,
=14.02, df=1,
<0.001, OR=3.65, 95% CI: 1.82 to 7.29,
=0.72; BD: 87.5%,
=16.0, df=1,
<0.001, OR=7.00, 95% CI: 2.49 to 19.70,
=1.07). We found no association between plasma orexin-A levels and any clinical symptoms, depression severity, or medication doses.
Our results suggest that plasma orexin-A levels are reduced in patients with BD.
This paper is a summary from the results of the first systematic survey of small Main-Belt Asteroids (MBAs) using 8.2 m Subaru telescope. We searched about 3 square-degree sky area near opposition ...and near the ecliptic. About 1100 moving objects down to
R∼26 mag (including very slow Kuiper Belt Objects) were detected. In this survey, the observational arc for each moving object was only 2 hours, so that only their semi-major axis (
a) and inclination (
I) were estimated statistically based on their apparent motions. We found that (1) the sky number density of MBAs is about 290 per square-degree down to
R∼24.4 mag (for MBAs), (2) the slope of the cumulative size distribution for detected MBAs ranging from 0.5 to 1 km in diameter is considerably shallower (about 1.2) than that for large MBAs (about 1.8) and (3) the shallowness of the size distribution slope for sub-km MBAs is more conspicuous in the outer part of the main-belt than in the inner part. These findings suggest that the number of small MBAs is much more depleted than an estimate extrapolated from the existing statistics of large asteroids. We also propose a new form of the power-law distribution with a size-dependent slope to express the observed sub-km MBA distribution.
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