241 research outputs found
Damage assessment of a full-scale bridge based on the response surface method
As a combination of statistical and mathematical techniques, response surface models have been recently found to be capable of substituting FE models in model updating iterations by using explicit mathematical functions to represent the relationship between the inputs and outputs of a physical system. However, the literature related to this topic is still scarce despite the wide employment of the response surface method in many engineering realms such as chemistry and industry. Due to that, this paper attempts to propose a systematic damage assessment procedure based on the model updating strategy using the response surface method. Instead of the qualitative evaluation traditionally used, here the 2(k) factorial design is employed to screen out non-significant updating parameters by quantitative statistical analysis, which considerably improves the screening reliability. Meanwhile, the central composite design is adopted to construct response surface models substituting original FE models during updating. The proposed method is used to detect the damage existing in an experimental full-scale bridge. The results demonstrate the merits of this method in its easy implementation and high computation efficiency, especially for the bridge case
Damage identification of a reinforced concrete frame by finite element model updating using damage parameterization
This paper develops a sensitivity-based updating method to identify the damage in a tested reinforced concrete (RC) frame modeled with a two-dimensional planar finite element (FE) by minimizing the discrepancies of modal frequencies and mode shapes. In order to reduce the number of unknown variables, a bidimensional damage (element) function is proposed, resulting in a considerable improvement of the optimization performance. For damage identification, a reference FE model of the undamaged frame divided into a few damage functions is firstly obtained and then a rough identification is carried out to detect possible damage locations, which are subsequently refined with new damage functions to accurately identify the damage. From a design point of view, it would be useful to evaluate, in a simplified way, the remaining bending stiffness of cracked beam sections or segments. Hence, an RC damage model based on a static mechanism is proposed to estimate the remnant stiffness of a cracked RC beam segment. The damage model is based on the assumption that the damage effect spreads over a region and the stiffness in the segment changes linearly. Furthermore, the stiffness reduction evaluated using this damage model is compared with the FE updating result. It is shown that the proposed bidimensional damage function is useful in producing a well-conditioned optimization problem and the aforementioned damage model can be used for an approximate stiffness estimation of a cracked beam segment
Effect of magnetic field correlation length on the gamma-ray pulsar halo morphology under anisotropic diffusion
Anisotropic diffusion is one of the potential interpretations for the
morphology of the Geminga pulsar halo. It interprets the observed
slow-diffusion phenomenon through a geometric effect, assuming the mean
magnetic field direction around Geminga is closely aligned with the line of
sight toward it. However, this direction should not extend further than the
correlation length of the turbulent magnetic field , which could be
pc or less. We first revisit the scenario and show that the halo
asymmetry predicted by this scenario is mainly contributed by the electrons
located beyond the ``core" section around Geminga, which has a length of
pc. Then, considering the directional variation of the magnetic field beyond
the core section, we take one magnetic field configuration as an example to
investigate the possible halo morphology. The predicted morphology has some
different features compared to the scenario. The current
experiments may already be able to test these features. In addition, we use a
semi-analytical method to solve the anisotropic propagation equation, which
offers significant convenience compared to numerical approaches.Comment: 15 pages, 7 figure
Features of the gamma-ray pulsar halo HESS J1831098
Gamma-ray pulsar halos are ideal indicators of cosmic-ray propagation in
localized regions of the Galaxy and electron injection from pulsar wind
nebulae. HESS~J1831098 is a candidate pulsar halo observed by both H.E.S.S.
and HAWC experiments. We adopt the flux map of the H.E.S.S. Galactic plane
survey and the spectrum measurements of H.E.S.S. and \textit{Fermi}-LAT to
study HESS~J1831098. We find that HESS~J1831098 meets all the criteria
for a pulsar halo. The diffusion coefficient inside the halo and the conversion
efficiency from the pulsar spin-down energy to the electron energy are both
similar to the Geminga halo, a canonical pulsar halo. The injection spectrum
can be well described by an exponentially-cutoff power law. However, the needed
power-law term is very hard with if the diffusion coefficient is
spatially and temporally independent. Considering the possible origins of the
slow-diffusion environment, we adopt the two-zone diffusion model and the
time-delayed slow-diffusion model. Both the models can interpret the H.E.S.S.
and \textit{Fermi}-LAT results with a milder . A modified injection time
profile may have a similar effect.Comment: 15 pages (one column), 4 figures, 1 tabl
Effectiveness of laparoscopic sleeve gastrectomy for weight loss and obesity-associated co-morbidities: a 3-year outcome from Mainland Chinese patients
AbstractBackgroundLaparoscopic sleeve gastrectomy (LSG) is becoming a stand-alone bariatric surgery for obesity, but its effectiveness for Mainland Chinese patients remains unclear.ObjectivesTo evaluate the effectiveness and safety of LSG for Mainland Chinese patientsSettingA tertiary hospitalMethodsRetrospective analysis of patients admitted for LSG between January 2011 and February 2012 was performed. Medium-term outcome measures were: total weight loss (%TWL), excess weight loss (%EWL), co-morbidities, improvement, and complications.ResultsSeventy patients (body mass index [BMI] 40.8±5.9 kg/m2) underwent LSG, comprising 40 women and 30 men. The most common co-morbidity was diabetes (n = 29, 41.4%). Lost to follow-up rate for weight loss was 15.7%, 31.4%, and 41% at 1, 2, and 3 years. The %TWL was 34.4±6.1, 34.7±6.2 and 33.7±7.1 at 1, 2, and 3 years. The %EWL increased to 77.1±13.0, 77.9±12.2 and 77.2±13.1 at 1, 2, and 3years. The proportions of patients having successful weight loss were 100% or 85% at 3 years according the definition of %TWL>10% or %EWL>50%. Approximately 79.3%, 51.7%, and 44.8% of patients completed follow-up for glycemic control at each time point, respectively. The proportions of patients with optimal glycemic control (fasting blood glucose [FBG]<5.6 mmol/L; hemoglobin A1C [HbA1C]<6.5%) were 47.9%, 60.0%, and 69.2% at 1, 2, and 3years. The weight loss and glycemic control effect may be greater in the high BMI group (≥40 kg/m2). Early and late complications occurred in 8.6% and 7.1% of patients during follow-up.ConclusionsLSG is effective in weight loss and glycemic control and is safe for Mainland Chinese obese patients, especially for patients with a BMI≥40 kg/m2
A stochastic model updating method for parameter variability quantification based on response surface models and Monte Carlo simulation
Stochastic model updating must be considered for quantifying uncertainties inherently existing in real-world engineering structures. By this means the statistical properties,instead of deterministic values, of structural parameters can be sought indicating the parameter variability. However, the implementation of stochastic model updating is much more complicated than that of deterministic methods particularly in the aspects of theoretical complexity and low computational efficiency. This study attempts to propose a simple and cost-efficient method by decomposing a stochastic updating process into a series of deterministic ones with the aid of response surface models and Monte Carlo simulation. The response surface models are used as surrogates for original FE models in the interest of programming simplification, fast response computation and easy inverse optimization. Monte Carlo simulation is adopted for generating samples from the assumed or measured probability distributions of responses. Each sample corresponds to an individual deterministic inverse process predicting the deterministic values of parameters. Then the parameter means and variances can be statistically estimated based on all the parameter predictions by running all the samples. Meanwhile, the analysis of variance approach is employed for the evaluation of parameter variability significance. The proposed method has been demonstrated firstly on a numerical beam and then a set of nominally identical steel plates tested in the laboratory. It is found that compared with the existing stochastic model updating methods, the proposed method presents similar accuracy while its primary merits consist in its simple implementation and cost efficiency in response computation and inverse optimization
An earthquake slip zone is a magnetic recorder
International audienceDuring an earthquake, the physical and the chemical transformations along a slip zone lead to an intense deformation within the gouge layer of a mature fault zone. Because the gouge contains ferromagnetic minerals, it has the capacity to behave as a magnetic recorder during an earthquake. This constitutes a conceivable way to identify earthquakes slip zones. In this paper, we investigate the magnetic record of the Chelungpu fault gouge that hosts the principal slip zone of the Chi-Chi earthquake (Mw 7.6, 1999, Taiwan) using Taiwan Chelungpu-fault Drilling Project core samples. Rock magnetic investigation pinpoints the location of the Chi-Chi mm-thick principal slip zone within the 16-cm thick gouge at ~1 km depth. A modern magnetic dipole of Earth magnetic field is recovered throughout this gouge but not in the wall rocks nor in the two other adjacent fault zones. This magnetic record resides essentially in two magnetic minerals; magnetite in the principal slip zone, and neoformed goethite elsewhere in the gouge. We propose a model where magnetic record: 1) is preserved during inter-seismic time, 2) is erased during co-seismic time and 3) is imprinted during post-seismic time when fluids cooled down. We suggest that the identification of a stable magnetic record carried by neoformed goethite may be a signature of friction-heating process in seismic slip zone
Successful and efficient DNA extraction from processed pangolin scales
A successful method for total DNA extraction from crude and processed pangolin scales was established. After pretreatment in the soaking solution for cleansing, the scales were prepared into fine powders and treated with PBS buffer containing 0.1% collagenase and 0.1% trypsin for 24 h, followed by digestion with proteinase K at 55°C for 120 h. Phenol-chloroform extraction was used to obtain the total DNA. PCR amplification for mitochondrial cytochrome b (cytb) gene was successful using the extracted DNA as the template, and sequencing of the amplified fragments confirmed Manis origin of the scale samples. With an efficiency up to 100%, this method is expected to provide a powerful tool in molecular identification of processed as well as crude pangolin scales
miRTarBase update 2014: an information resource for experimentally validated miRNA-target interactions
MicroRNAs (miRNAs) are small non-coding RNA molecules capable of negatively regulating gene expression to control many cellular mechanisms. The miRTarBase database (http://mirtarbase.mbc.nctu.edu.tw/) provides the most current and comprehensive information of experimentally validated miRNA-target interactions. The database was launched in 2010 with data sources for >100 published studies in the identification of miRNA targets, molecular networks of miRNA targets and systems biology, and the current release (2013, version 4) includes significant expansions and enhancements over the initial release (2010, version 1). This article reports the current status of and recent improvements to the database, including (i) a 14-fold increase to miRNA-target interaction entries, (ii) a miRNA-target network, (iii) expression profile of miRNA and its target gene, (iv) miRNA target-associated diseases and (v) additional utilities including an upgrade reminder and an error reporting/user feedback system
The LAMOST Survey of Background Quasars in the Vicinity of the Andromeda and Triangulum Galaxies -- II. Results from the Commissioning Observations and the Pilot Surveys
We present new quasars discovered in the vicinity of the Andromeda and
Triangulum galaxies with the LAMOST during the 2010 and 2011 observational
seasons. Quasar candidates are selected based on the available SDSS, KPNO 4 m
telescope, XSTPS optical, and WISE near infrared photometric data. We present
509 new quasars discovered in a stripe of ~135 sq. deg from M31 to M33 along
the Giant Stellar Stream in the 2011 pilot survey datasets, and also 17 new
quasars discovered in an area of ~100 sq. deg that covers the central region
and the southeastern halo of M31 in the 2010 commissioning datasets. These 526
new quasars have i magnitudes ranging from 15.5 to 20.0, redshifts from 0.1 to
3.2. They represent a significant increase of the number of identified quasars
in the vicinity of M31 and M33. There are now 26, 62 and 139 known quasars in
this region of the sky with i magnitudes brighter than 17.0, 17.5 and 18.0
respectively, of which 5, 20 and 75 are newly-discovered. These bright quasars
provide an invaluable collection with which to probe the kinematics and
chemistry of the ISM/IGM in the Local Group of galaxies. A total of 93 quasars
are now known with locations within 2.5 deg of M31, of which 73 are newly
discovered. Tens of quasars are now known to be located behind the Giant
Stellar Stream, and hundreds behind the extended halo and its associated
substructures of M31. The much enlarged sample of known quasars in the vicinity
of M31 and M33 can potentially be utilized to construct a perfect astrometric
reference frame to measure the minute PMs of M31 and M33, along with the PMs of
substructures associated with the Local Group of galaxies. Those PMs are some
of the most fundamental properties of the Local Group.Comment: 26 pages, 6 figures, AJ accepte
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