In order to model the fatigue crack propagation of engineering structures with high efficiency, a novel multi-grid (MG) reanalysis method is formulated in this study under the framework of the ...extended finite element method (XFEM). In the numerical approach, the MG is firstly used to establish connections between the mesh with no crack and the meshes with crack. The transfer operators are constructed only in the initial MG analysis and will be reused in the crack propagation analysis. Then, the equilibrium equations of crack propagation can be efficiently solved through the MG iterations. Several numerical examples are investigated to verify the validity of this method and it is shown that the presented algorithm is very accurate and can efficiently reduce the computational cost.
•MG reanalysis and XFEM are combined for fatigue crack growth analysis.•This algorithm can achieve high level of accuracy through MG iterations.•Huge amount of computational cost can be saved.
We investigate the thermodynamics of Schwarzschild–Tangherlini black hole in the context of the generalized uncertainty principle (GUP). The corrections to the Hawking temperature, entropy and the ...heat capacity are obtained via the modified Hamilton–Jacobi equation. These modifications show that the GUP changes the evolution of the Schwarzschild–Tangherlini black hole. Specially, the GUP effect becomes susceptible when the radius or mass of the black hole approaches the order of Planck scale, it stops radiating and leads to a black hole remnant. Meanwhile, the Planck scale remnant can be confirmed through the analysis of the heat capacity. Those phenomena imply that the GUP may give a way to solve the information paradox. Besides, we also investigate the possibilities to observe the black hole at the Large Hadron Collider (LHC), and the results demonstrate that the black hole cannot be produced in the recent LHC.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
•Ensemble learning is utilized to predict the remaining fatigue life.•Multiple machine learning methods are aggregated to improve the performance.•The present algorithm is vry effective and stable.
...An effective approach is proposed to predict the remaining fatigue life (RFL) of structures with stochastic parameters. The extended finite element method (XFEM) was firstly used to produce a large amount of datasets associated with structural responses and RFL. Then, a RFL prediction model was developed using the ensemble learning algorithm, which employed multiple machine-learning algorithms to learn useful degradation patterns of the structures from the XFEM datasets. Several numerical examples were investigated to evaluate the performance of proposed RFL prediction approach. The analysis results demonstrate that the ensemble learning is able to effectively predict the RFL of the structures with stochastic parameters.
In this work, we proposed a novel approach for the prediction of residual useful life (RUL) of structures through appropriately combining the phase field method and deep-learning. In this new ...approach, the phase field method is firstly utilized to obtain the structural responses of crack growth, which are further preserved as images. Then, the convolutional neural network (CNN) is constructed to establish a predictive model. The proposed approach is a hybrid model of both physical and data-driven techniques, which can build a bridge between traditional computational fracture mechanics and deep learning algorithms. Several numerical cases are studied to evaluate the prediction performance of the proposed approach. The analysis results demonstrate that the present approach is able to predict the RUL of the structures with high level of accuracy.
•Phase field method is used to generate images containing structural information.•CNN is trained and validated for the RUL prediction of structures.•This hybrid approach can achieve high level of prediction accuracy.
Extraction of essential oil from
Cuminum cyminum seeds using a combination of organic solvent with low boiling point and steam distillation was explored. The effect of different parameters, such as ...particle size (40, 60, 80
mesh), temperature (°C) 10, 15, 20 and extraction time (3, 5, 8
h), on the extraction yield was investigated using three-level orthogonal array design. The experimental results showed that the temperature had the largest effect on the yield of the extract (oleoresin), followed by extraction time and particle size. The optimum parameters, such as temperature, particle size, and extraction time were in turn 20
°C, 80
mesh, and 8
h. Essential oil of
C. cyminum seeds obtained by supercritical fluid extraction (SFE), hydrodistillation (HD), combination technology of organic solvent with low boiling point and steam distillation (OS-SD) were further analysed by gas chromatographic/mass spectrometric detection to compare the extraction methods. Forty-five compounds in the
C. cyminum essential oil were identified, showing that the composition of the extraction by different methods was mostly similar, whereas relative concentration of the identified compounds was apparently different. General characteristics of the
C. cyminum essential oil obtained by different methods were further compared, and OS-SD was considered as the optimum process among the three processes to obtain
C. cyminum essential oil for high quality, simple technology and low cost.
•XFEM and CA are combined to deal with fatigue growth analysis.•Accurate results can be obtained using only a small number of basic vectors.•The computational effort savings of presented algorithm is ...significant.
This study aims to reduce the computational cost in the simulation of fatigue crack growth process. Extended finite element method and combined approximations (CA) are integrated to form an efficient algorithm for such analysis. In the CA approach, binomial series are used as high quality basis vectors for the reduced basis expression and then crack propagation path can be predicted without solving the complete set of system equations. The validity of presented algorithm is fully investigated through several numerical examples. From these results, it is shown that the presented algorithm is very accurate and can save huge amounts of computational effort.
The extension of the cosmic-ray spectrum beyond 1 petaelectronvolt (PeV; 10
electronvolts) indicates the existence of the so-called PeVatrons-cosmic-ray factories that accelerate particles to PeV ...energies. We need to locate and identify such objects to find the origin of Galactic cosmic rays
. The principal signature of both electron and proton PeVatrons is ultrahigh-energy (exceeding 100 TeV) γ radiation. Evidence of the presence of a proton PeVatron has been found in the Galactic Centre, according to the detection of a hard-spectrum radiation extending to 0.04 PeV (ref.
). Although γ-rays with energies slightly higher than 0.1 PeV have been reported from a few objects in the Galactic plane
, unbiased identification and in-depth exploration of PeVatrons requires detection of γ-rays with energies well above 0.1 PeV. Here we report the detection of more than 530 photons at energies above 100 teraelectronvolts and up to 1.4 PeV from 12 ultrahigh-energy γ-ray sources with a statistical significance greater than seven standard deviations. Despite having several potential counterparts in their proximity, including pulsar wind nebulae, supernova remnants and star-forming regions, the PeVatrons responsible for the ultrahigh-energy γ-rays have not yet been firmly localized and identified (except for the Crab Nebula), leaving open the origin of these extreme accelerators.
Free-electron lasers have been successfully operated with ultrahigh brightness and excellent transverse coherence at X-ray wavelengths. One of the next goals for further improvements is full ...coherence. An obvious approach is to seed the free-electron laser interaction using a conventional source that has good temporal coherence. Here, we show the first lasing of a free-electron laser with an echo-enabled harmonic generation scheme, which shows great promise for producing coherent lasing at short wavelengths, even in the X-ray regime. The experiment was conducted at a test facility that combines a 135.4 MeV electron accelerator with an amplifier consisting of a series of undulator magnets. Lasing was achieved at the third harmonic of the seed with a gain of ∼100,000 over spontaneous radiation. The measurements show typical exponential growth and excellent spectral characteristics, as well as good intensity stability.
High-energy photons from the Crab Nebula
The Crab Nebula contains a pulsar that excites the surrounding gas to emit high-energy radiation. The combination of the pulsar's youth and nearby location ...makes the nebula the brightest gamma-ray source in the sky. The LHAASO Collaboration report observations of this source at energies of tera– to peta–electron volts, extending the spectrum of this prototypical object. They combine these data with observations at lower energies to model the physics of the emission process. The multiwave-length data can be explained by a combination of synchrotron radiation and inverse Compton scattering.
Science
, abg5137, this issue p.
425
Detection of the Crab Nebula at peta–electron volt energies constrains the gamma-ray emission mechanism.
The Crab Nebula is a bright source of gamma rays powered by the Crab Pulsar’s rotational energy through the formation and termination of a relativistic electron-positron wind. We report the detection of gamma rays from this source with energies from 5 × 10
−4
to 1.1 peta–electron volts with a spectrum showing gradual steepening over three energy decades. The ultrahigh-energy photons imply the presence of a peta–electron volt electron accelerator (a pevatron) in the nebula, with an acceleration rate exceeding 15% of the theoretical limit. We constrain the pevatron’s size between 0.025 and 0.1 parsecs and the magnetic field to ≈110 microgauss. The production rate of peta–electron volt electrons, 2.5 × 10
36
ergs per second, constitutes 0.5% of the pulsar spin-down luminosity, although we cannot exclude a contribution of peta–electron volt protons to the production of the highest-energy gamma rays.
Background
Various minimally invasive approaches have been described for infected necrotizing pancreatitis. This article describes a modified minimal‐access retroperitoneal pancreatic necrosectomy ...(MARPN) procedure assisted by gas insufflation.
Methods
This retrospective, observational study documented patients who had undergone a step‐up MARPN between 1 January 2010 and 31 December 2016. A minimum follow‐up of 1 year was required for inclusion. The step‐up approach involved percutaneous catheter drainage followed by the modified MARPN and necrosectomy. If more than one access site was needed it was categorized as complex MARPN.
Results
Of 212 patients with infected necrotizing pancreatitis, 164 (77·4 per cent) underwent a step‐up approach. The median number of percutaneous catheter drains and MARPN procedures was 3 (range 1–7) and 1 (1–6) respectively. Ninety patients (54·9 per cent) underwent complex MARPN. For residual necrosis after MARPN, three patients (1·8 per cent) underwent sinus tract gastroscopy, and 11 (6·7 per cent) had sinography combined with a tube change. However, operations in 13 patients (7·9 per cent) required conversion to open surgery. Postoperative complications developed in 103 patients (62·8 per cent). The mortality rate was 6·1 per cent (10 deaths).
Conclusion
A step‐up approach using a modified MARPN for infected necrotizing pancreatitis is a reasonable option.
Antecedentes
Los procedimientos mínimamente invasivos se han convertido en los más frecuentes para el tratamiento de necrosis pancreáticas infectadas. El objetivo de este estudio fue presentar un procedimiento de necrosectomía pancreática retroperitoneal de acceso mínimo (minimal‐access retroperitoneal pancreatic necrosectomy, MARPN) modificado y asistido mediante insuflación de gases, así como evaluar su seguridad y eficacia.
Métodos
Se realizó un análisis retrospectivo y observacional de los datos de un hospital desde el 1 de enero de 2010 hasta el 31 de diciembre de 2016. Se incluyeron en el análisis todos los pacientes en los que realizó un abordaje por etapas, que consistía en el drenaje percutáneo mediante la colocación de un catéter seguido de un procedimiento MARPN modificado, en los que se dispusiese de un seguimiento postoperatorio mínimo de 1 año. El MARPN en el lado derecho y la necrosectomía realizada a través de más de un acceso se clasificaron como MARPN complejo. Se evaluaron los resultados radiológicos y quirúrgicos.
Resultados
De 212 pacientes con necrosis pancreática infectada, en 164 (77,4%) se realizó un abordaje por etapas. La mediana del número de drenajes percutáneos y procedimientos MARPN fue 3 (rango, 1‐7) y 1 (rango, 1‐6), respectivamente. En 90 pacientes (54,9%) se realizó un MARPN complejo. Para la exéresis de necrosis residual después de un MARPN, en 3 pacientes (1,8%) se realizó mediante gastroscopia y en 11 pacientes (6,7%) con un recambio de drenaje bajo control radiológico. En 13 pacientes (7,9%) fue necesaria la reconversión a cirugía abierta. Hubo complicaciones postoperatorias en 103 pacientes (62,8%). La tasa de mortalidad fue del 6,1% (n = 10).
Conclusión
El abordaje por etapas con un MARPN modificado es seguro y efectivo en el tratamiento de la necrosis pancreática infectada.
Minimally invasive approaches have been used increasingly in the management of infected necrotizing pancreatitis. This study presents a modified minimal‐access retroperitoneal pancreatic necrosectomy procedure assisted by carbon dioxide insufflation, instead of saline. A clear field of view without necrotic debris floating in saline makes the technique safe and efficient.
High degree of success
VIDEO
Presented in part to the Joint Congress of the Sixth Biennial Congress of the Asian–Pacific Hepato‐Pancreato‐Biliary Association and the 29th Meeting of the Japanese Society of Hepato‐Biliary‐Pancreatic Surgery, Yokohama, Japan, June 2017
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