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排序方式： 共有716条查询结果，搜索用时 15 毫秒
61.
Athanasios Iliopoulos John G. Michopoulos 《International journal for numerical methods in engineering》2013,95(4):313-330
Full‐field strain measurement techniques are based on computing the spatial derivatives of numerical or functional approximations of the underlying displacement fields extracted from digital imaging methods. These methods implicitly assume that the medium satisfies the strain compatibility conditions, which are only true in the case of a continuum body that remains continuum throughout its deformation history. In the present work, we introduce a method that can be used to calculate the strain components directly from typical digital imaging data, without the need of the continuum hypothesis and the need for displacement field differentiation. Thus, it enables the measurement of strain fields from imaged surfaces that may or may not contain discontinuities. Numerical comparisons are performed on the basis synthetic data produced from an analytical solution for an elastically orthotropic open‐hole domain in tension. For performance comparison purposes, the mean absolute error distributions are calculated for the cases of both the traditional meshless random grid method, and the direct strain method introduced herein. It is established that the more refined representation of strain provided by our present approach is more accurate everywhere in the domain, but most importantly, near its boundaries. Published 2013. This article is a US Government work and is in the public domain in the USA. 相似文献
62.
63.
Nikitas Siannas Christina Zacharaki Polychronis Tsipas Dong Jik Kim Wassim Hamouda Cosmin Istrate Lucian Pintilie Martin Schmidbauer Catherine Dubourdieu Athanasios Dimoulas 《Advanced functional materials》2024,34(8):2311767
Synapses play a vital role in information processing, learning, and memory formation in the brain. By emulating the behavior of biological synapses, electronic synaptic devices hold the promise of enabling high-performance, energy-efficient, and scalable neuromorphic computing. Ferroelectric memristive devices integrate the characteristics of both ferroelectric and memristive materials and present a far-reaching potential as artificial synapses. Here, it is reported on a new ferroelectric device on silicon, a field-effect memristor, consisting of an epitaxial ultrathin ferroelectric Hf0.5Zr0.5O2 film sandwiched between an epitaxial highly doped oxide semiconductor SrTiO3-δ and a top metal. Upon a low voltage of less than 2 V, the field-effect modulation in the semiconductor enables to access multiple states. The device works in a large time domain ranging from milliseconds down to tens of nanoseconds. By gradually switching the polarization by identical pulses, the ferroelectric diode devices can dynamically adjust the synaptic strength to mimic short- and long-term memory plasticity. Ionic contributions due to redox processes in the oxide semiconductor beneficially influence the device operation and retention. 相似文献
64.
Athanasios Drosos;Agapi Dima;Panagiotis Kandylis;Theano Petsi;Poonam S. Nigam;Athanasios A. Koutinas;Maria Kanellaki; 《Starch - St?rke》2024,76(3-4):2300044
Composite biocatalysts (CB) consisting of amylases and Saccharomyces cerevisiae immobilized separately on bacterial nanocellulose (BNC) are used for the process of simultaneous saccharification and fermentation (SSF) of starch (5%, w/v) for bioethanol production. Parameters such as: i) addition of phosphates and/or divalent metal-ions salts during the co-immobilization process of the amylases, ii) required co-immobilization time, iii) fermentation temperature and initial pH of starch, and iv) CB as single or double freeze-dried are studied. The utilization of double freeze-dried CB exhibits fermentation efficiency 89.9% and ethanol yield 0.51 g ethanol g−1 starch while the single freeze-dried CB 81.1% and 0.46 g ethanol g−1 starch, respectively. In the case of double freeze-dried CB, the fermentation efficiency decreases by only 27.1% in two-recycling batches, while in the single freeze-dried one decreases by 51.3%. The application of double freeze-dried CB can be used for: i) the eco-friendly biosynthesis of value-added bioproducts; ii) the promising option for fuel-grade bioethanol through starchy wastes or foodstuff starchy residues treatment, and iii) the implementation of industrialization. Finally, to simulate an industrial process of one-step SSF of starch by applying a CB model, a technoeconomic analysis is evaluated, where using BNCs makes the bioprocess cost-effective and environmentally favorable, simultaneously. 相似文献
65.
66.
Ana Paula Barreira Dora Agapito Thomas Panagopoulos Maria Helena Guimarães 《Urban Research & Practice》2017,10(2):156-177
The number of cities experiencing population decline has been increasing worldwide. Despite the existence of theoretical propositions of shrinkage as an opportunity to increase levels of residential satisfaction, the issue has not been addressed empirically. This article contributes to fill this gap by assessing, through survey, the residential satisfaction of inhabitants of four shrinking Portuguese cities.
Data were analysed by means of a tree-decision approach: the Chi-squared Automatic Interaction Detection analysis. A sense of safety is the feature that best discriminates inhabitants’ level of residential satisfaction. The results show that shrinkage due to deindustrialisation processes is detrimental to residential satisfaction. 相似文献
67.
Athanasios C. Rakitzis Christian H. Weiß Philippe Castagliola 《Quality and Reliability Engineering International》2017,33(2):413-430
The zero‐inflated Poisson distribution serves as an appropriate model when there is an excessive number of zeros in the data. This phenomenon frequently occurs in count data from high‐quality processes. Usually, it is assumed that these counts exhibit serial independence, while a more realistic assumption is the existence of an autocorrelation structure between them. In this work, we study control charts for monitoring correlated Poisson counts with an excessive number of zeros. Zero‐inflation in the process is captured via appropriate integer‐valued time series models. Extensive numerical results are provided regarding the performance of the considered charts in the detection of changes in the mean of the process as well as the effects of zero‐inflation on them. Finally, a real‐data practical application is given. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
68.
Calvin D'Souza Michael Apicella Ahmad El-kharouf Emmanuel Stamatakis Martin Khzouz Athanasios Stubos Evangelos I. Gkanas 《国际能源研究杂志》2020,44(14):11597-11613
In light of stricter emissions regulations and depleting fossil fuel reserves, fuel cell vehicles (FCVs) are one of the leading alternatives for powering future vehicles. An open-cathode, air-cooled proton exchange membrane fuel cell (PEMFC) stack provides a relatively simple electric generation system for a vehicle in terms of system complexity and number of components. The temperature within a PEMFC stack is critical to its level of performance and the electrochemical efficiency. Previously created computational models to study and predict the stack temperature have been limited in their scale and the inaccurate assumption that temperature is uniform throughout. The present work details the creation of a numerical model to study the temperature distribution of an 80-cell Ballard 1020ACS stack by simulating the cooling airflow across the stack. Using computational fluid dynamics, a steady-state airflow simulation was performed using experimental data to form boundary conditions where possible. Additionally, a parametric study was performed to investigate the effect of the distance between the stack and cooling fan on stack performance. Model validation was performed against published results. The temperature distribution across the stack was identical for the central 70% of the cells, with eccentric temperatures observed at the stack extremities, while the difference between coolant and bipolar plate temperatures was approximately 10°C at the cooling channel outlets. The results of the parametric study showed that the fan-stack distance has a negligible effect on stack performance. The assumptions regarding stack temperature uniformity and measurement were challenged. Lastly, the hypothesis regarding the negligible effect of fan-stack distance on stack performance was confirmed. 相似文献
69.
The current work presents a parametric study, which involves different generalized nonlinear mechanical formulations with different damping characteristics to account for the interaction between a monopile‐supported offshore wind turbine and the surrounding soil. The novelty of the study lies in the fact that recently developed nonlinear mechanical models used so far for the simulation of high‐damping rubber isolators are introduced to describe the nonlinear hysteretic soil behavior. More specifically, the first generalized mechanical model consists of a combination of elastoplastic and trilinear elastic elements (labeled as model 3), while the second model consists of trilinear hysteretic models connected in parallel with trilinear elastic springs and hysteretic dampers used to ensure that the unloading stiffness will be as close as possible to the initial stiffness of the system (labeled as model 4). These newly developed models are compared with well‐known models within the industry, namely, a model that comprises elastoplastic elements (labeled as model 1) and a model that comprises trilinear elastic springs (labeled as model 2). All these models provide exactly the same effective stiffness, but on the other hand different levels of damping are involved in each one of them. The goal of the present work is 3‐fold, introducing novel mechanical models for the simulation of soil behavior, to investigate the effect of different soil damping levels in the response of offshore wind turbines and to highlight the limitations of the commonly used models within the industry. To this end, the differences between the response due to different levels of damping characteristics and modeling approaches are shown, highlighting the importance of soil damping in the overall response of the system. 相似文献
70.
Manlio Bacco Marco Colucci Alberto Gotta Charilaos Kourogiorgas Athanasios D. Panagopoulos 《International Journal of Satellite Communications and Networking》2019,37(4):331-342
The use of unmanned aerial vehicles (UAVs) is rising in several application fields. This work deals with the communication challenges in UAV swarms, or flying ad hoc network (FANET), when taking into account non–line‐of‐sight scenarios. The use of satellites is a necessity in such operating conditions; thus, this work provides architectural considerations and performance assessments when several (FANETs) share an uplink random access satellite channel, fed with M2M/IoT traffic generated from on‐board sensors, to be reliably delivered to a remote ground destination. 相似文献