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نتیجه جستجو - Anisotropic

تعداد مقالات یافته شده: 16
ردیف عنوان نوع
1 Layer number dependent optical and electrical properties of CVD grown two-dimensional anisotropic WS2
خواص نوری و الکتریکی وابسته به تعداد لایه WS2 ناهمسانگرد دوبعدی رشد CVD-2021
Engineering 2D transition metal dichalcogenides with precise control over layer number enable tuning of exciting optical and electrical properties at the nanoscale level. We report controlled one-step chemical vapour deposition growth of WS2 monolayer, bilayer, and trilayer for large scale manufacturing and demonstrate layer dependent changes in their work function, photoluminescence, and electrical conductivity. Raman, photoluminescence, and fluorescence imaging revealed that the base WS2 monolayer contains alternating triangular domains with different emission properties. It is observed that bilayer and trilayer grow selectively on less luminescent facet leading to fan-like morphology for second and third layers. We have systematically demonstrated that desired growth and areal coverage of bilayer and trilayer can be achieved by controlling WO3 precursor content. Kelvin probe force microscopic studies suggest a higher work function of thicker layers as compared to the monolayer. It was found that work function increases by 0.04 eV when thickness increases from monolayer to bilayer. FET device measurement on mono and bilayer shows n-type characteristics and two-fold higher photo-current in monolayer in comparison to the bilayer. The studied thickness dependence of the work function of WS2 is vital to the fabrication of metal contacts for WS2 based electronic and optoelectronic devices.
Keywords: CVD growth | 2D materials | PL segmentation | Optoelectronics | Transition metal dichalcogenides | KPFM
مقاله انگلیسی
2 Defect-engineering-enhanced electrical manipulation of anisotropic excitons in two-dimensional ReS2
دستکاری الکتریکی اکسیتون های ناهمسانگرد با نقص مهندسی در ReS2 دو بعدی-2021
Engineering the photoluminescence (PL) properties, such as emission peaks, intensity, and lifetime, is highly desirable for widespread applications. Electric control is a facile and feasible method, and electrical manipulation of the PL properties with a high efficiency becomes increasingly important. ReS2 has excellent environmental stability, distinctive interlayer decoupling, and strong anisotropic properties. Herein, taking ReS2 as a prototype material, we propose a novel strategy to enhance electrical control of anisotropic excitons in ReS2 by defect engineering. Sulfur vacancies have been introduced controllably by mild argon plasma treatment, and contribute to the anisotropic defect-related exciton emission whose polarization direction is almost the same as those of the excitons along the Re–S atomic chains. However, the conversion from the neutral excitons to the defect-related excitons significantly modulate the radiation recombination behavior under a lateral electric field. The defect engineering-enhanced electrical manipulation of anisotropic excitons paves the way towards an exciton engineering in new 2D electronic and optoelectronic devices.
Keywords: Photoluminescence | Anisotropic | Defect engineering | Electric control
مقاله انگلیسی
3 Coupled elasto-viscoplastic and damage model accounting for plastic anisotropy and damage evolution dependent on loading conditions
الاستو ویسکوپلاستیک همراه و مدل آسیب محاسبه ناهمسانگردی پلاستیک و تکامل آسیب وابسته به شرایط بارگذاری-2021
This work presents an unconventional fully coupled elasto-viscoplastic and damage constitutive model that is suitable for investigating the failure mechanism of metallic materials. The constitutive equations are developed within a finite elastoplasticity framework under the assumption of hypoelastic-based plasticity. Anisotropic plastic potential and plastic-induced anisotropy are modelled by means of the Hill48 yield criterion and a Chaboche-type non-linear kinematic hardening law, respectively. A modified Voce-type law is assumed for the isotropic hardening behaviour. A novel law is proposed to account for an evolution of the damage depending on the loading directions. The proposed model was implemented via user subroutine for the commercial finite elements (FE) software Abaqus/Standard and used for the prediction of the cyclic failure of lead-free solder materials, the crack formation in anisotropic AISI 316L steel specimens and the description of the failure behaviour of carbon steel notched round bars and flat grooved plates.
Keywords: Rate-dependent plasticity | Damage anisotropic evolution | Plastic anisotropy | Kinetic logarithmic spin | Hypoelastic-based plasticity
مقاله انگلیسی
4 Impact of Cattaneo law of heat conduction on an anisotropic Darcy- Bénard convection with a local thermal nonequilibrium model
تأثیر قانون اجرای Cattaneo از انتقال گرما در یک همرفت ناهمسانگرد Darcy- Bnnard با یک مدل عدم تعادل حرارتی موضعی-2020
The impact of Cattaneo heat flux law of heat conduction on the onset of thermal convection in an anisotropic (both mechanical and thermal) porous medium under a local thermal nonequilibrium (LTNE) condition is investigated. In the fluid phase, Fourier law of heat transfer is invoked. The results are analyzed for oxides of aluminium and copper solid skeletons. Contrary to the standard LTNE Darcy porous convection in an anisotropic porous layer, instability is triggered as an oscillatory convection under certain governing parametric values. The thermal and mechanical anisotropies of the porous medium display stabilizing and destabilizing influence on the onset of convection, respectively. There occurs a threshold value of scaled-interphase heat transfer coefficient at which the instability shifts from stationary to oscillatory convection. The threshold value decreases with an increase in solid thermal relaxation time and mechanical anisotropy parameters, while it rises with an upsurge in thermal anisotropy parameters. The effect of mechanical as well as thermal (fluid phase) anisotropy and solid thermal relaxation time parameters is to increase the convection cell size but a mixed performance is seen with solid thermal anisotropy parameter.
Keywords: Anisotropy | Porous medium | Linear stability | Cattaneo effect | Local thermal nonequilibrium
مقاله انگلیسی
5 Validity of Kirchhoff’s law for semitransparent films made of anisotropic materials
اعتبار قانون Kirchhoff برای فیلمهای نیمه شفاف ساخته شده از مواد ناهمسانگرد-2020
Kirchhoff’s law relates the emittance and absorptance of an object and has played an important role in radiative heat transfer calculations for many engineering applications. Along with the advancement of metamaterials, two-dimensional materials, and micro/nanoscale thermal radiation, Kirchhoff’s law has been revisited by several groups. Some studies also questioned the derivations and applicability of the statement of Kirchhoff’s law that appears in prevalent radiative heat transfer textbooks. The present study begins with a short review of Kirchhoff’s law for isotropic objects and its validity for both hemispherical emittance and directional emittance. Then, this study formulates Kirchhoff’s law for opaque anisotropic materials, considering both co-polarization and cross-polarization, and then for semitransparent films. It is shown that for macroscopic objects, as long as the Helmholtz reciprocity can be established, conven- tional expressions of Kirchhoff’s law can be applied for engineering thermal analysis and design even with anisotropic media and metamaterials. Numerical examples and results are provided, based on a nat- ural hyperbolic material and a magneto-optical material, to illustrate the reciprocity and applicability of Kirchhoff’s law.
Keywords: Absorptance | Anisotropy | Emittance | Kirchhoff’s law | Optical reciprocity
مقاله انگلیسی
6 A constitutive law for the viscous and tertiary creep responses of ice to applied stress
یک قانون اساسی برای واکنش خزش چسبناک یخ و سوم به استرس کاربردی-2020
Given the initial (secondary creep) viscous response of ice to applied stress, the subsequent tertiary creep is described by an orthotropic fabric evolution relation motivated by crystal rotation arguments. That is, the ice is described as a non-simple anisotropic fluid with dependence on the evolving deformation. Extension and modification of previous formulations are proposed, in which a general orthotropic flow law for stress includes terms which are quadratic functions of the strain-rate tensor, compared to previously analysed relations in which only linear in the strain-rate tensor terms were considered. Ice response functions in the extended law are constructed in such a way that the validity equalities and inequalities between the instantaneous directional viscosities at each stage of the tertiary creep are satisfied, and correlations with families of idealised uni-axial and simple shear tertiary creep curves for different applied stresses are possible. It is shown for a range of free parameters in the proposed orthotropic model how accurately the assumed uni-axial and shear creep curves can be approximated by the constructed response functions.
Keywords: Polar ice | Viscous creep | Anisotropic response | Orthotropy | Constitutive law
مقاله انگلیسی
7 Prediction of displacement in the equine third metacarpal bone using a neural network prediction algorithm
پیش بینی جابجایی در استخوان metacarpal سوم اسب با استفاده از الگوریتم پیش بینی شبکه عصبی-2019
Bone is a nonlinear, inhomogeneous and anisotropic material. To predict the behavior of bones expert systems are employed to reduce the computational cost and to enhance the accuracy of simulations. In this study, an artificial neural network (ANN) was used for the prediction of displacement in long bones followed by ex-vivo experiments. Three hydrated third metacarpal bones (MC3) from 3 thoroughbred horses were used in the experiments. A set of strain gauges were distributed around the midshaft of the bones. These bones were then loaded in compression in an MTS machine. The recordings of strains, load, Load exposure time, and displacement were used as ANN input parameters. The ANN which was trained using 3,250 experimental data points from two bones predicted the displacement of the third bone (R2 ≥ 0.98). It was suggested that the ANN should be trained using noisy data points. The proposed modification in the training algorithm makes the ANN very robust against noisy inputs measurements. The performance of the ANN was evaluated in response to changes in the number of input data points and then by assuming a lack of strain data. A finite element analysis (FEA) was conducted to replicate one cycle of force-displacement experimental data (to gain the same accuracy produced by the ANN). The comparison of FEA and ANN displacement predictions indicates that the ANN produced a satisfactory outcome within a couple of seconds, while FEA required more than 160 times as long to solve the same model (CPU time: 5 h and 30 min).
Keywords: Artificial neural network (ANN) | Displacement prediction | Finite element analysis (FEA) | Expert system | Long bones | Equine third metacarpal bone (MC3)
مقاله انگلیسی
8 Ultrasound image segmentation using a novel multi-scale Gaussian kernel fuzzy clustering and multi-scale vector field convolution
قطعه بندی تصویر اولتراسوند با استفاده از یک خوشه بندی فازی هسته ای گاوسی چند مقیاسی و پیچیدگی میدان بردار چند مقیاسی-2019
Ultrasound imaging is most popular technique used for breast cancer screening. Lesion segmentation is challenging step in characterization of breast ultrasound (US) based Computer Aided Diagnosis (CAD) systems due to presence of speckle noise, shadowing effect etc. The aim of this study is to develop an automatic lesion segmentation technique in breast US with high accuracy even in presence of noises, artifacts and multiple lesions. This article presents a novel clustering method called Multi-scale Gaussian Kernel induced Fuzzy C -means (MsGKFCM) for segmentation of lesions in automatically extracted Region of Interest (ROI) in US to delimit the border of the mass. Further, a hybrid approach using MsGKFCM and Multi-scale Vector Field Convolution (MsVFC) is proposed to obtain an accurate lesion margin in breast US images. Initially, the images are filtered using speckle reducing anisotropic diffusion (SRAD) technique. Subsequently, MsGKFCM is applied on filtered images to segment the mass and detect an appropriate cluster center. The detected cluster center is further used by MsVFC to determine the accurate lesion margin. The proposed technique is evaluated on 127 US images using measures such as Jaccard Index, Dice similarity, Shape similarity, Hausdroffdifference, Area difference, Accuracy, F -measure and analysis of variance (ANOVA) test. The empirical results suggest that the proposed approach can be used as an expert system to assist medical professionals by providing objective evidences in breast lesion detection. Results obtained are so far looking promising and effective in comparison to state-of-the-art algorithms.
Keywords: Ultrasound image segmentation | Speckle reduction | Multi-scale Gaussian kernel induced fuzzy | C -means | Multi-scale vector field convolution
مقاله انگلیسی
9 Improving the knowledge transfer from research to industry by developing demand-oriented design guidelines for fibre-reinforced plastics
بهبود دانش انتقال از تحقیقات به صنعت با ایجاد دستورالعمل طراحی با توجه به تقاضا برای پلاستیک تقویت شده فیبر-2018
Design guidelines as a knowledge documentation form is no longer a new topic in industry and science. The first one was already developed in 1954, and since then their number has been growing steadily. Today, design guidelines are published in numerous books, publications and specialist articles on various topics. Through the successful dissemination of design guidelines for traditional materials in industry, this concept of knowledge documentation was also adopted identically for fibre-reinforced plastics. However, there is a significant difference between designing with isotropic classical metals and anisotropic fibre-reinforced plastics. With the latter, the freedom of design is significant greater what allows individual design solutions and thus increases the complexity of design process. This, in turn, places different demands and expectations on design guidelines for this group of materials. The comprehensive analysis as well as interviews with industrial representatives showed, that current design guidelines for fiber-reinforced plastics do not meet the requirements of the industry. Some important aspects, which have a significant influence on product properties and therefore have to be considered in design, are missing holistically. Design guidelines are formulated in a general way similar to those for classic metals, which at most leads to the acquisition of general knowledge but allows not sufficiently its application in specific situations. Furthermore, there is no uniform specification as to how the knowledge should be documented in design guidelines in order to ensure their benefits through the application. This leads to different documentation forms, structure and depth of detail. This paper presents requirements on design guidelines for fibre-reinforced plastics in order to facilitate a good knowledge transfer in industrial fields of application and proposes a solution for a knowledge management system, which supports design engineers in different product development processes by providing relevant situation-specific information.
Keywords : Design guidelines for fibre-reinforced plastics ، knowledge management system ، knowledge transfer
مقاله انگلیسی
10 آنالیزی از پارامترهای ساختار الکترونیک، خواص جذب،NBO ، QTAIM، NMR از جذب هیدروژن سولفیددر مکان های مختلف از سطح خارجی نانولوله الومینیوم فسفید: یک مطالعه DFT
سال انتشار: 2015 - تعداد صفحات فایل pdf انگلیسی: 17 - تعداد صفحات فایل doc فارسی: 38
محاسبه تئوری تابع چگالی DFT در لایه B3LYP/6-31G* برای بررسی خواص جذبی و توصیف کوانتوم مولکولی از جذب H2S در سطح خارجی از نانولوله تک دیواره الومینیوم فسفیدALPNT ایجاد شد. فرکانس ارتعاشی و خواص فیزیکی مانند ممان دو قطبی، پتانسیل شیمیایی، سختی شیمیایی، و خواص شیمیایی الکترون دوستی برای تمام صورتبندی ها به صورت سیستماتیک بیان شد. همچنین برهمکنش گاز H2S و ALPNT در 5 توصیف فعالیت مانند انرژی تعادل سراسری (DESE(AB)) ، تغییرات انرژی منحصر به پذیرنده (DEA(B)) ، تغییرات انرژی منحصر به دهنده (DEB(A))، تفاوت الکترون دوستی جهانی در ALPNT و H2S گازی (Dw) و انتقال بار (DN) توضیح داده می شود. تمام جذب ها دارای فرایند بی ضرر الکترونیکی و برخوردهای قابل اغماض در انرژی گاز نانولوله ALP است. محاسبات اربیتال پیوند طبیعی مشتق شده از محاسبات اربیتال اتم طبیعی است. جذب فیزیکی مولکول H2S در سطحی از نانولوله ALP اولیه همراه با انرژی جذبی در حدود 20-کیلو ژول بر مول است. تئوری AIM همچنین برای امتحان کردن خواصی از نقاط بحرانی پیوند استفاده می شود. این کار با دانسیته الکترونی و لاپلاسین انجام می شود. انرژی جذب مولکول H2S برای جلوگیری از بازگشت ALPNT خیلی بزرگ نیست. بنابراین سنسور دارای زمان بازگشت کوتاهی است. ساختار الکترونی ALPNT اولیه و گاز H2S جذب شده بر مدل ALPNTبا کمک محاسبات DFT برای پارامترحفاظت شیمیایی (CS) از اتم 27Al و 31P امتحان می شود. پارامترهای CS ایزوتروپی و غیر ایزوتروپی تقسیم شده بر روی لایه ها در دتکتور شبیه به محیط الکترونیک به وسیله مکان اتم در هر لایه ایجاد می شود.
کلمات کلیدی: نانولوله های فسفید آلومینیوم | سولفید هیدروژن | نظریه کاربردی تراکم | NBO | NMR | تراکم حالت
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