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[en] Two random sequential adsorption (RSA) methods for the generation of the representative volume element (RVE) were developed for the short fiber reinforced elastomer composites (SFECs) with large fiber aspect ratio. These two RSA methods use two different fiber intersection test methods respectively (the ‘straightforward method’ developed by Rahman and the method of Tian et al). Also, a new iteration method was developed to realize geometric periodicity. The maximum fiber fraction that can be reached by two RSA methods were obtained respectively and compared with the theoretical and experimental formulas by Evans and Gibson. The results show that the ‘straightforward method’ may result in misjudgments in some special cases, especially when the fiber aspect ratio is large. Therefore, the RSA method using the ‘straightforward method’ is not exactly a perfect RSA method. In contrast, there is no fiber overlap found in the RVEs established by the RSA method using the fiber intersection test method of Tian et al. Moreover, the maximum fiber volume fraction that can be generated by this RSA method is close to the theoretical limits when the fiber aspect ratio is larger than 50 and meets the requirement of common SFECs with large fiber aspect ratio. Therefore, the RSA method using the fiber intersection test method of Tian et al is considered to be suitable for the satisfactory generation of the RVE for SFECs with large fiber aspect ratios. (paper)
[en] The purpose of the NSTX Center Stack Upgrade project is to expand the NSTX operational space and thereby the physics basis for next-step ST facilities. The plasma aspect ratio (ratio of plasma major to minor radius) of the upgrade is increased to 1.5 from the original value of 1.26, which increases the cross sectional area of the center stack by a factor of ∼ 3 and makes possible higher levels of performance and pulse duration.
[en] Nanoimprint lithography using vertically aligned carbon nanostructures as stamps is reported. The functionality of the stamp is demonstrated through lift-off and etch-back processes after pattern replication. The imprint process is robust and the stamp structures survived more than 50 consecutive imprints. In this paper we demonstrate this for feature sizes ranging from 80 nm to 200 μm where the aspect ratio of the individual nanostructures surpasses 1:5 with a pitch down to 100 nm. This demonstration opens up the possibility of utilizing vertically grown carbon nanostructures for manufacturing extremely high aspect ratio and small pitch stamps for nanoimprint lithography.
[en] The present study aims to analyze the buckling behavior of Euler–Bernoulli nanobeam in conjunction with a novel fractional nonlocal model namely conformable fractional nonlocal model. Fractional models are getting more popular among the researchers because of its applicability and fixability to handle many complex physical phenomena which are not possible to model with integer operators. Also, the main advantage of fractional models over integer model is its applicability to handle both the integer and noninteger operators which makes it much more flexible in term of real-world application. In this regards, the nonlocal constitutive relation is developed in conjunction with conformable fractional derivatives and fractional strain energy to analyze the buckling behavior of Euler–Bernoulli Nanobeam. In this study, the Simply Supported-Simply Supported (SS), Clamped-Simply Supported, and Clamped-Clamped boundary conditions are taken into the investigation with the help of the Differential Quadrature Method (DQM). Critical buckling load parameters are computed for the SS, CS, and CC boundary conditions from generalized eigenvalue problem. Graphical, as well as tabular results, are calculated by using MATLAB programmes and effects of various parameters such as fractional parameter, nonlocal parameter, aspect ratio on critical buckling load parameters extensively studied. (paper)
[en] Highlights: • Wall jet data are presented and differences with free jet are highlighted. • Symmetry properties are imposed on 3D velocity measurements by suitable averaging. • Mean vorticity components are estimated by interpolation of velocity measurements. • The axial vorticity is related to the development of saddle back velocity profiles. • Axial vorticity equation terms provide insight/understanding on flow development. - Abstract: Experimental results on the near field development of a turbulent rectangular wall jet with aspect ratio 10 that issues from a sharp-edged orifice at Reh ∼ 23,000 are presented and discussed, in comparison with results obtained in a free jet with identical initial conditions. Hot wire X-probe measurements on cross plane grids provide information on the 3D characteristics of the flow field. This work, besides presenting the main features of the jet, focuses on the effect of vorticity on the development of specific flow field characteristics. Mean vorticity components were estimated by interpolation and derivation from the mean and turbulent velocity measurements and the symmetries of the flow field were imposed by suitable averaging. Several terms of the axial vorticity equation are presented and discussed to uncover some complex flow physics, related e.g. to axis switching and the formation of a dumbbell shape of the jet outline, in the early stages of development.
[en] Highlights: • Hashin-Hansen model is developed for tensile modulus of polymer/CNT nanocomposites. • Nanoparticles network is assumed as a third phase above percolation threshold. • A good agreement is reported between the experimental results and the predictions. • The relations between modulus and main parameters are justified. - Abstract: In this paper, a conventional Hashin-Hansen model is developed to analyze the tensile modulus of polymer/CNT nanocomposites above the percolation threshold. This model for composites containing dispersed particles utilizes the aspect ratio of the nanofiller (α), the number of nanotubes per unit area (N), the percolation threshold () and the modulus of the filler network (EN), assuming that the filler network constitutes a third phase in the nanocomposites. The experimental results and the predictions agree well, verifying the proposed relations between the modulus and the other parameters in the Hashin-Hansen model. Moreover, large values of “α”, “N” and “EN” result in an improved modulus of the polymer/CNT nanocomposites, while a low percolation threshold results in a high modulus.
[en] A new scheme of toggle magnetoresistance random access memory (MRAM) based on magnetostatically coupled (MSC) bilayers without antiferromagnetic coupling is investigated. Analysis shows that the toggle-MRAM operation and necessary storage lifetime can be achieved by choosing an appropriate aspect ratio for MSC bilayers having reasonable area and thickness. The attenuation factor defined as the ratio of the effective MSC field to the demagnetizing field is found to be essential to obtain the toggle-mode operation
[en] In this report, a design method is proposed for in-plane MEMS electrostatic energy harvesters with comb drives. Dependent on the device layer thickness and the achievable aspect ratio of the DRIE process, either the overlapping-area-change or the gap-closing converter has higher output power than the other. Two prototypes of MEMS electret energy harvesters are developed to verify the present design method
[en] The four-field-period device TJ-II has a major radius of 1.5 m and an average plasma radius of 0.10--0.25 m, with a typical plasma aspect ratio AP of 10. In the infinite aspect ratio, helically symmetric limit, the region of the stability to low-n modes has been shown to extend to average betas of at least 40%, for a relatively highly indented plasma. It is possible to approximate the helically symmetric limit from the actual TJ-II parameters increasing the number of toroidal periods NT and choosing the major radius RO such as to obtain a constant helical pitch h = NT/RO. In this way the aspect ratio per period is fixed. In this work we analyze a shear-less TJ-II configuration with a rotational transform per period of 0.36 and a vacuum magnetic well of 3.5%. By taking for NT the values NT = 3, 4, 5, 8, 10, 11, 12, 19 and 100 a sequence of equilibria is generated. These equilibria are calculated with the fixed boundary version of the VMEC code. The Mercier stability properties are then analyzed