Results 1 - 10 of 6648
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[en] The present work is focused on the experimental study of flame dynamics in preheated meso-scale straight channels of various aspect ratios (2, 5, 12 and 15) and inlet dimensions.Premixed methane-air mixture were used for the reported experiments. To maintain a positive wall temperature gradient inside the channel, the lower part of the rectangular channels were heated at a constant temperature using an external electric heater. Laminar premixed flames were stabilized inside these channels. Various flame propagation modes such as concave, planar, and convex flames with respect to unburned mixture. Concave flames lead to flashback whereas convex flames lead to blowout. Increase in aspect ratio and decrease of flow velocity leads to flame flashback. (paper)
[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] 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] The aspect ratio (AR) of the vertical axis wind rotors defined in this paper as the ratio between the height and the diameter of the rotor is an important factor when considering the performance of the rotors. However, choosing the most appropriate AR when designing a wind rotor, based on literature review, is not fully reliable as different sources point out contradictory data. This paper presents an analysis regarding the influence of the AR on rotors performance based on experimental data. (paper)
[en] Channel holes (CH) and common source line (CSL) etch are two of key process challenges in 3D NAND. With the increase of stacked layers, the aspect ratio become larger than 50:1. One of key issues is CSL tilting to CH, leading to serious word-line leakage and block fail in array. In this work, it is demonstrated that trapped charges brought by CH etch process can affect the CSL slit etch process seriously, and lead to CSL tilting issue. Charging model was used to explain the phenomenon and is validated by experiments. An approach by removing the backside films for charges release via poly-Si deposition film is proposed to solve this issue. This work provides effective approach to solve the special deep trench tilting issue in 3D NAND memory processes development. (paper)