561 research outputs found
A-priori Validation of Subgrid-scale Models for Astrophysical Turbulence
We perform a-priori validation tests of subgrid-scale (SGS) models for the
turbulent transport of momentum, energy and passive scalars. To this end, we
conduct two sets of high-resolution hydrodynamical simulations with a
Lagrangian code: an isothermal turbulent box with rms Mach number of 0.3, 2 and
8, and the classical wind tunnel where a cold cloud traveling through a hot
medium gradually dissolves due to fluid instabilities. Two SGS models are
examined: the eddy diffusivity (ED) model wildly adopted in astrophysical
simulations and the "gradient model" due to Clark et al. (1979). We find that
both models predict the magnitude of the SGS terms equally well (correlation
coefficient > 0.8). However, the gradient model provides excellent predictions
on the orientation and shape of the SGS terms while the ED model predicts
poorly on both, indicating that isotropic diffusion is a poor approximation of
the instantaneous turbulent transport. The best-fit coefficient of the gradient
model is in the range of [0.16, 0.21] for the momentum transport, and the
turbulent Schmidt number and Prandtl number are both close to unity, in the
range of [0.92, 1.15].Comment: ApJ accepted; analysis code available at
https://github.com/huchiayu/Lapriori.j
Improved Antireflection Properties of an Optical Film Surface with Mixing Conical Subwavelength Structures
Based on finite difference time domain method, an optical film surface with mixing conical subwavelength structures is numerically investigated to improve antireflection property. The mixing conical subwavelength structure is combined with the pure periodic conical subwavelength structures and the added small conical structures in the gap between the pure periodic conical subwavelength structures. The antireflection properties of two types of subwavelength structures with different aspect ratios in spectral range of 400–800 nm are analyzed and compared. It is shown that, for the mixing type, the average reflectance is decreased and the variances of the reflectance are evidently smaller. When the added structure with a better aspect ratio exists, the average reflectance of the surface can be below 0.30%. Obviously, the antireflection properties of the optical film surface with mixing conical subwavelength structures can be improved
Interference-Aware Deployment for Maximizing User Satisfaction in Multi-UAV Wireless Networks
In this letter, we study the deployment of Unmanned Aerial Vehicle mounted
Base Stations (UAV-BSs) in multi-UAV cellular networks. We model the multi-UAV
deployment problem as a user satisfaction maximization problem, that is,
maximizing the proportion of served ground users (GUs) that meet a given
minimum data rate requirement. We propose an interference-aware deployment
(IAD) algorithm for serving arbitrarily distributed outdoor GUs. The proposed
algorithm can alleviate the problem of overlapping coverage between adjacent
UAV-BSs to minimize inter-cell interference. Therefore, reducing co-channel
interference between UAV-BSs will improve user satisfaction and ensure that
most GUs can achieve the minimum data rate requirement. Simulation results show
that our proposed IAD outperforms comparative methods by more than 10% in user
satisfaction in high-density environments.Comment: 5 pages, 3 figures, to appear in IEEE Wireless Communications Letter
Twin-Free GaAs Nanosheets by Selective Area Growth: Implications for Defect-Free Nanostructures
Highly perfect, twin-free GaAs nanosheets grown on (111)B surfaces by selective area growth (SAG) are demonstrated. In contrast to GaAs nanowires grown by (SAG) in which rotational twins and stacking faults are almost universally observed, twin formation is either suppressed or eliminated within properly oriented nanosheets are grown under a range of growth conditions. A morphology transition in the nanosheets due to twinning results in surface energy reduction, which may also explain the high twin-defect density that occurs within some III–V semiconductor nanostructures, such as GaAs nanowires. Calculations suggest that the surface energy is significantly reduced by the formation of {111}-plane bounded tetrahedra after the morphology transition of nanowire structures. By contrast, owing to the formation of two vertical {11̅0} planes which comprise the majority of the total surface energy of nanosheet structures, the energy reduction effect due to the morphology transition is not as dramatic as that for nanowire structures. Furthermore, the surface energy reduction effect is mitigated in longer nanosheets which, in turn, suppresses twinning
Bian Zheng Lun Zhi
Background. Limited scientific evidence supports the positive effects of traditional Chinese medicine (TCM) for treating dysmenorrhea. Thus, an observation period of 3 months could verify the ancient indication that TCM treatments effectively alleviate menstrual cramps in women with primary dysmenorrhea or endometriosis. Methods. A prospective, nonrandomized study (primary dysmenorrhea and endometriosis groups) was conducted in women with dysmenorrhea for more than three consecutive menstrual cycles. All patients received TCM prescriptions based on bian zheng lun zhi theory 14 days before menstruation for a period of 12 weeks. Pain intensity was evaluated using a 10-cm visual analogue scale and two validated questionnaires (the Menstrual Distress Questionnaire and the World Health Organization Quality of Life questionnaire). Results. Of the initial 70 intent-to-treat participants, the women with dysmenorrhea reported significant alleviation of cramps during menstruation after the 12-week TCM treatment. Mixed model analysis revealed that TCM prescriptions were more effective in alleviating fatigue, hot flashes, dizziness, painful breasts, excitement, and irritability in the primary dysmenorrhea group (N=36) than in the endometriosis group (N=34). Conclusion. TCM prescriptions based on syndrome differentiation theory might be a potentially viable choice for treating painful menstruation and premenstrual symptoms after ruling out endometriosis
Prevalence of restless legs syndrome in migraine patients with and without aura: a cross-sectional, case-controlled study
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