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51.
A method to identify complex Young’s modulus of viscoelastic materials using forced longitudinal vibration of slender rods is proposed.The method differs from the beam one.Experimental tests were carried out at room temperature with different lengths in 108 mm, 100 mm,90 mm,83.5 mm,80 mm.74.5 mm,70 mm for the polycarbonate bars,and the curves of ratios A2/A1 between two ends of a viscoelastic bar versus frequencies are obtained, furthermore,the corresponding 3 dB bandwidth and the storage and loss modulus can be calculated.Sufficient number of obtained complex Young’s modulus at different frequency allows us to calculate other ones using the least square method.If the step of the tested frequency is 5 Hz,the maximum error of results can be less than 6%.By comparison with the measurement methods which the previous literature mentioned,this new method simplifies the calculation,and the physical meaning appears apparently and clearly. 相似文献
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53.
Nakiboğlu G Rudenko O Hirschberg A 《The Journal of the Acoustical Society of America》2012,131(1):749-765
When one swings a short corrugated pipe segment around one's head, it produces a musically interesting whistling sound. As a musical toy it is called a "Hummer" and as a musical instrument, the "Voice of the Dragon." The fluid dynamics aspects of the instrument are addressed, corresponding to the sound generation mechanism. Velocity profile measurements reveal that the turbulent velocity profile developed in a corrugated pipe differs notably from the one of a smooth pipe. This velocity profile appears to have a crucial effect both on the non-dimensional whistling frequency (Strouhal number) and on the amplitude of the pressure fluctuations. Using a numerical model based on incompressible flow simulations and vortex sound theory, excellent predictions of the whistling Strouhal numbers are achieved. The model does not provide an accurate prediction of the amplitude. In the second part of the paper the sound radiation from a Hummer is discussed. The acoustic measurements obtained in a semi-anechoic chamber are compared with a theoretical radiation model. Globally the instrument behaves as a rotating (Leslie) horn. The effects of Doppler shift, wall reflections, bending of the tube, non-constant rotational speed on the observed frequency, and amplitude are discussed. 相似文献
54.
For given integers we ask whether every large graph with a sufficiently small number of k‐cliques and k‐anticliques must contain an induced copy of every l‐vertex graph. Here we prove this claim for with a sharp bound. A similar phenomenon is established as well for tournaments with . 相似文献
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Madeleine Soyeur Supervisory Editor Gerald E. Brown Supervisory Editor Avraham Gal Supervisory Editor Karlheinz Langanke Supervisory Editor Larry McLerran Supervisory Editor Achim Richter Supervisory Editor Johanna Stachel Supervisory Editor Isao Tanihata Supervisory Editor 《Nuclear Physics A》2001,690(4):331-338
57.
In this paper, we investigate the relationship between the information presentation format and project control. Furthermore, the effects of some system conditions, namely the number of projects to be controlled and the level of time pressure, on the quality of the project control decisions are analyzed. Information provided by Earned Value Analysis is used to monitor and control projects, and simulation is applied to replicate and model the uncertain project environments. Software is developed to generate random cost figures, to present the data in different visual forms and to collect users’ responses. Having performed the experiments, the statistical significance of the results is tested. 相似文献
58.
Esther Azizi Felix Pavlotsky Iris Vered Avraham I. Kudish 《Photochemistry and photobiology》2009,85(5):1240-1244
To characterize the relationship between occupational sun exposure and seasonal variations in serum 25-OH-D3, four consecutive measurements of 25-OH-D3, one per season, were taken in 122 outdoor and 104 indoor Israeli workers. Continuous UVB measurements, taken in Beer Sheva, Israel, provided the average daily standard erythema dose (SED) of ambient solar UVB. The average daily exposure of the outdoor and indoor workers to solar UVB was 4.4 ± 1.6 h (4.0–37.6 SED) and 0.9 ± 0.5 h (0.6–8.2 SED), respectively. At each season mean 25-OH-D3 were significantly higher among outdoor workers than among indoor workers. Mean 25-OH-D3 increased significantly from spring to autumn in both gender and occupational groups. Adjusting for confounders, high (>median) 25-OH-D3 among males was significantly associated with occupational sun exposure in the autumn (odds ratio [OR] 4.31; 95% confidence interval [CI] 1.4–13.3), and among females in the spring (OR 3.35; 95% CI 1.53–7.32). Among this working population optimal vitamin D status (≥30 ng mL−1 ) was approached only in summer by males working either outdoor or indoor. In the rest of the year 25-OH-D3 ranged between ≥20.0 and 29.0 ng mL−1 . Monitoring 25-OH-D3 may disclose undesirable vitamin D status following reduced sun exposure for skin cancer prevention among outdoor workers. 相似文献
59.
Joseph Kreimer Dimitri Golenko-Ginzburg Avraham Mehrez 《The Journal of the Operational Research Society》1988,39(9):847-853
The question of allocation of control points in stochastic dynamic-programming models from different areas is considered. A widely used approach is to choose equal time intervals between successive control points. Conditions under which this choice may cease to be optimal are discussed. Two different approaches to statement and solution of a production-control problem are presented. 相似文献
60.
Given an arbitrary n×n matrix A with complex entries, we characterize all inertia triples (abc) that are attained by the Lyapunov transform AH+ HA*, as H varies over the set of all n× n positive definite matrices. 相似文献