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71.
《中国颗粒学报》2008,6(6)
A two-dimensional discrete element model (DEM) simulation of cohesive polygonal particles has been developed to assess the benefit of point source vibration to induce flow in wedge-shaped hoppers. The particle-particle interaction model used is based on a multi-contact principle.The first part of the study investigated particle discharge under gravity without vibration to determine the critical orifice size (Be) to just sustain flow as a function of particle shape. It is shown that polygonal-shaped particles need a larger orifice than circular particles. It is also shown that Be decreases as the number of particle vertices increases. Addition of circular particles promotes flow of polygons in a linear manner.The second part of the study showed that vibration could enhance flow, effectively reducing Be. The model demonstrated the importance of vibrator location (height), consistent with previous continuum model results, and vibration amplitude in enhancing flow. 相似文献
72.
Clear effects criterion is one of the important rules for selecting optimal fractional factorial designs, and it has become
an active research issue in recent years. Tang et al. derived upper and lower bounds on the maximum number of clear two-factor
interactions (2fi’s) in 2
n−(n−k) fractional factorial designs of resolutions III and IV by constructing a 2
n−(n−k) design for given k, which are only restricted for the symmetrical case. This paper proposes and studies the clear effects problem for the asymmetrical
case. It improves the construction method of Tang et al. for 2
n−(n−k) designs with resolution III and derives the upper and lower bounds on the maximum number of clear two-factor interaction
components (2fic’s) in 4
m
2
n
designs with resolutions III and IV. The lower bounds are achieved by constructing specific designs. Comparisons show that
the number of clear 2fic’s in the resulting design attains its maximum number in many cases, which reveals that the construction
methods are satisfactory when they are used to construct 4
m
2
n
designs under the clear effects criterion.
This work was supported by the National Natural Science Foundation of China (Grant Nos. 10571093, 10671099 and 10771123),
the Research Foundation for Doctor Programme (Grant No. 20050055038) and the Natural Science Foundation of Shandong Province
of China (Grant No. Q2007A05). Zhang’s research was also supported by the Visiting Scholar Program at Chern Institute of Mathematics. 相似文献
73.
74.
本文首次用熔融法生长了Dy3 + :ThO2 晶体 ,详细研究了其光谱特性。通过 12K下格位选择激发下的发射光谱测量 ,利用晶场理论 ,确定了Dy3 + 在ThO2 中的格位对称性为C3v。列表给出了Dy3 + :ThO2 的晶场能级结构。测量和讨论了 4 F9/ 2 能级的寿命。 相似文献
75.
The rapid development of high-speed trains like the TGV or the ICE in recent years results in high dynamic loads causing vibrations which propagate from the train-track structure into the ground and further into nearby buildings. In this context it is important to develop rigid tracks with improved dynamic behaviour and to investigate possible means of vibration reduction. The boundary element method in frequency and time domain is used to simulate train-track structures subjected to dynamic loading and the reduction of vibrations which for instance can be achieved via a trench running parallel to the rigid track. In this context the non-causality error, which arises when the time-domain BEM algorithm is applied to mathematically concave domains, is discussed and the substructure method is proposed as a solution to this problem. A two-layered cylindrical elastic structure on a half-space with a trench is added as an example of a possible application. 相似文献
76.
A mathematical model is developed to study periodic-impact motions and bifurcations in dynamics of a small vibro-impact pile driver. Dynamics of the small vibro-impact pile driver can be analyzed by means of a three-dimensional map, which describes free flight and sticking solutions of the vibro-impact system, between impacts, supplemented by transition conditions at the instants of impacts. Piecewise property and singularity are found to exist in the Poincaré map. The piecewise property is caused by the transitions of free flight and sticking motions of the driver and the pile immediately after the impact, and the singularity of map is generated via the grazing contact of the driver and the pile immediately before the impact. These properties of the map have been shown to exhibit particular types of sliding and grazing bifurcations of periodic-impact motions under parameter variation. The influence of piecewise property, grazing singularities and parameter variation on the performance of the vibro-impact pile driver is analyzed. The global bifurcation diagrams for the impact velocity of the driver versus the forcing frequency are plotted to predict much of the qualitative behavior of the actual physical system, which enable the practicing engineer to select excitation frequency ranges in which stable period one single-impact response can be expected to occur, and to predict the larger impact velocity and shorter impact period of such response. 相似文献
77.
K.A. Schmidt M. Bergström G.B. Hagemann B. Herskind G. Sletten P.G. Varmette J. Domscheit H. Hübel S.W. Ødegård S. Frattini A. Bracco B. Million M.P. Carpenter R.V.F. Janssens T.L. Khoo T. Lauritsen C.J. Lister S. Siem I. Wiedenhöver D.J. Hartley L.L. Riedinger A. Maj W.C. Ma R. Terry 《The European Physical Journal A - Hadrons and Nuclei》2001,12(1):15-28
High-spin properties of the nucleus 169Hf have been studied through the fusion evaporation reaction 96Zr(76Ge,3n)169Hf at a beam energy of 310 MeV. The known rotational bands have been extended considerably and 6 new bands have been established,
four of which form coupled bands with pronounced M1 connections. Quasiparticle assignments are suggested for the new band structures, and it appears that coupling to vibrational
degrees of freedom plays a role. Both coupled bands involve the excitation of quasiprotons. In the region of highest spin,
a large alignment gain is interpreted in terms of a mixed crossing where an h
9/2 and an h
11/2 quasiproton provide the two signatures of the aligning configuration.
Received: 23 March 2001 / Accepted: 20 September 2001 相似文献
78.
Ce‐doped Lu3Al5O12 optical ceramics co‐doped with Mg2+ are fabricated by solid‐state reaction method and further optimized by an air‐annealing process. Mg2+ co‐doping leads to a significant decrease of thermoluminescence intensity above room temperature and an increase of scintillation light yield (LY) value and fast component content even if the overall scintillation efficiency decreases. Scintillation LY of ~21900 ph/MeV has been achieved with a short shaping time of 1 μs, and the ratio of LY values for 1 μs and 10 μs shaping times was as high as 79%. The acceleration of scintillation response induced by Mg2+ co‐doping and the role of Ce4+ ions in the scintillation mechanism are discussed.
79.
《Physics letters. A》2014,378(32-33):2436-2442
The band structure of a nacreous composite material is studied by two proposed models, where an ultrawide low frequency band gap is observed. The first model (tension-shear chain model) with two phases including brick and mortar is investigated to describe the wave propagation in the nacreous composite material, and the dispersion relation is calculated by transfer matrix method and Bloch theorem. The results show that the frequency ranges of the pass bands are quite narrow, because a special tension-shear chain motion in the nacreous composite material is formed by some very slow modes. Furthermore, the second model (two-dimensional finite element model) is presented to investigate its band gap by a multi-level substructure scheme. Our findings will be of great value to the design and synthesis of vibration isolation materials in a wide and low frequency range. Finally, the transmission characteristics are calculated to verify the results. 相似文献
80.
Jessica Dubois Sofya Kulikova Lucie Hertz-Pannier Jean-François Mangin Ghislaine Dehaene-Lambertz Cyril Poupon 《Magnetic resonance imaging》2014