Modélisation et simulation numérique du changement de phase liquide–vapeur en cavitéModeling and numerical simulation of liquid–vapor phase change in an enclosed cavity

A model for the simulation of boiling flow with phase change in a closed cavity is presented. A front-tracking method is used to deal with the liquid–vapor interface. The liquid phase is incompressible while the vapor phase is weakly compressible and obeys to the perfect gas law. This model can deal with large density ratio (${\rho }_l/{\rho }_v?1000$) flows while accounting for the saturation curve. Computations are performed on a 1D validation case, idealizing a pressure cooker. Results are compared with a low Mach number approximation. To cite this article: V. Daru et al., C. R. Mecanique 334 (2006).     

Performance evaluation of traveling wave ultrasonic motor based on a model with visco-elastic friction layer on stator

A new visco-elastic contact model of traveling wave ultrasonic motor (TWUSM) is proposed. In this model, the rotor is assumed to be rigid body and the friction material on stator teeth surface to be visco-elastic body. Both load characteristics of TWUSM, such as rotation speed, torque and efficiency, and effects of interface parameters between stator and rotor on output characteristic of TWUSM can be calculated and simulated numerically by using MATLAB method based on this model. This model is compared with that one of compliant slider and rigid stator. The results show that this model can obtain bigger stall torque. The simulated results are compared with test results, and found that their load characteristics have good agreement.     

Relationship between Rayleigh wave polarization and state of stress

This research develops an analytical model (using Stroh's formalism) to predict the affect of applied stress on the wave speed and the polarization of Rayleigh surface waves. Simulation results are then used to demonstrate that the polarization of a Rayleigh wave (which is reference-free) could be more sensitive than wave speed as an indicator of the state of stress.     

Diophantine approximation with prime variables and mixed powers

The Ramanujan Journal - Suppose that $$\lambda _1, \lambda _2, \lambda _3, \lambda _4$$ are positive real numbers and $$\frac{\lambda _1}{\lambda _2}$$ is irrational and algebraic. Let $$\mathcal...     

On the combinatorics of the Boros-Moll polynomials

The Boros-Moll polynomials arise in the evaluation of a quartic integral. The original double summation formula does not imply the fact that the coefficients of these polynomials are positive. Boros and Moll proved the positivity by using Ramanujan’s Master Theorem to reduce the double sum to a single sum. Based on the structure of reluctant functions introduced by Mullin and Rota along with an extension of Foata’s bijection between Meixner endofunctions and bi-colored permutations, we find a combinatorial proof of the positivity. In fact, from our combinatorial argument one sees that it is essentially the binomial theorem that makes it possible to reduce the double sum to a single sum.     

Finite <Emphasis Type="Italic">p</Emphasis>-groups all of whose maximal abelian subgroups are soft

A subgroup A of a p-group G is said to be soft in G if C _G (A) = A and |N _G (A/A| = p. In this paper we determined finite p-groups all of whose maximal abelian subgroups are soft; see Theorem A and Proposition 2.4.     

Hybrid variable neighbourhood approaches to university exam timetabling

In this paper, we investigate variable neighbourhood search (VNS) approaches for the university examination timetabling problem. In addition to a basic VNS method, we introduce variants of the technique with different initialisation methods including a biased VNS and its hybridisation with a Genetic Algorithm. A number of different neighbourhood structures are analysed. It is demonstrated that the proposed technique is able to produce high quality solutions across a wide range of benchmark problem instances. In particular, we demonstrate that the Genetic Algorithm, which intelligently selects appropriate neighbourhoods to use within the biased VNS, produces the best known results in the literature, in terms of solution quality, on some of the benchmark instances. However, it requires relatively large amount of computational time. Possible extensions to this overall approach are also discussed.     

Silica spheres coated with C18‐modified gold nanoparticles for capillary LC and pressurized CEC separations

Nonporous monodispersed silica spheres of 1.3 μm were coated with gold nanoparticles (AuNPs) and subsequently coated with n‐octadecanethiol. By transmission electron microscopy analysis, the average diameter of the AuNPs on the silica spheres was determined to be 12 nm. The chromatographic and electrochromatographic properties of self‐assembled n‐octadecanethiol AuNP‐coated silica microspheres (C18‐AuNPs‐SiO₂) were investigated using a group of nonpolar PAHs. The stationary phase appears to display a characteristic reversed‐phase behavior. Higher separation efficiency and shorter separation times were obtained using pressurized CEC (pCEC) compared with capillary LC (CLC). A maximum column efficiency of about 2.5×10⁵ plates per meter and less than 18 min separation time for benzene were obtained in pCEC while only 66 507 plates per meter and an analysis time of nearly 100 min were observed in CLC mode. A chemical stability test of the C18‐AuNPs‐SiO₂ stationary phase under extremely high and low pH conditions demonstrated that it is stable at pH 12 and 1 for at least 60 h. The results confirm that C18‐AuNPs‐SiO₂ possesses a high rigidity to withstand high packing pressures and can be used as a good stationary phase for CLC and pCEC.     

Electrochemical deposition of nano-structured ZnO on the nanocrystalline TiO2 film and its characterization

One-dimensional structure of ZnO nanorod arrays on nanocrystalline TiO₂/ITO conductive glass substrates has been fabricated by cathodic reduction electrochemical deposition methods in the three-electrode system, with zinc nitrate aqueous solution as the electrolyte, and were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and photoluminescence (PL) spectra. The effects of film substrates, electrolyte concentration, deposition time, and methenamine (HMT) addition on ZnO deposition and its luminescent property were investigated in detail. The results show that, compared with on the ITO glass substrate, ZnO is much easily achieved by electrochemical deposition on the TiO₂ nanoparticle thin films. ZnO is hexagonally structured wurtzite with the c-axis preferred growth, and further forms nanorod arrays vertically on the substrates. It is favorable to the growth of ZnO to extend the deposition time, to increase the electrolyte concentration, and to add a certain amount of HMT in the system, consequently improving the crystallinity and orientation of ZnO arrays. It is demonstrated that the obtained ZnO arrays with high crystallinity and good orientation display strong band-edge UV (375 nm) and weak surface-state-related green (520 nm) emission peaks.     

Permanent gold nanoparticle coatings on polyelectrolyte multilayer modified capillaries for open-tubular capillary electrochromatography

This paper reports on a new strategy to coat fused silica capillaries through ionic adsorption of gold nanoparticles (AuNPs) on a polyelectrolyte multilayer (PEM) modified capillary wall. The coating was constructed in situ by alternating rinses with positively charged poly(diallydimethylammonium chloride), negatively charged poly(sodium-4-styrenesulfonate), and positively charged AuNPs. After self-assembly of n-octadecanethiol onto the surface of AuNPs, the modified capillary was investigated as a new medium for the separation of neutral analytes and proteins in open-tubular capillary electrochromatography (OT-CEC). The surface coverage of the capillary wall was increased using the high density of AuNPs which were dynamically capped with 4-dimethylaminopyridine (DMAP). The chromatographic performance of the column coated with positively charged AuNPs was remarkably improved compared with a column modified with negatively charged AuNPs. The coating was robust over more than 810 runs in this study and also showed high stability against 0.01 M NaOH, 0.01 M HCl, and electrolyte concentrations up to 70 mM. The run-to-run, day-to-day, and capillary-to-capillary reproducibilities of electroosmotic flow were satisfying with relative standard deviation values of less than 1% in all cases. The AuNP-coated PEM modified capillary column not only showed good performance for neutral analytes but also was suitable for the analysis of both basic and acidic proteins.