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991.
Newtonian liquids and non-Newtonian soft solids were squeezed between parallel glass plates by a constant force F applied at time t=0. The plate separation h(t) and the squeeze-rate
were measured for different amplitudes of plate roughness in the range 0.3–31 m. Newtonian liquids obeyed the relation Vh
3
of Stephan (1874) for large plate separations. Departures from this relation that occurred when h approached the roughness amplitude were attributed to radial liquid permeation through the rough region. Most non-Newtonian materials showed boundary-slip that varied with roughness amplitude. Some showed slip that varied strongly during the squeezing process. Perfect slip (zero boundary shear stress) was not approached by any material, even when squeezed by optically-polished plates. If the plates had sufficient roughness amplitude (e.g. about 30 m), boundary slip was practically absent, and the dependence of V on h was close to that predicted by no-slip theory of a Herschel-Bulkley fluid in squeeze flow (Covey and Stanmore 1981, Adams et al. 1994). 相似文献
992.
The problem of the mixing of hot turbulent gases in an axisymmetric channel with a lateral surface of arbitrary shape and a pre-swirled flow is considered. The flowfields and the temperature and concentration distributions are calculated for various inlet conditions. 相似文献
993.
M. Ciavarella G. Murolo J.R. Barber 《Journal of the mechanics and physics of solids》2004,52(6):1247-1265
The Weierstrass series comprises a system of superposed self-affine sine waves that can be used to define a simple idealization of a two-dimensional fractal rough surface profile. The load-compliance relation for the contact of this profile with a rigid plane is here estimated using Westergaard's solution for the contact of a single sine wave with a plane and various approximations concerning the interaction of the different terms in the series. These approximations are compared with a numerical solution for the contact of the profile defined by the first few terms of the series. Once the load-compliance relation is established, the electrical contact resistance can be determined, using an analogy between the conduction and incremental elastic contact problems. The results show that these simple estimates give quite good predictions of the relations between load, compliance and contact resistance. They also confirm that these relations are largely determined by the coarse scale features of the surface profile, in contrast to the predictions of classical asperity model theories. 相似文献
994.
995.
We construct an explicit bundle with flat connection on the configuration space of n points on a complex curve. This enables one to recover the ‘1-formality’ isomorphism between the Lie algebra of the prounipotent completion of the pure braid group of n points on a surface and an explicitly presented Lie algebra, and to extend it to a morphism from the full braid group of the surface to the semidirect product of the associated group with the symmetric group Sn. 相似文献
996.
In this paper the Wiener–Hopf (or Riemann–Hilbert) factorization of a class of symbols important in applications is studied. The symbols in this class involve outer functions that appear in applications such as diffraction by strip gratings and infinite-dimensional integrable systems. The method proposed is based on the reduction of a vector Riemann–Hilbert to a scalar problem on an appropriate Riemann surface. Two examples are given leading to the Riemann sphere and to an elliptic curve. 相似文献
997.
Xianwen Ren Lu‐Tao Weng Kai‐Mo Ng Chi‐Ming Chan 《Surface and interface analysis : SIA》2013,45(7):1158-1165
The effects of argon (Ar) and a mixture of Ar and oxgyen(Ar/O2) plasmas on amorphous and semi‐crystalline poly(bisphenol A hexane ether) thin films were investigated by time‐of‐flight secondary ion mass spectroscopy (ToF‐SIMS) and principal component analysis (PCA). PCA results of the ToF‐SIMS spectra indicate that an Ar/O2 plasma produced less physical sputtering and had a higher chemical reactivity than did an Ar plasma, regardless of whether an amorphous or a crystalline surface was involved. However, the chemical differences between the Ar‐ and Ar/O2‐plasma‐treated semi‐crystalline films were much smaller. The observed results can be explained by the higher resistance of the polymer crystalline regions to physical sputtering and chemical etching. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
998.
Xia Xin Li Xiao Yan Bai Shi‐Ling Yuan 《Journal of Dispersion Science and Technology》2013,34(4):519-524
Via chemical adsorption, various films were assembled onto silicon surfaces. The structures and properties of the monolayer‐ or bilayer‐modified silicon surfaces, such as Si‐C10H20 CH2OC(O)CF3, Si‐C10H20CH2OH, and Si‐C10H20‐CH2‐NH‐C18H37, were investigated by various techniques. x‐ray photoelectron spectroscopy (XPS) gave clear proofs of the formation of octadecylamine layer and other kinds of layers on silicon surfaces. The contact angle measurements showed that the wettability of silicon surfaces was dominated by the terminal functional groups of the attached layers. Atomic force microscopy (AFM) observations showed that interesting patterns have formed on the monolayer‐ or bilayer‐modified silicon surfaces. Electrochemical impedance spectra (EIS) measurements showed that the Si‐C10H20CH2‐NH‐C18H37 has a better ability to prevent charge transfer as compared with that of Si‐C10H20CH2OH, which may find applications in the area of surface passivations. 相似文献
999.
Jeanne M. Hankett Yuwei Liu Xiaoxian Zhang Chi Zhang Zhan Chen 《Journal of Polymer Science.Polymer Physics》2013,51(5):311-328
Industrial plastics, biomedical polymers and numerous other polymeric systems are contacted with water for everyday functions and after disposal. Probing the interfacial molecular interactions between widely used polymers and water yields valuable information that can be extrapolated to macroscopic polymer/water interfacial behaviors so scientists can better understand polymer bio-compatibility, hygroscopic tendencies and improve upon beneficial polymer behavior in water. There is an ongoing concerted effort to elucidate the molecular level behaviors of polymers in water by using sum frequency generation vibrational spectroscopy (SFG). SFG stands out for its utility in probing buried interfaces in situ and in real time without disrupting interfacial chemistry. Included in this review are SFG water interfacial studies performed on poly(methacrylate) and (acrylate)s, poly(dimethyl siloxane)s, poly(ethylene glycol)s, poly(electrolyte)s and other polymer types. The driving forces behind common water/polymer interfacial molecular features will be discussed as well as unique molecular reorientation phenomena and resulting macroscopic behaviors from microscopic polymer rearrangement. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013 相似文献
1000.
Dr. Hristiyan A. Aleksandrov Dr. Francesc Viñes Wiebke Ludwig Dr. Swetlana Schauermann Prof. Dr. Konstantin M. Neyman 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(4):1335-1345
Palladium is crucial for industry‐related applications such as heterogeneous catalysis, energy production, and hydrogen technologies. In many processes, atomic H and C species are proposed to be present in the surface/near‐surface area of Pd, thus noticeably affecting its chemical activity. This study provides a detail and unified view on the interactions of the H and C species with Pd nanoparticles (NPs), which is indispensable for insight into their catalytic properties. Density functional calculations of the interplay of C and H atoms at various concentrations and sites on suitable Pd NPs have been performed, accompanied by catalysis‐relevant experiments on oxide‐supported bare and C‐modified Pd NPs. It is shown that on a Pd79 NP a subsurface C atom destabilizes nearby atoms H at low coverage. Our experiments confirm that H atoms bind more weakly on C‐containing Pd NPs than on C‐free NPs. Various factors related to the presence of both H and C atoms on a Pd79 surface, which may influence the penetration of H atoms from the surface into the subsurface area, have been investigated. Carbon atoms facilitate the subsurface penetration of atomic H both thermodynamically and kinetically when the surface is densely covered by H atoms. Moreover, subsurface H atoms are also energetically favored, even in the absence of C atoms, when several facets of the NP are covered by H atoms. 相似文献