We analyze a model of an interface fluctuating above a
rough substrate. It is based on harmonic crystals, or lattice
free fields, indexed by d ,
d 3. The phenomenon for
which we want to get precise quantitative estimates is the
repulsion effect of the substrate on the interface: the
substrate is itself a random field, but its randomness is
quenched (this generalizes
the widely considered case of a flat deterministic substrate).
With respect to [2] in which the substrate has been taken to be
an IID field, here the substrate is an harmonic crystal, as the
interface, and as such it is strongly correlated. We obtain the
leading asymptotic behavior of the model in the limit of a very
extended substrate: we show in particular that, to leading
order, the effect of an IID substrate cannot be distinguished
from the effect of an harmonic crystal substrate. We observe
however that, unlike in the IID substrate case, annealed and
quenched models display sharply different features. 相似文献
The 1 D one-band Hubbard model with different repulsive on-site interactions on even (U+V > 0) and odd (U-V > 0) sites, supplemented by the correlated-hopping term (t* > 0), describing the modification of the electron hopping by the presence of other particles on the sites, is considered as a 1 D model for CuO systems. The ground state phase diagram is studied within the framework of the bosonization technique and renormalization group analysis valid for weak coupling. Depending on the choice of model parameters, the following sequences of phase transitions with increasing bandfilling occur: 1) metal-insulator-metal (for t* ? U/4); 2) metal-insulator-metal-superconductor $ ({\rm for}U/4 < t * \le U/\sqrt 8);3) $metal-superconductor-metal-insulator-metal-superconductor $ ({\rm for}U/\sqrt 8 \le t * < (U + V)/\sqrt 8){\rm and}4) $metal-superconductor $ ({\rm for}(U + V)/\sqrt 8 \le t*) $. 相似文献
For the SOS model defined by the Hamiltonian
, where
x,
x,{1,2,...},h>0,xd,d2 it is shown that in the low-temperature region an infinite sequence of first-order phase transitions takes place whenh»0 and the temperature is fixed. 相似文献
Via NMR-spectroscopy the relative reactivity of N-heterocyclic silylenes (NHSi) and carbenes (NHC) was studied. Reaction of sterically crowded bis-N-heterocyclic Pd(0) carbene complexes with free N-heterocyclic silylenes led to complete displacement of the N-heterocyclic carbene, which is unexpected knowing that usually a silylene is a weaker bound ligand compared to a carbene. High-level DFT calculations on a small model system and the experimentally used complexes confirm the experimental findings and indicate that steric interactions play an important role in the substitution reaction. 相似文献
C-Si reductive elimination from Pt(R)(SiPh3)(PMe3)2 (R=Me, Pr) was theoretically studied with the density functional theory. For comparisons with the experiment, substitution of PMe3 with diphenylacetylene was taken into account. The calculated activation barriers in the C-Si elimination step after the ligand exchange were 22.0 and 28.9 kcal mol−1 for R=Me and Pr, respectively, which explains the reactivity difference reported experimentally. In order to analyze the energy difference, we optimized transition states of several model complexes, and examined the influence of the steric repulsion between R and the other ligands. Comparisons of the geometries and the barrier heights reveal that the steric repulsion and the Si-alkyl bond energy are important factors controlling the reaction rate. 相似文献
Particle–particle separation in biotechnology has gained interest over the years due to the large number of processes that yield particle mixtures. Direct isolation of the product-containing particles is a logical and efficient downstream processing route in these processes. Dissolved-air flotation is applicable for these separations when the particles that require separation have different interactions with the air bubbles and/or differ in aggregation behaviour.
In this work, model particles consisting of micrometer-sized protein-coated polystyrene particles were used to investigate the requirements for the application of dissolved-air flotation for particle–particle separation in biotechnology. These model particles have heterogeneous surfaces with surface groups (brushes) that extend out into the solution. Therefore, steric (or brush) repulsion and so-called hydrophobic interactions between the particles need to be taken into account. The flotation behaviour of the protein-coated particles was related to the size of the aggregates and the foaming behaviour of the proteins. Prediction of their aggregation behaviour was performed on the basis of calculations of the Van der Waals, electrostatic, hydrophobic and brush interactions. The brush interaction force proves to be essential for the prediction of the aggregation behaviour of the particles. 相似文献
The X-ray crystal structures of 1,1-di(p-methylphenyl)-2,2-dinitroethylene (2), 1,1-di(p-methoxylphenyl)-2,2-dinitroethylene (3), 1,1-di(p-fluorophenyl)-2,2- dinitroethylene (4), 1,1-di(p-chlorophenyl)-2,2-dinitroethylene (5), and 1-phenyl-1- (p-nitrophenyl)-2,2-dinitroethylene (6) are reported and compared with that of 1,1-diphenyl-2,2-dinitroethylene (1). Owing to steric repulsion between the aryl rings, the single bond lengths between C(1) and the two ring carbons atoms are longer than the normal sp2–sp2 bond distance of 1.46 Å. For 4–6 in which the aryl rings contain electron-withdrawing substituents (F, Cl, NO2), the double bonds between C(1) and C(2) are shorter than those in 2 and 3, whose aryl rings containing electron-donating substituents. Furthermore, the steric repulsion between the aryl rings and C
NO2 fragments results in an appreciable twist about the central double bond. The two aryl rings of compounds 1–6 make dihedral angles of 77.7, 66.6, 62.8, 80.9, 82.0, and 71.2°, and the two C
NO2 fragments make dihedral angles of 68.5, 67.8, 65.9, 76.9, 73.0, and 71.9°, respectively. 相似文献
The purpose of this work was to evaluate the possibility of adding tea saponin (TS) to reduce the synthetic surfactant concentration, and maintain or improve the shelf stability of nanoemulsions. The Zanthoxylum bungeanum essential oil (2.5 wt%) loaded oil-in-water nanoemulsions were co-stabilized by Tween 40 (0.5–2.5 wt%) and TS (0.1–5 wt%). A combination of several analytical techniques, such as dynamic laser scattering, interfacial tension, zeta potential, and transmission electron microscope, were used for the characterization of nanoemulsions. Low levels of TS (0.1–0.5 wt%) with Tween 40 had significant effects on the emulsification, and a nanoemulsion with the smallest droplet diameter of 89.63 ± 0.67 nm was obtained. However, in the presence of high TS concentration (0.5–5 wt%), micelles generated by the non-adsorbed surfactants in the aqueous lead to droplets growth. In addition, the combinations of Tween 40 and TS at the high level (>3.5 wt%) exerted a synergistic effect on stabilizing the nanoemulsions and preventing both Ostwald ripening and coalescence. The negative charged TS endowed the droplets with electrostatic repulsion and steric hinderance appeared to prevent flocculation and coalescence. These results would provide a potential application of natural TS in the preparation and stabilization of nanoemulsions containing essential oil. 相似文献