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991.
X-Chromosome inactivation is the process whereby one of the two X-chromosomes in female cells is silenced to prevent the cell producing too much of any X-linked proteins and RNA. The proposed blocking-factor mechanism of X-inactivation is not well understood and hence is the subject of much current research. In this paper we investigated the nature of the phase transition predicted to exist in the spontaneous symmetry breaking model of X-inactivation proposed by Nicodemi and Prisco [Mario Nicodemi, Antonella Prisco, Symmetry breaking model for x-chromosome inactivation, Phs. Rev. Lett. 98 (2007) 108104]. Finite size effects were investigated by using an on lattice Monte Carlo simulation. From the scaling it is concluded that the transition is in general abrupt. The critical temperature of the system was determined to be 1.68±0.01E0/kB in the thermodynamic limit when the concentration C=0.025 blocking-factors per lattice site. 相似文献
992.
Theoretical analysis on the local critical stress and size effect for interfacial debonding in particle reinforced rheological materials 总被引:1,自引:0,他引:1
The mechanisms of interfacial debonding of particle reinforced rheological materials are studied. Based on an energy criterion,
a simple formula of local critical stress for interfacial debonding is derived and expressed in terms of the interfacial energy.
The particle size effect on interface debonding can then be analyzed easily owing to the fact that critical stress is inversely
proportional to the square root of particle radius. By taking PP/CaCO3 system as an example, the present energy criterion is compared with the mechanical debonding criterion, and it is found that
under the condition that bond strength is equal to matrix strength and particle radius not over 0.2μm, the mechanical debonding
criterion can be automatically satisfied if the energy criterion is satisfied. A relation between critical time and interface
energy is calculated by using the energy criterion. The influences of the particle volume fraction and the parlicle size,
the loading rate and the relaxation time of the matrix on the critical time of interfacial debonding are also discussed.
Supported by the National Natural Science Foundation of China (19632030 and 19872007) and Natural Science Foundation of Jiangsu
Province. 相似文献
993.
James P. Johansen Alejandro M. CastroPablo M. Carrica 《International Journal of Multiphase Flow》2010
Measurements of gas volume fraction, bubble velocity, chord length and bubble size distributions were performed on the research vessel Athena II operating in Saint Andrew Bay in the gulf coast near Panama City, FL. Double tipped sapphire optical local phase-detection probes were used to acquire indicator functions downstream of the breaking bow wave, behind the masker and at the stern. These indicator functions were also taken at different depths, operating speeds and headings respect to the waves. The data processing includes the computation of velocity of individual bubbles and chord lengths, resulting in chord length distributions. These chord length distributions are used to obtain bubble size distributions using a novel procedure described in detail herein. Uncertainty analysis is performed for gas volume fraction, average bubble velocity and chord length. The results indicate that air entrainment increases with ship speed and sailing against the waves at all positions. The bow wave exhibits unsteady breaking that creates bubble clouds, which were characterized and identified by signal processing. At the stern a very strong dependence of bubble size with depth was found, with evidence that small bubbles (smaller than 500 μm) are transported through the bottom of the hull and reach the transom. The roller present at the transom, the associated strong unsteadiness and bubble entrainment are well captured, as indicated by the stern results, showing the frothy nature of the upper layer. 相似文献
994.
M. Sánchez‐Chaves M. Fernández‐García M. L. Cerrada 《Journal of Polymer Science.Polymer Physics》2007,45(9):1026-1036
The crystalline structure exhibited by terpolymers obtained through chemical modification with benzoyl chloride from an ethylene‐vinyl alcohol copolymer with a molar fraction in vinyl alcohol of 68%, EVOH68, has been studied by either wide angle X‐ray diffraction or small angle X ray scattering experiments and differential scanning calorimetry. The type of crystal lattice developed has been found to be strongly dependent on modification degree and thermal history. A highly‐disordered crystalline lattice with very small crystallites has been found for the quenched specimen with the highest benzoate content while the rest of fast cooled samples crystallized into an orthorhombic lattice. On the other hand, a monoclinic crystal cell has been observed in the slowly cooled specimens with low benzoate incorporation. At the last given thermal treatment, this monoclinic lattice evolves and seems to be transformed into an orthorhombic‐like crystal for the terpolymer with the highest modification ratio. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1026–1036, 2007 相似文献
995.
Yury Dikansky Arthur Zakinyan Marita Bedganian 《Journal of magnetism and magnetic materials》2009,321(10):1433-1435
A new method of particle size analysis of micrometer-sized particles is discussed. The improved method of sedimentation analysis with magnetic fluids has the potential and versatility to characterize polydisperse systems. 相似文献
996.
The superconducting transition temperature and grain size of dc sputtered Nb films are systematically investigated. The results
show that the superconductivity is closely related to the grain size, rather than to the scattering strength of electrons
or the surface layer proximity effect of the films.
Supported by the National Basic Research Program of China (Grant No. 2006CB-91304), and the Knowledge Innovation Project of
Chinese Academy of Sciences
Contributed by ZHANG DianLin 相似文献
997.
Niels M. B. Smeets Tom G. T. Jansen Timo J. J. Sciarone Johan P. A. Heuts Jan Meuldijk Alex M. Van Herk 《Journal of polymer science. Part A, Polymer chemistry》2010,48(5):1038-1048
The effect a Co(II) based catalytic chain transfer agent (CCTA) has on the course of the polymerization and the product properties of an emulsion polymerization is governed by the intrinsic activity and the partitioning behavior of the catalyst. The effect on the conversion time history, the molecular weight distribution and the particle size distribution is evaluated in batch emulsion polymerization of methyl methacrylate for three different CCTAs, which cover a range of intrinsic activities and partitioning behaviors. It was demonstrated that radical desorption from the particle phase to the aqueous phase preceded by chain transfer is the main kinetic event controlling the course of the polymerization and the product properties in terms of the particle size distribution. The experimental results show that the aqueous phase solubility of the CCTA is the key parameter controlling the course of the polymerization and the particle size distribution. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1038–1048, 2010 相似文献
998.
Magnusson Martin H. Deppert Knut Malm Jan-Olle Bovin Jan-Olov Samuelson Lars 《Journal of nanoparticle research》1999,1(2):243-251
Gold nanoparticles are of great interest for various nanoelectronic applications, e.g., for making single electron transistors or very fine leads to molecular size entities. For this and other applications, it is important that all particles have controllable size and shape. In this paper, we describe the production of size-selected gold aerosol particles in the 20nm range made by evaporation in a high-temperature tube furnace and subsequent size selection. To obtain spherical particles, it was necessary to reshape the particles at high temperature, which was investigated for temperatures between 25°C and 1200°C. High-resolution transmission electron microscopy showed that the degree of crystallinity became higher for higher reshaping temperature. During reshaping at high temperature, an anomalous charging behavior was discovered, whereby negatively as well as positively charged particles became multiply negatively charged. Possible mechanisms for explaining this thermally activated phenomenon are discussed. 相似文献
999.
George W. Scherer 《Journal of Sol-Gel Science and Technology》1994,1(3):285-291
For materials with high porosity, the hydraulic radius (r
h
) is not proportional to the characteristic dimension of the pore space. Techniques (e.g., NMR) that measure r
h
will give much larger pore sizes than techniques (e.g., thermoporometry) that measure pore entry radii. In this note, estimates of the relation between hydraulic radius and pore size of gel networks are obtained from cell models. The constant in the Kozeny equation, which relates permeability to r
h
, is strongly density-dependent at low densities. For gels it is suggested that the permeability is more directly related to the mesh size of the network than to the hydraulic radius. The mesh size is also critical for immobilization of dyes or enzymes in a gel, and r
h
is a misleading measure of the ability of a network to entrap a large molecule. 相似文献
1000.