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21.
《Composite Interfaces》2013,20(6):523-544
The influence of coal tar pitch on the formation of the mesophase composites from coal and pitch blends, the development of porous structure during carbonization, and the texture of matter in the pore walls has been studied using X-rays and scanning electronic microscopy (SEM). The influence of the coal-tar pitch on the structure of a coal plastic layer formed during the pyrolysis process of four Polish coals has been monitored. It was determined that, during pyrolysis of three mixtures of Z, S and K coals with coal-tar pitch, more porous composites are formed, and a denser composite is formed from P coal–pitch mixture. Based on a study of the texture of composites and carbonizates, it is suggested that during carbonization of coal Z with a coal-pitch in the plastic state there is a nematic mesophase formed, and when heating P coal–pitch mixtures, a cholesteric one is formed. 相似文献
22.
《Composite Interfaces》2013,20(7-9):647-668
This paper aims at introducing a new natural composite used as soil stabilizer with particular application in geotechnical engineering. The fibers introduced in the present study could be used as effective soil reinforcement. This research proves the feasibility of the use of modified jute/polypropylene in lime and cement composites and studies their effects on the tensile and compressive strength of the matrix. In general, the optimal mechanical performance of natural composites and durability depends on the optimization of the interfacial bond between natural fiber and matrix. Since the fibers and matrices are chemically different, strong adhesion at their interfaces is needed for an effective transfer of stress and bond distribution throughout an interface. In this paper a theoretical approach for the identification of elastic modulus in composite interfaces is proposed in detail with a reasonable error. The theoretical approach is based on the method using a sum of least squares criterion. The approach is applied through optimization techniques, using analytical sensitivities and correlating adhesion with Young's modulus. The validity and potentiality of the proposed technique is discussed and the results demonstrated the versatility, accuracy, and efficiency of the presented approach. The applied method also appears to be a simple way of predicting the modulus of elasticity in composite interfaces. This leads to a discussion of the most promising stabilization methods for soil reinforcement and the outlook for the future. 相似文献
23.
We consider possible tests of the Einstein Equivalence Principle for physical systems in which quantum-mechanical vacuum energies cannot be neglected. Specific tests include a search for the manifestation of non-metric effects in Lamb-shift transitions of hydrogenic atoms and in anomalous magnetic moments of massive leptons. We discuss how current experiments already set bounds on the violation of the equivalence principle in this sector and how new (high-precision) measurements of these quantities could provide further information to this end. 相似文献
24.
A new Planckian type distribution for cosmologies with photon creation is derived using thermodynamics and semiclassical considerations. This spectrum is preserved during the evolution of the universe and compatible with the present spectral shape of the cosmic microwave background radiation (CMBR). Accordingly, the widely spread feeling that cosmologies with continuous photon creation are definitely ruled out by the COBE limits on deviation of the CMBR spectrum from blackbody shape should be reconsidered. It is argued that a crucial test for this kind of cosmologies is provided by measurements of the CMBR temperature at high redshifts. For a given redshift z greater than zero, the temperature is smaller than the one predicted by the standard FRW model. 相似文献
25.
26.
Boris Petrovichev Malcolm Gray David McClelland 《General Relativity and Gravitation》1998,30(7):1055-1074
We model the behaviour of single-bounce delay-line dual recycled Sagnac-based interferometer and compare its performance with that of single-bounce Michelson-based system. Geometric imperfections such as mirror tilt and curvature mismatch can strongly influence the performance of the Sagnac device due to the inherently smaller free spectral range (FSR) and higher order mode spacing. This leads to a greater number of higher order modes near, or within the signal band in the signal recycling cavity of the instrument. The important consequence of that is, in general, a greater sensitivity of a Sagnac system to nonideal parameters and imperfections of various kind affecting the performance of a real interferometer. A number of optical configurations have also been examined numerically to determine the best possible optical arrangement, in the presence of such geometric imperfections. We show that there is an optimum choice for the nominal radius of curvature of the end mirrors which results from balancing the loss due to mirror tilt against that due to curvature mismatch. 相似文献
27.
The evolution of a class of inhomogeneous spherically symmetric universe models possessing a varying cosmological term and a material fluid, with an adiabatic index either constant or not, is studied. 相似文献
28.
《Quaestiones Mathematicae》2013,36(1):125-131
We prove several Banach spaces properties of E φ [0, 1], many of them concerning to the Δ2 condition and the presence of c 0 and l 1 in those Banach spaces. 相似文献
29.
《Quaestiones Mathematicae》2013,36(4):539-545
The Padé table of 2 F 1(a, 1; c; z) is normal for c > a > 0 (cf. [4]). For m ≥ n - 1 and c ? Z-, the denominator polynomial Q mn (z) in the [m/n] Padé approximant P mn (z)/Q mn (z) for 2 F 1(a, 1; c; z) and the remainder term Q mn (z)2 F 1(a, 1; c; z)-Pmn (z) were explicitly evaluated by Padé (cf. [2], [6] or [9]). We show that for c > a > 0 and m ≥ n - 1, the poles of Pmn (z)/Qmn (z) lie on the cut (1,∞). We deduce that the sequence of approximants Pmn (z)/Qmn (z) converges to 2 F 1(a, 1; c; z) as m → ∞, n/m → ρ with 0 < ρ ≤ 1, uniformly on compact subsets of the unit disc |z| < 1 for c > a > 0. 相似文献
30.
Christof Wetterich 《General Relativity and Gravitation》1998,30(1):159-172
A nonlocal form of the effective gravitational action could cure the unboundedness of euclidean gravity with Einstein action. On sub-horizon length scales the modified gravitational field equations seem compatible with all present tests of general relativity and post-Newtonian gravity. They induce a difference in the effective Newtonian constant between regions of space with vanishing or nonvanishing curvature scalar (or Ricci tensor). In cosmology they may lead to a value < 1 for the critical density after inflation. The simplest model considered here appears to be in conflict with nucleosynthesis, but generalizations consistent with all cosmological observations seem conceivable. 相似文献