Filtration in highly porous cellular materials

When studying filtration for materials with a high porosity (higher than 0.80) and large pore sizes (1–5 mm), the capillary model structure, traditionally used in powder metallurgy, cannot be regarded as adequate to the actual processes that occur. The physical picture of the motion of a liquid in a layer of highly porous cellular material can be defined as the flow of a liquid around a spatial framework (the "external" problem of hydrodynamics). For pressure filtering in a highly porous cellular material, three characteristic types of motion of the liquid are observed: laminar undetached flow (Re < 1), detached vortex-free flow (1 < Re < 10), and detached vortex flow (Re > 10). RITTs of Powder Metallurgy. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 48–50, April, 1998.     

Sodium NMR relaxation in porous materials

The NMR relaxation of hydrogen nuclei of a fluid in a porous material is generally interpreted in terms of the Brownstein-Tarr model, in which the relaxation rate of the signal is inversely proportional to the pore size. We have investigated whether this model can be applied to the relaxation of Na nuclei in a NaCl solution in a porous material. The results indicate that the ion distribution over the pores can be obtained from an analysis of the Na NMR signal decay, if the pore sizes are roughly below 1 microm. This information is very useful for studies of combined moisture and ion transport in porous building materials.     

Acoustical characteristics of porous materials

The diversity of porous materials is noted. However, this study is particularly relevant to the use of sound absorbent materials in architectural acoustics. The theory of sound propagation within an idealised porous material consisting of a rigid matrix through which run parallel cylindrical pores normal to the surface is reviewed. Extensions to pores of arbitrary orientation and cross-section are achieved by introducing physically-measura ble microstructural constants rather than phenomenological bulk parameters that might be frequency dependent. By comparison of several theories that account for sound propagation within an elastically-framed porous material a basis is laid for an improved formulation, that takes into account both viscosity and heat conduction.The application of various propagation theories to model the reflection and transmission of sound at porous boundaries is considered. Particular attention is paid to the common assumption of local reaction and to the adequacy of modelling the porous interface as that of a quasi-homogeneous fluid. Finally the most widely used methods of measuring acoustical characteristics of porous materials at normal and oblique incidence and of obtaining their values by empirical means are surveyed.     

Wormhole Solutions in Superstring Theory

The wormhole is discussed in 4-dimensional superstring theory; the correspondingwormhole equation is deduced, from which both the analytical and numericalsolutions are given with three different cases of cosmological constant.     

X-ray-induced secondary electron emission in porous materials

Electron emission induced by X-ray radiation in secondary-emission porous materials was investigated.     

Temperature pattern dynamics in shocked porous materials

The physical fields in porous materials under strong shock wave reaction are very complicated. We simulate such systems using the grain contact material point method. The complex temperature fields in the material are treated with the morphological characterization. To compare the structures and evolution of characteristic regimes under various temperature thresholds, we introduce two concepts, structure similarity and process similarity. It is found that the temperature pattern dynamics may show high similarity under various conditions. Within the same material, the structures and evolution of high-temperature regimes may show high similarity if the shock strength and temperature threshold are chosen appropriately. For process similarity in materials with high porosity, the required temperature threshold increases parabolically with the impact velocity. When the porosity becomes lower, the increasing rate becomes higher. For process similarity in different materials, the required temperature threshold and the porosity follow a power-law relationship in some range.     

Geodesics in the Wormhole Gravitational Field

Journal of Experimental and Theoretical Physics - The structure of spacetime near a wormhole (WH) and possible observational consequences are investigated theoretically. In connection with the...     

Decay of mesoscopically localized vibrations in porous materials

The low-temperature decay of a vibrational eigenstate of a crystalline mesoscopic particle surrounded by other such particles of approximately the same size is considered. The decay time is determined by the anharmonicity and the coupling between adjacent mesoscopic particles. Under some limiting conditions for particles of a typical size of 50 Å the decay time at low temperatures can be several milliseconds. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 1, 51–56 (10 January 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Salt transport and crystallization in porous building materials

Salt weathering is a major cause of deterioration of porous building materials. To obtain information about the mechanisms underlying these damage processes we have studied the moisture and ion transport. We measured the time evolution of NaCl saturated samples of fired-clay brick during one-sided drying using Nuclear Magnetic Resonance. The moisture content and amount of dissolved Na ions could be measured quantitatively as a function of position. The NaCl concentration profiles obtained from these data reflect the competition between advection to the surface and redistribution by diffusion. By representing the measured moisture and NaCl profiles in an efflorescence pathway diagram (EPD) also the crystallization can be taken into account.     

Wormhole solution in Bergmann-Wagoner scalar-tensor gravitational theory

We give a Euclidean wormhole solution in the vacuum Bergmann-Wagoner scalar-tensor gravitational theory. We show that this wormhole, unlike others, has complex charge and is a baby universe (half a wormhole).     

Microstructure and texture of cementitious porous materials

We have characterized the microstructure of different cementitious materials (white and Portland cement pastes, mortars, concretes) by different magnetic resonance techniques. In particular, we show how the measurement of proton nuclear magnetic spin-lattice relaxation as a function of magnetic field strength (and hence nuclear Larmor frequency) can provide reliable information on the dynamics of proton species at the surface of CSH, the specific surface area and the pore size distribution throughout the progressive hydration of cement-based materials. The measurement does not require any drying temperature modification and is sufficiently fast to be applied continuously during the progressive hydration of the material. Coupling this method with the standard proton nuclear spin relaxation and high-resolution NMR allows us to follow the development of microscale texture within the material.     

Characterization of porous materials by small-angle scattering

Characterization of porous materials by small-angle scattering has been extensively pursued for several years now as the pores are often of mesoscopic size and compatible with the length scale accessible by the technique using both neutrons and X-rays as probing radiation. With the availability of ultra small-angle scattering instruments, one can investigate porous materials in the sub-micron length scale. Because of the increased accessible length scale vis-a-vis the multiple scattering effect, conventional data analysis procedures based on single scattering approximation quite often fail. The limitation of conventional data analysis procedures is also pronounced in the case of thick samples and long wavelength of the probing radiation. Effect of multiple scattering is manifested by broadening the scattering profile. Sample thickness for some technologically important materials is often significantly high, as the experimental samples have to replicate all its essential properties in the bulk material. Larger wavelength of the probing radiation is used in some cases to access large length scale and also to minimize the effect of double Bragg reflections.     

具有旋量场的量子虫洞

本文利用Hawking-Page的边界条件讨论了具有费米场的量子虫洞,导出了相应的Wheeler-DeWitt方程,计算了虫洞波函数,由虫洞波函数的分析,发现虫洞在a=0处出现几率密度为零,虫洞基态最可几半径为Planck尺度.     

Energy of a Charged Wormhole

The Møller energy(due to matter and fields including gravity) distribution of the traversable Lorentzian wormhole space-time by the scalar field or electric charged is studied in two different approaches of gravity such as general relativity and tele-parallel gravity. The results are found exactly the same in these different approximations. The energy found in tele-parallel gravity is also independent of the tele-parallel dimensionless coupling constant, which means that it is valid in any tele-parallel model. Our results sustains that (a) the importance of the energy-momentum definitions in the evaluation of the energy distribution of a given space-time and (b) the viewpoint of Lassner that the Møller energy-momentum complex is a powerful concept of energy and momentum.