СONCEPT AND CALCULATION OF THE LIMIT TRANSVERSE SIZE OF CAPILLARIES

Porous medium are products of processing in food, agricultural, chemical and many other industries. Calculations of processes with wet porous medium are based on capillary properties of the liquid in a pore space. The capillary properties of liquids in porous media are established in pore models in the form of thin tubes of circular or slit transverse sections. The intensity of the processes occurring in it depends on the nature of the filling of the pore space with liquid. Filling with liquid and the formation of a capillary layer is possible only in small pores. However, there is no analytical justification for the transverse pore size, more than which it cannot be filled with liquid by capillary forces. With this in mind, the concept of the limiting transverse size of a capillary for a liquid under conditions of complete wetting is introduced. The limiting size calculation is based on two conditions: the shape of the axial section of the meniscus surface has the appearance of a semicircle and its extremum point is located at the level of the free surface of the fluid supplying the capillary. A capillary column cannot form in larger pores. The absence of formulas for calculating capillaries of the limiting sizes can introduce a significant error into the analytical calculation of the moisture content in the capillary layer of a liquid in porous media and moisture transfer processes. The aim of the study was to obtain formulas for calculating the limiting (largest) sizes of capillaries of a circular, flat slit section and annular transverse sections with complete wetting of their walls. For the conditions above, it was identified that the limiting distance between the walls was independent from annular capillary diameter. The formulas for the limiting transverse sizes of the flat slit and annular capillaries turned out to be the same under the assumptions above. This indicates a weak dependence of the limiting size of a slit capillary on the curvature of its transverse section. Examples of calculations of capillaries of the limiting sizes are performed.Porous medium are products of processing in food, agricultural, chemical and many other industries. Calculations of processes with wet porous medium are based on capillary properties of the liquid in a pore space. The capillary properties of liquids in porous media are established in pore models in the form of thin tubes of circular or slit transverse sections. The intensity of the processes occurring in it depends on the nature of the filling of the pore space with liquid. Filling with liquid and the formation of a capillary layer is possible only in small pores. However, there is no analytical justification for the transverse pore size, more than which it cannot be filled with liquid by capillary forces. With this in mind, the concept of the limiting transverse size of a capillary for a liquid under conditions of complete wetting is introduced. The limiting size calculation is based on two conditions: the shape of the axial section of the meniscus surface has the appearance of a semicircle and its extremum point is located at the level of the free surface of the fluid supplying the capillary. A capillary column cannot form in larger pores. The absence of formulas for calculating capillaries of the limiting sizes can introduce a significant error into the analytical calculation of the moisture content in the capillary layer of a liquid in porous media and moisture transfer processes. The aim of the study was to obtain formulas for calculating the limiting (largest) sizes of capillaries of a circular, flat slit section and annular transverse sections with complete wetting of their walls. For the conditions above, it was identified that the limiting distance between the walls was independent from annular capillary diameter. The formulas for the limiting transverse sizes of the flat slit and annular capillaries turned out to be the same under the assumptions above. This indicates a weak dependence of the limiting size of a slit capillary on the curvature of its transverse section. Examples of calculations of capillaries of the limiting sizes are performed

Optical control of electron spin coherence in CdTe/(Cd,Mg)Te quantum wells

Optical control of the spin coherence of quantum well electrons by short laser pulses with circular or linear polarization is studied experimentally and theoretically. For that purpose the coherent electron spin dynamics in a n-doped CdTe/(Cd,Mg)Te quantum well structure was measured by time-resolved pump-probe Kerr rotation, using resonant excitation of the negatively charged exciton (trion) state. The amplitude and phase shifts of the electron spin beat signal in an external magnetic field, that are induced by laser control pulses, depend on the pump-control delay and polarization of the control relative to the pump pulse. Additive and non-additive contributions to pump-induced signal due to the control are isolated experimentally. These contributions can be well described in the framework of a two-level model for the optical excitation of the resident electron to the trion.Comment: 15 pages, 18 figure

Electronic Structure and Thermoelectric Prospects of Phosphide Skutterudites

The prospects for high thermoelectric performance in phosphide skutterudites are investigated based on first principles calculations. We find that stoichiometric CoP_3 differs from the corresponding arsenide and antimonide in that it is metallic. As such the band structure must be modified if high thermopowers are to be achieved. In analogy to the antimonides it is expected that this may be done by filling with La. Calculations for LaFe_4P_12 show that a gap can in fact be opened by La filling, but that the valence band is too light to yield reasonable p-type thermopowers at appropriate carrier densities; n-type La filled material may be more favorable.Comment: 3 pages, 3 figures, 1 tabl

DEFORMATION FEATURES OF UNIAXIAL COMPRESSION OF SAMPLES FROM THE POTATO TUBERS FLESH

The article analyzes the deformation mechanism under uniaxial compression of cylindrical samples cut from the pulp of potato tuber. In its typical S-shaped stress-strain diagram, three characteristic zones of different types of dominant deformation can be distinguished. Clarified the boundary between the second and third zones. The rationale for changing the type of deformations in each zone by adding a new type to the previous one is presented. Grounded elastic deformation in the first zone, which is associated with stretching of the cell membranes. In the second zone, the destruction of individual cells distributed in the sample volume occurs and in the third zone — the predominant gradual unification of these destructions. An explanation is given of the characteristic brittle fracture of the sample with significant residual deformations at the end of the third zone. The erroneous determination of the deformations of the second and third zones as plastic (yield) was noted. In this regard, a new term was introduced — modulus of rigidity Z. The change in the modulus of stiffness Z with increasing irreversible deformations indicates structural changes in the flesh of the sample due to its gradually collapsing cell structure. The reason for straightening diagrams for samples from fresh, hard potato tubers is explained. Taking into account the type of deformations by zones allows us to reasonably proceed to the creation of criteria for quantitative assessments of the degree of flaccidity of potato tubers.The article analyzes the deformation mechanism under uniaxial compression of cylindrical samples cut from the pulp of potato tuber. In its typical S-shaped stress-strain diagram, three characteristic zones of different types of dominant deformation can be distinguished. Clarified the boundary between the second and third zones. The rationale for changing the type of deformations in each zone by adding a new type to the previous one is presented. Grounded elastic deformation in the first zone, which is associated with stretching of the cell membranes. In the second zone, the destruction of individual cells distributed in the sample volume occurs and in the third zone — the predominant gradual unification of these destructions. An explanation is given of the characteristic brittle fracture of the sample with significant residual deformations at the end of the third zone. The erroneous determination of the deformations of the second and third zones as plastic (yield) was noted. In this regard, a new term was introduced — modulus of rigidity Z. The change in the modulus of stiffness Z with increasing irreversible deformations indicates structural changes in the flesh of the sample due to its gradually collapsing cell structure. The reason for straightening diagrams for samples from fresh, hard potato tubers is explained. Taking into account the type of deformations by zones allows us to reasonably proceed to the creation of criteria for quantitative assessments of the degree of flaccidity of potato tubers

SU(4) and SU(2) Kondo Effects in Carbon Nanotube Quantum Dots

We study the SU(4) Kondo effect in carbon nanotube quantum dots, where doubly degenerate orbitals form 4-electron ``shells''. The SU(4) Kondo behavior is investigated for one, two and three electrons in the topmost shell. While the Kondo state of two electrons is quenched by magnetic field, in case of an odd number of electrons two types of SU(2) Kondo effect may survive. Namely, the spin SU(2) state is realized in the magnetic field parallel to the nanotube (inducing primarily orbital splitting). Application of the perpendicular field (inducing Zeeman splitting) results in the orbital SU(2) Kondo effect.Comment: 5 pages. Some material was previously posted in cond-mat/0608573, v

Stability of Nonlinear Normal Modes in the FPU-β\beta Chain in the Thermodynamic Limit

All possible symmetry-determined nonlinear normal modes (also called by simple periodic orbits, one-mode solutions etc.) in both hard and soft Fermi-Pasta-Ulam-$\beta$ chains are discussed. A general method for studying their stability in the thermodynamic limit, as well as its application for each of the above nonlinear normal modes are presented

Orthogonality of Biphoton Polarization States

Orthogonality of two-photon polarization states belonging to a single frequency and spatial mode is demonstrated experimentally, in a generalization of the well-known anti-correlation 'dip' experiment.Comment: Submitted to Phys.Rev.Let

Stability analysis of dynamical regimes in nonlinear systems with discrete symmetries

We present a theorem that allows to simplify linear stability analysis of periodic and quasiperiodic nonlinear regimes in N-particle mechanical systems (both conservative and dissipative) with different kinds of discrete symmetry. This theorem suggests a decomposition of the linearized system arising in the standard stability analysis into a number of subsystems whose dimensions can be considerably less than that of the full system. As an example of such simplification, we discuss the stability of bushes of modes (invariant manifolds) for the Fermi-Pasta-Ulam chains and prove another theorem about the maximal dimension of the above mentioned subsystems