Transient Nucleation near the Mean-Field Spinodal

Nucleation is considered near the pseudospinodal in a one-dimensional $\phi^4$ model with a non-conserved order parameter and long-range interactions. For a sufficiently large system or a system with slow relaxation to metastable equilibrium, there is a non-negligible probability of nucleation occurring before reaching metastable equilibrium. This process is referred to as transient nucleation. The critical droplet is defined to be the configuration of maximum likelihood that is dynamically balanced between the metastable and stable wells. Time-dependent droplet profiles and nucleation rates are derived, and theoretical results are compared to computer simulation. The analysis reveals a distribution of nucleation times with a distinct peak characteristic of a nonstationary nucleation rate. Under the quench conditions employed, transient critical droplets are more compact than the droplets found in metastable equilibrium simulations and theoretical predictions.Comment: 7 Pages, 5 Figure

Photoinduced 3D orientational order in side chain liquid crystalline azopolymers

We apply experimental technique based on the combination of methods dealing with principal refractive indices and absorption coefficients to study the photoinduced 3D orientational order in the films of liquid crystalline (LC) azopolymers. The technique is used to identify 3D orientational configurations of trans azobenzene chromophores and to characterize the degree of ordering in terms of order parameters. We study two types of LC azopolymers which form structures with preferred in-plane and out-of-plane alignment of azochromophores, correspondingly. Using irradiation with the polarized light of two different wavelengths we find that the kinetics of photoinduced anisotropy can be dominated by either photo-reorientation or photoselection mechanisms depending on the wavelength. We formulate the phenomenological model describing the kinetics of photoinduced anisotropy in terms of the isomer concentrations and the order parameter tensor. We present the numerical results for absorption coefficients that are found to be in good agreement with the experimental data. The model is also used to interpret the effect of changing the mechanism with the wavelength of the pumping light.Comment: uses revtex4 28 pages, 10 figure

Unwinding of a cholesteric liquid crystal and bidirectional surface anchoring

We examine the influence of bidirectional anchoring on the unwinding of a planar cholesteric liquid crystal induced by the application of a magnetic field. We consider a liquid crystal layer confined between two plates with the helical axis perpendicular to the substrates. We fixed the director twist on one boundary and allow for bidirectional anchoring on the other by introducing a high-order surface potential. By minimizing the total free energy for the system, we investigate the untwisting of the cholesteric helix as the liquid crystal attempts to align with the magnetic field. The transitions between metastable states occur as a series of pitchjumps as the helix expels quarter or half-turn twists, depending on the relative sizes of the strength of the surface potential and the bidirectional anchoring. We show that secondary easy axis directions can play a significant role in the unwinding of the cholesteric in its transition towards a nematic, especially when the surface anchoring strength is large

Light Induced Structures in Liquid Crystalline Side-Chain Polymers with Azobenzene Functional Groups

We applied ellipsometry to study the distribution of azobenzene fragments in the films of two types of comblike polymers with azobenzene moieties in the side chains before and after ultraviolet ~UV! light irradiation. The polymer with an alkyl chain at the end of the azobenzene fragment forms structures with preferred homeotropic alignment of the fragments. Irradiation of this polymer with nonpolarized UV light at normal incidence induces a homeotropic alignment of azobenzene fragments. Oblique irradiation induces tilted structures. Polarized UV light irradiation at normal beam incidence induces biaxial structures with a fanlike distribution of azobenzene fragments and preferably out-of-plane alignment. The polymer with polar nitro group at the end of the azobenzene moiety shows preferential in-plane orientation. The degenerate in-plane alignment is retained for normal irradiation with nonpolarized UV light. Excitation with polarized light provides highly ordered in-plane alignment of the azobenzene fragments perpendicular to the UV light polarization. Re-orientation of the fragments under a second UV exposure with orthogonal polarization involves out-of-plane rotation of the fragments.</p

Characteristics of tissue expression of extracellular matrix proteolytic enzymes and their inhibitors in patients with bladder cancer

Objectives. Levels and expression of matrix metalloproteases 2 (MMP-2), MMP-9, MMP-14 and tissue inhibitor of metalloproteinases 1 (TIMP-1), TIMP-2 were studied by immunohistochemistry in tumor and surrounding tissues in 73 patients with superficial bladder cancer (BC) ТаN0M0 and Т1N0M0 depending on the disease characteristics. Results. The study showed the initial increase in the number of tumor cells expressing MMP-2, MMP-9 and MMP-14 and their tissue inhibitors, compared to histologically unchanged tissues and tumor-adjacent tissues. The number of MMP-9 producing tumor cells was maximal. Tissue expression of TIMP-1 and TIMP-2 in tumor cells in superficial BC patients was higher than in unchanged tissues and in tumor-adjacent tissues. The ratio of MMP and TIMP expression differed, and the proteolytic potential of MMP was higher than that of TIMP.Conclusion. The study demonstrated the influence of the primary bladder cancer stage (from Ta to T1), tumor differentiation grade (from G1 to G2) and prognosis of the disease course (from favorable to intermediate) on the enhancing expression of MMP-9 and TIMP-1 in tumor tissues in superficial BC