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Full-Text Articles in Physics

Discotic Micellar Nematic And Lamellar Phases Under Shear-Flow, J. T. Mang, Satyendra Kumar, B. Hammouda Dec 1994

Discotic Micellar Nematic And Lamellar Phases Under Shear-Flow, J. T. Mang, Satyendra Kumar, B. Hammouda

Physics Publications

Small-angle neutron scattering was employed to study the effect of shear flow on the nematic (N) and lamellar (L(alpha)) phases in aqueous solutions of cesium perfluoro-octanoate. Shear rates as high as similar to 4000 s(-1) were used. The N phase was found to align with the director in the direction of the gradient velocity. The L, phase oriented with lamellae parallel to the shear plane. This change in equilibrium orientation is attributed, primarily, to changes in the value of the Ericksen viscosity parameter at. Subtle shear-rate-dependent director reorientations were also observed in the proximity of the N-to-L(alpha ...


X-Ray Studies Of The Hexatic Phase In Liquid-Crystals With A Crystal-B-Hexatic-B-Smectic-A Phase Sequence, Ewa Gorecka, Li Chen, Wieslaw Pyzuk, Adam Krowczynski, Satyendra Kumar Oct 1994

X-Ray Studies Of The Hexatic Phase In Liquid-Crystals With A Crystal-B-Hexatic-B-Smectic-A Phase Sequence, Ewa Gorecka, Li Chen, Wieslaw Pyzuk, Adam Krowczynski, Satyendra Kumar

Physics Publications

Free-standing monodomain thick films of three liquid crystalline compounds were examined by x-ray scattering. These compounds exhibit a unique enantiotropic crystal-B-hexatic-B-smectic-A phase sequence with no evidence of herringbone order. The hexatic order parameter Cg changes in the hexatic phase with critical exponent beta=0.15+/-0.03. Temperature dependence of the in-plane positional order correlation length suggests a strongly first-order hexatic-B to crystal-B phase transition with indiscernible enthalpy change.


Experimental-Observation Of A Transition Between 2 Uniaxial Nematic Liquid-Crystal Phases, G. Nounesis, Satyendra Kumar, S. Pfeiffer, R. Shashidhar, C. W. Garland Jul 1994

Experimental-Observation Of A Transition Between 2 Uniaxial Nematic Liquid-Crystal Phases, G. Nounesis, Satyendra Kumar, S. Pfeiffer, R. Shashidhar, C. W. Garland

Physics Publications

The experimental observation of a phase transition between two uniaxial nematic liquid-crystalline phases is reported. High-resolution x-ray scattering and ac calorimetric studies on binary mixtures of octyl- and decyloxyphenyl-nitrobenzoyloxy benzoates show evidence of a first-order transition between two nematic phases with different types of short-range smectic order. This transition is observed in the vicinity of the termination of the smectic-Ad-smectic-A1 phase boundary, in accordance with theoretical predictions.


Surface-Layer Phase-Transitions In Nematic Liquid-Crystals, Natasha Kothekar, David W. Allender, R. M. Hornreich Apr 1994

Surface-Layer Phase-Transitions In Nematic Liquid-Crystals, Natasha Kothekar, David W. Allender, R. M. Hornreich

Physics Publications

Surface-layer transitions in nematogenic materials characterized by a preferential planar surface interaction linear in the order parameter have been studied theoretically at temperatures above the bulk transition (T(NI)). The coupled Euler-Lagrange nonlinear differential equations obtained from the Landau-de Gennes free energy were solved exactly by numerical integration. This problem had been studied previously employing various limits and approximations with several differences in the phase diagram reported. The exact results allow one to determine which of these differences are artifacts of the approximations used and which are dependent upon the ratio of elastic constants. It is found, for physically relevant ...


Surface-Induced Discrete Smectic Order In The Isotropic-Phase Of 12cb In Cylindrical Pores, Germano S. Iannacchione, Joseph T. Mang, Satyendra Kumar, Daniele Finotello Mar 1994

Surface-Induced Discrete Smectic Order In The Isotropic-Phase Of 12cb In Cylindrical Pores, Germano S. Iannacchione, Joseph T. Mang, Satyendra Kumar, Daniele Finotello

Physics Publications

No abstract provided.


A Rigorous Treatment Of O(Α 6mc 2) Qed Corrections To The Fine Structure Splittings Of Helium, T. Zhang, Gordon W. F. Drake Jan 1994

A Rigorous Treatment Of O(Α 6mc 2) Qed Corrections To The Fine Structure Splittings Of Helium, T. Zhang, Gordon W. F. Drake

Physics Publications

Relativistic formulae for the energy level shifts due to electron self-energy corrections are derived within the external potential Bethe-Salpeter formalism. A rigorous treatment of QED corrections to the fine structure splittings of helium is carried out. Although some individual self-energy diagrams give contributions of order α 6mc 2, they are shown to sum to zero. In addition, the α 6mc 2 correction from vertex modifications in the presence of Coulomb photons does not contribute. Therefore, a rigorous treatment of all QED corrections of order α 6mc 2 to the fine structure splittings of helium now appears to be complete. © 1994 ...


Lamb Shifts And Hyperfine Structure In Li+6 And Li+7: Theory And Experiment, E. Riis, A. G. Sinclair, O. Poulsen, Gordon W. F. Drake Jan 1994

Lamb Shifts And Hyperfine Structure In Li+6 And Li+7: Theory And Experiment, E. Riis, A. G. Sinclair, O. Poulsen, Gordon W. F. Drake

Physics Publications

High-precision laser-resonance measurements accurate to ±0.5 MHz or better are reported for transitions among the 1s2s 3S1-1s2p 3PJ hyperfine manifolds for each of J=0, 1, and 2 in both Li+6 and Li+7. A detailed analysis of hyperfine structure is performed for both the S and P states, using newly calculated values for the magnetic dipole and electric quadrupole coupling constants, and the hyperfine shifts subtracted from the measurements. The resulting transition frequencies are then analyzed on three different levels. First, the isotope shifts in the fine-structure splittings are calculated from the relativistic reduced mass and recoil ...


High-Precision Calculations Of The Zeeman Effect In The 2 3pj, 2 1p1, 2 3s1, And 3 3pj States Of Helium, Z. C. Yan, Gordon W. F. Drake Jan 1994

High-Precision Calculations Of The Zeeman Effect In The 2 3pj, 2 1p1, 2 3s1, And 3 3pj States Of Helium, Z. C. Yan, Gordon W. F. Drake

Physics Publications

The g factors for the Zeeman effect, including relativistic corrections up to order 2 a.u., are calculated to high precision for the 2 3PJ, 2 1P1, 2 3S1, and 3 3PJ states of helium, using variational wave functions constructed from doubled Hylleraas-type basis sets. Our results clarify the present disagreements among the existing theoretical values for the g factors. The experimental values of the fine-structure splittings for the helium 3 3PJ states, measured by Yang et al. [Phys. Rev. A 32, 2249 (1985); 33, 1725 (1986)], are reanalyzed, using our improved g factors. © 1994 The American Physical Society.