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Full-Text Articles in Physics

Critical-Behavior At The Nematic To Smectic-A Transition In A Nonpolar Liquid-Crystal With Wide Nematic Range, Li Chen, J. D. Brock, J. Huang, Satyendra Kumar Oct 1991

Critical-Behavior At The Nematic To Smectic-A Transition In A Nonpolar Liquid-Crystal With Wide Nematic Range, Li Chen, J. D. Brock, J. Huang, Satyendra Kumar

Physics Publications

High-resolution x-ray scattering experiments to study the critical smectic-A fluctuations in the nematic phase have been performed on a mixture of two nonpolar, two-benzene-ring compounds. The ratio T(NA)/T(NI) (= 0.885) for this mixture is much smaller than for previously studied similar materials. The smectic correlation lengths parallel and perpendicular to the smectic-layer normal are found to diverge anisotropically with characteristic exponents-nu parallel-to = 0.75 +/- 0.03, nu perpendicular-to = 0.65 +/- 0.03, and the susceptibility with gamma = 1.24 +/- 0.05.


Determination Of The Liquid-Crystal Surface Elastic-Constant K24, David W. Allender, G. P. Crawford, J. W. Doane Sep 1991

Determination Of The Liquid-Crystal Surface Elastic-Constant K24, David W. Allender, G. P. Crawford, J. W. Doane

Physics Publications

Analysis of the Frank free energy for nematics confined to cylindrical regions indicates that the director pattern is dependent on the surface elastic constant K24 if there is weak normal anchoring and escape along the cylinder axis. Using deuterium nuclear-magnetic-resonance techniques on samples of submicrometer-size cavities in Nuclepore membranes, we report the first measurement of K24.


Finite Molecular Anchoring In The Escaped-Radial Nematic Configuration: A 2-H-Nmr Study, G. P. Crawford, David W. Allender, J. William Doane, M. Vilfan, I. Vilfan Aug 1991

Finite Molecular Anchoring In The Escaped-Radial Nematic Configuration: A 2-H-Nmr Study, G. P. Crawford, David W. Allender, J. William Doane, M. Vilfan, I. Vilfan

Physics Publications

The director-field configuration of a nematic liquid crystal confined to cylindrical cavities of polycarbonate Nuclepore membranes ranging from 0.3 to 0.05-mu-m in radius is determined using deuterium nuclear magnetic resonance (H-2 NMR). Spectral patterns from cavities of radius 0.3-mu-m reveal the escaped-radial configuration with singular point defects, but as the cylinder size is decreased, the elastic energy imposed by the curvature of the confining walls competes with the anchoring energy to tilt the directors away from their preferred perpendicular anchoring direction, preventing the expected transition to the planar-radial configuration. A surface fitting parameter is directly determined by ...


Absence Of The Incommensurate Smectic-A Phase In Db7ocn+8ocb Mixtures, Satyendra Kumar, Li Chien, V. Surendranath Jul 1991

Absence Of The Incommensurate Smectic-A Phase In Db7ocn+8ocb Mixtures, Satyendra Kumar, Li Chien, V. Surendranath

Physics Publications

The results of a high-resolution x-ray-diffraction study of the smectic phases in mixtures of DB7OCN and 8OCB show that the incommensurate smectic-Ai2 phase, previously reported in this mixture, is in fact a coexistence of the partially bilayer smectic-Ad and the bilayer smectic-A2phases at a first-order phase transition between them.


Nematic-Isotropic Phase-Transition In A Liquid-Crystal Droplet, S. Kralj, S. Zumer, David W. Allender Mar 1991

Nematic-Isotropic Phase-Transition In A Liquid-Crystal Droplet, S. Kralj, S. Zumer, David W. Allender

Physics Publications

Possible phases in a nematic liquid crystal confined to a spherical submicrometer droplet embedded in a solid polymer are analyzed in terms of a Landau-de Gennes theory. For a droplet with a radial structure we show that the strength of the nematic-polymer interfacial interaction affects the nematic-paranematic (partially ordered isotropic phase) phase transition and may in addition induce a boundary-layer nematic phase. This boundary layer phase exists only in a narrow (approximately 0.1 K) temperature interval above the nematic phase for a restricted range of interfacial interactions. Also in the radial structure the degree of ordering is suppressed close ...


Microcalorimetric Study Of Nematic-To-Neat-Soap And Nematic-To-Isotropic Phase Transitions In A Lyotropic Liquid Crystal, T. S. Shin, Satyendra Kumar Feb 1991

Microcalorimetric Study Of Nematic-To-Neat-Soap And Nematic-To-Isotropic Phase Transitions In A Lyotropic Liquid Crystal, T. S. Shin, Satyendra Kumar

Physics Publications

The results of specific-heat measurements at the nematic- (N) to-neat-soap (NS) and nematic-to-isotropic (I) phase transitions in binary mixtures of cesium-perfluoro-octanoate and water are reported. The ratio of specific-heat amplitudes above and below the N-NS transition, A+/A-, and the specific-heat exponent α remain ∼1.0 and ≤0.02, respectively, suggesting 3D XY-type behavior. At the first-order N-I transition, vanishing latent heat and coexistence range at low concentration indicate the existence of a Landau point.


A Unified Treatment Of The Non-Relativistic And Relativistic Hydrogen Atom I: The Wavefunctions, R. A. Swainson, Gordon W. F. Drake Jan 1991

A Unified Treatment Of The Non-Relativistic And Relativistic Hydrogen Atom I: The Wavefunctions, R. A. Swainson, Gordon W. F. Drake

Physics Publications

In this and the following two papers in this series it is shown how the radial part of non-relativistic and relativistic hydrogenic bound-state calculations involving the Green functions can be presented in a unified manner. The angular part of such calculations, being well understood, is performed in the standard way. In this, the first paper, it is shown how a suitable linear transformation of the two relativistic radial wavefunctions allows the pair of relativistic coupled differential equations to be written as two uncoupled second-order equations which are simple generalizations of the corresponding non-relativistic equation. This transformation is presented in a ...


Quantum Defects And The 1/N Dependence Of Rydberg Energies: Second-Order Polarization Effects, Gordon W. F. Drake, R. A. Swainson Jan 1991

Quantum Defects And The 1/N Dependence Of Rydberg Energies: Second-Order Polarization Effects, Gordon W. F. Drake, R. A. Swainson

Physics Publications

The principal result of this paper is a general expression for the second-order dipole polarization energy of a Rydberg electron resulting from the term -1/r4 in the asymptotic potential, where 1 is the core polarizability. It is shown that the second-order term contributes even as well as odd powers of 1/n in a 1/n expansion of the energies for Rydberg states. The results are used to extend the interpretation of the terms in a quantum-defect expansion. It is shown that the Ritz expansion for the quantum defect, which contains only even inverse powers of the effective quantum ...


Variational Calculation For The Ground State Of Lithium And The Qed Corrections For Li-Like Ions, D. K. Mckenzie, Gordon W. F. Drake Jan 1991

Variational Calculation For The Ground State Of Lithium And The Qed Corrections For Li-Like Ions, D. K. Mckenzie, Gordon W. F. Drake

Physics Publications

High-precision variational calculations using multiple basis sets in Hylleraas coordinates are presented for the 1s22s 2S state of lithium. The variational bound of -7.478 060 326(10) a.u. for the nonrelativistic energy is in good agreement with our revised experimental value of -7.47 806 034(20) a.u., thereby resolving a long-standing disrepancy. Two-electron calculations of the QED corrections are extended to three-electron systems and compared with other results. The comparison for Li-like ions up to U89+ suggests a simple interpretation for the ''screening of the Lamb shift'' recently calculated by Cheng, Johnson, and Sapirstein [Phys. Rev ...


Erratum: Expectation Values Of Rp For Arbitrary Hydrogenic States (Physical Review A (1991) 43, 11, (6432)), Gordon W. F. Drake, R. A. Swainson Jan 1991

Erratum: Expectation Values Of Rp For Arbitrary Hydrogenic States (Physical Review A (1991) 43, 11, (6432)), Gordon W. F. Drake, R. A. Swainson

Physics Publications

No abstract provided.


Measurement Of The N=2 Lamb Shift In He+ By The Anisotropy Method, A. Van Wijngaarden, J. Kwela, Gordon W. F. Drake Jan 1991

Measurement Of The N=2 Lamb Shift In He+ By The Anisotropy Method, A. Van Wijngaarden, J. Kwela, Gordon W. F. Drake

Physics Publications

A high-precision measurement of the 2s 2S1/22p 2P1/2 Lamb shift in He+ by the quenching-anisotropy method is reported. The theory and experimental method are described in detail. The measured value of 14042.520.16 MHz (11 parts per million) rivals the accuracy of Lamb-shift measurements in hydrogen by microwave resonance. By subtracting the known low-order terms in the Lamb shift, we interpret the results as a measurement of the order (Z)6mc2 and higher contributions to the electron self-energy GSE(Z). The various contributions to the Lamb shift are discussed, and a revised value for GSE(Z) at ...


A Unified Treatment Of The Non-Relativistic And Relativistic Hydrogen Atom Ii: The Green Functions, R. A. Swainson, Gordon W. F. Drake Jan 1991

A Unified Treatment Of The Non-Relativistic And Relativistic Hydrogen Atom Ii: The Green Functions, R. A. Swainson, Gordon W. F. Drake

Physics Publications

This is the second in a series of three papers in which it is shown how the radial part of non-relativistic and relativistic hydrogenic bound-state calculations involving the Green functions can be presented in a unified manner. In this paper the nonrelativistic Green function is examined in detail; new functional forms are presented and a clear mathematical progression is shown to link these and most other known forms. A linear transformation of the four radial parts of the relativistic Green function is given which allows for the presentation of this function as a simple generalization of the non-relativistic Green function ...


A Unified Treatment Of The Non-Relativistic And Relativistic Hydrogen Atom: Iii. The Reduced Green Functions, R. A. Swainson, Gordon W. F. Drake Jan 1991

A Unified Treatment Of The Non-Relativistic And Relativistic Hydrogen Atom: Iii. The Reduced Green Functions, R. A. Swainson, Gordon W. F. Drake

Physics Publications

The last in a series of three papers in which it is shown how the radial part of non-relativistic and relativistic hydrogenic bound-state calculations involving the Green functions can be presented in a unified manner. The work presented here is concerned with the reduced Green functions which arise in second-order stationary state perturbation theory. Using a simple linear transformation of the four radial parts of the relativistic reduced Green function it is shown how the non-relativistic and relativistic functions are special instances of the solution of a general second-order differential equation. The general solution of this equation is exhibited in ...