Biomedical subjects

C Rosenblatt

Publications and source records attributed to C Rosenblatt.

At least 19 recordsLinked to original sources

PubMed2000

Freedericksz transition in an anticlinic liquid crystal

It is shown experimentally that a very-long-pitch, surface-stabilized, anticlinic liquid crystal undergoes a two-step electric-field-induced transition to the synclinic phase. The liquid crystal remains undistorted below a threshold field E(th). For E>E(th), a Freedericksz transition occurs, wherein molecules in adjacent smectic layers undergo unequal azimuthal rotations about the layer normal. At higher fields a transition to the synclinic phase occurs via solitary waves.

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PubMed2000

Collapse dynamics of liquid bridges investigated by time-varying magnetic levitation

Using a novel technique that facilitates temporal control over the total body force on a liquid, an unexpected scaling relationship was discovered for the collapse time of a liquid bridge. A paramagnetic liquid was suspended between the tips of two collinear rods in a strong magnetic field gradient that was adjusted to compensate gravity. A sudden change of the magnet current, corresponding to a change of Bond number, resulted in a deformation and ultimate collapse of the liquid bridge. The collapse time was found to be independent of the bridge length when other parameters were held constant.

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PubMed2000

Bend elasticity of mixtures of V-shaped molecules in ordinary nematogens

Freedericksz measurements were performed on mixtures of a nematic mesogen and a V-shaped molecule. The bend elastic constant was found to decrease significantly with increasing concentration of the V-shaped molecule. The results are discussed theoretically, taking into account the detailed structure of the molecules.

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PubMed2000

Interlayer interactions in enantiomeric anticlinic liquid crystalline mixtures

The interlayer interaction coefficient U in the anticlinic phase of enantiomeric binary mixtures was determined by measuring the threshold electric field for the onset of solitary waves. U was found to increase with decreasing temperature in the anticlinic phase for a given enantiomer excess X. The ratio U(X,straight theta)/U(X=1,straight theta), where straight theta is the polar angle, was found to be significantly smaller for mixtures with low enantiomer excess than for the optically pure material. The observed behavior is analyzed using a mean-field model for dipole-dipole interactions in adjacent layers.

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PubMed2000

Freedericksz transition in an anticlinic liquid crystal

The Freedericksz geometry is used to show experimentally that a very-long-pitch, surface stabilized, anticlinic liquid crystal undergoes a two-step electric-field-induced transition to the synclinic phase. The liquid crystal remains undistorted below the threshold field E(th). For E>E(th), a Freedericksz transition occurs, wherein molecules in adjacent smectic layers undergo unequal azimuthal rotations about the layer normal, resulting in a nonzero polarization that couples to the applied field. Measurements of E(th) as a function of temperature are reported. Related quasielastic light scattering measurements demonstrate that acoustic Goldstone mode fluctuations are quenched by a dc electric field E>E(th). At high fields a transition to the synclinic phase occurs via solitary waves.

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PubMed2000

Electric field-induced acoustic-optic mode coupling in an anticlinic liquid crystal

A dc electric field was applied perpendicular to the tilt plane of a pitch-compensated (unwound helix) anticlinic liquid crystal. By means of quasielastic light scattering, the field was found to couple the acoustic and optic Goldstone modes, resulting in an increase of the relaxation time tau(beta) of the acousticlike eigenmode. Elastic constants were estimated from the relaxation time data.

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PubMed1999

Stability of Magnetically Levitated Liquid Bridges of Arbitrary Volume Subjected to Axial and Lateral Gravity.

The paramagnetic fluid composed of manganese chloride tetrahydrate dissolved in water was used to form bridges held between two parallel collinear rods. Magnetic levitation was used to control the effective gravity felt by the bridges. Their stability was studied as a function of Bond number and volume of the supported liquid. Data are compared with theoretical predictions for liquid bridges as well as with experimental results, where available. Copyright 1999 Academic Press.

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PubMed1996