In this paper, thin films of some fatty acids and fatty acid-cholesterol mixtures were investigated as biological membrane simple models, in order to establish the thermal neutron irradiation influence on these systems, while in the smectic C liquid crystal state. Samples are nonlinear dielectrics with a weak conduction, and nonlinear optical media. They generally present some memore effects. Cholesterol modifies these properties depending on its percentage in mixture and saturated or unsaturated character of the acid. After exposed to a flow of thermal neutrons, texture and behavioral changes, in terms of content of cholesterol in mixtures, and depending on the number of carbon atoms, were emphasized.
This paper presents the effect of thermal neutrons irradiation on some properties of one of the most common long-chain fatty acids, found in combined form in natural animal and vegetable fats, the stearic acid, with role in the biological membrane. Microscopic aspect, electric current and optical properties under laser beam change by irradiation. These changes can offer information both for biology and technique.
The influence of the cholesterol amount in mixtures with fatty acids, in balance with the action of different external perturbations, is the aim of this paper. Samples were investigated as cells containing thin films in the smectic C liquid crystal state, sandwiched between transparent electrodes. D.c. electric fields, weak laser beams, thermal neutrons flows were applied on the samples and their response was studied.
A variety of self-organized patterns were observed in liquid crystal modulators, generated because of their large and controllable nonlinearity. In this work, we investigated some fatty acids and mixtures with cholesterol, which showed, under certain conditions, thermotropic mesomorphism and a large sensitivity to the optical field. Depending on the transverse profile of the laser beam, a self-phase modulation and external self-focusing - illustrating the nonlinear wave propagation - were observed. A ring pattern, due to the steady-state far-field diffraction intensity distribution of the Gaussian beam of a helium-neon laser, transmitted through the samples, was experimentally and computer studied. This is useful both for building new photonic devices and for explaining some processes from the biological membrane.
Phase-coherent control of photocurrent magnitude and directionality in semiconductors using lineraly chirped pulses is proposed and analysed. Measurable photocurrents can be generated for the pulsewidth shorter than the dephasing time of the excited carriers.
Last years, lasers' applications in medicine and biology were fully enriched by using computer facilities. Our studies were focused on the nonlinear behavior of some substances important for the living matter, as for example fatty acids and their mixtures with cholesterol and some drugs. The experimental data were computer processed and some computer models of the phenomena were built.
Sandwich 25micrometers -thick cells with transparent electrodes, filled with some fatty acids (FA) important for the biological membrane (BM), and their mixtures with cholesterol, in the liquid crystal (LC) state, were subjected to a flow of thermal neutrons (4.15 x 1012 neutrons/cm2). Microstructural aspects, electric behaviour and nonlinear optical effects under lower power laser beams were studied before and after irradiation. The laser interaction with FA in the LC state shows the influence of the thermal neutrons irradiation on the electric conduction and the molecular arrangements in the LC systems. Before irradiation, a lens-like effect u nder a He-Ne laser beam has been noticed in the unsaturated (UFA) acids; due to the self-phase modulation effect, a ring pattern appear in far field. The presence of cholesterol (ch) in mixtures modified these effects. After irradiation, the optical nonlinear effects change their feature, increasing in UFA and occurring also in some saturated acids (SFA). These changes are in agreement with the microscopical aspects, the color modifications, and with the electrical state change. The mixture samples are analyzed too. A month after irradiation, SFA seem to slowing return to the initial state, but UFA samples do not come back to the state before irradiation. The nonlinear optical behavior changes dramatically. Ch slightly modifies these changes.
In this paper, we present a study of pure arachidonic acid, arachidic acid, other fatty acids (FA) and mixtures with cholesterol (Ch) in different ratio of compounds, having smectic C liquid crystal (LC) properties. Very thin systems (`membranes') of FA and mixtures, manufactured by us, were subjected to some electrical measurements, that show a new distribution, induced by Ch, of the space charge in the system. The FA and mixtures' samples were also sandwiched between two glass plates of transparent SnO2 electrodes and studied under dc and ac electric fields. The hysteresis curves of the current versus the applied voltage exhibited a nonlinear dielectric feature and a negative resistance. We studied the change of the fundamental IR and second harmonic pulsed beam of a Nd3+ glass laser, in the time domain, after passing through our samples; the optical output power of a He-Ne laser beam ((lambda) equals 6328 angstroms, Pmax equals 20 mW), from the LC cells situated between parallel and crossed polarizers was registered. A nonlinear optical behavior of the samples and some memory effects were emphasized. Also a correlation between the electric and optical nonlinearity of the samples seems to be possible.
The role of the fatty acids in the biological membrane structure and properties is partially known. They can exhibit a mesogenic feature and behavior in terms of the temperature, the presence of many acids of cholesterol, or other important substances for the metabolism, of external stimuli etc. We studied the arachidic, lauric, elaidic, arachidonic and butiric acids. The most important seems to be the arachidonic acid, a forerunner of phospholipids. This is an unsaturated fatty acid,with four double bounds. We found that it displayed liquid crystalline properties between 4-20 grades centrigrades; in mixture with other fatty acids or cholesterol, these properties change. The paper present considerations on the biological role of the fatty acids and mixtures, in interactions with some physical fields experimental results and some theoretical considerations.
The work addresses the problem of a CO2 laser dynamics control in the presence of Gaussian white noise in the cavity losses. We improve the delayed continuous feedback method by introducing memory of the previous states. The method proves a powerful one that works for otherwise chaotic dynamics and regular dynamics equally well and it is robust with respect to noise.
Pure fatty acids and mixtures, which can be found in the biological membrane, were prepared and studied in interaction with electric, magnetic and optic fields, under different temperature conditions. All the samples displayed a smectic C liquid crystalline texture, and ferroelectric behavior. The nonlinear electric and optic features of their response have been emphasized and correlated. Theoretical considerations are meant to explain this behavior, in connection with the living matter processes.
Dependence on a n applied external electric field of the current intensity through samples of fatty acids with mesomorphic behavior was investigated. The time dependence of intensity for a potential step applied to the sample, was used to determine the specific space charge. Electric conduction was analyzed based on the experimental results.
The engineering education in optics needs new computer aided methods, to increase the information in this field and to facilitate thus the students work. We organized in our computational laboratory two workshops in flexible computer aided learning and interactive physics. Packages of the CUPS series and Interactive Physics simulations were exemplified. Teachers, researchers, students, engineers and technical staff participated in; the interest of the participants was remarkable, and it materialized in two new research projects, involving the 'Politehnica' University, the Research and Technology Ministry and the 'MATPUR' Enterprise of Pure Materials.
Arachidonic acid (AA) samples and mixtures of arachidonic acid - cholesterol (AA-C) were manufactured and subjected to external electric cw or pulsatory optical laser fields. The polarizing microscope showed a pseudohomeotropic smectic C texture for AA at 10 degree(s)C and smectic C textures with fibers for mixtures AA-C at room temperature. The dependences I equals I(U) at t degree(s)C equals const. and I equals I(t) at U equals const., t being time, showed that samples are dielectrics with a weak conduction (I approximately equals 10-9 A, U equals 0 - 40V). Pure acid samples present an electric hysteresis which disappears when cholesterol is added. The current occurred when the electric field is applied, decreases in time, and tends to a constant value. When the temperature was 19 degree(s)C, a cw focussed laser radiation from a He-Ne laser ((lambda) equals 632.8 nm, P equals 20 mW) determined a lenselike effect in AA, but no effect in mixtures. At the same temperature, the samples were crossed by some green pulses ((lambda) equals 532 nm, (tau) equals 200 microsecond(s) ) furnished by an experimental setup containing a Nd3+ glass laser and a KDP crystal for the second harmonic generation. The shape and extension of the pulse in the time domain, displayed on a sampling oscilloscope, are some indications of the cholesterol percentage.
In `optoelectronic devices' area, a new domain occurred: organic and biological optoelectronics. Since 1988 our researches axed on this exciting theme and several works materialize the results we obtained. In this paper, we used the lauric acid, a fatty acid, which can be found, for example, under an esterified form, in the cocobutter.
Saturated and unsaturated fatty acids and mixtures of fatty acids and fatty acid-cholesterol in electric and optic fields were investigated. In the mesomorphic state, they are nonlinear dielectrics and nonlinear optical media. These properties are influenced by cholesterol.
Unsaturated fatty acids arachidonicurn and elaidicwn acids with liquid crystal Sit properties were investigated. These aci4s have an important role in biologicel membrane.The electrical meastie' rements showed nonlinear dielectrical properties and ferroelectri.city.Optical nonlinear behaviour, dependent on temperature, distan— ce, cell thickness, incidence angle and incident optical laser po.•wer was aimlised.Phe samplçs Were ittilised like nonlinear lens and in an all—optical bistable device.
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