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Results for “DIELECTRIC ABSORPTION”

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At least 19 recordsLinked to original sources
PubMed1987

"Resonances" in the dielectric absorption of DNA?

An attempt was made to confirm previous reports of resonant-like dielectric absorption of plasmid DNA in aqueous solutions at 1-10 GHz. The dielectric properties of the sample were measured using an automatic network analyzer with two different techniques. One technique used an open-ended coaxial probe immersed in the sample; the other employed a coaxial transmission line. No resonances were observed that could be attributed to the sample; however, resonance-type artifacts were prominent in the probe measurements. The coaxial line technique appears to be less susceptible to such artifacts. We note two important sources of error in the calibration of the automatic network analyzer using the probe technique.

DNA, Bacterial↗
PubMed2004

Theoretical evaluation of dielectric absorption of microwave energy at the scale of nucleic acids.

A theoretical model is proposed for the evaluation of dielectric properties of the cell nucleus between 0.3 and 3 GHz, as a function of its nucleic acids (NA) concentration (CNA). It is based on literature data on dielectric properties of DNA solutions and nucleoplasm. In skeletal muscle cells, the specific absorption rate (SAR) ratio between nucleoplasm and cytoplasm is found to be larger than one for CNA above 30 mg/ml. A nearly linear relationship is found between CNA and this nucleocytoplasmic SAR ratio. Considering the nanoscale of the layer of condensed counterions and bound water molecules at the NA-solution interface, the power absorption per unit volume is evaluated at this precise location. It is found to be between one and two orders of magnitude above that in muscle tissue as a whole. Under realistic microwave (MW) exposure conditions, however, these SAR inhomogeneities do not generate any significant thermal gradient at the scale considered here. Nevertheless, the question arises of a possible biological relevance of nonnegligible and preferential heat production at the location of the cell nucleus and of the NA molecules.

Absorption↗
PubMed2003

Geometrical-optics code for computing the optical properties of large dielectric spheres.

Absorption of electromagnetic radiation by absorptive dielectric spheres such as snow grains in the near-infrared part of the solar spectrum cannot be neglected when radiative properties of snow are computed. Thus a new, to our knowledge, geometrical-optics code is developed to compute scattering and absorption cross sections of large dielectric particles of arbitrary complex refractive index. The number of internal reflections and transmissions are truncated on the basis of the ratio of the irradiance incident at the nth interface to the irradiance incident at the first interface for a specific optical ray. Thus the truncation number is a function of the angle of incidence. Phase functions for both near- and far-field absorption and scattering of electromagnetic radiation are calculated directly at any desired scattering angle by using a hybrid algorithm based on the bisection and Newton-Raphson methods. With these methods a large sphere's absorption and scattering properties of light can be calculated for any wavelength from the ultraviolet to the microwave regions. Assuming that large snow meltclusters (1-cm order), observed ubiquitously in the snow cover during summer, can be characterized as spheres, one may compute absorption and scattering efficiencies and the scattering phase function on the basis of this geometrical-optics method. A geometrical-optics method for sphere (GOMsphere) code is developed and tested against Wiscombe's Mie scattering code (MIE0) and a Monte Carlo code for a range of size parameters. GOMsphere can be combined with MIE0 to calculate the single-scattering properties of dielectric spheres of any size.

Journal Article↗
PubMed2026

Morphology-Encoded Colorimetric Hydrogen Sensing Using Embedded Reactive Pd Absorbers in Fabry-Perot Cavities.

Chemical reactions offer a powerful strategy for generating visible optical responses through localized changes in absorption, dielectric environment, and interfacial wetting. A palladium (Pd)-embedded Fabry-Perot cavity is introduced as a reaction-active optical platform in which structural color is governed by intracavity absorption coupled with reaction-induced dielectric perturbation. Positioning Pd within the dielectric spacer creates a spatially controllable reactive absorber whose vertical location relative to the standing-wave field dictates wavelength-selective absorption within the cavity. The morphology of the embedded Pd layer provides an additional design parameter by modulating both optical loss and interfacial wetting. Under hydrogen exposure in the presence of oxygen, catalytic water formation at the Pd/polymer interface generates localized dielectric heterogeneity and interfacial water droplets, thereby perturbing the optical path length and amplifying the visible response. As a result, the cavity exhibits pronounced, morphology-dependent color transitions that are inaccessible through dielectric-layer engineering or Pd/PdH refractive-index changes alone, enabling direct visual hydrogen sensing under ambient light, as well as flexible optical devices capable of large-area patterning. These findings establish a design framework for reaction-active optical cavities that translate localized chemistry into a colorimetric hydrogen sensing mechanism.

Fabry–Perot resonator↗
PubMed2003

Effects of the counterion on dielectric spectroscopy of a montmorillonite suspension over the frequency range 10(5)-10(10) Hz.

Dielectric measurements were carried out on suspensions of montmorillonite clay exchanged with three different counterions: sodium, ammonium, and tetramethylammonium (TMA). Only two dielectric absorption peaks could be identified for the clay sample with the TMA counterion, whereas three peaks were found for the two inorganic counterions. The dielectric process observed at around 10 GHz is due to the orientation of bulk water molecules, judging from the relaxation time and relaxation strength. The relaxation strength of the process occurring at around 10 MHz was compared with the coefficient of adiabatic compressibility obtained from ultrasound velocity measurements. The increase in the relaxation strength with decreasing compressibility indicates that the process at around 10 MHz is caused by the orientation of bound water molecules on the clay samples. The relaxation strength of the process occurring at around 10 MHz for the TMA sample was remarkably small. Furthermore, the network structure of the bound water molecules can be characterized by a property peculiar to the TMA sample, taking into account the value of its Cole-Cole parameter. Results for the relaxation strength of the process occurring at around 100 kHz were compared with those for electrophoretic mobility. This comparison revealed that discrimination between bound ions and ions in the diffuse double layer is important, and both the relaxation and electrophoretic results could be satisfactorily explained by surface polarization of the clay.

Journal Article↗
PubMed2000

Theory of Cerenkov and transition radiation from layered structures

A scattering theoretical approach is used to describe the generation of both transition and Cerenkov radiation due to the passage of fast electrons through layered, in general absorptive, dielectrics. It leads to a considerable improvement over the coherent summation method usually employed. Reflection of the produced radiation from the layer interfaces is now properly taken into account and absorption of radiation, if present, is automatically taken care of. The usual restriction that the energy of the produced photons must be small relative to the initial electron energy is lifted. In contrast to existing theories the production of Cerenkov radiation, if it takes place, is included as well. Our expressions for radiation production feature the eigenmodes of the Helmholtz equation for the dielectric and we discuss how the latter can be obtained by means of a transfer matrix formalism. A numerical evaluation shows that under the appropriate conditions our results are in agreement with those from the coherent summation formalism. Finally, we present numerical results that give an impression of the relative yields for transition and Cerenkov radiation.

Journal Article↗
PubMed2004

Pulse centroid velocity of the Poynting vector.

The evolution of the pulse centroid velocity of the Poynting vector for both ultrawideband rectangular and ultrashort Gaussian envelope pulses is presented as a function of the propagation distance in a dispersive, absorptive dielectric material. The index of refraction of the material is described by the Lorentz-Lorenz formula in which a single-resonance Lorentz model is used to describe the mean molecular polarizability. The results show that, as the propagation distance increases above a value that is on the order of an absorption depth at the pulse carrier frequency, the centroid velocity of an ultrawideband/ultrashort pulse tends toward the rate at which the Brillouin precursor travels through the medium. For small propagation distances when the carrier frequency of the optical pulse lies in the absorption band of the material, the centroid velocity can take on superluminal and negative values.

Journal Article↗
PubMed2004

Detection of bioradicals by in vivo L-band electron spin resonance spectrometry.

The applications of in vivo electron paramagnetic resonance (EPR) or electron spin resonance (ESR) spectroscopy have been impressive over a relatively short period despite the many obstacles which had to be overcome, such as dielectric absorption and biodestruction. The loop-gap resonators and modified loop coil systems have emerged as the most suitable resonators for in vivo EPR experiments. This paper briefly discusses instrumental aspects as a prelude to several examples related to the in vivo monitoring and detection of bioradicals. Recent progress in detection of bioradicals induced by drugs or chemicals is discussed with regard to nitrosocompounds, nitric oxide and metals in vivo. A clinical EPR application is also discussed.

Animals↗
PubMed1984

Picosecond relaxations in hydrated lysozyme observed by mm-wave spectroscopy.

Dielectric absorption measurements at mm-wave frequencies (50 GHz. . . 150 GHz) are reported for lysozyme at different hydration levels. The measurements were extended over the temperature range from liquid helium to room temperature using the untuned cavity technique. For dried lysozyme (water content less than or equal to 0.5%, w/w) a nearly linear increase with frequency and an exponential increase with temperature of the absorption coefficient is observed between 50 K and 300 K. This frequency and temperature dependence is described by relaxation processes in asymmetric double-well potentials with relaxation times in the picosecond range. Hydration yields a nearly frequency-independent contribution to the absorption, which arises only at temperatures above 120 K. The frequency independence indicates relaxation rates for the bound water that are small compared to mm-wave frequencies. Thereby the contribution of bound water can clearly be distinguished from the fast intrinsic processes. An assignment of these picosecond relaxations to the NH . . . OC hydrogen bond of the peptide backbone is suggested.

Muramidase↗
PubMed2004

Role of multipole moment of the probe in apertureless near-field optical microscopy.

The model of apertureless near-field optical microscope is developed taking into account the multipole moment of probe. In the case of samples with small dielectric absorption, the multipole moments are shown to be responsible for the appearance of additional resonances in the spectrum of scattered signal. The influence of multipole moments is especially pronounced in the near-field microscopy with modulation of tip-sample distance. A good agreement of the theoretical results with experimental data in the case of resonant interaction of the probe and sample is demonstrated.

Algorithms↗
PubMed2003

Dielectric relaxation behavior of a liquid crystal showing an unusual type of antiferroelectric-ferroelectric-antiferroelectric phase sequence.

The temperature and frequency dependent dielectric relaxation behavior of a liquid crystalline (S)-(+)-1-methylheptyl 4-[2-(4-alkoxyphenyl) thiophene-5-carbonylthiooxy] benzoate system is reported. Interesting successive antiferroelectric-ferroelectric-antiferroelectric (AF-FE-AF) phase transitions are observed in this system resembling the successive phase transitions observed in crystalline Rochelle salt. The smectic-C* (SmC*) to AF1 phase transition (around 103.0 degrees C) is first order in nature, predicted from the use of Orihara and Ishibashi theory. It is also found that a contribution of the ferroelectric SmC* phase ordering penetrates even in the antiferroelectric AF1 (SmC(*)(A)) and AF2 (SmC(*)(A)) phases very close to the SmC*-AF1 and SmC*-AF2 phase boundaries (critical regions). It is suggested that this type of mixing of AF and FE phases might cause surface induced ferroelectric- or ferroelectric-type ordering near the AF-FE phase transitions. A soft mode with Debye-type dispersion was observed in the SmA phase. The thermal behaviors of dielectric dispersion, absorption, and dielectric strength in different phases are also reported and discussed.

Journal Article↗
PubMed1999

Optical properties of an ionic-type phononic crystal

An ionic-type phononic crystal composed of two ferroelectric media with opposite spontaneous polarization aligned periodically in a superlattice structure was studied theoretically and experimentally. The coupling between vibrations of the superlattice and the electromagnetic waves results in various long-wavelength optical properties, such as microwave absorption, dielectric abnormality, and polariton excitation, that exist originally in ionic crystals. The results show that this artificial crystal structure can be used to simulate the microscopic physical processes in real crystals.

Journal Article↗