Wei, Yan-Zhen; Kumbharkhane, AC; Sadeghi, M; Sage, JT; Tian, WD; Champion, PM; Sridhar, S; McDonald, MJ
Protein hydration investigations with high-frequency dielectric spectroscopy Journal Article
In: The Journal of Physical Chemistry, vol. 98, no. 26, pp. 6644–6651, 1994.
@article{wei1994protein,
title = {Protein hydration investigations with high-frequency dielectric spectroscopy},
author = {Yan-Zhen Wei and AC Kumbharkhane and M Sadeghi and JT Sage and WD Tian and PM Champion and S Sridhar and MJ McDonald},
year = {1994},
date = {1994-01-01},
journal = {The Journal of Physical Chemistry},
volume = {98},
number = {26},
pages = {6644--6651},
publisher = {American Chemical Society},
abstract = {Water plays a unique and important role in biological processes. Since biological processes take place in aqueous media at relatively low biomolecular concentrations, interactions between biomol-ecules and water are often confined to an interfacial region surrounding the biomolecule. It is to be expected that a fraction of the water molecules find themselves in a local environment interacting strongly with the macromolecule. One expects the behavior of the hydration water to be influenced by the biomolecule, and in fact, water adsorbed during hydrationof dry protein is known to have properties different from those of bulk water. 1 Partially hydrated films of myoglobin, for instance, contain 0.38 g of noncrystallizing water/gram of protein. 2 Bound water was shown to be a crucial factor for stabilizing different conformational states of biomolecules. 3· 4 This water is believed to adsorb on the protein surface and activate …},
keywords = {Chemical & Biological Physics},
pubstate = {published},
tppubtype = {article}
}
Water plays a unique and important role in biological processes. Since biological processes take place in aqueous media at relatively low biomolecular concentrations, interactions between biomol-ecules and water are often confined to an interfacial region surrounding the biomolecule. It is to be expected that a fraction of the water molecules find themselves in a local environment interacting strongly with the macromolecule. One expects the behavior of the hydration water to be influenced by the biomolecule, and in fact, water adsorbed during hydrationof dry protein is known to have properties different from those of bulk water. 1 Partially hydrated films of myoglobin, for instance, contain 0.38 g of noncrystallizing water/gram of protein. 2 Bound water was shown to be a crucial factor for stabilizing different conformational states of biomolecules. 3· 4 This water is believed to adsorb on the protein surface and activate …
Wei, Yan-Zhen; Sridhar, S
A new graphical representation for dielectric data Journal Article
In: The Journal of chemical physics, vol. 99, no. 4, pp. 3119–3124, 1993.
@article{wei1993new,
title = {A new graphical representation for dielectric data},
author = {Yan-Zhen Wei and S Sridhar},
year = {1993},
date = {1993-01-01},
journal = {The Journal of chemical physics},
volume = {99},
number = {4},
pages = {3119--3124},
publisher = {American Institute of Physics},
abstract = {A method of graphically representing complex dielectric data is described, which is particularly useful for situations where the Cole–Cole representation is unsuitable. The representation emphasizes the orientational dipolar contribution to the conductivity by plotting σχ‘=ωεv(ε’−ε∞) vs σχ’=ωεvε‘. We discuss the utility of the representation for conducting dielectrics and for studying multirelaxation processes, particularly modes with smaller amplitudes (absorption) at high frequencies. For a Debye relaxation with dc conductivity, this representation leads to a semicircle, whereas the Cole–Cole plot shows a divergence. Even in the absence of conductivity, this representation is useful particularly at high frequencies, where it enables the identification of multirelaxation processes not apparent in the Cole–Cole representation. A particularly striking example is the clear observation of two relaxation processes in dielectric data on 1‐propanol. We also show that in this σχ representation, all the well‐known functional forms such as Cole–Cole and Cole–Davidson, approach an asymptotic slope at high frequencies. Applications of the σχ representation to analysis of dielectric spectra taken up to 20 GHz are discussed for pure glycerol and LiCl/propanol solutions.},
keywords = {Chemical & Biological Physics},
pubstate = {published},
tppubtype = {article}
}
A method of graphically representing complex dielectric data is described, which is particularly useful for situations where the Cole–Cole representation is unsuitable. The representation emphasizes the orientational dipolar contribution to the conductivity by plotting σχ‘=ωεv(ε’−ε∞) vs σχ’=ωεvε‘. We discuss the utility of the representation for conducting dielectrics and for studying multirelaxation processes, particularly modes with smaller amplitudes (absorption) at high frequencies. For a Debye relaxation with dc conductivity, this representation leads to a semicircle, whereas the Cole–Cole plot shows a divergence. Even in the absence of conductivity, this representation is useful particularly at high frequencies, where it enables the identification of multirelaxation processes not apparent in the Cole–Cole representation. A particularly striking example is the clear observation of two relaxation processes in dielectric data on 1‐propanol. We also show that in this σχ representation, all the well‐known functional forms such as Cole–Cole and Cole–Davidson, approach an asymptotic slope at high frequencies. Applications of the σχ representation to analysis of dielectric spectra taken up to 20 GHz are discussed for pure glycerol and LiCl/propanol solutions.
Wei, Yan-Zhen; Sridhar, S
Relationships between the dielectric and structural properties of supercooled LiCl: RH2O solutions Journal Article
In: Journal of Molecular Liquids, vol. 56, pp. 259–273, 1993.
@article{wei1993relationships,
title = {Relationships between the dielectric and structural properties of supercooled LiCl: RH2O solutions},
author = {Yan-Zhen Wei and S Sridhar},
year = {1993},
date = {1993-01-01},
journal = {Journal of Molecular Liquids},
volume = {56},
pages = {259--273},
publisher = {Elsevier},
abstract = {The relation between the dynamics of dielectric relaxation, the glass-forming ability and properties in the supercooled state of LiCl:RH2O solutions are investigated, via measurements of the dielectric spectra between 45 MHz and 20 GHz and temperatures between 210 K and 300 K and concentrations R ≤ 20. For high concentration glass-forming solutions, a close correspondence between the temperature dependencies of the Cole-Cole relaxation time τC, the conductivity, and the viscosity, is observed. τC(T) is well-described by a power law form (T-TMC)γ, with TMC ∼ 205 K and γ ∼ 2, a form motivated by mode-coupling theory. The data suggest that non-Debye response at room temperature is associated with the ability to vitrify at low temperatures. A microscopic basis for the avoidance of crystallization is provided by obtaining from the dielectric data the mean radius available to a water molecule, which is shown to approach 1.9 Å in the highly concentrated solutions. This suggests strong confinement of water molecules by the ions, which prevents macroscopic crystallization from occurring when cooled.},
keywords = {Chemical & Biological Physics},
pubstate = {published},
tppubtype = {article}
}
The relation between the dynamics of dielectric relaxation, the glass-forming ability and properties in the supercooled state of LiCl:RH2O solutions are investigated, via measurements of the dielectric spectra between 45 MHz and 20 GHz and temperatures between 210 K and 300 K and concentrations R ≤ 20. For high concentration glass-forming solutions, a close correspondence between the temperature dependencies of the Cole-Cole relaxation time τC, the conductivity, and the viscosity, is observed. τC(T) is well-described by a power law form (T-TMC)γ, with TMC ∼ 205 K and γ ∼ 2, a form motivated by mode-coupling theory. The data suggest that non-Debye response at room temperature is associated with the ability to vitrify at low temperatures. A microscopic basis for the avoidance of crystallization is provided by obtaining from the dielectric data the mean radius available to a water molecule, which is shown to approach 1.9 Å in the highly concentrated solutions. This suggests strong confinement of water molecules by the ions, which prevents macroscopic crystallization from occurring when cooled.
Wei, Yan-Zhen; Chiang, Ping; Sridhar, S
Ion size effects on the dynamic and static dielectric properties of aqueous alkali solutions Journal Article
In: The Journal of chemical physics, vol. 96, no. 6, pp. 4569–4573, 1992.
@article{wei1992ion,
title = {Ion size effects on the dynamic and static dielectric properties of aqueous alkali solutions},
author = {Yan-Zhen Wei and Ping Chiang and S Sridhar},
year = {1992},
date = {1992-01-01},
journal = {The Journal of chemical physics},
volume = {96},
number = {6},
pages = {4569--4573},
publisher = {American Institute of Physics},
abstract = {Dielectric spectroscopy studies of aqueous ionic solutions ACl/H2O (A=Li, Rb, Cs) were carried out at frequencies between 45 MHz and 20 GHz, using recently developed coaxial measurement techniques. The behavior of the static dielectric constant εs0 and the dielectric relaxation time τD of the solutions were studied as functions of ion size and concentration. For moderate concentrations both εs0 and τD decrease linearly with solution conductivity. While the behavior of εs0 can be understood in terms of either static or Hubbard–Onsager kinetic polarization models, the experimental results for τD are at present not understood quantitatively in terms of these models. However we point out the good correlation of the τD data with empirical viscosity results, which suggests an alternative explanation based upon the solution viscosity, modified by ion size effects, which play an important role in the dielectric response. We also discuss the various length scales relevant to dielectric and conductivity processes in the solutions.},
keywords = {Chemical & Biological Physics},
pubstate = {published},
tppubtype = {article}
}
Dielectric spectroscopy studies of aqueous ionic solutions ACl/H2O (A=Li, Rb, Cs) were carried out at frequencies between 45 MHz and 20 GHz, using recently developed coaxial measurement techniques. The behavior of the static dielectric constant εs0 and the dielectric relaxation time τD of the solutions were studied as functions of ion size and concentration. For moderate concentrations both εs0 and τD decrease linearly with solution conductivity. While the behavior of εs0 can be understood in terms of either static or Hubbard–Onsager kinetic polarization models, the experimental results for τD are at present not understood quantitatively in terms of these models. However we point out the good correlation of the τD data with empirical viscosity results, which suggests an alternative explanation based upon the solution viscosity, modified by ion size effects, which play an important role in the dielectric response. We also discuss the various length scales relevant to dielectric and conductivity processes in the solutions.
Wei, Yanzhen; Sridhar, S
Biological applications of a technique for broadband complex permittivity measurements Proceedings Article
In: 1992 IEEE MTT-S Microwave Symposium Digest, pp. 1271–1274, IEEE 1992.
@inproceedings{wei1992biological,
title = {Biological applications of a technique for broadband complex permittivity measurements},
author = {Yanzhen Wei and S Sridhar},
year = {1992},
date = {1992-01-01},
booktitle = {1992 IEEE MTT-S Microwave Symposium Digest},
pages = {1271--1274},
organization = {IEEE},
abstract = {A broadband coax technique developed for the measurement of dielectric properties of biological substances up to at least 20 GHz is discussed. For water-based materials such as blood or muscle substitute phantoms, a 0.047 inch size probe is essential to minimize errors due to radiation. The data indicate the importance of dielectric volume of the constituents, and enable tailoring of phantoms and substitutes for use in biomedical applications.< >},
keywords = {Chemical & Biological Physics},
pubstate = {published},
tppubtype = {inproceedings}
}
A broadband coax technique developed for the measurement of dielectric properties of biological substances up to at least 20 GHz is discussed. For water-based materials such as blood or muscle substitute phantoms, a 0.047 inch size probe is essential to minimize errors due to radiation. The data indicate the importance of dielectric volume of the constituents, and enable tailoring of phantoms and substitutes for use in biomedical applications.< >
Liu, Ping; Rappaport, Carey M; Wei, Yan-zhen; Sridhar, S
Simulated biological materials at microwave frequencies for the study of electromagnetic hyperthermia Proceedings Article
In: 1992 14th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, pp. 272–273, IEEE 1992.
@inproceedings{liu1992simulated,
title = {Simulated biological materials at microwave frequencies for the study of electromagnetic hyperthermia},
author = {Ping Liu and Carey M Rappaport and Yan-zhen Wei and S Sridhar},
year = {1992},
date = {1992-01-01},
booktitle = {1992 14th Annual International Conference of the IEEE Engineering in Medicine and Biology Society},
volume = {1},
pages = {272--273},
organization = {IEEE},
abstract = {For the study of electromagnetic hyperthermia, it is necessary to simulate human biological materials in microwave frequencies. Using a new technique for the precise measurement of the dielectric properties of the simulated materials for frequencies up to 20 GHz, we have modified the previous simulation for high water content tissue at the frequency range 100-1000 MHz. We present new formulas for the frequency range 5-20 GHz. Modifications of composition for various frequencies are discussed.},
keywords = {Chemical & Biological Physics},
pubstate = {published},
tppubtype = {inproceedings}
}
For the study of electromagnetic hyperthermia, it is necessary to simulate human biological materials in microwave frequencies. Using a new technique for the precise measurement of the dielectric properties of the simulated materials for frequencies up to 20 GHz, we have modified the previous simulation for high water content tissue at the frequency range 100-1000 MHz. We present new formulas for the frequency range 5-20 GHz. Modifications of composition for various frequencies are discussed.
Sridhar, S
Experimental observation of scarred eigenfunctions of chaotic microwave cavities Journal Article
In: Physical review letters, vol. 67, no. 7, pp. 785, 1991.
@article{sridhar1991experimental,
title = {Experimental observation of scarred eigenfunctions of chaotic microwave cavities},
author = {S Sridhar},
year = {1991},
date = {1991-01-01},
journal = {Physical review letters},
volume = {67},
number = {7},
pages = {785},
publisher = {APS},
abstract = {The wave functions of Sinai-billiard-shaped microwave cavities are experimentally studied. Some of the general features observed are parity breaking in the lowest eigenstates,‘‘bouncing-ball’’states, and states with quasirectangular or quasicircular symmetry. The above features are associated with nonisolated periodic orbits. Some states are observed which can be associated with isolated periodic orbits, leading to scars. This work represents the first direct experimental observation of scarred eigenfunctions. At high frequencies the eigenfunctions are very complex, and are yet to be classified in a general scheme.},
keywords = {Chemical & Biological Physics},
pubstate = {published},
tppubtype = {article}
}
The wave functions of Sinai-billiard-shaped microwave cavities are experimentally studied. Some of the general features observed are parity breaking in the lowest eigenstates,‘‘bouncing-ball’’states, and states with quasirectangular or quasicircular symmetry. The above features are associated with nonisolated periodic orbits. Some states are observed which can be associated with isolated periodic orbits, leading to scars. This work represents the first direct experimental observation of scarred eigenfunctions. At high frequencies the eigenfunctions are very complex, and are yet to be classified in a general scheme.
Wei, Yan-Zhen; Sridhar, S
Dielectric spectroscopy up to 20 GHz of LiCl/H2O solutions Journal Article
In: The Journal of chemical physics, vol. 92, no. 2, pp. 923–928, 1990.
@article{wei1990dielectric,
title = {Dielectric spectroscopy up to 20 GHz of LiCl/H2O solutions},
author = {Yan-Zhen Wei and S Sridhar},
year = {1990},
date = {1990-01-01},
journal = {The Journal of chemical physics},
volume = {92},
number = {2},
pages = {923--928},
publisher = {American Institute of Physics},
abstract = {Detailed measurements of the complex dielectric function ε=ε’−iε‘ as functions of frequency between 45 MHz and 20 GHz and concentration c are presented and analyzed for LiCl/H2O solutions. In this frequency range, the dielectric response is due to free water molecules and the response of the bound water occurs at lower frequencies and is not observed. From the data, several parameters—the static and high frequency limiting values ε0 and ε∞, the dc conductivity σdc, the dielectric relaxation time τd, and the hydration number nhyd—are extracted. The dissociation is observed to be incomplete suggesting the presence of undissociated ion pairs. A dissociation parameter is inferred from the σdc data. A model which views the liquid as composed of free water, hydrated single ions, and hydrated ion pairs is used to analyze the ε0 data. With inclusion of the dissociation parameter, the model describes the data reasonably well for c≤5.1 M. At higher concentrations, a unique relaxation time is not observed indicating glasslike behavior.},
keywords = {Chemical & Biological Physics},
pubstate = {published},
tppubtype = {article}
}
Detailed measurements of the complex dielectric function ε=ε’−iε‘ as functions of frequency between 45 MHz and 20 GHz and concentration c are presented and analyzed for LiCl/H2O solutions. In this frequency range, the dielectric response is due to free water molecules and the response of the bound water occurs at lower frequencies and is not observed. From the data, several parameters—the static and high frequency limiting values ε0 and ε∞, the dc conductivity σdc, the dielectric relaxation time τd, and the hydration number nhyd—are extracted. The dissociation is observed to be incomplete suggesting the presence of undissociated ion pairs. A dissociation parameter is inferred from the σdc data. A model which views the liquid as composed of free water, hydrated single ions, and hydrated ion pairs is used to analyze the ε0 data. With inclusion of the dissociation parameter, the model describes the data reasonably well for c≤5.1 M. At higher concentrations, a unique relaxation time is not observed indicating glasslike behavior.
Wei, Yan-Zhen; Sridhar, S
Technique for measuring the frequency-dependent complex dielectric constants of liquids up to 20 GHz Journal Article
In: Review of scientific instruments, vol. 60, no. 9, pp. 3041–3046, 1989.
@article{wei1989technique,
title = {Technique for measuring the frequency-dependent complex dielectric constants of liquids up to 20 GHz},
author = {Yan-Zhen Wei and S Sridhar},
year = {1989},
date = {1989-01-01},
journal = {Review of scientific instruments},
volume = {60},
number = {9},
pages = {3041--3046},
publisher = {American Institute of Physics},
keywords = {Chemical & Biological Physics},
pubstate = {published},
tppubtype = {article}
}
Sridhar, S; Taborek, P
High-frequency structural relaxation in supercooled liquids Journal Article
In: The Journal of chemical physics, vol. 88, no. 2, pp. 1170–1176, 1988.
@article{sridhar1988high,
title = {High-frequency structural relaxation in supercooled liquids},
author = {S Sridhar and P Taborek},
year = {1988},
date = {1988-01-01},
journal = {The Journal of chemical physics},
volume = {88},
number = {2},
pages = {1170--1176},
publisher = {American Institute of Physics},
keywords = {Chemical & Biological Physics},
pubstate = {published},
tppubtype = {article}
}
SRIDHAR, SPP; KUMAR, R
Hemato-biochemical changes in calves during neonatal life Journal Article
In: Indian Journal Animal Health, pp. 105–109, 1988.
@article{sridhar1988hemato,
title = {Hemato-biochemical changes in calves during neonatal life},
author = {SPP SRIDHAR and R KUMAR},
year = {1988},
date = {1988-01-01},
journal = {Indian Journal Animal Health},
pages = {105--109},
keywords = {Chemical & Biological Physics},
pubstate = {published},
tppubtype = {article}
}
WEI, YAN-ZHEN; SRIDHAR, S
PROPERTIES OF SUPERCOOLED LiCl RH O SOLUTIONS Journal Article
In: 0000.
@article{weiproperties,
title = {PROPERTIES OF SUPERCOOLED LiCl RH O SOLUTIONS},
author = {YAN-ZHEN WEI and S SRIDHAR},
abstract = {The relation between the dynamics of dielectric relaxation, the glass-forming ability and properties in the supercooled state of LiCl: RH, O solutions are investigated, via measurements of the dielectric spectra between 45 MHz and 20 GHz and temperatures between 210 K and 300 K and concentrations R< 20. For high concentration glass-forming solutions, a close correspondence between the temperature dependencies of the Cole-Cole relaxation time t, the conductivity, and the viscosity, is observed.,(T) is well-described by a power law form (TT,)', with T.,-205 K and y-2, a form motivated by mode-coupling theory. The data suggest that non-Debye response at room temperature is associated with the ability to vitrify at low temperatures. A microscopic basis for the avoidance of crystallization is provided by obtaining from the dielectric data the mean radius available to a water molecule, which is shown to approach 19 …},
keywords = {Chemical & Biological Physics},
pubstate = {published},
tppubtype = {article}
}
The relation between the dynamics of dielectric relaxation, the glass-forming ability and properties in the supercooled state of LiCl: RH, O solutions are investigated, via measurements of the dielectric spectra between 45 MHz and 20 GHz and temperatures between 210 K and 300 K and concentrations R< 20. For high concentration glass-forming solutions, a close correspondence between the temperature dependencies of the Cole-Cole relaxation time t, the conductivity, and the viscosity, is observed.,(T) is well-described by a power law form (TT,)', with T.,-205 K and y-2, a form motivated by mode-coupling theory. The data suggest that non-Debye response at room temperature is associated with the ability to vitrify at low temperatures. A microscopic basis for the avoidance of crystallization is provided by obtaining from the dielectric data the mean radius available to a water molecule, which is shown to approach 19 …
Measuring Experimental Eigenvalues and Eigenfunctions
In closed or open billiard geometries, Maxwell’s equations can be written as (Ñ2 + k2) Ψ = 0, where in general Ψ = {Εi, Βj} is a vector field. In thin 2-D geometries bounded by parallel metallic plates in the x-y plane, the wave equation for the TM modes (Βz = 0) reduces to the time independent Schrodinger equation (Ñ2 + k2) Ψ = 0, for frequencies ƒ < c/2d, where d is the plate separation. This QM-E&M mapping with Ψ = Εz allows us to study 2-D problems in Quantum Chaos by suitably constructing classically chaotic geometries. Eigenvalues, eigenfunctions, scattering resonances and widths are measured and analyzed, yielding insights towards the quantum classical correspondence.