A psychophysical investigation of Beidler's mixture equation

Beidler's mixture equation (1971) describes the relationshipbetween the concentration and composition of a binary mixtureand the magnitude of the neural response. Later this equationwas generalized to a psychophysical level. The purpose of thepresent study is to show that Beidler's mixture equation canbe tested appropriately with indirect psychophysical methods,without the necessity of making assumptions about the magnitudeof the maximum responses to the single compounds which constitutethe mixture. Experiments were carried out using glucose andfructose as tastants. Concentrations of fructose and three equiratiomixture types containing glucose and fructose were matched inperceived sweetness intensities to five different glucose concentrationsusing the method of constant stimuli. The results showed thatBeidler's mixture equation describes accurately the taste interactionbetween glucose and fructose at low sweetness levels. At highsweetness levels the taste system is more efficient, as couldbe expected on the basis of Beidler's mixture equation, becausethe experimentally determined mixture concentrations were lowerthan those predicted by the mixture equation. The findings suggestthat glucose and fructose share common receptors, but that eitherone or both have additional secondary binding mechanisms.     

The dielectric properties of aqueous solutions of poly(ethylene glycol) and their influence on membrane structure

The dielectric constant of water is reduced drastically on addition of poly(ethylene glycol). The behaviour is not described by a linear mixture equation. The decreased dielectric constant can lead to the general perturbation of the membrane structure which is necessary in such a manner that a strong aggregation of membranes would lead to their fusion. The changed cation permeability in the presence of poly(ethylene glycol) can explained as the effect of the lowered dielectric constant on the transfer energy.     

Study of Bound Water of Poly-Adenine Using High Frequency Dielectric Measurements

The high frequency dielectric constant of poly-adenine (poly-A) was measured between 1 MHz and 1 GHz. The purpose of these experiments was to investigate the state of water molecules that are bound to the charged groups of the poly-A molecule. Analysis of the data using the Maxwell's mixture equation revealed the dielectric constant of bound water higher than we expected. Using Onsager's internal field in Debye's equation, we calculated the dielectric constant of water in the vicinity of a charged ion. The result of this computation demonstrates that the dielectric constant of bound water is much smaller than the normal value only in the immediate proximity of charged ions (within 2 Å). The dielectric constant increases rapidly to the normal value as the distance increases from 2 to 4 Å. This observation indicates that charged sites of polyions have only short range interactions with the surrounding water molecules. However, this conclusion pertains only to rotary diffusion of bound water since dielectric measurement is unable to detect translational diffusion.     

Microwave dielectric measurements of erythrocyte suspensions.

Complex dielectric constants of human erythrocyte suspensions over a frequency range from 45 MHz to 26.5 GHz and a temperature range from 5 to 40 degrees C have been determined with the open-ended coaxial probe technique using an automated vector network analyzer (HP 8510). The spectra show two separate major dispersions (beta and gamma) and a much smaller dispersion between them. The two major dispersions are analyzed with a dispersion equation containing two Cole-Cole functions by means of a complex nonlinear least squares technique. The parameters of the equation at different temperatures have been determined. The low frequency behavior of the spectra suggests that the dielectric constant of the cell membrane increases when the temperature is above 35 degrees C. The real part of the dielectric constant at approximately 3.4 GHz remains almost constant when the temperature changes. The dispersion shifts with temperature in the manner of a thermally activated process, and the thermal activation enthalpies for the beta- and gamma-dispersions are 9.87 +/- 0.42 kcal/mol and 4.80 +/- 0.06 kcal/mol, respectively.     

Temperature-dependent dielectric properties of slightly hydrated horn keratin

With an aim to reveal the mechanism of protein-water interaction in a predominantly two phase model protein system this study investigates the frequency and temperature dependence of dielectric constant epsilon' and loss factor epsilon' in cow horn keratin in the frequency range 30 Hz to 3 MHz and temperature range 30-200 degrees C at two levels of hydration. These two levels of hydration were achieved by exposing the sample to air at 50% relative humidity (RH) at ambient temperature and by evacuating the sample for 72 h at 105 degrees C. A low frequency dispersion (LFD) and an intermediate frequency alpha-dispersion were the two main dielectric responses observed in the air-dried sample. The LFD and the high frequency arm of the alpha-dispersion followed the same fractional power law of frequency. Within the framework of percolation cluster model these dispersions, respectively have been attributed to percolation of protons between and within the clusters of hydrogen-bonded water molecules bound to polar or ionizable protein components. The alpha-dispersion peak, which results from intra-cluster charge percolation conformed to Cole-Cole modified Debye equation. Temperature dependence of the dielectric constant in the air-dried sample exhibited peaks at 120 and 155 degrees C which have been identified as temperatures of onset of release of water bound to polar protein components in the amorphous and crystalline regions, respectively. An overall rise in the permittivity was observed above 175 degrees C, which has been identified as the onset of chain melting in the crystalline region of the protein.     

Formation of ECR Plasma in a Dielectric Plasma Guide under Self-Excitation of a Standing Ion-Acoustic Wave

The formation of a spatially localized plasma with a high brightness has been experimentally observed in a dielectric plasma guide under the electron cyclotron resonance discharge at the excitation of a standing ion-acoustic wave. The results obtained show the possibility of designing compact high-intensity radiation sources with a spectrum determined by the working gas or gas mixture type, high-intensity chemically active particle flow sources, and plasma thrusters for correcting orbits of light spacecraft.     

Activity coefficients of NaCl in trehalose-water and maltose-water mixtures at 298.15 K

The ionic mean activity coefficients of NaCl in trehalose-water and maltose-water mixtures have been experimentally determined at 298.15 K from emf measurements by electrochemical cell containing ion selective electrodes (ISE): Na-ISE/NaCl (m), sugar (Y%), H(2)O (100-Y%)/Cl-ISE. The electrolyte molality (m) ranged between 0.01 and 3 mol kg(-1), approximately, and the weight percent (Y%) of sugar in the mixture of solvents between 0, 10, 20, 30 and 40%. The system is considered as an electrolyte in a mixture of solvents and the data have been analysed by using the Debye-Hückel and Pitzer equations. The results obtained with both equations are in quite agreement with each other. The variation of the fit parameter from both equations were studied relative to the change in the dielectric properties of the mixture of solvents. Standard free energy of transference were comparatively discussed in terms of ion-solvent, ion-ion interactions and the hydration of both the electrolyte and the sugar.     

Modeling clustered long‐term survivors using marginal mixture cure model

There is a great deal of recent interests in modeling right‐censored clustered survival time data with a possible fraction of cured subjects who are nonsusceptible to the event of interest using marginal mixture cure models. In this paper, we consider a semiparametric marginal mixture cure model for such data and propose to extend an existing generalized estimating equation approach by a new unbiased estimating equation for the regression parameters in the latency part of the model. The large sample properties of the regression effect estimators in both incidence and the latency parts are established. The finite sample properties of the estimators are studied in simulation studies. The proposed method is illustrated with a bone marrow transplantation data and a tonsil cancer data.     

Polymerization of gamma-benzyl-L-glutamate N-carboxyanhydride: effects of conditions of polymer precipitation on the molecular weight distribution

Poly-γ-berizyl-L -glutamate prepared by polymerization of γ-benzyl-L -glutamate NCA in dimethylformamide (DMF) with the use of diisopropylamine as the initiator was precipitated from the polymerization mixture under different conditions. A portion of the almost completely polymerized solution was treated with an excess of isopropylamine and then precipitated into diethyl ether (sample A). The remaining portion of the polymerization mixture was concentrated in a rotating evaporator, stored at room temperature for a few days, and then diluted with DMF and precipitated into diethyl ether (sample B). The molecular weight distributions of the two polymer samples were determined by the chromatographic procedure of Baker and Williams. The molecular weight of sample B is roughly three times that of sample A. However both samples have the “most probable” distribution of molecular weight. The results are interpreted according to Bamford's polymerization mechanism.     

High-frequency dielectrical separation of microfossils

Wang Yu-xian 1981 12 15: High-frequency dielectrical separation of microfossils. Lethaia , Vol. 14, pp. 261–268. Oslo. ISSN 0024–1164.
Microfossils can be separated from matrix particles in washed and graded samples by making use of the different dielectric properties of these two components. The separators used represent a development of earlier bi-electrode mineral separators and apply a single-electrode high-frequency electromagnetic radiation field. The sample is immersed in a fluid, generally a mixture of CCl₄ and C₂H₅OH, calibrated to a given dielectric constant. One of the particle components, normally the mudstone matrix with the higher dielectric constant (15–20), is attracted to the loop-like electrode and lifted off into an immersed small vessel, whilst the calcareous microfossils (constant 8–13) are repelled and remain; similarly the fossils may be lifted off from remaining quartz particles (constant < 7). The paper presents the constants and frequencies applied for a range of washed samples (etched samples not yet considered) and some constraints of the method. An intermediate-frequency separator is also taken into use. * Microfossils, separation methods, sample preparation, dielectric separator .     

The properties of liquid water in electric and magnetic fields

A new model of liquid water is proposed, which involves the liquid-crystalline phase, namely, the presence of linearly ordered chains of water molecules and large clusters of these molecules. The presence of linearly ordered chains and clusters in liquid water makes itself evident after the exposure of water to low-frequency electromagnetic radiation. The kinetics of the linearly ordered chains is described by nonlinear excitations (solitons). A hydrodynamic equation describing the behavior of this model system was derived. On the basis of the model, the dimensions of clusters were determined (approximately 600 A). The calculated values of dielectric permeability in the range of low frequencies appeared to be close to their experimentally obtained values. A tenfold increase in the stationary value of dielectric permeability compared with the known value of the dielectric constant in the frequency range of 10(4)-10(6) Hz was predicted. The frequency dependence of dielectric permeability in this range was studied.     

Influence of State of Mixing of the Sample on Total Absorbed Energy in Microwave Cooking

The effects of the state of mixing on total absorbed energy (P) in microwave cooking were investigated. When water and oil were heated independently, both of P were almost equal and the effect of the dielectric loss factor (ε″) on P was negligible. P of a two-layer sample was almost equal to that of the water component alone and was affected by ε″. P of an emulsion sample was almost constant and equal to that of water alone whose volume was the same as the volume of the sample. The difference between P of a two-layer sample and that of an emulsion sample was thought to be affected by the increase in the water-oil interface area, and it was found that P of the water-oil mixture is influenced by the state of mixing.     

On the dielectric spectra of proteins in conducting media

The effect of conductivity on the dielectric measurements of proteins is studied. For that purpose the dielectric spectra (0.03–13 MHz) of serum albumin and myoglobin in solutions of varying conductivities were recorded. The results presented confirm that Maxwell's prediction of a threshold frequency in conducting materials also holds for protein solutions. The threshold frequency of a serum albumin solution is experimentally determined and the ionic screening of the electric field when performing dielectric spectra of these samples discussed. Three distinct frequency regions must be considered: a low frequency region where the sample behaves like a conductor; an intermediate region centered around the threshold frequency where the free charges partially screen the fixed charges; and a high frequency region where the sample behaves like a good dielectric. Dielectric measurements in the low frequency region defined above, are not possible.     

"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.     

Millimeter wave power density in aqueous biological samples

Power density distribution inside a water sample placed between two parallel lossy dielectric plates (Polystyrene) was calculated using Fresnel equations for the frequency range of 42.25-53.57 GHz. Due to the multiple internal reflections from the sample boundaries, the distribution of the power density within the thin sample is more uniform than that within a semi-infinite medium. The power density in a sample depends on the thicknesses of the sample and the adjacent dielectric plates. For the given frequency range the sample thickness optimal for power density uniformity varies between 0.28 and 0.33 mm. The front plate has a significant effect on the magnitude of the power density within the sample but little effect on the power density distribution. The thicker the rear plate, the greater is the non uniformity of the power density distribution within the sample. Based on the calculated data, we determined the dimension of an exposure chamber providing the optimal power density distribution uniformity for mm-wave irradiation.     

Time domain dielectric spectroscopy study of human cells. II. Normal and malignant white blood cells.

The dielectric properties of human lymphocyte suspensions were studied by time domain dielectric spectroscopy (TDDS). Nine populations of malignant and normal lymphocytes were investigated. Analysis of the dielectric parameters of cell structural parts were performed in the framework of Maxwell-Wagner mixture formula and the double-shell model of cell. The specific capacitance of the cell membranes was estimated by the Hanai-Asami-Koisumi formula. It was shown that the dielectric permittivity, capacitance and conductivity values of cell membranes are higher for normal lymphocytes than for the malignant ones. The difference of the same parameters for normal B- and T-cells is also discussed.     

Modeling loop reorganization free energies of acetylcholinesterase: a comparison of explicit and implicit solvent models

The treatment of hydration effects in protein dynamics simulations varies in model complexity and spans the range from the computationally intensive microscopic evaluation to simple dielectric screening of charge-charge interactions. This paper compares different solvent models applied to the problem of estimating the free-energy difference between two loop conformations in acetylcholinesterase. Molecular dynamics (MD) simulations were used to sample potential energy surfaces of the two basins with solvent treated by means of explicit and implicit methods. Implicit solvent methods studied include the generalized Born (GB) model, atomic solvation potential (ASP), and the distance-dependent dieletric constant. By using the linear response approximation (LRA), the explicit solvent calculations determined a free-energy difference that is in excellent agreement with the experimental estimate, while rescoring the protein conformations with GB or the Poisson equation showed inconsistent and inferior results. While the approach of rescoring conformations from explicit water simulations with implicit solvent models is popular among many applications, it perturbs the energy landscape by changing the solvent contribution to microstates without conformational relaxation, thus leading to non-optimal solvation free energies. Calculations applying MD with a GB solvent model produced results of comparable accuracy as observed with LRA, yet the electrostatic free-energy terms were significantly different due to optimization on a potential energy surface favored by an implicit solvent reaction field. The simpler methods of ASP and the distance-dependent scaling of the dielectric constant both produced considerable distortions in the protein internal free-energy terms and are consequently unreliable.     

Electrorotation and levitation of cells and colloidal particles

We review dielectrophoretic forces on cells and colloidal particles, emphasizing their use for manipulating and characterizing the electrical properties of suspended particles. Compared with dielectric spectroscopy, these methods offer a measure of independence from electrode artifacts and mixture theory. On the assumption that the particles can be modeled as uniform dielectric objects with effective dielectric properties, a simple theory can be developed for the frequency variation in the field-induced forces. For particles exhibiting counterion polarization, dielectrophoretic forces differ considerably from predictions of this theory at low frequencies, apparently because of double layer phenomena.     

Microwave absorption in oligomers of ethylene glycol

The dielectric properties of biologically and pharmaceutically important low-molecular weight ethylene glycols H(-OCH2CH2-)n -OH (n = 1,2,4,6) were investigated to clarify the effect of chain length on the dielectric properties. The measurement of dielectric constant and dielectric loss was carried out over the frequency range 200 MHz to 20 GHz at temperatures of 25 degrees C to 55 degrees C. It is found that in these molecules microwave dielectric losses are significant. The dispersion behaviour of these molecules can be represented by Cole-Cole equation. The dielectric properties of these homologous ethylene glycols are discussed in terms of the effects of chain length and intermolecular hydrogen bonds regarding the molecular conformations. These wide frequency range dielectric data have also been discussed in view of the suitable selection of the oligomer of ethylene glycol for cosmetic preparations and other pharmaceutical applications with the intention of protection of the skin from weak microwave radiations present in the surrounding environment. These systematic microwave dielectric data with frequency and temperature variation are not available and are provided in this paper.     

Importance of product inhibition in the kinetics of the acylase hydrolysis reaction by differential stopped flow microcalorimetry

The hydrolysis of N-acetyl-L-methionine, N-acetylglycine, N-acetyl-L-phenylalanine, and N-acetyl-L-alanine at 298.35K by porcine kidney acylase I (EC 3.5.1.14) was monitored by the heat released upon mixing of the substrate and enzyme in a differential stopped flow microcalorimeter. Values for the Michaelis constant (K(m)) and the catalytic constant (k(cat)) were determined from the progress of the reaction curve employing the integrated form of the Michaelis-Menten equation for each reaction mixture. When neglecting acetate product inhibition of the acylase, values for k(cat) were up to a factor of 2.3 larger than those values determined from reciprocal initial velocity-initial substrate concentration plots for at least four different reaction mixtures. In addition, values for K(m) were observed to increase linearly with an increase in the initial substrate concentration. When an acetate product inhibition constant of 600+/-31M(-1), determined by isothermal titration calorimetry, was used in the progress curve analysis, values for K(m) and k(cat) were in closer agreement with their values determined from the reciprocal initial velocity versus initial substrate concentration plots. The reaction enthalpies, Delta(r)H(cal), which were determined from the integrated heat pulse per amount of substrate in the reaction mixture, ranged from -4.69+/-0.09kJmol(-1) for N-acetyl-L-phenylalanine to -1.87+/-0.23kJmol(-1) for N-acetyl-L-methionine.