Damping Of Fluctuations Research Articles

Damping of Giant Resonances and Fluctuations of Nuclear Deformations

Damping of Giant Resonances and Fluctuations of Nuclear Deformations

Comparison of eddy-covariance measurements of CO2 fluxes by open- and closed-path CO2 analysers

Eddy fluxes of CO2 estimated using a sonic anemometer and a closed-path analyser were, on average, 16% lower than those obtained with the same anemometer and an adjacent open-path CO2 analyser. Covariances between vertical windspeed and CO2 density from the closed-path analyser were calculated using data points for CO2 that were delayed relative to anemometer data by the time required for a parcel of air to travel from the tube inlet to the CO2 sensor. Air flow in the intake tube was laminar. Densities of CO2 that had been corrected for spurious fluctuations arising from fluctuations in temperature and humidity were used in the flux calculations. Corrections for the cross-sensitivity of CO2 analysers to water vapour were also incorporated. Spectral analysis of the corrected CO2 signal from the closed-path analyser showed that damping of fluctuations in the sampling tube at frequencies f > 0.1 Hz caused the apparent loss in flux. The measured losses can be predicted accurately using theory that describes the damping of oscillations in a sampling tube. High-frequency response of the closed-path system can be improved substantially by ensuring turbulent flow in the tube, using a combination of high volumetric flow rate and small tube diameter. The analysis of attenuation of turbulent fluctuations in flow through tubes is applicable to the measurement of fluxes of other minor atmospheric constituents using the eddy covariance method.

Thermal-mechanical fluctuations of fluid membranes in confined geometries: the case of soft confinement

By definition, membrane or macromolecular assembly is an event of molecular confinement against the configurational entropy of a disordered state. Bilayer membranes under progressive confinement experience a continual damping of undulatory fluctuations, first interpreted as a steric force (Helfrich. Z. Naturforsch. 1978). This paper uses a new, diffusion-equation formalism based on the Feynman-type variational principle to describe how direct interbilayer forces - of hydration, electrostatic double layers, and van der Waals attraction - confine membrane fluctuations. We recover theoretical results to examine measured forces in multilamellar arrays showing that [open quotes]soft[close quotes] collisions, through long-range forces, create a mutual enhancement of both the direct forces and the undulatory steric interactions. Thus, there is yet another way to resolve the old, but false, dilemma to choose between steric and direct forces driving membrane assembly. One may develop a systematic connection between bilayer charge, hydration, and flexibility and the action of configurational entropic forces. The results make clear that one should measure forces between membranes or macromolecules in a way that allows them to express their native mechanical freedom. 15 refs., 3 figs.

Eddy-covariance CO2 flux measurements using open- and closed-path CO2 analysers: Corrections for analyser water vapour sensitivity and damping of fluctuations in air sampling tubes

Eddy-covariance CO2 flux measurements using open- and closed-path CO2 analysers: Corrections for analyser water vapour sensitivity and damping of fluctuations in air sampling tubes

Eddy-covariance CO2 flux measurements using open- and closed-path CO2 analysers: Corrections for analyser water vapour sensitivity and damping of fluctuations in air sampling tubes

Methods of calibrating infrared CO2 analysers for sensitivity to CO2 and water vapour are described. Equations to correct eddy covariance CO2 flux measurements are presented for: (i) analyser cross-sensitivity to water vapour and the effects of density fluctuations arising from atmospheric fluxes of water vapour and sensible heat, (ii) flux losses caused by signal processing and limited instrument frequency response for open- and closed-path CO2 analysers, and (iii) flux losses resulting from damping of concentration fluctuations in a tube used to sample air for closed-path CO2 analysers. Examples of flux corrections required for typical instruments are presented.

Adaptation to estuarine conditions in shore crabs Carcinus maenas (L.) in relation to body size

Analysis of the salt kinetics in a closed medium in which shore crabs Carcinus maenas (L.) are exposed to changes in salinity, yields information on the permeability and the halftime value for salinity adaptation. The latter value represents an index of the extent to which an animal is adapted to salinity fluctuations in its environment. At brackish-water salinities, the overall permeability to salt appears to be inversely related to the external salinity. Sudden changes in the medium salinity result in a rapid, temporary reduction of the permeability. The whole-animal permeability appears to be linearly related to animal weight. The area-specific permeabilities in small animals tends to be lower than those of larger ones. The halftime value for salinity adaptation is found to be independent of animal weight or external salinity. Therefore, small animals will have no disadvantage in the passive internal damping of fluctuations in environmental salinities. This explains why young animals, despite their high surface area:volume ratio, can survive in shallow coastal waters where environmental conditions are highly unstable.

ULTRASONIC ATTENUATION AND INTERNAL FRICTION DURING FERROELASTIC TRANSFORMATION OF Gd2(MoO4)3 CRYSTAL

The critical attenuation (as) of longitudinal ultrasonic propagation in the vicinity of the f erroelastic-f erroelectrie transformation of GMO has been measured at frequencies (f) 31, 50, 72 and 93 MHz. The proportional relation between as and f2 is established satisfactorily in so far as the shear type phase transition is concerned. In addition, the critical exponents for the attenuation is determined: ρ=1.52 for T-Tc>0.05 K and the crossover behavior is observed.Eesults are also reported on a internal friction investigation (at f=1 Hz, 150kHz) of the ferroelastic transition of GMO, which is suggested to be caused by the moving interphase boundary. The critical stress to move the boundary is determined and it is then confirmed that the mechanism of the ultrasonic attenuation of longitudinal wave in the 2-4°direction is just contributed by the fluctuation damping.

The collisionless damping of density fluctuations in an expanding universe

The best candidate for the dark matter is a massive collisionless non-baryonic relic of the early universe. The most natural type of initial density fluctuations expected are of the adiabatic rather than of the isothermal type. We calculate the temporal evolution of the (initially adiabatic) fluctuation spectrum by numerical integration of the coupled Einstein-Boltzmann equations for scalar perturbations in the metric and in the density of photons, neutrinos, and collisionless relics. Our output linear perturbation spectrum, which is itself input to the nonlinear problem of large scale structure formation, is shown to be characterized by two scales: the damping mass and the horizon mass when the energy density in relativistic particles equals that in nonrelativistic ones, M/sub H/eq. Collisionless relics which decouple when relativistic may be of two basic types if they are to dominate the mass of the universe: massive neutrinos of 10--100 eV, or massive gravitinos (or other weakly interacting particles) of mass about 1 keV. For massive neutrinos, both scales are of supercluster size; and the Zel'dovich pancake picture, in which a large scale is the first to collapse, is expected, regardless of initial spectrum. For massive gravitinos, the damping mass is of galactic scale. Depending uponmore » the initial spectrum, one can get either hierarchical clustering from the damping scale upward or fragmentation of the large M/sub H/eq scale. Collisionless relics which decouple when nonrelativistic have negligible damping masses; again, hierarchical clustering from very small scales or large scale fragmentation is possible in this adiabatic picture.« less

Principles of organic contaminant behavior during artificial recharge

The behavior of a variety of organic contaminants having low molecular weight has been observed during groundwater recharge with reclaimed water. The evidence is site-specific, but is believed to have broader implications regarding the general behavior of organic contaminants in groundwater. The movement of specific contaminants such as chloroform and chlorobenzene is retarded with respect to that of a conservative tracer such as chloride. The measured retardation factors are approximately 3 and 35 for chloroform and chlorobenzene, respectively. The retardation is caused by the sorption of the solute, apparently by the organic constituents of the soil material. The magnitude of the retardation factor of an organic solute can be predicted approximately from knowledge of the organic carbon content of the aquifer material and the octanol-water partition coefficient of the solute. Sorption also contributes to attenuation (damping) of concentration fluctuations. It is shown that the degree of attenuation depends strongly on the retardation factor, the distance traveled, and the hydrogeologic characteristics of the aquifer. There is evidence of biodegradation of organic solutes in the vicinity of the recharge well.

Applications of Larkin-Khmelnitzkii theory to static and dynamical critical phenomena in uniaxial ferroelectrics

The logarithmic correction factors to classical Landau theory due to order parameter fluctuations close to the Curie point are used to calculate various static and dynamic properties for small t ≡ |T — Tc|/Tc. The specific heat at constant polarization has below Tc a cusp ∞ |log t|-2/3. The leading term in the spin-lattice relaxation rate 1/Tt, varies as log t just as in classical theory and in agreement with experiment in colemanite. The damping of low-frequency longitudinal sound waves propagating perpendicular to the easy axis varies as t-1|logt|2/3 below Tc (relaxation damping) and as t-1|log t|-1/3 above Tc (fluctuation damping); the ratio of these two terms is material independent, analogously to recent experiments at the superfluid phase transition in helium II. Propagation of sound not perpendicular to the polar axis suppresses the damping due to the relaxation of the long-range order parameter and leaves only the fluctuation damping. The energy of 180° domain walls vanishes as t3/2|log t|1/2 whereas the domain width, just as in classical theory, remains constant. Earlier estimates of the size of the critical region (“Ginzburg criterion”) in triglycine sulfate are criticized.

Circulation and Temperature Structure in Large Marine Enclosures

Certain physical measurements intended to shed light on the circulation in large plastic enclosures (60–2000 m3) induced by the changing environment in which they are moored are described. Layers of dye were generally seen to diffuse vertically although some important advection effects were also observed. Estimates of an average coefficient of turbulent diffusivity yielded values in the range.05–.26 cm2∙s−1.Measurements taken with recording thermistor chains both inside and outside the enclosures show strong damping of external fluctuations with periods significantly less than 1 day. Various possible sources of mixing energy are considered and it is concluded that thermal forcing through the wall may be significant and could account for the observed range of coefficients.The significance of the observed mixing and circulation to the ecology of the enclosures is discussed. Of particular importance is the vertical mixing of nutrients that influences phytoplankton sinking rates and thus plays a crucial role in determining variations in algal concentration at different depths. Key words: mixing, enclosures, controlled ecosystem pollution experiment, circulation, temperature profiles

Excited States of 25Mg from the 27Al(d, α)25Mg Reaction and 2I+1 Rule

The excitation functions for the 27 Al(d, α) 25 Mg reaction leading up to the 14th level of the final nucleus were obtained at 90° (lab.) in the deuteron energy range from 5.7 to 8.0 MeV in steps of 25 keV. The average values of the excitation functions over the incident energies agree well with the 2 I +1 rule for the levels of which spins have been established. By using the 2 I +1 rule spins of the 10th, 11th, 12th, 13th and 14th excited states of 25 Mg were determined respectively as 5/2, 7/2, 9/2, 1/2 and 3/2 or 5/2, which are not in contradiction to the previous knowledge. Fluctuation damping coefficients N were calculated from the fluctuations in the excitation functions, and the validity for the use of N values as a guide to determine the nuclear spins was examined.

An isothermal calorimeter for solid-state reactions

The design and operation of an isothermal calorimeter is described. The calorimeter is suitable for studying solid-state reactions of long duration in the temperature range 40-300°C. Advantage is taken of the natural damping of thermal fluctuations in a massive body to achieve a temperature stability of better than ± 10−3 degC. In the temperature range 150-240°C the maximum sensitivity is 0·1 cal h−1.

On the Jeans Criterion in Relativistic Cosmology

The problem of gravitational instability in an expanding universe is studied. A physically meaningful discussion is given by using as a coordinate condition the generalized de Donder gauge condition. This technique allows the general relativistic discussion to be exactly analogous to the Newtonian treatment of Bonnor (1957), and an explicit Jeans criterion may consequently be obtained. An unexpected result is found for an isothermal model universe: damping of fluctuations of any given scale occurs after sufficient time has elapsed. Approximate analytic and exact numerical solutions of the perturbation equations are presented.

The electro-pneumatic brake system for steam road service

To describe the organic removal performance in an activated sludge process, the effect of biological adsorption (biosorption, hereinafter) of both soluble and particulate organic substances (SOS and POS, respectively, hereinafter) on the rate of organic removal must be taken into account. This study quantitatively investigated the biosorption of organic pollutants in the domestic wastewater by the activated sludge. The capability of biosorption and the rate of bio-oxidation of organic pollutants were formulated based on the experimental results as functions of both COD concentration and temperature. The biosorption capacity of activated sludge was proportional to COD concentration in the mixed liquor originated from the influent. The kinetic expressions were combined with the equation of longitudinal liquid mixing to set up the mathematical model to predict the effluent COD, and thus to clarify the effect of biosorption on the damping of influent fluctuations of both COD concentration and the inflow rate. The model was also successfully applied to assessing the effectiveness of MLSS control strategies in equalizing the effluent water quality.