Local High Frequency Research Articles

A genetic model for disruptive selection on colony social organisation, reproduction, and ecotype distribution in wood ants inhabiting different woodland habitats

Wood ants of theFormica rufa species complex are typically bound to woodland habitats and their eventual colonization of more open habitats depends on the presence of a sufficient number of woody plants. Computer simulations of the long-term development of large wood ant populations in woodland systems of differing structure were performed. A cellular, stochastic automation model simulated the alternatives of a compact, coherent woodland system and a fragmented, coarse-grained woodland system. The simulation of a compact woodland system gave evidence that disruptive selection alone may be sufficient to produce two distinct ectotypes, which are known asFormica rufa andFormica polyctena, even if there is a full fertility of the crosses. The simulation of a fragmented, coarse-grained woodland system has supported the view, that a high local frequency of nests with intermediate phenotypes might be explainable by a particular woodland pattern which favour mixed strategies. It was shown that queen dominance and intraspecific social parasitism are likely to be important factors in the dynamics of large wood ant populations.

Calculation of nuclear magnetic resonance order parameters in proteins by normal mode analysis. II. Contribution from localized high frequency motions

Nuclear magnetic resonance (NMR) order parameter S̃ 2 for spin pairs in protein is an important quantity for deducing protein static and dynamic three-dimensional structures from NMR experimental data. In the previous paper it has been shown that contribution from low frequency motions to the order parameter can be calculated reliably from normal mode analysis carried out in dihedral angle space for spin pairs for which a number of intervening dihedral angles (NIVDA) is 10 or less. However, it has been known that for spin pairs with NIVDA=0, high frequency motions also affect the value of the order parameter. In this paper we show that the effect of high frequency motions can be accounted for by a correction term to be added to the value obtained from normal mode analysis in dihedral angle space. A factor of the correction term determined by high frequency motions can be calculated by the usual normal mode analysis for a small peptide fragment which has the same local conformation as in protein.

Perpendicular ion acceleration by localized high frequency electric fields in magnetized plasmas

A basic process capable of explaining observations of fast perpendicular ions in a wide range of plasma environments is described. Spatial symmetry breaking perpendicular to the confining magnetic field is shown to cause irreversible energy gain for ions gyrating through an electric field having a nonuniform amplitude. The efficiency depends on the ratio of the ion Larmor radius to the scale length of the amplitude gradient, and on the scaled frequency ν≡ω/Ωi. A Landau resonance is not required, and there is no lower threshold on the electric field, because the mechanism is active in the linear regime. Theory, numerics, and particle-in-cell simulations are used to illustrate the interaction for electrostatic fields in the lower-hybrid range of frequencies, but the process does not depend on a particular type of mode.

A model for the 1/f noise corner frequency of FETs on semi-insulating substrates based on bulk phenomena: Theory and experiments

We have developed a formula for the 1/f noise corner frequency for GaAs MESFETs. The formula is based on a new theory where the 1/f noise is a bulk phenomena with localized high frequency variations and long range low frequency fluctuations in the substrate with the lowest frequency being constrained only by the thickness of the material. The model is based on employing a distributed equivalent circuit technique in evaluating the semi-insulating substrate. Preliminary results demonstrate a close consistency between modeled and measured data.

Vibrational neutron spectroscopy of collagen and model polypeptides

A pulsed source neutron spectrometer has been used to measure vibrational spectra (20-4000 cm-1) of dry and hydrated type I collagen fibers, and of two model polypeptides, polyproline II and (prolyl-prolyl-glycine)10, at temperatures of 30 and 120 K. the collagen spectra provide the first high resolution neutron views of the proton-dominated modes of a protein over a wide energy range from the low frequency phonon region to the rich spectrum of localized high frequency modes. Several bands show a level of fine structure approaching that of optical data. The principal features of the spectra are assigned. A difference spectrum is obtained for protein associated water, which displays an acoustic peak similar to pure ice and a librational band shifted to lower frequency by the influence of the protein. Hydrogen-weighted densities of states are extracted for collagen and the model polypeptides, and compared with published calculations. Proton mean-square displacements are calculated from Debye-Waller factors measured in parallel quasi-elastic neutron-scattering experiments. Combined with the collagen density of states function, these yield an effective mass of 14.5 a.m.u. for the low frequency harmonic oscillators, indicating that the extended atom approximation, which simplifies analyses of low frequency protein dynamics, is appropriate.

On the theory of 1/f noise of semi-insulating materials

The 1/f noise phenomena associated with devices involving semi-insulating materials, for instance GaAs MESFET's on semi-insulating GaAs, has long been a perplexing problem. In this particular case the 1/f noise corner frequency can be up to 100 MHz before the mean square noise current at the drain is dominated by the Nyquist noise associated with the channel conductance. No reasonable explanation has ever been given, although there are many different theories. 1/f noise is a common phenomena in nature and other devices involving semi-insulating materials. We propose here that this 1/f noise is a bulk phenomena associated with localized high frequency variations and long range low frequency fluctuations, the lowest frequency being limited only by the volume of the material. Specifically the proposal here is that injection of a current I into a semi-insulating material will result in a mean square noise voltage at the point of injection given by v/sub n//sup 2/~=2(kT/q)q/spl Delta/fR(/spl omega//sub c///spl omega/) Volts/sup 2/ where /spl omega//sub c/=1/t/sub t/, for the radian frequencies, /spl omega/, larger than /spl omega//sub c/ which is the reciprocal of the transit time of the carriers. For a long sample and long transit times then this 1/f noise voltage due to current injection will be larger than the Nyquist mean square noise of the sample alone as long as the DC voltage developed across the semi-insulating sample exceeds ((2kT/q)l/sup 2/(/spl omega///spl mu/))/sup 1/2/. This theory then gives the 1/f or 1//spl omega/ frequency dependence. The dc current I might be injected for instance by the substrate current in a GaAs MESFET being injected into the semi-insulating substrate, or gate current in an IGET being injected into the gate insulator.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Long time scale molecular dynamics subspace integration method applied to anharmonic crystals and glasses

A subspace dynamics method is presented to model long time dynamical events. The method involves determining a set of vectors that span the subspace of the long time dynamics. Specifically, the vectors correspond to real and imaginary low frequency normal modes of the condensed phase system. Most importantly, the normal mode derived vectors are only used to define the subspace of low frequency motions, and the actual time dependent dynamics is fully anharmonic. The resultant projected set of Newton’s equations is numerically solved for the subspace motions. Displacements along the coordinates outside the subspace are then constrained during the integration of the equations of motion in the reduced dimensional space. The method is different from traditional constraint methods in that it can systematically deduce and remove both local and collective high frequency motions of the condensed phase system with no a priori assumptions. The technique is well suited to removing large numbers of degrees of freedom, while only keeping the very low frequency global motions. The method is applied to highly anharmonic Lennard-Jones crystal and glass systems. Even in these systems with no intramolecular degrees of freedom or obvious separation of time scales, the subspace dynamics provides a speed up of approximately a factor of 5 over traditional molecular dynamics through use of a larger integration time step. In the cases illustrated here a single set of subspace vectors was adequate over the full time interval, although this is not expected to be true for all systems.

Vibrational contributions to rougheting; a study for the (111) and (100) FCC Lennard-Jones systems

It is well known that simple lattice-gas models of surfaces predict roughening temperatures ( T R) for close packed faces, as determined by the temperature at which step free energies vanish, to be above the melting point. Further, these models predict T R to scale as the ratio of the number of inplane bonds for different faces. Vibrational contributions, in the form of line tensions and step entropies calculated in the harmonic limit, to the roughening temperature are calculated for the (111) and (100) faces of a face center cubic Lennard-Jones system. Inclusion of these effects reduces T R significantly to temperatures below the melting point and brings T R for the (111) and (100) closer together in agreement with experiment. However, the ordering of T R switches from that expected, that is the (111) transition now occurs below that of the (100). Local density of state spectra show the 〈011〉 step on the (100) face to exhibit localized high frequency vibration modes above the bulk continuum.

Ultrasonic absorption and dynamic shear properties of the transition from dilute solution to the melt for polybutadiene

The frequency dependence of ultrasonic absorption ( α f 2 ∼ η eff ) and dynamic shear data ( G′, G″, η′ s) has been studied over a wide frequency range ( f = 10 4 – 10 9 Hz) in solutions (∅ = 0.03 – 0.8) of polybutadiene in 2-methyl butyl benzene and toluene as solvents and in the melt (∅ = 1). The ultrasonic spectra and the frequency dependence of the shear properties are both described in terms of subchain motions, entanglement effects and local motions. For increasing concentrations the crossover from dilute solution behaviour to the entanglement regime was detected. We have attempted to describe, in terms of the subchain concept, the influence of concentration on motions at frequencies above the entanglement region. The subchain motion in dilute solutions and between the entanglements have been described by combining the Muthukumar-Freed theory with relaxation times calculated by the Moiseev version of the Zimm theory taking into consideration the solvent quality. Deviations from the expected screening of the hydrodynamic interaction for the highest concentrations and the melt have been attempted in order to describe additional local high frequency relaxations connected to the dynamic glass transition. By comparing longitudinal ( η eff) and shear ( η′ s) measurements it was possible to clarify the influence of subchain motions on shear and bulk properties.

The 1984 Round Valley, California Earthquake Sequence

SUMMARY The 1984 November 23 ML 5.8 Round Valley earthquake is one in the.series of moderate earthquakes to have occurred in the Bishop-Mammoth Lakes, California area since 1978. This event and its aftershock sequence are particularly well recorded in that they occurred within a dense, local high frequency seismic network, and strong motion accelerograms, and regional and teleseismic digital seismograms are available for the main shock. We have derived the fault plane solution from the local and regional first motion data, inverted the teleseismic body wave data for the moment tensor solution, and fit regional surface waves for the low frequency moment. Unlike results for several of the earlier moderate events in the Bishop-Mammoth Lakes region, all results for the Round Valley main shock data sets give solutions consistent with left-lateral strike slip faulting on a near vertical N30E striking plane. The seismic moment of the main shock from the regional surface wave analysis is 7.9 X 101'Nt m. Measurements of the seismic moment from regional surface waves and teleseismic body waves have been converted to spectral level and combined with the acceleration spectra to give a composite source spectrum for the main shock. The spectrum shows a lower corner frequency at 0.2Hz associated with the overall faulting event, and a higher comer frequency at 4.0 Hz which may be associated with the subevents composing the but at a lower slope of w-l between the low and high frequency corners as postulated in models for complex or partial stress drop events. The Round Valley main shock was followed by a widespread and prolonged aftershock sequence. Because of the dense local, high gain permanent seismograph network operated jointly by the University of Nevada-Reno and the United States Geological Survey, accurate locations and fault plane solutions could be determined for the aftershocks beginning immediately after the main shock, and the temporal and spatial growth of the aftershock sequence could be followed in detail. The Round Valley sequence is characterized by the development of two conjugate planes of aftershock activity; one, a near vertical plane striking N30E associated with the main shock, and another which developed in the first 24 h of activity striking N40W and dipping 55NE. This shallow plane conforms to an extension of the Hilton Creek fault postulated by Malcome Clark, and may be the first indication of activity on this major Holocene structure since the recent period of earthquake activity began in 1978. Aftershocks defining the deeper near vertical plane tend to concentrate around the periphery of a 36-49 km2 area which appears to represent the slip surface of the main shock. Relating the seismic moment determined from regional surface waves to this slip area results in an average dislocation of 0.54-0.73 m and a stress drop of 1.5-2.3 MPa. Nearly 800 fault plane solutions for aftershocks were determined. A smaller subset which samples the aftershock zone both spatially and temporally shows that during the initial hours of the sequence, aftershocks occuring on the deeper, near vertical plane were predominantly left-lateral strike slip. Motion on the N40W plane was dominantly right-lateral to right-lateral oblique slip with a tendency for shallow normal displacement at its western extent. Fault plane solutions in the shallow crust above the two conjugate planes are more variable, suggesting complex brecciation of the shallow crustal block. Although the main shock and the bulk of aftershock activity is confined to the foot wall block of the Round Valley range front fault, this activity at the north end of the sequence area may represent activation of the hanging wall block of the range front fault.

Effect of friction on electron transfer: The two reaction coordinate case

Electron transfer is a very important reaction in many biological processes such as photosynthesis and oxidative phosphorylation. In many of these reactions, most of the interesting dynamics can be included by using two reaction coordinates: one fast (local high frequency vibration modes) and one slow (outersphere modes such as solvent polarization). We report a model to describe this problem, which uses path integral techniques to calculate electron transfer rates, and also to obtain the Fokker–Planck equations associated with this model. Different limiting cases lead to qualitatively different results such as exponential or nonexponential time decay for the donor survival probability. Conditions for the validity of the adiabatic or the nonadiabatic limits will be discussed. Application of this model to real systems is proposed, in particular for a porphyrin rigidly linked to a quinone, which is a very interesting model compound for primary events of photosynthesis. This model can also be used for other multicoordinate biological reactions such as ligand binding to heme proteins. Also, in the concluding part of Sec. III, we discuss the important limit where the fast vibronic mode is much faster than all the other nuclear modes coupled to the problem. In this limit the fast mode ‘‘renormalizes’’ the electronic matrix element, and this considerably simplifies the treatment of the problem, reducing it to coupling only to the slow modes.

Investigation of the homogeneity of solids with a linear regression model

Testing of the hemogeneity of solids is usually based on the comparison of the variance of measurements at several sample points with the variance of repeated measurements. In the case of destructive analytical methods, empirical mathematical models are needed because repetitions at the same subsample are impossible. Successful application of such models depends on the adequacy of the mathematical model and the type of distribution observed. Gradients and textures with low or medium local frequency require other tests than stochastic distributions with high local frequency. A simple regression model base on a 2 2 factorial allows conclusions about the type of distribution without great mathematical effort.

Entangled linear polymer chains in melts: n.m.r. and Rouse or reptation models; stress relaxation

This study deals with detailed descriptions proposed to analyse slow chain diffusional process effects on n.m.r. properties of nuclei linked to long linear polymer molecules in melts or in concentrated solutions. It aims to predict relationships among macroscopic viscoelastic properties and semi-local dynamical properties observed from n.m.r. These relationships are discussed considering two main models of low-frequency chain fluctuations in melts: a multiple relaxation-mode spectrum analogous to a Rouse model or a single relaxation-mode spectrum analogous to a reptation model. The two descriptions are compared with each other. The Rouse model was chosen because n.m.r. properties might be sensitive to the equilibration process of conformational fluctuations within a so-called ‘tube’ as well as to the reptation in a ‘tube’. Also, the Rouse model is more easily handled than the reptation one. Local molecular properties are transferred to the unusual n.m.r. semi-local space scale ( <30 A ̊ ) through the submolecule concept: every monomeric unit is supposed to have a uniform average orientational order within a given submolecule. Semi-local dynamical properties are analysed from the transition of the spin-system response from a pseudo-solid behaviour to a liquid-like one, induced by shortening polymer molecules or by slightly diluting them. This transition is currently observed from the transverse magnetic relaxation function of nuclei linked to entangled polymer chains. This spin-system response is contrasted to the longitudinal response only sensitive to local high relaxation frequency motions. Also, it is shown how stress-relaxation processes induced on a macroscopic scale can be monitored on a semi-local space scale from n.m.r. Relaxation rates of the transverse magnetization are shown to depend strongly upon both the initial stretching ratio λ of the polymer sample and the structure of its chain relaxation spectrum.

Seismic-Stratigraphic Mapping of Gulf Coast Stratigraphic Traps: ABSTRACT

The mappability of a seismic-stratigraphic trap depends not only on the thickness and the stratigraphic position of the objective unit, but the velocity contrast with nearby beds. Analysis of band-pass filtered sonic logs provides a useful technique for determining the portion of the frequency spectrum that carries the basic stratigraphic information. Depending on local stratigraphy, both high (75 to 125 hz) and low (0 to 10 hz) frequency components may be important in defining the trap. The filtered sonic can be used to predict the seismic mappability of stratigraphic units. Review of seismic-stratigraphic data over fields in the Gulf Coast indicates that determining the mappability of a feature depends on complete understanding of the trap. At Walker Creek field, Smackover porosity is not resolved with a 60-hz filtered sonic. Because the basic reservoir-seal relation is low frequency, however, the field limits are clearly expressed on real seismic-stratigraphic data. Alternatively, recognition of the pinch-out of the 20-ft (6.1 m) thick Spanish Camp Sand at South Lissie field serves as an excellent example of a trap expressed as a high frequency feature. These simple examples illustrate clearly that both high and low frequency components are required for successful seismic mapping of Gulf Coast stratigraphic traps. End_of_Article - Last_Page 1568------------

Hydrodynamic interactions and their effect on local high frequency processes in the polymer chain (Polarized luminescence, NMR)

A theoretical study has been made of the influence of hydrodynamic interactions on the mechanism of polarized luminescence and NMR of macromolecules in solution. The depolarization function for the luminescence Y ( T/ n) has been formulated (in which T - the absolute temperature; n - solvent viscosity) and equations have also been obtained for the spin-lattice relaxation time T 1 (in the high frequency range) for chains with strong hydrodynamic interactions, the chain consisting of 10, 30 or 100 segments modelled by a Gaussian sub-chain. The hydrodynamic interactions due to space effects have been found not to affect the shape of the Y ( T/ n) function in the range 1 < Y < 3 and the mol.wt. dependence of mobility (determined by polarizing luminescence) θ ω N for chains with a strong hydrodynamic interaction at small N values shows the behaviour typical of freely permeated chains. The change to the region in which θ ω N is practically independent of N in the presence of the hydrodynamic reaction is at N ≈ 5–6.

Further Progress with Oncolysis due to Local High Frequency Hyperthermia, Local X-Irradiation and Apathogenic Clostridia*

AbstractResults of tests on application of combined local high frequency hyperthermia, local X-irradiation and apathogenic Clostridia in treatment of Harding-Passey-Melanoma (HPM) in mice are presented and analyzed.

Ionospheric HF Doppler dispersion during the eclipse of 7 March 1970 and TID analysis

The amplitudes and phases (relative to a local high precision frequency standard) of WWV HF transmissions on 5, 10 and 15 MHz from Ft. Collins, Colorado, were recorded continuously during the period of the total solar eclipse on 7 March 1970. Changes in apparent Doppler frequency as small as 0.01 Hz could be detected. The goal of the experiment was to detect the passage of ionospheric acoustic-gravitational waves which were predicted by Chimonas and Hines (1970). Following a period of large phase and group path disturbance beginning at about 1600 UT, smaller phase path variations of a regular nature were observed after 1900 UT. Their periods, 25 min, correspond to the acoustic-gravitational wave period predicted by Chimonas (1970) for the solar eclipse-generated wave. The TID amplitude, ranging from 1 to 20 per cent of the mean electron density at reflection height, was computed by combining the phase path data with group path data ( Lerfald et al., 1970) and total electron content data ( Davis and Da Rosa, 1970). Although the available data are suggestive, the TID which occurred after 1900 UT cannot be unequivocally associated with the ionospheric acoustic gravitational wave predicted by Chimonas and Hines (1970).

Impacto de los sólidos suspendidos totales sobre la obstrucción en emisores de riego localizado de alta frecuencia

Este estudio a escala piloto evaluó el impacto de los sólidos suspendidos totales, SST, sobre la obstrucción en emisores de riego localizado de alta frecuencia, RLAF, empleando como tratamiento para mejorar la calidad de agua un filtro de grava de flujo ascendente con mantas sintéticas (FGAC Manta). El efluente de dicho tratamiento alimentó cuatro tipos de sistemas RLAF: Lyn, Autocompensado, Microjet y Cinta de riego, para evaluar la incidencia del aporte de los SST sobre cada uno de ellos. Para ello se evaluó el riesgo de obturación, el coeficiente de uniformidad (Cu), la concentración de sólidos depositados en las paredes de los conductos y el tamaño de partícula que ingresó a los RLAF. Los resultados mostraron que cuanto mayor fue la concentración de SST, menor fue el tiempo de riego alcanzado por las tecnologías RLAF. La relación de los SST aportados a los RLAF con el tamaño de partícula que ingresó a los conductos y emisores presentó partículas hasta de 129 micras, que contribuyen a la obturación de los emisores. El régimen laminar contribuye a la deposición de sólidos en los conductos de los emisores de las tecnologías RLAF afectando el Cu.

Localized vibrations at vacant sites in cubic crystals

The existence of localized high frequency modes at a vacancy is studied for models of copper, iron and sodium with central short range forces. The vacancy represents a softening of the crystal but some force constants increase under the atomic readjustment and these may produce localized modes. In copper a mode of symmetry A 2u , is found which is slightly above the continuum. No localized modes were found in iron or sodium. The perturbation of the dynamical matrix was too extensive to apply the Green function method so that the total spectrum could not be studied. A molecular approximation is used in which shells of atoms near the vacancy are free to vibrate. This gives a lower bound to the frequency which increases as more shells are released. The dynamical matrix is factored by use of symmetry coordinates, complete tables of which are given for the group O h . Up to 20 movable shells and 30 symmetry coordinates are considered. A method of combining the molecular calculations for the few strongly perturbed shells with the properties of the unperturbed crystal at larger distances is developed by an adaptation of the theory of “effective moduli”. It speeds convergence and gives the asymptotic behavior of the mode. The experimental observation of localized modes of a vacancy in a metal appears to be difficult.

Some experimental results concerning nonreciprocal East-West VLF wave propagation

Experimental data collected in recent years by Crombie [1958], and Reder et al. [1962], and theoretical work on VLF propagation by Wait [1960] have given strong evidence to the fact that VLF propagation is nonreciprocal in the east-w'es t and west-east direc Lioos. Experimental data rela ting to this topic are aL present sparse. This paper presents some experjmentflJ results obtained during the past 2 years which will substantiate the existing evidence as to this nonreciprocal propagation . Since D ecemb er 1961 , t he phftse of the VLF transmitter NPM (19.8 kc/s) located at Hawaii has been monitored and compar ed with a local high stability frequency source in Singapore, which is approximately 11,000 km away. The shortest propagation pftth is one which travels within 20 deg of an east to wes t direcLion. Th e relfttive phftse of GBR (distance 11,000 km) has also been monitored over the same period. While tbe diurnal variation of phase of GBR (16.0 kc/s) at t his iLe has undergone tbe usual trapezoidal pattern wiLh a (1fty to night excur ion of 1.1 to 1.3 cycles of phase, tbe diurnal phase of NPM has exhibited a double-humped paLLem regularly day after day (fig . 1). H is proposed in this paper that this form of diurnal phase variation is du e to the nonreciproci ty of VLF propagfttion in the east-west and west-eas t directions. Further evidence to support this conclusion has been obtained from: (a) short term monitoring of NPM at Gan in the M aldive I slands, and (b) from flight measurements of several thousand