Study of solar flares using cosmic radio noise on 25 Mc./s. at Ahmedabad (23°02′ N., 72°38′ E.)

The paper describes observations made at Ahmedabad of sudden cosmic noise absorptions (SCNA’s) on 25 Mc./s. associated with solar flares. The frequency distributions of solar flare attenuations, their times of growth and duration, etc., have been determined and the results are compared with similar observations made by other workers. It has been found that SCNA’s of 25 Mc./s. recorded at Ahmedabad in 1956–58 have been markedly larger in size and duration than those observed in Australia on 18·3 Mc./s. in 1950–51.     

Ein rauscharmet Empfänger in der Radioastronomie der Sonne

Summary A minimum-signal receiver has been set up to measure small fluctuations in the black radiation of the quiet sun. It has previously been almost impossible to use such receivers, because of the eleven-year sun-spot cycle, but signals from the quiet sun can now be received.The system described here consists of a broad-band receiver, operating within the limits 500–1000 Mcs. This receiver operates like a well known Dicke comparison-radiometer, but it is more sensitive than the usual Dicke-system. The minimum detectable temperature in the frequency-region 500–1000 Mc is <10^oK, if the receiver-bandwith is 2 Mc and the time-constant 1 sec.For special cases the broadband receiver is used in conjunction with a parametricpreamplifier at a fixed frequency (610 Mc) The receiver-system is switched to a parabolaantenna having a broadband helixfeed.Examples are given for radioastronomy-measurements of the sun including microbursts, oscillations of beginning radiobursts, and of noise comparison at different UHF-frequencies.

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Jetzt an der Radiosternwarte der Universität Bonn.     

Spread-F in the ionosphere over ahmedabad during the years 1954–57

From a study of spread-F or F-scatter at Ahmedabad during the four years 1954–57 of increasing sunspot activity, it was found that the time of its maximum occurrence receded from 03 hr. in low sunspot years to an hour or two before midnight in high sunspot years. This was particularly well seen in the winter and equinoctial months. Also, maximum spread-F activity which was found in summer in sunspot minimum mum years, occurred in equinoxes in maximum sunspot years. The frequency of occurrence of spread-F was found to be a maximum whenhpF₂ was in the range 300–350 km. F-scatter and F₂-stratification were found to be anti-correlated both in their diurnal and seasonal variations. The general trend was towards decreased spread-F with increased sunspot activity. It is concluded that (1) spread-F at Ahmedabad geomagnetic latitude (Φ=13·6° N) undergoes variations similar to those at equatorial stations, more so in high sunspot years, (2) the change-over from low-latitude type to middle-latitude type of variation of spread-F takes place at about geomagnetic latitude 22°, and (3) spread-F at Ahmedabad decreases with increase in magnetic activity, which is the reverse of that observed at high latitudes.     

The effect of Gaussian white noise on the fractality of fluctuations in the plasma of a symmetrical discharge

In this work we investigate the influence of white Gaussian noise on the fluctuations in the plasma of a symmetrical discharge using multifractal detrended fluctuation analysis. We observe that in the range of noise intensity used in our study, the multifractality strength is increased by the noise, at all values of the inter-anode voltage, both for original and filtered time-series. This is interpreted as a new positive influence of noise because this effect can be understood as an increasing in the predictability on the dynamics in a time-series. A constructive influence of noise can appear only for fluctuations with underlying chaotic dynamics. The shuffling analysis demonstrates that the multifractality is purely a consequence of the correlations of the fluctuations. The noise influence is also observed in the change of the position of the maximum in the singularity spectra. The multifractal detrended cross correlation between light intensity and current intensity demonstrates that the fluctuations in both parameters are generated by the same physical processes though they are very different in nature: one is a local parameter and the other is a global one.     

Noise-induced effects in nonlinear relaxation of condensed matter systems

Noise-induced phenomena characterise the nonlinear relaxation of nonequilibrium physical systems towards equilibrium states. Often, this relaxation process proceeds through metastable states and the noise can give rise to resonant phenomena with an enhancement of lifetime of these states or some coherent state of the condensed matter system considered. In this paper three noise induced phenomena, namely the noise enhanced stability, the stochastic resonant activation and the noise-induced coherence of electron spin, are reviewed in the nonlinear relaxation dynamics of three different systems of condensed matter: (i) a long-overlap Josephson junction (JJ) subject to thermal fluctuations and non-Gaussian, Lévy distributed, noise sources; (ii) a graphene-based Josephson junction subject to thermal fluctuations; (iii) electrons in a n-type GaAs crystal driven by a fluctuating electric field. In the first system, we focus on the switching events from the superconducting metastable state to the resistive state, by solving the perturbed stochastic sine-Gordon equation. Nonmonotonic behaviours of the mean switching time versus the noise intensity, frequency of the external driving, and length of the junction are obtained. Moreover, the influence of the noise induced solitons on the mean switching time behaviour is shown. In the second system, noise induced phenomena are observed, such as noise enhanced stability (NES) and stochastic resonant activation (SRA). In the third system, the spin polarised transport in GaAs is explored in two different scenarios, i.e. in the presence of Gaussian correlated fluctuations or symmetric dichotomous noise. Numerical results indicate an increase of the electron spin lifetime by rising the strength of the random fluctuating component. Furthermore, our findings for the electron spin depolarization time as a function of the noise correlation time point out (i) a non-monotonic behaviour with a maximum in the case of Gaussian correlated fluctuations, (ii) an increase up to a plateau in the case of dichotomous noise. The noise enhances the coherence of the spin relaxation process.     

Fractal space,cosmic strings and spontaneous symmetry breaking

The present paper is conceived within the framework of El Naschie's fractal-Cantorian program and proposes to develop a model of the fractal properties of spacetime. We show that, starting from the most fundamental level of elementary particles and rising up to the largest scale structure of the Universe, the fractal signature of spacetime is imprinted onto matter and fields via the common concept for all scales emanating from the physical spacetime vacuum fluctuations. The fractal structure of matter, field and spacetime (i.e. the nature and the Universe) possesses a universal character and can encompass also the well-known geometric structures of spacetime as Riemannian curvature and torsion and includes also, deviations from Newtonian or Einsteinian gravity (e.g. the Rössler conjecture). The leitmotiv of the paper is generated by cosmic strings as a fractal evidence of cosmic structures which are directly related to physical properties of a vacuum state of matter (VSM). We present also some physical aspects of a spontaneous breaking of symmetry and the Higgs mechanism in their relation with cosmic string phenomenology. Superconducting cosmic strings and the presence of cosmic inhomogeneities can induce to cosmic Josephson junctions (weak links) along a cosmic string or in connection with a cosmic string (self) interactions and thus some intermittency routes to a cosmic chaos can be explored. The key aspect of fractals in physics and of fractal geometry is to understand why nature gives rise to fractal structures. Our present answer is: because a fractal structure is a manifestation of the universality of self-organisation processes, as a result of a sequence of spontaneous symmetry breaking (SSB). Our conclusion is that it is very difficult to prescribe a certain type of fractal within an empty spacetime. Possibly, a random fractal (like a Brownian motion) characterises the structure of free space. The presence of matter will decide the concrete form of fractalisation. But, what does it mean the presence of matter? Can there exist a spacetime without matter or matter without spacetime? Possibly not, but consider on the other hand a space far removed from usual matter, or a space containing isolated small particles in which a very low density matter can exist. Very low density matter might be influenced by a fractal structure of space, for example in the sense that it is subject also to fluctuations structured by random fractals. Diffraction and diffusion experiments in an empty space and very low density matter could provide evidence of a fractal structure of space. However, at very high (Planck) densities, and a spacetime in which fluctuations represent also the source of matter and fields (which is very resonable within the context of a quantum gravity), we can assert that Einstein's dream of geometrising physics and El Naschie's hope to prove the fractalisation (or Cantorisation) of spacetime are fully realised.     

Quantum mechanics from cosmic fluctuations

We show that it is possible to derive Quantum Mechanics from cosmic fluctuations in the light of Santamato's geometric approach and a simple model in the Robertson–Walker geometry considered in that context.     

Noise-induced on–off intermittency in mutually coupled semiconductor lasers

Intermittent switches between low-frequency fluctuations and steady-state emission are experimentally observed in two bidirectionally coupled semiconductor lasers subject to common Gaussian noise applied to the laser pump currents. The time series analysis reveals power-law scalings typical for on–off intermittency near its onset, with critical exponents of −1 for the mean turbulent length versus noise intensity and −3/2 for probability distribution of laminar phases versus the laminar length. The same −1 power-law scaling is found by the power spectrum analysis for the signal-to-noise ratio versus the noise intensity.     

A calculation of the flux and energy spectrum of secondary electrons at high altitudes in the atmosphere

Calculations are carried out to determine the flux and energy spectra of secondary electrons which are produced by the cosmic radiation in the upper layers of the atmosphere. The calculations are valid to an atmospheric depth of about 10 g./cm.² Electron spectra are presented for different depths and locations where measurements of the electron flux have been carried out: Ft. Churchill, Manitoba; Sioux Falls, South Dakota; Palestine, Texas; and Hyderabad, India. The calculations are compared with observed electron fluxes during the ascents of balloon flights.     

The nuclear magnetic resonance spectra of four spin systems

The ring proton resonance spectra ofα, β andγ picolines have been studied at 40 Mc./sec. The spectra which belong to the classes ABCX, ABXY and A₂X₂ respectively have been completely analyzed to determine all the involved parameters.     

Interstellar hydrogen and cosmic background radiation

It is shown that a collection of photons with nearly the same frequency exhibits a “condensation” type of phenomenon corresponding to a peak intensity. The observed cosmic background radiation can be explained from this standpoint in terms of the radiation due to fluctuations in interstellar hydrogen.     

Dynamical analysis of a delayed singular prey–predator economic model with stochastic fluctuations

This article studies a delayed singular prey–predator economic model with stochastic fluctuations, which is described by differential‐algebraic equations due to a economic theory. Local stability and Hopf bifurcation condition are described on the delayed singular prey–predator economic model within deterministic environment. It reveals the sensitivity of the model dynamics on gestation time delay. A phenomenon of Hopf bifurcation occurs as the gestation time delay increases through a certain threshold. Subsequently, a singular stochastic prey–predator economic model with time delay is obtained by introducing Gaussian white noise terms to the above deterministic model system. The fluctuation intensity of population and harvest effort are calculated by Fourier transforms method. Numerical simulations are carried out to substantiate these theory analysis. © 2013 Wiley Periodicals, Inc. Complexity 19: 23–29, 2014     

The Noise Prediction Model SATIN

This paper presents the noise prediction model SATIN (Statistical Approach to Turbulence Induced Noise) which is based on Lighthill's acoustic analogy. It allows to predict both, the far‐field noise radiation as well as near‐field wall‐pressure fluctuations. Far‐field noise radiation may result from the scattering of wall‐pressure fluctuations at geometrical discontinuities and is therefore important for many practical problems. Within this paper, we focus on the calculation of far‐field noise radiation. The required input values of SATIN are local properties of turbulence, namely the turbulent kinetic energy and the integral length scale which can be obtained by steady solutions of the Reynolds‐averaged Navier‐Stokes equations with a two equation turbulence model. It is assumed that the turbulence is axisymmetric and homogenous, which is taken into account by introducing two anisotropy parameters. The validation of SATIN is done for trailing‐edge noise originating from a thin flat plate using measurements of a phased array. As expected, the anisotropic formulation of SATIN improves the prediction quality considerably compared to isotropic turbulence.     

Measurements of total electron content over Ahmedabad and Bombay from Beacon satellite data

The paper outlines the method used at Ahmedabad for determining the total electron content in the ionosphere from differential Faraday rotations of plane polarised radio waves on 40.010 and 41.010 Mc./s. transmitted by NASA satellite 64-64A. The observations made during the period October 1964 to April 1965 are utilised to determine the diurnal variation of the total electron content up to the satellite height which was about 1,000 km. over Ahmedabad and Bombay latitudes. The curve of total electron content up to the satellite height shows similarity to the curve of maximum electron density at the F2 peak. The total electron contents over Bombay are in general higher than those over Ahmedabad.     

Dynamics of transport under random fluxes on the boundary

The impact of boundary noise on the dynamical evolution of the scalar transport equation in shear flows is studied, taking off from earlier studies in shear-flow dispersion in internal waves, a mechanism for horizontal mixing in the ocean. In particular, we model a gravity current evolving under an assumed shear-flow. The transport equation is deterministic, with a noise term at the inlet boundary. This was motivated by observed seasonal fluctuations in some known sources of salty, dense water in the oceans, like the Red Sea overflow, as well as observed thermal and saline anomalies in the thermohaline circulation.The noises used were: Wiener white, Wiener colored, Lévy white, and Lévy colored noise. Lévy processes form a more general class of processes which are generally non-Gaussian in distribution, and may have infinitely many jumps in finite time. They have been used to model pollutant point-sources, the flight time of particles in vortices, and linear and nonlinear anomalous diffusion.The major finding was that white noises (Wiener and Lévy ) and colored Wiener noise all have the effect of impeding the diffusion process, by as much as 33%. However, colored Lévy noise (non-Gaussian, time-correlated) does not have this effect on diffusion. This would suggest that time-correlation is more important in distinguishing noises than the distribution of the process that produced the noise. This also explains why Lévy colored noise showed great sensitivity to the stability parameter α, while Lévy white noise is unaffected by its stability parameter.     

Investigations on the multiply charged nuclei of the primary cosmic radiation near the geomagnetic equator using nuclear emulsion

A nuclear emulsion stack was exposed over Hyderabad, India (geomagnetic latitudeλ=7·6° N) under a mean atmospheric depth of 6·8 g./cm.², on 24 March 1960. The relative and absolute intensities of Be and B nuclei and nuclei of charge Z?6 (the S-nuclei) have been determined in this stack. The intensities were extrapolated to the top of the atmosphere using measured fragmentation parameters involved in collisions of cosmic ray nuclei in graphite. The flux values of Be, B and S nuclei at the top of the atmosphere have been determined to be 0·025±0·011, 0·101±0·023 and 1·12±0·10 particles/m.² sec. sr. respectively. The ratios of intensities B/S, Be/S and Be/B have been found to be 0·09±0·02, 0·022±0·008 and 0·25±0·11 respectively. These ratios of intensities have been used (a) to compute the amount of matter traversed by the radiation before reaching the vicinity of the earth as 2·6±0·6 g./cm.², (b) to show that the Fermi mechanism of acceleration of particles is not efficient at these energies (1–10 GeV/n.) in interstellar space and (c) to show that preferential acceleration of H₁-nuclei (Z?20) is not of overwhelming importance. The derived source composition of nuclei of energy ?7·5 GeV/n suggests that N, O, F and H₃-nuclei (Z=10–15) have similar abundances in the universe and in cosmic rays, and that C and H₁-nuclei are overabundant in cosmic rays.     

Electron dynamical response in InP semiconductors driven by fluctuating electric fields

The complexity of electron dynamics in low-doped n-type InP crystals operating under fluctuating electric fields is deeply explored and discussed. In this study, we employ a multi-particle Monte Carlo approach to simulate the non-linear transport of electrons inside the semiconductor bulk. All possible scattering events of hot electrons in the medium, the main details of the band structure, as well as the heating effects, are taken into account. The results presented in this study derive from numerical simulations of the electron dynamical response to the application of a sub-Thz electric field, fluctuating for the superimposition of an external source of Gaussian correlated noise. The electronic noise features are statistically investigated by computing the correlation function of the velocity fluctuations, its spectral density and the variance, i.e. the total noise power, for different values of amplitude and frequency of the driving field. Our results show the presence of a cooperative non-linear behavior of electrons, whose dynamics is strongly affected by the field fluctuations. Moreover, the electrons self-organize among different valleys, giving rise to the reduction of the intrinsic noise. This counterintuitive effect critically depends on the relationship among the characteristic times of the external fluctuations and the temporal scales of complex phenomena involved in the electron dynamical response. In particular, the correlation time of the electric field fluctuations appears to be crucial both for the noise reduction effect and the appearance of an anomalous diffusion effect.     

Evidence of low-dimensional dynamics in a traffic noise time series

The noise level measurements were made at 10 s interval near a busy road which admits one-way traffic only. The time series thus obtained was analysed using non-linear dynamical techniques. The results of the analysis suggest that the underlying dynamical process could be deterministic. It appears that the data support periodic and quasiperiodic attractors. The presence of colour fluctuations in the time series could be attributed to shuttling of the dynamics between these two attractors.     

Untersuchungen über Elektronenströmungen

Summary The laws of conservation of energy and charge are used in a perturbation theory for longitudinal controlled streams of electrons. Space charge, the electromagnetic field and the relativistic change of mass are taken into account. The relations in the classical field are found from a matrix form. Impedances of the streams are used. On terminals they are identical with the impedances of the electronic device. It is shown, howNyquist's noise formula can be derived from the shot noise, for a system in thermal equilibrium with potential minimum in the electron streams and high transit time angles. For a system not in thermal equilibrium some noise formulas are presented. A simplification of the calculation of the noise convection currents of the electrons coming at the electrodes can be made. When in all emission points the emission fluctuations are concentrated in the streams with maximal transit time the noise in the convection currents has the same value as the real noise. When a potential minimum is present, the current is important, which passes over the potential minimum. The noise of this current must be concentrated in the streams with maximal transit time beginning in the potential minimum.     

On the stability and Hopf bifurcation of a delay-induced predator–prey system with habitat complexity

We study the effect of the degree of habitat complexity and gestation delay on the stability of a predator–prey model. It is observed that there is stability switches, and Hopf bifurcation occurs when the delay crosses some critical value. By applying the normal form theory and the center manifold theorem, the explicit formulae which determine the stability and direction of the bifurcating periodic solutions are determined. The qualitative dynamical behavior of the model system is verified with the published data of Paramecium aurelia (prey) and Didinium nasutum (predator) interaction. It is observed that the quantitative level of abundance of system populations depends crucially on the delay parameter if the gestation period exceeds some critical value. However, the fluctuations in the population levels can be controlled completely by increasing the degree of habitat complexity.