One-dimensional Propagation Model Research Articles

Origin of cosmic ray electrons and positrons

With experimental results of AMS on the spectra of cosmic ray (CR) $e^{-}$, $e^{+}$, $e^{-}+e^{+}$ and positron fraction, as well as new measurements of CR $e^{-}+e^{+}$ flux by HESS, one can better understand the CR lepton ($e^{-}$ and $e^{+}$) spectra and the puzzling electron-positron excess above $\sim$10 GeV. In this article, spectra of CR $e^{-}$ and $e^{+}$ are fitted with a physically motivated simple model, and their injection spectra are obtained with a one-dimensional propagation model including the diffusion and energy loss processes. Our results show that the electron-positron excess can be attributed to uniformly distributed sources that continuously inject into the galactic disk electron-positron with a power-law spectrum cutting off near 1 TeV and a triple power-law model is needed to fit the primary CR electron spectrum. The lower energy spectral break can be attributed to propagation effects giving rise to a broken power-law injection spectrum of primary CR electrons with a spectral hardening above $\sim$40 GeV.

Infrared-laser-induced ultrafast modulation on the spectrum of an extreme-ultraviolet attosecond pulse.

We present a theoretical investigation of the isolated extreme-ultraviolet (XUV) attosecond pulse propagating in the ionizing gas induced by a synchronized strong infrared (IR) laser, with the numerical solution of the nonadiabatic one-dimensional propagation model. Upon scanning the relative delay between the XUV and the IR pulse, it is found that the delay-dependent XUV transmission spectrogram exhibits the unique pattern that is controllable by the chirp of the XUV pulse. Furthermore, we demonstrate that this kind of spectrum modulation can be attributed to the term of the light energy loss involved in the propagation equation. The characteristics of the spectrum modulation dependent on the XUV chirp might provide an all-optical way for the reconstruction of the XUV spectral phase.

One-Dimensional Model for Propagation of a Pressure Wave in a Model of the Human Arterial Network: Comparison of Theoretical and Experimental Results

Pulse wave evaluation is an effective method for arteriosclerosis screening. In a previous study, we verified that pulse waveforms change markedly due to arterial stiffness. However, a pulse wave consists of two components, the incident wave and multireflected waves. Clarification of the complicated propagation of these waves is necessary to gain an understanding of the nature of pulse waves in vivo. In this study, we built a one-dimensional theoretical model of a pressure wave propagating in a flexible tube. To evaluate the applicability of the model, we compared theoretical estimations with measured data obtained from basic tube models and a simple arterial model. We constructed different viscoelastic tube set-ups: two straight tubes; one tube connected to two tubes of different elasticity; a single bifurcation tube; and a simple arterial network with four bifurcations. Soft polyurethane tubes were used and the configuration was based on a realistic human arterial network. The tensile modulus of the material was similar to the elasticity of arteries. A pulsatile flow with ejection time 0.3 s was applied using a controlled pump. Inner pressure waves and flow velocity were then measured using a pressure sensor and an ultrasonic diagnostic system. We formulated a 1D model derived from the Navier-Stokes equations and a continuity equation to characterize pressure propagation in flexible tubes. The theoretical model includes nonlinearity and attenuation terms due to the tube wall, and flow viscosity derived from a steady Hagen-Poiseuille profile. Under the same configuration as for experiments, the governing equations were computed using the MacCormack scheme. The theoretical pressure waves for each case showed a good fit to the experimental waves. The square sum of residuals (difference between theoretical and experimental wave-forms) for each case was <10.0%. A possible explanation for the increase in the square sum of residuals is the approximation error for flow viscosity. However, the comparatively small values prove the validity of the approach and indicate the usefulness of the model for understanding pressure propagation in the human arterial network.

A static network level model for the information propagation in vehicular ad hoc networks

In this paper, we present a network level model to describe the information propagation in vehicular ad hoc networks (VANETs). The approach utilizes an existing one-dimensional propagation model to evaluate information travel times on the individual arcs of the network. Traffic flow characteristics are evaluated by a static traffic assignment model. Upper and lower bounds are developed for the time of information propagation between two nodes in a network. We show that the bounds yield good (typically within 5%) estimates of the true time lag for the lower penetration rates (<10%), which makes them particularly useful in the initial deployment stages of vehicle-to-vehicle (V2V) communication. Furthermore, our lower bound reveals that – quite surprisingly – for sufficiently low penetration rates, more equipped vehicles on the road does not necessarily promote the fast propagation of information. As an application of the bounds, we formulate a resource allocation model in which communication devices can be installed along roads to promote wireless propagation. A set of efficient heuristic algorithms is developed to solve the resource allocation problem. Numerical results are given throughout.

Excitation of acoustic waves from cylindrical polyvinylidene fluoride (PVDF) film confined in a concentric wall

This paper investigates acoustic wave radiation from cylindrical polyvinylidene fluoride (PVDF) film mounted inside a concentric wall with a small air gap. In such a structure, propagation is allowed only in the gap between the film and the wall surface, and the wave propagates in the axial direction of the cylinder. The radiation impedance of the cylindrical transducer inside the concentric wall has been calculated using a one-dimensional propagation model. After calculating the mechanical impedance of the cylindrical PVDF film, the generated acoustic wave has been calculated as a function of frequency with various air gaps between the PVDF film and the wall. It has been found that the excited acoustic wave becomes stronger for a narrower air gap and shows a maximum at a specific air gap. This phenomenon has been explained as the match between the transducer impedance and the radiation impedance of the air gap. When the gap is too small, the radiation impedance exceeds the transducer's mechanical impedance, the acoustic wave radiation decreases with the decreasing gap, and the resonance frequency increases due to loading by the imaginary part of the excessive radiation impedance. All these theoretical results have been experimentally confirmed.

The role of time scale separation in a nonequilibrium roughening transition

In this work we analyze the role of time scale separation between the external driving and the avalanche relaxation dynamics in a one-dimensional model of propagation of innovations among economic agents. When the time scales are separated the model presents a nonequilibrium roughening transition. We show that when avalanche overlapping is permitted, only a rough phase is observed.

“Buzz-saw” noise: A comparison of measurement with prediction

Accurate prediction of “buzz-saw” noise in a turbofan inlet duct necessitates consideration of nonlinear acoustics, modelling a complete fan blade set, modelling an acoustic liner, and calculations at high frequencies. A recent series of papers has described new work concerning the application of one-dimensional propagation models to the prediction of buzz-saw noise. A numerical model, termed the frequency domain numerical solution or FDNS, has been developed. It can be used to calculate the nonlinear propagation of the rotor-alone pressure field in either a rigid or acoustically-lined inlet duct. From this the in-duct noise level of the buzz-saw tones can be determined. In previous work, validation of this method by comparison with in-duct noise measurements has been limited to rigid inlet ducts, because of the lack of availability of suitable measurements from lined ducts. In this article new measurements of buzz-saw noise in an acoustically-lined inlet duct are utilized. A comparison of measurements of buzz-saw noise in a lined inlet duct, and noise predictions from numerical simulations by the FDNS is presented. The detailed measurements reveal the effect of an acoustic liner on buzz-saw noise. The suitability of the numerical model to be used to provide realistic noise predictions for supersonic ducted fans is also examined.

Nonequilibrium phase transition in a model for the propagation of innovations among economic agents.

We characterize the different morphological phases that occur in a simple one-dimensional model of propagation of innovations among economic agents [X. Guardiola et al., Phys. Rev E 66, 026121 (2002)]. We show that the model can be regarded as a nonequilibrium surface growth model. This allows us to demonstrate the presence of a continuous roughening transition between a flat (system size independent fluctuations) and a rough phase (system size dependent fluctuations). Finite-size scaling studies at the transition strongly suggest that the dynamic critical transition does not belong to directed percolation and, in fact, critical exponents do not seem to fit in any of the known universality classes of nonequilibrium phase transitions. Finally, we present an explanation for the occurrence of the roughening transition and argue that avalanche driven dynamics is responsible for the novel critical behavior.

Pressure Fluctuations on the Impeller Blades of a Centrifugal Turbomachine: a Comparative Analysis Between Air and Water Tests

In this paper a comparison between pressure fluctuations measurements in the time domain is proposed. These measurements were carried out on two centrifugal turbomachines, a fan with air and a pump with water. In order to gather a better understanding of their internal acoustics, time records of the pressure fluctuations were made on the blades in the outlet of the impellers and near the volute tongue. These showed that the flow is very unsteady at the impeller outlet and in the tongue region. An analysis of the pressure fluctuations and their propagation showed that the main noise sources are caused by the blade-tongue interactions and depend on the fluid type. In the case of the pump, the hydraulic nature of the noise source is dominant. Using a one-dimensional propagation model, it is possible to explain some differences in the behaviour of the turbomachines which is related in particular to the different sound speeds.

NUMERICAL EXPERIMENTS ON ACOUSTIC RECIPROCITY IN COMPRESSIBLE POTENTIAL FLOWS IN DUCTS

A reciprocity theorem for the scattering matrix for the propagation of acoustic modes in a duct with acoustically hard walls or with acoustically absorbing walls has been given in a companion publication. It was found that for a source at a specified end of the duct, suitably scaled reflection matrices in direct and reverse flow have a reciprocal relationship. Scaled transmission matrices obtained for direct flow and reversed flow with simultaneous switching of source location from one end to the other also have a reciprocal relationship. A reverse flow theorem for the equivalent one-dimensional propagation model, which is a good approximation to the three-dimensional model at low frequencies, was also obtained. In this case, using reciprocity and acoustic power conservation arguments it is additionally found that the acoustic power transmission coefficient is the same for a source at either end of the duct for a given flow direction. This result leads to an invariance theorem which relates acoustic power propagated due to sources of equal pressure amplitude at the two ends of the duct. A numerical verification of these reciprocal relationships is given here for propagation in axially symmetric (circular and annular) ducts with multi-modal propagation and at low frequencies when a one-dimensional model is appropriate.

Role of passive electrical properties during action potential restitution in intact heart.

Action potential duration (APD) restitution is classically attributed to membrane ionic currents; however, the role of cell-to-cell coupling in restitution is poorly understood. To test the hypothesis that passive electrical properties of multicellular preparations influence restitution, spatial gradients of transmembrane voltage were measured with high spatial (0.83 mm), voltage (1 mV), and temporal (0.5 ms) resolutions using voltage-sensitive dye in Langendorff-perfused guinea pig ventricle. At short premature coupling intervals, APD failed to shorten in cells located near (< 3 mm) the site of pacing corresponding to the site of earliest repolarization, deviating from classical restitution. In contrast, APD shortened exponentially with increasing stimulus prematurity when pacing was remote from the identical recording site. The mechanism responsible for nonexponential restitution was investigated in a one-dimensional propagation model using the dynamic Luo-Rudy formulation of the ventricular cell and was found to be attributable to depolarizing axial current present in regions of steep repolarization gradients. Moreover, axial current loading attenuated spatial gradients of repolarization that were prominent in the absence of cell-to-cell coupling. These data demonstrate that 1) in contrast to restitution in isolated cells, restitution in multicellular tissue is influenced by axial current from neighboring cells, and 2) in normal myocardium, axial current between cells attenuates dispersion of repolarization during premature stimulation of the heart.

Alfvén-Jeans and Magnetosonic Modes in Multispecies Self-Gravitating Dusty Plasmas

Perpendicularly propagating electromagnetic waves in magnetized, multispecies, self-gravitating dusty plasmas are investigated in terms of their wave dispersion properties as well as with respect to their susceptibility to gravitational collapse. In particular, waves on the ordinary as well as extraordinary mode branches are considered. Within the one-dimensional propagation model employed, all modes except the ordinary mode produce density perturbations that can be unstable to gravitational collapse. The wavelengths that are unstable are comparable to the well-known Jeans length for a neutral gas/dust, but there are interesting modifications due to the presence of a magnetic field and charged particles. Furthermore, the effects of the gravitational coupling of a multicomponent plasma to a neutral dust are discussed.

Experimental studies of the propagation of combustion in solids

The application of thermal methods to the study of steady-state combustion is described. Such methods provide a route to information on heat transfer and chemical kinetics which forms a basis for the implementation of numerical models. The experimental results from thermal analysis and temperature profile analysis have been examined within the context of a simple pseudo one-dimensional model of propagation offering some confirmation of the validity of the approach.

The Mexico Earthquake of September 19, 1985—Earthquake Behavior of Soft Sites in Mexico City

From the september 19, 1985 earthquake there are several acceleration records for the soft (lake bed) sites in Mexico City. One-dimensional propagation models of the incident seismic accelerations incorporate the wave propagation profiles at three of those sites. The undamped computed surface acceleration spectra compare well with the recorded ones for two sites. The other one does not produce adequate results, which is probably due to incomplete information on the shear wave velocities. Further investigation with the site impulse function indicates that the surface accelerations during the september 19, 1985 event had a frequency content determined, to a certain extent, by the natural periods of the site. Direct inspection of the recorded spectra for the september 19, 1985 earthquake at the studied sites shows that the relation between spectral periods corresponds to the closed form solution of an homogeneous layer with a fixed base. This relation may be different for other earthquakes recorded at these sites.