Injection Rate Of Particles Research Articles

γ-ray emission from PWNe interacting with molecular clouds

We consider a situation in which a pulsar is formed inside or close to a high-density region of a molecular cloud. Right after birth, the pulsar was very active and accelerated hadrons and leptons to very high energies. Hadrons diffuse through the supernova remnant and some of them are trapped in the nearby cloud interacting with the matter. We extend a recent timedependent model for the γ radiation of pulsar wind nebulae (PWNe) to describe this more complicated astrophysical scenario. The typical calculations have been performed for two objects, IC 443 and W41, which have recently been discovered as sources of TeV γ -rays. In this model the low-energy TeV emission should be correlated with the birth place of the pulsar and the region of dense soft radiation rather than with its present position, provided that the injection rate of relativistic particles into the PWN has been much more efficient at early times. The high-energy TeV emission should be correlated with the location of dense clouds which were able to capture high-energy hadrons due to their strong magnetic fields.

Nonlinear Diffusive Shock Acceleration with Magnetic Field Amplification

We introduce a Monte Carlo model of nonlinear diffusive shock acceleration that allows for the generation of large-amplitude magnetic turbulence, i.e., ΔB B0, where B0 is the ambient magnetic field. The model is the first to include strong wave generation, efficient particle acceleration to relativistic energies in nonrelativistic shocks, and thermal particle injection in an internally self-consistent manner. We find that the upstream magnetic field B0 can be amplified by large factors and show that this amplification depends strongly on the ambient Alfven Mach number. We also show that, in the nonlinear model, large increases in B do not necessarily translate into a large increase in the maximum particle momentum a particular shock can produce, a consequence of high-momentum particles diffusing in the shock precursor where the large amplified field converges to the low ambient value. To deal with the field growth rate in the regime of strong fluctuations, we extend to strong turbulence a parameterization that is consistent with the resonant quasi-linear growth rate in the weak turbulence limit. We believe our parameterization spans the maximum and minimum range of the fluctuation growth, and within these limits we show that the nonlinear shock structure, acceleration efficiency, and thermal particle injection rates depend strongly on the yet to be determined details of wave growth in strongly turbulent fields. The most direct application of our results will be to estimate magnetic fields amplified by strong cosmic-ray modified shocks in supernova remnants.

A supersonic gas injection system for fuelling and probing fusion plasmas

The large gas reservoir surrounding the H-1NF plasma leads to difficulties in achieving the density control required to maximize the plasma temperature. We have designed and tested an alternative fuelling system which uses a double conical nozzle to generate a directed flow of particles into the plasma without adding to the gas inventory in the rest of the vacuum vessel. By using a closed plenum at a programmable pressure and a piezo-electric valve, the particle flux can be dynamically changed in a controlled and quantitative manner. Measurements of the gas jet using constant temperature hot wire anemometry show that, for plenum pressures between 500 and 1000 Torr, the particle injection rate (helium) ranges between 2 × 1020 and 4 × 1020 s−1 with half-cone angles between 5° and 20°. The system has been installed on the H-1NF device and first plasma results indicate localized gas injection consistent with test tank anemometry measurements.

Derivation of electric potential patterns in the inner magnetosphere from Cluster EDI data: Initial results

Electric potential patterns are derived in the inner magnetosphere at 4 < L < 10 using 2 years of data from the Electron Drift Instrument (EDI) on Cluster. First, we examine the relations between the electric field and the following three parameters to understand how the potential patterns are organized: BZ component of the interplanetary magnetic field (IMF), Kp index, and Dst index. From these correlations we can determine the effect of the interplanetary electric field (IEF) on the inner magnetospheric electric field as measured by Cluster. Next, the electric field is related to a quantity proportional to the injection rate of the plasma sheet particles, F(Dst*) ≡ (dDst*/dt + 0.13Dst*), where the effect of the magnetopause current is removed in Dst*. Then we develop a method to obtain potential patterns. An inverse problem is solved by adjusting a trade‐off parameter for smoothness of the result. The obtained potential patterns for three controlling parameters, IMF BZ, Kp index, and F(Dst*), are attached as supplemental material. We discuss the following features from these potential patterns: (1) potential drop, (2) rotation of the direction of the convection electric field, (3) dawn‐dusk asymmetry of the strength of the electric field, and (4) size of the last closed equipotential (LCE). This initial study is relevant to the development of an empirical model of inner magnetospheric convection in the equatorial plane.

자기폭풍 기간 중 정지궤도 공간에서의 입자 유입률과 Dst 지수 사이의 상관관계

자기폭풍(magnetic storm)과 서브스톰(substorm)의 인과관계를 규명하기 위하여 서브스톰 확장기 활동(substorm expansive activity)의 전형적인 지시자로 알려진 정지궤도 위성에서 관측된 양성자 플럭스(proton flux)의 무분산 입자유입률(dispersionless particle injection rate)과 Dst 지수와의 상관관계를 조사하였다. 본 연구에 이용된 자기폭풍은 1996년에서 2000년까지 5년 동안에 일어난 것으로 자기폭풍 기간 중 Dst의 최소값인 <TEX>$Dst_{min}$</TEX>의 크기에 따라 대규모(<TEX>$-200nT{$\leq$}Dst_{min}{$\leq$}-100nT$</TEX>), 중규모(<TEX>$-100nT{\leq}Dst_{min}{\leq}-50nT$</TEX>), 소규모 자기폭풍(<TEX>$-50nT{\leq}Dst_{min}{\leq}-30nT$</TEX>)의 3단계로 구분하였다. 양성자 플럭스는 LANL의 정지궤도 위성에서 관측된 자료 중에서 주로 환전류(ring current)를 구성하는 입자의 에너지에 해당하는 50keV에서 670keV 범위의 6개 에너지 채널의 자료를 이용하였다. 그리고 입자유입은 자정 부근에서 주로 일어나므로 18:00~04:00MLT구간에서 관측된 자료만을 이용하였다. 한편 내부 자기권으로 유입되는 입자에너지를 추정하기 위하여 양성자 플럭스 비(<TEX>$f_{max}/f_{ave}$</TEX>)를 조사하였다. 여기서, <TEX>$f_{ave}$</TEX> 및 <TEX>$f_{max}$</TEX>는 각각 입자유입이 일어나기 전 후의 양성자 플럭스의 양을 나타낸다. 한편 자기폭풍 기간 동안에 1 ~ 2개의 인공위성 관측으로부터 내부 자기권으로 유입되는 총 에너지량을 추정하는 것이 불가능하다는 것이 알려졌다. 그러나 총 에너지 유입량은 적어도 플럭스 비와 유입횟수에 비례할 것이다. 따라서 내부 자기권으로 유입되는 에너지의 양을 간접적으로 추정하기 위해서 이들의 곱으로 정의되는 총 에너지 유입률 지수(total energy injection parameter, TEIP)를 제안하였다. 특히 서브스톰이 자기폭풍의 발달에 기여하는 정도를 알기 위하여 자기폭풍을 두 구간, 즉 주상(main phase)과 회복기(recovery phase)로 나누어 조사하였다. 양성자의 무분산 유입자료와 자기폭풍 기간 중 Dst<TEX>$_{min}$</TEX> 값을 비교해 본 결과 다음과 같은 특성이 확인되었다. 첫째, 주상기간 중 입자들의 평균 유입횟수는 자기폭풍의 크기에 비례하여 증가하는 경향을 나타내며 유입휫수와 <TEX>$Dst_{min}$</TEX> 사이에는 높은 상관관계(0.83)가 있었다. 둘째, 주상기간 중 자기폭풍의 크기가 클수록 플럭스 비 (<TEX>$f_{max}/f_{ave}$</TEX>는 대체로 증가하는 경향을 나타냈다. 그리고 75~113keV 에너지 채널에서의 <TEX>$Dst_{min}$</TEX> 값과 플럭스 비의 상관계수는 0.74로서 가장 높았으며 나머지 에너지 채널 역시 비교적 높은 상관관계를 나타냈다. 셋째, 주상기간 중 총 에너지 유입률 지수와 <TEX>$Dst_{min}$</TEX> 사이에 높은 상관관계가 확인되었다. 특히 환전류를 구성하는 주요 입자의 에너지 영역(75~l13keV)에서 가장 높은(0.80) 상관계수를 기록했다. 넷째, 회복기 중에 일어나는 입자들의 유입은 자기폭풍의 지속시간을 연장시키는 경향을 보이며 큰 자기폭풍일수록 현저했다. 주상에서 관측된 이러한 특성은 서브스톰 확장기 활동이 자기폭풍의 발달과 밀접한 관계가 있음을 시사한다. To examine the causal relationship between geomagnetic storm and substorm, we investigate the correlation between dispersionless particle injection rate of proton flux observed from geosynchronous satellites, which is known to be a typical indicator of the substorm expansion activity, and Dst index during magnetic storms. We utilize geomagnetic storms occurred during the period of 1996 ~ 2000 and categorize them into three classes in terms of the minimum value of the Dst index (<TEX>$Dst_{min}$</TEX>); intense (<TEX>$-200nT{$\leq$}Dst_{min}{$\leq$}-100nT$</TEX>), moderate(<TEX>$-100nT{\leq}Dst_{min}{\leq}-50nT$</TEX>), and small (<TEX>$-50nT{\leq}Dst_{min}{\leq}-30nT$</TEX>) -30nT)storms. We use the proton flux of the energy range from 50 keV to 670 keV, the major constituents of the ring current particles, observed from the LANL geosynchronous satellites located within the local time sector from 18:00 MLT to 04:00 MLT. We also examine the flux ratio (<TEX>$f_{max}/f_{ave}$</TEX>) to estimate particle energy injection rate into the inner magnetosphere, with <TEX>$f_{ave}$</TEX> and <TEX>$f_{max}$</TEX> being the flux levels during quiet and onset levels, respectively. The total energy injection rate into the inner magnetosphere can not be estimated from particle measurements by one or two satellites. However, the total energy injection rate should be at least proportional to the flux ratio and the injection frequency. Thus we propose a quantity, “total energy injection parameter (TEIP)”, defined by the product of the flux ratio and the injection frequency as an indicator of the injected energy into the inner magnetosphere. To investigate the phase dependence of the substorm contribution to the development of magnetic storm, we examine the correlations during the two intervals, main and recovery phase of storm separately. Several interesting tendencies are noted particularly during the main phase of storm. First, the average particle injection frequency tends to increase with the storm size with the correlation coefficient being 0.83. Second, the flux ratio (<TEX>$f_{max}/f_{ave}$</TEX>) tends to be higher during large storms. The correlation coefficient between <TEX>$Dst_{min}$</TEX> and the flux ratio is generally high, for example, 0.74 for the 75~113 keV energy channel. Third, it is also worth mentioning that there is a high correlation between the TEIP and <TEX>$Dst_{min}$</TEX> with the highest coefficient (0.80) being recorded for the energy channel of 75~113 keV, the typical particle energies of the ring current belt. Fourth, the particle injection during the recovery phase tends to make the storms longer. It is particularly the case for intense storms. These characteristics observed during the main phase of the magnetic storm indicate that substorm expansion activity is closely associated with the development of mangetic storm.

The Effects of Pipe Curvature on the Flow Characteristics of Solid-liquid Two-phase Mixture in an Experimental Flexible Hose System

ABSTRACT The flexible hose system, which smoothly connects the buffer system and the miner in the deep sea lifting system, maximizes the action radius of the miner and prevents the lifting pipe from being twisted or broken. In order to predict and prevent accidents such as pipe clogging and to minimize the required power through the system, it is important to understand the flowing characteristics of manganese nodules and seawater in a flexible hose system. In this study a lab-scale flexible hose apparatus has been designed and manufactured to analyze the effects of pipe curvature on the flow characteristics of solid-liquid two-phase mixture in a flexible hose. The experiments for solid-liquid two-phase flow in a flexible hose has been performed by changing experimental factors, such as particle size, particle injection rate, hose shape and two-phase mixture velocity. The experimental results show that the increase of discharged volume fraction and diameter of the solid particles causes the pressure drop in the hose and the increase of the minimum velocity to transport the solid particles in the identical flexible hose. In the case of the solid-liquid two-phase mixture velocity more than 1.5 m/sec, the more the shape of the flexible hose becomes curved, the more the pressure drop in the hose increases. When it is lower than 1.5 m/sec, it was confirmed that the more the shape of the flexible hose becomes linear, the stronger the accumulation phenomenon becomes and the more the pressure drop in the hose increases.

An Experimental Analysis on Hydraulic Lifting of Solids through a Small-scale Vertical Tube

ABSTRACT A lab-scale hydraulic pumping system with 3.64 m straight pipe section has been designed and manufactured to analyze flowing characteristics of solid-liquid two-phase mixture in a vertical tube. The experiments for solid-liquid two-phase flow in the vertical tube have been performed by systematically changing experimental factors, such as pipe diameter, particle size, particle injection rate and two-phase mixture velocity. As results, it has been confirmed that pressure drop and hydraulic gradient in the tube increase because of increase in in-situ volume fraction of solid particles when particle injection rates are increased. Also, as the size of the solid particle becomes larger, the settling velocity of the solid particle group increases and pressure drop also increases in the tube. The other hand, as the tube diameter becomes larger, the pressure drop and the hydraulic gradient decrease.

Energetic Particle Events: Efficiency of Interplanetary Shocks as 50 keV &lt;E&lt; 100 MeV Proton Accelerators

We have studied the injection rate of shock-accelerated protons in long-lasting particle events by tracing back the magnetohydrodynamic conditions at the shock under which protons are accelerated. This tracing back is carried out by -tting the observed Nux and anisotropy pro-les at di†erent energies, considering the magnetic connection between the shock and the observer, and modeling the propagation of the shock and of the particles along the interplanetary magnetic -eld. A focused-di†usion transport equation that includes the e†ects of adiabatic deceleration and solar wind convection has been used to model the evolution of the particle population. The mean free path and the injection rate have been derived by requiring consistency with the observed Nux and anisotropy pro-les for di†erent energies, in the upstream region of the events. We have extended the energy range of previous models down to 50 keV and up to D100 MeV. We have analyzed four proton events, representative of west, central merid- ian, and east scenarios. The spectra of the injection rate of shock-accelerated protons derived for these events show that for energies higher than 2 MeV the shock becomes a less efficient proton accelerator. We have related the derived injection rates to the evolution of the strength of the shock, particularly to the normalized downstream-upstream velocity ratio (VR), the magnetic -eld ratio, and the angle As h Bn . a result, we have derived an empirical relation of the injection rate with respect to the normalized veloc- ity ratio (log Q P VR), but we have not succeeded with the other two parameters. The Q(VR) relation allows us to determine the injection rate of shock-accelerated particles along the shock front and throughout its dynamical expansion, reproducing multispacecraft observations for one of the simulated events. This relation allows us to analyze the inNuence of the corotation e†ect on the modeled particle Nux and anisotropy pro-les. Subject headings: acceleration of particles E interplanetary medium E MHD E shock waves E Sun: particle emission

Radiation drag in relativistic active galactic nucleus jets

We present the first comprehensive study of radiation drag imposed on both cold and relativistic plasma components in a jet propagating at relativistic speeds through a dense radiation field. Earlier work showed that radiation drag acting on the cold plasma alone drops very fast with distance from the central source and can affect the jet dynamics only very close to the central source (up to 10–30 gravitational radii), and only if the jet plasma is strongly dominated by electron-positron pairs. In the case of radiation drag acting on a jet through relativistic electrons/positrons, the distance dependence can be much flatter, actually being determined by the distance dependence of the injection rate of relativistic particles. However, we show that such radiation drag can be dynamically important only for magnetically dominated jets in which the injection luminosity of relativistic electrons/positrons exceeds the kinetic luminosity of the jet. Our studies are performed using a radiation tensor formalism, which is the most suitable and elegant method for calculating both forces and cooling rates resulting from Compton scattering of an ambient radiation field by relativistic plasma in a jet. Simple analytic formulae, derived using this method, allow one to make quick estimates of dynamical and radiative effects resulting from the interaction of relativistic jets with different external radiation field distributions.

Energy Spectrum of Shock-Accelerated Particles.

We have quantified the injection rate of low-energy particles (90-1000 keV) at the front of three interplanetary shocks detected by ISEE-3 spacecraft. We have used a MHD code to simulate the shock propagation and the focused-diffusion equation for particle propagation. This allows us to quantify the injection rate of particles, Q, at the shock by fitting the observed flux and anisotropy at different energies. We relate the variations of the efficiency of the particle acceleration with the interplanetary magnetic field and plasma conditions in the shock front region magnetically connected with the observer. Particularly, with the MHD strength of the shock, the interplanetary magnetic field-shock normal angle, the extent of the shock, and the heliolongitude of the parent solar activity that generates the shock.

Energy spectrum of low-energy fluxes of particles accelerated by interplanetary shocks

The injection rate of particles at the front of interplanetary shocks has usually been studied locally, around the shock passage by the observer's position, but little is known of how the efficiency of the particle-acceleration process evolves as the shock propagates from the Sun to the Earth. In many events accelerated particles are observed long in advance of the arrival of the shock (from 5 hours to 2 days), and they show large anisotropies. We have used a compound shock-particle model to derive the injection rate of particles at the shock front and their energy spectrum, as a function of time, by fitting the observed particle fluxes and anisotropies between 100 and 1000 keV. We have studied three individual low-energy particle events taken as representatives of West, Central Meridian and East events.

The spectral turnover of the 'filled-center' supernova remnant 3C 58: Implications for when acceleration occurs

view Abstract Citations (15) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Spectral Turnover of the "Filled-Center" Supernova Remnant 3C 58: Implications for When Acceleration Occurs Green, D. A. Abstract IRAS observations the 'filled-center' supernova remnant 3C 58 are used to derived upper limits of 0.4, 0.4, 0.8, and 1.5 Jy for its infrared flux density at 12, 25, 60, and 100 micrometers, respectively. These values imply a break in the spectrum of 3C58 above a few tens of gigahertz -- two orders of magnitude below the break in the spectrum of the Crab Nebula -- with a change of spectral index across the break for 3C58 of more than 0.5. This is similar to previous results for another 'filled-center' remnant, G74.9+1.2, from radio observations alone. This implies that their emission is not dominated by a constant injection rate of particles with a power-law distribution. Either the break is due to synchrotron losses in the past, with little particle injection in recent times or it is intrinsic to the acceleration mechanism at work (presumably from a central neutron star). Publication: The Astrophysical Journal Supplement Series Pub Date: February 1994 DOI: 10.1086/191908 Bibcode: 1994ApJS...90..817G Keywords: Crab Nebula; Interstellar Matter; Mathematical Models; Particle Acceleration; Supernova Remnants; Ephemeris Time; Flux Density; Infrared Astronomy Satellite; Light Curve; Maximum Likelihood Estimates; Power Spectra; Astrophysics; ISM: SUPERNOVA REMNANTS; ACCELERATION OF PARTICLES; RADIATION MECHANISMS: NONTHERMAL full text sources ADS | data products SIMBAD (6)

Radio Emission From Snr 1987A

AbstractDiffusive acceleration of electrons by the blast wave of SNR 1987A is shown to provide a reasonable fit to observations of the radio emission since it reappeared in 1990 July. As well as determining the diffusion coefficient in this model, the observations indicate that the compression ratio of the gas subshock embedded in the blast wave is ~2.7, much lower than the value of 4 expected of a strong shock front. We propose that protons accelerated by the shock front itself cause the weakening of the subshock by both heating and accelerating the upstream plasma, producing a structure with a precursor to the gas subshock. Preliminary calculations using a fluid model for the energetic particle population indicate that these effects can significantly weaken the subshock just a few years after the explosion, if the same rate of particle injection is assumed as in other models of the acceleration of cosmic rays.Subject headings: acceleration of particles — ISM: individual (SNR 1987 A) — radio continuum: ISM — shock waves

The Spectral Turnover of the “Filled-Center” Supernova Remnant 3C 58: Implications for When Acceleration Occurs

AbstractIRASobservations the “filled-center” supernova remnant 3C 58 are used to derived upper limits of 0.4, 0.4, 0.8, and 1.5 Jy for its infrared flux density at 12, 25, 60, and 100 μm, respectively. These values imply a break in the spectrum of 3C58 above a few tens of gigahertz—two orders of magnitude below the break in the spectrum of the Crab Nebula—with a change of spectral index across the break for 3C 58 of more than 0.5. This is similar to previous results for another “filled-center” remnant, G74.9+1.2, from radio observations alone. This implies that their emission isnotdominated by a constant injection rate of particles with a power-law distribution. Either the break is due to synchrotron losses in the past, with little particle injection in recent times or it is intrinsic to the acceleration mechanism at work (presumably from a central neutron star).Subject headings: acceleration of particles — ISM: individual (3C 58) — radiation mechanisms: nonthermal — supernova remnants

Upper limits on the infrared flux density of the ‘filled-centre’ supernova remnant 3C58

Upper limits of 0.4, 0.4, 0.8 and 1.5 Jy for the infrared flux density of the ‘filled-centre’ supernova remnant 3C58 are derived from IRAS observations at 12, 25, 60 and 100 μm respectively. These limits are considerably below the infrared flux densities predicted for 3C58 by Reynolds & Chevalier. They are consistent with a break in the spectrum of 3C58 at ≈ 50 GHz, which is two orders of magnitude below the break in the spectrum of the Crab nebula. The change of spectral index across the break for 3C58 is more than 0.5, which implies that the emission from 3C58 is not dominated by a constant injection rate of particles with a power-law distribution. Either the break is intrinsic to the acceleration mechanism at work – presumably from a central neutron star – or it is due to synchrotron losses in the past, with little if any particle injection in recent times.

Diffusive acceleration of electrons in SN 1987A

We suggest that synchrotron radiation emitted by electrons undergoing diffusive acceleration at the supernova blast wave is the cause of the reappearance of radio emission from SN 1987A in 1990 July. Making reasonable assumptions concerning adiabatic losses and the magnetic field in the preexplosion stellar wind, we find the light curve and spectrum which would be produced by a constant rate of particle injection occurring in a localized region of the shock front; i.e., in a clump or knot. Observations indicate that two such clumps have been encountered to date. From the observed delay in the switch-on of the emission between 843 MHz and 4.8 GHz we find a spatial diffusion coefficient for electrons of κ<SUB>normal</SUB>_ = 2 x 10^20^ m^2^ s^-1^. This value agrees with that found for the second clump and is substantially greater than the Bohm value. Estimating the magnetic field to be 10^-7 T and assuming the diffusion coefficient is constant leads to the conclusion that the shock encountered the first clump on about day 900 and the second clump on day 1190. From the observed spectrum we find the compression ratio of the shock responsible for electron acceleration to be ~2.7. This implies strong modification of the shock front which may be due to the acceleration of cosmic rays.

Long-term effects of an interplanetary shock on the flux and anisotropy profiles of the associated low-energy particle event

A large energetic storm particle event associated with an interplanetary shock was detected by ISEE-3 on 24 April, 1979. We have studied the effects of this shock on the flux and anisotropy profiles in the upstream region of the particle event, and we have developed a propagation model that permits to reproduce the observations. This model includes particle injection, both at the Sun and at the shock, therefore it allows to study the parameters for the interplanetary propagation of low-energy particles, the particle injection rates, and to relate them to the conditions at the shock front.

Effects of particle loading on a reduced pressure inductively coupled radio frequency plasma torch

Our previous attempts in the modeling of the heat transfer and fluid flow in radio frequency (RF) plasma torches considered dilute particle-loading conditions. It was assumed that the injected particles have no effect on the plasma temperature and velocity profiles. However, in practice, the plasma deposition process is carried out under fairly high loading conditions to achieve high energy efficiency. The plasma gas experiences significant local cooling and deceleration due to high particle injection rates. To this end, a numerical model has been developed which considers the coupling effects between the plasma temperature and velocity fields and injected particles. In this study, effort has been focused on the particle-loading effect in an inductively coupled RF plasma torch under a reduced pressure environment. The temperature and flow fields in an inductively coupled RF plasma torch are solved using an axisymmetric, variable property formulation of the Navier-Stokes equations. Pseudo two-dimensional electrical and magnetic field equations were considered. In addition, an integral constraint condition is used to maintain a specified discharge power in the plasma torch. The interaction between the plasma gas and injected particles is considered using the well-known “Particle-Source-In-Cell” (PSI-Cell) method. The exchanged mass, momentum, and energy between the plasma gas and injected particles are accounted for through additional source terms in the governing equations. The effect of particle loading on the resulting torch flow, thermal profiles, and particle-melting characteristics are presented and discussed.

Particle Transport Across the Transpired Turbulent Boundary Layer

The results of the experimental and theoretical investigation are presented to determine the effects of surface inclination and density of particulates on deposition control by transpiration. Effects of the particle size and injection rate were reported in a recent paper by Kozlu and Louis (1986). The purpose of this work is to obtain a better insight into the deposition process by investigating the different aspects of the problem. An application of the work is the control of deposition of small particles (0.5–3 μm) contributing most of the mass of the solid carryover entering turbines burning fuels derived from coal. Experimental study is carried out in a wind tunnel facility containing a porous transpired section. Similar flows and particle motions are achieved by choosing the proper Reynolds and Stokes numbers which are representative of the conditions found in industrial gas turbines. The study after reviewing the effects of size and injection rates on deposition determines the interaction between transpiration and the inertial impaction of particulates using the glass particles. Tests were also conducted on the inclined plate with coal particles to determine the density effects on the particle concentration profiles and consequently on the arrival rates. Experimental data are used to predict the concentration profiles of particulates for different density values. For inclined plate experiments, the turbulent Schmidt numbers obtained from the experiments are in agreement with the theoretical prediction of Tchen (1947) as found in the flat plate.

Meridian chains of magnetometers as a powerful “remote sensing” tool in determining electromagnetic quantities in the ionosphere on a global scale

The meridian chains of magnetometers have proven to be a powerful tool in determining the distribution of the ionospheric currents, the field‐aligned currents, the electric potential, the Joule heat production rate, and the auroral particle injection rate over the entire polar region, with a time resolution of about 5 minutes or even less. A brief history behind the development of this remote sensing method is given, which includes the pioneering efforts by K. Birkeland and S. Chapman, the Second Polar Year projects, IGY efforts, IMS meridian chains, and finally, the computer code developments during and after the IMF Data Analysis Phase. There is still much to improve in this remote sensing method, but it has become complementary to in‐situ satellite observations.