WorldWideScience

Sample records for dust grain charging

  1. Photoelectric charging of dust grains

    International Nuclear Information System (INIS)

    Ignatov, A. M.

    2009-01-01

    Photoemission from the surface of a dust grain in vacuum is considered. It is shown that the cutoff in the energy spectrum of emitted electrons leads to the formation of a steady-state electron cloud. The equation describing the distribution of the electric potential in the vicinity of a dust grain is solved numerically. The dust grain charge is found as a function of the grain size.

  2. Experiments on Dust Grain Charging

    Science.gov (United States)

    Abbas, M. N.; Craven, P. D.; Spann, J. F.; Tankosic, D.; LeClair, A.; West, E. A.

    2004-01-01

    Dust particles in various astrophysical environments are charged by a variety of mechanisms generally involving collisional processes with other charged particles and photoelectric emission with UV radiation from nearby sources. The sign and the magnitude of the particle charge are determined by the competition between the charging processes by UV radiation and collisions with charged particles. Knowledge of the particle charges and equilibrium potentials is important for understanding of a number of physical processes. The charge of a dust grain is thus a fundamental parameter that influences the physics of dusty plasmas, processes in the interplanetary medium and interstellar medium, interstellar dust clouds, planetary rings, cometary and outer atmospheres of planets etc. In this paper we present some results of experiments on charging of dust grains carried out on a laboratory facility capable levitating micron size dust grains in an electrodynamic balance in simulated space environments. The charging/discharging experiments were carried out by exposing the dust grains to energetic electron beams and UV radiation. Photoelectric efficiencies and yields of micron size dust grains of SiO2, and lunar simulates obtained from NASA-JSC will be presented.

  3. Experimental Study of Dust Grain Charging

    Science.gov (United States)

    Spann, James F; Venturini, Catherine C.; Comfort, Richard H.; Mian, Abbas M.

    1999-01-01

    The results of an experimental study of the charging mechanisms of micron size dust grains are presented. Individual dust grains are electrodynamically suspended and exposed to an electron beam of known energy and flux, and to far ultraviolet radiation of known wavelength and intensity. Changes in the charge-to-mass ratio of the grain are directly measured as a function of incident beam (electron and/or photon), grain size and composition. Comparisons of our results to theoretical models that predict the grain response are presented.

  4. Dust grain charging in a wake of other grains

    International Nuclear Information System (INIS)

    Miloch, W. J.; Block, D.

    2012-01-01

    The charging of dust grain in the wake of another grains in sonic and supersonic collisionless plasma flows is studied by numerical simulations. We consider two grains aligned with the flow, as well as dust chains and multiple grain arrangements. It is found that the dust charge depends significantly on the flow speed, distance between the grains, and the grain arrangement. For two and three grains aligned, the charges on downstream grains depend linearly on the flow velocity and intergrain distance. The simulations are carried out with DiP3D, a three dimensional particle-in-cell code with both electrons and ions represented as numerical particles [W. J. Miloch et al., Phys. Plasmas 17, 103703 (2010)].

  5. Charging of dust grains in a plasma with negative ions

    International Nuclear Information System (INIS)

    Mamun, A.A.; Shukla, P.K.

    2003-01-01

    The role of negative ions on the charging of dust grains in a plasma is examined. Two models for negative ion distributions are considered. These are streaming negative ions and Boltzmannian negative ions. It is found that the effects of the negative ion number density, negative ion charge, and negative ion streaming speed significantly affect the dust grain surface potential or the dust grain charge

  6. The grain charging and the dust acoustic wave instability

    International Nuclear Information System (INIS)

    Varma, Ram K.

    2001-01-01

    The stability of the steady charging state of the assembly of dust grains in a plasma is analyzed using, besides the equations of continuity and momentum balance, also the equations of thermal energy balance with the grain charging terms for both the electron and ion species. The grain charging terms account for the energy exchange between the dust grains and the electron and ion fluids. The grains are taken to be immobile for the purpose of this analysis. Two limiting cases are analyzed: (i) f(≡4πn d λ D 2 a) >1 (n d is the dust number density, λ D plasma Debye length, and a, the grain radius). The steady grain charge state is found to be stable in the case f o is unaffected. On the other hand, in the limit f>>1, the state is found to be unstable provided γ q (≡q o e/aT e ) e -T i )/T e (T e , T i are electron and ion temperatures). A coherent charging of the dust grains results as a consequence of this instability until γ q ≅(1/2) (T e -T i )/T i . Next, by letting the grain charges be mobile, so that the perturbation of dust number density is nonzero, we examine the stability of the dust-acoustic wave (DAW). The DAW is found to be unstable, also in the f>>1 case, while stable in the f<<1. The instability of the DAW also implies a concomitant grain charge growth, which would again be of a coherent nature

  7. Adiabatic motion of charged dust grains in rotating magnetospheres

    International Nuclear Information System (INIS)

    Northrop, T.G.; Hill, J.R.

    1983-01-01

    Dust grains in the ring systems and rapidly rotating magnetospheres of the outer planets such as Jupiter and Saturn may be sufficiently charged that the magnetic and electric forces on them are comparable with the gravitational force. The adiabatic theory of charged particle motion has previously been applied to electrons and atomic size particles. But it is also applicable to these charged dust grains in the micrometer and smaller size range. We derive here the guiding center equation of motion, drift velocity, and parallel equation of motion for these grains in a rotating magnetosphere. The effects of periodic grain charge-discharge have not been treated previously and have been included in this analysis. Grain charge is affected by the surrounding plasma properties and by the grain plasma velocity (among other factors), both of which may vary over the gyrocircle. The resulting charge-discharge process at the gyrofrequency destroys the invariance of the magnetic moment and causes a grain to move radially. The magnetic moment may increase or decrease, depending on the gyrophase of the charge variation. If it decreases, the motion is always toward synchronous radius for an equatorial grain. But the orbit becomes circular before the grain reaches synchronous radius, a conclusion that follows from an exact constant of the motion. This circularization can be viewed as a consequence of the gradual reduction in the magnetic moment. This circularization also suggests that dust grains leaving Io could not reach the region of the Jovian ring, but several effects could change that conclusion. Excellent qualitative and quantitative agreement is obtained between adiabatic theory and detailed numerical orbit integrations

  8. Charging of dust grains in a plasma with negative ions

    International Nuclear Information System (INIS)

    Kim, Su-Hyun; Merlino, Robert L.

    2006-01-01

    The effect of negative ions on the charging of dust particles in a plasma is investigated experimentally. A plasma containing a very low percentage of electrons is formed in a single-ended Q machine when SF 6 is admitted into the vacuum system. The relatively cold Q machine electrons (T e ≅0.2 eV) readily attach to SF 6 molecules to form SF 6 - negative ions. Calculations of the dust charge indicate that for electrons, negative ions, and positive ions of comparable temperatures, the charge (or surface potential) of the dust can be positive if the positive ion mass is smaller than the negative ion mass and if ε, the ratio of the electron to positive ion density, is sufficiently small. The Q machine plasma is operated with K + positive ions (mass 39 amu) and SF 6 - negative ions (mass 146 amu), and also utilizes a rotating cylinder to dispense dust into the plasma column. Analysis of the current-voltage characteristics of a Langmuir probe in the dusty plasma shows evidence for the reduction in the (magnitude) of the negative dust charge and the transition to positively charged dust as the relative concentration of the residual electrons is reduced. Some remarks are offered concerning experiments that could become possible in a dusty plasma with positive grains

  9. Charging of dust grains in a plasma with negative ions

    Science.gov (United States)

    Kim, Su-Hyun; Merlino, Robert L.

    2006-05-01

    The effect of negative ions on the charging of dust particles in a plasma is investigated experimentally. A plasma containing a very low percentage of electrons is formed in a single-ended SF6 is admitted into the vacuum system. The relatively cold (Te≈0.2eV ) readily attach to SF6 molecules to form SF6- negative ions. Calculations of the dust charge indicate that for electrons, negative ions, and positive ions of comparable temperatures, the charge (or surface potential) of the dust can be positive if the positive ion mass is smaller than the negative ion mass and if ɛ, the ratio of the electron to positive ion density, is sufficiently small. The K+ positive ions (mass 39amu) and SF6- negative ions (mass 146amu), and also utilizes a rotating cylinder to dispense dust into the plasma column. Analysis of the current-voltage characteristics of a Langmuir probe in the dusty plasma shows evidence for the reduction in the (magnitude) of the negative dust charge and the transition to positively charged dust as the relative concentration of the residual electrons is reduced. Some remarks are offered concerning experiments that could become possible in a dusty plasma with positive grains.

  10. Simulation study of spheroidal dust gains charging: Applicable to dust grain alignment

    International Nuclear Information System (INIS)

    Zahed, H.; Sobhanian, S.; Mahmoodi, J.; Khorram, S.

    2006-01-01

    The charging process of nonspherical dust grains in an unmagnetized plasma as well as in the presence of a magnetic field is studied. It is shown that unlike the spherical dust grain, due to nonhomogeneity of charge distribution on the spheroidal dust surface, the resultant electric forces on electrons and ions are different. This process produces some surface charge density gradient on the nonspherical grain surface. Effects of a magnetic field and other plasma parameters on the properties of the dust particulate are studied. It has been shown that the alignment direction could be changed or even reversed with the magnetic field and plasma parameters. Finally, the charge distribution on the spheroidal grain surface is studied for different ambient parameters including plasma temperature, neutral collision frequency, and the magnitude of the magnetic field

  11. A note on dust grain charging in space plasmas

    Science.gov (United States)

    Rosenberg, M.; Mendis, D. A.

    1992-01-01

    Central to the study of dust-plasma interactions in the solar system is the electrostatic charging of dust grains. While previous calculations have generally assumed that the distributions of electrons and ions in the plasma are Maxwellian, most space plasmas are observed to have non-Maxwellian tails and can often be fit by a generalized Lorentzian (kappa) distribution. Here we use such a distribution to reevaluate the grain potential, under the condition that the dominant currents to the grain are due to electron and ion collection, as is the case in certain regions of space. The magnitude of the grain potential is found to be larger than that in a Maxwellian plasma as long as the electrons are described by a kappa distribution: this enhancement increased with ion mass and decreasing electron kappa. The modification of the grain potential in generalized Lorentzian plasmas has implications for both the physics (e.g., grain growth and disruption) and the dynamics of dust in space plasmas. These are also briefly discussed.

  12. Charging properties of a dust grain in collisional plasmas

    International Nuclear Information System (INIS)

    Khrapak, S.A.; Morfill, G.E.; Khrapak, A.G.; D'yachkov, L.G.

    2006-01-01

    Charging related properties of a small spherical grain immersed in a collisional plasma are investigated. Asymptotic expressions for charging fluxes, grain surface potential, long range electrostatic potential, and the properties of grain charge fluctuations due to the discrete nature of the charging process are obtained. These analytical results are in reasonable agreement with the available results of numerical modeling

  13. Photoemission Experiments for Charge Characteristics of Individual Dust Grains

    Science.gov (United States)

    Abbas, M. M.; Spann, James F., Jr.; Craven, Paul D.; West, E.; Pratico, Jared; Scheianu, D.; Tankosic, D.; Venturini, C. C.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    Photoemission experiments with UV radiation have been performed to investigate the microphysics and charge characteristics of individual isolated dust grains of various compositions and sizes by using the electrodynamic balance facility at NASA Marshall Space Flight Center. Dust particles of 1 - 100 micrometer diameter are levitated in a vacuum chamber at pressures approx. 10(exp -5) torr and exposed to a collimated beam of UV radiation in the 120-300 nanometers spectral range from a deuterium lamp source with a MgF2 window. A monochromator is used to select the UV radiation wavelength with a spectral resolution of 8 nanometers. The electrodynamic facility permits measurements of the charge and diameters of particles of known composition, and monitoring of photoemission rates with the incident UV radiation. Experiments have been conducted on Al2O3 and silicate particles, and in particular on JSC-1 Mars regolith simulants, to determine the photoelectron yields and surface equilibrium potentials of dust particles when exposed to UV radiation in the 120-250 micrometers spectral range. A brief discussion of the experimental procedure, the results of photoemission experiments, and comparisons with theoretical models will be presented.

  14. Attraction of likely charged nano-sized grains in dust-electron plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Vishnyakov, Vladimir I., E-mail: eksvar@ukr.net [Physical-Chemical Institute for Environmental and Human Protection, Odessa 65082 (Ukraine)

    2016-01-15

    Dust-electron plasma, which contains only the dust grains and electrons, emitted by them, is studied. Assumption of almost uniform spatial electrons distribution, which deviates from the uniformity only near the dust grains, leads to the grain charge division into two parts: first part is the individual for each grain “visible” charge and the second part is the common charge of the neutralized background. The visible grain charge can be both negative and positive, while the total grain charge is only positive. The attraction of likely charged grains is possible, because the grain interaction is determined by the visible charges. The equilibrium state between attraction and repulsion of grains is demonstrated.

  15. Dust grain charges in a nuclear-track plasma and the formation of dynamic vortex dust structures

    International Nuclear Information System (INIS)

    Rykov, V.A.; Khudyakov, A.V.; Filinov, V.S.; Vladimirov, V.I.; Deputatova, L.V.; Krutov, D.V.; Nefedov, A.P.; Fortov, V.E.

    2002-01-01

    Results are presented from Monte Carlo calculations of the electric charge of dust grains in a plasma produced during the slowing down of the radioactive decay products of californium nuclei in neon. The dust grain charging is explained for the first time as being due to the drift of electrons and ions in an external electric field. It is shown that the charges of the grains depend on their coordinates and strongly fluctuate with time. The time-averaged grain charges agree with the experimental data obtained on ordered liquidlike dust structures in a nuclear-track plasma. The time-averaged dust grain charges are used to carry out computer modeling of the formation of dynamic vortex structures observed in experiments. Evidence is obtained of the fact that the electrostatic forces experienced by the dust grains are potential in character

  16. Effects of dust grain charge fluctuation on obliquely propagating dust-acoustic potential in magnetized dusty plasmas

    International Nuclear Information System (INIS)

    Mamun, A.A.; Hassan, M.H.A.

    1999-05-01

    Effects of dust grain charge fluctuation, obliqueness and external magnetic field on finite amplitude dust-acoustic solitary potential in a magnetized dusty plasma, consisting of electrons, ions and charge fluctuating dust grains, have been investigated by the reductive perturbation method. It has been shown that such a magnetized dusty plasma system may support dust-acoustic solitary potential on a very slow time scale involving the motion of dust grains, whose charge is self-consistently determined by local electron and ion currents. The effects of dust grain charge fluctuation, external magnetic field and obliqueness are found to modify the properties of this dust-acoustic solitary potential significantly. The implications of these results to some space and astrophysical dusty plasma systems, especially to planetary ring-systems and cometary tails, are briefly mentioned. (author)

  17. Experimental Investigation of Charging Properties of Interstellar Type Silica Dust Grains by Secondary Electron Emissions

    Science.gov (United States)

    Tankosic, D.; Abbas, M. M.

    2013-01-01

    The dust charging by electron impact is an important dust charging processes in astrophysical and planetary environments. Incident low energy electrons are reflected or stick to the grains charging the dust grains negatively. At sufficiently high energies electrons penetrate the grains, leading to excitation and emission of electrons referred to as secondary electron emission (SEE). Available classical theoretical models for calculations of SEE yields are generally applicable for neutral, planar, or bulk surfaces. These models, however, are not valid for calculations of the electron impact charging properties of electrostatically charged micron/submicron-size dust grains in astrophysical environments. Rigorous quantum mechanical models are not yet available, and the SEE yields have to be determined experimentally for development of more accurate models for charging of individual dust grains. At the present time, very limited experimental data are available for charging of individual micron-size dust grains, particularly for low energy electron impact. The experimental results on individual, positively charged, micron-size lunar dust grains levitated carried out by us in a unique facility at NASA-MSFC, based on an electrodynamic balance, indicate that the SEE by electron impact is a complex process. The electron impact may lead to charging or discharging of dust grains depending upon the grain size, surface potential, electron energy, electron flux, grain composition, and configuration (Abbas et al, 2010, 2012). In this paper, we discuss SEE charging properties of individual micron-size silica microspheres that are believed to be analogs of a class of interstellar dust grains. The measurements indicate charging of the 0.2m silica particles when exposed to 25 eV electron beams and discharging when exposed to higher energy electron beams. Relatively large size silica particles (5.2-6.82m) generally discharge to lower equilibrium potentials at both electron energies

  18. Measurements of Charging of Apollo 17 Lunar Dust Grains by Electron Impact

    Science.gov (United States)

    Abbas, Mian M.; Tankosic, Dragana; Spann, James F.; Dube, Michael J.

    2008-01-01

    It is well known since the Apollo missions that the lunar surface is covered with a thick layer of micron size dust grains with unusually high adhesive characteristics. The dust grains observed to be levitated and transported on the lunar surface are believed to have a hazardous impact on the robotic and human missions to the Moon. The observed dust phenomena are attributed to the lunar dust being charged positively during the day by UV photoelectric emissions, and negatively during the night by the solar wind electrons. The current dust charging and the levitation models, however, do not fully explain the observed phenomena, with the uncertainty of dust charging processes and the equilibrium potentials of the individual dust grains. It is well recognized that the charging properties of individual dust grains are substantially different from those determined from measurements made on bulk materials that are currently available. An experimental facility has been developed in the Dusty Plasma Laboratory at MSFC for investigating the charging and optical properties of individual micron/sub-micron size positively or negatively charged dust grains by levitating them in an electrodynamic balance in simulated space environments. In this paper, we present the laboratory measurements on charging of Apollo 17 individual lunar dust grains by a low energy electron beam. The charging rates and the equilibrium potentials produced by direct electron impact and by secondary electron emission process are discussed.

  19. Charging of Individual Micron-Size Interstellar/Planetary Dust Grains by Secondary Electron Emissions

    Science.gov (United States)

    Tankosic, D.; Abbas, M. M.

    2012-01-01

    Dust grains in various astrophysical environments are generally charged electrostatically by photoelectric emissions with UV/X-ray radiation, as well as by electron/ion impact. Knowledge of physical and optical properties of individual dust grains is required for understanding of the physical and dynamical processes in space environments and the role of dust in formation of stellar and planetary systems. In this paper, we discuss experimental results on dust charging by electron impact, where low energy electrons are scattered or stick to the dust grains, thereby charging the dust grains negatively, and at sufficiently high energies the incident electrons penetrate the grain leading to excitation and emission of electrons referred to as secondary electron emission (SEE). Currently, very limited experimental data are available for charging of individual micron-size dust grains, particularly by low energy electron impact. Available theoretical models based on the Sternglass equation (Sternglass, 1954) are applicable for neutral, planar, and bulk surfaces only. However, charging properties of individual micron-size dust grains are expected to be different from the values measured on bulk materials. Our recent experimental results on individual, positively charged, micron-size lunar dust grains levitated in an electrodynamic balance facility (at NASA-MSFC) indicate that the SEE by electron impact is a complex process. The electron impact may lead to charging or discharging of dust grains depending upon the grain size, surface potential, electron energy, electron flux, grain composition, and configuration (e.g. Abbas et al, 2010). Here we discuss the complex nature of SEE charging properties of individual micron-size lunar dust grains and silica microspheres.

  20. Positive column of a glow discharge in neon with charged dust grains (a review)

    Energy Technology Data Exchange (ETDEWEB)

    Polyakov, D. N., E-mail: cryolab@ihed.ras.ru; Shumova, V. V.; Vasilyak, L. M. [Russian Academy of Sciences, Joint Institute for High Temperatures (Russian Federation)

    2017-03-15

    The effect of charged micron-size dust grains (microparticles) on the electric parameters of the positive column of a low-pressure dc glow discharge in neon has been studied experimentally and numerically. Numerical analysis is carried out in the diffusion-drift approximation with allowance for the interaction of dust grains with metastable neon atoms. In a discharge with a dust grain cloud, the longitudinal electric field increases. As the number density of dust grains in an axisymmetric cylindrical dust cloud rises, the growth of the electric field saturates. It is shown that the contribution of metastable atoms to ionization is higher in a discharge with dust grains, in spite of the quenching of metastable atoms on dust grains. The processes of charging of dust grains and the dust cloud are considered. As the number density of dust grains rises, their charge decreases, while the space charge of the dust cloud increases. The results obtained can be used in plasma technologies involving microparticles.

  1. Positive column of a glow discharge in neon with charged dust grains (a review)

    International Nuclear Information System (INIS)

    Polyakov, D. N.; Shumova, V. V.; Vasilyak, L. M.

    2017-01-01

    The effect of charged micron-size dust grains (microparticles) on the electric parameters of the positive column of a low-pressure dc glow discharge in neon has been studied experimentally and numerically. Numerical analysis is carried out in the diffusion-drift approximation with allowance for the interaction of dust grains with metastable neon atoms. In a discharge with a dust grain cloud, the longitudinal electric field increases. As the number density of dust grains in an axisymmetric cylindrical dust cloud rises, the growth of the electric field saturates. It is shown that the contribution of metastable atoms to ionization is higher in a discharge with dust grains, in spite of the quenching of metastable atoms on dust grains. The processes of charging of dust grains and the dust cloud are considered. As the number density of dust grains rises, their charge decreases, while the space charge of the dust cloud increases. The results obtained can be used in plasma technologies involving microparticles.

  2. Charge and Levitation of Grains in Plasma Sheath with Dust Thermic Emission

    International Nuclear Information System (INIS)

    Wu Haicheng; Xie Baisong

    2005-01-01

    By taking into account thermic emission current from hot dust surface, the problem involved in dust charging and levitation of dust grains in plasma sheath has been researched. The results are compared to that without including thermal emission current while the system parameters are same. It is found that the thermal emission current has played a significant role on modifying the dust charging and balance levitations. Both of the charging numbers of dust and the dust radius in balance are dramatically reduced. The stability of dust levitation is also analyzed and discussed.

  3. Laboratory Measurements of Charging of Apollo 17 Lunar Dust Grains by Low Energy Electrons

    Science.gov (United States)

    Abbas, Mian M.; Tankosic, Dragana; Spann, James F.; Dube, Michael J.; Gaskin, Jessica

    2007-01-01

    It is well recognized that the charging properties of individual micron/sub-micron size dust grains by various processes are expected to be substantially different from the currently available measurements made on bulk materials. Solar UV radiation and the solar wind plasma charge micron size dust grains on the lunar surface with virtually no atmosphere. The electrostatically charged dust grains are believed to be levitated and transported long distances over the lunar terminator from the day to the night side. The current models do not fully explain the lunar dust phenomena and laboratory measurements are needed to experimentally determine the charging properties of lunar dust grains. An experimental facility has been developed in the Dusty Plasma Laboratory at NASA Marshall Space Flight Center MSFC for investigating the charging properties of individual micron/sub-micron size positively or negatively charged dust grains by levitating them in an electrodynamic balance in simulated space environments. In this paper, we present laboratory measurements on charging of Apollo 17 individual lunar dust grains by low energy electron beams in the 5-100 eV energy range. The measurements are made by levitating Apollo 17 dust grains of 0.2 to 10 micrometer diameters, in an electrodynamic balance and exposing them to mono-energetic electron beams. The charging rates and the equilibrium potentials produced by direct electron impact and by secondary electron emission processes are discussed.

  4. Laboratory Studies of Charging Properties of Dust Grains in Astrophysical/Planetary Environments

    Science.gov (United States)

    Tankosic, D.; Abbas, M. M.

    2012-01-01

    Dust grains in various astrophysical environments are generally charged electrostatically by photoelectric emissions with UV/X-ray radiation, as well as by electron/ion impact. Knowledge of physical and optical properties of individual dust grains is required for understanding of the physical and dynamical processes in space environments and the role of dust in formation of stellar and planetary systems. In this paper we focus on charging of individual micron/submicron dust grains by processes that include: (a) UV photoelectric emissions involving incident photon energies higher than the work function of the material and b) electron impact, where low energy electrons are scattered or stick to the dust grains, thereby charging the dust grains negatively, and at sufficiently high energies the incident electrons penetrate the grain leading to excitation and emission of electrons referred to as secondary electron emission (SEE). It is well accepted that the charging properties of individual micron/submicron size dust grains are expected to be substantially different from the bulk materials. However, no viable models for calculation of the charging properties of individual micron size dust grains are available at the present time. Therefore, the photoelectric yields, and secondary electron emission yields of micron-size dust grains have to be obtained by experimental methods. Currently, very limited experimental data are available for charging of individual micron-size dust grains. Our experimental results, obtained on individual, micron-size dust grains levitated in an electrodynamic balance facility (at NASA-MSFC), show that: (1) The measured photoelectric yields are substantially higher than the bulk values given in the literature and indicate a particle size dependence with larger particles having order-of-magnitude higher values than for submicron-size grains; (2) dust charging by low energy electron impact is a complex process. Also, our measurements indicate that

  5. Coagulation of dielectric dust grains due to variable asymmetric charging

    International Nuclear Information System (INIS)

    Manweiler, Jerry W.; Armstrong, Thomas P.; Cravens, Thomas E.

    1998-01-01

    Observational evidence of electrical forces acting significantly on small solids is present for both the modern solar system in Saturn's rings and the ancient solar system in chondritic meteorites. It is likely that grain-grain coagulation rates are affected by the distribution of charges on small grains. Plasma particle impacts and photoelectric effects can provide the charges. It appears that some charging is inevitable and that plasma grain interactions need to be evaluated to determine the size of the effect on coagulation rates. We apply the results of our previous charging work to models of the protoplanetary nebula. It is expected that the protoplanetary nebula is weakly ionized except in certain instances and locations such as: solar flares in the interior, ultraviolet radiation at the outer boundary, and during enhanced luminosity of the star. Since the grains we study are non-conducting and show strong dipole moments in flowing plasma, we modify the geometric cross sections to include the effects of flowing plasma on non-conducting grains with plasma mediated shielding. This paper provides results showing how plasma flow affects the processes involved in charging the grains--total charge and charge distribution. We calculate the modifications to the cross sections and subsequent changes in the coagulation rates

  6. Charging of Dust Grains in a Nuclear-Induced Plasma at High Pressures

    International Nuclear Information System (INIS)

    Pal’, A. F.; Starostin, A. N.; Filippov, A. V.

    2001-01-01

    The process of dust-grain charging in plasmas produced by radioactive decay products or spontaneous fission fragments in air and xenon at high pressures is studied numerically in the hydrodynamic approximation. It is shown that, at sufficiently high rates of gas ionization, the dust grains in air are charged by electrons rather than ions, so that the grain charge in air is comparable to that in electropositive gases. The results of numerical calculations based on a complete model agree well with the experimental data. The time evolution of the grain charge is investigated, and the characteristic time scales on which the grains acquire an electric charge are established. The validity of approximate theories of dust-grain charging in electropositive and electronegative gases at high pressures is examined

  7. On Dust Charging Equation

    OpenAIRE

    Tsintsadze, Nodar L.; Tsintsadze, Levan N.

    2008-01-01

    A general derivation of the charging equation of a dust grain is presented, and indicated where and when it can be used. A problem of linear fluctuations of charges on the surface of the dust grain is discussed.

  8. LUNAR DUST GRAIN CHARGING BY ELECTRON IMPACT: COMPLEX ROLE OF SECONDARY ELECTRON EMISSIONS IN SPACE ENVIRONMENTS

    International Nuclear Information System (INIS)

    Abbas, M. M.; Craven, P. D.; LeClair, A. C.; Spann, J. F.; Tankosic, D.

    2010-01-01

    Dust grains in various astrophysical environments are generally charged electrostatically by photoelectric emissions with radiation from nearby sources, or by electron/ion collisions by sticking or secondary electron emissions (SEEs). The high vacuum environment on the lunar surface leads to some unusual physical and dynamical phenomena involving dust grains with high adhesive characteristics, and levitation and transportation over long distances. Knowledge of the dust grain charges and equilibrium potentials is important for understanding a variety of physical and dynamical processes in the interstellar medium, and heliospheric, interplanetary/planetary, and lunar environments. It has been well recognized that the charging properties of individual micron-/submicron-size dust grains are expected to be substantially different from the corresponding values for bulk materials. In this paper, we present experimental results on the charging of individual 0.2-13 μm size dust grains selected from Apollo 11 and 17 dust samples, and spherical silica particles by exposing them to mono-energetic electron beams in the 10-200 eV energy range. The dust charging process by electron impact involving the SEEs discussed is found to be a complex charging phenomenon with strong particle size dependence. The measurements indicate substantial differences between the polarity and magnitude of the dust charging rates of individual small-size dust grains, and the measurements and model properties of corresponding bulk materials. A more comprehensive plan of measurements of the charging properties of individual dust grains for developing a database for realistic models of dust charging in astrophysical and lunar environments is in progress.

  9. Lunary Dust Grain Charging by Electron Impact: Complex Role of Secondary Electron Emissions in Space Environments

    Science.gov (United States)

    Abbas, M. M.; Tankosic, D.; Crave, P. D.; LeClair, A.; Spann, J. F.

    2010-01-01

    Dust grains in various astrophysical environments are generally charged electrostatically by photoelectric emissions with radiation from nearby sources, or by electron/ion collisions by sticking or secondary electron emissions (SEES). The high vacuum environment on the lunar surface leads to some unusual physical and dynamical phenomena involving dust grains with high adhesive characteristics, and levitation and transportation over long distances. Knowledge of the dust grain charges and equilibrium potentials is important for understanding a variety of physical and dynamical processes in the interstellar medium, and heliospheric, interplanetary/ planetary, and lunar environments. It has been well recognized that the charging properties of individual micron-/submicron-size dust grains are expected to be substantially different from the corresponding values for bulk materials. In this paper, we present experimental results on the charging of individual 0.2-13 m size dust grains selected from Apollo 11 and 17 dust samples, and spherical silica particles by exposing them to mono-energetic electron beams in the 10-200 eV energy range. The dust charging process by electron impact involving the SEES discussed is found to be a complex charging phenomenon with strong particle size dependence. The measurements indicate substantial differences between the polarity and magnitude of the dust charging rates of individual small-size dust grains, and the measurements and model properties of corresponding bulk materials. A more comprehensive plan of measurements of the charging properties of individual dust grains for developing a database for realistic models of dust charging in astrophysical and lunar environments is in progress.

  10. Instability of dust ion-acoustic waves in a dusty plasma containing elongated and rotating charged dust grains

    International Nuclear Information System (INIS)

    Shukla, P.K.; Tskhakaya, D.D.

    2001-01-01

    The dispersion properties of the dust ion-acoustic waves (DIAWs) in an unmagnetized dusty plasma is examined when the plasma constituents are electrons, ions, and charged dust grains which are elongated and rotating. Since the dipole moment of elongated and rotating dust grains is nonzero, significant modifications of the DIAW spectrum emerge. It is found that the DIAWs are subjected to an instability when the DIAW frequency approximately equals the angular rotation frequency of the elongated dust grains. The relevance of our investigation to enhanced fluctuations in space and laboratory dusty plasmas is pointed out

  11. Complex Role of Secondary Electron Emissions in Dust Grain Charging in Space Environments: Measurements on Apollo 11 and 17 Dust Grains

    Science.gov (United States)

    Abbas, M. M.; Tankosic, D.; Spann, J. F.; LeClair, A. C.

    2010-01-01

    Dust grains in various astrophysical environments are generally charged electrostatically by photoelectric emissions with radiation from nearby sources, or by electron/ion collisions by sticking or secondary electron emissions. Knowledge of the dust grain charges and equilibrium potentials is important for understanding of a variety of physical and dynamical processes in the interstellar medium (ISM), and heliospheric, interplanetary, planetary, and lunar environments. The high vacuum environment on the lunar surface leads to some unusual physical and dynamical phenomena involving dust grains with high adhesive characteristics, and levitation and transportation over long distances. It has been well recognized that the charging properties of individual micron/submicron size dust grains are expected to be substantially different from the corresponding values for bulk materials and theoretical models. In this paper we present experimental results on charging of individual dust grains selected from Apollo 11 and Apollo 17 dust samples by exposing them to mono-energetic electron beams in the 10- 400 eV energy range. The charging rates of positively and negatively charged particles of approximately 0.2 to 13 microns diameters are discussed in terms of the secondary electron emission (SEE) process, which is found to be a complex charging process at electron energies as low as 10-25 eV, with strong particle size dependence. The measurements indicate substantial differences between dust charging properties of individual small size dust grains and of bulk materials.

  12. Charged dust in planetary magnetospheres: Hamiltonian dynamics and numerical simulations for highly charged grains

    Science.gov (United States)

    Schaffer, L.; Burns, J. A.

    1994-01-01

    We use a combination of analytical and numerical methods to investigate the dynamics of charged dust grains in planetary magnetospheres. Our emphasis is on obtaining results valid for particles that are not necessarily dominated either by gravitational or electromagnetic forces. A Hamiltonian formulation of the problem yields exact results, for all values of charge-to-mass ratio, when we introduce two constraints: particles remain in the equatorial plane and the magnetic field is taken as axially symmetric. In particular, we obtain locations of equilibrium points, the frequencies of stable periodic orbits, the topology of separatrices in phase space, and the rate of longitudinal drift. These results are significant for specific applications: motion in the nearly aligned dipolar field of Saturn, and the trajectories of arbitrarily charged particles in complex magnetic fields for limited periods of time after ejection from parent bodies. Since the model is restrictive, we also use numerical integrations of the full three-dimensional equations of motion and illustrate under what conditions the constrained problem yields reasonable results. We show that a large fraction of the intermediately charged and highly charged (gyrating) particles will always be lost to a planet's atmosphere within a few hundred hours, for motion through tilted-dipole magnetic fields. We find that grains must have a very high charge-to-mass ratio in order to be mirrored back to the ring plane. Thus, except perhaps at Saturn where the dipole tilt is very small, the likely inhabitants of the dusty ring systems are those particles that are either nearly Keplerian (weakly charged) grains or grains whose charges place them in the lower end of the intermediate charge zone. Fianlly, we demonstrate the effect of plasma drag on the orbits of gyrating particles to be a rapid decrease in gyroradius followed by a slow radial evolution of the guiding center.

  13. Mechanisms of dust grain charging in plasma with allowance for electron emission processes

    Energy Technology Data Exchange (ETDEWEB)

    Mol’kov, S. I.; Savin, V. N., E-mail: moped@onego.ru [Petrozavodsk State University (Russian Federation)

    2017-02-15

    The process of dust grain charging is described with allowance for secondary, ion-induced, photoelectric, and thermal electron emission from the grain surface. The roughness of the grain surface is taken into account. An intermediate charging regime involving ion–atom collisions and electron ionization in the perturbed plasma region is analyzed using the moment equations and Poisson’s equation. A calculation method is proposed that allows one to take into account the influence of all the above effects and determine the radius of the plasma region perturbed by the dust grain.

  14. Effect of non-Maxwellian particle trapping and dust grain charging on dust acoustic solitary waves

    International Nuclear Information System (INIS)

    Rubab, N.; Murtaza, G.; Mushtaq, A.

    2006-01-01

    The role of adiabatic trapped ions on a small but finite amplitude dust acoustic wave, including the effect of adiabatic dust charge variation, is investigated in an unmagnetized three-component dusty plasma consisting of electrons, ions and massive micron sized negatively charged dust particulates. We have assumed that electrons and ions obey (r,q) velocity distribution while the dust species is treated fluid dynamically. It is found that the dynamics of dust acoustic waves is governed by a modified r dependent Korteweg-de Vries equation. Further, the spectral indices (r,q) affect the charge fluctuation as well as the trapping of electrons and ions and consequently modify the dust acoustic solitary wave

  15. Stability Dust-Ion-Acoustic Wave In Dusty Plasmas With Stream -Influence Of Charge Fluctuation Of Dust Grains

    International Nuclear Information System (INIS)

    Atamaniuk, Barbara; Zuchowski, Krzysztof

    2006-01-01

    There is a quickly increasing wealth of experimental data on so-called dusty plasmas i. e. ionized gases or usual plasmas that contain micron sized charged particles. Interest in these structures is driven both by their importance in many astrophysical as well as commercial situations. Among them are linear and nonlinear wave phenomena. We consider the influence of dust charge fluctuations on stability of the ion-acoustic waves when the stream of particles is present. It is assumed that all grains of dust have equal masses but charges are not constant in time-they may fluctuate in time. The dust charges are not really independent of the variations of the plasma potentials. All modes will influence the charging mechanism, and feedback will lead to several new interesting and unexpected phenomena. The charging of the grains depends on local plasma characteristics. If the waves disturb these characteristic, then charging of the grains is affected and the grain charge is modified, with a resulting feedback on the wave mode. In case considering here, when temperature of electrons is much greater then the temperature of the ions and temperature of electrons is not great enough for further ionization of the ions, we show that stability of the acoustic wave depends only one phenomenological coefficient

  16. Laboratory Studies on the Charging of Dust Grains in a Plasma

    Science.gov (United States)

    Xu, Wenjun

    1993-01-01

    The charging of dust grains by the surrounding plasma is studied in a dusty plasma device (DPD) (Xu, W., B. Song, R. L. Merlino, and N. D'Angelo, Rev. Sci. Instrum., 63, 5266, 1992). The dusty plasma device consists of a rotating-drum dust dispersal device used in conjunction with an existing Q-machine, to produce extended, steady state, magnetized plasma columns. The dust density in the dust chamber is controlled by the drum rotation speed. The device is capable of generating a dusty plasma in which as much as about 90% of the negative charge is attached to the dust grains of 1-10mu m size. Measurements of the dust parameter eta, the percentage of negative charge on free electrons in the dusty plasma, are presented. The dust parameter eta is found to depend on the rotational speed of the dust chamber, plasma density and the type and size of different dust. The dust parameter eta is calculated from a pair of Langmuir curves taken with and without dust under the same conditions. The operation of the dust chamber as described above has been confirmed by the agreement between the measurements of eta and the direct mechanical measurements consisting of weighing dust samples collected within the rotation dust chamber, at different rotation rates. By varying the ratio d/lambda_ {rm D} between the intergrain distance and the plasma Debye length, the effects predicted by Goertz and Ip (Goertz, C. K., and W-H. Ip, Geophys. Res. Lett., 11, 349, 1984), and subsequently reanalyzed in a more general fashion by Whipple et al. (Whipple, E. C., T. G. Northrop, and D. A. Mendis, J. Geophys. Rev., 90, 7405, 1985), as "isolated" dust grains become "closely packed" grains, have been demonstrated experimentally (Xu, W., N. D'Angelo, and R. L. Merlino, J. Geophys. Rev., 98, 7843, 1993). Similar results are presented and compared for two types of dust, kaolin and Al_2O _3, which have been studied in the experiment.

  17. PHOTOELECTRIC CHARGING OF DUST GRAINS IN THE ENVIRONMENT OF YOUNG STELLAR OBJECTS

    International Nuclear Information System (INIS)

    Pedersen, Andreas; Gomez de Castro, Ana I.

    2011-01-01

    The evolution of disks around young stellar objects (YSOs) is deeply affected by the YSOs' ultraviolet (UV) radiation field especially in the 500-1100 A spectral range. The two dominant processes are: the photodissociation of H 2 molecules in the Werner and Lyman bands, and the emission of photoelectrons from dust grains when high energy photons are absorbed. Photoelectrons are an important source of gas heating. In this paper, dust grain charging when exposed to various possible UV fields in the YSOs' environment is investigated. Numerical simulations of the evolution of photoelectrons in the electric field created by the charged dust grains are carried out to obtain the charging profile of dust grains. From the simulations it appears that the different spectra produce significant quantitative and qualitative differences in the charging processes. Both the UV background and the Ae-Herbig star radiation field produce a relatively slow charging of dust grains due to the low fraction of sufficiently energetic photons. The radiation field of T Tauri stars (TTSs) is harder due to the release of magnetic energy in the dense magnetospheric environment. These numerical results have been used to propose a new simple analytical model for grain charging in the atmosphere of protostellar disks around TTSs susceptible to be used in any disk modeling. It has been found that the yield decreases exponentially with the dust charge and that two populations of photoelectrons are produced: a low energy population with mean kinetic energy E = 2.5 eV and a high energy population with E = 5.5-6 eV; the energy dispersion within the populations is ∼1.3 eV (T ∼ 1.5 x 10 4 K). The high energy population is susceptible of dissociating the H 2 and ionizing some low ionization potential species, such as the Mg. These results add an additional role to dust on the chemistry of the layers just below the H 2 photoionization front. This photoelectic yield has been applied to a simple evaluation

  18. Charging and heat collection by a positively charged dust grain in a plasma.

    Science.gov (United States)

    Delzanno, Gian Luca; Tang, Xian-Zhu

    2014-07-18

    Dust particulates immersed in a quasineutral plasma can emit electrons in several important applications. Once electron emission becomes strong enough, the dust enters the positively charged regime where the conventional orbital-motion-limited (OML) theory can break down due to potential-well effects on trapped electrons. A minimal modification of the trapped-passing boundary approximation in the so-called OML(+) approach is shown to accurately predict the dust charge and heat collection flux for a wide range of dust size and temperature.

  19. Fluctuations of the charge on a dust grain in a plasma

    International Nuclear Information System (INIS)

    Cui, C.; Goree, J.

    1994-01-01

    A dust grain in a plasma acquires an electric charge by collecting electron and ion currents. These currents consist of discrete charges, causing the charge to fluctuate around an equilibrium value (Q). Electrons and ions are collected at random intervals and in a random sequence, with probabilities that depend on the grain's potential. The authors developed a model for these probabilities and implemented it in a numerical simulation of the collection of individual ions and electrons, yielding a time series Q(t) for the grain's charge. Electron emission from the grain is not included, although it could be added easily to the method. They obtained the power spectrum and the rms fluctuation level, as well as the distribution function of the charge. Most of the power in the spectrum lies at frequencies much lower than 1/τ, the inverse charging time. The rms fractional fluctuation level varies as 0.5 |left-angle N right-angle | -1/2 , where left-angle N right-angle = left-angle Q right-angle/e is the average number of electron charges on the grain. This inverse square-root scaling means that fluctuations are most important for small grains. They also show that very small grains can experience fluctuations to neutral and positive polarities, even in the absence of electron emission

  20. Stochastic charging of dust grains in planetary rings: Diffusion rates and their effects on Lorentz resonances

    Science.gov (United States)

    Schaffer, L.; Burns, J. A.

    1995-01-01

    Dust grains in planetary rings acquire stochastically fluctuating electric charges as they orbit through any corotating magnetospheric plasma. Here we investigate the nature of this stochastic charging and calculate its effect on the Lorentz resonance (LR). First we model grain charging as a Markov process, where the transition probabilities are identified as the ensemble-averaged charging fluxes due to plasma pickup and photoemission. We determine the distribution function P(t;N), giving the probability that a grain has N excess charges at time t. The autocorrelation function tau(sub q) for the strochastic charge process can be approximated by a Fokker-Planck treatment of the evolution equations for P(t; N). We calculate the mean square response to the stochastic fluctuations in the Lorentz force. We find that transport in phase space is very small compared to the resonant increase in amplitudes due to the mean charge, over the timescale that the oscillator is resonantly pumped up. Therefore the stochastic charge variations cannot break the resonant interaction; locally, the Lorentz resonance is a robust mechanism for the shaping of etheral dust ring systems. Slightly stronger bounds on plasma parameters are required when we consider the longer transit times between Lorentz resonances.

  1. Onset of turbulence induced by electron nonthermality in a complex plasma in presence of positively charged dust grains

    Directory of Open Access Journals (Sweden)

    Susmita Sarkar

    2018-03-01

    Full Text Available In this paper onset of turbulence has been detected from the study of non linear dust acoustic wave propagation in a complex plasma considering electrons nonthermal and equilibrium dust charge positive. Dust grains are charged by secondary electron emission process. Our analysis shows that increase in electron nonthermality makes the grain charging process faster by reducing the magnitude of the nonadiabaticity induced pseudo viscosity. Consequently nature of dust charge variation changes from nonadiabatic to adiabatic one. For further increase of electron nonthermality, this pseudo viscosity becomes negative and hence generates a turbulent grain charging behaviour. This turbulent grain charging phenomenon is exclusively the outcome of this nonlinear study which was not found in linear analysis.

  2. Laboratory Measurements on Charging of Individual Micron-Size Apollo-11 Dust Grains by Secondary Electron Emissions

    Science.gov (United States)

    Tankosic, D.; Abbas, M. M.

    2012-01-01

    Observations made during Apollo missions, as well as theoretical models indicate that the lunar surface and dust grains are electrostatically charged, levitated and transported. Lunar dust grains are charged by UV photoelectric emissions on the lunar dayside and by the impact of the solar wind electrons on the nightside. The knowledge of charging properties of individual lunar dust grains is important for developing appropriate theoretical models and mitigating strategies. Currently, very limited experimental data are available for charging of individual micron-size size lunar dust grains in particular by low energy electron impact. However, experimental results based on extensive laboratory measurements on the charging of individual 0.2-13 micron size lunar dust grains by the secondary electron emissions (SEE) have been presented in a recent publication. The SEE process of charging of micron-size dust grains, however, is found to be very complex phenomena with strong particle size dependence. In this paper we present some examples of the complex nature of the SEE properties of positively charged individual lunar dust grains levitated in an electrodynamic balance (EDB), and show that they remain unaffected by the variation of the AC field employed in the above mentioned measurements.

  3. Effect of electron emission on the charge and shielding of a dust grain in a plasma: A continuum theory

    International Nuclear Information System (INIS)

    D'yachkov, L. G.; Khrapak, A. G.; Khrapak, S. A.

    2008-01-01

    The continuum approximation is used to analyze the effect of electron emission from the surface of a spherical dust grain immersed in a plasma on the grain charge by assuming negligible ionization and recombination in the disturbed plasma region around the grain. A parameter is introduced that quantifies the emission intensity regardless of the emission mechanism (secondary, photoelectric, or thermionic emission). An analytical expression for the grain charge Z d is derived, and a criterion for change in the charge sign is obtained. The case of thermionic emission is examined in some detail. It is shown that the long-distance asymptotic behavior of the grain potential follows the Coulomb law with a negative effective charge Z eff , regardless of the sign of Z d . Thus, the potential changes sign and has a minimum if Z d > 0, which implies that attraction is possible between positively charged dust grains

  4. Development of a self-consistent model of dust grain charging at elevated pressures using the method of moments

    International Nuclear Information System (INIS)

    Filippov, A.V.; Dyatko, N.A.; Pal', A.F.; Starostin, A.N.

    2003-01-01

    A model of dust grain charging is constructed using the method of moments. The dust grain charging process in a weakly ionized helium plasma produced by a 100-keV electron beam at atmospheric pressure is studied theoretically. In simulations, the beam current density was varied from 1 to 10 6 μA/cm 2 . It is shown that, in a He plasma, dust grains of radius 5 μm and larger perturb the electron temperature only slightly, although the reduced electric field near the grain reaches 8 Td, the beam current density being 10 6 μA/cm 2 . It is found that, at distances from the grain that are up to several tens or hundreds of times larger than its radius, the electron and ion densities are lower than their equilibrium values. Conditions are determined under which the charging process may be described by a model with constant electron transport coefficients. The dust grain charge is shown to be weakly affected by secondary electron emission. In a beam-produced helium plasma, the dust grain potential calculated in the drift-diffusion model is shown to be close to that calculated in the orbit motion limited model. It is found that, in the vicinity of a body perturbing the plasma, there may be no quasineutral plasma presheath with an ambipolar diffusion of charged particles. The conditions for the onset of this presheath in a beam-produced plasma are determined

  5. Anomalous transport of charged dust grains in a magnetized collisional plasma: A molecular dynamics study

    Science.gov (United States)

    Bezbaruah, Pratikshya; Das, Nilakshi

    2018-05-01

    Anomalous diffusion of charged dust grains immersed in a plasma in the presence of strong ion-neutral collision, flowing ions, and a magnetic field has been observed. Molecular Dynamics simulation confirms the deviation from normal diffusion in an ensemble of dust grains probed in laboratory plasma chambers. Collisional effects are significant in governing the nature of diffusion. In order to have a clear idea on the transport of particles in a real experimental situation, the contribution of streaming ions and the magnetic field along with collision is considered through the relevant interaction potential. The nonlinear evolution of Mean Square Displacement is an indication of the modification in particle trajectories due to several effects as mentioned above. It is found that strong collision and ion flow significantly affect the interparticle interaction potential in the presence of the magnetic field and lead to the appearance of the asymmetric type of Debye Hückel (D H) potential. Due to the combined effect of the magnetic field, ion flow, and collision, dusty plasma exhibits a completely novel behavior. The coupling parameter Γ enhances the asymmetric D H type potential arising due to ion flow, and this may drive the system to a disordered state.

  6. Charge and potential of a dust grain versus the intergrain distance and establishment of the latter in a low-pressure plasma

    International Nuclear Information System (INIS)

    Sysun, A. V.; Sysun, V. I.; Khakhaev, A. D.; Shelestov, A. S.

    2008-01-01

    Results from experimental studies of ordered dust structures in plasma are reviewed. The experimental conditions and the data on the grain size and intergrain distance in plasma dust crystals are analyzed. It is shown that intergrain distance is a function of the grain size. The range of the ratio of the dust grain size to the Debye radius within which plasma dust crystals can form is determined. A volume cell surrounding a dust grain in plasma is considered. It is found that the potential and charge of the grain depend substantially on the intergrain distance. The charge, potential, and potential energy of a dust grain in a plasma dust crystal, as well as the electrostatic force exerted by the plasma field on the grain, are calculated by the method of molecular dynamics as functions of the intergrain distance. The corresponding analytic approximations and the criterion for the establishment of a steady-state intergrain distance are proposed.

  7. On the role of electron quantum tunneling in charging of dust grains in complex plasma

    International Nuclear Information System (INIS)

    Tyshetskiy, Yu.O.; Vladimirov, S.V.

    2011-01-01

    The aim of this work is calculate ion additional current associated with the quantum tunneling of plasma electrons, that are classically forbidden to overcome the repulsive potential barrier, onto the negatively charged grain. We compare this additional quantum tunneling current with the classical electron current from plasma onto the grain and analyze how this additional current affects the self-consistent equilibrium grain charge for different plasma parameters and grain sizes.

  8. Bistable intrinsic charge fluctuations of a dust grain subject to secondary electron emission in a plasma.

    Science.gov (United States)

    Shotorban, B

    2015-10-01

    A master equation was formulated to study intrinsic charge fluctuations of a grain in a plasma as ions and primary electrons are attached to the grain through collisional collection, and secondary electrons are emitted from the grain. Two different plasmas with Maxwellian and non-Maxwellian distributions were considered. The fluctuations could be bistable in either plasma when the secondary electron emission is present, as two stable macrostates, associated with two stable roots of the charge net current, may exist. Metastablity of fluctuations, manifested by the passage of the grain charge between two macrostates, was shown to be possible.

  9. Study of effect of grain size on dust charging in an RF plasma using three-dimensional PIC-MCC simulations

    International Nuclear Information System (INIS)

    Ikkurthi, V. R.; Melzer, A.; Matyash, K.; Schneider, R.

    2008-01-01

    A 3-dimensional Particle-Particle Particle-Mesh (P 3 M) code is applied to study the charging process of micrometer size dust grains confined in a capacitive RF discharge. In our model, particles (electrons and ions) are treated kinetically (Particle-in-Cell with Monte Carlo Collisions (PIC-MCC)). In order to accurately resolve the plasma particles' motion close to the dust grain, the PIC technique is supplemented with Molecular Dynamics (MD), employing an an analytic electrostatic potential for the interaction with the dust grain. This allows to self-consistently resolve the dust grain charging due to absorption of plasma electrons and ions. The charging of dust grains confined above lower electrode in a capacitive RF discharge and its dependence on the size and position of the dust is investigated. The results have been compared with laboratory measurements

  10. CHARGED DUST GRAIN DYNAMICS SUBJECT TO SOLAR WIND, POYNTING–ROBERTSON DRAG, AND THE INTERPLANETARY MAGNETIC FIELD

    Energy Technology Data Exchange (ETDEWEB)

    Lhotka, Christoph; Bourdin, Philippe; Narita, Yasuhito, E-mail: christoph.lhotka@oeaw.ac.at, E-mail: philippe.bourdin@oeaw.ac.at, E-mail: yasuhito.narita@oeaw.ac.at [Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8042 Graz (Austria)

    2016-09-01

    We investigate the combined effect of solar wind, Poynting–Robertson drag, and the frozen-in interplanetary magnetic field on the motion of charged dust grains in our solar system. For this reason, we derive a secular theory of motion by the means of an averaging method and validate it with numerical simulations of the unaveraged equations of motions. The theory predicts that the secular motion of charged particles is mainly affected by the z -component of the solar magnetic axis, or the normal component of the interplanetary magnetic field. The normal component of the interplanetary magnetic field leads to an increase or decrease of semimajor axis depending on its functional form and sign of charge of the dust grain. It is generally accepted that the combined effects of solar wind and photon absorption and re-emmision (Poynting–Robertson drag) lead to a decrease in semimajor axis on secular timescales. On the contrary, we demonstrate that the interplanetary magnetic field may counteract these drag forces under certain circumstances. We derive a simple relation between the parameters of the magnetic field, the physical properties of the dust grain, as well as the shape and orientation of the orbital ellipse of the particle, which is a necessary conditions for the stabilization in semimajor axis.

  11. Study of the Effects of the Electric Field on Charging Measurements on Individual Micron-size Dust Grains by Secondary Electron Emissions

    Science.gov (United States)

    Tankosic, D.; Abbas, M. M.

    2013-01-01

    The dust charging by electron impact is an important dust charging process in Astrophysical, Planetary, and the Lunar environments. Low energy electrons are reflected or stick to the grains charging the dust grains negatively. At sufficiently high energies electrons penetrate the grain leading to excitation and emission of electrons referred to as secondary electron emission (SEE). Available theoretical models for the calculation of SEE yield applicable for neutral, planar or bulk surfaces are generally based on Sternglass Equation. However, viable models for charging of individual dust grains do not exist at the present time. Therefore, the SEE yields have to be obtained by some experimental methods at the present time. We have conducted experimental studies on charging of individual micron size dust grains in simulated space environments using an electrodynamic balance (EDB) facility at NASA-MSFC. The results of our extensive laboratory study of charging of individual micron-size dust grains by low energy electron impact indicate that the SEE by electron impact is a very complex process expected to be substantially different from the bulk materials. It was found that the incident electrons may lead to positive or negative charging of dust grains depending upon the grain size, surface potential, electron energy, electron flux, grain composition, and configuration. In this paper we give a more elaborate discussion about the possible effects of the AC field in the EDB on dust charging measurements by comparing the secondary electron emission time-period (tau (sub em) (s/e)) with the time-period (tau (sub ac) (ms)) of the AC field cycle in the EDB that we have briefly addressed in our previous publication.

  12. COSMIC DUST AGGREGATION WITH STOCHASTIC CHARGING

    International Nuclear Information System (INIS)

    Matthews, Lorin S.; Hyde, Truell W.; Shotorban, Babak

    2013-01-01

    The coagulation of cosmic dust grains is a fundamental process which takes place in astrophysical environments, such as presolar nebulae and circumstellar and protoplanetary disks. Cosmic dust grains can become charged through interaction with their plasma environment or other processes, and the resultant electrostatic force between dust grains can strongly affect their coagulation rate. Since ions and electrons are collected on the surface of the dust grain at random time intervals, the electrical charge of a dust grain experiences stochastic fluctuations. In this study, a set of stochastic differential equations is developed to model these fluctuations over the surface of an irregularly shaped aggregate. Then, employing the data produced, the influence of the charge fluctuations on the coagulation process and the physical characteristics of the aggregates formed is examined. It is shown that dust with small charges (due to the small size of the dust grains or a tenuous plasma environment) is affected most strongly

  13. Charged dust structures in plasmas

    International Nuclear Information System (INIS)

    Cramer, N.F.; Vladimirov, S.V.

    1999-01-01

    We report here on theoretical investigations of the mechanical-electrostatic modes of vibration of a dust-plasma crystal, extending earlier work on the transverse modes of a horizontal line of grains (where the ions flow vertically downward to a plane horizontal cathode), the modes of two such lines of grains, and the modes of a vertical string of grains. The last two arrangements have the unique feature that the effect of the background plasma on the mutual grain interaction is asymmetric because of the wake downstream of the grains studied in. The characteristic frequencies of the vibrations are dependent on the parameters of the plasma and the dust grains, such as the Debye length and the grain charge, and so measurement of the frequencies could provide diagnostics of these quantities. Although the current boom in dusty plasma research is driven mainly by such industrial applications as plasma etching, sputtering and deposition, the physical outcomes of investigations in this rapidly expanding field cover many important topics in space physics and astrophysics as well. Examples are the interaction of dust with spacecraft, the structure of planetary rings, star formation, supernova explosions and shock waves. In addition, the study of the influence of dust in environmental research, such as in the Earth's ionosphere and atmosphere, is important. The unique binding of dust particles in a plasma opens possibilities for so-called super-chemistry, where the interacting bound elements are not atoms but dust grains

  14. A Van der Pol-Mathieu equation for the dynamics of dust grain charge in dusty plasmas

    International Nuclear Information System (INIS)

    Momeni, M; Kourakis, I; Moslehi-Fard, M; Shukla, P K

    2007-01-01

    The chaotic profile of dust grain dynamics associated with dust-acoustic oscillations in a dusty plasma is considered. The collective behaviour of the dust plasma component is described via a multi-fluid model, comprising Boltzmann distributed electrons and ions, as well as an equation of continuity possessing a source term for the dust grains, the dust momentum and Poisson's equations. A Van der Pol-Mathieu-type nonlinear ordinary differential equation for the dust grain density dynamics is derived. The dynamical system is cast into an autonomous form by employing an averaging method. Critical stability boundaries for a particular trivial solution of the governing equation with varying parameters are specified. The equation is analysed to determine the resonance region, and finally numerically solved by using a fourth-order Runge-Kutta method. The presence of chaotic limit cycles is pointed out. (fast track communication)

  15. Alignment of dust grains in ionized regions

    Science.gov (United States)

    Anderson, Nels; Watson, William D.

    1993-01-01

    The rate at which charged dust grains in a plasma are torqued by passing ions and electrons is calculated. When photo-emission of electrons is not important, attraction of ions by the grain monopole potential increases the rate at which the grains' spins are dealigned by nearly an order of magnitude. Consequently, the energy density of the magnetic field required to align grains in an H II region may be increased by about an order of magnitude. In contrast, electric dipole and quadrupole moments are unlikely to produce large dealignment rates for grains of modest length-to-width ratio. Nonetheless, for positively charged grains these higher-order moments likely prevent monopole repulsion of ions from reducing the dealignment rate far below that for neutral grains. The presence of positive grain charge therefore does not greatly facilitate grain alignment in an H II region.

  16. Fractal dust grains in plasma

    International Nuclear Information System (INIS)

    Huang, F.; Peng, R. D.; Liu, Y. H.; Chen, Z. Y.; Ye, M. F.; Wang, L.

    2012-01-01

    Fractal dust grains of different shapes are observed in a radially confined magnetized radio frequency plasma. The fractal dimensions of the dust structures in two-dimensional (2D) horizontal dust layers are calculated, and their evolution in the dust growth process is investigated. It is found that as the dust grains grow the fractal dimension of the dust structure decreases. In addition, the fractal dimension of the center region is larger than that of the entire region in the 2D dust layer. In the initial growth stage, the small dust particulates at a high number density in a 2D layer tend to fill space as a normal surface with fractal dimension D = 2. The mechanism of the formation of fractal dust grains is discussed.

  17. Charging of Single Micron Sized Dust Grains by Secondary Electron Emission: A Laboratory Study

    Science.gov (United States)

    Spann, James F., Jr.; Venturini, Catherine C.; Comfort, R. H.

    1998-01-01

    We present the details of a new laboratory study whose objective is to experimentally study the interaction of micron sized particles with plasmas and electromagnetic radiation. Specifically, to investigate under what conditions and to what extent do particles of various compositions and sizes become charged, or discharged, while exposed to an electron beam and ultraviolet radiation environment The emphasis is the study of the two charging mechanisms, secondary emission of electrons and photoelectric effect. The experiment uses a technique known as electrodynamic suspension of particles. With this technique, a single charged particle is electrodynamically levitated and then exposed to a controlled environment. Its charge to mass ratio is directly measured. Viscous drag measurements and the light scattering measurements characterize its size and optical characteristics. The environment to which the particle is expose may consist of room temperature and pressure or a rarefied atmosphere where only one major gaseous constituent is present, or, as in this case, a vacuum environment under electron bombardment or UV radiation . In addition, the environment can be cycled as part of the experiment. Therefore, using this technique, a single particle can be repeatedly exposed to a controlled environment and its response measured, or a single particle can be exposed to similar environments with minor differences and its response measured as a function of only the changed environmental conditions.

  18. Grain dust and the lungs.

    Science.gov (United States)

    Chan-Yeung, M.; Ashley, M. J.; Grzybowski, S.

    1978-01-01

    Grain dust is composed of a large number of materials, including various types of grain and their disintegration products, silica, fungi, insects and mites. The clinical syndromes described in relation to exposure to grain dust are chronic bronchitis, grain dust asthma, extrinsic allergic alveolitis, grain fever and silo-filler's lung. Rhinitis and conjunctivitis are also common in grain workers. While the concentration and the quality of dust influence the frequency and the type of clinical syndrome in grain workers, host factors are also important. Of the latter, smoking is the most important factor influencing the frequency of chronic bronchitis. The role of atopy and of bronchial hyperreactivity in grain dust asthma has yet to be assessed. Several well designed studies are currently being carried out in North America not only to delineate the frequency of the respiratory abnormalities, the pathogenetic mechanisms and the host factors, but also to establish a meaningful threshold limit concentration for grain dust. Images p1272-a PMID:348288

  19. Charged dust in saturn's magnetosphere

    International Nuclear Information System (INIS)

    Mendis, D.A.; Hill, J.R.; Houpis, H.L.F.

    1983-01-01

    Gravito-electrodynamic theory of charged dust grains is used to explain a variety of phenomena in those portions of the Saturnian ring system that are known to be dominated by fine (micron- and submicron-sized) dust, and in which collisional forces and Coulomb drag can be neglected. Among the phenomena discussed are the formation and evolution of the rotating near-radial spokes in the B-ring, the formation of waves in the F-ring, the cause of eccentricities of certain isolated ringlets, and the origin and morphology of the broad diffuse E-ring. Several novel processes predicted by the gravitoelectrodynamic theory, including 'magneto-gravitational capture' of exogenic dust by the magnetosphere, '1:1 magneto-gravitational orbital resonances' of charged dust with nearby satellites, and 'gyro-orbital resonances,' are used to explain individual observations. The effect of a ring current associated with this charged dust is also evaluated. Finally, the cosmogonic implications of the magneto-gravitational theory are briefly discussed. While several (although not all) of these processes have been discussed by one or more of the present authors elsewhere, the purpose of this paper is to synthesize all these processes within the framework of gravito-electrodynamics, and also to show its range of applicability within Saturn's ring system

  20. Dipole-dipole interaction of dust grains in plasmas

    International Nuclear Information System (INIS)

    Tskhakaya, D.D.; Shukla, P.K.

    2005-01-01

    Complete screening of the negative dust grain charge by a cloud of trapped ions in plasmas is investigated. In the external electric field, the compound dust particle - 'dust grain + ion cloud' acquires a dipole moment due to displacement of the centers of positive and negative charges in the opposite directions. By analogy to the Van der Waals potential, the dipole-dipole interaction of the compound dust particles can have an attractive behavior. It is shown that the dipole-dipole attractive force can exceed the shadowing force that is connected with the reciprocal interception of ions by the neighboring dust grains

  1. Physics of dust grains in hot gas

    International Nuclear Information System (INIS)

    Draine, B.T.; Salpeter, E.E.

    1979-01-01

    Charging of dust grains in hot (10 4 --10 9 K) plasma is studied, including photoelectron and secondary electron emission, field emission, and transmission of electrons and ions through the grain; resulting grain potentials are (for T > or approx. = 10 5 K) considerably smaller in magnitude than found by Burke and Silk. Even so, large electrostatic stresses can cause ion field emission and rapid destruction of small grains in very hot gas. Rapid rotation can also disrupt small grains, but damping (by microwave emission) usually limits the centrifugal stress to acceptable values for plasma densities n/sub H/ -3 . Sputtering rates are estimated for grains in hot gas, based upon a semiempirical fit to experimental data. Predicted sputtering rates for possible grain constituents are similar to estimates by Barlow, but in some cases differ significantly. Useful approximation formulae are given for the drag forces acting on a grain with arbitrary Mach number

  2. [Asthma due to grain dust].

    Science.gov (United States)

    Baur, X; Preisser, A; Wegner, R

    2003-06-01

    The actual literature as well as two case reports described in detail show that grain dust induces asthmatic reactions and ODTS which are obviously not of allergic origin. For diagnosis occupational-type exposure tests are decisive whereas allergological testing usually is not. Endotoxins which are present in the grain dust samples in high concentrations have to be regarded as the major causative components. To avoid irreversible lung function impairment a comprehensive early diagnosis is necessary. Generally, a remarkable reduction of exposure to dust with high levels of airborne endotoxin in agriculture has to be achieved since in many workplaces corresponding exposures are still rather high.

  3. Physical properties of five grain dust types.

    OpenAIRE

    Parnell, C B; Jones, D D; Rutherford, R D; Goforth, K J

    1986-01-01

    Physical properties of grain dust derived from five grain types (soybean, rice, corn, wheat, and sorghum) were measured and reported. The grain dusts were obtained from dust collection systems of terminal grain handling facilities and were assumed to be representative of grain dust generated during the handling process. The physical properties reported were as follows: particle size distributions and surface area measurements using a Coulter Counter Model TAII; percent dust fractions less tha...

  4. Efficient radiative transfer in dust grain mixtures

    OpenAIRE

    Wolf, S.

    2002-01-01

    The influence of a dust grain mixture consisting of spherical dust grains with different radii and/or chemical composition on the resulting temperature structure and spectral energy distribution of a circumstellar shell is investigated. The comparison with the results based on an approximation of dust grain parameters representing the mean optical properties of the corresponding dust grain mixture reveal that (1) the temperature dispersion of a real dust grain mixture decreases substantially ...

  5. Photoemission of Single Dust Grains for Heliospheric Conditions

    Science.gov (United States)

    Spann, James F., Jr.; Venturini, Catherine C.; Abbas, Mian M.; Comfort, Richard H.

    2000-01-01

    Initial results of an experiment to measure the photoemission of single dust grains as a function of far ultraviolet wavelengths are presented. Coulombic forces dominate the interaction of the dust grains in the heliosphere. Knowledge of the charge state of dust grains, whether in a dusty plasma (Debye length grains is primarily determined by primary electron and ion collisions, secondary electron emission and photoemission due to ultraviolet sunlight. We have established a unique experimental technique to measure the photoemission of individual micron-sized dust grains in vacuum. This technique resolves difficulties associated with statistical measurements of dust grain ensembles and non-static dust beams. The photoemission yield of Aluminum Oxide 3-micron grains For wavelengths from 120-300 nm with a spectral resolution of 1 nm FWHM is reported. Results are compared to interplanetary conditions.

  6. The dust acoustic wave in a bounded dusty plasma with strong electrostatic interactions between dust grains

    International Nuclear Information System (INIS)

    Shukla, Nitin; Shukla, P.K.

    2011-01-01

    The dispersion relation for the dust acoustic wave (DAW) in an unmagnetized dusty plasma cylindrical waveguide is derived, accounting for strong electrostatic interactions between charged dust grains. It is found that the boundary effect limits the radial extent of the DAW. The present result should be helpful for understanding the frequency spectrum of the DAW in a dusty plasma waveguide with strongly coupled charged dust grains. - Highlights: → We study the dust acoustic wave (DAW) in a bounded plasma. → We account for interactions between dust grains. → The boundary effect limits the radial extent of the DAW.

  7. Bounded dust-acoustic waves in a cylindrically bounded collisional dusty plasma with dust charge variation

    International Nuclear Information System (INIS)

    Wei Nanxia; Xue Jukui

    2006-01-01

    Taking into account the boundary, particle collisions, and dust charging effects, dust-acoustic waves in a uniform cylindrically bounded dusty plasma is investigated analytically, and the dispersion relation for the dust-acoustic wave is obtained. The effects of boundary, dust charge variation, particle collision, and dust size on the dust-acoustic wave are discussed in detail. Due to the bounded cylindrical boundary effects, the radial wave number is discrete, i.e., the spectrum is discrete. It is shown that the discrete spectrum, the adiabatic dust charge variation, dust grain size, and the particle collision have significant effects on the dust-acoustic wave

  8. Physical properties of five grain dust types.

    Science.gov (United States)

    Parnell, C B; Jones, D D; Rutherford, R D; Goforth, K J

    1986-01-01

    Physical properties of grain dust derived from five grain types (soybean, rice, corn, wheat, and sorghum) were measured and reported. The grain dusts were obtained from dust collection systems of terminal grain handling facilities and were assumed to be representative of grain dust generated during the handling process. The physical properties reported were as follows: particle size distributions and surface area measurements using a Coulter Counter Model TAII; percent dust fractions less than 100 micron of whole dust; bulk density; particle density; and ash content. PMID:3709482

  9. IONIZATION AND DUST CHARGING IN PROTOPLANETARY DISKS

    Energy Technology Data Exchange (ETDEWEB)

    Ivlev, A. V.; Caselli, P. [Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstr. 1, D-85748 Garching (Germany); Akimkin, V. V., E-mail: ivlev@mpe.mpg.de [Institute of Astronomy of the Russian Academy of Sciences, Pyatnitskaya Street 48, 119017 Moscow (Russian Federation)

    2016-12-10

    Ionization–recombination balance in dense interstellar and circumstellar environments is a key factor for a variety of important physical processes, such as chemical reactions, dust charging and coagulation, coupling of the gas with magnetic field, and development of instabilities in protoplanetary disks. We determine a critical gas density above which the recombination of electrons and ions on the grain surface dominates over the gas-phase recombination. For this regime, we present a self-consistent analytical model, which allows us to calculate exactly the abundances of charged species in dusty gas, without making assumptions on the grain charge distribution. To demonstrate the importance of the proposed approach, we check whether the conventional approximation of low grain charges is valid for typical protoplanetary disks, and discuss the implications for dust coagulation and development of the “dead zone” in the disk. The presented model is applicable for arbitrary grain-size distributions and, for given dust properties and conditions of the disk, has only one free parameter—the effective mass of the ions, shown to have a small effect on the results. The model can be easily included in numerical simulations following the dust evolution in dense molecular clouds and protoplanetary disks.

  10. Discrete stochastic charging of aggregate grains

    Science.gov (United States)

    Matthews, Lorin S.; Shotorban, Babak; Hyde, Truell W.

    2018-05-01

    Dust particles immersed in a plasma environment become charged through the collection of electrons and ions at random times, causing the dust charge to fluctuate about an equilibrium value. Small grains (with radii less than 1 μm) or grains in a tenuous plasma environment are sensitive to single additions of electrons or ions. Here we present a numerical model that allows examination of discrete stochastic charge fluctuations on the surface of aggregate grains and determines the effect of these fluctuations on the dynamics of grain aggregation. We show that the mean and standard deviation of charge on aggregate grains follow the same trends as those predicted for spheres having an equivalent radius, though aggregates exhibit larger variations from the predicted values. In some plasma environments, these charge fluctuations occur on timescales which are relevant for dynamics of aggregate growth. Coupled dynamics and charging models show that charge fluctuations tend to produce aggregates which are much more linear or filamentary than aggregates formed in an environment where the charge is stationary.

  11. Kuiper Belt Dust Grains as a Source of Interplanetary Dust Particles

    Science.gov (United States)

    Liou, Jer-Chyi; Zook, Herbert A.; Dermott, Stanley F.

    1996-01-01

    The recent discovery of the so-called Kuiper belt objects has prompted the idea that these objects produce dust grains that may contribute significantly to the interplanetary dust population. In this paper, the orbital evolution of dust grains, of diameters 1 to 9 microns, that originate in the region of the Kuiper belt is studied by means of direct numerical integration. Gravitational forces of the Sun and planets, solar radiation pressure, as well as Poynting-Robertson drag and solar wind drag are included. The interactions between charged dust grains and solar magnetic field are not considered in the model. Because of the effects of drag forces, small dust grains will spiral toward the Sun once they are released from their large parent bodies. This motion leads dust grains to pass by planets as well as encounter numerous mean motion resonances associated with planets. Our results show that about 80% of the Kuiper belt grains are ejected from the Solar System by the giant planets, while the remaining 20% of the grains evolve all the way to the Sun. Surprisingly, the latter dust grains have small orbital eccentricities and inclinations when they cross the orbit of the Earth. This makes them behave more like asteroidal than cometary-type dust particles. This also enhances their chances of being captured by the Earth and makes them a possible source of the collected interplanetary dust particles; in particular, they represent a possible source that brings primitive/organic materials from the outer Solar System to the Earth. When collisions with interstellar dust grains are considered, however, Kuiper belt dust grains around 9 microns appear likely to be collisionally shattered before they can evolve toward the inner part of the Solar System. The collision destruction can be applied to Kuiper belt grains up to about 50 microns. Therefore, Kuiper belt dust grains within this range may not be a significant part of the interplanetary dust complex in the inner Solar

  12. Measurements of Lunar Dust Charging Properties by Electron Impact

    Science.gov (United States)

    Abbas, Mian M.; Tankosic, Dragana; Craven, Paul D.; Schneider, Todd A.; Vaughn, Jason A.; LeClair, Andre; Spann, James F.; Norwood, Joseph K.

    2009-01-01

    Dust grains in the lunar environment are believed to be electrostatically charged predominantly by photoelectric emissions resulting from solar UV radiation on the dayside, and on the nightside by interaction with electrons in the solar wind plasma. In the high vacuum environment on the lunar surface with virtually no atmosphere, the positive and negative charge states of micron/submicron dust grains lead to some unusual physical and dynamical dust phenomena. Knowledge of the electrostatic charging properties of dust grains in the lunar environment is required for addressing their hazardous effect on the humans and mechanical systems. It is well recognized that the charging properties of individual small micron size dust grains are substantially different from the measurements on bulk materials. In this paper we present the results of measurements on charging of individual Apollo 11 and Apollo 17 dust grains by exposing them to mono-energetic electron beams in the 10-100 eV energy range. The charging/discharging rates of positively and negatively charged particles of approx. 0.1 to 5 micron radii are discussed in terms of the sticking efficiencies and secondary electron yields. The secondary electron emission process is found to be a complex and effective charging/discharging mechanism for incident electron energies as low as 10-25 eV, with a strong dependence on particle size. Implications of the laboratory measurements on the nature of dust grain charging in the lunar environment are discussed.

  13. Nonlinear periodic waves in dusty plasma with variable dust charge

    International Nuclear Information System (INIS)

    Yadav, Lakhan Lal; Bharuthram, R.

    2002-01-01

    Using the reductive perturbation method, we present a theory of nonlinear periodic waves, viz. the cnoidal waves, in a dusty plasma consisting of electrons, ions, and cold dust grains with charge fluctuations, which in the limiting case reduce to dust acoustic solitons. It is found that the frequency of the dust acoustic cnoidal wave increases with its amplitude. The dust charge fluctuations are found to affect the characteristics of the cnoidal waves

  14. Dynamics of interplanetary dust grains

    International Nuclear Information System (INIS)

    Lamy, P.L.

    1975-01-01

    The interaction of spherical grains of various materials-three silicates (quartz, obsidian and andesite), water-ice and iron - whose radii lie in the micronic and submicronic range with the interplanetary medium is solved. This includes: the interaction with the solar radiation field which is solved using Mie scattering theory and taking into account the precise dependence of the optical properties of the five materials upon wavelength; the interaction with the solar wind: corpuscular tangential drag is found to be always important and may even be larger than the Poynting-Robertson drag; the interaction with the interplanetary magnetic field is investigated in terms of a diffusion or random walk through a series of electromagnetic scatterings, leading to a Chapman-Komolgorov equation (i.e., a generalized Liouville equation). Numerical results are presented for these interactions spanning the entire solar system with circularity of elliptical orbits, direct or retrograde, with grains of various materials and sizes and giving -probably for the first time - a clear global picture of the interaction of dust grains with the interplanetary medium. The dynamics of the grains is then investigated using the theory of general perturbations and the numerical integration of trajectories of circum-solar grains

  15. TRAJECTORIES AND DISTRIBUTION OF INTERSTELLAR DUST GRAINS IN THE HELIOSPHERE

    International Nuclear Information System (INIS)

    Slavin, Jonathan D.; Frisch, Priscilla C.; Müller, Hans-Reinhard; Heerikhuisen, Jacob; Pogorelov, Nikolai V.; Reach, William T.; Zank, Gary

    2012-01-01

    The solar wind carves a bubble in the surrounding interstellar medium (ISM) known as the heliosphere. Charged interstellar dust grains (ISDG) encountering the heliosphere may be diverted around the heliopause or penetrate it depending on their charge-to-mass ratio. We present new calculations of trajectories of ISDG in the heliosphere, and the dust density distributions that result. We include up-to-date grain charging calculations using a realistic UV radiation field and full three-dimensional magnetohydrodynamic fluid + kinetic models for the heliosphere. Models with two different (constant) polarities for the solar wind magnetic field (SWMF) are used, with the grain trajectory calculations done separately for each polarity. Small grains a gr ∼ gr ∼> 1.0 μm, pass into the inner solar system and are concentrated near the Sun by its gravity. Trajectories of intermediate size grains depend strongly on the SWMF polarity. When the field has magnetic north pointing to ecliptic north, the field de-focuses the grains resulting in low densities in the inner heliosphere, while for the opposite polarity the dust is focused near the Sun. The ISDG density outside the heliosphere inferred from applying the model results to in situ dust measurements is inconsistent with local ISM depletion data for both SWMF polarities but is bracketed by them. This result points to the need to include the time variation in the SWMF polarity during grain propagation. Our results provide valuable insights for interpretation of the in situ dust observations from Ulysses.

  16. The effect of dust charge inhomogeneity on low-frequency modes in a strongly coupled plasma

    International Nuclear Information System (INIS)

    Farid, T.; Mamun, A.A.; Shukla, P.K.

    2000-01-01

    An analysis of low-frequency modes accounting for dust grain charge fluctuation and equilibrium grain charge inhomogeneity in a strongly coupled dusty plasma is presented. The existence of an extremely low frequency mode, which is due to the inhomogeneity in the equilibrium dust grain charge, is reported. Besides, the equilibrium dust grain charge inhomogeneity makes the dust-acoustic mode unstable. The strong correlations in the dust fluid significantly drive a new mode as well as the existing dust-acoustic mode. The applications of these results to recent experimental and to some space and astrophysical situations are discussed

  17. The equilibrium and oscillations of dust grains in a discharge

    International Nuclear Information System (INIS)

    Cramer, N.F.; Vladimirov, S.V.

    2000-01-01

    Full text: In a vertically oriented laboratory discharge plasma, dust particles are negatively charged and usually levitate in the sheath or pre-sheath region under the balance of gravitational, electrostatic (due to the sheath electric field) and plasma (such as the ion drag) forces. The ion flow, in addition to a direct (dragging) influence, is also responsible for the generation of associated collective plasma processes which can strongly affect the vertical arrangement of the grains, such as in the case of supersonic flows when a wake field is generated. Under some circumstances, the grains may form into a stable regular structure, the dust-plasma crystal, which can support a variety of lattice waves. The mechanism of formation of the crystal is still not well understood. The charge of the dust particles appears mainly due to electron and ion current onto the grain surfaces. The dependence of the dust particle charge on the sheath parameters has an important effect on the oscillations and equilibrium of dust grains in the vertical plane, leading to a possible disruption of the equilibrium position of the particle. Recent experiments at Sydney have shown the formation of the crystalline and liquid states of arrays of dust grains, and the self-excitation of vertical oscillations of the grains. To model these experiments, we have studied the interaction of dust grains with the plasma, including the charging of the grain, with a number of different models. A fluid model of the plasma to study the dust trapping, disruptions of the equilibrium, and the modes of transverse waves (vertically polarized) in arrays of grains in a dust-plasma crystal. It is found that for a grain radius greater than a critical value, there is no equilibrium position. Possible vertical oscillations about the stable equilibrium may develop high amplitudes, thus leading to a fall of the oscillating grain onto the electrode when the potential barrier is overcome. It is found that the charge

  18. Collisionless damping of nonlinear dust ion acoustic wave due to dust charge fluctuation

    International Nuclear Information System (INIS)

    Ghosh, Samiran; Chaudhuri, Tushar K.; Sarkar, Susmita; Khan, Manoranjan; Gupta, M.R.

    2002-01-01

    A dissipation mechanism for the damping of the nonlinear dust ion acoustic wave in a collisionless dusty plasma consisting of nonthermal electrons, ions, and variable charge dust grains has been investigated. It is shown that the collisionless damping due to dust charge fluctuation causes the nonlinear dust ion acoustic wave propagation to be described by the damped Korteweg-de Vries equation. Due to the presence of nonthermal electrons, the dust ion acoustic wave admits both positive and negative potential and it suffers less damping than the dust acoustic wave, which admits only negative potential

  19. Cosmic gamma-ray burst from intergalactic relativistic dust grains

    International Nuclear Information System (INIS)

    Dasgupta, A.K.

    1979-01-01

    Charged dust grains of radii a approximately 3 x 10 -6 approximately 3 x 10 -5 cm may acquire relativistic energy (>10 18 eV) in the intergalactic medium. In order to attain relativistic energy, dust grains have to move in and out ('scattering') of the magnetic field of the medium. A relativistic grain of radius a -5 cm with Lorentz factor γ approximately 10 3 approaching the Earth will break up either due to electrostatic charge or due to sputtering about 150 approximately 100 km, and may scatter solar photons via a fluorescence process. Dust grains may also melt into droplets in the solar vicinity and may contribute towards observed gamma-ray bursts. (Auth.)

  20. Extracting lunar dust parameters from image charge signals produced by the Lunar Dust Experiment

    Science.gov (United States)

    Stanley, J.; Kempf, S.; Horanyi, M.; Szalay, J.

    2015-12-01

    The Lunar Dust Experiment (LDEX) onboard the Lunar Atmosphere and Dust Environment Explorer (LADEE) is an impact ionization dust detector used to characterize the lunar dust exosphere generated by the impacts of large interplanetary particles and meteor streams (Horanyi et al., 2015). In addition to the mass and speed of these lofted particles, LDEX is sensitive to their charge. The resulting signatures of impact events therefore provide valuable information about not only the ambient plasma environment, but also the speed vectors of these dust grains. Here, impact events produced from LDEX's calibration at the Dust Accelerator Laboratory are analyzed using an image charge model derived from the electrostatic simulation program, Coulomb. We show that parameters such as dust grain speed, size, charge, and position of entry into LDEX can be recovered and applied to data collected during LADEE's seven-month mission.

  1. Solitons in dusty plasmas with positive dust grains

    International Nuclear Information System (INIS)

    Baluku, T. K.; Hellberg, M. A.; Mace, R. L.

    2008-01-01

    Although ''typical'' micrometer-sized dust grains in a space or laboratory plasma are often negatively charged because of collisions with the mobile electrons, there are environments in which grains may take on a positive charge. We consider a dusty plasma composed of electrons, positive ions and positive dust grains, and use the fluid dynamic paradigm to identify existence domains in parameter space for both dust-acoustic (DA) and dust-modified ion-acoustic (DIA) solitons. Only positive potential DA solitons are found. This represents an expected antisymmetry with the case of negative dust, where previously only negative solitons were reported. However, whereas for negative dust DIA solitons of either sign of potential may exist, we find that for the case of positive dust, DIA solitons are restricted to positive potentials only. The results for both positive and negative dust are consistent with an hypothesis that, in the absence of flows, the sign(s) of the soliton potential coincide(s) with the sign(s) of the species whose inertia is included in the calculation; i.e., the cold, supersonic species present in the plasma

  2. Small amplitude variable charge dust Bernstein-Greene-Kruskal double layers

    Energy Technology Data Exchange (ETDEWEB)

    Amour, Rabia [Plasma Physics Group, Theoretical Physics Laboratory, Faculty of Sciences - Physics, U.S.T.H.B, Bab-Ezzouar, B.P. 32, El Alia, Algiers 16111 (Algeria); Tribeche, Mouloud [Plasma Physics Group, Theoretical Physics Laboratory, Faculty of Sciences - Physics, U.S.T.H.B, Bab-Ezzouar, B.P. 32, El Alia, Algiers 16111 (Algeria)], E-mail: mouloud-tribeche@lycos.com

    2009-05-11

    A first theoretical attempt is made to investigate small amplitude, variable charge dust Bernstein-Greene-Kruskal (BGK) double layers (DLs). The nature of the dust BGK-DLs (compressive or rarefactive), their strength and thickness depend sensitively on the net negative charge residing on the grain surface, the dust grain dynamics and, more interestingly, on the ion-to-electron temperatures ratio.

  3. Small amplitude variable charge dust Bernstein-Greene-Kruskal double layers

    International Nuclear Information System (INIS)

    Amour, Rabia; Tribeche, Mouloud

    2009-01-01

    A first theoretical attempt is made to investigate small amplitude, variable charge dust Bernstein-Greene-Kruskal (BGK) double layers (DLs). The nature of the dust BGK-DLs (compressive or rarefactive), their strength and thickness depend sensitively on the net negative charge residing on the grain surface, the dust grain dynamics and, more interestingly, on the ion-to-electron temperatures ratio.

  4. Exact solutions for rotating charged dust

    International Nuclear Information System (INIS)

    Islam, J.N.

    1984-01-01

    Earlier work by the author on rotating charged dust is summarized. An incomplete class of exact solutions for differentially rotating charged dust in Newton-Maxwell theory for the equal mass and charge case that was found earlier is completed. A new global exact solution for cylindrically symmetric differentially rotating charged dust in Newton-Maxwell theory is presented. Lastly, a new exact solution for cylindrically symmetric rigidly rotating charged dust in general relativity is given. (author)

  5. TRAJECTORIES AND DISTRIBUTION OF INTERSTELLAR DUST GRAINS IN THE HELIOSPHERE

    Energy Technology Data Exchange (ETDEWEB)

    Slavin, Jonathan D. [Harvard-Smithsonian Center for Astrophysics, MS 83, 60 Garden Street, Cambridge, MA 02138 (United States); Frisch, Priscilla C. [Department of Astronomy and Astrophysics, University of Chicago, 5460 S. Ellis Avenue, Chicago, IL 60637 (United States); Mueller, Hans-Reinhard [Department of Physics and Astronomy, Dartmouth College, Hanover, NH 03755 (United States); Heerikhuisen, Jacob; Pogorelov, Nikolai V. [Department of Physics and Center for Space Physics and Aeronomic Research, University of Alabama, Huntsville, AL 35899 (United States); Reach, William T. [Universities Space Research Association, MS 211-3, Moffett Field, CA 94035 (United States); Zank, Gary [Department of Physics and Center for Space Plasma and Aeronomic Research, University of Alabama, Huntsville, AL 35805 (United States)

    2012-11-20

    The solar wind carves a bubble in the surrounding interstellar medium (ISM) known as the heliosphere. Charged interstellar dust grains (ISDG) encountering the heliosphere may be diverted around the heliopause or penetrate it depending on their charge-to-mass ratio. We present new calculations of trajectories of ISDG in the heliosphere, and the dust density distributions that result. We include up-to-date grain charging calculations using a realistic UV radiation field and full three-dimensional magnetohydrodynamic fluid + kinetic models for the heliosphere. Models with two different (constant) polarities for the solar wind magnetic field (SWMF) are used, with the grain trajectory calculations done separately for each polarity. Small grains a {sub gr} {approx}< 0.01 {mu}m are completely excluded from the inner heliosphere. Large grains, a {sub gr} {approx}> 1.0 {mu}m, pass into the inner solar system and are concentrated near the Sun by its gravity. Trajectories of intermediate size grains depend strongly on the SWMF polarity. When the field has magnetic north pointing to ecliptic north, the field de-focuses the grains resulting in low densities in the inner heliosphere, while for the opposite polarity the dust is focused near the Sun. The ISDG density outside the heliosphere inferred from applying the model results to in situ dust measurements is inconsistent with local ISM depletion data for both SWMF polarities but is bracketed by them. This result points to the need to include the time variation in the SWMF polarity during grain propagation. Our results provide valuable insights for interpretation of the in situ dust observations from Ulysses.

  6. Stochastic diffusion of dust grains by the interplanetary magnetic field

    International Nuclear Information System (INIS)

    Hassan, M.H.A.; Wallis, M.K.

    1983-10-01

    The effects of the sectored Interplanetary Magnetic Field on charged dust grains orbiting around the sun under radiation pressure and Poynting-Robertson drag forces are examined for initially circular and non-inclined orbits. The distribution function of the charged grains satisfies a Fokker-Planck equation in which the sectored field is taken as a source of stochastic impulses. By adopting the integrals of the impulse-free motion as variable parameters, the Fokker-Planck equation can be properly treated as a diffusion equation. Analytic solutions of the resulting diffusion equation show that dust grains injected near the ecliptic plane are scattered strongly to high helio-latitudes. The scattering is more pronounced for small grains injected at large distances from the Sun. (author)

  7. Excitation of collective plasma modes during collisions between dust grains and the formation of dust plasma crystals

    International Nuclear Information System (INIS)

    Goree, J.A.; Morfill, G.; Tsytovich, V.N.

    1998-01-01

    Dust plasma crystals have recently been produced in experiments in a number of laboratories. For dust crystallization to occur, there should exist an efficient mechanism for the cooling of the dust plasma component. It is shown that the excitation of collective plasma modes during collisions between the grains may serve as the required cooling mechanism. The excitation of dust sound waves is found to be most efficient. It is shown that the cooling of dust grains via the excitation of collective plasma modes can be even more efficient than that due to collisions with neutral particles, which was previously considered to be the only mechanism for cooling of the dust plasma component. At present, the first experiments are being carried out to study collisions between individual dust grains. High efficiency of the excitation of plasma modes caused by collisions between dust grains is attributed to the coherent displacement of the plasma particles that shield the grains. it is shown that the excitation efficiency is proportional to the fourth power of the charge of the dust grains and to a large power of their relative velocity, and is independent of their mass. The results obtained can be checked in experiments studying how the binary collisions between dust grains and the pressure of the neutral component influence the dust crystallization

  8. Influence of grain charge gradients on the dynamics of macroparticles in an electrostatic trap

    Energy Technology Data Exchange (ETDEWEB)

    Vaulina, O. S., E-mail: olga.vaulina@bk.ru [Russian Academy of Sciences, Joint Institute for High Temperatures (Russian Federation)

    2017-03-15

    An analytical model of anomalous heating of charged dust grains (macroparticles) caused by their stochastic motion in a bounded plasma volume is proposed. Analytical expressions allowing one to describe the pumping (heating) of interacting grains with additional stochastic energy due to grain charge gradients are derived. The analytical results are verified by numerical simulation of the problem. It is shown that spatial variations in the charges of dust grains can lead to their anomalous heating in laboratory plasma.

  9. Dust Spectroscopy and the Nature of Grains

    Science.gov (United States)

    Tielens, A. G. G. M.

    2006-01-01

    Ground-based, air-borne and space-based, infrared spectra of a wide variety of objects have revealed prominent absorption and emission features due to large molecules and small dust grains. Analysis of this data reveals a highly diverse interstellar and circumstellar grain inventory, including both amorphous materials and highly crystalline compounds (silicates and carbon). This diversity points towards a wide range of physical and chemical birthsites as well as a complex processing of these grains in the interstellar medium. In this talk, I will review the dust inventory contrasting and comparing both the interstellar and circumstellar reservoirs. The focus will be on the processes that play a role in the lifecycle of dust in the interstellar medium.

  10. Electrons scattered inside small dust grains of various materials

    International Nuclear Information System (INIS)

    Richterova, Ivana; Beranek, Martin; Pavlu, Jiri; Nemecek, Zdenek; Safrankova, Jana

    2010-01-01

    The dust grain charge in an electron beam is given by a difference in numbers of electrons that fall onto the grain and those leaving it. Electrons with energies exceeding 1 keV can penetrate through submicron-sized dust grains. If the grain is small enough, a yield of these electrons reaches unity but they leave a part of their energy inside the grain and this energy excites secondary electrons. The paper presents a hybrid Monte Carlo code that simulates paths of the primary electrons inside a spherical grain and provides the yield of scattered electrons and their energy spectrum as a function of the grain size and material. This code is based on the Richterovaet al. [Phys. Rev. B 74, 235430 (2006)] model but it includes several corrections important for light materials like carbon or ice. The model was verified using experimental results obtained on large planar samples. For spherical samples, we have found that the yield of scattered electrons reaches unity for 50 nm Au grains illuminated by 5 keV electrons, whereas the same effect can be observed on ≅1000 nm carbon grains.

  11. Nonlinear screening of dust grains and structurization of dusty plasma

    International Nuclear Information System (INIS)

    Tsytovich, V. N.; Gusein-zade, N. G.

    2013-01-01

    A review of theoretical ideas on the physics of structurization instability of a homogeneous dusty plasma, i.e., the formation of zones with elevated and depressed density of dust grains and their arrangement into different structures observed in laboratory plasma under microgravity conditions, is presented. Theoretical models of compact dust structures that can form in the nonlinear stage of structurization instability, as well as models of a system of voids (both surrounding a compact structure and formed in the center of the structure), are discussed. Two types of structures with very different dimensions are possible, namely, those smaller or larger than the characteristic mean free path of ions in the plasma flow. Both of them are characterized by relatively regular distributions of dust grains; however, the first ones usually require external confinement, while the structures of the second type can be self-sustained (which is of particular interest). In this review, they are called dust clusters and self-organized dust structures, respectively. Both types of the structures are characterized by new physical processes that take place only in the presence of the dust component. The role of nonlinearities in the screening of highly charged dust grains that are often observed in modern laboratory experiments turns out to be great, but these nonlinearities have not received adequate study as of yet. Although structurization takes place upon both linear and nonlinear screening, it can be substantially different under laboratory and astrophysical conditions. Studies on the nonlinear screening of large charges in plasma began several decades ago; however, up to now, this effect was usually disregarded when interpreting the processes occurring in laboratory dusty plasma. One of the aims of the present review was to demonstrate the possibility of describing the nonlinear screening of individual grains and take it into account with the help of the basic equations for the

  12. Plasma kinetics around a dust grain in an ion flow

    International Nuclear Information System (INIS)

    Maiorov, S.A.; Vladimirov, S.V.; Cramer, N.F.

    2000-01-01

    Full text: In a typical laboratory discharge, dust particles are negatively charged and usually levitate in the sheath or pre-sheath region under the balance of gravitational, electrostatic (due to the sheath electric field) and plasma (such as the ion drag) forces. The ion flow provides not only a direct (dragging) influence, but is also responsible for the generation of associated collective plasma processes which can strongly affect the vertical arrangement of the dust grains. The complete problem of the plasma dynamics around a macroscopic body in the presence of plasma flows is highly nonlinear and therefore its numerical analysis is of major importance. Among various numerical methods, direct integration of the equations of motion of the plasma particles represents a numerical experiment whose significance approaches experiments in the laboratory. Here, we present for the first time the results of a self-consistent molecular dynamics (MD) three-dimensional (3D) simulation of the kinetics of plasma particles (electrons and ions) around a dust grain, taking into account the dust charging. The core of the method includes consideration of the time evolution of the system consisting of positively ('ions') and negatively ('electrons') charged particles confined in a simulation box together with a macroscopic absorbing grain ('dust particle') with infinite mass and an initial (negative) charge. The ions are introduced in the system as a uniform flow defined by its Mach number and the ion temperature. The paths of the ions and electrons are determined through numerical integration of the equations of motion. We demonstrate that the plasma kinetics around a dust grain in the presence of an ion flow involves a strong ion focusing behind the grain. We have also confirmed that the most important of the processes involved is the ion time-scale; the kinetics of the electrons follows a Boltzmann distribution with good agreement. We note that the time constraints involved

  13. Multiple void formation in plasmas containing multispecies charged grains

    International Nuclear Information System (INIS)

    Liu, Y. H.; Chen, Z. Y.; Bogaerts, A.; Yu, M. Y.

    2006-01-01

    Self-organized separation of charged-dust species in two-dimensional dusty plasmas is studied by means of molecular-dynamics simulation. The multispecies dust grains, interacting through a screened Coulomb potential with a long-range attractive component, are confined by an external quadratic potential and subjected to a radially outward ion drag force. It is found that, in general, the species are spatially separated by bandlike dust-free (or void) regions, and grains of the same species tend to populate a common shell. At large ion drag and/or large plasma screening, a central disklike void as well as concentric bandlike voids separating the different species appear. Because of the outward drag and the attractive component of the dust-dust interaction forces, highly asymmetrical states consisting of species-separated dust clumps can also exist despite the fact that all the forces are either radial or central

  14. Dust grains from the heart of supernovae

    Science.gov (United States)

    Bocchio, M.; Marassi, S.; Schneider, R.; Bianchi, S.; Limongi, M.; Chieffi, A.

    2016-03-01

    Dust grains are classically thought to form in the winds of asymptotic giant branch (AGB) stars. However, there is increasing evidence today for dust formation in supernovae (SNe). To establish the relative importance of these two classes of stellar sources of dust, it is important to know the fraction of freshly formed dust in SN ejecta that is able to survive the passage of the reverse shock and be injected in the interstellar medium. With this aim, we have developed a new code, GRASH_Rev, that allows following the dynamics of dust grains in the shocked SN ejecta and computing the time evolution of the mass, composition, and size distribution of the grains. We considered four well-studied SNe in the Milky Way and Large Magellanic Cloud: SN 1987A, CasA, the Crab nebula, and N49. These sources have been observed with both Spitzer and Herschel, and the multiwavelength data allow a better assessment the mass of warm and cold dust associated with the ejecta. For each SN, we first identified the best explosion model, using the mass and metallicity of the progenitor star, the mass of 56Ni, the explosion energy, and the circumstellar medium density inferred from the data. We then ran a recently developed dust formation model to compute the properties of freshly formed dust. Starting from these input models, GRASH_Rev self-consistently follows the dynamics of the grains, considering the effects of the forward and reverse shock, and allows predicting the time evolution of the dust mass, composition, and size distribution in the shocked and unshocked regions of the ejecta. All the simulated models aagree well with observations. Our study suggests that SN 1987A is too young for the reverse shock to have affected the dust mass. Hence the observed dust mass of 0.7-0.9 M⊙ in this source can be safely considered as indicative of the mass of freshly formed dust in SN ejecta. Conversely, in the other three SNe, the reverse shock has already destroyed between 10-40% of the

  15. Strongly coupled Coulomb systems with positive dust grains: thermal and UV-induced plasmas

    International Nuclear Information System (INIS)

    Samarian, A.A.

    2000-01-01

    Full text: A plasma containing macroscopic dust particles or grains (often referred to as a dusty or colloidal or complex plasma) has the feature that grains may be charged by electron or ion flux or by photo- or thermoelectron emission. Electron emission from a grain surface produces a positive charge; capture of electrons produces the reverse effect making the dust grains negatively charged. Most dusty plasma research is concerned with the ordered dust structures (so-called 'plasma crystal') in glow discharges. The dust grains in these experiments were found to carry a negative charge due to the higher mobility of electrons as compared to ions in the discharge plasma. In recent years, in parallel with the study of the properties of plasma crystals under discharge conditions, attempts to obtain a structure from positively charged dust grains have been made, and structure formation processes for various charging mechanisms, particularly thermoelectron emission and photoemission, have been investigated. In this paper we review the essential features of strongly coupled plasmas with positive dust grains. An ordered structure of CeO 2 grains has been experimentally observed in a combustion products jet. The grains were charged positively and suspended in the plasma flow. Their charge is about 10 3 a and the calculated value of a Coulomb coupling parameter Γ is >10, corresponding to a plasma liquid. The ordered structures of Al 2 O 3 dust grains in propellant combustion products plasma have been observed for the first time. These structures were found in the sheath boundary of condensation region. The obtained data let us estimate the value of parameter Γ =3-40, corresponding to the plasma liquid state. The possibility is studied of the formation of ordered dust grain structures in thermal plasma. The range of the required values of the coupling parameter Γ is calculated using the results of diagnostic measurements carried out in thermal plasma with grains of

  16. A Dust Grain Photoemission Experiment

    Science.gov (United States)

    Venturini, C. C.; Spann, J. F., Jr.; Abbas, M. M.; Comfort, R. H.

    2000-01-01

    A laboratory experiment has been developed at Marshall Space Flight Center to study the interaction of micron-sized particles with plasmas and FUV radiation. The intent is to investigate the conditions under which particles of various compositions and sizes become charged, or discharged, while exposed to an electron beam and/or UV radiation. This experiment uses a unique laboratory where a single charged micron size particle is suspended in a quadrupole trap and then subjected to a controlled environment. Tests are performed using different materials and sizes, ranging from 10 microns to 1 micron, to determine the particle's charge while being subjected to an electron beam and /or UV radiation. The focus of this presentation will be on preliminary results from UV photoemission tests, but past results from electron beam, secondary electron emission tests will also be highlighted. A monochromator is used to spectrally resolve UV in the 120 nm to 300 nm range. This enables photoemission measurements as a function of wavelength. Electron beam tests are conducted using I to 3 micron sized aluminum oxide particles subjected to energies between 100 eV to 3 KeV. It was found that for both positive and negative particles the potential tended toward neutrality over time with possible equilibrium potentials between -0.8 Volts and 0.8 Volts.

  17. Exposure to grain dust in Great Britain.

    Science.gov (United States)

    Spankie, Sally; Cherrie, John W

    2012-01-01

    Airborne grain dust is a complex mixture of fragments of organic material from grain, plus mineral matter from soil, and possible insect, fungal, or bacterial contamination or their toxic products, such as endotoxin. In the 1990s, grain workers in Britain were frequently exposed to inhalable dust >10 mg.m(-3) (8 h), with particularly high exposures being found at terminals where grain was imported or exported and in drying operations (personal exposure typically approximately 20 mg.m(-3)). Since then, the industry has made substantial progress in improving the control of airborne dust through better-designed processes, increased automation, and an improved focus on product quality. We have used information from the published scientific literature and a small survey of industry representatives to estimate current exposure levels. These data suggest that current long-term exposure to inhalable dust for most workers is on average less than approximately 3 mg.m(-3), with perhaps 15-20% of individual personal exposures being >10 mg.m(-3). There are no published data from Britain on short-term exposure during cleaning and other tasks. We have estimated average levels for a range of tasks and judge that the highest levels, for example during some cleaning activities and certain process tasks such as loading and packing, are probably approximately10 mg.m(-3). Endotoxin levels were judged likely to be dust levels are <10 mg.m(-3). There are no published exposure data on mycotoxin, respirable crystalline silica, and mite contamination but these are not considered to present widespread problems in the British industry. Further research should be carried out to confirm these findings.

  18. Residual dust charges in discharge afterglow

    International Nuclear Information System (INIS)

    Coueedel, L.; Mikikian, M.; Boufendi, L.; Samarian, A. A.

    2006-01-01

    An on-ground measurement of dust-particle residual charges in the afterglow of a dusty plasma was performed in a rf discharge. An upward thermophoretic force was used to balance the gravitational force. It was found that positively charged, negatively charged, and neutral dust particles coexisted for more than 1 min after the discharge was switched off. The mean residual charge for 200-nm-radius particles was measured. The dust particle mean charge is about -5e at a pressure of 1.2 mbar and about -3e at a pressure of 0.4 mbar

  19. Measurements of Photoelectric Yield and Physical Properties of Individual Lunar Dust Grains

    Science.gov (United States)

    Abbas, M. M.; Tankosic, D.; Craven, P. D.; Spann, J. F.; LeClair, A.; West, F. A.; Taylor, L.; Hoover, R.

    2005-01-01

    Micron size dust grains levitated and transported on the lunar surface constitute a major problem for the robotic and human habitat missions for the Moon. It is well known since the Apollo missions that the lunar surface is covered with a thick layer of micron/sub-micron size dust grains. Transient dust clouds over the lunar horizon were observed by experiments during the Apollo 17 mission. Theoretical models suggest that the dust grains on the lunar surface are charged by the solar UV radiation as well as the solar wind. Even without any physical activity, the dust grains are levitated by electrostatic fields and transported away from the surface in the near vacuum environment of the Moon. The current dust charging and the levitation models, however, do not fully explain the observed phenomena. Since the abundance of dust on the Moon's surface with its observed adhesive characteristics is believed to have a severe impact on the human habitat and the lifetime and operations of a variety of equipment, it is necessary to investigate the phenomena and the charging properties of the lunar dust in order to develop appropriate mitigating strategies. We will present results of some recent laboratory experiments on individual micro/sub-micron size dust grains levitated in electrodynamic balance in simulated space environments. The experiments involve photoelectric emission measurements of individual micron size lunar dust grains illuminated with UV radiation in the 120-160 nm wavelength range. The photoelectric yields are required to determine the charging properties of lunar dust illuminated by solar UV radiation. We will present some recent results of laboratory measurement of the photoelectric yields and the physical properties of individual micron size dust grains from the Apollo and Luna-24 sample returns as well as the JSC-1 lunar simulants.

  20. Ion trapping within the dust grain plasma sheath

    International Nuclear Information System (INIS)

    Jovanovic, D.; Shukla, P.K.

    2002-01-01

    One of the most important and still unresolved problems in the physics of dusty plasmas is the determination of the dust charge. The grains are not directly accessible to measurements and it is necessary to have a reliable theoretical model of the electron and ion dynamics inside the Debye sphere for the interpretation of the relevant experimental data, which include also the effects of the surrounding electron and ion clouds. Recent computer simulations [6] and laboratory experiments [9] indicate that the plasma sheath is dominated by trapped ions, orbiting the grain on closed trajectories at distances smaller than the Debye radius, that cannot be accounted for by the classical theories. We present the first analytical, fully self-consistent, calculations of the electrostatic shielding of a charged dust grain in a collisional plasma. In the regime when the mean free path for the ion-dust collisions is larger than that for the ion-neutral collisions, we solve the kinetic equation for the ions, coupled with Boltzmann distributed electrons and Poisson's equation. The ion velocity distribution function, in the form of a spherically symmetric ion hole, is found to be anisotropic in the presence of charge-exchange collisions. The number of trapped ions and their spatial distribution are determined from the interplay between the collective plasma interaction and the collisional trapping/de-trapping. The stationary state results from the self-tuning of the trapped ion density by the feedback based on the nonlocality of the collisional integral, and on the ion mixing in the radial direction along elongated orbits. Our results confirm the existence of a strong Debye shielding of the dust charge, allowing also the over-population of the trapped ion distribution (ion hump)

  1. Composite grains: Application to circumstellar dust

    Directory of Open Access Journals (Sweden)

    D. B. Vaidya

    2011-09-01

    Full Text Available Using the discrete dipole approximation (DDA we calculate the absorption efficiency of the composite grain, made up of a host silicate spheroid and inclusions of graphite, in the spectral region 5.0-25.0μm. We study the absorption as a function of the voulume fraction of the inclusions. In particular, we study the variation in the 10.0μm and 18.0μm emission features with the volume fraction of the inclusions. Using the extinction efficiencies, of the composite grains we calculate the infrared fluxes at several dust temperatures and compare the model curves with the observed infrared emission curves (IRAS-LRS, obtained for circumstellar dust shells around oxygen rich M-type stars.

  2. Dust grain resonant capture: A statistical study

    Science.gov (United States)

    Marzari, F.; Vanzani, V.; Weidenschilling, S. J.

    1993-01-01

    A statistical approach, based on a large number of simultaneous numerical integrations, is adopted to study the capture in external mean motion resonances with the Earth of micron size dust grains perturbed by solar radiation and wind forces. We explore the dependence of the resonant capture phenomenon on the initial eccentricity e(sub 0) and perihelion argument w(sub 0) of the dust particle orbit. The intensity of both the resonant and dissipative (Poynting-Robertson and wind drag) perturbations strongly depends on the eccentricity of the particle while the perihelion argument determines, for low inclination, the mutual geometrical configuration of the particle's orbit with respect to the Earth's orbit. We present results for three j:j+1 commensurabilities (2:3, 4:5 and 6:7) and also for particle sizes s = 15, 30 microns. This study extends our previous work on the long term orbital evolution of single dust particles trapped into resonances with the Earth.

  3. Prevalence of IgE antibodies to grain and grain dust in grain elevator workers

    Energy Technology Data Exchange (ETDEWEB)

    Lewis, D.M.; Romeo, P.A.; Olenchock, S.A.

    1986-04-01

    IgE-mediated allergic reactions have been postulated to contribute to respiratory reactions seen in workers exposed to grain dusts. In an attempt better to define the prevalence of IgE antibodies in workers exposed to grain dusts, we performed the radioallergosorbent test (RAST) on worker sera using both commercial allergens prepared from grain and worksite allergens prepared from grain dust samples collected at the worksite. We found that the two types of reagents identified different populations with respect to the specificity of IgE antibodies present. The RAST assay performed using worksite allergens correlated well with skin test procedures. These results may allow us to gain better understanding of allergy associated with grain dust exposure, and document the utility of the RAST assay in assessment of occupational allergies.

  4. Prevalence of IgE antibodies to grain and grain dust in grain elevator workers.

    Science.gov (United States)

    Lewis, D M; Romeo, P A; Olenchock, S A

    1986-01-01

    IgE-mediated allergic reactions have been postulated to contribute to respiratory reactions seen in workers exposed to grain dusts. In an attempt better to define the prevalence of IgE antibodies in workers exposed to grain dusts, we performed the radioallergosorbent test (RAST) on worker sera using both commercial allergens prepared from grain and worksite allergens prepared from grain dust samples collected at the worksite. We found that the two types of reagents identified different populations with respect to the specificity of IgE antibodies present. The RAST assay performed using worksite allergens correlated well with skin test procedures. These results may allow us to gain better understanding of allergy associated with grain dust exposure, and document the utility of the RAST assay in assessment of occupational allergies. PMID:3709478

  5. Prevalence of IgE antibodies to grain and grain dust in grain elevator workers

    International Nuclear Information System (INIS)

    Lewis, D.M.; Romeo, P.A.; Olenchock, S.A.

    1986-01-01

    IgE-mediated allergic reactions have been postulated to contribute to respiratory reactions seen in workers exposed to grain dusts. In an attempt better to define the prevalence of IgE antibodies in workers exposed to grain dusts, we performed the radioallergosorbent test (RAST) on worker sera using both commercial allergens prepared from grain and worksite allergens prepared from grain dust samples collected at the worksite. We found that the two types of reagents identified different populations with respect to the specificity of IgE antibodies present. The RAST assay performed using worksite allergens correlated well with skin test procedures. These results may allow us to gain better understanding of allergy associated with grain dust exposure, and document the utility of the RAST assay in assessment of occupational allergies

  6. Laboratory Measurements of Optical and Physical Properties of Individual Lunar Dust Grains

    Science.gov (United States)

    Abbas, M. M.; Tankosic, D.; Craven, P. D.; Hoover, R. B.

    2006-01-01

    The lunar surface is covered with a thick layer of sub-micron/micron size dust grains formed by meteoritic impact over billions of years. The fine dust grains are levitated and transported on the lunar surface, and transient dust clouds over the lunar horizon were observed by experiments during the Apollo 17 mission. Theoretical models suggest that the dust grains on the lunar surface are charged by the solar UV radiation as well as the solar wind. Even without any physical activity, the dust grains are levitated by electrostatic fields and transported away from the surface in the near vacuum environment of the Moon. The current dust charging and levitation models, however, do not fully explain the observed phenomena. Since the abundance of dust on the Moon's surface with its observed adhesive characteristics has the potential of severe impact on human habitat and operations and lifetime of a variety of equipment, it is necessary to investigate the charging properties and the lunar dust phenomena in order to develop appropriate mitigating strategies. Photoelectric emission induced by the solar UV radiation with photon energies higher than the work function of the grain materials is recognized to be the dominant process for charging of the lunar dust, and requires measurements of the photoelectric yields to determine the charging and equilibrium potentials of individual dust grains. In this paper, we present the first laboratory measurements of the photoelectric yields of individual sub-micron/micron size dust grains selected from sample returns of Apollo 17, and Luna 24 missions, as well as similar size dust grains from the JSC-1 simulants. The experimental results were obtained on a laboratory facility based on an electrodynamic balance that permits a variety of experiments to be conducted on individual sub-micron/micron size dust grains in simulated space environments. The photoelectric emission measurements indicate grain size dependence with the yield

  7. Enhanced electromagnetic emission from plasmas containing positive dust grains and electrons

    International Nuclear Information System (INIS)

    Shukla, P.K.; Shukla, Nitin; Stenflo, L.

    2007-01-01

    Large amplitude high-frequency (HF) electromagnetic (EM) waves can scatter off dust-acoustic waves in plasmas containing positive dust grains and electrons, and can thus be responsible for HF enhanced electromagnetic emissions (EEE). An expression for the ensemble average of the squared HF-EEE vector potential is therefore derived, following the standard parametric interaction formalism and adopting the Rostoker superposition principle. The results should be useful for deducing the dust plasma parameters (e.g. the dust number density and dust charge) in situ, and HF intense EM beams can thus be used for diagnosis of positive dust-electron plasmas in space and laboratories

  8. Studies on plasma profiles and its effect on dust charging in hydrogen plasma

    Science.gov (United States)

    Kakati, B.; Kausik, S. S.; Saikia, B. K.; Bandyopadhay, M.

    2010-02-01

    Plasma profiles and its influence on dust charging are studied in hydrogen plasma. The plasma is produced in a high vacuum device by a hot cathode discharge method and is confined by a cusped magnetic field cage. A cylindrical Espion advanced Langmuir probe having 0.15 mm diameter and 10.0 mm length is used to study the plasma parameters for various discharge conditions. Optimum operational discharge parameters in terms of charging of the dust grains are studied. The charge on the surface of the dust particle is calculated from the capacitance model and the current by the dust grains is measured by the combination of a Faraday cup and an electrometer. Unlike our previous experiments in which dust grains were produced in-situ, here a dust dropper is used to drop the dust particles into the plasma.

  9. Studies on plasma profiles and its effect on dust charging in hydrogen plasma

    International Nuclear Information System (INIS)

    Kakati, B; Kausik, S S; Saikia, B K; Bandyopadhay, M

    2010-01-01

    Plasma profiles and its influence on dust charging are studied in hydrogen plasma. The plasma is produced in a high vacuum device by a hot cathode discharge method and is confined by a cusped magnetic field cage. A cylindrical Espion advanced Langmuir probe having 0.15 mm diameter and 10.0 mm length is used to study the plasma parameters for various discharge conditions. Optimum operational discharge parameters in terms of charging of the dust grains are studied. The charge on the surface of the dust particle is calculated from the capacitance model and the current by the dust grains is measured by the combination of a Faraday cup and an electrometer. Unlike our previous experiments in which dust grains were produced in-situ, here a dust dropper is used to drop the dust particles into the plasma.

  10. Scientists Detect Radio Emission from Rapidly Rotating Cosmic Dust Grains

    Science.gov (United States)

    2001-11-01

    current radio astronomy research, and the idea was largely forgotten. In the 1990s this perception began to change when scientists and engineers designed sensitive instruments to detect the faint afterglow of the Big Bang, which is seen in the Universe as the Cosmic Microwave Background Radiation. While making detailed maps of this faint and cold radiation, scientists also detected signals at approximately the same wavelength and intensity as the background radiation, but clearly emanating from within the Milky Way's galactic plane. The researchers expected to detect some emission from the Milky Way, but what they encountered was much brighter than anticipated. This discovery caused some concern among researchers because of the need to have a very clear "window" on the Universe to study the background radiation in great detail. If there were a source of radio emission in our own galactic "back yard," then studies of the microwave background radiation would need to recognize these emissions and correct for them. "We want to be clear, however, that nothing we have found invalidates the current interpretation of the Cosmic Microwave Background Radiation," assured Finkbeiner. "Nobody has done anything wrong in neglecting these signals - so far." Scientists considered several plausible mechanisms for this anomalous emission, but these theories failed to explain the observed spatial distribution of this emission across the sky. This predicament prompted theorists to rethink the spinning dust idea, leading to a 1998 model by Bruce Draine (Princeton University) and Alex Lazarian (University of Wisconsin), which proposed rotational dust-grain emission as an important mechanism. Draine and Lazarian assumed that small dust grains, perhaps having no more than 100 atoms each, would populate many interstellar dust clouds in the Galaxy. Each grain would have a small electric dipole and would therefore react to the charged ions that race through the clouds at tremendous speeds. As an ion

  11. Nonlinear dust acoustic waves in a charge varying dusty plasma with suprathermal electrons

    International Nuclear Information System (INIS)

    Tribeche, Mouloud; Bacha, Mustapha

    2010-01-01

    Arbitrary amplitude dust acoustic waves in a dusty plasma with a high-energy-tail electron distribution are investigated. The effects of charge variation and electron deviation from the Boltzmann distribution on the dust acoustic soliton are then considered. The dust charge variation makes the dust acoustic soliton more spiky. The dust grain surface collects less electrons as the latter evolves far away from their thermodynamic equilibrium. The dust accumulation caused by a balance of the electrostatic forces acting on the dust grains is more effective for lower values of the electron spectral index. Under certain conditions, the dust charge fluctuation may provide an alternate physical mechanism causing anomalous dissipation, the strength of which becomes important and may prevail over that of dispersion as the suprathermal character of the plasma becomes important. Our results may explain the strong spiky waveforms observed in auroral plasmas.

  12. Busting dust: from cosmic grains to terrestrial microbes

    International Nuclear Information System (INIS)

    Mendis, D.A.

    2001-01-01

    Electrostatic charging can have important consequences for both the growth and disruption of microparticulates immersed in a plasma. In this topical review, my emphasis is on the latter process, while I extend the term microparticulates not only to include ordinary inanimate cosmic or terrestrial dust but also to include terrestrial microbes whose sizes range from tens of nanometers (viruses) to tens of micrometers (bacteria). Following a description of the basic mechanism of electrostatic disruption of a solid body, I will discuss the role of size, shape and surface irregularity on the process. I will also consider the mitigating role of electric field emission of electrons on the disruption process of a negatively charged grain as its size falls below a critical size. I will conclude by reviewing some early evidence for the electrostatic disruption of cosmic grains, and the very recent evidence for the electrostatic disruption of the bacterial cell membranes in terrestrial sterilization experiments. (orig.)

  13. Computer simulation of dust grain evolution

    Science.gov (United States)

    Liffman, K.

    1989-01-01

    The latest results are reported from a Monte Carlo code that is being developed at NASA Ames. The goal of this program, is to derive from the observed and presumed properties of the interstellar medium (ISM) the following information: (1) the size spectrum of interstellar dust; (2) the chemical structure of interstellar dust; (3) interstellar abundances; and (4) the lifetime of a dust grain in the ISM. Presently this study is restricted to refractory interstellar material, i.e., the formation and destruction of ices are not included in the program. The program is embedded in an analytic solution for the bulk chemical evolution of a two-phase interstellar medium in which stars are born in molecular clouds, but new nucleosynthesis products and stellar return are entered into a complementary intercloud medium. The well-mixed matter of each interstellar phase is repeatedly cycled stochastically through the complementary phase and back. Refractory dust is created by thermal condensation as stellar matter flows away from sites of nucleosynthesis such as novae and supernovae and/or from the matter returned from evolved intermediate stars. The history of each particle is traced by standard Monte Carlo techniques as it is sputtered and fragmented by supernova shock waves in the intercloud medium. It also accretes an amorphous mantle of gaseous refractory atoms when its local medium joins with the molecular cloud medium. Finally it encounters the possibility of astration (destruction by star formation) within the molecular clouds.

  14. Potential around a dust grain in collisional plasma

    Energy Technology Data Exchange (ETDEWEB)

    Moulick, R., E-mail: moulick@gmail.com; Goswami, K. S. [Centre of Plasma Physics - Institute for Plasma Research Sonapur, Guwahati, Assam 782402 (India)

    2015-04-15

    The ion neutral collision can lead to interesting phenomena in dust charging, totally different from the expectations based on the traditional orbit motion limited theory. The potential around a dust grain is investigated for the collisional plasma considering the presence of ion neutral collisions. Fluid equations are solved for the one dimensional radial coordinate. It is observed that with the gradual increase in ion neutral collision, the potential structure around the dust grain changes its shape and is different from the usual Debye-Hückel potential. The shift however starts from a certain value of ion neutral collision and the electron-ion density varies accordingly. The potential variation is interesting and reconfirms the fact that there exists a region of attraction for negative charges. The collision modeling is done for the full range of plasma, i.e., considering the bulk and the sheath jointly. The potential variation with collision is also shown explicitly and the variation is found to cope up with the earlier observations.

  15. On the theory of dynamics of dust grain in plasma

    Science.gov (United States)

    Stepanenko, A. A.; Krasheninnikov, S. I.

    2013-03-01

    The dynamics of rotationally symmetric dust grains in plasma embedded in a magnetic field are of concern. The general expressions for forces and torques acting on dust are found. It is shown that dust spinning is determined by torques related to both the Lorentz force (dominant for relatively small grains) and the gyro-motion of plasma particles impinging the grain (which prevails for large grains). The stability of grain spinning is analyzed and it is shown that, for some cases (e.g., oblate spheroid), there is no stable dynamic equilibrium of grain spinning.

  16. Acute symptoms following exposure to grain dust in farming.

    Science.gov (United States)

    Manfreda, J; Holford-Strevens, V; Cheang, M; Warren, C P

    1986-01-01

    History of acute symptoms (cough, wheezing, shortness of breath, fever, stuffy nose, and skin itching/rash) following exposure to grain dust was obtained from 661 male and 535 female current and former farmers. These symptoms were relatively common: 60% of male and 25% of female farmers reported at least one such symptom on exposure to grain dust. Association of cough, wheezing, shortness of breath, and stuffy nose with skin reactivity and capacity to form IgE is consistent with an allergic nature of these symptoms. Barley and oats dust were perceived as dust most often producing symptoms. On the other hand, grain fever showed a different pattern, i.e., it was not associated with either skin reactivity or total IgE. Smoking might modify the susceptibility to react to grain dust with symptoms. Only those who reported wheezing on exposure to grain dust may have an increased risk to develop chronic airflow obstruction. PMID:3709486

  17. Simulating galactic dust grain evolution on a moving mesh

    Science.gov (United States)

    McKinnon, Ryan; Vogelsberger, Mark; Torrey, Paul; Marinacci, Federico; Kannan, Rahul

    2018-05-01

    Interstellar dust is an important component of the galactic ecosystem, playing a key role in multiple galaxy formation processes. We present a novel numerical framework for the dynamics and size evolution of dust grains implemented in the moving-mesh hydrodynamics code AREPO suited for cosmological galaxy formation simulations. We employ a particle-based method for dust subject to dynamical forces including drag and gravity. The drag force is implemented using a second-order semi-implicit integrator and validated using several dust-hydrodynamical test problems. Each dust particle has a grain size distribution, describing the local abundance of grains of different sizes. The grain size distribution is discretised with a second-order piecewise linear method and evolves in time according to various dust physical processes, including accretion, sputtering, shattering, and coagulation. We present a novel scheme for stochastically forming dust during stellar evolution and new methods for sub-cycling of dust physics time-steps. Using this model, we simulate an isolated disc galaxy to study the impact of dust physical processes that shape the interstellar grain size distribution. We demonstrate, for example, how dust shattering shifts the grain size distribution to smaller sizes resulting in a significant rise of radiation extinction from optical to near-ultraviolet wavelengths. Our framework for simulating dust and gas mixtures can readily be extended to account for other dynamical processes relevant in galaxy formation, like magnetohydrodynamics, radiation pressure, and thermo-chemical processes.

  18. LUNAR SURFACE AND DUST GRAIN POTENTIALS DURING THE EARTH’S MAGNETOSPHERE CROSSING

    Energy Technology Data Exchange (ETDEWEB)

    Vaverka, J.; Richterová, I.; Pavlu, J.; Šafránková, J.; Němeček, Z., E-mail: jana.safrankova@mff.cuni.cz [Department of Surface and Plasma Science, Faculty of Mathematics and Physics, Charles University in Prague, V Holešovičkách 2, 180 00 Prague (Czech Republic)

    2016-07-10

    Interaction between the lunar surface and the solar UV radiation and surrounding plasma environment leads to its charging by different processes like photoemission, collection of charged particles, or secondary electron emission (SEE). Whereas the photoemission depends only on the angle between the surface and direction to the Sun and varies only slowly, plasma parameters can change rapidly as the Moon orbits around the Earth. This paper presents numerical simulations of one Moon pass through the magnetospheric tail including the real plasma parameters measured by THEMIS as an input. The calculations are concentrated on different charges of the lunar surface itself and a dust grain lifted above this surface. Our estimations show that (1) the SEE leads to a positive charging of parts of the lunar surface even in the magnetosphere, where a high negative potential is expected; (2) the SEE is generally more important for isolated dust grains than for the lunar surface covered by these grains; and (3) the time constant of charging of dust grains depends on their diameter being of the order of hours for sub-micrometer grains. In view of these results, we discuss the conditions under which and the areas where a levitation of the lifted dust grains could be observed.

  19. Interaction between dust grains near a conducting wall

    International Nuclear Information System (INIS)

    Ignatov, A.M.

    2003-01-01

    The effect of a conducting electrode on the interaction of dust grains in an ion flow is discussed. It is shown that two grains levitating above the electrode at the same height may attract one another. This results in the instability of a dust layer

  20. Dust Coagulation in Infalling Protostellar Envelopes I. Compact Grains

    Science.gov (United States)

    Yorke, H.; Lin, D.; Suttner, G.

    1999-01-01

    Dust plays a key role in the optical, thermodynamic and gas dynamical behavior of collapsing molecular cores. Because of relative velocities of the individual dust grains, coagulation and shattering can modify the grain size distribution and -- due to corresponding changes in the medium's opacity significantly -- influence the evolution during early phases of star formation.

  1. Nonextensive electron and ion dust charging currents

    International Nuclear Information System (INIS)

    Amour, Rabia; Tribeche, Mouloud

    2011-01-01

    The correct nonextensive electron and ion charging currents are presented for the first time based on the orbit motion limited approach. For -1< q<1, where q measures the amount of plasma nonextensivity, the nonextensive electron charging current is expressed in terms of the hypergeometric function. The variable dust charge is expressed in terms of the Lambert function and we take advantage of this transcendental function to investigate succinctly the effects of nonextensive charge carriers. The obtained formulas bring a possibility to build theories on nonlinear collective process in variable charge nonextensive dusty plasmas.

  2. Carbohydrate and protein contents of grain dusts in relation to dust morphology.

    Science.gov (United States)

    Dashek, W V; Olenchock, S A; Mayfield, J E; Wirtz, G H; Wolz, D E; Young, C A

    1986-01-01

    Grain dusts contain a variety of materials which are potentially hazardous to the health of workers in the grain industry. Because the characterization of grain dusts is incomplete, we are defining the botanical, chemical, and microbial contents of several grain dusts collected from grain elevators in the Duluth-Superior regions of the U.S. Here, we report certain of the carbohydrate and protein contents of dusts in relation to dust morphology. Examination of the gross morphologies of the dusts revealed that, except for corn, each dust contained either husk or pericarp (seed coat in the case of flax) fragments in addition to respirable particles. When viewed with the light microscope, the fragments appeared as elongated, pointed structures. The possibility that certain of the fragments within corn, settled, and spring wheat were derived from cell walls was suggested by the detection of pentoses following colorimetric assay of neutralized 2 N trifluoroacetic acid hydrolyzates of these dusts. The presence of pentoses together with the occurrence of proteins within water washings of grain dusts suggests that glycoproteins may be present within the dusts. With scanning electron microscopy, each dust was found to consist of a distinct assortment of particles in addition to respirable particles. Small husk fragments and "trichome-like" objects were common to all but corn dust. Images FIGURE 4. FIGURE 5. PMID:3709476

  3. Formation of dust grains with impurities in red giant winds

    Science.gov (United States)

    Dominik, Carsten

    1994-01-01

    Among the several proposed carriers of diffuse interstellar bands (DIB's) are impurities in small dust grains, especially in iron oxide grains (Huffman 1977) and silicate grains (Huffman 1970). Most promising are single ion impurities since they can reproduce the observed band widths (Whittet 1992). These oxygen-rich grains are believed to originate mostly in the mass flows from red giants and in supernovae ejecta (e.g. Gehrz 1989). A question of considerable impact for the origin of DIB's is therefore, whether these grains are produced as mainly clean crystals or as some dirty materials. A formalism has been developed that allows tracking of the heterogeneous growth of a dust grain and its internal structure during the dust formation process. This formalism has been applied to the dust formation in the outflow from a red giant star.

  4. Effect of Stochastic Charge Fluctuations on Dust Dynamics

    Science.gov (United States)

    Matthews, Lorin; Shotorban, Babak; Hyde, Truell

    2017-10-01

    The charging of particles in a plasma environment occurs through the collection of electrons and ions on the particle surface. Depending on the particle size and the plasma density, the standard deviation of the number of collected elementary charges, which fluctuates due to the randomness in times of collisions with electrons or ions, may be a significant fraction of the equilibrium charge. We use a discrete stochastic charging model to simulate the variations in charge across the dust surface as well as in time. The resultant asymmetric particle potentials, even for spherical grains, has a significant impact on the particle coagulation rate as well as the structure of the resulting aggregates. We compare the effects on particle collisions and growth in typical laboratory and astrophysical plasma environments. This work was supported by the National Science Foundation under Grant PHY-1414523.

  5. Laboratory Investigation of Space and Planetary Dust Grains

    Science.gov (United States)

    Spann, James

    2005-01-01

    Dust in space is ubiquitous and impacts diverse observed phenomena in various ways. Understanding the dominant mechanisms that control dust grain properties and its impact on surrounding environments is basic to improving our understanding observed processes at work in space. There is a substantial body of work on the theory and modeling of dust in space and dusty plasmas. To substantiate and validate theory and models, laboratory investigations and space borne observations have been conducted. Laboratory investigations are largely confined to an assembly of dust grains immersed in a plasma environment. Frequently the behaviors of these complex dusty plasmas in the laboratory have raised more questions than verified theories. Space borne observations have helped us characterize planetary environments. The complex behavior of dust grains in space indicates the need to understand the microphysics of individual grains immersed in a plasma or space environment.

  6. Observations of dusty plasmas with magnetized dust grains

    Science.gov (United States)

    Luo, Q.-Z.; D'Angelo, N.

    2000-11-01

    We report a newly observed phenomenon in a dusty plasma device of the \\mbox{Q-machine} type. At low plasma densities the time required by the plasma to return to its no-dust conditions, after the dust dispenser is turned off, can be as long as many tens of seconds or longer. A tentative interpretation of this observation in terms of magnetized dust grains is advanced. It appears that an important loss mechanism of fine dust grains is by ion drag along the magnetic field lines. The effect of ion drag is somewhat counteracted by the -µ∇B force present when the magnetic field has a mirror geometry.

  7. On interaction of large dust grains with fusion plasma

    International Nuclear Information System (INIS)

    Krasheninnikov, S. I.; Smirnov, R. D.

    2009-01-01

    So far the models used to study dust grain-plasma interactions in fusion plasmas neglect the effects of dust material vapor, which is always present around dust in rather hot and dense edge plasma environment in fusion devices. However, when the vapor density and/or the amount of ionized vapor atoms become large enough, they can alter the grain-plasma interactions. Somewhat similar processes occur during pellet injection in fusion plasma. In this brief communication the applicability limits of the models ignoring vapor effects in grain-plasma interactions are obtained.

  8. Laboratory Measurements of Optical Properties of Micron Size Individual Dust Grains

    Science.gov (United States)

    Abbas, M. M.; Craven, P. D.; Spann, J. F.; Tankosic, D.; LeClair, A.; Witherow, W. K.; Camata, R.; Gerakines, P.

    2003-01-01

    A laboratory program is being developed at NASA Marshall Space Flight Center for experimental determination of the optical and physical properties individual dust grains in simulated astrophysical environments. The experimental setup is based on an electrodynamic balance that permits levitation of single 0.1 - 10 micron radii dust grains in a cavity evacuated to pressures of approx. 10(exp -6) torr. The experimental apparatus is equipped with observational ports for measurements in the UV, visible, and infrared spectral regions. A cryogenic facility for cooling the particles to temperature of approx. 10-50K is being installed. The current and the planned measurements include: dust charging processes, photoelectric emissions and yields with UV irradiation, radiation pressure measurements, infrared absorption and scattering properties, and condensation processes, involving the analogs of cosmic dust grains. Selected results based on photoemissions, radiation pressure, and other laboratory measurements will be presented.

  9. Laboratory Investigations of the Physical and Optical Properties of the Analogs of Individual Cosmic Dust Grains

    Science.gov (United States)

    Abbas, M. M.; Tankosic, D.; Craven, P. D.; Spann, J. F.; LeClair, A.; West, E. A.

    2005-01-01

    Microdsub-micron size cosmic dust grains play an important role in the physical and dynamical process in the galaxy, the interstellar medium, and the interplanetary and planetary environments. The dust grains in various astrophysical environments are generally charged by a variety of mechanisms that include collisional process with electrons and ions, and photoelectric emissions with UV radiation. The photoelectric emission process is believed to be the dominant process in many astrophysical environments with nearby UV sources, such as the interstellar medium, diffuse clouds, the outer regions of the dense molecular clouds, interplanetary medium, dust in planetary environments and rings, cometary tails, etc. Also, the processes and mechanisms involved in the rotation and alignment of interstellar dust grains are of great interest in view of the polarization of observed starlight as a probe for evaluation of the galactic magnetic field.

  10. Effect of Dust Grains on Solitary Kinetic Alfven Wave

    International Nuclear Information System (INIS)

    Li Yangfang; Wu, D. J.; Morfill, G. E.

    2008-01-01

    Solitary kinetic Alfven wave has been studied in dusty plasmas. The effect of the dust charge-to-mass ratio is considered. We derive the Sagdeev potential for the soliton solutions based on the hydrodynamic equations. A singularity in the Sagdeev potential is found and this singularity results in a bell-shaped soliton. The soliton solutions comprise two branches. One branch is sub-Alfvenic and the soliton velocities are much smaller than the Alfven speed. The other branch is super-Alfvenic and the soliton velocities are very close to or greater than the Alfven speed. Both compressive and rarefactive solitons can exist in each branch. For the sub-Alfvenic branch, the rarefactive soliton is a bell shape curve which is much narrower than the compressive one. In the super-Alfvenic branch, however, the compressive soliton is bell-shaped and the rarefactive one is broadened. We also found that the super-Alfvenic solitons can develop to other structures. When the charge-to-mass ratio of the dust grains is sufficiently high, the width of the rarefactive soliton will increase extremely and an electron density depletion will be observed. When the velocity is much higher than the Alfven speed, the bell-shaped soliton will transit to a cusped structure.

  11. Collective attraction of equal-sign charged grains in plasmas

    International Nuclear Information System (INIS)

    Tsytovich, V.N.; Morfill, G.E.

    2002-01-01

    It is shown that, in the presence of many grains embedded in a plasma, any two grains with the same charge sign can attract each other. The attraction is caused by collective effects. Both the strength of attraction and the distance at which the attraction is located depend on the average dust density. In the limit of strong collective interaction, the potential energy of interaction is found to be equal to the Coulomb interaction with an amplitude periodically changing its sign at a sequence of interdust distances. The condition for collective effects to dominate lead to a threshold condition that is fulfilled in existing experiments. The effect of collective attraction is applied for the physical interpretation of the observed phenomenon of the formation of dust crystals in laboratory experiments

  12. Experimental Investigations of the Physical and Optical Properties of Individual Micron/Submicron-Size Dust Grains in Astrophysical Environments

    Science.gov (United States)

    Abbas, M. M.; Tankosic, D.; LeClair, A.

    2014-01-01

    Dust grains constitute a significant component of matter in the universe, and play an important and crucial role in the formation and evolution of the stellar/planetary systems in interstellar dust clouds. Knowledge of physical and optical properties of dust grains is required for understanding of a variety of processes in astrophysical and planetary environments. The currently available and generally employed data on the properties of dust grains is based on bulk materials, with analytical models employed to deduce the corresponding values for individual small micron/submicron-size dust grains. However, it has been well-recognized over a long period, that the properties of individual smallsize dust grains may be very different from those deduced from bulk materials. This has been validated by a series of experimental investigations carried out over the last few years, on a laboratory facility based on an Electrodynamic Balance at NASA, which permits levitation of single small-size dust grains of desired composition and size, in vacuum, in simulated space environments. In this paper, we present a brief review of the results of a series of selected investigations carried out on the analogs of interstellar and planetary dust grains, as well as dust grains obtained by Apollo-l1-17 lunar missions. The selected investigations, with analytical results and discussions, include: (a) Direct measurements of radiation on individual dust grains (b) Rotation and alignments of dust grains by radiative torque (c) Charging properties of dust grains by: (i) UV Photo-electric emissions (ii) Electron Impact. The results from these experiments are examined in the light of the current theories of the processes involved.

  13. Measurement of photoemission and secondary emission from laboratory dust grains

    Science.gov (United States)

    Hazelton, Robert C.; Yadlowsky, Edward J.; Settersten, Thomas B.; Spanjers, Gregory G.; Moschella, John J.

    1995-01-01

    The overall goal of this project is experimentally determine the emission properties of dust grains in order to provide theorists and modelers with an accurate data base to use in codes that predict the charging of grains in various plasma environments encountered in the magnetospheres of the planets. In general these modelers use values which have been measured on planar, bulk samples of the materials in question. The large enhancements expected due to the small size of grains can have a dramatic impact upon the predictions and the ultimate utility of these predictions. The first experimental measurement of energy resolved profiles of the secondary electron emission coefficient, 6, of sub-micron diameter particles has been accomplished. Bismuth particles in the size range of .022 to .165 micrometers were generated in a moderate pressure vacuum oven (average size is a function of oven temperature and pressure) and introduced into a high vacuum chamber where they interacted with a high energy electron beam (0.4 to 20 keV). Large enhancements in emission were observed with a peak value, delta(sub max) = 4. 5 measured for the ensemble of particles with a mean size of .022 micrometers. This is in contrast to the published value, delta(sub max) = 1.2, for bulk bismuth. The observed profiles are in general agreement with recent theoretical predictions made by Chow et al. at UCSD.

  14. Long-range interaction between dust grains in plasma

    Directory of Open Access Journals (Sweden)

    D.Yu. Mishagli

    2014-03-01

    Full Text Available The nature of long-range interactions between dust grains in plasma is discussed. The dust grain interaction potential within a cell model of dusty plasma is introduced. The attractive part of inter-grain potential is described by multipole interaction between two electro-neutral cells. This allowed us to draw an analogy with molecular liquids where attraction between molecules is determined by dispersion forces. Also main ideas of the fluctuation theory for electrostatic field in cell model are formulated, and the dominating contribution to attractive part of inter-grain potential is obtained.

  15. Effects of grain dust on lungs prior to and following dust remediation.

    Science.gov (United States)

    Pahwa, Punam; Dosman, James A; McDuffie, Helen H

    2008-12-01

    To determine longitudinal estimates of pulmonary function decline in Canadian grain elevator workers before and after dust control by analyzing data collected from five regions of Canada over 15 years. Declines in forced expired volume in one second and forced vital capacity before and after dust control were estimated by using a generalized estimating equations approach. For grain workers who were in the grain industry for 20 or more years both before and after dust control: the mean annual loss of forced expired volume in one second was greatest among current smoking grain workers followed by ex-smokers and nonsmokers, respectively. Similar results were obtained for forced vital capacity. Grain dust control was effective in reducing decline in the lung function measurements among grain workers in all smoking and exposure categories.

  16. Effect of confining wall potential on charged collimated dust beam in low-pressure plasma

    International Nuclear Information System (INIS)

    Kausik, S. S.; Kakati, B.; Saikia, B. K.

    2013-01-01

    The effect of confining wall potential on charged collimated dust beam in low-pressure plasma has been studied in a dusty plasma experimental setup by applying electrostatic field to each channel of a multicusp magnetic cage. Argon plasma is produced by hot cathode discharge method at a pressure of 5×10 −4 millibars and is confined by a full line cusped magnetic field confinement system. Silver dust grains are produced by gas-evaporation technique and move upward in the form of a collimated dust beam due to differential pressure maintained between the dust and plasma chambers. The charged grains in the beam after coming out from the plasma column enter into the diagnostic chamber and are deflected by a dc field applied across a pair of deflector plates at different confining potentials. Both from the amount of deflection and the floating potential, the number of charges collected by the dust grains is calculated. Furthermore, the collimated dust beam strikes the Faraday cup, which is placed above the deflector plates, and the current (∼pA) so produced is measured by an electrometer at different confining potentials. The experimental results demonstrate the significant effect of confining wall potential on charging of dust grains

  17. Effect of confining wall potential on charged collimated dust beam in low-pressure plasma

    Energy Technology Data Exchange (ETDEWEB)

    Kausik, S. S.; Kakati, B.; Saikia, B. K. [Centre of Plasma Physics, Institute for Plasma Research, Sonapur 782 402 (India)

    2013-05-15

    The effect of confining wall potential on charged collimated dust beam in low-pressure plasma has been studied in a dusty plasma experimental setup by applying electrostatic field to each channel of a multicusp magnetic cage. Argon plasma is produced by hot cathode discharge method at a pressure of 5×10{sup −4} millibars and is confined by a full line cusped magnetic field confinement system. Silver dust grains are produced by gas-evaporation technique and move upward in the form of a collimated dust beam due to differential pressure maintained between the dust and plasma chambers. The charged grains in the beam after coming out from the plasma column enter into the diagnostic chamber and are deflected by a dc field applied across a pair of deflector plates at different confining potentials. Both from the amount of deflection and the floating potential, the number of charges collected by the dust grains is calculated. Furthermore, the collimated dust beam strikes the Faraday cup, which is placed above the deflector plates, and the current (∼pA) so produced is measured by an electrometer at different confining potentials. The experimental results demonstrate the significant effect of confining wall potential on charging of dust grains.

  18. Effect of confining wall potential on charged collimated dust beam in low-pressure plasma

    Science.gov (United States)

    Kausik, S. S.; Kakati, B.; Saikia, B. K.

    2013-05-01

    The effect of confining wall potential on charged collimated dust beam in low-pressure plasma has been studied in a dusty plasma experimental setup by applying electrostatic field to each channel of a multicusp magnetic cage. Argon plasma is produced by hot cathode discharge method at a pressure of 5×10-4 millibars and is confined by a full line cusped magnetic field confinement system. Silver dust grains are produced by gas-evaporation technique and move upward in the form of a collimated dust beam due to differential pressure maintained between the dust and plasma chambers. The charged grains in the beam after coming out from the plasma column enter into the diagnostic chamber and are deflected by a dc field applied across a pair of deflector plates at different confining potentials. Both from the amount of deflection and the floating potential, the number of charges collected by the dust grains is calculated. Furthermore, the collimated dust beam strikes the Faraday cup, which is placed above the deflector plates, and the current (˜pA) so produced is measured by an electrometer at different confining potentials. The experimental results demonstrate the significant effect of confining wall potential on charging of dust grains.

  19. Ion drag force on dust grains in the magnetized edge plasma

    International Nuclear Information System (INIS)

    Matyash, K.; Schneider, R.; Ikkurthi, V.R.; Melzer, A.

    2009-01-01

    A 3-dimensional Particle-Particle Particle-Mesh (P3M) code [K. Matyash, R. Schneider, F. Taccogna, D. Tskhakaya, J. Nucl. Mater. 363-365 (2007) 458] is applied to simulate a small-size (smaller than a Debye length) spherical dust grain confined in the magnetized plasma near the material wall of a tokamak. Plasma particles (electrons and ions) are treated kinetically (Particle-in-Cell with Monte Carlo Collisions (PIC MCC)), which allows to resolve self-consistently the electrostatic sheath in front of the wall. In order to describe accurately the plasma particles' motion close to the dust grain, the PIC technique is supplemented with Molecular Dynamics (MD), employing an analytic electrostatic potential for the interaction with the dust grain. The charging of a spherical, conducting dust grain confined in the sheath potential close to the wall of a tokamak is simulated. A magnetic field normal to the wall was investigated. The ion drag force resulting from dust grain collisions with the streaming ions is calculated. This force is critical for a realistic description of the dust particle dynamics and transport in fusion plasmas.

  20. The temperature of large dust grains in molecular clouds

    Science.gov (United States)

    Clark, F. O.; Laureijs, R. J.; Prusti, T.

    1991-01-01

    The temperature of the large dust grains is calculated from three molecular clouds ranging in visual extinction from 2.5 to 8 mag, by comparing maps of either extinction derived from star counts or gas column density derived from molecular observations to I(100). Both techniques show the dust temperature declining into clouds. The two techniques do not agree in absolute scale.

  1. Photoelectric Emission Measurements on the Analogs of Individual Cosmic Dust Grains

    Science.gov (United States)

    Abbas, M. M.; Tankosic, D.; Craven, P. D.; Spann, J. F.; LeClair, A.; West, E. A.; Weingartner, J. C.; Tielens, A. G. G. M.; Nuth, J. a.; Camata, R. P.

    2006-01-01

    The photoelectric emission process is considered to be the dominant mechanism for charging of cosmic dust grains in many astrophysical environments. The grain charge and equilibrium potentials play an important role in the dynamical and physical processes that include heating of the neutral gas in the interstellar medium, coagulation processes in the dust clouds, and levitation and dynamical processes in the interplanetary medium and planetary surfaces and rings. An accurate evaluation of photoelectric emission processes requires knowledge of the photoelectric yields of individual dust grains of astrophysical composition as opposed to the values obtained from measurements on flat surfaces of bulk materials, as it is generally assumed on theoretical considerations that the yields for the small grains are much different from the bulk values. We present laboratory measurements of the photoelectric yields of individual dust grains of silica, olivine, and graphite of approx. 0.09-5 micrometer radii levitated in an electrodynamic balance and illuminated with ultraviolet radiation at 120-160 nm wavelengths. The measured yields are found to be substantially higher than the bulk values given in the literature and indicate a size dependence with larger particles having order-of-magnitude higher values than for submicron-size grains.

  2. Effect of energetic electrons on dust charging in hot cathode filament discharge

    Science.gov (United States)

    Kakati, B.; Kausik, S. S.; Saikia, B. K.; Bandyopadhyay, M.

    2011-03-01

    The effect of energetic electrons on dust charging for different types of dust is studied in hydrogen plasma. The hydrogen plasma is produced by hot cathode filament discharge method in a dusty plasma device. A full line cusped magnetic field cage is used to confine the plasma elements. To study the plasma parameters for various discharge conditions, a cylindrical Langmuir probe having 0.15 mm diameter and 10.0 mm length is used. An electronically controlled dust dropper is used to drop the dust particles into the plasma. For different discharge conditions, the dust current is measured using a Faraday cup connected to an electrometer. The effect of secondary emission as well as discharge voltage on charging of dust grains in hydrogen plasma is studied with different dust.

  3. Effect of energetic electrons on dust charging in hot cathode filament discharge

    International Nuclear Information System (INIS)

    Kakati, B.; Kausik, S. S.; Saikia, B. K.; Bandyopadhyay, M.

    2011-01-01

    The effect of energetic electrons on dust charging for different types of dust is studied in hydrogen plasma. The hydrogen plasma is produced by hot cathode filament discharge method in a dusty plasma device. A full line cusped magnetic field cage is used to confine the plasma elements. To study the plasma parameters for various discharge conditions, a cylindrical Langmuir probe having 0.15 mm diameter and 10.0 mm length is used. An electronically controlled dust dropper is used to drop the dust particles into the plasma. For different discharge conditions, the dust current is measured using a Faraday cup connected to an electrometer. The effect of secondary emission as well as discharge voltage on charging of dust grains in hydrogen plasma is studied with different dust.

  4. Infrared emission from isolated dust clouds in the presence of very small dust grains

    Science.gov (United States)

    Lis, Dariusz C.; Leung, Chun M.

    1991-01-01

    Models of the effects of small grain-generated temperature fluctuations on the IR spectrum and surface brightness of externally heated interstellar dust clouds are presently constructed on the basis of a continuum radiation transport computer code which encompasses the transient heating of small dust grains. The models assume a constant fractional abundance of large and small grains throughout the given cloud. A comparison of model results with IRAS observations indicates that the observed 12-25 micron band emissions are associated with about 10-A radius grains, while the 60-100 micron emission is primarily due to large grains which are heated under the equilibrium conditions.

  5. Nonextensive dust acoustic waves in a charge varying dusty plasma

    Science.gov (United States)

    Bacha, Mustapha; Tribeche, Mouloud

    2012-01-01

    Our recent analysis on nonlinear nonextensive dust-acoustic waves (DA) [Amour and Tribeche in Phys. Plasmas 17:063702, 2010] is extended to include self-consistent nonadiabatic grain charge fluctuation. The appropriate nonextensive electron charging current is rederived based on the orbit-limited motion theory. Our results reveal that the amplitude, strength and nature of the nonlinear DA waves (solitons and shocks) are extremely sensitive to the degree of ion nonextensivity. Stronger is the electron correlation, more important is the charge variation induced nonlinear wave damping. The anomalous dissipation effects may prevail over that dispersion as the electrons evolve far away from their Maxwellian equilibrium. Our investigation may be of wide relevance to astronomers and space scientists working on interstellar dusty plasmas where nonthermal distributions are turning out to be a very common and characteristic feature.

  6. Ochratoxin A in grain dust--estimated exposure and relations to agricultural practices in grain production.

    Science.gov (United States)

    Halstensen, Anne Straumfors; Nordby, Karl-Christian; Elen, Oleif; Eduard, Wijnand

    2004-01-01

    Ochratoxin A (OTA) is a nephrotoxin frequently contaminating grains. OTA inhalation during grain handling may therefore represent a health risk to farmers, and was the subject of this study. Airborne and settled grain dust was collected during grain work on 84 Norwegian farms. Climate and agricultural practices on each farm were registered. Penicillium spp., Aspergillus spp. and OTA in settled dust were measured. Settled dust contained median 4 microg OTA/kg dust (range 2-128), correlating with Penicillium spp. (median 40 cfu/mg; range 0-32000, rs =0.33; p grain species, districts and agricultural practices. Penicillium levels, but not OTA levels, were higher in storage than in threshing dust (p=0.003), and increased with storage time (rs =0.51, p dust during threshing and median 7 mg/m3 (range 1-110) dust during storage work, equalling median 3.7 pg/m3 (range 0.6-200) and median 40 pg/m3 (range 2-14000) OTA, respectively (p grain work was low, although varying by more than 1,000-fold. However, the farmers may occasionally be highly exposed, particularly during handling of stored grain.

  7. Disintegration of Dust Aggregates in Interstellar Shocks and the Lifetime of Dust Grains in the ISM

    Science.gov (United States)

    Dominik, C.; Jones, A. P.; Tielens, A. G. G. M.; Cuzzi, Jeff (Technical Monitor)

    1994-01-01

    Interstellar grains are destroyed by shock waves moving through the ISM. In fact, the destruction of grains may be so effective that it is difficult to explain the observed abundance of dust in the ISM as a steady state between input of grains from stellar sources and destruction of grains in shocks. This is especially a problem for the larger grains. Therefore, the dust grains must be protected in some way. Jones et al. have already considered coatings and the increased post-shock drag effects for low density grains. In molecular clouds and dense clouds, coagulation of grains is an important process, and the largest interstellar grains may indeed be aggregates of smaller grains rather than homogeneous particles. This may provide a means to protect the larger grains, in that, in moderate velocity grain-grain collisions in a shock the aggregates may disintegrate rather than be vaporized. The released small particles are more resilient to shock destruction (except in fast shocks) and may reform larger grains later, recovering the observed size distribution. We have developed a model for the binding forces in grain aggregates and apply this model to the collisions between an aggregate and fast small grains. We discuss the results in the light of statistical collision probabilities and grain life times.

  8. Effects of dust-charge fluctuations on the potential of an array of projectiles in a partially ionized dusty plasma

    International Nuclear Information System (INIS)

    Ali, S.; Nasim, M.H.; Murtaza, G.

    2003-01-01

    The expressions for the Debye and the wake potential are derived by incorporating dust-charge fluctuations of a single projectile, as well as of an array of dust grain projectiles, propagating through a partially ionized dusty plasma with a constant velocity. Numerically, the effects of the dust-charge fluctuations and the dust-neutral collisions on the electrostatic potential for a single, three, six and ten projectiles are examined. The dust-charge relaxation rate modifies the shape of the Debye as well as the wake potential. For smaller values of the relaxation rates a potential well is formed instead of Debye potential

  9. Experimental Phase Functions of Millimeter-sized Cosmic Dust Grains

    Energy Technology Data Exchange (ETDEWEB)

    Muñoz, O.; Moreno, F.; Guirado, D.; Escobar-Cerezo, J. [Instituto de Astrofísica de Andalucía, CSIC, Glorieta de la Astronomía s/n, E-18008 Granada (Spain); Vargas-Martín, F. [Department of Electromagnetism and Electronics, University of Murcia, E-30100 Murcia (Spain); Min, M. [SRON Netherlands Institute for Space Research, Sobornnelaan 2, 3584 CA Utrecht (Netherlands); Hovenier, J. W. [Astronomical Institute “Anton Pannekoek,” University of Amsterdam, Science Park 904, 1098 XH, Amsterdam (Netherlands)

    2017-09-01

    We present the experimental phase functions of three types of millimeter-sized dust grains consisting of enstatite, quartz, and volcanic material from Mount Etna, respectively. The three grains present similar sizes but different absorbing properties. The measurements are performed at 527 nm covering the scattering angle range from 3° to 170°. The measured phase functions show two well-defined regions: (i) soft forward peaks and (ii) a continuous increase with the scattering angle at side- and back-scattering regions. This behavior at side- and back-scattering regions is in agreement with the observed phase functions of the Fomalhaut and HR 4796A dust rings. Further computations and measurements (including polarization) for millimeter-sized grains are needed to draw some conclusions about the fluffy or compact structure of the dust grains.

  10. Phototelectric Emission Measurements on the Analogs of Individual Cosmic Dust Grains

    Science.gov (United States)

    Abbas, Mian M.; Tankosic, D.; Craven, P. D.; Spann, J. F.; LeClair, A.; West, E. A.; Weingartner, J. C.; Tielens, A. G. G. M.; Nuth, J. A.; Camata, R. P.; hide

    2005-01-01

    The photoelectric emission process is considered to be the dominant mechanism for charging of cosmic dust grains in many astrophysical environments. The grain charge and the equilibrium potentials play an important role in the dynamical and physical processes that include heating of the neutral gas in the interstellar medium, coagulation processes in the dust clouds, and levitation and dynamical processes in the interplanetary medium and planetary surfaces and rings. An accurate evaluation of photoelectric emission processes requires knowledge of the photoelectric yields of individual dust grains of astrophysical composition as opposed to the values obtained from measurements on flat surfaces of bulk materials, as it is generally assumed on theoretical considerations that the yields for the small grains are much higher than the bulk values. We present laboratory measurements of the photoelectric yields of individual dust grains of silica, olivine, and graphite of approximately 0.09 to 8 microns radii levitated in an electrodynamic balance and illuminated with W radiation at 120 to 160 nm wavelengths. The measured values and the size dependence of the yields are found to be substantially different from the bulk values given in the literature.

  11. The effects of variable dust size and charge on dust acoustic waves propagating in a hybrid Cairns–Tsallis complex plasma

    Science.gov (United States)

    El-Taibany, W. F.; El-Siragy, N. M.; Behery, E. E.; Elbendary, A. A.; Taha, R. M.

    2018-05-01

    The propagation characteristics of dust acoustic waves (DAWs) in a dusty plasma consisting of variable size dust grains, hybrid Cairns-Tsallis-distributed electrons, and nonthermal ions are studied. The charging of the dust grains is described by the orbital-motion-limited theory and the size of the dust grains obeys the power law dust size distribution. To describe the nonlinear propagation of the DAWs, a Zakharov-Kuznetsov equation is derived using a reductive perturbation method. It is found that the nonthermal and nonextensive parameters influence the main properties of DAWs. Moreover, our results reveal that the rarefactive waves can propagate mainly in the proposed plasma model while compressive waves can be detected for a very small range of the distribution parameters of plasma species, and the DAWs are faster and wider for smaller size dust grains. Applications of the present results to dusty plasma observations are briefly discussed.

  12. Exposure to grain dust and microbial components in the Norwegian grain and compound feed industry.

    Science.gov (United States)

    Halstensen, Anne Straumfors; Heldal, Kari Kulvik; Wouters, Inge M; Skogstad, Marit; Ellingsen, Dag G; Eduard, Wijnand

    2013-11-01

    The aim of this study was to extensively characterize grain workers' personal exposure during work in Norwegian grain elevators and compound feed mills, to identify differences in exposures between the workplaces and seasons, and to study the correlations between different microbial components. Samples of airborne dust (n = 166) were collected by full-shift personal sampling during work in 20 grain elevators and compound feed mills during one autumn season and two winter seasons. The personal exposure to grain dust, endotoxins, β-1→3-glucans, bacteria, and fungal spores was quantified. Correlations between dust and microbial components and differences between workplaces and seasons were investigated. Determinants of endotoxin and β-1→3-glucan exposure were evaluated by linear mixed-effect regression modeling. The workers were exposed to an overall geometric mean of 1.0mg m(-3) inhalable grain dust [geometric standard deviation (GSD) = 3.7], 628 endotoxin units m(-3) (GSD = 5.9), 7.4 µg m(-3) of β-1→3-glucan (GSD = 5.6), 21 × 10(4) bacteria m(-3) (GSD = 7.9) and 3.6 × 10(4) fungal spores m(-3) (GSD = 3.4). The grain dust exposure levels were similar across workplaces and seasons, but the microbial content of the grain dust varied substantially between workplaces. Exposure levels of all microbial components were significantly higher in grain elevators compared with all other workplaces. The grain dust exposure was significantly correlated (Pearson's r) with endotoxin (rp = 0.65), β-1→3-glucan (rp = 0.72), bacteria (rp = 0.44) and fungal spore (rp = 0.48) exposure, whereas the explained variances were strongly dependent on the workplace. Bacteria, grain dust, and workplace were important determinants for endotoxin exposure, whereas fungal spores, grain dust, and workplace were important determinants for β-1→3-glucan exposure. Although the workers were exposed to a relatively low mean dust level, the microbial exposure was high. Furthermore, the

  13. Artist rendering of dust grains colliding at low speeds

    Science.gov (United States)

    2003-01-01

    Clues to the formation of planets and planetary rings -- like Saturn's dazzling ring system -- may be found by studying how dust grains interact as they collide at low speeds. To study the question of low-speed dust collisions, NASA sponsored the COLLisions Into Dust Experiment (COLLIDE) at the University of Colorado. It was designed to spring-launch marble-size projectiles into trays of powder similar to space or lunar dust. COLLIDE-1 (1998) discovered that collisions below a certain energy threshold eject no material. COLLIDE-2 was designed to identify where the threshold is. In COLLIDE-2, scientists nudged small projectiles into dust beds and recorded how the dust splashed outward (video frame at top; artist's rendering at bottom). The slowest impactor ejected no material and stuck in the target. The faster impactors produced ejecta; some rebounded while others stuck in the target.

  14. Aspergillus candidus: a respiratory hazard associated with grain dust.

    Science.gov (United States)

    Krysinska-Traczyk, E; Dutkiewicz, J

    2000-01-01

    The concentration of Aspergillus candidus in samples of grain dust and of air polluted with grain dust was found to be large (respectively 3.0 x 10(5) - 3.0 x 10(9) cfu/g and 5.0 x 10(3) - 6.47 x 10(5) cfu/m(3)) and proved to be significantly greater compared to samples of other organic dusts (pgrain workers reacted significantly more frequently to extract of A. candidus in the leukocyte migration inhibition test (pdusts. It was concluded that Aspergillus candidus, because of its common occurrence and strong immunomodulating properties, poses an important occupational hazard for grain handling workers

  15. Studies of dust grain properties in infrared reflection nebulae.

    Science.gov (United States)

    Pendleton, Y J; Tielens, A G; Werner, M W

    1990-01-20

    We have developed a model for reflection nebulae around luminous infrared sources embedded in dense dust clouds. The aim of this study is to determine the sizes of the scattering grains. In our analysis, we have adopted an MRN-like power-law size distribution (Mathis, Rumpl, and Nordsieck) of graphite and silicate grains, but other current dust models would give results which were substantially the same. In the optically thin limit, the intensity of the scattered light is proportional to the dust column density, while in the optically thick limit, it reflects the grain albedo. The results show that the shape of the infrared spectrum is the result of a combination of the scattering properties of the dust, the spectrum of the illuminating source, and foreground extinction, while geometry plays a minor role. Comparison of our model results with infrared observations of the reflection nebula surrounding OMC-2/IRS 1 shows that either a grain size distribution like that found in the diffuse interstellar medium, or one consisting of larger grains, can explain the observed shape of the spectrum. However, the absolute intensity level of the scattered light, as well as the observed polarization, requires large grains (approximately 5000 angstroms). By adding water ice mantles to the silicate and graphite cores, we have modeled the 3.08 micrometers ice band feature, which has been observed in the spectra of several infrared reflection nebulae. We show that this ice band arises naturally in optically thick reflection nebulae containing ice-coated grains. We show that the shape of the ice band is diagnostic of the presence of large grains, as previously suggested by Knacke and McCorkle. Comparison with observations of the BN/KL reflection nebula in the OMC-1 cloud shows that large ice grains (approximately 5000 angstroms) contribute substantially to the scattered light.

  16. PROPERTIES OF DUST GRAINS PROBED WITH EXTINCTION CURVES

    International Nuclear Information System (INIS)

    Nozawa, Takaya; Fukugita, Masataka

    2013-01-01

    Modern data of the extinction curve from the ultraviolet to the near-infrared are revisited to study properties of dust grains in the Milky Way (MW) and the Small Magellanic Cloud (SMC). We confirm that the graphite-silicate mixture of grains yields the observed extinction curve with the simple power-law distribution of the grain size but with a cutoff at some maximal size: the parameters are tightly constrained to be q = 3.5 ± 0.2 for the size distribution a –q and the maximum radius a max = 0.24 ± 0.05 μm, for both MW and SMC. The abundance of grains, and hence the elemental abundance, is constrained from the reddening versus hydrogen column density, E(B – V)/N H . If we take the solar elemental abundance as the standard for the MW, >56% of carbon should be in graphite dust, while it is dust /ρ H = 1 / (120 +10 -16 ) for the MW and 1 / (760 +70 -90 ) for the SMC under the elemental abundance constraints. We underline the importance of the wavelength dependence of the extinction curve in the near-infrared in constructing the dust model: if A λ ∝λ –γ with γ ≅ 1.6, the power-law grain-size model fails, whereas it works if γ ≅ 1.8-2.0.

  17. Thirteen years of Aeolian dust dynamics in a desert region (Negev desert, Israel): analysis of horizontal and vertical dust flux, vertical dust distribution and dust grain size

    NARCIS (Netherlands)

    Offer, Z.Y.; Goossens, D.

    2004-01-01

    At Sede Boqer (northern Negev desert, Israel), aeolian dust dynamics have been measured during the period 1988–2000. This study focuses on temporal records of the vertical and horizontal dust flux, the vertical distribution of the dust particles in the atmosphere, and the grain size of the

  18. GEMS Revealed: Spectrum Imaging of Aggregate Grains in Interplanetary Dust

    Science.gov (United States)

    Keller, L. P.; Messenger, S.; Christoffersen, R.

    2005-01-01

    Anhydrous interplanetary dust particles (IDPs) of cometary origin contain abundant materials that formed in the early solar nebula. These materials were transported outward and subsequently mixed with molecular cloud materials and presolar grains in the region where comets accreted [1]. GEMS (glass with embedded metal and sulfides) grains are a major component of these primitive anhydrous IDPs, along with crystalline Mg-rich silicates, Fe-Ni sulfides, carbonaceous material, and other trace phases. Some GEMS grains (5%) are demonstrably presolar based on their oxygen isotopic compositions [2]. However, most GEMS grains are isotopically solar and have bulk chemical compositions that are incompatible with inferred compositions of interstellar dust, suggesting a solar system origin [3]. An alternative hypothesis is that GEMS grains represent highly irradiated interstellar grains whose oxygen isotopic compositions were homogenized through processing in the interstellar medium (ISM) [4]. We have obtained the first quantitative X-ray maps (spectrum images) showing the distribution of major and minor elements in individual GEMS grains. Nanometer-scale chemical maps provide critical data required to evaluate the differing models regarding the origin of GEMS grains.

  19. COMPARTMENTALIZATION OF THE INFLAMMATORY RESPONSE TO INHALED GRAIN DUST

    Science.gov (United States)

    Interleukin (IL)-1beta, IL-6, IL-8, tumor necrosis factor (TNF)-alpha, and the secreted form of the IL-1 receptor antagonist (sIL-1RA) are involved in the inflammatory response to inhaled grain dust. Previously, we found considerable production of these cytokines in the lower...

  20. Stochastic histories of dust grains in the interstellar medium

    International Nuclear Information System (INIS)

    Liffman, K.; Clayton, D.D.

    1989-01-01

    The purpose is to study an evolving system of refractory dust grains within the Interstellar Medium (ISM). This is done via a combination of Monte Carlo processes and a system of partial differential equations, where refractory dust grains formed within supernova remnants and ejecta from high mass loss stars are subjected to the processes of sputtering and collisional fragmentation in the diffuse media and accretion within the cold molecular clouds. In order to record chemical detail, the authors take each new particle to consist of a superrefractory core plus a more massive refractory mantle. The particles are allowed to transfer to and fro between the different phases of the interstellar medium (ISM) - on a time scale of 10(exp 8) years - until either the particles are destroyed or the program finishes at a Galaxy time of 6x10(exp 9) years. The resulting chemical and size spectrum(s) are then applied to various astrophysical problems with the following results. For an ISM which has no collisional fragmentation of the dust grains, roughly 10 percent by mass of the most refractory material survives the rigors of the ISM intact, which leaves open the possibility that fossilized isotopically anomalous material may have been present within the primordial solar nebula. Stuctured or layered refractory dust grains within the model cannot explain the observed interstellar depletions of refractory material. Fragmentation due to grain-grain collisions in the diffuse phase plus the accretion of material in the molecular cloud phase can under certain circumstances cause a bimodal distribution in grain size

  1. Dust charging and charge fluctuations in a weakly collisional radio-frequency sheath at low pressure

    International Nuclear Information System (INIS)

    Piel, Alexander; Schmidt, Christian

    2015-01-01

    Models for the charging of dust particles in the bulk plasma and in the sheath region are discussed. A new model is proposed that describes collision-enhanced ion currents in the sheath. The collisions result in a substantial reduction of the negative charge of the dust. Experimental data for the dust charge in the sheath can be described by this model when a Bi-Maxwellian electron distribution is taken into account. Expressions for the dust charging rate for all considered models are presented and their influence on the rise of the kinetic dust temperature is discussed

  2. Dust grain characterization — Direct measurement of light scattering

    Science.gov (United States)

    BartoÅ, P.; Pavlů, J.

    2018-01-01

    Dust grains play a key role in dusty plasma since they interact with the plasma we can use them to study plasma itself. The grains are illuminated by visible light (e.g., a laser sheet) and the situation is captured with camera. Despite of simplicity, light scattering on similar-to-wavelength sized grains is complex phenomenon. Interaction of the electromagnetic wave with material has to be computed with respect to Maxwell equations — analytic solution is nowadays available only for several selected shapes like sphere, coated sphere, or infinite cylinder. Moreover, material constants needed for computations are usually unknown. For computation result verification and material constant determination, we designed and developed a device directly measur­ing light scattering profiles. Single dust grains are trapped in the ultrasonic field (so called "acoustic levitation") and illuminated by the laser beam. Scattered light is then measured by a photodiode mounted on rotating platform. Synchronous detection is employed for a noise reduction. This setup brings several benefits against conventional methods: (1) it works in the free air, (2) the measured grain is captured for a long time, and (3) the grain could be of arbitrary shape.

  3. Large dust grains in the wind of VY Canis Majoris

    Science.gov (United States)

    Scicluna, P.; Siebenmorgen, R.; Wesson, R.; Blommaert, J. A. D. L.; Kasper, M.; Voshchinnikov, N. V.; Wolf, S.

    2015-12-01

    Massive stars live short lives, losing large amounts of mass through their stellar wind. Their mass is a key factor determining how and when they explode as supernovae, enriching the interstellar medium with heavy elements and dust. During the red supergiant phase, mass-loss rates increase prodigiously, but the driving mechanism has proven elusive. Here we present high-contrast optical polarimetric-imaging observations of the extreme red supergiant VY Canis Majoris and its clumpy, dusty, mass-loss envelope, using the new extreme-adaptive-optics instrument SPHERE at the VLT. These observations allow us to make the first direct and unambiguous detection of submicron dust grains in the ejecta; we derive an average grain radius ~0.5 μm, 50 times larger than in the diffuse ISM, large enough to receive significant radiation pressure by photon scattering. We find evidence for varying grain sizes throughout the ejecta, highlighting the dynamical nature of the envelope. Grains with 0.5 μm sizes are likely to reach a safe distance from the eventual explosion of VY Canis Majoris; hence it may inject upwards of 10-2 M⊙ of dust into the ISM. Based on observations made with European Southern Observatory (ESO) telescopes at the La Silla Paranal Observatory under program 60.A-9368(A).Appendix A is available in electronic form at http://www.aanda.org

  4. PROPERTIES OF DUST GRAINS PROBED WITH EXTINCTION CURVES

    Energy Technology Data Exchange (ETDEWEB)

    Nozawa, Takaya; Fukugita, Masataka [Kavli Institute for the Physics and Mathematics of the Universe (WPI), University of Tokyo, Kashiwa 277-8583 (Japan)

    2013-06-10

    Modern data of the extinction curve from the ultraviolet to the near-infrared are revisited to study properties of dust grains in the Milky Way (MW) and the Small Magellanic Cloud (SMC). We confirm that the graphite-silicate mixture of grains yields the observed extinction curve with the simple power-law distribution of the grain size but with a cutoff at some maximal size: the parameters are tightly constrained to be q = 3.5 {+-} 0.2 for the size distribution a {sup -q} and the maximum radius a{sub max} = 0.24 {+-} 0.05 {mu}m, for both MW and SMC. The abundance of grains, and hence the elemental abundance, is constrained from the reddening versus hydrogen column density, E(B - V)/N{sub H}. If we take the solar elemental abundance as the standard for the MW, >56% of carbon should be in graphite dust, while it is <40% in the SMC using its available abundance estimate. This disparity and the relative abundance of C to Si explain the difference of the two curves. We find that 50%-60% of carbon may not necessarily be in graphite but in the amorphous or glassy phase. Iron may also be in the metallic phase or up to {approx}80% in magnetite rather than in silicates, so that the Mg/Fe ratio in astronomical olivine is arbitrary. With these substitutions, the parameters of the grain size remain unchanged. The mass density of dust grains relative to hydrogen is {rho}{sub dust}/{rho}{sub H}= 1 / (120{sup +10}{sub -16}) for the MW and 1 / (760{sup +70}{sub -90}) for the SMC under the elemental abundance constraints. We underline the importance of the wavelength dependence of the extinction curve in the near-infrared in constructing the dust model: if A{sub {lambda}}{proportional_to}{lambda}{sup -{gamma}} with {gamma} {approx_equal} 1.6, the power-law grain-size model fails, whereas it works if {gamma} {approx_equal} 1.8-2.0.

  5. Laboratory Studies of the Optical Properties and Condensation Processes of Cosmic Dust Grains

    Science.gov (United States)

    Abbas, M. M.; Craven, P. D.; Spann, J. F.; Tankosic, D.; LeClair, A.; West, E.; Sheldon, R.; Witherow, W. K.; Gallagher, D. L.; Adrian, M. L.

    2002-01-01

    A laboratory facility for conducting a variety of experiments on single isolated dust particles of astrophysical interest levitated in an electrodynamics balance has been developed at NASA/Marshall Space Flight Center. The objective of the research is to employ this experimental technique for studies of the physical and optical properties of individual cosmic dust grains of 0.1-100 micron size in controlled pressure/temperatures environments simulating astrophysical conditions. The physical and optical properties of the analogs of interstellar and interplanetary dust grains of known composition and size distribution will be investigated by this facility. In particular, we will carry out three classes of experiments to study the micro-physics of cosmic dust grains. (1) Charge characteristics of micron size single dust grains to determine the photoelectric efficiencies, yields, and equilibrium potentials when exposed to UV radiation. (2) Infrared optical properties of dust particles (extinction coefficients and scattering phase functions) in the 1-30 micron region using infrared diode lasers and measuring the scattered radiation. (3) Condensation experiments to investigate the condensation of volatile gases on colder nucleated particles in dense interstellar clouds and lower planetary atmospheres. The condensation experiments will involve levitated nucleus dust grains of known composition and initial mass (or m/q ratio), cooled to a temperature and pressure (or scaled pressure) simulating the astrophysical conditions, and injection of a volatile gas at a higher temperature from a controlled port. The increase in the mass due to condensation on the particle will be monitored as a function of the dust particle temperature and the partial pressure of the injected volatile gas. The measured data will permit determination of the sticking coefficients of volatile gases and growth rates of dust particles of astrophysical interest. Some preliminary results based on

  6. Dust charging processes with a Cairns-Tsallis distribution function with negative ions

    International Nuclear Information System (INIS)

    Abid, A. A.; Khan, M. Z.; Yap, S. L.; Terças, H.; Mahmood, S.

    2016-01-01

    Dust grain charging processes are presented in a non-Maxwellian dusty plasma following the Cairns-Tsallis (q, α)–distribution, whose constituents are the electrons, as well as the positive/negative ions and negatively charged dust grains. For this purpose, we have solved the current balance equation for a negatively charged dust grain to achieve an equilibrium state value (viz., q d  = constant) in the presence of Cairns-Tsallis (q, α)–distribution. In fact, the current balance equation becomes modified due to the Boltzmannian/streaming distributed negative ions. It is numerically found that the relevant plasma parameters, such as the spectral indexes q and α, the positive ion-to-electron temperature ratio, and the negative ion streaming speed (U 0 ) significantly affect the dust grain surface potential. It is also shown that in the limit q → 1 the Cairns-Tsallis reduces to the Cairns distribution; for α = 0 the Cairns-Tsallis distribution reduces to pure Tsallis distribution and the latter reduces to Maxwellian distribution for q → 1 and α = 0

  7. Dust charging processes with a Cairns-Tsallis distribution function with negative ions

    Energy Technology Data Exchange (ETDEWEB)

    Abid, A. A., E-mail: abidaliabid1@hotmail.com [Applied Physics Department, Federal Urdu University of Arts, Science and Technology, Islamabad Campus, Islamabad 45320 (Pakistan); Khan, M. Z., E-mail: mzk-qau@yahoo.com [Applied Physics Department, Federal Urdu University of Arts, Science and Technology, Islamabad Campus, Islamabad 45320 (Pakistan); Plasma Technology Research Center, Department of Physics, Faculty of Science, University of Malaya, Kuala Lumpur 50603 (Malaysia); Yap, S. L. [Plasma Technology Research Center, Department of Physics, Faculty of Science, University of Malaya, Kuala Lumpur 50603 (Malaysia); Terças, H., E-mail: hugo.tercas@tecnico.ul.pt [Physics of Information Group, Instituto de Telecomunicações, Av. Rovisco Pais, Lisbon 1049-001 (Portugal); Mahmood, S. [Science Place, University of Saskatchewan, Saskatoon, Saskatchewan S7N5A2 (Canada)

    2016-01-15

    Dust grain charging processes are presented in a non-Maxwellian dusty plasma following the Cairns-Tsallis (q, α)–distribution, whose constituents are the electrons, as well as the positive/negative ions and negatively charged dust grains. For this purpose, we have solved the current balance equation for a negatively charged dust grain to achieve an equilibrium state value (viz., q{sub d} = constant) in the presence of Cairns-Tsallis (q, α)–distribution. In fact, the current balance equation becomes modified due to the Boltzmannian/streaming distributed negative ions. It is numerically found that the relevant plasma parameters, such as the spectral indexes q and α, the positive ion-to-electron temperature ratio, and the negative ion streaming speed (U{sub 0}) significantly affect the dust grain surface potential. It is also shown that in the limit q → 1 the Cairns-Tsallis reduces to the Cairns distribution; for α = 0 the Cairns-Tsallis distribution reduces to pure Tsallis distribution and the latter reduces to Maxwellian distribution for q → 1 and α = 0.

  8. Stochastic histories of dust grains in the interstellar medium

    International Nuclear Information System (INIS)

    Liffman, K.

    1988-01-01

    The purpose of this thesis is to study an evolving system of SU-perNOva CONdensateS (SUNOCONS) within the Interstellar Medium (ISM). This is done via a Monte Carlo process where refractory dust grains formed within supernova remnants are subjected to the processes of sputtering and collisional fragmentation in the diffuse phase and accretion within the cold molecular cloud phase. In order to record chemical detail, we take each new particle to consist of a superrefractory core plus a more massive refractory mantle. The particles are allowed to transfer to and from between the different phases of the ISM until either the particles are destroyed or the program finishes. The resulting chemical and size spectrum(s) are then applied to various astrophysical problems with the following results: (1) after six thousand million years roughly 10 to 20% by mass of the most refractory material (Al 2 O 3 ) survives the rigors of the ISM intact, which leaves open the possibility that fossilized isotopically anomalous material may have been present within the primordial solar nebula. (2) structured or layered refractory dust grains within our model cannot explain the observed interstellar depletions of refractory material. (3) fragmentation due to grain-grain collisions in the diffuse phase plus the accretion of material in the molecular cloud phase can under certain circumstances cause a biomodal distribution in grain size

  9. Radiation condensation instability of compressional electromagnetic modes in magnetoplasmas containing charged dust impurities

    International Nuclear Information System (INIS)

    Shukla, P K; Eliasson, B; Kopp, A

    2006-01-01

    We report on an investigation into the radiation condensation (RC) instability of low-frequency (in comparison with the electron gyrofrequency) compressional electromagnetic waves in a magnetized plasma containing charged dust impurities. By using a two-fluid model, supplemented by the Faraday and Ampere laws, we derive a new dispersion relation. The latter is numerically analysed to examine the role of charged dust grains on the growth rate of the RC instability. The relevance of our investigation to density condensation in the next generation tokamak edges and on solar prominences is discussed

  10. Secondary Electron Emission from Dust and Its Effect on Charging

    Science.gov (United States)

    Saikia, B. K.; Kakati, B.; Kausik, S. S.; Bandyopadhyay, M.

    2011-11-01

    Hydrogen plasma is produced in a plasma chamber by striking discharge between incandescent tungsten filaments and the permanent magnetic cage [1], which is grounded. The magnetic cage has a full line cusped magnetic field geometry used to confine the plasma elements. A cylindrical Langmuir probe is used to study the plasma parameters in various discharge conditions. The charge accumulated on the dust particles is calculated using the capacitance model and the dust current is measured by the combination of a Faraday cup and an electrometer at different discharge conditions. It is found Secondary electron emission from dust having low emission yield effects the charging of dust particles in presence of high energetic electrons.

  11. Secondary Electron Emission from Dust and Its Effect on Charging

    International Nuclear Information System (INIS)

    Saikia, B. K.; Kakati, B.; Kausik, S. S.; Bandyopadhyay, M.

    2011-01-01

    Hydrogen plasma is produced in a plasma chamber by striking discharge between incandescent tungsten filaments and the permanent magnetic cage [1], which is grounded. The magnetic cage has a full line cusped magnetic field geometry used to confine the plasma elements. A cylindrical Langmuir probe is used to study the plasma parameters in various discharge conditions. The charge accumulated on the dust particles is calculated using the capacitance model and the dust current is measured by the combination of a Faraday cup and an electrometer at different discharge conditions. It is found Secondary electron emission from dust having low emission yield effects the charging of dust particles in presence of high energetic electrons.

  12. A Wealth of Dust Grains in Quasar Winds

    Science.gov (United States)

    2007-01-01

    [figure removed for brevity, see original site] Click on image for larger poster version This plot of data captured by NASA's Spitzer Space Telescope reveals dust entrained in the winds rushing away from a quasar, or growing black hole. The quasar, called PG2112+059, is located deep inside a galaxy 8 billion light-years away. Astronomers believe the dust might have been forged in the winds, which would help explain where dust in the very early universe came from. The data were captured by Spitzer's infrared spectrograph, an instrument that splits apart light from the quasar into a spectrum that reveals telltale signs of different minerals. Each type of mineral, or dust grain, has a unique signature, as can be seen in the graph, or spectrum, above. The strongest features are from the mineral amorphous olivine, or glass (purple); the mineral forsterite found in sand (blue); and the mineral corundum found in rubies (light blue). The detection of forsterite and corundum is highly unusual in galaxies without quasars. Therefore, their presence is a key clue that these grains might have been created in the quasar winds and not by dying stars as they are in our Milky Way galaxy. Forsterite is destroyed quickly in normal galaxies by radiation, so it must be continually produced to be detected by Spitzer. Corundum is hard, and provides a seed that softer, more common minerals usually cover up. As a result, corundum is usually not seen in spectra of galaxies. Since Spitzer did detect the mineral, it is probably forming in a clumpy environment, which is expected in quasar winds. All together, the signatures of the unusual minerals in this spectrum point towards dust grains forming in the winds blowing away from quasars.

  13. Grain dust and respiratory health in South African milling workers.

    Science.gov (United States)

    Bachmann, M; Myers, J E

    1991-01-01

    Respiratory health was investigated in 224 grain milling workers. The likelihood of respiratory symptoms and chronic airflow limitation was raised for workers exposed to dust independent of the effects of smoking. Smokers were more likely than non-smokers to respond to a bronchodilator at the end of the working week. Dust was more strongly associated with most abnormal outcomes than was smoking. Subjective categories of exposure to dust were more strongly associated with most abnormal outcomes than were objective categories. The prevalence of all symptoms at the time of a survey conducted at the mill six years before was higher in workers who subsequently left the mill than in those who remained employed although the differences were not significant. PMID:1931723

  14. Nasal lavage cellularity, grain dust, and airflow obstruction.

    Science.gov (United States)

    Blaski, C A; Watt, J L; Quinn, T J; Thorne, P S; Schwartz, D A

    1996-04-01

    To evaluate the clinical utility of nasal lavage (NL), we performed post-work shift NL on 172 grain workers and 78 postal worker control subjects. The grain worker group included a higher percentage of current smokers (25.7% vs 16.7%) and a lower percentage of former smokers (21.15% vs 35.9%) compared with the postal workers. The control subjects included more female workers and were slightly older than the grain workers. Compared with the postal workers, the grain workers were exposed to significantly greater concentrations of total dust (0.1 +/- 0.0 vs 6.8 +/- 1.4 mg/m3; mean +/- SEM) and total endotoxin (4.3 +/- 0.8 vs 2,372.4 +/- 653.8 endotoxin units/m3). NL from gain workers showed a higher concentration of total cells (55,000 +/- 14,000 vs 25,000 +/- 5,000 cells per milliliter; p=0.03), a higher concentration of squamous epithelial cells (17,029.0 +/- 4,177 .0 vs 7,103.7 +/- 1,479.8 cells per milliliter; p=0.03), and a higher concentration of neutrophils (40,058.0 +/- 12,803.2 vs 17,891.0 +/- 3,822.3 cells per milliliter; p=0.10) compared with postal workers. Importantly, these differences in NL cellularity between grain workers and postal workers were observed within the three strata of smokers. To further assess the importance of total cells, squamous epithelial cells, and neutrophils in the NL fluid of grain workers, we investigated the relationship between these cell concentrations and (1) measures of dust and endotoxin exposure during the work shift. (2) spirometric measures of airflow obtained immediately before the NL, and (3) work-related respiratory symptoms. The concentration of total cells, the concentration of squamous epithelial cells, or the concentration of neutrophils in the NL was not associated with ambient levels of dust or endotoxin, with baseline or cross-shift changes in lung function, or with work-related respiratory symptoms. These findings suggest that increased NL cellularity may be seen in workers exposed to high dust levels

  15. The destruction and growth of dust grains in interstellar space

    International Nuclear Information System (INIS)

    Barlow, M.J.

    1978-01-01

    The processes governing the destruction and growth of dust grains in interstellar space are investigated with a view to establishing the conditions required for the existence of ice mantles. In this paper sputtering by particles with energies in the eV to GeV range is considered. Previous sputtering yield estimates which were based on theoretical considerations are shown to be greatly in error for incident particle energies of less than 1 keV. Empirical formulae for the sputtering threshold energy and the sputtering yield are derived from the extensive experimental data available. The sputtering of grains in H II regions, in the inter-cloud medium, and in shock waves produced by cloud-cloud collisions and by supernova remnants, is investigated. Of these, supernova remnants are shown to be the most important, leading to lifetimes of approximately 2 x 10 8 yr for ice grains and between 5 to 20 x 10 8 yr for refractory grains. Destruction rates are estimated for grains bombarded by MeV and GeV cosmic rays. It is shown that collision cascade sputtering dominates evaporative sputtering produced by thermal spikes. It is also shown that even if all electron excitation energy loss in a grain material could be transferred to the lattice particles, the observed cosmic ray flux spectrum could not cause significant destruction of ice grains. (author)

  16. Effects of grain size distribution on the interstellar dust mass growth

    OpenAIRE

    Hirashita, Hiroyuki; Kuo, Tzu-Ming

    2011-01-01

    Grain growth by the accretion of metals in interstellar clouds (called `grain growth') could be one of the dominant processes that determine the dust content in galaxies. The importance of grain size distribution for the grain growth is demonstrated in this paper. First, we derive an analytical formula that gives the grain size distribution after the grain growth in individual clouds for any initial grain size distribution. The time-scale of the grain growth is very sensitive to grain size di...

  17. Modulation instability of ion thermal waves in a pair-ion plasma containing charged dust impurities

    International Nuclear Information System (INIS)

    Sabry, R.

    2008-01-01

    Modulation instability of ion thermal waves (ITWs) is investigated in a plasma composed of positive and negative ions as well as a fraction of stationary charged (positive or negative) dust impurities. For this purpose, a linear dispersion relation and a nonlinear Schroedinger equation are derived. The latter admits localized envelope solitary wave solutions of bright (pulses) and dark (holes, voids) type. The envelope soliton depends on the intrinsic plasma parameters. It is found that modulation instability of ITWs is significantly affected by the presence of positively/negatively charged dust grains. The findings of this investigation should be useful in understanding the stable electrostatic wave packet acceleration mechanisms in pair-ion plasma, and also enhances our knowledge on the occurrence of instability associated to the existence of charged dust impurities in pair-ion plasmas. Our results should be of relevance for laboratory plasmas.

  18. Pentoxifylline does not alter the response to inhaled grain dust.

    Science.gov (United States)

    Jagielo, P J; Watt, J L; Quinn, T J; Knapp, H R; Schwartz, D A

    1997-05-01

    Pentoxifylline (PTX) has been shown to reduce sepsis-induced neutrophil sequestration in the lung and inhibit endotoxin-mediated release of tumor necrosis factor-alpha (TNF-alpha). Previously, we have shown that endotoxin appears to be the principal agent in grain dust causing airway inflammation and airflow obstruction following grain dust inhalation. To determine whether PTX affects the physiologic and inflammatory events following acute grain dust inhalation, 10 healthy, nonsmoking subjects with normal airway reactivity were treated with PTX or placebo (PL) followed by corn dust extract (CDE) inhalation (0.08 mL/kg), using a single-blinded, crossover design. Subjects received PTX (1,200 mg/d) or PL for 4 days prior to CDE inhalation and 400 mg PTX or PL on the exposure day. Both respiratory symptoms and declines in FEV1 and FVC occurred following CDE exposure in both groups, but there were no significant differences in the frequency of symptoms or percent declines from baseline in the FEV1 and FVC at any of the time points measured in the study. Elevations in peripheral blood leukocyte and neutrophil concentrations and BAL total cell, neutrophil, TNF-alpha, and interleukin-8 concentrations were measured 4 h following exposure to CDE in both the PTX- and PL-treated subjects, but no significant differences were found between treatment groups. These results suggest that pretreatment with PTX prior to inhalation of CDE, in the doses used in this study, does not alter the acute physiologic or inflammatory events following exposure to inhaled CDE.

  19. Obliquely propagating cnoidal waves in a magnetized dusty plasma with variable dust charge

    International Nuclear Information System (INIS)

    Yadav, L. L.; Sayal, V. K.

    2009-01-01

    We have studied obliquely propagating dust-acoustic nonlinear periodic waves, namely, dust-acoustic cnoidal waves, in a magnetized dusty plasma consisting of electrons, ions, and dust grains with variable dust charge. Using reductive perturbation method and appropriate boundary conditions for nonlinear periodic waves, we have derived Korteweg-de Vries (KdV) equation for the plasma. It is found that the contribution to the dispersion due to the deviation from plasma approximation is dominant for small angles of obliqueness, while for large angles of obliqueness, the dispersion due to magnetic force becomes important. The cnoidal wave solution of the KdV equation is obtained. It is found that the frequency of the cnoidal wave depends on its amplitude. The effects of the magnetic field, the angle of obliqueness, the density of electrons, the dust-charge variation and the ion-temperature on the characteristics of the dust-acoustic cnoidal wave are also discussed. It is found that in the limiting case the cnoidal wave solution reduces to dust-acoustic soliton solution.

  20. Effect of dust size distribution on ion-acoustic solitons in dusty plasmas with different dust grains

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Dong-Ning; Yang, Yang; Yan, Qiang [Northwest Normal University, College of Physics and Electronic Engineering (China); Wang, Xiao-Yun [Lanzhou Jiao Tong University, Department of Mathematics and Physics (China); Duan, Wen-Shan, E-mail: duanws@126.com [Northwest Normal University, College of Physics and Electronic Engineering (China)

    2017-02-15

    Theoretical studies are carried out for ion acoustic solitons in multicomponent nonuniform plasma considering the dust size distribution. The Korteweg−de Vries equation for ion acoustic solitons is given by using the reductive perturbation technique. Two special dust size distributions are considered. The dependences of the width and amplitude of solitons on dust size parameters are shown. It is found that the properties of a solitary wave depend on the shape of the size distribution function of dust grains.

  1. Catalysis by Dust Grains in the Solar Nebula

    Science.gov (United States)

    Kress, Monika E.; Tielens, Alexander G. G. M.

    1996-01-01

    In order to determine whether grain-catalyzed reactions played an important role in the chemistry of the solar nebula, we have applied our time-dependent model of methane formation via Fischer-Tropsch catalysis to pressures from 10(exp -5) to 1 bar and temperatures from 450 to 650 K. Under these physical conditions, the reaction 3H2 + CO yields CH4 + H2O is readily catalyzed by an iron or nickel surface, whereas the same reaction is kinetically inhibited in the gas phase. Our model results indicate that under certain nebular conditions, conversion of CO to methane could be extremely efficient in the presence of iron-nickel dust grains over timescales very short compared to the lifetime of the solar nebula.

  2. Methanol extract of grain dust shows complement fixing activity and other characteristics similar to tannic acid.

    Science.gov (United States)

    Skea, D; Broder, I

    1986-01-01

    We have found several similarities between tannic acid and grain dust extract prepared with methanol. Both formed a precipitate with IgG, and these interactions were inhibited by albumin. In addition, both preparations fixed complement; this activity was heat stable and was removed by prior adsorption of the preparations with hide powder. Adsorption with polyvinyl polypyrrolidone reduced the complement-fixing activity of tannic acid but not that of the methanol grain dust extract. The similarities between tannic acid and the methanol grain dust extract are consistent with the presence of a tannin or tanninlike material in grain dust. Images FIGURE 1. PMID:3709479

  3. Respiratory symptoms and ventilatory performance in workers exposed to grain and grain based food dusts.

    Science.gov (United States)

    Deacon, S P; Paddle, G M

    1998-05-01

    A health surveillance study of male grain food manufacturing workers used a respiratory health questionnaire and spirometry to assess the prevalence of work-related respiratory symptoms and impaired ventilatory performance. The prevalence of cough, breathlessness, wheeze and chest tightness was between 8-13% but was 20% for rhinitis. Rhinitis was the most common symptom with 37% of those reporting rhinitis describing this as work-related. A case-control analysis of workers reporting rhinitis did not identify any specific occupational activities associated with increased risk of rhinitis. Smoking habit and all respiratory symptoms apart from rhinitis had a significant effect upon ventilatory performance. Occupational exposure to raw grains, flour, ingredients and finished food was categorized as high, medium or low in either continuous or intermediate patterns. Multiple regression analysis confirmed the effects of height, age and smoking upon ventilatory performance. However, occupational exposure to grain, flour, food ingredients and cooked food dusts had no effect upon ventilatory performance. It is concluded that smoking habit is the major determinant of respiratory symptoms and impaired ventilatory function. The excess complaints of rhinitis warrant further study but it would appear that the current occupational exposure limits for grain, flour, food ingredients and cooked food dusts are adequate to protect workers against impairment of ventilatory performance.

  4. Technology and Policy for Suppressing Grain Dust Explosions in Storage Facilities

    National Research Council Canada - National Science Library

    1995-01-01

    To ensure workplace safety, grain handling facilities engage in a variety of activities to control the accumulation of grain dust, such as good housekeeping practices, pneumatic systems, and liquid additives...

  5. Relativistic Gas Drag on Dust Grains and Implications

    Energy Technology Data Exchange (ETDEWEB)

    Hoang, Thiem, E-mail: thiemhoang@kasi.re.kr [Korea Astronomy and Space Science Institute, Daejeon 34055 (Korea, Republic of); Korea University of Science and Technology, Daejeon, 34113 (Korea, Republic of)

    2017-09-20

    We study the drag force on grains moving at relativistic velocities through interstellar gas and explore its application. First, we derive a new analytical formula of the drag force at high energies and find that it is significantly reduced compared to the classical model. Second, we apply the obtained drag force to calculate the terminal velocities of interstellar grains by strong radiation sources such as supernovae and active galactic nuclei (AGNs). We find that grains can be accelerated to relativistic velocities by very luminous AGNs. We then quantify the deceleration of relativistic spacecraft proposed by the Breakthrough Starshot initiative due to gas drag on a relativistic lightsail. We find that the spacecraft’s decrease in speed is negligible because of the suppression of gas drag at relativistic velocities, suggesting that the lightsail may be open for communication during its journey to α Centauri without causing a considerable delay. Finally, we show that the damage to relativistic thin lightsails by interstellar dust is a minor effect.

  6. Trichothecene mycotoxins and their determinants in settled dust related to grain production.

    Science.gov (United States)

    Nordby, Karl-Christian; Halstensen, Anne Straumfors; Elen, Oleif; Clasen, Per-Erik; Langseth, Wenche; Kristensen, Petter; Eduard, Wijnand

    2004-01-01

    We hypothesise that inhalant exposure to mycotoxins causes developmental outcomes and certain hormone-related cancers that are associated with grain farming in an epidemiological study. The aim of the present study was to identify and validate determinants of measured trichothecene mycotoxins in grain dust as work environmental trichothecene exposure indicators. Settled grain dust was collected in 92 Norwegian farms during seasons of 1999 and 2000. Production characteristics and climatic data were studied as determinants of trichothecenes in settled dust samples obtained during the production of barley (N = 59), oats (N = 32), and spring wheat (N = 13). Median concentrations of trichothecenes in grain dust were grain dust in this study. Differences in cereal species, production properties and districts contributed less to explain mycotoxin concentrations. Fungal forecasts are validated as indicators of mycotoxin exposure of grain farmers and their use in epidemiological studies may be warranted.

  7. The role of endotoxin in grain dust exposure and airway obstruction.

    Science.gov (United States)

    Von Essen, S

    1997-05-01

    Grain dust exposure is a common cause of respiratory symptoms in grain workers, feed mill employees, and farmers. Many of these workers develop wheezing and acute and chronic bronchitis symptoms, which can be associated with obstructive changes on pulmonary function testing. It has recently been demonstrated that grain dust exposure causes neutrophilic airways inflammation and systemic symptoms related to release of interleukin-1, tumor necrosis factor, interleukin-6, and other mediators of inflammation. Although grain dust is a heterogenous substance, endotoxin has received the greatest amount of attention as a possible cause of the airway inflammation that occurs after grain dust exposure. Although endotoxin undoubtedly causes a portion of the changes seen after grain dust exposure, it is becoming clear that other substances play a role as well.

  8. SECONDARY EMISSION FROM NON-SPHERICAL DUST GRAINS WITH ROUGH SURFACES: APPLICATION TO LUNAR DUST

    International Nuclear Information System (INIS)

    Richterová, I.; Němeček, Z.; Beránek, M.; Šafránková, J.; Pavlů, J.

    2012-01-01

    Electrons impinging on a target can release secondary electrons and/or they can be scattered out of the target. It is well established that the number of escaping electrons per primary electron depends on the target composition and dimensions, the energy, and incidence angle of the primary electrons, but there are suggestions that the target's shape and surface roughness also influence the secondary emission. We present a further modification of the model of secondary electron emission from dust grains which is applied to non-spherical grains and grains with defined surface roughness. It is shown that the non-spherical grains give rise to a larger secondary electron yield, whereas the surface roughness leads to a decrease in the yield. Moreover, these effects can be distinguished: the shape effect is prominent for high primary energies, whereas the surface roughness predominantly affects the yield at the low-energy range. The calculations use the Lunar Highlands Type NU-LHT-2M simulant as a grain material and the results are compared with previously published laboratory and in situ measurements.

  9. Formation of dust grains in the ejecta of SN 1987A

    International Nuclear Information System (INIS)

    Kozasa, Takashi; Hasegawa, Hiroichi; Nomoto, Kenichi

    1989-01-01

    Formation of dust grains in the ejecta of SN 1987A is investigated on the basis of a theory of homogeneous nucleation and grain growth. The formation of dust grains in the gas ejected from a heavy element-rich mantle is considered, including the effects of latent heat released during grain growth and of radiation from the photosphere. It is shown that dust grains can condense in the heavy-element-rich mantle, and that the time of formation strongly depends on the temperature structure in the ejecta. Moreover, the formation of dust grains is retarded by the strong SN radiation field and the effect of latent heat deposited during grain growth. 41 refs

  10. Something from nothing: self-charging of identical grains

    Science.gov (United States)

    Shinbrot, Troy; Yoshimatsu, Ryuta; Nuno Araujo, Nuno; Wurm, Gerhard; Herrmann, Hans

    We investigate the electrostatic charging of an agitated bed of identical grains using simulations, mathematical modeling, and experiments. We simulate charging with a discrete-element model including electrical multipoles and find that infinitesimally small initial charges can grow exponentially rapidly. We propose a mathematical Turing model that defines conditions for exponential charging to occur and provides insights into the mechanisms involved. Finally, we confirm the predicted exponential growth in experiments using vibrated grains under microgravity, and we describe novel predicted spatiotemporal states that merit further study. I acknowledge support from NSF/DMR, award 1404792.

  11. Influence of the interaction of ions-dust grains on ion acoustic wave and dust acoustic wave

    International Nuclear Information System (INIS)

    Hua Jianjun; Liu Jinyuan; Ma Tengcai

    2004-01-01

    Based on a set of hydrodynamic equations and a linear time-dependent perturbation theory, the influence of the interaction of ions-dust grains on ion acoustic wave IAW and dust acoustic wave DAW in dusty plasma is analyzed. The results show that the interaction makes IAW more stable and DAW less stable

  12. Size Distribution and Rate of Dust Generated During Grain Elevator Handling

    Science.gov (United States)

    Dust generated during grain handling is an air pollutant that produces safety and health hazards. This study was conducted to characterize the particle size distribution (PSD) of dust generated during handling of wheat and shelled corn in the research elevator of the USDA Grain Marketing and Product...

  13. Laboratory-based grain-shape models for simulating dust infrared spectra

    NARCIS (Netherlands)

    Mutschke, H.; Min, M.; Tamanai, A.

    2009-01-01

    Context. Analysis of thermal dust emission spectra for dust mineralogy and physical grain properties depends on comparison spectra, which are either laboratory-measured infrared extinction spectra or calculated extinction cross sections based on certain grain models. Often, the agreement between

  14. Occupational asthma and IgE sensitization to grain dust.

    Science.gov (United States)

    Park, H S; Nahm, D H; Suh, C H; Kwon, O Y; Kim, K S; Lee, S W; Chung, H K

    1998-06-01

    To evaluate type I hypersensitivity to grain dust (GD), its prevalence and relationship to respiratory dysfunction, we studied clinical and immunologic features, including skin prick tests (SPT), serum specific IgE, and bronchoprovocation tests of 43 employees working in the animal feed industry. To further characterize IgE-mediated reaction, SDS-PAGE and electroblot studies were performed. Our survey revealed that 15 (34.9%) subjects had work-related skin response (> or =2+ of A/H ratio) to GD, thirteen (30.2%) had high specific IgE antibody against GD. The specific IgE antibody was detected more frequently in symptomatic workers (40%) than in asymptomatic workers (11%). Significant association was found between specific IgE antibody and atopy or smoking (pdust mite, storage mite and corn dust. Immunoblot analysis showed 8 IgE binding components within GD ranging from 13.5 to 142.5 kDa. Two bands (13.5, 33 kDa) were bound to the IgE from more than 50% of the 14 sera tested. In conclusion, these findings suggest that GD inhalation could induce IgE-mediated bronchoconstriction in exposed workers.

  15. DUST DYNAMICS IN PROTOPLANETARY DISK WINDS DRIVEN BY MAGNETOROTATIONAL TURBULENCE: A MECHANISM FOR FLOATING DUST GRAINS WITH CHARACTERISTIC SIZES

    Energy Technology Data Exchange (ETDEWEB)

    Miyake, Tomoya; Suzuki, Takeru K.; Inutsuka, Shu-ichiro, E-mail: miyake.tomoya@e.mbox.nagoya-u.ac.jp, E-mail: stakeru@nagoya-u.jp [Department of Physics, Nagoya University, Nagoya, Aichi 464-8602 (Japan)

    2016-04-10

    We investigate the dynamics of dust grains of various sizes in protoplanetary disk winds driven by magnetorotational turbulence, by simulating the time evolution of the dust grain distribution in the vertical direction. Small dust grains, which are well-coupled to the gas, are dragged upward with the upflowing gas, while large grains remain near the midplane of a disk. Intermediate-size grains float near the sonic point of the disk wind located at several scale heights from the midplane, where the grains are loosely coupled to the background gas. For the minimum mass solar nebula at 1 au, dust grains with size of 25–45 μm float around 4 scale heights from the midplane. Considering the dependence on the distance from the central star, smaller-size grains remain only in an outer region of the disk, while larger-size grains are distributed in a broader region. We also discuss the implications of our result for observations of dusty material around young stellar objects.

  16. In Situ Sampling of Relative Dust Devil Particle Loads and Their Vertical Grain Size Distributions.

    Science.gov (United States)

    Raack, Jan; Reiss, Dennis; Balme, Matthew R; Taj-Eddine, Kamal; Ori, Gian Gabriele

    2017-04-19

    During a field campaign in the Sahara Desert in southern Morocco, spring 2012, we sampled the vertical grain size distribution of two active dust devils that exhibited different dimensions and intensities. With these in situ samples of grains in the vortices, it was possible to derive detailed vertical grain size distributions and measurements of the lifted relative particle load. Measurements of the two dust devils show that the majority of all lifted particles were only lifted within the first meter (∼46.5% and ∼61% of all particles; ∼76.5 wt % and ∼89 wt % of the relative particle load). Furthermore, ∼69% and ∼82% of all lifted sand grains occurred in the first meter of the dust devils, indicating the occurrence of "sand skirts." Both sampled dust devils were relatively small (∼15 m and ∼4-5 m in diameter) compared to dust devils in surrounding regions; nevertheless, measurements show that ∼58.5% to 73.5% of all lifted particles were small enough to go into suspension (grain size classification). This relatively high amount represents only ∼0.05 to 0.15 wt % of the lifted particle load. Larger dust devils probably entrain larger amounts of fine-grained material into the atmosphere, which can have an influence on the climate. Furthermore, our results indicate that the composition of the surface, on which the dust devils evolved, also had an influence on the particle load composition of the dust devil vortices. The internal particle load structure of both sampled dust devils was comparable related to their vertical grain size distribution and relative particle load, although both dust devils differed in their dimensions and intensities. A general trend of decreasing grain sizes with height was also detected. Key Words: Mars-Dust devils-Planetary science-Desert soils-Atmosphere-Grain sizes. Astrobiology 17, xxx-xxx.

  17. Plasma flow around and charge distribution of a dust cluster in a rf discharge

    Science.gov (United States)

    Schleede, J.; Lewerentz, L.; Bronold, F. X.; Schneider, R.; Fehske, H.

    2018-04-01

    We employ a particle-in-cell Monte Carlo collision/particle-particle particle-mesh simulation to study the plasma flow around and the charge distribution of a three-dimensional dust cluster in the sheath of a low-pressure rf argon discharge. The geometry of the cluster and its position in the sheath are fixed to the experimental values, prohibiting a mechanical response of the cluster. Electrically, however, the cluster and the plasma environment, mimicking also the experimental situation, are coupled self-consistently. We find a broad distribution of the charges collected by the grains. The ion flux shows on the scale of the Debye length strong focusing and shadowing inside and outside the cluster due to the attraction of the ions to the negatively charged grains, whereas the electron flux is characterized on this scale only by a weak spatial modulation of its magnitude depending on the rf phase. On the scale of the individual dust potentials, however, the electron flux deviates in the vicinity of the cluster strongly from the laminar flow associated with the plasma sheath. It develops convection patterns to compensate for the depletion of electrons inside the dust cluster.

  18. Non-Markovian dynamics of dust charge fluctuations in dusty plasmas

    Science.gov (United States)

    Asgari, H.; Muniandy, S. V.; Ghalee, Amir; Ghalee

    2014-06-01

    Dust charge fluctuates even in steady-state uniform plasma due to the discrete nature of the charge carriers and can be described using standard Langevin equation. In this work, two possible approaches in order to introduce the memory effect in dust charging dynamics are proposed. The first part of the paper provides the generalization form of the fluctuation-dissipation relation for non-Markovian systems based on generalized Langevin equations to determine the amplitudes of the dust charge fluctuations for two different kinds of colored noises under the assumption that the fluctuation-dissipation relation is valid. In the second part of the paper, aiming for dusty plasma system out of equilibrium, the fractionalized Langevin equation is used to derive the temporal two-point correlation function of grain charge fluctuations which is shown to be non-stationary due to the dependence on both times and not the time difference. The correlation function is used to derive the amplitude of fluctuations for early transient time.

  19. Inertia-Centric Stability Analysis of a Planar Uniform Dust Molecular Cloud with Weak Neutral-Charged Dust Frictional Coupling

    Science.gov (United States)

    K. Karmakar, P.; Borah, B.

    2014-05-01

    This paper adopts an inertia-centric evolutionary model to study the excitation mechanism of new gravito-electrostatic eigenmode structures in a one-dimensional (1-D) planar self-gravitating dust molecular cloud (DMC) on the Jeans scale. A quasi-neutral multi-fluid consisting of warm electrons, warm ions, neutral gas and identical inertial cold dust grains with partial ionization is considered. The grain-charge is assumed not to vary at the fluctuation evolution time scale. The neutral gas particles form the background, which is weakly coupled with the collapsing grainy plasma mass. The gravitational decoupling of the background neutral particles is justifiable for a higher inertial mass of the grains with higher neutral population density so that the Jeans mode frequency becomes reasonably large. Its physical basis is the Jeans assumption of a self-gravitating uniform medium adopted for fiducially analytical simplification by neglecting the zero-order field. So, the equilibrium is justifiably treated initially as “homogeneous”. The efficacious inertial role of the thermal species amidst weak collisions of the neutral-charged grains is taken into account. A standard multiscale technique over the gravito-electrostatic equilibrium yields a unique pair of Korteweg-de Vries (KdV) equations. It is integrated numerically by the fourth-order Runge-Kutta method with multi-parameter variation for exact shape analyses. Interestingly, the model is conducive for the propagation of new conservative solitary spectral patterns. Their basic physics, parametric features and unique characteristics are discussed. The results go qualitatively in good correspondence with the earlier observations made by others. Tentative applications relevant to space and astrophysical environments are concisely highlighted.

  20. The effects of nedocromil sodium on the response to grain dust in West Australian grain workers.

    Science.gov (United States)

    Blainey, A D; Musk, A W; Ryan, G; Phillips, M J; Buccilli, C; Troon, S; Kidd, G

    1990-01-01

    Seasonal grain workers in Western Australia who develop respiratory symptoms after exposure to grain dust develop concomitant changes in lung function and bronchial responsiveness to methacholine. The mechanisms underlying these changes are not known. A detailed study was undertaken of seasonal grain workers in Western Australia to evaluate the effect of nedocromil sodium (Fisons, United Kingdom) on these changes to see if they could be prevented by this drug. Forty seven subjects participated. Symptoms and forced expiratory volume in one second (FEV1) were recorded before the study and before, during, and after each working shift, and bronchial responsiveness to methacholine was measured at the beginning and end of the study. Twenty three subjects received nedocromil and 22 received a placebo in a double blind design; there was no difference in baseline characteristics between the two groups. At the end of the study, no differences were found between the nedocromil and placebo groups in the prevalence of symptoms or development of new symptoms during the study. The drug had no effect on changes in methacholine PD20 or FEV1. As in previous studies, new symptoms developing during the season were more common in atopic subjects and were associated with a fall in methacholine PD20. It is concluded that nedocromil has no effect on the development of new symptoms in grain workers. The mechanisms underlying these symptoms require further study. PMID:2171630

  1. Electrostatic Charging and Particle Interactions in Microscopic Insulating Grains

    Science.gov (United States)

    Lee, Victor

    In this thesis, we experimentally investigate the electrostatic charging as well as the particle interactions in microscopic insulating grains. First, by tracking individual grains accelerated in an electric field, we quantitatively demonstrate that tribocharging of same-material grains depends on particle size. Large grains tend to charge positively, and small ones tend to charge negatively. Theories based on the transfer of trapped electrons can explain this tendency but have not been validated. Here we show that the number of trapped electrons, measured independently by a thermoluminescence technique, is orders of magnitude too small to be responsible for the amount of charge transferred. This result reveals that trapped electrons are not responsible for same-material tribocharging of dielectric particles. Second, same-material tribocharging in grains can result in important long-range electrostatic interactions. However, how these electrostatic interactions contribute to particle clustering remains elusive, primarily due to the lack of direct, detailed observations. Using a high-speed camera that falls with a stream charged grains, we observe for the first time how charged grains can undergo attractive as well as repulsive Kepler-like orbits. Charged particles can be captured in their mutual electrostatic potential and form clusters via multiple bounces. Dielectric polarization effects are directly observed, which lead to additional attractive forces and stabilize "molecule-like" arrangements of charged particles. Third, we have developed a new method to study the charge transfer of microscopic particles based on acoustic levitation techniques. This method allows us to narrow the complex problem of many-particle charging down to precise charge measurements of a single sub-millimeter particle colliding with a target plate. By simply attaching nonpolar groups onto glass surfaces, we show that the contact charging of a particle is highly dependent on

  2. The flow of interstellar dust through the solar system: the role of dust charging

    International Nuclear Information System (INIS)

    Sterken, V. J.; Altobelli, N.; Schwehm, G.; Kempf, S.; Srama, R.; Strub, P.; Gruen, E.

    2011-01-01

    Interstellar dust can enter the solar system through the relative motion of the Sun with respect to the Local Interstellar Cloud. The trajectories of the dust through the solar system are not only influenced by gravitation and solar radiation pressure forces, but also by the Lorentz forces due to the interaction of the interplanetary magnetic field with the charged dust particles. The interplanetary magnetic field changes on two major time scales: 25 days (solar rotation frequency) and 22 years (solar cycle). The short-term variability averages out for regions that are not too close (>∼2 AU) to the Sun. This interplanetary magnetic field variability causes a time-variability in the interstellar dust densities, that is correlated to the solar cycle.In this work we characterize the flow of interstellar dust through the solar system using simulations of the dust trajectories. We start from the simple case without Lorentz forces, and expand to the full simulation. We pay attention to the different ways of modeling the interplanetary magnetic field, and discuss the influence of the dust parameters on the resulting flow patterns. We also discuss the possibilities of using this modeling for prediction of dust fluxes for different space missions or planets, and we pay attention to where simplified models are justified, and where or when a full simulation, including all forces is necessary. One of the aims of this work is to understand measurements of spacecraft like Ulysses, Cassini and Stardust.

  3. Saharan dust plume charging observed over the UK

    Science.gov (United States)

    Harrison, R. Giles; Nicoll, Keri A.; Marlton, Graeme J.; Ryder, Claire L.; Bennett, Alec J.

    2018-05-01

    A plume of Saharan dust and Iberian smoke was carried across the southern UK on 16th October 2017, entrained into an Atlantic cyclone which had originated as Hurricane Ophelia. The dust plume aloft was widely noticed as it was sufficiently dense to redden the visual appearance of the sun. Time series of backscatter from ceilometers at Reading and Chilbolton show two plumes: one carried upwards to 2.5 km, and another below 800 m into the boundary layer, with a clear slot between. Steady descent of particles at about 50 cm s‑1 continued throughout the morning, and coarse mode particles reached the surface. Plumes containing dust are frequently observed to be strongly charged, often through frictional effects. This plume passed over atmospheric electric field sensors at Bristol, Chilbolton and Reading. Consistent measurements at these three sites indicated negative plume charge. The lower edge plume charge density was (‑8.0 ± 3.3) nC m‑2, which is several times greater than that typical for stratiform water clouds, implying an active in situ charge generation mechanism such as turbulent triboelectrification. A meteorological radiosonde measuring temperature and humidity was launched into the plume at 1412 UTC, specially instrumented with charge and turbulence sensors. This detected charge in the boundary layer and in the upper plume region, and strong turbulent mixing was observed throughout the atmosphere’s lowest 4 km. The clear slot region, through which particles sedimented, was anomalously dry compared with modelled values, with water clouds forming intermittently in the air beneath. Electrical aspects of dust should be included in numerical models, particularly the charge-related effects on cloud microphysical properties, to accurately represent particle behaviour and transport.

  4. Study of Charge Distribution in a Dust Beam using a Faraday Cup Assembly

    International Nuclear Information System (INIS)

    Kausik, S.S.; Dutta, P.; Chakraborty, M.; Kakati, M.; Saikia, B.K.

    2005-01-01

    A Faraday cup assembly is employed to study the charge distribution in a dust beam. The Faraday Cup scans the dust beam across its diameter and the dust particle current is noted in an Electrometer. The variation of the pico ampere current, carried by the charged dust particles in the beam, is studied with change in the gas pressure. The observations provide an insight into the variation of the charge to mass ratio in a dust beam

  5. Work Tasks as Determinants of Grain Dust and Microbial Exposure in the Norwegian Grain and Compound Feed Industry

    NARCIS (Netherlands)

    Straumfors, Anne; Heldal, Kari Kulvik; Wouters, Inge M; Eduard, Wijnand

    OBJECTIVES: The grain and compound feed industry entails inevitable risks of exposure to grain dust and its microbial content. The objective of this study was therefore to investigate task-dependent exposure differences in order to create knowledge basis for awareness and exposure reducing measures

  6. Relaxing the Small Particle Approximation for Dust-grain opacities in Carbon-star Wind Models

    OpenAIRE

    Mattsson, Lars; Höfner, Susanne

    2010-01-01

    We have computed wind models with time-dependent dust formation and grain-size dependent opacities, where (1) the problem is simplified by assuming a fixed dust-grain size, and where (2) the radiation pressure efficiency is approximated using grain sizes based on various means of the actual grain size distribution. It is shown that in critical cases, the effect of grain sizes can be significant. For well-developed winds, however, the effects on the mass-loss rate and the wind speed are small.

  7. Composition of extracts of airborne grain dusts: lectins and lymphocyte mitogens.

    Science.gov (United States)

    Olenchock, S A; Lewis, D M; Mull, J C

    1986-01-01

    Airborne grain dusts are heterogeneous materials that can elicit acute and chronic respiratory pathophysiology in exposed workers. Previous characterizations of the dusts include the identification of viable microbial contaminants, mycotoxins, and endotoxins. We provide information on the lectin-like activity of grain dust extracts and its possible biological relationship. Hemagglutination of erythrocytes and immunochemical modulation by antibody to specific lectins showed the presence of these substances in extracts of airborne dusts from barley, corn, and rye. Proliferation of normal rat splenic lymphocytes in vitro provided evidence for direct biological effects on the cells of the immune system. These data expand the knowledge of the composition of grain dusts (extracts), and suggest possible mechanisms that may contribute to respiratory disease in grain workers. PMID:3709474

  8. NUMERICAL SIMULATIONS OF SUPERNOVA DUST DESTRUCTION. I. CLOUD-CRUSHING AND POST-PROCESSED GRAIN SPUTTERING

    International Nuclear Information System (INIS)

    Silvia, Devin W.; Smith, Britton D.; Michael Shull, J.

    2010-01-01

    We investigate through hydrodynamic simulations the destruction of newly formed dust grains by sputtering in the reverse shocks of supernova (SN) remnants. Using an idealized setup of a planar shock impacting a dense, spherical clump, we implant a population of Lagrangian particles into the clump to represent a distribution of dust grains in size and composition. We then post-process the simulation output to calculate the grain sputtering for a variety of species and size distributions. We explore the parameter space appropriate for this problem by altering the overdensity of the ejecta clumps and the speed of the reverse shocks. Since radiative cooling could lower the temperature of the medium in which the dust is embedded and potentially protect the dust by slowing or halting grain sputtering, we study the effects of different cooling methods over the timescale of the simulations. In general, our results indicate that grains with radii less than 0.1 μm are sputtered to much smaller radii and often destroyed completely, while larger grains survive their interaction with the reverse shock. We also find that, for high ejecta densities, the percentage of dust that survives is strongly dependent on the relative velocity between the clump and the reverse shock, causing up to 50% more destruction for the highest velocity shocks. The fraction of dust destroyed varies widely across grain species, ranging from total destruction of Al 2 O 3 grains to minimal destruction of Fe grains (only 20% destruction in the most extreme cases). C and SiO 2 grains show moderate to strong sputtering as well, with 38% and 80% mass loss. The survival rate of grains formed by early SNe is crucial in determining whether or not they can act as the 'dust factories' needed to explain high-redshift dust.

  9. Rapid formation of large dust grains in the luminous supernova 2010jl.

    Science.gov (United States)

    Gall, Christa; Hjorth, Jens; Watson, Darach; Dwek, Eli; Maund, Justyn R; Fox, Ori; Leloudas, Giorgos; Malesani, Daniele; Day-Jones, Avril C

    2014-07-17

    The origin of dust in galaxies is still a mystery. The majority of the refractory elements are produced in supernova explosions, but it is unclear how and where dust grains condense and grow, and how they avoid destruction in the harsh environments of star-forming galaxies. The recent detection of 0.1 to 0.5 solar masses of dust in nearby supernova remnants suggests in situ dust formation, while other observations reveal very little dust in supernovae in the first few years after explosion. Observations of the spectral evolution of the bright SN 2010jl have been interpreted as pre-existing dust, dust formation or no dust at all. Here we report the rapid (40 to 240 days) formation of dust in its dense circumstellar medium. The wavelength-dependent extinction of this dust reveals the presence of very large (exceeding one micrometre) grains, which resist destruction. At later times (500 to 900 days), the near-infrared thermal emission shows an accelerated growth in dust mass, marking the transition of the dust source from the circumstellar medium to the ejecta. This provides the link between the early and late dust mass evolution in supernovae with dense circumstellar media.

  10. Solar wind radiation damage in lunar dust grains and the characteristics of the ancient solar wind

    International Nuclear Information System (INIS)

    Borg, J.; Chaumont, J.

    1980-01-01

    Current understanding of the exposure history of lunar dust grains to the ancient solar wind is reviewed, the work being based mostly on a Monte Carlo statistical code, describing the 'gardening' effects of the meteorite bombardment in the lunar regolith, and on analytical models, yielding the lifetimes of the grains against various types of destruction processes. Families of lunar dust grains are identified, and evidence is presented showing that lunar dust grains were not partially shielded from solar wind ions. Results of solar wind simulation experiments are used to interpret the thickness distribution of the amorphous coatings of solar wind radiation-damaged material observed on 1-micron lunar dust grains. It is argued that such distributions reflect the speed distribution of the ancient solar wind as averaged over periods of approximately 5000 years in duration, and that the ancient solar wind is less energetic than the present day solar wind

  11. Dust acoustic and drift waves in a non-Maxwellian dusty plasma with dust charge fluctuation

    Science.gov (United States)

    Zakir, U.; Haque, Q.; Imtiaz, N.; Qamar, A.

    2015-12-01

    > ) on the wave dispersion and instability are presented. It is found that the presence of the non-thermal electron and ion populations reduce the growth rate of the instability which arises due to the dust charging effect. In addition, the nonlinear vortex solutions are also obtained. For illustration, the results are analysed by using the dusty plasma parameters of Saturn's magnetosphere.

  12. Wool and grain dusts stimulate TNF secretion by alveolar macrophages in vitro.

    Science.gov (United States)

    Brown, D M; Donaldson, K

    1996-06-01

    The aim of the study was to investigate the ability of two organic dusts, wool and grain, and their soluble leachates to stimulate secretion of tumour necrosis factor (TNF) by rat alveolar macrophages with special reference to the role of lipopolysaccharide (LPS). Rat alveolar macrophages were isolated by bronchoalveolar lavage (BAL) and treated in vitro with whole dust, dust leachates, and a standard LPS preparation. TNF production was measured in supernatants with the L929 cell line bioassay. Both wool and grain dust samples were capable of stimulating TNF release from rat alveolar macrophages in a dose-dependent manner. The standard LPS preparation caused a dose-dependent secretion of TNF. Leachates prepared from the dusts contained LPS and also caused TNF release but leachable LPS could not account for the TNF release and it was clear that non-LPS leachable activity was present in the grain dust and that wool dust particles themselves were capable of causing release of TNF. The role of LPS in wool dust leachates was further investigated by treating peritoneal macrophages from two strains of mice, LPS responders (C3H) and LPS non-responders (C3H/HEJ), with LPS. The non-responder mouse macrophages produced very low concentrations of TNF in response to the wool dust leachates compared with the responders. LPS and other unidentified leachable substances present on the surface of grain dust, and to a lesser extent on wool dust, are a trigger for TNF release by lung macrophages. Wool dust particles themselves stimulate TNF. TNF release from macrophages could contribute to enhancement of inflammatory responses and symptoms of bronchitis and breathlessness in workers exposed to organic dusts such as wool and grain.

  13. Work Tasks as Determinants of Grain Dust and Microbial Exposure in the Norwegian Grain and Compound Feed Industry.

    Science.gov (United States)

    Straumfors, Anne; Heldal, Kari Kulvik; Wouters, Inge M; Eduard, Wijnand

    2015-07-01

    The grain and compound feed industry entails inevitable risks of exposure to grain dust and its microbial content. The objective of this study was therefore to investigate task-dependent exposure differences in order to create knowledge basis for awareness and exposure reducing measures in the Norwegian grain and compound feed industry. A total of 166 samples of airborne dust were collected by full-shift personal sampling during work in 20 grain elevators and compound feed mills during one autumn season and two winter seasons. The personal exposure to grain dust, endotoxins, β-1→3-glucans, bacteria, and fungal spores was quantified and used as individual outcomes in mixed models with worker nested in company as random effect and different departments and tasks as fixed effects. The exposure levels were highest in grain elevator departments. Exposure to endotoxins was particularly high. Tasks that represented the highest and lowest exposures varied depending on the bioaerosol component. The most important determinants for elevated dust exposure were cleaning and process controlling. Cleaning increased the dust exposure level by a factor of 2.44 of the reference, from 0.65 to 1.58mg m(-3), whereas process controlling increased the dust exposure level by a factor of 2.97, from 0.65 to 1.93mg m(-3). Process controlling was associated with significantly less grain dust exposure in compound feed mills and the combined grain elevators and compound feed mills, than in grain elevators. The exposure was reduced by a factor of 0.18 and 0.22, from 1.93 to 0.34mg m(-3) and to 0.42mg m(-3), respectively, compared with the grain elevators. Inspection/maintenance, cleaning, and grain rotation and emptying were determinants of higher exposure to both endotoxin and β-1→3-glucans. Seed winnowing was in addition a strong determinant for endotoxin, whereas mixing of animal feed implied higher β-1→3-glucan exposure. Cleaning was the only task that contributed significantly to

  14. Dexamethasone attenuates grain sorghum dust extract-induced increase in macromolecular efflux in vivo.

    Science.gov (United States)

    Akhter, S R; Ikezaki, H; Gao, X P; Rubinstein, I

    1999-05-01

    The purpose of this study was to determine whether dexamethasone attenuates grain sorghum dust extract-induced increase in macromolecular efflux from the in situ hamster cheek pouch and, if so, whether this response is specific. By using intravital microscopy, we found that an aqueous extract of grain sorghum dust elicited significant, concentration-dependent leaky site formation and increase in clearance of FITC-labeled dextran (FITC-dextran; mol mass, 70 kDa) from the in situ hamster cheek pouch (P grain sorghum dust extract- and substance P-induced increases in macromolecular efflux from the in situ hamster cheek pouch in a specific fashion.

  15. Grain sorghum dust increases macromolecular efflux from the in situ nasal mucosa.

    Science.gov (United States)

    Gao, X P

    1998-04-01

    The purpose of this study was to determine whether an aqueous extract of grain sorghum dust increases macromolecular efflux from the nasal mucosa in vivo and, if so, whether this response is mediated, in part, by substance P. Suffusion of grain sorghum dust extract on the in situ nasal mucosa of anesthetized hamsters elicits a significant increase in clearance of fluorescein isothiocyanate-labeled dextran (FITC-dextran; mol mass, 70 kDa; P grain sorghum dust elicits neurogenic plasma exudation from the in situ nasal mucosa.

  16. Effect of Different Size Dust Grains on the Properties of Solitary Waves in Space Environments

    International Nuclear Information System (INIS)

    Elwakil, S.A.; Zahran, M.A.; El-Shewy, E.K.; Abdelwahed, H.G.

    2009-01-01

    Propagation of nonlinear dust-acoustic (DA) waves in an unmagnetized collisionless dusty plasma consisting of dust grains obey power law dust size distribution and nonthermal ions are investigated. For nonlinear DA waves, a reductive perturbation method was employed to obtain a Korteweg-de Vries (KdV) equation for the first-order potential. The effects of a dust size distribution, dust radius and the non-thermal distribution of ions on the soliton amplitude, width and energy of electrostatic solitary structures are presented

  17. Nonstationary stochastic charge fluctuations of a dust particle in plasmas.

    Science.gov (United States)

    Shotorban, B

    2011-06-01

    Stochastic charge fluctuations of a dust particle that are due to discreteness of electrons and ions in plasmas can be described by a one-step process master equation [T. Matsoukas and M. Russell, J. Appl. Phys. 77, 4285 (1995)] with no exact solution. In the present work, using the system size expansion method of Van Kampen along with the linear noise approximation, a Fokker-Planck equation with an exact Gaussian solution is developed by expanding the master equation. The Gaussian solution has time-dependent mean and variance governed by two ordinary differential equations modeling the nonstationary process of dust particle charging. The model is tested via the comparison of its results to the results obtained by solving the master equation numerically. The electron and ion currents are calculated through the orbital motion limited theory. At various times of the nonstationary process of charging, the model results are in a very good agreement with the master equation results. The deviation is more significant when the standard deviation of the charge is comparable to the mean charge in magnitude.

  18. Diffusion coefficients of Fokker-Planck equation for rotating dust grains in a fusion plasma

    Science.gov (United States)

    Bakhtiyari-Ramezani, M.; Mahmoodi, J.; Alinejad, N.

    2015-11-01

    In the fusion devices, ions, H atoms, and H2 molecules collide with dust grains and exert stochastic torques which lead to small variations in angular momentum of the grain. By considering adsorption of the colliding particles, thermal desorption of H atoms and normal H2 molecules, and desorption of the recombined H2 molecules from the surface of an oblate spheroidal grain, we obtain diffusion coefficients of the Fokker-Planck equation for the distribution function of fluctuating angular momentum. Torque coefficients corresponding to the recombination mechanism show that the nonspherical dust grains may rotate with a suprathermal angular velocity.

  19. Determination of parameters for hypervelocity dust grains encountered in near-Earth space

    Science.gov (United States)

    Tanner, William G.; Maag, Carl R.; Alexander, W. Merle; Sappenfield, Patricia

    1993-01-01

    Primarily interest was in the determination of the population of micrometeoroids and space debris and interpretation of the hole size in a thin film or in a micropore foam returned from space with theoretical calculations describing the event. In order to augment the significance of the theoretical calculations of the impact event, an experiment designed to analyze the charge production due to hypervelocity impacts on thin films also produced data which described the penetration properties of micron and sub-micron sized projectiles. The thin film penetration sites in the 500 A and 1000 A aluminum films were counted and a size distribution function was derived. In the case of the very smallest dust grains, there were no independent measurements of velocities like that which existed for the larger dust grains (d(sub p) is less than or equal to 1 micron). The primary task then became to assess the relationship between the penetration hole and the particle diameter of the projectile which made the hole. The most promising means to assess the measure of the diameters of impacting grains came in the form of comparing cratering mechanics to penetration mechanics. Future experimentation will produce measurements of the cratering as opposed to the penetrating event. Particles encountered by surfaces while being flown in space will degrade that surface in a systematic manner even when the impact is with small hypervelocity particles, d(sub p) is less than or equal to 10 microns. Though not to a degree which would precipitate a catastrophic failure of a system, the degradation of the materials comprising the interconnected system will occur. It is the degradation of the optical system and the subsequent embrittlement of other materials that can lead to degradation if not to failure. It is to this end that research was conducted to compare the primary consequences for experiments which will be flown to those which have been returned.

  20. Neurogenic plasma exudation mediates grain dust-induced tissue injury in vivo.

    Science.gov (United States)

    Gao, X P; Von Essen, S; Rubinstein, I

    1997-02-01

    The purpose of this study was to determine whether an aqueous extract of grain sorghum dust (GDE) elicits neurogenic plasma exudation in the oral mucosa in vivo. Using intravital microscopy, we found that GDE elicited significant, concentration-dependent leaky site formation and an increase in clearance of fluorescein isothiocyanate-labeled dextran (FITC-dextran; mol mass 70 kDa) from the hamster cheek pouch (P grain sorghum dust elicits immediate oral mucosa inflammation in vivo.

  1. Shotgun pyrosequencing metagenomic analyses of dusts from swine confinement and grain facilities.

    Science.gov (United States)

    Boissy, Robert J; Romberger, Debra J; Roughead, William A; Weissenburger-Moser, Lisa; Poole, Jill A; LeVan, Tricia D

    2014-01-01

    Inhalation of agricultural dusts causes inflammatory reactions and symptoms such as headache, fever, and malaise, which can progress to chronic airway inflammation and associated diseases, e.g. asthma, chronic bronchitis, chronic obstructive pulmonary disease, and hypersensitivity pneumonitis. Although in many agricultural environments feed particles are the major constituent of these dusts, the inflammatory responses that they provoke are likely attributable to particle-associated bacteria, archaebacteria, fungi, and viruses. In this study, we performed shotgun pyrosequencing metagenomic analyses of DNA from dusts from swine confinement facilities or grain elevators, with comparisons to dusts from pet-free households. DNA sequence alignment showed that 19% or 62% of shotgun pyrosequencing metagenomic DNA sequence reads from swine facility or household dusts, respectively, were of swine or human origin, respectively. In contrast only 2% of such reads from grain elevator dust were of mammalian origin. These metagenomic shotgun reads of mammalian origin were excluded from our analyses of agricultural dust microbiota. The ten most prevalent bacterial taxa identified in swine facility compared to grain elevator or household dust were comprised of 75%, 16%, and 42% gram-positive organisms, respectively. Four of the top five swine facility dust genera were assignable (Clostridium, Lactobacillus, Ruminococcus, and Eubacterium, ranging from 4% to 19% relative abundance). The relative abundances of these four genera were lower in dust from grain elevators or pet-free households. These analyses also highlighted the predominance in swine facility dust of Firmicutes (70%) at the phylum level, Clostridia (44%) at the Class level, and Clostridiales at the Order level (41%). In summary, shotgun pyrosequencing metagenomic analyses of agricultural dusts show that they differ qualitatively and quantitatively at the level of microbial taxa present, and that the bioinformatic analyses

  2. Shotgun pyrosequencing metagenomic analyses of dusts from swine confinement and grain facilities.

    Directory of Open Access Journals (Sweden)

    Robert J Boissy

    Full Text Available Inhalation of agricultural dusts causes inflammatory reactions and symptoms such as headache, fever, and malaise, which can progress to chronic airway inflammation and associated diseases, e.g. asthma, chronic bronchitis, chronic obstructive pulmonary disease, and hypersensitivity pneumonitis. Although in many agricultural environments feed particles are the major constituent of these dusts, the inflammatory responses that they provoke are likely attributable to particle-associated bacteria, archaebacteria, fungi, and viruses. In this study, we performed shotgun pyrosequencing metagenomic analyses of DNA from dusts from swine confinement facilities or grain elevators, with comparisons to dusts from pet-free households. DNA sequence alignment showed that 19% or 62% of shotgun pyrosequencing metagenomic DNA sequence reads from swine facility or household dusts, respectively, were of swine or human origin, respectively. In contrast only 2% of such reads from grain elevator dust were of mammalian origin. These metagenomic shotgun reads of mammalian origin were excluded from our analyses of agricultural dust microbiota. The ten most prevalent bacterial taxa identified in swine facility compared to grain elevator or household dust were comprised of 75%, 16%, and 42% gram-positive organisms, respectively. Four of the top five swine facility dust genera were assignable (Clostridium, Lactobacillus, Ruminococcus, and Eubacterium, ranging from 4% to 19% relative abundance. The relative abundances of these four genera were lower in dust from grain elevators or pet-free households. These analyses also highlighted the predominance in swine facility dust of Firmicutes (70% at the phylum level, Clostridia (44% at the Class level, and Clostridiales at the Order level (41%. In summary, shotgun pyrosequencing metagenomic analyses of agricultural dusts show that they differ qualitatively and quantitatively at the level of microbial taxa present, and that the

  3. Ochratoxin A and citrinin loads in stored wheat grains: impact of grain dust and possible prediction using ergosterol measurement.

    Science.gov (United States)

    Tangni, E K; Pussemier, L

    2006-02-01

    Crop storage should be carried out under hygienic conditions to ensure safe products, but sometimes grain dust which has settled from previous storage may be left over and incorporated to the following stored grains. This paper describes the results obtained using a lab model developed in order to assess the impact of grain dust incorporation for its direct contribution as a contaminant but also as an inoculum in stored wheat. Settled grain dust (4 samples) released from Belgian grain storages were collected and analysed by HPLC for ergosterol, ochratoxin A (OTA) and citrinin (CIT) content. For OTA and for ergosterol, there was a high degree of variability in concentrations found in the dust samples (from 17.3-318 ng g(-1) and from 39-823 microg g(-1), respectively) whilst for CIT, the range was less significant (from 137-344 ng g(-1)). Incorporation of grain dust into wheat storage contributed to an increase in the concentrations of mycotoxins in the stored grain. Dust acts as a contaminant and as an inoculum. According to these two ways, patterns of mycotoxin generation vary with the nature of the mycotoxin, the mycotoxigenic potential of dust and the water activity of the wheat. OTA and CIT showed a very versatile image when considering the amounts of toxins produced under the selected experimental conditions. The development of a robust tool to forecast the mycotoxigenicity of dust was based on the determination of ergosterol content as a general marker of fungal biomass. Present results suggest that this predictive tool would only be valid for predicting the contamination level of CIT and OTA at reasonable moisture content (14-20%). The potential risk of having highly contaminated batches from stock to stock may thus occur and this paper discusses possible pathways leading to OTA and CIT contamination either under wet or dry storage conditions. We therefore, recommend taking precautionary measures not only by controlling and maintaining moisture at a

  4. Recommendations for reducing the effect of grain dust on the lungs. Canadian Thoracic Society Standards Committee.

    Science.gov (United States)

    Becklake, M; Broder, I; Chan-Yeung, M; Dosman, J A; Ernst, P; Herbert, F A; Kennedy, S M; Warren, P W

    1996-11-15

    To assess the appropriateness of the current Canadian standards for exposure to grain dust in the workplace. The current permissible exposure limit of 10 mg of total grain dust per cubic metre of air (expressed as mg/m3) as an 8-hour time-weighted average exposure, or a lower permissible exposure limit. Acute symptoms of grain-dust exposure, such as cough, phlegm production, wheezing and dyspnea, similar chronic symptoms, and spirometric deficits revealing obstructive or restrictive disease. Articles published from 1924 to December 1993 were identified from Index Medicus and the bibliographies of pertinent articles. Subsequent articles published from 1994 (when the recommendations were approved by the Canadian Thoracic Society Standards Committee) to June 1996 were retrieved through a search of MEDLINE, and modification of the recommendations was not found to be necessary. Studies of interest were those that linked measurements of total grain dust levels to the development of acute and chronic respiratory symptoms and changes in lung function in exposed workers. Papers on the effects of grain dust on workers in feed mills were not included because other nutrients such as animal products may have been added to the grain. Unpublished reports (e.g., to Labour Canada) were included as sources of information. A high value was placed on minimizing the biological harm that grain dust has on the lungs of grain workers. A permissible exposure limit of 5 mg/m3 would control the short-term effects of exposure to grain dust on workers. Evidence is insufficient to determine what level is needed to prevent long-term effects. The economic implications of implementing a lower permissible exposure limit have not been evaluated. The current Canadian standards for grain-dust exposure should be reviewed by Labour Canada and the grain industry. A permissible exposure level of 5 mg/m3 is recommended to control short-term effects. Further measurements that link the levels of exposure to

  5. Injurious effects of wool and grain dusts on alveolar epithelial cells and macrophages in vitro.

    Science.gov (United States)

    Brown, D M; Donaldson, K

    1991-01-01

    Epidemiological studies of workers in wool textile mills have shown a direct relation between the concentration of wool dust in the air and respiratory symptoms. Injurious effects of wool dust on the bronchial epithelium could be important in causing inflammation and irritation. A pulmonary epithelial cell line in vitro was therefore used to study the toxic effects of wool dust. Cells of the A549 epithelial cell line were labelled with 51Cr and treated with whole wool dusts and extracts of wool, after which injury was assessed. Also, the effects of grain dust, which also causes a form of airway obstruction, were studied. The epithelial injury was assessed by measuring 51Cr release from cells as an indication of lysis, and by monitoring cells which had detached from the substratum. No significant injury to A549 cells was caused by culture with any of the dusts collected from the air but surface "ledge" dust caused significant lysis at some doses. Quartz, used as a toxic control dust, caused significant lysis at the highest concentration of 100 micrograms/well. To determine whether any injurious material was soluble the dusts were incubated in saline and extracts collected. No extracts caused significant injury to epithelial cells. A similar lack of toxicity was found when 51Cr labelled control alveolar macrophages were targets for injury. Significant release of radiolabel was evident when macrophages were exposed to quartz at concentrations of 10 and 20 micrograms/well, there being no significant injury with either wool or grain dusts. These data suggest that neither wool nor grain dust produce direct injury to epithelial cells, and further studies are necessary to explain inflammation leading to respiratory symptoms in wool and grain workers. PMID:2015211

  6. Induction of histamine release in vitro from rat peritoneal mast cells by extracts of grain dust.

    Science.gov (United States)

    Warren, C P; Holford-Strevens, V

    1986-01-01

    The ability of extracts of grain dust and wheat to induce histamine release from rat peritoneal cells was investigated. Some grain dusts, with a high endotoxin content, were found to produce cytotoxic histamine release. Extract of wheat dust, with a low endotoxin release, produced noncytotoxic histamine release from peritoneal cells but not from purified mast cells. This reaction was dependent on the presence of phosphatidyl serine. The agent did not appear to be a lectin because histamine release was not enhanced by passive sensitization of mast cells with IgE. The activity occurred only over a narrow range of concentrations of the extract of wheat. The cause was unclear. PMID:2423321

  7. [The epidemiological validation of the MPEL for grain dust in the atmosphere].

    Science.gov (United States)

    Pinigin, M A; Cherepov, E M; Safiulin, A A; Petrova, I V; Mukhambetova, L Kh; Osipova, E M; Veselov, A P

    1998-01-01

    The use of calculating and gravimetric methods for examining the grain dust pollution of the ambient air at the site of an elevator determined the maximum single, mean daily, and mean annual concentrations at different distances from the source of dust emission. The mean ratio of these concentrations was 12.1:4.3:1, respectively. The calculated concentration-effect and concentration-time relationships provided evidence for the maximum single, mean daily, and mean annual allowable concentrations for grain dust in the ambient air.

  8. Inter-grain coupling and grain charge in dusty plasma Coulomb crystals

    International Nuclear Information System (INIS)

    Smith, M. A.; Goodrich, J.; Mohideen, U.; Rahman, H. U.; Rosenberg, M.; Mendis, D. A.

    1998-01-01

    We have studied the lattice structure and grain charge of dusty plasma Coulomb crystals formed in rectangular conductive grooves as a function of plasma temperature and density. The crystal appears to be made of mutually repulsive columns of grains confined by the walls of the groove. The columns are oriented along the direction of the electrode sheath electric field. A simple phenomenological model wherein the inter-grain spacing results from an attractive electric field induced dipole-dipole force balanced by a repulsive monopole Coulomb force is consistent with observed features of the Coulomb crystal

  9. Levels of fungi and mycotoxins in the samples of grain and grain dust collected from five various cereal crops in eastern Poland.

    Science.gov (United States)

    Krysińska-Traczyk, Ewa; Perkowski, Juliusz; Dutkiewicz, Jacek

    2007-01-01

    During combine harvesting of 5 various cereal crops (rye, barley, oats, buckwheat, corn) 24 samples of grain and 24 samples of settled grain dust were collected on farms located in the Lublin province of eastern Poland. The samples were examined for the concentration of total microfungi, Fusarium species, deoxynivalenol (DON), nivalenol (NIV), and ochratoxin A (OTA). Microfungi able to grow on malt agar were present in 79.2% of grain samples and in 91.7% of grain dust samples in the concentrations of 1.0-801.3x10(3) cfu/g and 1.5-12440.0x10(3) cfu/g, respectively. The concentration of microfungi in grain dust samples was significantly greater than in grain samples (pgrain samples and from 58.3% of grain dust samples in the concentrations of 0.1-375.0x10(3) cfu/g and 4.0-7,700.0x10(3) cfu/g, respectively. They were found in all samples of grain and grain dust from rye, barley and corn, but only in 0-16.7% of samples of grain and grain dust from oats and buckwheat. DON was found in 79.2% of grain samples and in 100% of grain dust samples in the concentrations of 0.001-0.18 microg/g and 0.006-0.283 microg/g, respectively. NIV was detected in 62.5% of grain samples and in 94.4% of grain dust samples in the concentrations of 0.004-0.502 microg/g and 0.005-0.339 microg/g, respectively. OTA was detected in 58.3% of grain samples and in 91.7% of grain dust samples in the concentrations of 0.00039- 0.00195 microg/g and 0.00036-0.00285 microg/g, respectively. The concentrations of DON, total fusariotoxins (DON+NIV) and OTA were significantly greater in grain dust samples than in grain samples (pgrain and dust was significantly correlated with the concentrations of DON (pgrain and dust was significantly correlated with the concentration of total fusariotoxins (pgrain dust collected from 5 various cereals on farms in eastern Poland was not large, the persistent presence of these mycotoxins in over 90% of examined samples poses a potential health risk of chronic respiratory

  10. Analytical study of spheroidal dust grains in plasma

    International Nuclear Information System (INIS)

    Zahed, H.; Mahmoodi, J.; Sobhanian, S.

    2006-01-01

    Using the modified spheroidal equations, the potential of a spheroidal conducting grain, floated in a plasma, is calculated. The electric field and capacitance for both prolate and oblate spheroidal grains are investigated. The solutions, obtained up to the second-order approximation, show that the plasma screening causes the equipotential surfaces around the grain to be more elongated or flattened than the potential spheroids of the Laplace equation. This leads to the variation of the plasma concentration around the grain

  11. Presence of specific IgG antibody to grain dust does not go with respiratory symptoms.

    Science.gov (United States)

    Park, H S; Suh, C H; Nahm, D H; Kim, H Y

    1999-02-01

    A high prevalence of work-related symptoms in relation to grain dust exposure has been reported in grain dust workers, but the role of the specific IgG antibody is unknown. To study the possible role of specific IgG (sIgG) and specific IgG4 (sIgG4) in the development of work-related symptoms, sIgG and sIgG4 subclass antibodies against grain dust antigens were determined by ELISA in sera from 43 workers and 27 non-exposed controls. They were compared with results of specific IgE antibodies, exposure intensity and the presence of respiratory symptoms. SIgG and sIgG4 antibodies were detectable in almost all sera of exposed workers, and the prevalence were significantly higher than those of controls (pgrain dust exposure and may unlikely play a role in the etiology of respiratory symptoms.

  12. Size and density sorting of dust grains in SPH simulations of protoplanetary discs

    Science.gov (United States)

    Pignatale, F. C.; Gonzalez, J.-F.; Cuello, Nicolas; Bourdon, Bernard; Fitoussi, Caroline

    2017-07-01

    The size and density of dust grains determine their response to gas drag in protoplanetary discs. Aerodynamical (size × density) sorting is one of the proposed mechanisms to explain the grain properties and chemical fractionation of chondrites. However, the efficiency of aerodynamical sorting and the location in the disc in which it could occur are still unknown. Although the effects of grain sizes and growth in discs have been widely studied, a simultaneous analysis including dust composition is missing. In this work, we present the dynamical evolution and growth of multicomponent dust in a protoplanetary disc using a 3D, two-fluid (gas+dust) smoothed particle hydrodynamics code. We find that the dust vertical settling is characterized by two phases: a density-driven phase that leads to a vertical chemical sorting of dust and a size-driven phase that enhances the amount of lighter material in the mid-plane. We also see an efficient radial chemical sorting of the dust at large scales. We find that dust particles are aerodynamically sorted in the inner disc. The disc becomes sub-solar in its Fe/Si ratio on the surface since the early stage of evolution but sub-solar Fe/Si can be also found in the outer disc-mid-plane at late stages. Aggregates in the disc mimic the physical and chemical properties of chondrites, suggesting that aerodynamical sorting played an important role in determining their final structure.

  13. Orbital-motion-limited theory of dust charging and plasma response

    International Nuclear Information System (INIS)

    Tang, Xian-Zhu; Luca Delzanno, Gian

    2014-01-01

    The foundational theory for dusty plasmas is the dust charging theory that provides the dust potential and charge arising from the dust interaction with a plasma. The most widely used dust charging theory for negatively charged dust particles is the so-called orbital motion limited (OML) theory, which predicts the dust potential and heat collection accurately for a variety of applications, but was previously found to be incapable of evaluating the dust charge and plasma response in any situation. Here, we report a revised OML formulation that is able to predict the plasma response and hence the dust charge. Numerical solutions of the new OML model show that the widely used Whipple approximation of dust charge-potential relationship agrees with OML theory in the limit of small dust radius compared with plasma Debye length, but incurs large (order-unity) deviation from the OML prediction when the dust size becomes comparable with or larger than plasma Debye length. This latter case is expected for the important application of dust particles in a tokamak plasma

  14. MULTIGRAIN: a smoothed particle hydrodynamic algorithm for multiple small dust grains and gas

    Science.gov (United States)

    Hutchison, Mark; Price, Daniel J.; Laibe, Guillaume

    2018-05-01

    We present a new algorithm, MULTIGRAIN, for modelling the dynamics of an entire population of small dust grains immersed in gas, typical of conditions that are found in molecular clouds and protoplanetary discs. The MULTIGRAIN method is more accurate than single-phase simulations because the gas experiences a backreaction from each dust phase and communicates this change to the other phases, thereby indirectly coupling the dust phases together. The MULTIGRAIN method is fast, explicit and low storage, requiring only an array of dust fractions and their derivatives defined for each resolution element.

  15. Cometary and interstellar dust grains - Analysis by ion microprobe mass spectrometry and other techniques

    Science.gov (United States)

    Zinner, Ernst

    1991-01-01

    A survey of microanalytical measurements on interplanetary dust particles (IDPs) and interstellar dust grains from primitive meteorites is presented. Ion-microprobe mass spectrometry with its capability to determine isotopic compositions of many elements on a micron spatial scale has played a special role. Examples are measurements of H, N, and O isotopes and refractory trace elements in IDPs; C, N, Mg, and Si isotopes in interstellar SiC grains; and C and N isotopes and H, N, Al, and Si concentrations in interstellar graphite grains.

  16. Ultraviolet interstellar linear polarization. I - Applicability of current dust grain models

    Science.gov (United States)

    Wolff, Michael J.; Clayton, Geoffrey C.; Meade, Marilyn R.

    1993-01-01

    UV spectropolarimetric observations yielding data on the wavelength-dependence of interstellar polarization along eight lines of sight facilitate the evaluation of dust grain models previously used to fit the extinction and polarization in the visible and IR. These models pertain to bare silicate/graphite grains, silicate cores with organic refractory mantles, silicate cores with amorphous carbon mantles, and composite grains. The eight lines-of-sight show three different interstellar polarization dependences.

  17. Gravitational collapse of charged dust shell and maximal slicing condition

    International Nuclear Information System (INIS)

    Maeda, Keiichi

    1980-01-01

    The maximal slicing condition is a good time coordinate condition qualitatively when pursuing the gravitational collapse by the numerical calculation. The analytic solution of the gravitational collapse under the maximal slicing condition is given in the case of a spherical charged dust shell and the behavior of time slices with this coordinate condition is investigated. It is concluded that under the maximal slicing condition we can pursue the gravitational collapse until the radius of the shell decreases to about 0.7 x (the radius of the event horizon). (author)

  18. Analysis of the Effect of Prevailing Weather Conditions on the Occurrence of Grain Dust Explosions.

    Science.gov (United States)

    Sanghi, Achint; Ambrose, R P Kingsly

    2016-07-27

    Grain dust explosions have been occurring in the U.S. for the past twenty years. In the past ten years, there have been an average of ten explosions a year, resulting in nine fatalities and 93 injuries. In more than half of these cases, the ignition source remains unidentified. The effect of ambient humidity on the likelihood of a dust explosion has been discussed for many years. However, no investigation into a possible link between the two has been carried out. In this study, we analyzed local weather data and grain dust explosions during the period 2006 to 2014 to measure potential relationships between the two events. The 84 analyzed explosions do not show any trend with regard to prevailing temperatures, or relative or absolute humidity. In addition, the ignition source could not be identified in 54 of the incidents. The majority of grain dust explosion incidents occurred at grain elevator facilities, where the dust generation potential was high compared with grain processing industries. Copyright© by the American Society of Agricultural Engineers.

  19. Enhanced neutrophil chemotactic activity after bronchial challenge in subjects with grain dust-induced asthma.

    Science.gov (United States)

    Park, H S; Jung, K S

    1998-03-01

    There have been few reports suggesting involvement of neutrophils in induction of bronchoconstriction after inhalation of grain dust. To understand the role of neutrophils in pathogenesis of grain dust-induced asthma. We observed serum neutrophil chemotactic activity during grain dust-bronchoprovocation tests in six asthmatic subjects with positive bronchial challenges (group I). They were compared with those of six symptomatic subjects from the same workplace with negative bronchial challenges (group II). After grain dust inhalation, serum neutrophil chemotactic activity significantly increased at 30 minutes (P = .028), and then decreased to baseline level at 240 minutes (P = .028) in five subjects of group I having isolated early asthmatic responses. Enhanced neutrophil chemotactic activity was persistent for up to 240 minutes in one asthmatic subject having both early and late asthmatic responses. There was, however, no significant change in serum neutrophil chemotactic activity during bronchial challenges in subjects of group II. Pre-incubation of sera with anti-interleukin-8 (IL-8) antibody did not affect the neutrophil chemotactic activity results of group I subjects. These results suggest that enhanced neutrophil chemotactic activity distinct from IL-8 may contribute to significant bronchoconstriction induced by grain dust.

  20. Grain size effect on Sr and Nd isotopic compositions in eolian dust. Implications for tracing dust provenance and Nd model age

    International Nuclear Information System (INIS)

    Feng Jinliang; Zhu Liping; Zhen Xiaolin; Hu Zhaoguo

    2009-01-01

    Strontium (Sr) and neodymium (Nd) isotopic compositions enable identification of dust sources and reconstruction of atmospheric dispersal pathways. The Sr and Nd isotopic compositions in eolian dust change systematically with grain size in ways not yet fully understood. This study demonstrates the grain size effect on the Sr and Nd isotopic compositions in loess and 2006 dust fall, based on analyses of seven separated grain size fractions. The analytical results indicate that Sr isotopic ratios strongly depend on the grain size fractions in samples from all types of eolian dust. In contrast, the Nd isotopic ratios exhibit little variation in loess, although they vary significantly with grain size in samples from a 2006 dust fall. Furthermore, Nd model ages tend to increase with increasing grain size in samples from all types of eolian dust. Comparatively, Sr isotopic compositions exhibit high sensitively to wind sorting, while Nd isotopic compositions show greater sensitively to dust origin. The principal cause for the different patterns of Sr and Nd isotopic composition variability with grain size appears related to the different geochemical behaviors between rubidium (Rb) and Sr, and the similar geochemical behaviors between samarium (Sm) and Nd. The Nd isotope data indicate that the various grain size fractions in loess have similar origins for each sample. In contrast, various provenance components may separate into different grain size fractions for the studied 2006 dust fall. The Sr and Nd isotope compositions further confirm that the 2006 dust fall and Pleistocene loess in Beijing have different sources. The loess deposits found in Beijing and those found on the Chinese Loess Plateau also derive from different sources. Variations between Sr and Nd isotopic compositions and Nd model ages with grain size need to be considered when directly comparing analyses of eolian dust of different grain size. (author)

  1. Size and density distribution of very small dust grains in the Barnard 5 cloud

    Science.gov (United States)

    Lis, Dariusz C.; Leung, Chun Ming

    1991-01-01

    The effects of the temperature fluctuations in small graphite grains on the energy spectrum and the IR surface brightness of an isolated dust cloud heated externally by the interstellar radiation field were investigated using a series of models based on a radiation transport computer code. This code treats self-consistently the thermal coupling between the transient heating of very small dust grains and the equilibrium heating of conventional large grains. The model results were compared with the IRAS observations of the Barnard 5 (B5) cloud, showing that the 25-micron emission of the cloud must be produced by small grains with a 6-10 A radius, which also contribute about 50 percent to the observed 12-micron emission. The remaining 12 micron flux may be produced by the polycyclic aromatic hydrocarbons. The 60-and 100-micron radiation is dominated by emission from large grains heated under equilibrium conditions.

  2. EVIDENCE FOR H{sub 2} FORMATION DRIVEN DUST GRAIN ALIGNMENT IN IC 63

    Energy Technology Data Exchange (ETDEWEB)

    Andersson, B-G; De Buizer, J.; Charcos-Llorens, M. [SOFIA Science Center, USRA, NASA Ames Research Center, M.S. N211-3 Moffett Field, CA 94035 (United States); Piirola, V. [Finnish Centre for Astronomy with ESO, University of Turku, Väisäläntie 20, FI-21500 Piikkiö (Finland); Clemens, D. P. [Institute for Astrophysical Research, Boston University, Boston, MA 02215 (United States); Uomoto, A. [Observatories of the Carnegie Institution, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Geballe, T. R. [Gemini Observatory, Northern Operations Center, 670 N. A' ohoku Place, Hilo, HI 96720 (United States); Lazarian, A.; Hoang, T. [Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, WI 53706 (United States); Vornanen, T., E-mail: bg@sofia.usra.edu [Tuorla Observatory, University of Turku, Väisäläntie 20, FI-21500 Piikkiö (Finland)

    2013-10-01

    In the interstellar medium (ISM), molecular hydrogen is expected to form almost exclusively on the surfaces of dust grains. Due to that molecule's large formation energy (–4.5 eV), several dynamical effects are likely associated with the process, including the alignment of asymmetric dust grains with the ambient magnetic field. Such aligned dust grains are, in turn, believed to cause the broadband optical/infrared polarization observed in the ISM. Here, we present the first observational evidence for grain alignment driven by H{sub 2} formation, by showing that the polarization of the light from stars behind the reflection nebula IC 63 appears to correlate with the intensity of H{sub 2} fluorescence. While our results strongly suggest a role for 'Purcell rockets' in grain alignment, additional observations are needed to conclusively confirm their role. By showing a direct connection between H{sub 2} formation and a probe of the dust characteristics, these results also provide one of the first direct confirmations of the grain-surface formation of H{sub 2}. We compare our observations to ab initio modeling based on Radiative Torque Alignment (RAT) theory.

  3. The role of endotoxin in grain dust-induced lung disease.

    Science.gov (United States)

    Schwartz, D A; Thorne, P S; Yagla, S J; Burmeister, L F; Olenchock, S A; Watt, J L; Quinn, T J

    1995-08-01

    To identify the role of endotoxin in grain dust-induced lung disease, we conducted a population-based, cross-sectional investigation among grain handlers and postal workers. The study subjects were selected by randomly sampling all grain facilities and post offices within 100 miles of Iowa City. Our study population consisted of 410 grain workers and 201 postal workers. Grain workers were found to be exposed to higher concentrations of airborne dust (p = 0.0001) and endotoxin (p = 0.0001) when compared with postal workers. Grain workers had a significantly higher prevalence of work-related (cough, phlegm, wheezing, chest tightness, and dyspnea) and chronic (usual cough or phlegm production) respiratory symptoms than postal workers. Moreover, after controlling for age, gender, and cigarette smoking status, work-related respiratory symptoms were strongly associated with the concentration of endotoxin in the bioaerosol in the work setting. The concentration of total dust in the bioaerosol was marginally related to these respiratory problems. After controlling for age, gender, and cigarette smoking status, grain workers were found to have reduced spirometric measures of airflow (FEV1, FEV1/FVC, and FEF25-75) and enhanced airway reactivity to inhaled histamine when compared with postal workers. Although the total dust concentration in the work environment appeared to have little effect on these measures of airflow obstruction, higher concentrations of endotoxin in the bioaerosol were associated with diminished measures of airflow and enhanced bronchial reactivity. Our results indicate that the concentration of endotoxin in the bioaerosol may be particularly important in the development of grain dust-induced lung disease.

  4. Cometary dust: the diversity of primitive refractory grains.

    Science.gov (United States)

    Wooden, D H; Ishii, H A; Zolensky, M E

    2017-07-13

    Comet dust is primitive and shows significant diversity. Our knowledge of the properties of primitive cometary particles has expanded significantly through microscale investigations of cosmic dust samples (anhydrous interplanetary dust particles (IDPs), chondritic porous (CP) IDPs and UltraCarbonaceous Antarctic micrometeorites, Stardust and Rosetta ), as well as through remote sensing ( Spitzer IR spectroscopy). Comet dust are aggregate particles of materials unequilibrated at submicrometre scales. We discuss the properties and processes experienced by primitive matter in comets. Primitive particles exhibit a diverse range of: structure and typology; distribution of constituents; concentration and form of carbonaceous and refractory organic matter; Mg- and Fe-contents of the silicate minerals; sulfides; existence/abundance of type II chondrule fragments; high-temperature calcium-aluminium inclusions and ameboid-olivine aggregates; and rarely occurring Mg-carbonates and magnetite, whose explanation requires aqueous alteration on parent bodies. The properties of refractory materials imply there were disc processes that resulted in different comets having particular selections of primitive materials. The diversity of primitive particles has implications for the diversity of materials in the protoplanetary disc present at the time and in the region where the comets formed.This article is part of the themed issue 'Cometary science after Rosetta'. © 2017 The Authors.

  5. Laboratory Experiments on Rotation of Micron Size Cosmic Dust Grains with Radiation

    Science.gov (United States)

    Abbas, M. M.; Craven, P. D.; Spann, J. F.; Tankosic, D.; LeClair, A.; Gallagher, D. L.; West, E.; Weingartner, J.; Witherow, W. K.

    2004-01-01

    The processes and mechanisms involved in the rotation and alignment of interstellar dust grains have been of great interest in astrophysics ever since the surprising discovery of the polarization of starlight more than half a century ago. Numerous theories, detailed mathematical models and numerical studies of grain rotation and alignment along the Galactic magnetic field have been presented in the literature. In particular, the subject of grain rotation and alignment by radiative torques has been shown to be of particular interest in recent years. However, despite many investigations, a satisfactory theoretical understanding of the processes involved in grain rotation and alignment has not been achieved. As there appears to be no experimental data available on this subject, we have carried out some unique experiments to illuminate the processes involved in rotation of dust grains in the interstellar medium. In this paper we present the results of some preliminary laboratory experiments on the rotation of individual micron/submicron size nonspherical dust grains levitated in an electrodynamic balance evacuated to pressures of approx. 10(exp -3) to 10(exp -5) torr. The particles are illuminated by laser light at 5320 A, and the grain rotation rates are obtained by analyzing the low frequency (approx. 0-100 kHz) signal of the scattered light detected by a photodiode detector. The rotation rates are compared with simple theoretical models to retrieve some basic rotational parameters. The results are examined in the light of the current theories of alignment.

  6. THE JCMT GOULD BELT SURVEY: EVIDENCE FOR DUST GRAIN EVOLUTION IN PERSEUS STAR-FORMING CLUMPS

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Michael Chun-Yuan; Francesco, J. Di; Johnstone, D.; Broekhoven-Fiene, H. [Department of Physics and Astronomy, University of Victoria, Victoria, BC, V8P 1A1 (Canada); Sadavoy, S. [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany); Hatchell, J. [Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom); Mottram, J. C.; Hogerheijde, M. R. [Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands); Kirk, H. [NRC Herzberg Astronomy and Astrophysics, 5071 West Saanich Road, Victoria, BC, V9E 2E7 (Canada); Buckle, J.; Salji, C. [Astrophysics Group, Cavendish Laboratory, J J Thomson Avenue, Cambridge, CB3 0HE (United Kingdom); Berry, D. S.; Currie, M. J.; Jenness, T. [Joint Astronomy Centre, 660 North A‘ohōkū Place, University Park, Hilo, HI-96720 (United States); Fich, M.; Tisi, S. [Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario, N2L 3G1 (Canada); Nutter, D.; Quinn, C. [School of Physics and Astronomy, Cardiff University, The Parade, Cardiff, CF24 3AA (United Kingdom); Pattle, K. [Jeremiah Horrocks Institute, University of Central Lancashire, Preston, Lancashire, PR1 2HE (United Kingdom); Pineda, J. E. [European Southern Observatory (ESO), Garching (Germany); and others

    2016-07-20

    The dust emissivity spectral index, β , is a critical parameter for deriving the mass and temperature of star-forming structures and, consequently, their gravitational stability. The β value is dependent on various dust grain properties, such as size, porosity, and surface composition, and is expected to vary as dust grains evolve. Here we present β , dust temperature, and optical depth maps of the star-forming clumps in the Perseus Molecular Cloud determined from fitting spectral energy distributions to combined Herschel and JCMT observations in the 160, 250, 350, 500, and 850 μ m bands. Most of the derived β and dust temperature values fall within the ranges of 1.0–2.7 and 8–20 K, respectively. In Perseus, we find the β distribution differs significantly from clump to clump, indicative of grain growth. Furthermore, we also see significant localized β variations within individual clumps and find low- β regions correlate with local temperature peaks, hinting at the possible origins of low- β grains. Throughout Perseus, we also see indications of heating from B stars and embedded protostars, as well evidence of outflows shaping the local landscape.

  7. The Importance of Physical Models for Deriving Dust Masses and Grain Size Distributions in Supernova Ejecta. I. Radiatively Heated Dust in the Crab Nebula

    Science.gov (United States)

    Temim, Tea; Dwek, Eli

    2013-01-01

    Recent far-infrared (IR) observations of supernova remnants (SNRs) have revealed significantly large amounts of newly condensed dust in their ejecta, comparable to the total mass of available refractory elements. The dust masses derived from these observations assume that all the grains of a given species radiate at the same temperature, regardless of the dust heating mechanism or grain radius. In this paper, we derive the dust mass in the ejecta of the Crab Nebula, using a physical model for the heating and radiation from the dust. We adopt a power-law distribution of grain sizes and two different dust compositions (silicates and amorphous carbon), and calculate the heating rate of each dust grain by the radiation from the pulsar wind nebula. We find that the grains attain a continuous range of temperatures, depending on their size and composition. The total mass derived from the best-fit models to the observed IR spectrum is 0.019-0.13 Solar Mass, depending on the assumed grain composition. We find that the power-law size distribution of dust grains is characterized by a power-law index of 3.5-4.0 and a maximum grain size larger than 0.1 micron. The grain sizes and composition are consistent with what is expected for dust grains formed in a Type IIP supernova (SN). Our derived dust mass is at least a factor of two less than the mass reported in previous studies of the Crab Nebula that assumed more simplified two-temperature models. These models also require a larger mass of refractory elements to be locked up in dust than was likely available in the ejecta. The results of this study show that a physical model resulting in a realistic distribution of dust temperatures can constrain the dust properties and affect the derived dust masses. Our study may also have important implications for deriving grain properties and mass estimates in other SNRs and for the ultimate question of whether SNe are major sources of dust in the Galactic interstellar medium and in

  8. Semi-analytic variable charge solitary waves involving dust phase-space vortices (holes)

    Energy Technology Data Exchange (ETDEWEB)

    Tribeche, Mouloud; Younsi, Smain; Amour, Rabia; Aoutou, Kamel [Plasma Physics Group, Faculty of Sciences-Physics, Theoretical Physics Laboratory, University of Bab-Ezzouar, USTHB BP 32, El Alia, Algiers 16111 (Algeria)], E-mail: mtribeche@usthb.dz

    2009-09-15

    A semi-analytic model for highly nonlinear solitary waves involving dust phase-space vortices (holes) is outlined. The variable dust charge is expressed in terms of the Lambert function and we take advantage of this transcendental function to investigate the localized structures that may occur in a dusty plasma with variable charge trapped dust particles. Our results which complement the previously published work on this problem (Schamel et al 2001 Phys. Plasmas 8 671) should be of basic interest for experiments that involve the trapping of dust particles in ultra-low-frequency dust acoustic modes.

  9. Semi-analytic variable charge solitary waves involving dust phase-space vortices (holes)

    International Nuclear Information System (INIS)

    Tribeche, Mouloud; Younsi, Smain; Amour, Rabia; Aoutou, Kamel

    2009-01-01

    A semi-analytic model for highly nonlinear solitary waves involving dust phase-space vortices (holes) is outlined. The variable dust charge is expressed in terms of the Lambert function and we take advantage of this transcendental function to investigate the localized structures that may occur in a dusty plasma with variable charge trapped dust particles. Our results which complement the previously published work on this problem (Schamel et al 2001 Phys. Plasmas 8 671) should be of basic interest for experiments that involve the trapping of dust particles in ultra-low-frequency dust acoustic modes.

  10. Large dust grains in the wind of VY Canis Majoris

    OpenAIRE

    Scicluna, P.; Siebenmorgen, R.; Wesson, R.; Blommaert, J. A. D. L; Kasper, M.; Voshchinnikov, N. V.; Wolf, S.

    2015-01-01

    Massive stars live short lives, losing large amounts of mass through their stellar wind. Their mass is a key factor determining how and when they explode as supernovae, enriching the interstellar medium with heavy elements and dust. During the red supergiant phase, mass-loss rates increase prodigiously, but the driving mechanism has proven elusive. Here we present high-contrast optical polarimetric-imaging observations of the extreme red supergiant VY Canis Majoris and its clumpy, dusty, mass...

  11. Toxigenic Fusarium spp. as determinants of trichothecene mycotoxins in settled grain dust.

    Science.gov (United States)

    Halstensen, Anne Straumfors; Nordby, Karl-Christian; Klemsdal, Sonja Sletner; Elen, Oleif; Clasen, Per-Erik; Eduard, Wijnand

    2006-12-01

    Trichothecenes are immunosuppressive mycotoxins produced mainly by Fusarium spp. and often are detected as natural contaminants of grain and other agricultural products. Exposure to trichothecenes through inhalation during grain work may represent possible health risks for grain farmers. We aimed, therefore, to investigate the level of Fusarium spp. and trichothecenes in settled grain dust collected during work on 92 Norwegian farms. Mycotoxins were determined by gas chromatography-mass spectrometry, whereas the Fusarium spp. were identified and quantified both by species-specific semiquantitative polymerase chain reaction (PCR) and by cultivation. All potential trichothecene-producing molds in the grain dust were quantified using a PCR assay specific for tri5, the gene coding for trichodiene synthase that catalyzes the first step in the trichothecene biosynthesis. We performed correlation analysis between mold-DNA and mycotoxins to assess whether the PCR-detected DNA could be used as indicators of the mycotoxins. The methodological problem of detecting small amounts of airborne mycotoxins during grain work may then be avoided. Whereas the trichothecene-producing Fusarium species in grain dust could not be identified or quantified to a sufficient extent by cultivation, all investigated Fusarium spp. could be specifically detected by PCR and quantified from the DNA agarose gel band intensities. Furthermore, we observed a strong correlation between the trichothecenes HT-2 toxin (HT-2) or T-2 toxin (T-2) and DNA specific for tri5 (r = 0.68 for HT-2 and r = 0.50 for T-2; p grain dust during work, but the use of Fusarium-DNA as indicators for trichothecenes should be used cautiously.

  12. Charge-fluctuation-induced heating of dust particles in a plasma.

    Science.gov (United States)

    Vaulina, O S; Khrapak, S A; Nefedov, A P; Petrov, O F

    1999-11-01

    Random charge fluctuations are always present in dusty plasmas due to the discrete nature of currents charging the dust particle. These fluctuations can be a reason for the heating of the dust particle system. Such unexpected heating leading to the melting of the dust crystals was observed recently in several experiments. In this paper we show by analytical evaluations and numerical simulation that charge fluctuations provide an effective source of energy and can heat the dust particles up to several eV, in conditions close to experimental ones.

  13. Laboratory Experiments on Rotation and Alignment of the Analogs of Interstellar Dust Grains by Radiation

    Science.gov (United States)

    Abbas, M. M.; Craven, P. D.; Spann, J. F.; Tankosic, D.; LeClair, A.; Gallagher, D. L.; West, E. A.; Weingartner, J. C.; Witherow, W. K.; Tielens, A. G. G. M.

    2004-01-01

    The processes and mechanisms involved in the rotation and alignment of interstellar dust grains have been of great interest in astrophysics ever since the surprising discovery of the polarization of starlight more than half a century ago. Numerous theories, detailed mathematical models, and numerical studies of grain rotation and alignment with respect to the Galactic magnetic field have been presented in the literature. In particular, the subject of grain rotation and alignment by radiative torques has been shown to be of particular interest in recent years. However, despite many investigations, a satisfactory theoretical understanding of the processes involved in subject, we have carried out some unique experiments to illuminate the processes involved in the rotation of dust grains in the interstellar medium. In this paper we present the results of some preliminary laboratory experiments on the rotation of individual micron/submicron-sized, nonspherical dust grains levitated in an electrodynamic balance evacuated to pressures of approximately 10(exp -3) to 10(exp -5) torr. The particles are illuminated by laser light at 5320 A, and the grain rotation rates are obtained by analyzing the low-frequency (approximately 0 - 100 kHz) signal of the scattered light detected by a photodiode detector. The rotation rates are compared with simple theoretical models to retrieve some basic rotational parameters. The results are examined in light of the current theories of alignment.

  14. Dust grain dynamics due to nonuniform and nonstationary high-frequency radiations in cold magnetoplasmas

    Directory of Open Access Journals (Sweden)

    A. K. Nekrasov

    2006-03-01

    Full Text Available A general nonlinear theory for low-frequency electromagnetic field generation due to high-frequency nonuniform and nonstationary electromagnetic radiations in cold, uniform, multicomponent, dusty magnetoplasmas is developed. This theory permits us to consider the nonlinear action of all waves that can exist in such plasmas. The equations are derived for the dust grain velocities in the low-frequency nonlinear electric fields arising due to the presence of electromagnetic cyclotron waves travelling along the background magnetic field. The dust grains are considered to be magnetized as well as unmagnetized. Different regimes for the dust particle dynamics, depending on the spatio-temporal change of the wave amplitudes and plasma parameters, are discussed. It is shown that induced nonlinear electric fields can have both an electrostatic and electromagnetic nature. Conditions for maximum dust acceleration are found. The results obtained may be useful for understanding the possible mechanisms of dust grain dynamics in astrophysical, cosmic and laboratory plasmas under the action of nonuniform and nonstationary electromagnetic waves.

  15. Neutrophilic respiratory tract inflammation and peripheral blood neutrophilia after grain sorghum dust extract challenge.

    Science.gov (United States)

    Von Essen, S G; O'Neill, D P; McGranaghan, S; Olenchock, S A; Rennard, S I

    1995-11-01

    To determine if inhalation of grain sorghum dust in the laboratory would cause neutrophilic upper and lower respiratory tract inflammation in human volunteers, as well as systemic signs of illness. Prospective. University of Nebraska Medical Center. Thirty normal volunteers. Inhalation challenge with 20 mL of a nebulized solution of filter-sterilized grain sorghum dust extract (GSDE). One group received prednisone, 20 mg for 2 days, prior to the challenge. Bronchoscopy with bronchoalveolar lavage (BAL) was performed 24 h after challenge, with samples collected as bronchial and alveolar fractions. Findings included visible signs of airways inflammation, quantified as the bronchitis index. The percentage of bronchial neutrophils was significantly increased in those challenged with GSDE vs the control solution, Hanks' balanced salt solution (40.3 +/- 4.5% vs 14.3 +/- 5.1%, p grain dust extract. To explain the increase in peripheral blood neutrophil counts, the capacity of the peripheral blood neutrophils to migrate in chemotaxis experiments was examined. The results demonstrate an increase in peripheral blood neutrophils and an increase in chemotactic responsiveness. Inhalation challenge with a grain dust extract causes respiratory tract inflammation and a peripheral blood neutrophilia. One reason for this may be an increase in activated peripheral blood neutrophils.

  16. H2O grain size and the amount of dust in Mars' residual North polar cap

    Science.gov (United States)

    Kieffer, H.H.

    1990-01-01

    In Mars' north polar cap the probable composition of material residual from the annual condensation cycle is a mixture of fine dust and H2O grains of comparable size and abundance. However, metamorphism of such material will gradually lower its albedo by increasing the size of the H2O grains only. If the cap is undergoing net annual sublimation (as inferred from water vapor observations), late summer observations should be of old ice with H2O grain sizes of 100 ??m or more. Ice of this granularity containing 30% fine dust has a reflectivity similar to that of dust alone; the observed albedo and computed ice grain size imply dust concentrations of 1 part per 1000 or less. The brightness of the icy areas conflicts with what would be expected for a residual cap deposited by an annual cycle similar to that observed by Viking and aged for thousands of years. The residual cap surface cannot be "old dirty' ice. It could be old, coarse, and clean; or it could be young, fine, and dirty. This brings into question both the source of the late summer water vapor and the formation rate of laminated terrain. -Author

  17. [The status of the body protective systems in children in atmospheric pollution by grain dust].

    Science.gov (United States)

    Mukhambetova, L Kh; Petrova, I V; Pinigin, M A; Leshchenko, G M; Shekhter, O V; Safiulin, A A; Astakhova, L F

    1998-01-01

    The use of noninvasive methods has revealed changes in the detoxification and immune systems in children exposed to grain dust-polluted ambient air. Impaired detoxification and immunity may be considered to be a manifestation of the common pathological mechanism responsible for reduced resistance to adverse factors and they lead to the increased risk of nonspecific infectious processes and allergy in the population.

  18. Effect of Ion Streaming on Diffusion of Dust Grains in Dissipative System

    Science.gov (United States)

    Begum, M.; Das, N.

    2018-01-01

    The presence of strong electric fields in the sheath region of laboratory complex plasma induces an ion drift and perturbs the field around dust grains. The downstream focusing of ions leads to the formation of oscillatory kind of attractive wake potential which superimpose with the normal Debye-Hückel (DH) potential. The structural properties of complex plasma and diffusion coefficient of dust grains in the presence of such a wake potential have been investigated using Langevin dynamics simulation in the subsonic regime of ion flow. The study reveals that the diffusion of dust grains is strongly affected by the ion flow, so that the diffusion changes its character in the wake potential to the DH potential dominant regimes. The dependence of the diffusion coefficient on the parameters, such as the neutral pressure, dust grain size, ion flow velocity, and Coulomb coupling parameter, have been calculated for the subsonic regime by using the Green-Kubo expression, which is based on the integrated velocity autocorrelation function. It is found that the diffusion and the structural property of the system is intimately connected with the interaction potential and significantly get affected in the presence of ion flow in the subsonic regime.

  19. Growth and sedimentation of dust grains in the primitive solar nebular

    International Nuclear Information System (INIS)

    Battaglia, A.

    1987-01-01

    Formation of the planets in the solar system is envisioned to occur via a gravitational instability in a thin layer of dust located at the midplane of the primitive solar nebula. The break-up of the dust layer gives rise to seed plants (planetesimals) that, through successive collisions, eventually form the present-day planets. This thesis addresses the problem of the formation of the dust layer, beginning with a configuration in which the dust particles are uniformly mixed with the nebula's turbulent gas. To describe the properties of turbulence in the primitive solar nebula, models by Canuto et al. (1987) and by Cabot et al. (1987) are used. The available results concerning calculation of the velocity of particles embedded in a turbulent fluid were found to be unsatisfactory; therefore, a new formalism was developed to express the latter quantity in terms of the properties of the turbulence in the fluid. Following the space-time evolution of the grains, formalism was developed that simulates the simultaneous processes of collisions and sedimentation of the dust grains in the primitive solar nebula. It is concluded that, for the model of the primitive solar nebula considered, the formation of a dust layer at midplane is very unlikely

  20. Grain Size Distribution and Health Risk Assessment of Metals in Outdoor Dust in Chengdu, Southwestern China.

    Science.gov (United States)

    Chen, Mengqin; Pi, Lu; Luo, Yan; Geng, Meng; Hu, Wenli; Li, Zhi; Su, Shijun; Gan, Zhiwei; Ding, Sanglan

    2016-04-01

    A total of 27 outdoor dust samples from roads, parks, and high spots were collected and analyzed to investigate the contamination of 11 metals (Cr, Mn, Co, Ni, Cu, Zn, As, Sr, Cd, Sb, and Pb) in Chengdu, China. The results showed that the samples from the high spots exhibited the highest heavy metal level compared with those from the roads and the parks, except for Ni, Cu, and Pb. The dust was classified into five grain size fractions. The mean loads of each grain size fraction of 11 determined metals displayed similar distribution, and the contribution of median size (63-125, 125-250, 250-500 μm) fractions accounted for more than 70% of overall heavy metal loads. The health risk posed by the determined metals to human via dust ingestion, dermal contact, and inhalation was investigated. Oral and respiratory bioaccessible parts of the metals in dust were extracted using simulated stomach solution and composite lung serum. The mean bioaccessibilities of 11 investigated metals in the gastric solution were much higher than those in the composite lung serum, especially Zn, Cd, and Pb. Ingestion was the most important exposure pathway with percentage greater than 70% for both children and adults. Risk evaluation results illustrated that children in Chengdu might suffer noncarcinogenic risk when exposed to outdoor dust. Given that the cancer risk values of Pb and Cr larger than 1 × 10(-4), potential carcinogenic risk might occur for Chengdu residents through outdoor dust intake.

  1. Variable charge dust acoustic solitary waves in a dusty plasma with a q-nonextensive electron velocity distribution

    International Nuclear Information System (INIS)

    Amour, Rabia; Tribeche, Mouloud

    2010-01-01

    A first theoretical work is presented to study variable charge dust acoustic solitons within the theoretical framework of the Tsallis statistical mechanics. Our results reveal that the spatial patterns of the variable charge solitary wave are significantly modified by electron nonextensive effects. In particular, it may be noted that for -1 d becomes more negative and the dust grains localization (accumulation) less pronounced. The electrons are locally expelled and pushed out of the region of the soliton's localization. This electron depletion becomes less effective as the electrons evolve far away from their thermal equilibrium. The case q>1 provides qualitatively opposite results: electron nonextensivity makes the solitary structure more spiky. Our results should help in providing a good fit between theoretical and experimental results.

  2. Comparison of dust related respiratory effects in Dutch and Canadian grain handling industries: a pooled analysis.

    Science.gov (United States)

    Peelen, S J; Heederik, D; Dimich-Ward, H D; Chan-Yeung, M; Kennedy, S M

    1996-08-01

    Four previously conducted epidemiological studies in more than 1200 grain workers were used to compare exposure-response relations between exposure to grain dust and respiratory health. The studies included Dutch workers from an animal feed mill and a transfer grain elevator and Canadian workers from a terminal grain elevator and the docks. Relations between forced expiratory volume in one second (FEV1) and exposure were analysed with multiple regression analysis corrected for smoking, age, and height. Exposure variables examined included cumulative and current dust exposure and the numbers of years a subject was employed in the industry. Sampling efficiencies of the Dutch and Canadian measurement techniques were compared in a pilot study. Results of this study were used to correct slopes of exposure-response relations for differences in dust fractions sampled by Dutch and Canadian personal dust samplers. Negative exposure-response relations were shown for regressions of FEV1 on cumulative and current exposure and years employed. Slopes of the exposure-response relations differed by a factor of three to five between industries, apart from results for cumulative exposure. Here the variation in slopes differed by a factor of 100, from -1 to -0.009 ml/mg.y/m3. The variation in slopes between industries reduced to between twofold to fivefold when the Dutch transfer elevator workers were not considered. There was evidence that the small exposure-response slope found for this group is caused by misclassification of exposure and a strong healthy worker effect. Alternative, but less likely explanations for the variation in slopes were differences in exposure concentrations, composition of grain dust, exposure characteristics, and measurement techniques. In conclusion, this study showed moderately similar negative exposure-response relations for four different populations from different countries, despite differences in methods of exposure assessment and exposure estimation.

  3. Airborne and Grain Dust Fungal Community Compositions Are Shaped Regionally by Plant Genotypes and Farming Practices.

    Science.gov (United States)

    Pellissier, Loïc; Oppliger, Anne; Hirzel, Alexandre H; Savova-Bianchi, Dessislava; Mbayo, Guilain; Mascher, Fabio; Kellenberger, Stefan; Niculita-Hirzel, Hélène

    2016-01-29

    Chronic exposure to airborne fungi has been associated with different respiratory symptoms and pathologies in occupational populations, such as grain workers. However, the homogeneity in the fungal species composition of these bioaerosols on a large geographical scale and the different drivers that shape these fungal communities remain unclear. In this study, the diversity of fungi in grain dust and in the aerosols released during harvesting was determined across 96 sites at a geographical scale of 560 km(2) along an elevation gradient of 500 m by tag-encoded 454 pyrosequencing of the internal transcribed spacer (ITS) sequences. Associations between the structure of fungal communities in the grain dust and different abiotic (farming system, soil characteristics, and geographic and climatic parameters) and biotic (wheat cultivar and previous crop culture) factors were explored. These analyses revealed a strong relationship between the airborne and grain dust fungal communities and showed the presence of allergenic and mycotoxigenic species in most samples, which highlights the potential contribution of these fungal species to work-related respiratory symptoms of grain workers. The farming system was the major driver of the alpha and beta phylogenetic diversity values of fungal communities. In addition, elevation and soil CaCO3 concentrations shaped the alpha diversity, whereas wheat cultivar, cropping history, and the number of freezing days per year shaped the taxonomic beta diversity of these communities. Copyright © 2016, American Society for Microbiology. All Rights Reserved.

  4. Airborne and Grain Dust Fungal Community Compositions Are Shaped Regionally by Plant Genotypes and Farming Practices

    Science.gov (United States)

    Pellissier, Loïc; Oppliger, Anne; Hirzel, Alexandre H.; Savova-Bianchi, Dessislava; Mbayo, Guilain; Mascher, Fabio; Kellenberger, Stefan

    2016-01-01

    Chronic exposure to airborne fungi has been associated with different respiratory symptoms and pathologies in occupational populations, such as grain workers. However, the homogeneity in the fungal species composition of these bioaerosols on a large geographical scale and the different drivers that shape these fungal communities remain unclear. In this study, the diversity of fungi in grain dust and in the aerosols released during harvesting was determined across 96 sites at a geographical scale of 560 km2 along an elevation gradient of 500 m by tag-encoded 454 pyrosequencing of the internal transcribed spacer (ITS) sequences. Associations between the structure of fungal communities in the grain dust and different abiotic (farming system, soil characteristics, and geographic and climatic parameters) and biotic (wheat cultivar and previous crop culture) factors were explored. These analyses revealed a strong relationship between the airborne and grain dust fungal communities and showed the presence of allergenic and mycotoxigenic species in most samples, which highlights the potential contribution of these fungal species to work-related respiratory symptoms of grain workers. The farming system was the major driver of the alpha and beta phylogenetic diversity values of fungal communities. In addition, elevation and soil CaCO3 concentrations shaped the alpha diversity, whereas wheat cultivar, cropping history, and the number of freezing days per year shaped the taxonomic beta diversity of these communities. PMID:26826229

  5. DUST PROPERTIES AND DISK STRUCTURE OF EVOLVED PROTOPLANETARY DISKS IN Cep OB2: GRAIN GROWTH, SETTLING, GAS AND DUST MASS, AND INSIDE-OUT EVOLUTION

    International Nuclear Information System (INIS)

    Sicilia-Aguilar, Aurora; Henning, Thomas; Dullemond, Cornelis P.; Bouwman, Jeroen; Sturm, Bernhard; Patel, Nimesh; Juhász, Attila

    2011-01-01

    We present Spitzer/Infrared Spectrograph spectra of 31 T Tauri stars (TTS) and IRAM/1.3 mm observations for 34 low- and intermediate-mass stars in the Cep OB2 region. Including our previously published data, we analyze 56 TTS and 3 intermediate-mass stars with silicate features in Tr 37 (∼4 Myr) and NGC 7160 (∼12 Myr). The silicate emission features are well reproduced with a mixture of amorphous (with olivine, forsterite, and silica stoichiometry) and crystalline grains (forsterite, enstatite). We explore grain size and disk structure using radiative transfer disk models, finding that most objects have suffered substantial evolution (grain growth, settling). About half of the disks show inside-out evolution, with either dust-cleared inner holes or a radially dependent dust distribution, typically with larger grains and more settling in the innermost disk. The typical strong silicate features nevertheless require the presence of small dust grains, and could be explained by differential settling according to grain size, anomalous dust distributions, and/or optically thin dust populations within disk gaps. M-type stars tend to have weaker silicate emission and steeper spectral energy distributions than K-type objects. The inferred low dust masses are in a strong contrast with the relatively high gas accretion rates, suggesting global grain growth and/or an anomalous gas-to-dust ratio. Transition disks in the Cep OB2 region display strongly processed grains, suggesting that they are dominated by dust evolution and settling. Finally, the presence of rare but remarkable disks with strong accretion at old ages reveals that some very massive disks may still survive to grain growth, gravitational instabilities, and planet formation.

  6. Reduction of airborne radioactive dust by means of a charged water spray.

    Science.gov (United States)

    Bigu, J; Grenier, M G

    1989-07-01

    An electrostatic precipitator based on charged water spray technology has been used in an underground uranium mine to control long-lived radioactive dust and short-lived aerosol concentration in a mine gallery where dust from a rock breaking/ore transportation operation was discharged. Two main sampling stations were established: one upstream of the dust precipitator and one downstream. In addition, dust samplers were placed at different locations between the dust discharge and the end of the mine gallery. Long-lived radioactive dust was measured using cascade impactors and nylon cyclone dust samplers, and measurement of the radioactivity on the samples was carried out by conventional methods. Radon and thoron progeny were estimated using standard techniques. Experiments were conducted under a variety of airflow conditions. A maximum radioactive dust reduction of about 40% (approximately 20% caused by gravitational settling) at a ventilation rate of 0.61 m3/sec was obtained as a result of the combined action of water scrubbing and electrostatic precipitation by the charged water spray electrostatic precipitator. This represents the optimum efficiency attained within the range of ventilation rates investigated. The dust reduction efficiency of the charged water spray decreased with increasing ventilation rate, i.e., decreasing air residence time, and hence, reduced dust cloud/charged water droplets mixing time.

  7. Properties and Alignment of Interstellar Dust Grains toward Type Ia Supernovae with Anomalous Polarization Curves

    Energy Technology Data Exchange (ETDEWEB)

    Hoang, Thiem, E-mail: thiemhoang@kasi.re.kr [Korea Astronomy and Space Science Institute 776, Daedeokdae-ro, Yuseong-gu, Daejeon 34055 (Korea, Republic of); Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON M5S 3H8 (Canada); Institute of Theoretical Physics, Goethe Universität Frankfurt, D-60438 Frankfurt am Main (Germany)

    2017-02-10

    Recent photometric and polarimetric observations of Type Ia supernovae (SNe Ia) show unusually low total-to-selective extinction ratios ( R {sub V} < 2) and wavelengths of maximum polarization ( λ{sub max} < 0.4 μ m) for several SNe Ia, which indicates peculiar properties of interstellar (IS) dust in the SN-hosted galaxies and/or the presence of circumstellar (CS) dust. In this paper, we use an inversion technique to infer the best-fit grain size distribution and the alignment function of interstellar grains along the lines of sight toward four SNe Ia with anomalous extinction and polarization data (SN 1986G, SN 2006X, SN 2008fp, and SN 2014J). We find that to reproduce low values of R{sub V}, a significant enhancement in the mass of small grains of radius a < 0.1 μ m is required. For SN 2014J, a simultaneous fit to its observed extinction and polarization is unsuccessful if all the data are attributed to IS dust (model 1), but a good fit is obtained when accounting for the contribution of CS dust (model 2). For SN 2008fp, our best-fit results for model 1 show that in order to reproduce an extreme value of λ{sub max} ∼ 0.15 μ m, small silicate grains must be aligned as efficiently as big grains. For this case, we suggest that strong radiation from the SN can induce efficient alignment of small grains in a nearby intervening molecular cloud via the radiative torque (RAT) mechanism. The resulting time dependence polarization from this RAT alignment model can be tested by observing at ultraviolet wavelengths.

  8. New results in the theory of dust grain alignment

    Science.gov (United States)

    Cugnon, Pierre

    1989-01-01

    Two complementary approaches are used in an attempt to propose an appropriate formulation of the solution to the problem of magnetic alignment of grains in the diffuse and/or the more denser clouds, whatever the mechanism of rotational excitation can be. The interest of such a unified formulation is mainly that the same theoretical expression for polarization can be used everywhere, allowing for easier comparisons between regions where the physical conditions are highly different. The first consists in applying a Monte-Carlo method to a limited number of representative cases, for which all the torques acting on the grain are taken into account: impulsive random torques due to direct collisions with gas atoms, to evaporation of atoms from the surface, and to exo-energetic recombinations forming hydrogen molecules, followed by violent ejections from peculiar sites; magnetic torques. Three characteristic times are associated with these torques: the collisional damping time, the time necessary to change completely the actual sites configuration narrowly bound to the correlation time of the suprathermal torque; and the magnetic damping time. The second approach starts from a heuristic point of view. It consists in a generalization of results (Cugnon, 1983; see also Purcell and Spitzer, 1971; Greenberg, 1978) obtained for thermal alignment to the suprathermal case. It appears indeed that in two extreme cases, the thermal formulation may be used after redefinition of involved times and temperatures.

  9. New results in the theory of dust grain alignment

    International Nuclear Information System (INIS)

    Cugnon, P.

    1989-01-01

    Two complementary approaches are used in an attempt to propose an appropriate formulation of the solution to the problem of magnetic alignment of grains in the diffuse and/or the more denser clouds, whatever the mechanism of rotational excitation can be. The interest of such a unified formulation is mainly that the same theoretical expression for polarization can be used everywhere, allowing for easier comparisons between regions where the physical conditions are highly different. The first consists in applying a Monte-Carlo method to a limited number of representative cases, for which all the torques acting on the grain are taken into account: impulsive random torques due to direct collisions with gas atoms, to evaporation of atoms from the surface, and to exo-energetic recombinations forming hydrogen molecules, followed by violent ejections from peculiar sites; magnetic torques. Three characteristic times are associated with these torques: the collisional damping time, the time necessary to change completely the actual sites configuration narrowly bound to the correlation time of the suprathermal torque; and the magnetic damping time. The second approach starts from a heuristic point of view. It consists in a generalization of results (Cugnon, 1983; see also Purcell and Spitzer, 1971; Greenberg, 1978) obtained for thermal alignment to the suprathermal case. It appears indeed that in two extreme cases, the thermal formulation may be used after redefinition of involved times and temperatures

  10. TEMPERATURE SPECTRA OF INTERSTELLAR DUST GRAINS HEATED BY COSMIC RAYS. I. TRANSLUCENT CLOUDS

    Energy Technology Data Exchange (ETDEWEB)

    Kalvāns, Juris, E-mail: juris.kalvans@venta.lv [Engineering Research Institute “Ventspils International Radio Astronomy Center” of Ventspils University College, Inzenieru 101, Ventspils, LV-3601 (Latvia)

    2016-06-01

    Heating of whole interstellar dust grains by cosmic-ray (CR) particles affects the gas–grain chemistry in molecular clouds by promoting molecule desorption, diffusion, and chemical reactions on grain surfaces. The frequency of such heating, f{sub T}, s{sup −1}, determines how often a certain temperature T{sub CR}, K, is reached for grains hit by CR particles. This study aims to provide astrochemists with a comprehensive and updated data set on CR-induced whole-grain heating. We present calculations of f{sub T} and T{sub CR} spectra for bare olivine grains with radius a of 0.05, 0.1, and 0.2 μ m and such grains covered with ice mantles of thickness 0.1 a and 0.3 a . Grain shape and structure effects are considered, as well as 30 CR elemental constituents with an updated energy spectrum corresponding to a translucent cloud with A{sub V} = 2 mag. Energy deposition by CRs in grain material was calculated with the srim program. We report full T{sub CR} spectra for all nine grain types and consider initial grain temperatures of 10 K and 20 K. We also provide frequencies for a range of minimum T{sub CR} values. The calculated data set can be simply and flexibly implemented in astrochemical models. The results show that, in the case of translucent clouds, the currently adopted rate for heating of whole grains to temperatures in excess of 70 K is underestimated by approximately two orders of magnitude in astrochemical numerical simulations. Additionally, grains are heated by CRs to modest temperatures (20–30 K) with intervals of a few years, which reduces the possibility of ice chemical explosions.

  11. The Influence of Abrasion on Martian Dust Grains: Evidence from a Study of Antigorite Grains

    Science.gov (United States)

    Bishop, Janice L.; Drief, Ahmed; Dyar, M. Darby

    2003-01-01

    Grinding was shown to greatly affect the structure and a number of properties of antigorite grains in a study by Drief and Nieto. Grinding is likely to influence the structure of most clay mineral grains and has been shown recently to influence the structure of kaolinite. The antigorite structure includes curved waves of layered silicate as shown by D dony et al.. Our study was performed in order to characterize in detail changes in the mineral grains resulting from grinding and to assess the influence of physical processes on clay minerals on the surface of Mars. This project includes a combination of SEM, reflectance spectroscopy and Moessbauer spectroscopy.

  12. Global dynamics of dust grains in magnetic planets

    International Nuclear Information System (INIS)

    Inarrea, Manuel; Lanchares, Victor; Palacian, Jesus F.; Pascual, Ana I.; Salas, J. Pablo; Yanguas, Patricia

    2005-01-01

    We study the dynamics of a charged particle orbiting a rotating magnetic planet. The system is modelled by the Hamiltonian of the two-body problem perturbed by an axially-symmetric potential. The perturbation consists in a magnetic dipole field and a corotational electric field. After an averaging process we arrive at a one degree of freedom Hamiltonian system for which we obtain its relative equilibria and bifurcations. It is shown that the system exhibits a complex and rich dynamics. In particular, dramatic changes in the phase flow take place in the vicinity of a circular equatorial orbit, that in the case of Saturn is located inside the E-ring

  13. Global dynamics of dust grains in magnetic planets

    Energy Technology Data Exchange (ETDEWEB)

    Inarrea, Manuel [Universidad de La Rioja, Area de Fisica Aplicada, 26006 Logrono (Spain)]. E-mail: manuel.inarrea@dq.unirioja.es; Lanchares, Victor [Universidad de La Rioja, Departamento de Matematicas y Computacion, 26004 Logrono (Spain); Palacian, Jesus F. [Universidad Publica de Navarra, Departamento de Matematica e Informatica, 31006 Pamplona (Spain); Pascual, Ana I. [Universidad de La Rioja, Departamento de Matematicas y Computacion, 26004 Logrono (Spain); Salas, J. Pablo [Universidad de La Rioja, Area de Fisica Aplicada, 26006 Logrono (Spain); Yanguas, Patricia [Universidad Publica de Navarra, Departamento de Matematica e Informatica, 31006 Pamplona (Spain)

    2005-05-02

    We study the dynamics of a charged particle orbiting a rotating magnetic planet. The system is modelled by the Hamiltonian of the two-body problem perturbed by an axially-symmetric potential. The perturbation consists in a magnetic dipole field and a corotational electric field. After an averaging process we arrive at a one degree of freedom Hamiltonian system for which we obtain its relative equilibria and bifurcations. It is shown that the system exhibits a complex and rich dynamics. In particular, dramatic changes in the phase flow take place in the vicinity of a circular equatorial orbit, that in the case of Saturn is located inside the E-ring.

  14. Charging-delay effect on longitudinal dust acoustic shock wave in strongly coupled dusty plasma

    International Nuclear Information System (INIS)

    Ghosh, Samiran; Gupta, M.R.

    2005-01-01

    Taking into account the charging-delay effect, the nonlinear propagation characteristics of longitudinal dust acoustic wave in strongly coupled collisional dusty plasma described by generalized hydrodynamic model have been investigated. In the 'hydrodynamic limit', a Korteweg-de Vries Burger (KdVB) equation with a damping term arising due to dust-neutral collision is derived in which the Burger term is proportional to the dissipation due to dust viscosity through dust-dust correlation and charging-delay-induced anomalous dissipation. On the other hand, in the 'kinetic limit', a KdVB equation with a damping term and a nonlocal nonlinear forcing term arising due to memory-dependent strong correlation effect of dust fluid is derived in which the Burger term depends only on the charging-delay-induced dissipation. Numerical solution of integrodifferential equations reveals that (i) dissipation due to dust viscosity and principally due to charging delay causes excitation of the longitudinal dust acoustic shock wave in strongly coupled dusty plasma and (ii) dust-neutral collision does not appear to play any direct role in shock formation. The condition for the generation of shock is also discussed briefly

  15. Constraints on Circumstellar Dust Grain Sizes from High Spatial Resolution Observations in the Thermal Infrared

    Science.gov (United States)

    Bloemhof, E. E.; Danen, R. M.; Gwinn, C. R.

    1996-01-01

    We describe how high spatial resolution imaging of circumstellar dust at a wavelength of about 10 micron, combined with knowledge of the source spectral energy distribution, can yield useful information about the sizes of the individual dust grains responsible for the infrared emission. Much can be learned even when only upper limits to source size are available. In parallel with high-resolution single-telescope imaging that may resolve the more extended mid-infrared sources, we plan to apply these less direct techniques to interpretation of future observations from two-element optical interferometers, where quite general arguments may be made despite only crude imaging capability. Results to date indicate a tendency for circumstellar grain sizes to be rather large compared to the Mathis-Rumpl-Nordsieck size distribution traditionally thought to characterize dust in the general interstellar medium. This may mean that processing of grains after their initial formation and ejection from circumstellar atmospheres adjusts their size distribution to the ISM curve; further mid-infrared observations of grains in various environments would help to confirm this conjecture.

  16. Nonlinear waves in viscoelastic magnetized complex astroplasmas with polarized dust-charge variations

    Directory of Open Access Journals (Sweden)

    Papari Das

    2018-01-01

    Full Text Available A nonextensive nonthermal magnetized viscoelastic astrofluid, compositionally containing nonthermal electrons and ions together with massive polarized dust micro-spherical grains of variable electric charge, is allowed to endure weakly nonlinear perturbation around its equilibrium. The nonextensivity originating from the large-scale non-local effects is included via the Tsallis thermo-statistical distribution laws describing the lighter species. Assuming the equilibrium as a homogeneous hydrostatic one, the dust polarization effects are incorporated via the conventional homogeneous polarization force law. The perturbed fluid model evolves as a unique conjugate pair of coupled extended Korteweg-de Vries (e-KdV equations. A constructed numerical tapestry shows the collective excitations of a new pair of distinct classes of nonlinear mode structures in new parametric space. The first family indicates periodic electrostatic compressive eigenmodes in the form of soliton-chains. Likewise, the second one reveals gravitational rarefactive solitary patterns. Their microphysical multi-parametric dependencies of the eigen-patterns are illustratively analyzed and bolstered. The paper ends up with some promising implications and applications in the astro-cosmo-plasmic context of wave-induced accretive triggering processes responsible for gravitationally bounded (gravito-condensed astro-structure formation, such as stellesimals, planetsimals, etc.

  17. Nonlinear waves in viscoelastic magnetized complex astroplasmas with polarized dust-charge variations

    Science.gov (United States)

    Das, Papari; Karmakar, Pralay Kumar

    2018-01-01

    A nonextensive nonthermal magnetized viscoelastic astrofluid, compositionally containing nonthermal electrons and ions together with massive polarized dust micro-spherical grains of variable electric charge, is allowed to endure weakly nonlinear perturbation around its equilibrium. The nonextensivity originating from the large-scale non-local effects is included via the Tsallis thermo-statistical distribution laws describing the lighter species. Assuming the equilibrium as a homogeneous hydrostatic one, the dust polarization effects are incorporated via the conventional homogeneous polarization force law. The perturbed fluid model evolves as a unique conjugate pair of coupled extended Korteweg-de Vries (e-KdV) equations. A constructed numerical tapestry shows the collective excitations of a new pair of distinct classes of nonlinear mode structures in new parametric space. The first family indicates periodic electrostatic compressive eigenmodes in the form of soliton-chains. Likewise, the second one reveals gravitational rarefactive solitary patterns. Their microphysical multi-parametric dependencies of the eigen-patterns are illustratively analyzed and bolstered. The paper ends up with some promising implications and applications in the astro-cosmo-plasmic context of wave-induced accretive triggering processes responsible for gravitationally bounded (gravito-condensed) astro-structure formation, such as stellesimals, planetsimals, etc.

  18. Dust exposure in workers from grain storage facilities in Costa Rica.

    Science.gov (United States)

    Rodríguez-Zamora, María G; Medina-Escobar, Lourdes; Mora, Glend; Zock, Jan-Paul; van Wendel de Joode, Berna; Mora, Ana M

    2017-08-01

    About 12 million workers are involved in the production of basic grains in Central America. However, few studies in the region have examined the occupational factors associated with inhalable dust exposure. (i) To assess the exposure to inhalable dust in workers from rice, maize, and wheat storage facilities in Costa Rica; (ii) to examine the occupational factors associated with this exposure; and (iii) to measure concentrations of respirable and thoracic particles in different areas of the storage facilities. We measured inhalable (dust concentrations in 176 personal samples collected from 136 workers of eight grain storage facilities in Costa Rica. We also measured respirable (dust particles in several areas of the storage facilities. Geometric mean (GM) and geometric standard deviation (GSD) inhalable dust concentrations were 2.0mg/m 3 and 7.8 (range=dust concentrations were associated with job category [GM for category/GM for administrative staff and other workers (95% CI)=4.4 (2.6, 7.2) for packing; 20.4 (12.3, 34.7) for dehulling; 109.6 (50.1, 234.4) for unloading in flat bed sheds; 24.0 (14.5, 39.8) for unloading in pits; and 31.6 (18.6, 52.5) for drying], and cleaning task [15.8 (95% CI: 10.0, 26.3) in workers who cleaned in addition to their regular tasks]. Higher area concentrations of thoracic dust particles were found in wheat (GM and GSD=4.3mg/m 3 and 4.5) and maize (3.0mg/m 3 and 3.9) storage facilities, and in grain drying (2.3mg/m 3 and 3.1) and unloading (1.5mg/m 3 and 4.8) areas. Operators of grain storage facilities showed elevated inhalable dust concentrations, mostly above international exposure limits. Better engineering and administrative controls are needed. Copyright © 2017 Elsevier GmbH. All rights reserved.

  19. CURVED WALLS: GRAIN GROWTH, SETTLING, AND COMPOSITION PATTERNS IN T TAURI DISK DUST SUBLIMATION FRONTS

    Energy Technology Data Exchange (ETDEWEB)

    McClure, M. K.; Calvet, N.; Hartmann, L.; Ingleby, L. [Department of Astronomy, The University of Michigan, 500 Church Street, 830 Dennison Building., Ann Arbor, MI 48109 (United States); D' Alessio, P. [Centro de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, 58089 Morelia, Michoacán (Mexico); Espaillat, C. [Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Sargent, B. [Center for Imaging Science and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623 (United States); Watson, D. M. [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States); Hernández, J., E-mail: melisma@umich.edu, E-mail: ncalvet@umich.edu, E-mail: lhartm@umich.edu, E-mail: lingleby@umich.edu, E-mail: p.dalessio@astrosmo.unam.mx, E-mail: cespaillat@cfa.harvard.edu, E-mail: baspci@rit.edu, E-mail: dmw@pas.rochester.edu, E-mail: hernandj@cida.ve [Centro de Investigaciones de Astronomía (CIDA), Mérida 5101-A (Venezuela, Bolivarian Republic of)

    2013-10-01

    The dust sublimation walls of disks around T Tauri stars represent a directly observable cross-section through the disk atmosphere and midplane. Their emission properties can probe the grain size distribution and composition of the innermost regions of the disk, where terrestrial planets form. Here we calculate the inner dust sublimation wall properties for four classical T Tauri stars with a narrow range of spectral types and inclination angles and a wide range of mass accretion rates to determine the extent to which the walls are radially curved. Best fits to the near- and mid-IR excesses are found for curved, two-layer walls in which the lower layer contains larger, hotter, amorphous pyroxene grains with Mg/(Mg+Fe) = 0.6 and the upper layer contains submicron, cooler, mixed amorphous olivine and forsterite grains. As the mass accretion rates decrease from 10{sup –8} to 10{sup –10} M{sub ☉} yr{sup –1}, the maximum grain size in the lower layer decreases from ∼3 to 0.5 μm. We attribute this to a decrease in fragmentation and turbulent support for micron-sized grains with decreasing viscous heating. The atmosphere of these disks is depleted of dust with dust-gas mass ratios 1 × 10{sup –4} of the interstellar medium (ISM) value, while the midplane is enhanced to eight times the ISM value. For all accretion rates, the wall contributes at least half of the flux in the optically thin 10 μm silicate feature. Finally, we find evidence for an iron gradient in the disk, suggestive of that found in our solar system.

  20. CURVED WALLS: GRAIN GROWTH, SETTLING, AND COMPOSITION PATTERNS IN T TAURI DISK DUST SUBLIMATION FRONTS

    International Nuclear Information System (INIS)

    McClure, M. K.; Calvet, N.; Hartmann, L.; Ingleby, L.; D'Alessio, P.; Espaillat, C.; Sargent, B.; Watson, D. M.; Hernández, J.

    2013-01-01

    The dust sublimation walls of disks around T Tauri stars represent a directly observable cross-section through the disk atmosphere and midplane. Their emission properties can probe the grain size distribution and composition of the innermost regions of the disk, where terrestrial planets form. Here we calculate the inner dust sublimation wall properties for four classical T Tauri stars with a narrow range of spectral types and inclination angles and a wide range of mass accretion rates to determine the extent to which the walls are radially curved. Best fits to the near- and mid-IR excesses are found for curved, two-layer walls in which the lower layer contains larger, hotter, amorphous pyroxene grains with Mg/(Mg+Fe) = 0.6 and the upper layer contains submicron, cooler, mixed amorphous olivine and forsterite grains. As the mass accretion rates decrease from 10 –8 to 10 –10 M ☉ yr –1 , the maximum grain size in the lower layer decreases from ∼3 to 0.5 μm. We attribute this to a decrease in fragmentation and turbulent support for micron-sized grains with decreasing viscous heating. The atmosphere of these disks is depleted of dust with dust-gas mass ratios 1 × 10 –4 of the interstellar medium (ISM) value, while the midplane is enhanced to eight times the ISM value. For all accretion rates, the wall contributes at least half of the flux in the optically thin 10 μm silicate feature. Finally, we find evidence for an iron gradient in the disk, suggestive of that found in our solar system

  1. Charging effect at grain boundaries of MoS2

    Science.gov (United States)

    Yan, Chenhui; Dong, Xi; Li, Connie H.; Li, Lian

    2018-05-01

    Grain boundaries (GBs) are inherent extended defects in chemical vapor deposited (CVD) transition metal dichalcogenide (TMD) films. Characterization of the atomic structure and electronic properties of these GBs is crucial for understanding and controlling the properties of TMDs via defect engineering. Here, we report the atomic and electronic structure of GBs in CVD grown MoS2 on epitaxial graphene/SiC(0001). Using scanning tunneling microscopy/spectroscopy, we find that GBs mostly consist of arrays of dislocation cores, where the presence of mid-gap states shifts both conduction and valence band edges by up to 1 eV. Our findings demonstrate the first charging effect near GBs in CVD grown MoS2, providing insights into the significant impact GBs can have on materials properties.

  2. Radiation Pressure Measurements on Micron-Size Individual Dust Grains

    Science.gov (United States)

    Abbas, M. M.; Craven, P. D.; Spann, J. F.; Witherow, W. K.; West, E. A.; Gallagher, D. L.; Adrian, M. L.; Fishman, G. J.; Tankosic, D.; LeClair, A.

    2003-01-01

    Measurements of electromagnetic radiation pressure have been made on individual silica (SiO2) particles levitated in an electrodynamic balance. These measurements were made by inserting single charged particles of known diameter in the 0.2- to 6.82-micron range and irradiating them from above with laser radiation focused to beam widths of approximately 175- 400 microns at ambient pressures particle due to the radiation force is balanced by the electrostatic force indicated by the compensating dc potential applied to the balance electrodes, providing a direct measure of the radiation force on the levitated particle. Theoretical calculations of the radiation pressure with a least-squares fit to the measured data yield the radiation pressure efficiencies of the particles, and comparisons with Mie scattering theory calculations provide the imaginary part of the refractive index of SiO2 and the corresponding extinction and scattering efficiencies.

  3. DELIVERY OF DUST GRAINS FROM COMET C/2013 A1 (SIDING SPRING) TO MARS

    International Nuclear Information System (INIS)

    Tricarico, Pasquale; Samarasinha, Nalin H.; Sykes, Mark V.; Li, Jian-Yang; Farnham, Tony L.; Kelley, Michael S. P.; Farnocchia, Davide; Stevenson, Rachel; Bauer, James M.; Lock, Robert E.

    2014-01-01

    Comet C/2013 A1 (Siding Spring) will have a close encounter with Mars on 2014 October 19. We model the dynamical evolution of dust grains from the time of their ejection from the comet nucleus to the close encounter with Mars, and determine the flux at Mars. Constraints on the ejection velocity from Hubble Space Telescope observations indicate that the bulk of the grains will likely miss Mars, although it is possible that a few percent of the grains with higher velocities will reach Mars, peaking approximately 90-100 minutes after the close approach of the nucleus, and consisting mostly of millimeter-radius grains ejected from the comet nucleus at a heliocentric distance of approximately 9 AU or larger. At higher velocities, younger grains from submillimeter to several millimeters can also reach Mars, although an even smaller fraction of grains is expected have these velocities, with negligible effect on the peak timing. Using NEOWISE observations of the comet, we can estimate that the maximum fluence will be of the order of 10 –7 grains m –2 . We include a detailed analysis of how the expected fluence depends on the grain density, ejection velocity, and size-frequency distribution, to account for current model uncertainties and in preparation of possible refined model values in the near future

  4. Radiation Pressure Measurements on Micron Size Individual Dust Grains

    Science.gov (United States)

    Abbas, M. M.; Craven, P.D.; Spann, J. F.; Tankosic, D.; Witherow, W. K.; LeClair, A.; West, E.; Sheldon, R.; Gallagher, D. L.; Adrian, M. L.

    2003-01-01

    Measurements of electromagnetic radiation pressure have been made on individual silica (SiO2) particles levitated in an electrodynamic balance. These measurements were made by inserting single charged particles of known diameter in the 0.2 micron to 6.82 micron range and irradiating them from above with laser radiation focused to beam-widths of approx. 175-400 micron, at ambient pressures approx. 10(exp -3) to 10(exp -4) torr. The downward displacement of the particle due to the radiation force is balanced by the electrostatic force indicated by the compensating dc potential applied to the balance electrodes, providing a direct measure of the radiation force on the levitated particle. Theoretical calculations of the radiation pressure with a least-squares fit to the measured data yield the radiation pressure efficiencies of the particles, and comparisons with Mie scattering theory calculations provide the imaginary part of the refractive index of silica and the corresponding extinction and scattering efficiencies.

  5. Measuring the Dust Grains and Distance to X Persei Via Its X-ray Halo

    Science.gov (United States)

    Smith, Randall

    2006-09-01

    We propose to observe the X-ray halo of the high mass X-ray binary pulsar X Per to measure interstellar dust grains along the line of sight (LOS) and to determine the distance to X Per. The X-ray halo is formed by scattering from grains along the LOS, which for X Per appear to be concentrated in one molecular cloud. Unlike many other X-ray halo observations, this low-absorption high-latitude sightline is well-characterized from absorption spectroscopy done with HST, Copernicus, and FUSE. This halo observation will measure the distance to the cloud and the dust size distribution in it. We will also be able to determine the distance to X Per by measuring the time delayed pulses in the X-ray halo.

  6. Secondary charging effects due to icy dust particle impacts on rocket payloads

    Directory of Open Access Journals (Sweden)

    M. Kassa

    2012-03-01

    Full Text Available We report measurements of dust currents obtained with a small probe and a larger probe during the flight of the ECOMA-4 rocket through the summer polar mesosphere. The payload included two small dust probes behind a larger dust probe located centrally at the front. For certain phases of the payload rotation, the current registered by one of the small dust probes was up to 2 times the current measured with the larger probe, even though the effective collection area of the larger probe was 4 times that of the small one. We analyze the phase dependence of the currents and their difference with a model based on the assumption that the small probe was hit by charged dust fragments produced in collisions of mesospheric dust with the payload body. Our results confirm earlier findings that secondary charge production in the collision of a noctilucent cloud/Polar Summer Mesospheric Echo (NLC/PMSE dust particle with the payload body must be several orders of magnitude larger than might be expected from laboratory studies of collisions of pure ice particles with a variety of clean surfaces. An important consequence is that for some payload configurations, one should not assume that the current measured with a detector used to study mesospheric dust is simply proportional to the number density of ambient dust particles. The higher secondary charge production may be due to the NLC/PMSE particles containing multiple meteoric smoke particles.

  7. Atomic-scale simulation of dust grain collisions: Surface chemistry and dissipation beyond existing theory

    Science.gov (United States)

    Quadery, Abrar H.; Doan, Baochi D.; Tucker, William C.; Dove, Adrienne R.; Schelling, Patrick K.

    2017-10-01

    The early stages of planet formation involve steps where submicron-sized dust particles collide to form aggregates. However, the mechanism through which millimeter-sized particles aggregate to kilometer-sized planetesimals is still not understood. Dust grain collision experiments carried out in the environment of the Earth lead to the prediction of a 'bouncing barrier' at millimeter-sizes. Theoretical models, e.g., Johnson-Kendall-Roberts and Derjaguin-Muller-Toporov theories, lack two key features, namely the chemistry of dust grain surfaces, and a mechanism for atomic-scale dissipation of energy. Moreover, interaction strengths in these models are parameterized based on experiments done in the Earth's environment. To address these issues, we performed atomic-scale simulations of collisions between nonhydroxylated and hydroxylated amorphous silica nanoparticles. We used the ReaxFF approach which enables modeling chemical reactions using an empirical potential. We found that nonhydroxylated nanograins tend to adhere with much higher probability than suggested by existing theories. By contrast, hydroxylated nanograins exhibit a strong tendency to bounce. Also, the interaction between dust grains has the characteristics of a strong chemical force instead of weak van der Waals forces. This suggests that the formation of strong chemical bonds and dissipation via internal atomic vibration may result in aggregation beyond what is expected based on our current understanding. Our results also indicate that experiments should more carefully consider surface conditions to mimic the space environment. We also report results of simulations with molten silica nanoparticles. It is found that molten particles are more likely to adhere due to viscous dissipation, which supports theories that suggest aggregation to kilometer scales might require grains to be in a molten state.

  8. Collisionless damping of dust-acoustic waves in a charge varying dusty plasma with nonextensive ions

    Energy Technology Data Exchange (ETDEWEB)

    Amour, Rabia; Tribeche, Mouloud [Faculty of Physics, Theoretical Physics Laboratory (TPL), Plasma Physics Group (PPG), University of Bab-Ezzouar, USTHB, B.P. 32, El Alia, Algiers 16111 (Algeria)

    2014-12-15

    The charge variation induced nonlinear dust-acoustic wave damping in a charge varying dusty plasma with nonextensive ions is considered. It is shown that the collisionless damping due to dust charge fluctuation causes the nonlinear dust acoustic wave propagation to be described by a damped Korteweg-de Vries (dK-dV) equation the coefficients of which depend sensitively on the nonextensive parameter q. The damping term, solely due to the dust charge variation, is affected by the ion nonextensivity. For the sake of completeness, the possible effects of nonextensivity and collisionless damping on weakly nonlinear wave packets described by the dK-dV equation are succinctly outlined by deriving a nonlinear Schrödinger-like equation with a complex nonlinear coefficient.

  9. Collisionless damping of dust-acoustic waves in a charge varying dusty plasma with nonextensive ions

    International Nuclear Information System (INIS)

    Amour, Rabia; Tribeche, Mouloud

    2014-01-01

    The charge variation induced nonlinear dust-acoustic wave damping in a charge varying dusty plasma with nonextensive ions is considered. It is shown that the collisionless damping due to dust charge fluctuation causes the nonlinear dust acoustic wave propagation to be described by a damped Korteweg-de Vries (dK-dV) equation the coefficients of which depend sensitively on the nonextensive parameter q. The damping term, solely due to the dust charge variation, is affected by the ion nonextensivity. For the sake of completeness, the possible effects of nonextensivity and collisionless damping on weakly nonlinear wave packets described by the dK-dV equation are succinctly outlined by deriving a nonlinear Schrödinger-like equation with a complex nonlinear coefficient

  10. A grain of sand or a handful of dust?

    Science.gov (United States)

    Wagner, Fabian

    2013-03-01

    The recent paper by Girod et al (2013) analyses the implications of stringent global GHG mitigation targets for the intensities of, inter alia , broad consumption categories like food, shelter and transport. This type of scenario modeling analysis and inverse reasoning helps us to better understand the potential or required contribution of changes in consumption patterns to mitigation. This is welcome because while there is a growing literature on the behavioral and consumption dimensions of mitigation, there is still no widely accepted framework for studying systematically the interactions between supply and demand, behavior and technology, production and consumption. So we are left with the question: what do we need to do exactly to stabilize GHG concentrations? Intuitively, we take our cue from Aristotelian logic: if A implies B, then in order to avoid B we had better prevent A. At this level it is clear that we need either to decarbonize our energy systems to start with, or to suck out CO2 from the atmosphere. When multiple causes are at work, however, our neat Aristotelian picture is no longer appropriate (Cartwright 2003). Leaving capturing and storage aside, we need to decarbonize our systems, but we also need to reduce the energy intensity, change our personal habits, eat less meat, use more public transportation, etc. What is the right balance between these factors? Can we do just one thing, say, eat less meat, but not another, and still achieve some pretty ambitious mitigation goals? In other words, what are necessary and what are sufficient sets of measures to reach these goals? Let us first look at the question of necessary measures. This gets tricky when applied to individual consumers: it is somewhat akin to the notorious question whether a heap of sand is still a heap when you take away one grain (Sainsbury 2011). If you are inclined to say yes, think once more. What happens when you take away another one, and another one, and another one, and so

  11. The Challenge of Incorporating Charged Dust in the Physics of Flowing Plasma Interactions

    Science.gov (United States)

    Jia, Y.; Russell, C. T.; Ma, Y.; Lai, H.; Jian, L.; Toth, G.

    2013-12-01

    The presence of two oppositely charged species with very different mass ratios leads to interesting physical processes and difficult numerical simulations. The reconnection problem is a classic example of this principle with a proton-electron mass ratio of 1836, but it is not the only example. Increasingly we are discovering situations in which heavy, electrically charged dust particles are major players in a plasma interaction. The mass of a 1mm dust particle is about 2000 proton masses and of a 10 mm dust particle about 2 million proton masses. One example comes from planetary magnetospheres. Charged dust pervades Enceladus' southern plume. The saturnian magnetospheric plasma flows through this dusty plume interacting with the charged dust and ionized plume gas. Multiple wakes are seen downstream. The flow is diverted in one direction. The field aligned-current systems are elsewhere. How can these two wake features be understood? Next we have an example from the solar wind. When asteroids collide in a disruptive collision, the solar wind strips the nano-scale charged dust from the debris forming a dusty plasma cloud that may be over 106km in extent and containing over 100 million kg of dust accelerated to the solar wind speed. How does this occur, especially as rapidly as it appears to happen? In this paper we illustrate a start on understanding these phenomena using multifluid MHD simulations but these simulations are only part of the answer to this complex problem that needs attention from a broader range of the community.

  12. Experimental human exposure to inhaled grain dust and ammonia: towards a model of concentrated animal feeding operations.

    Science.gov (United States)

    Sigurdarson, Sigurdur T; O'Shaughnessy, Patrick T; Watt, Janet A; Kline, Joel N

    2004-10-01

    Ammonia and endotoxin-rich dust are present in high concentrations in swine confinement facilities; exposure to this environment is linked to workers' respiratory problems. We hypothesized that experimental exposure to ammonia and dust would impair pulmonary function, and that these exposures would be synergistic. We exposed six normal subjects and eight subjects with mild asthma to ammonia (16-25 ppm) and/or endotoxin-rich grain dust (4 mg/m3). Pulmonary function and exhaled NOx were measured before and after exposure. There was no significant change in pulmonary function in the normal subjects following any of the exposure conditions. Among asthmatics, a significant transient decrease in FEV1 was induced by grain dust, but was not altered by ammonia; increased bronchial hyperreactivity was also noted in this group. In a vulnerable population, exposure to grain dust results in transient airflow obstruction. Short-term exposure to ammonia does not increase this response.

  13. Size distribution of dust grains: A problem of self-similarity

    International Nuclear Information System (INIS)

    Henning, TH.; Dorschner, J.; Guertler, J.

    1989-01-01

    Distribution functions describing the results of natural processes frequently show the shape of power laws. It is an open question whether this behavior is a result simply coming about by the chosen mathematical representation of the observational data or reflects a deep-seated principle of nature. The authors suppose the latter being the case. Using a dust model consisting of silicate and graphite grains Mathis et al. (1977) showed that the interstellar extinction curve can be represented by taking a grain radii distribution of power law type n(a) varies as a(exp -p) with 3.3 less than or equal to p less than or equal to 3.6 (example 1) as a basis. A different approach to understanding power laws like that in example 1 becomes possible by the theory of self-similar processes (scale invariance). The beta model of turbulence (Frisch et al., 1978) leads in an elementary way to the concept of the self-similarity dimension D, a special case of Mandelbrot's (1977) fractal dimension. In the frame of this beta model, it is supposed that on each stage of a cascade the system decays to N clumps and that only the portion beta N remains active further on. An important feature of this model is that the active eddies become less and less space-filling. In the following, the authors assume that grain-grain collisions are such a scale-invarient process and that the remaining grains are the inactive (frozen) clumps of the cascade. In this way, a size distribution n(a) da varies as a(exp -(D+1))da (example 2) results. It seems to be highly probable that the power law character of the size distribution of interstellar dust grains is the result of a self-similarity process. We can, however, not exclude that the process leading to the interstellar grain size distribution is not fragmentation at all

  14. Charging-delay induced dust acoustic collisionless shock wave: Roles of negative ions

    International Nuclear Information System (INIS)

    Ghosh, Samiran; Bharuthram, R.; Khan, Manoranjan; Gupta, M. R.

    2006-01-01

    The effects of charging-delay and negative ions on nonlinear dust acoustic waves are investigated. It has been found that the charging-delay induced anomalous dissipation causes generation of dust acoustic collisionless shock waves in an electronegative dusty plasma. The small but finite amplitude wave is governed by a Korteweg-de Vries Burger equation in which the Burger term arises due to the charging-delay. Numerical investigations reveal that the charging-delay induced dissipation and shock strength decreases (increases) with the increase of negative ion concentration (temperature)

  15. Dynamic vortex dust structures in a nuclear-track plasma

    International Nuclear Information System (INIS)

    Rykov, V A; Khudyakov, A V; Filinov, V S; Vladimirov, V I; Deputatova, L V; Krutov, D V; Fortov, V E

    2003-01-01

    Results are presented from Monte Carlo calculations of the electric charge on dust grains in a plasma produced during the slowing down of radioactive decay products of californium nuclei in neon. The dust grain charging is explained as being due to the drift of electrons and ions in an external electric field. It is shown that the charges of the grains depend on their coordinates and strongly fluctuate with time. The time-averaged grain charges agree with the experimental data obtained on ordered liquid-like dust structures in a nuclear-track plasma. The time-averaged dust grain charges are used to carry out computer modelling of the formation of dynamic vortex structures observed in experiments. Evidence is obtained for the fact that the electrostatic forces experienced by the dust grains are potential in character. The paper is supplemented by a video clip showing the typical dynamics of the simulated vortex dust structure

  16. On the secondary charging effects and structure of mesospheric dust particles impacting on rocket probes

    Directory of Open Access Journals (Sweden)

    O. Havnes

    2007-03-01

    Full Text Available The dust probe DUSTY, first launched during the summer of 1994 (flights ECT–02 and ECT–07 from Andøya Rocket Range, northern Norway, was the first probe to unambiguously detect heavy charged mesospheric aerosols, from hereon referred to as dust. In ECT–02 the probe detected negatively charged dust particles in the height interval of 83 to 88.5 km. In this flight, the lower grid in the detector (Grid 2 measures both positive and negative currents in various regions, and we find that the relationship between the current measurements of Grid 2 and the bottom plate can only be explained by influence from secondary charge production on Grid 2. In ECT–07, which had a large coning, positive currents reaching the top grid of the probe were interpreted as due to the impact of positively charged dust particles. We have now reanalyzed the data from ECT–07 and arrived at the conclusion that the measured positive currents to this grid must have been mainly due to secondary charging effects from the impacting dust particles. The grid consists of a set of parallel wires crossed with an identical set of wires on top of it, and we find that if the observed currents were created from the direct impact of charged dust particles, then they should be very weakly modulated at four times the rocket spin rate ωR. Observations show, however, that the observed currents are strongly modulated at 2ωR. We cannot reproduce the observed large modulations of the impact currents in the dust layer if the currents are due only to the transfer of the charges on the impacted dust particles. Based on the results of recent ice cluster impact secondary charging experiments by Tomsic (2003, which found that a small fraction of the ice clusters, when impacting with nearly grazing incidence, carried away one negative charge −1e, we have arrived at the conclusion that similar, but significantly more effective, charging effects must be predominantly responsible for the

  17. On the secondary charging effects and structure of mesospheric dust particles impacting on rocket probes

    Directory of Open Access Journals (Sweden)

    O. Havnes

    2007-03-01

    Full Text Available The dust probe DUSTY, first launched during the summer of 1994 (flights ECT–02 and ECT–07 from Andøya Rocket Range, northern Norway, was the first probe to unambiguously detect heavy charged mesospheric aerosols, from hereon referred to as dust. In ECT–02 the probe detected negatively charged dust particles in the height interval of 83 to 88.5 km. In this flight, the lower grid in the detector (Grid 2 measures both positive and negative currents in various regions, and we find that the relationship between the current measurements of Grid 2 and the bottom plate can only be explained by influence from secondary charge production on Grid 2. In ECT–07, which had a large coning, positive currents reaching the top grid of the probe were interpreted as due to the impact of positively charged dust particles. We have now reanalyzed the data from ECT–07 and arrived at the conclusion that the measured positive currents to this grid must have been mainly due to secondary charging effects from the impacting dust particles. The grid consists of a set of parallel wires crossed with an identical set of wires on top of it, and we find that if the observed currents were created from the direct impact of charged dust particles, then they should be very weakly modulated at four times the rocket spin rate ωR. Observations show, however, that the observed currents are strongly modulated at 2ωR. We cannot reproduce the observed large modulations of the impact currents in the dust layer if the currents are due only to the transfer of the charges on the impacted dust particles. Based on the results of recent ice cluster impact secondary charging experiments by Tomsic (2003, which found that a small fraction of the ice clusters, when impacting with nearly grazing incidence, carried away one negative charge −1e, we have arrived at the conclusion that similar, but significantly more effective, charging effects must

  18. Planck early results. XX. New light on anomalous microwave emission from spinning dust grains

    DEFF Research Database (Denmark)

    Lähteenmäki, A.; Poutanen, T.; Natoli, P.

    2011-01-01

    by a combination of free-free radiation, cosmic microwave background, thermal dust, and electric dipole radiation from small spinning dust grains. The spinning dust spectra are the most precisely measured to date, and show the high frequency side clearly for the first time. The spectra have a peak in the range 20......-40 GHz and are detected at high significances of 17.1σ for Perseus and 8.4σ for ρ Ophiuchi. In Perseus, spinning dust in the dense molecular gas can account for most of the AME; the low density atomic gas appears to play a minor role. In ρ Ophiuchi, the ~30 GHz peak is dominated by dense molecular gas......, but there is an indication of an extended tail at frequencies 50-100 GHz, which can be accounted for by irradiated low density atomic gas. The dust parameters are consistent with those derived from other measurements. We have also searched the Planck map at 28.5 GHz for candidate AME regions, by subtracting a simple model...

  19. Measurement of net electric charge and dipole moment of dust aggregates in a complex plasma.

    Science.gov (United States)

    Yousefi, Razieh; Davis, Allen B; Carmona-Reyes, Jorge; Matthews, Lorin S; Hyde, Truell W

    2014-09-01

    Understanding the agglomeration of dust particles in complex plasmas requires knowledge of basic properties such as the net electrostatic charge and dipole moment of the dust. In this study, dust aggregates are formed from gold-coated mono-disperse spherical melamine-formaldehyde monomers in a radiofrequency (rf) argon discharge plasma. The behavior of observed dust aggregates is analyzed both by studying the particle trajectories and by employing computer models examining three-dimensional structures of aggregates and their interactions and rotations as induced by torques arising from their dipole moments. These allow the basic characteristics of the dust aggregates, such as the electrostatic charge and dipole moment, as well as the external electric field, to be determined. It is shown that the experimental results support the predicted values from computer models for aggregates in these environments.

  20. Heavy metal speciation in various grain sizes of industrially contaminated street dust using multivariate statistical analysis.

    Science.gov (United States)

    Yıldırım, Gülşen; Tokalıoğlu, Şerife

    2016-02-01

    A total of 36 street dust samples were collected from the streets of the Organised Industrial District in Kayseri, Turkey. This region includes a total of 818 work places in various industrial areas. The modified BCR (the European Community Bureau of Reference) sequential extraction procedure was applied to evaluate the mobility and bioavailability of trace elements (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) in street dusts of the study area. The BCR was classified into three steps: water/acid soluble fraction, reducible and oxidisable fraction. The remaining residue was dissolved by using aqua regia. The concentrations of the metals in street dust samples were determined by flame atomic absorption spectrometry. Also the effect of the different grain sizes (dust samples on the mobility of the metals was investigated using the modified BCR procedure. The mobility sequence based on the sum of the first three phases (for grain size) was: Cd (71.3)>Cu (48.9)>Pb (42.8)=Cr (42.1)>Ni (41.4)>Zn (40.9)>Co (36.6)=Mn (36.3)>Fe (3.1). No significant difference was observed among metal partitioning for the three particle sizes. Correlation, principal component and cluster analysis were applied to identify probable natural and anthropogenic sources in the region. The principal component analysis results showed that this industrial district was influenced by traffic, industrial activities, air-borne emissions and natural sources. The accuracy of the results was checked by analysis of both the BCR-701 certified reference material and by recovery studies in street dust samples. Copyright © 2015 Elsevier Inc. All rights reserved.

  1. Child-Langmuir flow in a planar diode filled with charged dust impurities

    International Nuclear Information System (INIS)

    Tang Xiaoyan; Shukla, Padma Kant

    2008-01-01

    The Child-Langmuir (CL) flow in a planar diode in the presence of stationary charged dust particles is studied. The limiting electron current density and other diode properties, such as the electrostatic potential, the electron flow speed, and the electron number density, are calculated analytically. A comparison of the results with the case without dust impurities reveals that the diode parameters mentioned above decrease with the increase of the dust charge density. Furthermore, it is found that the classical scaling of D -2 (the gap spacing D) for the CL current density remains exactly valid, while the scaling of V 3/2 (the applied gap voltage V) can be a good approximation for low applied gap voltage and for low dust charge density

  2. Self-organization and oscillation of negatively charged dust particles in a 2-dimensional dusty plasma

    Energy Technology Data Exchange (ETDEWEB)

    Song, Y.L. [College of Science, China Agricultural University, Beijing 100083 (China); Huang, F., E-mail: huangfeng@cau.edu.cn [College of Science, China Agricultural University, Beijing 100083 (China); Chen, Z.Y., E-mail: chenzy@mail.buct.edu.cn [Department of Physics, Beijing University of Chemical Technology, Beijing 100029 (China); State Key Laboratory of Laser Propulsion & Application, Beijing 101416 (China); Liu, Y.H. [School of Physics and Optoelectronic Engineering, Ludong University, Yantai 264025 (China); Yu, M.Y. [Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou 310027 (China); Institute for Theoretical Physics I, Ruhr University, D-44801 Bochum (Germany)

    2016-02-22

    Negatively charged dust particles immersed in 2-dimensional dusty plasma system are investigated by molecular dynamics simulations. The effects of the confinement potential and attraction interaction potential on dust particle self-organization are studied in detail and two typical dust particle distributions are obtained when the system reaches equilibrium. The average radial velocity (ARV), average radial force (ARF) and radial mean square displacement are employed to analyze the dust particles' dynamics. Both ARVs and ARFs exhibit oscillation behaviors when the simulation system reaches equilibrium state. The relationships between the oscillation and confinement potential and attraction potential are studied in this paper. The simulation results are qualitatively similar to experimental results. - Highlights: • Self-organization and oscillation of a 2-dimensional dusty plasma is investigated. • Effect of the confinement potential on dust self-organization and oscillation is given. • Effect of the attraction potential on dust self-organization and oscillation is studied.

  3. Self-organization and oscillation of negatively charged dust particles in a 2-dimensional dusty plasma

    International Nuclear Information System (INIS)

    Song, Y.L.; Huang, F.; Chen, Z.Y.; Liu, Y.H.; Yu, M.Y.

    2016-01-01

    Negatively charged dust particles immersed in 2-dimensional dusty plasma system are investigated by molecular dynamics simulations. The effects of the confinement potential and attraction interaction potential on dust particle self-organization are studied in detail and two typical dust particle distributions are obtained when the system reaches equilibrium. The average radial velocity (ARV), average radial force (ARF) and radial mean square displacement are employed to analyze the dust particles' dynamics. Both ARVs and ARFs exhibit oscillation behaviors when the simulation system reaches equilibrium state. The relationships between the oscillation and confinement potential and attraction potential are studied in this paper. The simulation results are qualitatively similar to experimental results. - Highlights: • Self-organization and oscillation of a 2-dimensional dusty plasma is investigated. • Effect of the confinement potential on dust self-organization and oscillation is given. • Effect of the attraction potential on dust self-organization and oscillation is studied.

  4. Grain dust-induced lung inflammation is reduced by Rhodobacter sphaeroides diphosphoryl lipid A.

    Science.gov (United States)

    Jagielo, P J; Quinn, T J; Qureshi, N; Schwartz, D A

    1998-01-01

    To further determine the importance of endotoxin in grain dust-induced inflammation of the lower respiratory tract, we evaluated the efficacy of pentaacylated diphosphoryl lipid A derived from the lipopolysaccharide of Rhodobacter sphaeroides (RsDPLA) as a partial agonist of grain dust-induced airway inflammation. RsDPLA is a relatively inactive compound compared with lipid A derived from Escherichia coli (LPS) and has been demonstrated to act as a partial agonist of LPS-induced inflammation. To assess the potential stimulatory effect of RsDPLA in relation to LPS, we incubated THP-1 cells with RsDPLA (0.001-100 micrograms/ml), LPS (0.02 microgram endotoxin activity/ml), or corn dust extract (CDE; 0.02 microgram endotoxin activity/ml). Incubation with RsDPLA revealed a tumor necrosis factor (TNF)-alpha stimulatory effect at 100 micrograms/ml. In contrast, incubation with LPS or CDE resulted in TNF-alpha release at 0.02 microgram/ml. Pretreatment of THP-1 cells with varying concentrations of RsDPLA before incubation with LPS or CDE (0.02 microgram endotoxin activity/ml) resulted in a dose-dependent reduction in the LPS- or CDE-induced release of TNF-alpha with concentrations of RsDPLA of up to 10 micrograms/ml but not at 100 micrograms/ml. To further understand the role of endotoxin in grain dust-induced airway inflammation, we utilized the unique LPS inhibitory property of RsDPLA to determine the inflammatory response to inhaled CDE in mice in the presence of RsDPLA. Ten micrograms of RsDPLA intratracheally did not cause a significant inflammatory response compared with intratracheal saline. However, pretreatment of mice with 10 micrograms of RsDPLA intratracheally before exposure to CDE (5.4 and 0.2 micrograms/m3) or LPS (7.2 and 0.28 micrograms/m3) resulted in significant reductions in the lung lavage concentrations of total cells, neutrophils, and specific proinflammatory cytokines compared with mice pretreated with sterile saline. These results confirm the LPS

  5. Physico-chemical characterization of grain dust in storage air of Bangalore.

    Science.gov (United States)

    Mukherjee, A K; Nag, D P; Kakde, Y; Babu, K R; Prdkash, M N; Rao, S R

    1998-06-01

    An Anderson personal cascade impactor was used to study the particle mass size distribution in the storage air of two major grain storage centers in Bangalore. Dust levels in storage air as well as the personal exposures of workers were determined along with a detailed study on the particle size distribution. Protein and carbohydrate content of the dust were also determined respectively in the phosphate buffer saline (PBS) and water extracts by using the standard analytical techniques. Personal exposures in both of the grain storage centers have been found to be much above the limit prescribed by ACGIH (1995-96). But the results of particle size analysis showed a higher particle mass distribution in the non-respirable size range. The mass median diameters (MMD) of the storage air particulate of both the centers were found to be beyond the respirable range. Presence of protein and carbohydrate in the storage air dust is indicative of the existence of glyco-proteins, mostly of membrane origin.

  6. From Dust Grains to Planetesimals: The Importance of the Streaming Instability in Protoplanetary Disks

    Science.gov (United States)

    Simon, Jacob B.; Armitage, Philip J.; Youdin, Andrew N.; Li, Rixin

    2016-01-01

    Planetesimals are the precursors to planets, and understanding their formation is an essential step towards developing a complete theory of planet formation. For small solid particles (e.g., dust grains) to coagulate into planetesimals, however, requires that these particles grow beyond centimeter sizes; with traditional coagulation physics, this is very difficult. The streaming instability, which is a clumping process akin to the pile-up of cars in a traffic jam, generates sufficiently high solid densities that the mutual gravity between the clumped particles eventually causes their collapse towards planetesimal mass and size scales. Exploring this transition from dust grains to planetesimals is still in its infancy but is extremely important if we want to understand the basics of planet formation. Here, I present a series of high resolution, first principles numerical simulations of protoplanetary disk gas and dust to study the clumping of particles via the streaming instability and the subsequent collapse towards planetesimals. These simulations have been employed to characterize the planetesimal population as a function of radius in protoplanetary disks. The results of these simulations will be crucial for planet formation models to correctly explain the formation and configuration of solar systems.

  7. Effect of ion suprathermality on arbitrary amplitude dust acoustic waves in a charge varying dusty plasma

    International Nuclear Information System (INIS)

    Tribeche, Mouloud; Mayout, Saliha; Amour, Rabia

    2009-01-01

    Arbitrary amplitude dust acoustic waves in a high energy-tail ion distribution are investigated. The effects of charge variation and ion suprathermality on the large amplitude dust acoustic (DA) soliton are then considered. The correct suprathermal ion charging current is rederived based on the orbit motion limited approach. In the adiabatic case, the variable dust charge is expressed in terms of the Lambert function and we take advantage of this transcendental function to show the existence of rarefactive variable charge DA solitons involving cusped density humps. The dust charge variation leads to an additional enlargement of the DA soliton, which is less pronounced as the ions evolve far away from Maxwell-Boltzmann distribution. In the nonadiabatic case, the dust charge fluctuation may provide an alternate physical mechanism causing anomalous dissipation the strength of which becomes important and may prevail over that of dispersion as the ion spectral index κ increases. Our results may provide an explanation for the strong spiky waveforms observed in auroral electric field measurements by Ergun et al.[Geophys. Res. Lett. 25, 2025 (1998)].

  8. [Effects of the grain size and thickness of dust deposits on soil water and salt movement in the hinterland of the Taklimakan Desert].

    Science.gov (United States)

    Sun, Yan-Wei; Li, Sheng-Yu; Xu, Xin-Wen; Zhang, Jian-Guo; Li, Ying

    2009-08-01

    By using mcirolysimeter, a laboratory simulation experiment was conducted to study the effects of the grain size and thickness of dust deposits on the soil water evaporation and salt movement in the hinterland of the Taklimakan Desert. Under the same initial soil water content and deposition thickness condition, finer-textured (grain size of dust deposits on soil water evaporation had an inflection point at the grain size 0.20 mm, i. e., increased with increasing grain size when the grain size was 0.063-0.20 mm but decreased with increasing grain size when the grain size was > 0.20 mm. With the increasing thickness of dust deposits, its inhibition effect on soil water evaporation increased, and there existed a logarithmic relationship between the dust deposits thickness and water evaporation. Surface soil salt accumulation had a negative correlation with dust deposits thickness. In sum, the dust deposits in study area could affect the stability of arid desert ecosystem.

  9. Interstellar silicate analogs for grain-surface reaction experiments: Gas-phase condensation and characterization of the silicate dust grains

    Energy Technology Data Exchange (ETDEWEB)

    Sabri, T.; Jäger, C. [Laboratory Astrophysics Group of the Max Planck Institute for Astronomy at the Friedrich Schiller University Jena Institute of Solid State Physics, Helmholtzweg 3, D-07743 Jena (Germany); Gavilan, L.; Lemaire, J. L.; Vidali, G. [Observatoire de Paris/Université de Cergy-Pontoise, 5 mail Gay Lussac, F-95000 Cergy-Pontoise (France); Mutschke, H. [Laboratory Astrophysics Group of the Astrophysical Institute and University Observatory, Friedrich Schiller University Jena Schillergässchen 3, D-07743 Jena (Germany); Henning, T., E-mail: tolou.sabri@uni-jena.de [Max Planck Institute for Astronomy Königstuhl 17, D-69117 Heidelberg (Germany)

    2014-01-10

    Amorphous, astrophysically relevant silicates were prepared by laser ablation of siliceous targets and subsequent quenching of the evaporated atoms and clusters in a helium/oxygen gas atmosphere. The described gas-phase condensation method can be used to synthesize homogeneous and astrophysically relevant silicates with different compositions ranging from nonstoichiometric magnesium iron silicates to pyroxene- and olivine-type stoichiometry. Analytical tools have been used to characterize the morphology, composition, and spectral properties of the condensates. The nanometer-sized silicate condensates represent a new family of cosmic dust analogs that can generally be used for laboratory studies of cosmic processes related to condensation, processing, and destruction of cosmic dust in different astrophysical environments. The well-characterized silicates comprising amorphous Mg{sub 2}SiO{sub 4} and Fe{sub 2}SiO{sub 4}, as well as the corresponding crystalline silicates forsterite and fayalite, produced by thermal annealing of the amorphous condensates, have been used as real grain surfaces for H{sub 2} formation experiments. A specifically developed ultra-high vacuum apparatus has been used for the investigation of molecule formation experiments. The results of these molecular formation experiments on differently structured Mg{sub 2}SiO{sub 4} and Fe{sub 2}SiO{sub 4} described in this paper will be the topic of the next paper of this series.

  10. Downwind changes in grain size of aeolian dust; examples from marine and terrestrial archives

    Science.gov (United States)

    Stuut, Jan-Berend; Prins, Maarten

    2013-04-01

    Aeolian dust in the atmosphere may have a cooling effect when small particles in the high atmosphere block incoming solar energy (e.g., Claquin et al., 2003) but it may also act as a 'greenhouse gas' when larger particles in the lower atmosphere trap energy that was reflected from the Earth's surface (e.g., Otto et al., 2007). Therefore, it is of vital importance to have a good understanding of the particle-size distribution of aeolian dust in space and time. As wind is a very size-selective transport mechanism, the sediments it carries typically have a very-well sorted grain-size distribution, which gradually fines from proximal to distal deposition sites. This fact has been used in numerous paleo-environmental studies to both determine source-to-sink changes in the particle size of aeolian dust (e.g., Weltje and Prins, 2003; Holz et al., 2004; Prins and Vriend, 2007) and to quantify mass-accumulation rates of aeolian dust (e.g., Prins and Weltje 1999; Stuut et al., 2002; Prins et al., 2007; Prins and Vriend, 2007; Stuut et al., 2007; Tjallingii et al., 2008; Prins et al., 2009). Studies on modern wind-blown particles have demonstrated that particle size of dust not only is a function of lateral but also vertical transport distance (e.g., Torres-Padron et al., 2002; Stuut et al., 2005). Nonetheless, there are still many unresolved questions related to the physical properties of wind-blown particles like e.g., the case of "giant" quartz particles found on Hawaii (Betzer et al., 1988) that can only originate from Asia but have a too large size for the distance they travelled through the atmosphere. Here, we present examples of dust particle-size distributions from terrestrial (loess) as well as marine (deep-sea sediments) sedimentary archives and their spatial and temporal changes. With this contribution we hope to provide quantitative data for the modelling community in order to get a better grip on the role of wind-blown particles in the climate system. Cited

  11. Indirect Charged Particle Detection: Concepts and a Classroom Demonstration

    Science.gov (United States)

    Childs, Nicholas B.; Horányi, Mihály; Collette, Andrew

    2013-01-01

    We describe the principles of macroscopic charged particle detection in the laboratory and their connections to concepts taught in the physics classroom. Electrostatic dust accelerator systems, capable of launching charged dust grains at hypervelocities (1-100 km/s), are a critical tool for space exploration. Dust grains in space typically have…

  12. Developing ISM Dust Grain Models with Precision Elemental Abundances from IXO

    Science.gov (United States)

    Valencic, L. A.; Smith, R. K.; Juet, A.

    2009-01-01

    The exact nature of interstellar dust grains in the Galaxy remains mysterious, despite their ubiquity. Many viable models exist, based on available IR-UV data and assumed elemental abundances. However, the abundances, which are perhaps the most stringent constraint, are not well known: modelers must use proxies in the absence of direct measurements for the diffuse interstellar medium (ISM). Recent revisions of these proxy values have only added to confusion over which is the best representative for the diffuse ISM, and highlighted the need for direct, high signal-to-noise measurements from the ISM itself. The International X-ray Observatory's superior facilities will enable high-precision elemental abundance measurements. We ill show how these results will measure both the overall ISM abundances and challenge dust models, allowing us to construct a more realistic picture of the ISM.

  13. Enforcing dust mass conservation in 3D simulations of tightly coupled grains with the PHANTOM SPH code

    Science.gov (United States)

    Ballabio, G.; Dipierro, G.; Veronesi, B.; Lodato, G.; Hutchison, M.; Laibe, G.; Price, D. J.

    2018-06-01

    We describe a new implementation of the one-fluid method in the SPH code PHANTOM to simulate the dynamics of dust grains in gas protoplanetary discs. We revise and extend previously developed algorithms by computing the evolution of a new fluid quantity that produces a more accurate and numerically controlled evolution of the dust dynamics. Moreover, by limiting the stopping time of uncoupled grains that violate the assumptions of the terminal velocity approximation, we avoid fatal numerical errors in mass conservation. We test and validate our new algorithm by running 3D SPH simulations of a large range of disc models with tightly and marginally coupled grains.

  14. Interactions of Dust Grains with Coronal Mass Ejections and Solar Cycle Variations of the F-Coronal Brightness

    Science.gov (United States)

    Ragot, B. R.; Kahler, S. W.

    2003-01-01

    The density of interplanetary dust increases sunward to reach its maximum in the F corona, where its scattered white-light emission dominates that of the electron K corona above about 3 Solar Radius. The dust will interact with both the particles and fields of antisunward propagating coronal mass ejections (CMEs). To understand the effects of the CME/dust interactions we consider the dominant forces, with and without CMEs. acting on the dust in the 3-5 Solar Radius region. Dust grain orbits are then computed to compare the drift rates from 5 to 3 Solar Radius. for periods of minimum and maximum solar activity, where a simple CME model is adopted to distinguish between the two periods. The ion-drag force, even in the quiet solar wind, reduces the drift time by a significant factor from its value estimated with the Poynting-Robertson drag force alone. The ion-drag effects of CMEs result in even shorter drift times of the large (greater than or approx. 3 microns) dust grains. hence faster depletion rates and lower dust-pain densities, at solar maxima. If dominated by thermal emission, the near-infrared brightness will thus display solar cycle variations close to the dust plane of symmetry. While trapping the smallest of the grains, the CME magnetic fields also scatter the grains of intermediate size (0.1-3 microns) in latitude. If light scattering by small grains close to the Sun dominates the optical brightness. the scattering by the CME magnetic fields will result in a solar cycle variation of the optical brightness distribution not exceeding 100% at high latitudes, with a higher isotropy reached at solar maxima. A good degree of latitudinal isotropy is already reached at low solar activity since the magnetic fields of the quiet solar wind so close to the Sun are able to scatter the small (less than or approx. 3 microns) grains up to the polar regions in only a few days or less, producing strong perturbations of their trajectories in less than half their orbital

  15. The surface reactivity of acrylonitrile with oxygen atoms on an analogue of interstellar dust grains

    Science.gov (United States)

    Kimber, Helen J.; Toscano, Jutta; Price, Stephen D.

    2018-06-01

    Experiments designed to reveal the low-temperature reactivity on the surfaces of interstellar dust grains are used to probe the heterogeneous reaction between oxygen atoms and acrylonitrile (C2H3CN, H2C=CH-CN). The reaction is studied at a series of fixed surface temperatures between 14 and 100 K. After dosing the reactants on to the surface, temperature-programmed desorption, coupled with time-of-flight mass spectrometry, reveals the formation of a product with the molecular formula C3H3NO. This product results from the addition of a single oxygen atom to the acrylonitrile reactant. The oxygen atom attack appears to occur exclusively at the C=C double bond, rather than involving the cyano(-CN) group. The absence of reactivity at the cyano site hints that full saturation of organic molecules on dust grains may not always occur in the interstellar medium. Modelling the experimental data provides a reaction probability of 0.007 ± 0.003 for a Langmuir-Hinshelwood style (diffusive) reaction mechanism. Desorption energies for acrylonitrile, oxygen atoms, and molecular oxygen, from the multilayer mixed ice their deposition forms, are also extracted from the kinetic model and are 22.7 ± 1.0 kJ mol-1 (2730 ± 120 K), 14.2 ± 1.0 kJ mol-1 (1710 ± 120 K), and 8.5 ± 0.8 kJ mol-1 (1020 ± 100 K), respectively. The kinetic parameters we extract from our experiments indicate that the reaction between atomic oxygen and acrylonitrile could occur on interstellar dust grains on an astrophysical time-scale.

  16. GEO Debris and Interplanetary Dust: Fluxes and Charging Behavior

    Science.gov (United States)

    Graps, A. L.; Green, S. F.; McBride, N. M.; McDonnell, J. A. M.; Drolshagen, G.; Svedhem, H.; Bunte, K. D.

    2005-08-01

    A population of cosmic dust mixed with a population of man-made debris exists within the Earth's magnetosphere. Measurements of these provide the data samples for studies of the interplanetary dust particles that travel through our magnetosphere from the outside and for studies of the local byproducts of our space endeavours. Even though instruments to detect natural meteoroids and space debris particles have been flown in Low Earth Orbits (LEO) and on interplanetary missions, very little information on the particle environment for Earth orbits above about 600 km altitude have been available. In particular, knowledge about particles smaller than 1 m in the geostationary (GEO) region was largely unknown before GORID. In September 1996, a dust/debris detector: GORID was launched into GEO as a piggyback instrument on the Russian Express-2 telecommunications spacecraft. The instrument began its normal operation in April 1997 and ended its mission in July 2002. The goal of this work was to use GORID's particle data to identify and separate the space debris from the interplanetary dust particles (IDPs) in GEO, to more finely determine the instrument's measurement characteristics and to derive impact fluxes. Here we present some results of that study. We give GORID flux distributions for debris and IDPs and then present intriguing debris clustering features that might be the result of electrostatic fragmentation of the rocket slag particles.

  17. On the secondary charging effects and structure of mesospheric dust particles impacting on rocket probes

    Energy Technology Data Exchange (ETDEWEB)

    Havnes, O.; Naesheim, L.I. [Inst. of Physics, Univ. of Tromso (Norway)

    2007-07-01

    The dust probe DUSTY, first launched during the summer of 1994 (flights ECT-02 and ECT-07) from Andoeya Rocket Range, northern Norway, was the first probe to unambiguously detect heavy charged mesospheric aerosols, from hereon referred to as dust. In ECT-02 the probe detected negatively charged dust particles in the height interval of 83 to 88.5 km. In this flight, the lower grid in the detector (Grid 2) measures both positive and negative currents in various regions, and we find that the relationship between the current measurements of Grid 2 and the bottom plate can only be explained by influence from secondary charge production on Grid 2. In ECT-07, which had a large coning, positive currents reaching the top grid of the probe were interpreted as due to the impact of positively charged dust particles. We have now reanalyzed the data from ECT-07 and arrived at the conclusion that the measured positive currents to this grid must have been mainly due to secondary charging effects from the impacting dust particles. The grid consists of a set of parallel wires crossed with an identical set of wires on top of it, and we find that if the observed currents were created from the direct impact of charged dust particles, then they should be very weakly modulated at four times the rocket spin rate {omega}{sub R}. Observations show, however, that the observed currents are strongly modulated at 2{omega}{sub R}. We cannot reproduce the observed large modulations of the impact currents in the dust layer if the currents are due only to the transfer of the charges on the impacted dust particles. Based on the results of recent ice cluster impact secondary charging experiments by Tomsic (2003), which found that a small fraction of the ice clusters, when impacting with nearly grazing incidence, carried away one negative charge - 1e, we have arrived at the conclusion that similar, but significantly more effective, charging effects must be predominantly responsible for the positive

  18. Dust Grains and the Luminosity of Circumnuclear Water Masers in Active Galaxies

    Science.gov (United States)

    Collison, Alan J.; Watson, William D.

    1995-01-01

    In previous calculations for the luminosities of 22 GHz water masers, the pumping is reduced and ultimately quenched with increasing depth into the gas because of trapping of the infrared (approximately equals 30-150 micrometers), spectral line radiation of the water molecule. When the absorption (and reemission) of infrared radiation by dust grains is included, we demonstrate that the pumping is no longer quenched but remains constant with increasing optical depth. A temperature difference between the grains and the gas is required. Such conditions are expected to occur, for example, in the circumnuclear masing environments created by X-rays in active galaxies. Here, the calculated 22 GHz maser luminosities are increased by more than an order of magnitude. Application to the well-studied, circumnuclear masing disk in the galaxy NGC 4258 yields a maser luminosity near that inferred from observations if the observed X-ray flux is assumed to be incident onto only the inner surface of the disk.

  19. Non-thermal desorption from interstellar dust grains via exothermic surface reactions

    Science.gov (United States)

    Garrod, R. T.; Wakelam, V.; Herbst, E.

    2007-06-01

    Aims:The gas-phase abundance of methanol in dark quiescent cores in the interstellar medium cannot be explained by gas-phase chemistry. In fact, the only possible synthesis of this species appears to be production on the surfaces of dust grains followed by desorption into the gas. Yet, evaporation is inefficient for heavy molecules such as methanol at the typical temperature of 10 K. It is necessary then to consider non-thermal mechanisms for desorption. But, if such mechanisms are considered for the production of methanol, they must be considered for all surface species. Methods: Our gas-grain network of reactions has been altered by the inclusion of a non-thermal desorption mechanism in which the exothermicity of surface addition reactions is utilized to break the bond between the product species and the surface. Our estimated rate for this process derives from a simple version of classical unimolecular rate theory with a variable parameter only loosely constrained by theoretical work. Results: Our results show that the chemistry of dark clouds is altered slightly at times up to 106 yr, mainly by the enhancement in the gas-phase abundances of hydrogen-rich species such as methanol that are formed on grain surfaces. At later times, however, there is a rather strong change. Instead of the continuing accretion of most gas-phase species onto dust particles, a steady-state is reached for both gas-phase and grain-surface species, with significant abundances for the former. Nevertheless, most of the carbon is contained in an undetermined assortment of heavy surface hydrocarbons. Conclusions: The desorption mechanism discussed here will be better constrained by observational data on pre-stellar cores, where a significant accretion of species such as CO has already occurred.

  20. Modelling dust transport in tokamaks

    International Nuclear Information System (INIS)

    Martin, J.D.; Martin, J.D.; Bacharis, M.; Coppins, M.; Counsell, G.F.; Allen, J.E.; Counsell, G.F.

    2008-01-01

    The DTOKS code, which models dust transport through tokamak plasmas, is described. The floating potential and charge of a dust grain in a plasma and the fluxes of energy to and from it are calculated. From this model, the temperature of the dust grain can be estimated. A plasma background is supplied by a standard tokamak edge modelling code (B2SOLPS5.0), and dust transport through MAST (the Mega-Amp Spherical Tokamak) and ITER plasmas is presented. We conclude that micron-radius tungsten dust can reach the separatrix in ITER. (authors)

  1. Electromagnetic scattering by a polydispersion of small charged cosmic dust particles

    Directory of Open Access Journals (Sweden)

    M. Kocifaj

    2011-09-01

    Full Text Available Some recent studies on extended red emissions suggest the presence of very small dust particles in the Universe. The sizes of these particles vary from 1 nm to some tens of nanometers, thus situating them deeply in the Rayleigh region if computations are made for visible or near infrared. The optical response of such particles can be a function of the surface charge. In this study we analyse the effect of surface electric potential on the total optical thickness and scattering phase function of the cosmic dust particles. The results are compared with those obtained for electrically neutral dust.

  2. Real-time PCR detection of toxigenic Fusarium in airborne and settled grain dust and associations with trichothecene mycotoxins.

    Science.gov (United States)

    Halstensen, Anne Straumfors; Nordby, Karl-Christian; Eduard, Wijnand; Klemsdal, Sonja Sletner

    2006-12-01

    Inhalation of immunomodulating mycotoxins produced by Fusarium spp. that are commonly found in grain dust may imply health risks for grain farmers. Airborne Fusarium and mycotoxin exposure levels are mainly unknown due to difficulties in identifying Fusarium and mycotoxins in personal aerosol samples. We used a novel real-time PCR method to quantify the fungal trichodiene synthase gene (tri5) and DNA specific to F. langsethiae and F. avenaceum in airborne and settled grain dust, determined the personal inhalant exposure level to toxigenic Fusarium during various activities, and evaluated whether quantitative measurements of Fusarium-DNA could predict trichothecene levels in grain dust. Airborne Fusarium-DNA was detected in personal samples even from short tasks (10-60 min). The median Fusarium-DNA level was significantly higher in settled than in airborne grain dust (p dust (r(s) = 0.20, p = 0.003). Both F. langsethiae-DNA and tri5-DNA were associated with HT-2 and T-2 toxins (r(s) = 0.24-0.71, p dust, and could thus be suitable as indicators for HT-2 and T-2. The median personal inhalant exposure to specific toxigenic Fusarium spp. was less than 1 genome m(-3), but the exposure ranged from 0-10(5) genomes m(-3). This study is the first to apply real-time PCR on personal samples of inhalable grain dust for the quantification of tri5 and species-specific Fusarium-DNA, which may have potential for risk assessments of inhaled trichothecenes.

  3. Motions in the relativistic fields of a charged dust

    International Nuclear Information System (INIS)

    Fonseca Teixeira, A.F. da.

    1980-04-01

    The general relativistic motion of arbitrarily charged test particles is investigated, in the spherically symmetric fields of a charged, static, incoherent matter with T 0 0 = const. The condition for existence of stable circular orbits is established, inside and outside the diffused source. The null geodesics are also investigated, as a limiting case. (Author) [pt

  4. The turbulent life of dust grains in the supernova-driven, multiphase interstellar medium

    Science.gov (United States)

    Peters, Thomas; Zhukovska, Svitlana; Naab, Thorsten; Girichidis, Philipp; Walch, Stefanie; Glover, Simon C. O.; Klessen, Ralf S.; Clark, Paul C.; Seifried, Daniel

    2017-06-01

    Dust grains are an important component of the interstellar medium (ISM) of galaxies. We present the first direct measurement of the residence times of interstellar dust in the different ISM phases, and of the transition rates between these phases, in realistic hydrodynamical simulations of the multiphase ISM. Our simulations include a time-dependent chemical network that follows the abundances of H+, H, H2, C+ and CO and take into account self-shielding by gas and dust using a tree-based radiation transfer method. Supernova explosions are injected either at random locations, at density peaks, or as a mixture of the two. For each simulation, we investigate how matter circulates between the ISM phases and find more sizeable transitions than considered in simple mass exchange schemes in the literature. The derived residence times in the ISM phases are characterized by broad distributions, in particular for the molecular, warm and hot medium. The most realistic simulations with random and mixed driving have median residence times in the molecular, cold, warm and hot phase around 17, 7, 44 and 1 Myr, respectively. The transition rates measured in the random driving run are in good agreement with observations of Ti gas-phase depletion in the warm and cold phases in a simple depletion model. ISM phase definitions based on chemical abundance rather than temperature cuts are physically more meaningful, but lead to significantly different transition rates and residence times because there is no direct correspondence between the two definitions.

  5. The colour of the solar corona and dust grains in it

    International Nuclear Information System (INIS)

    Ajmanov, A.K.; Nikolsky, G.M.

    1980-01-01

    The photometry of coronal negatives is carried out. The films were obtained at the March 7, 1970 and July 10, 1972 eclipses. A distribution of the coronal brightness in the red (635 mm), green (545 nm), and blue (455 nm) wavelength intervals up to distances of (6-7)Rsub(sun) is deduced (Figure 1). Colour indexes of the corona (the emission ratio red/blue-Csub(rb) and green/blue-Csub(gb)) have been obtained. We assume Csub(rb) = Csub(gb) = 1 in the inner corona ( = 1 μm. RED brightness is evaluated to be 4 x 10 -10 anti Bsub(sun). There is 1 grain of dust in the elementary volume with cross section of 1 cm 2 along the line of sight. The intensity of dust emission in wavelength interval 10 μm deduced by the authors is approximately 1 μ W cm -2 sm -1 . That is in agreement with Mankin et al. (1974) and Lena et al. (1974) observations. The whole dust mass of RED is -11 cm -3 . Determination of the colour of the solar corona have been made by a number of scientists (Tikhov, 1940, 1957; Allen, 1946; Blackwell, 1952; Michard, 1956; Sharonov, 1958; Nay et al. 1961). The corona colour was found to be somewhat redder than the Sun's. However this question is not finally settled to date. (orig.)

  6. Self-charging of identical grains in the absence of an external field

    Science.gov (United States)

    Yoshimatsu, R.; Araújo, N. A. M.; Wurm, G.; Herrmann, H. J.; Shinbrot, T.

    2017-01-01

    We investigate the electrostatic charging of an agitated bed of identical grains using simulations, mathematical modeling, and experiments. We simulate charging with a discrete-element model including electrical multipoles and find that infinitesimally small initial charges can grow exponentially rapidly. We propose a mathematical Turing model that defines conditions for exponential charging to occur and provides insights into the mechanisms involved. Finally, we confirm the predicted exponential growth in experiments using vibrated grains under microgravity, and we describe novel predicted spatiotemporal states that merit further study.

  7. Work-related asthma in a population exposed to grain, flour and other ingredient dusts.

    Science.gov (United States)

    Smith, T A; Lumley, K P

    1996-02-01

    The purpose of the study was to determine the prevalence and causation of work-related asthmatic symptoms in a population exposed to grain, flour and other ingredient dusts. Where workers complained of asthmatic symptoms which were the result of dust exposure, follow-up aimed to identify whether the symptoms were the result of sensitisation or of non-specific irritation. A questionnaire was presented to 3,450 workers who had exposure to dust during the course of flour milling (528), bread baking (1,756), cake baking (209) and other activities in food preparation (957). Those with positive responses were followed-up by taking a formal history, examination, skin prick testing and serial peak flow measurement. The overall prevalence of work-related asthmatic symptoms was 4.4% (153 out of 3,450). In the group who were followed-up (128 out of 153), non-specific respiratory irritation was thought to be the cause in 90 (2.6%), whilst sensitisation was responsible for symptoms in 12 (0.3%). Of the 12 cases due to sensitisation, the agents responsible were: fungal amylase (10 cases, all associated with bread baking), flour (one case, associated with flour packing), and grain (one case, associated with flour milling). Non-specific irritation is considerably more common than sensitisation as the cause of work-related asthmatic symptoms in flour milling, baking and other flour-based industries. The prevalence of sensitisation to flour is very low (less than 1 in 1,000) in all these industries. The principal sensitiser encountered in modern plant bakeries appears to be fungal amylase. The most important source of exposure to fungal amylase is probably the debagging, sieving, weighing and mixing of bread improvers.

  8. Effect of the radio frequency discharge on the dust charging process in a weakly collisional and fully ionized plasma

    Energy Technology Data Exchange (ETDEWEB)

    Motie, Iman [Department of Physics, Mashhad Branch, Islamic Azad University, Mashhad (Iran, Islamic Republic of); Bokaeeyan, Mahyar, E-mail: Mehyar9798@gmail.com [Department of Engineering, University of Applied Science and Technology (UAST)-Mohandesan Center, Mashhad (Iran, Islamic Republic of)

    2015-02-15

    A close analysis of dust charging process in the presence of radio frequency (RF) discharge on low pressure and fully ionized plasma for both weak and strong discharge's electric field is considered. When the electromagnetic waves pass throughout fully ionized plasma, the collision frequency of the plasma is derived. Moreover, the disturbed distribution function of plasma particles in the presence of the RF discharge is obtained. In this article, by using the Krook model, we separate the distribution function in two parts, the Maxwellian part and the perturbed part. The perturbed part of distribution can make an extra current, so-called the accretion rate of electron (or ion) current, towards a dust particle as a function of the average electron-ion collision frequency. It is proven that when the potential of dust grains increases, the accretion rate of electron current experiences an exponential reduction. Furthermore, the accretion rate of electron current for a strong electric field is relatively smaller than that for a weak electric field. The reasons are elaborated.

  9. Pantoea agglomerans: a mysterious bacterium of evil and good. Part II--Deleterious effects: Dust-borne endotoxins and allergens--focus on grain dust, other agricultural dusts and wood dust.

    Science.gov (United States)

    Dutkiewicz, Jacek; Mackiewicz, Barbara; Lemieszek, Marta Kinga; Golec, Marcin; Skórska, Czesława; Góra-Florek, Anna; Milanowski, Janusz

    2016-01-01

    Pantoea agglomerans, a Gram-negative bacterium developing in a variety of plants as epiphyte or endophyte is particularly common in grain and grain dust, and has been identified by an interdisciplinary group from Lublin, eastern Poland, as a causative agent of work-related diseases associated with exposure to grain dust and other agricultural dusts. The concentration of P. agglomerans in grain as well as in the settled grain and flour dust was found to be high, ranging from 10(4)-10(8) CFU/g, while in the air polluted with grain or flour dust it ranged from 10(3)-10(5) CFU/m(3) and formed 73.2-96% of the total airborne Gram-negative bacteria. The concentration of P. agglomerans was also relatively high in the air of the facilities processing herbs and other plant materials, while it was lower in animal farms and in wood processing facilities. Pantoea agglomerans produces a biologically-potent endotoxin (cell wall lipopolysaccharide, LPS). The significant part of this endotoxin occurs in dusts in the form of virus-sized globular nanoparticles measuring 10-50 nm that could be described as the 'endotoxin super-macromolecules'. A highly significant relationship was found (R=0.804, P=0.000927) between the concentration of the viable P. agglomerans in the air of various agricultural and wood industry settings and the concentration of bacterial endotoxin in the air, as assessed by the Limulus test. Although this result may be interfered by the presence of endotoxin produced by other Gram-negative species, it unequivocally suggests the primary role of the P. agglomerans endotoxin as an adverse agent in the agricultural working environment, causing toxic pneumonitis (ODTS). Numerous experiments by the inhalation exposure of animals to various extracts of P. agglomerans strains isolated from grain dust, including endotoxin isolated with trichloroacetic acid (LPS-TCA), endotoxin nanoparticles isolated in sucrose gradient (VECN), and mixture of proteins and endotoxin obtained

  10. Pantoea agglomerans : a mysterious bacterium of evil and good. Part II. Deleterious effects: Dust-borne endotoxins and allergens – focus on grain dust, other agricultural dusts and wood dust

    Directory of Open Access Journals (Sweden)

    Jacek Dutkiewicz

    2015-12-01

    Full Text Available Pantoea agglomerans , a Gram-negative bacterium developing in a variety of plants as epiphyte or endophyte is particularly common in grain and grain dust, and has been identified by an interdisciplinary group from Lublin, eastern Poland, as a causative agent of work-related diseases associated with exposure to grain dust and other agricultural dusts. The concentration of [i]P. agglomerans[/i] in grain as well as in the settled grain and flour dust was found to be high, ranging from 10 4 –10 8 CFU/g, while in the air polluted with grain or flour dust it ranged from 10 3 –10 5 CFU/m 3 and formed 73.2–96% of the total airborne Gram-negative bacteria. The concentration of P. agglomerans was also relatively high in the air of the facilities processing herbs and other plant materials, while it was lower in animal farms and in wood processing facilities. Pantoea agglomerans produces a biologically-potent endotoxin (cell wall lipopolysaccharide, LPS. The significant part of this endotoxin occurs in dusts in the form of virus-sized globular nanoparticles measuring 10–50 nm that could be described as the ‘endotoxin super-macromolecules’. A highly significant relationship was found (R=0.804, P=0.000927 between the concentration of the viable P. agglomerans in the air of various agricultural and wood industry settings and the concentration of bacterial endotoxin in the air, as assessed by the Limulus test. Although this result may be interfered by the presence of endotoxin produced by other Gram-negative species, it unequivocally suggests the primary role of the P. agglomerans endotoxin as an adverse agent in the agricultural working environment, causing toxic pneumonitis (ODTS. Numerous experiments by the inhalation exposure of animals to various extracts of P. agglomerans strains isolated from grain dust, including endotoxin isolated with trichloroacetic acid (LPS-TCA, endotoxin nanoparticles isolated in sucrose gradient (VECN, and mixture of

  11. Identification of a Compound Spinel and Silicate Presolar Grain in a Chondritic Interplanetary Dust Particle

    Science.gov (United States)

    Nguyen, A. N.; Nakamura-Messenger, K.; Messenger, S.; Keller, L. P.; Kloeck, W.

    2014-01-01

    Anhydrous chondritic porous interplanetary dust particles (CP IDPs) have undergone minimal parent body alteration and contain an assemblage of highly primitive materials, including molecular cloud material, presolar grains, and material that formed in the early solar nebula [1-3]. The exact parent bodies of individual IDPs are not known, but IDPs that have extremely high abundances of presolar silicates (up to 1.5%) most likely have cometary origins [1, 4]. The presolar grain abundance among these minimally altered CP IDPs varies widely. "Isotopically primitive" IDPs distinguished by anomalous bulk N isotopic compositions, numerous 15N-rich hotspots, and some C isotopic anomalies have higher average abundances of presolar grains (375 ppm) than IDPs with isotopically normal bulk N (<10 ppm) [5]. Some D and N isotopic anomalies have been linked to carbonaceous matter, though this material is only rarely isotopically anomalous in C [1, 5, 6]. Previous studies of the bulk chemistry and, in some samples, the mineralogy of select anhydrous CP IDPs indicate a link between high C abundance and pyroxene-dominated mineralogy [7]. In this study, we conduct coordinated mineralogical and isotopic analyses of samples that were analyzed by [7] to characterize isotopically anomalous materials and to establish possible correlations with C abundance.

  12. The Evolution of Dust in the Multiphase ISM: Grain Destruction Processes

    Science.gov (United States)

    Wolfire, Mark

    1999-01-01

    This proposal covered year one of a long term project in which we acquired the necessary hardware and softwaxe needed to calculate grain destruction processes in the interstellar medium (ISM). The long term goal of this research is to develop a model for the dust evolution in the ISM capable of explaining observations of elemental depletions, the grain size distribution, and the emission characteristics of the ISM from the X-ray through the FIR. We purchased a SUN Ultra 10 workstation and peripheral devices including an Exabyte Tape drive, HP Laser Printer, and Seagate External Hard Disk. The PI installed the hardware and Solaris operating system on the workstation and integrated the hardware into the network. Software was also purchased to enable connections to the workstation from a PC (Hummingbird Exceed). Additional freeware required to carry out the proposed program was installed on the system including compilers (g77, gcc, g++), editors (emacs), a markup language (LaTeX), and display programs (WIP, XV, SAOtng). We have also successfully modified the required plot files to work with our system which display the results of grain processing.

  13. Nonlinear localized dust acoustic waves in a charge varying dusty plasma with nonthermal ions

    International Nuclear Information System (INIS)

    Tribeche, Mouloud; Amour, Rabia

    2007-01-01

    A numerical investigation is presented to show the existence, formation, and possible realization of large-amplitude dust acoustic (DA) solitary waves in a charge varying dusty plasma with nonthermal ions. These nonlinear localized structures are self-consistent solutions of the collisionless Vlasov equation with a population of fast particles. The spatial patterns of the variable charge DA solitary wave are significantly modified by the nonthermal effects. The results complement and provide new insights into previously published results on this problem

  14. (KP) equation in warm dusty plasma with variable dust charge, two ...

    Indian Academy of Sciences (India)

    In this work, the propagation of nonlinear waves in warm dusty plasmas with variable dust charge, two-temperature ion and nonthermal electron is studied. By using the reductive perturbation theory, the Kadomstev–Petviashvili (KP) equation is derived. The energy of the soliton and the linear dispersion relation are obtained ...

  15. Dust particle charge and screening in the collisional RF plasma sheath

    NARCIS (Netherlands)

    Beckers, J.; Trienekens, D.J.M.; Kroesen, G.M.W.; Sprouse, G.D.

    2012-01-01

    Once immersed in plasma, a dust particle gathers a highly negative charge due to the net collection of free electrons. In most plasma's on earth and with particle sizes is in the micrometer range, the gravitational force is dominant and consequently the particle ends up within the plasma sheath

  16. A Monte Carlo model for the exposure history of lunar dust grains in the ancient solar wind

    International Nuclear Information System (INIS)

    Borg, J.; Comstock, G.M.; Langevin, Y.; Maurette, M.; Jouffrey, B.; Jouret, C.

    1976-01-01

    The theoretical motion of the individual dust grains in the lunar regolith is analyzed by using a Monte Carlo statistical code where the variables are the mass and speed distribution of meteorites at the lunar surface and the geometrical shape of impact craters. From these computations the detailed irradiation history of the grains in the ancient solar wind is traced back, over a period of 4 billion years, as a function of the grain-size. Then by combining this irradiation scheme with the results of solar wind simulation experiments, the time and depth dependent accumulation of solar wind effects in the theoretical grains (solar wind maturation) is inferred. Finally, the validity of these predictions is tentatively checked by discussing a variety of physical and chemical solar wind effects which are registered in the surface layers of lunar dust grains. Therefore these studies give a tentative scenario for the 'maturation' of the lunar regolith with respect to solar wind effects, but they also reveal useful guidelines to deduce meaningful information from such effects. In particular, they suggest a 'lunar skin' sampling technique for extracting dust grains in lunar core tubes which could help in deciphering the past activity of the ancient solar wind over a time scale of several billion years. (Auth.)

  17. Maximizing Ion Current by Space Charge Neutralization using Negative Ions and Dust Particles

    International Nuclear Information System (INIS)

    Smirnov, A.; Raitses, Y.; Fisch, N.J.

    2005-01-01

    Ion current extracted from an ion source (ion thruster) can be increased above the Child-Langmuir limit if the ion space charge is neutralized. Similarly, the limiting kinetic energy density of the plasma flow in a Hall thruster might be exceeded if additional mechanisms of space charge neutralization are introduced. Space charge neutralization with high-mass negative ions or negatively charged dust particles seems, in principle, promising for the development of a high current or high energy density source of positive light ions. Several space charge neutralization schemes that employ heavy negatively charged particles are considered. It is shown that the proposed neutralization schemes can lead, at best, only to a moderate but nonetheless possibly important increase of the ion current in the ion thruster and the thrust density in the Hall thruster

  18. Separation of mycotoxin-containing sources in grain dust and determination of their mycotoxin potential.

    Science.gov (United States)

    Palmgren, M S; Lee, L S

    1986-01-01

    Two distinct reservoirs of mycotoxins exist in fungal-infected cereal grains--the fungal spores and the spore-free mycelium-substrate matrix. Many fungal spores are of respirable size and the mycelium-substrate matrix can be pulverized to form particles of respirable size during routine handling of grain. In order to determine the contribution of each source to the level of mycotoxin contamination of dust, we developed techniques to harvest and separate mycelium-substrate matrices from spores of fungi. Conventional quantitative chromatographic analyses of separated materials indicated that aflatoxin from Aspergillus parasiticus, norsolorinic acid from a mutant of A. parasiticus, and secalonic acid D from Penicillium oxalicum were concentrated in the mycelium-substrate matrices and not in the spores. In contrast, spores of Aspergillus niger and Aspergillus fumigatus contained significant concentrations of aurasperone C and fumigaclavine C, respectively; only negligible amounts of the toxins were detected in the mycelium-substrate matrices of these two fungi. PMID:3709472

  19. IMPROVING THE MODEL OF EMISSION FROM SPINNING DUST: EFFECTS OF GRAIN WOBBLING AND TRANSIENT SPIN-UP

    International Nuclear Information System (INIS)

    Hoang, Thiem; Lazarian, A.; Draine, B. T.

    2010-01-01

    Observations continue to support the interpretation of the anomalous microwave foreground as electric dipole radiation from spinning dust grains as proposed by Draine and Lazarian. In this paper, we present a refinement of the original model by improving the treatment of a number of physical effects. First, we consider a disk-like grain rotating with angular velocity at an arbitrary angle with respect to the grain symmetry axis (i.e., grain wobbling) and derive the rotational damping and excitation coefficients arising from infrared emission, plasma-grain interactions, and electric dipole emission. The angular velocity distribution and the electric dipole emission spectrum for disk-like grains is calculated using the Langevin equation, for cases both with and without fast internal relaxation. Our results show that for fast internal relaxation, the peak emissivity of spinning dust, compared to earlier studies, increases by a factor of ∼2 for the warm neutral medium (WNM), the warm ionized medium (WIM), the cold neutral medium (CNM), and the photodissociation region, and by a factor ∼4 for reflection nebulae. The frequency at the emission peak also increases by factors ∼1.4 to ∼2 for these media. Without internal relaxation, the increase of emissivity is comparable, but the emission spectrum is more extended to higher frequency. The increased emission results from the non-sphericity of grain shape and from the anisotropy in damping and excitation along directions parallel and perpendicular to the grain symmetry axis. Second, we provide a detailed numerical study including transient spin-up of grains by single-ion collisions. The range of grain size in which single-ion collisions are important is identified. The impulses broaden the emission spectrum and increase the peak emissivity for the CNM, WNM, and WIM, although the increases are not as large as those due to the grain wobbling. In addition, we present an improved treatment of rotational excitation and

  20. Grain elevator workers show work-related pulmonary function changes and dose-effect relationships with dust exposure.

    Science.gov (United States)

    Corey, P; Hutcheon, M; Broder, I; Mintz, S

    1982-01-01

    The purpose of this study was to determine whether grain handlers underwent work-related changes in their pulmonary function and, if so, to examine the dose-effect relationships with dust exposure. The pulmonary function of grain handlers was measured at the beginning and end of work shifts over a period of one week, during which their exposure to dust was measured daily. The results showed changes indicative of a within-day obstructive change, in addition to a small restrictive defect occurring over the course of a week. Civic outside labourers who were examined as a control group showed a similar within-week obstructive change without any associated restriction of lung volume. The data on the grain handlers were also used to examine the dose-effect relationships of dust exposure, both on baseline pulmonary function and on within-day changes in these measurements. The baseline flow rates of workers who did not wear a mask were found to vary inversely with their average exposure to respirable dust. In addition, the flow rates underwent a within-day decrease that varied directly with their corresponding exposure to respirable dust and was unrelated to mask wearing. The median of the slopes for this relationship indicated that 50% of the subjects had a decrease of at least 923 ml/s in the value of their Vmax50%VC for each 1 mg/m3 increase in the concentration of respirable dust. Non-respirable dust did not have a measurable effect either on the baseline or the within-day changes in pulmonary function. The acute changes were unaffected by age, duration of employment, or extent of smoking. PMID:7138793

  1. Dust evolution, a global view: III. Core/mantle grains, organic nano-globules, comets and surface chemistry

    Science.gov (United States)

    2016-01-01

    Within the framework of The Heterogeneous dust Evolution Model for Interstellar Solids (THEMIS), this work explores the surface processes and chemistry relating to core/mantle interstellar and cometary grain structures and their influence on the nature of these fascinating particles. It appears that a realistic consideration of the nature and chemical reactivity of interstellar grain surfaces could self-consistently and within a coherent framework explain: the anomalous oxygen depletion, the nature of the CO dark gas, the formation of ‘polar ice’ mantles, the red wing on the 3 μm water ice band, the basis for the O-rich chemistry observed in hot cores, the origin of organic nano-globules and the 3.2 μm ‘carbonyl’ absorption band observed in comet reflectance spectra. It is proposed that the reaction of gas phase species with carbonaceous a-C(:H) grain surfaces in the interstellar medium, in particular the incorporation of atomic oxygen into grain surfaces in epoxide functional groups, is the key to explaining these observations. Thus, the chemistry of cosmic dust is much more intimately related with that of the interstellar gas than has previously been considered. The current models for interstellar gas and dust chemistry will therefore most likely need to be fundamentally modified to include these new grain surface processes. PMID:28083090

  2. Effects of exposure to grain dust in Polish farmers: work-related symptoms and immunologic response to microbial antigens associated with dust.

    Science.gov (United States)

    Skórska, C; Mackiewicz, B; Dutkiewicz, J; Krysińska-Traczyk, E; Milanowski, J; Feltovich, H; Lange, J; Thorne, P

    1998-01-01

    Medical examinations were performed in a group of 76 Polish farmers heavily exposed to grain dust during harvesting and threshing, and in a group of 63 healthy urban dwellers not exposed to organic dusts (controls). The examinations included: interview concerning the occurrence of respiratory disorders and work-related symptoms, physical examination, lung function tests, and allergological tests comprising skin prick test with 4 microbial antigens associated with grain dust and agar-gel precipitation test with 12 microbial antigens. As many as 34 farmers (44.7%) reported the occurrence of work-related symptoms during harvesting and threshing. The most common was dry cough reported by 20 individuals (26.3%). Dyspnoea was reported by 15 farmers (19.7%), tiredness by 12 (15.7%), chest tightness by 8 (10.5%), plugging of nose and hoarseness by 5 each (6. 5%). No control subjects reported these work-related symptoms. The mean spirometric values in the examined group of farmers were within the normal range, but a significant post-shift decrease of these values was observed after work with grain. The farmers showed a frequency of the positive early skin reactions to environmental allergens in the range of 10.8 - 45.5%, and a frequency of positive precipitin reactions in range of 3.9 - 40.8%. The control group responded to the majority of allergens with a significantly lower frequency of positive results compared to the farmers. The obtained results showed a high response of grain farmers to inhalant microbial allergens and indicate a potential risk of occupational respiratory diseases (such as allergic alveolitis, asthma, Organic Dust Toxic Syndrome) among this population

  3. Non-monotonic spatial distribution of the interstellar dust in astrospheres: finite gyroradius effect

    Science.gov (United States)

    Katushkina, O. A.; Alexashov, D. B.; Izmodenov, V. V.; Gvaramadze, V. V.

    2017-02-01

    High-resolution mid-infrared observations of astrospheres show that many of them have filamentary (cirrus-like) structure. Using numerical models of dust dynamics in astrospheres, we suggest that their filamentary structure might be related to specific spatial distribution of the interstellar dust around the stars, caused by a gyrorotation of charged dust grains in the interstellar magnetic field. Our numerical model describes the dust dynamics in astrospheres under an influence of the Lorentz force and assumption of a constant dust charge. Calculations are performed for the dust grains with different sizes separately. It is shown that non-monotonic spatial dust distribution (viewed as filaments) appears for dust grains with the period of gyromotion comparable with the characteristic time-scale of the dust motion in the astrosphere. Numerical modelling demonstrates that the number of filaments depends on charge-to-mass ratio of dust.

  4. Kinetic simulation of neutral/ionized gas and electrically charged dust in the coma of comet 67P/Churyumov-Gerasimenko

    International Nuclear Information System (INIS)

    Tenishev, Valeriy; Rubin, Martin; Combi, Michael R.

    2011-01-01

    The cometary coma is a unique phenomenon in the solar system being a planetary atmosphere influenced by little or no gravity. As a comet approaches the sun, the water vapor with some fraction of other gases sublimate, generating a cloud of gas, ice and other refractory materials (rocky and organic dust) ejected from the surface of the nucleus. Sublimating gas molecules undergo frequent collisions and photochemical processes in the near-nucleus region. Owing to its negligible gravity, comets produce a large and highly variable extensive dusty coma with a size much larger than the characteristic size of the cometary nucleus.The Rosetta spacecraft is en route to comet 67P/Churyumov-Gerasimenko for a rendezvous, landing, and extensive orbital phase beginning in 2014. Both, interpretation of measurements and safety consideration of the spacecraft require modeling of the comet's dusty gas environment.In this work we present results of a numerical study of multispecies gaseous and electrically charged dust environment of comet Chyuryumov-Gerasimenko. Both, gas and dust phases of the coma are simulated kinetically. Photolytic reactions are taken into account. Parameters of the ambient plasma as well as the distribution of electric/magnetic fields are obtained from an MHD simulation of the coma connected to the solar wind. Trajectories of ions and electrically charged dust grains are simulated by accounting for the Lorentz force and the nucleus gravity.

  5. Analysis of "Midnight" Tracks in the Stardust Interstellar Dust Collector: Possible Discovery of a Contemporary Interstellar Dust Grain

    Science.gov (United States)

    Westphal, A. J.; Allen, C.; Bajit, S.; Bastien, R.; Bechtel, H.; Bleuet, P.; Borg, J.; Brenker, F.; Bridges, J.; Brownlee, D. E.; hide

    2010-01-01

    In January 2006, the Stardust sample return capsule returned to Earth bearing the first solid samples from a primitive solar system body, Comet 81P/Wild2, and a collector dedicated to the capture and return of contemporary interstellar dust. Both collectors were approximately 0.1m(exp 2) in area and were composed of aerogel tiles (85% of the collecting area) and aluminum foils. The Stardust Interstellar Dust Collector (SIDC) was exposed to the interstellar dust stream for a total exposure factor of 20 m(exp 2) day. The Stardust Interstellar Preliminary Examination (ISPE) is a three-year effort to characterize the collection using nondestructive techniques.

  6. Acoustic Wave in a Dusty Plasma with Frequent Grain Charging Collisions

    International Nuclear Information System (INIS)

    Lee, Hee J.; Cho, Sang-Hoon

    2003-01-01

    The sink terms in the electron and ion continuity equations and the frictional terms in the momentum equations of a dusty plasma are obtained by taking moments of a kinetic equation which takes into account the grain charging collisions by electrons and ions. We show that an acoustic wave can propagate as a normal mode in the parameter regime where the frequencies of charging collisions are much greater than the wave frequency

  7. Magnetic diffusion and ionization fractions in dense molecular clouds: The role of charged grains

    International Nuclear Information System (INIS)

    Elmegreen, B.G.

    1979-01-01

    The ionization fraction is determined for dense molecular clouds by considering charge exchange, dissociative recombination, radiative recombination, and collisions between grains and charged species. The inclusion of grains tends to lower the ionization fraction for a given cosmic-ray ionization rate zeta and metal depletion delta. The observed values of the ionization fractions in dense cloud cores (i.e., -8 ) are obtained for reasonable values of zeta=10 -17 s -1 and delta=0.1.For temperatures less than 30 K, each grain alternates in charge between -e and 0. The resulting motion of the grains in a self-graviting cloud that contains a magnetic field will be periodic; their response to electromagnetic forces will depend on their instantaneous charge. This complex motion is calculated in order to determine the average viscous force between the grains and the neutral molecules in the cloud. The grain-neutral viscous force combines with the ion-neutral viscous force to regulate the motion of the neutral molecules relative to the magnetic field. The resultant The result neutral drift leads to a diffusion of the magnetic field out of the cloud. The time scale for this diffusion is calculated. Grain-related viscous forces dominate ion-related forces for ionization fractions less than 5 x 10 -8 . The magnetic diffusion time in a self-gravitating cloud that is supported by an internal magnetic field is shown to be at least 10 times larger thanthe free-fall time even when the ionization fraction is much less than 10 -8

  8. Hypervelocity dust impact craters on photovoltaic devices imaged by ion beam induced charge

    International Nuclear Information System (INIS)

    Yang, Changyi; Wu, Yiyong; Lv, Gang; Rubanov, Sergey; Jamieson, David N.

    2015-01-01

    Hypervelocity dust has a speed of greater than 5 km/s and is a significant problem for equipment deployed in space such as satellites because of impacts that damage vulnerable components. Photovoltaic (PV) arrays are especially vulnerable because of their large surface area and the performance can be degraded owing to the disruption of the structure of the junction in the cells making up the array. Satellite PV arrays returned to Earth after service in orbit reveal a large number of craters larger than 5 μm in diameter arising from hypervelocity dust impacts. Extensive prior work has been done on the analysis of the morphology of craters in PV cells to understand the origin of the micrometeoroid that caused the crater and to study the corresponding mechanical damage to the structure of the cell. Generally, about half the craters arise from natural micrometeoroids, about one third from artificial Al-rich debris, probably from solid rocket exhausts, and the remainder from miscellaneous sources both known and unknown. However to date there has not been a microscopic study of the degradation of the electrical characteristics of PV cells exposed to hypervelocity dust impacts. Here we present an ion beam induced charge (IBIC) pilot study by a 2 MeV He microbeam of craters induced on a Hamamatsu PIN diode exposed to artificial hypervelocity Al dust from a dust accelerator. Numerous 5–30 μm diameter craters were identified and the charge collection efficiency of the crater and surrounds mapped with IBIC with bias voltages between 0 and 20 V. At highest bias, it was found the efficiency of the crater had been degraded by about 20% compared to the surrounding material. The speed distribution achieved in the Al dust accelerator was peaked at about 4 km/s compared to 11–68 km/s for dust encountered in low Earth orbit. We are able to extrapolate the charge collection efficiency degradation rate of unbiased cells in space based on our current measurements and the

  9. Hypervelocity dust impact craters on photovoltaic devices imaged by ion beam induced charge

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Changyi [School of Physics, University of Melbourne, Parkville, VIC 3010 (Australia); Wu, Yiyong; Lv, Gang [National Key Laboratory of Materials Behavior and Evaluation Technology in Space Environments, Harbin Institute of Technology, Harbin (China); Rubanov, Sergey [Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, VIC 3010 (Australia); Jamieson, David N., E-mail: d.jamieson@unimelb.edu.au [School of Physics, University of Melbourne, Parkville, VIC 3010 (Australia)

    2015-04-01

    Hypervelocity dust has a speed of greater than 5 km/s and is a significant problem for equipment deployed in space such as satellites because of impacts that damage vulnerable components. Photovoltaic (PV) arrays are especially vulnerable because of their large surface area and the performance can be degraded owing to the disruption of the structure of the junction in the cells making up the array. Satellite PV arrays returned to Earth after service in orbit reveal a large number of craters larger than 5 μm in diameter arising from hypervelocity dust impacts. Extensive prior work has been done on the analysis of the morphology of craters in PV cells to understand the origin of the micrometeoroid that caused the crater and to study the corresponding mechanical damage to the structure of the cell. Generally, about half the craters arise from natural micrometeoroids, about one third from artificial Al-rich debris, probably from solid rocket exhausts, and the remainder from miscellaneous sources both known and unknown. However to date there has not been a microscopic study of the degradation of the electrical characteristics of PV cells exposed to hypervelocity dust impacts. Here we present an ion beam induced charge (IBIC) pilot study by a 2 MeV He microbeam of craters induced on a Hamamatsu PIN diode exposed to artificial hypervelocity Al dust from a dust accelerator. Numerous 5–30 μm diameter craters were identified and the charge collection efficiency of the crater and surrounds mapped with IBIC with bias voltages between 0 and 20 V. At highest bias, it was found the efficiency of the crater had been degraded by about 20% compared to the surrounding material. The speed distribution achieved in the Al dust accelerator was peaked at about 4 km/s compared to 11–68 km/s for dust encountered in low Earth orbit. We are able to extrapolate the charge collection efficiency degradation rate of unbiased cells in space based on our current measurements and the

  10. SEM Characterization of Extinguished Grains from Plasma-Ignited M30 Charges

    Science.gov (United States)

    Kinkennon, A.; Birk, A.; DelGuercio, M.; Kaste, P.; Lieb, R.; Newberry, J.; Pesce-Rodriguez, R.; Schroeder, M.

    2000-01-01

    M30 propellant grains that had been ignited in interrupted closed bomb experiments were characterize by scanning electron microscopy (SEM). Previous chemical analysis of extinguished grains had given no indications of plasma-propellant chemical interactions that could explain the increased burning rates that had been previously observed in full-pressure closed bomb experiments. (This does not mean that there is no unique chemistry occurring with plasma ignition. It may occur very early in the ignition event and then become obscured by the burning chemistry.) In this work, SEM was used to look at grain morphologies to determine if there were increases in the surface areas of the plasma-ignited grains which would contribute to the apparent increase in the burning rate. Charges were made using 30 propellant grains (approximately 32 grams) stacked in two tiers and in two concentric circles around a plastic straw. Each grain was notched so that, when the grains were expelled from the bomb during extinguishment, it could be determined in which tier and which circle each grain was originally packed. Charges were ignited in a closed bomb by either a nickel wire/Mylar-capillary plasma or black powder. The bomb contained a blowout disk that ruptured when the pressure reached 35 MPa, and the propellant was vented into a collection chamber packed with polyurethane foam. SEM analysis of the grains fired with a conventional black powder igniter showed no signs of unusual burning characteristics. The surfaces seemed to be evenly burned on the exteriors of the grains and in the perforations. Grains that had been subjected to plasma ignition, however, had pits, gouges, chasms, and cracks in the surfaces. The sides of the grains closest to the plasma had the greatest amount of damage, but even surfaces facing the outer wall of the bomb had small pits. The perforations contained gouges and abnormally burned regions (wormholes) that extended into the web. The SEM photos indicated that

  11. Nitrogen chemistry on dust grains: the formation of hydroxylamine, precursor to glycine

    Science.gov (United States)

    Vidali, Gianfranco; Lemaire, Jean Louis; Shi, Jianming; Hopkins, Tyler; Garrod, Rob; He, Jiao

    2015-08-01

    In ices coating dust grains in molecular clouds, nitrogen-containing molecules - mostly NH3 - are present in sizable quantity, up to 15-20% with respect to water ice, the largest component. We studied the oxidation of ammonia in a series of experiments using beams of oxygen and ammonia in various configurations (co-deposition and sequential deposition with various NH3:O ratios). We detected the formation of hydroxylamine (NH2OH) and other products, depending on the degree of oxidation. A simulation of a dense cloud with input from experimental data shows that on and in ices at 14 K and with modest activation energy for reaction, NH2OH is easily formed and its abundance never falls below a tenth of the NH3 abundance. Strategies for detection of hydroxylamine in the ISM will be presented.This work is supported by the NSF Astronomy and Astrophysics Division (grant No.1311958 to G.V.). R.T.G. acknowledges the support of the NASA Astrophysics Theory Program (grant No. NNX11AC38G).

  12. Self-confinement of finite dust clusters in isotropic plasmas.

    Science.gov (United States)

    Miloshevsky, G V; Hassanein, A

    2012-05-01

    Finite two-dimensional dust clusters are systems of a small number of charged grains. The self-confinement of dust clusters in isotropic plasmas is studied using the particle-in-cell method. The energetically favorable configurations of grains in plasma are found that are due to the kinetic effects of plasma ions and electrons. The self-confinement phenomenon is attributed to the change in the plasma composition within a dust cluster resulting in grain attraction mediated by plasma ions. This is a self-consistent state of a dust cluster in which grain's repulsion is compensated by the reduced charge and floating potential on grains, overlapped ion clouds, and depleted electrons within a cluster. The common potential well is formed trapping dust clusters in the confined state. These results provide both valuable insights and a different perspective to the classical view on the formation of boundary-free dust clusters in isotropic plasmas.

  13. Propagation of waves in a multicomponent plasma having charged ...

    Indian Academy of Sciences (India)

    Propagation of waves in a multicomponent plasma having charged dust particles has been investigated by various authors in recent times as the presence of charged dust grains give rise to a new kind of modes called dust modes and it has wide applications in magneto- sphere and space plasma [1–3]. In fact, Rao et al [4] ...

  14. Variable extinction in HD 45677 and the evolution of dust grains in pre-main-sequence disks

    Science.gov (United States)

    Sitko, Michael L.; Halbedel, Elaine M.; Lawrence, Geoffrey F.; Smith, J. Allyn; Yanow, Ken

    1994-01-01

    Changes in the UV extinction and IR emission were sought in the Herbig Ae/Be star candidate HD 45677 (= FS CMa) by comparing UV, optical, and IR observations made approximately 10 yr apart. HD 45677 varied significantly, becoming more than 50% brighter in the UV and optical than it was a decade ago. A comparison of the observations between epochs indicates that if the variations are due to changes in dust obscuration, the dust acts as a gray absorber into the near-IR and must be depleted in grains smaller than 1 micron. This is similar to the results obtained on the circumstellar disks of stars like Vega and Beta Pic, and suggests that radiation pressure may be responsible for the small-grain depletion. In addition, the total IR flux seems to have declined, indicating a decrease in the total mass of the dust envelope that contributes to the IR emission in this part of the spectrum. Due to the anomalous nature of the extinction, the use of normal extinction curves to deredden the spectral energy distributions of stars with circumstellar dust may lead to significant errors and should be used with great caution.

  15. Radial decoupling of small and large dust grains in the transitional disk RX J1615.3-3255

    Science.gov (United States)

    Kooistra, Robin; Kamp, Inga; Fukagawa, Misato; Menard, Francois; Momose, Munetake; Tsukagoshi, Takashi; Kudo, Tomoyuki; Kusakabe, Nobuhiko; Hashimoto, Jun; Abe, Lyu; hide

    2017-01-01

    We present H-band (1.6 micron) scattered light observations of the transitional disk RX J1615.3-3255, located in the approx. 1 Myr old Lupus association. From a polarized intensity image, taken with the HiCIAO instrument of the Subaru Telescope, we deduce the position angle and the inclination angle of the disk. The disk is found to extend out to 68 +/- 12 AU in scattered light and no clear structure is observed. Our inner working angle of 24 AU does not allow us to detect a central decrease in intensity similar to that seen at 30 AU in the 880 m continuum observations. We compare the observations with multiple disk models based on the spectral energy distribution (SED) and submm interferometry and find that an inner rim of the outer disk at 30 AU containing small silicate grains produces a polarized intensity signal which is an order of magnitude larger than observed. We show that a model in which the small dust grains extend smoothly into the cavity found for large grains is closer to the actual H-band observations. A comparison of models with different dust size distributions suggests that the dust in the disk might have undergone significant processing compared to the interstellar medium.

  16. Dust-Plasma Interactions

    International Nuclear Information System (INIS)

    Rosenberg, Marelene

    2005-01-01

    Our theoretical research on dust-plasma interactions has concentrated on three main areas: (a)studies of grain charging and applications; (b) waves and instabilities in weakly correlated dusty plasma with applications to space and laboratory plasmas; (c) waves in strongly coupled dusty plasmas.

  17. Effects of polymorphic variations in tumor necrosis factor alpha and occupational exposure to grain dust on longitudinal decline in pulmonary function.

    Science.gov (United States)

    Pahwa, Punam; Nakagawa, Kazuko; Koehncke, Niels; McDuffie, Helen H

    2009-01-01

    Longitudinal declines in pulmonary function are associated with individuals experiencing occupational exposure to organic dusts in combination with lifestyle factors such as cigarette smoking and with genetic factors, and interactions between these factors. To investigate the relationship between polymorphism of genes encoding Tumor Necrosis Factor Alpha (TNF-alpha) and longitudinal lung function decline in grain workers exposed to grain dust. Male grain handlers who participated in the Saskatchewan Grain Workers Surveillance Program from 2002 through 2005 provided demographic, occupational, lifestyle, and respiratory symptoms information as well as pulmonary function measurements and DNA for genotyping. Marginal models using the generalized estimating equations approach were fitted by using a SAS PROC GENMOD to predict the annual decline in Forced Expired Volume in one second (FEV(1)) and Forced Vital Capacity (FVC). Smoking intensity contributed to the decline in FEV(1.)Among *1/*1 homozygotes and *1/*2 heterozygotes, grain workers with grain industry had significantly lower FEV(1)declines compared to those of the other two exposure groups (>10 and 20 years in the grain industry). The annual declines in FEV(1)for grain workers who were either *1/*1 homozygote or *1/*2 heterozygote and had been in the grain industry for grain workers who were *2/*2 genotype and had been in the industry for grain industry is an effect modifier between TNF-alpha 308 genotype and longitudinal decline in FEV(1)in male subjects exposed to grain dust.

  18. On Influence of Neutrals on Dust Particle Charging in Complex Plasmas in the Presence of Electromagnetic Radiation

    International Nuclear Information System (INIS)

    Kopnin, S. I.; Morzhakova, A. A.; Popel, S. I.; Shukla, P. K.

    2011-01-01

    Effects associated with neutral component of complex (dusty) ionospheric plasmas which affect dust particle charging are studied. Microscopic ion currents on dust particles with taking into account ion-neutral interaction are presented. Calculations are performed both for the case of negative charges of dust particles, when the influence of Solar radiation on dust particle charging processes is negligible, and for the case of positive charges which is realized in the presence of sufficiently intensive UV or X-ray radiation. We also carry out investigation of the electron heating due to the photoelectric effect. We show that the efficiency of electron heating depends on the density of neutral component of the plasma. As result, we determine altitudes where the influence of the neutral plasma component on dust particle charging processes as well as the electron heating effect are significant and should be taken into account under consideration of the ionospheric complex plasmas. In particular, we show that the effects considered could be important for the description of noctilucent clouds, polar mesosphere summer echoes, and some other physical phenomena associated with dust particles in the ionosphere.

  19. Grain dust induces IL-8 production from bronchial epithelial cells: effect on neutrophil recruitment.

    Science.gov (United States)

    Park, H S; Suh, J H; Kim, S S; Kwon, O J

    2000-06-01

    There have been several investigations suggesting an involvement of activated neutrophils in the development of grain dust (GD)-induced occupational asthma. Interleukin-8 in the sputa from GD-induced asthmatic patients increased significantly after the exposure to GD. To confirm IL-8 production from bronchial epithelial cells when exposed to GD, and to evaluate the role of IL-8 on neutrophil recruitment. We cultured Beas-2B, a bronchial epithelial cell line. To observe GD-induced responses, four different concentrations ranging from 1 to 200 microg/mL of GD were incubated for 24 hours and compared with those without incubation of GD. To evaluate the effect of pro-inflammatory cytokines on IL-8 production and neutrophil chemotaxis, epithelial cells were incubated with peripheral blood mononuclear cell (PBMC) culture supernatant derived from subjects with GD-induced asthma exposed to 10 microg/mL of GD, and then compared with those without addition of PBMC supernatant. The level of released IL-8 in the supernatant was measured by enzyme-linked immunosorbent assay. Neutrophil chemotactic activity of the culture supernatant was determined by modified Boyden chamber method. Interleukin-8 production and neutrophil chemotactic activity from bronchial epithelial cells significantly increased with additions of GD in a dose-dependent manner (P < .05, respectively), and were significantly augmented with additions of PBMC supernatant (P < .05, respectively) at each concentration. Close correlation was noted between neutrophil chemotactic activity and IL-8 level (r = 0.87, P < .05). Compared with the untreated sample, pre-treatment of anti-IL-8 antibody induced a significant suppression (up to 67.2%) of neutrophil chemotactic activity in a dose-dependent manner. These results suggest that IL-8 produced from bronchial epithelial cells may be a major cytokine, which induces neutrophil migration into the airways when exposed to GD.

  20. Enhanced basophil histamine release and neutrophil chemotactic activity predispose grain dust-induced airway obstruction.

    Science.gov (United States)

    Park, H; Jung, K; Kang, K; Nahm, D; Cho, S; Kim, Y

    1999-04-01

    The pathogenic mechanism of grain dust (GD)-induced occupational asthma (OA) remains unclear. To understand further the mechanism of GD-induced OA. Fifteen employees working in a same GD industry, complaining of work-related respiratory symptoms, were enrolled and were divided into two groups according to the GD-bronchoprovocation test (BPT) result: six positive responders were grouped as group III, nine negative responders as group II and five healthy controls as group I. Serum GD-specific immunoglobulin (Ig)E (sIgE), specific IgG (sIgG) and specific IgG4 (sIgG4) antibodies were detected by enzyme-linked immunosorbent assay. Basophil histamine release was measured by the autofluorometric method, and changes of serum neutrophil chemotactic activity were observed by the Boyden chamber method. For clinical parameters such as degree of airway hyperresponsiveness to methacholine, duration of respiratory symptoms, exposure duration, and prevalences of serum sIgE, sIgG and sIgG4 antibodies, there were no significant differences between group II and III (P > 0.05, respectively). Serum neutrophil chemotactic activity increased significantly at 30 min and decreased at 240 min after the GD-BPT in group III subjects (P 0.05). Basophil histamine release induced by GD was significantly higher in group III than those of group I or group II (P < 0.05, respectively), while minimal release of anti-IgG4 antibodies was noted in all three groups. These results suggest that enhanced basophil histamine release and serum neutrophil chemotactic activity might contribute to the development of GD-induced occupational asthma.

  1. Assessment of Workers' Exposure to Grain Dust and Bioaerosols During the Loading of Vessels' Hold: An Example at a Port in the Province of Québec.

    Science.gov (United States)

    Marchand, Geneviève; Gardette, Marie; Nguyen, Kiet; Amano, Valérie; Neesham-Grenon, Eve; Debia, Maximilien

    2017-08-01

    Longshoremen are exposed to large amounts of grain dust while loading of grain into the holds of vessels. Grain dust inhalation has been linked to respiratory diseases such as chronic bronchitis, hypersensitivity, pneumonitis, and toxic pneumonitis. Our objective was to characterize the exposure of longshoremen to inhalable and total dust, endotoxins, and cultivable bacteria and fungi during the loading of grain in a vessel's hold at the Port of Montreal in order to assess the potential health risks. Sampling campaigns were conducted during the loading of two different types of grain (wheat and corn). Environmental samples of microorganisms (bacteria, fungus, and actinomycetes) were taken near the top opening of the ship's holds while personal breathing zone measurements of dust and endotoxins were sampled during the worker's 5-hour shifts. Our study show that all measurements are above the recommendations with concentration going up to 390 mg m-3 of total dust, 89 mg m-3 of inhalable fraction, 550 000 EU m-3 of endotoxins, 20 000 CFU m-3 of bacteria, 61 000 CFU m-3 of fungus and 2500 CFU m-3 of actinomycetes. In conclusion, longshoremen are exposed to very high levels of dust and of microorganisms and their components during grain loading work. Protective equipment needs to be enforced for all workers during such tasks in order to reduce their exposure. © The Author 2017. Published by Oxford University Press on behalf of the British Occupational Hygiene Society.

  2. Modulational instability of ultra-low-frequency shear dust Alfvén waves in a plasma medium of positive and negatively charged dust fluids

    International Nuclear Information System (INIS)

    Mamun, A. A.

    2014-01-01

    The propagation of finite amplitude ultra-low-frequency shear dust Alfvén (SDA) waves, and their modulational instability in a magnetized plasma medium of positive and negatively charged dust fluids have been theoretically investigated by using the reductive perturbation method. The derivative nonlinear Schrödinger equation is derived to examine the stability analysis of such SDA waves. It is found that the SDA waves propagating in such an opposite polarity dust plasma medium are modulationally unstable, and that the instability criterion and the growth rate of these unstable SDA waves in such a novel opposite polarity dust plasma medium are found to be significantly different from those in electron–ion or electron–positron plasma media. The implications of the present investigation in different space environments and laboratory devices are briefly discussed.

  3. Induced charge of spherical dust particle on plasma-facing wall in non-uniform electric field

    International Nuclear Information System (INIS)

    Tomita, Y.; Smirnov, R.; Zhu, S.

    2005-01-01

    Induced charge of a spherical dust particle on a plasma-facing wall is investigated analytically, where non-uniform electric field is applied externally. The one-dimensional non-uniform electrostatic potential is approximated by the polynomial of the normal coordinate toward the wall. The bipolar coordinate is introduced to solve the Laplace equation of the induced electrostatic potential. The boundary condition at the dust surface determines the unknown coefficients of the general solution of the Laplace equation for the induced potential. From the obtained potential the surface induced charge can be calculated. This result allows estimating the effect of the surrounding plasma, which shields the induced charge. (author)

  4. Dust Acoustic Solitons in the Dusty Plasma of the Earth's Ionosphere

    International Nuclear Information System (INIS)

    Kopnin, S.I.; Kosarev, I.N.; Popel, S.I.; Yu, M.Y.

    2005-01-01

    Stratified structures that are observed at heights of 80-95 km in the lower part of the Earth's ionosphere are known as noctilucent clouds and polar mesosphere summer echoes. These structures are thought to be associated with the presence of vast amounts of charged dust or aerosols. The layers in the lower ionosphere where there are substantial amounts of dust are called the dusty ionosphere. The dust grains can carry a positive or a negative charge, depending on their constituent materials. As a rule, the grains are ice crystals, which may contain metallic inclusions. A grain with a sufficiently large metallic content can acquire a positive charge. Crystals of pure ice are charged negatively. The distribution of the dust grains over their charges has a profound impact on the ionizational and other properties of dust structures in the dusty ionosphere. In the present paper, a study is made of the effect of the sign of the dust charge on the properties of dust acoustic solitons propagating in the dusty ionosphere. It is shown that, when the dust charge is positive, dust acoustic solitons correspond to a hill in the electron density and a well in the ion density. When the dust is charged negatively, the situation is opposite. These differences in the properties of dust acoustic solitons can be used to diagnose the plasmas of noctilucent clouds and polar mesosphere summer echoes

  5. SPITZER survey of dust grain processing in stable discs around binary post-AGB stars

    NARCIS (Netherlands)

    Gielen, C.; van Winckel, H.; Min, M.; Waters, L.B.F.M.; Lloyd Evans, T.

    2008-01-01

    Aims. We investigate the mineralogy and dust processing in the circumbinary discs of binary post-AGB stars using high-resolution TIMMI2 and SPITZER infrared spectra. Methods: We perform a full spectral fitting to the infrared spectra using the most recent opacities of amorphous and crystalline dust

  6. Grain Boundaries Act as Solid Walls for Charge Carrier Diffusion in Large Crystal MAPI Thin Films.

    Science.gov (United States)

    Ciesielski, Richard; Schäfer, Frank; Hartmann, Nicolai F; Giesbrecht, Nadja; Bein, Thomas; Docampo, Pablo; Hartschuh, Achim

    2018-03-07

    Micro- and nanocrystalline methylammonium lead iodide (MAPI)-based thin-film solar cells today reach power conversion efficiencies of over 20%. We investigate the impact of grain boundaries on charge carrier transport in large crystal MAPI thin films using time-resolved photoluminescence (PL) microscopy and numerical model calculations. Crystal sizes in the range of several tens of micrometers allow for the spatially and time resolved study of boundary effects. Whereas long-ranged diffusive charge carrier transport is observed within single crystals, no detectable diffusive transport occurs across grain boundaries. The observed PL transients are found to crucially depend on the microscopic geometry of the crystal and the point of observation. In particular, spatially restricted diffusion of charge carriers leads to slower PL decay near crystal edges as compared to the crystal center. In contrast to many reports in the literature, our experimental results show no quenching or additional loss channels due to grain boundaries for the studied material, which thus do not negatively affect the performance of the derived thin-film devices.

  7. The Lunar Dust Environment

    Science.gov (United States)

    Szalay, Jamey Robert

    Planetary bodies throughout the solar system are continually bombarded by dust particles, largely originating from cometary activities and asteroidal collisions. Surfaces of bodies with thick atmospheres, such as Venus, Earth, Mars and Titan are mostly protected from incoming dust impacts as these particles ablate in their atmospheres as 'shooting stars'. However, the majority of bodies in the solar system have no appreciable atmosphere and their surfaces are directly exposed to the flux of high speed dust grains. Impacts onto solid surfaces in space generate charged and neutral gas clouds, as well as solid secondary ejecta dust particles. Gravitationally bound ejecta clouds forming dust exospheres were recognized by in situ dust instruments around the icy moons of Jupiter and Saturn, and had not yet been observed near bodies with refractory regolith surfaces before NASA's Lunar Dust and Environment Explorer (LADEE) mission. In this thesis, we first present the measurements taken by the Lunar Dust Explorer (LDEX), aboard LADEE, which discovered a permanently present, asymmetric dust cloud surrounding the Moon. The global characteristics of the lunar dust cloud are discussed as a function of a variety of variables such as altitude, solar longitude, local time, and lunar phase. These results are compared with models for lunar dust cloud generation. Second, we present an analysis of the groupings of impacts measured by LDEX, which represent detections of dense ejecta plumes above the lunar surface. These measurements are put in the context of understanding the response of the lunar surface to meteoroid bombardment and how to use other airless bodies in the solar system as detectors for their local meteoroid environment. Third, we present the first in-situ dust measurements taken over the lunar sunrise terminator. Having found no excess of small grains in this region, we discuss its implications for the putative population of electrostatically lofted dust.

  8. EXPLORING THE ROLE OF SUB-MICRON-SIZED DUST GRAINS IN THE ATMOSPHERES OF RED L0–L6 DWARFS

    Energy Technology Data Exchange (ETDEWEB)

    Hiranaka, Kay; Cruz, Kelle L.; Baldassare, Vivienne F. [Hunter College, Department of Physics and Astronomy, City University of New York, 695 Park Ave, New York, NY 10065 (United States); Douglas, Stephanie T. [American Museum of Natural History, Department of Astrophysics, Central Park West at 79th Street, New York, NY 10024 (United States); Marley, Mark S., E-mail: khiranak@hunter.cuny.edu [NASA Ames Research Center, MS-245-3, Moffett Field, CA 94035 (United States)

    2016-10-20

    We examine the hypothesis that the red near-infrared colors of some L dwarfs could be explained by a “dust haze” of small particles in their upper atmospheres. This dust haze would exist in conjunction with the clouds found in dwarfs with more typical colors. We developed a model that uses Mie theory and the Hansen particle size distributions to reproduce the extinction due to the proposed dust haze. We apply our method to 23 young L dwarfs and 23 red field L dwarfs. We constrain the properties of the dust haze including particle size distribution and column density using Markov Chain Monte Carlo methods. We find that sub-micron-range silicate grains reproduce the observed reddening. Current brown dwarf atmosphere models include large-grain (1–100 μ m) dust clouds but not sub-micron dust grains. Our results provide a strong proof of concept and motivate a combination of large and small dust grains in brown dwarf atmosphere models.

  9. Influence of Addition of Briquettes with Dust Content into the Charge of Electric Induction Furnace on Cast Iron Quality

    Directory of Open Access Journals (Sweden)

    Pribulová A.

    2012-09-01

    Full Text Available Foundry dust from blasting and grinding of castings contain a high amount of iron, ergo it is possible its recycling in foundry process. Dust was compacted by briquetting, two kinds of briquettes were prepared (A contained 95% magnetic part of dust from casting blasting +5% bentonite and B contained 95% mixture of dust from casting grinding and magnetic part of dust from casting blasting + 5% bentonite and used as a part of charge into the electric induction furnace. It was found that addition of briquettes has had an influence of a chemical composition of cast iron above all on content of sulphur, phosphorus and silicon. It was not reflected in decrease in tensile strength and in microstructure. Yield of metal from briquettes was not lower then 70%.

  10. Influence of Addition of Briquettes with Dust Content into the Charge of Electric Induction Furnace on Cast Iron Quality

    Directory of Open Access Journals (Sweden)

    A. Pribulová

    2012-09-01

    Full Text Available Foundry dust from blasting and grinding of castings contain a high amount of iron, ergo it is possible its recycling in foundry process.Dust was compacted by briquetting, two kinds of briquettes were prepared (A contained 95% magnetic part of dust from casting blasting+5% bentonite and B contained 95% mixture of dust from casting grinding and magnetic part of dust from casting blasting + 5%bentonite and used as a part of charge into the electric induction furnace. It was found that addition of briquettes has had an influence of a chemical composition of cast iron above all on content of sulphur, phosphorus and silicon. It was not reflected in decrease in tensile strength and in microstructure. Yield of metal from briquettes was not lower then 70%.

  11. THE STRUCTURE OF PRE-TRANSITIONAL PROTOPLANETARY DISKS. II. AZIMUTHAL ASYMMETRIES, DIFFERENT RADIAL DISTRIBUTIONS OF LARGE AND SMALL DUST GRAINS IN PDS 70 {sup ,}

    Energy Technology Data Exchange (ETDEWEB)

    Hashimoto, J.; Wisniewski, J. [Department of Physics and Astronomy, The University of Oklahoma, 440 West Brooks Street, Norman, OK 73019 (United States); Tsukagoshi, T. [College of Science, Ibaraki University, Bunkyo 2-1-1, Mito 310-8512 (Japan); Brown, J. M. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 78, Cambridge, MA 02138 (United States); Dong, R. [Astronomy Department, University of California, Berkeley, CA 94720 (United States); Muto, T. [Division of Liberal Arts, Kogakuin University, 1-24-2, Nishi-Shinjuku, Shinjuku-ku, Tokyo 163-8677 (Japan); Zhu, Z. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Ohashi, N.; Kudo, T.; Egner, S.; Guyon, O. [Subaru Telescope, 650 North A' ohoku Place, Hilo, HI 96720 (United States); Kusakabe, N.; Akiyama, E. [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Abe, L. [Laboratoire Hippolyte Fizeau, UMR6525, Universite de Nice Sophia-Antipolis, 28, avenue Valrose, F-06108 Nice Cedex 02 (France); Brandner, W.; Carson, J.; Feldt, M. [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany); Brandt, T. [Astrophysics Department, Institute for Advanced Study, Princeton, NJ (United States); Currie, T. [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON (Canada); Grady, C. A., E-mail: jun.hashimoto@ou.edu [Eureka Scientific, 2452 Delmer, Suite 100, Oakland, CA 96002 (United States); and others

    2015-01-20

    The formation scenario of a gapped disk, i.e., transitional disk, and its asymmetry is still under debate. Proposed scenarios such as disk-planet interaction, photoevaporation, grain growth, anticyclonic vortex, eccentricity, and their combinations would result in different radial distributions of the gas and the small (sub-μm size) and large (millimeter size) dust grains as well as asymmetric structures in a disk. Optical/near-infrared (NIR) imaging observations and (sub-)millimeter interferometry can trace small and large dust grains, respectively; therefore multi-wavelength observations could help elucidate the origin of complicated structures of a disk. Here we report Submillimeter Array observations of the dust continuum at 1.3 mm and {sup 12}CO J = 2 → 1 line emission of the pre-transitional protoplanetary disk around the solar-mass star PDS 70. PDS 70, a weak-lined T Tauri star, exhibits a gap in the scattered light from its disk with a radius of ∼65 AU at NIR wavelengths. However, we found a larger gap in the disk with a radius of ∼80 AU at 1.3 mm. Emission from all three disk components (the gas and the small and large dust grains) in images exhibits a deficit in brightness in the central region of the disk, in particular, the dust disk in small and large dust grains has asymmetric brightness. The contrast ratio of the flux density in the dust continuum between the peak position to the opposite side of the disk reaches 1.4. We suggest the asymmetries and different gap radii of the disk around PDS 70 are potentially formed by several (unseen) accreting planets inducing dust filtration.

  12. The Structure of Pre-Transitional Protoplanetary Disks. II Azimuthal Asymmetries, Different Radial Distributions of Large and Small Dust Grains in PDS 70

    Science.gov (United States)

    Hashimoto, J.; Tsukagoshi, T.; Brown, J. M.; Dong, R.; Muto, T.; Zhu, Z.; Wisniewski, J.; Ohashi, N.; Kudo, T.; Kusakabe, N.; hide

    2015-01-01

    The formation scenario of a gapped disk, i.e., transitional disk, and its asymmetry is still under debate. Proposed scenarios such as disk-planet interaction, photoevaporation, grain growth, anticyclonic vortex, eccentricity, and their combinations would result in different radial distributions of the gas and the small (sub-micron size) and large (millimeter size) dust grains as well as asymmetric structures in a disk. Optical/near-infrared (NIR) imaging observations and (sub-)millimeter interferometry can trace small and large dust grains, respectively; therefore multi-wavelength observations could help elucidate the origin of complicated structures of a disk. Here we report Submillimeter Array observations of the dust continuum at 1.3 mm and CO-12 J = 2 yields 1 line emission of the pre-transitional protoplanetary disk around the solar-mass star PDS 70. PDS 70, a weak-lined T Tauri star, exhibits a gap in the scattered light from its disk with a radius of approx. 65 AU at NIR wavelengths. However, we found a larger gap in the disk with a radius of approx. 80 AU at 1.3 mm. Emission from all three disk components (the gas and the small and large dust grains) in images exhibits a deficit in brightness in the central region of the disk, in particular, the dust disk in small and large dust grains has asymmetric brightness. The contrast ratio of the flux density in the dust continuum between the peak position to the opposite side of the disk reaches 1.4. We suggest the asymmetries and different gap radii of the disk around PDS 70 are potentially formed by several (unseen) accreting planets inducing dust filtration.

  13. On the height variation of the E-region cowling conductivity – effect of charged dust particles

    Directory of Open Access Journals (Sweden)

    P. Muralikrishna

    2006-11-01

    Full Text Available Height profiles of the Cowling conductivity in the electrojet region, estimated using the atmospheric parameters given by the existing models like CIRA or MSIS and measured electron density profiles, consistently show the heights of the electrojet current intensity peak to be more than 3 km below those estimated from in-situ measurements using magnetometers on board sounding rockets. Kulkarni and Muralikrishna (2005 attempted to explain this to be due to the effect of neutral dust particles. They reported that neutral dust particles, when they exist in sufficient numbers, can modify the collision parameters, especially in the lower E-region, where dust particles of meteoric origin are known to exist in large numbers, and thereby can modify the Cowling conductivity profile in the electrojet region. This work is extended here to include the effect of charged dust particles. Dust particles can become charged negatively by the attachment of ambient free electrons, and can thus reduce the number density of free electrons especially below the electrojet peak. This can alter the vertical profile of the east-west Hall current driven by the vertical Hall polarization field, thereby causing a net reduction in the electrojet current. Such a decrease in the electrojet current may be observed on the ground magnetograms. This mechanism, as proposed here, can operate only during periods of strong meteor shower activity, when the dust particle density at the assumed deposit height of 103 km can reach extreme values (for example, 5×104 cm−3 of 1-µm diameter dust particles. Such a dense dust layer may even cause a reversal in the normally upward vertical Hall polarization field, within the dust layer, causing a reversal of the electrojet currents below the current peak.

  14. The Electric Environment of Martian Dust Devils

    Science.gov (United States)

    Barth, E. L.; Farrell, W. M.; Rafkin, S. C.

    2017-12-01

    While Martian dust devils have been monitored through decades of observations, we have yet to study their possible electrical effects from in situ instrumentation. However, evidence for the existence of active electrodynamic processes on Mars is provided by laboratory studies of analog material and field campaigns of dust devils on Earth. We have enabled our Mars regional scale atmospheric model (MRAMS) to estimate an upper limit on electric fields generated through dust devil circulations by including charged particles as defined from the Macroscopic Triboelectric Simulation (MTS) code. MRAMS is used to investigate the complex physics of regional, mesoscale, and microscale atmospheric phenomena on Mars; it is a 3-D, nonhydrostatic model, which permits the simulation of atmospheric flows with large vertical accelerations, such as dust devils. MTS is a 3-D particle code which quantifies charging associated with swirling, mixing dust grains; grains of pre-defined sizes and compositions are placed in a simulation box and allowed to move under the influence of winds and gravity. Our MRAMS grid cell size makes our results most applicable to dust devils of a few hundred meters in diameter. We have run a number of simulations to understand the sensitivity of the electric field strength to the particle size and abundance and the amount of charge on each dust grain. We find that Efields can indeed develop in Martian dust convective features via dust grain filtration effects. The overall value of these E-fields is strongly dependent upon dust grain size, dust load, and lifting efficiency, and field strengths can range from 100s of mV/m to 10s of kV/m.

  15. Hypervelocity Dust Injection for Plasma Diagnostic Applications

    Science.gov (United States)

    Ticos, Catalin

    2005-10-01

    Hypervelocity micron-size dust grain injection was proposed for high-temperature magnetized plasma diagnosis. Multiple dust grains are launched simultaneously into high temperature plasmas at several km/s or more. The hypervelocity dust grains are ablated by the electron and ion fluxes. Fast imaging of the resulting luminous plumes attached to each grain is expected to yield local magnetic field vectors. Combination of multiple local magnetic field vectors reproduces 2D or even 3D maps of the internal magnetic field topology. Key features of HDI are: (1) a high spatial resolution, due to a relatively small transverse size of the elongated tail, and (2) a small perturbation level, as the dust grains introduce negligible number of particles compared to the plasma particle inventory. The latter advantage, however, could be seriously compromised if the gas load from the accelerator has an unobstructed access to the diagnosed plasma. Construction of a HDI diagnostic for National Spherical Torus Experiment (NSTX), which includes a coaxial plasma gun for dust grain acceleration, is underway. Hydrogen and deuterium gas discharges inside accelerator are created by a ˜ 1 mF capacitor bank pre-charged up to 10 kV. The diagnostic apparatus also comprises a dust dispenser for pre-loading the accelerator with dust grains, and an imaging system that has a high spatial and temporal resolution.

  16. The evolution of grain mantles and silicate dust growth at high redshift

    Science.gov (United States)

    Ceccarelli, Cecilia; Viti, Serena; Balucani, Nadia; Taquet, Vianney

    2018-05-01

    In dense molecular clouds, interstellar grains are covered by mantles of iced molecules. The formation of the grain mantles has two important consequences: it removes species from the gas phase and promotes the synthesis of new molecules on the grain surfaces. The composition of the mantle is a strong function of the environment that the cloud belongs to. Therefore, clouds in high-zeta galaxies, where conditions - like temperature, metallicity, and cosmic ray flux - are different from those in the Milky Way, will have different grain mantles. In the last years, several authors have suggested that silicate grains might grow by accretion of silicon-bearing species on smaller seeds. This would occur simultaneously with the formation of the iced mantles and be greatly affected by its composition as a function of time. In this work, we present a numerical study of the grain mantle formation in high-zeta galaxies, and we quantitatively address the possibility of silicate growth. We find that the mantle thickness decreases with increasing redshift, from about 120 to 20 layers for z varying from 0 to 8. Furthermore, the mantle composition is also a strong function of the cloud redshift, with the relative importance of CO, CO2, ammonia, methane, and methanol highly varying with z. Finally, being Si-bearing species always a very minor component of the mantle, the formation of silicates in molecular clouds is practically impossible.

  17. Collision and recombination driven instabilities in variable charged ...

    Indian Academy of Sciences (India)

    The dust-acoustic instability driven by recombination of electrons and ions on the surface of charged and variably-charged dust grains as well as by collisions in dusty plasmas with significant pressure of background neutrals have been theoretically investigated. The recombination driven instability is shown to be dominant ...

  18. Anomalous g-Factors for Charged Leptons in a Fractional Coarse-Grained Approach

    International Nuclear Information System (INIS)

    Helayël-Neto, J. A.; Weberszpil, J.

    2014-01-01

    We here propose to extend the concept of helicity to include it in a fractional scenario and we write down the left- and the right-handed Weyl equations from first principles in this extended framework. Next, by coupling the different fractional Weyl sectors by means of a mass parameter, we arrive at the fractional version of Dirac's equation which, whenever coupled to an external electromagnetic field and reduced to the nonrelativistic regime, yields a fractional Pauli-type equation. From the latter, we are able to present an explicit expression for the gyromagnetic ratio of charged fermions in terms of the fractionality parameter. We then focus our efforts to relate the coarse-grained property of space-time to fractionality and to the (g-2) anomalies of the different leptonic species

  19. Nonlinear ion acoustic waves in a quantum degenerate warm plasma with dust grains

    International Nuclear Information System (INIS)

    Dubinov, A. E.; Kolotkov, D. Yu.; Sazonkin, M. A.

    2011-01-01

    A study is made of the propagation of ion acoustic waves in a collisionless unmagnetized dusty plasma containing degenerate ion and electron gases at nonzero temperatures. In linear theory, a dispersion relation for isothermal ion acoustic waves is derived and an exact expression for the linear ion acoustic velocity is obtained. The dependence of the linear ion acoustic velocity on the dust density in a plasma is calculated. An analysis of the dispersion relation reveals parameter ranges in which the problem has soliton solutions. In nonlinear theory, an exact solution to the basic equations is found and examined. The analysis is carried out by Bernoulli’s pseudopotential method. The ranges of the phase velocities of periodic ion acoustic waves and the velocities of solitons are determined. It is shown that these ranges do not overlap and that the soliton velocity cannot be lower than the linear ion acoustic velocity. The profiles of the physical quantities in a periodic wave and in a soliton are evaluated, as well as the dependence of the critical velocity of solitons on the dust density in a plasma.

  20. Influence of orientation mismatch on charge transport across grain boundaries in tri-isopropylsilylethynyl (TIPS) pentacene thin films.

    Science.gov (United States)

    Steiner, Florian; Poelking, Carl; Niedzialek, Dorota; Andrienko, Denis; Nelson, Jenny

    2017-05-03

    We present a multi-scale model for charge transport across grain boundaries in molecular electronic materials that incorporates packing disorder, electrostatic and polarisation effects. We choose quasi two-dimensional films of tri-isopropylsilylethynyl pentacene (TIPS-P) as a model system representative of technologically relevant crystalline organic semiconductors. We use atomistic molecular dynamics, with a force-field specific for TIPS-P, to generate and equilibrate polycrystalline two-dimensional thin films. The energy landscape is obtained by calculating contributions from electrostatic interactions and polarization. The variation in these contributions leads to energetic barriers between grains. Subsequently, charge transport is simulated using a kinetic Monte-Carlo algorithm. Two-grain systems with varied mutual orientation are studied. We find relatively little effect of long grain boundaries due to the presence of low impedance pathways. However, effects could be more pronounced for systems with limited inter-grain contact areas. Furthermore, we present a lattice model to generalize the model for small molecular systems. In the general case, depending on molecular architecture and packing, grain boundaries can result in interfacial energy barriers, traps or a combination of both with qualitatively different effects on charge transport.

  1. Small vs. large dust grains in transitional disks: do different cavity sizes indicate a planet?. SAO 206462 (HD 135344B) in polarized light with VLT/NACO

    Science.gov (United States)

    Garufi, A.; Quanz, S. P.; Avenhaus, H.; Buenzli, E.; Dominik, C.; Meru, F.; Meyer, M. R.; Pinilla, P.; Schmid, H. M.; Wolf, S.

    2013-12-01

    Context. Transitional disks represent a short stage of the evolution of circumstellar material. Studies of dust grains in these objects can provide pivotal information on the mechanisms of planet formation. Dissimilarities in the spatial distribution of small (μm-size) and large (mm-size) dust grains have recently been pointed out. Aims: Constraints on the small dust grains can be obtained by imaging the distribution of scattered light at near-infrared wavelengths. We aim at resolving structures in the surface layer of transitional disks (with particular emphasis on the inner 10-50 AU), thus increasing the scarce sample of high-resolution images of these objects. Methods: We obtained VLT/NACO near-IR high-resolution polarimetric differential imaging observations of SAO 206462 (HD 135344B). This technique allows one to image the polarized scattered light from the disk without any occulting mask and to reach an inner working angle of ~0.1″. Results: A face-on disk is detected in H and Ks bands between 0.1″ and 0.9″. No significant differences are seen between the H and Ks images. In addition to the spiral arms, these new data allow us to resolve for the first time an inner disk cavity for small dust grains. The cavity size (≃28 AU) is much smaller than what is inferred for large dust grains from (sub-)mm observations (39 to 50 AU). This discrepancy cannot be ascribed to any resolution effect. Conclusions: The interaction between the disk and potential orbiting companion(s) can explain both the spiral arm structure and the discrepant cavity sizes for small and large dust grains. One planet may be carving out the gas (and, thus, the small grains) at 28 AU, and generating a pressure bump at larger radii (39 AU), which holds back the large grains. We analytically estimate that, in this scenario, a single giant planet (with a mass between 5 and 15 MJ) at 17 to 20 AU from the star is consistent with the observed cavity sizes. Based on observations collected at the

  2. Suprathermal grains: on intergalactic magnetic fields

    International Nuclear Information System (INIS)

    Dasgupta, A.K.

    1979-01-01

    Charged dust grains of radii a approximately equal to 3 x 10 -6 to approximately 3 x 10 -5 cm may be driven out of the galaxy due to radiation pressure of starlight. Once clear of the main gas-dust layer, dust grains may then escape into intergalactic space. Such grains are virtually indestructible-being evaporated only during formation. The dust grains, once injected into the intergalactic medium, may acquire suprathermal energy, thus 'suprathermal grains' in collision with magnetized cloud by the Fermi process. In order to attain relativistic energy, suprathermal grains have to move in and out ('scattering') of the magnetic field of the medium. It is now well established that high energy cosmic rays are of the order 10 20 eV or more. It has been speculated that these high energy (> = 10 18 eV) cosmic ray particles are charged dust grains, of intergalactic origin. This is possible only if there exists a magnetic field in the intergalactic medium. (Auth.)

  3. Dissipative dust-acoustic shock waves in a varying charge electronegative magnetized dusty plasma with trapped electrons

    Energy Technology Data Exchange (ETDEWEB)

    Bacha, Mustapha [Faculty of Physics, Theoretical Physics Laboratory, Plasma Physics Group, University of Bab-Ezzouar, USTHB, B.P. 32, El Alia, Algiers 16111 (Algeria); Tribeche, Mouloud, E-mail: mouloudtribeche@yahoo.fr, E-mail: mtribeche@usthb.dz [Faculty of Physics, Theoretical Physics Laboratory, Plasma Physics Group, University of Bab-Ezzouar, USTHB, B.P. 32, El Alia, Algiers 16111 (Algeria); Algerian Academy of Sciences and Technologies, Algiers (Algeria)

    2016-08-15

    The combined effects of an oblique magnetic field and electron trapping on dissipative dust-acoustic waves are examined in varying charge electronegative dusty plasmas with application to the Halley Comet plasma (∼10{sup 4} km from the nucleus). A weakly nonlinear analysis is carried out to derive a modified Korteweg-de Vries-Burger-like equation. Making use of the equilibrium current balance equation, the physically admissible values of the electron trapping parameter are first constrained. We then show that the Burger dissipative term is solely due to the dust charge variation process. It is found that an increase of the magnetic field obliqueness or a decrease of its magnitude renders the shock structure more dispersive.

  4. THE FORMATION OF THE PRIMITIVE STAR SDSS J102915+172927: EFFECT OF THE DUST MASS AND THE GRAIN-SIZE DISTRIBUTION

    International Nuclear Information System (INIS)

    Bovino, S.; Banerjee, R.; Grassi, T.; Schleicher, D. R. G.

    2016-01-01

    Understanding the formation of the extremely metal-poor star SDSS J102915+172927 is of fundamental importance to improve our knowledge on the transition between the first and second generation of stars in the universe. In this paper, we perform three-dimensional cosmological hydrodynamical simulations of dust-enriched halos during the early stages of the collapse process including a detailed treatment of the dust physics. We employ the astrochemistry package krome coupled with the hydrodynamical code enzo assuming grain-size distributions produced by the explosion of core-collapse supernovae (SNe) of 20 and 35 M ⊙ primordial stars, which are suitable to reproduce the chemical pattern of the SDSS J102915+172927 star. We find that the dust mass yield produced from Population III SNe explosions is the most important factor that drives the thermal evolution and the dynamical properties of the halos. Hence, for the specific distributions relevant in this context, the composition, the dust optical properties, and the size range have only minor effects on the results due to similar cooling functions. We also show that the critical dust mass to enable fragmentation provided by semi-analytical models should be revised, as we obtain values one order of magnitude larger. This determines the transition from disk fragmentation to a more filamentary fragmentation mode, and suggests that likely more than one single SN event or efficient dust growth should be invoked to get such high dust content.

  5. THE FORMATION OF THE PRIMITIVE STAR SDSS J102915+172927: EFFECT OF THE DUST MASS AND THE GRAIN-SIZE DISTRIBUTION

    Energy Technology Data Exchange (ETDEWEB)

    Bovino, S.; Banerjee, R. [Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, D-21029 Hamburg (Germany); Grassi, T. [Niels Bohr Institute and Centre for Star and Planet Formation, Øster Voldgade 5-7, DK-1350 Copenhagen (Denmark); Schleicher, D. R. G., E-mail: stefano.bovino@uni-hamburg.de [Departamento de Astronomía, Facultad Ciencias Físicas y Matemáticas, Universidad de Concepción, Av. Esteban Iturra s/n Barrio Universitario, Casilla 160, Concepción (Chile)

    2016-12-01

    Understanding the formation of the extremely metal-poor star SDSS J102915+172927 is of fundamental importance to improve our knowledge on the transition between the first and second generation of stars in the universe. In this paper, we perform three-dimensional cosmological hydrodynamical simulations of dust-enriched halos during the early stages of the collapse process including a detailed treatment of the dust physics. We employ the astrochemistry package krome coupled with the hydrodynamical code enzo assuming grain-size distributions produced by the explosion of core-collapse supernovae (SNe) of 20 and 35 M {sub ⊙} primordial stars, which are suitable to reproduce the chemical pattern of the SDSS J102915+172927 star. We find that the dust mass yield produced from Population III SNe explosions is the most important factor that drives the thermal evolution and the dynamical properties of the halos. Hence, for the specific distributions relevant in this context, the composition, the dust optical properties, and the size range have only minor effects on the results due to similar cooling functions. We also show that the critical dust mass to enable fragmentation provided by semi-analytical models should be revised, as we obtain values one order of magnitude larger. This determines the transition from disk fragmentation to a more filamentary fragmentation mode, and suggests that likely more than one single SN event or efficient dust growth should be invoked to get such high dust content.

  6. Grain-Scale Supercharging and Breakdown on Airless Regoliths

    Science.gov (United States)

    Zimmerman, M. I.; Farrell, W. M.; Hartzell, C.M.; Wang, X.; Horanyi, M.; Hurley, D. M.; Hibbitts, K.

    2016-01-01

    Interactions of the solar wind and emitted photoelectrons with airless bodies have been studied extensively. However, the details of how charged particles interact with the regolith at the scale of a single grain have remained largely uncharacterized. Recent efforts have focused upon determining total surface charge under photoemission and solar wind bombardment and the associated electric field and potential. In this work, theory and simulations are used to show that grain-grain charge differences can exceed classical sheath predictions by several orders of magnitude, sometimes reaching dielectric breakdown levels. Temperature-dependent electrical conductivity works against supercharging by allowing current to leak through individual grains; the balance between internal conduction and surface charging controls the maximum possible grain-to-grain electric field. Understanding the finer details of regolith grain charging, conductive equilibrium, and dielectric breakdown will improve future numerical studies of space weathering and dust levitation on airless bodies.

  7. Effects of Ca doping and O deficiency on the charge distribution in the vicinity of a 45° [001] grain boundary in YBa2Cu3O7

    KAUST Repository

    Schwingenschlö gl, Udo; Schuster, Cosima B.

    2012-01-01

    The charge redistribution at grain boundaries is critical for the applicability of high-T c superconductors in electronic devices, because it determines the transport across the material. We investigate the charge transfer and the alterations

  8. Hamiltonian Formulation and Perturbations for Dust Motion Around Cometary Nuclei

    Science.gov (United States)

    Jiang, Yu; Schmidt, Juergen; Baoyin, Hexi; Li, Hengnian; Li, Junfeng

    2017-12-01

    In this paper we analyze the dynamical behavior of large dust grains in the vicinity of a cometary nucleus. To this end we consider the gravitational field of the irregularly shaped body, as well as its electric and magnetic fields. Without considering the effect of gas friction and solar radiation, we find that there exist grains which are static relative to the cometary nucleus; the positions of these grains are the stable equilibria. There also exist grains in the stable periodic orbits close to the cometary nucleus. The grains in the stable equilibria or the stable periodic orbits won't escape or impact on the surface of the cometary nucleus. The results are applicable for large charge dusts with small area-mass ratio which are near the cometary nucleus and far from the Solar. It is found that the resonant periodic orbit can be stable, and there exist stable non-resonant periodic orbits, stable resonant periodic orbits and unstable resonant periodic orbits in the potential field of cometary nuclei. The comet gravity force, solar gravity force, electric force, magnetic force, solar radiation pressure, as well as the gas drag force are all considered to analyze the order of magnitude of these forces acting on the grains with different parameters. Let the distance of the dust grain relative to the mass centre of the cometary nucleus, the charge and the mass of the dust grain vary, respectively, fix other parameters, we calculated the strengths of different forces. The motion of the dust grain depends on the area-mass ratio, the charge, and the distance relative to the comet's mass center. For a large dust grain (> 1 mm) close to the cometary nucleus which has a small value of area-mass ratio, the comet gravity is the largest force acting on the dust grain. For a small dust grain (< 1 mm) close to the cometary nucleus with large value of area-mass ratio, both the solar radiation pressure and the comet gravity are two major forces. If the a small dust grain which is

  9. Neutrophil infiltration and release of IL-8 in airway mucosa from subjects with grain dust-induced occupational asthma.

    Science.gov (United States)

    Park, H S; Jung, K S; Hwang, S C; Nahm, D H; Yim, H E

    1998-06-01

    The immuno-pathological mechanism for occupational asthma induced by grain dust (GD) remains to be clarified. There have been few reports suggesting the involvement of neutrophils inducing bronchoconstriction after inhalation of GD. To further understand the role of neutrophil in the pathogenesis of GD-induced asthma. We studied the phenotype of leucocytes of the bronchial mucosa in patients with GD-induced asthma. Bronchial biopsy specimens were obtained by fibreoptic bronchoscopy from six subjects with GD-induced asthma. Six allergic asthma patients sensitive to house dust mite were enrolled as controls. Bronchial biopsy specimens were examined by immunohistochemistry with a panel of monoclonal antibodies to tryptase-containing mast cell (AA1), activated eosinophil (EG2), pan T-lymphocyte (CD3) and neutrophil elastase (NE). Induced sputum was collected before and after the GD-bronchoprovocation test. The IL-8 level in the sputum was measured using ELISA. There was a significant increase in the number of AA1+ and NE+ cells in bronchial mucosa of GD-induced asthma, compared with those of allergic asthma (P=0.01, P=0.01, respectively). No significant differences were observed in the number of EG2+ and CD3+ cells (P = 0.13, P=0.15, respectively). IL-8 was abundant in the sputum of all GD-induced asthma patients and significantly increased after the bronchial challenges compared with the baseline value (P = 0.03). These findings support the view that neutrophil recruitment together with mast cells may contribute to the bronchoconstriction induced by GD. A possible involvement of IL-8 was suggested.

  10. A comparative study of the grain-size distribution of surface dust and stormwater runoff quality on typical urban roads and roofs in Beijing, China.

    Science.gov (United States)

    Shen, Zhenyao; Liu, Jin; Aini, Guzhanuer; Gong, Yongwei

    2016-02-01

    The deposition of pollutants on impervious surfaces is a serious problem associated with rapid urbanization, which results in non-point-source pollution. Characterizing the build-up and wash-off processes of pollutants in urban catchments is essential for urban planners. In this paper, the spatial variation and particle-size distributions of five heavy metals and two nutrients in surface dust were analyzed, and the runoff water first-flush effect (FF30) and event-mean concentrations (EMCs) of 10 common constituents were characterized. The relationships between runoff variables and stormwater characteristics were examined from three typical urban impervious surfaces in Beijing, China. Dust on road surfaces with smaller grain sizes had higher pollutant concentrations, whereas concentrations of Mn, Zn, Fe, and TP in roof surface dust increased with grain size. Particles with grain sizes of 38-74 and 125-300 μm contributed most to the total pollutant load in roads, while particles with the smallest grain sizes (roads. The maximum intensity (I max) and the antecedent dry days (ADD) were critical parameters for EMCs in roads, while ADD was the only dominant parameter for EMCs on our studied roof. The rainfall intensity (RI) and maximum intensity (I max) were found to be the parameters with the strongest correlation to the first-flush effect on both roads and roofs. Significant correlations of total suspended solids (TSS) concentration in runoff with grain-size fractions of surface dust indicated that coarser particles (74-300 μm) are most likely to contribute to the solid-phase pollutants, and finer particles (<38 μm) are likely the main source of dissolved pollutants.

  11. The dust motion inside the magnetized sheath - The effect of drag forces

    International Nuclear Information System (INIS)

    Pandey, B. P.; Samarian, A.; Vladimirov, S. V.

    2010-01-01

    The isolated charged dust inside the magnetized plasma sheath moves under the influence of the electron and ion drag force and the sheath electrostatic field. The charge on the dust is a function of its radius as well as the value of the ambient sheath potential. It is shown that the charge on the dust determines its trajectory and dust performs the spiraling motion inside the sheath. The location of the turning spiral is determined by the number of negative charge on the dust, which in turn is a function of the dust radius. The back and forth spiraling motion finally causes the dust to move in a small, narrow region of the sheath. For a bigger dust particle, the dust moves closer to the sheath presheath boundary suggesting that the bigger grains, owing to the strong repulsion between the wall and dust, will be unable to travel inside the sheath. Only small, micron-sized grains can travel closer to the wall before repulsion pushes it back toward the plasma-sheath boundary. The temporal behavior of the spiraling dust motion appears like a damped harmonic oscillation, suggesting that the plasma drag force causes dissipation of the electrostatic energy. However, after initial damping, the grain keeps oscillating although with much smaller amplitude. The possible application of the present results to the ongoing sheath experiments is discussed.

  12. Effect of external magnetic field and variable dust electrical charge on the shape and propagation of solitons in the two nonthermal ions dusty plasma

    International Nuclear Information System (INIS)

    Ghalambor Dezfuly, S.; Dorranian, D.

    2012-01-01

    In this manuscript, the effect of dust electrical charge, nonthermal ions, and external magnetic field on the shape and propagation of solitons in dusty plasma with two nonthermal ions is studied theoretically. Using the reductive perturbation theory, the Zakharov-Kuznetsov equation for propagation of dust acoustic waves is extracted. Results show that external magnetic field does not affect the amplitude of solitary wave but width of solitons are effectively depend on the magnitude of external magnetic field. With increasing the charge of dust particles the amplitude of solution will increase while their width will decrease. Increasing the nonthermal ions lead to opposite effect.

  13. Electron energy distribution function, effective electron temperature, and dust charge in the temporal afterglow of a plasma

    International Nuclear Information System (INIS)

    Denysenko, I. B.; Azarenkov, N. A.; Kersten, H.

    2016-01-01

    Analytical expressions describing the variation of electron energy distribution function (EEDF) in an afterglow of a plasma are obtained. Especially, the case when the electron energy loss is mainly due to momentum-transfer electron-neutral collisions is considered. The study is carried out for different EEDFs in the steady state, including Maxwellian and Druyvesteyn distributions. The analytical results are not only obtained for the case when the rate for momentum-transfer electron-neutral collisions is independent on electron energy but also for the case when the collisions are a power function of electron energy. Using analytical expressions for the EEDF, the effective electron temperature and charge of the dust particles, which are assumed to be present in plasma, are calculated for different afterglow durations. An analytical expression for the rate describing collection of electrons by dust particles for the case when the rate for momentum-transfer electron-neutral collisions is independent on electron energy is also derived. The EEDF profile and, as a result, the effective electron temperature and dust charge are sufficiently different in the cases when the rate for momentum-transfer electron-neutral collisions is independent on electron energy and when the rate is a power function of electron energy.

  14. PROTOPLANETARY DISK MASSES IN IC348: A RAPID DECLINE IN THE POPULATION OF SMALL DUST GRAINS AFTER 1 Myr

    International Nuclear Information System (INIS)

    Lee, Nicholas; Williams, Jonathan P.; Cieza, Lucas A.

    2011-01-01

    We present a 1.3 mm continuum survey of protoplanetary disks in the 2-3 Myr old cluster, IC348, with the Submillimeter Array. We observed 85 young stellar objects and detected 10 with 1.3 mm fluxes greater than 2 mJy. The brightest source is a young embedded protostar driving a molecular outflow. The other nine detections are dusty disks around optically visible stars. Our millimeter flux measurements translate into total disk masses ranging from 2 to 6 Jupiter masses. Each detected disk has strong mid-infrared emission in excess of the stellar photosphere and has Hα equivalent widths larger than the average in the cluster and indicative of ongoing gas accretion. The disk mass distribution, however, is shifted by about a factor of 20 to lower masses, compared to that in the ∼1 Myr old Taurus and Ophiuchus regions. These observations reveal the rapid decline in the number of small dust grains in disks with time and probably their concomitant growth beyond millimeter sizes. Moreover, if IC348 is to form planets in the same proportion as detected in the field, these faint millimeter detections may represent the best candidates in the cluster to study the progression from planetesimals to planets.

  15. Electrostatic forces on grains near asteroids and comets

    Directory of Open Access Journals (Sweden)

    Hartzell Christine

    2017-01-01

    Full Text Available Dust on and near the surface of small planetary bodies (e.g. asteroids, the Moon, Mars’ moons is subject to gravity, cohesion and electrostatic forces. Due to the very low gravity on small bodies, the behavior of small dust grains is driven by non-gravitational forces. Recent work by Scheeres et al. has shown that cohesion, specifically van der Waals force, is significant for grains on asteroids. In addition to van der Waals cohesion, dust grains also experience electrostatic forces, arising from their interaction with each other (through tribocharging and the solar wind plasma (which produces both grain charging and an external electric field. Electrostatic forces influence both the interactions of grains on the surface of small bodies as well as the dynamics of grains in the plasma sheath above the surface. While tribocharging between identical dielectric grains remains poorly understood, we have recently expanded an existing charge transfer model to consider continuous size distributions of grains and are planning an experiment to test the charge predictions produced. Additionally, we will present predictions of the size of dust grains that are capable of detaching from the surface of small bodies.

  16. Infrared observations of an outburst of small dust grains from the nucleus of Comet P/Halley 1986 III at perihelion

    Science.gov (United States)

    Gehrz, R. D.; Johnson, C. H.; Magnuson, S. D.; Ney, E. P.; Hayward, T. L.

    1995-01-01

    A close examination of the 0.7- to 23-micron infrared data base acquired by Gehrz and Ney (1992), suggests that the nucleus of Comet P/Halley 1986 III emitted a burst of small dust grains during a 3-day period commencing within hours of perihelion passage on 1986 February 9.46 UT. The outburst was characterized by significant increases in the coma's grain color temperature T(sub obs), temperature excess (superheat: S = T(sub obs)/T(sub BB)), infrared luminosity, albedo, and 10-micron silicate emission feature strength. These changes are all consistent with the sudden ejection from the nucleus of a cloud of grains with radii of approximately 0.5 micron. This outburst may have produced the dust that was responsible for some of the tail streamers photographed on 1986 February 22 UT. The peak of the dust outburst occurred about 3 days before a pronounced increase in the water production rate measured by the Pioneer Venus Orbiter Ultraviolet Spectrometer. We suggest that jets that release large quantities of small particles may be largely responsible for some of the variable infrared behavior that has been reported for P/Halley and other comets during the past two decades. Such jets may also account for some of the differences IR Type I and IR Type II comets.

  17. Grain dust induces IL-8 production from bronchial epithelial cells: the effect of dexamethasone on IL-8 production.

    Science.gov (United States)

    Park, H S; Suh, J H; Kim, H Y; Kwon, O J; Choi, D C

    1999-04-01

    Recent publications have suggested an active participation of neutrophils to induce bronchoconstriction after inhalation of grain dust (GD). To further understand the role of neutrophils in the pathogenesis of GD-induced asthma, this investigation was designed to determine whether human bronchial epithelial cells could produce IL-8 production and to observe the effect of dexamethasone on IL-8 production. We cultured Beas-2B, a bronchial epithelial cell line. To observe GD-induced responses, four concentrations (1 to 200 microg/mL) of GD were incubated for 24 hours and compared with those without incubation of GD. To evaluate the effect of pro-inflammatory cytokines on IL-8 production, epithelial cells were incubated with peripheral blood mononuclear cell (PBMC) culture supernatant, which was derived from the culture of PBMC from a GD-induced asthmatic subject under the exposure to 10 microg/mL of GD, and compared with those cultured without addition of PBMC supernatant. The level of released IL-8 in the supernatant was measured by enzyme-linked immunosorbent assay. To evaluate the effect of dexamethasone on IL-8 production, four concentrations (5 to 5000 ng/mL) of dexamethasone were pre-incubated for 24 hours and the same experiments were repeated. There was significant production of IL-8 from bronchial epithelial cells with additions of GD in a dose-dependent manner (P < .05), which was significantly augmented with additions of PBMC supernatant (P < .05) at each concentration. Compared with the untreated sample, pretreatment of dexamethasone could induced a remarkable inhibitions (15% to 55%) of IL-8 production from bronchial epithelial cells in a dose-dependent manner. These results suggest that IL-8 production from bronchial epithelial cells may contribute to neutrophil recruitment occurring in GD-induced airway inflammation. The downregulation of IL-8 production by dexamethasone from bronchial epithelial cells may contribute to the efficacy of this compound in

  18. Segregation of O2 and CO on the surface of dust grains determines the desorption energy of O2

    Science.gov (United States)

    Noble, J. A.; Diana, S.; Dulieu, F.

    2015-12-01

    Selective depletion towards pre-stellar cores is still not understood. The exchange between the solid and gas phases is central to this mystery. The aim of this paper is to show that the thermal desorption of O2 and CO from a submonolayer mixture is greatly affected by the composition of the initial surface population. We have performed thermally programmed desorption (TPD) experiments on various submonolayer mixtures of O2 and CO. Pure O2 and CO exhibit almost the same desorption behaviour, but their desorption differs strongly when mixed. Pure O2 is slightly less volatile than CO, while in mixtures, O2 desorbs earlier than CO. We analyse our data using a desorption law linking competition for binding sites with desorption, based on the assumption that the binding energy distribution of both molecules is the same. We apply Fermi-Dirac statistics in order to calculate the adsorption site population distribution, and derive the desorbing fluxes. Despite its simplicity, the model reproduces the observed desorption profiles, indicating that competition for adsorption sites is the reason for lower temperature O2 desorption. CO molecules push-out or `dislodge' O2 molecules from the most favourable binding sites, ultimately forcing their early desorption. It is crucial to consider the surface coverage of dust grains in any description of desorption. Competition for access to binding sites results in some important discrepancies between similar kinds of molecules, such as CO and O2. This is an important phenomenon to be investigated in order to develop a better understanding of the apparently selective depletion observed in dark molecular clouds.

  19. Cross-shift changes in blood inflammatory markers occur in the absence of airway obstruction in workers exposed to grain dust.

    Science.gov (United States)

    Borm, P J; Schins, R P; Derhaag, T J; Kant, I; Jorna, T H

    1996-04-01

    Grain dust is well known to cause both acute and chronic respiratory disorders, and endotoxins are considered key components in this. Since endotoxins are known to elicit proinflammatory mediators, we investigated cytokine (tumor necrosis factor [TNF], interleukin-6, interleukin-8) release and a number of proinflammatory and anti-inflammatory proteins (soluble TNF receptors, lipopolysaccharide (LPS) binding protein, bactericidal permeability increasing protein (BPI), C-reactive protein) in plasma of workers exposed to grain dust. In two surveys during 1 week, lung function was measured daily before and after the shift, using flow-volume curves and/or forced oscillation measurements. On Monday and Friday, blood samples (30 mL) were drawn and cytokine release was determined by enzyme-linked immunosorbent assay in supernatant of isolated monocytes or whole blood culture, either unstimulated or on the ex vivo stimulation with 3 ng/mL or 1,000 ng/mL endotoxin. Individual exposures were determined from stationary dust measurements at every workplace combined with personal task analysis during all shifts. In both surveys, no cross-week change in lung function parameters was observed. In the first survey (average exposure: 20.2 mg/m3), monocyte spontaneous TNF release was increased sevenfold cross week (pdust exposure (r=0.62) of that week and the increase in soluble TNF receptor 75 kD (r=0.85). In the second survey, where average exposure was much lower (3.67 mg/m3), impedance parameters indicated a significant improvement of airway function, and cross-week changes in inflammatory markers were minimal. Therefore, we conclude that inflammatory events can be used to monitor adverse respiratory effects of moderate grain dust exposure.

  20. Characteristic study of head-on collision of dust-ion acoustic solitons of opposite polarity with kappa distributed electrons

    Science.gov (United States)

    Parveen, Shahida; Mahmood, Shahzad; Adnan, Muhammad; Qamar, Anisa

    2016-09-01

    The head on collision between two dust ion acoustic (DIA) solitary waves, propagating in opposite directions, is studied in an unmagnetized plasma constituting adiabatic ions, static dust charged (positively/negatively) grains, and non-inertial kappa distributed electrons. In the linear limit, the dispersion relation of the dust ion acoustic (DIA) solitary wave is obtained using the Fourier analysis. For studying characteristic head-on collision of DIA solitons, the extended Poincaré-Lighthill-Kuo method is employed to obtain Korteweg-de Vries (KdV) equations with quadratic nonlinearities and investigated the phase shifts in their trajectories after the interaction. It is revealed that only compressive solitary waves can exist for the positive dust charged concentrations while for negative dust charge concentrations both the compressive and rarefactive solitons can propagate in such dusty plasma. It is found that for specific sets of plasma parameters, the coefficient of nonlinearity disappears in the KdV equation for the negative dust charged grains. Therefore, the modified Korteweg-de Vries (mKdV) equations with cubic nonlinearity coefficient, and their corresponding phase shift and trajectories, are also derived for negative dust charged grains plasma at critical composition. The effects of different plasma parameters such as superthermality, concentration of positively/negatively static dust charged grains, and ion to electron temperature ratio on the colliding soliton profiles and their corresponding phase shifts are parametrically examined.

  1. Application of Principal Component Analysis in Assessment of Relation Between the Parameters of Technological Quality of Wheat Grains Treated with Inert Dusts Against Rice Weevil (Sitophilus oryzae L.

    Directory of Open Access Journals (Sweden)

    Marija Bodroža-Solarov

    2011-01-01

    Full Text Available Quality parameters of several wheat grain lots (low vitreous and high vitreous grains,non-infested and infested with rice weevils, (Sitophilus oryzae L. treated with inert dusts(natural zeolite, two diatomaceous earths originating from Serbia and a commercial productProtect-It® were investigated. Principal component analysis (PCA was used to investigatethe classification of treated grain lots and to assess how attributes of technological qualitycontribute to this classification. This research showed that vitreousness (0.95 and test weight(0.93 contributed most to the first principal component whereas extensigraph area (-0.76contributed to the second component. The determined accountability of the total variabilityby the first component was around 55%, while with the second it was 18%, which meansthat those two dimensions together account for around 70% of total variability of the observedset of variables. Principal component analysis (PCA of data set was able to distinguishamong the various treatments of wheat lots. It was revealed that inert dust treatments producedifferent effects depending on the degree of endosperm vitreousness.

  2. Screening in weakly ionized dusty plasmas; effect of dust density perturbations

    International Nuclear Information System (INIS)

    Tolias, P.; Ratynskaia, S.

    2013-01-01

    The screening of the charge of a non-emitting dust grain immersed in a weakly ionized dusty plasma is studied on the basis of a self-consistent hydrodynamic description. The dust number density is considered large enough so that the test grain is not isolated from other grains and dust collective effects are important. Not only dust charge perturbations but also dust density perturbations are taken into account, the latter are shown to have a strong effect on both the short and long range part of the potential. The realization of collective attraction via the newly obtained potential is discussed, a mechanism that could be central to the understanding of phase-transitions and self-organization processes in dusty plasmas.

  3. Effects of dust size distribution on dust negative ion acoustic solitary waves in a magnetized dusty plasma

    International Nuclear Information System (INIS)

    Ma, Yi-Rong; Qi, Xin; Sun, Jian-An; Duan, Wen-Shan; Yang, Lei

    2013-01-01

    Dust negative ion acoustic solitary waves in a magnetized multi-ion dusty plasma containing hot isothermal electron, ions (light positive ions and heavy negative ions) and extremely massive charge fluctuating dust grains are investigated by employing the reductive perturbation method. How the dust size distribution affect the height and the thickness of the nonlinear solitary wave are given. It is noted that the characteristic of the solitary waves are different with the different dust size distribution. The magnitude of the external magnetic field also affects the solitary wave form

  4. Measurements, characterizing and reduction of dust during combustion of energy grain; Maetning, karaktaerisering och reduktion av stoft vid eldning av spannmaal

    Energy Technology Data Exchange (ETDEWEB)

    Roennbaeck, Marie; Johansson, Linda; Claesson, Frida; Johansson, Mathias

    2008-07-01

    There is a potential for cereal grain for combustion use in Sweden, as well as for other agricultural fuels with similar qualities. Today, grain is combusted mainly in small-scale appliances. As all fast growing crops, the ash content is higher compared to wood fuels, resulting in a higher emission of particles. There are no limits for particle emission from appliances smaller than 500 kW in Sweden today. Nevertheless, it is important to consider these emissions because dust from small scale combustion of biofuels is one of the larger sources of particles to air in Sweden and in Europe today. Lately, is has been observed that the ultra fine particles (< 0.1 mum) is a cause of increased mortality. During large-scale combustion, the flue gas is cleaned from particles by electrostatic or fabric filters. During small-scale combustion primary measures is preferred by economical reasons. Particles can be reduced by design of the appliances or control of the combustion process. It might also be possible to reduce particles by use of additives that ties the volatile matters to the bottom ash and/or causes them leave as gas instead of particles. The aim of this project is to characterize and reduce particle emissions from combustion of cereal grain by use of additives. Limestone and kaolin were tested in a burner for oat grain. Particle emission was measured as total dust, as mass size distributed and as number size distributed. Fuel, bottom ash and dust were characterized chemically. In the flue gas carbon monoxide, carbon dioxide, oxygen, hydrocarbons, nitrogen oxide, sulphur dioxide and hydrogen chloride was measured. Equilibrium calculations were performed for combustion with and without additives. The combustion was not negatively influenced by the additives. The results confirm that lime stone reduces emissions of acidifying and corrosive gases such as sulphur dioxide and hydrogen chloride. Both lime stone and kaolin increase the ash fusion temperature. Results from

  5. Will Organic Synthesis Within Icy Grains or on Dust Surfaces in the Primitive Solar Nebula Completely Erase the Effects of Photochemical Self Shielding?

    Science.gov (United States)

    Nuth, Joseph A., III; Johnson, Natasha M.

    2012-01-01

    There are at least 3 separate photochemical self-shielding models with different degrees of commonality. All of these models rely on the selective absorption of (12))C(16)O dissociative photons as the radiation source penetrates through the gas allowing the production of reactive O-17 and O-18 atoms within a specific volume. Each model also assumes that the undissociated C(16)O is stable and does not participate in the chemistry of nebular dust grains. In what follows we will argue that this last, very important assumption is simply not true despite the very high energy of the CO molecular bond.

  6. Physics of interstellar dust

    CERN Document Server

    Krugel, Endrik

    2002-01-01

    The dielectric permeability; How to evaluate grain cross sections; Very small and very big particles; Case studies of Mie calculus; Particle statistics; The radiative transition probability; Structure and composition of dust; Dust radiation; Dust and its environment; Polarization; Grain alignment; PAHs and spectral features of dust; Radiative transport; Diffuse matter in the Milky Way; Stars and their formation; Emission from young stars. Appendices Mathematical formulae; List of symbols.

  7. Exposure to field vs. storage wheat dust: different consequences on respiratory symptoms and immune response among grain workers.

    Science.gov (United States)

    Barrera, Coralie; Wild, Pascal; Dorribo, Victor; Savova-Bianchi, Dessislava; Laboissière, Audrey; Pralong, Jacques A; Danuser, Brigitta; Krief, Peggy; Millon, Laurence; Reboux, Gabriel; Niculita-Hirzel, Hélène

    2018-05-26

    The aim of this study was to understand the differential acute effects of two distinct wheat-related dusts, such as field or stored wheat dust handling, on workers' health and how those effects evolved at 6 month intervals. Exposure, work-related symptoms, changes in lung function, and blood samples of 81 workers handling wheat and 61 controls were collected during the high exposure season and 6 months after. Specific IgG, IgE, and precipitins against 12 fungi isolated from wheat dust were titrated by enzyme-linked immunosorbent assay, dissociation-enhanced lanthanide fluorescence immunoassay, and electrosyneresis. The level of fungi was determined in the workers' environment. Levels of exhaled fraction of nitrogen monoxide (F E NO) and total IgE were obtained. Exposure response associations were investigated by mixed logistic and linear regression models. The recent exposure to field wheat dust was associated with a higher prevalence for five of six self-reported airway symptoms and with a lower F E NO than those in the control population. Exposure to stored wheat dust was only associated with cough. No acute impact of exposure on respiratory function was observed. Exposure to field wheat dust led to workers' sensitization against the three field fungi Aureobasidum, Cryptococcus, and Phoma, although exposure to storage wheat dust was associated with tolerance. The level of Ig remained stable 6 months after exposure. The clinical picture of workers exposed to field or storage wheat dust differed. The systematic characterization of the aerosol microbial profile may help to understand the reasons for those differences.

  8. Solitary waves of the Kadomstev-Petviashvili equation in warm dusty plasma with variable dust charge, two temperature ion and nonthermal electron

    International Nuclear Information System (INIS)

    Pakzad, Hamid Reza

    2009-01-01

    The propagation of nonlinear waves in warm dusty plasmas with variable dust charge, two temperature ion and nonthermal electron is studied. By using the reductive perturbation theory, the Kadomstev-Petviashivili (KP) equation is derived. Existence of rarefactive and compressive solitons is analyzed.

  9. Thin Static Charged Dust Majumdar–Papapetrou Shells with High Symmetry in D ≥ 4

    Czech Academy of Sciences Publication Activity Database

    Čermák, Martin; Zouhar, M.

    2012-01-01

    Roč. 51, č. 8 (2012), s. 2455-2469 ISSN 0020-7748 Institutional research plan: CEZ:AV0Z20410507 Keywords : Majumdar–Papapetrou * Kastor–Traschen * higher dimensional thin charged shell Subject RIV: BE - Theoretical Physics Impact factor: 1.086, year: 2012

  10. Effects of Ca doping and O deficiency on the charge distribution in the vicinity of a 45° [001] grain boundary in YBa2Cu3O7

    KAUST Repository

    Schwingenschlögl, Udo

    2012-02-01

    The charge redistribution at grain boundaries is critical for the applicability of high-T c superconductors in electronic devices, because it determines the transport across the material. We investigate the charge transfer and the alterations of the electronic states due to local doping of a normal-state 45°-tilted [001] grain boundary in YBa 2Cu 3O 7 by means of first-principles calculations. Considering Ca doping and O deficiency as prototypical modifications we demonstrate that the redistribution of the charge carriers in the CuO 2 planes displays a very complex spatial pattern, which deviates even qualitatively from the naive expectation. Copyright © EPLA, 2012.

  11. THERMODYNAMICS AND CHARGING OF INTERSTELLAR IRON NANOPARTICLES

    Energy Technology Data Exchange (ETDEWEB)

    Hensley, Brandon S. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Draine, B. T., E-mail: brandon.s.hensley@jpl.nasa.gov [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)

    2017-01-10

    Interstellar iron in the form of metallic iron nanoparticles may constitute a component of the interstellar dust. We compute the stability of iron nanoparticles to sublimation in the interstellar radiation field, finding that iron clusters can persist down to a radius of ≃4.5 Å, and perhaps smaller. We employ laboratory data on small iron clusters to compute the photoelectric yields as a function of grain size and the resulting grain charge distribution in various interstellar environments, finding that iron nanoparticles can acquire negative charges, particularly in regions with high gas temperatures and ionization fractions. If ≳10% of the interstellar iron is in the form of ultrasmall iron clusters, the photoelectric heating rate from dust may be increased by up to tens of percent relative to dust models with only carbonaceous and silicate grains.

  12. Grain dust originating from organic and conventional farming as a potential source of biological agents causing respiratory diseases in farmers.

    Science.gov (United States)

    Zukiewicz-Sobczak, Wioletta A; Cholewa, Grażyna; Krasowska, Ewelina; Chmielewska-Badora, Jolanta; Zwoliński, Jacek; Sobczak, Paweł

    2013-12-01

    Agricultural producers are exposed to a number of different health risks associated with their work environment. The objective of the study was to assess the degree of colonization by fungi in terms of quantity and in terms of variety of species the samples taken from the settled dust from combine threshing of rye cultivation from organic and conventional farms in the Province of Lublin. This paper is a preliminary quantitative assessment of the species of fungi colonizing the samples of settled dust collected during combine threshing from organic and conventional farms in the Province of Lublin. One of the stages of the project was the classification of biosafety BSL (biosafety level) of selected isolates and API ZYM tests to evaluate the potential ability of isolates to cause adverse health effects. To determine the concentration and composition of fungi in collected samples plate dilution method was used with two media: Malt Agar and Potato Dextrose Agar. MOST COMMONLY ISOLATED FUNGI IN SETTLED DUST SAMPLES COLLECTED DURING COMBINE THRESHING FROM ORGANIC FARMS, ON PDA MEDIUM WERE: Alternaria alternata and Aureobasidium pullulans. Cultures on MA medium were dominated by Alternaria alternata, Mycelia sterilia and Fusarium poae. In samples of dust from conventional crops, the predominant species was Alternaria alternata on PDA medium and on MA medium. The obtained results show a potential risk of people involved in agricultural work.

  13. Stardust Interstellar Preliminary Examination X: Impact Speeds and Directions of Interstellar Grains on the Stardust Dust Collector

    Science.gov (United States)

    Sterken, Veerle J.; Westphal, Andrew J.; Altobelli, Nicolas; Grun, Eberhard; Hillier, Jon K.; Postberg, Frank; Allen, Carlton; Stroud, Rhonda M.; Sandford, S. A.; Zolensky, Michael E.

    2014-01-01

    On the basis of an interstellar dust model compatible with Ulysses and Galileo observations, we calculate and predict the trajectories of interstellar dust (ISD) in the solar system and the distribution of the impact speeds, directions, and flux of ISD particles on the Stardust Interstellar Dust Collector during the two collection periods of the mission. We find that the expected impact velocities are generally low (less than 10 km per second) for particles with the ratio of the solar radiation pressure force to the solar gravitational force beta greater than 1, and that some of the particles will impact on the cometary side of the collector. If we assume astronomical silicates for particle material and a density of 2 grams per cubic centimeter, and use the Ulysses measurements and the ISD trajectory simulations, we conclude that the total number of (detectable) captured ISD particles may be on the order of 50. In companion papers in this volume, we report the discovery of three interstellar dust candidates in the Stardust aerogel tiles. The impact directions and speeds of these candidates are consistent with those calculated from our ISD propagation model, within the uncertainties of the model and of the observations.

  14. Dynamics of dust in astrophysical plasma and implications

    Science.gov (United States)

    Hoang, Thiem

    2012-06-01

    novel acceleration mechanism induced by charge fluctuations for very small grains using Monte Carlo simulations. Grain velocities from these new acceleration mechanisms are necessary for understanding dust coagulation in protoplanetary disks and formations of planets.

  15. From dust to life

    Science.gov (United States)

    Wickramasinghe, Chandra

    After initially challenging the dirty-ice theory of interstellar grains, Fred Hoyle and the present author proposed carbon (graphite) grains, mixtures of refractory grains, organic polymers, biochemicals and finally bacterial grains as models of interstellar dust. The present contribution summarizes this trend and reviews the main arguments supporting a modern version of panspermia.

  16. Interstellar Dust in the Heliosheath: Tentative Discovery of the Magnetic Wall of the Heliosphere

    Science.gov (United States)

    Frisch, P. C.

    2005-12-01

    The evident identification of interstellar dust grains entrained in the magnetic wall of the heliosphere is reported. It is shown that the distribution of dust grains causing the weak polarization of light from nearby stars is consistent with polarization by small charged interstellar dust grains captured in the heliosphere magnetic wall (Tinbergen 1982, Frisch 2005). There is an offset between the deflected small charged polarizing dust grains, radius less than 0.2 microns, and the undeflected large grain population, radius larger than 0.2 microns. The region of maximum polarization is towards ecliptic coordinates lambda,beta = 295,0 deg, which is offset along the ecliptic longitude by about 35 deg from the heliosphere nose and extends to low ecliptic latitudes where the heliosphere magnetic wall is expected. An offset is also found between the best aligned dust grains, near lambda=281 deg to 220 deg, and the upwind direction of the undeflected inflow of large grains seen by Ulysses and Galileo. In the aligned-grain region, the polarization strength anti-correlates with ecliptic latitude, indicating that the magnetic wall was predominantly at negative ecliptic latitudes when these data were acquired. These data are consistent with model predictions for an interstellar magnetic field which is tilted by 60 deg with respect to the ecliptic plane, and parallel to the galactic plane. References: Tinbergen, 1982: AA, v105, p53; Frisch, 2005: to appear in ApJL.

  17. Screening of a dust particle charge in a humid air plasma created by an electron beam

    Science.gov (United States)

    Filippov, A. V.; Derbenev, I. N.; Kurkin, S. A.

    2018-01-01

    A kinetic model has been developed for charged particle reactions in a humid air plasma produced by a fast electron beam. The model includes over 550 reactions with electrons, 33 positive ion species and 14 negative ion species. The model has been tested by solving 48 non-steady state equations for number densities of charged particles in humid air electron beam plasma, and by comparing with the available experimental data. The system of 48 steady state equations has been solved by iterative method in order to define the main ion species of the humid air plasma. A reduced kinetic model has been developed to describe the processes with the main ions and electrons. Screening constants have been calculated on the basis of the reduced system by means of Leverrier-Fadeev method. The dependencies of screening constants on gas ionization rates have been found for the rates from 10 to 1018 cm-3s-1 and the fraction of water molecules from 0 to 2%. The analysis of the constants has revealed that one of them is close to the inverse Debye length, and the other constants are defined by the inverse diffusion lengths passed by ions in the characteristic times of the attachment, recombination, and ion conversion. Pure imaginary screening constants appear at low rates of gas ionization.

  18. Nonplanar electrostatic shock waves in an opposite polarity dust ...

    Indian Academy of Sciences (India)

    M Amina

    2017-05-30

    May 30, 2017 ... comparison to electrons and ions) charged dust grains is called dusty ... and quark-gluon plasma [34], proton–neutron stars [35], dark-matter halos .... which is obtained by transforming the independent vari- ables ζ and τ to.

  19. Influence of Non-Maxwellian Particles on Dust Acoustic Waves in a Dusty Magnetized Plasma

    International Nuclear Information System (INIS)

    Nouri Kadijani, M.; Zareamoghaddam, H.

    2013-01-01

    In this paper an investigation into dust acoustic solitary waves (DASWs) in the presence of superthermal electrons and ions in a magnetized plasma with cold dust grains and trapped electrons is discussed. The dynamic of both electrons and ions is simulated by the generalized Lorentzian (κ) distribution function (DF). The dust grains are cold and their dynamics are studied by hydrodynamic equations. The basic set of fluid equations is reduced to modified Korteweg-de Vries (mKdV) equation using Reductive Perturbation Theory (RPT). Two types of solitary waves, fast and slow dust acoustic soliton (DAS) exist in this plasma. Calculations reveal that compressive solitary structures are possibly propagated in the plasma where dust grains are negatively (or positively) charged. The properties of DASs are also investigated numerically. (physics of gases, plasmas, and electric discharges)

  20. Glacial and interglacial eolian dust dispersal patterns across the Chinese Loess Plateau inferred from decomposed loess grain-size records.

    NARCIS (Netherlands)

    Prins, M.A.; Vriend, M.G.A.

    2007-01-01

    Previous studies have indicated that a genetically meaningful decomposition (unmixing) of loess grainsize distributions can be accomplished with the end-member modeling algorithm EMMA. The independent decomposition of two series of loess grain-size records from the NE Tibetan Plateau and Loess

  1. Studies on Charge Variation and Waves in Dusty Plasmas

    Science.gov (United States)

    Kausik, Siddhartha Sankar

    Plasma and dust grains are both ubiquitous ingredients of the universe. The interplay between them has opened up a new and fascinating research domain, that of dusty plasmas, which contain macroscopic particles of solid matter besides the usual plasma constituents. The research in dusty plasmas received a major boost in the early eighties with Voyager spacecraft observation on the formation of Saturn rings. Dusty plasmas are defined as partially or fully-ionized gases that contain micron-sized particles of electrically charged solid material, either dielectric or conducting. The physics of dusty plasmas has recently been studied intensively because of its importance for a number of applications in space and laboratory plasmas. This thesis presents the experimental studies on charge variation and waves in dusty plasmas. The experimental observations are carried out in two different experimental devices. Three different sets of experiments are carried out in two different experimental devices. Three different sets of experiments are carried out to study the dust charge variation in a filament discharge argon plasma. The dust grains used in these experiments are grains of silver. In another get of experiment, dust acoustic waves are studied in a de glow discharge argon plasma. Alumina dust grains are sprinkled in this experiment. The diagnostic tools used in these experiments are Langmuir probe and Faraday cup. The instruments used in these experiments are electrometer, He-Ne laser and charge coupled device (CCD) camera. Langmuir probe is used to measure plasma parameters, while Faraday cup and electrometer are used to measure very low current (~pA) carried by a collimated dust beam. He-Ne laser illuminates the dust grains and CCD camera is used to capture the images of dust acoustic waves. Silver dust grains are produced in the dust chamber by gas-evaporation technique. Due to differential pressure maintained between the dust and plasma chambers, the dust grains move

  2. Formation and dissociation of dust molecules in dusty plasma

    International Nuclear Information System (INIS)

    Yan Jia; Feng Fan; Liu Fucheng; Dong Lifang; He Yafeng

    2016-01-01

    Dust molecules are observed in a dusty plasma experiment. By using measurements with high spatial resolution, the formation and dissociation of the dust molecules are studied. The ion cloud in the wake of an upper dust grain attracts the lower dust grain nearby. When the interparticle distance between the upper dust grain and the lower one is less than a critical value, the two dust grains would form a dust molecule. The upper dust grain always leads the lower one as they travel. When the interparticle distance between them is larger than the critical value, the dust molecule would dissociate. (paper)

  3. Inverse Relationship of Marine Aerosol and Dust in Antarctic Ice with Fine-Grained Sediment in the South Atlantic Ocean: Implications for Sea-Ice Coverage and Wind Strength

    Directory of Open Access Journals (Sweden)

    Sharon L. Kanfoush

    2012-03-01

    Full Text Available This research seeks to test the hypothesis that natural gamma radiation (NGR from Ocean Drilling Program Site 1094, which displays variability over the last glacial-interglacial cycle similar to dust in the Vostok ice core, reflects fine-grained terrigenous sediment delivered by eolian processes. Grain size was measured on 400 samples spanning 0–20 m in a composite core. Accumulation of the <63μ size fraction at Site 1094 and dust in Vostok exhibit a negative correlation, suggesting the fine sediments are not dominantly eolian. However the technique used for grain size measurements cannot distinguish between terrigenous and biogenous materials; therefore it is possible much fine-grained material is diatoms. An inverse correlation between fine sediments and NGR supports this interpretation, and implies terrigenous materials were at times diluted by microfossils from high biological productivity. Fine marine sediments correlate positively with temperature and negatively with marine aerosol Na+ in Vostok. One plausible explanation is extensive sea-ice of cold intervals steepened ocean-continent temperature gradients, intensified winds, and led to increased transport of dust and marine aerosol to Antarctica yet also reduced biological productivity at Site 1094. Such a reduction despite increases in NGR, potentially representing Fe-rich dust influx, would require light limitation or stratification associated with sea-ice.

  4. Physical Alteration of Martian Dust Grains, Its Influence on Detection of Clays and Identification of Aqueous Processes on Mars

    Science.gov (United States)

    Bishop, Janice L.; Drief, Ahmed; Dyar, Darby

    2003-01-01

    Clays, if present on Mars, have been illusive. Determining whether or not clay minerals and other aqueous alteration species are present on Mars provides key information about the extent and duration of aqueous processes on Mars. The purpose of this study is to characterize in detail changes in the mineral grains resulting from grinding and to assess the influence of physical processes on clay minerals on the surface of Mars. Physical alteration through grinding was shown to greatly affect the structure and a number of properties of antigorite and kaolinite. This project builds on an initial study and includes a combination of SEM, HRTEM, reflectance and M ssbauer spectroscopies. Grain size was found to decrease, as expected, with grinding. In addition, nanophase carbonate, Si-OH and iron oxide species were formed.

  5. Ultraviolet Imaging Telescope images of the reflection nebula NGC 7023 - Derivation of ultraviolet scattering properties of dust grains

    Science.gov (United States)

    Witt, Adolf N.; Petersohn, Jens K.; Bohlin, Ralph C.; O'Connell, Robert W.; Roberts, Morton S.; Smith, Andrew M.; Stecher, Theodore P.

    1992-01-01

    The Ultraviolet Imaging Telescope as part of the Astro-1 mission, was used to obtain high-resolution surface brightness distribution data in six ultraviolet wavelength bands for the bright reflection nebula NGC 7023. From the quantitative comparison of the measured surface brightness gradients ratios of nebular to stellar flux, and detail radial surface brightness profiles with corresponding data from the visible, two major conclusions results: (1) the scattering in the near- and far-ultraviolet in this nebula is more strongly forward-directed than in the visible; (2) the dust albedo in the ultraviolet for wavelengths not less than 140 nm is identical to that in the visible, with the exception of the 220 nm bump in the extinction curve. In the wavelengths region of the bump, the albedo is reduced by 25 to 30 percent in comparison with wavelengths regions both shorter and longer. This lower albedo is expected, if the bump is a pure absorption feature.

  6. DustEM: Dust extinction and emission modelling

    Science.gov (United States)

    Compiègne, M.; Verstraete, L.; Jones, A.; Bernard, J.-P.; Boulanger, F.; Flagey, N.; Le Bourlot, J.; Paradis, D.; Ysard, N.

    2013-07-01

    DustEM computes the extinction and the emission of interstellar dust grains heated by photons. It is written in Fortran 95 and is jointly developed by IAS and CESR. The dust emission is calculated in the optically thin limit (no radiative transfer) and the default spectral range is 40 to 108 nm. The code is designed so dust properties can easily be changed and mixed and to allow for the inclusion of new grain physics.

  7. Exobiological implications of dust aggregation in planetary atmospheres: An experiment for the gas-grain simulation facility

    Science.gov (United States)

    Huntington, J. L.; Schwartz, D. E.; Marshall, J. R.

    1991-01-01

    The Gas-Grain Simulation Facility (GGSF) will provide a microgravity environment where undesirable environmental effects are reduced, and thus, experiments involving interactions between small particles and grains can be more suitably performed. Slated for flight aboard the Shuttle in 1992, the ESA glovebox will serve as a scientific and technological testbed for GGSF exobiology experiments as well as generating some basic scientific data. Initial glovebox experiments will test a method of generating a stable, mono-dispersed cloud of fine particles using a vibrating sprinkler system. In the absence of gravity and atmospheric turbulence, it will be possible to determine the influence of interparticle forces in controlling the rate and mode of aggregation. The experimental chamber can be purged of suspended matter to enable multiple repetitions of the experiments. Of particular interest will be the number of particles per unit volume of the chamber, because it is suspected that aggregation will occur extremely rapidly if the number exceeds a critical value. All aggregation events will be recorded on high-resolution video film. Changes in the experimental procedure as a result of surprise events will be accompanied by real-time interaction with the mission specialist during the Shuttle flight.

  8. The influence of secondary electron emission on the floating potential of tokamak-born dust

    International Nuclear Information System (INIS)

    Vaverka, J; Richterová, I; Vyšinka, M; Pavlů, J; Šafránková, J; Němeček, Z

    2014-01-01

    Dust production and its transport into the core plasma is an important issue for magnetic confinement fusion. Dust grains are charged by various processes, such as the collection of plasma particles and electron emissions, and their charge influences the dynamics of the dust. This paper presents the results of calculations of the surface potential of dust grains in a Maxwellian plasma. Our calculations include the charging balance of a secondary electron emission (SEE) from the dust. The numerical model that we have used accounts for the influence of backscattered electrons and takes into account the effects of grain size, material, and it is also able to handle both spherical and non-spherical grains. We discuss the role of the SEE under tokamak conditions and show that the SEE is a leading process for the grains crossing the scrape-off layer from the edge to core plasma. The results of our calculations are relevant for materials related to fusion experiments in ITER. (paper)

  9. Frontiers in In-Situ Cosmic Dust Detection and Analysis

    International Nuclear Information System (INIS)

    Sternovsky, Zoltan; Auer, Siegfried; Drake, Keith; Gruen, Eberhard; Horanyi, Mihaly; Le, Huy; Xie Jianfeng; Srama, Ralf

    2011-01-01

    In-situ cosmic dust instruments and measurements played a critical role in the emergence of the field of dusty plasmas. The major breakthroughs included the discovery of β-meteoroids, interstellar dust particles within the solar system, Jovian stream particles, and the detection and analysis of Enceladus's plumes. The science goals of cosmic dust research require the measurements of the charge, the spatial, size and velocity distributions, and the chemical and isotopic compositions of individual dust particles. In-situ dust instrument technology has improved significantly in the last decade. Modern dust instruments with high sensitivity can detect submicron-sized particles even at low impact velocities. Innovative ion optics methods deliver high mass resolution, m/dm>100, for chemical and isotopic analysis. The accurate trajectory measurement of cosmic dust is made possible even for submicron-sized grains using the Dust Trajectory Sensor (DTS). This article is a brief review of the current capabilities of modern dust instruments, future challenges and opportunities in cosmic dust research.

  10. Comet C2012 S1 (ISON): Observations of the Dust Grains From SOFIA and of the Atomic Gas From NSO Dunn and Mcmath-Pierce Solar Telescopes

    Science.gov (United States)

    Wooden, Diane H.; Woodward, Charles E.; Harker, David E.; Kelley, Michael S. P.; Sitko, Michael; Reach, William T.; De Pater, Imke; Gehrz, Robert D.; Kolokolova, Ludmilla; Cochran, Anita L.; hide

    2013-01-01

    Comet C/2012 S1 (ISON) is unique in that it is a dynamically new comet derived from the Oort cloud reservoir of comets with a sun-grazing orbit. Infrared (IR) and visible wavelength observing campaigns were planned on NASA's Stratospheric Observatory For Infrared Astronomy (SOFIA) and on National Solar Observatory Dunn (DST) and McMath-Pierce Solar Telescopes, respectively. We highlight our SOFIA (+FORCAST) mid- to far-IR images and spectroscopy (approx. 5-35 microns) of the dust in the coma of ISON are to be obtained by the ISON-SOFIA Team during a flight window 2013 Oct 21-23 UT (r_h approx. = 1.18 AU). Dust characteristics, identified through the 10 micron silicate emission feature and its strength, as well as spectral features from cometary crystalline silicates (Forsterite) at 11.05-11.2 microns, and near 16, 19, 23.5, 27.5, and 33 microns are compared with other Oort cloud comets that span the range of small and/or highly porous grains (e.g., C/1995 O1 (Hale-Bopp) and C/2001 Q4 (NEAT) to large and/or compact grains (e.g., C/2007 N4 (Lulin) and C/2006 P1 (McNaught)). Measurement of the crystalline peaks in contrast to the broad 10 and 20 micron amorphous silicate features yields the cometary silicate crystalline mass fraction, which is a benchmark for radial transport in our protoplanetary disk. The central wavelength positions, relative intensities, and feature asymmetries for the crystalline peaks may constrain the shapes of the crystals. Only SOFIA can look for cometary organics in the 5-8 micron region. Spatially resolved measurements of atoms and simple molecules from when comet ISON is near the Sun (r_hmeasures 4 settings: Na I, K, C2 to sample cometary organics (along with Mg I), and [OI] as a proxy for activity from water (along with Si I and Fe I). State-of-the-art instruments that will also be employed include IBIS, which is a Fabry-Perot spectral imaging system that concurrently measures lines of Na, K, Ca II, or Fe, and ROSA (CSUN/QUB), which is a

  11. Landau damping in bi-dust ion-acoustic waves

    International Nuclear Information System (INIS)

    Castro, E.; Puerta, J.; Martin, P.; Cereceda, C.

    2006-01-01

    Ion acoustic dust waves in a bi-dust plasma are analyzed in this paper. In order to model this system, we assume the existence of two different kinds of grains, each characterized by a different radius. Relative velocities between grains and charge fluctuations are neglected. In order to derive the dispersion relation of this system, we use the well known hybrid fluid-kinetic model, in which ions are treated kinetically and other species as fluids. In this plasma, waves with non-relative velocities between species leads to damped waves with frequency modes, defined by the grain radius. The induced damping ratio is studied as a function of the grain and ion densities. (Author)

  12. Time-Dependent Dust Formation in Novae

    Directory of Open Access Journals (Sweden)

    Kyung-Won Suh

    1991-06-01

    Full Text Available The dust formation processes in novae are investigated with close attention to recent infrared observations. Using mainly the classical nucleation theory, we have calculated the time scales of dust formation and growth in the environments of novae. Those time scales roughly resemble the typical observations. We have classified the dust-forming novae into three classes according to their explosion properties and the thermodynamic properties of dust grains. Oxygen grains from much later than carbon grains because of their thermodynamic properties. The effect of grain formation to the efficiency of stellar winds to drive the material outward is tested with newly obtained Planck mean values of dust grains.

  13. Dust-acoustic shock waves in a charge varying electronegative magnetized dusty plasma with nonthermal ions: Application to Halley Comet plasma

    Energy Technology Data Exchange (ETDEWEB)

    Tribeche, Mouloud; Bacha, Mustapha [Plasma Physics Group (PPG), Theoretical Physics Laboratory (TPL), Faculty of Physics, University of Bab-Ezzouar, USTHB, B. P. 32, El Alia, Algiers 16111 (Algeria)

    2013-10-15

    Weak dust-acoustic waves (DAWs) are addressed in a nonthermal charge varying electronegative magnetized dusty plasmas with application to the Halley Comet. A weakly nonlinear analysis is carried out to derive a Korteweg-de Vries-Burger equation. The positive ion nonthermality, the obliqueness, and magnitude of the magnetic field are found to modify the dispersive and dissipative properties of the DA shock structure. Our results may aid to explain and interpret the nonlinear oscillations that may occur in the Halley Comet Plasma.

  14. Non-ideal dust acoustic waves

    International Nuclear Information System (INIS)

    Konefka, F; Contreras, J P; Puerta, J; Castro, E; MartIn, P

    2008-01-01

    The dispersion relation for dust acoustic waves (DA waves) functionally depends on the state equation for the charged dust grains. The ideal gas equation is usually used for studying the effect of temperature on this dispersion relation. However, since the space occupied by the grains can be important in high-density plasmas, the non-ideal effects can be important in this case. This paper analyses the dispersion relation for DA waves, when more precise state equations are used as those described for Pade approximants. The correction to the usual wave equation has been determined and the break point in density, where the ideal gas-state equation has been found. The non-ideal effects are more important for short wavelength ones, and the limits where those effects become important are also studied. Since there are several experimental results for these kinds of waves, the importance of the non-ideal effects in these cases is analysed in detail.

  15. DC Glow Discharge Plasma, Containing Dust Particles: Self Organization and Peculiarities of Behavior

    International Nuclear Information System (INIS)

    Molotkov, V.I.; Pustyl'nik, M.Y.; Torchinskij, V.M.; Fortov, V.E.

    2003-01-01

    Dust particles, immersed in a plasma, acquire charge due to which they may be electrostatically trapped in a plasma. The energy of the interaction of the dust particles may be enough to transfer the dust component to nonideal and even crystalline state. This phenomenon is observed in various plasmas. In the present work a review of the investigations of strongly nonideal dusty plasma of the dc glow discharge striations is given. The formation of plasma crystals, liquids and plasma liquid crystals is considered. Typical phenomenon a for the dc discharge dusty plasma, such as coexistence of different phases in a single structure, convective motions, dust acoustic instability, are underlined. Results of the experiments on different external influences on dusty plasma structures are stated. It is shown that external influences may be used for measuring of the particle charge and field of forces acting on a dust grain levitating in a plasma. (author)

  16. Avinash-Shukla mass limit for the maximum dust mass supported against gravity by electric fields

    Science.gov (United States)

    Avinash, K.

    2010-08-01

    The existence of a new class of astrophysical objects, where gravity is balanced by the shielded electric fields associated with the electric charge on the dust, is shown. Further, a mass limit MA for the maximum dust mass that can be supported against gravitational collapse by these fields is obtained. If the total mass of the dust in the interstellar cloud MD > MA, the dust collapses, while if MD < MA, stable equilibrium may be achieved. Heuristic arguments are given to show that the physics of the mass limit is similar to the Chandrasekar's mass limit for compact objects and the similarity of these dust configurations with neutron and white dwarfs is pointed out. The effect of grain size distribution on the mass limit and strong correlation effects in the core of such objects is discussed. Possible location of these dust configurations inside interstellar clouds is pointed out.

  17. Spectro-Polarimetry of Fine-Grained Ice and Dust Surfaces Measured in the Laboratory to Study Solar System Objects and Beyond

    Science.gov (United States)

    Poch, O.; Cerubini, R.; Pommerol, A.; Thomas, N.; Schmid, H. M.; Potin, S.; Beck, P.; Schmitt, B.; Brissaud, O.; Carrasco, N.; Szopa, C.; Buch, A.

    2017-12-01

    The polarization of the light is very sensitive to the size, morphology, porosity and composition of the scattering particles. As a consequence, polarimetric observations could significantly complement observations performed in total light intensity, providing additional constraints to interpret remote sensing observations of Solar System and extra-solar objects. This presentation will focus on measurements performed in the laboratory on carefully characterized surface samples, providing reference data that can be used to test theoretical models and predict or interpret spectro-polarimetric observations. Using methods developed in the Laboratory for Outflow Studies of Sublimating Materials (LOSSy) at the University of Bern, we produce well-characterized and reproducible surfaces made of water ice particles having different grain sizes and porosities, as well as mineral/organic dusts, pure or mixed together, as analogues of planetary or small bodies surfaces. These surface samples are illuminated with a randomly polarized light source simulating the Sun. The polarization of their scattered light is measured at multiple phase angles and wavelengths, allowing to study the shape of the polarimetric phase curves and their spectral dependence, with two recently developed setups: The POLarimeter for Icy Samples (POLICES), at the University of Bern, allows the measurement of the weak polarization of ice surfaces from 400 to 800 nm, with direct application to icy satellites. Using a precision Stokes polarimeter, this setup is also used to study the spectral variations of circular polarization in the light scattered by biotic versus abiotic surfaces. The Spectrogonio radiometer with cHanging Angles for Detection Of Weak Signals (SHADOWS), at IPAG (University of Grenoble Alpes), measures linear polarization spectra from 0.35 to 5 μm in the light scattered by dark meteorite powders or icy samples, with application to primitive objects of the Solar System (asteroids, comets).

  18. Electromagnetically Interacting Dust Streams During Ulysses' Second Jupiter Encounter

    International Nuclear Information System (INIS)

    Krueger, H.; Forsyth, R.J.; Graps, A.L.; Gruen, E.

    2005-01-01

    The Jupiter system is a source of collimated burst-like streams of electrically charged 10-nm dust particles. In 2004 the Ulysses spacecraft had its second flyby at Jupiter and from late 2002 to early 2005 it measured a total of 24 dust streams between 0.8 and 3.4 AU from the planet. The grains show strong coupling to the interplanetary magnetic field: their impact directions correlate with the orientation and strength of the interplanetary magnetic field vector (namely its tangential and radial components) and they occur at 26 day intervals, closely matching the solar rotation period. Ulysses measured the dust streams over a large range in jovian latitude (+75 deg. to -35 deg.). Enhanced dust emission was measured along the jovian equator

  19. Dust in protoplanetary disks: observations*

    Directory of Open Access Journals (Sweden)

    Waters L.B.F.M.

    2015-01-01

    Full Text Available Solid particles, usually referred to as dust, are a crucial component of interstellar matter and of planet forming disks surrounding young stars. Despite the relatively small mass fraction of ≈1% (in the solar neighborhood of our galaxy; this number may differ substantially in other galaxies that interstellar grains represent of the total mass budget of interstellar matter, dust grains play an important role in the physics and chemistry of interstellar matter. This is because of the opacity dust grains at short (optical, UV wavelengths, and the surface they provide for chemical reactions. In addition, dust grains play a pivotal role in the planet formation process: in the core accretion model of planet formation, the growth of dust grains from the microscopic size range to large, cm-sized or larger grains is the first step in planet formation. Not only the grain size distribution is affected by planet formation. Chemical and physical processes alter the structure and chemical composition of dust grains as they enter the protoplanetary disk and move closer to the forming star. Therefore, a lot can be learned about the way stars and planets are formed by observations of dust in protoplanetary disks. Ideally, one would like to measure the dust mass, the grain size distribution, grain structure (porosity, fluffiness, the chemical composition, and all of these as a function of position in the disk. Fortunately, several observational diagnostics are available to derive constrains on these quantities. In combination with rapidly increasing quality of the data (spatial and spectral resolution, a lot of progress has been made in our understanding of dust evolution in protoplanetary disks. An excellent review of dust evolution in protoplanetary disks can be found in Testi et al. (2014.

  20. Threshold voltage variation depending on single grain boundary and stored charges in an adjacent cell for vertical silicon–oxide–nitride–oxide–silicon NAND flash memory

    Science.gov (United States)

    Oh, Hyeongwan; Kim, Jiwon; Baek, Rock-Hyun; Lee, Jeong-Soo

    2018-04-01

    The effects of single grain boundary (SGB) position and stored electron charges in an adjacent cell in silicon–oxide–nitride–oxide–silicon (SONOS) structures on the variations of threshold voltage (V th) were investigated using technology computer-aided design (TCAD) simulation. As the bit line voltage increases, the SGB position causing the maximum V th variation was shifted from the center to the source side in the channel, owing to the drain-induced grain barrier lowering effect. When the SGB is located in the spacer region, the potential interaction from both the SGB and the stored electron charges in the adjacent cell becomes significant and thus resulting in larger V th variation. In contrast, when the SGB is located at the center of the channel, the peak position of potential barrier is shifted to the center, so that the influence of the adjacent cell is diminished. As the gate length is scaled down to 20 nm, the influence of stored charges in adjacent cells becomes significant, resulting in larger V th variations.

  1. The nonlinear dustgrain-charging on large amplitude electrostatic waves in a dusty plasma with trapped ions

    Directory of Open Access Journals (Sweden)

    Y.-N. Nejoh

    1998-01-01

    Full Text Available The nonlinear dustgrain-charging and the influence of the ion density and temperature on electrostatic waves in a dusty plasma having trapped ions are investigated by numerical calculation. This work is the first approach to the effect of trapped ions in dusty plasmas. The nonlinear variation of the dust-charge is examined, and it is shown that the characteristics of the dustcharge number sensitively depend on the plasma potential, Mach number, dust mass-to-charge ratio, trapped ion density and temperature. The fast and slow wave modes are shown in this system. An increase of the ion temperature decreases the dust-charging rate and the propagation speed of ion waves. It is found that the existence of electrostatic ion waves sensitively depends on the ion to electron density ratio. New findings of the variable-charge dust grain particles, ion density and temperature in a dusty plasma with trapped ions are predicted.

  2. Numerical simulation of electron-beam-induced current near a silicon grain boundary and impact of a p-n junction space charge region

    Energy Technology Data Exchange (ETDEWEB)

    Corkish, R.; Altermatt, P.P.; Heiser, G. [Photovoltaics Special Research Centre, University of New South Wales, 2052 Sydney (Australia)

    2001-01-01

    Three-dimensional numerical simulations of electron-beam-induced current (EBIC) near a vertical silicon grain boundary are demonstrated. They are compared with an analytical model which excludes the effect of carrier generation other than in the bulk base region of a solar cell structure. We demonstrate that in a wide range of solar cell structures recombination in the space charge region (SCR) significantly affects the EBIC results and hence needs to be included in the data evaluation. Apart from these findings, simulations of a realistic silicon solar cell structure (thick emitter, field-dependent mobility, etc.) are demonstrated.

  3. Dust in H II regions

    International Nuclear Information System (INIS)

    Isobe, S.

    1977-01-01

    Several pieces of evidence indicate that H II regions may contain dust: 1) the continuum light scattered by dust grains (O'Dell and Hubbard, 1965), 2) thermal radiation from dust grains at infrared wavelengths (Ney and Allen, 1969), 3) the abnormal helium abundance in some H II regions (Peimbert and Costero, 1969), etc. Although observations of the scattered continuum suggest that the H II region cores may be dust-free, dust grains and gas must be well mixed in view of the infrared observations. This difficulty may be solved by introducing globules with sizes approximately 0.001 pc. These globules and the molecular clouds adjacent to H II regions are the main sources supplying dust to H II regions. (Auth.)

  4. Evolution of interstellar grains

    International Nuclear Information System (INIS)

    Greenberg, J.M.

    1984-01-01

    The principal aim of this chapter is to derive the properties of interstellar grains as a probe of local physical conditions and as a basis for predicting such properties as related to infrared emissivity and radiative transfer which can affect the evolution of dense clouds. The first sections will develop the criteria for grain models based directly on observations of gas and dust. A summary of the chemical evolution of grains and gas in diffuse and dense clouds follows. (author)

  5. Reconciling structural and thermodynamic predictions using all-atom and coarse-grain force fields: the case of charged oligo-arginine translocation into DMPC bilayers.

    Science.gov (United States)

    Hu, Yuan; Sinha, Sudipta Kumar; Patel, Sandeep

    2014-10-16

    Using the translocation of short, charged cationic oligo-arginine peptides (mono-, di-, and triarginine) from bulk aqueous solution into model DMPC bilayers, we explore the question of the similarity of thermodynamic and structural predictions obtained from molecular dynamics simulations using all-atom and Martini coarse-grain force fields. Specifically, we estimate potentials of mean force associated with translocation using standard all-atom (CHARMM36 lipid) and polarizable and nonpolarizable Martini force fields, as well as a series of modified Martini-based parameter sets. We find that we are able to reproduce qualitative features of potentials of mean force of single amino acid side chain analogues into model bilayers. In particular, modifications of peptide-water and peptide-membrane interactions allow prediction of free energy minima at the bilayer-water interface as obtained with all-atom force fields. In the case of oligo-arginine peptides, the modified parameter sets predict interfacial free energy minima as well as free energy barriers in almost quantitative agreement with all-atom force field based simulations. Interfacial free energy minima predicted by a modified coarse-grained parameter set are -2.51, -4.28, and -5.42 for mono-, di-, and triarginine; corresponding values from all-atom simulations are -0.83, -3.33, and -3.29, respectively, all in units of kcal/mol. We found that a stronger interaction between oligo-arginine and the membrane components and a weaker interaction between oligo-arginine and water are crucial for producing such minima in PMFs using the polarizable CG model. The difference between bulk aqueous and bilayer center states predicted by the modified coarse-grain force field are 11.71, 14.14, and 16.53 kcal/mol, and those by the all-atom model are 6.94, 8.64, and 12.80 kcal/mol; those are of almost the same order of magnitude. Our simulations also demonstrate a remarkable similarity in the structural aspects of the ensemble of

  6. Electrical Evolution of a Dust Plume from a Low Energy Lunar Impact: A Model Analog to LCROSS

    Science.gov (United States)

    Farrell, W. M.; Stubbs, T. J.; Jackson, T. L.; Colaprete, A.; Heldmann, J. L.; Schultz, P. H.; Killen, R. M.; Delory, G. T.; Halekas, J. S.; Marshall, J. R.; hide

    2011-01-01

    A Monte Carlo test particle model was developed that simulates the charge evolution of micron and sub-micron sized dust grains ejected upon low-energy impact of a moderate-size object onto a lunar polar crater floor. Our analog is the LCROSS impact into Cabeus crater. Our primary objective is to model grain discharging as the plume propagates upwards from shadowed crater into sunlight.

  7. Dust in cosmic plasma environments

    International Nuclear Information System (INIS)

    Mendis, D.A.

    1979-01-01

    Cosmic dust is invariably immersed in a plasma and a radiative environment. Consequently, it is charged to some electrostatic potential which depends on the properties of the environment as well as the nature of the dust. This charging affects the physical and dynamical properties of the dust. In this paper the basic aspects of this dust-plasma interaction in several cosmic environments - including planetary magnetospheres, the heliosphere and the interstellar medium - are discussed. The physical and dynamical consequences of the interaction, as well as the pertinent observational evidence, are reviewed. Finally, the importance of the surface charge during the condensation process in plasma environments is stressed. (Auth.)

  8. Threshold separation distance for attractive interaction between dust particles

    International Nuclear Information System (INIS)

    Jabdaraghi, R. Najafi; Sobhanian, S.

    2008-01-01

    Interaction between dust grains in a dusty plasma could be both repulsive and attractive. The Coulomb interaction between two negatively charged dust particulates and the electrostatic force between them are repulsive, while the shadowing force affecting them is attractive. We show in this paper that in some experimental conditions, there is some grain separation zone for which the attractive shadowing force is larger than the repulsive forces between them. In experimental conditions, for the grains separation distance r = 0.4 cm the shadowing force is almost equal to the electrostatic force between them and for r>0.4 cm the shadowing force exceeds the electrostatic force. So the resultant interaction force will be attractive. The possibility of dust crystal formation in this zone and also the motion of dust particles in the resultant potential of the form V = -(a/r)+(b/r 2 ) will be discussed. This form of potential comes from the combination electrostatic (F es (c/r 3 )) and shadowing (F shadow = -(d/r 2 )) forces.

  9. Molecules and dust in Cassiopeia A

    DEFF Research Database (Denmark)

    Biscaro, Chiara; Cherchneff, Isabelle

    2016-01-01

    We study the dust evolution in the supernova remnant Cassiopeia A. We follow the processing of dust grains that formed in the Type II-b supernova ejecta by modelling the sputtering of grains. The dust is located in dense ejecta clumps that are crossed by the reverse shock. We also investigate......-rich clumps that correspond to the outermost carbon-rich ejecta zone. We consider the various dust components that form in the supernova, several reverse shock velocities and inter-clump gas temperatures, and derive grain-size distributions and masses for the dust as a function of time. Both non...... and size, and the shock velocity in the clump. A Type II-b SN forms small grains that are sputtered within the clumps and in the inter-clump medium. For Cas A, silicate grains do not survive thermal sputtering in the inter-clump medium, while alumina, silicon carbide, and carbon dust may survive...

  10. Summary of the results from the Lunar Dust Experiment (LDEX) onboard the Lunar Atmosphere and Dust Environment (LADEE) Mission

    Science.gov (United States)

    Horanyi, Mihaly

    2016-07-01

    The Lunar Dust Experiment (LDEX) onboard the Lunar Atmosphere and Dust Environment Explorer (LADEE) mission (9/2013 - 4/2014) discovered a permanently present dust cloud engulfing the Moon. The size, velocity, and density distributions of the dust particles are consistent with ejecta clouds generated from the continual bombardment of the lunar surface by sporadic interplanetary dust particles. Intermittent density enhancements were observed during several of the annual meteoroid streams, especially during the Geminids. LDEX found no evidence of the expected density enhancements over the terminators where electrostatic processes were predicted to efficiently loft small grains. LDEX is an impact ionization dust detector, it captures coincident signals and full waveforms to reliably identify dust impacts. LDEX recorded average impact rates of approximately 1 and 0.1 hits/minute of particles with impact charges of q > 0.5 and q > 5 fC, corresponding to particles with radii of a > 0.3 and a> 0.7~μm, respectively. Several of the yearly meteor showers generated sustained elevated levels of impact rates, especially if their radiant direction intersected the lunar surface near the equatorial plane, greatly enhancing the probability of crossing their ejecta plumes. The characteristic velocities of dust particles in the cloud are on the order of ~100 m/s which we neglect compared to the typical spacecraft speeds of 1.6 km/s. Hence, with the knowledge of the spacecraft orbit and attitude, impact rates can be directly turned into particle densities as functions of time and position. LDEX observations are the first to identify the ejecta clouds around the Moon sustained by the continual bombardment of interplanetary dust particles. Most of the dust particles generated in impacts have insufficient energy to escape and follow ballistic orbits, returning to the surface, 'gardening' the regolith. Similar ejecta clouds are expected to engulf all airless planetary objects, including

  11. Formation and dissociation of dust molecules in dusty plasma

    Science.gov (United States)

    Yan, Jia; Feng, Fan; Liu, Fucheng; Dong, Lifang; He, Yafeng

    2016-09-01

    Dust molecules are observed in a dusty plasma experiment. By using measurements with high spatial resolution, the formation and dissociation of the dust molecules are studied. The ion cloud in the wake of an upper dust grain attracts the lower dust grain nearby. When the interparticle distance between the upper dust grain and the lower one is less than a critical value, the two dust grains would form a dust molecule. The upper dust grain always leads the lower one as they travel. When the interparticle distance between them is larger than the critical value, the dust molecule would dissociate. Project supported by the National Natural Science Foundation of China (Grant Nos. 11205044 and 11405042), the Natural Science Foundation of Hebei Province, China (Grant Nos. A2011201006 and A2012201015), the Research Foundation of Education Bureau of Hebei Province, China (Grant No. Y2012009), the Program for Young Principal Investigators of Hebei Province, China, and the Midwest Universities Comprehensive Strength Promotion Project, China.

  12. Lunar Dust Mitigation Screens

    Science.gov (United States)

    Knutson, Shawn; Holloway, Nancy

    With plans for the United States to return to the moon, and establish a sustainable human presence on the lunar surface many issues must be successfully overcome. Lunar dust is one of a number of issues with the potential to create a myriad of problems if not adequately addressed. Samples of dust brought back from Apollo missions show it to be soft, yet sharp and abrasive. The dust consists of a variety of morphologies including spherical, angular blocks, shards, and a number of irregular shapes. One of the main issues with lunar dust is its attraction to stick to anything it comes in contact with (i.e. astronauts, equipment, habitats, etc.). Ionized radiation from the sun strikes the moon's surface and creates an electrostatic charge on the dust. Further, the dust harbors van der Waals forces making it especially difficult to separate once it sticks to a surface. During the Apollo missions, it was discovered that trying to brush the lunar dust from spacesuits was not effective, and rubbing it caused degradation of the suit material. Further, when entering the lunar module after moonwalks, the astronauts noted that the dust was so prolific inside the cabin that they inhaled and ingested it, causing at least one of them, Harrison "Jack" Schmidt, to report irritation of the throat and lungs. It is speculated that the dust could also harm an astronaut's nervous and cardiovascular systems, especially during an extended stay. In addition to health issues, the dust can also cause problems by scouring reflective coatings off of thermal blankets, and roughening surfaces of windows and optics. Further, panels on solar cells and photovoltaics can also be compromised due to dust sticking on the surfaces. Lunar dust has the capacity to penetrate seals, interfere with connectors, as well as mechanisms on digging machines, all of which can lead to problems and failure. To address lunar dust issues, development of electrostatic screens to mitigate dust on sur-faces is currently

  13. Origins of GEMS Grains

    Science.gov (United States)

    Messenger, S.; Walker, R. M.

    2012-01-01

    Interplanetary dust particles (IDPs) collected in the Earth s stratosphere contain high abundances of submicrometer amorphous silicates known as GEMS grains. From their birth as condensates in the outflows of oxygen-rich evolved stars, processing in interstellar space, and incorporation into disks around new stars, amorphous silicates predominate in most astrophysical environments. Amorphous silicates were a major building block of our Solar System and are prominent in infrared spectra of comets. Anhydrous interplanetary dust particles (IDPs) thought to derive from comets contain abundant amorphous silicates known as GEMS (glass with embedded metal and sulfides) grains. GEMS grains have been proposed to be isotopically and chemically homogenized interstellar amorphous silicate dust. We evaluated this hypothesis through coordinated chemical and isotopic analyses of GEMS grains in a suite of IDPs to constrain their origins. GEMS grains show order of magnitude variations in Mg, Fe, Ca, and S abundances. GEMS grains do not match the average element abundances inferred for ISM dust containing on average, too little Mg, Fe, and Ca, and too much S. GEMS grains have complementary compositions to the crystalline components in IDPs suggesting that they formed from the same reservoir. We did not observe any unequivocal microstructural or chemical evidence that GEMS grains experienced prolonged exposure to radiation. We identified four GEMS grains having O isotopic compositions that point to origins in red giant branch or asymptotic giant branch stars and supernovae. Based on their O isotopic compositions, we estimate that 1-6% of GEMS grains are surviving circumstellar grains. The remaining 94-99% of GEMS grains have O isotopic compositions that are indistinguishable from terrestrial materials and carbonaceous chondrites. These isotopically solar GEMS grains either formed in the Solar System or were completely homogenized in the interstellar medium (ISM). However, the

  14. Dust in flowing magnetized plasma

    International Nuclear Information System (INIS)

    Pandey, Birendra P.; Samarian, Alex A.; Vladimirov, Sergey V.

    2009-01-01

    Plasma flows occur in almost every laboratory device and interactions of flowing plasmas with near-wall impurities and/or dust significantly affects the efficiency and lifetime of such devices. The charged dust inside the magnetized flowing plasma moves primarily under the influence of the plasma drag and electric forces. Here, the charge on the dust, plasma potential, and plasma density are calculated self-consistently. The electrons are assumed non-Boltzmannian and the effect of electron magnetization and electron-atom collisions on the dust charge is calculated in a self-consistent fashion. For various plasma magnetization parameters viz. the ratio of the electron and ion cyclotron frequencies to their respective collision frequencies, plasma-atom and ionization frequencies, the evolution of the plasma potential and density in the flow region is investigated. The variation of the dust charge profile is shown to be a sensitive function of plasma parameters. (author)

  15. ORIGIN OF DUST AROUND V1309 SCO

    International Nuclear Information System (INIS)

    Zhu, Chunhua; Lü, Guoliang; Wang, Zhaojun

    2013-01-01

    The origin of dust grains in the interstellar medium is still an unanswered problem. Nicholls et al. found the presence of a significant amount of dust around V1309 Sco, which may originate from the merger of a contact binary. We investigate the origin of dust around V1309 Sco and suggest that these dust grains are produced in the binary-merger ejecta. By means of the AGBDUST code, we estimate that ∼5.2 × 10 –4 M ☉ dust grains are produced with a radii of ∼10 –5 cm. These dust grains are mainly composed of silicate and iron grains. Because the mass of the binary merger ejecta is very small, the contribution of dust produced by binary merger ejecta to the overall dust production in the interstellar medium is negligible. However, it is important to note that the discovery of a significant amount of dust around V1309 Sco offers a direct support for the idea that common-envelope ejecta provides an ideal environment for dust formation and growth. Therefore, we confirm that common envelope ejecta can be important source of cosmic dust

  16. The effect of dust size distribution on the damping of the solitary waves in a dusty plasma

    International Nuclear Information System (INIS)

    Yang, Xue; Xu, Yan-Xia; Qi, Xin; Wang, Cang-Long; Duan, Wen-Shan; Yang, Lei

    2013-01-01

    The effect of the dust size distribution on the damping rate of the solitary wave in a dusty plasma is investigated in the present paper. It is found that the damping rate increases as either the mean radius of dust grains increases or as the total number density of the dust grains increases. The damping rate is less for usual dusty plasma (about which the number density of the smaller dust grains is larger than that of the larger dust grains) than that of the unusual dusty plasma (about which the number density of the larger dust grains is larger than that of the smaller dust grains)

  17. Stochastic heating of dust particles in complex plasmas as an energetic instability of a harmonic oscillator with random frequency

    Energy Technology Data Exchange (ETDEWEB)

    Marmolino, Ciro [Dipartimento di Scienze e Tecnologie dell' Ambiente e del Territorio-DiSTAT, Universita del Molise, Contrada Fonte Lappone, I-86090 Pesche (Italy)

    2011-10-15

    The paper describes the occurrence of stochastic heating of dust particles in dusty plasmas as an energy instability due to the correlations between dust grain charge and electric field fluctuations. The possibility that the mean energy (''temperature'') of dust particles can grow in time has been found both from the self-consistent kinetic description of dusty plasmas taking into account charge fluctuations [U. de Angelis, A. V. Ivlev, V. N. Tsytovich, and G. E. Morfill, Phys. Plasmas 12(5), 052301 (2005)] and from a Fokker-Planck approach to systems with variable charge [A. V. Ivlev, S. K. Zhdanov, B. A. Klumov, and G. E. Morfill, Phys. Plasmas 12(9), 092104 (2005)]. Here, a different derivation is given by using the mathematical techniques of the so called multiplicative stochastic differential equations. Both cases of ''fast'' and ''slow'' fluctuations are discussed.

  18. Dust acoustic shock wave at high dust density

    International Nuclear Information System (INIS)

    Ghosh, Samiran; Sarkar, Susmita; Khan, Manoranjan; Avinash, K.; Gupta, M. R.

    2003-01-01

    Dust acoustic (DA) shock wave at high dust density, i.e., the dust electroacoustic (DEA) or dust Coulomb (DC) shock wave has been investigated incorporating the nonadiabatic dust charge variation. The nonlinear DEA (DC) shock wave is seen to be governed by the Korteweg-de Vries Burger equation, in which the Burger term is proportional to the nonadiabaticity generated dissipation. It is seen that the shock strength decreases but after reaching minimum, it increases as the dust space charge density |q d n d | increases and the shock strength of DA wave is greater than that of DEA (DC) wave. Moreover the DEA (DC) shock width increases appreciably with increase mass m i of the ion component of the dusty plasma but for DA shock wave the effect is weak

  19. Cosmological simulation with dust formation and destruction

    Science.gov (United States)

    Aoyama, Shohei; Hou, Kuan-Chou; Hirashita, Hiroyuki; Nagamine, Kentaro; Shimizu, Ikkoh

    2018-06-01

    To investigate the evolution of dust in a cosmological volume, we perform hydrodynamic simulations, in which the enrichment of metals and dust is treated self-consistently with star formation and stellar feedback. We consider dust evolution driven by dust production in stellar ejecta, dust destruction by sputtering, grain growth by accretion and coagulation, and grain disruption by shattering, and treat small and large grains separately to trace the grain size distribution. After confirming that our model nicely reproduces the observed relation between dust-to-gas ratio and metallicity for nearby galaxies, we concentrate on the dust abundance over the cosmological volume in this paper. The comoving dust mass density has a peak at redshift z ˜ 1-2, coincident with the observationally suggested dustiest epoch in the Universe. In the local Universe, roughly 10 per cent of the dust is contained in the intergalactic medium (IGM), where only 1/3-1/4 of the dust survives against dust destruction by sputtering. We also show that the dust mass function is roughly reproduced at ≲ 108 M⊙, while the massive end still has a discrepancy, which indicates the necessity of stronger feedback in massive galaxies. In addition, our model broadly reproduces the observed radial profile of dust surface density in the circum-galactic medium (CGM). While our model satisfies the observational constraints for the dust extinction on cosmological scales, it predicts that the dust in the CGM and IGM is dominated by large (>0.03 μm) grains, which is in tension with the steep reddening curves observed in the CGM.

  20. The simplest model of a dust cloud in a plasma

    International Nuclear Information System (INIS)

    Ignatov, A.M.

    1998-01-01

    A cloud consisting of a finite number of dust grains in a plasma is considered. It is shown that the absorption of the plasma by the dust grains gives rise to the formation of a plasma flow toward to the cloud. The drag force produced by this flow acts upon the dust grains and counterbalances the electrostatic repulsing force. The distribution of the grain density inside the cloud is determined. The characteristic size of the cloud is estimated as r D 3/2 /a 1/2 , where r D is the plasma Debye radius, and a is the size of the dust grains

  1. Nonlinear dust-acoustic structures in space plasmas with superthermal electrons, positrons, and ions

    Energy Technology Data Exchange (ETDEWEB)

    Saberian, E., E-mail: e.saberian@neyshabur.ac.ir [University of Neyshabur, Department of Physics, Faculty of Basic Sciences (Iran, Islamic Republic of); Esfandyari-Kalejahi, A.; Afsari-Ghazi, M. [Azarbaijan Shahid Madani University, Department of Physics, Faculty of Sciences (Iran, Islamic Republic of)

    2017-01-15

    Some features of nonlinear dust-acoustic (DA) structures are investigated in a space plasma consisting of superthermal electrons, positrons, and positive ions in the presence of negatively charged dust grains with finite-temperature by employing a pseudo-potential technique in a hydrodynamic model. For this purpose, it is assumed that the electrons, positrons, and ions obey a kappa-like (κ) distribution in the background of adiabatic dust population. In the linear analysis, it is found that the dispersion relation yield two positive DA branches, i.e., the slow and fast DA waves. The upper branch (fast DA waves) corresponds to the case in which both (negatively charged) dust particles and (positively charged) ion species oscillate in phase with electrons and positrons. On the other hand, the lower branch (slow DA waves) corresponds to the case in which only dust particles oscillate in phase with electrons and positrons, while ion species are in antiphase with them. On the other hand, the fully nonlinear analysis shows that the existence domain of solitons and their characteristics depend strongly on the dust charge, ion charge, dust temperature, and the spectral index κ. It is found that the minimum/maximum Mach number increases as the spectral index κ increases. Also, it is found that only solitons with negative polarity can propagate and that their amplitudes increase as the parameter κ increases. Furthermore, the domain of Mach number shifts to the lower values, when the value of the dust charge Z{sub d} increases. Moreover, it is found that the Mach number increases with an increase in the dust temperature. Our analysis confirms that, in space plasmas with highly charged dusts, the presence of superthermal particles (electrons, positrons, and ions) may facilitate the formation of DA solitary waves. Particularly, in two cases of hydrogen ions H{sup +} (Z{sub i} = 1) and doubly ionized Helium atoms He{sup 2+} (Z{sub i} = 2), the mentioned results are the same

  2. Perturbed soliton excitations of Rao-dust Alfvén waves in magnetized dusty plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Kavitha, L., E-mail: louiskavitha@yahoo.co.in [Department of Physics, School of Basic and Applied Sciences, Central University of Tamil Nadu, Thiruvarur 610 101 (India); The Abdus Salam International Centre for Theoretical Physics, Trieste (Italy); Lavanya, C.; Senthil Kumar, V. [Department of Physics, Periyar University, Salem, Tamil Nadu 636 011 (India); Gopi, D. [Department of Chemistry, Periyar University, Salem 636 011 (India); Center for Nanoscience and Nanotechnology, Periyar University, Salem, Tamil Nadu 636 011 (India); Pasqua, A. [Department of Physics, University of Trieste, Trieste (Italy)

    2016-04-15

    We investigate the propagation dynamics of the perturbed soliton excitations in a three component fully ionized dusty magnetoplasma consisting of electrons, ions, and heavy charged dust particulates. We derive the governing equation of motion for the two dimensional Rao-dust magnetohydrodynamic (R-D-MHD) wave by employing the inertialess electron equation of motion, inertial ion equation of motion, the continuity equations in a plasma with immobile charged dust grains, together with the Maxwell's equations, by assuming quasi neutrality and neglecting the displacement current in Ampere's law. Furthermore, we assume the massive dust particles are practically immobile since we are interested in timescales much shorter than the dusty plasma period, thereby neglecting any damping of the modes due to the grain charge fluctuations. We invoke the reductive perturbation method to represent the governing dynamics by a perturbed cubic nonlinear Schrödinger (pCNLS) equation. We solve the pCNLS, along the lines of Kodama-Ablowitz multiple scale nonlinear perturbation technique and explored the R-D-MHD waves as solitary wave excitations in a magnetized dusty plasma. Since Alfvén waves play an important role in energy transport in driving field-aligned currents, particle acceleration and heating, solar flares, and the solar wind, this representation of R-D-MHD waves as soliton excitations may have extensive applications to study the lower part of the earth's ionosphere.

  3. Parameterizing the interstellar dust temperature

    Science.gov (United States)

    Hocuk, S.; Szűcs, L.; Caselli, P.; Cazaux, S.; Spaans, M.; Esplugues, G. B.

    2017-08-01

    The temperature of interstellar dust particles is of great importance to astronomers. It plays a crucial role in the thermodynamics of interstellar clouds, because of the gas-dust collisional coupling. It is also a key parameter in astrochemical studies that governs the rate at which molecules form on dust. In 3D (magneto)hydrodynamic simulations often a simple expression for the dust temperature is adopted, because of computational constraints, while astrochemical modelers tend to keep the dust temperature constant over a large range of parameter space. Our aim is to provide an easy-to-use parametric expression for the dust temperature as a function of visual extinction (AV) and to shed light on the critical dependencies of the dust temperature on the grain composition. We obtain an expression for the dust temperature by semi-analytically solving the dust thermal balance for different types of grains and compare to a collection of recent observational measurements. We also explore the effect of ices on the dust temperature. Our results show that a mixed carbonaceous-silicate type dust with a high carbon volume fraction matches the observations best. We find that ice formation allows the dust to be warmer by up to 15% at high optical depths (AV> 20 mag) in the interstellar medium. Our parametric expression for the dust temperature is presented as Td = [ 11 + 5.7 × tanh(0.61 - log 10(AV) ]χuv1/5.9, where χuv is in units of the Draine (1978, ApJS, 36, 595) UV field.

  4. Effect of grain size on charge and spin correlations in Bi{sub 0.5}Ca{sub 0.5}MnO{sub 3} manganite nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Ade, Ramesh; Singh, Rajender, E-mail: rssp@uohyd.ernet.in

    2016-11-15

    In this work we report the electron spin resonance (ESR) and magnetization (M) studies to understand the effect of grain size (GS) on the charge ordering and spin correlations in Bi{sub 0.5}Ca{sub 0.5}MnO{sub 3} manganite synthesized by sol–gel method. The suppression of charge ordering (CO), long-range antiferromagnetic (AFM) state, shifting of ferromagnetic (FM)-cluster glass (CG) transition towards higher temperatures and evolution of different magnetic correlations with decrease in GS are discussed in view of the changes in surface to volume ratio of nano-grains. - Highlights: • Effect of grain size on charge and spin correlations in Bi{sub 0.5}Ca{sub 0.5}MnO{sub 3} are studied. • The samples with GS 27, 450 and 1080 nm were synthesized by sol–gel method. • The temperature dependent electron spin resonance (ESR) and magnetization measurements were carried out. • The evolution of different magnetic correlations with decrease in GS are ascribed to increase in surface to volume ratio of grains.

  5. Nonuniform charging effects on ion drag force in drifting dusty plasmas

    International Nuclear Information System (INIS)

    Chang, Dong-Man; Chang, Won-Seok; Jung, Young-Dae

    2006-01-01

    The nonuniform polarization charging effects on the ion drag force are investigated in drifting dusty plasmas. The ion drag force due to the ion-dust grain interaction is obtained as a function of the dust charge, ion charge, plasma temperature, Mach number, Debye length, and collision energy. The result shows that the nonuniform charging effects enhance the momentum transfer cross section as well as the ion drag force. It is found that the momentum transfer cross section and the ion drag force including nonuniform polarization charging effects increase with increasing the Mach number and also the ion drag force increases with increasing the temperature. In addition, it is found that the ion drag force is slightly decreasing with an increase of the Debye length

  6. A Microphysically-based Approach to Inferring Porosity, Grain Size, and Dust Abundance in the Seasonal Caps from Atmospherically-corrected TES Spectra

    Science.gov (United States)

    Eluszkiewicz, J.; Titus, T. N.

    2003-01-01

    One of the highlights of the TES observations in the polar regions has been the identification of a "cryptic" region in the south where CO2 appears to be in the form of a solid slab rather than a fluffy frost. While the exact mechanism(s) by which the cryptic region is formed are still subject of some debate, it appears certain that a type of rapid metamorphism related to the high volatility of CO2 ice is involved. The high volatility of CO2 ice under martian conditions has several Solar System analogs (N2 on Triton and Pluto, SO2 on Io), thus making the martian cryptic region somewhat less cryptic and certainly non-unique among planetary objects. In an endmember scenario, both the formation and the spectral properties of the cryptic region (and of other areas in the seasonal caps) can be quantitatively modeled by considering sintering of an ensemble of quasi-spherical CO2 grains. This model includes the special case of instanteneous slab formation, which occurs when the grains are sufficiently small (in the submicron range) so that their sintering timescale is short relative to the deposition timescale (a situation analogous to the "sintering" of water droplets falling into a pond).

  7. Oxidant enhancement in martian dust devils and storms: storm electric fields and electron dissociative attachment.

    Science.gov (United States)

    Delory, Gregory T; Farrell, William M; Atreya, Sushil K; Renno, Nilton O; Wong, Ah-San; Cummer, Steven A; Sentman, Davis D; Marshall, John R; Rafkin, Scot C R; Catling, David C

    2006-06-01

    Laboratory studies, numerical simulations, and desert field tests indicate that aeolian dust transport can generate atmospheric electricity via contact electrification or "triboelectricity." In convective structures such as dust devils and dust storms, grain stratification leads to macroscopic charge separations and gives rise to an overall electric dipole moment in the aeolian feature, similar in nature to the dipolar electric field generated in terrestrial thunderstorms. Previous numerical simulations indicate that these storm electric fields on Mars can approach the ambient breakdown field strength of approximately 25 kV/m. In terrestrial dust phenomena, potentials ranging from approximately 20 to 160 kV/m have been directly measured. The large electrostatic fields predicted in martian dust devils and storms can energize electrons in the low pressure martian atmosphere to values exceeding the electron dissociative attachment energy of both CO2 and H2O, which results in the formation of the new chemical products CO/O- and OH/H-, respectively. Using a collisional plasma physics model, we present calculations of the CO/O- and OH/H- reaction and production rates. We demonstrate that these rates vary geometrically with the ambient electric field, with substantial production of dissociative products when fields approach the breakdown value of approximately 25 kV/m. The dissociation of H2O into OH/H- provides a key ingredient for the generation of oxidants; thus electrically charged dust may significantly impact the habitability of Mars.

  8. The role of electrostatic charging of small and intermediate sized bodies in the solar system

    International Nuclear Information System (INIS)

    Mendis, D.A.

    1981-01-01

    The role of electrostatic charging of small and intermediate sized bodies in the solar system is reviewed. These bodies include planetary, interplanetary and cometary dust as well as cometary nuclei (at large heliocentric distances), asteroids and the larger bodies in the Saturnian ring system. While this charging has both physical and dynamical consequences for the small dust grains, it has only physical consequences for the larger bodies. The main physical consequences for the small grains are electrostatic erosion (''chipping'') and disruption, whereas for the larger bodies they include electrostatic levitation and blow-off of fine loose dust from their surfaces. A large variety of solar system phenomena, recently observed by the Pioneer and Voyager deep space probes as well as the HEOS-2 earth satellite, are explained in terms of these processes. Certain peculiar features observed in the dust tails of comets as well as the spatial orientation of the zodiacal dust cloud may also be explained along these lines. The possible electrostatic erosion of the dust mantles of new comets as well as the electrostatic 'polishing' of the smaller asteroids are also discussed. (Auth.)

  9. Laboratory Studies of the Optical Properties and Condensation Processes of Cosmic Dust Particles

    Science.gov (United States)

    Abbas, Mian M.; Craven, Paul D.; Spann, James F.; Tankosic, Dragana; Six, N. Frank (Technical Monitor)

    2002-01-01

    A laboratory facility for levitating single isolated dust particles in an electrodynamics balance has been developing at NASA/Marshall Space Flight Center for conducting a variety of experimental, of astrophysical interest. The objective of this research is to employ this innovative experimental technique for studies of the physical and optical properties of the analogs of cosmic grains of 0.2-10 micron size in a chamber with controlled pressure/temperatures simulating astrophysical environments. In particular, we will carry out three classes of experiments to investigate the microphysics of the analogs of interstellar and interplanetary dust grains. (1) Charge characteristics of micron size single dust grains to determine the photoelectric efficiencies, yields, and equilibrium potentials when exposed to UV radiation. These measurements will provide the much-needed photoelectric emission data relating to individual particles as opposed to that for the bulk materials available so far. (2) Infrared optical properties of dust particles obtained by irradiating the particles with radiation from tunable infrared diode lasers and measuring the scattered radiation. Specifically, the complex refractive indices, the extinction coefficients, the scattering phase functions, and the polarization properties of single dust grains of interest in interstellar environments, in the 1-25 micron spectral region will be determined. (3) Condensation experiments to investigate the deposition of volatile gases on colder nucleated particles in dense interstellar clouds and lower planetary atmospheres. The increase in the mass or m/q ratio due to condensation on the particle will be monitored as a function of the dust particle temperature and the partial pressure of the injected volatile gas. The measured data wild permit determination of the sticking efficiencies of volatile gases of astrophysical interest. Preliminary results based on photoelectric emission experiments on 0.2-6.6 micron

  10. Wood Dust

    Science.gov (United States)

    Learn about wood dust, which can raise the risk of cancers of the paranasal sinuses and nasal cavity. High amounts of wood dust are produced in sawmills, and in the furniture-making, cabinet-making, and carpentry industries.

  11. Rapid and cyclic dust accumulation during MIS 2 in Central Asia inferred from loess OSL dating and grain-size analysis.

    Science.gov (United States)

    Li, Yun; Song, Yougui; Lai, Zhongping; Han, Li; An, Zhisheng

    2016-09-02

    Due to lack of reliable proxies from the Westerlies-dominant region, the strength change of Northern Hemisphere Westerlies remains poorly understood. The aim of this study is to provide a reliable paleoclimatic proxy about the Northern Hemisphere Westerlies change. Here we report a 30.7 m thick loess section from the Ili basin directly controlled by the Westerlies. Based on optically stimulated luminescence (OSL) and high resolution grain-size records, we reconstruct the change history of the Westerlies strength during the last glacial period (mainly Marine Isotope Stages 2, MIS2), being similar with the Westerlies index recorded in the Qinghai Lake sediments. Within error limits, all ages are in stratigraphic order. We further compare the climatic records among the Ili loess, Qinghai Lake and the NGRIP, their similarity shows a good climatic coupling relationship among the Central Asia, East Asia and the North Atlantic, and the Westerlies plays a critical influence in