The size distribution of interstellar dust particles as determined from polarization: Spheroids

1995 ◽  
Vol 444 ◽  
pp. 293 ◽  
Author(s):  
Sang-Hee Kim ◽  
P. G. Martin
Keyword(s):  
Size Distribution ◽  
Interstellar Dust ◽  
Dust Particles

The size distribution of interstellar dust particles as determined from extinction

1994 ◽  
Vol 422 ◽  
pp. 164 ◽  
Author(s):  
Sang-Hee Kim ◽  
P. G. Martin ◽  
Paul D. Hendry
Keyword(s):  
Size Distribution ◽  
Interstellar Dust ◽  
Dust Particles

scholarly journals Quantum tunneling observed without its characteristic large kinetic isotope effects

2015 ◽  
Vol 112 (24) ◽  
pp. 7438-7443 ◽  
Author(s):  
Tetsuya Hama ◽  
Hirokazu Ueta ◽  
Akira Kouchi ◽  
Naoki Watanabe
Keyword(s):  
Chemical Kinetics ◽  
Quantum Tunneling ◽  
Interstellar Dust ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
State Theory ◽  
Dust Particles ◽  
Interplanetary Dust Particles ◽  
Chemical Systems ◽  
Kinetic Isotope

Classical transition-state theory is fundamental to describing chemical kinetics; however, quantum tunneling is also important in explaining the unexpectedly large reaction efficiencies observed in many chemical systems. Tunneling is often indicated by anomalously large kinetic isotope effects (KIEs), because a particle’s ability to tunnel decreases significantly with its increasing mass. Here we experimentally demonstrate that cold hydrogen (H) and deuterium (D) atoms can add to solid benzene by tunneling; however, the observed H/D KIE was very small (1–1.5) despite the large intrinsic H/D KIE of tunneling (≳100). This strong reduction is due to the chemical kinetics being controlled not by tunneling but by the surface diffusion of the H/D atoms, a process not greatly affected by the isotope type. Because tunneling need not be accompanied by a large KIE in surface and interfacial chemical systems, it might be overlooked in other systems such as aerosols or enzymes. Our results suggest that surface tunneling reactions on interstellar dust may contribute to the deuteration of interstellar aromatic and aliphatic hydrocarbons, which could represent a major source of the deuterium enrichment observed in carbonaceous meteorites and interplanetary dust particles. These findings could improve our understanding of interstellar physicochemical processes, including those during the formation of the solar system.

scholarly journals Ortho and Parahydrogen in Interstellar Material

1979 ◽  
Vol 34 (2) ◽  
pp. 163-166 ◽  
Author(s):  
Robert R. Reeves ◽  
Paul Harteck
Keyword(s):  
Interstellar Dust ◽  
Dynamic Equilibrium ◽  
Exothermic Reaction ◽  
Statistical Weight ◽  
Dust Particles ◽  
Minor Role ◽  
Interstellar Space ◽  
Special Cases ◽  
Temperature Equilibrium ◽  
A Minor

Abstract Since H2 is the most abundant molecule in the universe, the ratio of orthohydrogen molecules to parahydrogen in interstellar space is of interest. H2, formed by any exothermic reaction will be in the ratio of 3: 1 according to their statistical weight. This corresponds to the high temperature equilibrium. At the low prevailing temperatures of interstellar space, the thermo-dynamic equilibrium should be shifted to the parahydrogen side. In the gas phase this shift can occur only over chemical reactions which are close to thermally neutral. In addition, it can be concluded that two ion scrambling reactions dominate the process and these both involve positive hydrogen ions. In special cases, surface catalysis on interstellar dust particles may add to the equilibrating process. The highly forbidden process of transition by radiation J = 1(ortho) → J = O(para) + hv can only play a minor role in this catalysis

scholarly journals Streaming instability of multiple particle species in protoplanetary disks

2018 ◽  
Vol 618 ◽  
pp. A75 ◽  
Author(s):  
Noemi Schaffer ◽  
Chao-Chin Yang ◽  
Anders Johansen
Keyword(s):  
Particle Size ◽  
Size Distribution ◽  
Protoplanetary Disks ◽  
Single Species ◽  
Stokes Number ◽  
Dust Particles ◽  
Particle Sizes ◽  
Particle Species ◽  
Streaming Instability ◽  
Large Particles

The radial drift and diffusion of dust particles in protoplanetary disks affect both the opacity and temperature of such disks, as well as the location and timing of planetesimal formation. In this paper, we present results of numerical simulations of particle-gas dynamics in protoplanetary disks that include dust grains with various size distributions. We have considered three scenarios in terms of particle size ranges, one where the Stokes number τs = 10−1−100, one where τs = 10−4−10−1, and finally one where τs = 10−3−100. Moreover, we considered both discrete and continuous distributions in particle size. In accordance with previous works we find in our multispecies simulations that different particle sizes interact via the gas and as a result their dynamics changes compared to the single-species case. The larger species trigger the streaming instability and create turbulence that drives the diffusion of the solid materials. We measured the radial equilibrium velocity of the system and find that the radial drift velocity of the large particles is reduced in the multispecies simulations and that the small particle species move on average outwards. We also varied the steepness of the size distribution, such that the exponent of the solid number density distribution, dN∕da ∝ a−q, is either q = 3 or q = 4. Overall, we find that the steepness of the size distribution and the discrete versus continuous approach have little impact on the results. The level of diffusion and drift rates are mainly dictated by the range of particle sizes. We measured the scale height of the particles and observe that small grains are stirred up well above the sedimented midplane layer where the large particles reside. Our measured diffusion and drift parameters can be used in coagulation models for planet formation as well as to understand relative mixing of the components of primitive meteorites (matrix, chondrules and CAIs) prior to inclusion in their parent bodies.

Effect of an Arbitrary Dust Size Distribution Dust Particles for Vortex-Like Ion Distribution Dusty Plasma

2009 ◽  
Vol 52 (3) ◽  
pp. 517-522
Author(s):  
Wei Ju-Na ◽  
Shi Yu-Ren ◽  
He Guang-Jun ◽  
Jiang Xin ◽  
Duan Wen-Shan ◽  
...  
Keyword(s):  
Size Distribution ◽  
Dusty Plasma ◽  
Dust Particles ◽  
Ion Distribution ◽  
Dust Size Distribution

scholarly journals Study of Cosmic Dust Particles on Board LDEF and MIR Space Station

1991 ◽  
Vol 126 ◽  
pp. 11-14
Author(s):  
J.C. Mandeville
Keyword(s):  
Size Distribution ◽  
Good Accuracy ◽  
Space Station ◽  
Cosmic Dust ◽  
Orbital Debris ◽  
Dust Particles ◽  
Chemical Identification ◽  
Near Earth Space ◽  
Solid Objects ◽  
Long Duration

AbstractInterplanetary and near-earth space contains solid objects whose size distribution continuously covers the interval from submicron sized particles to km sized asteroids or comets. Two French experiments partly devoted to the detection of cosmic dust have been flown recently in space. One on the NASA Long Duration Exposure Facility (LDEF), and one on the Soviet MIR Space Station. A variety of sensors and collecting devices will make possible the study of cosmic particles after recovery of exposed material. Flux mass distribution is expected to be derived from craters counts, with a good accuracy. Remnants of particles, suitable for chemical identification are expected to be found within stacked foil detectors. Discrimination between extraterrestrial particles and man-made orbital debris will be possible.

scholarly journals Dust Measurements in the Outer Solar System

1994 ◽  
Vol 160 ◽  
pp. 367-380
Author(s):  
Eberhard Grün
Keyword(s):  
Solar System ◽  
Interstellar Dust ◽  
Thermal Emission ◽  
Scattered Light ◽  
Interplanetary Dust ◽  
Dust Particles ◽  
Spatial Density ◽  
Outer Solar System ◽  
The Sun

In-situ measurements of micrometeoroids provide information on the spatial distribution of interplanetary dust and its dynamical properties. Pioneers 10 and 11, Galileo and Ulysses spaceprobes took measurements of interplanetary dust from 0.7 to 18 AU distance from the sun. Distinctly different populations of dust particles exist in the inner and outer solar system. In the inner solar system, out to about 3 AU, zodiacal dust particles are recognized by their scattered light, their thermal emission and by in-situ detection from spaceprobes. These particles orbit the sun on low inclination (i ≤ 30°) and moderate eccentricity (e ≤ 0.6) orbits. Their spatial density falls off with approximately the inverse of the solar distance. Dust particles on high inclination or even retrograde trajectories dominate the dust population outside about 3 AU. The dust detector on board the Ulysses spaceprobe identified interstellar dust sweeping through the outer solar system on hyperbolic trajectories. Within about 2 AU from Jupiter Ulysses discovered periodic streams of dust particles originating from within the jovian system.

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