Circular polarization in star- formation regions: implications for biomolecular homochirality

Strong infrared circular polarization resulting from dust scattering in reflection nebulae in the Orion OMC-1 star-formation region has been observed. Circular polarization at shorter wavelengths might have been important in inducing chiral asymmetry in interstellar organic molecules that could be subsequently delivered to the early Earth by comets, interplanetary dust particles, or meteors. This could account for the excess of L-amino acids found in the Murchison meteorite and could explain the origin of the homochirality of biological molecules.     

Stress fields of the overriding plate at convergent margins and beneath active volcanic arcs

Tectonic stress fields in the overriding plate at convergent plate margins are complex and vary on local to regional scales. Volcanic arcs are a common element of overriding plates. Stress fields in the volcanic arc region are related to deformation generated by subduction and to magma generation and ascent processes. Analysis of moment tensors of shallow and intermediate depth earthquakes in volcanic arcs indicates that the seismic strain field in the arc region of many convergent margins is subhorizontal extension oriented nearly perpendicular to the arc. A process capable of generating such a globally consistent strain field is induced asthenospheric corner flow below the arc region.     

Trench-parallel anisotropy produced by foundering of arc lower crust

Many volcanic arcs display fast seismic shear-wave velocities parallel to the strike of the trench. This pattern of anisotropy is inconsistent with simple models of corner flow in the mantle wedge. Although several models, including slab rollback, oblique subduction, and deformation of water-rich olivine, have been proposed to explain trench-parallel anisotropy, none of these mechanisms are consistent with all observations. Instead, small-scale convection driven by the foundering of dense arc lower crust provides an explanation for the trench-parallel anisotropy, even in settings with orthogonal convergence and no slab rollback.     

Helium-3 from the mantle: primordial signal or cosmic dust?

Helium-3 in hotspot magmas has been used as unambiguous evidence for the existence of a primordial, undegassed reservoir deep in the Earth's mantle. However, a large amount of helium-3 is delivered to the Earth's surface by interplanetary dust particles (IDPs). Recycling of deep-sea sediments containing these particles to the mantle, and eventual incorporation in magma, can explain the high helium-3/helium-4 ratios of hotspot magmas. Basafts with high helium-3/helium-4 ratios may represent degassing of helium introduced by ancient (probably 1.5 to 2.0 billion years old) pelagic sediments rather than degassing of primordial lower mantle material brought to the surface in plumes. Influx of IDPs can also explain the neon and siderophile compositions of mantle samples.     

Internal mixture of sea salt, silicates, and excess sulfate in marine aerosols

Individual aerosol particles from the remote marine atmosphere were investigated by scanning electron microscopy and electron microprobe analysis. A large fraction of the silicate mineral component of the aerosol was found to be internally mixed with sea-salt aerosol particles. This observation explains the unexpected similarity in the size distributions of silicates and sea salt that has been observed in remote marine aerosols. Reentrainment of dust particles previously deposited onto the sea surface and collision between aerosol particles can be excluded as possible source mechanisms for these internally mixed aerosols. The internal mixing could be produced by processes within clouds, including droplet coalescence. Cloud processes may also be responsible for the observed enrichment of excess (nonsea-salt) sulfate on sea-salt particles.     

Origin of Saturn's E Ring: Self-Sustained, Naturally

Saturn's diffuse E ring spans the region between 3 and 8 saturnian radii (R(s)), has its peak brightness near the orbit of the satellite Enceladus (3.95 R(s)), and is thought to be composed primarily of icy particles 1.0 +/- 0.3 micrometers in radius. Such particles are shown to move periodically along highly elliptical paths that cross the orbits of several saturnian satellites; the resulting energetic collisions of E ring particles with embedded satellites are capable of sustaining the E ring at its current optical depth. With several reasonable assumptions, this model naturally selects Enceladus as the primary source of ring material and may also provide mechanisms that explain the generation of the unusual amount of submicrometer dust in the neighboring F and G rings, the excess of OH molecules observed within the E ring, and the orbital brightness variations of nearby satellites.     

Zodiacal dust and deep-sea sediments

The recent detection of radioactive Al(26) in marine sediments has led to the conclusion that it is brought into the earth's atmosphere by micrometeorites which have been exposed, in interplanetary space, to solar high-energy protons. The Al(26) method is not precise enough to yield directly a reliable value for the mass accretion rate to the earth to better than about 3 orders of magnitude, but is sufficiently accurate to allow a crucial decision between two widely differing of interplanetary dust which have been proposed to explain observations of the zodiacal light. The two models lead to Al(26) concentrations which would differ by about 5 orders of magnitude. Thus, the presence of Al(26) is consistent with the zodiacal dust model with particles of some tens of microns rather then with submicron particles. From this model a mass accretion to the earth then be calculated which is set at 1250 (upper limit, 2500; lower limit, 250) tons per day, or 2.8 x 10(-15) g/cm(2) sec, or 4.5 x 10(11) g over the earth per This value does not depend on the flux of the solar high-energy particles, which may be uncertain by an order of magnitude or more. The presence of Al(26) supports the idea that an important fraction of the dust is stony in composition material density, and thus eliminates some more exotic dust models, as such one consisting entirely of carbon grains. We may also conclude that the accreted dust particles have been in the solar system and exposed to protons from solar high-energy particles for a time interval which is greater than a significant of the Al(26) half-life (0.74 x 10(6) years).     

吉林市6种街道绿化树种叶片滞尘特性研究

[目的]研究树种叶片滞尘特性,为滞尘型绿地树种的选择提供参考。[方法]通过水浸法和图像法,测定吉林市6种常见街道绿化树种的单位叶面积滞尘量、叶片固着颗粒物粒径组成,分析微结构与叶片滞尘的关系。[结果]1能够较长时间稳定地固着于叶片表面的粉尘以小粒径颗粒物为主,6种树木叶片固着PM_(10)的数量比例均超过97.76%;叶片累计固着PM_(2.5)的数量比例均超过65.33%。2在各树种滞尘量比较中,大粒径颗粒物发挥了重要作用。6种树木叶片固着PM_(10)的体积比例为47.87%~78.22%,体积最大的是金焰绣线菊(Spiraea×bumalda cv.Cold flame),最小的是杏(Prunus armeniaca L.);叶片固着PM_(2.5)的体积比例为4.41%~14.66%,比例最大的是紫丁香(Syringa oblata Lindl.),最小的是杏。36种街道绿化树种叶片滞留颗粒物、PM_(2.5)、PM_(10)总量差异显著,树种滞尘存在特异性,表现在滞尘量及粒径组成两方面。4叶片微结构对较小颗粒物(粒径20μm)滞留具有重要影响。通常,叶片的皱褶、凹凸程度越大,固着颗粒物量越多。[结论]能够较长时间稳定地固着于树种叶片表面的粉尘以小颗粒物为主,固着量和粒径组成与叶片表面微结构有关。     

The formation of chondrules: petrologic tests of the shock wave model

Chondrules are millimeter-sized rounded igneous rocks within chondritic meteorites. Their textures and fractionated mineral chemistries suggest that they formed by repeated, localized, brief (minutes to hours) melting of cold aggregates of mineral dust in the protoplanetary nebula. Astrophysical models of chondrule formation have been unable to explain the petrologically diverse nature of chondrites. However, a nebular shock wave model for chondrule formation agrees with many of the observed petrologic and geochemical properties of chondrules and shows how particles within the nebula are sorted by size and how rims around chondrules are formed. It also explains the volatile-rich nature of chondrule rims and the chondrite matrix.     

Retrofitting Sprinkler Systems for Suppressing Dust Generated by Moving Vehicles Inside Farms

Fugitive dust is one of the well known problems in agriculture and it affects both humans and machine producing quality.Dust problems can seriously cause harmful diseases to workers and ruin expensive equipments. In this study, a dust formation generated in open environment by vehicles was analyzed on unpaved roads. Formed dust was measured by calculating total forces on the PM10 (airborne particles smaller than 10 mm) of dust particles, such as air velocity, gravity forces and air turbulence generated by the moving vehicle. The water fogger nozzle discharge was measured to determine the approximate droplets quantity in the air. The loggers were used to suppress the generated dust in an open environment via installing a proposed automatic suppression system which opens automatically when vehicles pass under the system.The relationship between water droplet speed and ability of collecting fugitive dust showed that high air temperature above 40℃ and wind speed above 10 m s-1 have negative effects on the system's ability of collecting dust due to evaporation of small radius droplets and/or drifting water droplets away from the effective area. The overall system efficiency was found to be 85% and the proposed dust suppression system was found to be a satisfying solution for reducing fugitive dust hazards.     

Comet or asteroid shower in the late Eocene?

The passage of a comet shower approximately 35 million years ago is generally advocated to explain the coincidence during Earth's late Eocene of an unusually high flux of interplanetary dust particles and the formation of the two largest craters in the Cenozoic, Popigai and the Chesapeake Bay. However, new platinum-group element analyses indicate that Popigai was formed by the impact of an L-chondrite meteorite. Such an asteroidal projectile is difficult to reconcile with a cometary origin. Perhaps instead the higher delivery rate of extraterrestrial matter, dust, and large objects was caused by a major collision in the asteroid belt.     

An astronomical 2175 angstrom feature in interplanetary dust particles

The 2175 angstrom extinction feature is the strongest (visible-ultraviolet) spectral signature of dust in the interstellar medium. Forty years after its discovery, the origin of the feature and the nature of the carrier(s) remain controversial. Using a transmission electron microscope, we detected a 5.7-electron volt (2175 angstrom) feature in interstellar grains embedded within interplanetary dust particles (IDPs). The carriers are organic carbon and amorphous silicates that are abundant in IDPs and in the interstellar medium. These multiple carriers may explain the enigmatic invariant central wavelength and variable bandwidth of the astronomical 2175 angstrom feature.     

Carbon and nitrogen isotopic anomalies in an anhydrous interplanetary dust particle

Because hydrogen and nitrogen isotopic anomalies in interplanetary dust particles have been associated with carbonaceous material, the lack of similar anomalies in carbon has been a major conundrum. We report here the presence of a 13C depletion associated with a 15N enrichment in an anhydrous interplanetary dust particle. Our observations suggest that the anomalies are carried by heteroatomic organic compounds. Theoretical models indicate that low-temperature formation of organic compounds in cold interstellar molecular clouds can produce carbon and nitrogen fractionations, but it remains to be seen whether the specific effects observed here can be reproduced.     

Effect of water on the composition of partial melts of greenstone and amphibolite

Closed-system partial melts of hydrated, metamorphosed arc basalts and andesites (greenstones and amphibolites), where only water structurally bound in metamorphic minerals is available for melting (dehydration melting), are generally water-undersaturated, coexist with plagioclase-rich, anhydrous restites, and have compositions like island arc tonalites. In contrast, water-saturated melting at water pressures of 3 kilobars yields strongly peraluminous, low iron melts that coexist with an amphibolebearing, plagioclase-poor restite. These melt compositions are unlike those of most natural silicic rocks. Thus, dehydration melting over a range of pressures in the crust of island arcs is a plausible mechanism for the petrogenesis of islands arc tonalite, whereas water-saturated melting at pressure of 3 kilobars and above is not.     

Magnesium isotopic composition of interplanetary dust particles

The magnesium isotopic composition of some extraterrestrial dust particles has been measured. The particles are believed to be samples of interplanetary dust, a significant fraction of which originated from the disaggregation of comets and may contain preserved isotopic anomalies. Improvements in mass spectrometric and sample preparation techniques have made it possible to measure the magnesium isotopic composition of the dust particles, which are typically 10 micrometers in size and contain on the order of 10(-10) gram of magnesium. Of the 13 samples analyzed, nine have the terrestrial magnesium isotopic composition within 2 parts per thousand, and one shows isotopic mass fractionation of 1.1 percent per mass unit. A subset of the particles, described as chondritic aggregates, are very close to normal isotopic composition, but their normalized isotopic ratios appear to show nonlinear effects of 3 to 4 parts per thousand, which is near the present limit of detection for samples of this size. The isotopic composition of calcium was also determined in one particle and found to be normal within 2 percent. It is clear that the isotopic composition of interplanetary dust particles can be determined with good precision. Collection of dust particles during the earth's passage through a comet tail or an intense meteor stream may permit laboratory analysis of material from a known comet.     

Growth and sintering of fullerene nanotubes

Carbon nanotubes produced in arcs have been found to have the form of multiwalled fullerenes, at least over short lengths. Sintering of the tubes to each other is the predominant source of defects that limit the utility of these otherwise perfect fullerene structures. The use of a water-cooled copper cathode minimized such defects, permitting nanotubes longer than 40 micrometers to be attached to macroscopic electrodes and extracted from the bulk deposit. A detailed mechanism that features the high electric field at (and field-emission from) open nanotube tips exposed to the arc plasma, and consequent positive feedback effects from the neutral gas and plasma, is proposed for tube growth in such arcs.     

An Explanation for Neptune's Ring Arcs

The Voyager mission revealed a complex system of rings and ring arcs around Neptune and uncovered six new satellites, four of which occupy orbits well inside the ring region. Analysis of Voyager data shows that a radial distortion with an amplitude of approximately 30 kilometers is traveling through the ring arcs, a perturbation attributable to the nearby satellite Galatea. Moreover, the arcs appear to be azimuthally confined by a resonant interaction with the same satellite, yielding a maximum spread in ring particle semimajor axes of 0.6 kilometer and a spread in forced eccentricities large enough to explain the arcs' 15-kilometer radial widths. Additional ring arcs discovered in the course of this study give further support to this model.     

6种丁香属植物滞尘能力评价及叶表微形态学解释

  目的  筛选滞尘能力较强的丁香属Syringa植物，促进丁香在城市绿化中生态功能的发挥。  方法  以6种丁香属植物为研究材料，在满叶期通过3级滤膜过滤法测定植物经过不同孔径的滤膜后滞留的各直径颗粒物，并对丁香属植物叶表面微观结构进行观察，探究叶片微观结构对植物滞尘效应的影响。  结果  ①丁香属植物对不同粒径颗粒物的滞尘能力存在显著差异(P＜0.05)，对于满叶期，6种丁香单位叶面积滞尘能力从大到小排序为什锦丁香S. chinensis、北京丁香S. pekinensis、欧丁香S. vulgaris、紫丁香S. oblata、暴马丁香S. reticulata var. amurensis、白丁香S. oblata var. alta。②什锦丁香单位叶面积滞尘能力最强，通过微观结构观察发现什锦丁香叶片上表面沟槽纵深，下表面气孔周围褶皱密集，有助于滞留颗粒物。③从偏相关系数来看，叶表微结构各参数与单位叶面积总颗粒滞留量(UTSP)和直径为0.2~2.5 μm颗粒物滞留量(UPM_2.5)均未达显著相关(P＞0.05)。  结论  沟槽的深度可能是影响植物滞尘的原因之一，在治理城市空气污染时，什锦丁香可作为优良的园林滞尘灌木树种。图2表3参26     

沸腾颗粒层除尘器内设预荷电装置的初步研究

对沸滕颗粒层除尘器内设预荷电装置，让待净化的尘粒首先荷电（称为预荷电）然后再通过滤层进行分离的净化方式进行了理论分析，分析显示设预荷电装置可改进除尘器的性能，为证实理论分析的正确性及该技术的实用性，还介绍了该技术的试用情况。     

Refractory minerals in interplanetary dust

A newly studied interplanetary dust particle contains a unique set of minerals that closely resembles assemblages in the refractory, calcium- and aluminum-rich inclusions in carbonaceous chondrite meteorites. The set of minerals includes diopside, magnesium- aluminum spinel, anorthite, perovskite, and fassaite. Only fassaite has previously been identified in interplanetary dust particles. Diopside and spinel occur in complex symplectic intergrowths that may have formed by a reaction between condensed melilite and the solar nebula gas. The particle represents a new link between interplanetary dust particles and carbonaceous chondrites; however, the compositions of its two most abundant refractory phases, diopside and spinel, differ in detail from corresponding minerals in calcium- and aluminum-rich inclusions.