Heavy element affinities in Apollo 17 samples

²⁰⁴Pb, Bi, Tl and Zn in samples from Apollo 17 exhibit relationships not found in samples from other sites.²⁰⁴Pb, Tl and Zn in residues remaining after dilute acid leaching are correlated with one another. Orange soil 74220, which is enriched in²⁰⁴Pb, Tl and Zn, is included in these relationships. In addition the submicron metallic phase generally associated with agglutinate formation is correlated with all three of these elements; this relationship has already been reported for²⁰⁴Pb in other samples. Thus, orange soil and agglutinates appear to be involved in concentrating heavy volatile metals. A process other than mixing is required to account for this. As a consequence of the isolation of the landing site by the surrounding massifs, local supply and recycling of volatile trace elements in soils may account for some of the interelement relations.     

合肥地区沙尘暴降尘过程的大气细粒子谱观测研究

2010年3月20日至3月28日,利用大气细粒子谱分析仪对合肥地区大气细粒子谱进行连续在线观测.观测过程涵盖整个沙尘暴降尘期、间歇性降雨期及晴好天气粒子浓度增长期.颗粒物数浓度分析表明,沙尘暴降尘期内核模态(Nucleation mode, 5~20 nm)、爱根核模态(Aitken mode, 20~100 nm)和积聚模态(Accumulation mode, 100~1000 nm)粒子浓度分别为898 cm-3、3424 cm-3、1587 cm-3,并未明显高于间歇性降雨期(粒子浓度分别为255 cm-3、1509 cm-3、1213 cm-3)和晴好天气粒子浓度增长期(粒子浓度分别为706 cm-3、4891 cm-3、2468 cm-3);沙尘暴降尘期粗粒子模态(Coarse mode, 1~10 μm) 粒子值达到 48 cm-3,浓度远高于其他观测期.粒谱分析表明:合肥地区大气细粒子谱呈典型双峰结构,第一峰值出现在10~20 nm之间,第二峰值出现在100 nm左右,而且不同天气条件下细粒子谱峰值位置略有不同;沙尘暴降尘期,粒径10 nm以下和400 nm以上粒子浓度值高于间歇性降雨期和晴好天气粒子浓度增长期,而并非只有粗粒子模态粒子浓度高于其他时段.     

Anhysteretic remanent magnetization: model of grain size distribution of spherical magnetite grains

A phenomenological model based on a linear relationship between the magnetic coercivity field and the reciprocal of the grain diameter is applied to explain the anhysteretic remanent magnetization (ARM) imparted to artificial samples with different concentrations of a very well characterized magnetite powder. By analyses of scanning electron microscopy images, the spherically shaped single domain synthetic magnetite is found to follow a lognormal grain size distribution with ~86 nm of mean diameter. The proposed model, fitted to ARM measurements up to a peak alternating field of 100 mT, yields a very good agreement. The coercivity behaviour predicted by micromagnetism theory disagrees with the experimental results of this work. A likely explanation for the discrepancy is that the magnetite particles, which consist of a mixture of grains in coherent rotation and curling modes, produce similar observations as domain processes.     

Inert gases from Apollo 11 and Apollo 12 fines: Reversals in the trends of relative element abundances

On the basis of the⁴He/²⁰Ne ratios in feldspathic particles from Apollo 11, basaltic fragments from Apollo 11, and magnetic separates from Apollo 12 fines, one expects the former to have the highest, and the Apollo 12 material to have the lowest⁸⁴Kr/¹³²Xe ratios. This is not the case; the⁸⁴Kr/¹³²Xe ratios from sample 12070 are substantially greater than those from the feldspathic and basaltic fragments in 10084. The trend-reversal in the feldspathic particles could be due to the trapping of genuine primordial lunar Kr and Xe. The reversal in the Apollo 11 basaltic fragments might be due to periodicnear-quantitative loss of the lighter gases by impact heating, with the Apollo 11 fines containing a relatively large proportion of strongly heated fragments.     

Particle size distribution of bed materials in the sandy river bed of alluvial rivers

The particle size distribution of bed materials in the sandy river bed of alluvial rivers is important in the study of topics such as friction, river bed evolution, erosion, and siltation. It also can reflect the dependency relation between river bed sediment and flow intensity. In this paper, the critical pattern of sediment movement in the near-wall region of a sandy river bed was analyzed. According to the principle of momentum balance, the critical settling-rising condition of bed material in a sandy river bed was found to be instantaneous turbulent velocity equal to 2.7 times the sediment settling velocity in quiescent water. Based on a vertical instantaneous turbulent velocity with a Gaussian distribution, a theoretical relation for calculating the particle size distribution of bed materials in a sandy river bed without pre-known characteristic grain sizes was developed by solving a stochastic equation. The for-mula is verified using measured data, and the results show that the proposed formula was in accordance with the measured data. This study has theoretical significance and practical value for determining the bed material particle size distribution of the sandy bed of alluvial rivers.     

Alteration of an Apollo 12 sample by adsorption of water vapor

The adsorption of water vapor caused radical changes in the surface characteristics of an Apollo 12 lunar fines sample. In the initial state, the sample had a relatively low specific surface area and no inherent porosity as deduced from the adsorption isotherms of nitrogen and argon. However, the sample interacted strongly with water vapor, particularly at high relative pressures, and irreversibly retained, in vacuum, a quantity of water much larger than can be explained by a simple chemisorption process. The interaction with water vapor more than doubled the specific surface area and created a pore system. The suggested explanation is that water penetrates the severely radiation damaged, amorphous surface layers of the particles and creates pores by leaching out channels or forcing apart adherent particles. Lunar fines from the Apollo 11, 12 and 14 missions have markedly different reactivities toward water vapor, an observation which remains unexplained at the present time.     

Particle track record in Apollo 15 deep core from 54 to 80 cm depths

Particle track measurements have been made in nearly 500 individual grains from 13 levels in the 54–80 cm depth range of the Apollo 15 deep core. They reveal a wide range of track densities at all depths and some systematic variations within layers, indicating that both predepositional mixing and subsequent layering are present and that separate sub-layers exist within larger regions where no sub-layers are visible. Minimum track densities are inferred to be useful measures of maximum residence times for undisturbed layers. Using the observed minimum track densities we conclude that the average deposition rate in this section of soil column was ≥ 0.4 cm/million years.     

A prediction method for the size distribution of saltating particles above a mixed-size bed

In aeolian saltation, the sand bed is a mixture of sand particle with a wide range of particle sizes. Generally, the particle size distribution (PSD) of saltating particles is ignored by previous aeolian transport models, which will result in differences between predictions and observations. To better understand the saltation process, a prediction method of the PSD of saltating particles was proposed in this article. The probability of contact between incident sand and bed sand was introduced into the particle-bed collision process. An artificial PSD of the incident saltating particles was set as the initial condition. A stochastic particle-bed collision model considering contact probability was then used in each iteration step to calculate a new PSD of saltating particles. Finally, the PSD of saltating particles can be determined when aeolian saltation reaches a steady state (saltation is in a steady state when its primary characteristics, such as horizontal mass flux and the concentration of saltating particles, remain approximately constant over time and distance). Meanwhile, according to the experimental results, a calculation formula for the contact parameter n is given, which characterizes the shielding effect of particles on each other. That is, if soil PSD and friction velocity were given, the PSD of saltating particles can be determined. Our results do not depend on the initial conditions, and the predicted results are consistent with the experimental results. It indicated that our method can be used to determine the PSD of saltating particles. © 2020 John Wiley & Sons, Ltd.     

Particle size distribution of cataclastic fault materials from Southern California: A 3-D study

The particle size distributions of fault gouge from the San Andreas, the San Gabriel, and the Lopez Canyon faults in Southern California were measured using sieving and Coulter-Counter techniques over a range of particle sizes from 2 m to 16 mm. The distributions were found to be power law (fractal) for the smaller fragments and log-normal by mass for sizes near and above the peak size. The apparent fractal dimensionD of the smaller particles in gouge samples from the San Andreas fault, the San Gabriel fault and the Lopez Canyon gouge were 2.4–3.6, 2.6–2.9 and 2.4–3.0, respectively. The averageD for the Lopez Canyon gouge was 2.7±0.2, which is in agreement with earlier studies of this gouge using planar 2-D sections. The fractal dimension of the finer fragments from all three faults is observed to be correlated with the peak fragment size, with finer gouges tending to have a largerD. A computer automaton is used to show that this observation may be explained as resulting from a fragmentation process which has a grinding limit at which particle reduction stops.     

Trapped solar and cosmogenic noble gas abundances in Apollo 15 and 16 deep drill samples

Abundances and isotopic compositions of all the stable noble gases have been measured in 19 different depths of the Apollo 15 deep drill core, 7 different depths of the Apollo 16 deep drill core, and in several surface fines and breccias. All samples analyzed from both drill cores contain large concentrations of solar wind implanted gases, which demonstrates that even the deepest layers of both cores have experienced a lunar surface history. For the Apollo 15 core samples, trapped⁴He concentrations are constant to within a factor of two; elemental ratios show even greater similarities with mean values of⁴He/²²Ne= 683±44,²²Ne/³⁶Ar= 0.439±0.057,³⁶Ar/⁸⁴Kr= 1.60±0.11·10³, and⁸⁴Kr/¹³²Xe= 5.92±0.74. Apollo 16 core samples show distinctly lower⁴He contents,⁴He/²²Ne(567±74), and²²Ne/³⁶Ar(0.229±0.024), but their heavy-element ratios are essentially identical to Apollo 15 core samples. Apollo 16 surface fines also show lower values of⁴He/²²Ne and²²Ne/³⁶Ar. This phenomenon is attributed to greater fractionation during gas loss because of the higher plagioclase contents of Apollo 16 fines. Of these four elemental ratios as measured in both cores, only the²²Ne/³⁶Ar for the Apollo 15 core shows an apparent depth dependance. No unambiguous evidence was seen in these core materials of appreciable variations in the composition of the solar wind. Calculated concentrations of cosmic ray-produced²¹Ne,⁸⁰Kr, and¹²⁶Xe for the Apollo 15 core showed nearly flat (within a factor of two) depth profiles, but with smaller random concentration variations over depths of a few cm. These data are not consistent with a short-term core accretion model from non-irradiated regolith. The Apollo 15 core data are consistent with a combined accretion plus static time of a few hundred million years, and also indicate variable pre-accretion irradiation of core material. The lack of large variations in solar wind gas contents across core layers is also consistent with appreciable pre-accretion irradiation. Depth profiles of cosmogenic gases in the Apollo 16 core show considerably larger concentrations of cosmogenic gases below ～65 cm depth than above. This pattern may be interpreted either as an accretionary process, or by a more recent deposition of regolith to the upper ～70 cm of the core. Cosmogenic gas concentrations of several Apollo 16 fines and breccias are consistent with ages of North Ray Crater and South Ray Crater of ～50·10⁶ and ～2·10⁶ yr, respectively.     

Heat diffusion and size reduction of a spherical magma chamber

An analytical solution is derived for the size reduction of a spherical magma chamber cooling by conduction. The use of moving boundary conditions and the constraint of a spherical symmetry allow one to ignore the details of the heat redistribution processes which take place within the magma chamber. The dependence of the solution on the initial conditions is investigated. A simple solution is found for short time, which is shown to be valid for times long enough to make it useful in the volcanological context. Moreover, the general solution confirms that the hydrothermal contribution to heat transfer in Phlegraean Fields cannot be extremely important.     

Estimation of average size of submicron particles from the number of all and uncharged particles

Summary Recently one of the authors introduced for a polydisperse aerosol the useful concept of the equivalent radius which is computed from a monodisperse substitute aerosol with the same fraction of charged nuclei as the actual.In this paper the result of a theoretical and experimental investigation into the agreement between equivalent and average radius of polydisperse aerosols are presented. It is shown that for normal conditions as is to be expected in practice the equivalent radius represents a very good estimate of the average size of submicron particles in polydisperse aerosols.

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Zusammenfassung Einer der Authoren hat jüngst den nützlichen Begriff des äquivalenten Radius für polydisperse Aerosole eingeführt, welcher für ein monodisperses Ersatz-Aerosol mit dem gleichen Bruchteil von geladenen Teilchen als das wirkliche Aerosol berechnet wird.In der vorliegenden Arbeit werden die Resultate einer theoretischen und experimentellen Untersuchung der Uebereinstimmung des äquivalenten und mittleren Radius für polydisperse Aerosole mitgeteilt. Es wird gezeigt, dass unter normalen Bedingungen, wie sie in der Praxis zu erwarten sind, der äquivalente Radius eine sehr gute Abschätzung für den mittleren Radius von sub-mikroskopischen Teilchen in polydispersen Aerosolen vorstellt.

     

Particle size characteristics of suspended sediment in hillslope runoff and stream flow

This study examines the particle size characteristics of hillslope soils and fluvial suspended sediments in an agricultural catchment. Samples of surface runoff and stream flow were collected periodically and analysed for the size distributions of the effective (undispersed) sediment. This sediment was subsequently dispersed and the ultimate size distributions determined. The median effective particle size of stream suspended sediment was considerably coarser than the median ultimate particle size, indicating that most of the load included a substantial proportion of aggregates. Moreover, the proportion of fine material (i.e. silt and clay) increased, and the proportion of sand-sized material decreased, with increasing discharge. This decrease in sediment size with increased flow, which is contrary to the traditional assumption of a positive discharge/particle size relationship, is thought to reflect: (i) the influx of silt and clay, predominantly the former, originating on the catchment slopes and brought to the stream by overland flow along vehicle wheelings, roads and tracks; and (ii) erosion of fine material from the channel bed and banks. During large storms, however, the proportion of sand-sized sediment increased during the rising limb of the hydrograph, as a result of the entrainment of coarser source material from the valley floor during overbank flooding. The stream suspended sediment was finer than the catchment soils and considerably finer than material eroding from the catchment slopes during storms. The degree of clay and silt enrichment in the suspended sediments was largely the result of preferential deposition of the coarser fraction during the transport and delivery of sediment from its source to basin outlet. The data from this study confirm that a significant mode of sediment transport in fluvial systems is in the form of aggregates, and that the dispersed sediment size distribution is inappropriate for determining the transportability of sediment by flow. © 1997 by John Wiley & Sons, Ltd.     

The effect of interstitial gaseous pressure on the thermal conductivity of a simulated Apollo 12 lunar soil sample

The thermal conductivity of a simulated Apollo 12 lunar soil sample was measured with a needle probe under vacuum. The result showed that the sample, with bulk densities of 1.70–1.85 g cm^?3 held in a vertical cylinder (2.54 cm in diameter and 6.99 cm long) has a thermal conductivity ranging from 8.8 to 10.9 mW m^?1 K^?1. This is comparable to the lunar regolith's thermal conductivity as determined in situ. Besides the dense packing of the soil particles, an enhanced intergranular thermal contact, due to the self-compression of the sample, is necessary to raise the sample's thermal conductivity from the level of loose soil (< 5 mW m^?1 K^?1) to that of the lunar regolith deeper than 35 cm (～ 10 mW m^?1 K^?1). A model of the lunar regolith, a thin layer of loose soil resting on a compacted self-compressed substratum, is consistent with the lunar regolith's surface structure as deduced from an observation of the lunar surface's brightness temperature. Martian regolith surface structure is similar, except that its surface layer may be missing in places because of aeolian activity. Measurements of thermal conductivity under simulated martian surface conditions showed that the thermal properties of loose and compacted soils agreed with the two peak values of the martian surface's thermal inertia as observed from “Viking” orbiters, suggesting that drifted loose soil and exposed compacted soil are responsible for the bimodal distribution of the martian surface's thermal inertia near zero elevation. For compacted soil exposed to the martian surface to have the same thermal conductivity as that buried under the surface layer, a cohesion of the soil particles must be assumed.     

Bubble size distribution in surface wave breaking entraining process

From the similarity theorem, an expression of bubble population is derived as a function of the air en-trainment rate, the turbulent kinetic energy (TKE) spectrum density and the surface tension. The bubble size spectrum that we obtain has a dependence of a?2.5 nd on the bubble radius, in which nd is positive and dependent on the form of TKE spectrum within the viscous dissipation range. To relate the bubble population with wave parameters, an expression about the air entrainment rate is deduced by intro-ducing two statistical relations to wave breaking. The bubble population vertical distribution is also derived, based on two assumptions from two typical observation results.     

Experimental study of the settling of twin spherical particles released side by side: The impact of particle size,fluid viscosity,initial spacing,and particle density

The settling of solid particles in a fluid is an important process that needs to be considered in many fields of research. For example, the interactions among particles and between particles and the surrounding fluid are important topics in studying suspended sediment transport and water clarification. In this paper, the settling processes and interactions of twin spherical particles released side by side were experimentally studied. The Reynolds number varied in the range of 1-300, which is wit...     

On the grain size dependence of the behavicur of fine magnetic particles in rocks

The grain size dependence of the ratio of saturation remanent magnetization to saturation magnetization (J _R :J _S ), weak field susceptibility (X ₀), thermoremanent magnetization (TRM) and its stability against AF demagnetization are interpreted in terms of nucleation theory. It is concluded that each of these parameters exhibits grain size dependence due to two effects. The first is the increasing difficulty with which domain walls are neucleated as grain size decreases. The second is an intrinsic grain size dependence of the parameters in multidomain particles.