Observed Size Distribution Research Articles

Yarkovsky depletion and asteroid collisional evolution

The orbital parameters of small asteroids change with time, as a consequence of the so-called Yarkovsky effect. This leads to a steady removal of objects from the Main Belt, which takes place when the objects reach one of the major resonant regions in the orbital elements space. The process may influence the evolution of the inventory and size distribution of Main Belt asteroids, but it has not been taken into account by classical models of the collisional evolution of the asteroid population. In this paper we discuss the role of the Yarkovsky effect in producing the current observed size distribution. We show that adding Yarkovsky effect to purely collisional mechanisms may increase the removal of objects at sizes around 1 km by a factor of about 2 with respect to a purely collisional scenario. Moreover, waves in the size distribution may also be produced. However, taking also into account current uncertainties in the efficiency of purely collisional mechanisms, the role of the Yarkovsky effect seems not dominant, and cannot be unambiguously determined.

The Evolution of Disk Galaxies in the GOODS-South Field: Number Densities and Size Distribution

We examine the evolution of the sizes and number densities of disk galaxies using the high-resolution images obtained by the Great Observatories Origins Deep Survey (GOODS) with the Advanced Camera for Surveys on the Hubble Space Telescope. The multiwavelength images are used to classify galaxies based on their rest-frame B-band morphologies out to redshift . In order to minimize the effect of selection biases, we confine our z ∼ 1.25 analysis to galaxies that occupy the region of the magnitude-size plane where the survey is ∼90% complete at all redshifts. The observed size distribution is consistent with a lognormal distribution as seen for the disk galaxies in the local universe and does not show any significant evolution over the redshift range . We 0.25 ≤ z ≤ 1.25 find that the number densities of disk galaxies remains fairly constant over this redshift range, although a modest evolution by a factor of 4 may be possible within the 2 j uncertainties. Subject headings: galaxies: evolution — galaxies: formation — galaxies: fundamental parameters — galaxies: structure

Landslides, sandpiles, and self-organized criticality

Abstract. Power-law distributions of landslides and rockfalls observed under various conditions suggest a relationship of mass movements to self-organized criticality (SOC). The exponents of the distributions show a considerable variability, but neither a unique correlation to the geological or climatic situation nor to the triggering mechanism has been found. Comparing the observed size distributions with models of SOC may help to understand the origin of the variation in the exponent and finally help to distinguish the governing components in long-term landslide dynamics. However, the three most widespread SOC models either overestimate the number of large events drastically or cannot be consistently related to the physics of mass movements. Introducing the process of time-dependent weakening on a long time scale brings the results closer to the observed statistics, so that time-dependent weakening may play a major part in the long-term dynamics of mass movements.

Aerosol Growth in a Steady-State, Continuous Flow Chamber: Application to Studies of Secondary Aerosol Formation

An analytical solution for the steady-state aerosol size distribution achieved in a steady-state, continuous flow chamber is derived, where particle growth is occurring by gas-to-particle conversion and particle loss is occurring by deposition to the walls of the chamber. The solution is presented in the case of two condensing species. By fitting the predicted steady-state aerosol size distribution to that measured, one may infer information about the nature of the condensing species from the calculated values of the species's molecular weights. The analytical solution is applied to three sets of experiments on secondary organic aerosol formation carried out in the U.S. Environmental Protection Agency irradiated continuous flow reactor, with parent hydrocarbons: toluene, f -pinene, and a mixture of toluene and f -pinene. Fits to the observed size distributions are illustrated by assuming two condensing products for each parent hydrocarbon; this is a highly simplified picture of secondary organic aerosol formation, which is known to involve considerably more than two condensing products. While not based on a molecular-level model of the gas-to-particle conversion process, the model does allow one to evaluate the extent to which the observed size distribution agrees with that based on a simple, two-component picture of condensation, and to study the sensitivity of those size distributions to variation of the essential properties of the condensing compounds, such as molecular weight. An inherent limitation of the steady-state experiment is that it is not possible to calculate the vapor pressures of the condensing species.

Dependence of solar radiative forcing of forest fire aerosol on ageing and state of mixture

Abstract. During airborne in situ measurements of particle size distributions in a forest fire plume originating in Northern Canada, an accumulation mode number mean diameter of 0.34 mm was observed over Lindenberg, Germany on 9 August 1998. Realizing that this is possibly the largest value observed for this property in a forest fire plume, scenarios of plume ageing by coagulation are considered to explain the observed size distribution, concluding that the plume dilution was inhibited in parts of the plume. The uncertainties in coagulation rate and transition from external to internal mixture of absorbing forest fire and non-absorbing background particles cause uncertainties in the plume's solar instantaneous radiative forcing of 20-40% and of a factor of 5-6, respectively. Including information compiled from other studies on this plume, it is concluded that the plume's characteristics are qualitatively consistent with a radiative-convective mixed layer.

Moment‐based simulation of microphysical properties of sulfate aerosols in the eastern United States: Model description, evaluation, and regional analysis

A six‐moment microphysics module for sulfate aerosols based on the quadrature method of moments has been incorporated in a host 3‐D regional model, the Multiscale Air Quality Simulation Platform. Model performance was examined and evaluated by comparison with in situ observations over the eastern United States for a 40‐day period from 19 July to 28 August 1995. The model generally reproduces the spatial patterns (sulfate mixing ratios and wet deposition) over the eastern United States and time series variations of sulfate mass concentrations. The model successfully captured the observed size distribution in the accumulation mode (radius 0.1–0.5 μm), in which the sulfate is predominately located, while underestimating the nucleation and coarse modes on the basis of the size distributions retrieved from the modeled six moments at the Great Smoky Mountains (GSM). This is consistent with better model performance on the effective radius (ratio of third to second moment, important for light scattering) than on number‐mean and mass‐mean radii. However, the model did not predict some of the moments well, especially the higher moments and during the dust events. Aerosol components other than sulfate such as dust and organics appear to have contributed substantially to the observed aerosol loading at GSM. The model underpredicted sulfate mixing ratios by 13% with about 50% of observations simulated to within a factor of 2. One of the reasons for this underestimation may be overprediction of sulfate wet deposition. Sulfate mass concentrations and number concentrations were high in the source‐rich Ohio River valley, but number concentrations were also high over the mid‐Atlantic coast (New Jersey area). Most (77%) sulfate amount was below 2.6 km, whereas most sulfate number (>52%) was above 2.6 km except over Ohio River valley (41%). These results demonstrate the accuracy, utility, practicality, and efficiency of moment‐based methods for representing aerosol microphysical processes in large‐scale chemical transport models.

Study of particle size distribution and formation mechanism of radioactive aerosols generated in high-energy neutron fields

The size distributions of 38Cl, 39Cl, 82Br and 84Br aerosols generated by irradiations of argon and krypton gases containing di-octyl phthalate (DOP) aerosols with 45 MeV and 65 MeV quasi-monoenergetic neutrons were measured in order to study the formation mechanism of radioactive particles in high energy radiation fields. The effects of the size distribution of the radioactive aerosols on the size of the added DOP aerosols, the energy of the neutrons and the kinds of nuclides were studied. The observed size distributions of the radioactive particles were explained by attachment of the radioactive atoms generated by the neutron-induced reactions to the DOP aerosols.

Atmospheric dust aerosol over the Tibetan Plateau

Cascade impactor and bulk samples of atmospheric aerosol particles were collected at three sites on the Tibetan Plateau: Udaoliang (September 1993 to May 1994) and Lhasa and Gongga (May 1998). The average dust concentration at these groundbased sites was 82 μg m−3; this is lower than the lowest average concentration observed over the nine major Chinese deserts (arithmetic mean value of 270 μg m−3), and it also is lower than that over the Loess Plateau (170 μg m−3). The elemental mass‐particle size distributions for several major dust‐derived elements (Al, Ca, Fe, K, Mn, Si, and Ti) were approximately lognormal, but those for Al, Fe, and Ti differed from Ca, K, and Si. Dry deposition velocities calculated from the observed size distributions and a two‐layer deposition model averaged 2.7 cm−1 for Al, Fe, and Ti. For Ca, K, and Si, which appear to be more strongly affected by local Tibetan sources, the average calculated dry deposition velocity was 4.3 cm s−1. Wet deposition fluxes estimated from scavenging ratios indicate that less than 10% of the total deposition on the Tibetan Plateau is attributable to wet removal during the 9 months for which data are available. The yearly mean dust deposition rate (local plus remote and dry plus wet) is estimated to be of the order of ∼100 g m−2 yr−1, which is lower than that onto the Chinese desert regions (320 g m−2 yr−1) or the Loess Plateau (250 g m−2 yr−1), suggesting that the sources upwind of China, and the Tibetan Plateau itself, are not major sources for Asian dust.

Feasibility of estimating stem size distribution from measurement on the largest trees in even-aged pure stands

Reconstruction of the size distribution of trees in stands provides critical information for assessing the effects of environmental changes on forests and for forest management. For furthering a method of such reconstruction, feasibility of estimating size distribution in stem volume from measurement of the largest trees was examined for even-aged pure stands of Pinus banksiana Lamb.and Larix gmelinii (Rupr.) Rupr. We tested what percentage of the largest trees should be included in obtaining a frequency distribution in stem volume that is not statistically different from the observed size distribution patterns. The –3/2 power, beta-type, and adjusted beta-type distribution functions were applied. Comparison of the observed stem frequencies and those estimated from measurement of the largest trees in a stand suggested that (i) the –3/2 power distribution, beta-type distribution, or adjusted beta-type distribution may be used for reconstruction of stem size variation in pure stands, if the overall size variation could be approximated by one of these functions; (ii) we can be at least 95% sure that the tree size pattern be expressed successfully with the –3/2 power distribution with tree samples of only the largest 20% in the stand, or with the beta-type distribution with the largest 30% in the stand; and (iii) the reliability decreases somewhat for the adjusted beta-type distribution. The second observation implies that reconstruction of the temporal changes in stand structure may be reliable up to the time when the stand density was about five times that of the trees used for fitting the –3/2 power distribution curve. Reliability may be warranted up to the stand density of about three times as the number of trees used for fitting the beta-type distribution. Other considerations and limitations are also discussed.

The host haloes of Lyman-break galaxies and submillimetre sources

We use the observed sizes and star formation rates of Lyman-break galaxies (LBGs) to understand their properties expected in the hierarchical scenario of galaxy formation. The observed size distribution constrains the masses (or circular velocities) of the host haloes of LBGs from below, because small haloes can only host galaxies with small sizes. The observed star formation distribution constrains the masses from above, because the number density of massive haloes in duty cycle is too low to host all the observed galaxies. Assuming a flat CDM model with a cosmological constant (Omega (Lambda) = 0.7), we find that consistency with observations requires the circular velocities of LBG host haloes to be in the range 100-300 km s(-1). The star formation in these haloes is efficient; a large fraction of all the gas in them can form stars on a time-scale of about 10-20 per cent of the Hubble time at redshift of 3. The predicted comoving correlation length of these objects is similar to3 h(-1) Mpc, and the predicted velocity dispersion of their stellar contents is typically 70 km s(-1).

A Growth Curve for the Newt Triturus cristatus

-I constructed Von Bertalanffy growth curves for a population of crested newts (Triturus cristatus) in northern France. Data were collected through capture-recapture of individually recognized newts over a six year period. The assumption that year to year growth diminishes with size following a linear negative relationship was tested and could not be rejected. Observations on seasonal growth were used to estimate average size of one year old juveniles. Inclusion of these data increased the precision with which the parameters in the Von Bertalanffy model were estimated. The parameter defining growth curve shape was not convincingly different for males and females. Asymptotic body size was significantly larger for females than for males. Comparison with growth curves estimated from published data indicated significant differences between populations, with slower growth and smaller size at maturation in Norwegian T cristatus than in French T: cristatus. l , l. 34, o. 2, pp. 227-232, 2000 i t e Study of A phibians and Reptiles A wide range in body size is usually observed in mature individuals of long-lived organisms characterized by indeterminate growth. One reason for this phenomenon is that natural selection favors reproduction commencing at an early age. However, as larger individuals may produce more offspring than smaller ones, investment in early reproductive activity may reduce growth and diminish lifetime reproductive success (Stearns, 1992). Parameters in the tradeoff between growth and reproduction are under strong selection as well as under the influence of environmental and phylogenetic constraints. As data accumulate for amphibians, we will be in a better position to evaluate patterns of geographical variation in life history parameters, and develop testable hypotheses about how life history attributes evolve in natural populations (e.g., Reznick et al., 1990; Manly, 1998). I here contribute to the growing data set with the analysis of individual growth and sexual size dimorphism in a population of the crested newt from France (Triturus cristatus). Capture-recapture data allow retrospective sexing of juveniles and the reconstruction of largely gender-specific post-metamorphic growth trajectories. Variation in growth parameters is documented through comparison with populations of crested newts experiencing different climatic conditions, and with a phylogenetically closely related species, the marbled newt, T marmoratus (Arntzen and Sp rreboom, 1989; Zajc and Arntzen, 1999). MATERIAL AND METHODS I estimated population parameters of T cristatus at an aquatic breeding site near Ambleteuse in northwestern France. Metamorphosis is in the year newts are born and larvae and efts had age 0. The observed size distributions indicated that juveniles had age 1 (see Arntzen and Teuis, 1993 for details). Because the population was newly established, adult newts had age <2 at pond age 2. Because adults were at least two years old (two years being the minimum age of maturation observed in the wild-Dolmen, 1983; Francillon-Vieillot et al., 1990; Arntzen and Teunis, 1993), I concluded that they were two years old. Extending this approach, adult newts first encountered at pond age 3 were 2.5 ? 0.5 yr old, etc. The accuracy of the age estimate declined with more annual cohorts contributing to the breeding population. By combining individual recognition (by pattern mapping, Hagstr6m, 1977) with capture-recapture for age determination and juvenile sex identification I avoided bodily harm of newts. 227 This content downloaded from 157.55.39.231 on Thu, 06 Oct 2016 04:43:12 UTC All use subject to http://about.jstor.org/terms

Collisional Evolution of the Outer Asteroid Belt

We present numerical results obtained by simulations of the collisional process between outer belt asteroids and scattered planetesimals from the Uranus–Neptune zone during their accretion period. We obtained final size distributions for the Hildas dominated by the collisional process with planetesimals, and as a consequence of this result, the observed population appears to be complete or nearly complete at sizes≥10 km in radius. In the proposed scenario, the elongated shapes of the largest Hildas should not be the result of a collisional process but could be primordial. The results obtained for the Trojan asteroids, for different initial masses, show that the final size distribution is dominated by the cometesimal bombardment, but in opposition to the Hilda asteroids, the observed size distribution appears to be incomplete for r<30 km. These results make it possible to assume that the initial mass of the asteroid belt was 4–6 times that at present.

A Dynamical Model for the Growth and Size Distribution of Multiple Metastatic Tumors

Metastasis is the spread of tumors culminating in the establishment of one or more secondary tumors at remote sites. In deciding the best treatment for cancer therapy, estimations of the colony size of metastatic tumors and predictions of the future spread of colonies are needed. A dynamical model for the colony size distribution of multiple metastatic tumors is presented here. The dynamics is described by equations that incorporate both the colonization by metastasis and the growth of each colony. When the colony growth is subject to the Gompertz function, the explicit solution obtained tends to an asymptotic stable distribution that shows a monotonically decreasing or U-shaped pattern according to the values of clinically significant parameters, such as the colonization coefficient and the fractal dimension of blood vessels. This predicted colony size distribution agrees well with successive data of a clinically observed size distribution of multiple metastatic tumors of liver cancer. The combined analysis of the theoretical colony size distribution and clinical data will give useful information on the diagnosis and the therapy for cancer patients.

Comparing the Evolution of the Galaxy Disk Sizes with Cold Dark Matter Models: The Hubble Deep Field.

The intrinsic sizes of the field galaxies with I</=26 in the Hubble and ESO New Technology Telescope (NTT) Deep Fields are shown as a function of their redshifts and absolute magnitudes using photometric redshifts derived from the multicolor catalogs and are compared with the cold dark matter (CDM) predictions. Extending to the lower luminosities and to the higher z that our previous analysis performed on the NTT field alone, we find the distribution of the galaxy disk sizes at different cosmic epochs is within the range predicted by typical CDM models. However, the observed size distribution of faint (MB>-19) galaxies is skewed with respect to the CDM predictions, and an excess of small-size disks (Rd<2 kpc) is already present at z approximately 0.5. The excess persists up to z approximately 3 and involves brighter galaxies. Such an excess may be reduced if luminosity-dependent effects, like starburst activity in interacting galaxies, are included in the physical mechanisms governing the star formation history in CDM models.

On the Size Distribution of Asteroid Families: The Role of Geometry

The steep slopes of the size distributions of the presently known asteroid families have long represented a debated problem. The reason is that it is not easy to reproduce them by the usual modeling techniques based on the application of standard power-laws as suggested by laboratory experiments. In this paper, we suggest that the failures of the previous models were due to the fact that geometric effects were not taken into account. In other words, the finite sizes of the parent bodies and the fact that fragments tend to have convex shapes cannot be disregarded. Following this approach, we find that steep size distributions are necessarily produced by fragmentations of the parent bodies. Moreover, we have been able to reproduce fairly well the observed size distributions of the major families, and we have also obtained some reasonable constraints on the original sizes of the parent bodies. Some anomalous mass depletions, probably due to injection of fragments in nearby resonances have also been found, not unexpectedly, in a few cases (Maria, Themis).

A differentiation method for separating a mixture of suspended particle size distributions

Abstract. A simple method is proposed to partition a mixture of two populations in suspended particle size data. The method, termed here "the differentiation method" is based on the function of the lognormal distribution. Suspended material in marine or estuarine situations often consists of difficult-to-interpret complex populations. The treatment of particle size data by the method described enables the confirmation of the lognormal law and also the demonstration of the occurrence of a combination of a number of populations which may not be distinguished by the classical Gaussian transformation or automatic methods. A simple combination of graphical and numerical techniques permits the decomposition and the easy determination of the various statistical parameters (median diameter, mean diameter, etc...). The method is applied to interpret observed size distributions of suspended particulate matter in the Seine estuary. The method enables the determination of the relative sizes of the constituent sub-populations that comprise the total suspended matter. In the example used to illustrate the method, particles are shown to be resuspended as a function of different hydrodynamic parameter.

The effect of wind direction on the observed size distribution of particle adsorbed polycyclic aromatic hydrocarbons on an inner city sampling site.

An investigation of the variability in the size distribution of particle adsorbed polycyclic aromatic hydrocarbons (PAHs) on an inner city sampling site showed differences depending on the wind direction. Particle size distributions of PAHs from outdoor air sampling were measured in Munich from 1994 to 1997. The sampling site is located northeast of a crossing with heavy traffic and southwest of a large inner city park. Depending on the wind direction, three different size distributions of particle adsorbed PAHs were observed. The maximum PAH concentration on very small particles (geometric mean diameter 75 nm) was observed with wind from west to southwest coming directly from the crossing area or the roads with heavy traffic. The maximum PAH concentration on particles with geometric mean diameter of 260 nm was found on days with wind from the built-up area north of the sampling site. On particles with geometric mean diameter of 920 nm the maximum PAH concentration was found on days with main wind directions from northeast to east. On these days the wind is blowing from the direction of the city park nearby. The distribution of particle adsorbed PAHs within different particle size classes is substantially influenced by the distance of the sampling site from strong sources of PAH loaded particulate matter.

Submicrometer and Supermicrometer Particulate Emission from Spark Ignition Vehicles

Abstract: Particulate emissions from 11 gasoline powered and 2 liquefied petroleum (LPG) powered passenger vehicles were characterised during the Accelerated Simulation Mode driving cycles on a chassis dynamometer. The test fleet consisted of 10 catalyst-equipped vehicles operated with unleaded gasoline (5 Ford Falcons and 5 Holden Commodores), 2 LPG powered vehicles (both Ford Falcons), and 1 older type noncatalyst vehicle operated with leaded gasoline. Particulate characterisation included determination of total particulate number concentration and size distribution using the Scanning Mobility Particle Sizer (SMPS) and the Aerodynamic Particle Sizer (APS). The average particle number concentrations in the SMPS range for all modes was lower for Ford Falcons and somewhat higher for Commodores, with values of 1.5x104 and 4.1x104 cm-3, respectively. This difference is significant and was observed for all modes. The number concentration levels were higher for the LPG fuelled cars (8.4x104 cm-3) and for the leaded gasoline powered vehicle (7.9x105 cm-3). There was not a significant variation in particle count median diameter in the SMPS and the APS ranges, either for different operating conditions of the vehicles investigated, or between different vehicle groups. The observed size distributions were bimodal with average values of CMD ranged from 39.1 to 60.2nm in the SMPS range and from 0.9 to 1.4µm in the APS range. The results obtained from this study can be used as a first order estimation towards emission inventories for vehicle groups included in the investigations.

Collisional Models and Scaling Laws: A New Interpretation of the Shape of the Main-Belt Asteroid Size Distribution

Numerical models of the collisional evolution of the main-belt asteroids lead to a new interpretation of the shape of the observed size distribution. Using recent hydrocode predictions of shattering and disruption criteria as starting points, we adjust the size–strength scaling relation for asteroidal strengths within our collisional model until a best least-squares fit to the observed size distribution is obtained. We show for the first time general agreement between the predictions of hydrocodes, results of numerical collisional models, and the observed size distribution of the main-belt population.

Ice crystal nucleation and growth in contrails forming at low ambient temperatures

A model of ice crystal nucleation and growth in a diluting aircraft exhaust plume is used to evaluate the physical processes responsible for the ice number densities and size distributions measured on May 4, 1996. Predicted ice crystal size distributions are compared with observations at about 70 seconds plume age. The simulated crystals grow to about 2 µm radius within 2–3 seconds, then remain approximately constant in size until 30–60 seconds plume age when crystal sublimations begins. The calculated crystal size distribution has approximately the same volume mode radius as the observed size distribution (1–2 µm); however, the model does not predict as many crystals larger than 2 µm radius as indicated by the measurements. Due to the low ambient temperature (−61°C), large ice supersaturations are generated in the plume, and all exhaust soot particles and ambient aerosols entrained into the plume before about 1 second plume age are activated to ice nuclei. The simulations indicate that if the soot particle emission index is on the order of 2×1012 particles (kg fuel)−1 or lower and freshly nucleated sulfate aerosols are too small to freeze in the young plume, then the majority of the contrail ice crystals may be nucleated on ambient aerosols entrained into the exhaust plume.