자연주의적 탐구조사(Naturalistic Inquiry)

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Using Multivariate Statistics

Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

The Theory of Island Biogeography

We review recent determinations of the present-day mass function (PDMF) and initial mass function (IMF) in various components of the Galaxy—disk, spheroid, young, and globular clusters—and in conditions characteristic of early star formation. As a general feature, the IMF is found to depend weakly on the environment and to be well described by a power-law form forM , and a lognormal form below, except possibly for m!1 early star formation conditions. The disk IMF for single objects has a characteristic mass around M , m!0.08 c and a variance in logarithmic mass , whereas the IMF for multiple systems hasM , and . j!0.7 m!0.2 j!0.6 c The extension of the single MF into the brown dwarf regime is in good agreement with present estimates of L- and T-dwarf densities and yields a disk brown dwarf number density comparable to the stellar one, n!n! BD " pc !3 .T he IMF of young clusters is found to be consistent with the disk fi eld IMF, providing the same correction 0.1 for unresolved binaries, confirming the fact that young star clusters and disk field stars represent the same stellar population. Dynamical effects, yielding depletion of the lowest mass objects, are found to become consequential for ages!130 Myr. The spheroid IMF relies on much less robust grounds. The large metallicity spread in the local subdwarf photometric sample, in particular, remains puzzling. Recent observations suggest that there is a continuous kinematic shear between the thick-disk population, present in local samples, and the genuine spheroid one. This enables us to derive only an upper limit for the spheroid mass density and IMF. Within all the uncertainties, the latter is found to be similar to the one derived for globular clusters and is well represented also by a lognormal form with a characteristic mass slightly larger than for the disk, M , ,e xcluding as ignif icant population of m!0.2-0.3 c brown dwarfs in globular clusters and in the spheroid. The IMF characteristic of early star formation at large redshift remains undetermined, but different observational constraints suggest that it does not extend below!1M , .T hese results suggest a characteristic mass for star formation that decreases with time, from conditions prevailing at large redshift to conditions characteristic of the spheroid (or thick disk) to present-day conditions.Theseconclusions,however, remain speculative, given the large uncertainties in the spheroid and early star IMF determinations. These IMFs allow a reasonably robust determination of the Galactic present-day and initial stellar and brown dwarf contents. They also have important galactic implications beyond the Milky Way in yielding more accurate mass-to-light ratio determinations. The mass-to-light ratios obtained with the disk and the spheroid IMF yield values 1.8-1.4 times smaller than for a Salpeter IMF, respectively, in agreement with various recent dynamical determinations. This general IMF determination is examined in the context of star formation theory. None of the theories based on a Jeans-type mechanism, where fragmentation is due only to gravity, can fulfill all the observational constraints on star formation and predict a large number of substellar objects. On the other hand, recent numerical simulations of compressible turbulence, in particular in super-Alfvenic conditions, seem to reproduce both qualitatively and quantitatively the stellar and substellar IMF and thus provide an appealing theoretical foundation. In this picture, star formation is induced by the dissipation of large-scale turbulence to smaller scales through radiative MHD shocks, producing filamentary structures. These shocks produce local nonequilibrium structures with large density contrasts, which collapse eventually in gravitationally bound objects under the combined influence of turbulence and gravity. The concept of a single Jeans mass is replaced by a distribution of local Jeans masses, representative of the lognormal probability density function of the turbulent gas. Objects below the mean thermal Jeans mass still have a possibility to collapse, although with a decreasing probability.

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Galactic stellar and substellar initial mass function

In the 1980s, exosomes were described as vesicles of endosomal origin secreted from reticulocytes. Interest increased around these extracellular vesicles, as they appeared to participate in several cellular processes. Exosomes bear proteins, lipids, and RNAs, mediating intercellular communication between different cell types in the body, and thus affecting normal and pathological conditions. Only recently, scientists acknowledged the difficulty of separating exosomes from other types of extracellular vesicles, which precludes a clear attribution of a particular function to the different types of secreted vesicles. To shed light into this complex but expanding field of science, this review focuses on the definition of exosomes and other secreted extracellular vesicles. Their biogenesis, their secretion, and their subsequent fate are discussed, as their functions rely on these important processes.

/pdf/biogenesis-secretion-and-intercellular-interactions-of-4pskmvujl3.pdf

Biogenesis, Secretion, and Intercellular Interactions of Exosomes and Other Extracellular Vesicles

We present our findings on the photometric variability of the impact spots of comet Shoemaker-Levy 9 (SL 9) in the Jovian atmosphere. Extensive imaging and differential photometry of impact spots in the methane band (8950/90 A) have enabled us to conservatively extract their photometric contribution from that of Jupiter. In this methane band, the SL 9 spots appear brighter than the surrounding Jovian surface because they lie above the main concentrations of methane that overlie the cloud tops. Our observations of two well-observed and isolated spots, H and Q1, indicate that spots experience a photometric growth that initially approximates a power law in time of index 0.3 and then appears to level off in the case of the H spot. We consider two explanations for the brightening of spots: (1) the dispersal of high optical depth core regions and (2) the coagulation of dust from the atomized or fragmented cometary ejecta. The former has been rejected because one spot, H, which was disrupted by a cyclonic storm, exhibited no discontinuity in its rate of photometric growth that would correspond to the disruption. We adopt the second as a working hypothesis because the growth of grains is consistent with our observations and has been cited as the cause for the observed changes in the integrated optical depth in the near-IR and the UV. We propose a simple model in which sites for grain nucleation are provided by the chemical interaction of cometary material and the shocked Jovian atmosphere and in which grain growth is restrained by the diminishing availability of raw materials for grain formation on timescales inversely proportional to the original aerosol density. This model, applied to a volumetric power-law distribution of aerosols, can produce an integrated scattering amplitude growth rate closely resembling our observations.

/pdf/the-photometric-growth-of-two-shoemaker-levy-9-impact-sites-16ib0weo14.pdf

The photometric growth of two shoemaker-levy 9 impact sites on jupiter

On the issues associated with applying traditional Lagrangian mechanics to the material point method.

Discussion: CHD pile performance: part I – physical modelling

Nature regulars give their recommendations for relaxed, inspiring holiday reading and viewing — from climate-change history to Isaac Newton the detective.

/pdf/a-break-from-the-bench-55mhctab5g.pdf

Michael E. Brown

Papers

The photometric growth of two shoemaker-levy 9 impact sites on jupiter

On the issues associated with applying traditional Lagrangian mechanics to the material point method.

Discussion: CHD pile performance: part I – physical modelling

A break from the bench