14 research outputs found
Does nitrate deposition following astrophysical ionizing radiation events pose an additional threat to amphibians?
It is known that amphibians are especially susceptible to the combination of
heightened UVB radiation and increased nitrate concentrations. Various
astrophysical events have been suggested as sources of ionizing radiation that
could pose a threat to life on Earth, through destruction of the ozone layer
and subsequent increase in UVB, followed by deposition of nitrate. In this
study, we investigate whether the nitrate deposition following an ionizing
event is sufficiently large to cause an additional stress beyond that of the
heightened UVB previously considered. We have converted predicted nitrate
depositions to concentration values, utilizing data from the New York State
Department of Environmental Conservation Acid Rain Monitoring Network web site.
Our results show that the increase in nitrate concentration in bodies of water
following the most intense ionization event likely in the last billion years
would not be sufficient to cause a serious additional stress on amphibian
populations and may actually provide some benefit by acting as fertilizer.Comment: This version is a longer, more detailed draft of an article submitted
to the journal Astrobiolog
Statistical properties of the Burgers equation with Brownian initial velocity
We study the one-dimensional Burgers equation in the inviscid limit for
Brownian initial velocity (i.e. the initial velocity is a two-sided Brownian
motion that starts from the origin x=0). We obtain the one-point distribution
of the velocity field in closed analytical form. In the limit where we are far
from the origin, we also obtain the two-point and higher-order distributions.
We show how they factorize and recover the statistical invariance through
translations for the distributions of velocity increments and Lagrangian
increments. We also derive the velocity structure functions and we recover the
bifractality of the inverse Lagrangian map. Then, for the case where the
initial density is uniform, we obtain the distribution of the density field and
its -point correlations. In the same limit, we derive the point
distributions of the Lagrangian displacement field and the properties of
shocks. We note that both the stable-clustering ansatz and the Press-Schechter
mass function, that are widely used in the cosmological context, happen to be
exact for this one-dimensional version of the adhesion model.Comment: 42 pages, published in J. Stat. Phy
The Alvarez impact theory of mass extinction; limits to its applicability and the âgreat expectations syndromeâ
For the past three decades, the Alvarez impact theory of mass extinction, causally related to catastrophic meteorite impacts, has been recurrently applied to multiple extinction boundaries. However, these multidisciplinary research efforts across the globe have been largely unsuccessful to date, with one outstanding exception: the Cretaceous-Paleogene boundary. The unicausal impact scenario as a leading explanation, when applied to the complex fossil record, has resulted in force-fitting of data and interpretations ("great expectations syndrome". The misunderstandings can be grouped at three successive levels of the testing process, and involve the unreflective application of the impact paradigm: (i) factual misidentification, i.e., an erroneous or indefinite recognition of the extraterrestrial record in sedimentological, physical and geochemical contexts, (ii) correlative misinterpretation of the adequately documented impact signals due to their incorrect dating, and (iii) causal overestimation when the proved impact characteristics are doubtful as a sufficient trigger of a contemporaneous global cosmic catastrophe. Examples of uncritical belief in the simple cause-effect scenario for the Frasnian-Famennian, Permian-Triassic, and Triassic-Jurassic (and the Eifelian-Givetian and Paleocene-Eocene as well) global events include mostly item-1 pitfalls (factual misidentification), with Ir enrichments and shocked minerals frequently misidentified. Therefore, these mass extinctions are still at the first test level, and only the F-F extinction is potentially seen in the context of item-2, the interpretative step, because of the possible causative link with the Siljan Ring crater (53 km in diameter). The erratically recognized cratering signature is often marked by large timing and size uncertainties, and item-3, the advanced causal inference, is in fact limited to clustered impacts that clearly predate major mass extinctions. The multi-impact lag-time pattern is particularly clear in the Late Triassic, when the largest (100 km diameter) Manicouagan crater was possibly concurrent with the end-Carnian extinction (or with the late Norian tetrapod turnover on an alternative time scale). The relatively small crater sizes and cratonic (crystalline rock basement) setting of these two craters further suggest the strongly insufficient extraterrestrial trigger of worldwide environmental traumas. However, to discuss the kill potential of impact events in a more robust fashion, their location and timing, vulnerability factors, especially target geology and palaeogeography in the context of associated climate-active volatile fluxes, should to be rigorously assessed. The current lack of conclusive impact evidence synchronous with most mass extinctions may still be somewhat misleading due to the predicted large set of undiscovered craters, particularly in light of the obscured record of oceanic impact events
Galaxy redshift abundance periodicity from Fourier analysis of number counts N(z) using SDSS and 2dF GRS galaxy surveys
Perturbation theory in Lagrangian hydrodynamics for a cosmological fluid with velocity dispersion
The Alvarez Impact Theory of Mass Extinction; Limits to its Applicability and the âGreat Expectations Syndromeâ
Disentangling the cosmic web I: morphology of isodensity contours
We apply Minkowski functionals and various derived measures to decipher the morphological properties of large-scale structure seen in simulations of gravitational evolution. Minkowski functionals of isodensity contours serve as tools to test global properties of the density field. Furthermore, we identify coherent objects at various threshold levels and calculate their partial Minkowski functionals. We propose a set of two derived dimensionless quantities, planarity and filamentarity, which reduce the morhological information in a simple and intuitive way. Several simulations of the gravitational evolution of initial power-law spectra provide a framework for systematic tests of our method. (orig.)Available from TIB Hannover: RR 4697(1194) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman