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Complex Population Dynamics in Mussels Arising from Density-Linked Stochasticity
Population fluctuations are generally attributed to the deterministic consequences of strong non-linear interactions among organisms, or the effects of random stochastic environmental variation superimposed upon the deterministic skeleton describing population change. Analysis of the population dynamics of the mussel Mytilus californianus taken in 16 plots over 18-years found no evidence that these processes explained observed strong fluctuations. Instead, population fluctuations arose because environmental stochasticity varied with abundance, which we term density-linked stochasticity. This phenomenon arises from biologically relevant mechanisms: recruitment variation and transmission of disturbance among neighboring individuals. Density-linked stochasticity is probably present frequently in populations, as it arises naturally from several general ecological processes, including stage structure variation with density, ontogenetic niche shifts, and local transmission of stochastic perturbations. More thoroughly characterizing and interpreting deviations from the mean behavior of a system will lead to better ecological prediction and improved insight into the important processes affecting populations and ecosystems.</p
The structure of one-relator relative presentations and their centres
Suppose that G is a nontrivial torsion-free group and w is a word in the
alphabet G\cup\{x_1^{\pm1},...,x_n^{\pm1}\} such that the word w' obtained from
w by erasing all letters belonging to G is not a proper power in the free group
F(x_1,...,x_n). We show how to reduce the study of the relative presentation
\^G= to the case n=1. It turns out that an
"n-variable" group \^G can be constructed from similar "one-variable" groups
using an explicit construction similar to wreath product. As an illustration,
we prove that, for n>1, the centre of \^G is always trivial. For n=1, the
centre of \^G is also almost always trivial; there are several exceptions, and
all of them are known.Comment: 15 pages. A Russian version of this paper is at
http://mech.math.msu.su/department/algebra/staff/klyachko/papers.htm . V4:
the intoduction is rewritten; Section 1 is extended; a short introduction to
Secton 5 is added; some misprints are corrected and some cosmetic
improvements are mad
Revealing nascent proteomics in signaling pathways and cell differentiation.
Regulation of gene expression at the level of protein synthesis is a crucial element in driving how the genetic landscape is expressed. However, we are still limited in technologies that can quantitatively capture the immediate proteomic changes that allow cells to respond to specific stimuli. Here, we present a method to capture and identify nascent proteomes in situ across different cell types without disturbing normal growth conditions, using O-propargyl-puromycin (OPP). Cell-permeable OPP rapidly labels nascent elongating polypeptides, which are subsequently conjugated to biotin-azide, using click chemistry, and captured with streptavidin beads, followed by digestion and analysis, using liquid chromatography-tandem mass spectrometry. Our technique of OPP-mediated identification (OPP-ID) allows detection of widespread proteomic changes within a short 2-hour pulse of OPP. We illustrate our technique by recapitulating alterations of proteomic networks induced by a potent mammalian target of rapamycin inhibitor, MLN128. In addition, by employing OPP-ID, we identify more than 2,100 proteins and uncover distinct protein networks underlying early erythroid progenitor and differentiation states not amenable to alternative approaches such as amino acid analog labeling. We present OPP-ID as a method to quantitatively identify nascent proteomes across an array of biological contexts while preserving the subtleties directing signaling in the native cellular environment
Mandatory Disclosure and Individual Investors: Evidence From the Jobs Act
One prominent justification for the mandatory disclosure rules that define modern securities law is that these rules encourage individual investors to participate in stock markets. Mandatory disclosure, the theory goes, gives individual investors access to information that puts them on a more equal playing field with sophisticated institutional shareholders. Although this reasoning has long been cited by regulators and commentators as a basis for mandating disclosure, recent work has questioned its validity. In particular, recent studies contend that individual investors are overwhelmed by the amount of information required to be disclosed under current law, and thus they cannot—and do not—use that information to analyze the companies that they own.
Using a recent change in the law that allows firms to disclose less information before their initial public offering (“IPO”), we examine whether reduced disclosure leads to less trading by individual investors. Our results show that, immediately following the IPO, individual investors are less likely to trade in the stocks of the firms that provide less disclosure—but that this difference disappears after two weeks of trading. Our findings have important implications for the lawmakers now examining whether, and how, to change the mandatory disclosure rules that have served as the basis of federal securities law for generations
Towards Understanding Photoperiodic Response in Grasses
In many plants, day length is the critical environmental parameter that controls flowering time. In long day plants, such as Arabidopsis and ryegrass (Lolium perenne), increasing day length in spring signals flowering, while in short day plants like rice, flowering is accelerated when days become shorter. Recently, significant progress has been made in understanding the molecular genetic mechanisms that govern this response. Most results have been obtained in the model plant Arabidopsis where CONSTANS (CO) is a critical candidate gene. Upstream of it is the GIGANTEA (GI) gene which is associated with the circadian clock mechanism (1). The FT gene is the immediate downstream genetic target of CO, and is a direct promoter of flowering (2). Characteristically, all three genes show circadian expression, albeit in different phases, and both the CO and FT genes are up-regulated under long-day (inductive) conditions. Work in ryegrass should help reveal both the conserved and divergent segments of the photoperiod response between different plant species
Mandatory Disclosure and Individual Investors: Evidence from the Jobs Act
One prominent justification for the mandatory disclosure rules that define modem securities law is that these rules encourage individual investors to participate in stock markets. Mandatory disclosure, the theory goes, gives individual investors access to information that puts them on a more equal playing field with sophisticated institutional shareholders. Although this reasoning has long been cited by regulators and commentators as a basis for mandating disclosure, recent work has questioned its validity. In particular, recent studies contend that individual investors are overwhelmed by the amount of information required to be disclosed under current law, and thus they cannot and do not use that information to analyze the companies that they own.
Using a recent change in the law that allows firms to disclose less information before their initial public offering ( IPO ), we examine whether reduced disclosure leads to less trading by individual investors. Our results show that, immediately following the IPO, individual investors are less likely to trade in the stocks of the firms that provide less disclosure but that this difference disappears after two weeks of trading. Our findings have important implications for the lawmakers now examining whether, and how, to change the mandatory disclosure rules that have served as the basis of federal securities law for generations
First principles based atomistic modeling of phase stability in PMN-xPT
We have performed molecular dynamics simulations using a shell model
potential developed by fitting first principles results to describe the
behavior of the relaxor-ferroelectric (1-x)PbMg1/3Nb2/3O3-xPbTiO3 (PMN-xPT) as
function of concentration and temperature, using site occupancies within the
random site model. In our simulations, PMN is cubic at all temperatures and
behaves as a polar glass. As a small amount of Ti is added, a weak polar state
develops, but structural disorder dominates, and the symmetry is rhombohedral.
As more Ti is added the ground state is clearly polar and the system is
ferroelectric, but with easy rotation of the polarization direction. In the
high Ti content region, the solid solution adopts ferroelectric behavior
similar to PT, with tetragonal symmetry. The ground state sequence with
increasing Ti content is R-MB-O-MC-T. The high temperature phase is cubic at
all compositions. Our simulations give the slope of the morphotropic phase
boundaries, crucial for high temperature applications. We find that the phase
diagram PMN-xPT can be understood within the random site model.Comment: 27 pages, 9 figure
Skeletal Structural Basis of Density Banding in the Reef Coral Montastrea Annularis
Density banding in coral skeletons can provide for reconstruction of the coral\u27s growth en- vironment over long periods. The physical differ- ences between low and high density portions of a skeletal band are not well understood. The skeletal architecture of M. annularis from Southeast Flor- ida, the Florida Keys, St. Croix, the Bahamas, and Mexico was compared in X-ray revealed high den- sity (HD), low density (LD), and stress HD bands. Density changes arose from differences in the size, but not spacing, of exothecal structural elements (horizontal dissepiments and vertical costae). En- dothecal architecture size (e.g., columella, dissepi- ments, septa) was relatively constant between den- sity band types. Results have implications for studies of coral growth, sclerochronology, and iso- topic/trace element composition
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