Chaotic scalar fields as models for dark energy

We consider stochastically quantized self-interacting scalar fields as suitable models to generate dark energy in the universe. Second quantization effects lead to new and unexpected phenomena is the self interaction strength is strong. The stochastically quantized dynamics can degenerate to a chaotic dynamics conjugated to a Bernoulli shift in fictitious time, and the right amount of vacuum energy density can be generated without fine tuning. It is numerically observed that the scalar field dynamics distinguishes fundamental parameters such as the electroweak and strong coupling constants as corresponding to local minima in the dark energy landscape. Chaotic fields can offer possible solutions to the cosmological coincidence problem, as well as to the problem of uniqueness of vacua.Comment: 30 pages, 3 figures. Replaced by final version accepted by Phys. Rev.

Conformation of a Polyelectrolyte Complexed to a Like-Charged Colloid

We report results from a molecular dynamics (MD) simulation on the conformations of a long flexible polyelectrolyte complexed to a charged sphere, \textit{both negatively charged}, in the presence of neutralizing counterions in the strong Coulomb coupling regime. The structure of this complex is very sensitive to the charge density of the polyelectrolyte. For a fully charged polyelectrolyte the polymer forms a dense two-dimensional "disk", whereas for a partially charged polyelectrolyte the monomers are spread over the colloidal surface. A mechanism involving the \textit{overcharging} of the polyelectrolyte by counterions is proposed to explain the observed conformations.Comment: 4 pages, 4 figures (6 EPS files

On the algebraic K-theory of the complex K-theory spectrum

Let p>3 be a prime, let ku be the connective complex K-theory spectrum, and let K(ku) be the algebraic K-theory spectrum of ku. We study the p-primary homotopy type of the spectrum K(ku) by computing its mod (p,v_1) homotopy groups. We show that up to a finite summand, these groups form a finitely generated free module over a polynomial algebra F_p[b], where b is a class of degree 2p+2 defined as a higher Bott element.Comment: Revised and expanded version, 42 pages

Degeneration rate of preantral follicles in the ovaries of goats

The degeneration rate of ovarian preantral follicles in goats, and the distribution in the follicular classes (primordial, primary or secondary) was assessed. Ovaries from adult goats were collected at a local slaughterhouse. To evaluate the morphology of the caprine preantral follicles in situ, one fragment from each ovary was fixed individually in Carnoy for 12 h, sectioned serially at a thickness of 7 μm and stained with Periodic Acid Shiff-hematoxylin. Preantral follicles were then classified according to the stage of development. Preantral follicles were classified individually either as morphologically normal; as Type 1 degenerated follicles (only the oocyte was degenerated); or as Type 2 degenerated follicles (when degeneration occurred at both oocyte and granulosa cells). The total examined was 235 primordial, 195 primary and 101 secondary follicles. The distribution of degenerated follicles as primordial, primary and secondary follicles was 8.5, 14.3 and 16.8%, respectively. When Types 1 and 2 degenerated follicles were pooled, secondary follicles were significantly more degenerated than primordial and primary follicles. When degeneration Types 1 and 2 was compared in each follicular class, a higher (P<0.05) percentage of Type 1 degeneration was observed in primordial and primary follicles. Conversely, secondary follicles were significantly more affected by Type 2 degeneration. When the follicular classes were taken together, a significantly higher percentage of Type 1 degenerated preantral follicles was observed when compared with Type 2 degenerated follicles (P<0.05). In conclusion, a low percentage of degenerated preantral follicles was observed and secondary follicles were more affected by degeneration than primordial follicles. Thus, primordial follicles constitute a large and potentially valuable source of oocytes for reproductive programs after in vitro growth and maturation

Can forest management based on natural disturbances maintain ecological resilience?

Given the increasingly global stresses on forests, many ecologists argue that managers must maintain ecological resilience: the capacity of ecosystems to absorb disturbances without undergoing fundamental change. In this review we ask: Can the emerging paradigm of natural-disturbance-based management (NDBM) maintain ecological resilience in managed forests? Applying resilience theory requires careful articulation of the ecosystem state under consideration, the disturbances and stresses that affect the persistence of possible alternative states, and the spatial and temporal scales of management relevance. Implementing NDBM while maintaining resilience means recognizing that (i) biodiversity is important for long-term ecosystem persistence, (ii) natural disturbances play a critical role as a generator of structural and compositional heterogeneity at multiple scales, and (iii) traditional management tends to produce forests more homogeneous than those disturbed naturally and increases the likelihood of unexpected catastrophic change by constraining variation of key environmental processes. NDBM may maintain resilience if silvicultural strategies retain the structures and processes that perpetuate desired states while reducing those that enhance resilience of undesirable states. Such strategies require an understanding of harvesting impacts on slow ecosystem processes, such as seed-bank or nutrient dynamics, which in the long term can lead to ecological surprises by altering the forest's capacity to reorganize after disturbance

Key taxa in food web responses to stressors: the Deepwater Horizon oil spill

Identifying key taxa in the response of ecosystems to perturbations relies on quantifying both their sensitivity to stressors and their importance in the overall web of interactions. If sensitive taxa occupy key network positions, then they may decrease the capacity of ecosystems to resist perturbations. Despite widespread concern for coastal marshes after the 2010 Deepwater Horizon oil spill in the Gulf of Mexico, impacts on individual taxa were variable, and the effects on the overall marsh food web have not been assessed. Here, we synthesize published studies on trophic relationships and oil sensitivity to identify critical taxa in the response of marsh food webs to the oil spill. Taxa such as carnivorous marsh fishes are expected to enhance resilience, while gulls, terns, and omnivorous snails may destabilize the food web. Our framework for identifying key taxa can be applied to other environmental stressors or ecosystems if both the sensitivity of individual taxa to a stressor and the food web structure are known

Microbial Mats from the Khor Al-Adaid Sabkha, Qatar: Morphotypes and Association with Authigenic Minerals

The sabkhas (i.e., salt flats) of Qatar are among the rare places on Earth where carbonate and sulfate minerals similar to those constituting economically important hydrocarbon reservoirs are still forming today, under the arid conditions that characterize the coastline of the country. Since the 1960's, the sabkhas of Qatar have been studied with great interest as a modern analogue for ancient sedimentary sequences (e.g., Wells, 1962; Illing & Taylor, 1995; Alsharhan & Kendall, 2003). The results of these studies provided important insights for formulating stratigraphic models of subsurface hydrocarbon reservoirs. Notable examples of gas and oil reservoirs that formed in arid, evaporitic environments include the Permo-Triassic Khuff (which is estimated to contain about 15-20% of the world's gas reserves and is of fundamental importance for the economy of Qatar), the Jurassic Arab formations, and the Triassic Kurra Chine, all of the Middle East, and the Permian Zechstein of Northern Europe. Although extremely valuable, most of these early studies were based on purely physical and chemical approaches, which may have not fully captured the complexity of the mineralization processes occurring in the sabkha environment. Indeed, research conducted in more recent years has shown that microorganisms play an important and, as yet, poorly understood role for the mineralization processes occurring in these evaporitic environments (Bontognali et al., 2010; Bontognali et al., 2012; Bontognali et al., 2014; Brauchli et al., 2015; Paulo & Dittrich, 2013; Strohmenger et al., 2011). Here we present the results of a field campaign conducted in the Khor Al-Adaid sabkha, which is located in the southeast of Qatar, in a large tidal embayment composed of two shallow inland lagoons. The main goal of the field campaign was to identify regions of the intertidal zone that are particularly rich in microbial mats, and that represent ideal sites at which to study microbe-mineral interactions. Three sites of interest have been defined.qscienc

Single-nucleus RNA sequencing of pre-malignant liver reveals disease-associated hepatocyte state with HCC prognostic potential

Current approaches to staging chronic liver diseases have limited utility for predicting liver cancer risk. Here, we employed single-nucleus RNA sequencing (snRNA-seq) to characterize the cellular microenvironment of healthy and pre-malignant livers using two distinct mouse models. Downstream analyses unraveled a previously uncharacterized disease-associated hepatocyte (daHep) transcriptional state. These cells were absent in healthy livers but increasingly prevalent as chronic liver disease progressed. Copy number variation (CNV) analysis of microdissected tissue demonstrated that daHep-enriched regions are riddled with structural variants, suggesting these cells represent a pre-malignant intermediary. Integrated analysis of three recent human snRNA-seq datasets confirmed the presence of a similar phenotype in human chronic liver disease and further supported its enhanced mutational burden. Importantly, we show that high daHep levels precede carcinogenesis and predict a higher risk of hepatocellular carcinoma development. These findings may change the way chronic liver disease patients are staged, surveilled, and risk stratified