Zeno and Anti Zeno effect for a two level system in a squeezed bath

We discuss the appearance of Zeno (QZE) or anti-Zeno (QAE) effect in an exponentially decaying system. We consider the quantum dynamics of a continuously monitored two level system interacting with a squeezed bath. We find that the behavior of the system depends critically on the way in which the squeezed bath is prepared. For specific choices of the squeezing phase the system shows Zeno or anti-Zeno effect in conditions for which it would decay exponentially if no measurements were done. This result allows for a clear interpretation in terms of the equivalent spin system interacting with a fictitious magnetic field.Comment: 18 pages, 7 figures;added references for section 4;changes in the nomenclatur

Expansion-Free Evolving Spheres Must Have Inhomogeneous Energy Density Distributions

In a recent paper a systematic study on shearing expansion-free spherically symmetric distributions was presented. As a particular case of such systems, the Skripkin model was mentioned, which corresponds to a nondissipative perfect fluid with a constant energy density. Here we show that such a model is inconsistent with junction conditions. It is shown that in general for any nondissipative fluid distribution, the expansion-free condition requires the energy density to be inhomogeneous. As an example we consider the case of dust, which allows for a complete integration.Comment: 8 pages, Latex. To appear in Phys. Rev.D. Typos correcte

Non Abelian BF theories with sources and 2-D gravity

We study the interaction of non-Abelian topological $BF$ theories defined on two dimensional manifolds with point sources carrying non-Abelian charges. We identify the most general solution for the field equations on simply and multiply connected two-manifolds. Taking the particular choice of the so-called extended Poincar\'e group as the gauge group we discuss how recent discussions of two dimensional gravity models do fit in this formalism.Comment: 20 pages, Latex, To appear in Phys Rev D5

Layer Features of the Lattice Gas Model for Self-Organized Criticality

A layer-by-layer description of the asymmetric lattice gas model for 1/f-noise suggested by Jensen [Phys. Rev. Lett. 64, 3103 (1990)] is presented. The power spectra of the lattice layers in the direction perpendicular to the particle flux is studied in order to understand how the white noise at the input boundary evolves, on the average, into 1/f-noise for the system. The effects of high boundary drive and uniform driving force on the power spectrum of the total number of diffusing particles are considered. In the case of nearest-neighbor particle interactions, high statistics simulation results show that the power spectra of single lattice layers are characterized by different $\beta_x$ exponents such that $\beta_x \to 1.9$ as one approaches the outer boundary.Comment: LaTeX, figures upon reques

Reptilian Heart Development And The Molecular Basis Of Cardiac Chamber Evolution

The emergence of terrestrial life witnessed the need for more sophisticated circulatory systems. This has evolved in birds, mammals and crocodilians into complete septation of the heart into left and right sides, allowing separate pulmonary and systemic circulatory systems, a key requirement for the evolution of endothermy(1-3). However, the evolution of the amniote heart is poorly understood. Reptilian hearts have been the subject of debate in the context of the evolution of cardiac septation: do they possess a single ventricular chamber or two incompletely septated ventricles(4-7)? Here we examine heart development in the red-eared slider turtle, Trachemys scripta elegans (a chelonian), and the green anole, Anolis carolinensis (a squamate), focusing on gene expression in the developing ventricles. Both reptiles initially form a ventricular chamber that homogenously expresses the T-box transcription factor gene Tbx5. In contrast, in birds and mammals, Tbx5 is restricted to left ventricle precursors(8,9). In later stages, Tbx5 expression in the turtle (but not anole) heart is gradually restricted to a distinct left ventricle, forming a left-right gradient. This suggests that Tbx5 expression was refined during evolution to pattern the ventricles. In support of this hypothesis, we show that loss of Tbx5 in the mouse ventricle results in a single chamber lacking distinct identity, indicating a requirement for Tbx5 in septation. Importantly, misexpression of Tbx5 throughout the developing myocardium to mimic the reptilian expression pattern also results in a single mispatterned ventricular chamber lacking septation. Thus ventricular septation is established by a steep and correctly positioned Tbx5 gradient. Our findings provide a molecular mechanism for the evolution of the amniote ventricle, and support the concept that altered expression of developmental regulators is a key mechanism of vertebrate evolution

Do early-successional weeds facilitate or compete with seedlings in forest restoration? Disentangling abiotic versus biotic factors

Semi-arid forests need cost-effective restoration strategies to address their severe degradation. Tree shelters are often used to minimize abiotic and biotic stress during seedling establishment. We asked if early-successional weeds act as a natural shelter by facilitating native seedlings, contingent on abiotic and biotic stressors and seedling ecological strategy. We conducted a manipulative weed exclusion experiment at a semi-arid site in South Texas targeted for large-scale forest restoration to discern the net effect of weeds on the growth and survival of target thornscrub tree and shrub seedlings. We assessed the roles of contrasting seedling ecological strategies (fast vs. slow growth habit), temporal variation in abiotic stress, microclimate and mammalian herbivory in modulating weed–seedling interactions. Ungulate herbivory on seedlings was common, of similar frequency across most species, but not diminished by the presence of weed neighbours. On average, seedlings growing adjacent to weed neighbours experienced modest but non-significant increases in both height and mortality after 6 months, relative to weed-excluded areas. However, seedlings without significant herbivory and adjacent to weed neighbours grew more vigorously (increased height and branching) during hot and dry periods, particularly those species with a fast growth habit. Although seedling light-saturated photosynthetic capacity (Asat) and air temperature were unaffected by weed presence during hot and dry periods, afternoon light levels were reduced by approximately 50%, possibly indicative of lower leaf temperatures and improved seedling water status. Our results show that realizing the facilitative potential of weeds in semi-arid forest restoration requires minimizing mammalian herbivory and temporally separating competition for resources. Managing for intermediate but not excessive levels of forb canopy cover is likely required to reduce high radiation loads and reduce transpiration without adverse competitive effects. Longer-term experiments manipulating cover crop identity, cover and mammalian herbivory will inform whether forbs can be effectively exploited to enhance restoration success at large scales

Mir-132/212 is required for maturation of binocular matching of orientation preference and depth perception

MicroRNAs (miRNAs) are known to mediate post-transcriptional gene regulation, but their role in postnatal brain development is still poorly explored. We show that the expression of many miRNAs is dramatically regulated during functional maturation of the mouse visual cortex with miR-132/212 family being one of the top upregulated miRNAs. Age-downregulated transcripts are significantly enriched in miR-132/miR-212 putative targets and in genes upregulated in miR-132/212 null mice. At a functional level, miR-132/212 deletion affects development of receptive fields of cortical neurons determining a specific impairment of binocular matching of orientation preference, but leaving orientation and direction selectivity unaltered. This deficit is associated with reduced depth perception in the visual cliff test. Deletion of miR-132/212 from forebrain excitatory neurons replicates the binocular matching deficits. Thus, miR-132/212 family shapes the age-dependent transcriptome of the visual cortex during a specific developmental window resulting in maturation of binocular cortical cells and depth perception

Overview: Recent advances in the understanding of the northern Eurasian environments and of the urban air quality in China – a Pan-Eurasian Experiment (PEEX) programme perspective

The Pan-Eurasian Experiment (PEEX) Science Plan, released in 2015, addressed a need for a holistic system understanding and outlined the most urgent research needs for the rapidly changing Arctic-boreal region. Air quality in China, together with the long-range transport of atmospheric pollutants, was also indicated as one of the most crucial topics of the research agenda. These two geographical regions, the northern Eurasian Arctic-boreal region and China, especially the megacities in China, were identified as a "PEEX region". It is also important to recognize that the PEEX geographical region is an area where science-based policy actions would have significant impacts on the global climate. This paper summarizes results obtained during the last 5 years in the northern Eurasian region, together with recent observations of the air quality in the urban environments in China, in the context of the PEEX programme. The main regions of interest are the Russian Arctic, northern Eurasian boreal forests (Siberia) and peatlands, and the megacities in China. We frame our analysis against research themes introduced in the PEEX Science Plan in 2015. We summarize recent progress towards an enhanced holistic understanding of the land-atmosphere-ocean systems feedbacks. We conclude that although the scientific knowledge in these regions has increased, the new results are in many cases insufficient, and there are still gaps in our understanding of large-scale climate-Earth surface interactions and feedbacks. This arises from limitations in research infrastructures, especially the lack of coordinated, continuous and comprehensive in situ observations of the study region as well as integrative data analyses, hindering a comprehensive system analysis. The fast-changing environment and ecosystem changes driven by climate change, socio-economic activities like the China Silk Road Initiative, and the global trends like urbanization further complicate such analyses. We recognize new topics with an increasing importance in the near future, especially "the enhancing biological sequestration capacity of greenhouse gases into forests and soils to mitigate climate change" and the "socio-economic development to tackle air quality issues".Peer reviewe