Stability and dynamical behavior in a lake-model and implications for regime shifts in real lakes

A modified abstract version of the Comprehensive Aquatic Simulation Model (CASM) is found to exhibit three types of folded bifurcations due to nutrient loading. The resulting bifurcation diagrams account for nonlinear dynamics such as regime shifts and cyclic changes between clear-water state and turbid state that have actually been observed in real lakes. In particular, pulse-perturbation simulations based on the model presented suggest that temporal behaviors of real lakes after biomanipulations can be explained by pulse-dynamics in complex ecosystems, and that not only the amplitude (manipulated abundance of organisms) but also the phase (timing) is important for restoring lakes by biomanipulation. Ecosystem management in terms of possible irreversible changes in ecosystems induced by regime shifts is also discussed. (c) 2007 Elsevier B.V All rights reserved.

On the limits of spectral methods for frequency estimation

An algorithm is presented which generates pairs of oscillatory random time series which have identical periodograms but differ in the number of oscillations. This result indicates the intrinsic limitations of spectral methods when it comes to the task of measuring frequencies. Other examples, one from medicine and one from bifurcation theory, are given, which also exhibit these limitations of spectral methods. For two methods of spectral estimation it is verified that the particular way end points are treated, which is specific to each method, is, for long enough time series, not relevant for the main result.

Pattern formation of chevrons in the conduction regime in homeotropically aligned liquid crystals

We report on chevrons (herringbonelike patterns) observed in homeotropically aligned liquid crystals with high electric conductivity. We focus our attention on two types of chevrons observed in the conduction regime. The threshold voltage and the characteristic double periodicity of chevrons (i.e., the short wavelength lambda(1) of the striated rolls and the long wavelength lambda(2) Of the chevron bands) have been measured as functions of the applied electric frequency f. With the aid of a crossed polarizer set, we have, in addition, determined the director field which shows a periodic in-plane rotation for our chevrons (with a wavelength lambda(2)) We arrived at the types of chevrons after qualitatively different bifurcation sequences with increasing voltage. The frequency dependence of lambda(2) also shows a qualitatively different behavior with respect to the two types of chevrons. The experimental results are discussed in terms of recent theoretical investigations.

Nonlinear excitations in strongly-coupled plasma lattices: envelope solitons, kinks and intrinsic localized modes

Ensembles of charged particles (plasmas) are a highly complex form of matter, most often modeled as a many-body system characterized by weak inter-particle interactions (electrostatic coupling). However, strongly-coupled plasma configurations have recently been produced in laboratory, either by creating ultra-cold plasmas confined in a trap or by manipulating dusty plasmas in discharge experiments. In this paper, the nonlinear aspects involved in the motion of charged dust grains in a one-dimensional plasma monolayer (crystal) are discussed. Different types of collective excitations are reviewed, and characteristics and conditions for their occurrence in dusty plasma crystals are discussed, in a quasi-continuum approximation. Dust crystals are shown to support nonlinear kink-shaped supersonic solitary longitudinal excitations, as well as modulated envelope localized modes associated with longitudinal and transverse vibrations. Furthermore, the possibility for intrinsic localized modes (ILMs) — Discrete Breathers (DBs) — to occur is investigated, from first principles. The effect of mode-coupling is also briefly considered. The relation to previous results on atomic chains, and also to experimental results on strongly-coupled dust layers in gas discharge plasmas, is briefly discussed.

Creation of persistent, straight, 2 mm long laser driven channels in underdense plasmas

The experimental study of the behavior of deuterium plasma with densities between 2 X 1018 and 2 x 10(20) cm(-3), subjected to a 6 TW, 30 ps, 3 X 10(18) W cm(-2) laser pulse, is presented Conclusive experimental proof that a single straight channel is generated when the laser pulse interacts with the lowest densities is provided This channel shows no small-scale longitudinal density modulations, extends up to 2 mm in length and persists for up to 150 ps after the peak of the interaction Bifurcation of the channel after 1 mm propagation distance is observed for the first time For higher density interactions, above the relativistic self-focusing threshold, bubblelike structures are observed to form at late times These observations have implications for both laser wakefield accelerators and fast ignition inertial fusion studies (C) 2010 American Institute of Physics [doi 10 1063/1 3505305]

The PRISMA statement for reporting systematic reviews and meta-analyses of studies that evaluate health care interventions: Explanation and elaboration

Systematic reviews and meta-analyses are essential to summarize evidence relating to efficacy and safety of health care interventions accurately and reliably. The clarity and transparency of these reports, however, is not optimal. Poor reporting of systematic reviews diminishes their value to clinicians, policy makers, and other users. Since the development of the QUOROM (QUality Of Reporting Of Meta-analysis) Statement-a reporting guideline published in 1999-there have been several conceptual, methodological, and practical advances regarding the conduct and reporting of systematic reviews and meta-analyses. Also, reviews of published systematic reviews have found that key information about these studies is often poorly reported. Realizing these issues, an international group that included experienced authors and methodologists developed PRISMA ( Preferred Reporting Items for Systematic reviews and Meta-Analyses) as an evolution of the original QUOROM guideline for systematic reviews and meta-analyses of evaluations of health care interventions. The PRISMA Statement consists of a 27-item checklist and a four-phase flow diagram. The checklist includes items deemed essential for transparent reporting of a systematic review. In this Explanation and Elaboration document, we explain the meaning and rationale for each checklist item. For each item, we include an example of good reporting and, where possible, references to relevant empirical studies and methodological literature. The PRISMA Statement, this document, and the associated Web site (http://www.prisma-statement.org/) should be helpful resources to improve reporting of systematic reviews and metaanalyses.

Probing magnetic order in ultracold lattice gases

A forthcoming challenge in ultracold lattice gases is the simulation of quantum magnetism. That involves both the preparation of the lattice atomic gas in the desired spin state and the probing of the state. Here we demonstrate how a probing scheme based on atom-light interfaces gives access to the order parameters of nontrivial quantum magnetic phases, allowing us to characterize univocally strongly correlated magnetic systems produced in ultracold gases. This method, which is also nondemolishing, yields spatially resolved spin correlations and can be applied to bosons or fermions. As a proof of principle, we apply this method to detect the complete phase diagram displayed by a chain of (rotationally invariant) spin-1 bosons.

Ground state of low-dimensional dipolar gases: Linear and zigzag chains

We study the ground-state phase diagram of ultracold dipolar gases in highly anisotropic traps. Starting from a one-dimensional geometry, by ramping down the transverse confinement along one direction, the gas reaches various planar distributions of dipoles. At large linear densities, when the dipolar gas exhibits a crystal-like phase, critical values of the transverse frequency exist below which the configuration exhibits transverse patterns. These critical values are found by means of a classical theory, and are in full agreement with classical Monte Carlo simulations. The study of the quantum system is performed numerically with Monte Carlo techniques and shows that the quantum fluctuations smoothen the transition and make it completely disappear in a gas phase. These predictions could be experimentally tested and would allow one to reveal the effect of zero-point motion on self-organized mesoscopic structures of matter waves, such as the transverse pattern of the zigzag chain.

Bilinear-biquadratic spin-1 chain undergoing quadratic Zeeman effect

The Heisenberg model for spin-1 bosons in one dimension presents many different quantum phases, including the famous topological Haldane phase. Here we study the robustness of such phases in front of a SU(2) symmetry-breaking field as well as the emergence of unique phases. Previous studies have analyzed the effect of such uniaxial anisotropy in some restricted relevant points of the phase diagram. Here we extend those studies and present the complete phase diagram of the spin-1 chain with uniaxial anisotropy. To this aim, we employ the density-matrix renormalization group together with analytical approaches. The complete phase diagram can be realized using ultracold spinor gases in the Mott insulator regime under a quadratic Zeeman effect.

Physicochemical Characterization of Morpholinium Cation Based Protic Ionic Liquids Used As Electrolytes

New protic ionic liquids (PILs) based on the morpholinium, N-methylmorpholinium, and N-ethyl morpholinium cations have been synthesized through a simple and atom-economic neutralization reaction between N-alkyl morpholine and formic acid. Their densities, refractive indices, thermal properties, and electrochemical windows have been measured. The temperature dependence of their dynamic viscosity and ionic conductivity have also been determined. The results allow us to classify them according to a classical Walden diagram and to evaluate their “fragility”. In addition, morpholinium based PILs exhibit a large electrochemical window as compared to other protic ionic liquids (up 2.91 V) and possess relatively high ionic conductivities of 10-16.8 mS·cm-1 at 25 °C and 21-29 mS·cm-1 at 100 °C, and a residual conductivity close to 1.0 mS·cm-1 at -15 °C. PIL-water mixtures exhibit high ionic conductivities up to 65 mS·cm-1 at 25 °C and 120 mS·cm-1 at 100 °C for morpholinium formate with water weight fraction ww = 0.6. Morpholinium based PILs studied in this work have a low cost and low toxicity, are good ionic liquids, and prove extremely fragile. They have wide applicable perspectives as electrolytes for fuel cell devices, thermal transfer fluids, and acid-catalyzed reaction media as replacements of conventional solvents.

Phase behavior of mixtures of colloidal platelets and nonadsorbing polymers

The phase behavior of a model system of colloidal platelets and nonadsorbing polymers is studied using computer simulations and perturbation theory. The equation of state for the pure platelet reference system is obtained by Monte Carlo simulations, and the free volume fraction accessible to polymers is measured by a trial insertion method. The free volume fraction is also calculated using scaled particle theory. Subsequently, the phase diagram for platelet-polymer mixtures is calculated. For a platelet aspect ratio L/D=0.1 and a polymer to platelet size ratio d/D>0.2, we observe coexistence between two isotropic phases with different densities. For smaller polymers d/D

A 330-360 GHz spectral survey of G34.3+0.15 - III. The outer halo

We have undertaken a 330-360 GHz molecular line survey of the halo gas surrounding the hot core associated with G34.26+0.15. In contrast to our molecular line survey of the hot core itself, where 338 lines from at least 38 species were detected, only 18 lines from 9 species were detected in the halo. The lines are mainly single transitions of simple di atomic and triatomic molecules. Lower limits to their column densities have been evaluated by an LTE method. In the case of methanol, where four transitions were detected, the rotation temperature and column density have been evaluated by the rotation diagram technique. We have modified the previous depth-dependent chemical model developed in Paper II to calculate the column densities observed along a general line of sight drawn through the model cloud. The model is also extended to produce beam-averaged column densities for better comparison with those observed. We compare the model column densities with those observed and make recommendations for future depth-dependent chemical modelling of hot cores.

A 330-360 GHz spectral survey of G 34.3+0.15 .1. Data and physical analysis

A 330--360 GHz spectral survey of the hot molecular core associated with the 'cometary' ultracompact HII region G 34.3+/-0.15 observed with the James Clerk Maxwell Telescope has detected 338 spectral lines from at least 35 distinct chemical species plus 19 isotopomers. 70 lines remain unidentified. Chemical abundance and rotation temperature have been determined by rotation diagram analysis for 12 species, and lower limits to abundance found for 38 others.

Detection of Entanglement in Ultracold Lattice Gases

Probing non trivial magnetic ordering in quantum magnets realized with ultracold lattice gases demands detection methods with some spatial resolution built on it. Here we demonstrate that the Faraday matter-light interface provides an experimentally feasible tool to distinguish indubitably different quantum phases of a given many-body system in a non-demolishing way. We illustrate our approach by focussing on the Heisenberg chain for spin-1 bosons in the presence of a SU(2) symmetry breaking field. We explain how using the light signal obtained via homodyne detection one can reconstruct the phase diagram of the model. Further we show that the very same technique that provides a direct experimentally measurable signal of different order parameters can be extended to detect also the presence of multipartite entanglement in such systems.

The chemical composition of two supergiants in the dwarf irregular galaxy WLM

The chemical composition of two stars in WLM has been determined from high-quality Ultraviolet-Visual Echelle Spectrograph (UVES) data obtained at the VLT-UT2. The model atmospheres analysis shows that they have the same metallicity, [Fe/H] = - 0.38 +/- 0.20 (+/- 0.29). Reliable magnesium abundances are determined from several lines of two ionization states in both stars resulting in [Mg/Fe] = - 0.24 +/- 0.16 (+/- 0.28). This result suggests that the [alpha(Mg)/Fe] ratio in WLM may be suppressed relative to solar abundances ( also supported by differential abundances relative to similar stars in NGC 6822 and the Small Magellanic Cloud [SMC]). The absolute Mg abundance, [Mg/H] = -0.62, is high relative to what is expected from the nebulae though, where two independent spectroscopic analyses of the H II regions in WLM yield [O/H] = - 0.89. Intriguingly, the oxygen abundance determined from the O I lambda6158 feature in one WLM star is [O/H] = - 0.21 +/- 0.10 (+/- 0.05), corresponding to 5 times higher than the nebular oxygen abundance. This is the first time that a significant difference between stellar and nebular oxygen abundances has been found, and currently, there is no simple explanation for this difference. The two stars are massive supergiants with distances that clearly place them in WLM. They are young ( less than or equal to 10 Myr) and should have a similar composition to the ISM. Additionally, differential abundances suggest that the O/Fe ratio in the WLM star is consistent with similar stars in NGC 6822 and the SMC, galaxies where the average stellar oxygen abundances are in excellent agreement with the nebular results. If the stellar abundances reflect the true composition of WLM, then this galaxy lies well above the metallicity-luminosity relationship for dwarf irregular galaxies. It also suggests that WLM is more chemically evolved than currently interpreted from its color-magnitude diagram. The similarities between the stars in WLM and NGC 6822 suggest that these two galaxies may have had similar star formation histories.