Daily entropy of dissolved oxygen reveals different energetic regimes and drivers among high‐mountain stream types

High‐resolution time series of dissolved oxygen (DO) have revealed different ecosystem energetics regimes across various stream types. Ecosystem energetic regimes are relevant to better understand the transformation and retention of nutrients and carbon in stream ecosystems. However, the patterns and controls of stream energetics in high‐mountain landscapes remain largely unknown. Here we monitored percent DO saturation (every 10 min) over 2 years in a glacier‐fed, krenal (groundwater‐fed) and a nival (snowmelt‐fed) stream as they are typical for the high mountains. We used daily Shannon entropy to explore the temporal dynamics of stream water DO and to infer information on the ecosystem energetics and on the potential drivers. We found that discharge modulated the drivers of DO variations at daily and seasonal scales. Elevated bed movement along with high turbidity and very high gas exchange rates drove the daily DO patterns in the glacier‐fed stream during snow and ice melt, whereas light seemed to drive DO dynamics in the krenal and nival streams. We found a window of favorable conditions for potential gross primary production (GPP) during the onset of the snowmelt in the glacier‐fed stream, whereas potential GPP seemed to extend over longer periods in the krenal and nival streams. Our findings suggest how the energetic regimes of these high‐mountain streams may change in the future as their biological and physical drivers change owing to climate warming

Quantitative Determination of Temperature in the Approach to Magnetic Order of Ultracold Fermions in an Optical Lattice

We perform a quantitative simulation of the repulsive Fermi-Hubbard model using an ultracold gas trapped in an optical lattice. The entropy of the system is determined by comparing accurate measurements of the equilibrium double occupancy with theoretical calculations over a wide range of parameters. We demonstrate the applicability of both high-temperature series and dynamical mean-field theory to obtain quantitative agreement with the experimental data. The reliability of the entropy determination is confirmed by a comprehensive analysis of all systematic errors. In the center of the Mott insulating cloud we obtain an entropy per atom as low as 0.77k(B) which is about twice as large as the entropy at the Neel transition. The corresponding temperature depends on the atom number and for small fillings reaches values on the order of the tunneling energy

The measurement of primary productivity in a high-rate oxidation pond (HROP)

A high-rate oxidation pond is studied as a model system for comparing 14C and oxygen evolution methods as tools for measuring primary productivity in hypertrophic aquatic systems. Our results indicate that at very dense algal populations (up to 5 mg chl. a l−1) and high photosynthetic rates, 14C based results may severely underestimate primary productivity, unless a way is found to keep incubation times very short. Results obtained with our oxygen electrode were almost an order of magnitude higher than those obtained by all 14C procedures. These higher values correspond fairly well with a field-tested computer-simulation model, as well as with direct harvest data obtained at the same pond when operated under similar conditions. The examination of the size-fractionation of the photosynthetic activity underscored the important contribution of nannoplanktonic algae to the total production of the syste

Säume wirken sich positiv auf die Gliedertiere aus

Im Rahmen des Teilprojektes «Wirkung neu angelegter Säume auf die Laufkäfer- und Spinnenfauna» wurden die Auswirkungen der Säume auf die Bodenarthropoden, insbesondere Laufkäfer und Spinnen, untersucht. Im Klettgau (SH) und in Litzibuch (AG) wurden jeweils zwei Säume und als Vergleichselemente zwei Buntbrachen und zwei Wegrandstreifen herangezogen. Die ausgewählten Bioindikatoren Laufkäfer und Spinnen, sowie als Beifänge Wanzen und Zikaden, wurden mit Bodenfallen erfasst. An 12 Standorten konnten insgesamt 21’000 Laufkäfer aus 93 Arten, 11’000 Spinnen aus 100 Arten, 44 Wanzenarten mit 1’691 Individuen sowie 29 Zikadenarten mit 270 Individuen festgestellt werden. Im Vergleich mit den Buntbrachen und mit den Wegrandstreifen nahmen die Säume eine mittlere Stellung ein. Die Säume boten sowohl den für Brache typischen Arthropodenarten als auch Grünlandspezialisten einen Lebensraum an. Sie stellen eine wertvolle Ergänzung zu Buntbrachen und Wiesen dar. Ausserdem tragen sie somit zur Erhöhung und Erhaltung der Artenvielfalt von Laufkäfern, Bodenspinnen, Bodenwanzen sowie Zikaden in der Agrarlandschaft bei

Creating, moving and merging Dirac points with a Fermi gas in a tunable honeycomb lattice

Dirac points lie at the heart of many fascinating phenomena in condensed matter physics, from massless electrons in graphene to the emergence of conducting edge states in topological insulators [1, 2]. At a Dirac point, two energy bands intersect linearly and the particles behave as relativistic Dirac fermions. In solids, the rigid structure of the material sets the mass and velocity of the particles, as well as their interactions. A different, highly flexible approach is to create model systems using fermionic atoms trapped in the periodic potential of interfering laser beams, a method which so far has only been applied to explore simple lattice structures [3, 4]. Here we report on the creation of Dirac points with adjustable properties in a tunable honeycomb optical lattice. Using momentum-resolved interband transitions, we observe a minimum band gap inside the Brillouin zone at the position of the Dirac points. We exploit the unique tunability of our lattice potential to adjust the effective mass of the Dirac fermions by breaking inversion symmetry. Moreover, changing the lattice anisotropy allows us to move the position of the Dirac points inside the Brillouin zone. When increasing the anisotropy beyond a critical limit, the two Dirac points merge and annihilate each other - a situation which has recently attracted considerable theoretical interest [5-9], but seems extremely challenging to observe in solids [10]. We map out this topological transition in lattice parameter space and find excellent agreement with ab initio calculations. Our results not only pave the way to model materials where the topology of the band structure plays a crucial role, but also provide an avenue to explore many-body phases resulting from the interplay of complex lattice geometries with interactions [11, 12]

A comparison of benthic macroinvertebrate assemblages among different types of alpine streams

SUMMARY 1. Benthic macroinvertebrate assemblages were compared among a diverse array of firstorder alpine tundra streams of the Swiss Alps. 2. A principal components analysis separated sites into three main groups: rhithral streams, rhithral lake outlets, and kryal sites including outlets and streams. Rhithral streams contained the most diverse and taxon rich assemblages, being colonised by both non-insect taxa and Ephemeroptera, Plecoptera, Trichoptera and Diptera. 3. Rhithral lake outlets supported high densities of non-insect taxa such as Oligochaeta, Nemathelminthes and crustaceans. Despite low taxon richness, kryal sites had high Ephemeroptera and Plecoptera abundances. Chironomidae were most common at all sites. 4. Collector-gatherers were dominant at all sites, whereas filter-feeders were rare. Scrapers and shredders were more common in streams than lake outlets. 5. Water temperature and algal standing crops were higher at rhithral lake outlets than rhithral streams, perhaps providing more favourable habitat for non-insect taxa. Glacial runoff was the dominant factor influencing macroinvertebrate assemblages of kryal streams and kryal lake outlets. Alpine lakes influenced the environmental conditions of their outlets and, consequently, their macroinvertebrate assemblages unless being constrained by a glacial influence

ALA- and ALA-hexylester-induced protoporphyrin IX fluorescence and distribution in multicell tumour spheroids

Synthesis of protoporphyrin IX (PpIX) in intact murine mammary cancer cell spheroids is reported from optical sections obtained using a laser scanning confocal fluorescence microscope. EMT6 spheroids 275–350 μ m in diameter were incubated in 0.1–15 mM aminolevulinic acid (ALA) or 0.001–2 mM ALA-hexylester (h-ALA) to test the ability of both pro-drugs to diffuse into the spheroids and induce PpIX production. Spheroids incubated with ALA show significant fluorescence nonuniformity for all concentrations, with the outermost cells exhibiting greater porphyrin fluorescence. Comparable levels of fluorescence throughout the optical section are achieved with approximately 100-fold lower h-ALA concentrations, indicating that the interior cells maintain esterase activity and porphyrin synthesis and that h-ALA diffuses efficiently to the spheroid interior. Fluorescence gradients are less pronounced with h-ALA incubation, in part because of apparent saturation of esterase activity in the spheroid perimeter. Proliferating (Ki67 positive) and quiescent cell populations exhibit remarkably different h-ALA concentration dependencies. The incubation concentration resulting in maximum fluorescence with ALA is 10 mM, while the optimal concentration for h-ALA is 200-fold lower at 0.05 mM. Exceeding these optimal concentrations for both pro-drugs leads to an overall loss of fluorescence. © 2001 Cancer Research Campaign http://www.bjcancer.co

Artificial graphene as a tunable Dirac material

Artificial honeycomb lattices offer a tunable platform to study massless Dirac quasiparticles and their topological and correlated phases. Here we review recent progress in the design and fabrication of such synthetic structures focusing on nanopatterning of two-dimensional electron gases in semiconductors, molecule-by-molecule assembly by scanning probe methods, and optical trapping of ultracold atoms in crystals of light. We also discuss photonic crystals with Dirac cone dispersion and topologically protected edge states. We emphasize how the interplay between single-particle band structure engineering and cooperative effects leads to spectacular manifestations in tunneling and optical spectroscopies.Comment: Review article, 14 pages, 5 figures, 112 Reference

An efficient system for the generation of marked genetic mutants in members of the genus Burkholderia

To elucidate the function of a gene in bacteria it is vital that targeted gene inactivation (allelic replacement) can be achieved. Allelic replacement is often carried out by disruption of the gene of interest by insertion of an antibiotic-resistance marker followed by subsequent transfer of the mutant allele to the genome of the host organism in place of the wild-type gene. However, due to their intrinsic resistance to many antibiotics only selected antibiotic-resistance markers can be used in members of the genus Burkholderia, including the Burkholderia cepacia complex (Bcc). Here we describe the construction of improved antibiotic-resistance cassettes that specify resistance to kanamycin, chloramphenicol or trimethoprim effectively in the Bcc and related species. These were then used in combination with and/or to construct a series enhanced suicide vectors, pSHAFT2, pSHAFT3 and pSHAFT-GFP to facilitate effective allelic replacement in the Bcc. Validation of these improved suicide vectors was demonstrated by the genetic inactivation of selected genes in the Bcc species Burkholderia cenocepacia and B. lata, and in the non-Bcc species, B. thailandensis

Development of an erythropoietin prescription simulator to improve abilities for the prescription of erythropoietin stimulating agents: Is it feasible?

BACKGROUND: The increasing use of erythropoietins with long half-lives and the tendency to lengthen the administration interval to monthly injections call for raising awareness on the pharmacokinetics and risks of new erythropoietin stimulating agents (ESA). Their pharmacodynamic complexity and individual variability limit the possibility of attaining comprehensive clinical experience. In order to help physicians acquiring prescription abilities, we have built a prescription computer model to be used both as a simulator and education tool. METHODS: The pharmacokinetic computer model was developed using Visual Basic on Excel and tested with 3 different ESA half-lives (24, 48 and 138 hours) and 2 administration intervals (weekly vs. monthly). Two groups of 25 nephrologists were exposed to the six randomised combinations of half-life and administration interval. They were asked to achieve and maintain, as precisely as possible, the haemoglobin target of 11-12 g/dL in a simulated naïve patient. Each simulation was repeated twice, with or without randomly generated bleeding episodes. RESULTS: The simulation using an ESA with a half-life of 138 hours, administered monthly, compared to the other combinations of half-lives and administration intervals, showed an overshooting tendency (percentages of Hb values > 13 g/dL 15.8 ± 18.3 vs. 6.9 ± 12.2; P < 0.01), which was quickly corrected with experience. The prescription ability appeared to be optimal with a 24 hour half-life and weekly administration (ability score indexing values in the target 1.52 ± 0.70 vs. 1.24 ± 0.37; P < 0.05). The monthly prescription interval, as suggested in the literature, was accompanied by less therapeutic adjustments (4.9 ± 2.2 vs. 8.2 ± 4.9; P < 0.001); a direct correlation between haemoglobin variability and number of therapy modifications was found (P < 0.01). CONCLUSIONS: Computer-based simulations can be a useful tool for improving ESA prescription abilities among nephrologists by raising awareness about the pharmacokinetic characteristics of the various ESAs and recognizing the factors that influence haemoglobin variability