Effects of nitrogen on benthic diatom assemblages in high-elevation Central and Eastern Alpine lakes.

We explored patterns of benthic-diatom composition across 62 high-elevation Alpine lakes spanning a wide range of nitrogen (N) concentrations due to atmospheric deposition and background variation in lake and watershed characteristics (e.g., land cover, bedrock geology, lake depth, and elevation). Our goals were to (i) assess the effect of lake-water N concentration on benthic-diatom composition during late summer or fall conditions and (ii) identify policy- relevant response thresholds. The analyses were carried out on an existing data set of diatom and water-chemistry data (EMERGE set), integrated with new data. Multivariate and correlation analyses revealed associations between pH, N concentration, and benthic-diatom composition, but the effects of pH and N were confounded. However, partial correlation analysis allowed us to identify ‘N-responsive diatoms’, i.e., diatom taxa with non-spurious association with N. Focusing on these taxa, we detected a decline in the abundance of taxa preferring low N concentrations and an increase in the abundance of taxa preferring high N concentrations starting at NO 3 concentrations of approximately 5 μmol L -1 . We interpreted this shift as an effect of watershed N saturation due to atmospheric N deposition. Based on the results, we suggest a concentration threshold of 5 μmol NO 3 L -1 during late-summer or fall to prevent change in benthic diatoms in high-elevation Alpine lakes affected by N deposition

AUTOMATIC ASSESSMENT OF LAKE STATUS USING AN OPEN SOURCE APPROACH: LAKE LUGANO'S CASE STUDY

Abstract. Climate change and human activities are increasingly threatening water resources. In particular sub-alpine lakes are fundamental not only for tourism or other economical activities, but also as a source of water. In this context, there is a strong need to monitor such resources to understand, study and react to known and unknown impacts, so that appropriate mitigation actions can be taken. Unfortunately, although monitoring data already exist for many of these lakes, the information is archived in different formats and servers undermining the full exploitation of data and preventing a more efficient data management. The aim of this work is to improve this situation by implementing a system that integrates and standardizes data coming from different sources. In addition, the system integrates web based tools that estimate lake state indicators using open source software and standard. Thanks to this system, it will be possible to exploit the data potential more fully. This paper focuses on the achievements reached by the research carried out on Lake Lugano in the context of the project SIMILE after two years of work

Collision of impurities with Bose-Einstein condensates

open5noQuantum dynamics of impurities in a bath of bosons is a long-standing problem of solid-state, plasma, and atomic physics. Recent experimental and theoretical investigations with ultracold atoms focused on this problem, studying atomic impurities immersed in a atomic Bose-Einstein condensate (BEC) and for various relative coupling strengths tuned by the Fano-Feshbach resonance technique. Here we report extensive numerical simulations on a closely related problem: the collision between a bosonic impurity made of few 41K atoms and a BEC made of 87Rb atoms in a quasi one-dimensional configuration and under a weak harmonic axial confinement. For small values of the interspecies interaction strength (no matter the sign of it), we find that the impurity, which starts from outside the BEC, simply oscillates back and forth the BEC cloud, but the frequency of oscillation depends on the interaction strength. For intermediate couplings, after a few cycles of oscillation the impurity is captured by the BEC and strongly changes its amplitude of oscillation. In the strong interaction regime, if the interspecies interaction is attractive, a local maximum (bright soliton) in the density of BEC occurs where the impurity is trapped; instead, if the interspecies interaction is repulsive, the impurity is not able to enter in the BEC cloud and the reflection coefficient is close to one. On the other hand, if the initial displacement of the impurity is increased, the impurity is able to penetrate in the cloud leading to the appearance of a moving hole (dark soliton) in the BEC.openLingua, F.; Lepori, L.; Minardi, F.; Penna, V.; Salasnich, L.Lingua, F.; Lepori, Luca; Minardi, F.; Penna, V.; Salasnich, L

Two-kink bound states in the magnetically perturbed Potts field theory at T<Tc

The q-state Potts field theory with $2\le q\le 4$ in the low-temperature phase is considered in presence of a weak magnetic field h. In absence of the magnetic field, the theory is integrable, but not free at q>2: its elementary excitations - the kinks - interact at small distances, and their interaction can be characterized by the factorizable scattering matrix which was found by Chim and Zamolodchikov. The magnetic field induces the long-range attraction between kinks causing their confinement into the bound-states. We calculate the masses of the two-kink bound states in the leading order in |h| -> 0 expressing them in terms of the scattering matrix of kinks at h=0.Comment: 20 pages, no figures, v2: one section and references adde

't Hooft tensor for generic gauge group

We study monopoles in gauge theories with generic gauge group. Magnetic charges are in one-to-one correspondence with the second homotopy classes at spatial infinity (${\Pi}_2$), which are therefore identified by the 't Hooft tensor. We determine the 't Hooft tensor in the general case. These issues are relevant to the understanding of Color Confinement.Comment: 5 pages. Contribution to the Conference QCD08, Montpellier 7-12 July 2008 To appear in the proceeding

(3+1) Massive Dirac Fermions with Ultracold Atoms in Optical Lattices

We propose the experimental realization of (3+1) relativistic Dirac fermions using ultracold atoms in a rotating optical lattice or, alternatively, in a synthetic magnetic field. This approach has the advantage to give mass to the Dirac fermions by coupling the ultracold atoms to a Bragg pulse. A dimensional crossover from (3+1) to (2+1) Dirac fermions can be obtained by varying the anisotropy of the lattice. We also discuss under which conditions the interatomic potentials give rise to relativistically invariant interactions among the Dirac fermions

Management of patient dose and image noise in routine pediatric CT abdominal examinations

The aim was to propose a strategy for finding reasonable compromises between image noise and dose as a function of patient weight. Weighted CT dose index (CTDIw) was measured on a multidetector-row CT unit using CTDI test objects of 16, 24 and 32cm in diameter at 80, 100, 120 and 140kV. These test objects were then scanned in helical mode using a wide range of tube currents and voltages with a reconstructed slice thickness of 5mm. For each set of acquisition parameter image noise was measured and the Rose model observer was used to test two strategies for proposing a reasonable compromise between dose and low-contrast detection performance: (1) the use of a unique noise level for all test object diameters, and (2) the use of a unique dose efficacy level defined as the noise reduction per unit dose. Published data were used to define four weight classes and an acquisition protocol was proposed for each class. The protocols have been applied in clinical routine for more than one year. CTDIvol values of 6.7, 9.4, 15.9 and 24.5mGy were proposed for the following weight classes: 2.5-5, 5-15, 15-30 and 30-50kg with image noise levels in the range of 10-15HU. The proposed method allows patient dose and image noise to be controlled in such a way that dose reduction does not impair the detection of low-contrast lesions. The proposed values correspond to high- quality images and can be reduced if only high-contrast organs are assesse