Localization Effect in a 2D Superconducting Network without Disorder

The superconducting properties of a two-dimensional superconducting wire network with a new geometry have been measured as a function of the external magnetic field. The extreme localization effect recently predicted for this periodic lattice is revealed as a suppression of the critical current when the applied magnetic field corresponds to half a flux quantum per unit cell. For this particular magnetic field, the observed vortex state configuration is highly disordered.Comment: 6 pages, 2 eps figures, submitted to Physica C. Title change

Phase Diagram of the Bose-Hubbard Model with T_3 symmetry

In this paper we study the quantum phase transition between the insulating and the globally coherent superfluid phases in the Bose-Hubbard model with T_3 structure, the "dice lattice". Even in the absence of any frustration the superfluid phase is characterized by modulation of the order parameter on the different sublattices of the T_3 structure. The zero-temperature critical point as a function of a magnetic field shows the characteristic "butterfly" form. At fully frustration the superfluid region is strongly suppressed. In addition, due to the existence of the Aharonov-Bohm cages at f=1/2, we find evidence for the existence of an intermediate insulating phase characterized by a zero superfluid stiffness but finite compressibility. In this intermediate phase bosons are localized due to the external frustration and the topology of the T_3 lattice. We name this new phase the Aharonov-Bohm (AB) insulator. In the presence of charge frustration the phase diagram acquires the typical lobe-structure. The form and hierarchy of the Mott insulating states with fractional fillings, is dictated by the particular topology of the T_3 lattice. The results presented in this paper were obtained by a variety of analytical methods: mean-field and variational techniques to approach the phase boundary from the superconducting side, and a strongly coupled expansion appropriate for the Mott insulating region. In addition we performed Quantum Monte Carlo simulations of the corresponding (2+1)D XY model to corroborate the analytical calculations with a more accurate quantitative analysis. We finally discuss experimental realization of the T_3 lattice both with optical lattices and with Josephson junction arrays.Comment: 16 pages, 17 figure

Biological and physical forcing of carbonate chemistry in an upwelling filament off northwest Africa: Results from a Lagrangian study

The Mauritanian upwelling system is one of the most biologically productive regions of the world's oceans. Coastal upwelling transfers nutrients to the sun-lit surface ocean, thereby stimulating phytoplankton growth. Upwelling of deep waters also supplies dissolved inorganic carbon (DIC), high levels of which lead to low calcium carbonate saturation states in surface waters, with potentially adverse effects on marine calcifiers. In this study an upwelled filament off the coast of northwest Africa was followed using drifting buoys and sulphur hexafluoride to determine how the carbonate chemistry changed over time as a result of biological, physical and chemical processes. The initial pHtot in the mixed layer of the upwelled plume was 7.94 and the saturation states of calcite and aragonite were 3.4 and 2.2, respectively. As the plume moved offshore over a period of 9 days, biological uptake of DIC (37 ?mol kg?1) reduced pCO2 concentrations from 540 to 410 ?atm, thereby increasing pHtot to 8.05 and calcite and aragonite saturation states to 4.0 and 2.7 respectively. The increase (25 ?mol kg?1) in total alkalinity over the 9 day study period can be accounted for solely by the combined effects of nitrate uptake and processes that alter salinity (i.e., evaporation and mixing with other water masses). We found no evidence of significant alkalinity accumulation as a result of exudation of organic bases by primary producers. The ongoing expansion of oxygen minimum zones through global warming will likely further reduce the CaCO3 saturation of upwelled waters, amplifying any adverse consequences of ocean acidification on the ecosystem of the Mauritanian upwelling system

Model test of the DTI-Floating wind concept

This study aims to de-risk the development of the Deep Turbine Installation-Floating (DTI-F) concept, a hybrid spar buoy-based floating offshore wind turbine with the novelty of being able to raise up and lower down the tower plus nacelle set. The paper presents the design and construction of a Froude-scaled model based on the DTI-F concept, the experimental testing configurations and conditions, and the instrumentation used to measure motions and loads. The test campaign included free decay and stiffness decay tests, along with regular and irregular wave testing. In addition to the hydrodynamic characterisation, the resonance properties of the system with different mooring configurations, i.e. three and four lines, and three lines with a delta connection, were investigated. We present the Response Amplitude Operators (RAOs) in all 6 degrees of freedom for two different mooring configurations. This work is the first step towards the calibration and performance improvement for existing numerical models of the DTI-F concept

Informal formative assessment in inquiry-based science lessons

This paper is focused on the characterization of informal formative assessment conversations (i.e., interactions on-the-fly) from a methodological perspective. Interactions on-the-fly are unexpected teachable moments in which the teacher tries to probe students’ understanding and use that information to support their inquiry process. One of the coding systems used (ESRU framework) was adopted from the research literature (Ruiz-Primo & Furtak, 2007). Two other systems described here were developed and previously reported in two papers written by the authors (Correia, Nieminen, Serret, Hähkiöniemi, Viiri, & Harrison, in press; Nieminen, Hähkiöniemi, Leskinen, & Viiri, 2016). This paper presents these three coding systems together and discusses their features to characterize interactions on-the-fly. Examples for coding interactions on-the-fly from Finnish and English physics lessons are presented. For example, on the one hand, on-the-fly discussion proceeds as follows: The teacher initiates an on-the-fly episode by eliciting information using an open-ended (divergent) question, as the discussion progresses the teacher starts narrowing down the discussion using a closed-ended question (convergent), and closes the discussion by giving a short mini lecture. On the other hand, when guiding students’ inquiry, the teacher can collect information rapidly (quick interpretation) or he/she can use series of probing questions (further probing). In the former, the guidance is more authoritative as it is based on correspondence of the students’ and the teacher’s ideas. In the latter, guidance is based more on the student’s ideas representing more dialogic way to support learning

Search for histopathological characteristics of inflammatory juvenile conjunctival nevus in conjunctival nevi related to age : Analysis of 33 cases

Conjunctival nevi in young individuals can correspond to the entity named Inflammatory Juvenile Conjunctival Nevus (IJCN), presenting clinically as a rapid growth lesion, and showing at the histopathological study an inflammatory infiltrate surrounding the lesion. All these findings can suggest a diagnosis of malignancy. Due to a case of IJCN diagnosed in our Pathology department, we realized that this entity is rarely reported in the literature and histopathological diagnostic criteria are not well defined. The aim of our study is to compare the histopathological characteristics of conjunctival nevi in patients aged thirty years or less to those in patients above 30 years, looking for the findings described in IJCN. All the excisional specimens of resected conjunctival nevus in a tertiary hospital from 2000 to 2018 were retrieved from the Pathology department archives. Demographic data were recorded, and histopathological variables (histological type of nevus, lymphocytic infiltration, eosinophilic infiltration, presence of lymphoid follicles, stromal nevomelanocytic component, intraepithelial nevomelanocytic component, epithelial inclusions, quantity of goblet cells in epithelial inclusions, cellular atypia, mitoses and maturation of the lesion) were evaluated by three independent observers. Statistical analysis was performed comparing the two age groups. The study determined a significant predominance of the lymphocytic and eosinophilic infiltration in the group of patients aged thirty years or less respect to the elderly group. The percentage of stromal component of the lesion is larger in patients over thirty years compared to the younger group. There was no correlation between epithelial inclusions, maturation or cytological atypia and age groups. We found some histopathological differences in conjunctival nevi related to young age, some of them coincident with the ones described in IJCN, which histopathologically could lead to a misleading diagnosis. However, we did not find significant differences related to age in many of the described histopathological findings described in IJCN. Larger series with a greater number of cases would be of interest to characterize more precisely this lesion

Projective dynamics and classical gravitation

Given a real vector space V of finite dimension, together with a particular homogeneous field of bivectors that we call a "field of projective forces", we define a law of dynamics such that the position of the particle is a "ray" i.e. a half-line drawn from the origin of V. The impulsion is a bivector whose support is a 2-plane containing the ray. Throwing the particle with a given initial impulsion defines a projective trajectory. It is a curve in the space of rays S(V), together with an impulsion attached to each ray. In the simplest example where the force is identically zero, the curve is a straight line and the impulsion a constant bivector. A striking feature of projective dynamics appears: the trajectories are not parameterized. Among the projective force fields corresponding to a central force, the one defining the Kepler problem is simpler than those corresponding to other homogeneities. Here the thrown ray describes a quadratic cone whose section by a hyperplane corresponds to a Keplerian conic. An original point of view on the hidden symmetries of the Kepler problem emerges, and clarifies some remarks due to Halphen and Appell. We also get the unexpected conclusion that there exists a notion of divergence-free field of projective forces if and only if dim V=4. No metric is involved in the axioms of projective dynamics.Comment: 20 pages, 4 figure

Respiration, phytoplankton size and the metabolic balance in the Atlantic gyres

The balance between plankton photosynthesis (GPP) and community respiration (CR) in the euphotic zone (net community production, NCP) is an essential driver of the biological carbon pump. Deficient datasets and a lack of knowledge of the mechanisms regulating CR cause poor empirical models and oversimplified parameterisations that maintain NCP as one of the most important unknowns for projections of the carbon pump. One important unresolved issue is the unexpected lack of empirical relationships between CR and the biomass or size-structure of the phytoplankton, which undermines the use of remotely sensed observations to predict net community metabolism. Here we analyse the spatial variation of plankton metabolism, chlorophyll a concentration (Chla), pico- and nanophytoplankton abundance and size-fractionated primary production (14CPP) along a latitudinal (49°N–46°S) transect of 73 stations across the Atlantic Ocean (AMT-22 cruise). The use of depth-weighted rates (rates integrated to the depth of 0.1% PAR, divided by the regionally varying depth of integration) markedly improved the depiction of latitudinal patterns and the significance of relationships, over volumetric or integrated rates. Depth-weighted CR showed clear and consistent latitudinal patterns with relevance for the distribution of NCP. Depth-weighted Chla and CR exhibited a significant relationship (CRZ=1.42ChlaZ-0.21, r2 = 0.69, N=37, p<0.001) with potential for the difficult prediction of CR. A general ratio of 1.42 mmolO2 mgChla-1 d-1 and a threshold Chla for net heterotrophy of ca. 0.25 mgChla m-3 can be tentatively proposed for the Atlantic, although further analyses of spatial and seasonal variation are necessary. We observed unusually positive NCP rates in the central part of the N gyre, due to a marked decrease of CR in a patch of high Synechococcus spp. abundance and high 14CPP by large phytoplankton. However, no relationship was observed between size-fractionated 14CPP and CR or the GPP : CR ratio during the cruise, contradicting the hypothesis that food web functioning is determined by the phytoplankton size structure. Such independence, together with the persistence of distinct GPP : CR and 14CPP : NCP relationships in distinct biogeographic provinces suggest a resilience of trophic dynamics and the existence of alternative ecosystem states, whose implications for projections of the metabolic state of the ocean are discussed