Simulations of small-scale explosive events on the Sun

Small-scale explosive events or microflares occur throughout the chromospheric network of the Sun. They are seen as sudden bursts of highly Doppler shifted spectral lines of ions formed at temperatures in the range 2x10^4 - 5x10^5 K. They tend to occur near regions of cancelling photospheric magnetic fields and are thought to be directly associated with magnetic field reconnection. Recent observations have revealed that they have a bi-directional jet structure reminiscent of Petschek reconnection. In this paper compressible MHD simulations of the evolution of a current sheet to a steady Petschek, jet-like configuration are computed using the Versatile Advection Code. We obtain velocity profiles that can be compared with recent ultraviolet line profile observations. By choosing initial conditions representative of magnetic loops in the solar corona and chromosphere, it is possible to explain the fact that jets flowing outward into the corona are more extended and appear before jets flowing towards the chromosphere. This model can reproduce the high Doppler shifted components of the line profiles but the brightening at low velocities, near the centre of the bi-directional jet, cannot be explained by this simple MHD model.Comment: 16 pages, 8 figures. To be published in Solar Physic

Thermally induced coherence in a Mott insulator of bosonic atoms

Conventional wisdom is that increasing temperature causes quantum coherence to decrease. Using finite temperature perturbation theory and exact calculations for the strongly correlated bosonic Mott insulating state we show a practical counter-example that can be explored in optical lattice experiments: the short-range coherence of the Mott insulating phase can increase substantially with increasing temperature. We demonstrate that this phenomenon originates from thermally produced defects that can tunnel with ease. Since the near zero temperature coherence properties have been measured with high precision we expect these results to be verifiable in current experiments.Comment: 5 pages, 3 figure

Classification of hydro-meteorological conditions and multiple artificial neural networks for streamflow forecasting

Abstract. This paper presents the application of a modular approach for real-time streamflow forecasting that uses different system-theoretic rainfall-runoff models according to the situation characterising the forecast instant. For each forecast instant, a specific model is applied, parameterised on the basis of the data of the similar hydrological and meteorological conditions observed in the past. In particular, the hydro-meteorological conditions are here classified with a clustering technique based on Self-Organising Maps (SOM) and, in correspondence of each specific case, different feed-forward artificial neural networks issue the streamflow forecasts one to six hours ahead, for a mid-sized case study watershed. The SOM method allows a consistent identification of the different parts of the hydrograph, representing current and near-future hydrological conditions, on the basis of the most relevant information available in the forecast instant, that is, the last values of streamflow and areal-averaged rainfall. The results show that an adequate distinction of the hydro-meteorological conditions characterising the basin, hence including additional knowledge on the forthcoming dominant hydrological processes, may considerably improve the rainfall-runoff modelling performance

“I am not CF, I have CF”: Social Connection and Isolation During Young Adulthood With Cystic Fibrosis

Historically, individuals living with cystic fibrosis (CF) gathered strength and support attending summer camps, support groups, and community events. However, in 2003, medical guidelines recommended stringent separation of individuals with CF to reduce the risk of cross-infection and disease progression. This study seeks to examine the impact of these recommendations on the social experiences of young adults with CF. A qualitative, exploratory, grounded theory approach was employed to understand the experience of young adults living with CF, with specific emphasis on the impact of social connection and isolation on their lives. Semi-structured individual interviews were conducted with ten young adults aged 18 – 25 diagnosed with CF. An interview guide was used to elicit information about how individuals with CF understand, experience, and perceive contact and social isolation from others with CF, ways in which they experience their social worlds, and the impact isolation from others with CF has on their medical and psychosocial development during the young adult years. Interviews were digitally recorded, transcribed verbatim, and coded using grounded theory’s constant comparative method. Analysis identified the importance of social connection and isolation as a common theme, supported by young adults’ use of social media, familiarity with the infection prevention and control guidelines, relationships with their siblings, the value of their friendships, and supported autonomy. Participants struggled to define normal in their daily lives. Increased social work practitioners’ awareness of ways to support young adults with chronic illness to engage with the CF community may improve health and mental health outcomes

Two point correlations of a trapped interacting Bose gas at finite temperature

We develop a computationally tractable method for calculating correlation functions of the finite temperature trapped Bose gas that includes the effects of s-wave interactions. Our approach uses a classical field method to model the low energy modes and treats the high energy modes using a Hartree-Fock description. We present results of first and second order correlation functions, in position and momentum space, for an experimentally realistic system in the temperature range of $0.6T_c$ to $1.0T_c$. We also characterize the spatial coherence length of the system. Our theory should be applicable in the critical region where experiments are now able to measure first and second order correlations.Comment: 9 pages, 4 figure

Influence of sociality on allometric growth and morphological differentiation in sponge-dwelling alpheid shrimp

Eusocial societies are defined by a reproductive division of labour between breeders and nonbreeders that is often accompanied by morphological differentiation. Some eusocial taxa are further characterized by a subdivision of tasks among nonbreeders, often resulting in morphological differentiation among different groups (subcastes) that specialize on different sets of tasks. We investigated the possibility of morphological castes in eusocial shrimp colonies (Zuzalpheus, formerly part of Synalpheus) by comparing growth allometry and body proportions of three eusocial shrimp species with three pair-forming species (species where reproductive females and males occur in equal sex ratios). Allometry of eusocial species differed in several respects from that of pair-forming species in both lineages. First, allometry of fighting claw size among individuals other than female breeders was steeper in eusocial than in pair-forming species. Second, breeding females in eusocial colonies had proportionally smaller weapons (fighting claws) than females in pair-forming species. Finally, claw allometry changed with increasing colony size in eusocial species; large colonies showed a diphasic allometry of fighting claw and finger size, indicating a distinctive group of large individuals possessing relatively larger weapons than other colony members. Shrimp are thus similar to other eusocial animals in the morphological differentiation between breeders and nonbreeders, and in the indication that some larger nonbreeders might contribute more to defence than others. (C) 2008 The Linnean Society of London

Trends in Elasticity and Electronic Structure of Transition-Metal Nitrides and Carbides from First Principles

The elastic properties of the $B_1$-structured transition-metal nitrides and their carbide counterparts are studied using the {\it ab initio\} density functional perturbation theory. The linear response results of elastic constants are in excellent agreement with those obtained from numerical derivative methods, and are also consistent with measured data. We find the following trends: (1) Bulk moduli $B$ and tetragonal shear moduli $G^{\prime}=(C_{11}-C_{12})/2$, increase and lattice constants $a_{0}$ decrease rightward or downward on the Periodic Table for the metal component or if C is replaced by N; (2) The inequality $B > G^{\prime} > G > 0$ holds for $G=C_{44}$; (3) $G$ depends strongly on the number of valence electrons per unit cell ($Z_{V}$). From the fitted curve of $G$ as a function of $Z_{V}$, we can predict that MoN is unstable in $B_{1}$ structure, and transition-metal carbonitrides ($e.g.$ ZrC$_{x}$N$_{1-x}$) and di-transition-metal carbides ($e.g.$ Hf$_{x}$Ta$_{1-x}$C) have maximum $G$ at $Z_{V} \approx 8.3$.Comment: 4 pages, 2 figures, submitted to PRL. 2 typos in ref. 15 were correcte