On the formation of coronal cavities

A theoretical study of the formation of a coronal cavity and its relation to a quiescent prominence is presented. It is argued that the formation of a cavity is initiated by the condensation of plasma which is trapped by the coronal magnetic field in a closed streamer and which then flows down to the chromosphere along the field lines due to lack of stable magnetic support against gravity. The existence of a coronal cavity depends on the coronal magnetic field strength; with low strength, the plasma density is not high enough for condensation to occur. Furthermore, we suggest that prominence and cavity material is supplied from the chromospheric level. Whether a coronal cavity and a prominence coexist depends on the magnetic field configuration; a prominence requires stable magnetic support

Disruption of Helmet Streamers by Current Emergence

We have investigated the dynamic response of a coronal helmet streamer to the emergence from below of a current with its magnetic field in a direction opposite to the overlying streamer field. Once the emerging current moves into the closed region of the streamer, a current sheet forms between the emerging field and the streamer field, because the preexisting field and the newly emerging field have opposite polarities. Thus magnetic reconnection will occur at the flanks of the emerged structure where the current density is maximum. If the emerging current is large enough, the energy contained in the current and the reconnection will promptly disrupt the streamer. If the emerging current is small, the streamer will experience a stage of slow evolution. In this stage, slow magnetic reconnection occurring at the flanks of the emerged structure leads to the degeneration of the emerged current to a neutral point. Above this point, a new magnetic bubble will form. The resulting configuration resembles an inverse-polarity prominence. Depending on the initial input energy of the current, the resulting structure will either remain in situ, forming a quasi-static structure, or move upward, forming a coronal transient similar to coronal jets. The numerical method used in this paper can be used to construct helmet streamers containing a detached magnetic structure in their closed field region. The quasi-static solution may serve as a preevent corona for studying coronal mass ejection initiation

Disruption of Helmet Streamers by Current Emergence

We have investigated the dynamic response of a coronal helmet streamer to the emergence from below of a current with its magnetic field in a direction opposite to the overlying streamer field. Once the emerging current moves into the closed region of the streamer, a current sheet forms between the emerging field and the streamer field, because the preexisting field and the newly emerging field have opposite polarities. Thus magnetic reconnection will occur at the flanks of the emerged structure where the current density is maximum. If the emerging current is large enough, the energy contained in the current and the reconnection will promptly disrupt the streamer. If the emerging current is small, the streamer will experience a stage of slow evolution. In this stage, slow magnetic reconnection occurring at the flanks of the emerged structure leads to the degeneration of the emerged current to a neutral point. Above this point, a new magnetic bubble will form. The resulting configuration resembles an inverse-polarity prominence. Depending on the initial input energy of the current, the resulting structure will either remain in situ, forming a quasi-static structure, or move upward, forming a coronal transient similar to coronal jets. The numerical method used in this paper can be used to construct helmet streamers containing a detached magnetic structure in their closed field region. The quasi-static solution may serve as a preevent corona for studying coronal mass ejection initiation

Cooperation and sensitivity to social feedback during group interactions in schizophrenia

Patients with schizophrenia show reduced cooperation and less sensitivity to social cues in pairwise interactions, however, it remains unclear whether these mechanisms are also present in interactions within social groups. We used a public goods game to investigate cooperation and sensitivity to social feedback in group interactions in 27 patients with schizophrenia and 27 healthy controls. Participants played 40 trials in two conditions: 1) no fine (20 trials): participants had the choice of investing into the public good (i.e. cooperating) or not (i.e. defecting), 2) fine (20 trials): participants had the same choice but defectors could be punished by the other players. On the first trial, patients invested less in the public good than healthy controls. In the no fine condition, controls decreased their investments over time, but patients did not. The possibility of being fined for defecting and actually being fined led to significantly higher cooperation in both groups. This shows that the groups were equally sensitive to social enforcement and social feedback. Our findings suggest that patients tend to approach social group interactions with less cooperative behaviour, which could contribute to social dysfunction in daily-life. However, an intact sensitivity to social enforcement and feedback indicates that patients can adjust their behaviour accordingly in group interactions

Direct Observation of Sub-Poissonian Number Statistics in a Degenerate Bose Gas

We report the direct observation of sub-Poissonian number fluctuation for a degenerate Bose gas confined in an optical trap. Reduction of number fluctuations below the Poissonian limit is observed for average numbers that range from 300 to 60 atoms.Comment: 5 pages, 4 figure

A long-lived coronal X-ray arcade

A large, long-lived, soft X-ray emitting arch system observed during a Skylab mission is analyzed. The supposition is that these arches owe their stability to the stable coronal magnetic-field configuration. A global constant alpha force-free magnetic field analysis, is used to describe the arches which stayed in the same approximate position for several solar rotations. A marked resemblance is noted between the theoretical magnetic field configuration and the observed X-ray emmitting feature

Half-Metallic Ferrimagnetism in Mn_2VAl

We show that Mn_2VAl is a compound for which the generalized gradient approximation (GGA) to the exchange-correlation functional in density functional theory makes a qualitative change in predicted behavior compared to the usual local density approximation (LDA). Application of GGA leads to prediction of Mn_2VAl being a half-metallic ferrimagnet, with the minority channel being the conducting one. The electronic and magnetic structure is analyzed and contrasted with the isostructural enhanced semimetal Fe_2VAl.Comment: 5 pages, Latex, 6 postscript figures. Description and figures of the (minority) Fermi surfaces have been adde

Shifting Home Energy Consumption Through a Holistic Understanding of the Home System of Practice

This chapter describes the concept of the home system of practice, which can be used to provide a deeper understanding of the social system of the home and inform long-term solutions for enabling domestic energy reduction. More traditional methods have attempted to persuade occupants to change behaviour through the use of information campaigns and feedback technology. However, these interventions are usually short lived as they ignore the underlying reasons for practices to occur. A more effective solution is through practice-oriented design, which co-creates innovative technology with the user. In addition, the emergence and use of automated technology enables practices to act independently of the user. Yet, the success of automation is also reliant on an understanding of the home system of practice, occupant needs and skills

Slater-Pauling Behavior of the Half-Ferromagnetic Full-Heusler Alloys

Using the full-potential screened Korringa-Kohn-Rostoker method we study the full-Heusler alloys based on Co, Fe, Rh and Ru. We show that many of these compounds show a half-metallic behavior, however in contrast to the half-Heusler alloys the energy gap in the minority band is extremely small. These full-Heusler compounds show a Slater-Pauling behavior and the total spin-magnetic moment per unit cell (M_t) scales with the total number of valence electrons (Z_t) following the rule: M_t=Z_t-24. We explain why the spin-down band contains exactly 12 electrons using arguments based on the group theory and show that this rule holds also for compounds with less than 24 valence electrons. Finally we discuss the deviations from this rule and the differences compared to the half-Heusler alloys.Comment: 10 pages, 8 figures, revised figure 3, new text adde