300 research outputs found
Wave modes excited by photospheric p-modes and mode conversion in a multi-loop system
Context. Waves are ubiquitous in the solar corona and there are indications
that they are excited by photospheric p-modes. However, it is unclear how
p-modes in coronal loops are converted to sausage modes and transverse (kink)
modes, which are observed in the corona. Aims. We aim to investigate how those
wave modes are excited in the lower corona by photospheric acoustic waves.
Methods. We built 3D magnetohydrostatic loop systems with multiple inclinations
spanning from the photosphere to the lower corona. We then simulated these
atmospheres with the MANCHA code, in which we perturb the equilibrium with a
p-mode driver at the bottom of the domain. By splitting the velocity
perturbation into components longitudinal, normal, and azimuthal to the
magnetic flux surfaces we can study wave behavior. Results. In vertical flux
tubes, we find that deformed fast sausage surface waves and slow sausage body
waves are excited. In inclined flux tubes fast kink surface waves, slow sausage
body waves, and either a fast sausage surface wave or a plane wave are excited.
In addition, we calculate a wave conversion factor (0 C 1) from
acoustic to magnetic wave behavior by taking the ratio of the mean magnetic
energy flux to the sum of the mean magnetic and acoustic energy flux and
compare it to a commonly used theoretical conversion factor. We find that
between magnetic field inclinations of 10 to 30 those two
methods lie within 40%. For smaller inclinations the absolute deviation is
smaller than 0.1.Comment: 14 pages, 14 figure
Behavioral Neuroscience: Crawling Is a No-Brainer for Fruit Fly Larvae
SummaryHow are stereotyped behaviors organized in a simple nervous system? A new study in the Drosophila larva reports that the foraging routine can be performed in the absence of any input from the brain
Antecedents of Trust: Status and Power in Virtual Teams
Few empirical efforts have been made to observe hierarchical elements of leadership, namely status and power distinctively. Virtual teams as a form of geographically dispersed work arrangement offer significant opportunities for companies and organizations around the globe, but also pose additional challenges to the leadership and the team itself. Due to communication challenges status and power have special characteristics in virtual teams compared to traditional teams. In this investigation we examine how status and power of a leader impact trust building in virtual teams and in turn the teamâs performance. The results revealed that status of a leader has a positive influence on trust in the leader, while power of a leader had no unique effect on followersâ reactions. As members of diverse cultures have different perceptions of leaders, we found a moderating effect of culture but not for team size
The Role of Culture and Personality in the Leadership Process in Virtual Teams
Leadership is a key challenge of virtual teams. A particular leadership style, namely inspirational leadership, which is a sub-category of transformational leadership, has been found to be especially suited for the study of highly diverse teams. Virtual team leaders increasingly have to manage global virtual teams that contain members from different cultural backgrounds and value orientations. This study answers a call of incorporating the role of individual-level attributes and dispositions as moderators of inspirational leadership effects, considering cultural and individual values of followers in a virtual setting. Results reveal the importance of inspirational leadership influencing attitudinal outcomes (trust in leadership and cohesion). Furthermore, the effect of leadership is shown to be dependent on cultural as well as personal values of followers indicating the need to consider individual factors in the process of managing virtual teams
Conflict, Value Diversity, and Performance in Virtual Teams
While most studies investigating culture in the context of conflict in teams have been using culture dimensions such as collectivism this study centers on another measurement of culture, namely individual values. In this investigation we examined how individual value diversity influences the relationship between team conflict and performance in virtual teams. Assessing two types of conflict, namely task and process conflict, the results revealed that task conflict had no unique effect beyond the impact of process conflict. Contrary to previous findings relating to group culture, this study found that value diversity has no influence on the relationship between conflict and performance in virtual teams. While individuals come to groups with their own values, they may be less powerful predictors of their behavior in groups where there are strong prevailing group values and norms to act a certain way
A new measure for in vivo thrombin activity in comparison with in vitro thrombin generation potential in patients with hyper- and hypocoagulability
The thrombin generation potential is an in vitro measure for the capacity of an individual to generate thrombin and recognized as a reflection of a hypo- or hypercoagulable status. Measurement of the in vivo thrombin activity, however, may be of clinical significance. We evaluated a new assay for in vivo thrombin activity and compared it to the in vitro thrombin generation potential in patients with hemophilia A (N = 15), oral anticoagulation for atrial fibrillation (AF) (N = 20), subjects with active cancer (N = 21), and healthy volunteers (N = 10). Thrombin activity was measured with a commercially available oligonucleotide enzyme capture assay in argatroban-stabilized plasma samples. Thrombin generation potential was determined with a commercially available assay in citrated plasma. Thrombin activity was detected in 17 (30.4 %) patients (mean 0.30 mU/ml [SD 0.80]), and in 39 patients (69.6 %) no thrombin activity was present. In cancer patients, thrombin activity was detected in 11 patients (52 %) (range 0.14-5.00 mU/ml) and was particularly increased in 3 patients with vessel-invasive tumors (1.2, 1.5, and 5.0 mU/ml). In AF patients, thrombin activity was only measureable in two patients (10 %) (recent hematoma [0.4 mU/ml] and recent ischemic stroke [1.5 mU/ml]). Thrombin activity was detected in four patients (27 %) with hemophilia (range 0.29-1.75 mU/ml), all of whom had received a factor VIII infusion on the same day. Thrombin activity did not correlate with any of the parameters of the thrombin generation potential. Only patients in acute procoagulatory states or after clotting factor replacement had elevated in vivo thrombin activity, which was, however, unrelated to the in vitro thrombin generation potential
Cut-off of transverse waves through the solar transition region
Context. Transverse oscillations are ubiquitously observed in the solar
corona, both in coronal loops and open magnetic flux tubes. Numerical
simulations suggest that their dissipation could heat coronal loops,
counterbalancing radiative losses. These models rely on a continuous driver at
the footpoint of the loops. However, analytical works predict that transverse
waves are subject to a cut-off in the transition region. It is thus unclear
whether they can reach the corona, and indeed heat coronal loops. Aims. Our
aims are to determine how the cut-off of kink waves affects their propagation
into the corona, and to characterize the variation of the cut-off frequency
with altitude. Methods. Using 3D magnetohydrodynamic simulations, we modelled
the propagation of kink waves in a magnetic flux tube, embedded in a realistic
atmosphere with thermal conduction, that starts in the chromosphere and extends
into the corona. We drove kink waves at four different frequencies, and
determined whether they experienced a cut-off. We then calculated the altitude
at which the waves were cut-off, and compared it to the prediction of several
analytical models. Results. We show that kink waves indeed experience a cut-off
in the transition region, and we identified the analytical model that gives the
best predictions. In addition, we show that waves with periods shorter than
approximately 500 s can still reach the corona by tunnelling through the
transition region, with little to no attenuation of their amplitude. This means
that such waves can still propagate from the footpoints of loop, and result in
heating in the corona.Comment: Accepted for publication in A&A. 8 pages, 7 figure
A Simple Way to Incorporate Novelty Detection in World Models
Reinforcement learning (RL) using world models has found significant recent
successes. However, when a sudden change to world mechanics or properties
occurs then agent performance and reliability can dramatically decline. We
refer to the sudden change in visual properties or state transitions as {\em
novelties}. Implementing novelty detection within generated world model
frameworks is a crucial task for protecting the agent when deployed. In this
paper, we propose straightforward bounding approaches to incorporate novelty
detection into world model RL agents, by utilizing the misalignment of the
world model's hallucinated states and the true observed states as an anomaly
score. We first provide an ontology of novelty detection relevant to sequential
decision making, then we provide effective approaches to detecting novelties in
a distribution of transitions learned by an agent in a world model. Finally, we
show the advantage of our work in a novel environment compared to traditional
machine learning novelty detection methods as well as currently accepted RL
focused novelty detection algorithms
In vitro cultivation of primary intestinal cells from Eisenia fetida as basis for ecotoxicological studies
The earthworm Eisenia fetida is a commonly used model organism for unspecific soil feeders in ecotoxicological studies. Its intestinal cells are the first to encounter possible pollutants co-ingested by the earthworm, which makes them prime candidates for studies of toxic effects of environmental pollutants on the cellular as compared to the organismic level. In this context, the aim of this study was to demonstrate the suitability of preparations of primary intestinal E. fetida cells for in vitro ecotoxicological studies. For this purpose, a suitable isolation and cultivation protocol was established. Cells were isolated directly from the intestine, maintaining >85% viability during subsequent cultivations (up to 144âh). Exposure to established pollutants and soil elutriates comprising silver nanoparticles and metal ions (Cu(2+), Cd(2+)) induced a significant decrease in the metabolic activity of the cells. In case of microplastic particles (MP particles), namely 0.2, 0.5, 2.0, and 3.0â”m diameter polystyrene (PS) beads as well as 0.5 and 2.0â”m diameter polylactic acid (PLA) beads, no active uptake was observed. Slight positive as well as negative dose and size dependent effects on the metabolism were seen, which to some extent might correlate with effects on the organismic level
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