23,453 research outputs found
Magnetic fields around evolved stars: further observations of HO maser polarization
We aim to detect the magnetic field and infer its properties around four AGB
stars using HO maser observations. The sample we observed consists of the
following sources: the semi-regular variable RT Vir and the Mira variables AP
Lyn, IK Tau, and IRC+60370. We observed the 6 HO maser
rotational transition, in full-polarization mode, to determine its linear and
circular polarization. Based on the Zeeman effect, one can infer the properties
of the magnetic field from the maser polarization analysis. We detected a total
of 238 maser features, in three of the four observed sources. No masers were
found toward AP Lyn. The observed masers are all located between 2.4 and 53.0
AU from the stars. Linear and circular polarization was found in 18 and 11
maser features, respectively. We more than doubled the number of AGB stars in
which magnetic field has been detected from HO maser polarization, as our
results confirm the presence of fields around IK Tau, RT Vir and IRC+60370. The
strength of the field along the line of sight is found to be between 47 and 331
mG in the HO maser region. Extrapolating this result to the surface of the
stars, assuming a toroidal field ( r), we find magnetic fields
of 0.3-6.9 G on the stellar surfaces. If, instead of a toroidal field, we
assume a poloidal field ( r), then the extrapolated magnetic
field strength on the stellar surfaces are in the range between 2.2 and
115 G. Finally, if a dipole field ( r) is assumed, the
field strength on the surface of the star is found to be between 15.8 and
1945 G. The magnetic energy of our sources is higher than the thermal and
kinetic energy in the HO maser region of this class of objects. This leads
us to conclude that, indeed, magnetic fields probably play an important role in
shaping the outflows of evolved stars. (abridged)Comment: 15 pages, 5 figures, 7 tables. Accepted for publication in A&
Cosmic String Wakes in Scalar-Tensor Gravities
The formation and evolution of cosmic string wakes in the framework of a
scalar-tensor gravity are investigated in this work. We consider a simple model
in which cold dark matter flows past an ordinary string and we treat this
motion in the Zel'dovich approximation. We make a comaprison between our
results and previous results obtained in the context of General Relativity. We
propose a mechanism in which the contribution of the scalar field to the
evolution of the wakes may lead to a cosmological observation.Comment: Replaced version to be published in the Classical and Quantum Gravit
Upper bound for the conductivity of nanotube networks
Films composed of nanotube networks have their conductivities regulated by
the junction resistances formed between tubes. Conductivity values are enhanced
by lower junction resistances but should reach a maximum that is limited by the
network morphology. By considering ideal ballistic-like contacts between
nanotubes we use the Kubo formalism to calculate the upper bound for the
conductivity of such films and show how it depends on the nanotube
concentration as well as on their aspect ratio. Highest measured conductivities
reported so far are approaching this limiting value, suggesting that further
progress lies with nanowires other than nanotubes.Comment: 3 pages, 1 figure. Minor changes. Accepted for publication in Applied
Physics Letter
Adaptação de método para a extração de proteínas de sementes de cerejeira (Amburana cearensis (Fr.All.) A.C.Smith).
bitstream/CENARGEN/23201/1/cot064.pd
How daily negative affect and emotional exhaustion correlates with work engagement and presenteeism-constrained productivity
Exploring productivity loss due to presenteeism and how it can have an influence on employees’ productivity has been an important concern for human resource managers. Using the conservation of resources theory and the job demands-resources model, this study investigated how work engagement could mediate the relationship between both emotional exhaustion and negative affect and productivity loss due to presenteeism in a country experiencing an economic downturn. A total of 42 employees from a health care institution completed a 10-day diary survey (420 diary tasks). Multilevel linear modeling results, including power analyses, showed that negative affect and emotional exhaustion predicted productivity loss due to presenteeism positively, whereas work engagement predicted productivity loss negatively. Furthermore, we found that at a day-level, work engagement mediated the effects of emotional exhaustion and negative affect on productivity loss due to presenteeism. This study highlights the importance of promoting work engagement to reduce the effects of negative affect and emotional exhaustion on productivity loss due to presenteeism through intervention.info:eu-repo/semantics/acceptedVersio
- …