69 research outputs found
Reversals of the solar magnetic dipole in the light of observational data and simple dynamo models
Observations show that the photospheric solar magnetic dipole usually does
not vanish during the reversal of the solar magnetic field, which occurs in
each solar cycle. In contrast, mean-field solar dynamo models predict that the
dipole field does become zero. In a recent paper Moss et al. (2013) suggested
that this contradiction can be explained as a large-scale manifestation of
small-scale magnetic fluctuations of the surface poloidal field. Here we
compare this interpretation with WSO (Wilcox Solar Observatory) photospheric
magnetic field data in order to determine the amplitude of magnetic
fluctuations required to explain the phenomenon and to compare the results with
predictions from a simple dynamo model which takes these fluctuations into
account. We demonstrate that the WSO data concerning the magnetic dipole
reversals are very similar to the predictions of our very simple solar dynamo
model, which includes both mean magnetic field and fluctuations. The ratio
between the rms value of the magnetic fluctuations and the mean field is
estimated to be about 2, in reasonable agreement with estimates from sunspot
data. The reversal epoch, during which the fluctuating contribution to the
dipole is larger than that from the mean field, is about 4 months. The memory
time of the fluctuations is about 2 months. Observations demonstrate that the
rms of the magnetic fluctuations is strongly modulated by the phase of the
solar cycle. This gives additional support to the concept that the solar
magnetic field is generated by a single dynamo mechanism rather than also by
independent small-scale dynamo action. A suggestion of a weak nonaxsymmetric
magnetic field of a fluctuating nature arises from the analysis, with a
lifetime of about 1 year.Comment: 9 pages, 10 figures, accepted versio
Faktor-faktor yang Mempengaruhi Audit Report Lag pada Perusahaan yang Terdaftar di Bursa Efek Indonesia
This study aims to obtain empirical evidence about the factors that affect the audit report lag. Factors tested audit report lag is a measure of the company, the firm size, auditor turnover and profitability. The population in this study were 45 blue-chip companies listed in Indonesia Stock Exchange Year 2011-2012. Data were obtained from the blue-chip companys financial statementsin 2011-2012. Based onpurposive sampling method, samples were obtained by 33 companies and 2 years of data are used so that the sample companies to 66 companies. This hypothesis was tested using multiple regression analysis.The results ofthis study indicatethat company size, turnover and profitability auditors significant effect on audit report lag. While the size of the firm no effect on audit report lag.Keywords: Audit report lag, the size of the company, the size of the firm, the change of auditors and auditor turnover
Local models of stellar convection: Reynolds stresses and turbulent heat transport
We study stellar convection using a local three-dimensional MHD model, with
which we investigate the influence of rotation and large-scale magnetic fields
on the turbulent momentum and heat transport. The former is studied by
computing the Reynolds stresses, the latter by calculating the correlation of
velocity and temperature fluctuations, both as functions of rotation and
latitude. We find that the horisontal correlation, Q_(theta phi), capable of
generating horisontal differential rotation, is mostly negative in the southern
hemisphere for Coriolis numbers exceeding unity, corresponding to equatorward
flux of angular momentum in accordance with solar observations. The radial
component Q_(r phi) is negative for slow and intermediate rotation indicating
inward transport of angular momentum, while for rapid rotation, the transport
occurs outwards. Parametrisation in terms of the mean-field Lambda-effect shows
qualitative agreement with the turbulence model of Kichatinov & R\"udiger
(1993) for the horisontal part H \propto Q_(theta phi)/cos(theta), whereas for
the vertical part, V \propto Q_(r phi)/sin(theta), agreement only for
intermediate rotation exists. The Lambda-coefficients become suppressed in the
limit of rapid rotation, this rotational quenching being stronger for the V
component than for H. We find that the stresses are enhanced by the presence of
the magnetic field for field strengths up to and above the equipartition value,
without significant quenching. Concerning the turbulent heat transport, our
calculations show that the transport in the radial direction is most efficient
at the equatorial regions, obtains a minimum at midlatitudes, and shows a
slight increase towards the poles. The latitudinal heat transport does not show
a systematic trend as function of latitude or rotation.Comment: 26 pages, 20 figures, final published version. For a version with
higher resolution figures, see http://cc.oulu.fi/~pkapyla/publ.htm
Alpha effect and turbulent diffusion from convection
(abridged) Aims: To study turbulent transport coefficients that describe the
evolution of large-scale magnetic fields in turbulent convection. Methods: We
use the test field method together with 3D numerical simulations of turbulent
convection with shear and rotation to compute turbulent transport coefficients
describing the evolution of large-scale magnetic fields in mean-field theory in
the kinematic regime. 1D mean-field models are used with the derived turbulent
transport coefficients to compare with direct simulations. Results: The
alpha-effect increases monotonically as rotation increases. Turbulent
diffusivity, eta_t, is proportional to the square of the turbulent vertical
velocity. Whereas eta_t decreases approximately inversely proportional to the
wavenumber of the field, the alpha-effect and turbulent pumping show a more
complex behaviour. In the presence of shear and no rotation a small
alpha-effect is induced which does not seem to show any consistent trend as a
function of shear. If the shear is large enough, this small alpha is able to
excite a dynamo in the mean-field model. The coefficient responsible for
driving the shear-current effect shows several sign changes as a function of
depth but is also able to contribute to dynamo action in the mean-field model.
The growth rates in these cases are well below those in direct simulations
suggesting that an incoherent alpha-shear dynamo may also act in them. If both
rotation and shear are present, the alpha-effect is more pronounced. The
combination of the shear-current and Omega x J-effects is also stronger than in
the case of shear only, but subdominant to the alpha-shear dynamo. The results
of direct simulations are consistent with mean-field models where all of these
effects are taken into account without the need to invoke incoherent effects.Comment: 14 pages, 14 figures, minor changes to match with the published
versio
Active region formation through the negative effective magnetic pressure instability
The negative effective magnetic pressure instability operates on scales
encompassing many turbulent eddies and is here discussed in connection with the
formation of active regions near the surface layers of the Sun. This
instability is related to the negative contribution of turbulence to the mean
magnetic pressure that causes the formation of large-scale magnetic structures.
For an isothermal layer, direct numerical simulations and mean-field
simulations of this phenomenon are shown to agree in many details in that their
onset occurs at the same depth. This depth increases with increasing field
strength, such that the maximum growth rate of this instability is independent
of the field strength, provided the magnetic structures are fully contained
within the domain. A linear stability analysis is shown to support this
finding. The instability also leads to a redistribution of turbulent intensity
and gas pressure that could provide direct observational signatures.Comment: 19 pages, 10 figures, submitted to Solar Physic
Effects of core-valence and core-core correlation on the line strength of the resonance lines in Li i and Na i
The Maunder minimum (1645-1715) was indeed a grand minimum: a reassessment of multiple datasets
Aims.
Although the time of the Maunder minimum (1645–1715) is widely known as a period of extremely low solar activity, it is still being debated whether solar activity during that period might have been moderate or even higher than the current solar cycle (number 24). We have revisited all existing evidence and datasets, both direct and indirect, to assess the level of solar activity during the Maunder minimum.
Methods.
We discuss the East Asian naked-eye sunspot observations, the telescopic solar observations, the fraction of sunspot active days, the latitudinal extent of sunspot positions, auroral sightings at high latitudes, cosmogenic radionuclide data as well as solar eclipse observations for that period. We also consider peculiar features of the Sun (very strong hemispheric asymmetry of the sunspot location, unusual differential rotation and the lack of the K-corona) that imply a special mode of solar activity during the Maunder minimum.
Results.
The level of solar activity during the Maunder minimum is reassessed on the basis of all available datasets.
Conclusions.
We conclude that solar activity was indeed at an exceptionally low level during the Maunder minimum. Although the exact level is still unclear, it was definitely lower than during the Dalton minimum of around 1800 and significantly below that of the current solar cycle #24. Claims of a moderate-to-high level of solar activity during the Maunder minimum are rejected with a high confidence level
Multiphoton detachment of a negative ion by an elliptically polarized, monochromatic laser field
Aplikasi Panas sebagai Alternatif untuk Mengawetkan Kayu Heat Treatment AS An Alternative For Wood Preservation
Most of Indonesian wood species are classified as less durable, so preservation is needed. Wood preservation inIndonesiamainly depends on imported preservatives. The preservatives are not only toxic to wood destroying organism but also to humans and the environments. Therefore alternative to treat wood should be sought and developed in term of the preservatives used as well as the methods. One that can be proposed is treating wood at high temperature combine with environmentally friendly preservatives, as tried in this experiment.The wood species used in this experiment were rubber wood (Hevea Brasilliensis) and pine (Pinus merkusii). Both woods were treated with borax at two concentrations (3% and 5%) by cold-soaking method for 24 hours. The treated woods were subsequently air dried. Then those woods were treated at three levels of high temperature (180ºC, 200ºC, and 220ºC) in an oven for one hour. Finally, the treated wood samples were laboratory-tested by assessing their resistance to dry wood termites (Cryptotermes synocephalus Light.) and powder-post beetles (Heterobostrychus aequalis Wat).The results revealed that increases of heating temperature and concentration of preservatives resulted in more durable woods. In this regard their resistance to dry wood termite and powder-post beetles was increased as shown by smaller weight loss. Treating wood at temperature of 180ºC combined with borax at concentration of 3% resulted in 100% termite mortality on rubber wood and pine
- …