4,718 research outputs found
Can spicules be detected at disc centre in broad-band Ca II H filter imaging data ?
We estimate the formation height range contributing to broad-band and
narrow-band filter imaging data in Ca II H to investigate whether spicules can
be detected in such observations at the centre of the solar disc. We apply
spectral filters of FWHMs from 0.03 nm to 1 nm to observed Ca line profiles to
simulate Ca imaging data. We estimate the relative intensity contributions of
off-limb and on-disc structures. We compare the synthetic Ca filter imaging
data with intensity maps of Ca spectra at different wavelengths and temperature
maps at different optical depths. We determine the intensity response function
for the wavelengths covered by the filters of different FWHM.
The intensity emitted off the solar limb is about 5% of the intensity at disc
centre. For a 0.3 nm-wide Ca II H filter, up to about 1/3 of the off-limb
intensity comes from emission in Hepsilon. On the disc, only about 15% of the
intensity transmitted through a broad-band filter comes from the line-core
region. No traces of elongated fibrillar structures are visible in imaging data
at disc centre, opposite to the line-core images of the Ca spectra. The
response function for a 0.3 nm-wide filter peaks at about 200 km. Relative
contributions from atmospheric layers above 800 km are about 10%. The inversion
results suggest that the slightly enhanced emission around the photospheric
magnetic network in broad-band Ca imaging data is caused by a thermal canopy at
a height of about 600 km. Broad-band Ca II H imaging data do not trace upper
chromospheric structures such as spicules in observations at the solar disc
because of the too small relative contribution of the line core to the total
wavelength-integrated filter intensity.Comment: 10 pages, 11 figures, accepted for publication in A&
Spectroscopy at the solar limb: II. Are spicules heated to coronal temperatures ?
Spicules of the so-called type II were suggested to be relevant for coronal
heating because of their ubiquity on the solar surface and their eventual
extension into the corona. We investigate whether solar spicules are heated to
transition-region or coronal temperatures and reach coronal heights (>6 Mm)
using multi-wavelength observations of limb spicules in different chromospheric
spectral lines (Ca II H, Hepsilon, Halpha, Ca II IR at 854.2 nm, He I at 1083
nm). We determine the line width of individual spicules and throughout the
field of view and estimate the maximal height that different types of off-limb
features reach. We derive estimates of the kinetic temperature and the
non-thermal velocity from the line width of spectral lines from different
chemical elements. We find that most regular spicules reach a maximal height of
about 6 Mm above the solar limb. The majority of features found at larger
heights are irregularly shaped with a significantly larger lateral extension
than spicules. Both individual and average line profiles in all spectral lines
show a decrease in their line width with height above the limb with very few
exceptions. Both the kinetic temperature and the non-thermal velocity decrease
with height above the limb. We find no indications that the spicules in our
data reach coronal heights or transition-region or coronal temperatures.Comment: Accepted for publication in Solar Physics, 52 pages, 32 figure
The polarization signature of photospheric magnetic fields in 3D MHD simulations and observations at disk center
Before using 3D MHD simulations of the solar photosphere in the determination
of elemental abundances, one has to ensure that the correct amount of magnetic
flux is present in the simulations. The presence of magnetic flux modifies the
thermal structure of the solar photosphere, which affects abundance
determinations and the solar spectral irradiance. We compare the polarization
signals in disk-center observations of the solar photosphere in quiet-Sun
regions with those in Stokes spectra computed on the basis of 3D MHD
simulations having average magnetic flux densities of about 20, 56, 112 and 224
G. This approach allows us to find the simulation run that best matches the
observations. The observations were taken with the Hinode SP, TIP, POLIS and
the GFPI, respectively. We determine characteristic quantities of full Stokes
profiles in a few photospheric spectral lines in the visible (630 nm) and
near-infrared (1083 and 1565 nm). We find that the appearance of abnormal
granulation in intensity maps of degraded simulations can be traced back to an
initially regular granulation pattern with numerous bright points in the
intergranular lanes before the spatial degradation. The linear polarization
signals in the simulations are almost exclusively related to canopies of strong
magnetic flux concentrations and not to transient events of magnetic flux
emergence. We find that the average vertical magnetic flux density in the
simulation should be less than 50 G to reproduce the observed polarization
signals in the quiet Sun internetwork. A value of about 35 G gives the best
match across the SP, TIP, POLIS and GFPI observations.Comment: 12 pages, 11 figures; accepted for publication in Ap
Thermodynamic fluctuations in solar photospheric three-dimensional convection simulations and observations
Numerical 3D radiative (M)HD simulations of solar convection are used to
understand the physical properties of the solar photosphere. To validate this
approach, it is important to check that no excessive thermodynamic fluctuations
arise as a consequence of the partially incomplete treatment of radiative
transfer. We investigate the realism of 3D convection simulations carried out
with the Stagger code. We compared the characteristic properties of several
spectral lines in solar disc centre observations with spectra synthesized from
the simulations. We degraded the synthetic spectra to the spatial resolution of
the observations using the continuum intensity distribution. We estimated the
necessary spectral degradation by comparing atlas spectra with averaged
observed spectra. In addition to deriving a set of line parameters directly, we
used the SIR code to invert the spectra. Most of the line parameters from the
observational data are matched well by the degraded simulation spectra. The
inversions predict a macroturbulent velocity below 10 m/s for the simulation at
full spatial resolution, whereas they yield ~< 1000 m/s at a spatial resolution
of 0.3". The temperature fluctuations in the inversion of the degraded
simulation do not exceed those from the observational data (of the order of
100-200 K rms for -2<log tau<-0.5). The comparison of line parameters in
spatially averaged profiles with the averaged values of line parameters in
spatially resolved profiles indicates a significant change of (average) line
properties at a spatial scale between 0.13" and 0.3". Up to a spatial
resolution of 0.3", we find no indications of the presence of excessive
thermodynamic fluctuations in the 3D HD simulation. To definitely confirm that
simulations without spatial degradation contain fully realistic thermodynamic
fluctuations requires observations at even better spatial resolution.Comment: 21 pages, 15 figures + 2 pages Appendix, accepted for publication in
A&A; v2 version: corrected for an error in the calculation of stray-light
estimates, for details see the Corrigendum to A&A, 2013, 557, 109 (DOI:
10.1051/0004-6361/201321596). Corrected text and numbers are in bold font.
Apart from the stray-light estimates, nothing in the rest of the paper was
affected by the erro
A numerical study on reaction-diffusion problem using radial basis functions
In this paper, the collocation approach, based on the indirect radial basis functions on boundary value problems (IRBFB), is used to obtain a solution for the problem of a non-linear model of reaction-diffusion in porous catalysis pellets for the case of th-order reaction. One of the boundaries of porous slab is impermeable and the other one is held at constant concentration. We applied this method through the integration process on the boundary value reaction-diffusion problem. The Thiele modulus thus measures the relative importance of the diffusion and reaction phenomena. Interestingly, for the large Thiele modulus the IRBFB offer a reasonable solution. Numerical results and findings obtained by the comparison with finite difference method, show a good accuracy and appropriate convergence rate of IRBFB process
Designing a Model for Knowledge Socialization Using Sociability Processes of Human Resource Management: A Case Study
This study develops a model for knowledge socialization using sociability processes of human resources through an applied research approach. Two types of participants participated in this study. The first type included academic and industrial experts; the second type included employees and managers of Ansar Bank. Ten experts were asked to identify criteria and weigh the identified criteria. Using simple random sampling, the sample size was estimated at 207. Field and archival studies were used to collect data. Validity and reliability of the distributed questionnaire were confirmed by organizational experts. Using theoretical literature and surveying experts, 18 criteria were identified of which 12 criteria (desirable and joyful workplace, management and leadership support in sociability process, training courses, transparency in working relations, team work, organizational trustful climate, job description and job knowledge, tangible incentives, participatory system, informal technique, defined career path, individual values aligned with organizational value) were selected by screening for prioritization and analysis. Fuzzy AHP and structural equation modelling based on partial least squares were used for prioritization and weighting. Fuzzy AHP model showed that desirable workplace (0.163), participatory systems and brainstorming (0.149), transparency in working relations (0.114), and informal techniques (0.111) gained the highest weights; finally, PLS model showed that all 12 identified criteria were effective on socialization of knowledge management
Investigating the Effects of Several Parameters on the Growth of Chlorella vulgaris Using Taguchi's Experimental Approach
Algae are part of photosynthetic organisms that play an important role in the aquatics nutrition. Like plants, algae need water, light and CO2 to grow. Using Taguchi's experimental approach (5 factors in four levels with 16 runs), effects of several parameters (NaCl, sodium bicarbonate and iron concentrations as well as light and temperature) on the growth of Chlorella vulgaris was studied. Increasing the concentrations of NaCl and sodium bicarbonate resulted in corresponding decreases in the growth of C. vulgaris. Media with 30.0g l-1NaCl did not indicate any algal growth. Also, with 9.0 g l-1sodium bicarbonate, biomass production was decreased. Chlorella vulgaris showed different growing behaviors at the various concentrations of iron (Fe+2) and at the different temperatures of this study. Maximum biomass production (approximately 3.56 g dry matter) was obtained at the 0.0 g l-1 sodium bicarbonate, 10.0g l-1NaCl, 18.0 µmol l-1 iron and at 30±2 °C. Yellow and blue lights increased the algal growth. Analysis of variance showed that salinity (i.e., the NaCl concentration) had the highest impact on the biomass production.
Gully erosion zonation mapping using integrated geographically weighted regression with certainty factor and random forest models in GIS
© 2018 Elsevier Ltd Every year, gully erosion causes substantial damage to agricultural land, residential areas and infrastructure, such as roads. Gully erosion assessment and mapping can facilitate decision making in environmental management and soil conservation. Thus, this research aims to propose a new model by combining the geographically weighted regression (GWR) technique with the certainty factor (CF) and random forest (RF) models to produce gully erosion zonation mapping. The proposed model was implemented in the Mahabia watershed of Iran, which is highly sensitive to gully erosion. Firstly, dependent and independent variables, including a gully erosion inventory map (GEIM) and gully-related causal factors (GRCFs), were prepared using several data sources. Secondly, the GEIM was randomly divided into two groups: training (70%) and validation (30%) datasets. Thirdly, tolerance and variance inflation factor indicators were used for multicollinearity analysis. The results of the analysis corroborated that no collinearity exists amongst GRCFs. A total of 12 topographic, hydrologic, geologic, climatologic, environmental and soil-related GRCFs and 150 gully locations were used for modelling. The watershed was divided into eight homogeneous units because the importance level of the parameters in different parts of the watershed is not the same. For this purpose, coefficients of elevation, distance to stream and distance to road parameters were used. These coefficients were obtained by extracting bi-square kernel and AIC via the GWR method. Subsequently, the RF-CF integrated model was applied in each unit. Finally, with the units combined, the final gully erosion susceptibility map was obtained. On the basis of the RF model, distance to stream, distance to road and land use/land cover exhibited a high influence on gully formation. Validation results using area under curve indicated that new GWR–CF–RF approach has a higher predictive accuracy 0.967 (96.7%) than the individual models of CF 0.763 (76.3%) and RF 0.776 (77.6%) and the CF-RF integrated model 0.897 (89.7%). Thus, the results of this research can be used by local managers and planners for environmental management
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