119,357 research outputs found
ADAS analysis of the differential emission measure structure of the inner solar corona. II. A study of the `quiet Sun' inhomogeneities from SOHO CDS-NIS spectra
We present a study of the differential emission measure (DEM) of a `quiet
Sun' area observed in the extreme ultraviolet at normal incidence by the
Coronal Diagnostic Spectrometer (CDS) on the SOHO spacecraft. The data used for
this work were taken using the NISAT_S observing sequence. This takes the full
wavelength ranges from both the NIS channels (308-381 Angtr. and 513-633
Angst.) with the 2 arcsec by 240 arcsec slit, which is the narrowest slit
available, yielding the best spectral resolution. In this work we contrast the
DEM from subregions of 2 by 80 arcsec with that obtained from the mean
spectrum of the whole raster (20 by 240 arcsec). We find that the DEM
maintains essentially the same shape in the subregions, differing by a constant
factor between 0.5 and 2 from the mean DEM, except in areas were the electron
density is below cm and downflow velocities of 50 km/s
are found in the transition region. Such areas are likely to contain plasma
departing from ionisation equilibrium, violating the basic assumptions
underlying the DEM method. The comparison between lines of Li-like and Be-like
ions may provide further evidence of departure from ionisation equilibrium. We
find also that line intensities tend to be lower where velocities of the order
of 30 km/s or higher are measured in transition region lines. The DEM analysis
is also exploited to improve the line identification performed by Brooks et al
(1999) and to investigate possible elemental abundance variations from region
to region. We find that the plasma has composition close to photospheric in all
the subregions examined.Comment: 18 pages, 9 figures, 7 tables. Table 5 is available only online. A
copy of Table 5 can be found at http://webusers.ct.astro.it/acl/table5.dat.
The ReadMe file is at http://webusers.ct.astro.it/acl/ReadMe. Accepted by
Astronomy and Astrophysic
MADNESS: A Multiresolution, Adaptive Numerical Environment for Scientific Simulation
MADNESS (multiresolution adaptive numerical environment for scientific
simulation) is a high-level software environment for solving integral and
differential equations in many dimensions that uses adaptive and fast harmonic
analysis methods with guaranteed precision based on multiresolution analysis
and separated representations. Underpinning the numerical capabilities is a
powerful petascale parallel programming environment that aims to increase both
programmer productivity and code scalability. This paper describes the features
and capabilities of MADNESS and briefly discusses some current applications in
chemistry and several areas of physics
Theoretical and experimental bubble formation at a single orifice in a two-dimensional gas-fluidized bed
An earlier developed, first principles hydrodynamic model of gas-fluidized beds has been employed to study theoretically bubble formation at a single orifice in a two-dimensional bed. For several orifice discharge rates, theoretically predicted bubble sizes, formation times and shapes have been compared with experimental data obtained from triggered photographs. Besides, the present experimental and theoretical results were compared with predictions from two approximate models reported in the literature which are based on an idealized picture of the process of bubble formation. The advanced hydrodynamic model appears to predict the experimentally observed diameters, formation times and shapes of bubbles quite satisfactorily. The observed and calculated bubble diameters fall between the predictions from the two approximate models. Both the experimental and theoretical results clearly indicate that a strong leakage of bubble gas into the surrounding porous emulsion phase occurs, especially during the initial stage of bubble formatio
Bond orbital description of the strain induced second order optical susceptibility in silicon
We develop a theoretical model, relying on the well established sp3
bond-orbital theory, to describe the strain-induced in
tetrahedrally coordinated centrosymmetric covalent crystals, like silicon. With
this approach we are able to describe every component of the
tensor in terms of a linear combination of strain gradients and only two
parameters and which can be estimated theoretically. The
resulting formula can be applied to the simulation of the strain distribution
of a practical strained silicon device, providing an extraordinary tool for
optimization of its optical nonlinear effects. By doing that, we were able not
only to confirm the main valid claims known about in strained
silicon, but also estimate the order of magnitude of the generated
in that device
Measuring the use of information and communication technologies (ICTs) in the classroom
In 2003, the ICT Curriculum Integration Performance Measurement Instrument was developed from an extensive review of the contemporary international and Australian research pertaining to the definition and measurement of ICT curriculum integration in classrooms (Proctor, Watson, & Finger, 2003). The 45-item instrument that resulted was based on theories and methodologies identified by the literature review. This paper describes psychometric results from a large-scale evaluation of the instrument subsequently conducted, as recommended by Proctor, Watson and Finger (2003). The resultant 20-item, two-factor instrument, now called Learning With ICTs: Measuring ICT Use in the Curriculum is both statistically and theoretically robust. This paper should be read in association with the original paper published in Computers in the Schools (Proctor, Watson & Finger, 2003) that described in detail the theoretical framework underpinning the development of the instrument
Implementation of analytical Hartree-Fock gradients for periodic systems
We describe the implementation of analytical Hartree-Fock gradients for
periodic systems in the code CRYSTAL, emphasizing the technical aspects of this
task. The code is now capable of calculating analytical derivatives with
respect to nuclear coordinates for systems periodic in 0, 1, 2 and 3 dimensions
(i.e. molecules, polymers, slabs and solids). Both closed-shell restricted and
unrestricted Hartree-Fock gradients have been implemented. A comparison with
numerical derivatives shows that the forces are highly accurate.Comment: accepted by Comp. Phys. Com
Entanglement entropy of subtracted geometry black holes
We compute the entanglement entropy of minimally coupled scalar fields on
subtracted geometry black hole backgrounds, focusing on the logarithmic
corrections. We notice that matching between the entanglement entropy of
original black holes and their subtracted counterparts is only at the order of
the area term. The logarithmic correction term is not only different but also,
in general, changes sign in the subtracted case. We apply Harrison
transformations to the original black holes and find out the choice of the
Harrison parameters for which the logarithmic corrections vanish.Comment: 15 page
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