1,390 research outputs found
Equivariant Zariski Structures
A new class of noncommutative -algebras (for an algebraically closed
field) is defined and shown to contain some important examples of quantum
groups. To each such algebra, a first order theory is assigned describing
models of a suitable corresponding geometric space. Model-theoretic results for
these geometric structures are established (uncountable categoricity,
quantifier elimination to the level of existential formulas) and that an
appropriate dimension theory exists, making them Zariski structures
Genetic Algorithm Approach for Implementation of Job Scheduling Problem
A job scheduling maps and schedules the virtual machine (VM) resources to physical machines (VM) for getting the finest mapping result to achieve the proper system load balance. Job scheduling system tries to find the best suitable schedule in a system for VMs and PMs, by considering various on time restrictions into concern. The ultimate goal of job scheduling is to schedule adaptable virtual machines to physical machines, getting a suitable order in order to enhance resource utility. This research paper proposes an approach in order to discuss a Job Scheduling problem to progress resource utility with the help of Genetic Algorithm (GA).
DOI: 10.17762/ijritcc2321-8169.15067
The local dust foregrounds in the microwave sky: I. Thermal emission spectra
Analyses of the cosmic microwave background (CMB) radiation maps made by the
Wilkinson Microwave Anisotropy Probe (WMAP) have revealed anomalies not
predicted by the standard inflationary cosmology. In particular, the power of
the quadrupole moment of the CMB fluctuations is remarkably low, and the
quadrupole and octopole moments are aligned mutually and with the geometry of
the Solar system. It has been suggested in the literature that microwave sky
pollution by an unidentified dust cloud in the vicinity of the Solar system may
be the cause for these anomalies. In this paper, we simulate the thermal
emission by clouds of spherical homogeneous particles of several materials.
Spectral constraints from the WMAP multi-wavelength data and earlier infrared
observations on the hypothetical dust cloud are used to determine the dust
cloud's physical characteristics. In order for its emissivity to demonstrate a
flat, CMB-like wavelength dependence over the WMAP wavelengths (3 through 14
mm), and to be invisible in the infrared light, its particles must be
macroscopic. Silicate spheres from several millimetres in size and carbonaceous
particles an order of magnitude smaller will suffice. According to our
estimates of the abundance of such particles in the Zodiacal cloud and
trans-neptunian belt, yielding the optical depths of the order of 1E-7 for each
cloud, the Solar-system dust can well contribute 10 microKelvin (within an
order of magnitude) in the microwaves. This is not only intriguingly close to
the magnitude of the anomalies (about 30 microKelvin), but also alarmingly
above the presently believed magnitude of systematic biases of the WMAP results
(below 5 microKelvin) and, to an even greater degree, of the future missions
with higher sensitivities, e.g. PLANCK.Comment: 33 pages, 9 figures, 1 table. The Astrophysical Journal, 2009,
accepte
On the intensity contrast of solar photospheric faculae and network elements
Sunspots, faculae and the magnetic network contribute to solar irradiance
variations. The contribution due to faculae and the network is of basic
importance, but suffers from considerable uncertainty. We determine the
contrasts of active region faculae and the network, both as a function of
heliocentric angle and magnetogram signal. To achieve this, we analyze
near-simultaneous full disk images of photospheric continuum intensity and
line-of-sight magnetic field provided by the Michelson Doppler Interferometer
(MDI) on board the SOHO spacecraft. Starting from the surface distribution of
the solar magnetic field we first construct a mask, which is then used to
determine the brightness of magnetic features, and the relatively field-free
part of the photosphere separately. By sorting the magnetogram signal into
different bins we are able to distinguish between the contrasts of different
concentrations of magnetic field. We find that the contrasts of active region
faculae (large magnetogram signal) and the network (small signal) exhibit a
very different CLV, showing that the populations of magnetic flux tubes are
different. This implies that these elements need to be treated separately when
reconstructing variations of the total solar irradiance with high precision. We
have obtained an analytical expression for the contrast of photospheric
magnetic features as a function of both position on the disk and magnetic field
strength, by performing a 2-dimensional fit to the observations.Comment: 12 pages, 8 figures, uses aa.cl
Sunspot areas and tilt angles for solar cycles 7-10
Extending the knowledge about the properties of solar cycles into the past is
essential for understanding the solar dynamo. This paper aims at estimating
areas of sunspots observed by Schwabe in 1825-1867 and at calculating the tilt
angles of sunspot groups. The sunspot sizes in Schwabe's drawings are not to
scale and need to be converted into physical sunspot areas. We employed a
statistical approach assuming that the area distribution of sunspots was the
same in the 19th century as it was in the 20th century. Umbral areas for about
130,000 sunspots observed by Schwabe were obtained, as well as the tilt angles
of sunspot groups assuming them to be bipolar. There is, of course, no polarity
information in the observations. The annually averaged sunspot areas correlate
reasonably with sunspot number. We derived an average tilt angle by attempting
to exclude unipolar groups with a minimum separation of the two alleged
polarities and an outlier rejection method which follows the evolution of each
group and detects the moment it turns unipolar at its decay. As a result, the
tilt angles, although displaying considerable scatter, place the leading
polarity on average 5.85+-0.25 closer to the equator, in good agreement with
tilt angles obtained from 20th-century data sets. Sources of uncertainties in
the tilt angle determination are discussed and need to be addressed whenever
different data sets are combined. The sunspot area and tilt angle data are
provided online.Comment: accepted for publication in Astron. & Astrophy
Temporal relation between quiet-Sun transverse fields and the strong flows detected by IMaX/SUNRISE
Localized strongly Doppler-shifted Stokes V signals were detected by
IMaX/SUNRISE. These signals are related to newly emerged magnetic loops that
are observed as linear polarization features. We aim to set constraints on the
physical nature and causes of these highly Doppler-shifted signals. In
particular, the temporal relation between the appearance of transverse fields
and the strong Doppler shifts is analyzed in some detail. We calculated the
time difference between the appearance of the strong flows and the linear
polarization. We also obtained the distances from the center of various
features to the nearest neutral lines and whether they overlap or not. These
distances were compared with those obtained from randomly distributed points on
observed magnetograms. Various cases of strong flows are described in some
detail. The linear polarization signals precede the appearance of the strong
flows by on average 84+-11 seconds. The strongly Doppler-shifted signals are
closer (0.19") to magnetic neutral lines than randomly distributed points
(0.5"). Eighty percent of the strongly Doppler-shifted signals are close to a
neutral line that is located between the emerging field and pre-existing
fields. That the remaining 20% do not show a close-by pre-existing field could
be explained by a lack of sensitivity or an unfavorable geometry of the
pre-existing field, for instance, a canopy-like structure. Transverse fields
occurred before the observation of the strong Doppler shifts. The process is
most naturally explained as the emergence of a granular-scale loop that first
gives rise to the linear polarization signals, interacts with pre-existing
fields (generating new neutral line configurations), and produces the observed
strong flows. This explanation is indicative of frequent small-scale
reconnection events in the quiet Sun.Comment: 11 pages, 8 figure
From Solar to Stellar Brightness Variations: The Effect of Metallicity
Context. Comparison studies of Sun-like stars with the Sun suggest an
anomalously low photometric variability of the Sun compared to Sun-like stars
with similar magnetic activity. Comprehensive understanding of stellar
variability is needed, to find a physical reasoning for this observation. Aims.
We investigate the effect of metallicity and effective temperature on the
photometric brightness change of Sun-like stars seen at different inclinations.
The considered range of fundamental stellar parameters is sufficiently small so
the stars, investigated here, still count as Sun-like or even as solar twins.
Methods. To model the brightness change of stars with solar magnetic activity,
we extend a well established model of solar brightness variations, SATIRE
(which stands for Spectral And Total Irradiance Reconstruction), which is based
on solar spectra, to stars with different fundamental parameters. For that we
calculate stellar spectra for different metallicities and effective temperature
using the radiative transfer code ATLAS9. Results. We show that even a small
change (e.g. within the observational error range) of metallicity or effective
temperature significantly affects the photometric brightness change compared to
the Sun. We find that for Sun-like stars, the amplitude of the brightness
variations obtained for Str\"omgren (b + y)/2 reaches a local minimum for
fundamental stellar parameters close to the solar metallicity and effective
temperature. Moreover, our results show that the effect of inclination
decreases for metallicity values greater than the solar metallicity. Overall,
we find that an exact determination of fundamental stellar parameters is
crucially important for understanding stellar brightness changes.Comment: 12 pages, 12 figures, accepted in A&
Properties of sunspots in cycle 23: I. Dependence of brightness on sunspot size and cycle phase
In this paper we investigate the dependence of umbral core brightness, as
well as the mean umbral and penumbral brightness on the phase of the solar
cycle and on the size of the sunspot. Albregtsen & Maltby (1978) reported an
increase in umbral core brightness from the early to the late phase of solar
cycle from the analysis of 13 sunspots which cover solar cycles 20 and 21. Here
we revisit this topic by analysing continuum images of more than 160 sunspots
observed by the MDI instrument on board the SOHO spacecraft for the period
between 1998 March to 2004 March, i.e. a sizable part of solar cycle 23. The
advantage of this data set is its homogeneity, with no seeing fluctuations. A
careful stray light correction, which is validated using the Mercury transit of
7th May, 2003, is carried out before the umbral and penumbral intensities are
determined. The influence of the Zeeman splitting of the nearby NiI spectral
line on the measured 'continuum' intensity is also taken into account. We did
not observe any significant variation in umbral core, mean umbral and mean
penumbral intensities with solar cycle, which is in contrast to earlier
findings for the umbral core intensity. We do find a strong and clear
dependence of the umbral brightness on sunspot size, however. The penumbral
brightness also displays a weak dependence. The brightness-radius relationship
has numerous implications, some of which, such as those for the energy
transport in umbrae, are pointed out.Comment: 16 pages, 21 postscript figures, accepted for publication in A&
Transperineal ultrasonography in stress urinary incontinence
Background: The aim of our study is to assess, using transperineal ultrasonography, amount of bladder neck mobility using rotational angles; represented by the difference in the anterior (α angle) and posterior urethral angles (β angle) and proximal pubourethral distance at rest and straining, in stress urinary incontinence and control group, to ascertain if there are significant differences in their values between the groups.Methods: In all, 24 women with SUI (SUI group) and 20 continent women (control group) were included. Transperineal ultrasonography was performed at rest and straining (Valsalva manoeuver), and the threshold value for the urethral angles (α and β angles) and proximal pubourethral distance for each group were estimated.Results: A significant difference was found in calculating the numerical value of the increment of both α and β angles in both groups, at rest and at straining (rotation angle α and rotation angle β (Rα and Rβ)). Higher rotation angles were seen in the SUI group for both the α angle and the β angle compared with those of the control group; mean (SD) Rα SUI 29.37±7.46 vs. controls 10.83±3.46°; and Rβ SUI 27.97±7.47 vs. controls 13.00±3.16°; p<0.01. There was also significant difference in proximal pubourethral distance (<0.01) during resting and straining phases in patients with SUI.Conclusions: Rotational angles and pubourethral distance helps in evaluation of stress urinary incontinence and reduces the need of urodynamic studies
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