521 research outputs found
Solar rotation rate and its gradients during cycle 23
Available helioseismic data now span almost the entire solar activity cycle
23 making it possible to study solar-cycle related changes of the solar
rotation rate in detail. In this paper we study how the solar rotation rate, in
particular, the zonal flows change with time. In addition to the zonal flows
that show a well known pattern in the solar convection zone, we also study
changes in the radial and latitudinal gradients of the rotation rate,
particularly in the shear layer that is present in the immediate sub-surface
layers of the Sun. In the case of the zonal-flow pattern, we find that the band
indicating fast rotating region close to the equator seems to have bifurcated
around 2005. Our investigation of the rotation-rate gradients show that the
relative variation in the rotation-rate gradients is about 20% or more of their
average values, which is much larger than the relative variation in the
rotation rate itself. These results can be used to test predictions of various
solar dynamo models.Comment: To appear in ApJ. Fig 5 has been corrected in this versio
Antiulcerogenic activity of ethanolic leaf extract of Lasianthera africana
The effect of ethanolic leaf extract of Lasianthera africana on experimentally induced ulcer was studied in rats. The extract (1000 – 3000mg/kg) inhibited ethanol-induced, indomethacin – induced and reserpine –induced ulcer models in a dose dependent fashion. The various degrees of inhibitions were statistically significant (
How much do helioseismological inferences depend upon the assumed reference model?
We investigate systematic uncertainties in determining the profiles of the
solar sound speed, density, and adiabatic index by helioseismological
techniques. We find that rms uncertainties-averaged over the sun of ~ 0.2%-0.4%
are contributed to the sound speed profile by each of three sources: 1)the
choice of assumed reference model, 2) the width of the inversion kernel, and 3)
the measurements errors. The density profile is about an order of magnitude
less well determined by the helioseismological measurements. The profile of the
adiabatic index is determined to an accuracy of about 0.2% . We find that even
relatively crude reference models yield reasonably accurate solar parameters.Comment: Accepted for publication in ApJ . Related material at
http://www.sns.ias.edu/~jn
Solar cycle variation in solar f-mode frequencies and radius
Using data from the Global Oscillation Network Group (GONG) covering the
period from 1995 to 1998, we study the change with solar activity in solar
f-mode frequencies. The results are compared with similar changes detected from
the Michelson Doppler Imager (MDI) data. We find variations in f-mode
frequencies which are correlated with solar activity indices. If these changes
are due to variation in solar radius then the implications are that the solar
radius decreases by about 5 km from minimum to maximum activity.Comment: To appear in Solar Physic
Temporal variations of solar rotation rate at high latitudes
Frequency splitting coefficients from Global Oscillation Network Group (GONG)
and Michelson Doppler Imager (MDI) observations covering the period 1995--2001
are used to study temporal variations in the solar rotation rate at high
latitudes. The torsional oscillation pattern in the Sun is known to penetrate
to a depth of about with alternate bands of faster and slower
rotating plasma. At lower latitudes the bands move towards equator with time.
At higher latitudes, however, the bands appear to move towards the poles. This
is similar to the observed pole-ward movement of large scale magnetic fields at
high latitudes. This also supports theoretical results of pole-ward moving
bands at high latitudes in some mean field dynamo models. The polar rotation
rate is found to decrease between 1995 and 1999 after which it has started
increasing.Comment: To appear in ApJ Letter
Towards a Continuous Record of the Sky
It is currently feasible to start a continuous digital record of the entire
sky sensitive to any visual magnitude brighter than 15 each night. Such a
record could be created with a modest array of small telescopes, which
collectively generate no more than a few Gigabytes of data daily.
Alternatively, a few small telescopes could continually re-point to scan and
reco rd the entire sky down to any visual magnitude brighter than 15 with a
recurrence epoch of at most a few weeks, again always generating less than one
Gigabyte of data each night. These estimates derive from CCD ability and
budgets typical of university research projects. As a prototype, we have
developed and are utilizing an inexpensive single-telescope system that obtains
optical data from about 1500 square degrees. We discuss the general case of
creating and storing data from a both an epochal survey, where a small number
of telescopes continually scan the sky, and a continuous survey, composed of a
constellation of telescopes dedicated each continually inspect a designated
section of the sky. We compute specific limitations of canonical surveys in
visible light, and estimate that all-sky continuous visual light surveys could
be sensitive to magnitude 20 in a single night by about 2010. Possible
scientific returns of continuous and epochal sky surveys include continued
monitoring of most known variable stars, establishing case histories for
variables of future interest, uncovering new forms of stellar variability,
discovering the brightest cases of microlensing, discovering new novae and
supernovae, discovering new counterparts to gamma-ray bursts, monitoring known
Solar System objects, discovering new Solar System objects, and discovering
objects that might strike the Earth.Comment: 38 pages, 9 postscript figures, 2 gif images. Revised and new section
added. Accepted to PASP. Source code submitted to ASCL.ne
Changes in Solar Dynamics from 1995 to 2002
Data obtained by the GONG and MDI instruments over the last seven years are
used to study how solar dynamics -- both rotation and other large scale flows
-- have changed with time. In addition to the well known phenomenon of bands of
faster and slower rotation moving towards the equator and pole, we find that
the zonal flow pattern rises upwards with time. Like the zonal flows, the
meridional flows also show distinct solar activity related changes. In
particular, the anti-symmetric component of the meridional flow shows a
decrease in speed with activity. We do not see any significant temporal
variations in the dynamics of the tachocline region where the solar dynamo is
believed to be operating.Comment: To appear in ApJ, March 1 200
Determination of Radioactive Elements Concentrations in Soils of Selected Areas in Akwa Ibom State, Nigeria by Instrumental Neutron Activation Analysis
A determination of radioactive elements concentrations in soils in selected parts of Akwa Ibom state, Nigeria were carried out by Instrumental Neutron Activation Analysis (INAA) technique. The soil analysis was conducted at the Nigeria Nuclear Research Reactor (NIRR – 1) at center for Energy Research and Training (CERT), Ahmadu Bello University Zaria, Nigeria. Twenty elements that include short lives, intermediate lives and long lives radioactive elements were detected in soil samples used for the analysis. The obtained radionuclides includes Na, Ti, V, As K, Mn, Sb, Fe, Dy, Pa, Mg, Sc, Yb, Ce, Co, Sm etc. The results show that INAA of soil samples of the area under investigation gave concentration of 20.05+ 0.60ppm for K, 9.36+ 0.79ppm for Na, 5.73+ 0.50ppm for Fe, 5.38+ 0.62ppm for Cr, 4.24+ 0.25ppm for As and 3.65+ 0.32ppm for Sb, etc. Comparison of the result from this with other studies show difference in the number of elements obtained which is attributed to the difference in the geology of these areas. Keywords: Soil, INAA, concentration, Radionuclides and NIRR-
Bounds on the Magnetic Fields in the Radiative Zone of the Sun
We discuss bounds on the strength of the magnetic fields that could be buried
in the radiative zone of the Sun. The field profiles and decay times are
computed for all axisymmetric toroidal Ohmic decay eigenmodes with lifetimes
exceeding the age of the Sun. The measurements of the solar oblateness yield a
bound <~ 7 MG on the strength of the field. A comparable bound is expected to
come from the analysis of the splitting of the solar oscillation frequencies.
The theoretical analysis of the double diffusive instability also yields a
similar bound. The oblateness measurements at their present level of
sensitivity are therefore not expected to measure a toroidal field
contribution.Comment: 15 pages, 6 figure
Epistemological access through lecture materials in multiple modes and language varieties: the role of ideologies and multilingual literacy practices in student evaluations of such materials at a South African University
This paper seeks to address the ways in which ideology and literacy practices shape the responses of students to an ongoing initiative at the University of the Western Cape aimed at diversifying options for epistemological access, specifically the language varieties and the modes in which parts of the curriculum for a third year linguistics module are delivered. Students’ responses to the materials in English and in two varieties of Afrikaans and isiXhosa (as mediated in writing vs orally) are determined, and used as basis to problematize decisions on language variety and mode in language diversification initiatives in Higher Education in South Africa. The findings of the paper are juxtaposed against particular group interests in the educational use of a language as well as differences in the affordances and impact of different modes of language use. The paper suggests that beyond the euphoria of using languages other than English in South African Higher Education, several issues (such as entrenched language practices, beliefs and language management orientations) require attention if the goals of transformation in this sector are to be attained
- …