848 research outputs found
EFFECT OF PHYSICO-CHEMICAL CHARACTERISTICS OF WATER OF RIVER OGUN ON THE DISTRIBUTION AND ABUNDANCE OF AQUATIC INSECTS
This study was carried out to determine the abundance, composition, distribution of aquatic insects and physico – chemical factors of Ogun River. The aquatic insects were collected using sweep and pond net (0.5mm) from two study sites during February and middle April, 2012. The water samples and insects were collected once in a week. Insects were sampled using standard entomological methods, while water samples was analysed using standard Winkler’s titrimetric and APHA methods to determine the chemical properties. Water analyses were conducted in the laboratory of Ogun State Water Corporation, Abeokuta, Ogun State. While insects identifications were done in the laboratory in the Entomology Laboratory of the College of Natural Sciences, Federal University of Agriculture, Abeokuta, Nigeria. Results show that five orders and thirteen families were found with the highest number of aquatic insects from the order Odonata. The most abundant family were Coenagriidae and Libellulidae respectively. Physico – chemical values, water temperature, pH, Dissolved Oxygen ( DO), Conductivity and Nutrient were measured. Only conductivity had the greater value among the water quality parameters.Â
AN EVALUATION OF GENDER LEARNING OUTCOMES IN VOCATIONAL AND TECHNICAL EDUCATION USING CONTEMPORARY TEACHING STRATEGIES AMONGST SENIOR SECONDARY SCHOOL STUDENTS IN EKITI STATE, NIGERIA
The study evaluated the effects of power point presentation and gaming simulation on gender learning outcomes amongst senior secondary schools students offering Vocational and Technical education subjects in Ekiti State. The purpose was to find out whether there exists any disparity in gender learning outcomes using contemporary teaching strategies in Ekiti State Senior Secondary Schools in Vocational and Technical Education subjects. The study employed the Quazi experimental research design. The sample consisted of 47 senior secondary school student chosen from the three senatorial districts in Ekiti State. The instrument used to collect data was the Vocational and Technical Education Achievement Test (VTEAT). Two research questions and two hypotheses were formulated. Mean and standard deviation were used to analyze the data for answering the research questions while Analysis of Covariance (ANCOVA) was used to the hypotheses of no significance at 0.05 level of significance. Results of the study showed that students taught with contemporary teaching strategies had higher post test scores in the vocational and technical education achievement test than those taught with conventional method of teaching. There were also no significant difference in the performance of male students taught with contemporary teaching strategies and female students in the senior secondary schools. It was recommended that the teachers of vocational and technical education in senior secondary school should take the advantage of using the contemporary teaching strategies their teaching procedures on the basis of enriching their students academic success. Key Words: Contemporary teaching strategies, vocational and technical education, gender, learning outcome, senior secondary school students
Observer-Based Controller for Disturbance Decoupling of Max-plus Linear Systems with Applications to a High Throughput Screening System in Drug Discovery
Max-plus linear systems are often used to model timed discrete-event systems, which represent system operations as discrete sequences of events in time. This paper presents the observer-based controller to solve the disturbance decoupling problem for max-plus linear systems where only estimations of system states are available for the controller. This observer-based controller leads to a greater control input than the one obtained with the output feedback strategy based on just-in-time criterion. A high throughput screening system in drug discovery illustrates this main result by showing that the scheduling obtained from the observer-based controller solving the disturbance decoupling problem is better than the scheduling obtained from the output feedback controller
Dusty star forming galaxies at high redshift
The global star formation rate in high redshift galaxies, based on optical
surveys, shows a strong peak at a redshift of z=1.5, which implies that we have
already seen most of the formation. High redshift galaxies may, however, emit
most of their energy at submillimeter wavelengths if they contain substantial
amounts of dust. The dust would absorb the starlight and reradiate it as
far-infrared light, which would be redshifted to the submillimeter range. Here
we report a deep survey of two blank regions of sky performed at submillimeter
wavelengths (450 and 850-micron). If the sources we detect in the 850-micron
band are powered by star formation, then each must be converting more than 100
solar masses of gas per year into stars, which is larger than the maximum star
formation rates inferred for most optically-selected galaxies. The total amount
of high redshift star formation is essentially fixed by the level of background
light, but where the peak occurs in redshift for the submillimeter is not yet
established. However, the background light contribution from only the sources
detected at 850-micron is already comparable to that from the
optically-selected sources. Establishing the main epoch of star formation will
therefore require a combination of optical and submillimeter studies.Comment: 10 pages + 2 Postscript figures, under embargo at Natur
Diffuse Lyman Alpha Haloes around Lyman Alpha Emitters at z=3: Do Dark Matter Distributions Determine the Lyman Alpha Spatial Extents?
Using stacks of Ly-a images of 2128 Ly-a emitters (LAEs) and 24 protocluster
UV-selected galaxies (LBGs) at z=3.1, we examine the surface brightness
profiles of Ly-a haloes around high-z galaxies as a function of environment and
UV luminosity. We find that the slopes of the Ly-a radial profiles become
flatter as the Mpc-scale LAE surface densities increase, but they are almost
independent of the central UV luminosities. The characteristic exponential
scale lengths of the Ly-a haloes appear to be proportional to the square of the
LAE surface densities (r(Lya) \propto Sigma(LAE)^2). Including the diffuse,
extended Ly-a haloes, the rest-frame Ly-a equivalent width of the LAEs in the
densest regions approaches EW_0(Lya) ~ 200 A, the maximum value expected for
young (< 10^7 yr) galaxies. This suggests that Ly-a photons formed via shock
compression by gas outflows or cooling radiation by gravitational gas inflows
may partly contribute to illuminate the Ly-a haloes; however, most of their
Ly-a luminosity can be explained by photo-ionisation by ionising photons or
scattering of Ly-a photons produced in HII regions in and around the central
galaxies. Regardless of the source of Ly-a photons, if the Ly-a haloes trace
the overall gaseous structure following the dark matter distributions, it is
not surprising that the Ly-a spatial extents depend more strongly on the
surrounding Mpc-scale environment than on the activities of the central
galaxies.Comment: 7 pages, 4 figures, accepted for publication in MNRA
WR bubbles and HeII emission
We present the very first high quality images of the HeII 4686 emission in
three high excitation nebulae of the Magellanic Clouds. A fourth high
excitation nebula, situated around the WR star BAT99-2, was analysed in a
previous letter. Using VLT FORS data, we investigate the morphology of the ring
nebulae around the early-type WN stars BAT99-49 & AB7. We derive the total HeII
fluxes for each object and compare them with the most recent theoretical WR
models. Using Halpha, [OIII] and HeI 5876 images along with long-slit
spectroscopy, we investigate the physical properties of these ring nebulae and
find only moderate chemical enrichment. We also surveyed seven other LMC WR
stars but we failed to detect any HeII emission but note that the nebula around
BAT99-11 shows a N/O ratio and an oxygen abundance slightly lower than the LMC
values, while the nebula around BAT99-134 presents moderate chemical enrichment
similar to the one seen near BAT99-2, 49 and AB7. The third high excitation
nebula presented in this paper, N44C, does not harbor stars hotter than mid-O
main sequence stars. It was suggested to be a fossil X-ray nebula ionized but
our observations of N44C reveal no substantial changes in the excitation
compared to previous results reported in the literature.Comment: 13 pages, 8 figures (7 in jpg), accepted by A&A, also available from
http://vela.astro.ulg.ac.be/Preprints/P81/index.htm
The chemical composition of metal-poor emission-line galaxies in the Data Release 3 of the Sloan Digital Sky Survey
We have re-evaluated empirical expressions for the abundance determination of
N, O, Ne, S, Cl, Ar and Fe taking into account the latest atomic data and
constructing an appropriate grid of photoionization models with state-of-the
art model atmospheres. Using these expressions we have derived heavy element
abundances in the 310 emission-line galaxies from the Data Release 3 of
the Sloan Digital Sky Survey (SDSS)with an observed Hbeta flux F(Hbeta)> 1E-14
erg s^{-1} cm^{-2} and for which the [O III] 4363 emission line was detected at
least at a 2sigma level, allowing abundance determination by direct methods.
The oxygen abundance 12 + log O/H of the SDSS galaxies lies in the range from ~
7.1 (Zsun/30) to 8.5 (0.7 Zsun). The SDSS sample is merged with a sample of 109
blue compact dwarf (BCD) galaxies with high quality spectra, which contains
extremely low-metallicity objects. We use the merged sample to study the
abundance patterns of low-metallicity emission-line galaxies. We find that
extremely metal-poor galaxies (12 + log O/H < 7.6, i.e. Z < Zsun/12) are rare
in the SDSS sample. The alpha element-to-oxygen abundance ratios do not show
any significant trends with oxygen abundance, in agreement with previous
studies, except for a slight increase of Ne/O with increasing metallicity,
which we interpret as due to a moderate depletion of O onto grains in the most
metal-rich galaxies. The Fe/O abundance ratio is smaller than the solar value,
by up to 1 dex at the high metallicity end. (abridged)Comment: 17 pages, 12 figures. Accepted for publication in the Astronomy and
Astrophysic
The Subaru Ly-alpha blob survey: A sample of 100 kpc Ly-alpha blobs at z=3
We present results of a survey for giant Ly-alpha nebulae (LABs) at z=3 with
Subaru/Suprime-Cam. We obtained Ly-alpha imaging at z=3.09+-0.03 around the
SSA22 protocluster and in several blank fields. The total survey area is 2.1
square degrees, corresponding to a comoving volume of 1.6 x 10^6 Mpc^3. Using a
uniform detection threshold of 1.4 x 10^{-18} erg s^{-1} cm^{-2} arcsec^{-2}
for the Ly-alpha images, we construct a sample of 14 LAB candidates with
major-axis diameters larger than 100 kpc, including five previously known blobs
and two known quasars. This survey triples the number of known LABs over 100
kpc. The giant LAB sample shows a possible "morphology-density relation":
filamentary LABs reside in average density environments as derived from compact
Ly-alpha emitters, while circular LABs reside in both average density and
overdense environments. Although it is hard to examine the formation mechanisms
of LABs only from the Ly-alpha morphologies, more filamentary LABs may relate
to cold gas accretion from the surrounding inter-galactic medium (IGM) and more
circular LABs may relate to large-scale gas outflows, which are driven by
intense starbursts and/or by AGN activities. Our survey highlights the
potential usefulness of giant LABs to investigate the interactions between
galaxies and the surrounding IGM from the field to overdense environments at
high-redshift.Comment: MNRAS Letters accepted (6 pages, 4 figures, 2 tables
New abundance measurements in UKS 1927-177, a very metal-poor galaxy in the Local Group
We present new results from optical spectroscopy of the brightest Hii region
in the dwarf irregular galaxy UKS 1927-177 in Sagittarius (SagDIG). From high
signal-to-noise spectra, reddening-corrected line flux ratios have been
measured with typical uncertainties of a few percent, from which the oxygen
abundance is rediscussed, and new abundance estimates are derived for N and Ne.
The O abundance in SagDIG, estimated with the empirical abundance indicator R23
and other methods, is in the range 12+log(O/H)=7.26 to 7.50. The fact that
SagDIG is ~10 times closer than IZw18 makes it an ideal target to test the
hypothesis of the existence of young galaxies in the present-day universe.
Indeed, stellar photometry suggests that this galaxy may harbor a stellar
population older than a few Gyr, and possibly an old stellar component as well.
The case of SagDIG therefore supports the view that very low chemical
abundances can be maintained throughout the life of a dwarf stellar system,
even in the presence of multiple star formation episodes.Comment: 6 pages, 3 figures, accepted for publication in A&A, main journa
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