732 research outputs found
Demand for fish in Sub-Saharan Africa: the past and the future
The Sub-Saharan region of Africa accounted for only 5.5% of the world's demand for fish from 1989 to 1991, inspite of comprising 9% of the global population. This study was carried out to determine the future demand for fish in the Sub-Saharan region. Fish accounts for approximately 10% of animal protein consumed. It is prominent in the diet of the poor since cured and smoked fish is a cheaper source of protein than meat or eggs. The average per capita consumption in 1992 was about 8 kg compared to 30 kg globally. Fish is prominent in the diets of people near coastal areas and large inland water bodies and a total of 40% of fish consumed is freshwater fish. Consumption is rising in the coastal areas but falling inland, probably due to drought and overexploitation resulting in an inadequate supply. Aquaculture has not been widely adopted and does not contribute substantially to the region's supply. To determine future demand and trends, a regression analysis was carried out at the country level with FAO data on fish consumption from 1960 to 1992, using several proxies for disposable income, cost of fishery products, changes in tastes and national differences in the tradition of fish consumption. An aggregate increase in fish consumption of nearly 2.7% annually over the next few years was predicted with a strong correlation between increases in income, prices and population. Real income was a significant and positive determinant of fish consumption, even though consumption increaed more slowly than income. Given the high projected rate of population increase, the growth rate in overall fish consumption actually implies a reduction in per capita fish consumption of 0.31% annually. If technological progress can improve production and supply, aquaculture could have a significant impact on fish consumption in the region
Estudos sôbre a neutralização do caldo de cana nas usinas de açúcar: I - determinação do CaO e MgO totais e CaO disponível da Cal
This paper is the first of several papers about the studies of neutralization of sugar cane juice, after treatment with SO2 in the cane sugar fabrication. The present work reports a study about the chelatometric method for the determination of total calcium oxide and magnesium oxide of lime and the available lime. The proposed method (by EDTA titration) for determining available lime was compared with the method based on sulfuric acid titration, with good agreement. The results showed that the chelatometric method is rapid and affords good precision. For the study about the neutralization of sugar cane juice, after treatment with SO2, were employed samples of lime containing several per cent of available lime. The quantities of lime to be added, to one liter of treated juice, was calculated based in the total calcium oxide of the lime. The solid samples of lime were added to the juice slowly and the material shaken intermittently during the period of fifteen minutes after the addition of lime. The pH was determined both 15 minutes and 2 1/2 hours after the addition of lime. Them it was brought to ebullition, cooled at room temperature and the pH was again determined. The results permit to conclude that the samples containing small amounts of available lime showed the poorest neutralization. Even with samples containing high percentage of available lime it was not possible to obtain a juice with pH 7,0 after the treatment, probably due to the presence of carbonates in the samples of lime. This study showed that the principal characteristic of lime to be employed in the juice neutralization is the available lime.Neste trabalho, que faz parte de uma série de pesquisas relacionadas com a neutralização do caldo de cana nas usinas de açúcar, é descrita a técnica de determinação quelatométrica do CaO e MgO totais e CaO disponível da cal. Os resultados fornecidos pela técnica preconizada foram comparados com aqueles obtidos através do emprêgo de métodos usuais. São também apresentados os primeiros estudos efetuados a respeito da capacidade neutralizadora da cal, em função do seu teor em oxido de calcio total e disponível, quando empregada na forma solida, na neutralização do caldo de cana
Phase diagrams of the generalized spin-1/2 ladder under staggered field and dimerization: A renormalization group study
In the weak-coupling regime of the continuous theories, two sets of one-loop
renormalization group equations are derived and solved to disclose the phase
diagrams of the antiferromagnetic generalized two-leg spin-1/2 ladder under the
effect of (I) a staggered external magnetic field and (II) an explicit
dimerization. In model (I), the splitting of the SU(2) critical line into
U(1) and Z critical surfaces is observed; while in model (II), two critical
surfaces arising from their underlying critical lines with SU(2) and Z
characteristics merge into an SU(2) critical surface on the line where the
model attains its highest symmetry.Comment: 10 pages, 9 figure
Magnetization plateaux in dimerized spin ladder arrays
We investigate the ground state magnetization plateaux appearing in spin 1/2
two-leg ladders built up from dimerized antiferromagnetic Heisenberg chains and
dimerized zig-zag interchain couplings. Using both Abelian bosonization and
Lanczos methods we find that the system yields rather unusual plateaux and
exhibits massive and massless phases for specific choices or ``tuning'' of
exchange interactions. The relevance of this behavior in the study of
NH_4CuCl_3 is discussed.Comment: 9 pages, RevTeX, 11 postscript figure
2D-Coordination polymers based on 1H-indazole4-carboxylic acid and transition metal ions: magnetic, luminescence and biological properties
We report the formation of five novel multifunctional coordination polymers based on 1H-indazole-4-
carboxylic acid (HL). To the best of our knowledge, these complexes are the first examples of coordination
compounds constructed with this interesting ligand. These materials were synthesized by solvothermal
routes, possess different 2D-structures and show interesting magnetic properties due to the copper
compound showing an unusual spin-canted effect while the anisotropic cobalt material behaves as a fieldinduced single molecule magnet. MTT assays performed on human embryonic kidney (HEK293) and
mouse skin melanoma (B16-F10) cell lines indicated that the Cd-based compound was the only one
exhibiting dose-dependent toxicity on B16-F10 cells, most likely due to the release of toxic Cd(II). Cadmium
and zinc polymers exhibit interesting luminescence properties. The fact that zinc polymers did not exhibit
inherent toxicity against both cancer and non-cancerous cells make this new family an excellent candidate
for further investigation in the field of luminescent materials with biomedical applications.Junta de Andalucia
FQM-394
FQM-1484Red Guipuzcoana de Ciencia, Tecnologia e Innovacion
OF218/2018University of Basque Country
GIU 17/13Basque Government
IT1005-16Spanish Ministry of Science, Innovation and Universities (MCIU/AEI/FEDER, UE)
PGC2018-102052-A-C22
PGC2018-102052-B-C21Junta de Andalucia
FQM-394
FQM-1484European Union (EU)ESFGovernment of the Basque CountryFEDER/MCIU/AEI
RYC-2016-21042
JdC-201
Domain wall generation by fermion self-interaction and light particles
A possible explanation for the appearance of light fermions and Higgs bosons
on the four-dimensional domain wall is proposed. The mechanism of light
particle trapping is accounted for by a strong self-interaction of
five-dimensional pre-quarks. We obtain the low-energy effective action which
exhibits the invariance under the so called \tau-symmetry. Then we find a set
of vacuum solutions which break that symmetry and the five-dimensional
translational invariance. One type of those vacuum solutions gives rise to the
domain wall formation with consequent trapping of light massive fermions and
Higgs-like bosons as well as massless sterile scalars, the so-called branons.
The induced relations between low-energy couplings for Yukawa and scalar field
interactions allow to make certain predictions for light particle masses and
couplings themselves, which might provide a signature of the higher dimensional
origin of particle physics at future experiments. The manifest translational
symmetry breaking, eventually due to some gravitational and/or matter fields in
five dimensions, is effectively realized with the help of background scalar
defects. As a result the branons acquire masses, whereas the ratio of Higgs and
fermion (presumably top-quark) masses can be reduced towards the values
compatible with the present-day phenomenology. Since the branons do not couple
to fermions and the Higgs bosons do not decay into branons, the latter ones are
essentially sterile and stable, what makes them the natural candidates for the
dark matter in the Universe.Comment: 34 pages, 2 figures, JHEP style,few important refs. adde
The effects of non-universal extra dimensions on the radiative lepton flavor decays \mu\to e\gamma and \tau\to \mu\gamma in the two Higgs doublet model
We study the effect of non-universal extra dimensions on the branching ratios
of the lepton flavor violating processes \mu\to e\gamma and \tau\to \mu\gamma
in the general two Higgs doublet model. We observe that these effects are small
for a single extra dimension, however, in the case of two extra dimensions
there is a considerable enhancement in the additional contributions.Comment: 16 Pages, 9 Figure
Geometric Approach to Pontryagin's Maximum Principle
Since the second half of the 20th century, Pontryagin's Maximum Principle has
been widely discussed and used as a method to solve optimal control problems in
medicine, robotics, finance, engineering, astronomy. Here, we focus on the
proof and on the understanding of this Principle, using as much geometric ideas
and geometric tools as possible. This approach provides a better and clearer
understanding of the Principle and, in particular, of the role of the abnormal
extremals. These extremals are interesting because they do not depend on the
cost function, but only on the control system. Moreover, they were discarded as
solutions until the nineties, when examples of strict abnormal optimal curves
were found. In order to give a detailed exposition of the proof, the paper is
mostly self\textendash{}contained, which forces us to consider different areas
in mathematics such as algebra, analysis, geometry.Comment: Final version. Minors changes have been made. 56 page
Universal extra dimensions and Z->b bar-b
We study, at the one loop level, the dominant contributions from a single
universal extra dimension to the process (Z\to b\bar{b}). By resorting to the
gaugeless limit of the theory we explain why the result is expected to display
a strong dependence on the mass of the top-quark, not identified in the early
literature. A detailed calculation corroborates this expectation, giving rise
to a lower bound for the compactification scale which is comparable to that
obtained from the parameter. An estimate of the subleading corrections
is furnished, together with a qualitative discussion on the difference between
the present results and those derived previously for the non-universal case.Comment: 16 pages, 4 figures, revtex
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