557 research outputs found
Predictability and Non-Gaussian Characteristics of the North Atlantic Oscillation
AbstractThe North Atlantic Oscillation (NAO) is the dominant mode of climate variability over the North Atlantic basin and has a significant impact on seasonal climate and surface weather conditions. It is the result of complex and nonlinear interactions between many spatiotemporal scales. Here, the authors study the statistical properties of two time series of the daily NAO index. Previous NAO modeling attempts only considered Gaussian noise, which can be inconsistent with the system complexity. Here, it is found that an autoregressive model with non-Gaussian noise provides a better fit to the time series. This result holds also when considering time series for the four seasons separately. The usefulness of the proposed model is evaluated by means of an investigation of its forecast skill
Effect of Thiourea on Yield and Quality of Potato (Solanum tuberosum L.)
A field experiment was carried out to study the effect of five concentrations (0, 250, 500, 750 and 1000 mM) of thiourea application on mother tubers on yield and quality attributes of harvested potato, variety Spunta in the region of Chott-Mariem in Tunisia. Treated tubers (Đš = 50 mm) were planted in field after breaking dormancy at a spacing of 80 cm x 30 cm according to completely randomized design (CRD) in three replications. Quality attributes of potato tubers especially fresh matter and dry matter of plant, total reducing sugars in leaves, tuber yield, number and diameter of tubers per plant and number of sprouts per tuber was measured. Soluble proteins and starch content in potato tubers were also quantified.In general we noted that application of thiourea showed significant influence on yield and on quality of tubers comparing to control. Maximum tuber yield per plant, maximum number of tubers per plant and maximum starch content was recorded with 250 mM of thiourea. Moreover, highest dry matter of potato plant was found also at this concentration. While increasing dose of thiourea thereafter it showed slight significant improvement and do not affect significantly the diameter of tubers comparing to control
Response of sesame seedlings to different concentrations of humic acids or calcium nitrate at germination and early growth
This study was conducted in
order to evaluate the response of sesame
seeds (Sesamum indicum L.) to organic or
mineral fertilization. The effects of two
fertilizers, which were calcium nitrate and
humic acids were studied separately at
germination and early seedlings growth.
Different concentrations of humic acids
(HA0: 0, HA1: 500, HA2: 1000 and HA3:
2000 mg Lâ1) or calcium nitrate (CaN0: 0,
CaN1: 50, CaN2: 100 and CaN3: 200 mg Lâ1)
were applied distinctly to the growth media.
The experimental design was accomplished
in a completely randomized block design
with three replications. Germination
measurements, seedlings length, fresh
seedling weight, total chlorophylls and
carotenoids, total soluble proteins and
sugars were determined. Results showed
that humic acids applied at 1000 mg L-1 or
calcium nitrate applied at 100 mg L-1
reduced the mean germination time (3.5 and
3.61 days) and had the highest germination
index (GI) and the highest coefficient of
velocity (CV). The longest seedling was
obtained at the concentrations HA2 and
CaN2 (+22%). Total chlorophyll and
carotenoids were significantly higher in
seedlings receiving the HA2 and CaN2 and
these treatments increased total soluble
proteins content by 32%. Higher
concentrations of humic acids or calcium
nitrate HA3 and CaN3 delayed germination
and enhanced proline and total soluble
sugars, respectively, by 42% and 46%,
compared to control. These preliminary
results indicated that the use of fertilizers
should be optimized and they can be
transformed at high level to an abiotic stress
menacing plant productivity. On the other
hand, suitable concentrations of fertilizers
can be used in the future as a remedy to
improve growth under abiotic stress
Impeller optimization in crossflow hydraulic turbines
Crossflow turbines represent a valuable choice for energy recovery in aqueducts, due
to their constructive simplicity and good efficiency under variable head jump conditions. Several
experimental and numerical studies concerning the optimal design of crossflow hydraulic turbines
have already been proposed, but all of them assume that structural safety is fully compatible with
the sought after geometry. We show first, with reference to a specific study case, that the geometry
of the most efficient impeller would lead shortly, using blades with a traditional circular profile
made with standard material, to their mechanical failure. A methodology for fully coupled fluid
dynamic and mechanical optimization of the blade cross-section is then proposed. The methodology
assumes a linear variation of the curvature of the blade external surface, along with an iterative use of
two-dimensional (2D) computational fluid dynamic (CFD) and 3D structural finite element method
(FEM) simulations. The proposed methodology was applied to the design of a power recovery system
(PRS) turbine already installed in an operating water transport network and was finally validated
with a fully 3D CFD simulation coupled with a 3D FEM structural analysis of the entire impeller
Modélisation du rendement grain du pois chiche (Cicer arietinum L.) du type « kabuli » sous les conditions édapho-climatiques du semi-aride supérieur Tunisien
Un essai est conduit, in situ, en pots, sous des conditions Ă©dapho-climatiques contrĂŽlĂ©es du semi aride supĂ©rieur Tunisien. Le matĂ©riel vĂ©gĂ©tal est composĂ© de huit gĂ©notypes de pois chiche du type « kabuli ». Quatre doses dâirrigation ont Ă©tĂ© administrĂ©es, notamment, 100%, 75%, 50% et 25% de la rĂ©serve facilement utilisable (RFU). Les rĂ©sultats indiquent que seuls le poids des gousses/m2 et le nombre de graines/m2 ont des effets directs significatifs sur le rendement en graines. Le nombre de graines/m2, la biomasse aĂ©rienne, la dose dâirrigation et le poids de 100 graines ont prĂ©sentĂ© les effets indirects positifs les plus Ă©levĂ©s; alors que les dates de floraison prĂ©coce, de floraison et de maturitĂ© prĂ©coce et le poids des gousses/m2 ont prĂ©sentĂ© les effets indirects nĂ©gatifs les plus Ă©levĂ©s. La rĂ©gression linĂ©aire multiple « pas Ă pas » a permis de rĂ©duire le nombre de covariables qui expliquent le rendement en graines. Lâanalyse sĂ©quentielle de piste, fondĂ©e sur le classement des covariables en premier et second ordre sur la base de leurs effets directs les plus Ă©levĂ©s et de leurs colinĂ©aritĂ©s minimales, a montrĂ© que le poids des gousses/m2 et le nombre de graines/m2 ont des effets directs hautement significatifs et que lâindice de rĂ©colte et la biomasse aĂ©rienne ont les effets indirects les plus Ă©levĂ©s sur le rendement en graines
PHYSIOLOGICAL MECHANISMS FOR POTATO DORMANCY RELEASE AND SPROUTING: A REVIEW
Potato ( Solanum tuberosum \ua0L.) tubers undergo a period of
dormancy, during which visible bud growth is inhibited. The length of
the dormancy is determined by environmental, physiological and hormonal
control mechanisms. Dormancy is the final stage of tuber life, which
serves to preserve tubers as organs of vegetative reproduction under
unfavourable growth conditions. Since the duration of potato tuber
dormancy and sprouting time bear significant economic importance, this
review considers the regulation of dormancy and sprouting of potato by
phytohormones and reactive oxygen species. Two phytohormones, ABA and
ethylene suppress tuber sprouting; however, the exact role of ethylene
remains to be elucidated. Cytokinins and gibberellins are required for
bud breaking and sprout growth, respectively. The auxin seems to play a
role in vascular development. Thus, tuber dormancy and sprouting can be
controlled in potato by manipulation of Reactive Oxygen Species (ROS),
especially H2O2\ua0metabolism via the inhibition of catalase (CAT)
activity.The possible mechanisms by which CAT inhibitors or
H2O2\ua0overcome dormancy and promote sprouting in the potato tuber
are discussed.La pomme de terre ( Solanum tuberosum \ua0L.) conna\ueet une
p\ue9riode de dormance durant laquelle la germination des bourgeons
visibles est inhib\ue9e. La dur\ue9e de dormance est
d\ue9termin\ue9e par des m\ue9canismes de contr\uf4le
environnemental, physiologique and hormonal. La dormance est le stade
final de la vie des tubercules servant \ue0 pr\ue9server les
tubercules comme organes de reproduction v\ue9g\ue9tative sous
condition de germination d\ue9favorables. Etant donn\ue9 que la
dur\ue9e de la dormance des tubercules de la pomme de terre et le
temps de rejet rev\ueatent une importance \ue9conomique
significative, cette revue consid\ue8re la r\ue9gulation de la
dormance et le rejet de la pomme de terre par des hormones et
d\u2019esp\ue8ces r\ue9actives d\u2019oxyg\ue8ne (ROS). Deux
phytohormones\ua0; ABA et \ue9thyl\ue8ne emp\ueachent le rejet
des tubercules\ua0; par ailleurs, le r\uf4le extractif de
l\u2019\ue9thyl\ue8ne reste \ue0 \ue9lucider. Les cytokinines
and les gibb\ue9rellines sont n\ue9cessaires dans
l\u2019\ue9limination des bourgeons et la croissance des rejets,
respectivement. L\u2019auxine semble jouer un r\uf4le dans le
d\ue9veloppement vasculaire. Ainsi, la dormance et les rejets des
tubercules peuvent \ueatre contr\uf4l\ue9s par manipulation
d\u2019esp\ue8ces r\ue9actives d\u2019oxyg\ue8ne (ROS),
sp\ue9cialement le m\ue9tabolisme du H2O2\ua0\ue0 travers
l\u2019inhibition de l\u2019activit\ue9 de la catalase (CAT). Les
m\ue9canismes possibles par lesquels les inhibiteurs du CAT ou
H2O2\ua0 surmontent la dormance et facilitent le rejet de la pomme de
terre sont discut\ue9s
Germination and growth in control and primed seeds of pepper as affected by salt stress
Salinity is an important
abiotic stress which can affect crop
production in the world. One of the simplest
methods for improving salinity tolerance of
plants is seeds priming. This experiment
was conducted to evaluate the effects of
seeds priming with three solutions (KCl ,
NaCl and CaCl2) in germination and later
growth of three pepper (Capsicum annuum
L.) cultivars: Beldi, Baklouti and Anaheim
Chili. Seeds germination was conducted in a
completely randomized design under seven
salinity levels (0, 2, 4, 6, 8, 10 and 12 g L-1)
at room temperature for primed and control
seeds. Plants derived from these germinated
seeds (control and primed) were
transplanted and cultivated in a greenhouse
for 4 months and were irrigated permanently
with seven salinity levels (0, 2, 4, 6, 8, 10
and 12 g L-1). The results showed that
salinity affected all parameters under study
like total germination percentage and
chlorophyll level (a and b). As well, proline
content increased as response to increasing
salinity. The plants derived and grown from
primed seeds showed a considerable
tolerance to salt stress and gave better
results. In fact, priming improved the salt
resistance of pepper owing to more
chlorophyll and proline accumulation.
These results suggest that seed priming
induced possible physiological adjustments
in pepper seeds, especially in the early
stages of development, and could be used as
a suitable tool for improving germination
and growth characteristics under salt stress
conditions
Comportement agronomique d'une collection de pois (Pisum sativum L)
Agronomical Behaviour of a Pea Collection (Pisum sativum L.). This experience was achieved under greenhouse conditions. Twelve genotypes of pea were used (Asgrow, Jumbo, Lincoln, Merveille de Kelvedon, Purser, Rajai Torpe, Snajor Kosep, Korai,Wando, Rondo, local genotype, Major Kosep Korai and Surgevil). They were cultivated on peat during 5.5 months (from October to April). Some agronomical parameters were studied: resistance to diseases, (Powdery-mildew, mildew, top yellow virus, anthracnose, browning), fresh matter, number of branches/plant, number of flowers/plant, number of pods/ plant and the yield of grains /plant. Results showed that only the genotype Purser is resistant to all diseases and Surgevil is sensitive only to the Top Yellow virus. The local genotype is sensitive to three frequent diseases (Powdery-mildew, mildew and Anthracnose). With regard to vegetative growth, the highest yield of fresh matter do not contribute towards a high fertility rate. In fact, only the genotypes having a weak yield of fresh matter (Snajor Kosep Korai, Asgrow, Major Kosep Korai, Rajai Torpe and Purser) have the most important rate of fertility (> 30%). Within this group, the most important yield (> 9 g/plant) is a result of high: number of pods/plant (7.5 to 21.6) and of grains/pod (2.8 to 4.92). Finally, genotype Purser should be retained for farmers and programs of genetic amelioration for its resistance to diseases and agronomical performances
Elements Discrimination in the Study of Super-Heavy Elements using an Ionization Chamber
Dedicated ionization chamber was built and installed to measure the energy
loss of very heavy nuclei at 2.7 MeV/u produced in fusion reactions in inverse
kinematics (beam of 208Pb). After going through the ionization chamber,
products of reactions on 12C, 18O targets are implanted in a Si detector. Their
identification through their alpha decay chain is ambiguous when their
half-life is short. After calibration with Pb and Th nuclei, the ionization
chamber signal allowed us to resolve these ambiguities. In the search for rare
super-heavy nuclei produced in fusion reactions in inverse or symmetric
kinematics, such a chamber will provide direct information on the nuclear
charge of each implanted nucleus.Comment: submitted to NIMA, 10 pages+4 figures, Latex, uses elsart.cls and
grahpic
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