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Water reuse for irrigated agriculture in Jordan: challenges of soil sustainability and the role of management strategies
Reclaimed water provides an important contribution to the water balance in water-scarce Jordan, but the quality of this water presents both benefits and challenges. Careful management of reclaimed water is required to maximize the nutrient benefits while minimizing the salinity risks. This work uses a multi-disciplinary research approach to show that soil response to irrigation with reclaimed water is a function of the management strategies adopted on the farm by the water user. The adoption of management methods to maintain soil productivity can be seen to be a result of farmersâ awareness to potentially plant-toxic ions in the irrigation water (70% of Jordan Valley farmers identified salinization as a hazard from irrigation with reclaimed water). However, the work also suggests that farmersâ management capacity is affected by the institutional management of water. About a third (35%) of farmers in the Jordan Valley claimed that their ability to manage salinization was limited by water shortages. Organizational interviews revealed that institutional awareness of soil management challenges was quite high (34% of interviewees described salinization as a risk from water reuse), but strategies to address this challenge at the institutional level require greater development
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Manganese absorption by barley roots
An investigation of Mn uptake by five-day-old excised barley
roots revealed that a metabolically-mediated process was involved.
In short-term experiments, the rate of Mn absorption was comparable
to that of the macronutrient cations. Like other metabolically
absorbed cations, the Mn absorption rate was a direct function of
the ambient concentration and the pH.
An evaluation of mutual effects between Mn and other cations
revealed several specific regulatory effects. Of the alkali cations
studied, Li alone had a pronounced stimulatory effect while Na, K
and Rb markedly reduced the absorption of Mn. The alkaline earth
cations also exerted widely differing effects. Calcium appeared to
promote the absorption of Mn, whereas Mg had a highly inhibitive
effect. The combination of both Ca and Mg was even more inhibitory.
Strontium apparently was without effect and Ba had a moderately
depressive effect. Other polyvalent cations which were effective
inhibitors of Mn absorption were Feâșâș, Zn, Cu, Al and La. In
contrast, Feâșâșâș was virtually without effect. Manganese effectively
blocked the absorption of Li and Mg, but greatly enhanced that of Na,
K and Rb.
These diverse regulatory effects and many others reported in
the literature are explained by the following hypothesis: the cationic
environment at the extracellular surface of the membrane is believed
to control the specificity of the ion carrier. By attaching to critical
activation sites, cations induce conformational changes in the
carrier which modify its selective transport properties. The
accessibility or affinity of transport sites for a given ion would
depend on the particular configuration of the carrier. This mechanism,
together with the mutual competition between some ions for
the same transport site and the cationic maintenance of the cellular
membranes, would explain most, if not all, of the regulatory effects
exerted by cations on the ion absorption process
Atomic dynamics in evaporative cooling of trapped alkali atoms in strong magnetic fields
We investigate how the nonlinearity of the Zeeman shift for strong magnetic
fields affects the dynamics of rf field induced evaporative cooling in magnetic
traps. We demonstrate for the 87-Rb and 23-Na F=2 trapping states with wave
packet simulations how the cooling stops when the rf field frequency goes below
a certain limit (for the 85-Rb F=2 trapping state the problem does not appear).
We examine the applicability of semiclassical models for the strong field case
as an extension of our previous work [Phys. Rev. A 58, 3983 (1998)]. Our
results verify many of the aspects observed in a recent Rb experiment
[Phys. Rev. A 60, R1759 (1999)].Comment: 9 pages, RevTex, eps figures embedde
Realtime calibration of the A4 electromagnetic lead fluoride calorimeter
Sufficient energy resolution is the key issue for the calorimetry in particle
and nuclear physics. The calorimeter of the A4 parity violation experiment at
MAMI is a segmented calorimeter where the energy of an event is determined by
summing the signals of neighbouring channels. In this case the precise matching
of the individual modules is crucial to obtain a good energy resolution. We
have developped a calibration procedure for our total absorbing electromagnetic
calorimeter which consists of 1022 lead fluoride (PbF_2) crystals. This
procedure reconstructs the the single-module contributions to the events by
solving a linear system of equations, involving the inversion of a 1022 x
1022-matrix. The system has shown its functionality at beam energies between
300 and 1500 MeV and represents a new and fast method to keep the calorimeter
permanently in a well-calibrated state
The evolutionary status of the semiregular variable QYSge
Repeated spectroscopic observations made with the 6m telescope of yielded new
data on the radial-velocity variability of the anomalous yellow supergiant
QYSge. The strongest and most peculiar feature in its spectrum is the complex
profile of NaI D lines, which contains a narrow and a very wide emission
components. The wide emission component can be seen to extend from -170 to +120
km/s, and at its central part it is cut by an absorption feature, which, in
turn, is split into two subcomponents by a narrow (16km/s at r=2.5) emission
peak. An analysis of all the Vr values leads us to adopt for the star a
systemic velocity of Vr=-21.1 km/s, which corresponds to the position of the
narrow emission component of NaI. The locations of emission-line features of
NaI D lines are invariable, which point to their formation in regions that are
external to the supergiant's photosphere. Differential line shifts of about
10km/s are revealed. The absorption lines in the spectrum of QYSge have a
substantial width of FWHM~45 km/s. The method of model atmospheres is used to
determine the following parameters: Teff=6250K, lg g=2.0, and microturbulence
Vt=4.5km/s. The metallicity of the star is found to be somewhat higher than the
solar one with an average overabundance of iron-peak elements of [Met/H]=+0.20.
The star is found to be slightly overabundant in carbon and nitrogen,
[C/Fe]=+0.25, [N/Fe]=+0.27. The alpha-process elements Mg, Si, and Ca are
slightly overabundant [alpha/H]=+0.12. The strong sodium excess, [Na/Fe]=+0.75,
is likely to be due to the dredge-up of the matter processed in the NeNa cycle.
Heavy elements of the s-process are underabundant relative to the Sun. On the
whole, the observed properties of QYSge do not give grounds for including this
star into the group of RCrB or RVTau-type type objects.Comment: 29 pages, 8 figures, 4 tables; accepted by Astrophys. Bulleti
Vacuum Energy Density in the Quantum Yang - Mills Theory
Using the effective potential approach for composite operators, we have
formulated a general method of calculation of the truly non-perturbative
Yang-Mills vacuum energy density (this is, by definition, the Bag constant
apart from the sign). It is the main dynamical characteristic of the QCD ground
state. Our method allows one to make it free of the perturbative contributions
('contaminations'), by construction. We also perform an actual numerical
calculation of the Bag constant for the confining effective charge. Its choice
uniquely defines the Bag constant, which becomes free of all the types of the
perturbative contributions now, as well as possessing many other desirable
properties as colorless, gauge independence, etc. Using further the trace
anomaly relation, we develop a general formalism which makes it possible to
relate the Bag constant to the gluon condensate not using the weak coupling
solution for the corresponding function. Our numerical result for the
Bag constant shows a good agreement with other phenomenological estimates of
the gluon condensate.Comment: 28 pages and 4 figures, typos corrected, added new appendices and new
references in comparison with the published versio
Isospin breaking in the vector current of the nucleon
Extraction of the nucleon's strange form factors from experimental data
requires a quantitative understanding of the unavoidable contamination from
isospin violation. A number of authors have addressed this issue during the
past decade, and their work is reviewed here. The predictions from early models
are largely consistent with recent results that rely as much as possible on
input from QCD symmetries and related experimental data. The resulting bounds
on isospin violation are sufficiently precise to be of value to on-going
experimental and theoretical studies of the nucleon's strange form factors.Comment: 5 pages, 3 figures. Presented at the International Workshop "From
Parity Violation to Hadronic Structure and more...", Milos, Greece, 16-20 May
2006. Version 2 is only to update Refs. [21] and [25
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