82 research outputs found
Hydraulic falls under a floating ice plate due to submerged obstructions
AbstractSteady two-dimensional nonlinear flexural–gravity hydraulic falls past a submerged obstruction on the bottom of a channel are considered. The fluid is assumed to be ideal and is covered above by a thin ice plate. Cosserat theory is used to model the sheet of ice as a thin elastic shell, and boundary integral equation techniques are then employed to find critical flow solutions. By utilising a second obstruction, solutions with a train of waves trapped between two obstructions are investigated.</jats:p
Forest land fund and the quality of the trade of wood products
Maintenance and extension of forest area represent a major objective of the general strategy of environmental
protection. In the same time, a rational exploitation of wood production is an essential component of the economic
development of any country. In this context, the paper analyzes the evolution of forest areas in Romania and in other
representative European countries. The economic contribution of wood products is comparatively analyzed in terms of
the quality of the trade of such products, thus analyzing the ratio between the value of one imported tone and one
exported tone wood product for several countries
The interwar agriculture: ideal or trap
This paper intends to reveal considerable historic realities regarding the Romanian agriculture, which may be
considered the main reasons of the failure of implementing efficient strategies after the year of 1989. The well-known
sayings “Romania, the granary of Europe”, “The strong interwar Romanian Leu” and “Romania – peony of the interwar
period” are analyzed based on statistic data with the aim to divulge the truth about the Romanian agriculture in the
interwar period. Results indicate that the import of cereals (not wheat) in Europe was on average 5% from Romania,
which is an insignificant percentage for the consumption balance of the European continent. Moreover, two periods of
time are considered to compare the Romanian agriculture before and after 1989. The unstructured agriculture, the
exaggerated fragmentation of the agriculture land and the use of subsistence agriculture on many agricultural surfaces
of the country lead Romania to be declassified in the world hierarchy of the average cereal production, from position
number 8 occupied before 1989 to position number 14 in the hierarchy of the analyzed countries and regions for the
period 1990-2007
Assessment of Soil Quality along the Proposed Main Road through Ngorongoro and Northern Serengeti, Tanzania
A new road through northern Serengeti National Park is proposed to be built. The purpose of this study was to collect baseline data on soils along the route of the proposed road before its construction. The physicochemical properties were used to characterize the soil before the construction of the proposed road. Levels of soil macro-elements mainly potassium (K), calcium (Ca), magnesium (Mg) and sodium (Na), and physicochemical properties: electrical conductivity (EC), pH, organic carbon (OC), soil organic matter (SOM), total nitrogen (TN), cation exchange capacity (CEC), phosphorus (P), aluminium (Al) were determined. Also, heavy metals: cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), lead (Pb), manganese (Mn), mercury (Hg), nickel (Ni) and zinc (Zn) were analyzed. This study was done on the eastern (Ngorongoro District) and western (Serengeti District) segments of the proposed road. The ranges in average values obtained for the physicochemical parameters and metal concentrations in the soils were: 0.05–0.57 mS/m for EC, 6.5–7.9 for pH, 0.71–1.23% for OC, 0.30–0.74 g/kg for TN, 1.23–2.12% for SOM, 20.6–79.7 mg/kg for available P, 0.27–2.08 meq/100-g for available K, 9.89–30.3 meq/100-g for available Ca, 0.29–0.67 meq/100-g for available Mg, 0.06–1.35 meq/100-g for available Na, 11.04–33.12 meq/100-g for CEC, 46702.9–63963.3 mg/kg for Al, BDL for Cd, 24.70–101.55 mg/kg for Cr, 27.31–34.96 mg/kg for Cu, 32390.8–42439 mg/kg for Fe, 18.06–22.19 mg/kg for Pb, 957.1–1458.9 mg/kg for Mn, BDL for Hg, 20.24–32.52 mg/kg for Ni and 96.09–124.14 mg/kg for Zn. These observed levels indicate that the soils before road construction are unpolluted, moderately fertile and within the specifications of good agricultural soil. On the western segment of the proposed road, the soil will need application of fertilizers for better agricultural usage.
Keywords: Physicochemical properties; soil quality; total nitrogen; macro-elements; heavy metals
Vector/tensor duality in the five dimensional supersymmetric Green-Schwarz mechanism
The five dimensional version of the Green-Schwarz mechanism can be invoked to
cancel U(1) anomalies on the boundaries of brane world models. In five
dimensions there are two dual descriptions that employ either a two-form tensor
field or a vector field. We present the supersymmetric extensions of these dual
theories using four dimensional N=1 superspace. For the supersymmetrization of
the five dimensional Chern-Simons three form this requires the introduction of
a new chiral Chern-Simons multiplet. We derive the supersymmetric vector/tensor
duality relations and show that not only is the usual one/two-form duality
modified, but that there is also an interesting duality relation between the
scalar components. Furthermore, the vector formulation always contains singular
boundary mass terms which are absent in the tensor formulation. This apparent
inconsistency is resolved by showing that in either formulation the four
dimensional anomalous U(1) mass spectrum is identical, with the lowest lying
Kaluza-Klein mode generically obtaining a finite nonzero mass.Comment: 1+35 pages, LaTeX, 1 figure, references added, typos correcte
Moduli stabilization with positive vacuum energy
We study the effect of anomalous U(1) gauge groups in string theory
compactification with fluxes. We find that, in a gauge invariant formulation,
consistent AdS vacua appear breaking spontaneously supergravity. Non vanishing
D-terms from the anomalous symmetry act as an uplifting potential and could
allow for de Sitter vacua. However, we show that in this case the gravitino is
generically (but not always) much heavier than the electroweak scale. We show
that alternative uplifting scheme based on corrections to the Kahler potential
can be compatible with a gravitino mass in the TeV range.Comment: 20 pages, 1 figur
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