Distribution of North American ash species in the Drava River basin and Danube basin (Croatia)

There are two North American ash species which have been acclimatized in north Croatian forest ecosystems: the white ash (Fraxinus americana L.) and the green ash (F. pennsylvanica Marshall). In the lowlands forests of the Drava River basin and Danube basin a total number of 960 subcompartments with North American ash species were established. According to the collected dendrological material the green ash was determined in twenty subcompartments. In those subcompartments the white ash was not found. Accordingly, the distribution of an important neophyte for wood production in the Drava River basin and Danube basin has been mapped for the first time. North American ash species are present in small, mostly isolated depressions where they were planted at the beginning or in the middle of the 20th century. Also, they spontaneously spread to many locations and with other pioneer species colonize swamps and river islets. In these locations the green ash has a pioneer and reclamation role in preparing habitats for the arrival and success of the native narrow-leaved ash (F. angustifolia Vahl). The timber value of North American ash species is small because the trees are usually bent by wind, snow and ice. Also, the trees of North American ash species were more often pulled down than the trees of native species

Effect of Pressure on Superconducting Ca-intercalated Graphite CaC6_6

The pressure effect on the superconducting transition temperature ($T_c$) of the newly-discovered Ca-intercalated graphite compound CaC$_6$ has been investigated up to $\sim$ 16 kbar. $T_c$ is found to increase under pressure with a large relative ratio $\Delta$$T_c$/$T_c$ of $\approx$ +0.4 %/kbar. Using first-principles calculations, we show that the large and positive effect of pressure on $T_c$ can be explained in the scope of electron-phonon theory due to the presence of a soft phonon branch associated to in-plane vibrations of Ca atoms. Implications of the present findings on the current debate about the superconducting mechanism in graphite intercalation compounds are discussed.Comment: 6 pages, 5 figs, final PRB versio

Non-linear terms in 2D cosmology

In this work we investigate the behavior of two-dimensional (2D) cosmological models, starting with the Jackiw-Teitelboim (JT) theory of gravitation. A geometrical term, non-linear in the scalar curvature $R$, is added to the JT dynamics to test if it could play the role of dark energy in a 2D expanding universe. This formulation makes possible, first, the description of an early (inflationary) 2D universe, when the van der Waals (vdW) equation of state is used to construct the energy-momentum tensor of the gravitational sources. Second, it is found that for later times the non-linear term in $R$ can generate an old 2D universe in accelerated expansion, where an ordinary matter dominated era evolves into a decelerated/accelerated transition, giving to the dark energy effects a geometrical origin. The results emerge through numerical analysis, following the evolution in time of the scale factor, its acceleration, and the energy densities of constituents.Comment: tex file plus figures in two zipped files. To appear in Europhys. Let

Coexistence of two order parameters and a pseudogaplike feature in the iron-based superconductor LaFeAsO_(1-x)F_x

The nature and value of the order parameters (OPs) in the superconducting Fe-based oxypnictides REFeAsO_(1-x)F_x (RE = rare earth) are a matter of intense debate, also connected to the pairing mechanism which is probably unconventional. Point-contact Andreev-reflection experiments on LaFeAsO_(1-x)F_x gave us direct evidence of three energy scales in the superconducting state: a nodeless superconducting OP, Delta1 = 2.8-4.6 meV, which scales with the local Tc of the contact; a larger unconventional OP that gives conductance peaks at 9.8-12 meV, apparently closes below Tc and decreases on increasing the Tc of the contact; a pseudogaplike feature (i.e. a depression in the conductance around zero bias), that survives in the normal state up to T* ~ 140 K (close to the Neel temperature of the undoped compound), which we associate to antiferromagnetic spin fluctuations (AF SF) coexisting with superconductivity. These findings point toward a complex, unconventional nature of superconductivity in LaFeAsO_(1-x)F_x.Comment: 19 pages, 12 figures - one figure and some insets added, minor changes to the tex

Effects of Pasture Conditions in Spring on Seasonal Forage Productivity

Fifteen beef cow-calf producers in southern Iowa were selected based on locality, management level, historical date of grazing initiation and desire to participate in the project. In 1997 and 1998, all producers kept records of production and economic data using the Integrated Resource Management-Standardized Performance Analysis (IRM-SPA) records program. At the initiation of grazing on each farm in 1997 and 1998, Julian date, degree-days, cumulative precipitation, and soil moisture, phosphorus, and potassium concentrations were determined. Also determined were pH, temperature, and load-bearing capacity; and forage mass, sward height, morphology and dry matter concentration. Over the grazing season, forage production, measured both by cumulative mass and sward height, forage in vitro digestible dry matter concentration, and crude protein concentration were determined monthly. In the fall of 1996 the primary species in pastures on farms used in this project were cool-season grasses, which composed 76% of the live forage whereas legumes and weeds composed 8.3 and 15.3%, respectively. The average number of paddocks was 4.1, reflecting a low intensity rotational stocking system on most farms. The average dates of grazing initiation were May 5 and April 29 in 1997 and 1998, respectively, with standard deviations of 14.8 and 14.1 days. Because the average soil moisture of 23% was dry and did not differ between years, it seems that most producers delayed the initiation of grazing to avoid muddy conditions by initiating grazing at a nearly equal soil moisture. However, Julian date, degree-days, soil temperature and morphology index at grazing initiation were negatively related to seasonal forage production, measured as mass or sward height, in 1998. And forage mass and height at grazing initiation were negatively related to seasonal forage production, measured as sward height, in 1997. Moreover, the concentrations of digestible dry matter at the initiation of and during the grazing season and the concentrations of crude protein during the grazing season were lower than desired for optimal animal performance. Because the mean seasonal digestible dry matter concentration was negatively related to initial forage mass in 1997 and mean seasonal crude proteins concentrations were negatively related to the Julian date, degree-days, and morphology indeces in both years, it seems that delaying the initiation of grazing until pasture soils are not muddy, is limiting the quality as well as the quantity of pasture forage. In 1997, forage production and digestibility were positively related to the soil phosphorus concentration. Soil potassium concentration was positively related to forage digestibility in 1997 and forage production and crude protein concentration in 1998. Increasing the number of paddocks increased forage production, measured as sward height, in 1997, and forage digestible dry matter concentration in 1998. Increasing yields or the concentrations of digestible dry matter or crude protein of pasture forage reduced the costs of purchased feed per cow

Confinement effects on glass forming liquids probed by DMA

Many molecular glass forming liquids show a shift of the glass transition T-g to lower temperatures when the liquid is confined into mesoporous host matrices. Two contrary explanations for this effect are given in literature: First, confinement induced acceleration of the dynamics of the molecules leads to an effective downshift of T-g increasing with decreasing pore size. Second, due to thermal mismatch between the liquid and the surrounding host matrix, negative pressure develops inside the pores with decreasing temperature, which also shifts T-g to lower temperatures. Here we present dynamic mechanical analysis measurements of the glass forming liquid salol in Vycor and Gelsil with pore sizes of d=2.6, 5.0 and 7.5 nm. The dynamic complex elastic susceptibility data can be consistently described with the assumption of two relaxation processes inside the pores: A surface induced slowed down relaxation due to interaction with rough pore interfaces and a second relaxation within the core of the pores. This core relaxation time is reduced with decreasing pore size d, leading to a downshift of T-g proportional to 1/d in perfect agreement with recent differential scanning calorimetry (DSC) measurements. Thermal expansion measurements of empty and salol filled mesoporous samples revealed that the contribution of negative pressure to the downshift of T-g is small (<30%) and the main effect is due to the suppression of dynamically correlated regions of size xi when the pore size xi approaches