Lavbundsarealerne ved Fussingø

På engene ved Fussingø Hovedgård blev der i 1997-2001 gennemført en tværfaglig undersøgelse af forskellige græsmarksstrategier, som afgræsning, slæt eller driftsophør, ud fra ønsket om at kunne øge naturkvaliteten under miljøvenlig græsmarksdrift og samtidig forbedre landbrugsproduktionen under sådanne forhold. Med henblik på at få en generel beskrivelse af engarealerne er der indsamlet nøgledata vedrørende geologi, afstrømningsforhold, arealernes driftshistorie, klima, hydrologi og vegetationen på arealerne. Der er benyttet en kombination af ældre beskrivelser og nye registreringer. Engområdet er beliggende i en tunneldal, som stort set følger Skals å forløbet. Der er tørveaflejringer med mindre lag af ler og kalkgytje indlejret lokalt. I den øverste meter af jordlaget er humusindholdet ca. 60%. Der var et højt N-indhold i jorden, men med stor variation indenfor området (1,8-2,7%). Den potentielle netto kvælstof mineralisering var betydeligt højere end det niveau man normalt finder på mineraljord. Afstrømningsoplandet ved Fussingø er på 1948 ha, og det består af fire del-oplande, der afvander til Skals å systemet. Lavbundsarealet på 411 ha udgør 21% af det samlede oplandsareal. Lavbundsarealet består bl.a. af 44% vådområder, som ikke udnyttes landbrugsmæssigt, og af 20% vedvarende græsningsarealer. Engarealerne, som indgik i forsøget, blev i perioden før 1955 og i perioden efter 1987 drevet med græsmarksdrift. I den mellemliggende periode var der mere eller mindre intensiv drift af arealerne med både græsmarksdrift og salgsafgrøder. Klimaet i forsøgsperioden var specielt ved at nedbøren i forårsperioden var stigende gennem de år forsøget varede, og arealerne blev mere og mere fugtige i vækstperioden. Med hensyn til fugtighed var der betydelige forskelle i vandstand fra græsningsfold til græsningsfold. Vegetationen var kulturpræget på østarealet og naturpræget på vestarealet. En forklaring på dette forhold kan være, at der på østarealet var en højere N-mineralisering og et højere indhold af plantetilgængeligt K. Danske lavbundsarealer kan variere meget, og der er ikke grundige beskrivelser af alle lavbundsarealer som af arealerne på Fussingø. Man kan derfor ikke sige, hvor stor en del af de danske lavbundsarealer, der har samme forhold som arealerne, der indgik i undersøgelsen. Ud fra gamle kortoptegnelser er det tidligere vurderet, at en tredjedel af Danmarks lavbundsarealer har humusjord og dermed tilsvarende jordtype som engene ved Fussingø

Expressions 2020

https://openspace.dmacc.edu/expressions/1036/thumbnail.jp

From Network Structure to Dynamics and Back Again: Relating dynamical stability and connection topology in biological complex systems

The recent discovery of universal principles underlying many complex networks occurring across a wide range of length scales in the biological world has spurred physicists in trying to understand such features using techniques from statistical physics and non-linear dynamics. In this paper, we look at a few examples of biological networks to see how similar questions can come up in very different contexts. We review some of our recent work that looks at how network structure (e.g., its connection topology) can dictate the nature of its dynamics, and conversely, how dynamical considerations constrain the network structure. We also see how networks occurring in nature can evolve to modular configurations as a result of simultaneously trying to satisfy multiple structural and dynamical constraints. The resulting optimal networks possess hubs and have heterogeneous degree distribution similar to those seen in biological systems.Comment: 15 pages, 6 figures, to appear in Proceedings of "Dynamics On and Of Complex Networks", ECSS'07 Satellite Workshop, Dresden, Oct 1-5, 200

Correlated N-boson systems for arbitrary scattering length

We investigate systems of identical bosons with the focus on two-body correlations and attractive finite-range potentials. We use a hyperspherical adiabatic method and apply a Faddeev type of decomposition of the wave function. We discuss the structure of a condensate as function of particle number and scattering length. We establish universal scaling relations for the critical effective radial potentials for distances where the average distance between particle pairs is larger than the interaction range. The correlations in the wave function restore the large distance mean-field behaviour with the correct two-body interaction. We discuss various processes limiting the stability of condensates. With correlations we confirm that macroscopic tunneling dominates when the trap length is about half of the particle number times the scattering length.Comment: 15 pages (RevTeX4), 11 figures (LaTeX), submitted to Phys. Rev. A. Second version includes an explicit comparison to N=3, a restructured manuscript, and updated figure

Quantum Corrections to Dilute Bose Liquids

It was recently shown (A. Bulgac. Phys. Rev. Lett. {\bf 89}, 050402 (2002)) that an entirely new class of quantum liquids with widely tunable properties could be manufactured from bosons (boselets), fermions (fermilets) and their mixtures (ferbolets) by controlling their interaction properties by the means of a Feshbach resonance. We extend the previous mean--field analysis of these quantum liquids by computing the lowest order quantum corrections to the ground state energy and the depletion of the Bose--Einstein condensate and by estimating higher order corrections as well. We show that the quantum corrections are relatively small and controlled by the diluteness parameter $\sqrt{n|a|^3} \ll 1$, even though strictly speaking in this case there is no low density expansion.Comment: final published version, typos corrected, updated references and added one referenc

Constructing Entanglement Witness Via Real Skew-Symmetric Operators

In this work, new types of EWs are introduced. They are constructed by using real skew-symmetric operators defined on a single party subsystem of a bipartite dxd system and a maximal entangled state in that system. A canonical form for these witnesses is proposed which is called canonical EW in corresponding to canonical real skew-symmetric operator. Also for each possible partition of the canonical real skew-symmetric operator corresponding EW is obtained. The method used for dxd case is extended to d1xd2 systems. It is shown that there exist Cd2xd1 distinct possibilities to construct EWs for a given d1xd2 Hilbert space. The optimality and nd-optimality problem is studied for each type of EWs. In each step, a large class of quantum PPT states is introduced. It is shown that among them there exist entangled PPT states which are detected by the constructed witnesses. Also the idea of canonical EWs is extended to obtain other EWs with greater PPT entanglement detection power.Comment: 40 page

Scaling predictions for radii of weakly bound triatomic molecules

The mean-square radii of the molecules $^4$He$_3$, $^4$He$_2-^6$Li, $^4$He$_2-^7$Li and $^4$He$_2-^{23}$Na are calculated using a three-body model with contact interactions. They are obtained from a universal scaling function calculated within a renormalized scheme for three particles interacting through pairwise Dirac-delta interaction. The root-mean-square distance between two atoms of mass $m_A$ in a triatomic molecule are estimated to be of de order of ${\cal C}\sqrt{\hbar^2/[m_A(E_3-E_2)]}$, where $E_2$ is the dimer and $E_3$ the trimer binding energies, and ${\cal C}$ is a constant (varying from $\sim 0.6$ to $\sim 1$) that depends on the ratio between $E_2$ and $E_3$. Considering previous estimates for the trimer energies, we also predict the sizes of Rubidium and Sodium trimers in atomic traps.Comment: 7 pages, 2 figure

On the complexity of strongly connected components in directed hypergraphs

We study the complexity of some algorithmic problems on directed hypergraphs and their strongly connected components (SCCs). The main contribution is an almost linear time algorithm computing the terminal strongly connected components (i.e. SCCs which do not reach any components but themselves). "Almost linear" here means that the complexity of the algorithm is linear in the size of the hypergraph up to a factor alpha(n), where alpha is the inverse of Ackermann function, and n is the number of vertices. Our motivation to study this problem arises from a recent application of directed hypergraphs to computational tropical geometry. We also discuss the problem of computing all SCCs. We establish a superlinear lower bound on the size of the transitive reduction of the reachability relation in directed hypergraphs, showing that it is combinatorially more complex than in directed graphs. Besides, we prove a linear time reduction from the well-studied problem of finding all minimal sets among a given family to the problem of computing the SCCs. Only subquadratic time algorithms are known for the former problem. These results strongly suggest that the problem of computing the SCCs is harder in directed hypergraphs than in directed graphs.Comment: v1: 32 pages, 7 figures; v2: revised version, 34 pages, 7 figure

Narrow genetic base in forest restoration with holm oak (Quercus ilex L.) in Sicily

In order to empirically assess the effect of actual seed sampling strategy on genetic diversity of holm oak (Quercus ilex) forestations in Sicily, we have analysed the genetic composition of two seedling lots (nursery stock and plantation) and their known natural seed origin stand by means of six nuclear microsatellite loci. Significant reduction in genetic diversity and significant difference in genetic composition of the seedling lots compared to the seed origin stand were detected. The female and the total effective number of parents were quantified by means of maternity assignment of seedlings and temporal changes in allele frequencies. Extremely low effective maternity numbers were estimated (Nfe $\approx$ 2-4) and estimates accounting for both seed and pollen donors gave also low values (Ne $\approx$ 35-50). These values can be explained by an inappropriate forestry seed harvest strategy limited to a small number of spatially close trees