Photon bunching in parametric down-conversion with continuous wave excitation

The first direct measurement of photon bunching (g2 correlation function) in one output arm of a spontaneous-parametric-down-conversion source operated with a continuous pump laser in the single-photon regime is demonstrated. The result is in agreement with the statistics of a thermal field of the same coherence length, and shows the feasibility of investigating photon statistics with compact cw-pumped sources. Implications for entanglement-based quantum cryptography are discussed.Comment: 7 pages, 4 figures, expanded introduction and experimental details added. Accepted for publication in Phys.Rev.

The Status of the Wave Function in Dynamical Collapse Models

The idea that in dynamical wave function collapse models the wave function is superfluous is investigated. Evidence is presented for the conjecture that, in a model of a field theory on a 1+1 lightcone lattice, knowing the field configuration on the lattice back to some time in the past, allows the wave function or quantum state at the present moment to be calculated, to arbitrary accuracy so long as enough of the past field configuration is known.Comment: 35 pages, 11 figures, LaTex, corrected typos, some modifications made. to appear in Found. of Phys. Lett. Vol. 18, Nbr 6, Nov 2005, 499-51

Simulating causal collapse models

We present simulations of causal dynamical collapse models of field theories on a 1+1 null lattice. We use our simulations to compare and contrast two possible interpretations of the models, one in which the field values are real and the other in which the state vector is real. We suggest that a procedure of coarse graining and renormalising the fundamental field can overcome its noisiness and argue that this coarse grained renormalised field will show interesting structure if the state vector does on the coarse grained scale.Comment: 18 pages, 8 fugures, LaTeX, Reference added, discussion of probability distribution of labellings correcte

Disponibilité azotée et lessivage de l'azote dans un mull et un moder forestiers

International audienc

Index foliaire, paramètres foliaires et caractéristiques édaphiques stationnelles dans quelques peuplements forestiers de Lorraine belge

International audienc

Influence of logging traffic on the hydromorphic degradation of acid forest soils developed on loessic loam in middle Belgium

Modifications of soil physical parameters (bulk density, pore space pattern and clay dispersibility) induced by compaction in wheel-rutted areas due to mechanized forest exploitation was studied in loamy soils developed under beech stands in the loessic belt of middle Belgium. The consequences of surface waterlogging on pedological processes (especially the geochemical behaviour of iron and aluminium) were also investigated. The results show that rutted areas have: (1) a significant decrease of total porosity in the eluvial upper layers of the soil (0-30 cm depth), associated with an important lowering of the transmission pore volume and a decrease in macroporosity to about 6% of the total soil volume, i.e. to less than the current threshold value for root viability (10%); (2) a reduction of macropore space to about 9.5% in the lower illuvial horizons (30-50 cm depth); (3) a decrease of redox potential due to temporary waterlogging, inducing (a) the occurrence of reduced forms of iron, (b) a strong leaching of iron oxyhydroxides from the E(g) to the B(1g) horizon, (c) an increase of organically complexed iron forms in both the Es and B(tg) horizons, and (d) high solubility of Goethite and even of ferromagnesium minerals in the eluvial horizons; (4) an increase of clay dispersibility in both the E(g) and B(tg) horizons. These results provide clear evidence that on loessic materials soil compaction due to logging operations leads to rapid soil degradation through active hydromorphic processes.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Influence of the nature of clay minerals on the fixation of radiocaesium traces in an acid brown earth-podzol weathering sequence

The magnitude of radiocaesium fixation by micaceous clay minerals is affected by their transformation, which depends on weathering in soil. The net retention of radiocaesium traces was quantified by sorption-desorption experiments in the Various horizons of four sandy soils forming an acid brown earth-podzol weathering sequence derived from sandy sediments and characterized by marked changes in mineral composition. The features of the 2:1 minerals of the four soils, resulting from an aluminization process in depth and a desaluminization process towards the surface, had a strong influence on Cs+ fixation. Beneath the desaluminization front, which deepens from the acid brown earth to the podzol, hydroxy interlayered vermiculite was dominant and the Cs-137(+) fixation was the weakest. At the desaluminization front depth, vermiculite was responsible for the strongest Cs-137(+) fixation. In the upper layers, smectite appeared in the podzolized soils and the Cs-137(+) fixation decreased. The magnitude in Cs+ fixation therefore appeared as a tracer of the transformation process affecting the 2:1 clay minerals in the acid brown earth-podzol weathering sequence. This magnitude was positively correlated with the vermiculite content of the studied soil materials estimated by the rubidium saturation method

Weathering pattern in acid leached soils developed on Pleistocene loess of Central Belgium: contribution of isotitane assessment and Sr isotope methods

info:eu-repo/semantics/nonPublishe