Daylight quantum key distribution over 1.6 km

Quantum key distribution (QKD) has been demonstrated over a point-to-point $\sim1.6$-km atmospheric optical path in full daylight. This record transmission distance brings QKD a step closer to surface-to-satellite and other long-distance applications.Comment: 4 pages, 2 figures, 1 table. Submitted to PRL on 14 January 2000 for publication consideratio

Recommandations pour une agriculture plus écologique respectant les besoins socio - écono-miques locaux, région du Menabe Central, côte ouest de Madagascar

Dans le Menabe Central (côte ouest de Madagascar), les paysages forestiers deviennent toujours plus ouverts, le taux de déforestation avoisinant les 0,7 % . La déforestation étant notamment due à des défrichements pour l’agriculture qui est la principale activité de la région, une gestion agricole écologiquement durable apparaît comme une nécessité urgente. Afin de ne pas défavoriser les populations locales vivant dans des conditions socio-économiques difficiles (81,3 % de la population malgache vivait encore en - dessous du seuil de pauvreté en 2010), cet aménagement agricole doit également viser à proposer des  recommandations socio - économiquement rentables. Cette étude vise donc à confirmer l’hypothèse selon laquelle une agriculture plus écologique – permettant aux agriculteurs de se sédentariser sur leurs terres et diminuant les défrichements forestiers – qui fournirait des produits économiquement rentables sur le long terme répondrait aux nécessités socio-économiques et écologiques locales. La présente étude conclut en mettant en évidence quatre recommandations : i) La riziculture devrait être privilégiée ; ii) les techniques agro - forestières et les utilisations de fertilisants naturels devraient être encouragées ; iii) des alternatives permettant de diversifier le revenu des populations rurales, telle que la rizipisciculture, devraient être soutenues ; et iv) un aménagement des surfaces sylvicoles défrichées devrait être mis en place de manière participative.In the Central Menabe region on the west cost of Madagascar, traditional uses of forest resources create an increasingly open landscape. The current annual rate of loss of Malagasy dense dry forest, the natural forest type of the region, is 0.7 % . Agriculture represents the principal activity of people in Central Menabe, and the main reason for the decrease in forest cover. In the current difficult socio-economical context (81.3 % of the Malagasy population lived under the poverty line in 2010), where a threat to dry forests clearly exists, it is therefore urgent to propose scientifically-sound and participatory recommendations for ecologically sustainable and socio - economically profitable agricultural use of the Central Menabe landscape. The objective of this study is to confirm the hypothesis that a more sustainable form of agriculture – promoting farmers’ permanent use of cultivated fields – would generate high value economic products, and contribute to the socio - economic and environmental needs of the region. To meet this objective, the study answers three research questions: i) What are the principal products of the villager economy? ii) what is the role of traditional agriculture in deforestation?; and, iii) what is the potential for, and the expectations of the local populations towards, more sedentary agricultural techniques? The research uses methods from both social (scoring and questionnaires) and natural sciences (inventories and measures of clearings), and was carried out in six villages representative of the Central Menabe region. Two villages mainly practiced rice cultivation, two mainly carried out slash and burn cultivation (of maize, cassava and peanut), and two practiced both slash and burn and rice cultivation. Half of the villages were situated near a national road and have thus an easy access to regional markets; the three other villages were more remote. In total 120 inhabitants were involved in 72 different scoring exercises and 288 participated in a questionnaire survey. Mann-Whitney and chi - square tests were used to test for statistical significance in observed differences.Analyses confirm that rice is the main pillar of the villager economy in the region, and that – at the village scale – this product serves a strong commercial demand which is not always satisfied. Farmers take a weak interest in the consumption of products from slash and burn cultivation (low demand), although the majority of people that cultivate maize, cassava or peanut perceive slash and burn cultivation as a source of alimentary or financial security (subsistence or sale). Give

Free-space quantum key distribution

A working free-space quantum key distribution (QKD) system has been developed and tested over a 205-m indoor optical path at Los Alamos National Laboratory under fluorescent lighting conditions. Results show that free-space QKD can provide secure real-time key distribution between parties who have a need to communicate secretly.Comment: 5 pages, 2 figures, 2 tables. To be published in Physical review A on or about 1 April 199

Soil Microbial Community Changes in Wooded Mountain Pastures due to Simulated Effects of Cattle Grazing

The effect of cattle activity on pastures can be subdivided into three categories of disturbances: herbage removal, dunging and trampling. The objective of this study was to assess separately or in combination the effect of these factors on the potential activities of soil microbial communities and to compare these effects with those of soil properties and plant composition or biomass. Controlled treatments simulating the three factors were applied in a fenced area including a light gradient (sunny and shady situation): (i) repeated mowing; (ii) trampling; (iii) fertilizing with a liquid mixture of dung and urine. In the third year of the experiment, community level physiological profiles (CLPP) (Biolog Ecoplates™) were measured for each plots. Furthermore soil chemical properties (pH, total organic carbon, total nitrogen and total phosphorus), plant species composition and plant biomass were also assessed. Despite differences in plant communities and soil properties, the metabolic potential of the microbial community in the sunny and in the shady situations were similar. Effects of treatments on microbial communities were more pronounced in the sunny than in the shady situation. In both cases, repeated mowing was the first factor retained for explaining functional variations. In contrast, fertilizing was not a significant factor. The vegetation explained a high proportion of variation of the microbial community descriptors in the sunny situation, while no significant variation appeared under shady condition. The three components of cattle activities influenced differently the soil microbial communities and this depended on the light conditions within the wooded pasture. Cattle activities may also change spatially at a fine scale and short-term and induce changes in the microbial community structure. Thus, the shifting mosaic that has been described for the vegetation of pastures may also apply for below-ground microbial communitie

Practical free-space quantum key distribution over 1 km

A working free-space quantum key distribution (QKD) system has been developed and tested over an outdoor optical path of ~1 km at Los Alamos National Laboratory under nighttime conditions. Results show that QKD can provide secure real-time key distribution between parties who have a need to communicate secretly. Finally, we examine the feasibility of surface to satellite QKD.Comment: 5 pages, 2 figures, 2 tables. Submitted to Physics Review Letters, May 199

Tailoring Single and Multiphoton Probabilities of a Single Photon On-Demand Source

As typically implemented, single photon sources cannot be made to produce single photons with high probability, while simultaneously suppressing the probability of yielding two or more photons. Because of this, single photon sources cannot really produce single photons on demand. We describe a multiplexed system that allows the probabilities of producing one and more photons to be adjusted independently, enabling a much better approximation of a source of single photons on demand.Comment: 4 pages, LaTex, 2 figures, twocolumn and RevTex Style for PR

Theoretical efficient high capacity Quantum Key Distribution Scheme

A theoretical quantum key distribution scheme using EPR pairs is presented. This scheme is efficient in that it uses all EPR pairs in distributing the key except those chosen for checking eavesdroppers. The high capacity is achieved because each EPR pair carries 2 bits of key code.Comment: 3 pages and 1 figure, to appear in Physical Review