Purity-bounded uncertainty relations in multidimensional space -- generalized purity

Uncertainty relations for mixed quantum states (precisely, purity-bounded position-momentum relations, developed by Bastiaans and then by Man'ko and Dodonov) are studied in general multi-dimensional case. An expression for family of mixed states at the lower bound of uncertainty relation is obtained. It is shown, that in case of entropy-bounded uncertainty relations, lower-bound state is thermal, and a transition from one-dimensional problem to multi-dimensional one is trivial. Results of numerical calculation of the relation lower bound for different types of generalized purity are presented. Analytical expressions for general purity-bounded relations for highly mixed states are obtained.Comment: 12 pages, 2 figures. draft version, to appear in J. Phys. A Partially based on a poster "Multidimensional uncertainty relations for states with given generalized purity" presented on X Intl. Conf. on Quantum Optics'2004 (Minsk, Belarus, May 30 -- June 3, 2004) More actual report is to be presented on ICSSUR-2005, Besan\c{c}on, France and on EQEC'05, Munich. V. 5: amended article after referees' remark

Phase-space rotations and orbital Stokes parameters

We introduce the orbital Stokes parameters as a linear combination of a beam's second-order moments. Similar to the ones describing the field polarization and associated with beam energy and its spin angular momentum, the orbital Stokes parameters are related to the total beam width and its orbital angular momentum. We derive the transformation laws for these parameters during beam propagation through first-order optical systems associated with phase-space rotations. The values of the orbital Stokes parameters for Gaussian modes and arbitrary fields expressed as their linear superposition are obtained

Signal representation on the angular Poincare sphere, based on second-order moments

Based on the analysis of second-order moments, a generalized canonical representation of a two-dimensional optical signal is proposed, which is associated with the angular Poincare sphere. Vortex-free ( or zero-twist) optical beams arise on the equator of this sphere, while beams with a maximum vorticity ( or maximum twist) are located at the poles. An easy way is shown how the latitude on the sphere, which is a measure for the degree of vorticity, can be derived from the second-order moments. The latitude is invariant when the beam propagates through a first-order optical system between conjugate planes. To change the vorticity of a beam, a system that does not operate between conjugate planes is needed, with the gyrator as the prime representative of such a system. A direct way is derived to find an optical system ( consisting of a lens, a magnifier, a rotator, and a gyrator) that transforms a beam with an arbitrary moment matrix into its canonical form

Rhamphicarpa fistulosa, a widespread facultative hemi-parasitic weed, threatening rice production in Africa

Rhamphicarpa fistulosa is a facultative hemi-parasitic plant of the Orobanchaceae family, adapted to wet soils. Apart from tropical Australia, it is only found in sub-Saharan Africa, where it is considered a minor weed in cereal crops such as rice. Due to this status, the species has received only sporadic attention. Recent field observations and encounters with rice farmers in several African countries showed that R. fistulosa is, however, a more serious and increasing production constraint than previously thought. Results from a systematic literature review and a global herbarium study support this. The species has a broad distribution over Africa (at least 35 countries from Madagascar to Senegal and from Sudan to South Africa) and a wide range in altitude (0–2150 m a.s.l.) and environment (waterlogged swamps to moist free-draining uplands). Rhamphicarpa fistulosa is relatively independent and persistent because of the presumably wide host range, the facultative nature of its parasitism and its prolific seed (estimated 100 000 seeds m−2 under moderate infestation levels). Finally, R. fistulosa causes severe yield losses (average 60%) and high regional annual economic losses (estimated US $175 million), while effective control options are scant and awareness of the species among important R&D stakeholders is almost absent. An integrated approach is advocated to assist the rice sector to reduce current R. fistulosa-inflicted losses and to prevent further spread of the species into new areas

Loss of coherence in double-slit diffraction experiments

7 págs.; 3 figs.; PACS numberssd: 03.65.Yz, 03.65.Ta, 03.75.DgThe effects of incoherence and decoherence in a double-slit experiment are studied using both optical and quantum-phenomenological models. The results are compared with experimental data obtained with cold neutrons. ©2005 American Physical SocietyThis work was supported in part by MCyT Spaind under Contracts No. BFM2000-347 and No. BQU2003-8212. A.S.S. gratefully acknowledges partial support from the Consejería de Educación y Cultura of the Comunidad Autónoma de Madrid.Peer Reviewe

Food security under attack: Africa's struggle against parasitic weeds

Parasitic weeds invade around 1.34 million hectares of rainfed rice areas in Africa causing damages estimated at USD 200 million

A novel role for coagulation proteins in the development of proliferative vitreoretinopathy

Abstract In patients with retinal detachment, the major cause of recurrent redetachment is proliferative vitreoretinopathy (PVR, 5-10 %). PVR is characterized by the formation of fibrotic contractile membranes on either side of the retina, causing the retina to detach. The retinal pigment epithelium (RPE) has an important role in the homeostasis and functioning of the retina and forms the outer blood-retinal barrier by separating the retina from the blood vessels in the choroid. Coagulation proteins may come in contact with the RPE due to hemorrhage or breakdown of the blood-retinal barrier. We were the first to demonstrate that vitreous of patients with established PVR contains elevated levels of thrombin. Intravitreal thrombin (and to some extent factor Xa) can induce the release of a broad panel of cytokines, chemokines and growth factors by RPE which regulate local inflammatory and fibrotic responses, fitting PVR pathogenesis. These responses include the differentiation of monocytes into macrophages and that of RPE into myofibroblasts. Both cell types are abundantly present in fibrotic retinal membranes. The clinically available direct thrombin-inhibitor Dabigatran is able to inhibit the thrombin-induced release of cytokines, chemokines and growth factors and may thus be an interesting therapy for PVR development and other vitreoretinal disorders which are characterized by breakdown of the blood-retinal barrier. Currently, in the Rotterdam Eye Hospital, it has been found that Dabigatran reaches the eye in a potential effective concentration and a clinical trial with Dabigatran is planned with patients at risk for developing PVR