2,421 research outputs found

    Quantum coherence generated by interference-induced state selectiveness

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    The relations between quantum coherence and quantum interference are discussed. A general method for generation of quantum coherence through interference-induced state selection is introduced and then applied to `simple' atomic systems under two-photon transitions, with applications in quantum optics and laser cooling.Comment: 17 pages, 7 figures, to be published in Journal of Modern Optics' special issue on quantum interferenc

    The Functional Integral for a Free Particle on a Half-Plane

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    A free non-relativistic particle moving in two dimensions on a half-plane can be described by self-adjoint Hamiltonians characterized by boundary conditions imposed on the systems. The most general boundary condition is parameterized in terms of the elements of an infinite-dimensional matrix. We construct the Brownian functional integral for each of these self-adjoint Hamiltonians. Non-local boundary conditions are implemented by allowing the paths striking the boundary to jump to other locations on the boundary. Analytic continuation in time results in the Green's functions of the Schrodinger equation satisfying the boundary condition characterizing the self-adjoint Hamiltonian.Comment: 16 page

    A Free Particle on a Circle with Point Interaction

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    The quantum dynamics of a free particle on a circle with point interaction is described by a U(2) family of self-adjoint Hamiltonians. We provide a classification of the family by introducing a number of subfamilies and thereby analyze the spectral structure in detail. We find that the spectrum depends on a subset of U(2) parameters rather than the entire U(2) needed for the Hamiltonians, and that in particular there exists a subfamily in U(2) where the spectrum becomes parameter-independent. We also show that, in some specific cases, the WKB semiclassical approximation becomes exact (modulo phases) for the system.Comment: Plain TeX, 14 page

    Integrated transfers of terrigenous organic matter to lakes at their watershed level: A combined biomarker and GIS analysis

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    Terrigenous organic matter (TOM) transfer from a watershed to a lake plays a key role in contaminants fate and greenhouse gazes emission in these aquatic ecosystems. In this study, we linked physiographic and vegetation characteristics of a watershed with TOM nature deposited in lake sediments. TOM was characterized using lignin biomarkers as indicators of TOM sources and state of degradation. Geographical information system (GIS) also allowed us to integrate and describe the landscape morpho-edaphic characteristics of a defined drainage basin. Combining these tools we found a significant and positive relationship (R2 = 0.65, p < 0.002) between mean slope of the watershed and the terrigenous fraction estimated by Λ8 in recent sediments. The mean slope also correlated with the composition of TOM in recent sediments as P/(V + S) and 3,5Bd/V ratios significantly decreased with the steepness of the watersheds (R2 = 0.57, p < 0.021 and R2 = 0.71, p < 0.004, respectively). More precisely, areas with slopes comprised between 4° and 10° have a major influence on TOM inputs to lakes. The vegetation composition of each watershed influenced the composition of recent sediments of the sampled lakes. The increasing presence of angiosperm trees in the watershed influenced the export of TOM to the lake as Λ8 increased significantly with the presence of this type of vegetation (R2 = 0.44, p < 0.019). A similar relationship was also observed with S/V ratios, an indicator of angiosperm sources for TOM. The type of vegetation also greatly influenced the degradation state of OM. In this study, we were able to determine that low-sloped areas (0–2°) act as buffer zones for lignin inputs and by extension for TOM loading to sediments. The relative contribution of TOM from the soil organic horizons also increased in steeper watersheds. This study has significant implications in our understanding of the fate of TOM in lacustrine ecosystems

    Le programme intégré pour les produits de base

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    Homocysteine: A Potential Molecular Link Between Alzheimer\u27s Disease and Type 2 Diabetes Mellitus

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    In order to elucidate some of the mechanisms through which Alzheimer’s disease (AD) and Type II Diabetes Mellitus (T2DM) are linked, this study investigated the effects of elevated plasma homocysteine levels – a risk factor for AD – in a rat model of T2DM. Both elevated plasma homocysteine levels and T2DM are associated with cognitive deficits and are recognized as strong risk factors for the development of AD. The present experiment examined the effects of diet-induced hyperhomocysteinemia on the development of cognitive impairments and insulin-resistance, as well as on the insulin signaling cascade, in a diet-induced obese rat model of T2DM. Hyperhomocyteinemia was induced in both control-fed and high-fat diet plus fructose-fed (T2DM) animals using dietary supplementation of 2% methionine. Homocysteine levels were dramatically elevated in animals receiving methionine supplementation and a high-fat diet plus fructose and were significantly increased in animals receiving either high methionine or high fat plus fructose. Behavioral impairments were observed in all groups receiving treatment. Impaired glucose tolerance was observed in animals receiving either high methionine or high fat plus fructose diets; glucose intolerance was observed in animals receiving both treatments. Akt phosphorylation was reduced by 50% in groups receiving high methionine, regardless of high fat plus fructose. These findings strongly suggest that there are mechanisms at work by which homocysteine modulates the insulin signaling pathway and/or vice versa

    Le droit de l\u27integration economique socialiste

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    Four-Parameter Point-Interaction in 1-D Quantum Systems

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    We construct a four-parameter point-interaction for a non-relativistic particle moving on a line as the limit of a short range interaction with range tending toward zero. For particular choices of the parameters, we can obtain a delta-interaction or the so-called delta'-interaction. The Hamiltonian corresponding to the four-parameter point-interaction is shown to correspond to the four-parameter self-adjoint Hamiltonian of the free particle moving on the line with the origin excluded.Comment: 6 pages, Plain Tex file. BU-HEP-92-

    Dissociation between Cervical Mucus and Urinary Hormones during the Postpartum Return of Fertility in Breastfeeding Women

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    Identifying the return of fertility with cervical mucus observations is challenging during the postpartum period. Use of urinary measurements of estrogen and progesterone can assist in understanding the return to fertility during this period. The purposes of this study were to describe the postpartum return of fertility by an analysis of total estrogen (TE) and pregnanediol glucuronide (PDG) profiles and to correlate these profiles with cervical mucus observations. Twenty-six participants collected urine samples during the postpartum period and recorded mucus scores. TE and PDG hormones were analyzed and compared with mucus scores. During amenorrhea, mucus reflected TE changes in only 35 percent of women; after amenorrhea, typical mucus patterns were seen in 33 percent of cycles. We concluded that postpartum mucus and hormone profiles are significantly dissociated but that monitoring urinary hormones may assist in identifying the return of fertility. We also identified different hormonal patterns in the return to fertility. The postpartum period is a challenging time for identifying the return of fertility. The purposes of this study were to describe the hormonal patterns during the return of fertility and to correlate these patterns with cervical mucus observations. Twenty-six postpartum women collected urine samples and recorded mucus scores. Urinary estrogen and progesterone hormones were analyzed and compared with mucus scores. Before the return of menses, mucus reflected hormonal changes in only 35 percent women and after first menses in 33 percent of cycles. We found that hormone profiles do not correlate well with mucus observations during the postpartum return of fertility

    Perturbation Theory for Singular Potentials in Quantum Mechanics

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    We study perturbation theory in certain quantum mechanics problems in which the perturbing potential diverges at some points, even though the energy eigenvalues are smooth functions of the coefficient of the potential. We discuss some of the unusual techniques which are required to obtain perturbative expansions of the energies in such cases. These include a point-splitting prescription for expansions around the Dirichlet (fermionic) limit of the δ\delta-function potential, and performing a similarity transformation to a non-Hermitian potential in the Calogero-Sutherland model. As an application of the first technique, we study the ground state of the δ\delta-function Bose gas near the fermionic limit.Comment: LaTeX, 19 pages, no figure
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