Lifetimes of atoms trapped in an optical lattice in proximity of a surface

We study the lifetime of an atom trapped in an optical vertical lattice in proximity of a massive surface using a complex scaling approach. We analyze how the presence of the surface modifies the known lifetimes of Wannier-Stark states associated to Landau-Zener tunnelling. We also investigate how the existence of a hypothetical short-distance deviation from Newton's gravitational law could affect these lifetimes. Our study is relevant in order to discuss the feasibility of any atomic- interferometry experiment performed near a surface. Finally, the difficulties encountered in applying the complex-scaling approach to the atom-surface Casimir-Polder interaction are addressed.Comment: 10 pages, 8 figure

How Will Declining Rates of Marriage Reshape Eligibility for Social Security?

For most older people in the United States, Social Security is the major source of income: nine out of ten people age 65 or older receive benefits, which represent an average of 41 percent of their income. Largely as a result of Social Security, poverty rates for the elderly are at an all-time low, just 10 percent. But pockets of poverty persist: older unmarried persons, blacks, and Hispanics experience poverty rates in excess of 20 percent, and over 40 percent of all older single black women live in poverty. People quality for Social Security based either on their work record or their marital status. Most older women receive noncontributory Social Security spouse of widow benefits on the basis of their marital history. For these women, marital status is more important than employment status in shaping old-age financial security. However, the trend to marry and stay married has declined over time in the United States, particularly among black women. This, we hypothesize, means that fewer women will qualify for spouse and widow benefits in coming decades. As a result, Social Security benefits will shrink among the very population that currently reports higher poverty rates, older single women, particularly black women. In this policy brief, we ask: Compared to earlier cohorts, what proportion of white, black, and Hispanic women born in the 1940s, 1950s, and 1960s will enter old age without a marriage that qualifies them for Social Security spouse and widow benefits? We find that the proportion who will reach age 62 without a qualifying marriage, and thus be ineligible for Social Security spouse and widow benefits, is increasing modestly for whites and Hispanics but dramatically for African Americans. Most of these women will be eligible for retired worker benefits under Social Security, but those benefits are not likely to be as large as the benefits they would have received as spouses and widows, had they been eligible. We then discuss a range of policy alternatives, including the possibility of a minimum benefit.Social Security, spousal benefits, widow benefits, poverty, elderly, social welfare, income security.

LLuna - Designing a Distributed Virtual Presence System

This paper describes a research project on virtual presence, which strives to populate the Web. The Web is extended by a new layer that shows users on Web pages while they are present at virtual locations. The document first describes the requirements for a large-scale distributed system that fits to the Web. The requirements lead to design decisions, which build upon a publicly available messaging infrastructure. The paper presents a feature rich implementation and describes our experience with real users. It finally shows what virtual presence means for virtual communities

Fluorescence and phosphorescence from individual C60_{60} molecules excited by local electron tunneling

Using the highly localized current of electrons tunneling through a double barrier Scanning Tunneling Microscope (STM) junction, we excite luminescence from a selected C$_{60}$ molecule in the surface layer of fullerene nanocrystals grown on an ultrathin NaCl film on Au(111). In the observed luminescence fluorescence and phosphorescence spectra, pure electronic as well as vibronically induced transitions of an individual C$_{60}$ molecule are identified, leading to unambiguous chemical recognition on the single-molecular scale

Deficits in high- (>60 Hz) gamma-band oscillations during visual processing in schizophrenia

Current theories of the pathophysiology of schizophrenia have focused on abnormal temporal coordination of neural activity. Oscillations in the gamma-band range (>25 Hz) are of particular interest as they establish synchronization with great precision in local cortical networks. However, the contribution of high gamma (>60 Hz) oscillations toward the pathophysiology is less established. To address this issue, we recorded magnetoencephalographic (MEG) data from 16 medicated patients with chronic schizophrenia and 16 controls during the perception of Mooney faces. MEG data were analysed in the 25–150 Hz frequency range. Patients showed elevated reaction times and reduced detection rates during the perception of upright Mooney faces while responses to inverted stimuli were intact. Impaired processing of Mooney faces in schizophrenia patients was accompanied by a pronounced reduction in spectral power between 60–120 Hz (effect size: d = 1.26) which was correlated with disorganized symptoms (r = −0.72). Our findings demonstrate that deficits in high gamma-band oscillations as measured by MEG are a sensitive marker for aberrant cortical functioning in schizophrenia, suggesting an important aspect of the pathophysiology of the disorder

typifying four Ehrenberg names and a preliminary checklist of the African taxa

To comply with the new phylogeny within the Surirellales as supported by molecular and morphological data, re-evaluations and re-combinations of taxa from and within the genera Surirella, Cymatopleura, and Stenopterobia and with the re-established genus Iconella are necessary. Since the African diatom flora is rich with taxa from these genera, especially Iconella, and the authors have studied these taxa recently, describing also new taxa, a preliminary checklist of African Iconella and Surirella is here presented. 94 names are contained on this list. 57 taxa have been transferred to Iconella; 55 taxa were formerly ranked within Surirella and two taxa within Stenopterobia. 10 taxa have stayed within Surirella and six taxa have been transferred from Cymatopleura to Surirella. 20 Surirella and 1 Stenopterobia names are listed which are either unrevised or unrevisable since morphological data is missing. Four names and taxa described by Ehrenberg are here typified. Two had been transferred to Iconella already: Iconella bifrons (Ehrenb.) Ruck & Nakov and Iconella splendida (Ehrenb.) Ruck & Nakov. Two are re-transferred from Cymatopleura to Surirella: Surirella librile (Ehrenb.) Ehrenb. and Surirella undulata (Ehrenb.) Ehrenb.; both taxa are currently known by their younger synonyms: Cymatopleura solea (Bréb.) W. Smith and Cymatopleura elliptica (Bréb. ex Kützing) W. Smith. Lectotypes for Iconella bifrons, I. splendida, Surirella librile, and S. undulata were designated

THE ''FORGOTTEN'' PROCESS : the emission stimulated by matter waves.

submitted in European Journal of PhysicsIn a famous paper where he introduces the A and B coefficients, Einstein considered that atomic decays of excited atoms can be stimulated by light waves. Here we consider that atomic decays can also be stimulated by atomic waves. It is however necessary to change the Maxwell-Boltzmann statistics of thermal equilibrium into Bose-Einstein statistics and to introduce a coefficient C which complements the list of the coefficients introduced by Einstein. Stimulated emission of light can be considered as the first step towards the laser. Similarly, stimulated production of matter waves can be considered as the basic phenomenon for an atom-laser. Most of the results that we obtain here are not new. However, the method that we use remains very close to elementary classical physics and emphasizes the symmetry between electromagnetic and matter waves from various points of view

Alltag des Kindergartens im deutsch-deutschen Vergleich. [Symposion 8. Schule und Unterricht in Ost und West]

Das DFG-Projekt "Alltag des Kindergartens im deutsch-deutschen Vergleich", das gemeinsam vom "Zentrum für empirische pädagogische Forschung" und vom "Institut für Kleinkindpädagogik und familienbegleitende Kinderbetreuung (BIK)e.V." durchgeführt wird, hat in einem ersten Untersuchungsteil das Ziel, den Kindergartenalltag Ende 1993 in den neuen und alten Bundesländern in zentralen Dimensionen zu beschreiben, um eine Basis für die Erfassung von Veränderungsprozessen zu sichern. In einem zweiten Untersuchungsteil wird versucht, den Kindergartenalltag in der DDR kurz vor der Wende anhand schriftlicher Dokumente und retrospektiver Interviews zu rekonstruieren. Die Autoren gehen auf die Konzeption der Studie ein und präsentieren die Ergebnisse der Early Childhood Environmental Rating Scale (ECERS). Sie stellen die Elternarbeit aus der Sicht der Gruppenleiterin anhand der Ergebnisse der Interviews dar. Und klären die Frage: zwei Kindergartenwelten in Ost und West? Dabei konstatieren sie, dass auch im Jahre 1993, vier Jahre nach der Wende, sich der Kindergartenalltag in den neuen und den alten Bundesländern in bestimmten Aspekten beträchtlich unterscheiden. (DIPF/Orig./ah

Limited sinking of Phaeocystis during a 12 days sediment trap study

There is a controversy discussion about the contribution of the genus Phaeocystis to the vertical carbon export with evidence for and against sedimentation of Phaeocystis. So far, the presence of Phaeocystis in sinking matter was investigated with methods depending on morphological features (microscopy) and fast degradable substances (biochemical analyses). In this study, we determine the occurrence and abundance of Phaeocystis antarctica in short-term sediment traps and the overlying water column during a 12-day time period in the Atlantic sector of the Southern Ocean with 454-pyrosequencing and microscopy counting. In the sediment trap samples, we only found few sequences belonging to Phaeocystis, which was not reflecting the situation in the water column above. The cell counts showed the same results. We conclude that Phaeocystis cells are not generally transported downwards by active sinking or other sinking processes