23,783 research outputs found

    Light-emitting current of electrically driven single-photon sources

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    The time-dependent tunnelling current arising from the electron-hole recombination of exciton state is theoretically studied using the nonequilibrium Green's function technique and the Anderson model with two energy levels. The charge conservation and gauge invariance are satisfied in the tunnelling current. Apart from the classical capacitive charging and discharging behavior, interesting oscillations superimpose on the tunnelling current for the applied rectangular pulse voltage.Comment: 14 pages, 5 figure

    Naturalistic Metaphysics at Sea

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    In this paper I return to the mid-20th-century debate between Quine and Carnap on the status of metaphysics questions with an eye toward advancing contemporary debates about whether naturalists can coherently undertake substantive metaphysical inquiry. Following Huw Price, I take the debate between Quine and Carnap to hinge, in part, on whether human inquiry is functionally unified. However, unlike Price, I suggest that this question is not best understood as a question about the function(s) of descriptive discourse. This goes along with rejecting a “linguistic conception” of the starting point of metaphysical inquiry, which, although shared by Quine and Carnap, Price gives us no good reason to think is mandatory for naturalists. I sketch two reasons naturalists have to reject a particular manifestation of this linguistic conception in Quine’s work—his criterion of ontological commitment. Finally, I show how these reasons can help us identify the grains of truth in some recent critiques of “mainstream metaphysics of mind.

    The Lagrangian cobordism group of T2T^2

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    We compute the Lagrangian cobordism group of the standard symplectic 2-torus and prove that it is isomorphic to the Grothendieck group of its derived Fukaya category. The proofs use homological mirror symmetry for the 2-torus.Comment: 43 pages, 12 figures. V2: Result of computation of the cobordism group reformulated; further minor changes and corrections. V3: Updated such as to agree with accepted version. To appear in Selecta Mathematic

    Proposal for a correlation induced spin-current polarizer

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    We propose a spin polarizer device composed of a quantum dot connected to the spin polarized leads. The spin control of the current flowing through the device is entirely due to the Coulomb interactions present inside the dot. We show that the initial polarization present in the source lead can be reverted or suppressed just by manipulating the gate voltage acting on the dot, the presence of the external magnetic field is not required. The influence of the temperature and finite bias on the efficiency of the current spin switching effect is also discussed.Comment: 5 pages, 4 figures, title changed, rearranged figures, one reference added, discussion extension, accepted for Phys. Rev.

    An exponential continuous time GARCH process

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    In this paper we introduce an exponential continuous time GARCH(p,q) process. It is defined in such a way that it is a continuous time extension of the discrete time EGARCH(p,q) process. We investigate stationarity and moment properties of the new model. An instantaneous leverage effect can be shown for the exponential continuous time GARCH(p,p) model

    Migration and Statistics

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    The field of empirical migration and integration research is characterised by a wide range of research questions, theoretical approaches and data sets. Research based on official statistics has to deal with different data sets on migration and foreign population resulting in different numbers. Developments in official statistics concentrate on the improvement of data quality. The census 2010/2011 or the projected central population register are important issues, e.g. in respect of sampling and weighting of migrants in surveys. The concept of migration background in the microcensus is a mayor enhancement in population statistics and has become widely accepted. It is recommended to implement questions on migration background in the census 2010/2011 too. The most important accessible data sets in the field of empirical integration research are the microcensus and the German Socio-Economic Panel; there is still untapped potential for analysis in this area. The supplementation of large surveys with a migrant sample is an appreciated trend. Most important challenges for empirical migration and integration research are the development of sampling methods for migrant population (including onomastics and topomastics), studies on new and small migrant groups, research projects in the country of origin, longitudinal migrant surveys and the development of measurement instruments.Population, Migration, Integration, Migration Background

    Shadow Budgets, Fiscal Illusion and Municipal Spending: The Case of Germany

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    The paper investigates the existence of fiscal illusion in German municipalities with special focus on the revenues from local public enterprises. These shadow budgets tend to increase the misperception of municipal tax prices and seem to have been neglected in the literature. Therefore, an aggregated expenditure function has been estimated for all German independent cities applying an “integrated budget” approach, which means that revenues and expenditures of the core budget and the local public enterprises are combined to one single municipal budget. The estimation results suggest that a higher relative share of local public enterprise revenues might increase total per capita spending as well as spending for non-obligatory municipal goods and services. Empirical evidence for other sources of fiscal illusion is mixed but some indications for debt illusion, renter illusion or the flypaper effect could be found.fiscal illusion, municipal enterprises, panel data regression

    Mixed effect model for absolute log returns of ultra high frequency data

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    The influence of covariates on absolute log returns of ultra high frequency data is analysed. Therefore we construct a mixed effect model for the absolute log returns. The parameters are estimated in a state space approach. To analyse the correlation in these irregularly spaced data empirically, the variogram, known mainly from spatial statistics, will be used. In a small simulation study the performance of the estimators will be analysed. In the end we apply the model to IBM trade data and analyse the influence of the covariates
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