2,034 research outputs found

    Primes and prime ideals in short intervals

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    We prove the analog of Cram\'er's short intervals theorem for primes in arithmetic progressions and prime ideals, under the relevant Riemann Hypothesis. Both results are uniform in the data of the underlying structure. Our approach is based mainly on the inertia property of the counting functions of primes and prime ideals.Comment: minor change to Proposition

    Backscattering Differential Ghost Imaging in Turbid Media

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    In this Letter we present experimental results concerning the retrieval of images of absorbing objects immersed in turbid media via differential ghost imaging (DGI) in a backscattering configuration. The method has been applied, for the first time to our knowledge, to the imaging of small thin black objects located at different depths inside a turbid solution of polystyrene nanospheres and its performances assessed via comparison with standard imaging techniques. A simple theoretical model capable of describing the basic optics of DGI in turbid media is proposed.Comment: 5 pages, 6 figure

    How initial and boundary conditions affect protoplanetary migration in a turbulent sub-Keplerian accretion disc: 2D non viscous SPH simulations

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    Current theories on planetary formation establish that giant planet formation should be contextual to their quick migration towards the central star due to the protoplanets-disc interactions on a timescale of the order of 10510^5 years, for objects of nearly 10 terrestrial masses. Such a timescale should be smaller by an order of magnitude than that of gas accretion onto the protoplanet during the hierarchical growing-up of protoplanets by collisions with other minor objects. These arguments have recently been analysed using N-body and/or fluid-dynamics codes or a mixing of them. In this work, inviscid 2D simulations are performed, using the SPH method, to study the migration of one protoplanet, to evaluate the effectiveness of the accretion disc in the protoplanet dragging towards the central star, as a function of the mass of the planet itself, of disc tangential kinematics. To this purpose, the SPH scheme is considered suitable to study the roles of turbulence, kinematic and boundary conditions, due to its intrinsic advective turbulence, especially in 2D and in 3D codes. Simulations are performed both in disc sub-Keplerian and in Keplerian kinematic conditions as a parameter study of protoplanetary migration if moderate and consistent deviations from Keplerian Kinematics occur. Our results show migration times of a few orbital periods for Earth-like planets in sub-Keplerian conditions, while for Jupiter-like planets estimates give that about 10410^4 orbital periods are needed to half the orbital size. Timescales of planet migration are strongly dependent on the relative position of the planet with respect to the shock region near the centrifugal barrier of the disc flow.Comment: 12 pages, 18 figures, under review by MNRA

    PROFILI SOSPETTI. STRUMENTI DI IDENTIFICAZIONE CRIMINALE E PRATICHE DI CLASSIFICAZIONE: LA BANCA DATI NAZIONALE DEL DNA

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    The empirical research discussed in this thesis is aimed at investigating the establishment and implementation of the Italian DNA databank arranged on the base of the Pr\ufcm treaty and set up with the law n.85 of 30th June 2009. This archive of criminal DNA profiles operates as part of a broader set of tools for the regulation and the government of phenomena and situations that at some point have been presented as a problem and defined as a threat. The implementation of this \u201cinstrument\u201d has been taken into account as an exemplary moment of the production of a larger dispositif of securitization and has been contextualised within a broader process of constitution, development and integration of national databases in the European framework of police and judicial cross-border cooperation. At a more general level the inquiry deals with classifications that define certain "kinds of people" (the criminal, the recidivist, the suspect). Special attention has been devoted to the scientific knowledge that support and justifies them, to the political discourses that makes theme effective and to the technical instruments they use, particularly that peculiar kind of tools represented by genetic and biometrics databases used for personal identification in criminal investigations, and in the management of public security and borders in EU

    Class Transitions and Two Component Accretion Flow in GRS 1915+105

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    The light curve of the galactic micro-quasar GRS 1915+105 changes in at least thirteen different ways which are called classes. We present examples of the transitions from one class to another as observed by the IXAE instrument aboard the Indian Satellite IRS-P3. We find that the transitions are associated with changes in photon counts over a time-scale of only a few hours and they take place through unknown classes. Assuming that the transitions are caused by variation of the accretion rates, this implies that a significant fraction of the matter must be nearly freely falling in order to have such dramatic changes in such a short time.Comment: 9 pages, 6 figures, Astronomy and Astrophys. (in press
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