289 research outputs found

    A revision of the Generalized Uncertainty Principle

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    The Generalized Uncertainty Principle arises from the Heisenberg Uncertainty Principle when gravity is taken into account, so the leading order correction to the standard formula is expected to be proportional to the gravitational constant GN=LPl2G_N = L_{Pl}^2. On the other hand, the emerging picture suggests a set of departures from the standard theory which demand a revision of all the arguments used to deduce heuristically the new rule. In particular, one can now argue that the leading order correction to the Heisenberg Uncertainty Principle is proportional to the first power of the Planck length LPlL_{Pl}. If so, the departures from ordinary quantum mechanics would be much less suppressed than what is commonly thought.Comment: 6 pages, 1 figur

    The Spousal Notice and Consultation Requirement: A New Approach to State Regulation of Abortion

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    Historically, state government has regulated certain aspects of the marital relationship in order to further its interest in maintaining a stable and well-functioning societ

    Brane Cosmology and KK Gravitinos

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    The cosmology of KK gravitinos in models with extra dimensions is considered. The main result is that the production of such KK modes is not compatible with an epoch of non--standard expansion after inflation. This is so because the BBN constraint on the zero mode forces the reduced five dimensional Planck mass M5M_5 down to values much smaller than the usual four dimensional one, but this in turn implies many KK states available for a given temperature. Once these states are taken into account one finds that there is no M5M_5 for which the produced KK gravitinos satisfy BBN and overclosure constraints. This conclusion holds for both flat and warped models in which only gravity propagates in the full spacetime.Comment: 19 pages, references added, IoP styl

    Comparison between different types of bedding materials for horses

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    ArticleThe sports horse lives a large part of the time inside the pen in constant contact with the bedding. Therefore the bedding material can deeply affect the welfare and health of horses kept in pens. The materials have to ensure the realization of a double aim: to create a comforta ble and soft surface on which the animal can stand and relax; to give appropriate hygienic and sanitary conditions. Other important factors influence the choice, such as: the material must not be appetizing for the horse; the litter has to maintain a prope r level of moisture, so that the hoof is kept healthy, elastic and hydrated. Also the costs for material and litter management have to be taken into account. In the present study, different organic materials are compared: wood chips, hemp, rice, flax and c oconut. The trials took place in five box stalls, with square plan of 3 x 3 m. Environmental data were collected during the trials (air temperature and humidity, ammonia concentration, litter moisture). Management data were also collected, regarding the us e of bedding materials, working time, costs. In the paper the main results of the comparison between the different litter materials used in horses pens are presented

    Thick disk accretion in Kerr space-time with arbitrary spin parameters

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    In this paper we extend our previous works on spherically symmetric accretion onto black holes and super-spinars to the case in which the fluid has a finite angular momentum initially. We run 2.5D and 3D general relativistic hydrodynamic simulations of the accretion of a fat disk. We study how the accretion process changes by changing the values of the parameters of our model. We show that the value of the fluid angular momentum critically determines turn-on and off the production of powerful equatorial outflows around super-spinars. For corotating disks, equatorial outflows are efficiently generated, even for relatively low spin parameters or relatively large super-spinar radii. For counterrotating disks, equatorial outflows are instead significantly suppressed, and they are possible only in limited cases. We also study accretion around a tilted disk.Comment: 11 pages, 10 figure

    Natural extension of the Generalised Uncertainty Principle

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    We discuss a gedanken experiment for the simultaneous measurement of the position and momentum of a particle in de Sitter spacetime. We propose an extension of the so-called generalized uncertainty principle (GUP) which implies the existence of a minimum observable momentum. The new GUP is directly connected to the nonzero cosmological constant, which becomes a necessary ingredient for a more complete picture of the quantum spacetime.Comment: 4 pages, 1 figure, v2 with added references, revised and extended as published in CQ

    A note on the black hole information paradox in de Sitter spacetimes

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    The possibility of stable or quasi--stable Planck mass black hole remnants as solution to the black hole information paradox is commonly believed phenomenologically unacceptable: since we have to expect a black hole remnant for every possible initial state, the number of remnants should be infinite. This would lead to remnant pair production in any physical process with a total available energy roughly exceeding the Planck mass, against trivial evidences. In this note I point out that the number of remnants in our Universe could be finite, at least if the value of the cosmological constant is positive, as present observational data could indicate. Nevertheless, it is not clear if a huge but finite number of states is phenomenologically allowed.Comment: 4 pages, 1 figure. v3: refereed versio

    Periodic Orbits and Escapes in Dynamical Systems

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    We study the periodic orbits and the escapes in two different dynamical systems, namely (1) a classical system of two coupled oscillators, and (2) the Manko-Novikov metric (1992) which is a perturbation of the Kerr metric (a general relativistic system). We find their simple periodic orbits, their characteristics and their stability. Then we find their ordered and chaotic domains. As the energy goes beyond the escape energy, most chaotic orbits escape. In the first case we consider escapes to infinity, while in the second case we emphasize escapes to the central "bumpy" black hole. When the energy reaches its escape value a particular family of periodic orbits reaches an infinite period and then the family disappears (the orbit escapes). As this family approaches termination it undergoes an infinity of equal period and double period bifurcations at transitions from stability to instability and vice versa. The bifurcating families continue to exist beyond the escape energy. We study the forms of the phase space for various energies, and the statistics of the chaotic and escaping orbits. The proportion of these orbits increases abruptly as the energy goes beyond the escape energy.Comment: 28 pages, 23 figures, accepted in "Celestial Mechanics and Dynamical Astronomy

    Poultry farming solutions for a sustainable development of marshlands areas of South Iraq

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    ArticleThe Department of Agricultural, Food and Forestry Systems of University of Florence carried out cooperation projects in the South Iraq, funded by Italian Ministry of Foreign Affairs and International Coop eration, focused on the development of rural areas. All the proposed interventions were designed taking into account some key points, such as the development of sustainable farming systems, the protection of the environment, the empowerment of women role. Among the main activities, a particular importance is given to the simple solutions for poultry breeding that represents an important economic resource for many farmers and a source of food for a large segment of the population. Therefore the main aim of t he project was to define new building solutions to apply in the area of marshlands. A mobile poultry shelter was designed and built to meet the demand for meat and eggs from a typical rural family. This shelter was designed to be used for extensive breedin g, with animals free to graze outside during the day. A suitable self - building methodology was applied to obtain results from farmers without specific skills for wood construction thanks to which they learn the appropriate way to build poultry shelters. As conclusion, poultry breeding can be spread in the area of marshlands using the simple self - building structures presented in the study

    Effects of disorder on quantum fluctuations and superfluid density of a Bose-Einstein condensate in a two-dimensional optical lattice

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    We investigate a Bose-Einstein condensate trapped in a 2D optical lattice in the presence of weak disorder within the framework of the Bogoliubov theory. In particular, we analyze the combined effects of disorder and an optical lattice on quantum fluctuations and superfluid density of the BEC system. Accordingly, the analytical expressions of the ground state energy and quantum depletion of the system are obtained. Our results show that the lattice still induces a characteristic 3D to 1D crossover in the behavior of quantum fluctuations, despite the presence of weak disorder. Furthermore, we use the linear response theory to calculate the normal fluid density of the condensate induced by disorder. Our results in the 3D regime show that the combined presence of disorder and lattice induce a normal fluid density that asymptotically approaches 4/3 of the corresponding condensate depletion. Conditions for possible experimental realization of our scenario are also proposed.Comment: 8 pages, 0 figure. To appear in Physical Review
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