289 research outputs found
A revision of the Generalized Uncertainty Principle
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 $G_N = L_{Pl}^2$. 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 $L_{Pl}$. 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
Historically, state government has regulated certain aspects of the
marital relationship in order to further its interest in maintaining a stable
and wellfunctioning societ
Brane Cosmology and KK Gravitinos
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 nonstandard expansion after inflation. This is so because the BBN
constraint on the zero mode forces the reduced five dimensional Planck mass
$M_5$ 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 $M_5$ 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
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 spacetime with arbitrary spin parameters
In this paper we extend our previous works on spherically symmetric accretion
onto black holes and superspinars 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 turnon and off the production of powerful equatorial outflows
around superspinars. For corotating disks, equatorial outflows are efficiently
generated, even for relatively low spin parameters or relatively large
superspinar 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
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 socalled 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
The possibility of stable or quasistable 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
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
MankoNovikov 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
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 BoseEinstein condensate in a twodimensional optical lattice
We investigate a BoseEinstein 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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