62 research outputs found
Modeling usual and unusual anisotropic spheres
In this paper, we study anisotropic spheres built from known static spherical
solutions. In particular, we are interested in the physical consequences of a
"small" departure from a physically sensible configuration. The obtained
solutions smoothly depend on free parameters. By setting these parameters to
zero, the starting seed solution is regained. We apply our procedure in detail
by taking as seed solutions the Florides metrics, and the Tolman IV solution.
We show that the chosen Tolman IV, and also Heint IIa Durg IV,V perfect fluid
solutions, can be used to generate a class of parametric solutions where the
anisotropic factor has features recalling boson stars. This is an indication
that boson stars could emerge by "perturbing" appropriately a perfect fluid
solution (at least for the seed metrics considered). Finally, starting with
Tolman IV, Heint IIa and Durg IV,V solutions, we build anisotropic
gravastar-like sources with the appropriate boundary conditions.Comment: Final version published in IJMP
A7. SITUAZIONE NAZIONALE: CORPI IDRICI INTERESSATI DA CIANOBATTERI TOSSICI
I cianobatteri sono diffusi in moltissimi ambienti acquatici, dove possono produrre cianotossine con diversi
profili tossicologici. Il presente rapporto riporta le linee guida per la gestione delle fioriture di cianobatteri nelle
acque di balneazione, elaborate da un gruppo di esperti. La prima parte sintetizza le attuali conoscenze scientifiche su vari aspetti, fra cui la loro presenza nei laghi italiani, le caratteristiche chimiche e tossicologiche delle varie
cianotossine, gli effetti osservati sulla salute dell\u2019uomo e la valutazione del rischio. La seconda parte definisce le
linee guida per prevenire effetti dannosi per la salute dei bagnanti e gestire il rischio associato alle fioriture. Vengono
fornite indicazioni per pianificare attivit\ue0 di monitoraggio ambientale e sorveglianza sanitaria nelle aree a maggiore
criticit\ue0. Viene inoltre presentato un sistema di reportistica, ambientale e sanitario, anche allo scopo di uniformare le
informazioni a livello nazionale. Il rapporto \ue8 completato dalle indicazioni tecniche rivolte alle strutture territoriali
preposte.Cyanobacteria thrive in many aquatic environments, where they can produce cyanotoxins with different
toxicological profiles. This report provides the guidelines for the management of cyanobacterial blooms in bathing
water, put together by a group of experts. The first part summarizes the current scientific knowledge on various
aspects, including their presence in the Italian lakes, chemical and toxicological characteristics of different
cyanotoxins, the observed effects on human health and the risk assessment. The second part defines the guidelines to prevent harmful effects on the health of bathers and manage the risk associated with blooms. It provides
recommendations for planning environmental monitoring activities and a health surveillance system in most critical
areas. It also introduces an environmental and health reporting system, with the purpose to standardize the
information at national level too. The report is supplemented by technical information aimed at territorial authorities
in charge
DNA barcoding of Ceramiales (Rhodophyta) around the Maltese islands reveals hidden biodiversity in the central Mediterranean
The genetic biodiversity of Mediterranean macroalgae is
generally understudied, a fact which is especially important
in the case of morphologically cryptic taxa. As a result, it is
often challenging to compare DNA barcodes from
Mediterranean samples to references in online databases
since, very often, no close hits are available. At a regional
scale, of around 1124 records of algae in the Mediterranean
Sea, only 114 species have been barcoded.peer-reviewe
An inhomogeneous universe with thick shells and without cosmological constant
We build an exact inhomogeneous universe composed of a central flat Friedmann
zone up to a small redshift , a thick shell made of anisotropic matter, an
hyperbolic Friedmann metric up to the scale where dimming galaxies are observed
() that can be matched to a hyperbolic Lema\^{i}tre-Tolman-Bondi
spacetime to best fit the WMAP data at early epochs. We construct a general
framework which permits us to consider a non-uniform clock rate for the
universe. As a result, both for a uniform time and a uniform Hubble flow, the
deceleration parameter extrapolated by the central observer is always positive.
Nevertheless, by taking a non-uniform Hubble flow, it is possible to obtain a
negative central deceleration parameter, that, with certain parameter choices,
can be made the one observed currently. Finally, it is conjectured a possible
physical mechanism to justify a non-uniform time flow.Comment: Version published in Class. Quantum gra
Physically motivated uncertainty relations at the Planck length for an emergent non commutative spacetime
We derive new space-time uncertainty relations (STUR) at the fundamental
Planck length from quantum mechanics and general relativity (GR), both in
flat and curved backgrounds. Contrary to claims present in the literature, our
approach suggests that no minimal uncertainty appears for lengths, but instead
for minimal space and four-volumes. Moreover, we derive a maximal absolute
value for the energy density. Finally, some considerations on possible
commutators among quantum operators implying our STUR are done.Comment: Final version published in "Class. Quantum Grav.
Einstein, Planck and Vera Rubin: Relevant Encounters Between the Cosmological and the Quantum Worlds
In Cosmology and in Fundamental Physics there is a crucial question like: where the elusive substance that we call Dark Matter is hidden in the Universe and what is it made of? that, even after 40 years from the Vera Rubin seminal discovery [1] does not have a proper answer. Actually, the more we have investigated, the more this issue has become strongly entangled with aspects that go beyond the established Quantum Physics, the Standard Model of Elementary particles and the General Relativity and related to processes like the Inflation, the accelerated expansion of the Universe and High Energy Phenomena around compact objects. Even Quantum Gravity and very exotic Dark Matter particle candidates may play a role in framing the Dark Matter mystery that seems to be accomplice of new unknown Physics. Observations and experiments have clearly indicated that the above phenomenon cannot be considered as already theoretically framed, as hoped for decades. The Special Topic to which this review belongs wants to penetrate this newly realized mystery from different angles, including that of a contamination of different fields of Physics apparently unrelated. We show with the works of this ST that this contamination is able to guide us into the required new Physics. This review wants to provide a good number of these \u201cpaths or contamination\u201d beyond/among the three worlds above; in most of the cases, the results presented here open a direct link with the multi-scale dark matter phenomenon, enlightening some of its important aspects. Also in the remaining cases, possible interesting contacts emerges. Finally, a very complete and accurate bibliography is provided to help the reader in navigating all these issues
Seasonal changes of water quality in a tropical shallow and eutrophic reservoir in the metropolitan region of Recife (Pernambuco-Brazil)
- âŠ