10,756 research outputs found
First ECINEQ summer school on “New perspectives on the study of inequality, poverty and redistributionâ€
Twistor interpretation of slice regular functions
Given a slice regular function ,
with , it is possible to lift it to a
surface in the twistor space of (see~\cite{gensalsto}). In this paper we show that
the same result is true if one removes the hypothesis on the domain of the function . Moreover we find that if a
surface contains the image of the twistor
lift of a slice regular function, then has to be ruled by lines.
Starting from these results we find all the projective classes of algebraic
surfaces up to degree 3 in that contain the lift of a slice
regular function. In addition we extend and further explore the so-called
twistor transform, that is a curve in which,
given a slice regular function, returns the arrangement of lines whose lift
carries on. With the explicit expression of the twistor lift and of the twistor
transform of a slice regular function we exhibit the set of slice regular
functions whose twistor transform describes a rational line inside
, showing the role of slice regular functions not
defined on . At the end we study the twistor lift of a particular
slice regular function not defined over the reals. This example shows the
effectiveness of our approach and opens some questions.Comment: 29 page
The Impact of the Temporal Distribution of Communicating Civilizations on their Detectability
We use a statistical model to investigate the detectability (defined by the
requirement that they are in causal contact with us) of communicating
civilizations within a volume of the universe surrounding our location. If the
civilizations are located in our Galaxy, the detectability requirement imposes
a strict constraint on their epoch of appearance and their communicating
lifespan. This, in turn, implies that the fraction of civilizations of which we
can find any empirical evidence strongly depends on the specific features of
their temporal distribution. Our approach shed light on aspects of the problem
that can escape the standard treatment based on the Drake equation. Therefore,
it might provide the appropriate framework for future studies dealing with the
evolutionary aspects of the search for extraterrestrial intelligence (SETI).Comment: 17 pages, 1 figure. Accepted for publication in Astrobiolog
Cosmology from Planck
I briefly review some of the main scientific outputs expected from the
upcoming Planck mission. Planck will map the CMB sky with 5' resolution and
K sensitivity, with minimal foreground contribution and superb control on
systematics. It will collect the entire information enclosed in the temperature
primary anisotropy signal and will also get a good measurement of the polarized
component of the CMB. This will have profound implications on our knowledge of
the physics of the early universe and on the determination of cosmological
parameters.Comment: Proceedings of the Francesco Melchiorri Memorial Conference (Rome,
Italy, April 12-14 2006). To appear in New Astron. Re
On the real differential of a slice regular function
In this paper we show that the real differential of any injective slice
regular function is everywhere invertible. The result is a generalization of a
theorem proved by G. Gentili, S. Salamon and C. Stoppato, and it is obtained
thanks, in particular, to some new information regarding the first coefficients
of a certain polynomial expansion for slice regular functions (called
\textit{spherical expansion}), and to a new general result which says that the
slice derivative of any injective slice regular function is different from
zero. A useful tool proven in this paper is a new formula that relates slice
and spherical derivatives of a slice regular function. Given a slice regular
function, part of its singular set is described as the union of surfaces on
which it results to be constant.Comment: 23 pages, some adjustment in the structure of the sections, some
typos removed, last example reviewe
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