11,342 research outputs found
Kohn-Sham calculations combined with an average pair-density functional theory
A recently developed formalism in which Kohn-Sham calculations are combined
with an ``average pair density functional theory'' is reviewed, and some new
properties of the effective electron-electron interaction entering in this
formalism are derived. A preliminary construction of a fully self-consitent
scheme is also presented in this framework.Comment: submitted to Int. J. Mod. Phys. B (proceedings of the 30th
International Workshop on Condensed Matter Theories
The nearby Galaxy structure toward the Vela Gum nebula
We report on photometry and spectroscopy for MK classification
purposes carried out in the fields of five open clusters projected against the
Vela Gum in the Third Galactic Quadrant of the Galaxy. They are Ruprecht 20,
Ruprecht 47, Ruprecht 60, NGC 2660 and NGC 2910. We could improve/confirm the
parameters of these objects derived before. The spectroscopic parallax method
has been applied to several stars located in the fields of four out of the five
clusters to get their distances and reddenings. With this method we found two
blue stars in the field of NGC 2910 at distances that make them likely members
of Vela OB1 too. Also, projected against the fields of Ruprecht 20 and Ruprecht
47 we have detected other young stars favoring not only the existence of Puppis
OB1 and OB2 but conforming a young stellar group at kpc from the Sun
and extending for more than 6 kpc outward the Galaxy. If this is the case,
there is a thickening of the thin Galactic disk of more than 300 pc at just 2-3
kpc from the Sun. Ruprecht 60 and NGC 2660 are too old objects that have no
physical relation with the associations under discussion. An astonishing result
has been the detection in the background of Ruprecht 47 of a young star at the
impressive distance of 9.5 kpc from the Sun that could be a member of the
innermost part of the Outer Arm. Another far young star in the field of NGC
2660, at near 6.0 kpc, may become a probable member of the Perseus Arm or of
the inner part of the Local Arm. The distribution of young clusters and stars
onto the Third Galactic Quadrant agrees with recent findings concerning the
extension of the Local Arm as revealed by parallaxes of regions of star
formation. We show evidences too that added to previous ones found by our group
explain the thickening of the thin disk as a combination of flare and warp.Comment: Accepted for publication in New Astronom
Collective housing as a good way to reduce city fragmentation
Today the study of the fragmentation represents an important
occasion to meditate on the city and on the evolution of the
relational strategies of settlements. If we analyse in a critical way
our contemporary cities, we can see several interventions of the last
decades, that brought, more or less consciously, to discontinuity and
isolation (gated communities to the new ghettos). In this situation the
individual becomes part of a small community; but how long does it
can go on? Are the public and sharing spaces, in which we can open
ourselves to the city and in the same time we can develop a sense
of identity and belonging, well designed? Are they at human scale? A
tendency, that can be observed in the modern western cities, is the
intervention as collective living and cohousing that are producing urban
continuities and community relations trying to institute relationships
with the outside, always keeping their own differences and identities.
Anyway the architectonic results donât seem already innovative and
the general quality of the interventions remains of low level. The
innovative examples for collective living can certainly be considered
positive for what deals with functions, topics and sense of community:
spaces where liveability increases and where a rediscovered relation
between Man and Environment is at the centre of the project, have
been designed. So the lacking passage to completely solve, thanks to
the cohousing projects, the fragmentation of the city, deals with the
architectural aspect. Architects must underline the importance of the
architectonical results in terms of language and spatiality to increase
the integration capability of the intervention. In this case the design of
architecture has a fundamental role for the next development of the
city and for solving all the fragmented and inclusive situation
Power calculation for gravitational radiation: oversimplification and the importance of time scale
A simplified formula for gravitational-radiation power is examined. It is
shown to give completely erroneous answers in three situations, making it
useless even for rough estimates. It is emphasized that short timescales, as
well as fast speeds, make classical approximations to relativistic calculations
untenable.Comment: Three pages, no figures, accepted for publication in Astronomische
Nachrichte
The evolution of the Italian opposition in the last twenty years: has anything changed?
In order to understand the evolution of the Italian political system over the past two decades, we have to consider the changes undergone by one fundamental institutional actor, that is, the parliamentary opposition. Its transformation can in fact be used as a valid indicator of change in the whole political system and it will also help us to reflect on the possible transformation of the Italian model of democracy. The 20-year path that has brought Italy to the current political situation, with the emergence of three different poles of approximately equal strength; the rise of the Five Star Movement; and the creation of a grand coalition consisting of traditional political opponents will be reconstructed by re-examining the evolution of the political system from the perspective of the changing role and functions of the parliamentary opposition, thus contributing to a better understanding of the (new) political phase initiated by the outcome of the 2013 election
Spiral structure of the Third Galactic Quadrant and the solution to the Canis Major debate
With the discovery of the Sagittarius dwarf spheroidal (Ibata et al. 1994), a
galaxy caught in the process of merging with the Milky Way, the hunt for other
such accretion events has become a very active field of astrophysical research.
The identification of a stellar ring-like structure in Monoceros, spanning more
than 100 degrees (Newberg et al. 2002), and the detection of an overdensity of
stars in the direction of the constellation of Canis Major (CMa, Martin et al.
2004), apparently associated to the ring, has led to the widespread belief that
a second galaxy being cannibalised by the Milky Way had been found. In this
scenario, the overdensity would be the remaining core of the disrupted galaxy
and the ring would be the tidal debris left behind. However, unlike the
Sagittarius dwarf, which is well below the Galactic plane and whose orbit, and
thus tidal tail, is nearly perpendicular to the plane of the Milky Way, the
putative CMa galaxy and ring are nearly co-planar with the Galactic disk. This
severely complicates the interpretation of observations. In this letter, we
show that our new description of the Milky Way leads to a completely different
picture. We argue that the Norma-Cygnus spiral arm defines a distant stellar
ring crossing Monoceros and the overdensity is simply a projection effect of
looking along the nearby local arm. Our perspective sheds new light on a very
poorly known region, the third Galactic quadrant (3GQ), where CMa is located.Comment: 5 pages, 2 figures. Quality of Fig 1 has been degraded to make it
smaller. Original fig. available on request. accepted for publication in
MNRAS letter
Droplet minimizers for the Gates-Lebowitz-Penrose free energy functional
We study the structure of the constrained minimizers of the
Gates-Lebowitz-Penrose free-energy functional ,
non-local functional of a density field , , a
-dimensional torus of side length . At low temperatures, is not convex, and has two distinct global minimizers,
corresponding to two equilibrium states. Here we constrain the average density
L^{-d}\int_{{\cal T}_L}m(x)\dd x to be a fixed value between the
densities in the two equilibrium states, but close to the low density
equilibrium value. In this case, a "droplet" of the high density phase may or
may not form in a background of the low density phase, depending on the values
and . We determine the critical density for droplet formation, and the
nature of the droplet, as a function of and . The relation between the
free energy and the large deviations functional for a particle model with
long-range Kac potentials, proven in some cases, and expected to be true in
general, then provides information on the structure of typical microscopic
configurations of the Gibbs measure when the range of the Kac potential is
large enough
The interaction-strength interpolation method for main-group chemistry: benchmarking, limitations, and perspectives
We have tested the original interaction-strength-interpolation (ISI)
exchange-correlation functional for main group chemistry. The ISI functional is
based on an interpolation between the weak and strong coupling limits and
includes exact-exchange as well as the G\"orling-Levy second-order energy. We
have analyzed in detail the basis-set dependence of the ISI functional, its
dependence on the ground-state orbitals, and the influence of the
size-consistency problem. We show and explain some of the expected limitations
of the ISI functional (i.e. for atomization energies), but also unexpected
results, such as the good performance for the interaction energy of
dispersion-bonded complexes when the ISI correlation is used as a correction to
Hartree-Fock.Comment: 20 pages, 20 figure
Extremum principles in electromagnetic systems
Variational expressions and saddle-point (or "mini-max") principles for linear problems in electromagnetism are proposed. When conservative conditions are considered, well-known variational expressions for the resonant frequencies of a cavity and the propagation constant of a waveguide are revised directly in terms of electric and magnetic field vectors. In both cases the unknown constants are typefied as stationary (but not extremum) points of some energy-like functionals. On the contrary, if dissipation is involved then variational expressions achieve the extremum property. Indeed, we point out that a saddle-point characterizes the unique solution of Maxwell equations subject to impedance-like dissipative boundary conditions. In particular, we deal with the quasi-static problem and the time-harmonic case
The response of precipitation characteristics to global warming from climate projections
Abstract. We revisit the issue of the response of precipitation characteristics to
global warming based on analyses of global and regional climate model
projections for the 21st century. The prevailing response we identify can be
summarized as follows: increase in the intensity of precipitation events and
extremes, with the occurrence of events of "unprecedented" magnitude, i.e.,
a magnitude not found in the present-day climate; decrease in the number of light
precipitation events and in wet spell lengths; and increase in the number of dry
days and dry spell lengths. This response, which is mostly consistent across
the models we analyzed, is tied to the difference between precipitation
intensity responding to increases in local humidity conditions and
circulations, especially for heavy and extreme events, and mean precipitation
responding to slower increases in global evaporation. These changes in
hydroclimatic characteristics have multiple and important impacts on the
Earth's hydrologic cycle and on a variety of sectors. As examples we
investigate effects on potential stress due to increases in dry and wet
extremes, changes in precipitation interannual variability, and changes in
the potential predictability of precipitation events. We also stress how the
understanding of the hydroclimatic response to global warming can provide
important insights into the fundamental behavior of precipitation processes,
most noticeably tropical convection
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