412 research outputs found
On the Average Comoving Number Density of Halos
I compare the numerical multiplicity function given in Yahagi, Nagashima &
Yoshii (2004) with the theoretical multiplicity function obtained by means of
the excursion set model and an improved version of the barrier shape obtained
in Del Popolo & Gambera (1998), which implicitly takes account of total angular
momentum acquired by the proto-structure during evolution and of a non-zero
cosmological constant. I show that the multiplicity function obtained in the
present paper, is in better agreement with Yahagi, Nagashima & Yoshii (2004)
simulations than other previous models (Sheth & Tormen 1999; Sheth, Mo & Tormen
2001; Sheth & Tormen 2002; Jenkins et al. 2001) and that differently from some
previous multiplicity function models (Jenkins et al. 2001; Yahagi, Nagashima &
Yoshii 2004) it was obtained from a sound theoretical background
Mesophases in Nearly 2D Room-Temperature Ionic Liquids
Computer simulations of (i) a [C12mim][Tf2N] film of nanometric thickness
squeezed at kbar pressure by a piecewise parabolic confining potential reveal a
mesoscopic in-plane density and composition modulation reminiscent of
mesophases seen in 3D samples of the same room-temperature ionic liquid (RTIL).
Near 2D confinement, enforced by a high normal load, relatively long aliphatic
chains are strictly required for the mesophase formation, as confirmed by
computations for two related systems made of (ii) the same [C12mim][Tf2N]
adsorbed at a neutral solid surface and (iii) a shorter-chain RTIL
([C4mim][Tf2N]) trapped in the potential well of part i. No in-plane modulation
is seen for ii and iii. In case ii, the optimal arrangement of charge and
neutral tails is achieved by layering parallel to the surface, while, in case
iii, weaker dispersion and packing interactions are unable to bring aliphatic
tails together into mesoscopic islands, against overwhelming entropy and
Coulomb forces. The onset of in-plane mesophases could greatly affect the
properties of long-chain RTILs used as lubricants.Comment: 24 pages 10 figure
2D-Drop model applied to the calculation of step formation energies on a (111) substrate
A model is presented for obtaining the step formation energy for metallic
islands on (111) surfaces from Monte Carlo simulations. This model is applied
to homo (Cu/Cu(111), Ag/Ag(111)) and heteroepitaxy (Ag/Pt(111)) systems. The
embedded atom method is used to represent the interaction between the particles
of the system, but any other type of potential could be used as well. The
formulation can also be employed to consider the case of other single crystal
surfaces, since the higher barriers for atom motion on other surfaces are not a
hindrance for the simulation scheme proposed.Comment: 12 pages, LaTeX2e, 2 included EPS figures, submitted to Surface
Science Subj-clas
Improvements in the M-T relation and mass function and the measured Omega_m through clusters evolution
In this paper, I revisit the constraints obtained by several authors
(Reichart et al. 1999; Eke et al. 1998; Henry 2000) on the estimated values of
Omega_m, n and sigma_8 in the light of recent theoretical developments: 1) new
theoretical mass functions (Sheth & Tormen 1999, Sheth, Mo & Tormen 1999, Del
Popolo 2002b); 2) a more accurate mass-temperature relation, also determined
for arbitrary Omega_m and Omega_{\Lambda} (Voit 2000, Pierpaoli et al. 2001,
Del Popolo 2002a). Firstly, using the quoted improvements, I re-derive an
expression for the X-ray Luminosity Function (XLF), similarly to Reichart et
al. (1999), and then I get some constraints to \Omega_m and n, by using the
ROSAT BCS and EMSS samples and maximum-likelihood analysis. Then I re-derive
the X-ray Temperature Function (XTF), similarly to Henry (2000) and Eke et al.
(1999), re-obtaining the constraints on Omega_m, n, sigma_8. Both in the case
of the XLF and XTF, the changes in the mass function and M-T relation produces
an increase in Omega_m of \simeq 20% and similar results in sigma_8 and n.Comment: 34 pages, 11 encapsulated figures. Accepted by Ap
Controversy over the pharmacological treatments of storage symptoms in spinal cord injury patients: a literature overview
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Planetary migration in evolving planetesimals discs
In the current paper, we further improved the model for the migration of
planets introduced in Del Popolo et al. (2001) and extended to time-dependent
planetesimal accretion disks in Del Popolo and Eksi (2002). In the current
study, the assumption of Del Popolo and Eksi (2002), that the surface density
in planetesimals is proportional to that of gas, is released. In order to
obtain the evolution of planetesimal density, we use a method developed in
Stepinski and Valageas (1997) which is able to simultaneously follow the
evolution of gas and solid particles for up to 10^7 yrs. Then, the disk model
is coupled to migration model introduced in Del Popolo et al. (2001) in order
to obtain the migration rate of the planet in the planetesimal. We find that
the properties of solids known to exist in protoplanetary systems, together
with reasonable density profiles for the disk, lead to a characteristic radius
in the range 0.03-0.2 AU for the final semi-major axis of the giant planet.Comment: IJMP A in prin
Improvements in the X-ray luminosity function and constraints on the Cosmological parameters from X-ray luminous clusters
We show how to improve constraints on \Omega_m, \sigma_8, and the dark-energy
equation-of-state parameter, w, obtained by Mantz et al. (2008) from
measurements of the X-ray luminosity function of galaxy clusters, namely MACS,
the local BCS and the REFLEX galaxy cluster samples with luminosities L> 3
\times 10^{44} erg/s in the 0.1--2.4 keV band. To this aim, we use Tinker et
al. (2008) mass function instead of Jenkins et al. (2001) and the M-L
relationship obtained from Del Popolo (2002) and Del Popolo et al. (2005).
Using the same methods and priors of Mantz et al. (2008), we find, for a
\Lambda while the result of Mantz et al. (2008) gives
less tight constraints and
\sigma_8=0.78^{+0.11}_{-0.13}. In the case of a wCDM model, we find
\Omega_m=0.27^{+0.07}_{-0.06}, and
, while in Mantz et al. (2008) they are again less tight
\Omega_m=0.24^{+0.15}_{-0.07}, \sigma_8=0.85^{+0.13}_{-0.20} and
w=-1.4^{+0.4}_{-0.7}. Combining the XLF analysis with the f_{gas}+CMB+SNIa data
set results in the constraint \Omega_m=0.269 \pm 0.012, \sigma_8=0.81 \pm 0.021
and w=-1.02 \pm 0.04, to be compared with Mantz et al. (2008), \Omega_m=0.269
\pm 0.016, \sigma_8=0.82 \pm 0.03 and w=-1.02 \pm 0.06. The tightness of the
last constraints obtained by Mantz et al. (2008), are fundamentally due to the
tightness of the +CMB+SNIa constraints and not to their XLF analysis.
Our findings, consistent with w=-1, lend additional support to the
cosmological-constant model.Comment: 9 pages, 4 Figures. A&A accepted. Paper Subitted Previously To Mantz
et al 2009, arXiv:0909.3098 and Mantz et al 2009b, arXiv:0909.309
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