2,038 research outputs found
Closed-loop approach to thermodynamics
We present the closed loop approach to linear nonequilibrium thermodynamics
considering a generic heat engine dissipatively connected to two temperature
baths. The system is usually quite generally characterized by two parameters:
the output power and the conversion efficiency , to which we add a
third one, the working frequency . We establish that a detailed
understanding of the effects of the dissipative coupling on the energy
conversion process, necessitates the knowledge of only two quantities: the
system's feedback factor and its open-loop gain , the product of
which, , characterizes the interplay between the efficiency, the
output power and the operating rate of the system. By placing thermodynamics
analysis on a higher level of abstraction, the feedback loop approach provides
a versatile and economical, hence a very efficient, tool for the study of
\emph{any} conversion engine operation for which a feedback factor may be
defined
Assessment of the validity of intermolecular potential models used in molecular dynamics simulations by extended x-ray absorption fine structure spectroscopy:A case study of Sr2+ in methanol solution
Molecular dynamics simulations have been carried out for Sr2+ in methanol using different Sr2+ Lennard-Jones parameters and methanol models. X-ray absorption fine structure. (EXAFS) spectroscopy has been employed to assess the reliability of the ion-ion and ion-methanol potential functions used in the simulations. Radial distribution functions of Sr2+ in methanol have been. calculated for each simulation and compared with the EXAFS experimental data. This procedure has allowed the determinations of reliable Sr2+-methanol models which have been used in longer simulations providing an accurate description of the dynamic and structural properties of this system
No role for neutrons, muons and solar neutrinos in the DAMA annual modulation results
This paper summarizes in a simple and intuitive way why the neutrons, the
muons and the solar neutrinos cannot give any significant contribution to the
DAMA annual modulation results. A number of these elements have already been
presented in individual papers; they are recalled here. Afterwards, few simple
considerations are summarized which already demonstrate the incorrectness of
the claim reported in PRL 113 (2014) 081302.Comment: 11 pages, 1 tabl
Investigating Earth shadowing effect with DAMA/LIBRA-phase1
In the present paper the results obtained in the investigation of possible
diurnal effects for low-energy single-hit scintillation events of
DAMA/LIBRA-phase1 (1.04 ton yr exposure) have been analysed in terms
of an effect expected in case of Dark Matter (DM) candidates inducing nuclear
recoils and having high cross-section with ordinary matter, which implies low
DM local density in order to fulfill the DAMA/LIBRA DM annual modulation
results. This effect is due to the different Earth depths crossed by those DM
candidates during the sidereal day.Comment: 22 pages, 9 figures, 1 table; in publication on Eur. Phys. J.
Wetting and contact-line effects for spherical and cylindrical droplets on graphene layers: A comparative molecular-dynamics investigation
In Molecular Dynamics (MD) simulations, interactions between water molecules
and graphitic surfaces are often modeled as a simple Lennard-Jones potential
between oxygen and carbon atoms. A possible method for tuning this parameter
consists of simulating a water nanodroplet on a flat graphitic surface,
measuring the equilibrium contact angle, extrapolating it to the limit of a
macroscopic droplet and finally matching this quantity to experimental results.
Considering recent evidence demonstrating that the contact angle of water on a
graphitic plane is much higher than what was previously reported, we estimate
the oxygen-carbon interaction for the recent SPC/Fwwater model. Results
indicate a value of about 0.2 kJ/mol, much lower than previous estimations. We
then perform simulations of cylindrical water filaments on graphitic surfaces,
in order to compare and correlate contact angles resulting from these two
different systems. Results suggest that modified Young's equation does not
describe the relation between contact angle and drop size in the case of
extremely small systems and that contributions different from the one deriving
from contact line tension should be taken into account.Comment: To be published on Physical Review E (http://pre.aps.org/
Final model independent result of DAMA/LIBRA-phase1
The results obtained with the total exposure of 1.04 ton x yr collected by
DAMA/LIBRA-phase1 deep underground at the Gran Sasso National Laboratory (LNGS)
of the I.N.F.N. during 7 annual cycles (i.e. adding a further 0.17 ton x yr
exposure) are presented. The DAMA/LIBRA-phase1 data give evidence for the
presence of Dark Matter (DM) particles in the galactic halo, on the basis of
the exploited model independent DM annual modulation signature by using highly
radio-pure NaI(Tl) target, at 7.5 sigma C.L.. Including also the first
generation DAMA/NaI experiment (cumulative exposure 1.33 ton x yr,
corresponding to 14 annual cycles), the C.L. is 9.3 sigma and the modulation
amplitude of the single-hit events in the (2-6) keV energy interval is: (0.0112
\pm 0.0012) cpd/kg/keV; the measured phase is (144 \pm 7) days and the measured
period is (0.998 \pm 0.002) yr, values well in agreement with those expected
for DM particles. No systematic or side reaction able to mimic the exploited DM
signature has been found or suggested by anyone over more than a decade.Comment: 20 pages, 13 figures, 6 tables; in publication on Eur. Phys. J.
Model independent result on possible diurnal effect in DAMA/LIBRA-phase1
The results obtained in the search for possible diurnal effect in the
single-hit low energy data collected by DAMA/LIBRA-phase1 (total exposure: 1.04
ton x yr) deep underground at the Gran Sasso National Laboratory (LNGS) of the
I.N.F.N. are presented. At the present level of sensitivity the presence of any
significant diurnal variation and of diurnal time structures in the data can be
excluded for both the cases of solar and sidereal time. In particular, the
diurnal modulation amplitude expected, because of the Earth diurnal motion, on
the basis of the DAMA Dark Matter annual modulation results is below the
present sensitivity.Comment: 14 pages, 5 figures, 2 tables; in publication on Eur. Phys. J.
Dark Matter investigation by DAMA at Gran Sasso
Experimental observations and theoretical arguments at Galaxy and larger
scales have suggested that a large fraction of the Universe is composed by Dark
Matter particles. This has motivated the DAMA experimental efforts to
investigate the presence of such particles in the galactic halo by exploiting a
model independent signature and very highly radiopure set-ups deep underground.
Few introductory arguments are summarized before presenting a review of the
present model independent positive results obtained by the DAMA/NaI and
DAMA/LIBRA set-ups at the Gran Sasso National Laboratory of the INFN.
Implications and model dependent comparisons with other different kinds of
results will be shortly addressed. Some arguments put forward in literature
will be confuted.Comment: review article, 71 pages, 25 figures, 8 tables; v2: minor
modifications. In publication on the International Journal of Modern Physics
Type I Planet Migration in Nearly Laminar Disks
We describe 2D hydrodynamic simulations of the migration of low-mass planets
() in nearly laminar disks (viscosity parameter ) over timescales of several thousand orbit periods. We consider disk
masses of 1, 2, and 5 times the minimum mass solar nebula, disk thickness
parameters of and 0.05, and a variety of values and
planet masses. Disk self-gravity is fully included. Previous analytic work has
suggested that Type I planet migration can be halted in disks of sufficiently
low turbulent viscosity, for . The halting is due to a
feedback effect of breaking density waves that results in a slight mass
redistribution and consequently an increased outward torque contribution. The
simulations confirm the existence of a critical mass () beyond which migration halts in nearly laminar disks. For \alpha
\ga 10^{-3}, density feedback effects are washed out and Type I migration
persists. The critical masses are in good agreement with the analytic model of
Rafikov (2002). In addition, for \alpha \la 10^{-4} steep density gradients
produce a vortex instability, resulting in a small time-varying eccentricity in
the planet's orbit and a slight outward migration. Migration in nearly laminar
disks may be sufficiently slow to reconcile the timescales of migration theory
with those of giant planet formation in the core accretion model.Comment: 3 figures, accepted to ApJ
- …