142 research outputs found
Lattice-gas Monte Carlo study of adsorption in pores
A lattice gas model of adsorption inside cylindrical pores is evaluated with
Monte Carlo simulations. The model incorporates two kinds of site: (a line of)
``axial'' sites and surrounding ``cylindrical shell'' sites, in ratio 1:7. The
adsorption isotherms are calculated in either the grand canonical or canonical
ensembles. At low temperature, there occur quasi-transitions that would be
genuine thermodynamic transitions in mean-field theory. Comparison between the
exact and mean-field theory results for the heat capacity and adsorption
isotherms are provided
Dimensional Crossover of Dilute Neon inside Infinitely Long Single-Walled Carbon Nanotubes Viewed from Specific Heats
A simple formula for coordinates of carbon atoms in a unit cell of a
single-walled nanotube (SWNT) is presented and the potential of neon (Ne)
inside an infinitely long SWNT is analytically derived under the assumption of
pair-wise Lennard-Jones potential between Ne and carbon atoms. Specific heats
of dilute Ne inside infinitely long (5, 5), (10, 10), (15, 15) and (20, 20)
SWNT's are calculated at different temperatures. It is found that Ne inside
four kinds of nanotubes exhibits 3-dimensional (3D) gas behavior at high
temperature but different behaviors at low temperature: Ne inside (5, 5)
nanotube behaves as 1D gas but inside (10, 10), (15, 15), and (20, 20)
nanotubes behaves as 2D gas. Furthermore, at ultra low temperature, Ne inside
(5, 5) nanotube still displays 1D behavior but inside (10, 10), (15, 15), and
(20, 20) nanotubes behaves as lattice gas.Comment: 10 pages, 5 figure
Phonons and specific heat of linear dense phases of atoms physisorbed in the grooves of carbon nanotube bundles
The vibrational properties (phonons) of a one-dimensional periodic phase of
atoms physisorbed in the external groove of the carbon nanotube bundle are
studied. Analytical expressions for the phonon dispersion relations are
derived. The derived expressions are applied to Xe, Kr and Ar adsorbates. The
specific heat pertaining to dense phases of these adsorbates is calculated.Comment: 4 PS figure
Vibrations of a chain of Xe atoms in a groove of carbon nanotube bundle
We present a lattice dynamics study of the vibrations of a linear chain of Xe
adsorbates in groove positions of a bundle of carbon nanotubes. The
characteristic phonon frequencies are calculated and the adsorbate polarization
vectors discussed. Comparison of the present results with the ones previously
published shows that the adsorbate vibrations cannot be treated as completely
decoupled from the vibrations of carbon nanotubes and that a significant
hybridization between the adsorbate and the tube modes occurs for phonons of
large wavelengths.Comment: 3 PS figure
Simple Model of Capillary Condensation in porous media
We employ a simple model to describe the phase behavior of 4He and Ar in a
hypothetical porous material consisting of a regular array of infinitely long,
solid, parallel cylinders. We find that high porosity geometries exhibit two
transitions: from vapor to film and from film to capillary condensed liquid. At
low porosity, the film is replaced by a ``necking'' configuration, and for a
range of intermediate porosity there are three transitions: from vapor to film,
from film to necking and from necking to a capillary condensed phase.Comment: 14 pages, 7 figure
Audience spontaneous entrainment during the collective enjoyment of live performances: physiological and behavioral measurements
Cardiac synchrony is a crucial component of shared experiences, considered as an objective measure of emotional processes accompanying empathic interactions. No study has investigated whether cardiac synchrony among people engaged in collective situations links to the individual emotional evaluation of the shared experience. We investigated theatrical live performances as collective experiences evoking strong emotional engagement in the audience. Cross Recurrence Quantification Analysis was applied to obtain the cardiac synchrony of twelve spectators’ quartets attending to two live acting performances. This physiological measure was then correlated with spectators’ emotional intensity ratings. Results showed an expected increment in synchrony among people belonging to the same quartet during both performances attendance and rest periods. Furthermore, participants’ cardiac synchrony was found to be correlated with audience’s convergence in the explicit emotional evaluation of the performances they attended to. These findings demonstrate that the mere co-presence of other people sharing a common experience is enough for cardiac synchrony to occur spontaneously and that it increases in function of a shared and coherent explicit emotional experience
Lattice model of gas condensation within nanopores
We explore the thermodynamic behavior of gases adsorbed within a nanopore.
The theoretical description employs a simple lattice gas model, with two
species of site, expected to describe various regimes of adsorption and
condensation behavior. The model includes four hypothetical phases: a
cylindrical shell phase (S), in which the sites close to the cylindrical wall
are occupied, an axial phase (A), in which sites along the cylinder's axis are
occupied, a full phase (F), in which all sites are occupied, and an empty phase
(E). We obtain exact results at T=0 for the phase behavior, which is a function
of the interactions present in any specific problem. We obtain the
corresponding results at finite T from mean field theory. Finally, we examine
the model's predicted phase behavior of some real gases adsorbed in nanopores
Effect of continuous flow HTST treatments on donkey milk nutritional quality
Nutritional quality of raw donkey milk (DM) may be impaired during sanitization with the current batch holder pasteurization systems (62.5 degrees C for 30 min). In this paper, we present the preliminary results concerning the effects of high temperature for short time (HTST) protocols using an innovative in continuous low flow rate pasteurization plant (60 dm3/h) on B-vitamins group, antioxidant capacity, lysozyme and beta-lactoglobulin in DM. Lysozyme, beta-lactoglobulin and antioxidant power decreased after the thermal treatments, with characteristics depending on the extent of the heat treatment. The lysozyme content was substantially reduced between 20 and 60%, while the degradation of beta-lactoglobulin was lower (2-22%). No vitamin B1 and B12 were found in raw milk, whereas were detected vitamin B2 (0.17 mu mol/L), nicotinic acid (13.28 mu mol/L), B6 (2.06 mu mol/L) and B9 (0.75 mu mol/L). The heat treatments carried out with the innovative plant ensured vitamin retention, as no significant differences were found against the raw milk (p > 0.05). The preliminary results from this study represent a guidance to the establishment of DM pasteurization standards parameters with the perspective to improve DM nutritional quality
Rotational and Vibrational Dynamics of Interstitial Molecular Hydrogen
The calculation of the hindered roton-phonon energy levels of a hydrogen
molecule in a confining potential with different symmetries is systematized for
the case when the rotational angular momentum is a good quantum number. One
goal of this program is to interpret the energy-resolved neutron time of flight
spectrum previously obtained for HC. This spectrum gives direct
information on the energy level spectrum of H molecules confined to the
octahedral interstitial sites of solid C. We treat this problem of
coupled translational and orientational degrees of freedom a) by construction
of an effective Hamiltonian to describe the splitting of the manifold of states
characterized by a given value of and having a fixed total number of phonon
excitations, b) by numerical solutions of the coupled translation-rotation
problem on a discrete mesh of points in position space, and c) by a group
theoretical symmetry analysis. Results obtained from these three different
approaches are mutually consistent. The results of our calculations explain
several hitherto uninterpreted aspects of the experimental observations, but
show that a truly satisfactory orientational potential for the interaction of
an H molecule with a surrounding array of C atoms has not yet been
developed.Comment: 53 pages, 9 figures, to appear in Phys. Rev B (in press). Phys. Rev.
B (in press
Bose-Einstein Condensation of Helium and Hydrogen inside Bundles of Carbon Nanotubes
Helium atoms or hydrogen molecules are believed to be strongly bound within
the interstitial channels (between three carbon nanotubes) within a bundle of
many nanotubes. The effects on adsorption of a nonuniform distribution of tubes
are evaluated. The energy of a single particle state is the sum of a discrete
transverse energy Et (that depends on the radii of neighboring tubes) and a
quasicontinuous energy Ez of relatively free motion parallel to the axis of the
tubes. At low temperature, the particles occupy the lowest energy states, the
focus of this study. The transverse energy attains a global minimum value
(Et=Emin) for radii near Rmin=9.95 Ang. for H2 and 8.48 Ang.for He-4. The
density of states N(E) near the lowest energy is found to vary linearly above
this threshold value, i.e. N(E) is proportional to (E-Emin). As a result, there
occurs a Bose-Einstein condensation of the molecules into the channel with the
lowest transverse energy. The transition is characterized approximately as that
of a four dimensional gas, neglecting the interactions between the adsorbed
particles. The phenomenon is observable, in principle, from a singular heat
capacity. The existence of this transition depends on the sample having a
relatively broad distribution of radii values that include some near Rmin.Comment: 21 pages, 9 figure
- …