569 research outputs found
Quasi-chemical approximation for polyatomic mixtures
The statistical thermodynamics of binary mixtures of polyatomic species was
developed on a generalization in the spirit of the lattice-gas model and the
quasi-chemical approximation (QCA). The new theoretical framework is obtained
by combining: (i) the exact analytical expression for the partition function of
non-interacting mixtures of linear -mers and -mers (species occupying
sites and sites, respectively) adsorbed in one dimension, and its extension
to higher dimensions; and (ii) a generalization of the classical QCA for
multicomponent adsorbates and multisite-occupancy adsorption. The process is
analyzed through the partial adsorption isotherms corresponding to both species
of the mixture. Comparisons with analytical data from Bragg-Williams
approximation (BWA) and Monte Carlo simulations are performed in order to test
the validity of the theoretical model. Even though a good fitting is obtained
from BWA, it is found that QCA provides a more accurate description of the
phenomenon of adsorption of interacting polyatomic mixtures.Comment: 27 pages, 8 figure
Standard and inverse site percolation of straight rigid rods on triangular lattices: Isotropic and nematic deposition/removal
Numerical simulations and finite-size scaling analysis have been carried out
to study standard and inverse percolation of straight rigid rods on triangular
lattices. In the case of standard (inverse) percolation, the lattice is
initially empty(occupied) and linear -mers ( linear consecutive sites)
are randomly and sequentially deposited on(removed from) the lattice,
considering an isotropic and nematic scheme. The study is conducted by
following the behavior of four critical concentrations with the size ,
determined for a wide range of : [] standard isotropic[nematic]
percolation threshold [], and []
inverse isotropic[nematic] percolation threshold
[]. The obtained results indicate that:
[] exhibits a non-monotonous dependence
with . It decreases[increases], goes through a minimum[maximum] around , then increases and asymptotically converges towards a definite value for
large []; [] rapidly
increases[decreases] and asymptotically converges towards a definite value for
infinitely long -mers []; for
both models, the curves of standard and inverse percolation thresholds are
symmetric with respect to . Thus, a complementary property is
found (and ), which has not been observed in other regular lattices.
This condition is analytically validated by using exact enumeration of
configurations for small systems; and in all cases, the model presents
percolation transition for the whole range of
Critical behavior of repulsive linear -mers on triangular lattices
Monte Carlo (MC) simulations and finite-size scaling analysis have been
carried out to study the critical behavior in a submonolayer two-dimensional
gas of repulsive linear -mers on a triangular lattice at coverage
. A low-temperature ordered phase, characterized by a repetition of
alternating files of adsorbed -mers separated by adjacent empty sites,
is separated from the disordered state by a order-disorder phase transition
occurring at a finite critical temperature, . The MC technique was
combined with the recently reported Free Energy Minimization Criterion Approach
(FEMCA), [F. Rom\'a et al., Phys. Rev. B, 68, 205407, (2003)], to predict the
dependence of the critical temperature of the order-disorder transformation.
The dependence on of the transition temperature, , observed in MC
is in qualitative agreement with FEMCA. In addition, an accurate determination
of the critical exponents has been obtained for adsorbate sizes ranging between
and . For , the results reveal that the system does not belong
to the universality class of the two-dimensional Potts model with (,
monomers). Based on symmetry concepts, we suggested that the behavior observed
for and 3 could be generalized to include larger particle sizes ().Comment: 17 pages, 13 figure
Income Distribution in a Monetary Economy: A Ricardo-Keynes Synthesis
The paper provides a novel theory of income distribution and achieves an integration of monetary and value theories along Ricardian lines, extended to a monetary production economy as understood by Keynes. In a monetary economy, capital is a fund that must be maintained. This idea is captured in the circuit of capital as first defined by Marx. We introduce the circuit of fixed capital; this circuit is closed when the present value of prospective returns from employing it is equal to its supply price. In a steady-growth equilibrium with nominal wages and interest rates given, the equation that closes the circuit of fixed capital can be solved for prices, implying a definitive income distribution. Accordingly, the imputation for fixed capital costs is equivalent to that of a money contract of equal length, which is the payment per period that will repay the cost of the fixed asset, together with interest. It follows that if capital assets remain in use for a period longer than is required to amortize them, their earnings beyond that period have an element of pure rent
Surface phase transitions in one-dimensional channels arranged in a triangular cross-sectional structure: Theory and Monte Carlo simulations
Monte Carlo simulations and finite-size scaling analysis have been carried
out to study the critical behavior in a submonolayer lattice-gas of interacting
monomers adsorbed on one-dimensional channels arranged in a triangular
cross-sectional structure. The model mimics a nanoporous environment, where
each nanotube or unit cell is represented by a one-dimensional array. Two kinds
of lateral interaction energies have been considered: , interaction
energy between nearest-neighbor particles adsorbed along a single channel and
, interaction energy between particles adsorbed across
nearest-neighbor channels. For and , successive planes are
uncorrelated, the system is equivalent to the triangular lattice and the
well-known
ordered phase is found at low temperatures and a coverage, , of 1/3
. In the more general case ( and ), a
competition between interactions along a single channel and a transverse
coupling between sites in neighboring channels allows to evolve to a
three-dimensional adsorbed layer. Consequently, the and structures "propagate" along the
channels and new ordered phases appear in the adlayer. The Monte Carlo
technique was combined with the recently reported Free Energy Minimization
Criterion Approach (FEMCA), to predict the critical temperatures of the
order-disorder transformation. The excellent qualitative agreement between
simulated data and FEMCA results allow us to interpret the physical meaning of
the mechanisms underlying the observed transitions.Comment: 24 pages, 6 figure
Omission of postoperative radiation after breast conserving surgery: A progressive paradigm shift towards precision medicine
Radiation therapy is a standard therapeutic option in the post-operative setting for early breast cancer patients after breast conserving surgery, providing a substantial benefit in reducing the risk of local relapse with a consequent survival gain. Nevertheless, the reduction in the burden related to treatment is becoming crucial in modern oncology for both local and systemic therapies and investigational efforts are being put forward by radiations oncologists to identify a subset of women at very low risk to be potentially omitted from post-operative irradiation after breast conservation. Clinical factors, classical pathological parameters and new predictive scores derived from gene expression and next generation sequencing techniques are being integrated in the quest toward a reliable low-risk profile for breast cancer patients. We herein provide a comprehensive overview on the topic
Jamming and percolation in random sequential adsorption of straight rigid rods on a two-dimensional triangular lattice
Monte Carlo simulations and finite-size scaling analysis have been performed
to study the jamming and percolation behavior of linear -mers (also known as
rods or needles) on the two-dimensional triangular lattice, considering an
isotropic RSA process on a lattice of linear dimension and periodic
boundary conditions. Extensive numerical work has been done to extend previous
studies to larger system sizes and longer -mers, which enables the
confirmation of a nonmonotonic size dependence of the percolation threshold and
the estimation of a maximum value of from which percolation would no longer
occurs. Finally, a complete analysis of critical exponents and universality
have been done, showing that the percolation phase transition involved in the
system is not affected, having the same universality class of the ordinary
random percolation.Comment: 6 figure
Role of Hypertension in Aggravating Aβ Neuropathology of AD Type and Tau-Mediated Motor Impairment
Epidemiological evidence suggests that hypertension may accelerate the onset and progression of Alzheimer's disease (AD). In this study, we explored the role of hypertension in the neurodegenerative changes associated with Aβ and tau aggregation. We induced hypertension in APPswe
Tg2576 and P301L-tauTg mouse models. In Tg2576 mice, experimental hypertension was associated with
a significant increase of the accumulation of Amyloid-β (Aβ) peptides in brain
tissue and a significant reduction of Aβ peptides in serum (P < .05). These results
indicate that hypertension may promote AD-type Aβ neuropathology in Tg2576. In P301L-tauTg mice we found that the presence of hypertension was
significantly associated with aggravated motor function assessed by hindlimb
extension test (P = .01). These results suggest that hypertension may play a role
in accelerating the progression of motor dysfunction associated with tau-related
alterations. Our studies suggest that the management of blood pressure (BP)
may alleviate AD-type Aβ neuropathology and neurological disorders associated
with abnormal tau metabolism
Measurement of the structural behaviour of a 3D airless wheel prototype by means of optical non-contact techniques
Additive Manufacturing (AM) is becoming a widely employed technique also in mass production. In this field, compliances with geometry and mechanical performance standards represent a crucial constrain. Since 3D printed products exhibit a mechanical behaviour that is difficult to predict and investigate due to the complex shape and the inaccuracy in reproducing nominal sizes, optical non-contact techniques are an appropriate candidate to solve these issues. In this paper, 2D digital image correlation and thermoelastic stress analysis are combined to map the stress and the strain performance of an airless wheel prototype. The innovative airless wheel samples are 3D-printed by fused deposition modelling and stereolithography in poly-lactic acid and photopolymer resin, respectively. The static mechanical behaviour for different wheel-ground contact configurations is analysed using the aforementioned non-contact techniques. Moreover, the wheel-ground contact pressure is mapped, and a parametric finite element model is developed. The results presented in the paper demonstrate that several factors have great influence on 3D printed airless wheels: a) the type of material used for manufacturing the specimen, b) the correct transfer of the force line (i.e., the loading system), c) the geometric complexity of the lattice structure of the airless wheel. The work confirms the effectiveness of the proposed non-contact measurement procedures for characterizing complex shaped prototypes manufactured using AM
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