6,000 research outputs found
Fluid-solid transition in hard hyper-sphere systems
In this work we present a numerical study, based on molecular dynamics
simulations, to estimate the freezing point of hard spheres and hypersphere
systems in dimension D = 4, 5, 6 and 7. We have studied the changes of the
Radial Distribution Function (RDF) as a function of density in the coexistence
region. We started our simulations from crystalline states with densities above
the melting point, and moved down to densities in the liquid state below the
freezing point. For all the examined dimensions (including D = 3) it was
observed that the height of the first minimum of the RDF changes in an almost
continuous way around the freezing density and resembles a second order phase
transition. With these results we propose a numerical method to estimate the
freezing point as a function of the dimension D using numerical fits and
semiempirical approaches. We find that the estimated values of the freezing
point are very close to previously reported values from simulations and
theoretical approaches up to D = 6 reinforcing the validity of the proposed
method. This was also applied to numerical simulations for D = 7 giving new
estimations of the freezing point for this dimensionality.Comment: 13 pages, 10 figure
HPMC Hydrogel Formation Mechanisms Unveiled by the Evaluation of the Activation Energy
Aqueous solutions of hydroxypropyl methylcellulose (HPMC) show inverse thermoreversible gelation, i.e., they respond to small temperature variations exhibiting solâgel transition during heating, and reversibly gelâsol transition during cooling. According to the pertinent literature on HPMC aqueous systems, at room temperature, the loss modulus (Gâ) is higher than the storage modulus (Gâ). During the heating ramp, the viscoelastic response follows a peculiar path: initially, Gâ and Gâ smoothly decrease, then drop to a minimum and finally increase. Eventually, Gâ overcomes Gâ, indicating the gel formation. A recent explanation of this behaviour considers a twoâstep mechanism: first, phase separation occurs, then fibrils form from a polymer-rich phase and entangle, leading to a threeâdimensional network. Based on this, our research focuses on the rheological analysis of the different steps of the solâgel transition of an HPMC aqueous solution. We perform different viscoelastic tests: thermal ramps, time sweeps, and frequency sweeps at selected characteristic temperatures. We couple classical analysis of the SAOS experiments with an innovative approach based on the evaluation of the activation energy (Ea), made possible by the instrument intrinsic temperature oscillations around the target value. Results show that Ea can be a valid tool that contributes to further clarifying the peculiar microstructural evolution occurring in this kind of thermoreversible gel
Energetics and stability of dangling-bond silicon wires on H passivated Si(100)
We evaluate the electronic, geometric and energetic properties of quasi 1-D
wires formed by dangling bonds on Si(100)-H (2 x 1). The calculations are
performed with density functional theory (DFT). Infinite wires are found to be
insulating and Peierls distorted, however finite wires develop localized
electronic states that can be of great use for molecular-based devices. The
ground state solution of finite wires does not correspond to a geometrical
distortion but rather to an antiferromagnetic ordering. For the stability of
wires, the presence of abundant H atoms in nearby Si atoms can be a problem. We
have evaluated the energy barriers for intradimer and intrarow diffusion
finding all of them about 1 eV or larger, even in the case where a H impurity
is already sitting on the wire. These results are encouraging for using
dangling-bond wires in future devices.Comment: 8 pages, 6 figure
Decoherence in an accelerated universe
In this paper we study the decoherence processes of the semiclassical
branches of an accelerated universe due to their interaction with a scalar
field with given mass. We use a third quantization formalism to analyze the
decoherence between two branches of a parent universe caused by their
interaction with the vaccum fluctuations of the space-time, and with other
parent unverses in a multiverse scenario.Comment: 11 pages, 2 figure
Collaboration and Innovation Dynamics in Software Ecosystems: A Technology Management Research Perspective
Belnap-Dunn semantics for natural implicative expansions of Kleene's strong three-valued matrix with two designated values
27 p.A conditional is natural if it fulfils the three following conditions. (1) It coincides with the classical conditional when restricted to the classical values T and F; (2) it satisfies the Modus Ponens; and (3) it is assigned a designated value whenever the value assigned to its antecedent is less than or equal to the value assigned to its consequent. The aim of this paper is to provide a âbivalentâ Belnap-Dunn semantics for all natural implicative expansions of Kleene's strong 3-valued matrix with two designated elements. (We understand the notion ânatural conditionalâ according to N. Tomova, âA lattice of implicative extensions of regular Kleene's logicsâ, Reports on Mathematical Logic, 47, 173â182, 2012.)S
- âŠ