Abstract
We studied the behavior of mixtures of
173
Yb (with symmetry up to SU(6)) and
171
Yb (up to SU(2)) fermionic isotopes loaded in one-dimensional (1D) optical lattices. To do so, we solved the ...Schrödinger equation describing different systems using a diffusion Monte Carlo technique. We considered continuous Hamiltonians in which the interactions between atoms of different species (isotopes and/or spins) were modeled by contact potentials with parameters derived from their experimental scattering lengths. This implies that we can find both attractive and repulsive interactions between fermion pairs in the same cluster. The strength of those interactions can be changed by varying the transverse confinement, leading to different cluster behaviors. Only balanced clusters, i.e. with the same number of
173
Yb and
171
Yb atoms were considered. We found that the standard state for these clusters is a metallic-like one with different populations of
173
Yb–
171
Yb molecule-like pairs in each optical lattice potential well. However, for big enough clusters, insulator-like states are also possible.
The behaviour of fermion clusters with SU(N) symmetry loaded in one-dimensional optical lattices and described by continuous Hamiltonians was studied using a diffusion Monte Carlo (DMC) technique. ...The state diagrams of SU(6) and SU(2) arrangements with the same number of particles were calculated and found virtually identical. The only difference was the absence of a band insulator in the SU(N) case in the range of optical lattice depths considered (V0 = 0-12 ER; ER, recoil energy of the lattice) in the non-interacting limit for N > 2. The appearance of that state was signalled by a noticeable change in the shape of the momentum distributions in going from a metal to a band insulator.
Two decades after its unexpected discovery, the properties of the X (3872) exotic resonance are still under intense scrutiny. In particular, there are doubts about its nature as an ensemble of mesons ...or having any other internal structure. We use a diffusion Monte Carlo method to solve the many-body Schrödinger equation that describes this state as a ccnn ( n = u or d quark) system. This approach accounts for multiparticle correlations in physical observables avoiding the usual quark-clustering assumed in other theoretical techniques. The most general and accepted pairwise Coulomb + linear-confining + hyperfine spin-spin interaction, with parameters obtained by a simultaneous fit of around 100 masses of mesons and baryons, is used. The X (3872) contains light quarks whose constituent masses are given by the dynamical breaking of chiral symmetry. The same mechanism gives rise to Goldstone-boson exchange interactions between light quarks whose contribution, derived from a well extended chiral quark model, has been included in this analysis but plays a marginal role. It appears that a meson-meson molecular configuration is preferred but, contrary to the usual assumption of D0 D0* molecule for the X (3872), our formalism produces ωJ/ψ and ρJ/ψ clusters as the most stable ones, which could explain in a natural way all the observed features of the X (3872).
A study about topsoil antimony distribution and mobility from the soils to the biomass has been afforded in three abandoned Sb mining areas located at Extremadura. Physico-chemical characteristics of ...the soils and total antimony levels were measured in soils and autochthonous plant species (
Cytisus striatus,
Cistus ladanifer and
Dittrichia viscosa). Comparison with corresponding values in reference areas isolated from the mining activities is discussed. Antimony mobility in the soils was estimated by measuring the water extractable fraction; low results were obtained for the three soil areas, with no statistical differences. Plant ability to accumulate antimony was estimated by use of plant accumulation coefficients (PAC). Seasonal (spring vs. autumn) effects on the antimony content in the plant species.
Cytisus striatus from Mari Rosa mine presented antimony excluder characteristics, whereas
Dittrichia viscosa specimens growing in San Antonio mine showed a significant antimony bioaccumulation.
Bioaccumulation of antimony in vegetal species growing in mining areas.
Incorporating carbon nanoparticles (CNPs) into polymers can enhance their mechanical behavior; however, enhancement depends strongly on compatibility and homogeneous dispersion. Actual methods to ...succeed high dispersion and compatibility are complicated, have solvent‐associated problems, and long processing times. The present work proposes the increase of the dispersion and compatibility of CNPs in a polypropylene (PP) matrix to obtain a nanocomposite with high mechanical properties, using simple, fast, and green methodologies: the modification of the CNPs by cold propylene plasma and the synergistic effect resulting from mixtures of carbon nanofibers (CNFs) and graphene nanoplatelets (GNPs) with PP matrix by melt mixing. Mixtures of CNFs and GNPs in 9:1, 8:2, and 7:3 ratios at 1 and 5 wt/wt% with and without surface modification by cold propylene plasma were fabricated. The compatibility and dispersion of the CNPs in the PP matrix were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy, and the results were related to the mechanical properties. The results show that the use of mixtures improved the dispersion in the system and hindered the reagglomeration of CNPs, whereas surface modification with plasma promotes higher compatibility between the phases. The elastic modulus of PP reached an increase of 127.40% using a modified mixture by plasma in a 7:3 ratio (CNF:GNPs) at 5 wt/wt%, while when the CNPs were used individually, the modified CNFs and GNPs at 5 wt/wt%, reached 97.77% and 111.85%, respectively. In addition, a finite element analysis shows that the stresses in nanocomposites fabricated with mixtures of CNPs are supported to a greater extent by GNPs than CNFs due to their morphology with a low number of graphene sheets, which allows them to have greater flexibility.
Influence of methods for promoting dispersion and compatibility: melt mixing, cold plasma modification, and mixtures of carbon nanoparticles of different geometries on enhancing the elastic modulus of polypropylene nanocomposites with carbon nanofibers and graphene nanoplatelets.
Diffusion Monte Carlo calculations on the possibility of having self-bound one-dimensional droplets of SU(6) × SU(2) ultracold fermionic mixtures are presented. We found that, even though ...arrangements with attractive interactions with only two spin types are not self-bound, mixtures with at least three kinds of fermions form stable small drops. However, that stabilization decreases for very tight confinements, where a universal behavior is found for Fermi-Fermi and Fermi-Boson clusters including attractive and repulsive interactions.
Water on graphene surfaces Gordillo, M C; Martí, J
Journal of physics. Condensed matter,
07/2010, Letnik:
22, Številka:
28
Journal Article
Recenzirano
Odprti dostop
In this paper, we summarize the main results obtained in our group about the behavior of water confined inside or close to different graphene surfaces by means of molecular dynamics simulations. ...These include the inside and outside of carbon nanotubes, and the confinement inside a slit pore or a single graphene sheet. We paid special attention to some thermodynamical (binding energies), structural (hydrogen-bond distributions) and dynamic (infrared spectra) properties, and their comparison to their bulk counterparts.
Introduction
The first definition of PAS, enunciated by Richard Gardner in 1985, refers to a disorder originating in the context of legal conflicts related to child custody. Its main characteristic ...would be a smear campaign by the child towards a parent, in the absence of plausible arguments. In this context, the child would experience an oppositional and dichotomous feeling towards his or her parents. In recent years, the presence of PAS has become increasingly important, both in the legal and health fields, largely due to the controversy and debate surrounding its approval and recognition, and there is currently no consensus on the matter.
Objectives
The main objective of this work is to examine the current state of PAS in depth in the different fields in which it is emerging: the medical-scientific and legal spheres. The current controversies and debate, both scientific and legal, will be developed. Research will be carried out on the origin of the concept and its evolution, its symptomatic presentation, the neuropsychological consequences in minors, the role and legal value of expert reports, as well as the existing evaluation methods for the assessment of PAS.
Methods
An extensive literature review was carried out on the subject in question, extracting information mainly from scientific articles, but also from legislative documents, manuals and books.
Results
There are currently no specific laws regulating PAS in European countries. According to Article 10.2 of the Spanish Constitution, norms related to fundamental rights shall be interpreted according to the Universal Declaration of Human Rights. As a direct consequence of the chronic psychological stresses experienced by children, adaptive disorders may appear, often characterised by symptoms of anxiety and depression. In addition, a multitude of neuropsychological consequences have been observed not only in the affected child, but also in the adult he or she will become.
Conclusions
Currently, there is a fervent debate about the validity and recognition of PAS as a diagnostic entity, spanning different disciplines, ranging from health to social and legal. In Europe, professionals in the scientific field have not reached an agreement regarding the approval of PAS. On the one hand, there are those for whom PAS is a verified phenomenon; on the other hand, there are those who flatly reject the existence of this phenomenon. The latter consider PAS an unscientific construct, referring to it as “court syndrome” or “patriarchal alienation syndrome”.
Disclosure of Interest
None Declared
We use a diffusion Monte Carlo method to solve the many-body Schrödinger equation describing fully heavy tetraquark systems. This approach allows us to reduce the uncertainty of the numerical ...calculation at the percent level, accounts for multiparticle correlations in the physical observables, and avoids the usual quark clustering assumed in other theoretical techniques applied to the same problem. The interaction between particles was modeled by the most general and accepted potential-i.e., a pairwise interaction including Coulomb, linear-confining and hyperfine spin-spin terms. This means that, in principle, our analysis should provide some rigorous statements about the mass location of the all-heavy tetraquark ground states, which is particularly timely due to the very recent observation made by the LHCb Collaboration of some enhancements in the invariant mass spectra of J/ψ pairs. Our main results are as follows: (i) The cc¯c¯c, cc¯b¯b (bb¯c¯c), and bb¯b¯b lowest-lying states are located well above their corresponding meson-meson thresholds. (ii) The JPC = 0++ cc¯c¯c ground state with preferred quark-antiquark pair configurations is compatible with the enhancement(s) observed by the LHCb Collaboration. (iii) Our results for the cc¯c¯b and bb¯c¯b sectors seem to indicate that the 0+ and 1+ ground states are almost degenerate, with the 2+ located around 100 MeV above them. (iv) Smaller mass splittings for the cb¯c¯b system are predicted, with absolute mass values in reasonable agreement with other theoretical works. (v) The 1++ cb¯c¯b tetraquark ground state lies at its lowest S-wave meson-meson threshold, and it is compatible with a molecular configuration.
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