Solid-to-solid isostructural transition in the hard sphere/attractive Yukawa system

A thermodynamically consistent density functional-perturbation theory is used to study the isostructural solid-to-solid transition which takes place in the hard sphere/attractive Yukawa system when the Yukawa tail is sufficiently short-ranged. A comparison with results for the square well potential allows us to study the effect of the attractive potential form on the solid-solid transition. Reasonable agreement with simulations is found for the main transition properties as well as for the phase diagram evolution with the the range of the attractive potential.Comment: 14 pages, latex, 5 figures available upon request: ([email protected]

Identification of Mexican Maize Races (Zea mays L.) with Drought Tolerance using Osmotic Potential Experiments for Genetic Breeding

Received: July 13th, 2023 ; Accepted: September 23rd, 2023 ; Published: October 23rd, 2023 ; Correspondence: [email protected] (Zea mays L.) is the third most important cereal crop worldwide after wheat and rice per cultivated area with 249,225,876 hectares and the most important crop for number of harvested grain tons with 1,482,997,259 in 2021. Some native Mexican maize races could be a source for drought tolerance to improve commercial cultivars and hybrids. The experiments were conducted using various osmotic pressures (OP) induced by polyethylene glycol (PEG-6000) (0, -0.05, -0.15, -0.30 and -0.49 MPa) simulating an increase of drought stress in ten maize genotypes. The main objectives of this study were the evaluation of germination and seedling growth components in response to drought stress and the identification of sources of drought tolerance in Mexican maize races. Apachito-r showed an increased germination in 110.4%, Cristalino-079 had a decreased germination in 98.7% and Cristalino-279 reduced its germination in a 91.1% compared to the control. Apachito-r outstands in root length at -0.05 OP increasing 200.1% and at -0.49 increasing 129.8%. The values for stem length were decreasing as the OP was increasing and only Apachito-r showed a significant difference at -0.30 MPa decreasing 39.8% respect to its control. Cristalino-279 showed significant difference in the variable root fresh weight and its value outstand at -0.15 increasing 267.2%, at -0.30 increasing 281.6% and at -0.49 MPa increasing 189.3% compared to the control in water. The variable root dry weight had the highest value for Apachito-r at -0.05 MPa increasing in a 189.4%, decreasing at -0.15 in 72% and at -0.30 MPa in a 79.8% and increasing at -0.49 MPa in 112.3%. Also noteworthy are E-zapata-r increasing 190.5% and Cristalino-061 increasing 142.9% at -0.30. E-zapata-r at -0.49 increased 115.1%. Cristalino-279 showed significant difference in the variable stem fresh weight and its value outstand at -0.05, -0.15 and -0.30 MPa increasing 146.7%, 103.7% and 60.2% respectively. Finally, in stem dry weight the tendency was to decrease as OP was increasing, however Cristalino-279 showed differences at -0.30 decreasing in 89.5% and at -0.49 MPa increasing in a 143.5% respect to the control. The most drought tolerant genotypes were Cristalino-279, Apachito-r, Azul and 8-carreras-PP. The most tolerant genotypes showed greater root length, greater root fresh and dry weight, better germination and greater stem length. Resistant and susceptible genotypes are ideal material to understand the physical and chemical mechanisms related to drought tolerance. Cristalino-279 shows the best level of drought tolerance at all levels of osmotic pressure, this genotype can be used as a source of drought tolerance for the improvement of commercial maize

Geoestatística no estudo de modelagem temporal da precipitação.

A análise geoestatística é uma poderosa ferramenta utilizada em estudos de dependência espacial. No que tange à dependência temporal, poucas são as análises realizadas com essa metodologia. Neste trabalho foi utilizada a técnica de geoestatística para ajustar um modelo de série temporal de precipitação, cujo poder é avaliado em predizer valores futuros. O estudo foi realizado na Bacia do Rio Itapemirim em uma série de precipitação mensal de 1940 a 2006. O modelo geoestatístico foi comparado com um modelo de séries temporais de Box e Jenkins. O modelo geoestatístico ajustado foi aquele com 96 vizinhos utilizados na previsão e erro relativo absoluto médio de 80,46. A metodologia de geoestatistica apresentou melhores resultados na estimação da precipitação mensal, em relação ao modelo SARIMA (2,1,1)(0,1,1)12

Theoretical description of phase coexistence in model C60

We have investigated the phase diagram of the Girifalco model of C60 fullerene in the framework provided by the MHNC and the SCOZA liquid state theories, and by a Perturbation Theory (PT), for the free energy of the solid phase. We present an extended assessment of such theories as set against a recent Monte Carlo study of the same model [D. Costa et al, J. Chem. Phys. 118:304 (2003)]. We have compared the theoretical predictions with the corresponding simulation results for several thermodynamic properties. Then we have determined the phase diagram of the model, by using either the SCOZA, or the MHNC, or the PT predictions for one of the coexisting phases, and the simulation data for the other phase, in order to separately ascertain the accuracy of each theory. It turns out that the overall appearance of the phase portrait is reproduced fairly well by all theories, with remarkable accuracy as for the melting line and the solid-vapor equilibrium. The MHNC and SCOZA results for the liquid-vapor coexistence, as well as for the corresponding critical points, are quite accurate. All results are discussed in terms of the basic assumptions underlying each theory. We have selected the MHNC for the fluid and the first-order PT for the solid phase, as the most accurate tools to investigate the phase behavior of the model in terms of purely theoretical approaches. The overall results appear as a robust benchmark for further theoretical investigations on higher order C(n>60) fullerenes, as well as on other fullerene-related materials, whose description can be based on a modelization similar to that adopted in this work.Comment: RevTeX4, 15 pages, 7 figures; submitted to Phys. Rev.

Confirmation of Anomalous Dynamical Arrest in attractive colloids: a molecular dynamics study

Previous theoretical, along with early simulation and experimental, studies have indicated that particles with a short-ranged attraction exhibit a range of new dynamical arrest phenomena. These include very pronounced reentrance in the dynamical arrest curve, a logarithmic singularity in the density correlation functions, and the existence of `attractive' and `repulsive' glasses. Here we carry out extensive molecular dynamics calculations on dense systems interacting via a square-well potential. This is one of the simplest systems with the required properties, and may be regarded as canonical for interpreting the phase diagram, and now also the dynamical arrest. We confirm the theoretical predictions for re-entrance, logarithmic singularity, and give the first direct evidence of the coexistence, independent of theory, of the two coexisting glasses. We now regard the previous predictions of these phenomena as having been established.Comment: 15 pages,15 figures; submitted to Phys. Rev.

Global Equation of State of two-dimensional hard sphere systems

Hard sphere systems in two dimensions are examined for arbitrary density. Simulation results are compared to the theoretical predictions for both the low and the high density limit, where the system is either disordered or ordered, respectively. The pressure in the system increases with the density, except for an intermediate range of volume fractions $0.65 \le \nu \le 0.75$, where a disorder-order phase transition occurs. The proposed {\em global equation of state} (which describes the pressure {\em for all densities}) is applied to the situation of an extremely dense hard sphere gas in a gravitational field and shows reasonable agreement with both experimental and numerical data.Comment: 4 pages, 2 figure

Liquid-Solid Transition of Hard Spheres Under Gravity

We investigate the liquid-solid transition of two dimensional hard spheres in the presence of gravity. We determine the transition temperature and the fraction of particles in the solid regime as a function of temperature via Even-Driven molecular dynamics simulations and compare them with the theoretical predictions. We then examine the configurational statistics of a vibrating bed from the view point of the liquid-solid transition by explicitly determining the transition temperature and the effective temperature, T, of the bed, and present a relation between T and the vibration strength.Comment: 14 total pages, 4 figure

Correlation functions near Modulated and Rough Surfaces

In a system with long-ranged correlations, the behavior of correlation functions is sensitive to the presence of a boundary. We show that surface deformations strongly modify this behavior as compared to a flat surface. The modified near surface correlations can be measured by scattering probes. To determine these correlations, we develop a perturbative calculation in the deformations in height from a flat surface. Detailed results are given for a regularly patterned surface, as well as for a self-affinely rough surface with roughness exponent $\zeta$. By combining this perturbative calculation in height deformations with the field-theoretic renormalization group approach, we also estimate the values of critical exponents governing the behavior of the decay of correlation functions near a self-affinely rough surface. We find that for the interacting theory, a large enough $\zeta$ can lead to novel surface critical behavior. We also provide scaling relations between roughness induced critical exponents for thermodynamic surface quantities.Comment: 31 pages, 2 figure