HOPF BIFURCATION ANALYSIS FOR SIMPLE THIRD-ORDER QUADRATIC SYSTEMS

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Reconstructing the Density of States by History-Dependent Metadynamics

We present a novel method for the calculation of the energy density of states D(E) for systems described by classical statistical mechanics. The method builds on an extension of a recently proposed strategy that allows the free energy profile of a canonical system to be recovered within a pre-assigned accuracy,[A. Laio and M. Parrinello, PNAS 2002]. The method allows a good control over the error on the recovered system entropy. This fact is exploited to obtain D(E) more efficiently by combining measurements at different temperatures. The accuracy and efficiency of the method are tested for the two-dimensional Ising model (up to size 50x50) by comparison with both exact results and previous studies. This method is a general one and should be applicable to more realistic model systems

Growing spinach in a floating system with different volumes of aerated or non-aerated nutrient solution

Vegetables grown in a floating system may encounter problems of hypoxia at root level, especially in the summer when temperature is high. Depending on the species, oxygen deficiency may cause a lower yield due to a reduction in water and mineral uptake by the plants. On the other hand, plants under oxygen stress may reduce nitrate accumulation, thus ameliorating produce quality. In the present work spinach was grown in summer and autumn in a floating system in different volumes (252, 126 and 60 l per m2 of cultivated area) of aerated or non aerated nutrient solution. Aeration kept oxygen concentration at 7-8 mg l-1 while in the non aerated solution oxygen decreased gradually reaching at harvest, on average, values of 1.92 mg l-1 and 2.83 mg l 1 in summer and autumn respectively. Such levels of hypoxia did not affect yield and did not reduce nitrate accumulation either. On the contrary, in the summer cycle leaf nitrate content was significantly lower when the nutrient solution was aerated. Reduction of the volume of the solution to 60 l m-2 of cultivated area induced a decrease in nitrate accumulation without negative effect on yield. No significant aeration x volume interaction was observed

RNA denaturation: excluded volume, pseudoknots and transition scenarios

A lattice model of RNA denaturation which fully accounts for the excluded volume effects among nucleotides is proposed. A numerical study shows that interactions forming pseudoknots must be included in order to get a sharp continuous transition. Otherwise a smooth crossover occurs from the swollen linear polymer behavior to highly ramified, almost compact conformations with secondary structures. In the latter scenario, which is appropriate when these structures are much more stable than pseudoknot links, probability distributions for the lengths of both loops and main branches obey scaling with nonclassical exponents.Comment: 4 pages 3 figure

Defects-related early childhood caries as hints of possible maternal–fetal health issues: Evidence from medieval northern Italy

Developmental defects of enamel (DDE) are important markers of stress as they arise from the disruption of ameloblastic activity during enamel matrix secretion and mineralization. Defects on the crowns of the deciduous dentition provide insights into maternal–fetal health because they can emerge during intrauterine development as a result of gestational issues. The presence of previous defective enamel represents one of the most predisposing causes of caries development. Thus, circular caries on the deciduous dentition are considered an indicator of stress because of their ascertained relation with dental enamel defects. In bioarchaeological analysis, these lesions allow us to deepen the question of maternal–fetal health issues in the ancient period. Here, we present evidence of defects-related early childhood caries in three infants from a medieval cemetery in northern Italy. The findings in the dentitions of the three subjects were investigated with a multi-analytical approach, including macroscopic examination, microscopic observation, cone-beam computed tomography (CBCT), scanning electron microscopy (SEM), and histological sections. In the specimens analyzed, the lesions observed in the dentitions appeared to have arisen during the fetal period and then protracted in the postnatal life, suggesting the implication of in utero environment and maternal health in the etiology of defects

Three-dimensional antiferromagnetic q-state Potts models: application of the Wang-Landau algorithm

We apply a newly proposed Monte Carlo method, the Wang-Landau algorithm, to the study of the three-dimensional antiferromagnetic q-state Potts models on a simple cubic lattice. We systematically study the phase transition of the models with q=3, 4, 5 and 6. We obtain the finite-temperature phase transition for q= 3 and 4, whereas the transition temperature is down to zero for q=5. For q=6 there exists no order for all the temperatures. We also study the ground-state properties. The size-dependence of the ground-state entropy is investigated. We find that the ground-state entropy is larger than the contribution from the typical configurations of the broken-sublattice-symmetry state for q=3. The same situations are found for q = 4, 5 and 6.Comment: 9 pages including 9 eps figures, RevTeX, to appear in J. Phys.