Macrozoneamento climático para o arroz irrigado no Rio Grande do Sul.

bitstream/item/33533/1/documento-137.pd

Zoneamento agroclimático para pereira no Rio Grande do Sul.

bitstream/CPACT/10925/1/documento_182.pdf; bitstream/item/33625/1/documento-182.pd

Interplay of quantum and classical fluctuations near quantum critical points

For a system near a quantum critical point (QCP), above its lower critical dimension $d_L$, there is in general a critical line of second order phase transitions that separates the broken symmetry phase at finite temperatures from the disordered phase. The phase transitions along this line are governed by thermal critical exponents that are different from those associated with the quantum critical point. We point out that, if the effective dimension of the QCP, $d_{eff}=d+z$ ($d$ is the Euclidean dimension of the system and $z$ the dynamic quantum critical exponent) is above its upper critical dimension $d_C$, there is an intermingle of classical (thermal) and quantum critical fluctuations near the QCP. This is due to the breakdown of the generalized scaling relation $\psi=\nu z$ between the shift exponent $\psi$ of the critical line and the crossover exponent $\nu z$, for $d+z>d_C$ by a \textit{dangerous irrelevant interaction}. This phenomenon has clear experimental consequences, like the suppression of the amplitude of classical critical fluctuations near the line of finite temperature phase transitions as the critical temperature is reduced approaching the QCP.Comment: 10 pages, 6 figures, to be published in Brazilian Journal of Physic

Critical exponents and equation of state of the three-dimensional Heisenberg universality class

We improve the theoretical estimates of the critical exponents for the three-dimensional Heisenberg universality class. We find gamma=1.3960(9), nu=0.7112(5), eta=0.0375(5), alpha=-0.1336(15), beta=0.3689(3), and delta=4.783(3). We consider an improved lattice phi^4 Hamiltonian with suppressed leading scaling corrections. Our results are obtained by combining Monte Carlo simulations based on finite-size scaling methods and high-temperature expansions. The critical exponents are computed from high-temperature expansions specialized to the phi^4 improved model. By the same technique we determine the coefficients of the small-magnetization expansion of the equation of state. This expansion is extended analytically by means of approximate parametric representations, obtaining the equation of state in the whole critical region. We also determine a number of universal amplitude ratios.Comment: 40 pages, final version. In publication in Phys. Rev.

Responses of Solanum tuberosum L. to Water Deficit by Matric or Osmotic Induction.

Toselectpotatogenotypestoleranttowaterdeficit,systemstosimulatethisstresshavebeen used. Polyethylene glycol (PEG) is the main osmotic agent used for this purpose, but it causes an excessively severe stress. However, it is difficult to carry out an experiment that aims to compare plant responses under water deficit by osmotic or matric induction, and, thus,fewstudiescomparethesestress-inducingmechanisms.Therefore,theobjectiveofthis studywas to compare the responses of Agata, BRS Clara,C2406-03andCota genotypes to water deficit in both induction methods (matric or osmotic). The tests were carried out in a greenhouse, one using hydroponics (osmotic induction) and the other in pots with soil (matric induction). In both tests, the application of stressful conditions occurred at the beginning of tuberization. Assessments of gas exchange and shoot temperature were made throughout the exposure to stress. Also, samples were collected from leaves for analysis of osmotic potential and leaves and tubers for analysis of metabolite content. At the end of the potatoplantcycle,thenumberandweightoftuberswereevaluated.Inbothstressconditions, there were significant reductions in photosynthesis and transpiration rate compared to the respective normal hydration conditions. In addition, indicators such as metabolite levels (proline and soluble sugars) were significantly altered in plants exposed to different stress inductions. These data, together with the significant limitations in the growth of stressed plants, indicate that the experimental models induce similar responses. However, the water deficit by osmotic induction was more severe for the potato plants when compared to stress due to matric induction, mainly affecting tuber production. Therefore, the water deficit osmotic induction model can be recommended for phenotyping tolerance to this stress, due to the hydroponic system inducing greater tuber production per plant under optimal cultivation conditions