El arqueado de tallos en cultivo de rosas: su papel en los intercambios gaseosos a escala del cultivo

Se ha estudiado la influencia del arqueado de tallos (técnica del “pulmón”) en la tasa de transpiración (E) y en la capacidad fotosintética (Alm) de un cultivo de rosas (Rosa hybrida cv. Dallas) sin suelo bajo invernadero. E se evaluó por medio de una balanza electrónica en plantas desarrolladas y en plantas con tallos arqueados. Alm se midió, en hojas adultas, a saturación de luz en diferentes estratos foliares del tallo floral y del pulmón. Los resultados muestran que el pulmón juega un papel preponderante en la tasa de transpiración del cultivo. La contribución del tallo floral y del pulmón a la transpiración del cultivo era muy similar (*50%). Se ha observado una disminución de Alm desde las hojas de la cima del tallo floral (16.4 mmolco2m-2s-1) hasta las hojas del pulmón, llegando a valores muy bajos en los tallos arqueados más viejos (6 mmolco2m-2s-1). El papel que juega la superficie foliar del pulmón en la fotosíntesis del cultivo (contribución 30 %) es de menor alcance que el que ejerce en la tasa transpiración, lo que indica que posee una menor eficiencia de uso del agua que el tallo floral. Por otro lado, los resultados sugieren que los tallos del pulmón deben renovarse con frecuencia, debido a una disminución drástica de Alm con la edad y con el sombreo mutuo entre las hojas

Electron exchange model potential: Application to positronium-helium scattering

The formulation of a suitable nonlocal model potential for electron exchange is presented, checked with electron-hydrogen and electron-helium scattering, and applied to the study of elastic and inelastic scattering and ionization of ortho positronium (Ps) by helium. The elastic scattering and the $n = 2$ excitations of Ps are investigated using a three-Ps-state close-coupling approximation. The higher ($n\ge 3$) excitations and ionization of Ps atom are treated in the framework of Born approximation with present exchange. Calculations are reported of phase shifts, and elastic, Ps-excitation, and total cross sections. The present target elastic total cross section agrees well with experimental results at thermal to medium energies.Comment: 16 latex pages, 7 postscript figure

Influence of effective stress on swelling pressure of expansive soils

The volume change and shear strength behaviour of soils are controlled by the effective stress. Recent advances in unsaturated soil mechanics have shown that the effective stress as applicable to unsaturated soils is equal to the difference between the externally applied stress and the suction stress. The latter can be established based on the soil-water characteristic curve (SWCC) of the soil. In the present study, the evolution of swelling pressure in compacted bentonite-sand mixtures was investigated. Comparisons were made between magnitudes of applied suction, suction stress, and swelling pressure

Clinical pharmacodynamic factors in docetaxel toxicity

Neutropenia is the main dose-limiting toxicity occurring in docetaxel treatment. The objective of this study was to identify pharmacodynamic (PD) factors responsible for the neutropaenia caused by docetaxel. Data were obtained from 92 patients treated with docetaxel as a monochemotherapy in two different treatment centres. A semiphysiological population pharmacokinetic–pharmacodynamic (PK/PD) model was applied to describe the time course of neutrophils and the neutropaenic effect of docetaxel. The plasma docetaxel concentration was assumed to inhibit the proliferation of neutrophil precursors through a linear model: Drug effect=Slope × Conc. Slope corresponds to the patients' sensitivity to the neutropaenic effect of docetaxel. Covariate analysis was performed by testing the relationship between the patients' characteristics and Slope using the program NONMEM. The neutropaenic effect of docetaxel showed a high interindividual variability. Three significant PD covariates were identified: serum α1-acid glycoprotein levels (AAG), level of chemotherapy pretreatment, and treatment centre. Extensive pretreatment was associated with an increase in Slope values meaning a higher haematotoxicity. An increase in AAG was associated with a decrease of both Slope and docetaxel plasma clearance. Patients treated in one centre had both higher Slope and docetaxel clearance. The centre effect (most likely due to a bias in the PK part of the study between the two centres) reveals the robustness of the PK/PD model. Individual dosing of docetaxel should be based on previous chemotherapy but not on the AAG level since it has a similar influence on PD and PK docetaxel parameters. This methodology should be applied to further investigate elderly patients and to identify more precisely the characteristics of previous chemotherapy that contribute to the cumulative myelotoxicity

Some Notes on Granular Mixtures with Finite, Discrete Fractal Distribution

Why fractal distribution is so frequent? It is true that fractal dimension is always less than 3? Why fractal dimension of 2.5 to 2.9 seems to be steady-state or stable? Why the fractal distributions are the limit distributions of the degradation path? Is there an ultimate distribution? It is shown that the finite fractal grain size distributions occurring in the nature are identical to the optimal grading curves of the grading entropy theory and, the fractal dimension n varies between-¥ and ¥. It is shown that the fractal dimensions 2.2-2.9 may be situated in the transitional stability zone, verifying the internal stability criterion of the grading entropy theory. Micro computed tomography (μCT) images and DEM (distinct element method) studies are presented to show the link between stable microstructure and internal stability. On the other hand, it is shown that the optimal grading curves are mean position grading curves that can be used to represent all possible grading curves