Surface properties of sediments from two Argentinean reservoirs and the rate of phosphate release

This article reports the surface properties (electrophoretic mobility, surface charge and specific surface area (SSA)), and phosphate release rates of sediments from two Argentinean reservoirs. Even though sediments are a heterogeneous mixture of minerals with different charging behavior, electrophoresis reveals that all sediment particles are negatively charged in the pH range 3-9. Iron and aluminum oxides, which usually carry a net positive charge at low pH, seem to be forming aggregates with negatively charged minerals and/or carrying a net negative charge due to the presence of organic matter. The phosphate release rate increased by increasing pH and temperature, and depended linearly on the SSA of the sediments. These data, together with the high activation energy of the process, indicate that the rate-controlling process is a chemical reaction occurring at the solid-water interface, and not a diffusion process. The rate-controlling step seems to be the breaking of bonds between phosphate and surface groups, breaking that should be preceded by one or more deprotonation steps at the surface and favored by electrostatic repulsion between the negative charge surface and the phosphate anion.Fil: Borgnino, L.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Avena, Marcelo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; ArgentinaFil: de Pauli, Carlos Primo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin

[Antihypertensive effect and tolerability of slow-release nicardipine]

In order to evaluate the antihypertensive efficacy and tolerability of a new nicardipine formulation, 26 mild-to-moderate essential hypertensive patients were given slow-release nicardipine, 40 mg, twice daily for 6 weeks. Systolic (SBP) and diastolic (DBP) blood pressure were measured after a 1 week single-blind placebo run-in period and after 1, 2, 4 and 6 weeks of active treatment, just before the morning administration. After 1 week, nicardipine induced a significant blood pressure reduction (p less than 0.01), with a decrease in mean SBP/DBP values of -15/-11 mmHg (from baseline values of 165/104 to 150/93 mmHg) in supine and of -16/-12 mmHg (from 158/110 to 142/98 mmHg) in standing position. After 6 weeks the decrease was of -15/-12 mmHg in supine and of -15/-14 mmHg in standing position. The responder rate (DBP decrease of at least 10 mmHg) was 62% (16/26). Normalization rate (DBP less than 95 mmHg with a concomitant decrease of at least 10 mmHg) was 54% (14/26). Eleven patients reported adverse events (headache, peripheral oedema, palpitations, nausea, constipation, flush, dizziness and asthenia). Due to an improved pharmacokinetic profile, the slow-release formulation prolongs to 12 hours the antihypertensive effect of nicardipine, thus facilitating patient's complianc

Error due to atmospheric turbulence effects on solar diameter measurements performed with an astrolabe

Diameter measurements performed with the solar astrolabe are affected by instrumental and atmospheric effects. The problem is to know how these effects contribute to the error on diameter measurements. Thus, a numerical simulation is developed to bring some responses to this problem. For this purpose, synthetic images of the Sun similar to the ones obtained by the instrument through the Earth atmosphere are simulated. A fractal model is used to generate randomly perturbed wavefronts and therefore optical response of the whole system, atmosphere and instrument. Many sequences of solar images are then simulated for various observation conditions (Fried's parameter r0, spatial coherence outer scale $\mathit{L}_{0}$ and atmospheric characteristic times). They are used to define the time of contact of the direct and reflected solar images which is fundamental in the solar astrolabe experiment. It is then studied as a function of the observation conditions relatively to the experimental characteristics (exposure time)

Nitrendipine 20 mg once daily versus nicardipine slow release 40 mg twice daily in mild essential hypertension: evaluation by 24-hour ambulatory blood pressure monitoring

The extent and duration of the blood pressure (BP) lowering effect of 20 mg nitrendipine (NIT) once daily and 40 mg nicardipine slow release (NIC) twice daily were compared in 12 men (aged 39-55 years) with mild essential hypertension according to a randomized, cross over study. Twenty-four-hour non invasive ambulatory BP monitoring (Spacelabs 5200) was performed at the end of a 2-week placebo run-in and after 4 weeks of each active treatment; automatic BP measurements were programmed at 15-min intervals. Both treatments significantly (p less than .01) reduced mean 24-hour and daytime systolic (SBP) and diastolic (DBP) BP, but had different effects on daytime BP profiles. NIT decreased SBP and DBP (p less than .05) in 5 out of 8 two-hour subperiods (from 8 a.m. to 6 p.m.), followed by a loss of effect; NIC reduced SBP and DBP (p less than .05) in 7 out of 8 two-hour subperiods (from 8 a.m. to 10 p.m.). During the night-time, NIT reduced mean SBP (p less than .05) and NIC both mean SBP and DBP values (p less than .05; p less than .05 vs NIT for SBP). Heart rate was not affected by either treatment. Thus, after short-term treatment in mild essential hypertensives nitrendipine once daily was not as effective as nicardipine slow release twice daily in reducing blood pressure throughout the 24 hour