Rhenium distribution and behaviour in the salinity gradient of a highly stratified estuary and pristine riverine waters

The abundance and distribution of dissolved Re (DRe) has been determined in the freshwater part of the Krka River (Croatia), draining the karstic carbonate landscape, as well as in the salinity gradient of its highly stratified estuary. Due to low DRe concentration, the batch procedure consisting of pre-concentration step using an anion exchange resin (Dovex) and analysis of DRe in 8 M HNO 3 eluate using a high resolution inductively coupled plasma mass spectrometry (HR ICP-MS) was adopted. Due to the potential inconsistent recoveries, ranging from 60% to 87%, the quantification was performed by using the isotope dilution (ID) technique. The DRe concentration in the Krka River basically increased in the downstream direction, with the 6.2 pM at the spring site, reaching 11.9 pM before the estuarine region. The weathering of the surrounding carbonate lithology is assumed as the source of natural Re. The two specific anomalies were registered: a strong increase in DRe concentration due to the anthropogenic input near the town of Knin (27.5 pM) and a decrease at downstream site caused by the subterranean input of freshwater of the Zrmanja River leading to relatively low DRe concentration (8.5 pM). In the estuarine segment, a near-conservative behavior of DRe was found in the salinity gradient of the upper surface layer, with the DRe concentration ranging from 18 to 38 pM. An anthropogenic supply was suggested within the estuarine segment close to the urban area causing a small positive deviation from the conservative line. In the bottom seawater layer, a minor decrease of DRe concentration in the most upstream estuarine regions was evidenced, implying a potential weak scavenging of Re.

Extended galactic rotational velocity profiles in f(R) gravity background

An attempt has been made to explore the geometric effects of f(R) action on the galactic dynamics under the weak field approximation. The rotational velocity is calculated beyond the Einstein’s geometric theory of gravity. It is inspired by the cosmological geometric relation obtained in the power-law f(R) gravity model in vacuum. We analyse the action with a small positive deviation from the Einstein–Hilbert gravity action (taking R as $$f(R)\propto R^{1+\delta }$$f(R)∝R1+δ) at the galactic scales for the explanation of the flatness paradox associated with the clustered galactic dark matter. We obtain the contribution of a dynamical f(R) cosmological background geometry on accelerating the test mass. Furthermore, the integrated effective acceleration of the test mass due to a massive spherically symmetric source in f(R) background is calculated via the study of geodesics for the suitable spacetime metric and an equation for the effective rotational velocity has been developed. We test the viability of the proposed model by tracing the motion of a test mass far from the disk of galactic matter for smaller $$\delta $$δ. The possible galactic rotational velocity curves in f(R) background are discussed for the formula obtained with $$\delta<< 1$$δ<<1. We also obtain constraints on $$\delta $$δ$$O(10^{-6})$$O(10-6) confirmed by observations.

Activity Measurement of Liquid Sn-Ag-Bi Alloys by Fused Salt EMF Method

Activity of tin in liquid Sn-Ag-Bi alloys was derived by EMF measurement of galvanic cell with fused salts electrolyte in the temperature range of 700 to 900K in the whole composition range. Activity of tin at 900K shows very small positive deviation from Raoult’s low for Sn-Bi alloys. Activity of ternary alloys was measured along three pseudo binary systems of Sn-(Ag,Bi) (where xAg/xBi =1/3,1/1 and 3/1). Its concentration dependence is very complex. From the iso-activity curves in the ternary system excess free energy of mixing is derived using Darken’s method for Gibbs-Duhem equation

Arylphosphonic acids. II. General acid and general base catalysis of acetone enolization

We have measured the rate constants for the enolization of acetone catalyzed by 29 arylphosphonate dianions (ArPO32−) and by 20 arylphosphonic acids (ArPO3H2). An excellent Brønsted correlation is found for the former reaction, with most ortho substituted compounds falling on the line drawn for the meta and para compounds (β = 0.72). The largest deviation is found for o-iodo, whose small positive deviation is ascribed to a polarizability effect in the transition state. The arylphosphonic acids give a fairly good Brønsted plot (α = 0.37) but here the ortho substituents tend to react slightly faster than would be expected on the basis of their equilibrium acid strengths. Catalysis by the monoanion ArPO3H− is difficult to detect; such ions appear to be acting as general acids, not general bases, and do not appear to act as bifunctional catalysts; it is shown that protonating acetone is 3.4 × 104 times as effective as deprotonating ArPO3H−. The Brønsted coefficients (β) for the rate-controlling steps for the enolization of acetone by the principal routes are shown to be inversely related to the magnitude of the rate constants.