A novel hexagonal honeycomb K–Cr-oxalate anionic network with layers separated by a five-coordinated Cu(II)–pypn complex (pypn = N,N′-bis(2-pyridylmethyl)-1,3-propanediamine). Synthesis,characterisation, spectroscopy and crystal structure of {[KCr(C2O4)3][Cu(pypn)(H2O)](H2O)4}

A novel hexagonal-based honeycomb compound with overall formula {[KCr(C₂O₄)₃][Cu(pypn)(H₂O)](H₂O)₄} is reported in which pypn is with the tetradentate ligand (N,N′-bis(2-pyridylmethyl)-1,3-propanediamine). The [KCr(C₂O₄)₃]^2? moiety forms a hexagonal honeycomb structure, while the five-coordinated [Cu(pypn)(H₂O)]²⁺ moiety is located in between the layers, partly filling the holes in the cavities. The synthesis, X-ray crystal structure and some spectroscopic properties are presented. The coordination of Cr(III) is octahedral, with a CrO₆ chromophore, and the K⁺ ion is in a KO₆ environment (K–O distances vary from 2.36 to 2.48 ?). The [KCr(C₂O₄)₃]^2? layers have the K⁺ ions in a Λ conformation, while the Cr(III) ions in the Δ conformation. The geometry around the Cu(II) is five-coordinated with four nitrogens from the chelating pypn ligand in a plane and the apical position being occupied by the oxygen atom of the coordinating water molecule. The packing of the cationic and the anionic layers appears to be of special interest.     

Determinants of Domestic Water Use by Rural Households Without Access to Private Improved Water Sources in Benin: A Seemingly Unrelated Tobit Approach

This paper analyzes the determinants of domestic water use in rural areas. The focus is on households without access to private improved water sources. These households use either only free sources, only purchased sources or a combination of free and purchased sources. We also analyze households’ water use behaviors as a function of water availability by explicitly estimating domestic water use for both rainy and dry seasons. Using a Seemingly Unrelated Tobit approach to simultaneously account for the censored nature of water demand and the correlation of error terms between free and purchased water use equations, we find that purchased water demand is perfectly price inelastic due to water scarcity. The important determinants of water use are household size and composition, access to water sources, wealth and time required for fetching water. Nevertheless, the effects of these determinants vary between household types and seasons, and the policy implications of the findings are discussed.     

Effects of higher order nonlinearities on modulational instability in nonlinear oppositely directed coupler

We are motivated by recent studies in medium formed by two tunnel-coupled waveguides. One of the waveguides is manufactured from an ordinary dielectric, while the second has negative refraction. We present an investigation of the gain spectrum permitting modulation instability in the nonlinear optical coupler with a negative-index metamaterial channel whose non-linear response includes third- and fifth-order terms. The principal motivation for our analysis stems from the impact of the inevitable presence of the effective cubic–quintic nonlinearity. We emphasize the influence of higher order nonlinear terms, over the MI phenomena, and the outcome of its development achieved by using linear stability analysis. Gain spectrum investigation has been carried out for both anomalous and normal dispersion regime in the focusing and defocusing cases of nonlinearity and near-zero dispersion regime where higher order linear dispersive effects emerge. Our results show that the MI gain spectra consist of multiple spectral region which are symmetric to the zero point. Moreover, some spectra have a high cut-off frequency but a narrow spectral width, which is obviously beneficial to the generation of high-repetition-rate pulse trains.     

Interaction of Cocos nucifera cream casein with humic acid suspensions

Two caseins labelled as CaSMG (casein without fats) and CaMG (casein with fats) were extracted from coconut cream. Both caseins were used as coagulants for the aggregation of humic acid (HA) particles in synthetic water at pH = 6 during the jar-test essays. The optimum dosage of CaMG or CaSMG and the residual turbidities of treated water obtained depend on the type of used casein (CaMG or CaSMG) and the concentration of particles in solution. The optimal doses of CaMG and CaSMG are respectively 280 and 180 mg/L for solution S(1) (HA aqueous solution at 15 mg/L), and then 340 and 240 mg/L for solution S(2) (HA aqueous solution at 25 mg/L). The residual turbidities of treated water are respectively 6.88 and 3.85 NTU for solution S(1) and 4.52 and 2.53 NTU for solution S(2). The collected sediment volumes are respectively 1.2 and 1.5 mL for solutions S(1) and S(2). The electrophoretic mobility measurement and transmission electron microscopy images of flocs formed during the flocculation essays suggest that both caseins operate through both mechanisms (charge neutralisation and bridging process mechanism), this last one seems to be predominant. The aggregates formed are the large clusters and result from adsorption of HA particles by the casein molecules.     

Higher order dispersion effects in the noninstantaneous nonlinear Schrödinger equation

We present a systematic analysis of the effects, of higher-order dispersion, noninstantaneous nonlinear response, as well as stochastic coefficients in optical fiber. This study is motivated by recent experimental observation of a new modulational instability spectral window induced by fourth-order dispersion in a normally dispersive single-mode optical fiber. Analytical expression of pulse amplitude is deduced with the second-order gain nonuniformity and the stimulated-Brillouin scattering-induced third-order as well as fourth-order dispersion effects involved. The influence of stochasticity, as well as the delayed Raman response in the nonconventional sidebands obtained due to the fourth-order dispersion, is considered. We note that the shape of the spectrum, and in particular the relative intensities of the higher order harmonics, is highly sensitive to the initial presence of classical noise, and can therefore be taken as a signature that the MI is seeded by vacuum fluctuations. Some direct simulations to see the evolution of different continuous wave states are reported. These show the formation of modulation instability pulses as well as transitions from lower amplitude continuous wave states to higher amplitude continuous wave states. The present results fit well with recent experimental investigations.     

Estimating rural households' willingness to pay for water supply improvements: a Benin case study using a semi-nonparametric bivariate probit approach

This paper estimates households' willingness to pay (WTP) to improve rural water supply in Benin. Particular attention is given to the distribution of WTP, which is traditionally addressed using parametric assumptions. To avoid distributional assumptions, a semi-nonparametric bivariate probit approach is introduced. Results provide the first evidence that, in rural Benin, households wanting to improve water supply are willing to pay more than the current price. WTP for water supply is determined by wealth, education, and characteristics of existing and new water systems. Results indicate that a demand-driven management approach can contribute to water supply improvements and sustainability.     

Bestimmungsmethode der Konsistenzgrenzen mittels Wasseraufnahmeversuchen

Determination of Atterberg limits by means of water absorption tests. Atterberg‐limits‐tests, according to German standard DIN 18122 [1], are partially subjective and require relatively high work expended. This paper deals with a new and reliable testing method by means of efficient water absorption tests. Therein Atterberg limits are determined by the additional view of innercrystalline water absorption.     

Der Wasseraufnahmeversuch nach DIN 18132 in einem neu entwickelten Gerät

A new device for testing water absorption according to German standard DIN 18132. The water absorption test according to German standard DIN 18132 [1] was carried out so far in the so‐called Enslin‐Neff device [2], [3] after a maximum of 24 hours. Herein the water absorption of a sample material is read off by means of a graduated capillary glass measuring tube. With increasing duration of test the effect of evaporation on the reading rises. To correct this effect German standard DIN 18132 [1] quantifies evaporated water mass separately in the so‐called zero‐test. Despite this proceeding the error is usually relatively large. This paper deals with a new developed device, which eliminates the effect of evaporation on water absorption test. By means of a balancing system the actual water absorption is determined. On the basis of the test accuracy swelling material – smectite – are efficiently identified in soils.