Effective interactions and phase behaviour for a model clay suspension in an electrolyte

Since the early observation of nematic phases of disc-like clay colloids by Langmuir in 1938, the phase behaviour of such systems has resisted theoretical understanding. The main reason is that there is no satisfactory generalization for charged discs of the isotropic DLVO potential describing the effective interactions between a pair of spherical colloids in an electrolyte. In this contribution, we show how to construct such a pair potential, incorporating approximately both the non-linear effects of counter-ion condensation (charge renormalization) and the anisotropy of the charged platelets. The consequences on the phase behaviour of Laponite dispersions (thin discs of 30 nm diameter and 1 nm thickness) are discussed, and investigation into the mesostructure via Monte Carlo simulations are presented.Comment: LaTeX, 12 pages, 11 figure

The interplay between screening properties and colloid anisotropy: towards a reliable pair potential for disc-like charged particles

The electrostatic potential of a highly charged disc (clay platelet) in an electrolyte is investigated in detail. The corresponding non-linear Poisson-Boltzmann (PB) equation is solved numerically, and we show that the far-field behaviour (relevant for colloidal interactions in dilute suspensions) is exactly that obtained within linearized PB theory, with the surface boundary condition of a uniform potential. The latter linear problem is solved by a new semi-analytical procedure and both the potential amplitude (quantified by an effective charge) and potential anisotropy coincide closely within PB and linearized PB, provided the disc bare charge is high enough. This anisotropy remains at all scales; it is encoded in a function that may vary over several orders of magnitude depending on the azimuthal angle under which the disc is seen. The results allow to construct a pair potential for discs interaction, that is strongly orientation dependent.Comment: 13 pages, 19 figure

Pengaruh Kesejahteraan Petani Karet terhadap Pendidikan Anak di Desa Teratak Air Hitam Kecamatan Sentajo Raya Kabupaten Kuantan Singingi

This study aims to determine the influence of the welfare of rubber farmers to the education of children in the village of Teratak Air Hitam Sentajo Raya Sub-district Kuantan Singing District. The subjects of this study are farmers who have childrens that droped out from school. The total sample are 41 respondents using the method of Proposive Sampling. The data used for this study are primary data collected by using questionnaires and documentation. Data analysis technique used the chi square test analysis. The results of this study indicate that the, rubber farmers are prosperous it can be seen from the fulfillment of welfare indicators. On the other hand the education of children of rubber farmers is still low. This study found that there is no significant relationship between the rubber farmer's welfare and their children's education in the village of Teratak Air Hitam Sentajo Raya Sub-district Kuantan Singingi Regency

Theory of orientational ordering in colloidal molecular crystals

Freezing of charged colloids on square or triangular two-dimensional periodic substrates has been recently shown to realize a rich variety of orientational orders. We propose a theoretical framework to analyze the corresponding structures. A fundamental ingredient is that a non spherical charged object in an electrolyte creates a screened electrostatic potential that is anisotropic at any distance. Our approach is in excellent agreement with the known experimental and numerical results, and explains in simple terms the reentrant orientational melting observed in these so called colloidal molecular crystals. We also investigate the case of a rectangular periodic substrate and predict an unusual phase transition between orientationnaly ordered states, as the aspect ratio of the unit cell is changed.Comment: 4 pages, to appear in Phys. Rev. Let

Committed to restoring tropical forests: an overview of Brazil’s and Indonesia’s restoration targets and policies

The restoration of tropical forests has become a popular nature-based solution for climate change mitigation, protection of biodiversity, and improving the livelihoods of local populations. The Bonn Challenge and the UN Decade on Ecosystem Restoration underscore the international momentum of the restoration movement, with many countries committing to restore millions of hectares of deforested and degraded land in the next decade. Brazil and Indonesia are among the ones with the most ambitious restoration commitments globally. Since both their economies are highly dependent on the export of agricultural commodities, reconciling economic growth with environmental sustainability will be a major policy challenge. In this paper, we (a) identify the main restoration targets and the policies supporting their implementation in both countries, (b) provide a descriptive overview of these restoration-supportive policies, and (c) discuss the main challenges that Brazil and Indonesia face in the implementation of their restoration commitments. We find that Brazil has an explicit and dedicated strategy to achieve its restoration target, but that recent political developments have weakened environmental governance in the country, affecting the implementation of its restoration commitment. In the case of Indonesia, we find that the government has rather focused and progressed on the restoration of peatlands and mangroves, whereas its commitment to restore forestlands has yet to benefit from a dedicated plan that allows to coordinate policies and agencies’ efforts towards the achievement of its restoration target

Considerations in the determination of orientational order parameters from X-ray scattering experiments

An assessment of the data processing and analysis methods used to obtain the second- and fourth-rank orientational order parameters of liquid crystals from X-ray scattering experiments has been carried out, using experimental data from four extensively studied alkyl-cyanobiphenyls and calculated data generated from two general types of theoretical orientational distribution function. The application of a background subtraction and two different baseline correction methods to the scattering profiles is assessed, along with three different methods to analyse the processed data. The choice of baseline correction method is shown to have a significant effect: an offset to zero overestimates the order parameters from the experimental and calculated data sets, particularly for lower order parameters arising from broad distributions, whereas an offset to a value estimated from regions of low scattering intensity provides experimental values close to those reported from other experimental techniques. By contrast, the three different analysis methods are shown generally to result in relatively small absolute differences between the order parameters. We outline a straightforward general approach to experimental X-ray scattering data processing and analysis for uniaxial phases that results in order parameters that match well with those reported using other experimental techniques

Real-world assessment and characteristics of men with benign prostatic hyperplasia (BPH) in primary care and urology clinics in Spain

Objectives: To describe the real-world demographic and clinical characteristics of patients with lower urinary tract symptoms (LUTS) as a result of benign prostatic hyperplasia (BPH) in Spain. Methodology: This observational, retrospective, multicentre study conducted in primary care and urology clinics in Spain included men aged ≥50 years diagnosed (≤8 years prior to study visit) with LUTS caused by BPH. The primary endpoint was demographic and clinical characteristics; secondary endpoints included disease progression and diagnostic tests across both healthcare settings. Results: A total of 670 patients were included (primary care: n = 435; urology: n = 235). Most patients had moderate/severe LUTS (74.6%) and prostate volume >30 cc (81.7%), with no differences between settings. More patients had prostate-specific antigen (PSA) ≥1.5 ng/mL in primary care (74.5%) versus urology (67.7%). Progression criteria were prevalent (48.9%). Clinical criteria were more commonly used than the International Prostate Symptom Score (IPSS) to evaluate LUTS at diagnosis (primary care: clinical criteria 73.0%; IPSS: 26.9%; urology: clinical criteria 76.5%; IPSS: 23.4%). Proportion of patients with moderate/severe LUTS at diagnosis was lower using clinical criteria than IPSS, and the proportion of patients with 'worsening' LUTS (diagnosis to study visit) was higher when using clinical criteria versus IPSS. In both healthcare settings, the most commonly used diagnostic tests were general and urological clinical history and PSA. Conclusion: Demographic and clinical characteristics of patients with BPH in Spain were similar in primary care and urology; however, assessment criteria to evaluate LUTS severity differ and are not completely aligned with clinical guideline recommendations. Increased use of recommended assessments may enhance optimal BPH management