Evaluation of the effect of volcanic ash on the properties of concrete

Effect of volcanic ash on the properties of concrete was assessed in the study. Preliminary tests were carried out on the different properties of materials used. The concrete samples were prepared using 0%, 5%, 10%, and 15% volcanic ash replacements and nominal mix of 1:2:4 with a 0.5 w/c ratio. Concrete sample specimen was subjected to workability test. Thereafter, Cube mould of size 100mm x 100mm x100mm and cylinder mould of size 200mm x 100mm were used to cast a total of 405 concrete samples, 162 cubes were used to assess compressive strength test while 162 cylinders were used to determine the tensile strength by the split tensile method. The specimens were cured and tested at 7, 14, 21, 28, 56 and 90 days. The results show setting time and soundness test of Miango volcanic ash satisfied the necessary requirements. Also, increase in compressive strength and split tensile strength of about 7.99% and 6.14% respectively, for concrete samples with 10% volcanic ash replacements after 28days of curing. It was concluded that Miango volcanic ash retards the setting time of concrete and enhances the properties of concrete. Hence it was recommended that it should be used to produce a strong and dense concrete and serve as an admixture.Keywords: Concrete, compressive strength, volcanic ash, partial replacement, workabilit

Probing a critical length scale at the glass transition

We give evidence of a clear structural signature of the glass transition, in terms of a static correlation length with the same dependence on the system size which is typical of critical phenomena. Our approach is to introduce an external, static perturbation to extract the structural information from the system's response. In particular, we consider the transformation behavior of the local minima of the underlying potential energy landscape (inherent structures), under a static deformation. The finite-size scaling analysis of our numerical results indicate that the correlation length diverges at a temperature $T_c$, below the temperatures here the system can be equilibrated. Our numerical results are consistent with random first order theory, which predicts such a divergence with a critical exponent $\nu=2/3$ at the Kauzmann temperature, where the extrapolated configurational entropy vanishes.Comment: 5 pages, 5 figures, to appear in Phys. Rev. Lett. 2010

Static and dynamic heterogeneities in a model for irreversible gelation

We study the structure and the dynamics in the formation of irreversible gels by means of molecular dynamics simulation of a model system where the gelation transition is due to the random percolation of permanent bonds between neighboring particles. We analyze the heterogeneities of the dynamics in terms of the fluctuations of the intermediate scattering functions: In the sol phase close to the percolation threshold, we find that this dynamical susceptibility increases with the time until it reaches a plateau. At the gelation threshold this plateau scales as a function of the wave vector $k$ as $k^{\eta -2}$, with $\eta$ being related to the decay of the percolation pair connectedness function. At the lowest wave vector, approaching the gelation threshold it diverges with the same exponent $\gamma$ as the mean cluster size. These findings suggest an alternative way of measuring critical exponents in a system undergoing chemical gelation.Comment: 4 pages, 4 figure

Static and dynamic heterogeneities in irreversible gels and colloidal gelation

We compare the slow dynamics of irreversible gels, colloidal gels, glasses and spin glasses by analyzing the behavior of the so called non-linear dynamical susceptibility, a quantity usually introduced to quantitatively characterize the dynamical heterogeneities. In glasses this quantity typically grows with the time, reaches a maximum and then decreases at large time, due to the transient nature of dynamical heterogeneities and to the absence of a diverging static correlation length. We have recently shown that in irreversible gels the dynamical susceptibility is instead an increasing function of the time, as in the case of spin glasses, and tends asymptotically to the mean cluster size. On the basis of molecular dynamics simulations, we here show that in colloidal gelation where clusters are not permanent, at very low temperature and volume fractions, i.e. when the lifetime of the bonds is much larger than the structural relaxation time, the non-linear susceptibility has a behavior similar to the one of the irreversible gel, followed, at higher volume fractions, by a crossover towards the behavior of glass forming liquids.Comment: 9 pages, 3 figure

Reentrant phase diagram and pH effects in cross-linked gelatin gels

Experimental results have shown that the kinetics of bond formation in chemical crosslinking of gelatin solutions is strongly affected not only by gelatin and reactant concentrations but also by the solution pH. We present an extended numerical investigation of the phase diagram and of the kinetics of bond formation as a function of the pH, via Monte Carlo simulations of a lattice model for gelatin chains and reactant agent in solution. We find a reentrant phase diagram, namely gelation can be hindered either by loop formation, at low reactant concentrations, or by saturation of active sites of the chains via formation of single bonds with crosslinkers, at high reactant concentrations. The ratio of the characteristic times for the formation of the first and of the second bond between the crosslinker and an active site of a chain is found to depend on the reactant reactivity, in good agreement with experimental data.Comment: 8 pages, 8 figure

Conflict Resolution and Reconciliation in Sudan: Inter-Tribal Reconciliation Conferences in South Darfur State up to 2009.

This study explores and critically examines the role of indigenous mechanisms (the Inter-Tribal Reconciliation Conferences-ITRCs) in resolving tribal conflicts in South Darfur State of Western Sudan. The fundamental question raised by this study is: have these reconciliation conferences- 1989-2009- been able to address the root causes of the tribal conflicts and are they capable of serving the same role that they once did? Tribal leadership structures, such as Native Administration (NA) and their mechanisms of conflict resolution/management in Darfur, have been subjected to highly significant changes over time. The question is to what extent these changes further fuelled tribal conflicts and/or have negatively affected the capability of the NA and the ITRCs to deal with these conflicts? This thesis relies on archive records and reports of the ITRCs and data generated through interviews conducted with key informants. Through a detailed analysis the study: 1) presents a detailed account of the major conflicts and their causes in South Darfur; 2) identifies the changing identities of the protagonists and of the perceived causes; 3) assesses the effectiveness of the agreements reached by these conferences when considered alongside the causes identified. Analysis of the ITRCs shows that tribal conflicts in Darfur (from1980s), and South Darfur in particular, were connected to the wider political conflict in the Sudan and the region respectively. The analysis suggests that the history of neglect/marginalisation of the region by successive governments, and the political manipulation of the NA and local government, have negatively affected the performance of these institutions. The experience of the ITRCs indicates that they were unable to address the underlying causes of the tribal conflicts, such as land disputes, the manipulation of the NA and local government, rape and mass killings

Évaluation de l’impact du rejet des déchets phosphates dans la mer sur la biodiversité marine dans trois localités côtières au Togo à partir des biomarqueurs du stress oxydatif chez Sphyraena barracuda (HECKEL, 1843)

La pollution due aux rejets des déchets phosphatés à Kpémé par la Société Nouvelle des Phosphates du Togo (SNPT), concerne aussi les zones environnantes. Nous avons voulu dans ce travail déterminer l’impact de cette pollution dans ces zones sur la biodiversité marine. Les teneurs en métaux lourds toxiques (Cd et Pb) dans les organes de poissons à Gbodjomé (zone de référence), Agbodrafo, Goumoukopé et Aného sont déterminées par spectrophotométrie d’absorption atomique à la flamme ; de même que certains biomarqueurs du stress oxydatif. Dans l’ensemble, les résultats ont montré une altération des enzymes antioxydantes, du système de la glutathion et une induction de la peroxydation lipidique due à la présence du Cd et du Pb qui provoquent un stress oxydatif chez les poissons, et donc chez les espèces de la biodiversité marine de la côte togolaise des zones concernées. Les résultats de la présente étude indiquent que les zones environnantes sont touchées par le rejet des déchets à Kpémé et les impacts sur la biodiversité marine diminuent au fur et à mesure qu’on s’éloigne des sites de rejets vers l’aval à cause du sens d’écoulement de la mer. Aussi, peut-on déduire que les biomarqueurs du stress oxydatif sont des indicateurs de la pollution aquatique.Mots clés: Déchets phosphatés, pollution, Cd, Pb, bioaccumulatio

EFFECT OF ETHYL SALICYLIC ACID VAPOUR ON SPROUTING AND ROTS INCIDENCE OF POTATO TUBERS UNDER LONG-TERM STORAGE(a)

The effect of exposing of potato tubers cv. Di-amond to ethyl salicylic acid (ES) vapour for dif-ferent doses and different periods of exposing on rots incidence and sprouting of tubers under long term storage was studied. Expose of tubers to high doses of vapour (resulted from evaporation of 0.5 or 1 ml/ liter space) for 6 h led to appear a very strong harmful effect on exposed tubers stored for 4 months. All tubers were decayed, collapsed and severely infected by rot pathogens. Expose of tu-bers to middle dose (0.25 ml/liter space) for 6, 12, 24, or 48 h then stored for 4 months at ambient temperature showed variable effects. Six or 12 h exposing led to slight reduction of rot incidence but it had not effect on sprouting in comparison to non-exposed tubers. On the other hand, exposing, for 24 or 48 h suppressed sprouting completely and reduced to very great extent rots incidence (%). Storage of tubers exposed to 0.25 ml/ liter for 24 h at high relative humidity (~90%) or under cooling (6-8 Cْ ) did not cause any reduction in compound efficiency. Expose of tubers to low dose of ES vapour (0.125 ml/ liter space) for dif-ferent periods showed that exposing for 6 or 12 h led to stimulatory effect on sprouting without ef-fect on rots incidence. Twenty four hours exposing led to decrease rots incidence and sprouting.These results clearly indicated that ES vapour had variable effects on exposed tubers depend upon dose and period of exposing

Allosteric modulators targeting cannabinoid cb1 and cb2 receptors: Implications for drug discovery

Allosteric modulators of cannabinoid receptors hold great therapeutic potential, as they do not possess intrinsic efficacy, but instead enhance or diminish the receptor's response of orthosteric ligands allowing for the tempering of cannabinoid receptor signaling without the desensitization, tolerance and dependence. Allosteric modulators of cannabinoid receptors have numerous advantages over the orthosteric ligands such as higher receptor type selectivity, probe dependence and biased signaling, so they have a great potential to separate the therapeutic benefits from side effects own of orthosteric ligands. This review aims to give an overview of the CB1 and CB2 receptor allosteric modulators highlighting the structure-activity relationship and pharmacological profile of each classes, and their future promise