Berry Phases, Quantum Phase Transitions and Chern Numbers

We study the relation between Chern numbers and Quantum Phase Transitions (QPT) in the XY spin-chain model. By coupling the spin chain to a single spin, it is possible to study topological invariants associated to the coupling Hamiltonian. These invariants contain global information, in addition to the usual one (obtained by integrating the Berry connection around a closed loop). We compute these invariants (Chern numbers) and discuss their relation to QPT. In particular we show that Chern numbers can be used to label regions corresponding to different phases.Comment: Proceedings of The International Conference on Strongly Correlated Electron Systems (SCES'07). Accepted for publication in Physica

Response of beta diversity to pulses of Ordovician-Silurian mass extinction

Ecologists are increasingly using the fossil record of mass extinction to build predictive models for the ongoing biodiversity crisis. During mass extinctions, major depletions in global (i.e., gamma) diversity may reflect decrease in alpha diversity (i.e., local assemblages support fewer taxa), and/or decrease in beta diversity (such that similar pools of taxa are common to a greater number of local areas). Contrasting the effects of extinction on alpha and beta diversity is therefore central to understanding how global richness becomes depleted over these critical events. Here we investigate the spatial effects of mass extinction by examining changes in alpha, beta, and gamma diversity in brachiopod communities over both pulses of Ordovician-Silurian extinction (;445.2 and ;438.8 million years ago), which had dramatically different causal mechanisms. We furthermore reconstruct geographic range sizes for brachiopod genera to test competing models for drivers of beta diversity change. We find that: (1) alpha and beta diversity respond differently to extinction; (2) these responses differ between pulses of extinction; (3) changes in beta diversity associated with extinction are accompanied by changes in geographic range size; and (4) changes in global beta diversity were driven by the extinction of taxa with statistically small and large ranges, rather than range expansion/contraction in taxa that survive into the aftermath. A symptom of ongoing biotic crisis may therefore be the extinction of specific narrow- or wide-ranging taxa, rather than the global proliferation of opportunistic and ‘‘disaster’’ forms. In addition, our results illustrate that changes in beta diversity on these longer timescales may largely be dictated by emplacement and removal of barriers to dispersal. Lastly, this study reinforces the utility of the fossil record in addressing questions surrounding the role of global-scale processes (such as mass extinctions) in sculpting and assembling regional biotas

An Examination of the Factors Affecting Residential Property Values in Magodo Neighbourhood, Lagos State

Lagos State is steadily emerging a multi-nuclei metropolis giving rise to a number of business hubs and real estate submarkets. Notwithstanding, investment and return on property are normally adjudged as more juicy in some neighbourhoods such as Ikoyi, Victoria Island, Lekki-axis, Ikeja, Apapa, Isale Eko and Amuwo Odofin. Obviously, these neighbourhoods share similar characteristics in that they are at the centre of Lagos State business activities, the home to many industrial establishments, headquarters of several business formations, the destination of early morning traffic rush from various parts of the State. The relationship among accessibility, property values and land use patterns has been the pre-occupation of earliest theorists with indication that travel costs were traded off against rents, population densities and distances from the Central Business District. This study assesses the veracity of this proposition in Magodo neighbourhood property market and the impact of other factors such as locational, structural and neighbourhood characteristics. A total of 232 questionnaires were distributed to two study groups, the estate surveyors and valuers and Magodo residents. Response were presented and analysed with tables, percentages and relative importance index. It was found amongst other things that travel distance and cost does not affect residential property value as others factors do. It was recommended that property investors should consider those attributes that significantly affect property values while government should endeavour to harness development potentials in the study are

Effect of sulfate concentration and associated cation type on chloride-induced reinforcement corrosion

Effect of sulfate concentration and associated cation type on chloride-induced reinforcement corrosio

Effect of cement alkalinity on pore solution chemistry and chloride-induced reinforcement corrosion

This paper reports the results of a study conducted to evaluate the influence of cement alkalinity on the pore solution chemistry and chloride-induced reinforcement corrosion in ordinary and sulfate resisting Portland cement concretes. To evaluate the influence of cement alkalinity on the pore solution chemistry, cement paste specimens were prepared and admixed with fixed quantity of sodium chloride and various dosages of alkalinity (in the range of 0.4 to 1.4% Na2O equivalent). The pore solution was extracted and analyzed to determine the OH-, Cl- and SO4 -- concentrations. The influence of cement alkalinity on chloride-induced reinforcement corrosion was also assessed by measuring corrosion potentials and corrosion current density at regular intervals. The results indicated that the OH-, Cland SO4 -- concentrations of the pore solution increased with increasing alkali content of the cement. Further, the Cl-/OH- ratio decreased with increasing alkali content up to 0.8% Na2O and then increased with a further increase in the alkalinity. Furthermore, an improvement in the corrosion-resistance of the SRPC and OPC concrete specimens was noted with increasing alkali content of cement. However, the highest improvement was noted when the alkalinity was 0.8% Na2O equivalent

Suspension feeding in the enigmatic Ediacaran organism Tribrachidium demonstrates complexity of Neoproterozoic ecosystems

The first diverse and morphologically complex macroscopic communities appear in the late Ediacaran period, 575 to 541 million years ago (Ma). The enigmatic organisms that make up these communities are thought to have formed simple ecosystems characterized by a narrow range of feeding modes, with most restricted to the passive absorption of organic particles (osmotrophy). We test between competing feeding models for the iconic Ediacaran organism Tribrachidium heraldicum using computational fluid dynamics. We show that the external morphology of Tribrachidium passively directs water flow toward the apex of the organism and generates low-velocity eddies above apical “pits.” These patterns of fluid flow are inconsistent with osmotrophy and instead support the interpretation of Tribrachidium as a passive suspension feeder. This finding provides the oldest empirical evidence for suspension feeding at 555 to 550 Ma, ~10 million years before the Cambrian explosion, and demonstrates that Ediacaran organisms formed more complex ecosystems in the latest Precambrian, involving a larger number of ecological guilds, than currently appreciated.</p

Long-term effect of sulfate ions and associated cation type on chloride-induced reinforcement corrosion in Portland cement concretes

This paper reports the influence of sulfate concentration on chloride-induced reinforcement corrosion in Portland cement concretes (with C3A varying from 3.6% to 9.65%). The concrete specimens were exposed to mixed chloride and sulfate solutions for a period of 1200 days. The chloride was fixed at 5% NaCl for all solutions, while the sulfate concentration was varied to represent that noted in the sulfate-bearing soil and ground water. The study included an assessment of the effect of cation type associated with sulfate ions, namely Na+ and Mg2+, on chloride-induced reinforcement corrosion, an important factor that has received little attention. Reinforcement corrosion was evaluated by measuring corrosion potentials and corrosion current density at regular intervals. The results indicate that the presence of sulfate ions in the chloride solution did not influence the time to initiation of chloride-induced reinforcement corrosion, but the rate of corrosion increased with increasing sulfate concentration. Further, the rate of chloride-induced reinforcement corrosion in the concrete specimens exposed to sodium chloride plus magnesium sulfate solutions was more than that in the concrete specimens exposed to sodium chloride plus sodium sulfate solutions

Chloride-induced reinforcement corrosion in blended cement concretes expores to chloride-sulfate environments

This paper reports the results of a study conducted to investigate the influence of sulphate concentration and associated cation type on chloride-induced reinforcement corrosion in blended cement concretes. Reinforced concrete specimens were exposed to chloride plus sulphate solutions for a period of 1200 days. The exposure solutions contained a fixed concentration of 5% sodium chloride and the sulphate concentration was varied from 0 to 4% SO4 2 . The effect of cation type associated with sulphate ions, namely Naþ and Mgþþ, on chloride-induced reinforcement corrosion was also evaluated. Reinforcement corrosion was assessed by measuring corrosion potentials and corrosion current density at regular intervals. The results indicated that the presence of sulphate ions in the chloride solution increased the corrosion current density, but no significant effect on the time to initiation of reinforcement corrosion was noted. Further, the corrosion current density increased with increasing sulphate concentration and the period of exposure. The corrosion current density on steel in the blended cement concrete specimens was much less than that in the plain cement concrete specimens, indicating that the corrosion resistance of blended cements was much better than that of plain cements. The cation type associated with sulphate ions did not significantly influence either the initiation or rate of reinforcement corrosion

Гендерная парадигма в образовании: от теории к практике

Computational fluid dynamics (CFD) simulations of water flow were performed in COMSOL. A model of Parvancorina sagitta from Russia with relief increased by 15% was oriented at 0° to the current and was fixed to the lower surface of a half-cylinder. Three-dimensional, incompressible flow of water was simulated with a normal inflow velocity inlet at the upstream end of the half-cylinder and a zero-pressure outlet at the downstream end. Slip boundary conditions were assigned to the top and sides of the half-cylinder, and no-slip boundary conditions were assigned to the Parvancorina model and the lower surface of the half-cylinder. The domain was meshed using free tetrahedral elements and the shear stress transport turbulence model was used to solve the Reynolds-averaged Navier–Stokes equations. A stationary solver was used to compute the steady-state flow patterns. Simulations were performed with an inlet velocity of 0.1, 0.2, and 0.5 m/s

A low inflammatory, Langerhans cell-targeted microprojection patch to deliver ovalbumin to the epidermis of mouse skin

In a low inflammatory skin environment, Langerhans cells (LCs) - but not dermal dendritic cells (dDCs) - contribute to the pivotal process of tolerance induction. Thus LCs are a target for specific-tolerance therapies. LCs reside just below the stratum corneum, within the skin's viable epidermis. One way to precisely deliver immunotherapies to LCs while remaining minimally invasive is with a skin delivery device such as a microprojection arrays (MPA). Today's MPAs currently achieve rapid delivery (e.g. within minutes of application), but are focussed primarily at delivery of therapeutics to the dermis, deeper within the skin. Indeed, no MPA currently delivers specifically to the epidermal LCs of mouse skin. Without any convenient, pre-clinical device available, advancement of LC-targeted therapies has been limited. In this study, we designed and tested a novel MPA that delivers ovalbumin to the mouse epidermis (eMPA) while maintaining a low, local inflammatory response (as defined by low erythema after 24 h). In comparison to available dermal-targeted MPAs (dMPA), only eMPAs with larger projection tip surface areas achieved shallow epidermal penetration at a low application energy. The eMPA characterised here induced significantly less erythema after 24 h (p = 0.0004), less epidermal swelling after 72 h (p