Different methods of fluoride delivery in prevention of white spot lesions in orthodontics

Orthodontic patients on fixed appliances are at an increased risk of developing white spot lesions which can progress to frank cavitations. Fluoride application in different forms has been shown to be effective in the reduction of formation of white spot lesions. The aim of this short communication is to discuss different methods that have been used in prevention of white spot lesions in orthodontic patients. Daily mouth rinse using 0.05% sodium fluoride is the most efficacious method in prevention of white spot lesions. It is thereby recommended for use in conjunction with proper maintenance of oral hygiene.Keywords: Demineralisation; Fluoride; Glass Ionomer; Compomer; Orthodontic

A new model of the human atrial myocyte with variable T-tubule organization for the study of atrial fibrillation

Atrial fibrillation is the most common arrhythmia, yet treatment strategies are sub-optimal due to incomplete understanding of the underlying mechanisms. Spatiotemporal sub-cellular calcium cycling may play a critical role in the development of alternans and spontaneous activity, which may underlie arrhythmia in the human atria. In this study, we construct a novel electrophysiological model of the human atrial myocyte which incorporates new data on atrial intracellular structure and explicitly accounts for variations in T-tubule organization. The model reproduces spatio-temporal calcium dynamics associated with normal cardiac excitation. In preliminary simulations, the model demonstrates that a loss of T-tubules can promote both alternans and spontaneous calcium waves. The model produced in this study provides novel insight into arrhythmia mechanisms in the human atria and provides a platform for future investigation of proarrhythmic calcium dynamics

Application of a Catalytic Asymmetric Povarov Reaction using Chiral Ureas to the Synthesis of a Tetrahydroquinoline Library

A 2328-membered library of 2,3,4-trisubstituted tetrahydroquinolines was produced using a combination of solution- and solid-phase synthesis techniques. A tetrahydroquinoline (THQ) scaffold was prepared via an asymmetric Povarov reaction using cooperative catalysis to generate three contiguous stereogenic centers. A matrix of 4 stereoisomers of the THQ scaffold was prepared to enable the development of stereo/structure-activity relationships (SSAR) upon biological testing. A sparse matrix design strategy was employed to select library members to be synthesized with the goal of generating a diverse collection of tetrahydroquinolines with physicochemical properties suitable for downstream discovery.Chemistry and Chemical Biolog

Two-stage Lagrangian modeling of ignition processes in ignition quality tester and constant volume combustion chambers

The ignition characteristics of isooctane and n-heptane in an ignition quality tester (IQT) were simulated using a two-stage Lagrangian (TSL) model, which is a zero-dimensional (0-D) reactor network method. The TSL model was also used to simulate the ignition delay of n-dodecane and n-heptane in a constant volume combustion chamber (CVCC), which is archived in the engine combustion network (ECN) library (http://www.ca.sandia.gov/ecn). A detailed chemical kinetic model for gasoline surrogates from the Lawrence Livermore National Laboratory (LLNL) was utilized for the simulation of n-heptane and isooctane. Additional simulations were performed using an optimized gasoline surrogate mechanism from RWTH Aachen University. Validations of the simulated data were also performed with experimental results from an IQT at KAUST. For simulation of n-dodecane in the CVCC, two n-dodecane kinetic models from the literature were utilized. The primary aim of this study is to test the ability of TSL to replicate ignition timings in the IQT and the CVCC. The agreement between the model and the experiment is acceptable except for isooctane in the IQT and n-heptane and n-dodecane in the CVCC. The ability of the simulations to replicate observable trends in ignition delay times with regard to changes in ambient temperature and pressure allows the model to provide insights into the reactions contributing towards ignition. Thus, the TSL model was further employed to investigate the physical and chemical processes responsible for controlling the overall ignition under various conditions. The effects of exothermicity, ambient pressure, and ambient oxygen concentration on first stage ignition were also studied. Increasing ambient pressure and oxygen concentration was found to shorten the overall ignition delay time, but does not affect the timing of the first stage ignition. Additionally, the temperature at the end of the first stage ignition was found to increase at higher ambient pressure and oxygen concentration. Sensitivity analysis was performed using the TSL model to elucidate the reactions that control the overall ignition process. The present TSL modeling approach demonstrates the suitability of using detailed chemical kinetic models to provide insights into spray combustion processes

Variabilidad de rindes de trigo y fertilización nitrogenada

p.115-122En la primera parte del trabajo se presenta un modelo teórico de respuesta del cultivo de trigo a una serie de factores de producción. El objetivo del mismo es permitir la estimación del valor esperado de rinde, E (Y), y la varianza de rinde, V (Y), para cualquier nivel de uso de insumo. En la segunda parte se usa el modelo anterior para analizar el proceso de respuesta del cultivo de trigo al uso de fertilizante nitrogenado. Se utilizan datos experimentales correspondientes a la zona triguera II. Una función polinomial es ajustada a datos de ensayos llevados a cabo en la zona II Norte y en la zona II Sur. Una prueba estadística para detectar la presencia de heterocedasticidad (el Test de Park) permite estimar la influencia del nivel de fertilización nitrogenada sobre la variabilidad de rindes. Se concluye que (1) las dosis óptimas son considerablemente (30-50 por ciento) mayores en la zona II surque en la II Norte, (2) las diferencias (entre zonas) de dosis óptima son mayores cuanto menores son las relaciones de precio fertilizante-trigo y (3) la utilización de fertilizante nitrogenado no parece aumentad el riesgo económico de producción

Platelet quiescence in patients with acute coronary syndrome undergoing coronary artery bypass graft surgery

BACKGROUND: The optimal antiplatelet strategy for patients with acute coronary syndromes who require coronary artery bypass surgery remains unclear. While a more potent antiplatelet regimen will predispose to perioperative bleeding, it is hypothesized that through “platelet quiescence,” ischemic protection conferred by such therapy may provide a net clinical benefit. METHODS AND RESULTS: We compared patients undergoing coronary artery bypass surgery who were treated with a more potent antiplatelet inhibition strategy with those with a less potent inhibition through a meta-analysis. The primary outcome was all-cause mortality after bypass surgery. The analysis identified 4 studies in which the antiplatelet regimen was randomized and 6 studies that were nonrandomized. Combining all studies, there was an overall higher mortality with weaker strategies compared with more potent strategies (odds ratio, 1.38; 95% CI, 1.03–1.85; P=0.03). CONCLUSIONS: Our findings support the concept of platelet quiescence, in reducing mortality for patients with acute coronary syndrome requiring coronary artery bypass surgery. This suggests the routine up-front use of potent antiplatelet regimens in acute coronary syndrome, irrespective of likelihood of coronary artery bypass graft

Computational singular perturbation analysis of brain lactate metabolism

Lactate in the brain is considered an important fuel and signalling molecule for neuronal activity, especially during neuronal activation. Whether lactate is shuttled from astrocytes to neurons or from neurons to astrocytes leads to the contradictory Astrocyte to Neuron Lactate Shuttle (ANLS) or Neuron to Astrocyte Lactate Shuttle (NALS) hypotheses, both of which are supported by extensive, but indirect, experimental evidence. This work explores the conditions favouring development of ANLS or NALS phenomenon on the basis of a model that can simulate both by employing the two parameter sets proposed by Simpson et al. (J Cereb. Blood Flow Metab., 27:1766, 2007) and Mangia et al. (J of Neurochemistry, 109:55, 2009). As most mathematical models governing brain metabolism processes, this model is multi-scale in character due to the wide range of time scales characterizing its dynamics. Therefore, we utilize the Computational Singular Perturbation (CSP) algorithm, which has been used extensively in multi-scale systems of reactive flows and biological systems, to identify components of the system that (i) generate the characteristic time scale and the fast/slow dynamics, (ii) participate to the expressions that approximate the surfaces of equilibria that develop in phase space and (iii) control the evolution of the process within the established surfaces of equilibria. It is shown that a decisive factor on whether the ANLS or NALS configuration will develop during neuronal activation is whether the lactate transport between astrocytes and interstitium contributes to the fast dynamics or not. When it does, lactate is mainly generated in astrocytes and the ANLS hypothesis is realised, while when it doesn’t, lactate is mainly generated in neurons and the NALS hypothesis is realised. This scenario was tested in exercise conditions

A comprehensive combustion chemistry study of n-propylcyclohexane

Alkylated cycloalkanes are vital components in gasoline, aviation, and diesel fuels; however, their combustion chemistry has been less investigated compared to other hydrocarbon classes. In this work, the combustion kinetics of n-propylcyclohexane (n-Pch) was studied across a range of experiments including pressurized flow reactor (PFR), jet stirred reactor (JSR), shock tube (ST), and rapid compression machine (RCM). These experiments cover a wide range of conditions spanning low to intermediate to high temperatures, low to high pressures at lean to rich equivalence ratios. Stable intermediate species were measured in PFR over a temperature range of 550–850 K, pressure of 8.0 bar, equivalence ratio (φ) of 0.27, and constant residence time of 120 ms. The JSR was utilized to measure the speciation during oxidation of n-Pch at φ of 0.5–2.0, at atmospheric pressure, and across temperature range of 550–800 K. Ignition delay times (IDTs) for n-Pch were measured in the RCM and ST at temperatures ranging from 650 to 1200 K, at pressures of 20 and 40 bar, at φ=0.5,1.0. In addition, a comprehensive detailed chemical kinetic model was developed and validated against the measured experimental data. The new kinetic model, coupled with the breadth of data from various experiments, provides an improved understanding of n-Pch combustion

Variazioni sul tema della prigionia: La Captive di Chantal Akerman.

Properties of the hole-doped Ln1−xAxMnO3 (Ln=rare earth, A=alkaline earth, x<0.5) are compared with those of the electron-doped compositions (x>0.5). Charge ordering is the dominant interaction in the latter class of manganates unlike ferromagnetism and metallicity in the hole-doped materials. Properties of charge-ordered (CO) compositions in the hole- and electron-doped regimes, Pr0.64Ca0.36MnO3 and Pr0.36Ca0.64MnO3, differ markedly. Thus, the CO state in the hole-doped Pr0.64Ca0.36MnO3 is destroyed by magnetic fields and by substitution of Cr3+ or Ru4+ (3%) in the Mn site, while the CO state in the electron-doped Pr0.36Ca0.64MnO3 is essentially unaffected. It is not possible to induce long-range ferromagnetism in the electron-doped manganates by increasing the Mn-O-Mn angles up to 165 and 180° as in La0.33Ca0.33Sr0.34MnO3; application of magnetic fields and Cr/Ru substitution (3%) do not result in long-range ferromagnetism and metallicity. Application of magnetic fields on the Cr/Ru-doped, electron-doped manganates also fails to induce metallicity. These unusual features of the electron-doped manganates suggest that the electronic structure of these materials is likely to be entirely different from that of the hole-doped ones, as verified by first-principles linearized muffin-tin orbital calculations