Adsorption of Alkanethiols on Gold Surfaces: PM-IRRAS Study of the Influence of Terminal Functionality on Alkyl Chain Orientation

The present paper focuses on a simplified method to study the orientation and the anisotropy of two different alkanethiols self-assembled monolayers on gold surfaces. The alkanethiols of interest vary only by their terminal functionalities (COOH and COOCH₃), thus allowing one to highlight the influence of these ending chemical groups on the final orientation of the adsorbed molecules. 11-Mercaptoundecanoic acid [HS-(CH₂)₁₀-COOH] and the methyl-11-mercaptoundecanoate [HS-(CH₂)₁₀-COOCH₃] were grafted under adequate conditions to obtain a high grafting density on gold substrates. These latter, before and after the alkanethiol adsorption, were analyzed mainly by the polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS) technique to access orientation angles, and by atomic force microscopy (AFM) to check the homogeneity of the grafted layer.

By applying an original PM-IRRAS simplified method, the results showed an orientation closer to the normal of the surface plane in the case of the acid thiol compared with the ester one, which is probably because of the lateral hydrogen bonds established between the adjacent COOH functions. This method offers a direct and simple way to quantify the orientation angles in the alkanethiol nanofilms.     

A comparison of three turbulence models for the prediction of parallel lobed jets in perforated panel optimization

The general context of the present study is the design of high induction HVAC air diffusers by means of passive jet control. When the diffuser is a perforated panel with lobed orifices (Meslem et al. 2010), the optimization of jet induction consists in improving the orifice’s geometry, the spacing between orifices and their arrangement on the panel. In this study, the flow field of a turbulent twin cross-shaped jet is investigated numerically using the standard k-ε model, the Shear Stress Transport (SST) k-ω model and the Reynolds Stress Model (RSM). The results are compared with PIV measurements. The objective is to assess their capability and limitations to predict the significant features of twin jet flow when the flow is numerically resolved through a lobed diffuser. It is shown that the k-ε and RSM models are more appropriate for predicting potential jet core length, the change in jet centreline streamwise velocity, and flow expansion in the symmetry plane of the twin jet flow. However, these models overestimate the overall flow expansion and the jet volumetric flow rate. The SST k-ω model seems more appropriate for the prediction of such dynamic integral quantities. A high level of turbulent kinetic energy predicted by the k-ε and RSM models in the near field of jets is probably the reason for this overestimation of jet induction. The SST k-ω model would appear to be the most appropriate tool for optimizing orifice design, orifice to orifice spacing and relative orifice orientation on a perforated panel diffuser.     

Recovered memories in context: Thoughts and elaborations on Bowers and Farvolden (1996).

The recovered memory debate exposes several traditional and recent contradictions within psychology. Building on K. Bowers and P. Farvolden ( see record 83:27619), the nature of recovered memories has profoundly different meanings for therapeutic versus legal settings. Whereas memory can be distorted during the process of retrieval, certain techniques—such as nondirective writing—may be helpful in reducing suggestive influences in recall. Ironically, methods that have been found to produce the most accurate recollections of the past appear only subtly different from those that yield the greatest distortions. The recovered memory debate must ultimately be viewed within a cultural context, both in terms of the phenomenon and its treatment. The authors discuss parallels to other explanatory and therapeutic fads related to states of nonspecific distress. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Chemical composition,antimicrobial potential against cariogenic bacteria and cytotoxic activity of Tunisian Nigella sativa essential oil and thymoquinone

We investigate in this work the chemical composition by GC–EIMS, the antibacterial and the cytotoxic activities of Tunisian Nigella sativa essential oil and its bioactive compound, thymoquinone, were tested against various clinical cariogenic bacteria (n = 30). Eighty-four compounds were identified in the essential oil. The major one was p-cymene (49.48%) whereas thymoquinone represented only 0.79%. The essential oil (2.43 mg/disc) containing only 3.35 μg of thymoquinone showed pronounced dose dependant antibacterial activity against Streptococcus mitis, Streptococcus mutans, Streptococcus constellatus and Gemella haemolysans (15.5 ± 0.707 mm). However, pure thymoquinone compound (150 μg/disk) was active against all the studied strains especially S. mutans and S. mitis (24.5 ± 0.71 and 22 ± 1.41 mm inhibition zones, respectively).     

A matheuristic approach for optimizing mineral value chains under uncertainty

Optimization and Engineering - Mineral value chains, also known as mining complexes, involve mining, processing, stockpiling, waste management and transportation activities. Their optimization is...     

Advanced Measures to Characterize Mechanical Properties of Refractories

The thermomechanical modelling method is becoming an important tool nowadays for the refractory researchers,suppliers and end-users. On one hand,applications focus on the post-mortem thermomechanical analysis to interpret the occurred failure phenomena of refractories in service. On the other hand,a priori investigation is very helpful for the design of refractory lining concepts before putting them into effect; as a result it will minimize the probability of refractory lining premature failure and save costs for the refractory suppliers as well as for the end-users. For both investigation routines,suitable material constitutive models and testing approaches are of relevance. Existing material constitutive models often used for refractories are the fictitious crack model acting for tensile failure,the Mohr-Coulomb or Drucker-Prager model describing shear failure,and the Norton-Bailey model representing creep. To characterize the tensile and shear failure of refractories at room temperature and elevated temperatures,a wedge splitting test and a modified shear test can be applied,respectively. The creep behavior and corresponding creep parameters of refractories can be determined with an appropriate creep testing device at elevated loads. The proper application of material constitutive models and testing approaches allows for improving the thermo-mechanical modelling and the optimization of the lining design.