Improving the structural reliability of steel frames using posttensioned connections

In this paper, various moment-resisting steel frames (MRSFs) are subjected to 30 narrow-band motions scaled at different ground motion intensity levels in terms of spectral acceleration at first mode of vibration in order to perform incremental dynamic analysis for peak and residual interstory drift demands. The results are used to compute the structural reliability of the steel frames by means of hazard curves for peak and residual drifts. It is observed that the structures exceed the threshold residual drift of 0.5%, which is perceptible to human occupants, and it could lead to human discomfort according to recent investigations. For this reason, posttensioned connections (PTCs) are incorporated into the steel frames in order to improve the structural reliability. The results suggest that the annual rate of exceedance of peak and residual interstory drift demands are reduced with the use of PTC. Thus, the structural reliability of the steel frames with PTC is superior to that of the MRSFs. In particular, the residual drift demands tend to be smaller when PTCs are incorporated in the steel structures.Peer ReviewedPostprint (published version

Attractions between charged colloids at water interfaces

The effective potential between charged colloids trapped at water interfaces is analyzed. It consists of a repulsive electrostatic and an attractive capillary part which asymptotically both show dipole--like behavior. For sufficiently large colloid charges, the capillary attraction dominates at large separations. The total effective potential exhibits a minimum at intermediate separations if the Debye screening length of water and the colloid radius are of comparable size.Comment: 8 pages, 1 figure, revised version (one paragraph added) accepted in JPC

Theory of capillary-induced interactions beyond the superposition approximation

Within a general theoretical framework we study the effective, deformation-induced interaction between two colloidal particles trapped at a fluid interface in the regime of small deformations. In many studies, this interaction has been computed with the ansatz that the actual interface configuration for the pair is given by the linear superposition of the interface deformations around the single particles. Here we assess the validity of this approach and compute the leading term of the effective interaction for large interparticle separation beyond this so-called superposition approximation. As an application, we consider the experimentally relevant case of interface deformations owing to the electrostatic field emanating from charged colloidal particles. In mechanical isolation, i.e., if the net force acting on the total system consisting of the particles plus the interface vanishes, the superposition approximation is actually invalid. The effective capillary interaction is governed by contributions beyond this approximation and turns out to be attractive. For sufficiently small surface charges on the colloids, such that linearization is strictly valid, and at asymptotically large separations, the effective interaction does not overcome the direct electrostatic repulsion between the colloidal particles.Comment: Minor typos correcte

Detection and quantitation of additions of soybean proteins in cured-meat products by perfusion reversed-phase high-performance liquid chromatography

Perfusion liquid chromatography has been applied in this work to the determination of soybean proteins in commercially available cured meat products, enabling the detection of additions of soybean proteins in cured meat products to which the addition of these vegetable proteins is forbidden and the quantitation of soybean proteins in cured meat products to which the addition of these proteins is allowed up to a certain limit. The analytical methodology is based on a sample treatment (fat extraction and soybean protein solubilization) prior to chromatographic analysis. Fat extraction with acetone and soybean protein solubilization with a buffer solution at basic pH (pH 10 or 9) were necessary to obtain selective and sensitive conditions. Use of water-acetonitrile-trifluoroacetic acid or water-tetrahydrofuran-trifluoroacetic acid linear binary gradients at a flow rate of 3 mL/min, a temperature of 50 degrees C, and UV detection at 280 nm enabled chromatographic analysis of soybean proteins in cured meat products in less than 3 min.The authors thank the Comunidad Autónoma de Madrid\ud (Spain) for project 07G/0025/2003. Dr. C. García-Ruiz\ud also thanks the Ministerio de Ciencia y Tecnolog a for her\ud contract from the Ramón y Cajal program (RYC-2003-001). F. Castro-Rubio thanks the Ministerio de Educación\ud y Ciencia (Spain) for her predoctoral grant

Separation and online preconcentration by multistep stacking with large-volume injection of anabolic steroids by capillary electrokinetic chromatography using charged cyclodextrins and UV-absorption detection

The separation of three common anabolic steroids (methyltestosterone, methandrostenolone and testosterone) was performed for the first time by capillary EKC. Different charged CD derivatives and bile salts were tested as dispersed phases in order to achieve the separation. A mixture of 10 mmol/L succinylated-b-CD with 1 mmol/L bCD in a 50 mmol/L borate buffer (pH 9) enabled the separation of the three anabolic steroids in less than 9 min. Concentration LODs, obtained for these compounds with low absorption of UV light, were ~5610–5 mol/L. The use of online reverse migrating sample stacking with large-volume injection (the effective length of the capillary) enabled to improve the detection sensitivity. Sensitivity enhancement factors (SEFs) ranging from 95 (for testosterone) to 149 (for methyltestosterone) were achieved by single stacking preconcentration. Then, the possibilities of multistep stacking to improve the sensitivity for these analytes were investigated. SEFs obtained by double stacking preconcentration ranged from 138 to 185, enabling concentration LODs of 2.79610–7 mol/L (for methyltestosterone), 3.47610–7 mol/L (for testosterone) and 3.56610–7 mol/L (for methandrostenolone). Although online triple stacking preconcentration was achieved, its repeatability was very poor and SEFs for the studied analytes were not calculated

Effective interactions of colloids on nematic films

The elastic and capillary interactions between a pair of colloidal particles trapped on top of a nematic film are studied theoretically for large separations $d$. The elastic interaction is repulsive and of quadrupolar type, varying as $d^{-5}$. For macroscopically thick films, the capillary interaction is likewise repulsive and proportional to $d^{-5}$ as a consequence of mechanical isolation of the system comprised of the colloids and the interface. A finite film thickness introduces a nonvanishing force on the system (exerted by the substrate supporting the film) leading to logarithmically varying capillary attractions. However, their strength turns out to be too small to be of importance for the recently observed pattern formation of colloidal droplets on nematic films.Comment: 13 pages, accepted by EPJ