55,640 research outputs found
Symmetry-based HIV protease inhibitors containing (S,S) or (R,R) tartaric acid core structure
No full textwo series of symmetry-based HIV protease inhibitors containing (S,S) or (R,R) tartaric acid core structure were prepared and tested for inhibitory property against the enzyme. All compounds showed weak antiprotease activity
A probabilistic approach for dynamic positioning capability and operability predictions
No full textDetermining Dynamic Positioning capability for an offshore vessel is mandatory to identify the environmental forces the system can counteract, together with the operability in a specific operational area of interest. Conventional predictions evaluate the capability as a maximum sustainable wind speed at a predefined encounter angle for a given wind–wave correlation, not reflecting the effective wind and waves occurrence at the site. In this respect, a step forward is provided by the scatter diagram approach, allowing the evaluation of operability in a specific sea area, using a simplified method to predict wind speed from wave parameters. Here, using known wind–waves joint distributions for the long-term environmental conditions further improves the scatter diagram approach, assessing the operability of a Dynamic Positioning system through a Quasi-Monte Carlo sampling of the joint distribution. Analysing the results of the Quasi-Monte Carlo process, it is possible to obtain a site-specific capability plot, allowing the identification of critical wind speeds in a way that is familiar to operators in the offshore industry. The application of this novel method in the case of quasi-static calculations both to a reference supply vessel and a pipe-lay vessel shows the flexibility of the proposed approach for site-specific Dynamic Positioning capability predictions
The design of R/C framed buildings with non-linear isolation systems
No full textIn this paper a parametric study on R/C base isolated building structures with different types of non linear devices is presented. Devices having high dissipation capacity, typically based on the hysteresis of steel or of lead, or/and re-centring capacity, based on shape memory alloys, are considered. The seismic response is evaluated by means of non-linear dynamic analyses using artificially generated accelerograms (EC8, soil type B). The performances of the structural system are examined and compared on the basis of some response parameters (maximum and residual displacements and ductility demands in the isolation system, maximum stresses and drifts in the R/C structure). The results show that SMA-based isolation systems have better overall performances than Steel Hysteresis-based isolation systems, as well as reduced structural costs
Traversable wormholes with vanishing sound speed in f(R) gravity
No full textWe derive exact traversable wormhole solutions in the framework of f(R) gravity with no exotic matter and with stable conditions over the geometric fluid entering the throat. For this purpose, we propose power-law f(R) models and two possible approaches for the shape function b(r)/r. The first approach makes use of an inverse power-law function, namely
b
(
r
)
/
r
∼
r
−
1
−
β
b(r)/r∼r
−1−β
. The second one adopts Padé approximants, used to characterize the shape function in a model-independent way. We single out the P(0, 1) approximant where the fluid perturbations are negligible within the throat, if the sound speed vanishes at
r
=
r
0
r=r
0
. The former guarantees an overall stability of the geometrical fluid into the wormhole. Finally, we get suitable bounds over the parameters of the model for the above discussed cases. In conclusion, we find that small deviations from general relativity give stable solutions
Study of Atrp Process for the Grafting of Vinyl Monomers on PVC and PVDF
No full textSTUDY OF ATRP PROCESS FOR THE GRAFTING OF VINYL MONOMERS ON PVC AND PVDF
Sonia Lanzalaco, Onofrio Scialdone, Alessandro Galia, Rosalia Mauro, Flavia Lazzano Dipartimento di Ingegneria Chimica, Gestionale, Informatica, Meccanica,
Viale delle Scienze, Palermo
e-mail: [email protected]
ATRP (atom transfer radical polymerization) has been recently used to prepare graft copolymers with regularly-spaced polymer chains from polymeric macroinitiators that have pendant chemical groups containing radically transferable halogen atoms [1]. The halogen atom serves as initiation site for the polymerization of side chains. Furthermore, Matyjaszewsky and Gennaro showed that an externally applied electrochemical potential can reversibly activate the copper catalyst for this process and demonstrated the dynamic modulation of polymerization rates through electrochemical means, fostering precise temporal control over initiation, cessation, and rejuvenation of the living process [2].
Our group has recently studied the atom transfer radical graft copolymerization by using halogen macroinitiators (polyvinylidenefluoride (PVDF) and polyvinylchloride (PVC) ) in organic media and used electrochemical approach to investigate the polymer effectiveness as ATRP macroinitiator and to detect the relative population of the redox couple Cu(I)/Cu(II) during the copolymerization . In particular in order to achieve preliminary information on the grafting of polyhydroxyethylmethacrylate on PVC and PVDF catalyzed by copper complexes, a study on the behavior of the various components of the system, such as halogenated polymer (PVC or PVDF), copper catalyst (CuCl or CuBr), ligand (TPMA or Me6TREN) , was carried out by cyclic voltammetric, chronoamperometric and spectrophotometric experiments. Some grafting experiments were also carried out in the more promising operative conditions.
[1] J. F. Hester, P. Banerjee, Y. Y. Won, A. Aktakul, M. H. Acar, A. M. Mayes, Macromolecules, 2002, 35, 7652.
[2] A. J. D. Magenau, N. Strandwitz, A. Gennaro, K. Matyjaszewski, Science, 332 (2011) 81-84
Optimal thruster location on offshore DP vessels
No full textDuring the design process of an offshore vessel, the DP system is not representing one of the primary constraints for the general arrangement of the vessel. Usually the location of the thruster devices is driven by the internal spaces available, i.e. the thrusters position is not optimised to reach the maximum capability. This is also true for a conversion of an existing vessel. Nowadays almost all offshore vessels require the installation of a DP system on board, means that it could be worthy to study more in detail the arrangement of the thrusters in such a way to maximise the capability of the vessel to keep position with a determined amount of power installed on board. In the present work a procedure aimed to find an optimal thruster location on the hull during early design stage will be presented. Using a quasi-static approach for DP capability evaluation, an optimisation procedure based on genetic algorithm has been developed, considering the constraints given by the vessel geometry. The discussion is supported by a test case on a reference vessel, were the original layout is compared with two possible optimised configurations
A Monte Carlo approach for the fully probabilistic evaluation of operability in ship dynamic positioning scenarios
No full textThe Dynamic Positioning system allows a vessel to keep a precise position and heading during stationing operations in a rough sea by using onboard actuators only. During the design phase, it is mandatory to identify the capability of the system actuators to counteract the environmental forces. Conventional predictions are limited to the estimation of a maximum sustainable wind speed on predefined encounter angles by estimating the corresponding wave parameters with questionable standard deterministic correlations. The proposed approach aims at determining the dynamic positioning performances by using site-specific long-term environmental conditions which are modelled with joint distributions of wind and wave parameters. To this end, the operability of the dynamic positioning system is evaluated as a non-deterministic multidimensional Monte Carlo integration process, based on the sampling of environmental joint distributions. For each environmental condition, a quasi-static dynamic positioning analysis is performed solving the equilibrium between external forces and the vessel's actuators through a non-linear thrust allocation algorithm. The proposed methodology is applied to a reference offshore ship in five different operative geographic areas, highlighting the suitability of the calculation methodology for site-specific operability predictions
Letter from Carl Hayden to F. R. Goodman, County Engineer
No full textLetter from Carl Hayden to F. R. Goodman regarding the construction of new roads
6) Farella M., Michelotti A., Steenks M.H., Cimino R., Romeo R., Bosman F. The diagnostic value of pressure algometry in myofascial pain of the jaw muscl
No full text6) Farella M., Michelotti A., Steenks M.H., Cimino R., Romeo R., Bosman F. The diagnostic value of pressure algometry in myofascial pain of the jaw muscl
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