Determination of labile chlorine content in polychloroprene,chlorobutyl rubber and chlorinated ethylene-propylene copolymer by thermal dehydrochlorination combined with Me3 Al treatment

Summary The labile (allylic and/or tertiary) chlorine content of polychloroprene, chlorobutyl rubber, and chlorinated ethylene propylene copolymer has been determined by thermal dehydrochlurination combined with Me₃Al treatment. The difference between the extent of dehydrochlorination of virgin and Me₃ Al-treated polymers yielded the labile Cl content of these rubbers.     

Isothermal adsorption by biporous spherical particles in a restricted volume

A finite-difference method is used in examining the isothermal one-component adsorption by spherical particles in a restricted volume on the assumptions of nonlinear equilibrium and nonlinearity in the diffusion coefficient.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 50, No. 3, pp. 423–427, March, 1986.     

An Inverse Substrate Orientation for the Regioselective Acylation of 3′,5′‐Diaminonucleosides Catalyzed by Candida antarctica lipase B?

Candida antarctica lipase B (CAL-B) catalyzes the regioselective acylation of natural thymidine with oxime esters and also the regioselective acylation of an analogue, 3',5'-diamino-3',5'-dideoxythymidine with nonactivated esters. In both cases, acylation favors the less hindered 5'-position over the 3'-position by upto 80-fold. Computer modeling of phosphonate transition-state analogues for the acylation of thymidine suggests that CAL-B favors acylation of the 5'-position because this orientation allows the thymine ring to bind in a hydrophobic pocket and forms stronger key hydrogen bonds than acylation of the 3'-position. On the other hand, computer modeling of phosphonamidate analogues of the transition states for acylation of either the 3'- or 5'-amino groups in 3',5'-diamino-3',5'-dideoxythymidine shows similar orientations and hydrogen bonds and, thus, does not explain the high regioselectivity. However, computer modeling of inverse structures, in which the acyl chain binds in the nucleophile pocket and vice versa, does rationalize the observed regioselectivity. The inverse structures fit the 5'-, but not the 3'-intermediate thymine ring, into the hydrophobic pocket, and form a weak new hydrogen bond between the O-2 carbonyl atom of the thymine and the nucleophile amine only for the 5'-intermediate. A water molecule might transfer a proton from the ammonium group to the active-site histidine. As a test of this inverse orientation, we compared the acylation of thymidine and 3',5'-diamino-3',5'-dideoxythymidine with butyryl acyl donors and with isosteric methoxyacetyl acyl donors. Both acyl donors reacted at equal rates with thymidine, but the methoxyacetyl acyl donor reacted four times faster than the butyryl acyl donor with 3',5'-diamino-3',5'-dideoxythymidine. This faster rate is consistent with an inverse orientation for 3',5'-diamino-3',5'-dideoxythymidine, in which the ether oxygen atom of the methoxyacetyl group can form a similar hydrogen bond to the nucleophilic amine. This combination of modeling and experiments suggests that such lipase-catalyzed reactions of apparently close substrate analogues like alcohols and amines might follow different pathways.     

Unmanned aerial vehicles UAVs attitude,height, motion estimation and control using visual systems

This paper presents an implementation of an aircraft pose and motion estimator using visual systems as the principal sensor for controlling an Unmanned Aerial Vehicle (UAV) or as a redundant system for an Inertial Measure Unit (IMU) and gyros sensors. First, we explore the applications of the unified theory for central catadioptric cameras for attitude and heading estimation, explaining how the skyline is projected on the catadioptric image and how it is segmented and used to calculate the UAV’s attitude. Then we use appearance images to obtain a visual compass, and we calculate the relative rotation and heading of the aerial vehicle. Additionally, we show the use of a stereo system to calculate the aircraft height and to measure the UAV’s motion. Finally, we present a visual tracking system based on Fuzzy controllers working in both a UAV and a camera pan and tilt platform. Every part is tested using the UAV COLIBRI platform to validate the different approaches, which include comparison of the estimated data with the inertial values measured onboard the helicopter platform and the validation of the tracking schemes on real flights.     

Agent-oriented modeling and development of a system for crisis management

The management of crisis situations has been a challenging problem from different points of views, such as communication efficiency and avoiding casualties. This paper presents a novel approach that includes an interaction organization pattern for Multi-agent Systems (MASs) in crisis management, abstracted from several existing case studies in which the agents follow a sequence of interactions and the organization must optimize the use of human resources. The pattern considers an emergent organization of peers that adopt different roles according to the circumstances. The key features of the organization are its robustness, scalability (in terms of both agents and roles), flexibility to deal with a changing environment, and the efficient use of resources. In order to validate the organization, the paper presents its modeling and development with the Ingenias methodology, conforming the corresponding MAS. This development follows a model-driven approach, which allows a smooth transition from the specification to the code, and a low-cost testing of the system with different settings. Another key aspect is the application of metrics for validating and improving the MAS in terms of response time. The MAS has been tested with 600 agents representing 200 citizens, showing its performance.     

Model-based decoupling control method for dual-drive gantry stages: A case study with experimental validations

Industrial motion control of dual-drive gantry stages is usually performed by position controllers acting independently on each actuator. This approach neglects the unbalance and the mechanical coupling between actuators, leading to poor positioning performances. To overcome this drawback, a model-based decoupling control is proposed. Initially, a dynamic model of the gantry stage is proposed. Once identified and validated, such model is written in terms of a decoupling basis. Then, by model inversion, a feedback?feedforward decoupling control is presented. Experimental results show that, in comparison to the independent axis control approach, the proposed solution leads to improved motion control.     

MODEL-BASED ASSISTANT TOOL FOR THE SETTING-UP AND OPTIMIZATION OF CENTERLESS GRINDING PROCESS

Recent advances in process modeling allow for more accurate prediction of complex phenomena. A combination of different modeling approaches makes it possible to develop new products to set up, control and optimize machining operations. In the near future, a continuous improvement strategy should be adopted, as improvements to advanced models open up new opportunities for industrial applications. In particular, the efforts made by different research groups on grinding have given rise to significant developments in this area, some of which have recently been made into applied software. As an example of the necessity for process modeling and the viability of industrialized tools based on it, this article presents the work carried out on the development of an assistant tool for the setting up and optimization of the centerless grinding process, focusing on avoiding the main limitations of this process and optimizing productivity.