Constrained motion planning of nonholonomic systems

This paper addresses the constrained motion planning problem for nonholonomic systems represented by driftless control systems with output. The problem consists in defining a control function driving the system output to a desirable point at a given time instant, whereas state and control variables remain over the control horizon within prescribed bounds. The state and control constraints are handled by extending the control system with a pair of state equations driven by the violation of constraints, and adding regularizing perturbations. For the regularized system a Jacobian motion planning algorithm is designed, called imbalanced. Solutions of example constrained motion planning problems for the rolling ball illustrate the theoretical concepts.     

Nature of the Thermal pretransition of synthetic phospholipids: dimyristolyl- and dipalmitoyllecithin

The hydrated synthetic lecithins, dimyristoyl and dipalmitoyllecithins, undergo two thermal transitions, a broad low enthalpy "pretransition" prior to the sharp first-order "chain-melting" transition. Both phospholipids exhibit the same temperature-dependent structural changes associated with the thermal pretransition. At low temperatures, below the pretransition, a one-dimensional lamellar lattice is observed. The hydrocarbon chains are fully extended and tilted with respect to the plane of the lipid bilayer. The hydrocarbon chain packing displays a temperature dependence and the angle of tilt of the hydrocarbon chains decreases with increasing temperature, reaching a minimum value of 30 degrees at the pretransition temperature of both lecithins. The pretransition is associated with a structural transformation from a one-dimensional lamellar to a two-dimensional monoclinic lattice consisting of lipid lamellae distorted by a periodic ripple. The hydrocarbon chains remain tilted in the temperature range intermediate between the pretransition and chain-melting transition. The cell parameters of this two-dimensional lattice exhibit a compositional dependence. The a parameter (proportional to the lamellar repeat distance) increases with increasing water content, while the b parameter (a measure of the ripple periodicity) decreases with increasing water content. At the chain-melting transition, the hydrocarbon chains of the phospholipid melt and assume a liquid-like conformation and the lattice reverts to one-dimensional lamellar. These structural changes observed for dimyristoyl- and dipalmitoyllecithins may be a common feature of all synthetic lecithins exhibiting a thermal pretransition. The appearance of the pretransition and accompanying two-dimensional may arise from specific interactions between the choline moiety of the polar head group and the structured water matrix surrounding it.     

Silica gel supported zirconocene dichloride/methylalumoxane catalysts for ethylene polymerization: Effects of heterogenation on activity,polymer microstructure and product morphology

The system zirconocene dichloride/methylalumoxane was supported on silica in order to provide ethylene polymerization catalysts for suspension or gas phase processes. Highest activity was found for a sandwich-like, three layer anchoring of the zirconium centers on the support surface. The new catalyst systems show a decrease of activity compared to polymerization experiments in homogeneous phase. However, the molecular weights are increased and the weight distributions remain narrow by immobilization of the active catalyst sites. Those supported metallocene catalysts could find application for the synthesis of polyethylene materials with controlled rheology.     

Relative bioavailability of different butamirate citrate preparations after single dose oral administration to 18 healthy volunteers

The action of purified cathepsin D on hemoglobin was examined using micellar electrokinetic chromatographic separation of peptide products. Purified cathepsin D was incubated with hemoglobin in 40 mM Na-formate pH 3.1 at 37 degrees C for varying lengths of time. The reaction was stopped by the addition of the inhibitor pepstatin, and the peptide products were isolated from the reaction mixture by ultrafiltration with a 10,000 molecular weight cut-off (MWCO) microfuge type filter. Filtered samples were then separated in 100 mM Tris-Cl pH 8.5 containing sodium dodecyl sulfate (SDS) or Na-deoxycholate at micellar concentrations using a 50-microns (i.d.) fused-silica capillary. Detection was performed at 214 nm. It was found that Na-deoxycholate containing separations were superior in resolution and required less time. This technique was used to determine initial velocity (expressed as peak area per unit time) for nine peptides. Several peptides resulted after very short incubation times (< 10 min). This suggests that this approach may be useful for the determination of cathepsin D activity.     

The use of microwave irradiation for the easy synthesis of graphene-supported transition metal nanoparticles in ionic liquids

Stable ruthenium or rhodium metal nanoparticles were supported on chemically derived graphene (CDG) surfaces with small and uniform particle sizes (Ru 2.2 ± 0.4 nm and Rh 2.8 ± 0.5 nm) by decomposition of their metal carbonyl precursors by rapid microwave irradiation in a suspension of CDG in the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate. The graphene-supported hybrid nanoparticles were shown to be active and could be re-used at least 10 times as catalysts for the hydrogenation of cyclohexene and benzene under organic-solvent-free conditions with constant activities up to 1570 mol cyclohexane × (mol metal)⁻¹ × h⁻¹ at 4 bar and 75 °C.     

A new approach to the learning effect: Beyond the learning curve restrictions

In this paper, we bring into the scheduling field a new model of the learning effect, where in two ways the existing approach is generalized. First we relax one of the rigorous constraints, and thus in our model each job can provide different experience to the processor. Second we formulate the job processing time as a non-increasing k-stepwise function, that, in general, is not restricted to a certain learning curve, thereby it can accurately fit every possible shape of a learning function. Furthermore, we prove that the problem of makespan minimization with the considered model is polynomially solvable if every job provides the same experience to the processor, and it becomes NP-hard if the experiences are diversified. The most essential result is a pseudopolynomial time algorithm that solves optimally the makespan minimization problem with any function of an experience-based learning model reduced into the form of the k-stepwise function.     

Effects of charge density on the recognition properties of molecularly imprinted polyampholyte hydrogels

Molecularly imprinted polymers are synthetic materials designed to selectively bind to a templated molecule. In this study, the effect of including both positive and negative charges simultaneously into the hydrogel network on the selective recognition properties of the MIP is examined. Using 3-methacrylamidopropyl trimethylammonium chloride (MAPTAC) as a cationic monomer and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) as an anionic monomer, various ratios of positive to negative charges were tested. Selective recognition properties were dependant on the type of charged monomer that made up a majority of the hydrogel's mass. Additionally, polyampholyte MIPs exhibited less swelling than previously studied polyelectrolyte hydrogels.     

Resource optimal control in some single-machine scheduling problems

We consider a problem to schedule a set of jobs on a single machine under the constraint that the maximum job completion time does not exceed a given limit. Before a job is released for processing, it must undergo some preprocessing treatment which consumes resources. It is assumed that the release time of a job is a positive strictly decreasing continuous function of the amount of resources consumed. The objective is to minimize the total resource consumption. We show that ordering jobs in nonincreasing processing times yields an optimal solution. We then consider a bicriterion approach to the problem in which the maximum job completion time and the resource consumption are simultaneously minimized and present a polynomial time solution algorithm. Finally, we consider a related problem in which the job release times are given but the processing times are functions of the amount of resource consumed. We show that ordering jobs in nondecreasing release times gives an optimal solution and that the problem to minimize both the maximum completion time and resource consumption is polynomially solvable