The Least Action and the Metric of an Organized System

In this paper, we formulate the least action principle for organized system as the minimum of the total sum of the actions of all of the elements. This allows us to see how this most basic law of physics determines the development of the system towards states with less action — organized states. Also we state that the metric tensor can describe the specific state of the constraints of the system, which is its actual organization. With this the organization is defined in two ways: 1. quantitative: the action I; 2. qualitative: the metric tensor g _mn. These two measures can describe the level of development and the specifics of the organization of a system. We consider closed and open systems. This revised version was published online in May 2006 with corrected email address     

A Multiscale 3D Model of the Vacuum Arc Remelting Process

A three-dimensional, transient, multiscale model of the VAR process is presented, allowing novel simulations of the influence of fluctuations in arc behavior on the flow and heat transfer in the molten pool and the effect this has on the microstructure and defects. The transient behavior of the arc was characterized using the external magnetic field and surface current measurements, which were then used as transient boundary conditions in the model. The interactions of the magnetic field, turbulent metal flow, and heat transfer were modeled using CFD techniques and this “macro” model was linked to a microscale solidification model. This allowed the transient fluctuations in the dendritic microstructure to be predicted, allowing the first coupled three-dimensional correlations between macroscopic operational parameters and microstructural defects to be performed. It was found that convection driven by the motion of the arc caused local remelting of the mushy zone, resulting in variations in permeability and solute density. This causes variations in the local Rayleigh number, leading to conditions under which freckle solidification defects will initiate. A three-dimensional transient tracking of particle fall-in was also simulated, enabling predictions of “white spot” defects via quantification of the trajectory and dissolution of inclusions entering the melt.     

Non-invasive imaging of abdominal vascular pathologies

With the advent of ultrasound (US), Doppler and color-flow Doppler imaging, computed tomography (CT), and magnetic resonance angiography (MRA) the ability for non-invasive studies of the abdominal vasculature has been enhanced considerably. In this paper an overview on various abdominal vascular pathologies is presented. Because of the dramatic improvements in image quality, special emphasis is given on the potential role of breathhold contrast-enhanced three-dimensional (3D) MRA which appears to be a versatile non-invasive alternative to conventional angiography.     

Hysteresis Switching Design for Stabilization of a Class of Switched Neutral Systems

Stabilization of a class of switched neutral systems with discrete time‐varying delays is investigated in this paper. The upper bound of the derivative of the discrete time‐varying delay is an arbitrary given unknown constant. Each subsystem is not assumed stable. In order to avoid sliding modes and chattering, a hysteresis switching law is designed based on state space partition, which considers the information of both discrete delays and neutral delays sufficiently. The obtained delay‐dependent stabilization criterion is given in terms of linear matrix inequality by introducing free‐weighting matrices. Finally, a simulation example is given to motivate and exemplify the proposed strategy.     

L 2-gain analysis and control synthesis of uncertain switched linear systems subject to actuator saturation

This article addresses the L ₂-gain analysis and control synthesis problem for a class of uncertain switched linear systems with saturating actuators and external disturbances. First, when the controllers are pre-given, an analysis condition on disturbance tolerance is established under which the state trajectory starting from the origin will remain inside a bounded set. By this condition, the problem of estimating disturbance tolerance capability is formulated as a constrained optimisation problem. Then, the restricted L ₂-gain property is analysed over the set of tolerable disturbances. An upper bound on the restricted L ₂-gain is estimated by solving a constrained optimisation problem. Furthermore, when controller gain matrices are design variables, these optimisation problems can be adapted for controller design. All the results are achieved by utilising the multiple Lyapunov functions method and presented in terms of an LMI optimisation-based approach. A numerical example is given to show the effectiveness of the proposed method.     

Research results on the corrosion effects of liquid heavy metals Pb, Bi and Pb–Bi on structural materials with and without corrosion inhibitors

The following article is a summary of research results of structural material corrosion in liquid heavy metals in the Czech Republic. The effect of alloying elements on the corrosion resistance of various types of steel in lead (Pb), bismuth (Bi) and lead–bismuth (Pb–Bi) was examined. Furthermore, the effect of temperature, temperature gradient, liquid–alloy composition and the flow velocity on a particular material corrosion resistance with and without the use of a corrosion inhibitor Ti and Zr was described. Types of steel affected by inhibition and their maximum operating temperatures are listed.     

Particle size and support effects on the complete benzene oxidation by Co and Co–Pt catalysts

Monometallic cobalt and bimetallic Co–Pt samples of various particle sizes have been prepared using SiO₂ and synthetic kenyaite (layered silicate) as a support. They are characterized by elemental analysis, XRD, TPR, and XPS. Cobalt is introduced by two methods—classical impregnation and ammonia method. The ammonia method of preparation leads to the formation of finely dispersed Co₃O₄ on both supports. Besides, hardly reducible cobalt silicate phases appear predominantly on the SiO₂ support. The Co₃O₄ particle size varies between 5 and 20 nm, depending on the support. The monometallic Co samples prepared by ammonia method on both supports are more active in benzene combustion than the impregnated ones due to the finer dispersion of the easily reducible Co₃O₄. Addition of Pt improves the activity and the promoting effect is more evident for the impregnated sample. This is explained with the synergy effect of cobalt oxide species and Pt. The less promoting effect of Pt on the catalytic activity of the bimetallic kenyaite-supported samples is attributed to the stronger interaction between the Co oxide phase and Pt during the preparation process.     

A Galantamine–Curcumin Hybrid Decreases the Cytotoxicity of Amyloid-Beta Peptide on SH-SY5Y Cells

Misfolded amyloid beta (Aβ) peptides aggregate and form neurotoxic oligomers. Membrane and mitochondrial damages, calcium dysregulation, oxidative stress, and fibril deposits are among the possible mechanisms of Aβ cytotoxicity. Galantamine (GAL) prevents apoptosis induced by Aβ mainly through the ability to stimulate allosterically the α7 nAChRs and to regulate the calcium cytosolic concentration. Here, we examined the cytoprotective effects of two GAL derivatives, namely compounds 4b and 8, against Aβ cytotoxicity on the human neuroblastoma cell line SH-SY5Y. The protective effects were tested at simultaneous administration, pre-incubation and post-incubation, with Aβ. GAL and curcumin (CU) were used in the study as reference compounds. It was found that 4b protects cells in a similar mode as GAL, while compound 8 and CU potentiate the toxic effects of Aβ. Allosteric stimulation of α7 nAChRs is suggested as a possible mechanism of the cytoprotectivity of 4b. These and previous findings characterize 4b as a prospective non-toxic multi-target agent against neurodegenerative disorders with inhibitory activity on acetylcholinesterase, antioxidant, and cytoprotective properties.     

Depth-profiled characterization of complex refractive index of ion implanted optically transparent polymers using multilayer calculations and reflectance data

The material in the ion-modified surface layer formed in polymethylmethacrylate (PMMA) is optically characterized by calculations based on multilayer model and optical reflectance data. PMMA was subjected to a low energy (50 keV) silicon ion implantation at the fluences of 3.2 × 10¹⁵ cm⁻² and 3.2 × 10¹⁶ cm⁻². Both real and imaginary components of the complex refractive index of this optically transparent polymer are modeled in a geometry that includes a gradient of their in-depth spatial distribution.