Influence of mode coupling on mode group diversity multiplexing in multimode fibers

In this paper, the influence of mode coupling on mode group diversity multiplexing (MGDM) in multimode fibers is investigated. It is found experimentally, that in step index fibers mode coupling is very strong among the lowest mode groups. It is confirmed that mode coupling in graded index fibers is negligible. Theoretical and numerical investigation of the system performance in strong mode coupling conditions, indicates need for greater separation of the lowest MGDM channels.     

Quantum ball as an example of quantum Kähler manifold

Using the notion of the coherent state map we present a construction of the C^∗$C^{\ast }$-algebra which is considered as a quantum version of the unit ball in C^N${\mathbb{C}}^N$. The structure of the quantum ball as well as its physical interpretation is investigated. Applying the reduction procedure to the quantum ball we obtain the Heisenberg–Weyl algebra.     

Nonlinear dynamics of a regenerative cutting process

We examine the regenerative cutting process by using a single degree of freedom nonsmooth model with a friction component and a time delay term. Instead of the standard Lyapunov exponent calculations, we propose a statistical 0-1?test analysis for chaos detection. This approach reveals the nature of the cutting process signaling regular or chaotic dynamics. For the investigated deterministic model, we are able to show a transition from chaotic to regular motion with increasing cutting speed. For two values of time delay showing the different response, the results have been confirmed by the means of the spectral density and the multiscaled entropy.     

New Applications of the Boundary Element Method in Dynamics of Solids

The boundary element method (BEM) is developed and applied in new fields of dynamic fracture mechanics, dynamics of composite, elasto–plastic and piezoelectric materials. The BEM results are compared with solutions computed by the finite element method (FEM) showing high accuracy of the BEM. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Oxidative Stress in Mucopolysaccharidoses: Pharmacological Implications

Although mucopolysaccharidoses (MPS) are caused by mutations in genes coding for enzymes responsible for degradation of glycosaminoglycans, storage of these compounds is crucial but is not the only pathomechanism of these severe, inherited metabolic diseases. Among various factors and processes influencing the course of MPS, oxidative stress appears to be a major one. Oxidative imbalance, occurring in MPS and resulting in increased levels of reactive oxidative species, causes damage of various biomolecules, leading to worsening of symptoms, especially in the central nervous system (but not restricted to this system). A few therapeutic options are available for some types of MPS, including enzyme replacement therapy and hematopoietic stem cell transplantation, however, none of them are fully effective in reducing all symptoms. A possibility that molecules with antioxidative activities might be useful accompanying drugs, administered together with other therapies, is discussed in light of the potential efficacy of MPS treatment.     

Chiral Amplification in Nature: Studying Cell‐Extracted Chiral Carotenoid Microcrystals via the Resonance Raman Optical Activity of Model Systems

Carotenoid microcrystals, extracted from cells of carrot roots and consisting of 95 % of achiral β‐carotene, exhibit a very intense chiroptical (ECD and ROA) signal. The preferential chirality of crystalline aggregates that consist mostly of achiral building blocks is a newly observed phenomenon in nature, and may be related to asymmetric information transfer from the chiral seeds (small amount of α‐carotene or lutein) present in carrot cells. To confirm this hypothesis, we synthesized several model aggregates from various achiral and chiral carotenoids. Because of the sergeant‐and‐soldier behavior, a small number of chiral sergeants (α‐carotene or astaxanthin) force the achiral soldier molecules (β‐ or 11,11′‐[D₂]‐β‐carotene) to jointly form supramolecular assemblies of induced chirality. The chiral amplification observed in these model systems confirmed that chiral microcrystals appearing in nature might consist predominantly of achiral building blocks and their supramolecular chirality might result from the co‐crystallization of chiral and achiral analogues.     

Thermal diffusivity measurement of ceramic materials used in spraying of TBC systems

The basic goal of this article was thermal diffusivity characterization of ceramic materials used in thermal barrier coating (TBC) systems for depositions of the insulation layer and characterization of the materials’ morphology and remanufacturing process. The base material was oxide 8YSZ (ZrO_2? ×?8Y₂O₃), which is usually dedicated to deposition of an insulating top layer in TBC systems. The data related to thermal properties such as thermal diffusivity and thermal conductivity are widely presented in the literature, but there is lack of information about the morphological form of investigated materials, and the presented results vary widely. Data on thermal properties based on the literature sources are inadequate for the real morphological form of materials used in the experiment (e.g., massive or single crystalline material vs. plasma-sprayed coatings), which consequently gives an unsatisfactory accuracy of the obtained numerical simulations by MES methods. This article presents the characterization of thermal diffusivity of the commercial 8YSZ ceramic material synthesized or remanufactured by different routes, which is investigated in the forms of pressed powder pellet (two commercial nano-sized powders with different morphologies), sintered pellets (one commercial powder, solid-state co-precipitated reacted powder of 8YSZ type), and a two-layered coating system of In625?+?NiCrAlY/8YSZ type. The range of analysis included morphological investigations of different types of powders in initial conditions and after remanufacturing (sintering, thermal spraying) as well as the thermal diffusivity analysis by the laser flash method. The obtained data were corrected by porosity factor and compared to each other. The best similarity for obtained thermal diffusivity data was found for commercial powers of HOSP^TM type after pressing and sintering processes and calculated (2-layered model) value of thermal diffusivity for two-layered system of In625/8YSZ TBS system. The results showed that there are significant differences in thermal diffusivity values for materials with different morphological forms.

     

Vibrations of a Pendulum with Oscillating Support and Extra Torque

The motion of a driven planar pendulum with vertically periodically oscillating point of suspension and under the action of an additional constant torque is investigated. We study the influence of the torque strength on the transition to chaotic motions of the pendulum using Melnikov's analysis. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Abnormal solvent effects on hydrogen atom abstraction. 3. Novel kinetics in sequential proton loss electron transfer chemistry

[reaction: see text] A prolonged search involving several dozen phenols, each in numerous solvents, for an ArOH/2,2-diphenyl-1-picrylhydrazyl (dpph(*)) reaction that is first-order in ArOH but zero-order in dpph(*) has reached a successful conclusion. These unusual kinetics are followed by 2,2'-methylene-bis(4-methyl-6-tert-butylphenol), BIS, in five solvents (acetonitrile, benzonitrile, acetone, cyclohexanone, and DMSO). In 15 other solvents the reactions were first-order in both BIS and dpph(*) (i.e., the reactions followed "normal" kinetics). The zero-order kinetics indicate that in the five named solvents the BIS/dpph(*) reaction occurs by sequential proton loss electron transfer (SPLET). This mechanism is not uncommon for ArOH/dpph(*) reactions in solvents that support ionization, and normal kinetics have always been observed previously (see Litwinienko, G.; Ingold, K. U. J. Org. Chem. 2003, 68, 3433 and Litwinienko, G.; Ingold, K. U. J. Org. Chem. 2004, 69, 5888). The zero-order kinetics found for the BIS/dpph(*) reaction in five solvents, S, imply that BIS ionization has become the rate-determining step (rds, rate constants 0.20-3.3 s(-)(1)) in the SPLET reaction sequence: S + HOAr right harpoon over left harpoon S- HOAr SH(+) + (-)OAr SH(+) + (*)OAr + dpph(-) --> S + (*)OAr + dpph-H, where ArOH = BIS. Some properties specific to BIS that may be relevant to its relatively slow ionization in the five solvents are considered.     

Synthesis and reactivity of O-acyl selenophosphates

The synthesis of several new O-acyl selenophosphates were investigated. The stability and reactivity of the products were studied and related to their structure.