Functionalized oligopolysiloxanes by heterogeneously catalyzed equilibration polymerization reactions

Summary A new general procedure for preparation of functionalized oligopolysiloxanes of predetermined molecular weight is described. It utilizes heterogeneously catalyzed siloxane equilibration polymerization reactions which do not require troublesome and sometimes difficult post-preparative work-up procedures usually encountered with the well known homogeneously catalyzed corresponding reactions. The method is described using as example the preparation of , -telechelic vinyldimethylsiloxy-oligopolydimethylsiloxanes from octamethylcyclotetrasiloxane and 1,3-divinyltetramethyldisiloxane, but reference to the preparations of trimethylsiloxy-, dimethylsiloxy-and carboxypropyldimethylsiloxyoligopolydimethylsiloxanes, oligopolymethylhydridosiloxanes or their copolymers is also made.     

On the critical molecular chain length of polydimethylsiloxane

Because a study of the results reported for the chain dimensions of polydimethylsiloxane (PDMS), critical for the onset of this polymer's non-Newtonian flow behavior, obtained from the viscosity-molecular weight relationships available from the literature, clearly revealed that considerable differences exist between the reported data, a detailed analysis of these data was performed together with an additional examination of 10 new PDMS samples that were selected so as to have molecular weights that would fill the gaps observed in the polymer viscosity–chain length relationship constructed from the accepted literature data. The results obtained were analyzed by using several different procedures integrated into a recently described comparative method that could allow for determination of what is called the most realistic critical value, Z_wc. The latter was determined as 930 PDMS main-chain atoms, which corresponds to this polymer's degree of polymerization of 464.5 and the weight-average molecular weight of 34,500. It is not only shown that after elimination of some clearly erroneous data points from the previously reported relationships the obtained critical chain-length values could very well fit the earlier relationships, but also that appropriate “master” relationships were constructed including 48 pairs of the old and 10 pairs of the new data points. It is suggested that this relationship be accepted as the best-fit viscosity–polymer chain-length dependence for PDMS, and it is pointed out that the obtained PDMS critical chain-length value ranks this polymer's macromolecules as the most flexible of the corresponding long-chain molecules presently known. © 1993 John Wiley & Sons, Inc.     

Recent progress in road and lane detection: a survey

The problem of road or lane perception is a crucial enabler for advanced driver assistance systems. As such, it has been an active field of research for the past two decades with considerable progress made in the past few years. The problem was confronted under various scenarios, with different task definitions, leading to usage of diverse sensing modalities and approaches. In this paper we survey the approaches and the algorithmic techniques devised for the various modalities over the last 5 years. We present a generic break down of the problem into its functional building blocks and elaborate the wide range of proposed methods within this scheme. For each functional block, we describe the possible implementations suggested and analyze their underlying assumptions. While impressive advancements were demonstrated at limited scenarios, inspection into the needs of next generation systems reveals significant gaps. We identify these gaps and suggest research directions that may bridge them.     

Silicon neuron: digital hardware implementation of the quartic model

This paper presents an FPGA implementation of the quartic neuron model. This approach uses digital computation to emulate individual neuron behavior. We implemented the neuron model using fixed-point arithmetic operation. The neuron model’s computations are performed in arithmetic pipelines. It was designed in VHDL language and simulated prior to mapping in the FPGA. We show that the proposed FPGA implementation of the quartic neuron model can emulate the electrophysiological activities in various types of cortical neurons and is capable of producing a variety of different behaviors, with diversity similar to that of neuronal cells. The neuron family of this digital neuron can be modified by appropriately adjusting the neuron model’s parameters.     

Alumina Grown during Deposition of Thermal Barrier Coatings on NiCrAlY

The microstructure of Al₂O₃ formed by oxidation of a model NiCrAlY alloy during electron-beam physical vapor deposition of ZrO₂–7.6 mol% YO_1.5 is examined and compared with that formed on the bare substrate. The growth rate, morphology, and chemical composition of the oxide vary among the different constituents of the alloy surface and are further influenced by the O₂ partial pressure and the physical presence of the thermal barrier coating (TBC) layer. These differences, however, are largely limited to the outer oxide layer. The interplay between the TBC and the growing oxide leads to the formation of a fine-grain Al₂O₃–ZrO₂"mixed zone" within the thermally grown oxide. A mechanism is outlined to explain this behavior, based on the dissolution of ZrO₂ in a transient Al₂O₃ structure growing by outward diffusion of Al, and its subsequent reprecipitation when the metastable phase transforms to the stable α-Al₂O₃ form.     

Metastable Phase Selection and Partitioning for Zr(1−x)AlxO(2−x/2) Materials Synthesized with Liquid Precursors

Aqueous solutions of zirconium acetate and aluminum nitrate were spray pyrolyzed at 250°C and upquenched to different temperatures to yield metastable solid solutions of composition Zr_{(1− x )}Al_xO_{(2− x /2)}. An amorphous oxide forms first during pyrolysis which subsequently crystallizes as a single phase for x ≤ 0.57 (≤40 mol% Al₂O₃). The crystallization temperature increased with Al₂O₃ content. Electron diffraction, supported by Raman spectroscopy, indicates that the initial phase is tetragonal. At higher temperatures, the initial solid solation partitions to other metastable phases, viz., t -ZrO₂+γ-Al₂O₃, prior to achieving their equilibrium phase assemblage, m -ZrO₂+α-Al₂O₃. Partitioning yields a nanocomposite microstructure with grain sizes of 20–100 nm, compared to the 3 to 5 nm in the initial, single phase. Compositions containing 45 to 50 mol% Al₂O₃ concurrently crystallize and partition. The structure selected during crystallization and the partitioning phenomena are discussed in terms of diffusional constraints during crystallization, which are conceptually similar to those operating during rapid solidification.     

Motional heterogeneity of polystyrene-block-polybutadiene: a spin probe study

Polystyrene-block-polybutadiene copolymers (SB) with 0.5 mass fraction of styrene were studied by electron spin resonance (ESR) of nitroxide spin probes. The influence of the block length ( and ) and the solvation power of casting solvents on the motional dynamics of spin probe were measured over a wide temperature range. Two nitroxide radicals as spin probes were selected: 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl benzoate (BzONO) and 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl (Tempol). Irrespective of the spin probe used two ESR spectral components differing in their motional properties above the phase transition of polybutadiene blocks (PB) were observed. The fast component was assigned to spin probes located in polybutadiene-rich domains and the slow component to spin probes in polystyrene-rich domains. The range of two spectral components and the phase transition of the slow ESR component, T_5mT, depend on the block length. The influence of the interphase and accumulation of free volume in the interphase on the Tempol probe motion was investigated by changing copolymer morphology in the films casted from selective and nonselective solvents. The analysis of the motional heterogeneity from the ratio of the fast and slow motional component presents evidence that in the selective solvent for polystyrene (PS) blocks (2-butanone) the most irregular structure with a large interphase is formed. The difference in fast motion of spin probes indicates that the motional dynamic is related to the change of domain structure.     

On the analytical derivation of the Pareto-optimal set with applications to structural design

The Fritz John conditions for Pareto-optimality have been set in matrix form and used for introducing a procedure for the analytical derivation of the Pareto-optimal set in the design variables domain. Subsequently, the derivation of the Pareto-optimal set in the objective functions domain can be obtained, if possible, by a proper analytical derivation. Both the objective and constraint functions are assumed to be available in analytical form and twice differentiable and convex (or pseudo-convex). The proposed procedure to find the Pareto-optimal set is relatively simple. The computation of the determinant of a matrix is required. A symbolic manipulator can be exploited. If there are two design variables and two objective functions, the Pareto-optimal set can be easily computed by applying a simple formula derived in the paper. If the number of design variables equals the number of objective functions, the Pareto-optimal set in the design variables domain can be found by computing the product of the constraint functions times the determinant of the Jacobian of the objective functions. A number of case studies have been proposed to test the effectiveness of the proposed procedure. The optimal structural design of, respectively, a pair of compressed spheres, a cantilever with rectangular cross section have been faced and solved. Additionally the test problem proposed by Fonseca and Fleming has been addressed and solved analytically. Optimization problems with low dimensionality (2 or 3 design variables and 2 objective functions, 2 or more constraints) have been easily solved. The proposed procedure can be useful in the actual engineering practice at the earliest design stage. In this case the designer can be made aware on the proper design variables setting to obtain the desired tradeoff among conflicting objective functions.     

Ferritin Protein Regulates the Degradation of Iron Oxide Nanoparticles

Proteins implicated in iron homeostasis are assumed to be also involved in the cellular processing of iron oxide nanoparticles. In this work, the role of an endogenous iron storage protein—namely the ferritin—is examined in the remediation and biodegradation of magnetic iron oxide nanoparticles. Previous in vivo studies suggest the intracellular transfer of the iron ions released during the degradation of nanoparticles to endogenous protein cages within lysosomal compartments. Here, the capacity of ferritin cages to accommodate and store the degradation products of nanoparticles is investigated in vitro in the physiological acidic environment of the lysosomes. Moreover, it is questioned whether ferritin proteins can play an active role in the degradation of the nanoparticles. The magnetic, colloidal, and structural follow‐up of iron oxide nanoparticles and proteins in lysosome‐like medium confirms the efficient remediation of potentially harmful iron ions generated by nanoparticles within ferritins. The presence of ferritins, however, delays the degradation of particles due to a complex colloidal behavior of the mixture in acidic medium. This study exemplifies the important implications of intracellular proteins in processes of degradation and metabolization of iron oxide nanoparticles.