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Novel bulk SiOC/spodumene composites have been developed by spark plasma sintering (SPS) at relatively low temperature (1200–1400 °C). Spodumene is a cheap and natural available lithium aluminosilicate mineral which acts as meltable/active filler. At 1300–1400 °C, the Al migrates toward the glassy matrix producing a Si-Al-O network and the crystallization of α-cristobalite. The C free phase also experiences a deep transformation. The epitaxial growth of few-layered graphene over SiC particles occurs at 1400 °C. An increase in the phonon transport is observed (36%, 1.28 – 2.14 Wm−1K−1) associated to the reduction of the interface resistance between the partially crystallized SiO 2 matrix and the SiC nano-wires/graphene-like carbon conductive phase. The electrical conductivity increases (1.14 ×10−2 – 8.1 Sm−1) due to the densification reached and an increasing ordering degree of the tortuous C free phase with a high quality of interconnection and crystallization. Raman parameters are determinant to understand the thermal and electrical response. • Spodumene was used for the first time to rise k and σ of SiOC/spodumene composites. • Raman parameters and densification are crucial to understand phonon/electron response. • The epitaxial growth of few-layered graphene over SiC particles occurs at 1400 ºC. • k boosts by the reduction of the interface resistance between SiO 2 /SiC nano-wires/C. • rises by densification and increasing ordering degree of the tortuous C free phase. [ABSTRACT FROM AUTHOR]

Nano- and micro-indentation experiments have been used to evaluate the mechanical properties of dense silicon oxycarbide (SiOC) derived materials obtained by spark plasma sintering (SPS). The sintering temperature varied from 1300 to 1700 °C, with a pressure of 40 MPa. The relationship between the mechanical properties and densification, porosity, evolution of the composition, structure and crystallization depending on the SPS sintering temperature has been determined. The SiOC sample obtained at 1400 °C shows the highest values of hardness (12 GPa) and elastic modulus (95 MPa) in both nano- and micro-indentation tests. The SPS treatment produces a neat densification of the material without promoting the phase separation of the Si–O–C matrix. In terms of the elasto-plastic behaviour, h f /h max >0.5 and W el /W tot <0.7, in conjunction with AFM images, highlight the negligible formation of pile-ups. The elastic recovery is quite high, and is probably due to the flexible segregated carbon phase. The Vickers indentation patterns show the Hertzian cones typical of anomalous glasses. Some minor radial cracks can also be seen, and can be attributed to the presence of both stiffer Si–C bonds which reduce the propagation of cracks, and to carbon, which reduces the brittleness of the SiOC derived materials. [ABSTRACT FROM AUTHOR]

Dense SiOC-Si 3 N 4 composites have been obtained employing mixtures with 10 % of Si 3 N 4 (SN10) or 5 % Si 3 N 4 - and an extra amount of carbon-5 % carbon nanofibers- (SN5N5) using spark plasma sintering (SPS). SPS produces densification at 1300/1400 °C and delays the carbothermal reaction of SiO 2 /Si 3 N 4 up to 1600 °C. It is observed the formation of a percolating network of SiC nanodots/nanowires widespread all over the matrix decorated with graphene-like carbon generated by Joule heating during SPS. The evolution of the C free is studied by conventional/non-conventional Raman parameters. In this sense, SN5N5–16 and SN10–17 show a C free phase composed by large highly tortuous and ordered graphene layers with the highest degree of interconnection and crystallinity determinant for understanding the highest thermal and electrical conductivities (1.91 WmK−1 and 33.6 Sm−1). Finally, this material displays a low coefficient of thermal expansion (1.26×10−6 K−1), remarkable resistance against oxidation to 1400 °C and high absorptance (95.8 %). • SPS delays the carbothermal reaction of SiO 2 /Si 3 N 4 to 1600 ºC in SiOC-Si 3 N 4 mixtures. • SiC nano-dots/wires decorated with graphene-like carbon appear all over the matrix. • Conventional/Non-conventional Raman parameters clarify SiOC-Si 3 N 4 properties. • A percolating network of SiC/graphene and C free upwards k, σ and downwards CTE. • The SiOC-Si 3 N 4 composites display remarkable oxidation resistance up to 1400 ºC. [ABSTRACT FROM AUTHOR]

In this paper, we present a piecewise smooth system, that describes the dynamics of a single vehicle moving through a street that has a sequence of lights that turn on and off with a specific frequency. The model presents three dynamic ways: accelerated, decelerated and zero state. Besides, we show the description of the mathematical model used to simulate the system. The simulation was developed under an event-based scheme and implemented in Matlab. To make the numerical analysis, we take as a parameter study the cycle traffic light, which provides benefits to vehicular traffic system due to its configuration is achieved implementing optimization strategies for the phenomenon of green wave and reduces the travel time as the vehicle minimizes the number of stops along the road. Also, the stability was studied for the periodic orbits one and two. Finally, we made an approximation of fuel consumption. We assume that this is proportional to the mechanical energy produced by the motor. From this point of view, it can be concluded that it is possible to apply modeling and simulation strategies based on dynamic systems to understand the complex behaviors associated with the travel of vehicles in a traffic controlled by traffic lights. [ABSTRACT FROM AUTHOR]

Highlights • A Fresnel lens allowed performing materials thermal shock resistance tests. • Dense SiOC resisted 100 cycles at 1200 °C (37 °C s−1-28 °C s−1) of thermal shock test. • The absorptance remained fairly constant during aging test (94.78 to 95.96–96.09%). • High-temperature oxidation forms a protective silica layer preventing degradation. • Dense silicon oxycarbide is a potential candidate as high temperature solar receivers. Abstract Materials used as solar receivers in concentrated solar power technology must withstand severe operational conditions caused by concentrated solar radiation. For this solar technology several ceramic material candidates (silicon carbide, porous and dense silicon oxycarbide) have been subjected to thermal shock resistance test by using Fresnel lens, the equipment available, that concentrates the solar radiation more than 2600 times. Fast heating (37 °C s−1) and cooling rates (28 °C s−1) from 100 to 1200 °C and dwelling time of 10 min are employed. The evolution of materials surface has been evaluated during test by spectroscopic methods and both confocal and electronic microscopies. It has been obtained the surface map of each analyzed sample in order to evaluate the effect of the concentrated solar radiation on the surface and the relationship with their durability. The absorptance values were also determined before and after the ageing test using normal direction between 400 and 1100 nm. Concentrated solar radiation facilitates the decomposition of tested materials producing the formation of gaseous species (mainly CO and CO 2) and a dense SiO 2 layer which is formed over the material surface. SiC and porous silicon oxycarbide materials fail the thermal shock resistance test. SiC experiences a catastrophic break and in the case of porous silicon oxycarbide, gases generated can evolve easily through the pores producing a severe degradation of the material surface. However, dense silicon oxycarbide resists 100 cycles at 1200 °C due to the formation of a protective SiO 2 layer over the material surface and its dense microstructure that slow down the diffusion of the gases preventing bulk material from being degraded. The surface studies confirm the formation of a crystalline SiO 2 phase all over the surface. Furthermore, the very similar coefficients of thermal expansion of silicon oxycarbide and silica (≈0.4 × 10−6 °C), protects material against catastrophic failure. Finally, the absorptance values remain fairly constant before and after thermal shock test (94.78 to 95.96–96.09%). The high resistance of dense silicon oxycarbide materials to thermal shock under concentrated solar radiation makes these materials suitable candidates of being used as high temperature solar receivers. [ABSTRACT FROM AUTHOR]

This review summarizes the data published over the past two and a half decades on the mechanism of plastic deformation of bulk isotropic linear glassy polymers in uniaxial tension, compression, and shear at low deformation temperatures (Tdef < 0.6Tg) and moderate loading rates. The main attention is focused on studies concerning the numerical computer simulations of plasticity of organic polymer glasses. The plastic behavior of glassy polymers at nano-, micro-, and macrolevels in the range of macroscopic strains up to ≈100% is discussed. Plasticity mechanisms are compared for organic, inorganic, metallic, polymer, and nonpolymer glasses with different chemical structures and types of interparticle interactions. The general common mechanism of plasticity of glassy compounds, the nucleation of plasticity carriers in them, and the structure of such carriers and their dynamics are covered. Within the framework of the common plasticity mechanism, the specific features of deformation in glassy polymers are analyzed. Specifically, the participation of conformational transformations in macromolecules in the deformation response of polymer glasses, change in intensity of the yield peak with the thermomechanical prehistory of the sample, and the role of van der Waals interactions in the accumulation of excess potential energy by the sample under loading are considered. The role of free volume and structural and dynamic heterogeneities in the plasticity of glasses is also discussed. [ABSTRACT FROM AUTHOR]

In order to obtain dense silicon oxycarbide (SiOC) materials that maintain the properties of glass, non-conventional spark plasma sintering was used to sinter SiOC powders from 1300 to 1700 °C and with 40 MPa of pressure. The concurrence of electrical current, high pressure and low vacuum while the material is being heating produces a dense SiOC-derived material composed of a SiO 2 glassy matrix reinforced with SiC nanowires grown in situ , graphene-like carbon and turbostratic graphite. SiOC materials with high electrical and thermal response are obtained as a result of this new processing technique. Electrical resistivity undergoes an extraordinary decrease of five orders of magnitude from 1300 (1.0 × 10 5 Ω m) to 1700 °C (0.78 Ω m), ranging from insulate to semiconductor material; and thermal conductivity increases by 30%, for these sintering temperatures. [ABSTRACT FROM AUTHOR]

The position of a graphene nanoribbon on a solid substrate allows the chemical modification of only one of the nanoribbon sides. A method was proposed that enables the chemical modification of the other side, too. It was numerically modeled how a nanoribbon separated from a substrate rolls up into a roll and how the roll unrolls on a flat substrate. The dependences of the number of coils and the radii of rolls forming by hydrogenation on the nanoribbon length and width were determined. [ABSTRACT FROM AUTHOR]

Extensive molecular dynamics simulations of polybutylcarbosilane dendrimer melts were performed in a wide temperature range from 300 to 600 K. The melt macroscopic and structural characteristics were analyzed for the third up to the eighth generation dendrimers for the systems consisting of 8 and 27 dendrimer molecules in the simulation box. For every system, averaging was performed over 8 independent simulation runs and along equilibrium time trajectories of up to 5 ns. Calculated values of the thermal expansion coefficients, heat capacity, and self-diffusion coefficients are in a good agreement with experimental observations. Analysis of the molecular mass dependence of the gyration radius and shape factor, detailed radial density distributions of dendrimer structural units, mobility of the branching points, and intermolecular interaction energy allowed to shed light on the basics of distinction in behavior of low and high generation dendrimer melts and formulate the directions of further research. [ABSTRACT FROM AUTHOR]

• Novel SiOC/spodumene composites with tailorable CTE are obtained employing SPS. • Spodumene and SPS reduce the sintering temperature of the SiOC matrix at least 100 °C. • Spodumene promotes sintering of SiOC, then its phase separation and crystallization. • Low CTE (0.128 3 –1.902 × 10−6 K−1) is obtained at 1200 °C by the formation of β-spodumene. • The maximum values of h (11.5 GPa) and e (91 MPa) are reached at 1300 °C. Highly densified silicon oxycarbide (SiOC)/spodumene composites with low coefficient of thermal expansion (CTE) were obtained just selecting the spark plasma sintering temperature employed. For the first time we proposed the use of spodumene a cheap and natural available lithium aluminium silicate mineral as meltable/active filler for SiOC-derived composites, due to its powerful fluxing properties and also its very low CTE. SiOC/spodumene composites sintered at 1200 ⁰C display a very low CTE (0.128±0.004–1.902±0.002 × 10−6 K−1) due to the α,β-transformation of spodumene. At higher sintering temperatures the CTE increases to 3.288±0.004 × 10−6 and 4.516±0.006 × 10−6 K−1 (1300 and 1400 ⁰C) due to the β-SiC formation. In this range of temperature, spodumene promotes the phase separation of SiOC and subsequent crystallization of cristobalite and β-SiC. The maximum values of hardness (11.5 ± 0.5 GPa) and elastic modulus (91±4 MPa) are reached at 1300 ⁰C, where the SiOC/composite displays a neat densification and the lowest roughness (1.61±0.01 nm). [ABSTRACT FROM AUTHOR]

Highly densified bulk silicon oxycarbide—carbon composites (SiOC-C) reinforced with carbon black (CB), active carbon (AC) or graphite (GR) have been obtained through spark plasma sintering. Structural, mechanical, tribological and thermal properties of SiOC-C composites were researched. The SiOC-C composites reinforced with GR and CB tended to give β-SiC. Wear behavior at room temperature under dry conditions was determined by using a ball on plate configuration and stainless steel balls as counter bodies. The coefficient of friction of the composites decreases down to 40% and the wear rate is also reduced by 1 in the order of magnitude when compared to SiOC. A graphite-like carbon tribolayer is probably formed in the composites; this layer could be responsible for the observed enhancement of such tribological properties. These SiOC-C composites are promising candidates for use in harsh enviroments where an adequate tribological response is required at high temperatures. [ABSTRACT FROM AUTHOR]

The suitability of using mesoporous silicon oxycarbide materials as controlled drug delivery systems is reported here. The silicon oxycarbide materials are known for their nanostructured nature composed of silica and carbon nanodomains in an amorphous matrix. The SiOC present a large surface area and a bimodal porous structure with pores of 6 and 100 nm size. The surface modification of the SiOC with amino-containing silanes leads to a similar porous structure with the grafted silane adopting a specific configuration depending on the amount of silane. The availability of the amino groups to interact with the loaded drug molecule has been determined through infrared spectroscopy whereas the amount of drug adsorbed on the material has been calculated through UV–vis spectroscopy and thermogravimetry. The materials are biologically inactive but they can host a large amount of active drug molecules per cm 2 into their porous structure. The adsorption kinetics have been compared with mesoporous silica and mesoporous active carbon and we have deducted that the drug penetrates faster in the SiOC than in the AC and the adsorption mechanism occurs via acceptor–donor interactions between the drug molecules and the surface of the materials. [ABSTRACT FROM AUTHOR]

Abstract: Spark plasma sintering (SPS) technology has been employed to obtain nanocomposites of a silicon oxycarbide glass matrix (SiOC) reinforced with SiC, SiO2 or Al2O3 nanoparticles. The characterization of the obtained materials revealed a dependence on the structural characteristics of the precursors with the properties and the reactions taking place during sintering. In the materials reinforced with SiO2, the stoichiometry of the oxycarbide phase is independent on the carbon content in the SiOC whereas when reinforcing with Al2O3, the mullite phase formation occurs at expense of the SiOC metastable phase. The measured mechanical and electrical properties have been revealed to be dependent of the size of the carbon nanodomains. [Copyright &y& Elsevier]

The article discusses the contribution of the interactions involving molecular dynamic simulation of uniaxial compressive and tensile deformation to the increase in the potential energy of amorphous glassy polymethylene. Topics include the use of Verlet velocity algorithm for the integration of the equation of motion, the changes in the calculation of polymethylene density, and the effect of the modification in the bond angles energy to the deformation of energy storage.

Molecular dynamics simulation of glassy polymethylene (PM) plastic deformation is performed up to ɛ = 30% in uniaxial compression regime at a temperature of 50 K, which is ∼140 K below T of the polymer. All atoms of PM chains are represented explisitly (all-atom model). Calculations were performed for two series of samples with different molecular mass distribution of chains: Samples have average degree of polymerization DP ≈ 212 with Mn ≈ 3000 and Mw ≈ 9500 (the first series) and DP ≈ 350, Mn ≈ 5000 and Mw ≈ 9500 (the second series). Each sample contains 12288 -CH- monomeric units per computational sell. Nonaffine displacements of carbon atoms and conformational rearrangements in chains during deformation are visualized and analyzed. The transformation of relatively fragments of chains up to 16-20 monomer units length are basic structural units, non-conformational displacements of which controls plastic process. Relatively large nonaffine displacements are observed even in the range of low strains, which are usually interpreted as Hookean strains. In the range of yield tooth and steady plastic flow, the number of these displacements increases along with their amplitude. Conformational set of PM chains does not show a serious change during deformation. Analysis had shown that the number of conformational rearrangements of trans-gauche type in PM chains during deformation is small and such rearrangements do not play decisive role in the considered range of PM plasticity, even at ɛ > 15%, at the stage of the developed plastic flow. [ABSTRACT FROM AUTHOR]

Abstract: Dense silicon oxycarbide glasses (SiOC) have been produced by spark plasma sintering (SPS) of SiOC powders. Raw powders were obtained by pyrolysis under nitrogen at 1100°C of tetraethylorthosilcate/polydimethylsiloxane (TEOS/PDMS) hybrids. SPS experiments were carried out at 1300 and 1500°C at 10 and 80MPa and then were studied by chemical analysis, 29Si and 13C MAS NMR, ATR, Raman, XRD, FE-SEM, density, porosity, microhardness (H v) and thermal conductivity (K). The SiOC materials are formed by Si x OC4−x units within a silica matrix where silicon carbide and graphite nanodomains are also present. After the SPS treatment the silicon carbide crystallite size is close to 2.5nm. At 1300°C and 1500°C the carbon nanodomain size is close to 3nm and 2nm, respectively. H v values vary from 3.4 to 9.15GPa, for 30% and 1% of porosity, respectively. Finally, K is always close to 1.38Wm−1 K−1. [Copyright &y& Elsevier]

Carbon nanofibers/glass (CNF/G) nanocomposites were obtained from a glass powder of low melting point and pristine CNFs. Green bodies containing from 0 to 22 % (v/v) of CNFs were sintered under nitrogen atmosphere in the 550-700 °C temperature range with different holding times. A fully microstructure characterization, by means of Hg porosimetry and N adsorption, was carried out for understanding the CNFs/G composites behavior during the sintering process. This understanding is required to optimize the microstructural design of CNFs/glass nanocomposite materials. During sintering two different and simultaneous phenomena occur the matrix crystallization and the pore formation. The glass matrix crystallization temperature decreases from 650 to 550 °C, when CNFs concentration increases to 22 % (v/v). The glass matrix produces the CNFs degradation and generates gaseous species which lead to homogeneous or foamy materials. This depends on the CNFs concentration and thermal treatment conditions. Foamy nanocomposites present pore size distributions with pores <0.1 and close to 20 μm. The glass matrix wets the CNFs and produce their degradation been of 1 % of carbon loss in all nanocomposites. [ABSTRACT FROM AUTHOR]

Commercially available CNFs (diameter 30-300 nm) have been used to develop both bulk and coating epoxy nanocomposites by using a solvent-free epoxy matrix powder. Processing of both types of materials has been carried out by a double-step process consisting in an initial physical premix of all components followed by three consecutive extrusions. The extruded pellets were grinded into powder and sieved. Carbon nanofibers powder coatings were obtained by electrostatic painting of the extruded powder followed by a curing process based in a thermal treatment at 200 °C for 25 min. On the other hand, for obtaining bulk carbon nanofibers epoxy composites, a thermal curing process involving several steps was needed. Gloss and mechanical properties of both nanocomposite coatings and bulk nanocomposites were improved as a result of the processing process. FE-SEM fracture surface microphotographs corroborate these results. It has been assessed the key role played by the dispersion of CNFs in the matrix, and the highly important step that is the processing and curing of the nanocomposites. A processing stage consisted in three consecutive extrusions has reached to nanocomposites free of entanglements neither agglomerates. This process leads to nanocomposite coatings of enhanced properties, as it has been evidenced through gloss and mechanical properties. A dispersion limit of 1% has been determined for the studied system in which a given dispersion has been achieved, as the bending mechanical properties have been increased around 25% compared with the pristine epoxy resin. It has been also demonstrated the importance of the thickness in the nanocomposite, as it involves the curing stage. The complex curing treatment carried out in the case of bulk nanocomposites has reached to reagglomeration of CNFs. [ABSTRACT FROM AUTHOR]

Novel hierarchical micro-meso-macroporous fluorine-doped silicon oxycarbide derived materials have been obtained by HF etching of silicon oxycarbides pyrolyzed at different temperatures. The influence of etching time (1 or 24 h) and pyrolysis temperature (from 1100 to 1400 °C) on the selective removal of the silica nano-domains present in the silicon oxycarbide and the appearance of oxygen and fluorine functionalities have been determined and evaluated in terms of their electrochemical response. The insertion of fluorine in the silicon oxycarbide matrix (Si–O(F) bonds) and free carbon phase (C–F semi-ionic and C–F covalent bonds) was corroborated. The materials pyrolyzed at 1300–1400 °C and etched during 24 h show values of specific capacitance as high as 225-165 Fg-1 (0.1–30 Ag-1) using a symmetrical configuration and H 2 SO 4 1 M as electrolyte. These materials displayed energy density values of 28-19 Whkg−1 (0.1–45 kWkg-1). The hierarchical microstructure in conjunction with the oxygen and fluorine functionalities are essential in order to explain their good electrochemical response. In particular, those materials present the highest amount of meso (3–10 nm) and larger meso-macropores and the highest content of fluorine in their composition. Then, fluorine-doped silicon oxycarbide derived materials can be potentially used as electrodes for supercapacitors in the field of energy storage applications. [Display omitted] • Hierarchical micro-meso-macroporous F-doped SiOC-DC were obtained at R.T. • F is grafted into silicon oxycarbide (SiO(F)) and C free (C–F semi-ionic and covalent). • Functionalization (F,O) and meso-macropores explain the good electrochemical response. • The functionalities (F, O) increase the wettability and promotes Faradaic processes. • The presence of bigger slit-shape meso-macro channels enhances C s values. [ABSTRACT FROM AUTHOR]

This paper presents a reflector recognition and localization technique in three-dimensional (3-D) environments, using only times-of-flight (TOFs) data obtained from ultrasonic transducers. The recognition and localization technique is based on the principal component analysis applied to the TOF vectors originating from a sensor that contains two emitting transducers and several receivers. The two emitters simultaneously transmit two coded pulses that are detected later on and discriminated by the receivers, after being reflected in the environment. The proposed technique allows for the possibility of not only recognizing the reflectors, but also estimating approximately its localization referred to the sensor. This technique has been tested with three types of reflectors in 3-D environments: planes, edges, and corners. The achieved results are very satisfactory for reflectors located in the range 50-350 cm. [ABSTRACT FROM AUTHOR]

In this article the authors prove the equality of the Weil pairing, also known as the Jacobian, and the product over the curve's points of tame symbols of the corresponding idele components. It is known that the Jacobian of an algebraic curve with a distinguished point is canonically isomorphic to its dual Abelian variety. Thus, there is a pairing on the points of finite order of the Jacobian. In the general case, the equality was proved and it was non canonically reduced to the particular case of a curve over a finite field.

• Hierarchically micro-mesoporous SiOC-CD were obtained from HF etching of SiOC • Better electrochemical response when both micro and slit-shape mesopores are present • SiOC-DC materials pyrolyzed at 1200 °C display a C s of up to 100 Fg−1 at 40 Ag−1 • SiOC-DCmaterials pyrolyzed at 1200 °C show an energy density of up to 28 W h Kg−1 [Display omitted] Hierarchically micro/mesoporous silicon oxycarbide derived carbon (SiOC-DC) materials have been successfully prepared by HF selective removing of silica nano-domains present in SiOC. Dense carbon enriched SiOC materials are obtained by pyrolysis from 1100 to 1400 °C of novel sol-gel hybrids which contain both Si–H and Si-Ph bonds. The pyrolysis temperature deeply affects the etching process, major differences are observed between the sample pyrolyzed at 1100 °C and at higher temperatures. Those differences are directly associated to the evolution of the phase separation of SiOC into SiO 2 and SiC, which facilitates the selective extraction of silica nano-domains and the formation of micro/mesoporous SiOC-DC materials with high specific surface areas (SSAs) and high pore volumes. The SiOC-DC sample pyrolyzed at 1200 °C displays very promising results of specific capacitance (90–100 Fg−1 at 40 Ag−1), relatively high energy density (28 W h Kg−1) at a low power density (0.10 kW kg−1), and a significant performance at high power density (10 W h Kg−1 at 49 kW kg−1), taking into account the low potential window of inorganic liquid electrolyte used (0.9 V). We have found that the presence of micropores but even more, the presence of slit-shape mesopores (D meso 3–10 nm) is crucial in order to explain the electrochemical response of these materials. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations of two types of isolated siloxane dendrimers of various generations (from the 2nd to the 8th) have been performed for temperatures ranging from 150 K to 600 K. The first type of dendrimer molecules has short spacers consisting of a single oxygen atom. In the dendrimers of the second type, spacers are longer and comprised of two oxygen atoms separated by a single silicon atom. A comparative analysis of molecular macroscopic parameters such as the gyration radius and the shape factor as well as atom distributions within dendrimer interior has been performed for varying generation number, temperature, and spacer length. It has been found that the short-spacer dendrimers of the 7th and 8th generations have a stressed central part with elongated bonds and deformed valence angles. Investigation of the time evolution of radial displacements of the terminal Si atoms has shown that a fraction of the Si groups have a reduced mobility. Therefore, rather long time trajectories (of the order of tens of nanoseconds) are required to study dendrimer intramolecular dynamics. [ABSTRACT FROM AUTHOR]

The potential application of silicon oxycarbonitride (SiOCN), silicon oxycarbide (SiOC) and silicon oxycarbide–SiC (SiOC–SiC) for photothermal devices such as volumetric solar absorbers has been studied evaluating the response to thermal shock from a Fresnel lens. The accelerated ageing test comprises fast heating (32 °C min−1) and cooling rates (27 °C min−1) from 100 to 1000 °C and dwelling times of 10 min. Porous materials (SiOCNp and SiOCp) failed the thermal shock tests; they were massively degraded by the formation of a large depression in the focus of solar radiation. Dense materials (SiOCd and SiOC–SiCd) withstood 100 cycles of thermal shock ageing tests due to the formation of a protective silica layer. The absorptance values for dense materials remained fairly constant before and after thermal shock tests: from 94.5 to 94.3% for SiOCd and from 93.3 to 93.3% for SiOC–SiCd. These preliminary studies indicate their potential for high-temperature solar receiver applications. [ABSTRACT FROM AUTHOR]

The design of a material porous microstructure with interconnected micro-meso-macropores is a key issue for the successful development of carbon-derived materials for supercapacitor applications. Another important issue is the nature of these carbon materials. For those reasons, in this study, novel hierarchical micro-meso-macroporous silicon oxycarbide-derived carbon (SiOC-DC) was obtained via chlorine etching of carbon-enriched SiOC prepared via pyrolysis (1100–1400 °C) of sol-gel triethoxysilane/dimethyldiphenysiloxane hybrids. In addition, and for the first time, non-conventional Raman parameters combined with the analysis of their microstructural characteristics were considered to establish their relationships with their electrochemical response. The sample pyrolyzed at 1100 °C showed planar and less-defective carbon domains together with the largest specific surface area (SSA) and the highest volume of micro-meso-macropores, which upgraded their electrochemical response. This sample has the highest specific capacitance (Cs = 101 Fg−1 (0.2 Ag−1)), energy (Ed = 12–7 Wh−1 kg−1), and power densities (Pd = 0.32–35 kw kg−1), showing a good capacitance retention ratio up to 98% after 10,000 charge–discharge cycles at 0.5 Ag−1. At a pyrolysis temperature ≥ 1200 °C, the carbon domains were highly ordered and tortuous with a high degree of interconnection. However, SSA and pore volumes (micro-meso-macropores) were significantly reduced and downgraded the Cs, Ed, and Pd values. [ABSTRACT FROM AUTHOR]

Our previous paper (E.A. Zubova, I.A. Strelnikov, N.K. Balabaev, A.V. Savin, M.A. Mazo, and L.I. Manevich, Polym. Sci., Ser. A 59 (1) (2017)) addressed the simplest coarse-grained model of polyethylene and alkanes. The CH group in this united-atom model is replaced with a bead. In the framework of the model, nonbonded interactions are described by the Lennard-Jones potential (6-12), whereas the potential for bonded interactions accounts for the bonds between beads and for coarse grained angles and dihedral angles but not for the cross terms between them. We found the area of geometrical parameters of the model where all the three known crystalline phases of polyethylene are stable at low temperatures. We parametrized the force field of the model using the dynamic properties of the system, namely, the inelastic neutron scattering spectrum of the orthorhombic phase of polyethylene. However, the simplest model underestimates the value of the elastic modulus along the chains of the crystal by a factor of two. The derived setting angle of the molecules also differs appreciably from the experimental data. Moreover, the acoustic dispersion curves for the modes with the wave vector directed along the chain axis deviate from the experimental data at low frequencies. In the present study, we included the cross terms into the bonded interactions. This made it possible to reproduce the experimental elastic modulus along the chains of the crystal and to decrease the frequency range for the optical skeletal dispersion curve to proper values. As for the beads, we separated force centers for the bonded and nonbonded interactions, which enabled us to reproduce the optical skeletal curve and to bring the anisotropy of interchain interactions in line with the experiment. However, the model fails to reproduce the balance of interactions between the neighboring chains in the crystal. For this, a different form of the potential energy of van der Waals interactions seems to be needed. [ABSTRACT FROM AUTHOR]

More than 20 coarse-grained (CG) DNA models have been developed for simulating the behavior of this molecule under various conditions, including those required for nanotechnology. However, none of these models reproduces the DNA polymorphism associated with conformational changes in the ribose rings of the DNA backbone. These changes make an essential contribution to the DNA local deformability and provide the possibility of the transition of the DNA double helix from the B-form to the A-form during interactions with biological molecules. We propose a CG representation of the ribose conformational flexibility. We substantiate the choice of the CG sites (six per nucleotide) needed for the 'sugar' GC DNA model, and obtain the potentials of the CG interactions between the sites by the 'bottom-up' approach using the all-atom AMBER force field. We show that the representation of the ribose flexibility requires one non-harmonic and one three-particle potential, the forms of both the potentials being different from the ones generally used. The model also includes (i) explicit representation of ions (in an implicit solvent) and (ii) sequence dependence. With these features, the sugar CG DNA model reproduces (with the same parameters) both the B- and A- stable forms under corresponding conditions and demonstrates both the A to B and the B to A phase transitions. [ABSTRACT FROM AUTHOR]

In this paper, robust disturbance-feedback strategies for finite time-horizon problems are studied. Linear discrete-time systems subject to linear control, state constraints, and quadratic objective functions are considered. In addition, persistent disturbances, which enter the system additively and are contained in a polytopic set, act on the system. The synthesis of robust strategies leads in the case of the traditional robust state-feedback and open-loop min-max strategies to, respectively, nonconvex problems or conservatism. However, robust disturbance-feedback problems can easily be reformulated as convex problems and solved by tractable linear matrix inequalities. Hence this approach bypasses the nonconvexity issue while maintaining the advantages of feedback strategies. As a key result, it is shown that both sources of conservatism attributed to this approach, namely, the relaxation method and the affine parametrization, can be removed at the expense of an increase in computational effort. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A molecular-dynamics simulation of the low-temperature (∼100 K below T) plastic deformation of glassy polymethylene (PM) was conducted. A model system consisting of 64 chains containing 100 CH groups (the united-atoms approach) in each computational cell with periodic boundary conditions was considered. The behavior of 32 such cells was considered. Each cell was subjected to an active isothermal uniaxial compression at a constant temperature of T = 50 K to a strain of ɛ = 30%. An analysis showed that the inelastic deformation of glassy PM proceeded via nonaffine displacements ('gliding') of chain fragments comprising 11-13 sites -CH-. These displacements are correlated and directed mainly along chain axes. Only a small number of conformational rearrangements occur in chains during the deformation of the material. Conformational transitions add only small additional displacements to nonaffine atomic transformations. A free-volume analysis using Voronoi-Delaunay tessellation in the deformed polymer did not show its relation to local plastic rearrangements. [ABSTRACT FROM AUTHOR]

Examines the behavior of thermal expansion coefficients in models of solids with different pairwise interaction potentials. Evaluation of the role of various nonlinear effects caused by the specificity of pairwise potentials; Consideration of three types of pairwise potentials; Utilization of a system of units in which the size, weight, and interaction energy of particles are equal to zero.

This paper describes the implementation of a neural network control system for guiding a wheelchair, using an architecture based on a digital signal processor (DSP). We use a recurrent radial basis neural network as a system controller and a Kalman filter as identifier, which acts as propagator of the control errors to the neurocontroller. The hub of the algorithm architecture is a DSP of the company Texas Instruments (TMS320C31). The board has complete autonomy of action and is specifically designed for executing control algorithms in real time. Various practical tests have been carried out to check the correct functioning of the system when governing the output of the wheelchair. [Copyright &y& Elsevier]

Cobalt-silicon oxycarbide materials (Co–SiOC) have been produced through the polymer-derived ceramic route by incorporating Cobalt acetate in different proportions. HF etching of the obtained materials leads to obtaining C-rich Co–SiOC materials where the constituent phases present different characteristics. The SiO 2 units that were the most vulnerable to the chemical attack were the most tensioned ones which are connected at the edges of the graphitic planes. The carbonaceous nanostructures in the HF-etched materials present a different ordering degree which is related with the microstructural characteristics of the pyrolyzed precursors. In addition, the electrochemical performance turns out to be dependent not solely on the Co content but also to the graphitization degree of the carbonaceous phase. [ABSTRACT FROM AUTHOR]

We carry out a molecular dynamics simulation of the first stages of constrained melting in crystalline polyethylene (PE). When heated, the crystal undergoes two structural phase transitions: from the orthorhombic (O) phase to the monoclinic (M) phase, and then to the columnar (C), quasi-hexagonal, phase. The M phase represents the tendency to the parallel packing of planes of PE zigzags, and the C phase proves to be some kind of oriented melt. We follow both the transitions O→M and M→C in real time and establish that, at their beginning, the crystal tries (and fails) to pass into the partially ordered phases similar to the RI and RII phases of linear alkanes, correspondingly. We discuss the molecular mechanisms and driving forces of the observed transitions, as well as the reasons why the M and C phases in PE crystals substitute for the rotator phases in linear alkanes. [ABSTRACT FROM AUTHOR]

The coarse-grained model of polyethylene and alkanes (the united-atom model, in which each CH group is represented by a single bead) was proposed several decades ago. It is widely applied in molecular dynamics simulations. For different tasks, the models with different geometrical and force parameters are used. Until now, it was thought that the coarse-grained model of polyethylene cannot reproduce the orthorhombic crystalline phase, which is typical of this polymer. In the present study, we analyze the simplest coarse-grained model of polyethylene. In this model, the Lennard-Jones potential (6-12) is adopted for van der Waals interactions between the beads of different chains. Of the bonded interactions, only the 'valence' bonds between beads and the 'bond' and 'torsion' angles are taken into account, whereas the cross terms between them are disregarded. We consider the model variation in which the bead (the force center with the mass of a CH group) is displaced from the center of the carbon atom and all the interactions, both bonded and nonbonded, are defined by the positions of these beads. For this model, we find the area of geometrical parameters (the displacement value and the van der Waals radius of the bead) in which all the three known crystalline phases of polyethylene are at equilibrium at low temperatures. We choose the force field constants for the model so that its oscillation spectrum reproduces the low-frequency part of the inelastic neutron scattering spectrum of the orthorhombic polyethylene. It proved to be that this choice can be made unambiguously. We compare the dispersion curves in the terahertz range with experimental data on the Raman scattering and infrared spectroscopy, and discuss the advantages and disadvantages of the analyzed simplest coarse model. [ABSTRACT FROM AUTHOR]

A general method for generating complementary sets of four sequences of length 4N is presented. The proposed generator easily allows finding four orthogonal sets of four sequences each. The generated sequences have excellent correlation properties and offer an efficient hardware implementation of the corresponding correlators based on the efficient pulse compressor, which is also derived. [ABSTRACT FROM AUTHOR]

This paper presents a new methodology to obtain the line impedance of current railway tracks by using only short-circuit measurements. Open-circuit measurements required by conventional methodologies are discarded, since they cannot be carried out for railway tracks in service (electrically continuous and indefinite length). The mathematical basis of the proposed methodology is based on the transmission line theory but focused on the changes in track length. The proposal has been successfully applied to characterize the impedance of the high-speed railway line at the Spanish AVE Madrid-Valencia (Cuenca) and in the AVE Atocha-Chamartin tunnel (Madrid). Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Tetraethyl orthosilicate (TEOS)-polydimethyl siloxane (PDMS) ormosils with different amounts of Ti and Ca were prepared and characterized. Several surface properties such as specific surface area, porosity, fractality, dispersive and polar surface energies were determined and related with their in-vitro bioactivity. It has been found a dependence of the surface fractal dimension with the concentration of Ca ions that induce the appearance of rough surfaces. The dispersive surface energy, γ, increased with the incorporation of Ti or Ca and the presence of micropores, but Ca(NO) precipitates in the surface coming from non-incorporated Ca lead to a decrease of the surface energy values. In relation with the polar surface energy, it has been observed that all ormosil materials presented amphoteric character with a larger presence of base surface sites than acid ones. The basicity of the surface increased with the concentration of Ti and Ca, while the acidity decreased. The in-vitro bioactivity of the surface was estimated by soaking samples in simulated body fluid (SBF) and afterwards characterized by means of X-ray diffraction (TF-XRD) and field emission scanning electron microscopy (FE-SEM). It has been observed that in vitro bioactivity is related with the polar surface characteristics of these materials, being necessary for the bioactivity, the presence of a highly polar surface with intermediate base/acid ratio and specific roughness. [ABSTRACT FROM AUTHOR]

Abstract: Nowadays, many ultrasonic sensory systems are being developed to operate outdoors, where they are finding a variety of applications, such as local positioning, vehicle navigation or obstacle detection. To assure the reliable operation of these systems under any meteorological condition, it is necessary to achieve a thorough comprehension of the effects that the different atmospheric phenomena can have on the propagation of these acoustic waves. This paper deals with one of these phenomena, atmospheric refraction, and its influence on the performance of an ultrasonic system whose signals are detected by matched filtering. [Copyright &y& Elsevier]

The article presents a study on the transition of the simplest molecular dynamic model of a polymer crystal, polyethylene, to the high-temperature quasi-hexagonal phase. In the study, the researchers considered the mechanism of thermally induced orientational disordering in a polymer crystal consisting of flexible chains with the simplest model. They found that before transition, molecules have regions of rotations through 180 degrees although the orientation of their planes is retained.

This work presents the development and implementation of a Local Positioning System (LPS) based on the transmission of ultrasonic signals, proposed for indoor positioning of mobile robots. The LPS consists of several ultrasonic beacons located in the environment, all of them emitting periodically and simultaneously. A portable receiver collects all the transmissions and autonomously computes its position. Neither infrared nor radiofrequency are required for synchronization in the localization process, compared to other related works. Direct Sequence Code Division Multiple Access (DS-CDMA) techniques are used to allow simultaneous emission from several beacons; each one transmitting a different 255-bit Kasami code. The portable receiver can detect the time of arrival for the different signals coming from the beacons, by carrying out all the correlations with the emitted codes. Absolute position of the receiver is determined by hyperbolic trilateration, using the Differences in Times-of-Arrival (DTOA) between a reference beacon and the other ones. The main advantage of this proposal is to permit the coexistence of an unlimited number of portable receivers, what is useful in applications like multirobot cooperation. [Copyright &y& Elsevier]

In this paper we present a new method to guide mobile robots. An eye-control device based on electro-oculography (EOG) is designed to develop a system for assisted mobility. Control is made by means eye movements detected using electro-oculographic potential. Using an inverse eye model the saccadic eye movements can be detected and know where the user is looking. This control technique can be useful in multiple applications, but in this work it is used to guide a wheelchair for helping people with severe disabilities. The system consists of a standard electric wheelchair, an on-board computer, sensors and a graphical user interface. Finally, we comment on some experimental results and conclusions about electrooculographic guidance using ocular commands. [ABSTRACT FROM AUTHOR]