Dimensional Behavior Research Articles

Elaboration, by tape casting, and thermal characterization of a solid oxide fuel half-cell for low temperature applications

In the past years, a major interest has been devoted to decrease the working temperature of solid oxide fuel cell (SOFC) down to about 700 °C. In this respect, materials with a high ionic conduction at intermediate temperature have to be found and the processes to elaborate fuel cells, using these new materials, have to be developed. Apatite materials (La 10− x Sr x (SiO 4) 6O 2± δ ) are attractive candidates for solid electrolyte working at intermediate temperature. The ceramic powder was produced by solid state reaction and was tape cast to obtain green sheets. Concerning the cathode, a perovskite oxide (La 1− x Sr x Mn 1− y Co yO 3− δ ) has been chosen. The perovskite powder was also shaped by tape casting with the introduction of a pore forming agent (corn-starch) to obtain the required porosity in the sintered cathode. The co-firing of the electrolyte/cathode half-cell in air at 1400 °C–2 h gives a flat sample with a dense apatite (98.2%), a 42.7% porous cathode and neither delamination nor chemical reactivity between electrolyte and cathode materials. The dimensional behaviour of the electrolyte material is stable for an oxygen partial pressure ranging from 10 −10 to 0.21 atmosphere, from room temperature to 700 °C. The thermal expansion coefficients of the electrolyte and cathode materials are rather close (Δ α = 2.8 × 10 −6 K −1) under air.

Compressibility of Changi sand in K0consolidation

The one-dimensional compressibility of sand is an important property for the estimation of settlement or deformation of sand deposits. The <TEX>$K_0$</TEX> value of sand is also an important design parameter. Experimental results are presented in this paper to study the compressibility of sand in <TEX>$K_0$</TEX> consolidation tests. The <TEX>$K_0$</TEX> consolidation tests were carried out using a triaxial cell and a plane-strain apparatus. Specimens prepared using both the moist tamping and the water sedimentation methods were tested. The testing data demonstrate that the type of testing apparatus does not affect the <TEX>$K_0$</TEX> measurement if proper boundary conditions are imposed in the tests. The data also show that the compressibility and the <TEX>$K_0$</TEX> value of loose sand specimens prepared using the moist tamping method are very sensitive to the variation of void ratio. The <TEX>$K_0$</TEX> values measured from these tests do not agree with the <TEX>$K_0$</TEX> values calculated from Jaky's equation. The compressibility and <TEX>$K_0$</TEX> values of sand obtained from tests on specimens prepared using different preparation methods are different which may reflect the influence of soil fabrics or structures on the one dimensional compression behavior of sand.

Two dimensional versus one dimensional behavior for biased diffusion and aggregation in a network of channels

We present an extension to two dimensions of a one-dimensional model for a fluid that drags particles in a narrow channel [V. Ruiz Barlett, M. Hoyuelos, H.O. Mártin, Physica A 387 (2008) 4623–4629]. We consider a network of narrow channels on a strip. There is a flux rate J of particles that enter in the left end of the system; particles move to the right, up or down with a jumping rate P . When two particles collide, they produce a cluster that remains immobile because the size of the cluster is greater than the channel diameter. After some time, the accumulation of clusters plugs the system up. We analyze the clogging time against J / P with results obtained from numerical simulations and from a continuous description with approximate differential equations. A transition from a 2D to a 1D behaviour is observed for J / P ≪ 1 . The transition point depends on the value of the number of longitudinal channels in the network, w . For J / P ≫ 1 , we demonstrate analytically, and confirm numerically, that the clogging time behaves as ln w .

Redox stability of SOFC: Thermal analysis of Ni–YSZ composites

A re-oxidation of a Ni-based SOFC can seriously damage the cells. Important aspects of this thermomechanical instability are reduction–oxidation kinetics and the dimensional behaviour of the Ni–YSZ composites. These were investigated in the temperature range of 600–1000 °C and different combinations of reduction and oxidation temperatures. Automated temperature and gas change programmes were implemented in thermogravimetry and identically repeated using a high precision dilatometer to show the dimensional behaviour of the cermets simultaneously with the Degree of Oxidation (DoO) as a function of time during redox cycling. The activation energy for reduction was 84.4 kJ/mol and the kinetics was largely linear. Different kinetic models were fitted to the reduction data; the best agreement was found using the Avrami equation. On the re-oxidation, initially linear kinetics was observed, followed by a period of parabolic kinetics slowing down to logarithmic towards full DoO. The shifts in the kinetic shape with time depended on the temperature and DoO. The rate constants for oxidation were fitted to the data. The BET surface area of the cermets after different reduction and oxidation treatments was measured and show decrease of surface area with increasing reduction temperature and no significant differences in the surface area depending on the re-oxidation temperature in the range of 600–1000 °C.

Thermoelectric properties and electronic structure calculations of low thermal conductivity Zintl phase series M 16X 11 (M = Ca and Yb; X = Sb and Bi)

Zintl phases of type M 16X 11 (M = Ca and Yb; X = Sb and Bi) have been synthesized by both the flux or solid state reaction methods. In order to evaluate the potential of these phases for thermoelectrics, the electrical resistivity ( ρ), thermopower ( α) and thermal conductivity ( κ) have been measured on hot pressed samples over a wide temperature range of 10–1000 K. The ρ and α trends are typical of a degenerate semiconductor. However, α remains low (∼30 μV/K or less). Hall measurements indicate a rather low charge carrier mobility ∼3–7 cm 2/V s, except for Ca 16Sb 11. It is notable that low thermal conductivity values ranging from ∼2.5 to 0.8 W/m K are measured for these phases at higher temperatures up to 1273 K. Particularly for Yb 16Sb 11, the lattice part of thermal conductivity is found to be between 0.5 and 0.7 W/m K. However, the challenge in this M 16X 11 system is to achieve high thermopower. In order to understand more fully the measured transport properties, band structure calculations have been performed. Consistent with experimental data, these calculations suggest that all the systems are indeed metallic. The electronic structures for Ca-based phases show one dimensional metallic behavior with small and almost symmetric density of states around the Fermi level.

Engineering thermoresponsive polymeric nanoshells

This study describes a family of hollow nanoscale constructs able to display a large and reversible change in size, within a narrow temperature interval. These thermoresponsive nanostructures are generated by crosslinking functionalized amphiphilic molecules, such as poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblocks, while constrained to their particular micellar configuration. This contribution focuses on the generation of these supramolecular architectures, by intra-micellarly crosslinking PEO–PPO–PEO dimethacrylate amphiphiles, and investigates their temperature-dependent dimensional behavior. Spherical nanoshells displaying a 200 nm diameter at 15 °C, shrink sharply around 28 °C, generating a compact structure of approximately 40 nm at body temperature. Thermoresponsive nanotubes were created by generating them from rod-like micelles at higher temperatures. By varying the composition of the triblock, the transition temperature can be fine tuned, from around 25 °C to slightly above body temperature. Also, the nanoshells were rendered biodegradable by incorporating aliphatic oligoesters into their structure. Numerous applications for these nanostructures are foreseen in various biomedical areas, such as in drug and gene delivery, in the tissue engineering and in the biosensors field.

Low dimensional description of pedestrian-induced oscillation of the Millennium Bridge

When it opened to pedestrian traffic in the year 2000, London’s Millennium Bridge exhibited an unwanted, large side-to-side oscillation, which was apparently due to a resonance between the stepping frequency of walkers and one of the bridge modes. Models for this event, and similar events on other bridges, have been proposed. The model most directly addressing the synchronization mechanism of individual walkers and the resulting global response of the bridge-pedestrian system is the one developed by Eckhardt et al. [Phys. Rev. E 75, 021110 (2007)]. This model treats individual walkers with a phase oscillator description and is inherently high dimensional with system dimensionality (N+2), where N is the number of walkers. In the present work we use a method proposed by Ott and Antonsen [Chaos 18, 037113 (2008)] to reduce the model of Eckhardt et al. to a low dimensional dynamical system, and we employ this reduced description to study the global dynamics of the bridge/pedestrian interaction. More generally, this treatment serves as an interesting example of the possibility of low dimensional macroscopic behavior in large systems of coupled oscillators.

Dimensional Behavior of Ni–YSZ Composites during Redox Cycling

The dimensional behavior of Ni–yttria-stabilized zirconia (YSZ) cermets during redox cycling was tested in dilatometry within the temperature range . The effect of humidity on redox stability was investigated at intermediate and low temperatures. We show that both the sintering of nickel depending on temperature of the initial reduction and the operating conditions, and the temperature of reoxidation are very important for the size of the dimensional change. Cumulative redox strain (CRS) is shown to be correlated with temperature. Measured maximum CRS after three redox cycles varies within 0.25–3.2% dL/L in dry gas and respective temperature range of . A high degree of redox reversibility was reached at low temperature, however, reversibility is lost at elevated temperatures. We found that at , 6% steam and a very high ratio is detrimental for redox stability, whereas at no negative effect was observed. Pre-reduction at 1100 instead of more than doubled redox strain on reoxidation at . For samples similarly pre-reduced at , lowering the reoxidation temperature from or below reduces the redox strain to less than half.

A modified particle swarm optimization via particle visual modeling analysis

A particle is treated as a whole individual in all researches on particle swarm optimization (PSO) currently, these are not concerned with the information of every particle’s dimensional vector. A visual modeling method describing particle’s dimensional vector behavior is presented in this paper. Based on the analysis of visual modeling, the reason for premature convergence and diversity loss in PSO is explained, and a new modified algorithm is proposed to ensure the rational flight of every particle’s dimensional component. Meanwhile, two parameters of particle-distribution-degree and particle-dimension-distance are introduced into the proposed algorithm in order to avoid premature convergence. Simulation results of the new PSO algorithm show that it has a better ability of finding the global optimum, and still keeps a rapid convergence as with the standard PSO.

The effect of weave type on dimensional stability of woven fabrics

PurposeTesting the effect of machine washing and drying on dimensional stability produces information about the fabric types that satisfy consumers during end use. At present, it is a known fact that the weave patterns affect the dimensional stability property of woven fabrics. But the essential requirement is to determine the magnitude of this effect for weave types and establish the proper weave types for end use in definite tolerances. The purpose of this paper is to investigate the dimensional stability properties of 100 percent cotton woven fabrics as a function of weave type.Design/methodology/approachIn total, 12 woven fabrics with different weave derivatives are woven with 100 percent cotton and Ne 30/1 combed ring spun yarn for this investigation. These samples are then washed and dried according to domestic washing and drying standard test procedures. The shrinkage values are measured and then expressed as a percentage of the initial dimensions.FindingsIt was observed that weave pattern has a significant effect on the dimensional behavior of woven fabrics. Weave patterns with a high number of interlacings have lower shrinkage values. At the same time, lower yarn crimp values restricted the fabric shrinkage and resulted in better dimensional stability. According to one way ANOVA results, the effect of weave type on dimensional stability is found to be significant (p&lt;0.01). In addition to these, Pearson correlation analysis showed that there is an important, positive and fair relationship between the number of washing cycles and total shrinkage.Research limitations/implicationsThe study covers 100 percent cotton woven fabrics with one type of warp and weft sett. The only finishing treatment applied to the sample fabrics was desizing. No dyeing was carried out.Originality/valueUnderstanding the magnitude of the effect of weave type on dimensional stability of cotton woven fabrics produces more knowledge about products which satisfy the customers with respect to dimensional stability during usage.

Three dimensional simulation of a DC free burning arc. Application to lightning physics

One of the mechanisms assumed to be involved in the ignition channel cut off is associated with the development of instability. Like any other electric arc, lightning channels become unstable if the provided power is insufficient. In order to study this phenomenon, ONERA in collaboration with EDF has performed 3D simulations of a part of a lightning channel in order to compute the main characteristics of the arc and understand in the future the physical conditions for the ignition of instability. The model, based on the resistive magneto hydro dynamic equations, was adapted to the lightning channel context. In a first step, the results were compared to the experiment of Tanaka et al. [Tanaka, S., Sunabe, K., and Goda, Y., 2000. Three dimensional behaviour analysis of D.C. free arc column by image processing technique, XIII Int'l Conf on Gas Discharges and their applications, Glasgow.] on long electric arcs subjected to continuing current at mean sea level. A good agreement between computations and measurements was found for times greater than tens of millisecond. Results also showed that the internal resistance continuously decreases with time. Finally, this model was adapted to investigate the effects of altitude on the characteristics of the arc column. Results showed that the effects of altitudes are negligible for altitudes lower than 4 km.

Transverse laser-induced thermoelectric voltages in tilted La2−xSrxCuO4 thin films

The transverse laser-induced thermoelectric voltages in the tilted La2−xSrxCuO4 (LSCO) thin films are observed for the first time. The detected signals are demonstrated to originate from the anisotropy of thermoelectric power and depend on the Sr-doping level drastically. The largest voltage is observed in the LSCO films at x=0.15 under the irradiation of different lasers with the wavelength in the spectrum range from infrared to ultraviolet. The dependence of the signals on Sr-doping content is associated with a two dimensional charge transport behavior in LSCO films near the optimum doping content.

Low dimensional behavior of large systems of globally coupled oscillators

It is shown that, in the infinite size limit, certain systems of globally coupled phase oscillators display low dimensional dynamics. In particular, we derive an explicit finite set of nonlinear ordinary differential equations for the macroscopic evolution of the systems considered. For example, an exact, closed form solution for the nonlinear time evolution of the Kuramoto problem with a Lorentzian oscillator frequency distribution function is obtained. Low dimensional behavior is also demonstrated for several prototypical extensions of the Kuramoto model, and time-delayed coupling is also considered.

DIMENSIONAL TRANSITIONS OF DENSITY OF STATES AND HEAT CAPACITY IN SPHERICAL QUANTUM DOTS

We evaluate analytically and numerically the density of states (DOS) and the heat capacity in a spherical quantum dot formed by a spherical thin barrier. The control of the spherical barrier thickness or the potential barrier height is found to cause the dimensional transition from the three-dimensional (3D) behavior to the quasi-zero dimensional (Q0D) behavior in the DOS and the heat capacity. When the barrier is thick enough, the DOS shows the Q0D-like behavior but when the barrier is thin enough to allow electrons to tunnel through it, the temperature dependence of the heat capacity exhibits quite a distinct behavior depending on the electron density. Explicit numerical plots are given in the low density regime.

The effect of bonding layer properties on the dynamic behaviour of surface-bonded piezoelectric sensors

The dynamic behaviour of piezoelectric sensors depends on the bonding condition along the interface between the sensors and the host structure. This paper provides a comprehensive theoretical study of the effect of the bonding layer on the coupled electromechanical characteristics of a piezoelectric sensor bonded to an elastic substrate, which is subjected to a high frequency elastic wave. A sensor model with a viscoelastic bonding layer, which undergoes a shear deformation, is proposed to simulate the two dimensional electromechanical behaviour of the integrated system. Analytical solution of the problem is provided by using Fourier transform and solving the resulting integral equations in terms of the interfacial stress. Numerical simulation is conducted to study the effect of the bonding layer upon the dynamic response of the sensor under different loading frequencies. The results indicate that the modulus and the thickness of the bonding layer have significant effects on sensor response, but the viscosity of the bonding layer is relatively less important.

Low dimensional behavior in three-dimensional coupled map lattices

The analysis of one-, two-, and three-dimensional coupled map lattices is here developed under a statistical and dynamical perspective. We show that the three-dimensional CML exhibits low dimensional behavior with long range correlation and the power spectrum follows 1 / f noise. This approach leads to an integrated understanding of the most important properties of these universal models of spatiotemporal chaos. We perform a complete time series analysis of the model and investigate the dependence of the signal properties by change of dimension.

NONLINEAR ANALYSIS OF ONE AND TWO DIMENSIONAL CONSOLIDATION PROBLEMS FOR UNBOUNDED SATURATED SOIL MEDIA

Soil in general is not a linear material, in which the relation between stress and strain is more complicated than the simple, linearly elastic relation. To make accurate deformation analysis of clay deposits, the incremental Biot's theory of consolidation is used together with elasto-viscoplastic constitutive relations based on the critical state concept using the modified Cam-clay model. One and two dimensional consolidation problems were analyzed numerically by the infinite-finite elements. Results show that the proposed method can describe the effect of sample thickness on consolidation phenomena. Also the two dimensional behavior of a clay foundation during the construction of embankment was analyzed.

Evaluation of post-curing and laser manufacturing parameters on the properties of SOMOS 7110 photosensitive resin used in stereolithography

The degree of cure of parts produced by stereolithography (SL) depends on laser power, manufacturing parameters, resin photosensitivity characteristics, and so on. Usually parts require a post-cure process, such as ultraviolet radiation and/or thermal treatment to improve their degree of cure, and thermal, mechanical and chemical properties. In this study, we evaluated the influence of line hatch spacing, an important manufacturing parameter, in relation to the calorimetric, dilatometric and hardness behavior of SL parts. The post-cure processes of ultraviolet radiation, microwave irradiation and conventional heating were also investigated. A higher degree of cure in green specimens was obtained with a line hatch spacing of 0.05 mm. However, the utilization of line hatch spacings of 0.15 and 0.10 mm induced an inhomogeneous curing process in relation to the internal and surface specimen structure, and remarkable cure shrinkage. The post-cure processes, especially the thermal treatment, improved the degree of cure of green specimens built using line hatch spacing of 0.10 mm, minimizing the anisotropy inherent to this rapid manufacturing method, which permits a better control over the dimensional behavior of SOMOS 7110 parts.

Experimental studies of the kinematics of the stable and unstable human knee joint

In an experimental study the three dimensional kinematic behaviour of fourty knee joint specimen was investigated. We found a continous passive tibial rotation during flexion, so the terminus "screw home mechanism" should no longer be used. There was also an automatic adduction and medialisation movement of the tibia. We calculated the roll-gliding ratio separately for the medial and the lateral side. Only the lateral femoral condyle displayed increasing gliding with pure rolling near extension and pure gliding near flexion. We found little differences concerning qualitative characteristics but not in the amount of passive motions.

Ba2F2Fe2+0.5Fe3+S3: A Two-Dimensional Inhomogeneous Mixed Valence Iron Compound

The structure of the new mixed valence compound Ba2F2Fe1.5S3 was solved by means of single crystal X-ray analysis. It crystallizes in an orthorhombic cell, in the Pnma space group with the cell parameters a = 12.528(3) A, b = 18.852(4) A, and c = 6.0896(12) A. The structure is formed by the alternated stacking of fluorite type [Ba2F2]2+ blocks and the newly discovered [Fe1.5S3]2- blocks. This [Fe1.5S3]2- block exhibits a mixed valence of iron with Fe(+II) located in octahedrons and Fe(+III) in tetrahedrons. Preliminary susceptibility measurements suggest a low dimensional antiferromagnetic behavior.