Reappraisal of loading rate effects on sand behavior in view of seismic design for pile foundation

This study re-visits the effects of loading rate on sand behavior in view of seismic design of pile foundation. Based on an extensive literature review covering both element testing and model testing, the paper summarizes the current understanding of the loading rate effects. The paper then describes the development of test apparatus used in this study and presents the data obtained from a series of monotonically increasing triaxial compression tests on Toyoura sand, varying the strain rate in the range of 0.005%/s to 250%/s. A total of 36 tests were conducted on dry and saturated sand, both under drained and undrained conditions with two confining pressures. The experimental results confirm that the soil strength and the soil stiffness increase as the strain rate increase. This paper also concludes that the internal friction angle and deformation modulus increase when the strain rate is high. The implications of the loading rate effect on pile foundation design are then presented.     

Nanostructured poly(3-hexylthiophene-2,5-diyl) films with tunable dimensions through self-assembly with polystyrene

Poly(3-hexylthiophene-2,5-diyl) is among the most widely used conjugated polymers for opto-electronic applications. To enhance its properties, researchers have attempted to nanostructure this polymer using various processes including breath figure arrays, nanolithography and elaborated organic synthesis. We here demonstrate a simple process to nanostructure the conjugated polymer using self-assembly with polystyrene and selective removal of one of the phases. The influence of the molecular weight of each polymer on the thin film morphology was systematically studied by atomic force microscopy. Using this approach, we observe two types of nanostructure, namely, nanoporous and nanoisland structures, of which the dimensions can be tuned by modifying the molecular weight of each polymer in the blend. This simple process introduces a cost-effective alternative to produce thin films of conjugated polymer with average nano-features from 100 nm up to 500 nm which could be used in a wide range of applications.     

Enhancement in thermoelectric power factor of M/T/N and M/Bi/M/Bi/M (M and N = Cu or Ni) composite devices welded with T = Bi or Bi<Subscript>0.88</Subscript>Sb<Subscript>0.12</Subscript> alloy

The resultant thermoelectric power factors P of M/T/N and M/Bi/M/Bi/M (M and N = Cu or Ni) devices welded with T = Bi or Bi_0.88Sb_0.12 alloy were measured at 298 K and compared with P values calculated as a function of x by treating these devices as an electrical and thermal circuit, where x is the ratio of thickness of Bi or Bi-Sb alloy to the interval between two thermocouples. Consequently, the Seebeck coefficients of M/T/N devices were enhanced significantly in the middle range from x = 0.3 to 0.8, and the observed P values have a local maximum at small x below x = 0.35. The x-dependence of P values of M/T/N devices was found to be explained well by the simple model proposed here when an enhancement factor in and some reduction in thermal conductivity of pure metal were taken into the calculation. As a whole, however, the observed P values of double-layered M/Bi/M/Bi/M devices are lower than those of single-layered M/Bi/M, so that the macroscopic multi-layering of thermoelectric materials has no effect on the enhancement in P. The maximum P (= 22.1 mW/K²m) of Cu/Bi-Sb/Cu is 1.5 times larger than that of Cu/Bi/Cu and reached 3.6 times as large as the mean value of 5.7 and 6.6 mW/K²m of the high-performance bulk p- and n-type bismuth-telluride compounds.     

SIR Weighting Combining Diversity Using Matched Filter for Personal Communication Systems

We propose a novel SIR weighting postdetection combining diversity scheme with a new accurate SIR estimation method. The SIR is estimated and used as the weighting factor to compensate severe cochannel interference, one of the most important issues for PCS in terms of frequency utilization. Theimprovement offered by the proposal depends on SIR estimation accuracy.The SIR is, in this paper, estimated by a matched filter where theauto-correlation between received signal and unique word is calculated. Computer simulationsconfirm that the SIR of each diversity branch can be estimated easily andaccuratelyby the proposed SIR estimation method. The proposed diversity scheme achievesaperformance very close to that of ideal SINR weighting diversity underRayleighfading with severe cochannel interference. When average SIR = 10 dB and thenumber of branches(L)=4, the proposed diversity scheme lowers the requiredE_b/N₀ by 5 dB at BER = 1×10^-3compared to conventional maximal ratio combining diversity. This paper alsopresentsthe unique word length required to realize adequate performance, i.e.,robustnessagainst high-pitch Rayleigh fading.     

Deposition of BaTiO3 thin films by plasma MOCVD

Barium titanium trioxide (BaTiO₃) thin films were deposited on fused silica or silicon wafer substrate from barium dipivaloylmethanate (II) (Ba(dpm)₂) and titanium tetraisopropoxide (IV) (TTIP) used as precursors in an oxygen microwave plasma. The substrates were dielectrically heated and the substrate temperatures were around 900 K during the film deposition. The deposition was performed for 15 min and the deposits were identified as BaTiO₃ by means of X-ray diffraction, X-ray photoelectron spectroscopy, infrared spectroscopy, and ellipsometry. Oxygen and barium atoms and TiO and CO molecules were identified in the plasma. These species would produce higher deposition rates at lower substrate temperatures than those did in the usual thermal metalorganic chemical vapor deposition (MOCVD). The dielectric constant of the BaTiO₃ thin film that was directly deposited on the silicon wafer substrate was as low as 10¹ order of magnitude. Because the deposit reacted with the substrate and an interdiffusional layer was formed, the platinum layer was coated on the silicon wafer substrate in order to prevent the formation of an interdiffusional layer. The dielectric constant then increased to 10³ order of magnitude.     

Pulsed NMR study in nuclear ordered solid3He

The nuclear spin dynamics in nuclear spin ordered solid³He in low magnetic fields on the melting curve has been studied by pulsed NMR down to 0.6 mK. The free induction decay signals (FID) were measured in single crystals of solid³He at three operating frequencies of 920, 1380, and 1840 kHz. The FIDs were nonexponential and dependent on the rf pulse strength _p H ₁ t _w , where is the gyromagnetic ratio,H ₁ is the rf field strength, andt _w is the pulse width. At small _p they decayed almost linearly in time with a small exponential tail at the end. When _p was further increased they became shorter and neither exponential nor linear in time. At large _p they decayed very rapidly and sometimes could not be observed at all because of the dead time of the NMR detection system. Such behavior of the FID was observed in many different single crystals in the given temperature range at 920 kHz. Tsubota and Tsuneto have shown by solving the nonlinear equations of motion numerically that the motion of the nuclear spin becomes chaotic when the tipping angle exceeds a critical value. Comparing their result with our experimental results, we concluded that some of the results of the rapid decay of the FID at large _p might be attributed to the onset of the chaotic motion. At 1840 kHz it is expected that the nonlinear effects in the equations of motion become less effective than that at 920 kHz. In fact, at this operating frequency the FIDs even at large _p and the tipping angle-dependent frequency shift could be observed. These frequency shifts were in rather good agreement with Namaizawa's theory provided an effective tipping angle was taken into account.     

Size of plastic region owing to blunting of the precrack tip andJ lc value in several types of structural steels

In this study, a three-point bendJ _lc fracture-toughness test was carried out using four types of structural steels at room temperature. The values of (γ _p)V, which represent the width of the region where the voids are located just ahead of the crack tip, were measured by Beacham's method [9] with the help of a scanning electron microscope (SEM). The experimental (γ _p) values and the theoretical values obtained using the finite element method (FEM) or calculated fromK at initiation are in good agreement. It was found that there is a certain linear relationship between (γ _p)Vand the stretched zone width (SZW), and an experimental relationship betweenJ _lc andσ _flow·(γ _p)V which may be expressed by the following equation: $$J_{lc} = 44.1 + 0.35\sigma _{{\text{flow}}} \cdot (\gamma _{\text{p}} )V_c KJ$$ whereσ _flow is the average value of the yield stress and the ultimate tensile strength. (γ _p)V _c represents the critical value of (γ _p)V. The numerical constant 44.1 kJ m^?2 is considered to be aJ _lc value for brittle fracture of the material tested, according to the authors' previous results. It is possible to calculateJ _lc if (γ _p)V _c can be measured.     

Monte Carlo simulations of spectral albedo for artificial snowpacks composed of spherical and nonspherical particles

The optical properties of snowpacks composed of spherical and nonspherical particles artificially prepared in a cold laboratory are investigated by measuring spectral albedos. The measured spectral albedo in the spectral region lambda=0.35-2.5 microm is compared with the theoretically calculated albedo, for which a Monte Carlo radiative transfer model is employed for multiple scattering combined with the Mie theory and the ray-tracing technique for single scattering by snow particles. Since the spherical particles are a little aggregate, the effects of a cluster of the spheres on snow albedo are examined using a generalized multiparticle Mie-solution model [Appl. Opt. 34, 4573 (1995); J. Quant. Spectrosc. Radiat. Transf. 79-80, 1121 (2003)]. The snow albedo of a cluster of the spheres can be represented with that of the singe sphere slightly larger than its component of the cluster in case of small grains. The observed albedos for the spherical snow particles agree with the theoretically calculated ones for the snow grain size measured in the snow pit work. The snow albedos for the nonspherical particles, which were dendrites, are influenced by the branch width and the branch length, based on a comparison of the theoretically calculated albedo by using circular cylindrical snow particles and the observed albedo. The snow albedo in the near-infrared region depends on the branch width only when the branch length is sufficiently greater than the branch width. The comparison between the spherical and nonspherical snow particles indicates that the spectral albedo of the nonspherical particles can be represented by using an equal volume-area ratio sphere.     

Relation between microstructure, properties and spark plasma sintering (SPS) parameters of pure ultrafine WC powder

A combined experimental/numerical methodology is developed to fully consolidate pure ultrafine WC powder under a current-control mode. Three applied currents, 1900, 2100 and 2700 A, and a constant pressure of 20 MPa were employed as process conditions. The developed spark plasma sintering (SPS) finite-element model includes a moving-mesh technique to account for the contact resistance change due to sintering shrinkage and punch sliding. The effects of the heating rate on the microstructure and hardness were investigated in detail along the sample radius from both experimental and modeling points of view. The maximum hardness (2700 HV10) was achieved for a current of 1900 A at the core sample, while the maximum densification was achieved for 2100 and 2700 A. A direct relationship between the compact microstructure and both the sintering temperature and the heating rate was established.