Fast Pressure Quenches Near the λ- Line in 4He

The formation of topological defects during phase transitions was first discussed by Kibble¹ within a cosmological context. The idea was further developed by Zurek² for condensed matter systems, such as the λ-transition in ⁴He. The vortex density generated during a pressure quench through the transition is expected to be controlled by the quench rate, and can be determined from the attenuation of a second sound pulse. In previous experiments³ using mechanical means to generate the quench no vortex formation was observed. We increased the quench rate by four orders of magnitude using a hemispherical ugtrasonic transducer. No attenuation of second sound was observed, except for ambient conditions close to the λ-line and quench depth sufficient to also create cavitation.     

Characterization of unidirectional carbon fibre reinforced plastic laminates

The purpose of the present paper is to outline a set of recommended tests in order to characterize the behavior of carbon fibre reinforced plastic laminates. The tests outlined in this contribution are classification of visual defects, dimension and density, fibre and resin content, tensible strength, apparent interlaminar shear strength, in-plane shear modulus, dynamic torsion property, static bending property, dynamic bending property, and thermal expansion coefficient. As a selected example, results of two tensile tests on CFRP laminates are reported.     

Host (nanocavity of zeolite-Y)/guest (Mn(II), Co(II), Ni(II) and Cu(II) complexes of pentadendate Schiff-base ligand) nanocomposite materials (HGNM): application in the heterogeneous oxidation of cyclohexene

Transition metal (M = Mn(II), Co(II), Ni(II) and Cu(II)) complexes with pentadendate Schiff-base ligand; N,N′-bis(salicylidene)-2,6-pyridinediaminato, H₂ [sal-2,6-py]; was entrapped in the nanocavity of zeolite-Y by a two-step process in the liquid phase: (i) adsorption of bis(salicylaldiminato)metal(II); [M(sal)₂]-NaY; in the supercages of the zeolite, and (ii) in situ Schiff condensation of the metal(II) precursor complex with the corresponding 2,6-pyridinediamine; [M(sal-2,6-py)]-NaY. The new materials were characterised by several techniques: chemical analysis, spectroscopic methods (DRS, BET, FTIR and UV/Vis), conductometric and magnetic measurements. Analysis of the data indicates that the M(II) complexes are encapsulated in the nanodimensional pores of zeolite-Y and exhibit different from those of the free complexes, which can arise from distortions caused by steric effects due to the presence of sodium cations, or from interactions with the zeolite matrix. The Host–Guest Nanocomposite Materials (HGNM); [M(sal-2,6-py)]-NaY; catalyzes the oxidation of cyclohexene with tert-butylhydroperoxide (TBHP). Oxidation of cyclohexene with HGNM gave 2-cyclohexene-1-one, 2-cyclohexene-1-ol and 1-(tert-butylperoxy)-2-cyclohexene. [Mn(sal-2,6-py)]-NaY shows significantly higher catalytic activity than other catalysts.     

Accident and hazard prediction models for highway–rail grade crossings: a state-of-the-practice review for the USA

Railway Engineering Science - Highway–rail grade crossings (HRGCs) are one of the most dangerous segments of the transportation network. Every year numerous accidents are recorded at HRGCs...     

Three-dimensional geotechnical modeling of the soils in Riyadh city,KSA

A standard penetration test (SPT) was carried out for 700 samples from 143 boreholes in four districts in Riyadh city, Kingdom of Saudi Arabia (KSA). Rock quality designation (RQD) and unconfined compression strength (UCS) tests were also performed for 238 samples from 154 boreholes in 15 districts of the city. Three-dimensional (3D) models of the SPT, RQD, and UCS were produced using the Voxler 3 software package. Further, 333 soil samples collected from 106 boreholes in 11 districts were examined to spatially model the distinctive geotechnical patterns of the alluvial soils in two dimensions. Tests were carried out to determine the soil grain size distribution, natural water content (NWC%), Atterberg’s consistency limits [liquid limit (LL%), plastic limit (PL%), and plasticity index (PI%)], and soil–water chemical components (pH Cl⁻, SO₃²⁻, and CO₃⁻). Spatial maps of the geotechnical parameters were produced by applying the geostatistical ordinary kriging implemented in ArcGIS. Soil samples were classified according to the unified soil classification system (USCS), and a thickness of the silty clay layer was produced. Plasticity charts indicated that the soils are inorganic cohesive clays with low and moderate plasticity (CL). Soil strength parameters showed wide ranges of UCS (average 220, range 21.3–618 kg/cm²), SPT (average 39, 0–100 N), and RQD (average 44, 11–78%). UCS and SPT 3D models clarified a regional southeastward trend of increase. RQD 3D models showed poor to fair engineering quality of rocks (25–75%). The results presented here can help to establish geohazard zonation maps with construction favorability ratings for safe urban expansion.

     

Numerical simulation of two phase refrigerant flow through non-adiabatic capillary tubes using drift flux model

Journal of Mechanical Science and Technology - This research presents a drift flux model to simulate steady state refrigerant flow through horizontal lateral straight capillary tube-suction line...     

Dynamic cure kinetics of epoxy/TiO2/MWCNT hybrid nanocomposites

The effect of multi-walled carbon nanotubes (MWCNTs) on cure kinetic parameters of the epoxy/amine/TiO₂ (1 wt%) resin system was studied dynamically at four heating rates using DTA. The presence of MWCNT in various amounts (0.1, 0.2, 0.4 and 0.6 wt%) neither retarded nor accelerated the cure reaction of the epoxy/amine/TiO₂ system in a considerable extent. Addition of MWCNTs increased the extent of cure of the corresponding nanocomposites, especially at higher contents up to 0.4 wt% MWCNT filled composite. However, increasing the MWCNT content to 0.6 wt% adversely affected the extent of cure due to nanoparticle agglomeration. The fracture surface morphology of the nanocomposites revealed that the cracks deviated on reaching the MWCNTs, while propagating in the polymer matrix. Fractional extent of conversion (α) was calculated using genetic algorithm. Flynn–Wall–Ozawa and Kissinger methods were used to analyze the kinetic parameters. The presence of MWCNTs did not affect the autocatalytic cure mechanism of epoxy/amine/TiO₂ resin system and also did not cause any considerable barrier effect on the curing process. Activation energy data fitted well in the cubic polynomial regression equations and the changes of E _a with respect to α proved the autocatalytic cure mechanism, being followed by all the MWCNT-containing epoxy-based hybrid nanocomposites.     

Adaptive fuzzy controller for active tuned mass damper of a benchmark tall building subjected to seismic and wind loads

Active tuned mass dampers (ATMDs) are one of the most effective solutions for mitigation of destructive effects of earthquakes and strong winds in tall buildings. In order to achieve optimal performance, these systems are designed and tuned to mitigate effect of either wind or earthquake excitation. However, due to different frequency contents and intensities of wind and earthquake excitations, which will cause contrasting structural modes stimulation, the ATMD designed for one of these disturbances may not work optimally for the other one. This paper addresses a methodological simulation approach for adaptive control design of ATMDs in tall buildings located in regions with high level of seismic activity and recurrent strong winds. For this purpose, a multi‐objective adaptive genetic‐fuzzy controller is proposed for the control of an ATMD of a benchmark 76‐story building subjected to wind load and earthquake disturbances. Simulation results reveal that the optimal ATMD designed for earthquake disturbance does not work adequately for wind load disturbance and vice versa. Furthermore, the proposed adaptive controller has superior performance in suppressing base shear and inter‐story drifts induced by wind load and earthquake excitations. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis of Volcano‐Like CdS/Organic Nanocomposite

Cadmium sulfide/organic nanocomposites, which were based on long nanowires, were synthesized by a simple reaction between cadmium nitrate and thioglycolic acid (TGA) at room temperature. The products were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected‐area electron diffraction (SAED), Fourier transform infrared (FTIR) spectra, and thermogravimetric analysis (TG). The CdS/organic nanocomposites was decomposed into pure wurtzite CdS nanorods through hydrothermal treatment at 190°C. Photoluminescence (PL) spectra were used to study the optical properties of CdS/organic composite and pure CdS. It is found that the emission maximum of the CdS/TGA nanocomposite is significantly blue‐shifted, and the intensity is highly enhanced as compared to the luminescence spectrum of the bare CdS nanorods.