bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical and optical studies of gap states in self-assembled molecular aggregates
Authors: Burtman V. , Hukic G. , Ndobe A. S. , Drori T. , Vardeny Z. V.
Published: March 2007

We fabricated a variety of two-terminal devices using self-assembled monolayers (SAM) of solid-state mixtures comprised of molecular “wires” [1,4-methane-benzenedithiol (Me-BDT)] and molecular insulator “spacers” [1-pentanethiol], which were prepared at various molar concentrations ratio, r of wires/spacers, and sandwiched between two gold electrodes. The devices’ electrical transport was investigated at several r values using the bias voltage (V) dependencies of the conductance and differential conductance at various temperatures. In parallel, we also studied the UV-visible absorption and photoluminescence (PL) emission spectra of the SAM mixtures grown on silica transparent substrates. For r>10−3 we found that two-dimensional (2D) Me-BDT aggregates are formed in the SAM films leading to novel properties compared to SAM films of isolated Me-BDT molecules at concentrations 10−8< r<10−4, which we studied before [V. Burtman, A. S. Ndobe, and Z. V. Vardeny, J. Appl. Phys. 98, 034314 (2005)]. First, an Ohmic response in the current-voltage (I-V) characteristics is obtained up to V∼0.5 V, which results in a new band in the differential conductance spectrum around V=0. Second, a new subgap absorption band is formed at ∼2.4 eV, which is related to a new yellow/red PL emission band. The novel optical and electrical properties of the 2D Me-BDT aggregates are explained by the formation of an electronic continuum band in the Me-BDT energy gap, which is caused by weak in-plane charge delocalization among the molecules forming the aggregates. To verify this model we also studied SAM molecular aggregate diodes using Al electrodes. The 1-eV difference in the electrode work function between Au and Al metals results in a pronounced EF shift with respect to the aggregate-related continuum band in the gap, and consequently, dramatically changes the device I-V characteristics.
Interface microstructure engineering by high power impulse magnetron sputtering for the enhancement of adhesion
Authors: Ehiasarian A. P. , Wen J. G. , Petrov I.
Published: March 2007

An excellent adhesion of hard coatings to steel substrates is paramount in practically all application areas. Conventional methods utilize Ar glow etching or cathodic arc discharge pretreatments that have the disadvantage of producing weak interfaces or adding droplets, respectively. One tool for interface engineering is high power impulse magnetron sputtering (HIPIMS). HIPIMS is based on conventional sputtering with extremely high peak power densities reaching 3kWcm−2 at current densities of >2Acm−2. HIPIMS of Cr and Nb was used to prepare interfaces on 304 stainless steel and M2 high speed steel (HSS). During the pretreatment, the substrates were biased to Ubias=−600V and Ubias=−1000V in the environment of a HIPIMS of Cr and Nb plasma. The bombarding flux density reached peak values of 300mAcm−2 and consisted of highly ionized metal plasma containing a high proportion of Cr1+ and Nb1+. Pretreatments were also carried out with Ar glow discharge and filtered cathodic arc as comparison. The adhesion was evaluated for coatings consisting of a 0.3μm thick CrN base layer and a 4μm thick nanolayer stack of CrN∕NbN with a period of 3.4nm, hardness of HK0.025=3100, and residual stress of −1.8GPa. For HIPIMS of Cr pretreatment, the adhesion values on M2 HSS reached scratch test critical load values of LC=70N, thus comparing well to LC=51N for interfaces pretreated by arc discharge plasmas and to LC=25N for Ar etching. Cross sectional transmission electron microscopy studies revealed a clean interface and large areas of epitaxial growth in the case of HIPIMS pretreatment. The HIPIMS pretreatment promoted strong registry between the orientation of the coating and polycrystalline substrate grains due to the incorporation of metal ions and the preservation of crystallinity of the substrate. Evidence and conditions for the formation of cube-on-cube epitaxy and axiotaxy on steel and γ-TiAl substrates are presented.
Optimization of InGaAs(P) photovoltaic cells lattice matched to InP
Authors: Emziane M. , Nicholas R. J.
Published: March 2007

InP lattice-matched single-junction InGaAs(P) solar cells were simulated as a function of the doping concentrations and thicknesses of the active layers. Three band gaps of 0.74 eV (for InGaAs) and 1 and 1.2 eV (for InGaAsP) were considered and the behavior of the photovoltaic parameters of the corresponding devices was studied. It is shown that relatively thin structure layers having a doping concentration around 1017 cm−3 give the optimal device performance. The influence of various incident intensities and blackbody spectra was investigated and lead to an insight into the dependence of the device parameters on the illumination conditions. The dependence on the material band gap is also discussed.
Electrical characterization of superconducting single-photon detectors
Authors: Mattioli F. , Leoni R. , Gaggero A. , Castellano M. G. , Carelli P. , Marsili F. , Fiore A.
Published: March 2007

Superconducting meanders of NbN thin films have applications as single-photon detectors with high sensitivity in the infrared region. We report here a detailed analysis of the electrical characteristics of such meanders, by studying structures where each wire of the meander is separately contacted. The effect of heating on the superconducting-normal transition of adjacent stripes is evidenced. Moreover, the analysis of the switching current distribution of each wire highlights the high-critical current uniformity achieved by our meander process.
Deposition of epitaxial Ti2AlC thin films by pulsed cathodic arc
Authors: Rosén J. , Ryves L. , Persson P. O. Å. , Bilek M. M. M.
Published: March 2007

A multicathode high current pulsed cathodic arc has been used to deposit Ti2AlC thin films belonging to the group of nanolaminate ternary compounds of composition Mn+1AXn. The required stoichiometry was achieved by means of alternating plasma pulses from three independent cathodes. We present x-ray diffraction and transmission electron microscopy analysis showing that epitaxial single phase growth of Ti2AlC has been achieved at a substrate temperature of 900 °C. Our results demonstrate a powerful method for MAX phase synthesis, allowing for phase tuning within the Mn+1AXn system.
Improvement in the conversion efficiency of single-junction SiGe solar cells by intentional introduction of the compositional distribution
Authors: Tayanagi Misumi , Usami Noritaka , Pan Wugen , Ohdaira Keisuke , Fujiwara Kozo , Nose Yoshitaro , Nakajima Kazuo
Published: March 2007

We attempted to clarify the impact of the compositional distribution on recently reported improvement in the conversion efficiency of solar cells based on bulk multicrystalline SiGe. For this purpose, Si1−xGex/Si1−yGey multiple quantum well structures on heavily doped Si-on-insulator were employed as model crystals. The combination of x and y, the width of each layer, and the number of repetitions were systematically changed to study the influence of the introduction of Ge on photocarrier generation and carrier transport while keeping the average Ge composition as 0.03. Spatial modulation of the band structure leads to formation of quantum wells for holes and gives negative impact especially in the photocarrier collection from the n-type region. When the depth of wells was designed to be constant, short-circuit carrier density was found to show a maximum at appropriate compositional distribution due to the competition between the increase in the photocarrier generation and the decrease in the minority carrier diffusion length. Within a limited compositional range, the overall performance of the solar cell was revealed to be improved by the introduction of the compositional distribution compared with that based on uniform Si0.97Ge0.03. Therefore, intentional introduction of the compositional distribution is concluded to be useful for improvement in the solar cell performance if appropriate dispersion is chosen.
Calculating van der Waals-London dispersion spectra and Hamaker coefficients of carbon nanotubes in water fromab initiooptical properties
Authors: Rajter R. F. , French R. H. , Ching W. Y. , Carter W. C. , Chiang Y. M.
Published: March 2007

The van der Waals-London dispersion (vdW-Ld) spectra are calculated for the [9,3,m] metallic and [6,5,s] semiconducting single wall carbon nanotubes (SWCNTs), graphite, and graphene (a single carbon sheet of the graphite structure) using uniaxial optical properties determined from ab initio band structure calculations. The [9,3,m], exhibiting metallic optical properties in the axial direction versus semiconducting optical properties in the radial direction, highlights the strong anisotropic nature of metallic SWCNTs. Availability of both efficient ab initio local density band structure codes and sufficient computational power has allowed us to calculate the imaginary parts of the frequency dependent dielectric spectra, which are then easily converted to the required vdW-Ld spectra for Hamaker coefficient calculations. The resulting Hamaker coefficients, calculated from the Lifshitz quantum electrodynamic theory, show that neither graphite nor graphene are accurate model materials for estimating the Hamaker coefficients of SWCNTs. Additionally, Hamaker coefficients were calculated between pure radial-radial, radial-axial, and axial-axial components of both SWCNTs. Analysis of these coefficients reveals that the vdW-Ld interactions will depend on both chirality and the particular orientation between neighboring SWCNTs. The minimization of energy, with respect to orientation, predicts that vdW-Ld alignment forces will arise as a result of the anisotropic optical properties of SWCNTs.
Conductivity of AgI under high pressure
Authors: Hao Aimin , Gao Chunxiao , Li Ming , He Chunyuan , Huang Xiaowei , Zou Guangtian , Tian Yongjun , Ma Yanzhang
Published: March 2007

We carried out in situ conductivity measurements on silver iodide (AgI) under high pressure using a fabricated microcircuit on a diamond anvil cell (DAC). The result shows that the conductivity of AgI increases discontinuously by two orders of magnitude at 1.0 GPa, accompanying the transition from wurtzite/zinc-blende structure to AgI-III (NaCl structure). The conductivity gradually decreases with increasing pressure from 1.0 to 11 GPa, indicating the ionic conduction is impeded by the application of pressure. The conductivity changes very little with further pressure increase from 11 to 20 GPa, implying that the ionic conductivity decrease with pressure may be offset by the conductivity increase with pressure from the electronic process. Above 20 GPa, the conductivity starts to increase again, indicating that the electronic contribution becomes dominant. We calculated the ionic carrier concentration and the activation energy for ionic transport in AgI-III, and investigated the temperature and pressure dependence of conductivity above 20 GPa. Based on this experimental information, we predict that the metallization of AgI should occur at about 91 GPa.
Light emission and negative differential conductance of n-type nanoporous silicon with buried p-layer assistance
Authors: Lin Jia-Chuan , Tsai Wei-Chih , Chen Wei-Lun
Published: March 2007

The light-emission and current-voltage properties of n-type nanoporous silicon (n-NPS) with a hole assistance of buried p layer are explored. The influences of anodic current density on the formation, morphology, and properties of n-NPS are measured. Such n-NPS films have nanoscaled pores and high-aspect-ratio pillars. Since the anisotype junction is forward biased during the anodization process, many holes can drift straightupward from p layer and participate in the electrochemical reaction. At room temperature, high peak-to-valley current ratios of about 117.3 can be obtained in negative difference conductance region as well as strong visible light emissions are clearly observed under ultraviolet excitation.
Magnetic properties and tunneling magnetoresistance effect in Fe–CdFeS granular films
Authors: Liu K. W. , Zhang J. Y. , Shen D. Z. , Wu X. J. , Li B. H. , Li B. S. , Lu Y. M. , Fan X. W
Published: March 2007

Granular thin film samples composed of Fe clusters embedded in CdFeS were prepared with using low pressure metal organic chemical vapor deposition. Temperature dependence of the resistivity of the granular film follows well the relationship for the tunneling transport between the iron granules. A large negative magnetoresistance of about 2.2% at 0.1T was observed at room temperature due to the presence of Fe clusters. The hysteresis behavior observed in the magnetoresistance corresponded exactly to those of the hysteresis loop in the magnetization measurement, which evidently showed the correlation between the magnetoresistance and global magnetization in the sample.
Ultrafast nonlinear optical tuning of photonic crystal cavities
Authors: Fushman Ilya , Waks Edo , Englund Dirk , Stoltz Nick , Petroff Pierre , Vučković Jelena
Published: March 2007

The authors demonstrate fast (up to 20GHz), low-power (60fJ, 3ps pulses) modulation of photonic crystal cavities in GaAs containing InAs quantum dots. Rapid modulation through blueshifting of the cavity resonance is achieved via free-carrier injection by an above-band picosecond laser pulse. Slow tuning by several linewidths due to laser-induced heating is also demonstrated.
Giant magnetoimpedance: A label-free option for surface effect monitoring
Authors: Kurlyandskaya G. V. , Fal Miyar V. , Saad A. , Asua E. , Rodriguez J.
Published: March 2007

The change in magnetoimpedance (MI) during surface modification of the magnetic sensitive element caused by highly corrosive fluid was studied with the aim of creating a robust method to monitor the surface effects. A MI-based sensor prototype with an as-quenched FeCoSiB or FeCoCrSiB amorphous ribbon sensitive element was designed and calibrated for a frequency range of 0.5–10MHz at an intensity of the current of 10–60mA without bath for fluids. Measurements as a function of the exposure time were also made in a regime where chemical surface modification and sensing were not separated (in a bath for fluids). The MI variation was explained by the change of the surface magnetic anisotropy and the geometry of the sensitive element. A simple model was developed to describe MI change. It was shown that the magnetoimpedance effect can be employed as useful method to probe the electric features of surface-modified magnetic electrodes when the corrosive fluid, the material of the sensitive element, and the detection conditions are properly selected.
Heteroepitaxial growth and optical properties of ZnS nanowire arrays on CdS nanoribbons
Authors: Li Y. Q. , Tang J. X. , Wang H. , Zapien J. A. , Shan Y. Y. , Lee S. T.
Published: March 2007

The authors present the results of heteroepitaxial growth of single-crystalline ZnS nanowire arrays on CdS nanoribbon substrates by the metal-catalyzed vapor-liquid-solid growth method. ZnS nanowire arrays were vertically or crosswise aligned to the surface of CdS nanoribbon substrates. Room-temperature lasing from ZnS nanowire arrays was demonstrated. The present synthesis provides a new approach to the rational design of building blocks for nanodevices.
Temperature behavior of inhomogeneous Pt∕GaN Schottky contacts
Authors: Iucolano Ferdinando , Roccaforte Fabrizio , Giannazzo Filippo , Raineri Vito
Published: March 2007

In this letter, a correlation between the nanoscale localized electrical properties of the Pt∕GaN Schottky barrier and the temperature behavior of macroscopic Schottky diodes is demonstrated. Although a significant improvement of the ideality factor of the diodes is achieved after annealing at 400°C, local current-voltage measurements, performed with a biased tip of a conductive atomic force microscope, revealed the inhomogeneous nature of the barrier. Its nanoscale degree of homogeneity was quantitatively described by means of Tung’s model [Phys. Rev. B 45, 13509 (1992)], allowing the authors to explain the temperature dependence of the electrical characteristics of the macroscopic diodes.
High performance hard magnetic NdFeB thick films for integration into micro-electro-mechanical systems
Authors: Dempsey N. M. , Walther A. , May F. , Givord D. , Khlopkov K. , Gutfleisch O.
Published: March 2007

5 μ m thick NdFeB films have been sputtered onto 100mm Si substrates using high rate sputtering (18μm∕h). Films were deposited at ⩽500°C and then annealed at 750°C for 10min. While films deposited at temperatures up to 450°C have equiaxed grains, the size of which decreases with increasing deposition temperature, the films deposited at 500°C have columnar grains. The out-of-plane remanent magnetization increases with deposition temperature, reaching a maximum value of 1.4T, while the coercivity remains constant at about 1.6T. The maximum energy product achieved (400kJ∕m3) is comparable to that of high-quality NdFeB sintered magnets.
Focusing of light by a nanohole array
Authors: Huang Fu Min , Zheludev Nikolay , Chen Yifang , Javier Garcia de Abajo F.
Published: March 2007

The authors demonstrate a mechanism for focusing at optical frequencies based on the use of nanohole quasiperiodic arrays in metal screens. Using coherent illumination at 660nm and scanning aperture optical microscopy, ∼290nm “hot spots” were observed at a distance of ∼12.5μm from the array. Even smaller hot spots of about ∼200nm in waist were observed closer to the plane of the array.
Enhanced thermal conductivity of carbon fiber/phenolic resin composites by the introduction of carbon nanotubes
Authors: Kim Y. A. , Kamio S. , Tajiri T. , Hayashi T. , Song S. M. , Endo M. , Terrones M. , Dresselhaus M. S.
Published: March 2007

The authors report a significant enhancement in the thermal conductivity of a conventional carbon fiber/phenolic resin composite system when adding highly crystalline multiwalled carbon nanotubes. They demonstrate that 7wt% of carbon nanotubes dispersed homogeneously in a phenolic resin acted as an effective thermal bridge between adjacent carbon fibers and resulted in an enhancement of the thermal conductivity (e.g., from 250to393W∕mK). These results indicate that highly crystalline carbon nanotubes can be used as a multifunctional filler to enhance simultaneously the mechanical and thermal properties of the carbon fiber/phenolic resin composites.
Focused ion beam milling as a universal template technique for patterned growth of carbon nanotubes
Authors: Chen Ying , Chen Hua , Yu Jun , Williams James S. , Craig Vince
Published: March 2007

Focused ion beam (FIB) milling system has been used to create nanosized patterns as the template for patterned growth of carbon nanotubes on Si substrate surface without predeposition of metal catalysts. Carbon nanotubes only nucleate and grow on the template under controlled pyrolysis of iron phthalocyanine at 1000°C. The size, growth direction, and density of the patterned nanotubes can be controlled under different growth conditions and template sizes. Atomic force microscopy and electron microscopy analyses reveal that the selective growth on the FIB template is due to its special surface morphology and crystalline structure.
Particle tracking velocimetry using fast x-ray phase-contrast imaging
Authors: Im Kyoung-Su , Fezzaa K. , Wang Y. J. , Liu X. , Wang Jin , Lai M.-C.
Published: March 2007

The authors demonstrate the use of millisecond x-ray phase-contrast imaging for velocity measurement of particle-laden flows in an optically opaque vessel. Taking advantage of particle size polydispersity, this single-particle tracking approach is extremely effective on flows with tracer particles exhibiting a great size distribution ranging from 1μm to hundreds of micrometers, which is impossible for visible-light-based techniques. Furthermore, a tomographic reconstruction was applied to yield the three-dimensional flow velocity field and its particle size dependence with unprecedented sensitivity.
Floating gated silicon-on-insulator nonvolatile memory devices with Au nanoparticles embedded in SiO1.3N insulators by digital sputtering method
Authors: Lee Dong Uk , Lee Min Seung , Kim Jae-Hoon , Kim Eun Kyu , Koo Hyun-Mo , Cho Won-Ju , Kim Won Mok
Published: March 2007

Floating gated silicon-on-insulator nonvolatile memory devices with Au nanoparticles embedded in SiO1.3N insulators were fabricated. The tunneling SiO1.3N insulator, Au nanoparticles, and control SiO1.3N insulator were sequentially deposited by digital sputtering method at 300°C. The size of Au nanoparticles was controlled in the range of 1–5nm by adjusting the deposition thickness of Au layer and the density of Au nanoparticles was approximately 1.5×1012cm−2. A significant threshold voltage shift of fabricated floating gate memory devices was obtained due to the charging effects of Au particles and the memory window was larger than 2.5V.
Complete characterization of molecular vibration using frequency resolved gating
Authors: Xu Xiaoji G. , Konorov Stanislav O. , Zhdanovich Sergey , Hepburn John W. , Milner Valery
Published: March 2007

The authors propose a new approach to vibration spectroscopy based on the coherent anti-Stokes Raman scattering of broadband ultrashort laser pulses. The proposed method reveals both the amplitude and the phase of molecular vibrations by utilizing the cross-correlation frequency resolved optical gating (XFROG) technique. The spectrum of the anti-Stokes pulse is measured as a function of the time delay between the laser-induced molecular vibrations and a well characterized broadband femtosecond probe pulse. The iterative XFROG algorithm provides a simultaneous complete characterization of molecular vibrations both in frequency and time domains with high resolution. They demonstrate experimentally the feasibility of the proposed method and show one of its potential applications in disentangling the time behavior of a mixture of vibrationally excited molecules. The technique of femtosecond pulse shaping is used for further improvement of accuracy and stability against noise.
Post‐Coital Antifertility Activity of Hibiscus rosa-sinensis Linn. Roots
Authors: Vasudeva Neeru , Sharma S. K.
Published: March 2007

Ancient literature mentions the use of a number of plants/preparations for fertility regulation. Some local contraceptive agents have also been described in Ayurvedic and Unani texts. Documented experiments or clinical data are, however, lacking. Therefore, the present study was undertaken to explore the antifertility and estrogenic activity of ethanolic extract of the roots of Hibiscus rosa-sinensis Linn. A strong anti‐implantation (inhibition 100%) and uterotropic activity was observed at the dose level of 400 mg/kg body weight. Histological studies were carried out to confirm this effect.
Hydromagnetic Fluctuating Flow of a Viscoelastic Fluid in a Porous Channel
Authors: Ghosh Sushil Kumar
Published: March 2007

An exact periodic solution for the time dependent flow of a viscoelastic fluid in the presence of transverse magnetic field is derived. It is assumed that on one plate the fluid is injected with certain velocity and that it is sucked off at the other plate with the same velocity. Both plates are oscillating with a known velocity in their own plane. A perturbation method has been employed by treating the viscoelastic parameter to be small. Effects of viscoelastic parameter, cross-flow Reynolds number, frequency parameter, and Hartmann number on the velocity as well as wall shear stress of the flow are discussed here with graphs.
T-Stresses Across Static Crack Kinking
Authors: Li Xian-Fang , Xu L. Roy
Published: March 2007

This paper is concerned with the T-stress change before and after crack kinking in two-dimensional elastic solids. By using asymptotic analysis and the Westergaard stress function method, approximate analytical formulas for calculating the T-stress as well as stress intensify factors of an infinitesimal kink are given. Contributions from the T-stress before crack kinking, to the T-stress and the stress intensity factors of the kinked crack, are clearly described. It is noted that since the sign of the T-stress of a kinked open crack might be different from that of a main crack, simply using the sign of the T-stress before crack kinking is not sufficient to determine crack growth stability as observed in recent experiments.
Modeling Heterogeneous Media With Microstructures of Different Scales
Authors: Sun C. T. , Huang G. L.
Published: March 2007

The objective of this paper is to extend the framework of the continuum theory so that it can capture the properties that are embedded in the microstructure or nanostructure and still keep its simplicity and efficiency. The model thus developed is capable of accounting for local deformation of microstructures in solids especially their micro- (local) inertia effect. The essence underlying this approach is the introduction of a set of bridging functions that relate the local deformation of microstructures to the macrokinematic variables. Once the solution of the macroscopically homogeneous continuum is obtained, the solutions in the microstructures are obtained through the use of these bridging functions. Propagation of waves of different wavelengths is considered and the dispersion curve is used to evaluate the accuracy of the model. The model is also employed to study wave reflection and transmission at the boundary of two media with microstructures of very different scales.
Some Applications of Integrated Elasticity
Authors: Assaad A. T. , Sinclair G. B.
Published: March 2007

This paper examines the effects of relaxing the assumption of classical linear elasticity that the loads act in their entirety on the undeformed shape. Instead, loads here are applied incrementally as deformation proceeds, and resulting fields are integrated. A formal statement of the attendant integrated elasticity theory is provided. A class of problems is identified for which this formulation is amenable to solution in closed form. Some results from these configurations are compared with linear elasticity and experimentally measured data. The comparisons indicate that, as deformation increases, integrated elasticity is capable of tracking the physical response better than linear elasticity.
Identification of Linear Time-Varying Dynamical Systems Using Hilbert Transform and Empirical Mode Decomposition Method
Authors: Shi Z. Y. , Law S. S.
Published: March 2007

This paper addresses the identification of linear time-varying multi-degrees-of-freedom systems. The identification approach is based on the Hilbert transform and the empirical mode decomposition method with free vibration response signals. Three-different types of time-varying systems, i.e., smoothly varying, periodically varying, and abruptly varying stiffness and damping of a linear time-varying system, are studied. Numerical simulations demonstrate the effectiveness and accuracy of the proposed method with single- and multi-degrees-of-freedom dynamical systems.
A Discrete Quasi-Coordinate Formulation for the Dynamics of Elastic Bodies
Authors: D’Eleuterio G. M. T. , Barfoot T. D.
Published: March 2007

The discretized equations of motion for elastic systems are typically displayed in second-order form. That is, the elastic displacements are represented by a set of discretized (generalized) coordinates, such as those used in a finite-element method, and the elastic rates are simply taken to be the time-derivatives of these displacements. Unfortunately, this approach leads to unpleasant and computationally intensive inertial terms when rigid rotations of a body must be taken into account, as is so often the case in multibody dynamics. An alternative approach, presented here, assumes the elastic rates to be discretized independently of the elastic displacements. The resulting dynamical equations of motion are simplified in form, and the computational cost is correspondingly lessened. However, a slightly more complex kinematical relation between the rate coordinates and the displacement coordinates is required. This tack leads to what may be described as a discrete quasi-coordinate formulation.
Wavelet-Based Sensitivity Analysis of the Impulse Response Function for Damage Detection
Authors: Law S. S. , Li X. Y.
Published: March 2007

This paper discusses the extraction of the wavelet-based impulse response function from the acceleration response using the discrete wavelet transform (DWT). The analytical formulation of the sensitivity of the DWT coefficient of the impulse response function with respect to a system parameter is then presented for structural damage detection. A numerical example with a 31-bar plane truss structure is used to verify the proposed method with different damage scenarios with or without model error and noise effect.
Delamination Detection-Oriented Finite Element Model for a Fiber Reinforced Polymer Bonded Concrete Plate and Its Application With Vibration Measurements
Authors: Wu D. , Law S. S.
Published: March 2007

Delamination is a common type of damage in laminated fiber-reinforced polymer (FRP) composites. As FRP composites are becoming popular in upgrading and strengthening of civil concrete structures, the specific delamination damage, i.e., the FRP-concrete debonding, is considered more critical than inter-laminar delamination occurring in the FRP composites. A finite element formulation on the FRP-bonded concrete plate with this type of delamination fault is developed in the context of non-destructive evaluation from vibration measurements and compared with a two-layer solid element model. An adhesive interface where possible debonding could occur is introduced between the FRP and the concrete plates. A scalar damage parameter characterizing the delamination is incorporated into the formulation of a finite element model that is compatible with the vibration-based damage identification procedure. The formulated model is then applied to the prediction of FRP-concrete delaminations from modal test results based on the sensitivity analysis of uniform load surface curvature, which has been previously proposed by the authors. The validity of the methodology is demonstrated in two numerical examples. The first one is used to check the model accuracy, while the second one assesses the efficiency of the model-based identification method.
An Investigation of
Steady-State Dynamic Response of a Sphere-Plane Contact Interface With Contact
Loss
Authors: Ma Q.
L. , Kahraman A. , Perret-Liaudet J. , Rigaud E.
Published: March 2007

In this study, the dynamic behavior of an elastic sphere-plane contact interface is studied analytically and experimentally. The analytical model includes both a continuous nonlinearity associated with the Hertzian contact and a clearance-type nonlinearity due to contact loss. The dimensionless governing equation is solved analytically by using multi-term harmonic balance method in conjunction with discrete Fourier transforms. The accuracy of the dynamic model and solution methods is demonstrated through comparisons with experimental data and numerical solutions for both harmonic amplitudes of the acceleration response and the phase difference between the response and the force excitation. A single-term harmonic balance approximation is used to derive a criterion for contact loss to occur. The influence of harmonic external excitation f(τ) and damping ratio ζ on the steady state response is also demonstrated.
Hierarchical Corrugated Core Sandwich Panel Concepts
Authors: Kooistra Gregory W. , Deshpande Vikram , Wadley Haydn N. G.
Published: March 2007

The transverse compression and shear collapse mechanisms of a second order, hierarchical corrugated truss structure have been analyzed. The two competing collapse modes of a first order corrugated truss are elastic buckling or plastic yielding of the truss members. In second order trusses, elastic buckling and yielding of the larger and smaller struts, shear buckling of the larger struts, and wrinkling of the face sheets of the larger struts have been identified as the six competing modes of failure. Analytical expressions for the compressive and shear collapse strengths in each of these modes are derived and used to construct collapse mechanism maps for second order trusses. The maps are useful for selecting the geometries of second order trusses that maximize the collapse strength for a given mass. The optimization reveals that second order trusses made from structural alloys have significantly higher compressive and shear collapse strengths than their equivalent mass first order counterparts for relative densities less than about 5%. A simple sheet metal folding and dip brazing method of fabrication has been used to manufacture a prototype second order truss with a relative density of about 2%. The experimental investigation confirmed the analytical strength predictions of the second order truss, and demonstrate that its strength is about ten times greater than that of a first order truss of the same relative density.
Utilization of Synchronous Averaging for Inspection of Tooth Surface Undulations on Gears (Localization of Nonmesh Harmonic Components to Individual Gear)
Authors: Houjoh Haruo , Ratanasumawong Chanat , Matsumura Shigeki
Published: March 2007

Cyclic undulation of the gear tooth surface is one of the important sources of gear noise and vibration. It has been known that vibration caused by this source can appear at the nonmesh harmonic frequency components (ghost components). As there are no relationships between the frequency of this vibration and any gear specifications, the gear noise source is hard to detect. This paper proposes the utilization of the synchronous averaging technique for diagnosis of the source of nonmesh harmonic vibration components on a gear pair, and shows the possibility of using this technique for inspection of tooth surface undulation. The method for practically applying this technique is discussed in detail. Results demonstrated in the form of spectrum showed good agreement with the undulation assessed from precise tooth surface measurement over the whole surface of every tooth. The effect of the direction of the arrangement of cyclic undulation on tooth surface and gear vibration is also discussed in this paper. Finally the limitation to the synchronous averaging technique was discussed with respect to gear ratio.
Analytical Modeling for Stress-Strain Curve of a Porous NiTi
Authors: Zhao Ying , Taya Minoru
Published: March 2007

Two models for predicting the stress-strain curve of porous NiTi under compressive loading are presented in this paper. Porous NiTi shape memory alloy is considered as a composite composed of solid NiTi as matrix and pores as inclusions. Eshelby’s equivalent inclusion method and Mori-Tanaka’s mean-field theory are employed in both models. Two types of pore connectivity are investigated. One is closed cells (model 1); the other is where the pores are interconnected to each other forming an open-cell microstructure (model 2). We also consider two different shapes of pores, spherical and ellipsoidal. The stress-strain curves of porous shape memory alloy with spherical pores and ellipsoidal pores are compared. It is found that the ellipsoidal shape assumption is more reasonable than the assumption of spherical pores. Comparison of the stress-strain curves of the two models shows that use of open-cell microstructure (model-2) makes the predictions more agreeable to the experimental results of porous NiTi whose microstructure exhibits open-cell microstructure.
Nonstationary Response Envelope Probability Densities of Nonlinear Oscillators
Authors: Spanos P. D. , Sofi A. , Di Paola M.
Published: March 2007

The nonstationary random response of a class of lightly damped nonlinear oscillators subjected to Gaussian white noise is considered. An approximate analytical method for determining the response envelope statistics is presented. Within the framework of stochastic averaging, the procedure relies on the Markovian modeling of the response envelope process through the definition of an equivalent linear system with response-dependent parameters. An approximate solution of the associated Fokker-Planck equation is derived by resorting to a Galerkin scheme. Specifically, the nonstationary probability density function of the response envelope is expressed as the sum of a time-dependent Rayleigh distribution and of a series expansion in terms of a set of properly selected basis functions with time-dependent coefficients. These functions are the eigenfunctions of the boundary-value problem associated with the Fokker-Planck equation governing the evolution of the probability density function of the response envelope of a linear oscillator. The selected basis functions possess some notable properties that yield substantial computational advantages. Applications to the Van der Pol and Duffing oscillators are presented. Appropriate comparisons to the data obtained by digital simulation show that the method, being nonperturbative in nature, yields reliable results even for large values of the nonlinearity parameter.
Dynamic Stress Concentration of a Circular Cutout Buried in Semi-Infinite Plates Subjected to Flexural Waves
Authors: Fang Xueqian , Hu Chao , Huang Wenhu
Published: March 2007

In this paper, based on the theory of elastic thin plates, applying the image method and the wave function expansion method, multiple scattering of elastic waves and dynamic stress concentration in semi-infinite plates with a circular cutout are investigated, and the general solutions of this problem are obtained. As an example, the numerical results of dynamic stress concentration factors are graphically presented and discussed. Numerical results show that the analytical results of scattered waves and dynamic stress in semi-infinite plates are different from those in infinite plates when the distance ratio b∕a is comparatively small. In the region of low frequency and long wavelength, the maximum dynamic stress concentration factors occur on the illuminated side of scattered body with θ=π, but not on the side of cutout with θ=π∕2. As the incidence frequency increases (the wavelength becomes short), the dynamic stress on the illuminated side of cutout becomes little, and the dynamic stress on the shadow side becomes great.
An Asymptotic Framework for the Analysis of Hydraulic Fractures: The Impermeable Case
Authors: Mitchell S. L. , Kuske R. , Peirce A. P.
Published: March 2007

This paper presents a novel asymptotic framework to obtain detailed solutions describing the propagation of hydraulic fractures in an elastic material. The problem consists of a system of nonlinear integro-differential equations and a free boundary problem. This combination of local and nonlocal effects leads to transitions on a small scale near the crack tip, which control the behavior across the whole fracture profile. These transitions depend upon the dominant physical process(es) and are identified by simultaneously scaling the associated parameters with the distance from the tip. A smooth analytic solution incorporating several physical processes in the crucial tip region can be constructed using this new framework. In order to clarify the exposition of the new methodology, this paper is confined to considering the impermeable case in which only the two physical processes of viscous dissipation and structure energy release compete.
Research Productivity and Salaries of Academic Home Economists
Authors: Abdel‐Ghany Mohamed
Published: March 2007

The data for this study (N = 64) were collected by means of a questionnaire mailed to graduates who have earned doctoral degrees in specializations within home economics in 15 universities in the years 1970 through 1975. The first objective of this research was to examine the effect of the following variables on research productivity (measured by the total number of refereed publications): percent of time devoted to research; years of professional experience; the squared term of experience to account for diminishing returns; quality of graduate training; and a composite index measuring resources available for support of research. The standardized partial regression coefficients indicated that only the percent of time devoted to research exerted an important independent effect upon research productivity. The second objective was to determine the relationship between research productivity and salaries, controlling for other independent variables. The results revealed that there was no significant relationship between the two vari ables.
Junior High Home Economics Curriculum: Its Effect on Students' Knowledge, Attitude, and Behavior
Authors: Byrd‐Bredbenner Carol , Hsu O'Connell Lily , Shannon Barbara
Published: March 2007

The objective of this study was to determine the effect of nutrition instruction, using the curriculum Nutrition In a Changing World, A Curriculum for Home Economics, Grades 7‐9, on improving the nutrition knowledge, selected food/nutrition attitudes, and dietary behavior of junior high home economics students. There were three groups of students, one experimental and two control groups, at each grade level (seven through nine). The experimental group was pretested, taught the nutrition curriculum and posttested. One control group was only posttested to measure the effect of the pretest on posttest performance. A second control group was pretested and posttested. Neither control group received nutrition instruction until after the study was completed. Three instruments were used to collect data: a nutrition knowledge test, a food/nutrition attitude instrument, and a food frequency form. The results indicate that, at all grade levels, the experimental group had significantly improved knowledge scores. Little change in attitude scale scores was noted in grades seven and eight, while ninth grade experimental students scored significantly higher on the posttest for all attitude scales. Little improvement was seen in the posttest food frequency scores.
Nutrition Knowledge, Attitudes, and Food Purchasing Practices of Parents
Authors: Beavers Irene , Kelley Margaret , Flenner Jan
Published: March 2007

Objectives of this study were to ascertain nutrition attitudes, knowledge, and food pur chasing practices of preschoolers' parents and to compare attitudes, practices, and knowledge of parents by type of child care program, sex, age, education level, family size, residence, occupation, nutrition training, and money spent on food eaten at home and away from home. The target population was parents, both mothers and fathers, who had preschool children attending a licensed day care center or day care home. Data were analyzed from 1,769 questionnaires. Cronbach's alpha reliabilities were computed for knowledge, attitudes, and practices, and a total score for each parent was calculated for each scale. Pearson's product‐moment correlation was used to determine relation ships among the variables and knowledge, attitudes, and practices. Differences in atti tudes, knowledge, and practices were determined by one‐way analysis of variance. Findings indicated that nutrition attitudes were more highly related to food purchasing practices than was nutrition knowledge to food purchasing practices. Education level was the predominant variable influencing nutrition knowledge, and nutrition attitude was the primary variable influencing food purchasing practices.
Attitudes Toward Clothing, Body and Self: A Comparison of Two Groups
Authors: Ford Imogene M. , Drake Mary Frances
Published: March 2007

The purpose of this study was to determine (1) if two racial groups differed on self‐ esteem, body satisfaction, and clothing variables, and (2) if relationships existed among the variables. Two groups of subjects, 164 White and 68 Black collegiate females, were administered the Rosenberg Self‐Image Questionnaire, the Body Characteristic De scriptive Scale, the Sexually Attractive Clothing Measure, and the Clothing Opinion naire. Data were analyzed using analysis of variance and correlations. The two racial groups were significantly different on three variables (adequacy of money, use of sexu ally attractive clothing, and self‐esteem) and alike on the remaining three variables (body satisfaction, attitude toward unusual clothing, and flair in clothing). All the re lationships between variables were the same for both racial groups. Seven pairs of variables were significantly related. These findings illustrate the complexity of clothing research when different groups within a pluralistic society are compared.
Freedom and Conformity in Dress: A Two‐Dimensional Approach
Authors: Lowe Elizabeth D. , Buckley Hilda M.
Published: March 2007

This study attempted to explore the question of whether freedom and conformity are simply polar opposites, or rather, separate dimensions of dress. To this end, 112 subjects were asked to complete a questionnaire which included: (1) a self‐rating of freedom in dress, (2) items reflecting the components of freedom in dress (choice, restrictions, satisfactions) set forth by Lowe and Anspach, (3) items contained in Creekmore's Im portance of Clothing questionnaire dealing with the approval dimension of dress (i.e., the tendency to conform to gain approval), and (4) demographic items. Factor analysis of a self‐rating of freedom in dress and its components was used to develop a measure of freedom in dress which could be compared with the self‐rating. This alternative measure was not independent of the self‐rating, but rather suggested that choice was the most important component of freedom in dress. Pearson correlations between conformity and freedom, regardless of which measure was used, were so small that the angle repre senting this relationship was nearly orthogonal, suggesting that freedom is not the op posite of conformity, but rather a separate dimension of dress.
New technologies for chronic disease management and control: a systematic review
Authors: García-Lizana Francisca , Sarría-Santamera Antonio
Published: March 2007

We conducted a systematic review of the clinical effectiveness of interventions using information and communication technologies (ICTs) for managing and controlling chronic diseases. Electronic databases were searched for randomized clinical trials that assessed the effectiveness of ICTs (except for those that included only telephone communication) and measured some clinical indicator. Information was reviewed and assessed independently by two researchers. Of the 950 clinical trials identified, 56 studies were identified for potential inclusion. Of those, 24 were finally included: 5 studies in asthma, 3 in hypertension, 1 in home telecare, 7 in diabetes, 6 in heart failure and 2 in prevention heart disease. Overall, ICT applications did not show an improvement in clinical outcomes, although no adverse effects were identified. However, ICTs used in the detection and follow up of cardiovascular diseases provided better clinical outcomes, mortality reduction and lower health services utilization. Systems used for improving education and social support were also shown to be effective. At present the evidence about the clinical benefits of ICTs for managing chronic disease is limited.