bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of SrBi2Nb2O9 Thin Films Prepared by Sol Gel Technique
Authors: Ching-Prado E. , Pérez W. , Reynés-Figueroa A. , Katiyar R. S. , Ravichandran D. , Bhalla A. S. 
Published: April 2011

ABSTRACTThin films of SrBi2Nb2O9 (SBN) with thicknesses of 0.1, 0.2, and 0.4 μ were grown by Sol-gel technique on silicon, and annealed at 650°C. The SBN films were investigated by Raman scatering for the first time. Raman spectra in some of the samples present bands around 60, 167, 196, 222, 302, 451, 560, 771, 837, and 863 cm−1, which correspond to the SBN formation. The study indicates that the films are inhomogeneous, and only in samples with thicknesses 0.4 μ the SBN material was found in some places. The prominent Raman band around 870 cm−1, which is the A1g mode of the orthorhombic symmetry, is assigned to the symmetric stretching of the NbO6 octahedrals. The frequency of this band is found to shift in different places in the same sample, as well as from sample to sample. The frequency shifts and the width of the Raman bands are discussed in term of ions in non-equilibrium positions. FT-IR spectra reveal a sharp peak at 1260 cm−1, and two broad bands around 995 and 772 cm−1. The bandwidths of the latter two bands are believed to be associated with the presence of a high degree of defects in the films. The experimental results of the SBN films are compared with those obtained in SBT (T=Ta) films. X-ray diffraction and SEM techniques are also used for the structural characterization.
A Technique for the Measurement of d31 Coefficient of Piezoelectric Thin Films
Authors: Shepard Joseph F. , Moses Paul J. , Trolier-McKinstry Susan 
Published: April 2011

ABSTRACTThis paper describes a new technique by which the d31 coefficient of piezoelectric thin films can be characterized. Silicon substrates coated with lead-zirconate titanate (PZT) are flexed while clamped in a uniform load rig. When stressed, the PZT film produces an electric charge which is monitored together with the change in applied load. The mechanical stress and thus the transverse piezoelectric coefficient can then be calculated. Experiments were conducted as a function of poling field strength and poling time. Results are dependent upon the value of applied stress, which itself is dependent upon the mechanical properties of the silicon substrate. Because the substrate is anisotropie, limiting d31 values were calculated. In general, d31 was found to be ∼20 pC/N for field strengths above 130 kV/cm and poling times of less than 1 minute, d31 was increased more than a factor of three, to ∼77 pC/N, when poled at 200 kV/cm for ∼21 hours.
Complex Piezoelectric Coefficients of PZT Ceramics: Method for Direct Measurement of d33
Authors: Jordan T. L. , Ounaies Z. , Turner T. L. 
Published: April 2011

ABSTRACTA fiber-optic device is used to determine the magnitude and phase of the strain in the poling direction of lead zirconate titanate (PZT) ceramic wafers. This information yields the real and imaginary components of the piezoelectric strain coefficient d33. The measurement hardware and software are described and results from the measurements of d33 for PZT 4 and 5 H wafers are presented. This method has the advantages of being direct, inexpensive and relatively simple to use. Verification of the results is provided through the use of the resonance method.
Effects of Magnetic Field and Hydrostatic Pressure on Martensitic Transformations in Some Shape Memory Alloys
Authors: Kakcshita T. , Saburi T. , Shimizu K. 
Published: April 2011

ABSTRACTThe recent works carried by the author's group on the effects of magnetic field and hydrostatic pressure on martensitic transformation are reviewed, which mainly concerned with some shape memory allovs, such as Fe-Pt, Fe-Co-Ni-Ti, Ti-Ni and Cu-Al-Ni alloys. The works clarify the effects of magnetic field and hydrostatic pressure on martensitic transformation temperature, magnetoelastic martensitic transformation and morphology and arrangement of martensites and transformation process of athermal transformation. That is, transformation start temperatures in Fe-Pt and Fe-Ni alloys examined increase with increasing magnetic field, but are not affected in Ti-Ni and Cu-Al-Ni alloys. On the other hand, transformation start temperature decreases with increasing hydrostatic pressure in the Fe-Ni-Co-Ti alloy, but increases in Cu-Al-Ni alloys. The magnetic field and hydrostatic pressure dependences of the martensitic start temperature are in good agreement with those calculated by the equations proposed by our group. In the work on the ausaged Fe-Ni-Co-Ti alloy, the appearance of magnetoelastic martensitic transformation is newly found. In addition, several martensite plates grow nearly parallel to the direction of applied magnetic field in the specimen of an Fe-Ni alloy single crystal. Moreover, we found that in the Cu-Al-Ni alloys exhibiting an athermal martensitic transformation, isothermal holding at a temperature above Ms makes martensitic transformation to start and the incubation time increases with increasing ΔT = T − Ms (T represents holding temperature). The above results show that the magnetic field and hydrostatic pressure effectively control not only the transformation temperature but also the morphology and distribution of martensites induced, as in the case of uniaxtial stress and compression.
The Martensitic Transformation and Extra Reflections Appearing Prior to the Transformation in AuCd Alloy
Authors: Ohba T. , Otsuka K. 
Published: April 2011

ABSTRACTAuCd alloy is a typical martensitic alloy. The crystal structural of the ζ2' (trogonal) martensite was recently determined and the analysis indicated the possibility of phonon softening. Despite a large absorption coefficient of Cd phonon softening was actually observed by using an isotope 114Cd. In the present study, precise x-ray scattering studies were performed with a rotating anode x-ray source and synchrotron radiation at Photon Factory in KEK, using small crystals. The structure factors of the parent phase and the diffraction profiles along <110> direction were measured with four circle diffractometers. The structure factors decrease when approaching the transformation temperature. Superstructure reflections were observed prior to the onset of the transformation. They are very weak and rather sharp and appear at q = (1/3,1/3,0) within the experimental error, i. e. at the commensurate position.
High Electromechanical Coupling Piezoelectrics - How High Energy Conversion Rate is Possible
Authors: Uchino Kenji 
Published: April 2011

ABSTRACTA new category of piezoelectric ceramics with very high electromechanical coupling was discovered in a lead zinc niobate:lead titanate solid solution in a single crystal form. The maximum coupling factor k33 reaches 95%, which corresponds to the energy conversion rate twice as high as the conventional lead zirconate titanate ceramics. This paper reviews the previous studies on superior piezoelectricity in relaxor ferroelectric: lead titanate solid solutions and on the possible mechanisms of this high electromechanical coupling.
Thermotracttve Titanium-Nickel thin Films Formicroelectromechanical Systems and Active Composites
Authors: Grummon D. S. , Pence T. J. 
Published: April 2011

ABSTRACTThin films of thermoelastic titanium-nickel are of interest as a material basis for force-producing elements in microelectromechanical systems, and for active phases in mechanically-adaptive composite materials. The successful introduction of this material system into such application areas will depend on development of reliable thin film deposition protocols, together with the refinement of analytical models which successfully predict the response of active microstructures to a variety of dynamic thermal and mechanical stimuli. In the present paper we review some of our recent experimental and theoretical work which bear on these problems. With respect to thin film fabrication techniques we focus on problems of composition control and the manipulation of microstructure, with particular emphasis on opportunities afforded by amorphous precursor phases formed during low temperature processing, and the fine-grained, thermally stable crystalline microstructures obtainable using hot-substrate deposition. The films resulting from either approach retain the important thermomechanical response features of the well-known bulk-alloy system: shape memory and transformational superelasticity. The response can be modeled in terms of a continuum description augmented with internal variables that track fractional partitioning of the material between austenite and variants of the martensite.
Aging Influence on the Shape Memory Effects and Superelasticity in Titanium-Nickel Single Crystals
Authors: Chumlyakov Yu.I. , Kireeva I. V. , Lineytsev V. N. , Lwisyuk A. G. 
Published: April 2011

ABSTRACTOn the Ti-50.8%Ni, Ti-51%Ni and Ti-51.3%Ni (at.%) single crystals, the investigations of the shape memory effects (SME) and superelasticity (SE) have been carried out in order to find out the dependence on a size and a volume fraction of the Ti3Ni4 dispersive particles, a crystal orientation and a sign of applied stress. It is shown, that in crystals without particles the strong dependence of SME on an orientation and a sign of applied stress takes place and SE is not observed. Precipitation of the coherent particles of Ti3Ni4 of 50–100 nm in size leads to the reduction of SME, weakening of orientation dependence of σcr interval of stress-induced martensitic transformations (MT).
Model Tracking of Stress and Temperature Induced Martensitic Transformations for Assessing Superelasticity and Shape Memory Actuation
Authors: Wu X. , Pence T. J. , Grummon D. S. 
Published: April 2011

ABSTRACTBoth austenite/martensite transformations, and martensite/martensite variant reorientation are central to superelasticity and shape memory actuation. Here we discuss a simple model for tracking these transformations that is appropriate for device modeling. The approach is to augment conventional continuum mechanical descriptions with internal variables that track fractional partitioning of the material between austenite and the various martensite variants. A three-species model involving austenite and two complementary martensite variants provides sufficient generality to capture the martensite variant distributions that underlie shape memory, and the strain-accommodation associated with superelasticity. Transformations between all of these species can be tracked on the basis of triggering algorithms that reflect both tran sformation hysteresis and the variation of triggering stress with temperature. The algorithm described here is for temperature-dependent response resolved in a single direction. It requires only the following experimentally determined parameters: the four transformation temperatures Mf, Ms, As, Af, the transformation strain, the Young's modulus, and the transformation latent heat.
Compression-Induced Martensitic Transformations in Cu-Zn-Al Alloys with e/a > 1.50
Authors: Cuniberti A. , Romero R. 
Published: April 2011

ABSTRACTResults are reported about the pseudoelastic cycles β-martensite obtained by compression of β Cu-Zn-Al single crystals with electronic concentration 1.52. Stress-strain curves at different temperatures and in situ observations were carried out. The results are compared with those obtained from tension test.
The Effects of Biaxial Stress on the Ferroelectric Characteristics of PZT Thin Films
Authors: Shepard Joseph F. , Trolier-McKinstry Susan , Hendrickson Mary , Zeto Robert 
Published: April 2011

ABSTRACTThe design and implementation of microelectromechanical (MEMS) systems requires a sound understanding of the influence of film stress on both the ferroelectric and piezoelectric characteristics of thin films to be used for sensing and/or actuation. Experiments were conducted in which thin film samples of sol-gel derived PZT were subjected to applied biaxial stresses from -139 to 142 MPa. Films were characterized at known stress states (derived from known values of residual stress and large deflection plate theory) in terms of their ferroelectric polarization (saturated and remnant), dielectric constants, coercive field strengths, and tan δ. Results obtained indicate that domain wall motion in thin films contributes much less to the observed response than is typical for bulk PZT materials. Alternative mechanisms are proposed in an attempt to explain the discrepancies.
Frequency Effects on the Damping Capacity of Superelastic Nitinol
Authors: Jones H. N. 
Published: April 2011

ABSTRACTThe evolution of the stress-strain behavior of a superelastic NiTi alloy over a range of cyclic frequencies up to 10 Hz is presented. Due to the stress-strain hysteresis typical of these alloys work is dissipated as heat during every cycle. Also, the heat release and absorption induced by the cyclic phase transformation responsible for the superelastic effect causes the material to undergo a cyclic temperature history which is superimposed on the average temperature resulting from the dissipative nature of the stress-strain cycle. As the cyclic frequency is increased the imposed strain rate is also necessarily increased. The stress-strain loops at very low frequencies are under isothermal conditions. As the cyclic rate is increased nearly adiabatic conditions are achieved at the higher frequencies. This affects the hysteretic cyclic behavior and the damping capacity of the material.
Determination of the Upper Limit for the Cluster Moment Contributing the Giant Magneto Resistance in Laser Deposited Granular Cu-rich Thin Films
Authors: Madurga V. , Ortega R. J. , Vergara J. , Rao K. V. 
Published: April 2011

ABSTRACTWe have fabricated granular Cu95Co5 thin films by laser ablation-deposition. Within a regime of annealing temperatures, these samples exhibit Giant Magneto Resistance (GMR), typically 5% in 0.5 Tesla at 5 K. The magnetic hysteresis loops are found to show finite coercive fields in the whole temperature range 2 K - 300 K. Below 9 K, the field dependence of the MR shows a split maximum. We interpret the data in terms of coercivity arising from blocking phenomenon of single domain superparamagnetic Co clusters. A quantitative determination of the upper limit for the cluster moment contributing to GMR is estimated to be 17000 μB (a cluster size of 5 nm).
Synthesis and Properties of Magnetorheological (MR) Fluids for Active Vibration Control
Authors: Phulé Pradeep P. , Ginder John M. , Jatkar Arun D. 
Published: April 2011

ABSTRACTMagnetorheological (MR) fluids represent an exciting class ofsmart materials for use in active vibration control and other applications. This paper discusses some of the fundamental materials science concepts that define the scientific basis for designing MR fluids. Preliminary experimental data and observations concerning the synthesis as well as the rheological behavior of MR fluids based on carbonyl iron and iron oxide particulates are presented and discussed.
Conformational and Dynamic Properties of Polymer Loops and Their Mixtures at an Impenetrable Interface
Authors: Gulati H. S. , Driscoll D. C. , Jones R. L. , Spontak R. J. , Hall C. K. 
Published: April 2011

ABSTRACTIn this study we investigate the equilibrium conformational properties and dynamic relaxation behavior of polymer loops grafted at an interface using the discontinuous molecular dynamics simulation technique. Differences and similarities between the structural and dynamic properties of polymer loops and tails are identified. The conformational properties of mixtures of polymers loops and tails are also studied using the bond-fluctuation method. The effect of mixture composition on the conformational properties of the individual components in the mixture is discussed.
Concentrated DNA Rheology and Microrheology
Authors: Mason T. G. , Dhople A. , Wirtz D. 
Published: April 2011

ABSTRACTWe present mechanical measurements of the frequency-dependent linear viscoelastic storage and loss moduli,G′(ω) and G″(ω), and the yield stress, τy, and yield strain, γy, for calf thymus DNA (13 kbp) over a range of mitotically relevant concentrations fromCDNA= 1 to 10 mg/ml. For largeCDNA, we find a dominant plateau elasticity,G′p, at high ω. As ω decreases,G′ falls until it is equal toG′ at the crossover frequency, ωc, below whichG″ dominates. We measureG′p∼CDNA2.25and ωc∼CDNA−2.4, consistent with scaling exponents for classical polymer solutions. The mechanical |G*(ω)| agree well with those measured using a new microrheological technique based on video tracking microscopy of thermally-driven fluorescent colloidal spheres and a frequency-dependent Stokes-Einstein equation. We have developed this technique to probe how enzymes, typically available in small quantities, can affect the rheology of the DNA. Using it, we report preliminary measurements of a higher ωcfor a DNA network in which the ATP-powered enzyme Topoisomerase II transiently cuts and rebinds the DNA, thereby relaxing entanglements.
Late Stages of the Pearling Instability in Lipid Bilayers
Authors: Goveas J. L. , Milner S. T. , Russel W. B. 
Published: April 2011

ABSTRACTWe have studied the late stages of the “pearling instability” in lipid bilayers, which is brought on by applying laser tweezers to a cylindrical vesicle. This produces a front that propagates down the vesicle, leaving behind it bilayer-covered droplets separated by thin tubes, which appear under the microscope as pearls on a string. At later times, the “pearls” are observed to drift slowly towards the “trap” (the spot where the tweezers are applied, into which the surfactant is drawn). We model the hydrodynamics of the drifting pearls as a combination of translation of the string of pearls, and “slipping” of the bilayer skin over the pearls, to relate the speed of the pearls to the underlying flux of the surfactant into the trap.
Depinning of Fracture Fronts
Authors: Daguier P. , Nghiem B. , Bouchaud E. , Creuzet F. 
Published: April 2011

ABSTRACTBy studying the morphology of the fracture surfaces of both a metallic alloy and of a silicate glass for various very low crack propagation velocities, it is shown that the pin-ning/depinning scenario of a line moving through randomly distributed obstacles seems well adapted to describe fracture of heterogeneous materials. The crossover length separating the large length scales regime characterised by a roughness index ζ ≃ 0.78 and the small length scales one, for which ζc ≃ 0.5, is shown to decrease with the measured crack velocity as a power law, ξc ∞ v−φ, with ζ ≃ 1. ξc and v also vary with the pulling force as power laws, and the measured values of exponents ν and β are close to: ν ≃ 2 and β ≃ 2.
Temperature and Chemistry Effects in Porous-Media Electrokinetics
Authors: Pengra David B. , Wong Po-Zen 
Published: April 2011

ABSTRACTElectrokinetic phenomena in brine-saturated porous media, such as electroosmosis (fluid-flow induced by applied electric fields) and streaming current (the complementary process) depend on the density of ions adsorbed on the pore surface and the characteristic thickness of the diffuse space-charge layer λ. These, in turn, depend on brine chemistry, ambient temperature and possibly other parameters. We report on a series of measurements of natural rock and synthetic glass-bead samples: for one sample group, we varied the temperature over 0–50 ° C; for another, we changed the brine cation species. We find that the electrokinetic coefficients depend only weakly on temperature; this is shown to follow from the expected trends in λ, η, and σ. The chemistry dependence follows qualitatively but not quantitatively the predictions of the Debye-Hiickel approximation.
Annular Ringlike Arrays from Mixtures of Metal Nanoparticles
Authors: Ohara P. C. , Heath J. R. , Gelbart W. M. 
Published: April 2011

ABSTRACTWe describe a theory for hole nucleation in volatile, wetting, thin liquid films. Hole nucleation in this system can occur due to two independent driving forces: evaporation (volatile hole nucleation) and by disjoining pressure effects (non-volatile hole nucleation). Although a concerted combination of these two can be in effect, the cases are treated separately here and will be treated jointly in the context of a simulation elsewhere. Growing holes – dry areas of the solid surface which are otherwise wet by solvent – are conjectured to be responsible for the formation of close-packed 2D annular ringlike arrays from dilute solutions of nearly monodisperse, large (3–5nm diameter), organically passivated metal particles [1]. When organic solutions of these nanoparticles are evaporated on a solid carbon substrate (a TEM grid), the resulting sub-monolayer structures are annular ringlike arrays due to the pinning of the rim of an opening hole by a sufficient collection of particles.
Uncoiling of DNA by Double Chained Cationic Surfactants
Authors: Paradies H. H. , Clancy S. F. 
Published: April 2011

ABSTRACTDistearyldimethylammonium (DSDMA) X (X− = OH, H2PO4) interact with double stranded T4 DNA (166 kilobase pairs) below and above the CMC (1.5×10−6). Below the CMC of either DSDMA X where the cationic double-chained surfactants are in the monomeric state, T4 DNA and DSDMA+form a compact complex where all surfactant molecules are bound. Close to the CMC, particularly for DSDMA OH but also in the presence of , T4 DNA exhibits a condensed (globule) conformation, though some DNA molecules are in the more extended DNA conformation. Above the CMC of DSDMA X a plateau is reached (up to 3.0 × 10−6 M surfactant) revealing a penetration of DSDMA molecules into the DNA globules resulting in a loosening of the tightened state of DNA. The various stages of the transition from the condensed coil to the extended state of T4 DNA with changing DSDMA X concentrations was monitored by static and inelastic light scattering experiments which were supplemented by small-angle X-ray scattering measurements.
Photon Correlation Spectroscopy of Liquid Crystals Confined in Porous Matrices with Different Structure and Pore Size
Authors: Aliev F.M. , Plechakov I.V. 
Published: April 2011

ABSTRACTWe present the results of photon correlation spectroscopy investigations of the influence of confinement, interface, porous matrix structure, pore size and shape on the dynamic behavior of nematic liquid crystals (LC) dispersed in porous matrices with randomly oriented, interconnected pores (porous glasses) and parallel cylindrical pores (Anopore membranes). Investigations of LC in cylindrical pores together with studies in random porous matrices, makes it possible to separate the role of random structure and domain formation from the contributions due to existence of LC - solid pore wall interface and pure finite size effect in relaxation of order parameter or director fluctuations. In the temperature range below nematic - isotropie phase transition temperature we observed two overlapping relaxational processes which are satisfactorily described by the decay functionf(q,t) =a·exp(–t/τ1) + (1–a)·exp(–xz), wherex=ln(t/τ0)/ln(τ2/τ0) and τ0= 10−8s. For LC in 100 Å random pores the second term describing the slow process dominates, whereas for 200 Å and 2000 Å cylindrical pores as well as 1000 Å random pores the contribution from the first term (fast process) is more visible. Since the slow relaxational process which does not exist in the bulk LC and broad spectrum of relaxation times (10−6- 10)s appear not only for LC in random pores but in cylindrical as well, we conclude that differences in dynamical behavior of confined LC from that in the bulk are mainly due to the existence of the interface.