bluuebunny/crossref_metadata_2025 huggingface dataset:
Vibronically induced decay paths from the $\tilde C$C̃1B1-state of water and its isotopomers
Authors: Dixon Richard N. , Oliver Thomas A. A. , Cheng Lina , Cheng Yuan , Yuan Kaijun , Yang Xueming
Published: March 2013

The photochemistry of the water molecule has revealed a wealth of quantum phenomena, which arise from the involvement of several coupled electronic states with very different potential energy surfaces. Most recently, dissociation from single rotational levels of its $\tilde C$C̃1B1 state near 124 nm has been attributed to a vibronically coupled decay via the lower $\tilde A$Ã-state surface, despite a large vertical energy gap of 2.8 eV. Similar conclusions have been reached for subsequent experimental data for D2O. The present paper presents further experimental data for HOD and for both the H+OD(X) and D+OH(X) products. Unlike the cases for H2O and D2O, the vibrational populations for hydroxyl products do not follow a smooth distribution with v(OH/OD). In particular, for OH there is a clear alternation in population for all the strong peaks, with odd v favoured over even v. These experimental data are analysed using new MRCI+Q calculations, which have been used to generate potential surfaces and associated non-adiabatic matrix elements for transition from the adiabatic $\tilde C$C̃-state to lower unbound potential surfaces; and hence, to guide dynamical calculations using time-dependent wavepackets. It is concluded that although there is a minor contribution from the $\tilde C$C̃→ $\tilde A$Ã decay route, the major route follows $\tilde C$C̃→ 1A2 → $\tilde A$Ã. This is mediated through two regions of near degeneracy of the elusive 1A2 surface with $\tilde C$C̃ for short bonds ca. 0.8 Å; and between 1A2 and $\tilde A$Ã with long bonds ≥2 Å, thereby bridging the vertical energy gap. The striking population alternation for the D+OH(X) products is attributed to dynamic symmetry breaking on the 1A2 surface.
Texture development in Galfenol wire
Authors: Boesenberg A. J. , Restorff J. B. , Wun-Fogle M. , Sailsbury H. , Summers E.
Published: March 2013

Galfenol (Fe-Ga alloy) wire fabrication provides a low cost alternative to directional solidification methods. This work evaluates the compositional dependence of the wire drawing suitability of Fe-Ga and characterizes the microstructural and magnetic properties of these wires. Wire has been produced with Ga contents between 10 at. % and 17 at. % to allow determination of the ductile to brittle transition (DTBT) in wire manufacture. Published results on chill cast bend specimens indicated that a DTBT occurs at roughly 15 at. % Ga. This DTBT was observed under tensile loading with a corresponding change in fracture behavior from transverse fracture to intergranular fracture. For improved magnetostrictive performance, higher Ga contents are desired, closer to the 17 at. % Ga evaluated in this work. Electron backscattered diffraction B-H loop and resonance measurements as a function of magnetic field (to determine modulus and coupling factor) are presented for as-drawn, furnace, and direct current (DC) annealed wire. Galfenol wire produced via traditional drawing methods is found to have a strong 〈110〉 (α) texture parallel to the drawing direction. As-drawn wire was observed to have a lower magnetic permeability and larger hysteresis than DC annealed wire. This is attributed to the presence of a large volume of crystalline defects; such as vacancies and dislocations.
The crystal structure and magnetic properties of Pr117Co56.7Ge112
Authors: Liu J. , Smetana V. , Gschneidner K. A. , Miller G. J. , Pecharsky V. K.
Published: March 2013

The ternary intermetallic compound Pr117Co56.7Ge112 adopts the cubic Tb117Fe52Ge112-type related structure with the lattice parameter a = 29.330(3) Å. The compound exhibits one prominent magnetic transition at ∼10 K and two additional weak magnetic anomalies are observed at ∼26 K and ∼46 K in a 1 kOe applied field. At a higher field of 10 kOe, only one broad ferromagnetic-like transition remains at 12 K. The inverse magnetic susceptibility of Pr117Co56.7Ge112 obeys the Curie-Weiss law with a positive value of the paramagnetic Curie temperature (θP = 24 K), indicating that ferromagnetic interactions are dominant. The effective magnetic moment is 3.49 μB/Pr, which is close to the theoretical effective paramagnetic moment of 3.58 μB for the Pr3+ ion.
Structure, magnetism, and magnetic compensation behavior of Co50-xMn25Ga25+x and Co50-xMn25+xGa25 Heusler alloys
Authors: Li G. J. , Liu E. K. , Zhang Y. J. , Du Y. , Zhang H. W. , Wang W. H. , Wu G. H.
Published: March 2013

The structure, magnetism, magnetic compensation behavior, exchange interaction, and electronic structures of Co50-xMn25Ga25+x and Co50-xMn25+xGa25 (x = 0–25) alloys have been systematically investigated by both experiments and first-principles calculations. We found that all the samples exhibited body centered cubic structures with high degree of atomic ordering. With increasing Ga content, the composition dependence of lattice parameter shows a kink point at the middle composition in Co50-xMn25Ga25+x alloys, which can be attributed to the enhanced covalent hybridization between the main-group Ga and the transition-metal atoms. Moreover, a complicated magnetic competition has been revealed in Co50-xMn25Ga25+x alloys, which causes the Curie temperature dramatically decrease and results in a magnetic moment compensation behavior. In Co50-xMn25+xGa25 alloys, however, with increasing Mn content, an additional ferrimagnetic configuration is established in the native ferromagnetic matrix, which causes the molecular moment monotonously decrease and the exchange interaction enhance gradually. The electronic structure calculations indicate that the Co50-xMn25+xGa25 alloys are likely to be in a coexistence state of the itinerant and localized magnetism. Our study will be helpful to understand the nature of magnetic ordering as well as to tune magnetic compensation and electronic properties of Heusler alloys.
A ferroelectric–semiconductor-coupled solar cell with tunable photovoltage
Authors: Huang Fang , Liu Xiangxin
Published: March 2013

To confirm the feasibility of nanodipole photovoltaic devices, we designed a practicable method of phase segregation to extract CdS piezoelectric nanoparticles from CdSTe mixed film. The constituent components of such device are mixture of ferroelectric CdS nanodipoles and CdTe semiconductor absorber. We observed an analogous electric hysteresis of photovoltage in such devices. Piezoresponse grain boundaries are observed, which contribute significantly to the hysteresis behavior of photovoltage. Abnormal photovoltage polarity of CdS nanodipole devices is also observed. But such phenomena cannot be explained by classical junctional device theory. We believe these provide convincing evidence for the mechanism of nanodipoles.
Surface phonon polariton characteristic of honeycomb nanoporous GaN thin films
Authors: Cheah S. F. , Lee S. C. , Ng S. S. , Yam F. K. , Abu Hassan H. , Hassan Z.
Published: March 2013

Nanoporous GaN thin films with honeycomb structure were fabricated via ultra-violet assisted electrochemical etching approach. Under different anodization voltages, two nanoporous samples with different porosity were fabricated. Porosity and surface phonon polariton (SPP) characteristics of the fabricated samples were investigated using polarized infrared attenuated total reflection technique. It was found that the porosity of nanoporous GaN has great influence on its SPP resonant frequency. It can modulate the resonance frequency towards lower value.
Plasmonic enhancement of photocurrent in carbon nanotube by Au nanoparticles
Authors: Zhou Changjie , Wang Sheng , Sun Jinling , Wei Nan , Yang Leijing , Zhang Zhiyong , Liao Jianhui , Peng Lian-Mao
Published: March 2013

We demonstrate a strong photocurrent enhancement in carbon nanotube (CNT) photodetectors by coupling the CNT with a plasmonic nanostructure made of Au nanoparticles. Comparing with the device without coupling to Au nanoparticles, more than 3 times photocurrent enhancement is observed and attributed to the strong local field enhancement on the CNT. The plasmonic near-field coupling with CNTs with different diameters is also investigated and the results suggest that CNTs with larger diameter show stronger enhancement. This work demonstrates the potential to significantly improve the performance of CNT photoelectric devices using metallic nanoparticles that support surface plasmons.
Observation of the intrinsic Gilbert damping constant in Co/Ni multilayers independent of the stack number with perpendicular anisotropy
Authors: Song Hyon-Seok , Lee Kyeong-Dong , Sohn Jeong-Woo , Yang See-Hun , Parkin Stuart S. P. , You Chun-Yeol , Shin Sung-Chul
Published: March 2013

We investigate the intrinsic Gilbert damping constant in perpendicular magnetic anisotropy Co/Ni multilayer system by means of an all-optical method. We find that the intrinsic Gilbert damping constant does not depend on the stack number and the perpendicular magnetic anisotropy when the magnetic field is high enough. In contrast, the extrinsic Gilbert damping is strongly correlated with the inhomogeneous anisotropy distribution in the low-field regime, as observed in magneto-optical images. Intriguingly, the extrinsic Gilbert damping is consistently reduced with decreasing length scale in the measurements, providing a concrete means to determine the intrinsic Gilbert damping.
Ferroelectric memristor based on Pt/BiFeO3/Nb-doped SrTiO3 heterostructure
Authors: Hu Zhongqiang , Li Qian , Li Meiya , Wang Qiangwen , Zhu Yongdan , Liu Xiaolian , Zhao Xingzhong , Liu Yun , Dong Shuxiang
Published: March 2013

We report a continuously tunable resistive switching behavior in Pt/BiFeO3/Nb-doped SrTiO3 heterostructure for ferroelectric memristor application. The resistance of this memristor can be tuned up to 5 × 105% by applying voltage pulses at room temperature, which exhibits excellent retention and anti-fatigue characteristics. The observed memristive behavior is attributed to the modulation effect of the ferroelectric polarization reversal on the width of depletion region and the height of potential barrier of the p-n junction formed at the BiFeO3/Nb-doped SrTiO3 interface.
Non-uniform magnetization reversal in nanocomposite magnets
Authors: Li Z. B. , Zhang M. , Shen B. G. , Sun J. R.
Published: March 2013

Magnetization reversal and exchange coupling are investigated in Pr-Fe-B melt-spun ribbons. In nanocomposite magnets, not only does the coercivity decrease but also magnetization reversal becomes more non-uniform in hard grains. The non-uniform magnetization reversal, resulting in a deterioration of squareness in hysteresis loop and a drop of the maximum Henkel plot value, mainly is caused by random arrangement of easy axes and intergranular soft regions among hard grains even with well exchange coupling between soft-hard grains in these ribbons. It is expected that the uniformity in magnetization reversal could be improved with the perfection of easy axes alignment in anisotropy nanocomposites.
Highly mismatched N-rich GaN1−xSbx films grown by low temperature molecular beam epitaxy
Authors: Yu K. M. , Sarney W. L. , Novikov S. V. , Detert D. , Zhao R. , Denlinger J. D. , Svensson S. P. , Dubon O. D. , Walukiewicz W. , Foxon C. T.
Published: March 2013

We have grown N-rich, dilute Sb GaN1−xSbx alloys by low temperature molecular beam epitaxy. At low growth temperature of <100 °C the material loses crystallinity and becomes primarily amorphous with small crystallites of 2–5 nm at a Sb composition of >4 at. %. Despite the different microstructures found for GaN1−xSbx alloys with different composition, the absorption edge shifts continuously from 3.4 eV (GaN) to close to 1 eV for samples with Sb content >30 at. %. GaN1−xSbx alloys with less than 5 at. % Sb show sufficient bandgap reduction (∼2 eV), making them suitable for photoelectrochemical applications.
“Quadratic nexus” and the process of democratization and state-building in Albania and Kosovo: a comparison
Authors: Krasniqi Gëzim
Published: March 2013

This paper examines the interplay between internal and external actors in the process of democratization and state-building in Albania and Kosovo. It does so by using David J. Smith's “quadratic nexus” that links Brubaker's “triadic nexus” – nationalizing states, national minorities and external national homelands – to the institutions of an ascendant and expansive “Euro-Atlantic space”. The main argument of this paper is twofold. First, it argues the nexus remains a useful framework in the study of state-and nation-building provided that it moves beyond the “civic vs. ethnic” dichotomy. Today, many states with a mixture of civic and multi-ethnic elements involve this relational nexus. Second, while comparing Albania and Kosovo, this paper argues that all the four elements of the nexus have a different impact on the process of state- and nation-building and their relationship is more conflictual in Kosovo than in Albania.
Regulatory Policy Design for Agroecosystem Management on Public Rangelands
Authors: Melkonyan Tigran , Taylor Michael H.
Published: March 2013

This paper develops a model to analyze regulatory design for agroecosystem management on public rangeland. We define and compare the efficiency of the most prominent regulatory instruments on public rangeland—input regulation, cost‐sharing/taxation, and performance regulation. We show that given informational asymmetries between ranchers and regulators within federal land management agencies, performance regulation can achieve first‐best outcomes when regulators can perfectly monitor ranch‐level ecological conditions and do not face constraints due to budget limitations or restrictions on the level of penalties they can assess, but that under imperfect monitoring and/or budgetary/penalty constraints, input regulation and cost‐sharing/taxation can dominate performance regulation.
A rate-distortion theory for gene regulatory networks and its application to logic gate consistency
Authors: Facchetti Giuseppe , Iacono Giovanni , De Palo Giovanna , Altafini Claudio
Published: March 2013

Motivation: A gene regulatory network in which the modes (activation/inhibition) of the transcriptional regulations are known and in which gene expression assumes boolean values can be treated as a system of linear equations over a binary field, i.e. as a constraint satisfaction problem for an information code.

Results: For currently available gene networks, we show in this article that the distortion associated with the corresponding information code is much lower than expected from null models, and that it is close to (when not lower than) the Shannon bound determined by the rate-distortion theorem. This corresponds to saying that the distribution of regulatory modes is highly atypical in the networks, and that this atypicality greatly helps in avoiding contradictory transcriptional actions.

Choosing a boolean formalism to represent the gene networks, we also show how to formulate criteria for the selection of gates that maximize the compatibility with the empirical information available on the transcriptional regulatory modes. Proceeding in this way, we obtain in particular that non-canalizing gates are upper-bounded by the distortion, and hence that the boolean gene networks are more canalizing than expected from null models.

Contact:  altafini@sissa.it.

Supplementary information:  Supplementary data are available at Bioinformatics online.
Corynespora cassiicola f. sp. schinii, a Potential Biocontrol Agent for the Weed Schinus terebinthifolius in the United States
Authors: de Macedo Davi Mesquita , Pereira Olinto Liparini , Wheeler Gregory Sherman , Barreto Robert Weingart
Published: March 2013

Schinus terebinthifolius (Anacardiaceae), Brazilian peppertree (BP), is a major environmental weed in many tropical and subtropical areas of the globe, including Florida, Hawai'i, and Australia. This plant has been the target of a classical biocontrol project in the United States involving pathogens collected in Brazil for several years. A fungus was found in the Brazilian state of Espírito Santo causing leaf spots and severe foliage blight on BP. Examination of the morphology and internal transcribed spacer sequence analysis confirmed that the fungus is a strain of Corynespora cassiicola. Preliminary host-range tests involving 24 species, including 11 species in the family Anacardiaceae, were conducted with the fungus, and specificity toward BP was confirmed. Plants of Brazilian pepper tree from populations in Florida and Hawai'i included in the tests became severely diseased. Therefore, the recognition of a new forma specialis—Corynespora cassiicola f. sp. schinii—is proposed. The specificity of this forma specialis and the severity of the disease it caused in the field and under controlled conditions indicate that it has the potential for use as a biocontrol agent for BP in areas where it is an exotic invasive species.
Local governance responses to social inclusion for older ruralVictorians: Building resources, opportunities and capabilities
Authors: Winterton Rachel , Clune Samantha , Warburton Jeni , Martin John
Published: March 2013

Aim

To explore how local governance enables access to resources, creates opportunities and increases capability for older people in rural communities to experience social inclusion.

Method

Twenty‐six semi‐structured interviews were undertaken with community stakeholders across two rural communities in north‐eastVictoria. Stakeholders were drawn from local government, and a range of community groups and organisations, as identified in a scoping study.

Results

Through the provision of community resources (e.g. physical and human infrastructure, organisational partnerships), local services and supports offer social and productive environments for participation. They also build individual resources (e.g. health, skills, finances, networks) to enable older people to participate within these environments, and provide assistance to allow older people to use individual and community resources.

Conclusions

Community resources are integral in facilitating the development of older people's individual resources, and opportunities and capabilities for participation. These enable greater choice in participation, and contribute to the sustainability of community resources serving ageing populations.
Towards improved guidelines for drying flood‐damaged buildings
Authors: Lamond J. , Proverbs D. , Escarameia M. , Tagg A.
Published: March 2013

In the aftermath of flood events in the UK, the insurance and the drying and repair industry are frequently criticised for the speed with which households are able to return to their homes. Delays in restoration have been attributed to lack of guidance and the need for improved methods and processes for drying buildings. A critical appraisal of available guidance and other sources relating to drying of buildings was undertaken. The review was enhanced by targeted interviews with industry experts and was validated via a stakeholder consultation workshop. The study found that a wide range of guidance is available and that most issues surrounding the drying of buildings are well covered but some gaps were identified. The findings endorse the need for new guidance but also for research into specific technical aspects of the drying process, which will help to speed up flood restoration in the future.
Substance use disorders: a theory‐driven approach to the integration of genetics and neuroimaging
Authors: Karoly Hollis C. , Harlaar Nicole , Hutchison Kent E.
Published: March 2013

The etiology of substance use disorders is related to changes in neuronal systems involved in reward anticipation, negative affect, and withdrawal, as well as to alterations in inhibition and executive control. Genetic and epigenetic variation associated with individual differences in these mechanisms may be important for predicting the effectiveness of current treatments and informing future pharmacogenomic investigations. Genetic research efforts have increasingly involved the use of approaches that leverage neurobiological phenotypes to link changes at the molecular level (e.g., genetic and epigenetic variation) to changes in intermediate neuroimaging phenotypes, and ultimately to clinical outcomes. The current review summarizes recent efforts that utilize neuroimaging and genetic approaches in the context of a three‐stage model of addiction. In addition, this review explores how these approaches have been used to study the progression from impulsive, recreational substance use to the compulsive, addicted state. Finally, this review describes future ways that research may incorporate these approaches to examine important stage‐specific mechanisms of addiction.
Spatial modelling of road network development, population pressure and biophysical properties of upland crop and forest conversions in Lop Buri province, Thailand, 1989–2006
Authors: Patarasuk Risa , Fik Timothy J.
Published: March 2013

Over the past few decades, land use and land cover change has become a global concern. In the Lop Buri province of Thailand, rapid land cover change, specifically conversion of forests to agriculture, has occurred. The purpose of the study is to identify the predictors of land cover change in Lop Buri province for land that has been converted to upland crops or has undergone deforestation between 1989 and 2006. Four logistic regression models were constructed using spatially explicit biophysical and geo‐social data, to account for changes to upland crops and forest loss from1989–98 and 1998–2006. Across the four models, slope, distance to forest edge, distance to towns, distance to roads, population size, and population density in various stand‐alone and interactive forms were found to be the most consistent predictors of land cover change.
Turbulence Measurements in a Heated, Concave Boundary Layer Under High-Free-Stream Turbulence Conditions
Authors: Kestoras M. D. , Simon T. W.
Published: March 2013

Turbulence measurements for both momentum and heat transfer are taken in a lowvelocity, turbulent boundary layer growing naturally over a concave wall. The experiments are conducted with negligible streamwise acceleration and a nominal freestream turbulence intensity of ∼8 percent. Comparisons are made with data taken in an earlier study in the same test facility but with a 0.6 percent free-stream turbulence intensity. Results show that elevated free-stream turbulence intensity enhances turbulence transport quantities like uv and vt in most of the boundary layer. In contrast to the low-turbulence cases, high levels of transport of momentum are measured outside the boundary layer. Stable, Go¨rtlerlike vortices, present in the flow under low-turbulence conditions, do not form when the free-stream turbulence intensity is elevated. Turbulent Prandtl numbers, Prt, within the log region of the boundary layer over the concave wall increase with streamwise distance to values as high as 1.2. Profiles of Prt suggest that the increase in momentum transport with increased free-stream turbulence intensity precedes the increase in heat transport. Distributions of near-wall mixing length for momentum remain unchanged on the concave wall when free-stream turbulence intensity is elevated. Both for this level of free-stream turbulence and for the lower level, mixing length distributions increase linearly with distance from the wall, following the standard slope. However, when free-stream turbulence intensity is elevated, this linear region extends farther into the boundary layer, indicating the emerging importance of larger eddies in the wake of the boundary layer with the high-turbulence free stream. Because these eddies are damped by the wall, the influence of the wall grows with eddy size.
Controls and Diagnostics Committee Best 1994 Paper Award: Modeling for Control of Rotating Stall in High-Speed Multistage Axial Compressors
Authors: Feulner M. R. , Hendricks G. J. , Paduano J. D.
Published: March 2013

Using a two-dimensional compressible flow representation of axial compressor dynamics, a control-theoretic input–output model is derived, which is of general utility in rotating stall/surge active control studies. The derivation presented here begins with a review of the fluid dynamic model, which is a two-dimensional stage stacking technique that accounts for blade row pressure rise, loss, and deviation as well as blade row and interblade row compressible flow. This model is extended to include the effects of the upstream and downstream geometry and boundary conditions, and then manipulated into a transfer function form that dynamically relates actuator motion to sensor measurements. Key relationships in this input–output form are then approximated using rational polynomials. Further manipulation yields an approximate model in standard form for studying active control of rotating stall and surge. As an example of high current relevance, the transfer function from an array of jet actuators to an array of static pressure sensors is derived. Numerical examples are also presented, including a demonstration of the importance of proper choice of sensor and actuator locations, as well as a comparison between sensor types. Under a variety of conditions, it was found that sensor locations near the front of the compressor or in the downstream gap are consistently the best choices, based on a quadratic optimization criterion and a specific three-stage compressor model. The modeling and evaluation procedures presented here are a first step toward a rigorous approach to the design of active control systems for high-speed axial compressors.
Variable Geometry Pipe Diffusers
Authors: Salvage J. W.
Published: March 2013

Theoretical analyses and experimental results are reported for two unique variable geometry techniques used with pipe diffusers to enhance off-design performance. One technique mechanically closes the diffuser throat in an unusual manner. The other allows flow recirculation to close the throat artificially while attempting to improve diffuser inlet flow characteristics. Results clearly show that surge margin may be significantly improved by either method and that flow recirculation may offer improved efficiency.
Synthesis and Generation of Surfaces Milled by Ball Nose End Mills Under Tertiary Cutter Motion
Authors: You S. J. , Ehmann K. F.
Published: March 2013

The synthesis and generation of milled surfaces under tertiary cutter motion of the spindle with ball nose end mills was investigated and shown that a multitude of surface topographies can be generated. A basis for theoretical investigation was established by the derivation of the tooth path equations and the development of computer simulation models for ball nose end milling processes. The accuracy of the developed computer model and the feasibility of the tertiary cutter motion concept were subsequently authenticated and verified by the agreement between the experiments and the computer simulations.
Optimization Methods Applied to Selecting Support Positions in Fixture Design
Authors: Menassa R. J. , DeVries W. R.
Published: March 2013

This paper proposes optimization techniques to assist in the design and evaluation of fixtures for holding prismatic workpieces. This formulation of the fixturing design problem takes into account deflection of the workpiece subjected to assembly or machining loads. Using the minimization of the workpiece deflection at selected points as the design criterion, the design problem is determining the positions of the fixture supports. The Finite Element Method is used for calculating deflections that are the basis for the design objective function, and the Broyden-Fletcher-Goldfarb-Shanno optimization algorithm is used to determine the fixture support positions. In this paper the proposed objective function is developed and the method is illustrated with three numerical examples.
Inspection of Roller Bearing Surfaces with Laser Doppler Vibrometry
Authors: Georgeson J. D. , Lieu D. K.
Published: March 2013

Laser Doppler Vibrometry is presented as an effective method of measuring surface profiles of rolling contact bearing balls. An experimental setup and signal processing algorithm are used to obtain digitized surface profiles and statistical measurements of ball surfaces. Tests are made on two different grades of high precision balls and the results are compared. Measurements are presented that match lobed ball frequency results with a resolution of 0.025 microns. The method is well suited for a manufacturing environment because of its durability, simplicity, and high speed.
Signature of Machine Tool Errors on Surface Texture by DDS
Authors: Pandit S. M. , Shunmugam M. S.
Published: March 2013

The dynamic effect of machine tool errors leaves its signature on machined surfaces. This paper proposes an application of data dependent systems (DDS) methodology to recover this signature from the surfaces in a comprehensive manner and provides a realistic basis for machine-tool acceptance. The approach is illustrated by experimental results from three different lathes. It is shown that relative contributions due to the feed wavelength reveal the dynamic performance of the machine tools. The deviation from the nominal and the spread of the estimated feed wavelength quantify the accuracy and rigidity, the feed wavelength being precisely maintained with minimal spread in a machine tool with high accuracy and high rigidity. Presence of other wavelengths and their relative contribution to the RMS surface roughness serve as quantitative indicators of other machine tool errors.
Development of an Adaptive Force/Position Controller for Robot-Automated Composite Tape-Layering
Authors: Yao Y. L. , Wu S. M.
Published: March 2013

The quality of parts produced by a composite tape-laying process is sensitive to the contact force exerted and the abutment of adjacent tape courses kept when the tapes are laid. Thus, a prerequisite for a high performance laying process automated by means of industrial manipulators is the ability to regulate laying force and position precisely in the presence of robot motion inaccuracies and laying contour variations. An on-line adaptive force/position controller for robot-automated laying processes was presented. The contact force error normal to a laying surface is measured by a wrist sensor in real time, while the position error tangent to the surface is measured by sensors found in manipulator joints. Both are modeled as autoregressive (AR) processes, on the basis of which future errors in Cartesian coordinates are forecasted. Via a compliance selection matrix, both predicted errors are fed to joint actuators in a similar manner for taking compensatory actions. In view of the similarity, the force control portion of the scheme was implemented in an experiment using a three degree-of-freedom manipulator and the results indicated a 40 percent average reduction in contact force variations.
Ice Pressure Measurements Using PVDF Film
Authors: Joensuu A.
Published: March 2013

Piezoelectric ice pressure measuring devices have been constructed using polyvinylidene fluoride (PVDF) film. PVDF seems to be an appealing transducer material since it is light, thin, mechanically resistant and can be attached on surfaces with complicated geometries. Moreover, it is commercially available in large sheets. Dynamic ice pressure distribution can be monitored using various metalization patterns thus dividing the areas into many active cells. Because minimum mechanical deformation is needed for the piezoelectric phenomenon to take place, the device does not interfere with the quantity to be measured. It is believed that the material will help to shed light on the ice pressure formation process in crushing. The paper deals with full-scale experiments conducted using PVDF film on the contact surfaces of a test hammer and a cylindrical indentor, and describes the signal treatment used.
Vortices in Motionless Media
Authors: Winfree A. T.
Published: March 2013

Three-dimensional continua capable of recurrent local activation are observed—both in the laboratory and in mathematical models—to support persistent self-organizing patterns of activity most conveniently described in terms of vortex lines. These lines generally close in rings, which may be linked and knotted. In some cases they adopt stable configurations resembling tiny dynamos of millimeter dimensions. The dynamics of these “organizing centers” has been investigated in certain chemical reactions, in heart muscle, and numerically in digital computers. The pertinent mathematical principles appear to entail consequences of local reaction and neighborhood diffusion, in the form of a dependency of the vortex filament’s lateral motion upon its local geometry and, when too closely approached by another segment of vortex filament, upon the distance and orientation involved.
Fluid-Inertia Effects in Radial Flow Between Oscillating, Rotating Parallel Disks
Authors: Warinner D. K. , Pearson J. T.
Published: March 2013

An order-of-magnitude analysis is applied to the Navier-Stokes equations and the continuity equation for isothermal, radial fluid flow between oscillating and rotating disks. This analysis investigates the four basic cases of 1) steady, radial flow, 2) unsteady, radial flow, 3) steady, spiral flow, and 4) unsteady, spiral flow. It is shown that certain values of particular dimensionless parameters for general cases will reduce the Navier-Stokes equations to simplified forms and thus render them amenable to closed-form solutions for, say, the pressure distribution between oscillating, rotating disks. The analysis holds for laminar and turbulent flows and compressible and incompressible flows. The conditions that must be satisfied for one to reasonably neglect 1) rotation, 2) unsteady terms, and 3) convective terms are set forth. One result shown is that only rarely could one reasonably neglect the radial convective acceleration while retaining the radial local acceleration.
The Influence of Linear and Rotating Motions on the Friction of Polymers
Authors: Briscoe B. J. , Stolarski T. A.
Published: March 2013

A series of experiments are described where combined linear and rotating motions are imposed upon a polymer while it is in contact with a smooth and clean counterface. Friction data are presented for a series of polymers, which reflect the main tribological groups, for a range of linear and angular velocities. The main conclusion is that within certain ranges of contact conditions, which the paper defines in part, three polymers, PTFE, high density polythene and ultrahigh molecular weight polythene, exhibit a response which is markedly different from that of the other polymers investigated. For the PTFE group of polymers the measured force attains a pronounced maximum value as rotation is introduced. The other polymers show no such effect. The phenomena are associated with the natural tendency of PTFE type polymers to undergo reorientation of the matrix at the interface during sliding. The results suggest a method of sensing the nature of the energy dissipation process during sliding and also accounts for an artefact which may be observed with PTFE materials when their friction is monitored in a pin-on-disk configuration.
An Experimental Investigation of the Pressures at the Edge of a Gas Bearing Pocket
Authors: Boffey D. A. , Wilson P. M.
Published: March 2013

Pressure profiles measured across the film/pocket interface of an externally-pressurized air-lubricated circular thrust bearing are presented. One of the thrust pads was vibrated in an attempt to simulate a pneumatic hammer type motion. The results show that at the bearing surface the pressure perturbations in the pocket are generally much higher than those in the film. It is argued that these results tend to reconcile an earlier discrepancy between theory and experiment in the prediction of stability.
Detection of Delamination Cracks in Layered Fiber-Reinforced
Composite Plates
Authors: Karim M. R. , Kundu T. , Desai C. S.
Published: March 2013

In this paper, the dynamic response of delamination cracks in a layered fiber-reinforced composite plate is analytically studied. The plate is subjected to an antiplane loading and its surface response is computed in absence as well as in presence of delaminatioin cracks. To what extent the surface response is influenced by the presence of internal delamination cracks is investigated here. This study is important for nondestructive evaluation of internal damage in composites due to delamination. The problem is formulated in terms of integral equations in frequency domain. These equations are then solved by expanding the unknown crack opening displacement in a complete set of Chebychev’s polynomials, whose coefficients are solved by satisfying the traction-free condition at the crack surface. The time histories are obtained numerically by inverting the spectra via Fast Fourier Transform (FFT) routine. The results show significant influence of delamination crack geometries on the surface response of the plate.
Dynamic Deformation of Orthotropic Cylinders
Authors: Cederbaum G. , Heller R. A.
Published: March 2013

The theory of thick orthotropic shells is used here to analyze a cylinder subjected to dynamic loads. The formulation includes shear deformation and rotatory inertia effects similarly to the first-order, shear deformation, laminated plate theory. Dynamic line loads (along the longitudinal direction) and patch loads are considered. The time-dependent part of the load is a step pulse or a half-sine wave.
Stress Intensity Factors of Semi-Elliptical Cracks in a Tubular
Welded Joint Using Line Springs and 3D Finite Elements
Authors: Du Z.-Z. , Hancock J. W.
Published: March 2013

A tubular welded T-joint containing a series of semi-elliptical cracks of increasing depth located near the chord-brace intersection, has been analyzed using shell elements with the cracks modeled by the line spring concept of Rice and Levy [1]. The same problem has also been modeled with 20-noded bricks allowing the stress intensity factors to be determined by virtual crack extension. The direction of crack growth has been determined both using off-axis virtual crack extension and solutions for kinked cracks, to determine the orientation which maximize either the strain energy release rate G or KI. The calculated crack path agrees with reported experiments [2]. Finally, the stress intensity factors for straight and curved cracks in single welded joints have been compared in terms of their effective depth.
Liquid/Vapor Action in a Vessel During Blowdown
Authors: Moody F. J.
Published: March 2013

Vapor bubble rise forms the basis for a theoretical study of liquid/vapor action in a saturated system during blowdown. Methods are developed and demonstrated for predicting time and space dependent mixture properties. Graphs are presented for estimating the time-dependent mixture level during steam, water, and mixture blowdowns from 1000 psia. Theoretical mixture levels are compared with vapor blowdown experiments. Although calculations strongly depend upon bubble rise velocity in the liquid, reasonable agreement with data is shown.
Turbine Blade Vibration Due to Nozzle Wakes
Authors: Heymann F. J.
Published: March 2013

Turbine blade vibrations due to resonance with the nozzle passing frequency have been measured and discussed with primary emphasis on the relationships between the resonant stresses and the stage flow parameters. Vibratory stresses were measured in a full admission, single-stage, impulse steam turbine test facility. The blading was shrouded into 6-blade groups, designed to bring the out-of-phase tangential modes into resonance. Some comparisons are made between measured and predicted frequencies and mode shapes. The variation of stresses, with such parameters as stage torque, velocity ratio, and mass flow, was studied by testing at eleven different operating conditions. It was found that stresses increased with torque, but less than proportionately so. It was found that stresses varied with velocity ratio in a complicated fashion, reaching a maximum and then a minimum as velocity ratio is increased. These empirical results are interpreted qualitatively in the light of available theory. It is concluded that the apparent dependence on velocity ratio may also reflect a dependence on Mach number and a dependence on the number of wakes in simultaneous engagement with a given blade. The same rotor blading was tested with two sets of nozzle (stator) blades of different sizes, and some data were also obtained at various values of axial spacing between rotating and stationary blades. The interrelationship between the effects of relative sizes and spacing between the two blade rows is discussed.
A Research Study on Internal Corrosion of High-Pressure Boilers
Authors: Goldstein P.
Published: March 2013

The following report is the third and last in a series describing the progress of “A Research Study on Internal Corrosion of High Pressure Boilers.” The first report described the background, scope, and organization of the program as well as the test facility. The second report discussed the methods of testing and the results of the first six runs. This final report describes the results of the last six tests and discusses the conclusions drawn from all of Phases II and III. The scope and an outline of seven tests composing the newly scheduled Phase IV program are also included. The results of runs with three types of boiler water treatment, fouled heat transfer surfaces, and conditions simulating fresh water and seawater condenser leakage are included. Data relating to deposition and corrosion in these environments are presented with particular emphasis on the severe corrosion experienced with simulated seawater condenser leakage.
Polynuclear Hydrocarbon Emission From Coal-Fired Installations
Authors: Diehl E. K. , du Breuil F. , Glenn R. A.
Published: March 2013

Trace quantities of the polynuclear hydrocarbons have been identified in flue gases resulting from combustion or carbonaceous fuels. Some of these hydrocarbons, particularly benzo(a)pyrene, possess known carcinogenic properties and are of some concern in the overall assessment of the effects of atmospheric pollution. An investigation was carried out under a two-year grant received from the U. S. Public Health Service to determine the occurrence of polynuclear hydrocarbons in the flue gases from various coal-fired steam-generating installations. The paper describes the preliminary work leading to the development of satisfactory sampling and analytical procedures and gives the results obtained from sampling various field installations.
Regenerative Thermomagnetic Power
Authors: Resler E. L. , Rosensweig R. E.
Published: March 2013

Thermomagnetic power devices utilize the temperature dependence of magnetic moment to convert heat into organized energy. In an analogous manner thermoelectrostatic devices would utilize changes of electric moment to perform the same function and the analysis of each can be given in a single treatment. This paper, which analytically explores new considerations relevant to these energy conversion methods, is motivated by a search for increased performance. To begin, a basis for the treatment of the thermodynamics of polarizable substances is developed in a manner that stresses material parameters. Explicit thermodynamic functions are then derived corresponding to both a simple and a realistic equation of state. With this information power cycles are devised and evaluation is made of their thermodynamic efficiencies. An optimum regenerative cycle emerges and criteria for its attainment are considered. Finally, a power estimate accounting for thermal irreversibilities predicts the possibility of low specific weight. Using more general conversion techniques than were admitted in the past, the prospect for thermomagnetic and thermoelectrostatic energy conversion is greatly improved.
A Simple Proof That Generic 3-RPR Manipulators Have Two Aspects
Authors: Coste Michel
Published: March 2013

Avoiding singularities in the workspace of a parallel robot is an important issue. The case of 3-RPR planar robots is an important subject of theoretical studies. We study the singularities of planar 3-RPR robots by using a new parameterization of the singular locus in a modified workspace. This approach enables us to give a simple alternative proof of a result recently proved by Husty: the complement of the singular locus in the workspace of a generic 3-RPR manipulator has two connected components (called aspects); we also give a procedure to design a singularity-free path connecting any two points in the same aspect. The parameterization introduced in this paper, due to its simple geometric properties, proves to be useful for the study of the singularities of 3-RPR robots.
Effect of Design Parameters on Drop Test Performance of Wafer Level Chip Scale Packages
Authors: Tumne P. , Venkatadri V. , Kudtarkar S. , Delaus M. , Santos D. , Havens R. , Srihari K.
Published: March 2013

Today’s consumer market demands electronics that are smaller, faster, and cheaper. To cater to these demands, novel materials, new designs, and new packaging technologies are introduced frequently. Wafer level chip scale package (WLCSP) is one of the emerging package technologies that have the key advantages of reduced cost and smaller footprint. The portable consumer electronics are frequently dropped; hence, the emphasis of reliability is shifting toward the study of effects of mechanical shock loading increasingly. Mechanical loading typically induces brittle fractures (also known as intermetallic failures) between the solder bumps and the bond pads at the silicon die side. This type of failure mechanism is typically characterized by the board level drop test. WLCSP is a variant of the flip-chip interconnection technique. In WLCSPs, the active side of the die is inverted and connected to the printed circuit board (PCB) by solder balls. The size of these solder balls is typically large enough (300 μm pre-reflow for 0.5-mm pitch and 250 μm pre-reflow for 0.4-mm pitch) to avoid the use of underfill that is required for the flip-chip interconnects. Several variations are incorporated in the package design parameters to meet the performance, reliability, and footprint requirements of the package assembly. The design parameters investigated in this effort are solder ball compositions with different silver (Ag) contents, backside lamination with different thicknesses, WLCSP type—direct and redistribution layer (RDL), bond pad thickness, and sputtered versus electroplated under bump metallurgy (UBM) deposition methods for 8 × 8, 9 × 9, and 10 × 10 array sizes. The test vehicles built using these design parameters were drop tested using Joint Electron Devices Engineering Council (JEDEC) recommended test boards and conditions as per JESD22-B11. Cross-sectional analysis was used to identify, confirm, and segregate the intermetallic and bulk solder failures. The objective of this research was to quantify the effects and interactions of WLCSP design parameters through drop test. The drop test data were collected and treated as a right censored data. Further, it was analyzed by fitting empirical distributions using the grouped and ungrouped data approach. Data analysis showed that design parameters had a significant effect on the drop performance and played a vital role in influencing the package reliability.
Simulation of the Physics of Flight
Authors: Lane W. Brian
Published: March 2013

Computer simulations continue to prove to be a valuable tool in physics education. Based on the needs of an Aviation Physics course, we developed the PHYSics of FLIght Simulator (PhysFliS), which numerically solves Newton's second law for an airplane in flight based on standard aerodynamics relationships. The simulation can be used to pique students' interest, teach a number of physics concepts, and teach computational investigation techniques. This paper describes the development and operation of this simulation, illustrates an example study that can be performed using it, and suggests further ideas for its use.