bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimal Parameters of an Electromagnetic Actuator for Actively Controlling the Vibration of a Flexible Rotor-Shaft System
Authors: Das Anindya S. , Roy Tarapada , Dutt Jayanta K.
Published: April 2011

The present work deals with finding the optimum parameter of a control system that utilizes an electromagnetic actuator to actively attenuate the vibration amplitude of a flexible rotor-shaft-bearing system. The equations of motion of the rotor-shaft-bearing system is found out using the finite element method and the rotor-shaft is modelled by beam finite element taking into account of the effects like distributed inertia, flexural stiffness, gyroscopic effect and internal material damping. Optimum actuator location and the optimal set of actuator and control parameters are found out using Genetic Algorithm based approach, where the objective is to minimize response amplitude with least amount of control cost with a specified margin of stability. The control parameter found in this approach is quite efficient in achieving the desired objective.
Novel Sensor Placement for Damage Identification in a Cracked Complex Structure With Structural Variability
Authors: Hong Sung-Kwon , Epureanu Bogdan I. , Castanier Matthew P.
Published: April 2011

The focus of this work is on sensor placement for structural dynamic analysis and damage detection. In particular, novel sensor placement techniques are presented for the detection of cracks in ground vehicles and other complex structures. These techniques are designed to provide vibration characteristics for complex structures that have both cracks and structural variability (such as uncertainty in the geometry or the material properties). Such techniques are needed because structural variability affects the mode shapes of a structure, and thus the optimal sensor locations for detecting cracks are affected. Two approaches are developed and used: (a) parametric reduced order models (PROMs), and (b) bilinear mode approximation (BMA). Based on PROMs and BMA, a novel sensor placement method (which uses a derivative of the effective independent distributed vector algorithm) is used to determine the optimal sensor locations for complex structures with cracks and structural variability. The approach can also be used to estimate the crack length. The length is identified by using a few mode shapes and only a few selected measurement locations. The information from the sensors can be used to determine variations in mode shapes of the structure (between healthy and cracked states) for different crack lengths. The variation in mode shapes can then be used to identify the crack length. Numerical results are presented for a ground vehicle frame. The sensor placement method is applied first to find the optimal sensor locations for a structure with a crack and parameter variability, and then to identify the length of a crack.
Modeling of Cyclic Response of High Temperature Shape Memory Alloys Undergoing Viscoplastic Mechanisms
Authors: Chatzigeorgiou George , Chemisky Yves , Lagoudas Dimitris C.
Published: April 2011

In this work we present a constitutive model for High Temperature Shape Memory Alloys (HTSMAs), where the appearence of viscoplastic mechanisms during transformation influences the cyclic response of the actuator performance. Based on previous models developed for conventional SMAs, a Gibbs free energy potential is defined and the evolution equations for forward, reverse transformation, plasticity occuring during transformation, retained martensite and viscoplasticity are properly chosen. The calibration of the model is achieved with the help of experimental tests performed on TiPdNi alloy. The transformation behavior of the material is calibrated using fast load biased thermal cycling tests at selected stress levels with fast cooling/heating rate. The viscoplastic behavior of the HTSMA is captured with creep and uniaxial tests at appropriate temperature levels. Predictions of the model are compared with load biased thermal cycling tests at slow cooling/heating rate, where viscoplastic strains are significant.
Constitutive Modeling of Magneto-Thermo-Mechanical Response of Field-Induced Phase Transformations in NiMnCoIn Magnetic Shape Memory Alloys
Authors: Haldar Krishnendu , Lagoudas Dimitris C. , Basaran Burak , Karaman Ibrahim
Published: April 2011

In this work we model the magnetic field induced phase transformation (FIPT) of magnetic shape memory alloys (MS-MAs). The working principle of such materials is described by the cross coupling of mechanical, thermal and magnetic fields. The Thermo-magneto-mechanical constitutive equations are derived in a thermodynamic consistent way. A 3-D stress-field-temperature phase diagram is constructed using the model. The model is calibrated from the experimental data and the model predictions are compared with experimental results.
Dynamic Analysis of a Smart Base-Isolation System Based on MR Elastomers
Authors: Jung Hyung-Jo , Park Jeong-Su , Koo Jeong-Hoi
Published: April 2011

This paper presents a numerical investigation of a smart base isolation system employing magneto-rheological (MR) elastomers or an MR elastomer-based base isolation system. MR elastomers are a new class of smart materials whose elastic modulus or stiffness can be adjusted depending on the magnitude of the applied magnetic field. Hence, they can be used as controllable stiffness elements in engineering systems. The primary goal of this study is to investigate the dynamic performance of the smart base-isolation in mitigating excessive vibrations of a building structure under earthquake loadings. To this end, a five-story shear building model coupled with a smart base-isolation is developed. Using this model, a series of numerical simulations is performed to evaluate the effectiveness of the MR elastomer-based base isolation system under several historic seismic excitations. The results show that the proposed base isolation system outperform the conventional passive-type base isolation system in reducing the responses of the building structure for all seismic excitations considered in this study.
Piezoresistance Characterization of Poly(Dimethyl-Siloxane)-Multiwall Carbon Nanotube Composites
Authors: Rizvi Reza , Makaremi Sara , Botelho Steven , Biddiss Elaine , Naguib Hani
Published: April 2011

This study examines the piezoresistive behavior of polymer-conducting filler composites. Piezoresistive composites of Poly(dimethyl-siloxane)-Multiwall Carbon Nanotube (PDMS-MWNT) were prepared using a direct mixing approach. The dispersion and the electrical conductivity of the composites were characterized at various MWNT compositions. The piezoresistive behavior under compression was measured using an Instron Universal Tester/Digital Sourcemeter combination. Negative piezoresistive behavior was observed signifying a reducing mean inter-particulate distance in the composites. Moreover, the sensitivities increased at two compositional values of 3 and 5 wt% MWNT in PDMS, which was associated with the state of MWNT dispersion observed. Tensile piezoresistive behavior of the PDMS-MWNT adhered on a fabric substrate was also characterized. Positive piezoresistive values, indicating increasing inter-particulate distance, were observed. Significant challenges in the implementation of PDMS-MWNT as sensory materials in electronic-textile applications were observed as a result of this study and have been discussed.
Optimisation of an SMA-Based Morphing Architecture
Authors: Brindisi Angela , Ameduri Salvatore , Tiseo Barbara , Concilio Antonio
Published: April 2011

Aircraft morphing architectures are currently worldwide investigated to explore the possibility of attaining better performance while reducing weights, volumes and costs of the whole wing system. It is well-known that a 3-flap wing, for instance, shall pay a penalty up to 100% due to the insertion of mechanical devices in its body. Moreover, the insertion of nacelles, aimed at covering the mechanical devices, disturb the wing aerodynamics itself. Also, flapped wings are noisy. The introduction of deformable instead of the classical slotted and flapped wings may lead to significant enhancement also in this field. In the frame of the Joint European Initiative on Green Regional Aircraft, inside a cooperation with the University of Naples, Department of Aerospace Engineering, the authors with their colleagues came to the definition of novel architectures, aimed at those aims. These structures are characterized by load-bearing actuators, a concept that allows overcoming the classical paradox of smart structure systems: capability of bearing loads while attaining (very) large deformations.
Sensitivity of Magnetorheological Damper Behavior to Perturbations in Temperature
Authors: Cesmeci Sevki , Wilson Nicholas L. , Wereley Norman M. , Sahin Ismail
Published: April 2011

In this study, the temperature dependent dynamic behavior of a magnetorheological (MR) damper is characterized. Substantial effort has been devoted to developing an understanding of the dynamic behavior of MR dampers with virtually no emphasis on temperature effects. However, MR dampers can experience large variations in temperature during operation as a result of damper self-heating, which may cause significant perturbations to its damping and yield force. Temperature variations also induce stiffness changes in the pneumatic accumulator due to gas law effects. To model temperature dependent effects, an MR damper, which was designed and fabricated for a ground vehicle seat suspension application, was tested over temperatures ranging from 0 °C to 100 °C at a constant frequency of 4 Hz and a constant amplitude of 7.62 mm on an MTS-810 material testing system equipped with a temperature-controlled environmental chamber. To model the MR damper behavior, a parametric algebraic model was used due to its physically motivated, low computational cost and high accuracy. Temperature dependent model parameters are identified from the experimental data by using a curve fitting method. Perturbations in model parameters arising over the tested temperature range indicate that yield force and post-yield viscosity are strongly dependent on temperature. As operating temperature increased from 0°C to 100°C, the controllable yield force decreased by up to 20%, the post-yield damping decreased by over 60%, and the stiffness at high piston velocity also increased significantly.
Use of Nanoparticles for the Development of High-Performance Nanoresins
Authors: Gudapati Vamshi M. , Ghasemi-Nejhad Mehrdad N.
Published: April 2011

In this study, a brittle epoxy resin has successfully been toughened by very small concentrations of SiC and diamond nanoparticles. The tensile stress-strain response (based on the ASTM tensile tests for polymers) and the fracture energy release rate, GIC, (based on the ASTM Single-Edge-Notched-Bending, SENB, tests for polymers) of neat and nano-reinforced epoxy were characterized over a range of nanoparticle concentrations. The maximum elevation of the fracture toughness, GIC, occurred at a very small particle concentration of about 0.2% by weight, for both diamond and SiC nanoparticles). This was also manifested as higher tensile failure stress and strain. The elevation of fracture toughness is most likely due to crack front trapping of the particles that promoted subsequent local plastic deformation. Scanning electron micrographs of the fracture surfaces for samples tested in tension and fracture showed the transition of epoxy behavior from brittle-to-ductile-to-brittle with increasing weight percentage of nanoparticles. At higher particle concentrations, flaky fracture surface was observed and the fracture toughness dropped, attaining values similar to the unreinforced polymer, which is attributed to agglomeration of the nanoparticles.
Twist Control of Aerodynamic Profiles by a “Reactive” Method (Experimental Results)
Authors: Runge Jean-Baptiste , Osmont Daniel , Ohayon Roger
Published: April 2011

Active twist control of airfoils by means of embedded actuators has been widely studied during the last decade (NASA, University of Maryland, DLR, ONERA, …) To control the twist of the profile, an additional torsional moment is applied by means of these actuators. The method is very efficient but has some limitations because the actuators need an input of energy proportional to the torsional elastic energy which can be a high input. Rather than applying an additional torsional moment, it is proposed to modify the torsional moment by changing the location of the shear center of the profile by means of an internal mechanical system. The modification of the internal structure is not energy consuming compared with active control. This method needs an external force to be effective, so it is called a “reactive” control method. Experimental investigations have been done to verify the efficiency of the method proposed.
Smart Self Sealing Pressure Vessels and Structural Panels
Authors: Huston Dryver , Hurley David
Published: April 2011

Structural systems that autonomously repair damage have the potential for enhanced longevities and performance envelopes. This paper addresses the issue of autonomously sensing and controlling self-repair processes in structural systems. Such an approach has the potential to expand upon self healing materials technology to the development of engineered smart self-healing structural systems. This involves coordinating damage-sensing capabilities with control of the healing processes. Much of the conceptual underpinning of this work comes from biological systems that routinely combine sensing with healing actions that span multiple spatial and temporal scales. The specific details and modalities of the response depend on the extent and vital threat of the damage. Coordination of antagonistic repair and material remodeling processes with a self-aware sense of health is an essential part of the process. This paper describes the results of experimental and system development efforts that attempt to mimic some aspects of coordinated self-healing in structural systems. This research expands and demonstrates the enhancement of autonomous repair techniques through the coordinated damage sensing and directed repair activities with test bed pressure vessels and structural panels that have been damaged by puncture and drilling of holes. Acoustic emission, embedded optical and capacitance sensors detect the damage. Thermoplastic repair techniques are initiated upon repair detection and localization of damage. Autonomous leak repair in pneumatic pressure vessels and panels with perforations up to 3 mm upon detection and localization of the damage are demonstrated.
Towards Self-Sensing of DEAP Actuators: Capacitive Sensing Experimental Analysis
Authors: York Alexander , Seelecke Stefan
Published: April 2011

Dielectric Electro-Active Polymers (DEAP’s) have become attractive material for various actuation and sensing applications such as light weight and energy efficient valve and pumping systems. The materials ability to act as both and actuator and a sensor enable DEAP actuators to have “self-sensing” capabilities. This advancement provides low cost actuator systems that do not require external sensors for feedback control. This paper explores the capacitive sensing capabilities of a DEAP actuator under loading conditions typical for pumping and valve applications. The capacitive sensing capabilities of the actuator are tested using a method similar to that used by Jung et al. [1] which uses the DEAP actuator as a variable capacitor in a high pass filter circuit. This sensing circuit produces a direct voltage output when the actuator is displaced. The sensing response of this system is experimentally investigated under mechanical loading. The sensor is shown to have an effective sensitivity of .041 (V/Vexc) / mm. In addition, the initial results of a dual sensing and actuating system are presented.
Thermomechanical Models for NiTi Shape Memory Alloys and Their Applications
Authors: Sedla´k Petr , Frost Miroslav , Ben Zineb Tarak , Sˇittner Petr
Published: April 2011

Optimal design of SMA structures must be based on a deep knowledge of the material properties. As the SMA structures increase in complexity (stents, textiles, microdevices), modeling becomes increasingly involved. Macroscopic models of shape memory alloys are being developed with the ultimate aim to effectively simulate thermomechanical response of a constitutive material element. Computational robustness, stability, adaptability and reasonable computational time with respect to the modeling goal becomes however an issue which seems to play an ever increasing role. For instance, the non-proportional mechanical loading seems to be one of the most challenging issues for models of shape set wire structures as stents or textiles made of wires. Based on systematic experimental research of behavior of NiTi wires in uniaxial tension and tension-torsion tests, we discuss several weak aspects of the existing phenomenological models and describe here a SMA material model optimized for simulation of NiTi wire structures where combination of tension, torsion and bending strains dominate.
Canaries Development via Combinatorial Materials Science Techniques for Prognostics and Health Management in Electronics Systems
Authors: Quintero Aguilo Pedro O. , Valentin Ricky , Caceres Valencia Pablo
Published: April 2011

The design of a canary in a system aims at the detection of failures without causing an error in the system. The idea behind a canary is to have a system that will provide an early warning in a way that a fault-tolerant system will continue its intended function despite the potential presence of hardware errors. This paper presents methods to collect and analyze life-cycle environmental and usage data for in-situ health assessments. The FARM method is also provided to develop a canary life cycle monitoring plan, that encompasses the selection of environmental and usage parameters. The multidimensional failure space of a system is analyzed with combinatorial material science. A case study is presented to illustrate the methodology.
Preparation of TiO2 Polymer Nanodielectrics via a Solvent-Based Technique
Authors: Khodaparast Payam , Ounaies Zoubeida
Published: April 2011

The effect of adding surface-functionally treated TiO2 nanoparticles on dielectric properties of PVDF matrix was investigated. Porosity of the nanocomposite films showed to have an impact on dielectric permittivity results. Thermal annealing was proposed as an effective way to overcome the porosity problem. By combination of surface treatment of particles and thermal annealing of nanocomposite films, considerable enhancement in dielectric permittivity of TiO2-PVDF nanocomposites was achieved. The experimental results were far higher than theoretical values based on Maxwell model, indicating the presence of an active interphase with high dielectric constant in the system.
Computational Modeling and Experimental Characterization of Hyperelastic Thin Film NiTi for Neurovascular Microstent Applications
Authors: Chun Youngjae , Chang Hsin-yun , Lin Po-Yu , Mohanchandra K. P. , Emmons Michael C. , Seong Myunghoon , Levi Daniel S. , Tulloch Allan W. , Kealey Colin , Rigberg David A. , Lawrence Peter F. , Carman Gregory P.
Published: April 2011

A novel hyperelastic thin film NiTi covered neurovascular microstent was developed for treating wide-neck and fusiform neurovascular aneurysms. This device requires 300–500% recoverable elongation for both collapsing and deployment. Nonlinear buckling and static analysis of Finite Element Modeling (FEM: ANSYS software used) was applied for obtaining critical buckling stress and critical strain values depending on thickness, strut width and pore height. A maximum theoretical critical strain for one geometry as high as 316% while a different experimentally tested film was found to strain 600% elastically without any signs of permanent deformation.
Actuation and Charging Characteristics of Ionic Liquid-Ionic Polymer Transducers
Authors: Davidson Jacob D. , Goulbourne N. C.
Published: April 2011

Ionic polymer transducers (IPTs) are soft sensors and actuators which operate through a coupling of micro-scale chemical, electrical, and mechanical interactions. The use of an ionic liquid as solvent for an IPT has been shown to dramatically increase transducer lifetime in free-air use, while also allowing for higher applied voltages without electrolysis. In this work we model charge transport in an ionic liquid IPT by considering both the cation and anion of the ionic liquid as mobile charge carriers, a phenomenon which is unique to ionic liquid IPTs compared to their water-based counterparts. The electrochemical behavior of the large ionic liquid ions is described by use of a modified Nernst-Planck equation which accounts for steric effects in double layer packing. The method of matched asymptotic expansions is applied to solve the resulting system of equations, and analytical expressions are derived for the nonlinear charge transferred and capacitance of the IPT as a function of the applied voltage. The boundary layer ionic concentration and charge density profiles and the leading order dynamics are also computed for the ionic liquid IPT. A simple equivalent circuit model is constructed in order to facilitate a comparison with experimental results. The implications of these model results in regards to actuation and charging performance characteristics of ionic liquid IPTs are noted.
Structural Characteristics of Nanocomposites Fabricated With In-Situ Particle Synthesis Method
Authors: Tuncer Enis , Sauers Isidor , James D. Randy , Polizos Georgios , Ellis Alvin R. , More Karren I. , Cantoni Claudia
Published: April 2011

In this article we discuss fabrication of nanocomposites using an in-situ particle synthesis method. The nanocomposites discussed were prepared with solution based chemistry using a particle precursor mixture, which produces the nanoparticles. The nanocomposites presented were synthesized with titanium dioxide nanoparticles. The efforts of Oak Ridge National Laboratory to deliver better electrical insulation materials using nanotechnology are presented.
Polymer Nanocomposites for High Energy Storage Capacitors
Authors: Bestaoui-Spurr Naima , Adams Todd , Rhodes Christopher , Edmondson C. A. , Fontanella J. J. , Wintersgill M. C.
Published: April 2011

The dielectric properties of a composite system based on polyimide filled with zirconium orthophosphate, ZrO(H2PO4)2·xH2O (ZrP), layered materials has been studied. The dielectric constant and loss of the polyimide/filler were studied over a broad range of frequencies and volume fractions of the layered filler. The dielectric breakdown strengths of the composite films were determined, and an analysis was carried out using a Weibull distribution. The dielectric constant and loss for the composite increase with increasing loading of the layered compound, and water contributes to both the dielectric constant and loss. The dielectric strength exhibits a maximum at a loading of about 5 wt-%, and the effect of water is to decrease the dielectric strength.
Transfer of carbon nanosheet films to nongrowth, zero thermal budget substrates
Authors: Quinlan Ronald A. , Javier Artjay , Foos Edward E. , Buckley Leonard , Zhu Mingyao , Hou Kun , Widenkvist Erika , Drees Martin , Jansson Ulf , Holloway Brian C.
Published: April 2011

Carbon-based nanostructures and materials have become a popular subject of research due to their unique thermal, mechanical, electrical, and optical properties. For example, the strong C–C bonds of graphene-based systems allow for excellent thermal conduction at room temperature and the conjugation of the sp2 lattice enables extremely high electron mobility. However, the use of carbon nanostructures as a component in polymer composites, sensors, mirco-electro-mechanical systems, and both rigid and flexible electronics has been limited by several factors, including the incompatibility with standard photolithography techniques, the high temperatures required for the nanostructure growth, and the presence of—or complication—of removing noncarbon species. Here, the authors report on a novel method for the transfer of carbon nanosheets to a low or zero thermal budget substrate while maintaining their original morphology and electrical properties. Four-point probe measurements’ post-transfer shows the retention of in-plane conductivity and scanning electron microscopy reveals the preservation of the original vertical morphology. Raman spectroscopy measurements confirm the retention of the graphitic structure of the post-transfer nanosheet film. This new transfer technique builds on the ability to conformally coat nanosheets while maintaining the original ultrahigh surface area morphology and the ability to fully incorporate nanosheets into several polymers while maintaining the original nanostructure separation. For a demonstration of the usefulness of polymer filling, carbon nanosheets were used as an ultrahigh surface area electrode for the photoactive polymer poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] in proof of principle experiments of a nanosheet-based organic photovoltaic device.
Novel postetch process to realize high quality photonic crystals in InP
Authors: Shahid N. , Naureen S. , Li M. Y. , Swillo M. , Anand S.
Published: April 2011

Thermally driven reflow of material during annealing was positively used to obtain near-vertical sidewall profiles for high-aspect-ratio nanostructures in InP fabricated by dry etching. This is very promising for achieving high optical quality in photonic crystal (PhC) components. Nearly cylindrical profiles were obtained for high-aspect-ratio PhC holes with diameters as small as 200–350 nm. Mini stop bands (MSBs) in line-defect PhC waveguides were experimentally investigated for both as-etched and reshaped hole geometries, and their spectral characteristics were used to assess the quality of PhC fabrication. The spectral characteristics of the MSB in PhC waveguides with reshaped holes showed significant improvement in performance with a transmission dip as deep as 35 dB with sharp edges dropping in intensity more than 30 dB for ∼4 nm of wavelength change. These results show potential for using high extinction drop-filters in InP-based monolithic photonic integrated circuit applications. Finally, it is proposed that other nanostructure geometries may also benefit from this reshaping process.
Equations as Guides to Thinking and Problem Solving
Authors: Hewitt Paul G.
Published: April 2011

Science is the study of nature's rules. The most basic of these are the laws of physics, most of which are expressed in equation form. Physics equations show how concepts connect to one another. But does a study of these equations enhance student understanding? Not always, for too often in an introductory course students are tempted (or even encouraged) to memorize equations or keep them in a handy list and then, when confronted with a problem, to look for what might be a relevant equation and plug numbers into it. Little understanding results. Or worse, equations may take a backseat in an introductory course and get little or no attention at all (as some popular physics books boast no equations).
“Find-the-Flaw” Problems
Authors: Styer Daniel F.
Published: April 2011

A physics teacher assigns problems to his or her students not to keep them indoors during sunny days, but to strengthen and deepen their understanding of the universe. Every problem has not only an answer, but also a “moral to the story”—a reason why that question and that answer are interesting and probing. It is an unfortunate fact that our rush to find the answer can obscure the moral and, even worse, obscure the very idea that a moral exists. For more than a decade, I have assigned “find-the-flaw” physics problems in which the answer to the problem is given and where the only point of the problem is to build “moral of the story” insight.
The Challenge of Unconventional Superconductivity
Authors: Norman Michael R.
Published: April 2011

During the past few decades, several new classes of superconductors have been discovered that do not appear to be related to traditional superconductors. The source of the superconductivity of these materials is likely different from the electron-ion interactions that are at the heart of conventional superconductivity. Developing a rigorous theory for any of these classes of materials has proven to be a difficult challenge and will remain one of the major problems in physics in the decades to come.
HD 181068: A Red Giant in a Triply Eclipsing Compact Hierarchical Triple System
Authors: Derekas A. , Kiss L. L. , Borkovits T. , Huber D. , Lehmann H. , Southworth J. , Bedding T. R. , Balam D. , Hartmann M. , Hrudkova M. , Ireland M. J. , Kovács J. , Mező Gy. , Moór A. , Niemczura E. , Sarty G. E. , Szabó Gy. M. , Szabó R. , Telting J. H. , Tkachenko A. , Uytterhoeven K. , Benkő J. M. , Bryson S. T. , Maestro V. , Simon A. E. , Stello D. , Schaefer G. , Aerts C. , ten Brummelaar T. A. , De Cat P. , McAlister H. A. , Maceroni C. , Mérand A. , Still M. , Sturmann J. , Sturmann L. , Turner N. , Tuthill P. G. , Christensen-Dalsgaard J. , Gilliland R. L. , Kjeldsen H. , Quintana E. V. , Tenenbaum P. , Twicken J. D.
Published: April 2011

The Kepler satellite reveals details of the oscillations patterns of an evolved star in an exotic triple-star system.
Climbing in 190 Dimensions
Authors: Yarus Michael
Published: April 2011

Creation of an improved RNA-copying ribozyme offers hope of realizing RNA-catalyzed self-replication.
Rapid Insect Evolution by Symbiont Transfer
Authors: Jiggins Francis M. , Hurst Gregory D. D.
Published: April 2011

A symbiotic bacteria dramatically increases reproduction and survival in a common insect pest.
Electrons Surf Sound Waves To Connect the Quantum Dots
Authors: Cho Adrian
Published: April 2011

Physicists have used sound waves to transport individual electrons over significant distances between artificial atoms on a chip, they reported at the American Physical Society meeting.
Ice Is Predicted to Be Weirder Still
Authors: Cho Adrian
Published: April 2011

A team of theorists reported at the American Physical Society meeting that a film of ice only two molecules thick may form the oddest of all crystalline structures, a so-called quasicrystal, which lacks the exact repeatability of an ordinary crystal structure but preserves other symmetries of a crystal.
One Cool Way to Erase Information
Authors: Cho Adrian
Published: April 2011

While erasing information, a tiny system can sometimes generate less than the minimum amount of heat required by a principle of thermodynamics, physicists reported at the American Physical Society meeting.
Superconductivity's Smorgasbord of Insights: A Movable Feast
Authors: Cho Adrian
Published: April 2011

Resistance-free electric currents and their eventual explanation have influenced thinking far beyond solid state physics.
Acupuncture and Massage Therapy for Neuropathic Pain following Spinal Cord Injury: An Exploratory Study
Authors: Norrbrink Cecilia , Lundeberg Thomas
Published: April 2011

Objective

The study sought to explore the possibility of using acupuncture and massage therapy for relieving neuropathic pain following spinal cord injury (SCI).

Design

30 individuals with SCI and neuropathic pain were assigned to treatment of either massage or acupuncture, with 15 individuals in each group. Both groups received treatment twice weekly for 6 weeks. Treatments were evaluated at the end of treatment and 2 months later (follow-up).

Results

Data were analysed on an intention-to-treat basis. Within the groups, ratings of present pain, general pain, pain unpleasantness and coping improved significantly at the end of treatment after acupuncture compared to baseline values, and following massage therapy ratings of pain interference on the Multidimensional Pain Inventory improved. At follow-up no significant improvements were seen. Between-group differences were seen regarding ratings of worst pain intensity at the end of treatment, and regarding pain unpleasantness and coping with pain at follow-up, both in favour of acupuncture. At the end of treatment, eight of the 15 individuals receiving acupuncture and nine receiving massage reported an improvement on the Patient Global Impression of Change Scale, and at follow-up six patients in the acupuncture group and one patient in the massage group still reported a favourable effect from the treatment. Few side effects were reported and neither dropout from the study did this due to adverse events.

Conclusion

Neuropathic pain following SCI is often only partially responsive to most interventions. Results from this study indicate, however, that both acupuncture and massage therapy may relieve SCI neuropathic pain. For this reason, larger randomised controlled trials are warranted for assessing the long-term effects of these treatments.
Solitaire FR thrombectomy system: immediate results in 56 consecutive acute ischemic stroke patients
Authors: Machi Paolo , Costalat Vincent , Lobotesis Kyriakos , Lima Maldonado Igor , Vendrell Jean Francois , Riquelme Carlos , Bonafé Alain
Published: April 2011

Background and purpose

Prompt recanalization of cerebral arteries in patients diagnosed with acute ischemic stroke is known to be associated with a better clinical outcome. The aim of this study was to present our initial experience regarding the efficacy and safety of the Solitaire FR as a revascularization device.

Methods

56 consecutive patients presenting with acute ischemic stroke underwent intra-arterial therapy using the Solitaire FR revascularization device. Immediate angiographic results and early clinical outcomes are presented.

Results

Solitaire FR was successful in achieving recanalization in 50 out of 56 patients (89%) with a final Thrombolysis in Cerebral Infarction score ≥2b. Five out of 56 patients had procedure related complications: two asymptomatic subarachnoid hemorrhages, two thromboembolic events and one symptomatic intracranial hemorrhage (PH2). Thirty patients (53.5%) demonstrated at discharge a National Institutes of Health Stroke Scale Score of ≤1 or an improvement of at least 10 points from baseline, and 26 patients (46%) had a modified Rankin Score ≤2.

Conclusions

Solitaire FR is successful in achieving a high rate of arterial recanalization with a low complication rate. The Solitaire FR is a promising thrombectomy tool with a high degree of effectiveness, safety and ease of use.
Novel use of Onyx for treatment of intracranial vertebral artery dissection
Authors: Oh Daniel C , Hirsch Joshua A , Yoo Albert J
Published: April 2011

This report describes a patient who presented with subarachnoid hemorrhage and extensive right posterior inferior cerebellar artery territory infarct secondary to a dissecting aneurysm of the right intracranial vertebral artery. Urgent endovascular treatment was undertaken with plans for trapping of the diseased segment with coils. However, significant intralesional stenosis limited distal microcatheter access. Therefore, using proximal flow arrest and adjunctive coiling, the liquid embolic agent Onyx was injected within the pseudoaneurysm and was able to traverse the stenosis, resulting in proximal and distal parent vessel closure. There were no embolic complications. During the 3 month hospital stay, there was no rebleeding. The patient was discharged to skilled nursing facility and was lost to follow-up.
Mass media campaigns designed to support new pictorial health warnings on cigarette packets: evidence of a complementary relationship
Authors: Brennan Emily , Durkin Sarah J , Cotter Trish , Harper Todd , Wakefield Melanie A
Published: April 2011

Background

In Australia, introduction of pictorial health warnings on cigarette packets was supported by a televised media campaign highlighting illnesses featured in two of the warning labels—gangrene and mouth cancer.

Methods

Two studies examined whether the warnings and the television advertisements complemented one another. Population telephone surveys of two cross-sections of adult smokers measured changes in top-of-mind awareness of smoking-related health effects from before (2005; n=587) to after the pack warnings were introduced (2006; n=583). A second study assessed cognitive and emotional responses and intentions to quit after smokers watched one of the campaign advertisements, comparing outcomes of those with and without prior pack warning exposure.

Results

Between 2005 and 2006, the proportion of smokers aware that gangrene is caused by smoking increased by 11.2 percentage points (OR=23.47, p=0.000), and awareness of the link between smoking and mouth cancer increased by 6.6 percentage points (OR=2.00, p=0.006). In contrast, awareness of throat cancer decreased by 4.3 percentage points, and this illness was mentioned in the pack warnings but not the advertisements. In multivariate analyses, smokers who had prior exposure to the warnings were significantly more likely to report positive responses to the advertisements and stronger post-exposure quitting intentions.

Conclusions

Television advertisements and pictorial health warnings on cigarette packets may operate in a complementary manner to positively influence awareness of the health consequences of smoking and motivation to quit. Jurisdictions implementing pictorial warnings should consider the benefits of supportive mass media campaigns to increase the depth, meaning and personal relevance of the warnings.
The power-normal distribution: application to forest stands
Authors: Mønness Erik
Published: April 2011

Foresters have long sought distribution functions capable of modeling a tree distribution that have good fit, yield flexible models, and are easy to use. The power-normal (PN) distribution originates from the inverse Box–Cox transformation and might be proven to fulfill these requirements. The PN has similarities with Johnson’s system-bounded (SB) distribution and can be seen as a contender. The PN is used in this study to fit the frequency distributions of tree diameter and height. PN is flexible in describing different shapes of observed distributions as indicated by the certain areas in the skewness × kurtosis shape plane. The estimation of the parameters using maximum likelihood is straightforward and the resulting numerical properties are desirable. The shapes achieved by PN are very diverse, even though only three parameters are used. Johnson’s SB has four parameters and estimation is often susceptible to numerical problems when fitted by maximum likelihood estimation. Our results indicate that the performance of PN is superior to that of Johnson’s SB, as shown by the Kolmogorov–Smirnov statistic and visual inspection, particularly for fitting tree height distributions.
Examining 40-year stand development following vegetation control: white spruce planted in a trembling aspen dominated cutover
Authors: Fleming Robert L. , Smith Allister D.
Published: April 2011

Many of the major questions regarding stand establishment practices involve implications for longer-term ecosystem development. We examined 41-year treatment effects on stand composition and dynamics using a white spruce ( Picea glauca (Moench) Voss) planting, mechanical site preparation (MSP) – herbicide (2,4-D plus 2,4,5-T) trial in a trembling aspen ( Populus tremuloides Michx.) dominated mixedwood. Both barrel and blade MSP with planting increased total and white spruce year 41 stand-level biomass over that in untreated areas. Year 2 herbicide application reduced year 41 trembling aspen biomass without substantially increasing that of white spruce, resulting in total yields similar to those in untreated areas. Barrel MSP increased year 41 trembling aspen biomass over that of untreated areas whereas blade MSP reduced it. Herbicide-related declines in trembling aspen biomass persisted or increased with time whereas white spruce response to herbicide varied with time and MSP. By accounting for inherent growth patterns, age shift calculations gave more balanced temporal depictions of planted white spruce response than effect size or percentage gain calculations. With barrel MSP, stand composition demonstrated a degree of mixedwood homeostasis whereas with blading, trembling aspen composition declined unilaterally from year 20 to 41.
Spatial modeling of habitat trees based on line transect sampling and point pattern reconstruction
Authors: Bäuerle Heidi , Nothdurft Arne
Published: April 2011

An approach is presented for the spatial modeling of rare habitat trees surveyed by line transect sampling (LTS) in a protected area of the European Natura 2000 network. The observed tree pattern is defined as a realization of a thinned point process where the thinning can be modeled by a parametric detection function. A complete pattern is reconstructed using an optimization algorithm. The start configuration contains detected tree locations and randomly generated tree positions. Empirical cumulative distribution functions (ECDFs) for intertree and location-to-tree distances estimated from the original LTS are set as target characteristics. The same ECDFs are estimated by means of virtual LTS in the reconstruction. Tree positions are relocated during the optimization. The sum of squared deviations between the ECDFs from the original LTS and the virtual LTS in the reconstruction is considered as a contrast measure. A new configuration is accepted if the contrast is lowered compared with the previous state. The nonparametrically reconstructed habitat tree patterns are described by a log Gaussian Cox process model. Evaluations by means of line transect resamplings in a complete habitat pattern show small deviations between the second-order functional characteristics obtained from the true pattern and their analogs derived from the reconstructions.
Habitat selection and spatial relationships of black bears (Ursus americanus) with woodland caribou (Rangifer tarandus caribou) in northeastern Alberta
Authors: Latham A.D.M. , Latham M.C. , Boyce M.S.
Published: April 2011

Populations of woodland caribou ( Rangifer tarandus caribou (Gmelin, 1788)) have declined across much of their range. Wolves ( Canis lupus L., 1758) are believed to be responsible for the majority of mortality in adult female caribou; however, we hypothesize that other predators such as black bears ( Ursus americanus Pallas, 1780) may be important contributors to calf mortality. We assessed habitat selection by black bears and spatial relationships of caribou – black bears during the caribou calving season in northeastern Alberta, Canada. Black bears avoided bogs and fens, while selecting upland mixed woods and various industrial features. Conversely, caribou showed strong selection for bogs and fens relative to bears, supporting the hypothesis that caribou in the boreal forest attempt to minimize predation risk by selecting peatlands to avoid areas frequented by predators. However, habitat selection by individual black bears was highly variable and some bears selected habitats similar to those selected by caribou, i.e., bogs and fens. Bears that specialize on foraging in peatlands might be responsible for some of the predation on caribou calves. Because declines in caribou populations have resulted from a combination of high adult female and calf mortalities, management actions to conserve woodland caribou should consider the entire suite of potential predators rather than focusing only on wolves.
Gill morphology and acute hypoxia: responses of mitochondria-rich, pavement, and mucous cells in the Amazonian oscar (Astronotus ocellatus) and the rainbow trout (Oncorhynchus mykiss), two species with very different approaches to the osmo-respiratory compromise
Authors: Matey Victoria , Iftikar Fathima I. , De Boeck Gudrun , Scott Graham R. , Sloman Katherine A. , Almeida-Val Vera M.F. , Val Adalberto L. , Wood Chris M.
Published: April 2011

The hypoxia-intolerant rainbow trout ( Oncorhynchus mykiss (Walbaum, 1792)) exhibits increased branchial ion permeability and Na+influx during acute exposure to moderate hypoxia (Po2 = 80 torr; 1 torr = 133.3224 Pa), manifesting the usual trade-off between gas exchange and electrolyte conservation. In contrast, the hypoxia-tolerant oscar ( Astronotus ocellatus (Agassiz, 1831)) is unusual in exhibiting decreased branchial ion permeability to ions and Na+influx during acute exposure to severe hypoxia (Po2 = 10–20 torr). These different physiological approaches to the osmo-respiratory compromise correlate with rapid, oppositely directed changes in gill morphology. In oscar, pavement cells (PVCs) expanded, partially covering neighboring mitochondria-rich cells (MRCs), which were recessed and reduced in size. Those remaining open were transformed from “shallow-basin” to “deep-hole” forms with smaller openings, deeper apical crypts, and smaller numbers of subapical microvesicles, changes that were largely reversed during normoxic recovery. In contrast, moderate hypoxia caused outward bulging of MRCs in rainbow trout with increases in size, surface exposure, and number of subapical microvesicles, accompanied by PVC retraction. These changes were partially reversed during normoxic recovery. In both rainbow trout and oscar, hypoxia caused discharge of mucus from enlarged mucous cells (MCs). Rapid, divergent morphological changes play an important role in explaining two very different physiological approaches to the osmo-respiratory compromise.
Diets of two congeneric species of crayfish worm (Annelida: Clitellata: Branchiobdellidae) from western Canada
Authors: Gale K.S.P. , Proctor H.C.
Published: April 2011

Crayfish worms (Branchiobdellidae) are obligatory ectosymbionts of crustaceans, primarily crayfish. Little is known about their diets or ecology. A single crayfish can host several species and age classes of branchiobdellidans at one time, creating the potential for intra- and inter-specific competition. Coexistence of competitors can be promoted through dietary differences; therefore, we examined gut contents of Cambarincola chirocephalus Ellis, 1919 and Cambarincola vitreus Ellis, 1919, two species of branchiobdellidan occasionally found on the same host (the crayfish Orconectes virilis (Hagen, 1870) in Western Canada) to assess evidence of dietary niche partitioning. We also compared gut contents of conspecific adults and juveniles to determine whether diets differed with age. We found a range of diatoms and invertebrates, particularly rotifers, in the guts of both Cambarincola species. The species appear to have different diets, in that guts of C. chirocephalus contained more invertebrate material than did those of C. vitreus. There was no statistical difference in composition of gut contents between adult and juvenile conspecifics. We found very limited evidence of dietary niche expansion in C. vitreus in the absence of C. chirocephalus. The observed dietary differences between species may promote their continued coexistence in areas where their ranges overlap.
Fluctuations in lemming populations in north Yukon, Canada, 2007–2010
Authors: Krebs Charles J. , Reid Donald , Kenney Alice J. , Gilbert Scott
Published: April 2011

We estimated population density of brown lemmings ( Lemmus sibiricus (Kerr, 1792)), Greenland collared lemmings ( Dicrostonyx groenlandicus (Traill, 1823)), and tundra voles ( Microtus oeconomus (Pallas, 1776)) on Herschel Island from 2007 to 2010 by mark–recapture on three live-trapping areas. Limited data were also available from Komakuk Beach on the north Yukon coast. In contrast to most previous studies, brown and collared lemmings were partly out of phase. Brown lemmings on Herschel reached peak density in 2007–2008 and were low in 2009–2010, while collared lemmings were at peak density in 2007–2008 and again in 2010. Large adult male body size was characteristic of peak populations. Brown lemmings increased dramatically in the peak summer of 2008 and collared lemmings increased rapidly when winter breeding under the snow was successful in 2009–2010. By contrast, at Komakuk Beach, we could see no clear signs of fluctuations in these three species. Winter snow conditions may be too severe for population persistence on the coastal plain along the north coast of the Yukon. Further work is needed to unravel why peak lemming densities are so variable among sites and why lemming fluctuations are so pronounced on the arctic coastal plain of Alaska and virtually absent on the coastal plain of the north Yukon.