bluuebunny/crossref_metadata_2025 huggingface dataset:
Aerodynamic Control of Micro Air Vehicle Wings Using Electroactive Membranes
Authors: Hays Michael R. , Morton Jeffrey , Oates William S. , Dickinson Benjamin T.
Published: February 2012

Electrically controlled adaptive materials are ideal candidates for developing high agility micro-air-vehicles (MAV) due to their intrinsic multi-functionality. The dielectric elastomer VHB 4910 is one such material, where deformation occurs with an applied electric field. Here, we study the aerostructural response and control authority of a VHB 4910 membrane wing. An experimental membrane-wing platform was constructed by stretching VHB 4910 over a rigid elliptical wing-frame. The low Reynolds number (chord Reynolds number < 106) aerodynamics of the elliptical wing were characterized with different electrostatic fields applied. We observe an overall increase in lift with maximum gains of 20% at 4.5 kV, and demonstrate the ability to delay stall. Aerodynamic effects are investigated with membrane displacement and strain data obtained through visual image correlation (VIC). The VIC data is compared to a finite deforming finite element shell model to help understand structural shape changes under electrostatic fields and low Reynolds number aerodynamic flows. The model is formulated to directly input three dimensional membrane displacements to quantify aerodynamic loads on the electroactive membrane surface.
Design Study of Shape Memory Alloy Honeycombs for Energy Absorption
Authors: Watkins Ryan T. , Shaw John A. , Triantafyllidis Nicolas , Grummon David
Published: February 2012

Shape memory alloys (SMA), which exhibit the shape memory effect and superelasticity, utilize a reversible solid-solid state phase transformation to recover large strains. Likewise, honeycomb structures under in-plane loading take advantage of deformation kinematics to amplify the structure’s macroscopic strain. The combination of a sparse honeycomb structure made of an SMA material can recover larger deformations than would be possible with either conventional metal honeycombs or monolithic SMAs. NiTi honeycombs and corrugations of about 5% relative density with robust properties were demonstrated recently [1]. Potential future applications include high performance energy absorbers, light-weight deployable devices, and high stroke actuators. This numerical study focuses on the design of superelastic SMA hexagonal honeycombs under in-plane compression for application to reusable energy absorbers. A design study with respect to honeycomb geometric parameters was performed to gain a better understanding of the geometric effects on energy absorption characteristics. A nonlinear finite element method was used to simulate their mechanical response using a hysteretic, trilinear, constitutive law to model the superelastic behavior of SMAs. Bloch wave analysis was used to evaluate the stability characteristics of the honeycomb structure. The corresponding energy absorption characteristics, under constraints of local strain limits, structural stability and allowable force levels, were evaluated to determine the optimum honeycomb geometries. It was found that diamond-like honeycombs, with greater height than width, had the best energy absorption properties.
Formation and Encapsulation of Biomolecular Arrays for Developing Arrays of Membrane-Based Artificial Hair Cell Sensors
Authors: Sarles Stephen A. , Garrison Kevin L. , Young Taylor T. , Leo Donald J.
Published: February 2012

Recent research in our group has shown that artificial cell membranes formed at the base of a hair-like structure can be used to sense air flow in a manner similar to the mechanotransduction processes found in mammalian hair cells. Our previous work demonstrated that a single artificial hair cell can be formed in an open substrate. However, that study also motivated the need to develop fully-encapsulated devices that feature arrays of hair-cells. Since the transduction element in this concept is an artificial cell membrane, or lipid bilayer, this work investigates two parallel substrate designs for providing encapsulation and a method for forming arrays of bilayers. In one effort, a flexible substrate with internal compartments for hosting the biomolecules and mating cap are constructed and experimentally characterized. The regulated attachment method (RAM) is used to form interface bilayers within the sealed device. Capacitance measurements of the sealed interface bilayer show that the sealing cap slightly compresses the bottom insert and reduces the size of the enclosed bilayer. Single channel measurements of alamethicin peptides further verify that the sealed device, which is also leak-proof under water, can be used to detect the insertion and gating activity of transmembrane proteins in the membrane. The second effort pursued herein is the fabrication and initial testing of a method to form arrays of interface bilayers by using anchored hydrogel pads that support curved aqueous lenses in oil. In this fashion, the configuration of the array does not require manipulating droplets, but instead depends on the arrangement of the built-in gels used to support the aqueous lenses. As with RAM, mechanical force is used to promote contact of adjacent aqueous lenses held in the flexible substrate. Initial tests show that gel-supported lenses can be used for forming multiple lipid bilayers within the device and that these interfaces can be interrogated individually or collectively using an electrode switching circuit.
Material Characterization and Mid-Span Bending Capacity With Finite Element Simulated Predictions
Authors: Anderson Walter , Eshghinejad Ahmadreza , Elahinia Mohammad
Published: February 2012

Intelligent materials have been the subject of research for many years. Shape memory alloys (SMAs) are a type of intelligent material that has been targeted for many different uses; such as actuators, sensors and structural supports. SMAs are attractive as actuators due to their large energy density. Although a great deal of information is available on the axial load capacity and on the tip force for SMA tweezer-like devices, there is not enough information about the load capacity at mid-span, especially at the macro-level. Imposed displacement at mid-span experimental evaluation of an SMA beam in the austenitic and martensitic regimes has been studied. To this end, a specimen of near equi-atomic nitinol was heat-treated (shape set) into a ‘U’ shape and loaded into a custom test fixture such that the boundary conditions of the beam are approximated as roller-roller; and the sample was deformed at different temperatures while reaction forces were measured. The displacement is near maximum displacement of the U shape without causing a change in concavity, thus full-scale capacity is shown. Additionally, Unified Model (finite element) predictions of the experimental response are also presented, with good agreement. Due to the robust nature of the Unified Model, geometric parameter variations (wire diameter and radius of curvature) were then simulated to encompass the design envelop for such an actuator. The material properties needed as inputs to the Unified Model were obtained from constant temperature tensile tests of a specimen subjected to the same heat treatment (shape set straight). The resultant critical stresses were then extracted using the tangent method similar to the one described in ASTM F-2082. It is worth noting that the specimen was trained before the stress value extraction, but the transversely loaded specimen was not trained due to the difficulty involved (inherent uneven stress distribution). The contribution of this work is the presentation of experimental results for transverse (mid-span) loading of a nitinol wire and the simulation results allowing for design of a proper actuator with known constraints on force, displacement or temperature (2 of 3 needed). In other words, this work could be used as a type of 3D look-up table; e.g. for a desired force/displacement, the required temperatures are given. Future work includes developing a sensor-less control strategy for simultaneous force/displacement control.
A Theoretical and Experimental Study on the Dynamic Response of Ni-Mn-Ga Specimens for Energy Harvesting
Authors: Bruno Nickolaus M. , Ciocanel Constantin , Feigenbaum Heidi P. , Waldauer Alex
Published: February 2012

This paper presents experimental results and model predictions on power harvesting/sensing capabilities of magnetic shape memory alloys (MSMAs). The theoretical predictions are made using a refined thermodynamic based constitutive model, developed initially by Kiefer and Lagoudas. In an attempt to better predict the observed experimental response of the material at high frequencies, dynamic effects are included in the simulation. Furthermore, internal magnetic and external Lorentz forces are also included in the analysis and their effect on the material’s overall response is discussed. The experimental program is carried out at frequencies of up to 40Hertz in two control modes, i.e. load and displacement control. A comparison between the simulated and experimental material response and measured voltage outputs, over a range of frequencies, is presented and discussed.
Structural Load Bearing Supercapacitors Using a PEGDGE Based Solid Polymer Electrolyte Matrix
Authors: Gallagher Tanya M. , Ciocanel Constantin , Browder Cindy
Published: February 2012

The interest in developing multifunctional materials has greatly increased in the last decade. Power storage composites are just one class of multifunctional materials that has the potential to lead to significant size and weight reduction. Many electronic devices (i.e. laptops, cellphones, iPods, etc.) and mechanical systems that require or generate electrical power during operation (i.e., hybrid or fully electric cars, wind turbines, airplanes, etc.) could benefit substantially from these materials. While several types of power storage structural composites have been developed to date, i.e. composite batteries and fuel cells, structural load bearing super- and ultra-capacitors appear to be the most promising ones. To date, two classes of structural capacitors have been explored: dielectric and solid electrolyte capacitors; the former are suitable for applications where very high voltage bursts of electrical energy are needed, while the latter are suitable for applications where lower voltage levels are required (i.e. more general power storage/delivery applications). This paper describes the efforts made to develop and characterize electro-mechanically structural supercapacitors. The load-bearing supercapacitors discussed here have been made with carbon fiber weave electrodes and separators of various materials, glued together with a solid polymer electrolyte (SPE) matrix. Electrochemical characterization reported specific capacitances as high as 2.9μF/mm3 and energy densities as high as 4.9 kJ/g.
On the Maximum Damping Performance of Piezoelectric Switching Techniques
Authors: Neubauer Marcus , Han Xu
Published: February 2012

Piezoelectric shunt damping is a well known technique to damp the vibrations of mechanical structures. The design of the electrical shunt aims to maximize the energy dissipation. Beside linear networks, switching circuits are a technique that can adapt to varying excitation frequencies. In this paper, the maximum damping performance of the SSDI technique is analyzed and compared to linear LR-shunts. It is shown that it can perform about 60% better.
Micromechanics of a Smart Composite Actuator Embedded With Hollow Piezoelectric Fibers
Authors: Aimmanee Sontipee , Trakarnkulchai Supharoek , Aimmanee Pakinee
Published: February 2012

This paper presents a development of mathematical models for predicting the effective elastic and piezoelectric properties of a Smart Composite Actuator (SCA) reinforced with transversely isotropic piezoelectric hollow fibers. The models are established based on micromechanics of representative volume element of concentric cylinders or so-called concentric cylinder model (CCM). Five elastic constants and two piezoelectric coefficients are predicted as a function of fiber volume fraction, matrix volume fraction, and their constituents’ properties in the SCA. Numerical results of a chosen material system are obtained and discussed. The models can be found useful for developing a SCA or a novel hollow fiber-reinforced composite with the desired properties.
FlexLegs: Flexible Legs Actuated by Shape Memory Alloy
Authors: Villanueva Alex , Smith Colin , Priya Shashank , Bachman Richard
Published: February 2012

A flexible leg (FlexLeg) design using BiFlex actuators was designed, fabricated and characterized. BISMAC actuators are unidirectional flexible actuators capable of exhibiting high curvature. These actuators were modified to achieve bidirectional deformation. The new bidirectional actuators termed as “BiFlex” actuators, have proven the capability to achieve large deformation in two directions. The FlexLegs consist of six segments which can be actuated individually. Two different sets of legs were constructed to determine the effect of size. The small legs measure 35.8 mm in height and 63.2 mm in width and the large legs were 97.4 mm in height and 165.4 mm in width. The small FlexLegs achieved a maximum deformation of 12% and 4% in the x- and y-direction respectively using a power of 0.7 W while producing a maximum force of 0.023 N. They were also able to withstand a load of 1.18 N. The large FlexLegs had a maximum deformation of 57% and 39% in the x- and y-direction respectively using a power of 3 W while producing a force of 0.045 N. They were able to withstand a load of 0.25 N. The legs were also able to perform several walking algorithms consisting of stepping, crabbing and yawing.
Effect of Nano-Particle Filler Type on the Piezoresistance of Polyethylene Composites
Authors: Rizvi Reza , Cochrane Brendan , Biddiss Elaine , Naguib Hani
Published: February 2012

This study examines the piezoresistive behavior of polyethylene (PE) composites containing different types of nano-particle fillers. The fillers investigated are single-wall carbon nanotube (SWNT), multi-wall carbon nanotube (MWNT) and graphene nanoplatelets (GNP), which were dispersed in PE through melt blending in concentrations ranging between 0.5–10 wt%. The lowest percolation threshold and highest electrical conductivity was found for SWNT composites, followed by MWNT and GNP. The piezoresistance of the nano-particle-PE composites was investigated and a negative piezoresistance behavior was observed signifying a reducing mean inter-particulate distance in the composites. The highest sensitivity was exhibited by MWNT and SWNT composites at compositions closer to the percolation threshold. The time dependence of piezoresistivity was also investigated through stress relaxation and cyclic loading experiments.
Design and Test of an Adaptive Tuned Vibration Absorber for Reducing Cryogenic Cooler Vibrations
Authors: Sinko Robert , Karnes Michael , Koo Jeong-Hoi , Kim Young-Keun , Kim Kyung-Soo
Published: February 2012

The focuses of this study are to design an adaptive tuned vibration absorber based on a smart material known as magnetorheological elastomers (MRE) and to test its dynamic performance. A primary system replicating a cryogenic cooler was designed and fabricated in order to test the effectiveness of the vibration absorber. A hybrid magnetic system (electromagnet and permanent magnets) was also designed and fabricated in order to actuate the MRE as an adaptive stiffness element in the vibration absorber. Vibration testing was conducted on both the primary system and vibration absorber individually in order to characterize the behavior and verify the design constraints. Further testing was performed on the two degree of freedom system to measure and assess the feasibility of the MRE material for use in an application requiring an adaptive vibration absorber. The results show that by using a hybrid design for the electromagnet within the vibration absorber, the stiffness of the MRE material can be both increased and decreased above its nominal value; therefore demonstrating the feasibility of this design as an alternative adaptive vibration absorber.
Enhanced Energy Storage in Nanocomposites Through Aligned PZT Nanowires
Authors: Tang Haixiong , Sodano Henry A. , Lin Yirong
Published: February 2012

Nanocomposites consisting of a piezoceramic inclusion and polymer matrix offer a combination of electromechanical coupling with high toughness and ductility inherent to polymers. There is a wide range of applications for these types of materials due to their intrinsic piezoelectric and dielectric properties, such as vibration sensing, actuation, energy harvesting and capacitive energy storage. However, the relatively low piezoelectric strain coefficient and dielectric permittivity of these nanocomposites significantly limit their application in energy conversion and energy storage applications. There are mainly two coupled to improve the dielectric permittivity and electromechanical properties of piezoceramic nanocomposites, namely higher aspect ratio active inclusions and alignment of inclusions in the direction of the applied electric field. Previously, we have demonstrated that using higher aspect ratio lead zirconate titanate (PZT) nanowires (NWs) could significantly enhance the energy density and d33 coupling as compared to the samples with lower aspect ratio PZT nanorods [11]. In this paper, we will show that orientation of PZT NWs also influences energy storage capability of nanocomposite. Nanocomposites with aligned PZT NWs in the direction of the applied electric field show increased dielectric permittivity and energy density as compared to those with randomly dispersed inclusions. PZT NWs are hydrothermally synthesized, dispersed into a polyvinylidene fluoride (PVDF), cast into a film and then aligned through uniaxial stretching. Scanning electric microscopy (SEM) shows the PZT NWs are successfully aligned in direction of stretching. This work demonstrates that the energy storage and conversion capability of the nanocomposite can be significantly enhanced through the alignment of PZT NWs in the direction of the applied electric field. The findings of this research could lead to broad interest due to demonstration of developing piezoceramic nanocomposites with enhanced dielectric and electromechanical properties for next generation energy storage and conversion devices.
TIG Welding of Nickel-Titanium to 304 Stainless Steel
Authors: Fox Gordon , Hahnlen Ryan , Dapino Marcelo
Published: February 2012

Shape memory nickel-titanium (NiTi) is attractive for use in solid-state actuators as it exhibits large recoverable stresses, limited by its ultimate shear strength of over 120 ksi (960 MPa), and large recoverable strains, up to 8%. Broad application of NiTi is hindered by the expense, complexity, and lack of reliability in machining and joining it to structural materials. This paper investigates the use of orbital Tungsten Inert Gas (TIG) welding to join NiTi to 304 stainless steel (304 SS), a common structural material that can be readily machined and welded. Tubes of NiTi and 304 SS were joined using a nickel filler to mitigate the formation of brittle intermetallics. Both tubes had a 0.375 in (9.53 mm) outer diameter with wall thicknesses of 0.065 in and 0.075 in (1.7 mm and 1.9 mm) for the 304 SS and NiTi tubes, respectively. Viable joints were created and characterized through X-ray analysis, optical microscopy, hardness mapping, and strength testing. The joints had an average failure torque of 450 in-lb (52 N-m), corresponding to an ultimate shear strength of approximately 50 ksi (350 MPa). This was sufficient to detwin the NiTi in the tubes, which occurs at a shear stress of 16 ksi (110 MPa), and plastically deform the annealed 304 SS tubes. Optical microscopy and hardness mapping revealed a heat-affected zone 0.005 in (125 μm) wide with a maximum hardness of 817 HV. Outside of this heat-affected zone the hardness was not affected, indicating that no large-scale loss of superelastic or shape memory properties arises from TIG welding.
Plane PVDF-Foil Modules for Energy Harvesting of Dynamic Weight Forces
Authors: Bischur Enrico , Schwesinger Norbert
Published: February 2012

Plane PVDF-foil modules have been developed and successfully tested that generate electrical energy out of the mechanical energy of dynamic weight forces. For instance electrical energy can be generated, if people or vehicles pass such modules on a ground area. This method is based on the piezoelectric effect of stretched PVDF-foil. The energy conversion of the generator modules was investigated with regard to the remanent polarization of the PVDF material. Furthermore, the influence of the PVDF layer system was investigated on the energy conversion. The measured values are compared with values calculated analytically. It was found that a higher remanent polarization of the PVDF material lead to a better energy conversion. Even more electrical energy could be generated, if more PVDF layers were stacked above each other. If the values were normalized on the PVDF volume used in each case, the values of the electric energy were not constant. However, a maximum was observed at n = 21 layers. The measured energy values were higher than calculated values of the longitudinal piezoelectric effect. This could be caused by a simultaneous expansion of the PVDF film in a direction vertical to the direction of the mechanical load. These generator modules could be used as new energy source for emergency lighting, alarm systems, traffic sensors, etc.
Thermo-Mechanical Modeling of a Shape Memory Alloy Heat Engine
Authors: Churchill Christopher B. , Shaw John
Published: February 2012

Two thirds of the energy generated in the United States is currently lost as waste heat, representing a potentially vast source of green energy. Low Carnot efficiency is an inherent limitation of extracting energy from low-grade thermal sources (temperature gradients near or below 100C), and SMA heat engines could be useful for those applications where low weight and packaging are overriding considerations. Although many shape memory alloy (SMA) heat engines have been proposed to harvest this energy, and a few have been built and demonstrated in past decades, they have not been commercially successful. Some of the barriers to commercialization include their perceived low thermodynamic efficiency, high material cost, low material durability, complexities when using fluid baths, and the lack of robust constitutive models and design tools. Recent advances, however, in SMA longevity, reductions in materials costs (as production volumes have increased), and a better understanding of SMA behavior have stimulated new research on SMA heat engines. The Lightweight Thermal Energy Recovery System (LighTERS) is an ongoing ARPA-E funded collaboration between General Motors, HRL Laboratories, Dynalloy, Inc., and the University of Michigan. In the LighTERS engine (a refinement of the Dr. Johnson engine), a closed loop SMA spring element generates mechanical power by pulling itself between alternating hot and cold air regions. The first known thermo-mechanical model for this type of heat engine was developed in three stages. First, the constitutive and heat transfer relationships of an SMA spring form were characterized experimentally. Second, those relationships were used as inputs in a steady-state model of the heat engine, including both convective heat transfer and large-deformation mechanics. Finally, the model was validated successfully against measurements of a experimental heat engine built at HRL Labs.
Optimized Biodynamic Shock Attenuation Performance Using an Adaptive Seat Suspension
Authors: Singh Harinder J. , Wereley Norman M.
Published: February 2012

Design optimization-based techniques are presented for the minimization of biodynamic loads of a seated occupant subjected to a shock due to an initial velocity vertical impact. A 95th percentile male occupant was modeled using a multiple degree-of-freedom biodynamic lumped parameter model (BLPM) seated on a vertically stroking adaptive seat suspension with a semi-active magnetorheological energy absorber (MREA). The governing equations of motion of the adaptive MREA-based seat suspension with biodynamic lumped parameter model were developed. The variation of magnetorheological yield force with respect to the energy absorber stroke was shaped using cubic polynomial for the maximum shock attenuation. Three cost functions were devised with a common goal of minimizing biodynamic decelerations. Constraints were established based on limitation of MREA stroke and, yield force as well as stroking load. The MREA yield force and damper stroke were crucial parameters for improved biodynamic response mitigation to shock loads. A globally optimized biodynamic response was analyzed among several local optimum responses for better shock attenuation.
Insight Into Active Health Monitoring Methods Using Machine Learning
Authors: Reynolds Whitney , Doyle Derek , Arritt Brandon
Published: February 2012

Current satellite validation tests involve numerous procedures to qualify the space vehicle for the vibrations expected during launch and for exposure to the space environment. Structural Health Monitoring methods are being considered in an effort to truncate the number of validation tests required for satellite checkout. The most promising of these monitoring techniques uses an active wave-based method in which an active piezoelectric transducer propagates a Lamb wave through the structure, where it is then received by a second sensor and evaluated over time to detect structural changes. Thus far, this method has proven effective in locating structural defects in a complex satellite panel; however, the attributes associated with the first wave arrival change significantly as the wave travels through ribs and interfaces. This study establishes a method to identify important features in the sensor signal that may otherwise be missed. In this work, an FE model of a plate is developed, and variability is introduced for each state observation. Different states are modeled as masses distributed at 12 locations. Signals are obtained through an explicit time-domain analysis. Matching Pursuit Decomposition is used to extract physically significant parameters from the signal, the features are reduced to a more manageable subset, and Support Vector Machines are utilized to identify important features in the sensor signal. The results of the classification indicate that for a plate specimen the extracted feature corresponding to anti-symmetric wave mode interaction with damage does the best job of differentiating damage states.
Dynamic Thermo-Mechanical Properties of Shape Memory Alloy Nanowires Upon Multi-Axial Loading
Authors: Dhote Rakesh P. , Melnik Roderick V. N. , Zu Jean W.
Published: February 2012

In this paper, we study the behavior of shape memory alloy (SMA) nanowires subjected to multi-axial loading. We use the model developed in our earlier work to study the microstructure and mechanical properties of finite length nanowires. The phase field model with the Ginzburg-Landau free energy is used to model the phase transformation based on the chosen order parameter. The governing equations of the thermo-mechanical model are solved simultaneously for different loading cases. We observe that nanowire behaves in a stiff manner to axial load with complete conversion of the unfavorable martensite to the favorable one. The bending load aids the phase transformation by redistributing the martensitic variants based on the local axial stress sign. The nanowire behavior to multi-axial (axial and bending together) is stiffer axially than the axial loading case. The understanding of the behavior of nanowire to multi-axial loading will be useful in developing better SMA-based MEMS and NEMS devices.
Shape Memory Alloy Actuator Design: CASMART Collaborative Best Practices
Authors: Benafan Othmane , Brown Jeff , Calkins F. Tad , Kumar Parikshith , Stebner Aaron , Turner Travis , Vaidyanathan Raj , Webster John , Young Marcus L.
Published: February 2012

Upon examination of shape memory alloy (SMA) actuation designs, there are many considerations and methodologies that are common to them all. A goal of CASMART’s design working group is to compile the collective experiences of CASMART’s member organizations into a single medium that engineers can then use to make the best decisions regarding SMA system design. In this paper, a review of recent work toward this goal is presented, spanning a wide range of design aspects including evaluation, properties, testing, modeling, alloy selection, fabrication, actuator processing, design optimization, controls, and system integration. We have documented each aspect, based on our collective experiences, so that the design engineer may access the tools and information needed to successfully design and develop SMA systems. Through comparison of several case studies, it is shown that there is not an obvious single, linear route a designer can adopt to navigate the path of concept to product. SMA engineering aspects will have different priorities and emphasis for different applications.
Stimuli Triggered Deployment of Bio-Inspired Self-Healing Functionality
Authors: Trask Richard , Bond Ian , Norris Chris
Published: February 2012

The concept of self-healing materials has gained widespread acceptance in the research community. Over recent years a diverse array of bio-inspired self-healing concepts, from solid-state diffusion to liquid-phase healing in a broad range of engineering materials, embracing ceramics, polymers and fibre reinforced polymer composite materials have been proposed in the open literature. In this research study the liquid-phase healing of operational damage, namely impact damage, is being addressed. The challenge of self-healing advanced fibre reinforced polymer composites is ensuring healing success without degrading the host composite’s performance, a problem not encountered in the self-healing of generic polymeric systems. In the genre of self-healing fibre reinforced composite materials, autonomous healing has been undertaken by a healing medium already located within the damage zone and released through the damage site either passively or actively through human invention. This approach requires the ‘engineering’ control of the storage medium’s toughness for release and the development of bespoke resin chemistries to be compatible with the manufacturing route, to remain active whilst latent and then to recover full mechanical performance once a damage event occurs. This study has generated a proof of concept whereby the healing medium is only deployed to the damage site once a sensor has been triggered. In essence this study aims to develop stimuli triggered deployment of a healing medium held remotely in a storage reservoir to repair impact damage to a composite material. The principle of the concept is revolves around the ability of a reservoir to deliver a healing medium to a damage site via a network of vessels contained in the centerline of the composite laminate. A Labview controlled peristaltic pressure rig containing the reservoirs for the resin and hardener, their independent pumps, pressure gauges, control switches and indicators was developed. Through the application of an impact event successfully deliver and subsequent healing of the damage event was achieved showing the potential of this concept for minimising parasitic mass and maximising healing potential in fibre reinforced composite materials.
Seasonality in Ocean Microbial Communities
Authors: Giovannoni Stephen J. , Vergin Kevin L.
Published: February 2012

Spring Bloom

The spring bloom of plankton in northern seas develops apparently in response to increasing light and to winter weather, which make nutrients available at the surface. This seasonality is important on a global scale because it reflects a tipping point, driven by phytoplankton growth, between CO
2
production and carbon storage. The phenomenon is thus of particular interest in this era of carbon excess.
Giovannoni and Vergin
(p.
671
) review what is known about the dynamics of these highly ordered microbial plankton communities, discuss the specialist roles of certain taxa, and reflect on predictions for anthropogenic changes to the oceans and what these might mean for geochemical cycles driven by ocean microbiota.
Pigment Pattern Formation by Contact-Dependent Depolarization
Authors: Inaba Masafumi , Yamanaka Hiroaki , Kondo Shigeru
Published: February 2012

Cell culture experiments reveal that direct interactions between pigment cells play a key role in skin pattern formation.
Near-Field Deformation from the El Mayor–Cucapah Earthquake Revealed by Differential LIDAR
Authors: Oskin Michael E. , Arrowsmith J Ramon , Corona Alejandro Hinojosa , Elliott Austin J. , Fletcher John M. , Fielding Eric J. , Gold Peter O. , Garcia J. Javier Gonzalez , Hudnut Ken W. , Liu-Zeng Jing , Teran Orlando J.
Published: February 2012

Earthquakes from Above

Preparing for risks and hazards associated with large earthquakes requires detailed understanding of their mechanical properties. In addition to pinpointing the location and magnitude of earthquakes, postmortem analyses of the extent of rupture and amount of deformation are key quantities, but are not simply available from seismological data alone. Using a type of optical remote sensing, Light Detection and Ranging (LiDAR),

Oskin
et al.

(p.
702
) surveyed the surrounding area that ruptured during the 2010
M
w
7.2 El Mayor–Cucapah earthquake in Northern Mexico. Because this area had also been analyzed in 2006, a comparative analysis revealed slip rate and strain release on the shallow fault zone and a number of previously unknown faults. As remote imaging becomes cheaper and more common, differential analyses will continue to provide fault-related deformation data that complements modern seismological networks.
Structure-Based Mechanistic Insights into DNMT1-Mediated Maintenance DNA Methylation
Authors: Song Jikui , Teplova Marianna , Ishibe-Murakami Satoko , Patel Dinshaw J.
Published: February 2012

Close-Up of DNA Methylation

In eukaryotes, maintenance of genomic CpG methylation patterns is required for imprinting, retrotransposon silencing, and X-chromosome inactivation. The epigenetic mark needs to be faithfully maintained and propagated during repeated cell divisions in somatic cells by selective methylation of hemimethylated CpG dinucleotides following DNA replication, which is carried out by the enzyme DNMT1.

Song
et al.

(p.
709
) determined the crystal structure of mouse DNMT1 bound to a DNA duplex containing a hemimethylated CpG on the parental strand, such as would be found immediately after DNA replication. Together with a previous structure of the autoinhibited structure, the findings suggest that a combination of active and auto-inhibitory mechanisms ensures the high fidelity of DNMT1-mediated maintenance of DNA methylation.
Structural Insight into the Ion-Exchange Mechanism of the Sodium/Calcium Exchanger
Authors: Liao Jun , Li Hua , Zeng Weizhong , Sauer David B. , Belmares Ricardo , Jiang Youxing
Published: February 2012

Maintaining Equilibrium

Na
+
/Ca
2+
exchangers (NCX) are membrane transporters that maintain the homeostasis of cytosolic Ca
2+
and play an essential role in Ca
2+
signaling. Despite a long history of physiological work and a large body of functional data, the structural basis underlying the ion exchange mechanism of NCX is poorly understood.

Liao
et al.

(p.
686
; see the Perspective by

Abramson
et al.

) present a high-resolution crystal structure of an NCX from
Methanococcus jannaschii
and demonstrate that this archaeal NCX catalyzes Na
+
/Ca
2+
-exchange reactions similar to its eukaryotic counterpart. The structure clarifies the mechanism of ion exchange proteins and reveals the basis for the stoichiometry, cooperativity, and bidirectionality of the reaction.
A Molecular MoS
2
Edge Site Mimic for Catalytic Hydrogen Generation
Authors: Karunadasa Hemamala I. , Montalvo Elizabeth , Sun Yujie , Majda Marcin , Long Jeffrey R. , Chang Christopher J.
Published: February 2012

Edging In on MoS
2

Molybdenum disulfide is a widely used catalyst in the petrochemical industry that has recently shown promise for water-splitting applications. Its activity appears to be confined to edge sites with exposed disulfide groups, although the precise geometric details underlying the chemistry remain uncertain.

Karunadasa
et al.

(p.
698
) prepared a molecular complex modeling one of these edge sites, in which a triangular Mo-S-S unit is supported by metal coordination to five tethered pyridine rings. The molecule was characterized crystallographically and proved robustly active toward electrochemical generation of hydrogen from water, even when applied to crudely filtered seawater.
Imaginary Identities
Ancestors and Relatives
Genealogy, Identity, and Community

by Eviatar Zerubavel

Oxford University Press, Oxford, 2011. 238 pp. $24.95, £15.99. ISBN 9780199773954.
Authors: Tienda Marta
Published: February 2012

Zerubavel examines social and cultural aspects of how we understand kinship---and hence approach ethnicity, race, and nationalism.
Probing Frozen Molecular Embraces
Authors: Zwier Timothy S.
Published: February 2012

The conformation of the complex formed by a catalyst and its substrate was determined with a method that combined mass spectrometry and infrared spectroscopy.
Remembering to Be Tolerant
Authors: Lee June-Yong , Jameson Stephen C.
Published: February 2012

Self-tolerant T cells can be transiently reactivated.
High Hopes for Croatia's 'Warm Spring Harbor' Remain Unfulfilled
Authors: Tatalovic Mico
Published: February 2012

What was supposed to be a rising star in Eastern European science, the Mediterranean Institute for Life Sciences in Split, is mired in controversy and appears to be on the brink of collapse.
Indoor Ecosystems
Authors: Humphries Courtney
Published: February 2012

The microbial ecology of buildings gets a boost from a foundation and researchers trying to better understand the invisible communities in our homes, hospitals, and workspaces.
CD4 T Cell Antigens from Staphylococcus aureus Newman Strain Identified following Immunization with Heat-Killed Bacteria
Authors: Lawrence Paulraj K. , Rokbi Bachra , Arnaud-Barbe Nadège , Sutten Eric L. , Norimine Junzo , Lahmers Kevin K. , Brown Wendy C.
Published: February 2012

Staphylococcus aureusis a commensal bacterium associated with the skin and mucosal surfaces of humans and animals that can also cause chronic infection. The emergence of antibiotic-resistant strains such as methicillin-resistantS. aureus(MRSA) and strains causing chronic intramammary infections (IMI) in cows results in severe human and livestock infections. Conventional approaches to vaccine development have yielded only a few noneffective vaccines against MRSA or IMI strains, so there is a need for improved vaccine development. CD4 T lymphocytes are required for promoting gamma interferon (IFN-γ) mediated immunoglobulin isotype switching in B lymphocytes to produce high-affinity IgG antibodies and IFN-γ-mediated phagocyte activation for an effective resolution of bacterial infection. However, the lack of known CD4 T cell antigens fromS. aureushas made it difficult to design effective vaccines. The goal of this study was to identifyS. aureusproteins recognized by immune CD4 T cells. Using a reverse genetics approach, 43 antigens were selected from theS. aureusNewman strain. These included lipoproteins, proteases, transcription regulators, an alkaline shock protein, conserved-domain proteins, hemolysins, fibrinogen-binding protein, staphylokinase, exotoxin, enterotoxin, sortase, and protein A. Screening of expressed proteins for recall T cell responses in outbred, immune calves identified 13 proteins that share over 80% sequence identity among MRSA or IMI strains. These may be useful for inclusion in a broadly protective multiantigen vaccine against MRSA or IMI.
Epidemiological Significance of the Domestic Black Pig (Sus scrofa) in Maintenance of Bovine Tuberculosis in Sicily
Authors: Di Marco Vincenzo , Mazzone Piera , Capucchio Maria Teresa , Boniotti Maria Beatrice , Aronica Vincenzo , Russo Miriam , Fiasconaro Michele , Cifani Noemi , Corneli Sara , Biasibetti Elena , Biagetti Massimo , Pacciarini Maria Lodovica , Cagiola Monica , Pasquali Paolo , Marianelli Cinzia
Published: February 2012

Bovine tuberculosis (bTB) is an emerging disease among wild animals in many parts of the world. Wildlife reservoir hosts may thus represent a potential source of infection for livestock and humans. We investigated the role played by the Sicilian black pig, an autochthonous free- or semi-free-ranging domestic pig breed, as a potential source of bTB infection in an area where bTB prevalence in cattle is high. We initially performed a preliminary field study to assess the occurrence of bTB in such animals. We sampled 119 pigs at abattoir and found 6.7% and 3.4% of them to be affected by gross tuberculous-like lesions (TBL) and
Mycobacterium bovis
culture positive, respectively. We then proceeded to investigate the dissemination and characteristics of lesions in a second field study performed on 100 animals sampled from infected herds. Here, tissues collected at the abattoir were examined macroscopically, microscopically, and by culture tests. Most pigs with TBL showed generalized lesions in both gross and histological examinations (53% and 65.5%, respectively). Head lymph nodes were the most frequently affected in both localized and generalized TB cases observed macroscopically and microscopically.
M. bovis
was the most frequently isolated etiologic agent. The molecular characterization of isolates from both field studies by spoligotyping and analysis of 12 mycobacterial interspersed repetitive-unit–variable number tandem repeat (MIRU-VNTR) loci, followed by their comparison to isolates of cattle origin, suggested a potential transmission of mycobacteria from domestic animals to black pigs and vice versa. Our findings, along with ethological, ecological, and management considerations, suggest that the black pig might act as a bTB reservoir in the ecosystem under study. However, additional studies will be necessary to establish the true epidemiological significance of the Sicilian black pig.
RNA Synthesis by the Brome Mosaic Virus RNA-Dependent RNA Polymerase in Human Cells Reveals Requirements for
De Novo
Initiation and Protein-Protein Interaction
Authors: Subba-Reddy Chennareddy V. , Tragesser Brady , Xu Zhili , Stein Barry , Ranjith-Kumar C. T. , Kao C. Cheng
Published: February 2012

Brome mosaic virus (BMV) is a model positive-strand RNA virus whose replication has been studied in a number of surrogate hosts. In transiently transfected human cells, the BMV polymerase 2a activated signaling by the innate immune receptor RIG-I, which recognizes
de novo
-initiated non-self-RNAs. Active-site mutations in 2a abolished RIG-I activation, and coexpression of the BMV 1a protein stimulated 2a activity. Mutations previously shown to abolish 1a and 2a interaction prevented the 1a-dependent enhancement of 2a activity. New insights into 1a-2a interaction include the findings that helicase active site of 1a is required to enhance 2a polymerase activity and that negatively charged amino acid residues between positions 110 and 120 of 2a contribute to interaction with the 1a helicase-like domain but not to the intrinsic polymerase activity. Confocal fluorescence microscopy revealed that the BMV 1a and 2a colocalized to perinuclear region in human cells. However, no perinuclear spherule-like structures were detected in human cells by immunoelectron microscopy. Sequencing of the RNAs coimmunoprecipitated with RIG-I revealed that the 2a-synthesized short RNAs are derived from the message used to translate 2a. That is, 2a exhibits a strong
cis
preference for BMV RNA2. Strikingly, the 2a RNA products had initiation sequences (5′-GUAAA-3′) identical to those from the 5′ sequence of the BMV genomic RNA2 and RNA3. These results show that the BMV 2a polymerase does not require other BMV proteins to initiate RNA synthesis but that the 1a helicase domain, and likely helicase activity, can affect RNA synthesis by 2a.
Enhanced Susceptibility of Ago1/3 Double-Null Mice to Influenza A Virus Infection
Authors: Van Stry Melanie , Oguin Thomas H. , Cheloufi Sihem , Vogel Peter , Watanabe Makiko , Pillai Meenu R. , Dash Pradyot , Thomas Paul G. , Hannon Gregory J. , Bix Mark
Published: February 2012

RNA interference (RNAi) is a critical component of many cellular antiviral responses in plants, invertebrates, and mammals. However, its
in vivo
role in host protection from the negative-sense RNA virus influenza virus type A (flu) is unclear. Here we have examined the role of RNAi in host defense to flu by analyzing Argonaute 1 and 3 double-knockout mice deficient in components of the RNA-induced silencing complex. Compared to littermate controls, flu-infected double-knockout mice exhibited increased mortality, consistent with more severe alveolitis and pneumonitis. These data indicate that optimal resistance to flu requires Argonaute 1 and/or 3. Enhanced mortality of double-knockout mice was not associated either with increased viral replication or with differential pulmonary recruitment or function of innate and adaptive immune cells. Given the absence of detectable immune defects, our results support the notion that the enhanced flu susceptibility of double-knockout mice arises from an intrinsic impairment in the ability of lung cells to tolerate flu-elicited inflammation.
The Histone Deacetylase Inhibitor Valproic Acid Lessens NK Cell Action against Oncolytic Virus-Infected Glioblastoma Cells by Inhibition of STAT5/T-BET Signaling and Generation of Gamma Interferon
Authors: Alvarez-Breckenridge Christopher A. , Yu Jianhua , Price Richard , Wei Min , Wang Yan , Nowicki Michal O. , Ha Yoonhee P. , Bergin Stephen , Hwang Christine , Fernandez Soledad A. , Kaur Balveen , Caligiuri Michael A. , Chiocca E. Antonio
Published: February 2012

Tumor virotherapy has been and continues to be used in clinical trials. One barrier to effective viral oncolysis, consisting of the interferon (IFN) response induced by viral infection, is inhibited by valproic acid (VPA) and other histone deacetylase inhibitors (HDACi). Innate immune cell recruitment and activation have been shown to be deleterious to the efficacy of oncolytic herpes simplex virus (oHSV) infection, and in this report we demonstrate that VPA limits this deleterious response. VPA, administered prior to oHSV inoculation in an orthotopic glioblastoma mouse model, resulted in a decline in NK and macrophage recruitment into tumor-bearing brains at 6 and 24 h post-oHSV infection. Interestingly, there was a robust rebound of recruitment of these cells at 72 h post-oHSV infection. The observed initial decline in immune cell recruitment was accompanied by a reduction in their activation status. VPA was also found to have a profound immunosuppressive effect on human NK cellsin vitro. NK cytotoxicity was abrogated following exposure to VPA, consistent with downmodulation of cytotoxic gene expression of granzyme B and perforin at the mRNA and protein levels. In addition, suppression of gamma IFN (IFN-γ) production by VPA was associated with decreased STAT5 phosphorylation and dampened T-BET expression. Despite VPA-mediated immune suppression, mice were not at significantly increased risk for HSV encephalitis. These findings indicate that one of the avenues by which VPA enhances oHSV efficacy is through initial suppression of immune cell recruitment and inhibition of inflammatory cell pathways within NK cells.
CRM1-Dependent Trafficking of Retroviral Gag Proteins Revisited
Authors: Baluyot Mariju F. , Grosse Sarah A. , Lyddon Terri D. , Janaka Sanath K. , Johnson Marc C.
Published: February 2012

We analyzed the nuclear trafficking ability of Gag proteins from six retroviral genera. Contrary to a previous report, human immunodeficiency virus type 1 (HIV-1) Gag showed no propensity to cycle through the nucleus. The only Gag protein that displayed CRM1-dependent nuclear cycling was that of Rous sarcoma virus (RSV). Surprisingly, this cycling could be eliminated without compromising infectivity by replacing the RSV Gag N-terminal matrix (MA) domain with HIV MA.