bluuebunny/crossref_metadata_2025 huggingface dataset:
Genetic control of cell morphogenesis during Drosophila melanogaster cardiac tube formation
Authors: Medioni Caroline , Astier Martine , Zmojdzian Monika , Jagla Krzysztof , Sémériva Michel
Published: July 2008

Tubulogenesis is an essential component of organ development, yet the underlying cellular mechanisms are poorly understood. We analyze here the formation of the Drosophila melanogaster cardiac lumen that arises from the migration and subsequent coalescence of bilateral rows of cardioblasts. Our study of cell behavior using three-dimensional and time-lapse imaging and the distribution of cell polarity markers reveals a new mechanism of tubulogenesis in which repulsion of prepatterned luminal domains with basal membrane properties and cell shape remodeling constitute the main driving forces. Furthermore, we identify a genetic pathway in which roundabout, slit, held out wings, and dystroglycan control cardiac lumen formation by establishing nonadherent luminal membranes and regulating cell shape changes. From these data we propose a model for D. melanogaster cardiac lumen formation, which differs, both at a cellular and molecular level, from current models of epithelial tubulogenesis. We suggest that this new example of tube formation may be helpful in studying vertebrate heart tube formation and primary vasculogenesis.
ACTH Inhibits bTREK-1 K+ Channels through Multiple cAMP-dependent Signaling Pathways
Authors: Liu Haiyan , Enyeart Judith A. , Enyeart John J.
Published: July 2008

Bovine adrenal zona fasciculata (AZF) cells express bTREK-1 K+ channels that set the resting membrane potential and function pivotally in the physiology of cortisol secretion. Inhibition of these K+ channels by adrenocorticotropic hormone (ACTH) or cAMP is coupled to depolarization and Ca2+ entry. The mechanism of ACTH and cAMP-mediated inhibition of bTREK-1 was explored in whole cell patch clamp recordings from AZF cells. Inhibition of bTREK-1 by ACTH and forskolin was not affected by the addition of both H-89 and PKI(6–22) amide to the pipette solution at concentrations that completely blocked activation of cAMP-dependent protein kinase (PKA) in these cells. The ACTH derivative, O-nitrophenyl, sulfenyl-adrenocorticotropin (NPS-ACTH), at concentrations that produced little or no activation of PKA, inhibited bTREK-1 by a Ca2+-independent mechanism. Northern blot analysis showed that bovine AZF cells robustly express mRNA for Epac2, a guanine nucleotide exchange protein activated by cAMP. The selective Epac activator, 8-pCPT-2′-O-Me-cAMP, applied intracellularly through the patch pipette, inhibited bTREK-1 (IC50 = 0.63 μM) at concentrations that did not activate PKA. Inhibition by this agent was unaffected by PKA inhibitors, including RpcAMPS, but was eliminated in the absence of hydrolyzable ATP. Culturing AZF cells in the presence of ACTH markedly reduced the expression of Epac2 mRNA. 8-pCPT-2′-O-Me-cAMP failed to inhibit bTREK-1 current in AZF cells that had been treated with ACTH for 3–4 d while inhibition by 8-br-cAMP was not affected. 8-pCPT-2′-O-Me-cAMP failed to inhibit bTREK-1 expressed in HEK293 cells, which express little or no Epac2. These findings demonstrate that, in addition to the well-described PKA-dependent TREK-1 inhibition, ACTH, NPS-ACTH, forskolin, and 8-pCPT-2′-O-Me-cAMP also inhibit these K+ channels by a PKA-independent signaling pathway. The convergent inhibition of bTREK-1 through parallel PKA- and Epac-dependent mechanisms may provide for failsafe membrane depolarization by ACTH.
Nicotinic Receptor Interloop Proline Anchors β1-β2 and Cys loops in Coupling Agonist Binding to Channel Gating
Authors: Lee Won Yong , Free Chris R. , Sine Steven M.
Published: July 2008

Nicotinic acetylcholine receptors (AChRs) mediate rapid excitatory synaptic transmission throughout the peripheral and central nervous systems. They transduce binding of nerve-released ACh into opening of an intrinsic channel, yet the structural basis underlying transduction is not fully understood. Previous studies revealed a principal transduction pathway in which αArg 209 of the pre-M1 domain and αGlu 45 of the β1–β2 loop functionally link the two regions, positioning αVal 46 of the β1–β2 loop in a cavity formed by αPro 272 through αSer 269 of the M2–M3 loop. Here we investigate contributions of residues within and proximal to this pathway using single-channel kinetic analysis, site-directed mutagenesis, and thermodynamic mutant cycle analysis. We find that in contributing to channel gating, αVal 46 and αVal 132 of the signature Cys loop couple energetically to αPro 272. Furthermore, these residues are optimized in both their size and hydrophobicity to mediate rapid and efficient channel gating, suggesting naturally occurring substitutions at these positions enable a diverse range of gating rate constants among the Cys-loop receptor superfamily. The overall results indicate that αPro 272 functionally couples to flanking Val residues extending from the β1–β2 and Cys loops within the ACh binding to channel opening transduction pathway.
Public information affects breeding dispersal in a colonial bird: kittiwakes cue on neighbours
Authors: Boulinier Thierry , McCoy Karen D , Yoccoz Nigel G , Gasparini Julien , Tveraa Torkild
Published: July 2008

Habitat selection and dispersal behaviour are key processes in evolutionary ecology. Recent studies have suggested that individuals may use the reproductive performance of conspecifics as a source of public information on breeding patch quality for dispersal decisions, but experimental evidence is still limited for species breeding in aggregates, i.e. colonial species. We addressed this issue by manipulating the local breeding success of marked individuals and that of their neighbours on a series of breeding patches of a colonial seabird, the black-legged kittiwake (
Rissa tridactyla
). Based on previous observations in this species, we predicted that individuals that lost their eggs on successful patches would attend their nest and come back to it the year after at a higher rate than individuals that lost their eggs on patches where their neighbours were also in failure. As predicted, the attendance of breeders and prospectors was strongly affected by the local level of breeding success, resulting in differential site fidelity and recruitment. This suggests that individuals used information conveyed by conspecific breeding performance to make decisions relative to breeding site selection. This process can amplify the response of these populations to environmental change and may have contributed to the evolution of colonial breeding.
The type and timing of social information alters offspring production
Authors: Fletcher Robert J , Miller Christine W
Published: July 2008

The acquisition and use of information are essential for decision-making in an uncertain world. The use of social information, or information from the behaviour of others, may be a common and efficient mechanism to improve estimates of resource quality by animals. According to theory, social information cues with higher information content should have a greater influence on decision-making, and current information should be weighed more than prior information. However, experimental tests of these hypotheses remain scarce. We exposed female cactus bugs (
Chelinidea vittiger
) to different types of social information (the presence of conspecific eggs or nymphs) presented at different times (current or prior to egg laying) to determine the influence of social information on offspring production. We found that social information substantially altered the number of eggs produced. The presence of conspecific eggs, regardless of timing, consistently increased egg production, whereas nymphs only increased egg production when present during egg laying. We conclude that the type and timing of social information may have an important, yet unappreciated, influence on reproductive allocation.
Quantifying within- and between-animal variation and uncertainty associated with counts of
Escherichia coli
O157 occurring in naturally infected cattle faeces
Authors: Robinson S.E , Brown P.E , Wright E.J , Hart C.A , French N.P
Published: July 2008

Cattle faeces are considered the most important reservoir for human infection with
Escherichia coli
O157. We have previously described shedding of
E. coli
O157 in the faeces of naturally infected cattle cohorts. However, the data require further investigation to quantify the uncertainty and variability in the estimates previously presented. This paper proposes a method for analysing both the presence and the quantity of
E. coli
O157 in cattle faecal samples, using two isolation procedures, one of which enumerates
E. coli
O157. The combination of these two measurements, which are fundamentally different in nature and yet measuring a common outcome, has necessitated the development of a novel statistical model for ascertaining the contribution of the various components of variation (both natural and observation induced) and for judging the influence of explanatory variables. Most of the variation within the sampling hierarchy was attributable to multiple samples from the same animal. The contribution of laboratory-level variation was found to be low. After adjusting for fixed and random effects, short periods of increased intensity of shedding were identified in individual animals. We conclude that within-animal variation is greater than between animals over time, and studies aiming to elucidate the dynamics of shedding should focus resources, sampling more within than between animals. These findings have implications for the identification of persistent high shedders and for assessing their role in the epidemiology of
E. coli
O157 in cattle populations. The development of this non-standard statistical model may have many applications to other microbial count data.
Predicting species interactions from edge responses: mongoose predation on hawksbill sea turtle nests in fragmented beach habitat
Authors: Leighton Patrick A , Horrocks Julia A , Krueger Barry H , Beggs Jennifer A , Kramer Donald L
Published: July 2008

Because species respond differently to habitat boundaries and spatial overlap affects encounter rates, edge responses should be strong determinants of spatial patterns of species interactions. In the Caribbean, mongooses (
Herpestes javanicus
) prey on hawksbill sea turtle (
Eretmochelys imbricata
) eggs. Turtles nest in both open sand and vegetation patches, with a peak in nest abundance near the boundary between the two microhabitats; mongooses rarely leave vegetation. Using both artificial nests and hawksbill nesting data, we examined how the edge responses of these species predict the spatial patterns of nest mortality. Predation risk was strongly related to mongoose abundance but was not affected by nest density or habitat type. The product of predator and prey edge response functions accurately described the observed pattern of total prey mortality. Hawksbill preference for vegetation edge becomes an ecological trap in the presence of mongooses. This is the first study to predict patterns of predation directly from continuous edge response functions of interacting species, establishing a link between models of edge response and species interactions.
Differential reproductive success favours strong host preference in a highly specialized brood parasite
Authors: De Mársico María C , Reboreda Juan C
Published: July 2008

Obligate avian brood parasites show dramatic variation in the degree to which they are host specialists or host generalists. The screaming cowbirdMolothrus rufoaxillarisis one of the most specialized brood parasites, using a single host, the bay-winged cowbird (Agelaioides badius) over most of its range. Coevolutionary theory predicts increasing host specificity the longer the parasite interacts with a particular avian community, as hosts evolve defences that the parasite cannot counteract. According to this view, host specificity can be maintained if screaming cowbirds avoid parasitizing potentially suitable hosts that have developed effective defences against parasitic females or eggs. Specialization may also be favoured, even in the absence of host defences, if the parasite's reproductive success in alternative hosts is lower than that in the main host. We experimentally tested these hypotheses using as alternative hosts two suitable but unparasitized species: house wrens (Troglodytes aedon) and chalk-browed mockingbirds (Mimus saturninus). We assessed host defences against parasitic females and eggs, and reproductive success of the parasite in current and alternative hosts. Alternative hosts did not discriminate against screaming cowbird females or eggs. Egg survival and hatching success were similarly high in current and alternative hosts, but the survival of parasitic chicks was significantly lower in alternative hosts. Our results indicate that screaming cowbirds have the potential to colonize novel hosts, but higher reproductive success in the current host may favour host fidelity.
Experimental and Theoretical Analysis of Pulling Force in Pultrusion and Resin Injection Pultrusion (RIP)–Part I: Experimental
Authors: Li Shoujie , Xu Liqun , Ding Zhongman , Lee L. James , Engelen Herbert
Published: July 2008

Pulling force is the summation of resistance forces along a pultrusion die. Its mechanism is complicated because the impregnated resin inside the compressed fiber reinforcement changes from a liquid to a gel, and finally to a solid in the die. Two methods, a ‘mat tracer’method and a ‘short die length’ method, were used to determine the pulling force distribution. Results show that the downstream part of the die contributes little to the pulling force.

In order to predict the resistance force in both the injection die and the heating die, two models were developed in this study. A friction measurement device was designed to measure the friction coefficient between the composite and the mold surface. The effect of process variables, such as temperature, resin conversion, normal force, and line speed, on the friction coefficient was investigated and a friction coefficient model was proposed based on the experimental results. A volume change model of vinylester resin was also developed to predict the thermal expansion–polymerization shrinkage during curing. The parameters of the model were determined by dilatometry, thermomechanical analysis (TMA) and differential scanning calorimetry (DSC).
Curing Characteristics, Mechanical Properties and Oil Resistance of Styrene Butadiene Rubber/Epoxidized Natural Rubber Blends
Authors: Ismail H. , Suzaimah S. , Hairunezam H. M.
Published: July 2008

Styrene butadiene rubber (SBR)/epoxidized natural rubber (ENR) blends were prepared with an internal mixer, Haake Rheomix. The blends were prepared at 60 C at a rotor speed of 60 rpm. Curing characteristics, mechanical properties and oil resistance of the blends were studied. The scorch time, t2 and curing time, t90 were found to decrease with increasing ENR composition in the blends. The mechanical properties viz. tensile strength, tear strength and tensile modulus, M300 (modulus at 300% elongation) increase with increasing ENR composition in the blends. However, elongation at break, Eb shows an opposite trend. At similar immersion time, SBR/ENR blends with higher composition of ENR exhibit better oil resistance.
Performance of Polypropylene Blended with Different Grades of mPE
Authors: Qiu Guixue , Raue Frank , Ehrenstein Gottfried W.
Published: July 2008

Blending polypropylene (PP) with an elastomeric phase such as EPDM is often performed in order to increase its fracture toughness. With the availability of metallocene polymerized polyethylene (mPE), a new modifier with interesting mechanical properties can be chosen for blending with PP. The influence of mPE grades in PP/mPE blends on their rheological, thermal and mechanical properties was investigated in this research. Special emphasis is placed on the low temperature toughness of the blends. The result shows that the mPE grade with a high octene content has the lowest glass transition temperature (Tg) and highest toughening effect for PP.
A New Bimetallic Complex Catalyst for NBR Hydrogenation and Properties of Hydrogenated NBR
Authors: Yue Dong Mei , Shen Zeng Min , Xu Rui Qing , Wei Yung Kang
Published: July 2008

A new homogeneous bimetallic catalyst, based on Rh-Ru compounds, for the hydrogenation of acrylonitrile-butadiene copolymer(NBR) has been prepared. This paper described a study of the catalyst preparation and its hydrogenation process of NBR. The hydrogenation catalytic activity and selectivity of this bimetallic catalyst system (BMSC)was compared to two catalysts, RhCl(PPh3)3 and RuCl2(PPh3)3. NBR and hydrogenated NBR(HNBR) have also been characterized by infrared spectrum. The results showed that this new bimetallic complex catalyst offers good catalyst activity and excellent selectivity in NBR hydrogenation process to produce a highly saturated (98%) HNBR without gel formation. In addition, properties of the vulcanized HNBR have high tensile strength, elongation, tear strength and low permanent set. Its hot air ageing performance and oil swell test indicate that this HNBR is as good as those of current commercial products. Moreover, this new bimetallic complex catalyst, in conjunction with metal recovery system developed in this laboratory offers potential economic advantage in industrial applications.
Knowledge Gap in Characterization of Reinforcing Fillers, Structure-Processability Relation of Agglomerates
Authors: Nakajima N.
Published: July 2008

The ultimate objective of mixing rubber and reinforcing filler is the achievement of a desired degree of the filler dispersion. Therefore, an ease of breakdown of the agglomerates into aggregates represents one of the most important aspects of processability. The manner of the breakdown must be related to the structure of agglomerates, in addition to other factors such as mechanical and adsorptive interaction with rubber. However, hardly any investigation has been conducted on the morphology of the agglomerates. This paper proposes a possible morphological model for the reinforcing carbon black over the structure range of 10 nm-100 mm. The purpose of this presentation is to call attention to the need for research on the subject.
An Experimental and Numerical Investigation of the Free Edge Problem in Composite Laminates
Authors: Nailadi Chaitra L. , Adams Donald F. , Adams Daniel O.
Published: July 2008

A quasi-three-dimensional finite element analysis of a symmetric angle-ply [+454/-454] s laminate subjected to a uniform axial extension was conducted and the results compared with experimental data generated for this purpose. Singular finite elements were embedded around the interface/free edge and eight-noded quadrilateral elements were used elsewhere. The order of the singularity was obtained from a closed form elasticity solution. The order to the singularity compared well will those in previous published numerical analyses. The analyses predicted the presence of high interlaminar normal and shear strain concentrations along the free edge. The results were compared to experimental data obtained using the moiré interferometric technique. The experimental data consist of displacement patterns and an interlaminar normal strain concentration along the free edge. Favorable agreement between analysis and experiment is obtained only if the singular element is embedded in a small region around the singular point. Supported by a detailed literature review, the agreement between the analysis and the experimental data shows that a quasi-three-dimensional analysis is sufficiently accurate.
Quadric Surfaces Criterion for Composite Materials
Authors: Yeh Hsien-Liang
Published: July 2008

A new criterion, which is named the quadric surfaces criterion for composite materials, is proposed based on the form of quadratic surface associated with a second-degree polynomial. The three interaction terms (i.e., σIσj, σIτij, and σjτij) are included in the quadric surfaces criterion completely. However, no more biaxial tests are required for the determination of those coefficients of the three stress interaction terms.

Since the quadric surfaces criterion requires three yield strengths from simple tension, compression, and torsion tests, respectively, this criterion is applicable for ductile materials as well as brittle materials with different strengths in tension and compression. One unique feature of the quadric surfaces criterion is the ability to change its format depending upon what types of stresses are applied and what types of material strengths are considered. Thus, it is shown that the entire closed failure envelope of the quadric surfaces criterion is composed of piecewise quadric surfaces. For example, when a material is deformed in compression, the compressive strength should be the dominant critical strength, not the tensile strength. Accordingly, the failure function must be adjusted so that it can accommodate the compressive strength.

The validity of the quadric surfaces failure criterion is examined with experimental results from off-axis uniaxial strength tests of unidirectional fiber composites, and angle-ply laminated composites. Comparisons were made with other well-known an isotropic strength theories as well.
Elasto-Plastic Finite Element Analysis of Fully Clamped Laminated Thermoplastic Composite Plates
Authors: Karakuzu Ramazan , Aslan Züleyha , Yucel U. Kerim
Published: July 2008

In this paper, an elasto-plastic finite element analysis is carried out in woven steel fiber reinforced laminated thermoplastic composite plates subjected to transverse uniform loads. The laminated composite plate is clamped at all its edges. Numerical simulation is performed using the well-established commercial software ANSYS. To investigate the effects of ply number, orientation angle and bonding type for optimum design of fully clamped laminated composite plates, yielding loads and residual stresses are obtained. Three-load step is carried out for each analysis consecutively. The yielding transverse load is applied at first. Then, a series of load increments added until the load reaches “Yielding Load + 0.005 MPa”. At the last step the external load is released to obtain the residual stress components.
Domain-Driven Binding of Fibrin(Ogen) onto Silk Fibroin Biomaterials
Authors: Santin Matteo , Denyer Stephen P. , Lloyd Andrew W. , Motta Antonella
Published: July 2008

Studies have demonstrated that serum protein adsorption onto silk fibroin-based biomaterials dramatically changes when the conformation of this natural polymer is rearranged by engineering procedures. In the present study, attention was paid to the binding of fibrin(ogen) to fibroin fibers and regenerated films. The fibroin specimens were incubated either in human plasma or in a fibrinogen solution to which thrombinwas added to activate the polymerization of the precursor into the final product, fibrin. The experiments were carried out in the presence and absence of calcium to investigate the role of calcium-dependent enzymes in the binding process. The two types of samples were analyzed by SEM, the micrographs showed completely different interactions with fibrinogen. Films did not show any visible fibrin polymerization, whereas the fibers were bound to the fibrin bundles by calcium-independent mechanisms.
Imaging of Poly(N-Isopropyl Acrylamide-Co-Acrylic Acid)–Amino Acid Conjugates with Scanning Tunnelling Microscopy
Authors: Koçum Cengiz , Bulmuş Volga , Pişkin Erhan
Published: July 2008

A copolymer of N-isopropyl acrylamide (NIPAAm) and acrylic acid (AAc), Mw 1,400, AAc content of 3.1 mmol carboxylic acid groups per gram of the copolymer, was synthesised by a free radical polymerisation. Mono-, di-, and tripeptide conjugates of this copolymer were prepared by using the carboxylprotected alanine, glycine and serine, with a water-soluble carbodiimide. Scanning tunnelling microscope images of the conjugates were taken after each synthesis step. The average length and width of the copolymer with no amino acid were measured as 17 and 2.5 nm, respectively. The lengths of the mono-, di-, and tri-peptide conjugates were similar to the length of the copolymer chain while the widths were in the range of 3.0–3.2, 3.5–4.0 and 4.2–4.4 nm, respectively.
In vitro Release Behavior of Insulin from Biodegradable Hybrid Hydrogel Networks of Polysaccharide and Synthetic Biodegradable Polyester
Authors: Zhang Yeli , Chu Chih-Chang
Published: July 2008

The controlled release of insulin from a series of biodegradable hybrid hydrogel network containing dextran derivative of allyl isocyanate (dex-AI) and poly (D,L) lactide diacrylate macromer (PDLLAM) over a wide range of composition ratio was investigated. Laser confocal scanning microscope was used to understand the insulin dispersion and release mechanism in the hydrogels. We found that the dispersion of insulin in the hydrogel network appeared to become less homogeneous as the PDLLAM composition in the hydrogel increased. The increase in hydrogel degradability imparted by PDLLAM incorporation shifted the hydrogel to a more open structure at a later release time, which facilitated the release rate and extent of insulin. From the result of release kinetics study (i.e., diffusion coefficient), insulin release occurred through diffusion and degradation controlled mechanisms. In addition, a comparison of the release characteristics of indomethacin, insulin and bovine serum albumin from the hydrogel network showed that the following parameters determined the release kinetics: drugmolecular weight and size, hydrogel swellability and degradability, drug solubility in water and the hydrophobic interaction between drugs and thehydrogel network.
Discrete-Time Modal Control for Seismic Structures with Active Bracing System
Authors: Lu Lyan-Ywan
Published: July 2008

In this study, a shaking-table test was performed to verify a proposed discrete-time modal control method that is suitable for seismic control of structural systems and also easy for digital control implementation. The computation of the feedback gain is formulated in a discrete-time domain and is given in a concise matrix form. A method for generating the best achievable eigenvectors that are most consistent with the target values is also proposed. The test involves a full-scale three-story building model that is actively controlled by an active bracing system. The test results show that the proposed discrete-time modal control can be a very efficient and promising method for mitigating the seismic response of building structures. For the building model tested, the performance of the proposed method with only two feedback signals can be as effective as that of full state feedback control.
Vibration Isolation of Structural Systems Using Squeeze Mode ER Mounts
Authors: Hong S. R. , Choi S. B. , Jung W. J. , Jeong W. B.
Published: July 2008

This paper presents vibration control of flexible structures using squeeze mode ER mounts. After devising the squeeze mode ER mount, its field-dependent damping forces are evaluated at various exciting frequencies. The ER mounts are then incorporated with a flexible beam structure. The governing equation of motion is obtained and an optimal controller which represents controllable damping force is designed to attenuate unwanted structural vibration. The controller is experimentally realized and control responses are presented in the frequency domain. In addition, vibration control responses of a flexible frame structure integrating with the proposed ER mounts are investigated by experiment.
Three-Ports Micro ER Valve for ER Suspension Fabricated by Photolithography
Authors: Nakano Masami , Katou Teruo , Satou Akira , Miyata Kaoru , Matsushita Kouichi
Published: July 2008

A three-ports micro ER valve has been fabricated by photolithography, which is made of a patterned resist film between two-glass plates coated ITO electrode pattern. And one inlet channel (height h 1/4 0.1 mm, width w 1/4 2 mm) of the ER suspension diverges into two outlet channels having ER valves, so that the inflow of the ER suspension from the inlet port is divided into two outflows to the two outlet ports by synchronously controlling a pair of ER valves installed in the outlet channels. The PWM control strategy is applied to a pair of ER valves to change the flow rates, as proposed in our previous paper. The PWM control of each outlet micro ER valve can realize the almost same changing characteristics of flow rate with the duty ratio as that of a conventional valve. The switching characteristics of a pair of ER valves have been investigated by measuring the flow rates from both outlet ports and visualizing the micro-flow behavior of ER suspension in the ER valves.
Vibration Control Evaluation of a Commercial Vehicle Featuring MR Seat Damper
Authors: Han Y. M. , Nam M. H. , Han S. S. , Lee H. G. , Choi S. B.
Published: July 2008

This paper presents vibration control responses of a commercial vehicle installed with electro-rheological (ER) primary suspensions and a magneto-rheological (MR) seat damper. After formulating the governing equation of motion of the full-vehicle system associated ER and MR dampers, the sky-hook controllers are designed by imposing semi-active actuating conditions. The control algorithms are then implemented via the hardware-in-the-loop simulation, and control responses of vertical displacement and acceleration at the driver’s seat are evaluated under two road conditions; bump and random road.
The Development of Elastodynamic Components for Piezoelectrically Actuated Flapping Micro-Air Vehicles
Authors: Cox Adam , Monopoli Daniel , Cveticanin Dragan , Goldfarb Michael , Garcia Ephrahim
Published: July 2008

This paper describes the development of skeletal mechanisms and wings for the electromechanical emulation of mesoscale flapping flight. Specifically, three piezoelectrically actuated flexure-based mechanisms are described that transform the linear output of piezoelectric unimorph actuators into single-degree-of-freedom flapping motion, and experimental results are described that characterize their performance. Additionally, efforts in the development of aeroelastically tailored wings are described, and data is presented that characterizes how the ratio of bending to torsional natural frequencies of the wing influences wing lift and efficiency.
Implementation of a Thermodynamic Framework for Damage Mechanics of Solder Interconnects in Microelectronics Packaging
Authors: Basaran Cemal , Tang Hong
Published: July 2008

A thermodynamic framework for damage mechanics is proposed. The damage evolution function uses entropy as a damage metric. A damage-coupled viscoplastic model with kinematic and isotropic hardening is implemented in a commercial finite element code to simulate the thermo-mechanical behavior of eutectic solder interconnectsin micro electronics packaging. The damage, asan internal state variable, is coupled witha unified viscoplastic constitutive model to characterize the cyclic deterioration of the material under thermo-mechanic fatigue loads. Several computational simulations of uniaxial monotonic tensile and cyclic shear tests are conducted to validate the model with experimentalresults. The behavior of a Ball Grid Array (BGA) package under thermo-mechanic fatigue loading is also simulated and compared with experimental results.
Damage Process of Polycrystalline LSI Conductor Due to Atom Migration Induced by Electric Current and Stress
Authors: Shibutani Tadahiro , Kitamura Takayuki , Kawamura Futoshi
Published: July 2008

Electric current inducesatom transport along grain boundary (GB) and interface (IF) in an LSI conductor and it istermed ‘‘electromigration (EM)’’. The atom flow and the constraint of deformation bring about the stress on the GB, which induces another atom flow (stress-induced migration: SM) under no external load. The functional for the EM and SM in a polycrystalline material is derived where the deformation field and the atom flux are calculated by minimizing the functional on the basis of the variational principle. A numerical simulation method of damaging process is proposed, and the mechanism and mechanics of cavity growth isanalyzed by the method under an electric current without external load. The results obtained are as follows. (1) The efflux of atoms at the cavity tip is governed by the stress evoked by the electric current (SM), while the atoms are carried far away by the EM. (2) The GB/IF network strongly influences the atom flow near the cavity and acceleratesthe cavity growth. (3) The high IF diffusivity activates not only the atom transport along the IF but also those along the GBs connected with it. The cavity growth isaffected by the accelerated atom flow.
Fracture of Friction Lining of the Brake System at Car Braking
Authors: Heidarov Sh. G.
Published: July 2008

The problem of fracture mechanics for friction lining of the brakesystem has been considered. It is assumed that at a multifold brakingthe fracture of materials caused by a contact interaction and accompanied by joint action of power load and temperature takes place with friction. It is considered that there are cracks near the surface of the friction lining contact. By the methods of analytical function theory the problem considered is reduced to the system of singular integral equations and to the infinite system of linear algebraic equations. The procedure of defining stress-intensity factors is shown. In the calculations the function describing the roughness of the friction lining surface has been assumed to be a stationary random function with a zero average value and known dispersion.
Interface Debonding Model and its Application to the Mixed Mode Interface Fracture Toughness
Authors: Omiya Masaki , Kishimoto Kikuo , Yang Wei
Published: July 2008

The aim of this paper is to investigate the mixed mode fracture toughness of an interface crack. The crack propagation is simulated by modifying a cohesive interface model proposed by Ma and Kishimoto (Ma, F. and Kishimoto, K. (1996). A Continuum Interface Debonding Model and Application to Matrix Cracking of Composites, JSME Int. J. Series A, 39:496–507). Based on the internal variable theory of thermodynamics, a continuum interface constitutive model relating interface traction with interface separation has been developed. By introducing an interface damage variable, an evolution equation was derived to characterize the degradation of interfacial rigidity with interface debonding. This constitutive relation is embedded at the crack tip of the interface and the propagation of the interface crack is simulated by the Finite Element Method. The results show that the fracture toughness and fracture boundary curves of dissimilar materials depend on the definition of the characteristic length included in the interface stress intensity factors. By changing the characteristic length properly and normalizing with the critical stress intensity factors, the intrinsic fracture boundary curve can be obtained. This curve can be considered as the fracture criterion based on the interface stress intensity factors. The relation between the fracture toughness and the phase angle is also influenced by the characteristic length. By changing the phase angle, the fracture toughness data is located on the same trend curve and the numerical results are well consistent with the analytical decohesion energy for all material pairs.
Characteristics of Ultraviolet Cured Glass–Epoxy Textile Composites: Part 1: Experimental Procedures and Testing
Authors: Adanur Sabit , Arumugham Yuvaraj
Published: July 2008

Ultraviolet curing of composite samples with different number of layers was carried out and the limitations and advantages of the system were examined. The optimization of the photoinitiator concentration in the radiation curable formulation was studied.

The composite samples were cured in different environments to understand the phenomenon of oxygen quenching and establish ways to overcome this. Postcuring of ultraviolet cured composite samples was done to study the degree of polymerization achieved. A formulation was developed to enhance the mechanical properties of the ultraviolet cured composite samples. Composite samples were made using the conventional heat curing process and comparative studies were performed with the ultraviolet cured composite samples. Three point bending and impact tests were performed to obtain relevant properties. A curing system using ultraviolet radiation is proposed for use on a braiding machine, which can quicken the composite manufacturing and eliminate additional secondary processing.
Air Permeability of Multilayer Needle Punched Nonwoven Fabrics: Experimental Method
Authors: Mohammadi M. , Banks-Lee P. , Ghadimi Parviz
Published: July 2008

In many applications, fabric structure has a dominant influence on the performance characteristics of a material, particularly in controlling transport of flows. Experimental air permeability was determined for 12 multilayer, heterogeneous, needle punched nonwoven materials. Samples were produced using multiple layers of ceramic and glass fibers. The fibers used to produce the ceramic layers for all samples have approximately the same diameter and density as the fibers used to produce the glass layers for all samples. Therefore, the samples were assumed to be multilayer homogeneous fabrics. In this paper, the experimental permeability is measured usingstandard equipment and results are discussed as a function of fabric construction parameters. Results showed that increasingthe fraction of glass and/or the fraction of ceramic content, and increasingthe number of needle barbs all cause a decrease in air permeability. Statistical results showed that the experimental air permeability can be predicted with greater than 99% confidence when using fabric thickness, fraction of glass in the sample, and fabric density as independent variables in the model.
Factors Affecting the Performance of New Oxygen Scavenging Polymer for Packaging Applications
Authors: Solis James A. , Rodgers Brad D.
Published: July 2008

Chevron Phillips Chemical Company has developed an oxygen scavenging system based on a blend of ethylene methylacrylate cyclohexenylmethyl acrylate (EMCM) for use in both flexible and rigid packaging applications. This polymer distinguishes itself from other oxygen scavenging polymers in that scavenging is conducted without the generation of degradation products that may easily migrate out of the polymer matrix, which in turn could cause negative organoleptic effects in certain classes of foods. Also, through the use of a proprietary photoinitiator, the oxidation mechanism may be initiated by treating the polymer with commercially available ultraviolet light systems, without reducing typical packaging rates. This system allows the packager to incorporate the scavenger into the package structure, store the packaging raw material (e.g. film, cartons, or bottles) for an extended period of time, and then initiate scavenging at the most opportune time - just prior to filling. Once the filled package is sealed, the polymer will scavenge any residual headspace oxygen in the package as well as any fugitive oxygen that may permeate through the passive barrier in the structure. This paper discusses the scavenging system and examines some of the factors that affect the performance of the system which must be considered during application specific development work.
In situ Monitoring of Crack Growth in Mild Steel under Closure Conditions Using a Piezotransducer Array
Authors: Rajic N.
Published: July 2008

This paper reports on an experimental study into the application of surface-mounted piezotransducer elements to the detection of remote crack growth under loading conditions promoting severe closure. Crack growth is inferred from measurements of the acoustic power transmitted through lamb modes across wave paths bridging the crack. It is shown that the proposed arrangement is able to detect sub-millimetre crack growth despite the presence of closure, although variations in the degree of closure were found to cause large sporadic fluctuations in the transmitted acoustic power. Although informative of crack-state, these episodes could impair the proper interpretation of the sensor response data, highlighting the need for a cautious and robust approach to the application of the method. In the present implementation, the piezoceramic elements are placed in regions exposed to cyclic stress, raising the issue of element durability. More importantly, no evidence of piezoceramic degradation was found in the course of extended testing at working stress levels, bolstering confidence with respect to the application of these elements to long-term in situ health monitoring.
High Molecular Weight Film Resins with Increased Stiffness
Authors: Cribbs Leonard
Published: July 2008

High Molecular Weight, High Density Polyethylene (HMWHDPE) resins for film markets typically fall into a relatively narrow range of densities to provide the desired product functionality. For example, resins targeted for the tee shirt bag market require tear and puncture properties that require melt indices of around 0.05 dg/min and densities of around 0.950 g/cc. Development of these film resins and their respective bags has allowed for substitution of HMW-HDPE for paper in many markets. Additional substitution appears available, but it requires resins with both high strength and higher modulus. Using technology to produce bi-modal molecular weight distributions, film resins meeting these requirements have been produced.
Targeted Administration of Proteic Drugs. I. Preparation of Polymeric Nanoparticles
Authors: Chiellini Emo , Chiellini Elisabetta E. , Chiellini Federica , Solaro Roberto
Published: July 2008

The formulation of hybrid nanoparticles based on synthetic polymer-protein hybrid matrices for the targeted release of proteic drugs with antiviral activity such as a-interferon was investigated. Human serum albumin, alone, or in combination with myoglobin, and the hemiesters of alternating copolymers of maleic anhydride/alkyl vinyl ethers of oligo(ethylene glycol) were selected as proteic and synthetic components, respectively. Digalactosyl diacyl gycerol, a natural glycolipid selectively recognized by the asialofetuin receptor was used for the active targeting of liver hepatocytes. Nanoparticle suspensions were prepared either by slow solvent evaporation from biphase and triphase emulsions or by controlled coprecipitation. Nanoparticles, 0.1-0.3 gm in diameter, were obtained by the latter method, whereas the former one afforded heterogeneous micro and nanoparticle mixtures. Several techniques were tested to separate the nanoparticle dispersions from the suspending solution. The best results, in terms of a homogeneous distribution of mostly spherical nanoparticles, were obtained by centrifugation in the presence of modified cyclodextrins. After lyophilization of supernatant, the resulting fluffy powder was easily resuspendable in water.
Processing and Film Properties of Polypropylene Made Using Metallocene Catalysts
Authors: DeMeuse Mark T.
Published: July 2008

This paper will present results of both laboratory and pilot line evaluations of homopolymer polypropylenes produced using metallocene catalysts. The main focus of the work will be on the physical properties of the oriented films made from the isotactic homopolymer materials. Discussion will also be provided of processing issues that occur during the film manufacturing process.
Modeling and Compensation of Hysteresis in Piezoceramic Transducers for Vibration Control
Authors: Lee Soon-Hong , Royston Thomas J. , Friedman Gary
Published: July 2008

Hysteretic behavior in piezoceramic transducers is investigated theoretically and experimentally. The applicability of the rate-independent generalized Maxwell resistive capacitor (MRC) hysteresis model is established. Methods for MRC and inverse MRC online model identification are developed by first establishing that the MRC and its inverse are the same particular cases of the classical Preisach hysteresis model. This enables use of the extensive mathematical framework that has been developed for Preisach models. A method of incorporating the MRC model in a feed forward control scheme for hysteresis compensation is also presented. Experimental studies on a 1-3 piezoceramic composite support the theoretical developments and their applicability to piezoceramics.
Development of Semi-Active Suspension Systems Using ER Fluids for the Wheeled Vehicle
Authors: Suh M. S. , Yeo M. S.
Published: July 2008

This paper describes the performance estimation of semi-active suspension system using Electro-Rheological fluid-based damper, which is continuously variable according to the electric field strength. ER fluid characteristics are formulated by incorporating Bingham-plastic models and a dynamic model of ER damper is achieved. Then the ER damper is applied to the quarter car model. A sky-hook control algorithm is applied to improve the ride quality through computer simulation. Vibration tests are carried out to compare their performance with conventional passive suspension systems.
Experimental Investigation of E/M Impedance Health Monitoring for Spot-Welded Structural Joints
Authors: Giurgiutiu Victor , Reynolds Anthony , Rogers Craig A.
Published: July 2008

Health monitoring results obtained during fatigue testing of a spot-welded lap-shear structural-joint specimen using the electromechanical (E/M) impedance technique are presented. The test specimens were instrumented with piezoelectric wafer transducers, and the base E/M impedance signature was recorded in the 200-1,100 kHz frequency range. Fatigue testing was applied to initiate and propagate crack damage of controlled magnitude. Calibration tests using plain specimens were first performed to correlate stiffness decrease with damage progression and remaining life. During the subsequent health-monitoring tests, the decrease in structural stiffness was used to assess damage progression in the specimen. As damage progressed, the E/M impedance signatures were recorded at predetermined intervals. Signature data were processed, and the RMS impedance change was calculated. Damage index values were observed to increase as crack damage increases. The initiation and propagation of damage was successfully correlated with the E/M impedance measurements. Sensing and the localization principles of E/M impedance method were confirmed, and the rejection of spurious information was verified. These experiments demonstrated that the E/M impedance technique is a potentially powerful tool for damage detection, health monitoring, and NDE of spot-welded structural joints.
Factors Affecting the Mechanical Properties of Laminated Glass/Graphite-Epoxy Hybrid Composites
Authors: Adanur Sabit , Onal Levent
Published: July 2008

Mechanical properties of woven fabric reinforced glass/graphite-epoxy hybrid composite materials were evaluated. Three different material configurations, all based on the same volume fraction ratio (Vf), were used. The effect of production parameters on impact and stress–strain behavior was investigated. ANOVA analysis was performed to find the influence of each parameter on the mechanical properties and the relations between parameters. Thickness of the composite and hybrid combination had effect on stress–strain and impact properties. Molding pressure gave significant rate on stress properties. Failure mechanisms of the laminates were evaluated. Different failure behavior between hybrid and glass structures was observed. Obvious delamination zones were observed with some samples. Regression models for defined variables and mechanical properties were generated.