bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure of bacteriophage SPN1S endolysin reveals an unusual two‐module fold for the peptidoglycan lytic and binding activity
Authors: Park Yangshin , Lim Jeong‐A. , Kong Minsuk , Ryu Sangryeol , Rhee Sangkee
Published: February 2014

Bacteriophage SPN1S infects the pathogenic Gram‐negative bacterium Salmonella typhimurium and expresses endolysin for the release of phage progeny by degrading peptidoglycan of the host cell walls. Bacteriophage SPN1S endolysin exhibits high glycosidase activity against peptidoglycans, resulting in antimicrobial activity against a broad range of outer membrane‐permeabilized Gram‐negative bacteria. Here, we report a crystal structure of SPN1S endolysin, indicating that unlike most endolysins from Gram‐negative bacteria background, the α‐helical protein consists of two modular domains, a large and a small domain, with a concave groove between them. Comparison with other structurally homologous glycoside hydrolases indicated a possible peptidoglycan binding site in the groove, and the presence of a catalytic dyad in the vicinity of the groove, one residue in a large domain and the other in a junction between the two domains. The catalytic dyad was further validated by antimicrobial activity assay against outer membrane‐permeabilized Escherichia coli. The three‐helix bundle in the small domain containing a novel class of sequence motif exhibited binding affinity against outer membrane‐permeabilized E. coli and was therefore proposed as the peptidoglycan‐binding domain. These structural and functional features suggest that endolysin from a Gram‐negative bacterial background has peptidoglycan‐binding activity and performs glycoside hydrolase activity through the catalytic dyad.
A new pathway of exogenous fatty acid incorporation proceeds by a classical phosphoryl transfer reaction
Authors: Cronan John E.
Published: February 2014

The Firmicute bacteria readily incorporate exogenous fatty acids into their phospholipids. In some (but not all) family members incorporation of the fatty acids present in human serum precludes the use of fatty acid synthesis inhibitors to treat infections. However, the pathway(s) of exogenous fatty acid incorporation in these bacteria remained unknown, although it was thought to differ from known pathways. Parsons and co‐workers show that in Staphylococcus aureus exogenous fatty acids are activated by phosphoryl transfer from ATP to form acyl‐phosphates, a mixed anhydride suggested as a potential intermediate 70 years ago. This finding has important ramifications for the efficacy of treatment of S. aureus infections using inhibitors of fatty acid synthesis.
X‐ray structure of a novel endolysin encoded by episomal phage phiSM101 of Clostridium perfringens
Authors: Tamai Eiji , Yoshida Hiromi , Sekiya Hiroshi , Nariya Hirofumi , Miyata Shigeru , Okabe Akinobu , Kuwahara Tomomi , Maki Jun , Kamitori Shigehiro
Published: February 2014

Gram‐positive bacteria possess a thick cell wall composed of a mesh polymer of peptidoglycans, which provides physical protection. Endolysins encoded by phages infecting bacteria can hydrolyse peptidoglycans in the bacterial cell wall, killing the host bacteria immediately. The endolysin (Psm) encoded by episomal phage phiSM101 of enterotoxigenic Clostridium perfringens type A strain SM101 exhibits potent lytic activity towards most strains of Clostridium perfringens. Psm has an N‐terminal catalytic domain highly homologous to N‐acetylmuramidases belonging to the glycoside hydrolase 25 family, and C‐terminal tandem repeated bacterial Src homology 3 (SH3_3) domains as the cell wall‐binding domain. The X‐ray structure of full‐length Psm and a catalytic domain of Psm in complex with N‐acetylglucosamine were determined to elucidate the catalytic reaction and cell wall recognition mechanisms of Psm. The results showed that Psm may have adopted a neighbouring‐group mechanism for the catalytic hydrolysing reaction in which the N‐acetyl carbonyl group of the substrate was involved in the formation of an oxazolinium ion intermediate. Based on structural comparisons with other endolysins and a modelling study, we proposed that tandem repeated SH3_3 domains of Psm recognized the peptide side‐chains of peptidoglycans to assist the catalytic domain hydrolysing the glycan backbone.
Population fluctuations affect inference in ecological networks of multi‐species interactions
Authors: Wells Konstans , Feldhaar Heike , O’Hara Robert B.
Published: February 2014

Local abundance and population fluctuations are key factors affecting the realized interaction frequencies in biotic interactions, but they are commonly ignored when network metrics are calculated over aggregated sets of observations. Here we studied how abundance fluctuations (i.e. demographic and stochastic population dynamics in one of the trophic levels) may affect derived network‐level inferences in bipartite ecological networks. Variation at both the species and network level in network indices (d’, Dependence, Fisher's alpha diversity for both levels, H2’, weighted NODF) were strongly correlated with the extent of abundance fluctuations, with a strong effect of environmental stochasticity on all indices except NODF; this was the only index for which considerable variation was caused by varying carrying capacities among species. Binary connectance, in turn, does not take interaction frequency (and thus abundance) into account and was only influenced by abundance fluctuations at low population sizes if this led to non‐occurrence of ‘true’ interactions.

Overall, abundance and population dynamics are likely to play an important role in determining what is commonly observed and summarized into ecological networks. We suggest that ecological network inference should account for underlying population dynamics and uncertainty in what is observed as interaction frequencies, modelling mechanisms at operative organisational levels below the network rather than using aggregated data of observations. Modelling population dynamics may be a valuable tool in this field to conceptualize and tease apart different sources of variation and express uncertainty in our inference from small samples.
IgY Technology in aquaculture – a review
Authors: Baloch Abdul Rasheed , Zhang Xiao‐Ying , Schade Rüdiger
Published: February 2014

Since the discovery of IgY in egg yolk in late 1800s, many applications of this antibody in diagnostics and therapeutics have been reported in human and veterinary medicine. The mass use of antimicrobial agents in aquaculture has caused the resistance in certain bacteria, and these fish pathogens cause tremendous economic losses in aquaculture industry coupled with antibiotic resistance, consequently causing barriers in international trades. IgY antibodies have been developed for the treatment and prevention of certain fish diseases such as white spot syndrome in shrimp, vibriosis, enteric redmouth disease and edwardsiellosis. These antibodies are also developed for the recognition of developing and mature stages of Loma salmonae (microsporidia) in the farmed pacific salmon. Other uses of IgY in aquaculture include the development of sandwich ELISA for the detection of ciguatoxin (a poisonous organic compound) in the tissues of fish, and recently, potential sea food persevering properties of IgY have been revealed. Our review presents an analysis of the characteristics, extraction methods, therapeutic, detection, and seafood‐persevering applications of IgY antibodies in aquaculture.
Statistical Inference for High‐Dimensional Global Minimum Variance Portfolios
Authors: Glombek Konstantin
Published: February 2014

Many studies demonstrate that inference for the parameters arising in portfolio optimization often fails. The recent literature shows that this phenomenon is mainly due to a high‐dimensional asset universe. Typically, such a universe refers to the asymptotics that the sample size n + 1 and the sample dimension d both go to infinity while d ∕ n → c ∈ (0,1). In this paper, we analyze the estimators for the excess returns’ mean and variance, the weights and the Sharpe ratio of the global minimum variance portfolio under these asymptotics concerning consistency and asymptotic distribution. Problems for stating hypotheses in high dimension are also discussed. The applicability of the results is demonstrated by an empirical study. Copyright © 2014 John Wiley & Sons, Ltd.
Effect of soil aggregate size and dicyandiamide on N2O emissions and ammonia oxidizer abundance in a grazed pasture soil
Authors: Robinson A. , Di H. J. , Cameron K. C. , Podolyan A.
Published: February 2014

Nitrous oxide (N2O) is a potent greenhouse gas, which is mainly produced from agricultural soils. Ammonia oxidation is the rate‐determining step in N2O production, and the process is carried out by ammonia oxidizers, bacteria and archaea. Soil aggregate size has been shown to alter soil properties, which affect N2O emissions and bacterial communities. However, the effect of aggregate size on temporal and total N2O emissions and ammonia‐oxidizing bacteria (AOB) and archaea (AOA) is not fully understood. This incubation study investigated the effect of three different soil aggregate sizes on N2O emissions and ammonia oxidizer abundance under high urine‐N concentrations and the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), at reducing N2O emissions in different aggregate soils. It was found that temporal patterns of N2O emissions were affected by aggregate size with higher peak emissions in the large and medium aggregates. However, the total emissions were the same due to a ‘switch’ in emissions at day 66, after which smaller aggregates produced higher N2O emissions. It is suggested that the switch was caused by an increase in aggregate disruption in the small aggregates, following the urine application, due to their higher surface area to volume ratio. AOB and AOA abundances were not significantly affected by aggregate size. DCD was effective in reducing N2O emissions in all aggregate sizes by an average of 79%. These results suggest that similar ammonia oxidizer abundance is found in soils of different aggregate sizes, and the efficacy of DCD in reducing N2O emissions was not affected by aggregate size of the soil.
The Arabidopsis thaliana tandem zinc finger 1 (AtTZF1) protein in RNA binding and decay
Authors: Qu Jie , Kang Shin Gene , Wang Wei , Musier‐Forsyth Karin , Jang Jyan‐Chyun
Published: February 2014

The Arabidopsis thaliana tandem zinc finger 1 (AtTZF1) protein is characterized by two tandem‐arrayed CCCH‐type zinc fingers. We have previously found that AtTZF1 affects hormone‐mediated growth, stress and gene expression responses. While much has been learned at the genetic and physiological level, the molecular mechanisms underlying the effects of AtTZF1 on gene expression remain obscure. A human TZF protein, hTTP, is known to bind and trigger the degradation of mRNAs containing AU‐rich elements (AREs) at the 3′ untranslated regions. However, while the TZF motif of hTTP is characterized by CX8CX5CX3H‐X18‐CX8CX5CX3H, AtTZF1 contains an atypical motif of CX7CX5CX3H‐X16‐CX5CX4CX3H. Moreover, the TZF motif of AtTZF1 is preceded by an arginine‐rich (RR) region that is unique to plants. Using fluorescence anisotropy and electrophoretic mobility shift binding assays, we have demonstrated that AtTZF1 binds to RNA molecules with specificity and the interaction is dependent on the presence of zinc. Compared with hTTP, in which TZF is solely responsible for RNA binding, both TZF and RR regions of AtTZF1 are required to achieve high‐affinity RNA binding. Moreover, zinc finger integrity is vital for RNA binding. Using a plant protoplast transient expression analysis we have further revealed that AtTZF1 can trigger the decay of ARE‐containing mRNAs in vivo. Taken together, our results support the notion that AtTZF1 is involved in RNA turnover.
Experimental Comparisons of Sliding Mode Controlled Pneumatic Muscle and Cylinder Actuators
Authors: Jouppila Ville , Andrew Gadsden S. , Ellman Asko
Published: February 2014

Pneumatic muscle actuators offer a higher force-to-weight ratio compared to traditional cylinder actuators, and introduce stick-slip-free operation that offers an interesting option for positioning systems. Despite several advantages, pneumatic muscle actuators are commonly avoided in industrial applications, mainly due to rather different working principles. Due to the highly nonlinear characteristics of the muscle actuator and pneumatic system, a reliable control strategy is required. Although muscle actuators are widely studied, the literature lacks detailed studies where the performance for servo systems is compared with traditional pneumatic cylinders. In this paper, a pneumatic servo actuation system is compared with a traditional cylinder actuator. As the overall system dynamics are highly nonlinear and not well defined, a sliding mode control (SMC) strategy is chosen for the control action. In order to improve the tracking performance, an SMC strategy with an integral action (SMCI) is also implemented. The control algorithms are experimentally applied on the pneumatic muscle and the cylinder actuator, for the purposes of position tracking. The robustness of the systems are verified and compared by varying the applied loads.
High-Frequency and Low-Temperature Thermosonic Bonding of Lead-Free Microsolder Ball on Silver Pad Without Flux
Authors: Wang Fuliang , Li Junhui , Han Lei
Published: February 2014

Lead-free solder balls are environment friendly; however, they require a high bonding temperature, which causes problems in the microelectronics package industry. To reduce the bonding temperature, a 60 kHz high-frequency thermosonic bonding method is proposed and realized using a lab bonder. Experimental results showed that this method could be used to bond a 300 μm-diameter Sn–Ag–0.5Cu microsolder ball onto a silver pad without flux at a low temperature of 160 °C in 3 s. A ball shear test showed that the high frequency led to a high bonding strength of 58.8 MPa, and a dimpled structure was observed at the bonding interface by SEM. Compare with the reflow method or laser soldering method, the proposed method requires a low bonding temperature and leads to a high bonding strength.
Detection of Cavitation in a Venturi Injector With a Combined Method of Strain Gauges and Numerical Simulation
Authors: Xu Yuncheng , Chen Yan , He Jianqiang , Yan Haijun
Published: February 2014

The fertilizer suction capability of a Venturi injector is dependent on the vacuum pressure in the throat portion. As the vacuum level drops below the saturation vapor pressure, the pressure decreases to a particular value corresponding to the maximum pressure difference (Δpmax) between inlet and outlet pressures, and critical cavitation is likely to occur, leading to an unstable suction flow rate and low fertilization uniformity. A new method of using strain gauges to detect cavitation in Venturi injectors was explored experimentally and verified numerically under various operating conditions. The standard deviation (SD) of the measured strain values and the simulated values of the vapor-phase volume fraction (Vf) were used to evaluate the influence of cavitation. The results showed that both the rate of increase (ηm) of the average SD and the average growth rate (AGR) of the simulated cavitation length reach relatively large values at the maximum pressure difference (Δpmax), where the measured suction flow rate simultaneously reaches a maximum. In addition, SD and Vf shared similar variation trends at pressure differences larger than the corresponding Δpmax under various conditions. This new cavitation detection method has been proved to be feasible and reliable. It helps to determine accurately the value of Δpmax at different inlet pressures and to ensure that the Venturi injector runs in a safe operating-pressure range.
Numerical and Experimental Investigations of the Three-Dimensional-Flow Structure of Tandem Cascades in the Sidewall Region
Authors: Böhle Martin , Frey Thomas
Published: February 2014

Tandem blades can be superior to single blades, particularly when large turning angles are required. This is well documented in the open literature and many investigations have been performed on the 2D-flow of tandem cascades to date. However, much less information on the flow near the sidewalls is available. Thus, the question arises as to how the geometry of a tandem cascade should be chosen near the sidewall in order to minimize the flow losses for large turning angles. The present work examines the 3D-flow field in the region of the sidewall of two high turning tandem cascades. A large spacing ratio was chosen for the forward blade of the first tandem cascade ((t/l)1=1.92). The second tandem cascade possessed a smaller spacing ratio for the forward blades ((t/l)1=1.0). Both cascades had the same total spacing ratio of t/l=0.6. Flow phenomena, such as the corner stall of the 3D boundary layer near the sidewall, are examined using both numerical and experimental methods. The empirical correlations of Lieblein and Lei are applied. The flow topology of both tandem cascades is explained and the locations of loss onset are identified. In addition, oil pictures from experiments and streamline pictures of the numerical simulations are shown and discussed for the flow close to the sidewalls. Finally, design rules such as the aerodynamic load splitting and the spacing ratio of the forward- and aft-blades, etc. are taken into account. The examinations are performed for tandem cascades designed for flow turning of approximately 50 deg at a Reynolds number of 8×105. The tandem cascades consist of NACA65 blades with circular camber lines and an aspect ratio of b/l=1.0.
Experimental Investigation of Tensile Properties of SS316L and Fabrication of Micro/Mesochannel Features by Electrical-Assisted Embossing Process
Authors: Peng Linfa , Mai Jianming , Jiang Tianhao , Lai Xinmin , Lin Zhongqin
Published: February 2014

During the electrical-assisted forming process, a significant decrease in the flow stress of the metal is beneficial to reduce the required force for the deformation with high-density electrical current introduced through the materials. It is an alternative manufacturing process of traditional hot forming to improve the formability without the undesirable effects caused by elevated temperature, such as surface oxidation. In this study, tension tests and electrical-assisted embossing process (EAEP) experiments were performed to study the electroplastic (EP) effect with high-density pulse current applied to the specimen and demonstrate the advantage of EAEP. In the first section of this study, specimens with various grain sizes were well prepared and an experimental setup was established to study the flow stress of SS316L sheet in the electroplastic tensile test. Extra cooling system was developed and the temperature increase caused by resistive heating was controlled. Thermal influence caused by resistive heating was thereby reduced. The impacts of the pulse current parameters on the flow stress were investigated. It was observed that the flow stress of the SS316L specimens was significantly reduced by the electroplastic effect. In the second section, the EAEP was proposed to fabricate microchannel feature on metal workpiece. Experiments were conducted to demonstrate the feasibility and advantage of the novel process. The protrusion feature height and microstructure of the grain deformation were measured to investigate the effect of the process parameters, such as the current density, the die geometric dimension, and the grain size of the specimen. Larger feature height was measured owing to the higher density current, which meant the electroplastic effects were helpful in EAEP.
Stiffness Sensor for Cubic Nonlinear Elasticity Using Nonlinear Self-Excited Oscillation
Authors: Kokubun Yosuke , Yabuno Hiroshi
Published: February 2014

The present paper develops a nonlinear stiffness sensor for measuring cubic nonlinear elasticity. The measurement system consists of a vibrator with a control circuit. We apply linear-plus-nonlinear feedback to actuate the vibrator attached to a measurement object for inducing van der Pol type self-excited oscillation so that the response amplitude of the oscillation can be set arbitrarily by changing the nonlinear feedback gain. We focus on the fact that the nonlinear elasticity of the measurement object causes a natural frequency shift related to the magnitude of vibration amplitude of the vibrator. We can set the response amplitude to various values by changing the nonlinear feedback gain and measuring the shift of the response frequency depending on the magnitude of the response amplitude. As a result, based on the bend of the experimentally obtained backbone curve, the nonlinear elasticity of the measurement object is identified.
A Lookup-Table-Based Approach for Spatial Analysis of Contact Problems
Authors: Machado Margarida , Flores Paulo , Ambrósio Jorge
Published: February 2014

The aim of this work is to present an efficient methodology to deal with general 3D-contact problems. This approach embraces three steps: geometrical definition of 3D surfaces, detection of the candidate contact points, and evaluation of the contact forces. The 3D-contact surfaces are generated and represented by using parametric functions due to their simplicity and ease in handling freeform shapes. This task is carried during preprocessing, which is performed before starting the multibody analysis. The preprocessing procedure can be condensed into four steps: a regular and representative collection of surface points is extracted from the 3D-parametric surface; for each point the tangent vectors to the u and v directions of the parametric surface and the normal vector are computed; the geometrical information on each point is saved in a lookup table, including the parametric point coordinates, the corresponding Cartesian coordinates, and the components of the normal, tangent, and bitangent vectors; the lookup table is rearranged such that the u-v mapping is converted into a 2D matrix being this surface data saved as a direct access file. For the detection of the contact points, the relative distance between the candidate contact points is computed and used to check if the bodies are in contact. The actual contact points are selected as those that correspond to the maximum relative indentation. The contact forces are determined as functions of the indentation or pseudopenetration, impact velocity, and geometric and material properties of the contacting surfaces. In general, lookup tables are used to reduce the computation time in dynamic simulations. However, the application of these schemes involves an increase of memory needs. Within the proposed approach, the amount of memory used is significantly reduced as a result of a partial upload into memory of the lookup table. A slider-crank mechanism with a cup on the top of the slider and a marble ball are used as a demonstrative example. A contact pair is considered between a cup and a marble ball, the contact forces for which are computed using a dissipative contact model.
Porogen Templating Processes: An Overview
Authors: Hong Yifeng , Zhou Jack G. , Yao Donggang
Published: February 2014

Porous materials with well-defined pore shapes, sizes and distributions are highly desired in many emerging applications, particularly for biomedical materials and devices. However, conventional methods for processing porous materials only demonstrated limited capability in morphological control. One promising solution is the porogen templating process, where a structured porogen pattern is created first and subsequently used as a template or mold for generation of the desired porous material. Particularly, with solid freeform fabrication, porogen templates having complex internal structures can be additively fabricated, and they can then be used as molds for molding of porous materials and devices. This article attempts to offer a constructive overview on the state of the art of porogen patterning and inverse molding, with the goal of explaining the working mechanisms and providing unbiased accounts of the pros and cons of existing techniques and process variants. The article further intends to provide a fundamental understanding of the constituent elements and corresponding building blocks in porogen templating processes. An increased understanding of these elements will facilitate the development of more capable new processes.
Developing a Mobile Lower Limb Robotic Exoskeleton for Gait Rehabilitation
Authors: Guo Zhao , Yu Haoyong , Yin Yue H.
Published: February 2014

A new compact mobile lower limb robotic exoskeleton (MLLRE) has been developed for gait rehabilitation for neurologically impaired patients. This robotic exoskeleton is composed of two exoskeletal orthoses, an active body weight support (BWS) system attached to a motorized mobile base, allowing over-ground walking. The exoskeletal orthosis is optimized to implement the extension and flexion of human hip and knee joints in the sagittal plane. The motor-driven BWS system can actively unload human body weight and track the vertical displacement of the center of mass (COM). This system is compact and easy for therapist to help patient with different weight (up to 100 kg) and height (150–190 cm). Experiments were conducted to evaluate the performance of the robot with a healthy subject. The results show that MLLRE is a useful device for patient to achieve normal over-ground gait patterns.
Estimation of Low-Cycle Fatigue Life of Elbow Pipes Considering the Multi-Axial Stress Effect
Authors: Takahashi Koji , Ando Kotoji , Matsuo Kazuya , Urabe Yoshio
Published: February 2014

The stress states of elbow pipes are complex and different from those of straight pipes. Manson's universal slope method cannot predict the low-cycle fatigue lives of elbow pipes under combined cyclic bending and internal pressure. In this work, fatigue tests and finite element analysis showed that the multi-axial stress factor (i.e., ratio of axial stress to hoop stress) is quite high at elbows. This paper proposes a revised Manson's universal slope method that considers the multi-axial stress factor to predict the low-cycle fatigue lives of elbows under combined cyclic bending and internal pressure with considerably high accuracy.
Theoretical Predictions of Spectral Emissivity for Coal Ash Deposits
Authors: Liu Dong , Duan Yuan-Yuan , Yang Zhen , Yu Hai-Tong
Published: February 2014

Coal ash inevitably forms deposits as combustion residue on the walls and heat transfer surfaces of coal-fired boilers. Ash deposits decrease the boiler efficiency, reduce the generating capacity, and cause unscheduled outages. The radiative heat transfer is the major heat transfer mechanism in utility boilers; thus, the ash deposit emissivity is critical to boiler efficiency and safety. This paper presents a radiative transfer model to predict the spectral emissivities of coal ash deposits. The model includes the effects of the microstructure, chemical composition, and temperature. Typical ash deposit microstructures are generated using diffusion-limited aggregation (DLA). The radiative properties are then calculated using the generalized multiparticle Mie-solution (GMM). The combined GMM and DLA model predicts spectral emissivity better than the original Mie theory and Tien's dependent scattering theory with the average relative difference between predicted results and experimental data decreasing from 17.8% to 9.1% for sample 1 and from 18.6% to 4.2% for sample 2. Maxwell-Garnett (MG) effective medium theory is used to calculate the ash deposit optical constants based on the chemical compositions to include the effect of chemical composition. Increasing temperatures increase the particle diameters and particle volume fractions and, thus, the spectral emissivities. The spectral emissivity ultimately remains constant and less than one. The homogeneous slab model gives the upper limit of the ash deposit spectral emissivity.
Experimental Investigations of Droplet Deposition and Coalescence in Curved Pipes
Authors: Nguyen Hung , Wang Shoubo , Mohan Ram S. , Shoham Ovadia , Kouba Gene
Published: February 2014

Even though there have been several studies conducted by the industry on the use of different inlet devices for gas–liquid separation, there have been limited laboratory and field evaluations on the use of external piping configurations as flow conditioning devices upstream of a separator inlet. The results of a systematic study of droplet deposition and coalescence in curved pipe and pipe fittings are reported in this paper. A facility has been designed consisting of two main test sections: a fixed horizontal straight pipe section and an interchangeable 180 deg return pipe section (or curved pipe section) of the same length. Both inlet and outlet to the 180 deg return are horizontal, but the plane of the 180 deg return pipe section can pivot about the axis of the inlet horizontal pipe to an angle as much as 10 deg downwards allowing downward flow in the return section. Various pipe fittings of different radius of curvature can be installed for comparison in the 180 deg return. Fittings evaluated in this study included: 180 deg pipe bend, short elbow bend (with standard radius of curvature of 1.5D), long elbow bend (with custom radius of curvature of 6D), target tee bend, and cushion tee bend. Experiments have been carried out using water and air, and varying gas velocities and liquid loadings. In order to compare the performance of geometries, Droplet Deposition Fractions (DDF) were measured in the horizontal straight pipe section and in the 180 deg return pipe section as a measure of coalescence efficiency. The results demonstrate that higher DDF occurs for curved fittings as compared to the straight pipe section. The short elbow bend has approximately 10% DDF higher, whereas long elbow bend along with 180 deg pipe bend perform better (by 15–20% DDF) than straight pipe. It was found that the cushion tee and target tee bends can coalesce droplets at lower gas velocities but break up droplets at higher gas velocities. Additionally, no significant differences between DDF's in three different inclination angles of a curved pipe were observed. It can be concluded that 180 deg pipe bend or two 6D long radius elbow bend can serve as a droplet coalescer; a pair of cushion tees or target tees can also work as coalescers at low kinetic energy but as atomizers at high kinetic energy.
Experimental Characterization and Modelling Validation of Shape Memory Alloy Negator Springs
Authors: Spaggiari Andrea , Dragoni Eugenio , Tuissi Ausonio
Published: February 2014

This paper is aimed at the experimental characterization and modelling validation of shape memory alloy (SMA) negator springs. A Negator spring is a spiral spring made of strip of metal wound on the flat with an inherent curvature such that, in repose, each coil wraps tightly on its inner neighbour. The main feature of a Negator springs is the nearly-constant force displacement behaviour in the unwinding of the strip. Moreover the stroke is very long, theoretically infinite as it depends only on the length of the initial strip. A Negator spring made in SMA is built and experimentally tested to demonstrate the feasibility of this actuator. The shape memory Negator spring behaviour is predicted both with an analytical model and with a a finite element software. In both cases the material is modelled as elastic in austenitic range while an exponential continuum law is used to describe the martensitic behaviour. The experimental results confirms the applicability of this kind of geometry to the shape memory alloy actuators and the analytical model is confirmed to be a powerful design tool to dimension and predict the spring behaviour both in martensitic and austenitic range, as well as the finite element model developed.
Structural Damage Detection Based on Energy Transfer Between Intrinsic Modes
Authors: Ghazi Reza Mohammadi , Long James , Buyukozturk Oral
Published: February 2014

In this study, a new damage detection algorithm for specific types of damages such as breathing cracks, which are called “active discontinuities” in this paper, is proposed. The algorithm is based on the nonlinear behavior of this class of damages and hence, is more precise and sensitive to damage compared to other common linear methods. The active discontinuities can be regarded as additional degrees of freedom (DOFs) which need energy to be excited. Because the input energy of both the intact and the damaged structures is finite, the energy content of vibrating modes will be changed due to damage. Thus, the properties of distribution of energy between vibrating modes can be used as indices for detecting damage. An essential detectability condition using this concept is decomposing a signal such that no spurious mode imposed to its expansion. In order to satisfy this condition, Empirical Mode decomposition (EMD) is used to extract the vibrating modes since all nonlinearities in a signal are preserved while no spurious mode or assumption of stationarity is imposed on the problem. Prevention of mode mixing, which is an important drawback of EMD, is another necessary condition for robustness of the algorithm. A solution is proposed in this paper to satisfy this condition in which special constraints are imposed on the normal procedure of EMD. Then, the fourth central moment, kurtosis, is used to compare the distribution of energy between the modified vibrating modes. The algorithm is verified through experimental testing of a simple steel cantilever structure under various damage scenarios. Results demonstrate the efficacy of the method for detecting discontinuities in a real structure.
Free Vibration Analysis of Electrorheological Fluid Sandwich Shell Structures Subjected to Large Deformation
Authors: Mohammadi Farough , Sedaghati Ramin
Published: February 2014

Due to the small linear region in electrorheological (ER) fluid, vibration analysis of the sandwich structure containing ER fluid should be investigated in nonlinear region where the material properties depend on frequency, amplitude and electric field. In present work, the nonlinear equations of motion have been obtained using finite element technique. The nonlinear amplitude dependent stiffness matrices in equations of motion have been previously expressed by B and N notations. In B-notation an asymmetric amplitude dependent stiffness matrix is achieved. On the other hand in N-notation a symmetric form of the nonlinear stiffness matrices is achieved. The main problem in nonlinear vibration analysis of structure using direct integration technique is the time-consuming integrations, which should be performed for several times throughout this method. Due to numerous degrees of freedom in sandwich shell/plate structures, the computational costs in finite element modeling of sandwich shell/plate structures becomes more expensive. In this study, by considering kinetic and potential energies attributed to the elastic and ER fluid layers and using Lagrange equations, nonlinear finite element formulation has been derived for the ER based sandwich shell structures. Also a new technique is developed to represent the equations of motion in a new notation referred to as H-notation which fundamentally reduces the computational costs in nonlinear vibration damping analysis of sandwich shell structure. Finally, parametric study is conducted to show the effect of small/ large displacement, electric field intensities and core thickness ratio on damping behavior of the ER based sandwich shell structures for different boundary conditions.
A Dynamic Knee-Ankle-Foot Orthosis With Superelastic Actuators
Authors: Tian Feng , Elahinia Mohammad , Hefzy Mohamed Samir
Published: February 2014

A knee-ankle-foot orthosis (KAFO) spans the knee, ankle and foot, and assists in the walking motion of those who suffer neuromuscular deficiencies. KAFOs can be classified as passive, semi-dynamic and dynamic. Passive KAFOs lock the knee joint during the whole gait cycle. Semi dynamic KAFOs lock the knee joint during the stance phase. Dynamic KAFOs attempt to reproduce normal knee motions during the whole gait cycle. Two types of dynamic KAFOs have been reported in the literature. The first one is activated by using a pneumatic system, and the second one uses a spring mechanism. Both systems are bulky and controlled through complex control systems that limit their application as assistive devices. The purpose of our research is to develop a dynamic KAFO that is actuated easily by employing shape memory materials. Such an actuation system makes the KAFO lightweight and with a great commercialization potential. The purpose of this paper is to present a conceptual design for the knee actuator of a dynamic KAFO. This actuator uses torsional shape memory rods to match the stiffness of the knee joint of the KAFO with that of a normal knee joint during the walking gait cycle. Joint stiffness is measured by the moment around the joint per degree of joint rotation. The proposed actuator includes two parts that work independently during the two phases of the gait cycle. The first part engages only during the stance phase and the other works only during the swing phase. Each part is developed by combining a superelastic (SE) rod and a rotary spring in series. The conceptual design is verified by simulation. The simulation results show that the proposed knee actuator reproduces the stiffness of the normal knee joint during the whole gait cycle. It is thus possible to develop a novel dynamic KAFO that can provide normal knee stiffness characteristics to assist individuals with quadriceps deficiency.
Digital Energy Harvester for Random or Multimodal Structural Vibrations
Authors: Makihara Kanjuro , Yamamoto Yuta
Published: February 2014

A digital energy harvester that captures electrical energy from complicated random or multimodal vibrations is proposed. The novel energy harvester is digital, autonomous, and controlled by a self-powered microprocessor. The digital self-powered microprocessor automatically and synchronously changes the circuit components with the vibration phase, and can therefore achieve autonomous harvesting. The multifunctional and self-controlled microprocessor is only driven by the voltage of the piezoelectric transducer, and no external power is required. The harvester exhibits great potential and versatility and is applicable to many machines and devices.
A Bi-Stable von-Mises Truss for Morphing Applications Actuated Using Shape Memory Alloys
Authors: Barbarino Silvestro , Gandhi Farhan S. , Visdeloup Rodolphe
Published: February 2014

The present study focuses on a bi-stable von-Mises truss (VMT), with integrated Shape Memory Alloy (SMA) wires which are resistively heated to provide the actuation force to transition the VMT from one stable equilibrium condition to the other, and back. This coupled VMT-SMA system can potentially be used in structural morphing applications. The paper considers in detail the design of the system, equilibrium between the VMT and the SMA wires, the initial pre-stress required in the two SMA wires, explains how the active (heated) SMA wire drives the VMT beyond the unstable equilibrium state, and the VMT in moving to the second stable equilibrium state pre-stresses the passive (unheated) SMA wire. The two SMA wires switch roles in moving the VMT back from the second to the first stable equilibrium state. A prototype is designed and fabricated and the transition of the VMT from one equilibrium state to the other, and back, is experimentally demonstrated. The governing differential equation representing the VMT behavior is coupled with equations representing the SMA behavior based on the Brinson thermo-mechanical model. The numerical predictions of system displacements versus temperature and time show good correlation with experimental results.
Microfabrication for Packaged Biomolecular Unit Cells
Authors: Nguyen Mary-Anne , Sarles Andy
Published: February 2014

This paper focuses on developing a closed fluidic environment for packaging biomolecular unit cells, which consists of a synthetic lipid bilayer and other biomolecules contained in a near solid-state material with two regions that contain hydrophobic oil (i.e. nonpolar solvent) surrounding aqueous droplets. This research provides a stepping-stone towards an autonomic biomolecular material system, whereby a packaged system will allow for precise droplet interface bilayer (DIB) formation without the interference of outside contamination for long-term applications. Also, substrate materials need to maintain droplets and preserve the self-assembly and stimuli-responsive properties of biomolecules within the unit cell. A critical feature of an encapsulating material is that it does not absorb either of the liquid phases required to form DIBs. Oil depletion tests within sealed, polymeric substrates show that polydimethylsiloxane (PDMS) absorbs full volume of injected hexadecane in approximately 27 hours. However, polyurethane substrates maintain the original amount of oil injected even after several weeks. Bilayer lifetime is also monitored within an environment in which the oil is also depleting. The results of this test show the longevity of a DIB to be shorter than oil lifetime. The lipid-encased droplets disconnect after approximately 10 hours, when there is only approximately <60% amount of oil present. In addition, an initial microfluidic substrate is designed such that a single T-junction intersection can be used to form monodisperse droplets within a primary oil-filled channel and a downstream increase in channel width can be used to connect droplets to form DIBs.
Performance of Capsule-Type Micro Actuator Using Hydrogen Storage Alloys
Authors: Goto Kenta , Higuchi Takehiro , Fuchiwaki Ohmi , Nakao Wataru
Published: February 2014

Capsule-type micro actuator driven by the volume change of hydrogen storage alloys (HSA-CMA) was proposed to be applied as an actuator mounted on the joints of the super multilink manipulator to capture space debris. This actuator consists of a hollow sphere frame made of aluminum, a membrane of hydrogen storage alloys and a valve, and is compact and lightweight. The aim of this study was to evaluate the availability of HSA-CMA. Finite element analyses were performed to investigate the actuator displacement and the generating force as the static performance, and the obtained static performances were compared with that of other smart actuators. The analysis on the actuator displacement led to the design map of HSA-CMA. The comparison result suggests that HSA-CMA has the actuator displacement and the generating force as well or better than other smart actuators and that it is suitable for use in space.
Multiplexed Fiber Optic Temperature Monitoring Sensor Using Hard-Polymer-Clad Fiber and an Optical Time-Domain Reflectometer
Authors: Kim Hyeong Cheol , Lee Jung-Ryul
Published: February 2014

Optical fiber temperature sensing systems have incomparable advantages than the traditional electric cable based monitoring systems. As of now, fiber Bragg grating (FBG) sensors are most popular because of its wavelength domain multiplexing capability. However, grating writing process is complex and takes long time and photosensitive fibers for the typical grating writing process are expensive. In addition, sensing systems for FBGs are also expensive. Therefore, this study proposes multiplexed fiber optic temperature monitoring sensor system using an economical Optical Time-Domain Reflectometer (OTDR) and Hard-Polymer-Clad Fiber (HPCF). HPCF is a specific type of optical fiber, in which a hard polymer cladding made of fluoroacrylate acts as a protective coating for an inner silica core. An OTDR is an optical loss measurement system that provides optical loss and event distance measurement in real time. Multiplexed sensor nodes were economically and quickly made by locally stripping HPCF clad through photo-thermal and photo-chemical processes using a continuous/pulse hybrid-mode laser with 10 m intervals. The core length exposed was easily controlled by adjusting the laser beam diameter, and the exposed core created a backscattering signal in the OTDR attenuation trace. The backscattering peak was sensitive to the temperature variation. Since the elaborated HPCF temperature sensor was insensitive to strain applied to the sensor node and to temperature variation in the normal HPCF line, neither strain compensation nor isolation technique are required. These characteristics are important advantages for the use as structure-integrated temperature sensors. The performance characteristics of the sensor nodes include an operating range of up to 120 C, a resolution of 1.52 C, a tensile strain resistance of 13%.
Power Response of a Muscle Actuator Driven by a Regenerative, Enzymatic Pressurization Mechanism
Authors: Sutter Thomas M. , Creasy Terry S. , Dickerson Matthew B. , Justice Ryan S.
Published: February 2014

Inspired by the characteristics of biological muscles, rubber muscle actuators (RMAs) are lightweight and compliant structures that deliver high power/weight ratios and are currently under investigation for use in soft robotics, prosthetics, and specialized aircraft. RMA actuation is accomplished by inflating the structure’s air bladder, which results in the contraction of the muscle. In this proceedings paper, we describe the use of gaseous products from enzymatically-catalyzed reactions to pressurize and drive the motion of RMAs. Specifically, this paper details the power envelope of RMAs driven by the urease-catalyzed production of CO2, under dynamic loading conditions. The use of enzymatically catalyzed, gas-producing reactions is advantageous for powering RMAs, as these systems may be self-regulating and self-regenerating. Reaction design parameters for sizing the gas source to RMA power requirements and power envelope results are reported for gas-powered actuator dynamics tested on a linear motion test assembly. The power response to increasing loads reflects the partial pressure over the reaction slurry; therefore, the chemistry and reactor scale affect the entire structure’s efficiency. We outline the reactor space-time design constraints that facilitate a tailored power response for urease catalyzed gas generation sources.