Science.gov

Sample records for dynamic stability enhancement

  1. Visual stabilization dynamics are enhanced by standing flight velocity.

    PubMed

    Theobald, Jamie C; Ringach, Dario L; Frye, Mark A

    2010-06-23

    A flying insect must travel to find food, mates and sites for oviposition, but for a small animal in a turbulent world this means dealing with frequent unplanned deviations from course. We measured a fly's sensory-motor impulse response to perturbations in optic flow. After an abrupt change in its apparent visual position, a fly generates a compensatory dynamical steering response in the opposite direction. The response dynamics, however, may be influenced by superimposed background velocity generated by the animal's flight direction. Here we show that constant forward velocity has no effect on the steering responses to orthogonal sideslip perturbations, whereas constant parallel sideslip substantially shortens the lags and relaxation times of the linear dynamical responses. This implies that for flies stabilizing in sideslip, the control effort is strongly affected by the direction of background motion.

  2. The dynamics of mobile promoters: Enhanced stability in promoter regions.

    PubMed

    Rabbani, Mahnaz; Wahl, Lindi M

    2016-10-21

    Mobile promoters are emerging as a new class of mobile genetic elements, first identified by examining prokaryote genome sequences, and more recently confirmed by experimental observations in bacteria. Recent datasets have identified over 40,000 putative mobile promoters in sequenced prokaryote genomes, however only one-third of these are in regions of the genome directly upstream from coding sequences, that is, in promoter regions. The presence of many promoter sequences in non-promoter regions is unexplained. Here we develop a general mathematical model for the dynamics of mobile promoters, extending previous work to capture the dynamics both within and outside promoter regions. From this general model, we apply rigorous model selection techniques to identify which parameters are statistically justified in describing the available mobile promoter data, and find best-fit values of these parameters. Our results suggest that high rates of horizontal gene transfer maintain the population of mobile promoters in promoter regions, and that once established at these sites, mobile promoters are rarely lost, but are commonly copied to other genomic regions. In contrast, mobile promoter copies in non-promoter regions are more numerous and more volatile, experiencing substantially higher rates of duplication, loss and diversification. PMID:27460588

  3. Enhancement of amorphous celecoxib stability by mixing it with octaacetylmaltose: the molecular dynamics study.

    PubMed

    Grzybowska, K; Paluch, M; Wlodarczyk, P; Grzybowski, A; Kaminski, K; Hawelek, L; Zakowiecki, D; Kasprzycka, A; Jankowska-Sumara, I

    2012-04-01

    In this paper, we present a novel way of stabilization of amorphous celecoxib (CEL) against recrystallization by preparing binary amorphous celecoxib-octaacetylmaltose (CEL-acMAL) systems by quench-cooling of the molten phase. As far as we know this is the first application of carbohydrate derivatives with acetate groups to enhance the stability of an amorphous drug. We found that CEL in the amorphous mixture with acMAL is characterized by a much better solubility than pure CEL. We report very promising results of the long-term measurements of stability of the CEL-acMAL binary amorphous system with small amount of stabilizer during its storage at room temperature. Moreover, we examined the effect of adding acMAL on molecular dynamics of CEL in the wide temperature range in both the supercooled liquid and glassy states. We found that the molecular mobility of the mixture of CEL with 10 wt % acMAL in the glassy state is much more limited than that in the case of pure CEL, which correlates with the better stability of the amorphous binary system. By dielectric measurements and theoretical calculations within the framework of density functional theory (DFT), we studied the role of acMAL in enhancing the stability of amorphous CEL in mixtures and postulated which interactions between CEL and acMAL molecules can be responsible for preventing devitrification. PMID:22384922

  4. Delay and noise induced regime shift and enhanced stability in gene expression dynamics

    NASA Astrophysics Data System (ADS)

    Yang, Tao; Zhang, Chun; Zeng, Chunhua; Zhou, Guoqiong; Han, Qinglin; Tian, Dong; Zhang, Huili

    2014-12-01

    A quantitative model of autoregulatory gene expression involving a single gene with time delays and cross-correlated noise sources is investigated. The probability density and mean first passage time (MFPT) of the protein concentration are obtained. The impacts of multiplicative (σM) and additive (σA) noise intensities, cross-correlation intensity λ between two noises, time delays τ in the degradation process and θ in the synthesis process and time delay β in both processes on the probability density and MFPT of the regime shifts between high and low protein concentration states are discussed, respectively. These results indicate that (i) the regime shifts from a high (or low) protein concentration state to a low (or high) one can be induced by σM, λ and θ (or σA and β) (ii) the MFPT as a function of the noise intensity σM or σA exhibits one maximum value in the case of λ > 0 or θ > 0, this maximum is a signature of the noise's enhanced stability phenomenon for high protein concentration state; and (iii) τ and β can weaken the stability of high protein concentration state but, in contrast, λ and θ can enhance it in the gene expression dynamics.

  5. Silver-mediated base pairings: towards dynamic DNA nanostructures with enhanced chemical and thermal stability

    NASA Astrophysics Data System (ADS)

    Swasey, Steven M.; Gwinn, Elisabeth G.

    2016-04-01

    The thermal and chemical fragility of DNA nanomaterials assembled by Watson-Crick (WC) pairing constrain the settings in which these materials can be used and how they can be functionalized. Here we investigate use of the silver cation, Ag+, as an agent for more robust, metal-mediated self-assembly, focusing on the simplest duplex building blocks that would be required for more elaborate Ag+-DNA nanostructures. Our studies of Ag+-induced assembly of non-complementary DNA oligomers employ strands of 2-24 bases, with varied base compositions, and use electrospray ionization mass spectrometry to determine product compositions. High yields of duplex products containing narrowly distributed numbers of Ag+ can be achieved by optimizing solution conditions. These Ag+-mediated duplexes are stable to at least 60 mM Mg2+, higher than is necessary for WC nanotechnology schemes such as tile assemblies and DNA origami, indicating that sequential stages of Ag+-mediated and WC-mediated assembly may be feasible. Circular dichroism spectroscopy suggests simple helical structures for Ag+-mediated duplexes with lengths to at least 20 base pairs, and further indicates that the structure of cytosine-rich duplexes is preserved at high urea concentrations. We therefore propose an approach towards dynamic DNA nanomaterials with enhanced thermal and chemical stability through designs that combine sturdy silver-mediated ‘frames’ with WC paired ‘pictures’.

  6. End-use load control for power system dynamic stability enhancement

    SciTech Connect

    Dagle, J.E.; Winiarski, D.W.; Donnelly, M.K.

    1997-02-01

    Faced with the prospect of increasing utilization of the transmission and distribution infrastructure without significant upgrade, the domestic electric power utility industry is investing heavily in technologies to improve network dynamic performance through a program loosely referred to as Flexible AC Transmission System (FACTS). Devices exploiting recent advances in power electronics are being installed in the power system to offset the need to construct new transmission lines. These devices collectively represent investment potential of several billion dollars over the next decade. A similar development, designed to curtail the peak loads and thus defer new transmission, distribution, and generation investment, falls under a category of technologies referred to as demand side management (DSM). A subset of broader conservation measures, DSM acts directly on the load to reduce peak consumption. DSM techniques include direct load control, in which a utility has the ability to curtail specific loads as conditions warrant. A novel approach has been conceived by Pacific Northwest National Laboratory (PNNL) to combine the objectives of FACTS and the technologies inherent in DSM to provide a distributed power system dynamic controller. This technology has the potential to dramatically offset major investments in FACTS devices by using direct load control to achieve dynamic stability objectives. The potential value of distributed versus centralized grid modulation has been examined by simulating the western power grid under extreme loading conditions. In these simulations, a scenario is analyzed in which active grid stabilization enables power imports into the southern California region to be increased several hundred megawatts beyond present limitations. Modeling results show distributed load control is up to 30 percent more effective than traditional centralized control schemes in achieving grid stability.

  7. Dynamically stabilized magnetic skyrmions

    PubMed Central

    Zhou, Y.; Iacocca, E.; Awad, A. A.; Dumas, R. K.; Zhang, F. C.; Braun, H. B.; Åkerman, J.

    2015-01-01

    Magnetic skyrmions are topologically non-trivial spin textures that manifest themselves as quasiparticles in ferromagnetic thin films or noncentrosymmetric bulk materials. So far attention has focused on skyrmions stabilized either by the Dzyaloshinskii–Moriya interaction (DMI) or by dipolar interaction, where in the latter case the excitations are known as bubble skyrmions. Here we demonstrate the existence of a dynamically stabilized skyrmion, which exists even when dipolar interactions and DMI are absent. We establish how such dynamic skyrmions can be nucleated, sustained and manipulated in an effectively lossless medium under a nanocontact. As quasiparticles, they can be transported between two nanocontacts in a nanowire, even in complete absence of DMI. Conversely, in the presence of DMI, we observe that the dynamical skyrmion experiences strong breathing. All of this points towards a wide range of skyrmion manipulation, which can be studied in a much wider class of materials than considered so far. PMID:26351104

  8. DYNAMIC NEUROMUSCULAR STABILIZATION & SPORTS REHABILITATION

    PubMed Central

    Kobesova, Alena; Kolar, Pavel

    2013-01-01

    Dynamic neuromuscular (core) stability is necessary for optimal athletic performance and is not achieved purely by adequate strength of abdominals, spinal extensors, gluteals or any other musculature; rather, core stabilization is accomplished through precise coordination of these muscles and intra‐abdominal pressure regulation by the central nervous system. Understanding developmental kinesiology provides a framework to appreciate the regional interdependence and the inter‐linking of the skeleton, joints, musculature during movement and the importance of training both the dynamic and stabilizing function of muscles in the kinetic chain. The Dynamic Neuromuscular Stabilization (DNS) approach provides functional tools to assess and activate the intrinsic spinal stabilizers in order to optimize the movement system for both pre‐habilitation and rehabilitation of athletic injuries and performance. Level of Evidence: 5 PMID:23439921

  9. Ras enhances Myc protein stability.

    PubMed

    Sears, R; Leone, G; DeGregori, J; Nevins, J R

    1999-02-01

    Various experiments have demonstrated a collaborative action of Myc and Ras, both in normal cell growth control as well as during oncogenesis. We now show that Ras enhances the accumulation of Myc activity by stabilizing the Myc protein. Whereas Myc has a very short half-life when produced in the absence of mitogenic signals, due to degradation by the 26S proteasome, the half-life of Myc increases markedly in growth-stimulated cells. This stabilization is dependent on the Ras/Raf/MAPK pathway and is not augmented by proteasome inhibition, suggesting that Ras inhibits the proteasome-dependent degradation of Myc. We propose that one aspect of Myc-Ras collaboration is an ability of Ras to enhance the accumulation of transcriptionally active Myc protein.

  10. Dynamic stability of maglev systems

    SciTech Connect

    Cai, Y.; Chen, S.S.; Mulcahy, T.M.; Rote, D.M.

    1994-05-01

    Because dynamic instabilities are not acceptable in any commercial maglev system, it is important to consider dynamic instability in the development of all maglev systems. This study considers the stability of maglev systems based on experimental data, scoping calculations, and simple mathematical models. Divergence and flutter are obtained for coupled vibration of a three-degree-of-freedom maglev vehicle on a guideway consisting of double L-shaped aluminum segments. The theory and analysis developed in this study provides basic stability characteristics and identifies future research needs for maglev systems.

  11. Dynamic stability of maglev systems

    SciTech Connect

    Cai, Y.; Chen, S.S.; Mulcahy, T.M.; Rote, D.M.

    1992-09-01

    Since the occurrence of dynamic instabilities is not acceptable for any commercial maglev systems, it is important to consider the dynamic instability in the development of all maglev systems. This study is to consider the stability of maglev systems based on experimental data, scoping calculations and simple mathematical models. Divergence and flutter are obtained for coupled vibration of a three-degree-of-freedom maglev vehicle on the guideway which consists of double L-shaped aluminum segments attached to a rotating wheel. The theory and analysis developed in this study provides basic stability characteristics and identifies future research needs for maglev system.

  12. Dynamic stability of maglev systems

    SciTech Connect

    Cai, Y.; Chen, S.S.; Mulcahy, T.M.; Rote, D.M.

    1992-01-01

    Since the occurrence of dynamic instabilities is not acceptable for any commercial maglev systems, it is important to consider the dynamic instability in the development of all maglev systems. This study is to consider the stability of maglev systems based on experimental data, scoping calculations and simple mathematical models. Divergence and flutter are obtained for coupled vibration of a three-degree-of-freedom maglev vehicle on the guideway which consists of double L-shaped aluminum segments attached to a rotating wheel. The theory and analysis developed in this study provides basic stability characteristics and identifies future research needs for maglev system.

  13. Dynamic stability of detached solidification

    NASA Astrophysics Data System (ADS)

    Mazuruk, K.; Volz, M. P.

    2016-06-01

    A dynamic stability analysis model is developed for meniscus-defined crystal growth processes. The Young-Laplace equation is used to analyze the response of a growing crystal to perturbations to its radius and a thermal transport model is used to analyze the effect of perturbations on the evolution of the crystal-melt interface. A linearized differential equation is used to analyze radius perturbations but a linear integro-differential equation is required for the height perturbations. The stability model is applied to detached solidification under zero-gravity and terrestrial conditions. A numerical analysis is supplemented with an approximate analytical analysis, valid in the limit of small Bond numbers. For terrestrial conditions, a singularity is found to exist in the capillary stability coefficients where, at a critical value of the pressure differential across the meniscus, there is a transition from stability to instability. For the zero-gravity condition, exact formulas for the capillary stability coefficients are derived.

  14. Vehicle dynamic stability and rollover

    NASA Astrophysics Data System (ADS)

    Allen, R. W.; Szostak, H. T.; Klyde, D. H.; Rosenthal, T. J.; Owens, K. J.

    1992-06-01

    The report considers ground vehicle lateral/directional stability which is of primary concern in traffic safety. Lateral/directional dynamics involve yawing, rolling, and lateral acceleration motions, and stability concerns include spinout and rollover. The report describes accident analysis, vehicle testing, and computer simulation analysis designed to give insight into basic vehicle design variables that contribute to stability problems. The results of vehicle testing and simulation analysis indicate that a vehicle that has both a relatively low ratio of track width to center of gravity height and is equipped with tires which have a relatively high peak coefficient of friction will have a propensity to rollover during steering maneuvers on a flat surface. Vehicle testing and computer simulation analysis also indicate that directional stability is significantly influenced by the relationship between vehicle weight distribution and lateral load transfer distribution that is greater than or equal to the percent weight on the front axle.

  15. Basin stability in delayed dynamics

    PubMed Central

    Leng, Siyang; Lin, Wei; Kurths, Jürgen

    2016-01-01

    Basin stability (BS) is a universal concept for complex systems studies, which focuses on the volume of the basin of attraction instead of the traditional linearization-based approach. It has a lot of applications in real-world systems especially in dynamical systems with a phenomenon of multi-stability, which is even more ubiquitous in delayed dynamics such as the firing neurons, the climatological processes, and the power grids. Due to the infinite dimensional property of the space for the initial values, how to properly define the basin’s volume for delayed dynamics remains a fundamental problem. We propose here a technique which projects the infinite dimensional initial state space to a finite-dimensional Euclidean space by expanding the initial function along with different orthogonal or nonorthogonal basis. A generalized concept of basin’s volume in delayed dynamics and a highly practicable calculating algorithm with a cross-validation procedure are provided to numerically estimate the basin of attraction in delayed dynamics. We show potential applicabilities of this approach by applying it to study several representative systems of biological or/and physical significance, including the delayed Hopfield neuronal model with multistability and delayed complex networks with synchronization dynamics. PMID:26907568

  16. Basin stability in delayed dynamics

    NASA Astrophysics Data System (ADS)

    Leng, Siyang; Lin, Wei; Kurths, Jürgen

    2016-02-01

    Basin stability (BS) is a universal concept for complex systems studies, which focuses on the volume of the basin of attraction instead of the traditional linearization-based approach. It has a lot of applications in real-world systems especially in dynamical systems with a phenomenon of multi-stability, which is even more ubiquitous in delayed dynamics such as the firing neurons, the climatological processes, and the power grids. Due to the infinite dimensional property of the space for the initial values, how to properly define the basin’s volume for delayed dynamics remains a fundamental problem. We propose here a technique which projects the infinite dimensional initial state space to a finite-dimensional Euclidean space by expanding the initial function along with different orthogonal or nonorthogonal basis. A generalized concept of basin’s volume in delayed dynamics and a highly practicable calculating algorithm with a cross-validation procedure are provided to numerically estimate the basin of attraction in delayed dynamics. We show potential applicabilities of this approach by applying it to study several representative systems of biological or/and physical significance, including the delayed Hopfield neuronal model with multistability and delayed complex networks with synchronization dynamics.

  17. Dynamic stability of maglev systems

    SciTech Connect

    Cai, Y.; Chen, S.S.; Mulcahy, T.M.; Rote, D.M.

    1992-04-01

    Because dynamic instability is not acceptable for any commercial maglev systems, it is important to consider this phenomenon in the development of all maglev systems. This study considers the stability of maglev systems based on experimental data, scoping calculations, and simple mathematical models. Divergence and flutter are obtained for coupled vibration of a three-degree-of-freedom maglev vehicle on a guideway consisting of double L-shaped aluminum segments attached to a rotating wheel. The theory and analysis developed in this study identifies basic stability characteristics and future research needs of maglev systems.

  18. Molecular dynamics simulations on pars intercerebralis major peptide-C (PMP-C) reveal the role of glycosylation and disulfide bonds in its enhanced structural stability and function.

    PubMed

    Kaushik, Sandeep; Mohanty, Debasisa; Surolia, Avadhesha

    2012-01-01

    Fucosylation of Thr 9 in pars intercerebralis major peptide-C (PMP-C) enhances its structural stability and functional ability as a serine protease inhibitor. In order to understand the role of disulfide bonds and glycosylation on the structure and function of PMP-C, we have carried out multiple explicit solvent molecular dynamics (MD) simulations on fucosylated and non-fucosylated forms of PMP-C, both in the presence and absence of the disulfide bonds. Our simulations revealed that there were no significant structural changes in the native disulfide bonded forms of PMP-C due to fucosylation. On the other hand, the non-fucosylated form of PMP-C without disulfide bonds showed larger deviations from the starting structure than the fucosylated form. However, the structural deviations were restricted to the terminal regions while core β-sheet retained its hydrogen bonded structure even in absence of disulfide bonds as well as fucosylation. Interestingly, fucosylation of disulfide bonded native PMP-C led to a decreased thermal flexibility in the residue stretch 29-32 which is known to interact with the active site of the target proteases. Our analysis revealed that disulfide bonds covalently connect the residue stretch 29-32 to the central β-sheet of PMP-C and using a novel network of side chain interactions and disulfide bonds fucosylation at Thr 9 is altering the flexibility of the stretch 29-32 located at a distal site. Thus, our simulations explain for the first time, how presence of disulfide bonds between conserved cysteines and fucosylation enhance the function of PMP-C as a protease inhibitor.

  19. Stabilization strategies for unstable dynamics.

    PubMed

    Morasso, Pietro; Casadio, Maura; De Santis, Dalia; Nomura, Taishin; Rea, Francesco; Zenzeri, Jacopo

    2014-12-01

    The stabilization of the human standing posture was originally attributed to the stiffness of the ankle muscles but direct measurements of the ankle stiffness ruled out this hypothesis, leaving open the possibility for a feedback stabilization strategy driven by proprioceptive signals. This solution, however, could be implemented with two different kinds of control mechanisms, namely continuous or intermittent feedback. The debate is now settled and the latter solution seems to be the most plausible one. Moreover, stabilization of unstable dynamics is not limited to bipedal standing. Indeed many manipulation tasks can be described in the same framework and thus a very general protocol for addressing this kind of problems is the use of haptic virtual reality where instability is generated by some kind of divergent or saddle-like force field. Several studies demonstrated that human subjects can choose to adopt a stiffness or feedback strategy as a combination of biomechanical and task constraints and can learn to switch from one strategy to the other if it is feasible or to use one or the other is infeasible. Understanding such mechanisms is relevant, for example, for the design of novel ergonomic man-machine interfaces in difficult, unstable tasks. PMID:25453479

  20. 14 CFR 25.181 - Dynamic stability.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Dynamic stability. 25.181 Section 25.181 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Flight Stability § 25.181 Dynamic stability. (a) Any short...

  1. 14 CFR 25.181 - Dynamic stability.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Dynamic stability. 25.181 Section 25.181 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Flight Stability § 25.181 Dynamic stability. (a) Any short...

  2. 14 CFR 25.181 - Dynamic stability.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Dynamic stability. 25.181 Section 25.181 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Flight Stability § 25.181 Dynamic stability. (a) Any short...

  3. 14 CFR 23.181 - Dynamic stability.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Dynamic stability. 23.181 Section 23.181... STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Flight Stability § 23.181 Dynamic stability. (a) Any short period oscillation not including combined lateral-directional...

  4. 14 CFR 23.181 - Dynamic stability.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Dynamic stability. 23.181 Section 23.181... STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Flight Stability § 23.181 Dynamic stability. Link to an amendment published at 76 FR 75755, December 2, 2011. (a) Any short period...

  5. 14 CFR 25.181 - Dynamic stability.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Dynamic stability. 25.181 Section 25.181 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Flight Stability § 25.181 Dynamic stability. (a) Any short...

  6. 14 CFR 23.181 - Dynamic stability.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 1 2013-01-01 2013-01-01 false Dynamic stability. 23.181 Section 23.181... STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Flight Stability § 23.181 Dynamic stability. (a) Any short period oscillation not including combined lateral-directional...

  7. 14 CFR 25.181 - Dynamic stability.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 1 2013-01-01 2013-01-01 false Dynamic stability. 25.181 Section 25.181 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Flight Stability § 25.181 Dynamic stability. (a) Any short...

  8. Stability in dynamical systems I

    SciTech Connect

    Courant, E.D.; Ruth, R.D.; Weng, W.T.

    1984-08-01

    We have reviewed some of the basic techniques which can be used to analyze stability in nonlinear dynamical systems, particularly in circular particle accelerators. We have concentrated on one-dimensional systems in the examples in order to simply illustrate the general techniques. We began with a review of Hamiltonian dynamics and canonical transformations. We then reviewed linear equations with periodic coefficients using the basic techniques from accelerator theory. To handle nonlinear terms we developed a canonical perturbation theory. From this we calculated invariants and the amplitude dependence of the frequency. This led us to resonances. We studied the cubic resonance in detail by using a rotating coordinate system in phase space. We then considered a general isolated nonlinear resonance. In this case we calculated the width of the resonance and estimated the spacing of resonances in order to use the Chirikov criterion to restrict the validity of the analysis. Finally the resonance equation was reduced to the pendulum equation, and we examined the motion on a separatrix. This brought us to the beginnings of stochastic behavior in the neighborhood of the separatrix. It is this complex behavior in the neighborhood of the separatrix which causes the perturbation theory used here to diverge in many cases. In spite of this the methods developed here have been and are used quite successfully to study nonlinear effects in nearly integrable systems. When used with caution and in conjunction with numerical work they give tremendous insight into the nature of the phase space structure and the stability of nonlinear differential equations. 14 references.

  9. On the dynamic stability of grasping

    SciTech Connect

    Xiong, C.H.; Li, Y.F.; Ding, H.; Xiong, Y.L.

    1999-09-01

    Stability is one of the important properties that a robot hand grasp must possess to be able to perform tasks similar to those performed by human hands. This paper discusses the dynamic stability of a grasped object. To analyze the stability of grasps, the authors build the model of the dynamics of the grasped object in response to the small perturbances. Furthermore, they determine the conditions associated with the dynamic stability and discuss the effects of various factors on the grasp stability. A quantitative measure for evaluating grasps is then presented. Finally, the effectiveness of the proposed theory is verified via examples.

  10. The dynamical stability of reverberatory neural circuits.

    PubMed

    Tegnér, Jesper; Compte, Albert; Wang, Xiao-Jing

    2002-12-01

    The concept of reverberation proposed by Lorente de Nó and Hebb is key to understanding strongly recurrent cortical networks. In particular, synaptic reverberation is now viewed as a likely mechanism for the active maintenance of working memory in the prefrontal cortex. Theoretically, this has spurred a debate as to how such a potentially explosive mechanism can provide stable working-memory function given the synaptic and cellular mechanisms at play in the cerebral cortex. We present here new evidence for the participation of NMDA receptors in the stabilization of persistent delay activity in a biophysical network model of conductance-based neurons. We show that the stability of working-memory function, and the required NMDA/AMPA ratio at recurrent excitatory synapses, depend on physiological properties of neurons and synaptic interactions, such as the time constants of excitation and inhibition, mutual inhibition between interneurons, differential NMDA receptor participation at excitatory projections to pyramidal neurons and interneurons, or the presence of slow intrinsic ion currents in pyramidal neurons. We review other mechanisms proposed to enhance the dynamical stability of synaptically generated attractor states of a reverberatory circuit. This recent work represents a necessary and significant step towards testing attractor network models by cortical electrophysiology.

  11. Rational Design of Biobetters with Enhanced Stability.

    PubMed

    Courtois, Fabienne; Schneider, Curtiss P; Agrawal, Neeraj J; Trout, Bernhardt L

    2015-08-01

    Biotherapeutics are the fastest growing class of pharmaceutical with a rapidly evolving market facing the rise of biosimilar and biobetter products. In contrast to a biosimilar, which is derived from the same gene sequence as the innovator product, a biobetter has enhanced properties, such as enhanced efficacy or reduced immunogenicity. Little work has been carried out so far to increase the intrinsic stability of biotherapeutics via sequence changes, even though, aggregation, the primary degradation pathway of proteins, leads to issues ranging from manufacturing failure to immunological response and to loss of therapeutic activity. Using our spatial aggregation propensity tool as a first step to a rational design approach to identify aggregation-prone regions, biobetters of rituximab have been produced with enhanced stability by introducing site-specific mutations. Significant stabilization against aggregation was achieved for rituximab with no decrease in its binding affinity to the antigen.

  12. Biomechanics of Posterior Dynamic Stabilization Systems

    PubMed Central

    Erbulut, D. U.; Zafarparandeh, I.; Ozer, A. F.; Goel, V. K.

    2013-01-01

    Spinal rigid instrumentations have been used to fuse and stabilize spinal segments as a surgical treatment for various spinal disorders to date. This technology provides immediate stability after surgery until the natural fusion mass develops. At present, rigid fixation is the current gold standard in surgical treatment of chronic back pain spinal disorders. However, such systems have several drawbacks such as higher mechanical stress on the adjacent segment, leading to long-term degenerative changes and hypermobility that often necessitate additional fusion surgery. Dynamic stabilization systems have been suggested to address adjacent segment degeneration, which is considered to be a fusion-associated phenomenon. Dynamic stabilization systems are designed to preserve segmental stability, to keep the treated segment mobile, and to reduce or eliminate degenerative effects on adjacent segments. This paper aimed to describe the biomechanical aspect of dynamic stabilization systems as an alternative treatment to fusion for certain patients. PMID:23606975

  13. Report of the Stability and Dynamics Session

    NASA Technical Reports Server (NTRS)

    Alexander, Iwan; Chato, David; Collicott, Steven; Dadzic, Nihad; Duval, Walter; Garoff, Steven; Grayson, Gary; Hochstein, John; Kassemi, Mo; Nelson, Emily

    2003-01-01

    Important issues: Mass gauging; Stability dynamics of disconnected capillary surfaces; Slow capillary driven flow (i.e. wicking); Long-term material property evolution in micro-g; Dumping problem with freezing of dump lines.

  14. A discussion of dynamic stability measurement techniques

    NASA Technical Reports Server (NTRS)

    Johnson, W.

    1975-01-01

    Techniques for the measurement of the dynamic stability of linear systems are discussed. Particular attention is given to an analysis of the errors in the procedures, and to methods for calculating the system damping from the data. The techniques discussed include: transient decay, moving block analysis, spectral analysis, random decrement signatures, transfer function analysis, and parameter identification methods. The special problems of rotorcraft dynamic stability testing are discussed.

  15. Compressor Stability Enhancement Using Discrete Tip Injection

    NASA Technical Reports Server (NTRS)

    Suder, Kenneth L.; Hathaway, Michael D.; Thorp, Scott A.; Strazisar, Anthony J.; Bright, Michelle B.

    2001-01-01

    Mass injection upstream of the tip of a high-speed axial compressor rotor is a stability enhancement approach known to be effective in suppressing small in tip-critical rotors. This process is examined in a transonic axial compressor rotor through experiments and time-averaged Navier-Stokes CFD simulations. Measurements and simulations for discrete injection are presented for a range of injection rates and distributions of injectors around the annulus. The simulations indicate that tip injection increases stability by unloading the rotor tip and that increasing injection velocity improves the effectiveness of tip injection. For the tested rotor, experimental results demonstrate that at 70 percent speed the stalling flow coefficient can be reduced by 30 percent using an injected mass- flow equivalent to 1 percent of the annulus flow. At design speed, the stalling flow coefficient was reduced by 6 percent using an injected mass-fiow equivalent to 2 percent of the annulus flow. The experiments show that stability enhancement is related to the mass-averaged axial velocity at the tip. For a given injected mass-flow, the mass-averaged axial velocity at the tip is increased by injecting flow over discrete portions of the circumference as opposed to full-annular injection. The implications of these results on the design of recirculating casing treatments and other methods to enhance stability will be discussed.

  16. Stability of Dynamical Systems with Discontinuous Motions:

    NASA Astrophysics Data System (ADS)

    Michel, Anthony N.; Hou, Ling

    In this paper we present a stability theory for discontinuous dynamical systems (DDS): continuous-time systems whose motions are not necessarily continuous with respect to time. We show that this theory is not only applicable in the analysis of DDS, but also in the analysis of continuous dynamical systems (continuous-time systems whose motions are continuous with respect to time), discrete-time dynamical systems (systems whose motions are defined at discrete points in time) and hybrid dynamical systems (HDS) (systems whose descriptions involve simultaneously continuous-time and discrete-time). We show that the stability results for DDS are in general less conservative than the corresponding well-known classical Lyapunov results for continuous dynamical systems and discrete-time dynamical systems. Although the DDS stability results are applicable to general dynamical systems defined on metric spaces (divorced from any kind of description by differential equations, or any other kinds of equations), we confine ourselves to finite-dimensional dynamical systems defined by ordinary differential equations and difference equations, to make this paper as widely accessible as possible. We present only sample results, namely, results for uniform asymptotic stability in the large.

  17. Nutrient dynamics and food-web stability

    SciTech Connect

    DeAngelis, D.L.; Mulholland, P.J.; Palumbo, A.V.; Steinman, A.D.; Huston, M.A.; Elwood, J.W. )

    1989-01-01

    The importance of nutrient limitation and recycling in ecosystems is widely recognized. Nutrients, defined in the broad sense as all material elements vital to biological functions, are in such small supply that they limit production in many ecosystems. Such limitation can affect ecosystem properties, including the structure and dynamics of the food webs that link species through their feeding relationships. What are the effects of limiting nutrients on the stability of ecosystem food webs Most of the literature on food web stability centers around the dynamics of population numbers and/or biomasses. Nevertheless, a growing body of theoretical and empirical research considers the role that both nutrient limitation and recycling can play in stability. In this paper, it is the authors objective to summarize the current understanding of several important types of stability. The theoretical and empirical evidence relating these types of stability and nutrient cycling is described. A central generalization is produced in each case.

  18. Dynamic stability experiment of Maglev systems

    SciTech Connect

    Cai, Y.; Mulcahy, T.M.; Chen, S.S.

    1995-04-01

    This report summarizes the research performed on Maglev vehicle dynamic stability at Argonne National Laboratory during the past few years. It also documents magnetic-force data obtained from both measurements and calculations. Because dynamic instability is not acceptable for any commercial Maglev system, it is important to consider this phenomenon in the development of all Maglev systems. This report presents dynamic stability experiments on Maglev systems and compares their numerical simulation with predictions calculated by a nonlinear dynamic computer code. Instabilities of an electrodynamic system (EDS)-type vehicle model were obtained from both experimental observations and computer simulations for a five-degree-of-freedom Maglev vehicle moving on a guideway consisting of double L-shaped aluminum segments attached to a rotating wheel. The experimental and theoretical analyses developed in this study identify basic stability characteristics and future research needs of Maglev systems.

  19. Unifying dynamical and structural stability of equilibria

    NASA Astrophysics Data System (ADS)

    Arnoldi, Jean-François; Haegeman, Bart

    2016-09-01

    We exhibit a fundamental relationship between measures of dynamical and structural stability of linear dynamical systems-e.g. linearized models in the vicinity of equilibria. We show that dynamical stability, quantified via the response to external perturbations (i.e. perturbation of dynamical variables), coincides with the minimal internal perturbation (i.e. perturbations of interactions between variables) able to render the system unstable. First, by reformulating a result of control theory, we explain that harmonic external perturbations reflect the spectral sensitivity of the Jacobian matrix at the equilibrium, with respect to constant changes of its coefficients. However, for this equivalence to hold, imaginary changes of the Jacobian's coefficients have to be allowed. The connection with dynamical stability is thus lost for real dynamical systems. We show that this issue can be avoided, thus recovering the fundamental link between dynamical and structural stability, by considering stochastic noise as external and internal perturbations. More precisely, we demonstrate that a linear system's response to white-noise perturbations directly reflects the intensity of internal white-noise disturbance that it can accommodate before becoming stochastically unstable.

  20. Enhancement of stability in systems with metastable states

    SciTech Connect

    Spagnolo, B.; Augello, G.; Pizzolato, N.; Valenti, D.; Fiasconaro, A.

    2007-12-06

    The investigation of noise-induced phenomena in far from equilibrium systems is one of the approach used to understand the behaviour of physical and biological complex systems. Metastability is a generic feature of many nonlinear systems, and the problem of the lifetime of metastable states involves fundamental aspects of nonequilibrium statistical mechanics. The enhancement of the life-time of metastable states through the noise enhanced stability effect and the role played by the resonant activation phenomenon will be discussed in models of interdisciplinary physics: (i) Ising model (ii) Josephson junction; (iii) stochastic FitzHugh-Nagumo model; (iv) a population dynamics model, and (v) a market model with stochastic volatility.

  1. Enhanced Product Stability in the Hammerhead Ribozyme†

    PubMed Central

    Shepotinovskaya, Irina; Uhlenbeck, Olke C.

    2010-01-01

    The rate of dissociation of P1, the 5′ product of hammerhead cleavage, is 100–300-fold slower in full-length hammerheads than in hammerheads that either lack or have disrupting mutations in the loop-loop tertiary interaction. The added stability requires the presence of residue 17 at the 3′ terminus of P1 but not the 2′, 3′ terminal phosphate. Since residue 17 is buried within the catalytic core of the hammerhead in the x-ray structure, we propose that the enhanced P1 stability is the result of the cooperative folding of the hammerhead around this residue. However, since the P1 is fully stabilized above 2.5 mM MgCl2 while hammerhead activity continues to increase with increasing MgCl2, it is clear that the hammerhead structure in the transition state must differ from that of the product complex. The product stabilization assay is used to test our earlier proposal that different tertiary interactions modulate the cleavage rate by differentially stabilizing the core. PMID:20423112

  2. U31: Vehicle Stability and Dynamics: Electronic Stability Control

    SciTech Connect

    Petrolino, Joseph; Spezia, Tony; Arant, Michael; Delorenzis, Damon; LaClair, Tim J; Lim, Alvin; Pape, Doug

    2011-01-01

    A team led by NTRCI is working to improve the roll and yaw stability of heavy duty combination trucks through developing stability algorithms, assembling demonstration hardware, and investigating robust wireless communication. Modern electronic stability control (ESC) products automatically slow a vehicle rounding a corner too quickly or apply individual brakes when necessary to improve the steering characteristics of a vehicle. Air brake systems in North America provide no electronic communication between a tractor and semitrailer, limiting the degree to which control systems can be optimized. Prior research has demonstrated stability improvements where dynamic measurements and control commands are communicated between units of a vehicle. Three related activities were undertaken: (1) Develop an algorithm for the optimum yaw and roll control of a combination vehicle. Vehicle state parameters needed to control the vehicle and the proper brake response were determined. An integrated stability control for the tractor and semitrailer requires communication between the two units. Dynamic models were used to assess the algorithm. (2) Implement the ESC algorithm in the laboratory. Hardware components suitable for the harsh environment for measurement, sensor-to-controller communication, and semitrailer-to-tractor communication and brake actuation were specified and assembled as a working system. The goal was to collect the needed vehicle state information, transmit the information to the ESC system, and then actuate the brakes in response to controller commands. (3) Develop a wireless network with the data rate and reliability necessary to communicate dynamic signals for a vehicle stability control system. Adaptive connectivity-aware, multi-hop routing was selected because it can perform in the harsh environment where packet collisions and fading often will exist. The protocol is to give high priority to urgent messages.

  3. Mechanical stability of trees under dynamic loads.

    PubMed

    James, Kenneth R; Haritos, Nicholas; Ades, Peter K

    2006-10-01

    Tree stability in windstorms and tree failure are important issues in urban areas where there can be risks of damage to people and property and in forests where wind damage causes economic loss. Current methods of managing trees, including pruning and assessment of mechanical strength, are mainly based on visual assessment or the experience of people such as trained arborists. Only limited data are available to assess tree strength and stability in winds, and most recent methods have used a static approach to estimate loads. Recent research on the measurement of dynamic wind loads and the effect on tree stability is giving a better understanding of how different trees cope with winds. Dynamic loads have been measured on trees with different canopy shapes and branch structures including a palm (Washingtonia robusta), a slender Italian cypress (Cupressus sempervirens) and trees with many branches and broad canopies including hoop pine (Araucaria cunninghamii) and two species of eucalypt (Eucalyptus grandis, E. teretecornus). Results indicate that sway is not a harmonic, but is very complex due to the dynamic interaction of branches. A new dynamic model of a tree is described, incorporating the dynamic structural properties of the trunk and branches. The branch mass contributes a dynamic damping, termed mass damping, which acts to reduce dangerous harmonic sway motion of the trunk and so minimizes loads and increases the mechanical stability of the tree. The results from 12 months of monitoring sway motion and wind loading forces are presented and discussed.

  4. Dynamic postural stability for double-leg drop landing.

    PubMed

    Niu, Wenxin; Zhang, Ming; Fan, Yubo; Zhao, Qinping

    2013-01-01

    Dynamic postural stability has been widely studied for single-leg landing, but seldom considered for double-leg landing. This study aimed to evaluate the dynamic postural stability and the influence mechanism of muscle activities during double-leg drop landing. Eight recreationally active males and eight recreationally active females participated in this study and dropped individually from three heights (0.32 m, 0.52 m, and 0.72 m). Ground reaction force was recorded to calculate the time to stabilisation. Electromyographic activities were recorded for selected lower-extremity muscles. A multivariate analysis of variance was carried out and no significant influence was found in time to stabilisation between genders or limb laterals (P > 0.05). With increasing drop height, time to stabilisation decreased significantly in two horizontal directions and the lower-extremity muscle activities were enhanced. Vertical time to stabilisation was not significantly influenced by drop height. Dynamic postural stability improved by neuromuscular change more than that required due to the increase of drop height. Double-leg landing on level ground is a stable movement, and the body would often be injured before dynamic postural stability is impaired. It is understandable to protect tissues from mechanical injuries by the sacrifice of certain dynamic postural stability in the design of protective devices or athlete training.

  5. Dynamic stability experiment of Maglev systems

    SciTech Connect

    Cai, Y.; Chen, S.S.; Zhu, S.; Rote, D.M.

    1995-12-31

    This paper presents dynamic stability experiments on maglev systems and compares with predictions calculated by a nonlinear dynamic computer code. Instabilities of an electrodynamic system (EDS)-type vehicle model were obtained from both experimental observations and computer simulations for a five-degree-of-freedom maglev vehicle moving on a guideway consisting of double L-shaped aluminum segments attached to a rotating wheel. The experimental and theoretical analyses developed in this study identify basic stability characteristics and future research needs of maglev systems.

  6. Dynamic stability of electrodynamic maglev systems

    SciTech Connect

    Cai, Y.; Chen, S.S.; Mulcahy, T.M.; Rote, D.M.

    1997-01-01

    Because dynamic instabilities are not acceptable in any commercial maglev system, it is important to consider dynamic instability in the development of all maglev systems. This study considers the stability of maglev systems based on mathematical models and experimental data. Divergence and flutter are obtained for coupled vibration of a three-degree-of-freedom maglev vehicle on a guideway consisting of double L-shaped aluminum segments. The theory and analysis for motion-dependent magnetic-force-induced instability developed in this study provides basic stability characteristics and identifies future research needs for maglev systems.

  7. Dynamic stabilization of an optomechanical oscillator

    NASA Astrophysics Data System (ADS)

    Seok, H.; Wright, E. M.; Meystre, P.

    2014-10-01

    Quantum optomechanics offers the potential to investigate quantum effects in macroscopic quantum systems in extremely well-controlled experiments. In this paper we discuss one such situation, the dynamic stabilization of a mechanical system such as an inverted pendulum. The specific example that we study is a "membrane-in-the-middle" mechanical oscillator coupled to a cavity field via a quadratic optomechanical interaction, with cavity damping the dominant source of dissipation. We show that the mechanical oscillator can be dynamically stabilized by a temporal modulation of the radiation pressure force. We investigate the system both in the classical and quantum regimes highlighting similarities and differences.

  8. Enhanced stabilization of collagen by furfural.

    PubMed

    Lakra, Rachita; Kiran, Manikantan Syamala; Usha, Ramamoorthy; Mohan, Ranganathan; Sundaresan, Raja; Korrapati, Purna Sai

    2014-04-01

    Furfural (2-furancarboxaldehyde), a product derived from plant pentosans, has been investigated for its interaction with collagen. Introduction of furfural during fibril formation enhanced the thermal and mechanical stability of collagen. Collagen films treated with furfural exhibited higher denaturation temperature (Td) (p<0.04) and showed a 3-fold increase in Young's modulus (p<0.04) at higher concentration. Furfural and furfural treated collagen films did not have any cytotoxic effect. Rheological characterization showed an increase in shear stress and shear viscosity with increasing shear rate for treated collagen. Circular dichroism (CD) studies indicated that the furfural did not have any impact on triple helical structure of collagen. Scanning electron microscopy (SEM) of furfural treated collagen exhibited small sized porous structure in comparison with untreated collagen. Thus this study provides an alternate ecologically safe crosslinking agent for improving the stability of collagen for biomedical and industrial applications.

  9. Enhanced Mechanical Stability of Gold Nanotips through Carbon Nanocone Encapsulation

    NASA Astrophysics Data System (ADS)

    Cano-Marquez, Abraham G.; Schmidt, Wesller G.; Ribeiro-Soares, Jenaina; Gustavo Cançado, Luiz; Rodrigues, Wagner N.; Santos, Adelina P.; Furtado, Clascidia A.; Autreto, Pedro A. S.; Paupitz, Ricardo; Galvão, Douglas S.; Jorio, Ado

    2015-06-01

    Gold is a noble metal that, in comparison with silver and copper, has the advantage of corrosion resistance. Despite its high conductivity, chemical stability and biocompatibility, gold exhibits high plasticity, which limits its applications in some nanodevices. Here, we report an experimental and theoretical study on how to attain enhanced mechanical stability of gold nanotips. The gold tips were fabricated by chemical etching and further encapsulated with carbon nanocones via nanomanipulation. Atomic force microscopy experiments were carried out to test their mechanical stability. Molecular dynamics simulations show that the encapsulated nanocone changes the strain release mechanisms at the nanoscale by blocking gold atomic sliding, redistributing the strain along the whole nanostructure. The carbon nanocones are conducting and can induce magnetism, thus opening new avenues on the exploitation of transport, mechanical and magnetic properties of gold covered by sp2 carbon at the nanoscale.

  10. Enhanced Mechanical Stability of Gold Nanotips through Carbon Nanocone Encapsulation

    PubMed Central

    Cano-Marquez, Abraham G.; Schmidt, Wesller G.; Ribeiro-Soares, Jenaina; Gustavo Cançado, Luiz; Rodrigues, Wagner N.; Santos, Adelina P.; Furtado, Clascidia A.; Autreto, Pedro A.S.; Paupitz, Ricardo; Galvão, Douglas S.; Jorio, Ado

    2015-01-01

    Gold is a noble metal that, in comparison with silver and copper, has the advantage of corrosion resistance. Despite its high conductivity, chemical stability and biocompatibility, gold exhibits high plasticity, which limits its applications in some nanodevices. Here, we report an experimental and theoretical study on how to attain enhanced mechanical stability of gold nanotips. The gold tips were fabricated by chemical etching and further encapsulated with carbon nanocones via nanomanipulation. Atomic force microscopy experiments were carried out to test their mechanical stability. Molecular dynamics simulations show that the encapsulated nanocone changes the strain release mechanisms at the nanoscale by blocking gold atomic sliding, redistributing the strain along the whole nanostructure. The carbon nanocones are conducting and can induce magnetism, thus opening new avenues on the exploitation of transport, mechanical and magnetic properties of gold covered by sp2 carbon at the nanoscale. PMID:26083864

  11. Ceramic membranes with enhanced thermal stability

    DOEpatents

    Anderson, Marc A.; Xu, Qunyin; Bischoff, Brian L.

    1993-01-01

    A method of creating a ceramic membrane with enhanced thermal stability is disclosed. The method involves combining quantities of a first metal alkoxide with a second metal, the quantities selected to give a preselected metal ratio in the resultant membrane. A limited amount of water and acid is added to the combination and stirred until a colloidal suspension is formed. The colloid is dried to a gel, and the gel is fired at a temperature greater than approximately 400.degree. C. The porosity and surface area of ceramic membranes formed by this method are not adversely affected by this high temperature firing.

  12. 14 CFR 23.181 - Dynamic stability.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Flight Stability § 23.181 Dynamic... to meet the flight characteristic requirements of this part, the primary control requirements of... suddenly released, the response of the airplane must not exhibit any dangerous characteristics nor...

  13. Estimating Gait Stability: Asymmetrical Loading Effects Measured Using Margin of Stability and Local Dynamic Stability.

    PubMed

    Worden, Timothy A; Beaudette, Shawn M; Brown, Stephen H M; Vallis, Lori Ann

    2016-01-01

    Changes to intersegmental locomotor control patterns may affect body stability. Our study aimed to (a) characterize upper body dynamic stability in response to the unilateral addition of mass to the lower extremity and (b) evaluate the efficacy of 2 different stability measures commonly used in the literature to detect resulting symmetrical step pattern modifications across the weighted segments (spatial) and between epochs of the gait cycle (temporal). Young adults walked on a treadmill while unloaded or with weights applied unilaterally to their foot, shank, or thigh. Both margin of stability and local dynamic stability (LDS) estimates detected similar trends of distal segment weighting resulting in more unstable upper body movement compared to proximal weighting; however only LDS detected anteroposterior changes in upper body stability over time.

  14. Insect flight dynamics: Stability and control

    NASA Astrophysics Data System (ADS)

    Sun, Mao

    2014-04-01

    Insects can hover, fly forward, climb, and descend with ease while demonstrating amazing stability, and they can also maneuver in impressive ways as no other organisms can. Is their flight inherently stable? If so, how can they maneuver so well? In recent years, significant progress has been made in revealing the dynamic flight stability and flight control mechanisms of insects and has partially answered these questions. Here the most recent advances in this active area are reviewed. The aim is to provide the background necessary to do research in the area and raise questions that need to be addressed in the future. This review begins with an overview of the flapping kinematics and aerodynamics of insect flight. It is followed by a summary of the governing equations of insect motion and the simplified theoretical models used for analysis of dynamic stability and control. Next, the stability properties of hovering flight and forward flight are scrutinized. Then the flight control properties are explored, dealing in turn with flight stabilization control, steady-state control for changing from hovering to forward flight and from one forward-flight speed to another, and control for maneuvers near hovering. Finally, remarks are given on the state of the art of this research field and speculation is made on its outlook in the near future.

  15. Dynamics, stability, and control of maglev systems

    SciTech Connect

    Cai, Y.; Chen, S.S.; Rote, D.M.; Coffey, H.T.

    1993-01-01

    The dynamic response of maglev systems is important in several respects: Safety and ride quality, guideway design, and system costs. The dynamic response of vehicles is the key element in the determination of ride quality, and vehicle stability is one of the important elements relative to safety. To design a proper guideway that provides acceptable ride quality in the stable region, the vehicle dynamics must be understood. The trade-off between guideway smoothness and the levitation and control systems must be considered if maglev systems are to be economically feasible. This paper is a summary of our previous work on dynamics, stability and control of maglev systems. First of all, the importance of dynamics of vehicle/guideway of maglev systems is discussed. Emphasis is placed on the modeling vehicle/guideway interactions of maglev systems with a multicar, or multiload vehicle traversing on a single or double-span flexible guideway. Coupled effects of vehicle/guideway interactions in wide range of vehicle speeds with various vehicle and guideway parameters for maglev systems are investigated. Secondly, the alternative control designs of maglev vehicle suspension systems are investigated in this study to achieve safe, stable operation and acceptable ride comfort requires some form of vehicle motion control. Active and semi-active control law designs are introduced into primary and secondary suspensions of maglev vehicles. Finally, this paper discusses the stability of maglev systems based on experimental data, scoping calculations, and simple mathematical models. Divergence and flutter are obtained for coupled vibration of a three-degree-of-freedom maglev vehicle on a guideway consisting of double L-shaped aluminum segments. The theory and analysis developed in this study provides basic stability characteristics and identifies future research needs for maglev systems.

  16. Dynamics, stability, and control of maglev systems

    SciTech Connect

    Cai, Y.; Chen, S.S.; Rote, D.M.; Coffey, H.T.

    1993-06-01

    The dynamic response of maglev systems is important in several respects: Safety and ride quality, guideway design, and system costs. The dynamic response of vehicles is the key element in the determination of ride quality, and vehicle stability is one of the important elements relative to safety. To design a proper guideway that provides acceptable ride quality in the stable region, the vehicle dynamics must be understood. The trade-off between guideway smoothness and the levitation and control systems must be considered if maglev systems are to be economically feasible. This paper is a summary of our previous work on dynamics, stability and control of maglev systems. First of all, the importance of dynamics of vehicle/guideway of maglev systems is discussed. Emphasis is placed on the modeling vehicle/guideway interactions of maglev systems with a multicar, or multiload vehicle traversing on a single or double-span flexible guideway. Coupled effects of vehicle/guideway interactions in wide range of vehicle speeds with various vehicle and guideway parameters for maglev systems are investigated. Secondly, the alternative control designs of maglev vehicle suspension systems are investigated in this study to achieve safe, stable operation and acceptable ride comfort requires some form of vehicle motion control. Active and semi-active control law designs are introduced into primary and secondary suspensions of maglev vehicles. Finally, this paper discusses the stability of maglev systems based on experimental data, scoping calculations, and simple mathematical models. Divergence and flutter are obtained for coupled vibration of a three-degree-of-freedom maglev vehicle on a guideway consisting of double L-shaped aluminum segments. The theory and analysis developed in this study provides basic stability characteristics and identifies future research needs for maglev systems.

  17. Fluctuation-enhanced stability of a metapopulation

    NASA Astrophysics Data System (ADS)

    Nie, Lin-Ru; Mei, Dong-Cheng

    2007-11-01

    The simplified incidence function model with cross-correlated noises was employed to study the stability of a metapopulation perturbed by environments. Through numerically computing the stationary probability distribution function (PDF) and stochastically simulating the extinction time of a metapopulation, we found that: (i) The multiplicative noise intensity D inhibits the fluctuation of dynamic variable while the additive noise intensity α intensifies it, whether there is a correlation between the multiplicative noise and the additive noise; (ii) As the correlation strength (λ) between them is greater than zero, there is an optimal D in which the PDF curve deviates furthest from the extinction position, and another optimal D which maximally delays the extinction time of a metapopulation; (iii) For the constant D and α, the increment of λ not only upgrades the probability that patches are occupied by a metapopulation, but also delays the time that a metapopulation goes to extinction.

  18. Photovoltaic panel having enhanced conversion efficiency stability

    SciTech Connect

    Cannella, V. D.

    1985-10-01

    A photovoltaic panel for converting light into electrical energy has enhanced energy conversion efficiency stability. The panel includes a photovoltaic device having an active region formed from a semiconductor material which exhibits an energy conversion efficiency stability directly related to the operating temperature of the device. The panel also includes means for maintaining the operating temperature of the device upon exposure to light at an elevated temperature above the ambient temperature external to the device. The active region semiconductor material is preferably an amorphous semiconductor alloy such as, for example, an amorphous silicon alloy. The operating temperature elevating means can include a thermal insulating material such as glass wool, styrofoam, or cork applied to the back side of the device to minimize heat conduction from the device. The panel can also include an enclosure for enclosing the device having a transparent cover overlying the device to seal the enclosure and provide a still air space adjacent the device. The panel is thereby arranged to maintain the operating temperature of the device at a temperature which is from about twenty degrees Centigrade to about one hundred and fifty degrees Centigrade above the ambient temperature external to the device.

  19. Dynamics of a colloid-stabilized cream

    NASA Astrophysics Data System (ADS)

    Herzig, E. M.; Robert, A.; van 'T Zand, D. D.; Cipelletti, L.; Pusey, P. N.; Clegg, P. S.

    2009-01-01

    We use x-ray photon correlation spectroscopy to investigate the dynamics of a high-volume-fraction emulsion creaming under gravity. The dodecane-in-water emulsion has interfaces stabilized solely by colloidal particles (silica). The samples were observed soon after mixing: as the emulsion becomes compact we discern two regimes of aging with a crossover between them. The young emulsion has faster dynamics associated with creaming in a crowded environment accompanied by local rearrangements. The dynamics slow down for the older emulsion, although our studies show that motion is associated with large intermittent events. The relaxation rate, as seen from the intensity autocorrelation function, depends linearly on the wave vector at all times; however, the exponent associated with the line shape changes from 1.5 for young samples to less than 1 as the emulsion ages. The combination of ballisticlike dynamics, an exponent that drops below 1, and large intermittent fluctuations has not been reported before to our knowledge.

  20. Stability threshold approach for complex dynamical systems

    NASA Astrophysics Data System (ADS)

    Klinshov, Vladimir V.; Nekorkin, Vladimir I.; Kurths, Jürgen

    2016-01-01

    A new measure to characterize the stability of complex dynamical systems against large perturbations is suggested, the stability threshold (ST). It quantifies the magnitude of the weakest perturbation capable of disrupting the system and switch it to an undesired dynamical regime. In the phase space, the ST corresponds to the ‘thinnest site’ of the attraction basin and therefore indicates the most ‘dangerous’ direction of perturbations. We introduce a computational algorithm for quantification of the ST and demonstrate that the suggested approach is effective and provides important insights. The generality of the obtained results defines their vast potential for application in such fields as engineering, neuroscience, power grids, Earth science and many others where the robustness of complex systems is studied.

  1. Stability, complexity and robustness in population dynamics.

    PubMed

    Demongeot, J; Hazgui, H; Ben Amor, H; Waku, J

    2014-09-01

    The problem of stability in population dynamics concerns many domains of application in demography, biology, mechanics and mathematics. The problem is highly generic and independent of the population considered (human, animals, molecules,…). We give in this paper some examples of population dynamics concerning nucleic acids interacting through direct nucleic binding with small or cyclic RNAs acting on mRNAs or tRNAs as translation factors or through protein complexes expressed by genes and linked to DNA as transcription factors. The networks made of these interactions between nucleic acids (considered respectively as edges and nodes of their interaction graph) are complex, but exhibit simple emergent asymptotic behaviours, when time tends to infinity, called attractors. We show that the quantity called attractor entropy plays a crucial role in the study of the stability and robustness of such genetic networks. PMID:25107273

  2. Parachute Dynamic Stability Variations Due to Atmospheric Density

    NASA Astrophysics Data System (ADS)

    Ginn, J. M.; Braun, R. D.; Clark, I. G.

    2014-06-01

    Apparent inertia effects on parachute dynamics are investigated. Both static and dynamic stability are examined as a function of apparent inertia parameters. Conclusions are drawn describing changes in stability based on atmospheric density.

  3. Stabilization of avalanche processes on dynamical networks

    NASA Astrophysics Data System (ADS)

    Savitskaya, N. E.

    2016-02-01

    The stabilization of avalanches on dynamical networks has been studied. Dynamical networks are networks where the structure of links varies in time owing to the presence of the individual "activity" of each site, which determines the probability of establishing links with other sites per unit time. An interesting case where the times of existence of links in a network are equal to the avalanche development times has been examined. A new mathematical model of a system with the avalanche dynamics has been constructed including changes in the network on which avalanches are developed. A square lattice with a variable structure of links has been considered as a dynamical network within this model. Avalanche processes on it have been simulated using the modified Abelian sandpile model and fixed-energy sandpile model. It has been shown that avalanche processes on the dynamical lattice under study are more stable than a static lattice with respect to the appearance of catastrophic events. In particular, this is manifested in a decrease in the maximum size of an avalanche in the Abelian sandpile model on the dynamical lattice as compared to that on the static lattice. For the fixed-energy sandpile model, it has been shown that, in contrast to the static lattice, where an avalanche process becomes infinite in time, the existence of avalanches finite in time is always possible.

  4. Dynamical Stability of Slip-stacking Particles

    SciTech Connect

    Eldred, Jeffrey; Zwaska, Robert

    2014-09-04

    We study the stability of particles in slip-stacking configuration, used to nearly double proton beam intensity at Fermilab. We introduce universal area factors to calculate the available phase space area for any set of beam parameters without individual simulation. We find perturbative solutions for stable particle trajectories. We establish Booster beam quality requirements to achieve 97% slip-stacking efficiency. We show that slip-stacking dynamics directly correspond to the driven pendulum and to the system of two standing-wave traps moving with respect to each other.

  5. Dynamical stability of slip-stacking particles

    NASA Astrophysics Data System (ADS)

    Eldred, Jeffrey; Zwaska, Robert

    2014-09-01

    We study the stability of particles in slip-stacking configuration, used to nearly double proton beam intensity at Fermilab. We introduce universal area factors to calculate the available phase space area for any set of beam parameters without individual simulation. We find perturbative solutions for stable particle trajectories. We establish Booster beam quality requirements to achieve 97% slip-stacking efficiency. We show that slip-stacking dynamics directly correspond to the driven pendulum and to the system of two standing-wave traps moving with respect to each other.

  6. Beam stability & nonlinear dynamics. Formal report

    SciTech Connect

    Parsa, Z.

    1996-12-31

    his Report includes copies of transparencies and notes from the presentations made at the Symposium on Beam Stability and Nonlinear Dynamics, December 3-5, 1996 at the Institute for Theoretical Physics, University of California, Santa Barbara California, that was made available by the authors. Editing, reduction and changes to the authors contributions were made only to fulfill the printing and publication requirements. We would like to take this opportunity and thank the speakers for their informative presentations and for providing copies of their transparencies and notes for inclusion in this Report.

  7. Stochastic Dynamics Underlying Cognitive Stability and Flexibility.

    PubMed

    Ueltzhöffer, Kai; Armbruster-Genç, Diana J N; Fiebach, Christian J

    2015-06-01

    dopaminergic modulation of cognitive flexibility. These results show that stochastic dynamical systems can implement the basic computations underlying cognitive stability and flexibility and explain neurobiological bases of individual differences. PMID:26068119

  8. Stochastic Dynamics Underlying Cognitive Stability and Flexibility

    PubMed Central

    Ueltzhöffer, Kai; Armbruster-Genç, Diana J. N.; Fiebach, Christian J.

    2015-01-01

    dopaminergic modulation of cognitive flexibility. These results show that stochastic dynamical systems can implement the basic computations underlying cognitive stability and flexibility and explain neurobiological bases of individual differences. PMID:26068119

  9. Dynamic and galvanic stability of stretchable supercapacitors.

    PubMed

    Li, Xin; Gu, Taoli; Wei, Bingqing

    2012-12-12

    Stretchable electronics are emerging as a new technological advancement, since they can be reversibly stretched while maintaining functionality. To power stretchable electronics, rechargeable and stretchable energy storage devices become a necessity. Here, we demonstrate a facile and scalable fabrication of full stretchable supercapacitor, using buckled single-walled carbon nanotube macrofilms as the electrodes, an electrospun membrane of elastomeric polyurethane as the separator, and an organic electrolyte. We examine the electrochemical performance of the fully stretchable supercapacitors under dynamic stretching/releasing modes in different stretching strain rates, which reveal the true performance of the stretchable cells, compared to the conventional method of testing the cells under a statically stretched state. In addition, the self-discharge of the supercapacitor and the electrochemical behavior under bending mode are also examined. The stretchable supercapacitors show excellent cyclic stability under electrochemical charge/discharge during in situ dynamic stretching/releasing.

  10. High gain 1.3-μm GaInNAs SOA with fast gain dynamics and enhanced temperature stability

    NASA Astrophysics Data System (ADS)

    Fitsios, D.; Giannoulis, G.; Iliadis, N.; Korpijärvi, V.-M.; Viheriälä, J.; Laakso, A.; Dris, S.; Spyropoulou, M.; Avramopoulos, H.; Kanellos, G. T.; Pleros, N.; Guina, M.

    2014-03-01

    Semiconductor optical amplifiers (SOAs) are a well-established solution of optical access networks. They could prove an enabling technology for DataCom by offering extended range of active optical functionalities. However, in such costand energy-critical applications, high-integration densities increase the operational temperatures and require powerhungry external cooling. Taking a step further towards improving the cost and energy effectiveness of active optical components, we report on the development of a GaInNAs/GaAs (dilute nitride) SOA operating at 1.3μm that exhibits a gain value of 28 dB and combined with excellent temperature stability owing to the large conduction band offset between GaInNAs quantum well and GaAs barrier. Moreover, the characterization results reveal almost no gain variation around the 1320 nm region for a temperature range from 20° to 50° C. The gain recovery time attained values as short as 100 ps, allowing implementation of various signal processing functionalities at 10 Gb/s. The combined parameters are very attractive for application in photonic integrated circuits requiring uncooled operation and thus minimizing power consumption. Moreover, as a result of the insensitivity to heating issues, a higher number of active elements can be integrated on chip-scale circuitry, allowing for higher integration densities and more complex optical on-chip functions. Such component could prove essential for next generation DataCom networks.

  11. Passive Endwall Treatments for Enhancing Stability

    NASA Technical Reports Server (NTRS)

    Hathaway, Michael D.

    2007-01-01

    These lecture notes were presented at the von Karman Institutes lecture series on Advances in Axial Compressor Aerodynamics, May 2006. They provide a fairly extensive overview of what's been learned from numerous investigations of various passive casing endwall technologies that have been proposed for alleviating the stall limiting physics associated with the compressor endwall flow field. The lecture notes are organized to give an appreciation for the inventiveness and understanding of the earliest compressor technologists and to provide a coherent thread of understanding that has arisen out of the early investigations. As such the lecture notes begin with a historical overview of casing treatments from their infancy through the earliest proposed concepts involving blowing, suction and flow recirculation. A summary of lessons learned from these early investigations is provided at the end of this section. The lecture notes then provide a somewhat more in-depth overview of recent advancements in the development of passive casing treatments from the late 1990's through 2006, including advancements in understanding the flow mechanism of circumferential groove casing treatments, and the development of discrete tip injection and self-recirculating casing treatments. At the conclusion of the lecture notes a final summary of lessons learned throughout the history of the development of passive casing treatments is provided. Finally, a list of future needs is given. It is hoped that these lecture notes will be a useful reference for future research endeavors to improve our understanding of the fluid physics of passive casing treatments and how they act to enhance compressor stability, and that they will perhaps provide a springboard for future research activities in this area of interest

  12. Stability precision dynamic testing system on artillery

    NASA Astrophysics Data System (ADS)

    Wang, Chunyan; Li, Bo

    2014-12-01

    Dynamic feature of Weapon equipments is one of important performance index for evaluating the performance of the whole weapon system. The construction of target range in our country in fire control dynamic testing is relatively backward; therefore, it has greatly influenced the evaluation on the fire control system. In order to solve this problem, it's urgent to develop a new testing instrument so as to adjust to the armament research process and promote weapon system working more efficiently and thereby meeting the needs of modernization in national defense. This paper proposes a new measure which is used to test the stability precision of the fire control system, and it is installed on the moving base. Using the method, we develop a testing system which can test the stability precision of the fire control system and achieve a high precision results after testing. The innovation of the system is we can receive the image not only by CCD, but our eyes. It also adopts digital image-forming and image processing technique for real-time measurement and storing of the target information; it simultaneously adopts the method adjusting the platform and the corresponding fixture mounted on a sample to measure the stable precision and the precision of corner of stabilizator. In this paper, we make a description on the construction of the system and the idea of the designing of the optical system. Finally, we introduce the actual application of the system and testing results.

  13. Dynamic stability of an aerodynamically efficient motorcycle

    NASA Astrophysics Data System (ADS)

    Sharma, Amrit; Limebeer, David J. N.

    2012-08-01

    Motorcycles exhibit two potentially dangerous oscillatory modes known as 'wobble' and 'weave'. The former is reminiscent of supermarket castor shimmy, while the latter is a low frequency 'fish-tailing' motion that involves a combination of rolling, yawing, steering and side-slipping motions. These unwanted dynamic features, which can occur when two-wheeled vehicles are operated at speed, have been studied extensively. The aim of this paper is to use mathematical analysis to identify important stability trends in the on-going design of a novel aerodynamically efficient motorcycle known as the ECOSSE Spirit ES1. A mathematical model of the ES1 is developed using a multi-body dynamics software package called VehicleSim [Anon, VehicleSim Lisp Reference Manual Version 1.0, Mechanical Simulation Corporation, 2008. Available at http://www.carsim.com]. This high-fidelity motorcycle model includes realistic tyre-road contact geometry, a comprehensive tyre model, tyre relaxation and a flexible frame. A parameter set representative of a modern high-performance machine and rider is used. Local stability is investigated via the eigenvalues of the linearised models that are associated with equilibrium points of interest. A comprehensive study of the effects of frame flexibilities, acceleration, aerodynamics and tyre variations is presented, and an optimal passive steering compensator is derived. It is shown that the traditional steering damper cannot be used to stabilise the ES1 over its entire operating speed range. A simple passive compensator, involving an inerter is proposed. Flexibility can be introduced deliberately into various chassis components to change the stability characteristics of the vehicle; the implications of this idea are studied.

  14. Depth enhanced and content aware video stabilization

    NASA Astrophysics Data System (ADS)

    Lindner, A.; Atanassov, K.; Goma, S.

    2015-03-01

    We propose a system that uses depth information for video stabilization. The system uses 2D-homographies as frame pair transforms that are estimated with keypoints at the depth of interest. This makes the estimation more robust as the points lie on a plane. The depth of interest can be determined automatically from the depth histogram, inferred from user input such as tap-to-focus, or selected by the user; i.e., tap-to-stabilize. The proposed system can stabilize videos on the fly in a single pass and is especially suited for mobile phones with multiple cameras that can compute depth maps automatically during image acquisition.

  15. Stability at systems of usual differential equations in virus dynamics

    NASA Astrophysics Data System (ADS)

    Schröer, H.

    In this paper we discuss different models of differential equations systems, that describe virus dynamics in different situations (HIV-virus and Hepatitis B-virus). We inquire the stability of differential equations. We use theorems of the stability theory.

  16. Dynamic actin structures stabilized by profilin.

    PubMed Central

    Finkel, T; Theriot, J A; Dise, K R; Tomaselli, G F; Goldschmidt-Clermont, P J

    1994-01-01

    We describe the production and analysis of clonal cell lines in which we have overexpressed human profilin, a small ubiquitous actin monomer binding protein, to assess the role of profilin on actin function in vivo. The concentration of filamentous actin is increased in cells with higher profilin levels, and actin filament half-life measured in these cells is directly proportional to the steady-state profilin concentration. The distribution of actin filaments is altered by profilin overexpression. While parallel actin bundles crossing the cells are virtually absent in cells overexpressing profilin, the submembranous actin network of these cells is denser than in control cells. These results suggest that in vivo profilin regulates the stability, and thereby distribution, of specific dynamic actin structures. Images PMID:8108438

  17. Predator interference and stability of predator-prey dynamics.

    PubMed

    Přibylová, Lenka; Berec, Luděk

    2015-08-01

    Predator interference, that is, a decline in the per predator consumption rate as predator density increases, is generally thought to promote predator-prey stability. Indeed, this has been demonstrated in many theoretical studies on predator-prey dynamics. In virtually all of these studies, the stabilization role is demonstrated as a weakening of the paradox of enrichment. With predator interference, stable limit cycles that appear as a result of environmental enrichment occur for higher values of the environmental carrying capacity of prey, and even a complete absence of the limit cycles can happen. Here we study predator-prey dynamics using the Rosenzweig-MacArthur-like model in which the Holling type II functional response has been replaced by a predator-dependent family which generalizes many of the commonly used descriptions of predator interference. By means of a bifurcation analysis we show that sufficiently strong predator interference may bring about another stabilizing mechanism. In particular, hysteresis combined with (dis)appearance of stable limit cycles imply abrupt increases in both the prey and predator densities and enhanced persistence and resilience of the predator-prey system. We encourage refitting the previously collected data on predator consumption rates as well as for conducting further predation experiments to see what functional response from the explored family is the most appropriate.

  18. Enhancing probiotic stability in industrial processes

    PubMed Central

    Gueimonde, Miguel; Sánchez, Borja

    2012-01-01

    Background Manufacture of probiotic products involves industrial processes that reduce the viability of the strains. This lost of viability constitutes an economic burden for manufacturers, compromising the efficacy of the product and preventing the inclusion of probiotics in many product categories. Different strategies have been used to improve probiotic stability during industrial processes. These include technological approaches, such as the modification of production parameters or the reformulation of products, as well as microbiological approaches focused on the strain intrinsic resistance. Among the later, both selection of natural strains with the desired properties and stress-adaptation of strains have been widely used. Conclusion During recent years, the knowledge acquired on the molecular basis of stress-tolerance of probiotics has increased our understanding on their responses to industrial stresses. This knowledge on stress-response may nowadays be used for the selection of the best strains and industrial conditions in terms of probiotic stability in the final product. PMID:23990824

  19. Stability and surface dynamics of metal nanowires

    NASA Astrophysics Data System (ADS)

    Zhang, Chang-Hua

    In this thesis, we have systematically investigated the stability, surface dynamics, electronic transport, and growth of metal nanowires using a semiclassical free energy functional based on the mean-field interacting electron model, which is simple and general enough. In this model, the ionic degrees of freedom of the wire are modeled as an incompressible fluid, and the conducting electrons are treated as a Fermi gas confined within the wire with Dirichlet boundary conditions. In equilibrium, we prove that the electron-electron interaction is a second-order effect to the total grand canonical free energy, while the shell-correction to the noninteracting grand canonical free energy is a first-order effect. To leading order, the electron-electron interactions just renormalize the Weyl parameters, such as the average energy density, surface tension and mean curvature energy, but not the mesoscopic shell effect. This finding for open mesoscopic systems is a generalization of the well-known Strutinsky theorem for finite-Fermion systems. It is for this reason that self-consistent jellium calculations obtain essentially identical equilibrium mesoscopic effects as calculations based on the free-electron model. However, for systems out of equilibrium, the electron-electron interaction plays important roles. First of all, the Strutinsky theorem breaks down in the non-equilibrium case. Secondly, the gauge invariance condition is violated if the electron-electron interaction is not adequately included. We first derive a thermodynamic phase diagram for jellium nanowires, which predicts that cylindrical wires with certain "magic" conductance values are stable with respect to small perturbations up to remarkably high temperatures and high applied voltage. We have shown that Jahn-Teller-distorted wires can be stable. The derived sequence of stable cylindrical and elliptical geometries explains the experimentally observed shell and supershell structures for alkali metals. Highly

  20. Lift enhancement by bats' dynamically changing wingspan.

    PubMed

    Wang, Shizhao; Zhang, Xing; He, Guowei; Liu, Tianshu

    2015-12-01

    This paper elucidates the aerodynamic role of the dynamically changing wingspan in bat flight. Based on direct numerical simulations of the flow over a slow-flying bat, it is found that the dynamically changing wingspan can significantly enhance the lift. Further, an analysis of flow structures and lift decomposition reveal that the elevated vortex lift associated with the leading-edge vortices intensified by the dynamically changing wingspan considerably contributed to enhancement of the time-averaged lift. The nonlinear interaction between the dynamically changing wing and the vortical structures plays an important role in the lift enhancement of a flying bat in addition to the geometrical effect of changing the lifting-surface area in a flapping cycle. In addition, the dynamically changing wingspan leads to the higher efficiency in terms of generating lift for a given amount of the mechanical energy consumed in flight. PMID:26701882

  1. Lift enhancement by bats' dynamically changing wingspan.

    PubMed

    Wang, Shizhao; Zhang, Xing; He, Guowei; Liu, Tianshu

    2015-12-01

    This paper elucidates the aerodynamic role of the dynamically changing wingspan in bat flight. Based on direct numerical simulations of the flow over a slow-flying bat, it is found that the dynamically changing wingspan can significantly enhance the lift. Further, an analysis of flow structures and lift decomposition reveal that the elevated vortex lift associated with the leading-edge vortices intensified by the dynamically changing wingspan considerably contributed to enhancement of the time-averaged lift. The nonlinear interaction between the dynamically changing wing and the vortical structures plays an important role in the lift enhancement of a flying bat in addition to the geometrical effect of changing the lifting-surface area in a flapping cycle. In addition, the dynamically changing wingspan leads to the higher efficiency in terms of generating lift for a given amount of the mechanical energy consumed in flight.

  2. Mechanisms and enhancement of flame stabilization

    SciTech Connect

    Law, C.K.

    1993-01-01

    During the reporting period, useful contributions have been made in understanding the structure of laminar premixed and diffusion flames, with emphasis on the influence of aerodynamics and chemical kinetics. These contributions include (1) derivation of the missing closure condition for the activation energy asymptotic analysis of premixed flames, (2) identification of a dual extinction mode for radiation-affected flames, (3) formulation of a unified theory of fundamental flammability limits, and (4) demonstration that flame stabilization can be achieved in the absence of heat loss. These investigations have been conducted via experimental, analytical and computational approaches, with strong coupling between the individual components.

  3. 14 CFR 29.181 - Dynamic stability: Category A rotorcraft.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 1 2013-01-01 2013-01-01 false Dynamic stability: Category A rotorcraft. 29.181 Section 29.181 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF....181 Dynamic stability: Category A rotorcraft. Any short-period oscillation occurring at any speed...

  4. 14 CFR 29.181 - Dynamic stability: Category A rotorcraft.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Dynamic stability: Category A rotorcraft. 29.181 Section 29.181 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF....181 Dynamic stability: Category A rotorcraft. Any short-period oscillation occurring at any speed...

  5. 14 CFR 29.181 - Dynamic stability: Category A rotorcraft.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Dynamic stability: Category A rotorcraft. 29.181 Section 29.181 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF....181 Dynamic stability: Category A rotorcraft. Any short-period oscillation occurring at any speed...

  6. 14 CFR 29.181 - Dynamic stability: Category A rotorcraft.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Dynamic stability: Category A rotorcraft... TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY ROTORCRAFT Flight Flight Characteristics § 29.181 Dynamic stability: Category A rotorcraft. Any short-period oscillation occurring at any speed...

  7. 14 CFR 29.181 - Dynamic stability: Category A rotorcraft.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Dynamic stability: Category A rotorcraft... TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY ROTORCRAFT Flight Flight Characteristics § 29.181 Dynamic stability: Category A rotorcraft. Any short-period oscillation occurring at any speed...

  8. Dynamic Stabilization of a Quantum Many-Body Spin System

    NASA Astrophysics Data System (ADS)

    Hoang, T. M.; Gerving, C. S.; Land, B. J.; Anquez, M.; Hamley, C. D.; Chapman, M. S.

    2013-08-01

    We demonstrate dynamic stabilization of a strongly interacting quantum spin system realized in a spin-1 atomic Bose-Einstein condensate. The spinor Bose-Einstein condensate is initialized to an unstable fixed point of the spin-nematic phase space, where subsequent free evolution gives rise to squeezing and quantum spin mixing. To stabilize the system, periodic microwave pulses are applied that rotate the spin-nematic many-body fluctuations and limit their growth. The stability diagram for the range of pulse periods and phase shifts that stabilize the dynamics is measured and compares well with a stability analysis.

  9. Dynamic stabilization of a quantum many-body spin system.

    PubMed

    Hoang, T M; Gerving, C S; Land, B J; Anquez, M; Hamley, C D; Chapman, M S

    2013-08-30

    We demonstrate dynamic stabilization of a strongly interacting quantum spin system realized in a spin-1 atomic Bose-Einstein condensate. The spinor Bose-Einstein condensate is initialized to an unstable fixed point of the spin-nematic phase space, where subsequent free evolution gives rise to squeezing and quantum spin mixing. To stabilize the system, periodic microwave pulses are applied that rotate the spin-nematic many-body fluctuations and limit their growth. The stability diagram for the range of pulse periods and phase shifts that stabilize the dynamics is measured and compares well with a stability analysis. PMID:24033006

  10. Enhancing protein stability with extended disulfide bonds.

    PubMed

    Liu, Tao; Wang, Yan; Luo, Xiaozhou; Li, Jack; Reed, Sean A; Xiao, Han; Young, Travis S; Schultz, Peter G

    2016-05-24

    Disulfide bonds play an important role in protein folding and stability. However, the cross-linking of sites within proteins by cysteine disulfides has significant distance and dihedral angle constraints. Here we report the genetic encoding of noncanonical amino acids containing long side-chain thiols that are readily incorporated into both bacterial and mammalian proteins in good yields and with excellent fidelity. These amino acids can pair with cysteines to afford extended disulfide bonds and allow cross-linking of more distant sites and distinct domains of proteins. To demonstrate this notion, we preformed growth-based selection experiments at nonpermissive temperatures using a library of random β-lactamase mutants containing these noncanonical amino acids. A mutant enzyme that is cross-linked by one such extended disulfide bond and is stabilized by ∼9 °C was identified. This result indicates that an expanded set of building blocks beyond the canonical 20 amino acids can lead to proteins with improved properties by unique mechanisms, distinct from those possible through conventional mutagenesis schemes.

  11. Effects of pelvic stabilization on lumbar muscle activity during dynamic exercise.

    PubMed

    San Juan, Jun G; Yaggie, James A; Levy, Susan S; Mooney, Vert; Udermann, Brian E; Mayer, John M

    2005-11-01

    Many commonly utilized low-back exercise devices offer mechanisms to stabilize the pelvis and to isolate the lumbar spine, but the value of these mechanisms remains unclear. The purpose of this study was to examine the effect of pelvic stabilization on the activity of the lumbar and hip extensor muscles during dynamic back extension exercise. Fifteen volunteers in good general health performed dynamic extension exercise in a seated upright position on a lumbar extension machine with and without pelvic stabilization. During exercise, surface electromyographic activity of the lumbar multifidus and biceps femoris was recorded. The activity of the multifidus was 51% greater during the stabilized condition, whereas there was no difference in the activity of the biceps femoris between conditions. This study demonstrates that pelvic stabilization enhances lumbar muscle recruitment during dynamic exercise on machines. Exercise specialists can use these data when designing exercise programs to develop low back strength.

  12. Temporal stability in forest productivity increases with tree diversity due to asynchrony in species dynamics.

    PubMed

    Morin, Xavier; Fahse, Lorenz; de Mazancourt, Claire; Scherer-Lorenzen, Michael; Bugmann, Harald

    2014-12-01

    Theory predicts a positive relationship between biodiversity and stability in ecosystem properties, while diversity is expected to have a negative impact on stability at the species level. We used virtual experiments based on a dynamic simulation model to test for the diversity-stability relationship and its underlying mechanisms in Central European forests. First our results show that variability in productivity between stands differing in species composition decreases as species richness and functional diversity increase. Second we show temporal stability increases with increasing diversity due to compensatory dynamics across species, supporting the biodiversity insurance hypothesis. We demonstrate that this pattern is mainly driven by the asynchrony of species responses to small disturbances rather than to environmental fluctuations, and is only weakly affected by the net biodiversity effect on productivity. Furthermore, our results suggest that compensatory dynamics between species may enhance ecosystem stability through an optimisation of canopy occupancy by coexisting species. PMID:25212251

  13. Enhanced muscle activity during lumbar extension exercise with pelvic stabilization.

    PubMed

    Lee, Ho-Seong

    2015-12-01

    The purpose of this study was to investigate whether pelvic stabilization affects multifidus (MF) and iliocostalis lumborum (IL) muscle activities during dynamic extension exercise. Nine males (age, 25.1±6.3 yr; height, 176.6±2.4 cm; body mass, 74.9±6.7 kg) performed an isometric lumbar extension strength test and dynamic exercise in an upright seated position with or without pelvic stabilization. The electromyography and muscle strength of the MF and IL muscles were measured when the subjects performed the isometric lumbar extension strength test at the trunk angle 110°, 146°, and 182°. In addition, the trunk extensor muscle activities were measured using 50% muscle strength of maximum isometric strength during a dynamic trunk extension exercise. The MF and IL muscle activities were significantly higher at 110°, 146°, and 182° with pelvic stabilization than that without pelvic stabilization during the isometric lumbar extension strength test (P<0.05) and the dynamic exercise (P<0.05). These results suggest that the lumbar extension exercise with pelvic stabilization may be more effective for MF and IL muscle activity compared to that without pelvic stabilization.

  14. Enhanced muscle activity during lumbar extension exercise with pelvic stabilization

    PubMed Central

    Lee, Ho-Seong

    2015-01-01

    The purpose of this study was to investigate whether pelvic stabilization affects multifidus (MF) and iliocostalis lumborum (IL) muscle activities during dynamic extension exercise. Nine males (age, 25.1±6.3 yr; height, 176.6±2.4 cm; body mass, 74.9±6.7 kg) performed an isometric lumbar extension strength test and dynamic exercise in an upright seated position with or without pelvic stabilization. The electromyography and muscle strength of the MF and IL muscles were measured when the subjects performed the isometric lumbar extension strength test at the trunk angle 110°, 146°, and 182°. In addition, the trunk extensor muscle activities were measured using 50% muscle strength of maximum isometric strength during a dynamic trunk extension exercise. The MF and IL muscle activities were significantly higher at 110°, 146°, and 182° with pelvic stabilization than that without pelvic stabilization during the isometric lumbar extension strength test (P<0.05) and the dynamic exercise (P<0.05). These results suggest that the lumbar extension exercise with pelvic stabilization may be more effective for MF and IL muscle activity compared to that without pelvic stabilization. PMID:26730390

  15. Stability of the Dynamically Stabilized Two-Wheeled Vehicle Traveling on a Rough Road

    NASA Astrophysics Data System (ADS)

    Nakagawa, Chihiro; Nakano, Kimihiko; Suda, Yoshihiro; Hayashi, Ryuzo

    These days, the dynamically stabilized two-wheeled vehicles are investigated as a form of the new personal mobility vehicle. With the control theory of the inverted pendulum, they are kept in equilibrium. It is important to investigate the stability of the dynamically stabilized vehicle especially on a rough road. For this background, the authors investigate the responses of the inverted pendulum, which is stabilized by an optimal controller, to vertical vibrations. With theoretical analysis, numerical simulations and experiments using a large scale vibration exciter, stability to vertical vibration is examined. The results show the system dynamics are governed by the Mathieu equation, thus the amplitude ratio reaches its peak when the frequency of the forced vibration is twice the natural frequency of the controlled inverted pendulum system. The simulation using the parameter of the dynamically stabilized vehicle was also performed and unstable region for the vehicle was found.

  16. Dynamic stabilization in the double-well duffing oscillator

    PubMed

    Kim; Kim

    2000-06-01

    Bifurcations associated with stability of the saddle fixed point of the Poincare map, arising from the unstable equilibrium point of the potential, are investigated in a forced Duffing oscillator with a double-well potential. One interesting behavior is the dynamic stabilization of the saddle fixed point. When the driving amplitude is increased through a threshold value, the saddle fixed point becomes stabilized via a pitchfork bifurcation. We note that this dynamic stabilization is similar to that of the inverted pendulum with a vertically oscillating suspension point. After the dynamic stabilization, the double-well Duffing oscillator behaves as the single-well Duffing oscillator, because the effect of the central potential barrier on the dynamics of the system becomes negligible. PMID:11088331

  17. Enhanced thermal stability of Ag nanorods through capping

    SciTech Connect

    Bachenheimer, Lou; Elliott, Paul; Stagon, Stephen; Huang, Hanchen

    2014-11-24

    Ag nanorods may serve as sensors in the detection of trace amounts of chemical agents, even single molecules, through surface enhanced Raman spectroscopy (SERS). However, thermal coarsening of Ag nanorods near room temperature limits their applications. This letter proposes the use of a thin oxide capping layer to enhance the thermal stability of Ag nanorods beyond 100 °C. Using electron microscopy characterization and SERS tests, the authors show that the proposed method is effective in stabilizing both morphology and sensitivity of Ag nanorods. The results of this work extend the applicability of Ag nanorods as chemical sensors to higher temperatures.

  18. Enhancing Biopolymer Dynamics through Destruction

    NASA Astrophysics Data System (ADS)

    Ross, Jennifer

    2012-02-01

    Microtubules are cytoskeletal filaments that organize intracellular space structurally and through active transport along their lengths. They need to be organized and remodeled quickly during development of differentiated cells or in mitosis. Much work has focused on remodeling from the ends because these long polymers can stochastically disassemble through dynamic instability or be actively disassembled. Microtubule-severing enzymes are a novel class of microtubule regulators that create new ends by cutting the filament. Thus, these proteins add a new dimension to microtubule regulation by their ability to create new microtubule ends. Interestingly, despite their destructive capabilities, severing has the ability to create new microtubule networks in cells. We are interested in the inherent biophysical activities of these proteins and their ability to remodel cellular microtubule networks. Interestingly, despite their destructive capabilities, severing has the ability to create new microtubule networks in cells. We use two-color single molecule total internal reflection fluorescence imaging to visualize purified severing enzymes and microtubules in vitro. We have examined two families of severing enzymes to find that their biophysical activities are distinct giving them different network-regulating abilities.

  19. A Quasi-Steady Flexible Launch Vehicle Stability Analysis Using Steady CFD with Unsteady Aerodynamic Enhancement

    NASA Technical Reports Server (NTRS)

    Bartels, Robert E.

    2011-01-01

    Launch vehicles frequently experience a reduced stability margin through the transonic Mach number range. This reduced stability margin is caused by an undamping of the aerodynamics in one of the lower frequency flexible or rigid body modes. Analysis of the behavior of a flexible vehicle is routinely performed with quasi-steady aerodynamic lineloads derived from steady rigid computational fluid dynamics (CFD). However, a quasi-steady aeroelastic stability analysis can be unconservative at the critical Mach numbers where experiment or unsteady computational aeroelastic (CAE) analysis show a reduced or even negative aerodynamic damping. This paper will present a method of enhancing the quasi-steady aeroelastic stability analysis of a launch vehicle with unsteady aerodynamics. The enhanced formulation uses unsteady CFD to compute the response of selected lower frequency modes. The response is contained in a time history of the vehicle lineloads. A proper orthogonal decomposition of the unsteady aerodynamic lineload response is used to reduce the scale of data volume and system identification is used to derive the aerodynamic stiffness, damping and mass matrices. The results of the enhanced quasi-static aeroelastic stability analysis are compared with the damping and frequency computed from unsteady CAE analysis and from a quasi-steady analysis. The results show that incorporating unsteady aerodynamics in this way brings the enhanced quasi-steady aeroelastic stability analysis into close agreement with the unsteady CAE analysis.

  20. Stability analysis of dynamic thin shells

    NASA Astrophysics Data System (ADS)

    Lobo, Francisco S. N.; Crawford, Paulo

    2005-11-01

    We analyse the stability of generic spherically symmetric thin shells to linearized perturbations around static solutions. We include the momentum flux term in the conservation identity, deduced from the 'ADM' constraint and the Lanczos equations. Following the Ishak Lake analysis, we deduce a master equation which dictates the stable equilibrium configurations. Considering the transparency condition, we study the stability of thin shells around black holes, showing that our analysis is in agreement with previous results. Applying the analysis to traversable wormhole geometries, by considering specific choices for the form function, we deduce stability regions and find that the latter may be significantly increased by considering appropriate choices for the redshift function.

  1. Dynamic Colloidal Stabilization by Nanoparticle Halos

    NASA Astrophysics Data System (ADS)

    Karanikas, S.; Louis, A. A.

    2004-12-01

    We explore the conditions under which colloids can be stabilized by the addition of smaller particles. The largest repulsive barriers between colloids occur when the added particles repel each other with soft interactions, leading to an accumulation near the colloid surfaces. At lower densities these layers of mobile particles (nanoparticle halos) result in stabilization, but when too many are added, the interactions become attractive again. We systematically study these effects—accumulation repulsion, reentrant attraction, and bridging—by accurate integral equation techniques.

  2. Logic Dynamics for Deductive Inference -- Its Stability and Neural Basis

    NASA Astrophysics Data System (ADS)

    Tsuda, Ichiro

    2014-12-01

    We propose a dynamical model that represents a process of deductive inference. We discuss the stability of logic dynamics and a neural basis for the dynamics. We propose a new concept of descriptive stability, thereby enabling a structure of stable descriptions of mathematical models concerning dynamic phenomena to be clarified. The present theory is based on the wider and deeper thoughts of John S. Nicolis. In particular, it is based on our joint paper on the chaos theory of human short-term memories with a magic number of seven plus or minus two.

  3. Parametrics of submarine dynamic stability in the vertical plane

    SciTech Connect

    Papoulias, F.A.; Papanikolaou, S.

    1996-12-31

    The problem of dynamic stability of submersible vehicles in the dive plane is examined utilizing bifurcation techniques. The primary mechanism of loss of stability is identified in the form of generic Hopf bifurcations to periodic solutions. Stability of the resulting limit cycles is established using center manifold approximations and integral averaging. Parametric studies are performed with varying vehicle geometric properties. The methods described in this work could lead to techniques resulting in enlargement of the submerged operational envelope of a vehicle.

  4. Tethered naphthalene diimide intercalators enhance DNA triplex stability.

    PubMed

    Gianolio, D A; McLaughlin, L W

    2001-09-01

    Naphthalene diimides function as effective intercalators and when tethered to the 5'-terminus of a pyrimidine-rich oligonucleotide can contribute significantly to the overall stabilization of DNA triplexes. This stabilization can be further enhanced by alterations to the linker tethering the DNA sequence and the intercalator. Less flexible linkers, and particularly one with a phenyl ring present, appear to permit the stabilization afforded by the bound intercalator to be transferred more effectively to the three-stranded complex. The conjugate containing the phenyl linker exhibits a T(M) value that is increased by 28 degrees C relative to the unconjugated triplex. That the linker itself contributes to the observed stabilization is clear since introduction of the phenyl linker increases the observed T(M) by 11 degrees C relative to a simple flexible linker.

  5. The relationship between parameters of static and dynamic stability tests

    PubMed Central

    Karimi, Mohammad Taghi; Solomonidis, Stephan

    2011-01-01

    BACKGROUND: Stability is often described to be static (quiet standing) and dynamic (maintaining a stable position while undertake a prescribed movement). Many researchers have used only static tests to evaluate the stability of normal and handicapped subjects. However, it is important to evaluate the stability of subjects while undertaking various tasks (dynamic stability). It is not currently clear whether static balance can predict dynamic balance or not. Therefore, the aim of this research was to investigate the relationship between parameters of static and dynamic stability tests. METHODS: The current clinical trial study was carried out in the Bioengineering Unit of Strathclyde University during 2008 and 2009. The normal subjects with no history of musculoskeletal disorders from staff and students of the Unit were selected in this study. Twenty-five normal subjects were recruited to participate in this research project. They were asked to stand on a force plate in quiet standing and while undertaking various hand tasks. The functional stability of the subjects was measured while transverse and vertical reaching tasks were undertaken. The correlation between various parameters of stability in quiet standing and functional hand tasks was evaluated using Pearson correlation. RESULTS: There was no significant correlation between static and dynamic stability parameters. The Pearson correlation coefficients for all parameters regarding the static and dynamic tests were less than 0.46. CONCLUSIONS: As there was no correlation between stability parameters in quiet standing and while performing various hand tasks, it is not practical to discuss ability of the subjects to control their balance while undertaking various hand tasks based on static balance ability. PMID:22091270

  6. Dynamics and stability of wind turbine generators

    NASA Technical Reports Server (NTRS)

    Hinrichsen, E. N.; Nolan, P. J.

    1981-01-01

    Synchronous and induction generators are considered. A comparison is made between wind turbines, steam, and hydro units. The unusual phenomena associated with wind turbines are emphasized. The general control requirements are discussed, as well as various schemes for torsional damping such as speed sensitive stabilizer and blade pitch control. Integration between adjacent wind turbines in a wind farm is also considered.

  7. Animal flight dynamics II. Longitudinal stability in flapping flight.

    PubMed

    Taylor, G K; Thomas, A L R

    2002-02-01

    Stability is essential to flying and is usually assumed to be especially problematic in flapping flight. If so, problems of stability may have presented a particular hurdle to the evolution of flapping flight. In spite of this, the stability of flapping flight has never been properly analysed. Here we use quasi-static and blade element approaches to analyse the stability provided by a flapping wing. By using reduced order approximations to the natural modes of motion, we show that wing beat frequencies are generally high enough compared to the natural frequencies of motion for a quasi-static approach to be valid as a first approximation. Contrary to expectations, we find that there is noting inherently destabilizing about flapping: beating the wings faster simply amplifies any existing stability or instability, and flapping can even enhance stability compared to gliding at the same air speed. This suggests that aerodynamic stability may not have been a particular hurdle in the evolution of flapping flight. Hovering animals, like hovering helicopters, are predicted to possess neutral static stability. Flapping animals, like fixed wing aircraft, are predicted to be stable in forward flight if the mean flight force acts above and/or behind the centre of gravity. In this case, the downstroke will always be stabilizing. The stabilizing contribution may be diminished by an active upstroke with a low advance ratio and more horizontal stroke plane; other forms of the upstroke may make a small positive contribution to stability. An active upstroke could, therefore, be used to lower stability and enhance manoeuvrability. Translatory mechanisms of unsteady lift production are predicted to amplify the stability predicted by a quasi-static analysis. Non-translatory mechanisms will make little or no contribution to stability. This may be one reason why flies, and other animals which rely upon non-translatory aerodynamic mechanisms, often appear inherently unstable.

  8. Enhanced Luminescent Stability through Particle Interactions in Silicon Nanocrystal Aggregates.

    PubMed

    Miller, Joseph B; Dandu, Naveen; Velizhanin, Kirill A; Anthony, Rebecca J; Kortshagen, Uwe R; Kroll, Daniel M; Kilina, Svetlana; Hobbie, Erik K

    2015-10-27

    Close-packed assemblies of ligand-passivated colloidal nanocrystals can exhibit enhanced photoluminescent stability, but the origin of this effect is unclear. Here, we use experiment, simulation, and ab initio computation to examine the influence of interparticle interactions on the photoluminescent stability of silicon nanocrystal aggregates. The time-dependent photoluminescence emitted by structures ranging in size from a single quantum dot to agglomerates of more than a thousand is compared with Monte Carlo simulations of noninteracting ensembles using measured single-particle blinking data as input. In contrast to the behavior typically exhibited by the metal chalcogenides, the measured photoluminescent stability shows an enhancement with respect to the noninteracting scenario with increasing aggregate size. We model this behavior using time-dependent density functional theory calculations of energy transfer between neighboring nanocrystals as a function of nanocrystal size, separation, and the presence of charge and/or surface-passivation defects. Our results suggest that rapid exciton transfer from "bright" nanocrystals to surface trap states in nearest-neighbors can efficiently fill such traps and enhance the stability of emission by promoting the radiative recombination of slowly diffusing excited electrons.

  9. New Insight into Cataract Formation: Enhanced Stability through Mutual Attraction

    SciTech Connect

    Stradner, A.; Schurtenberger, P.; Foffi, G.; Dorsaz, N.; Thurston, G.

    2007-11-09

    Small-angle neutron scattering experiments and molecular dynamics simulations combined with an application of concepts from soft matter physics to complex protein mixtures provide new insight into the stability of eye lens protein mixtures. Exploring this colloid-protein analogy we demonstrate that weak attractions between unlike proteins help to maintain lens transparency in an extremely sensitive and nonmonotonic manner. These results not only represent an important step towards a better understanding of protein condensation diseases such as cataract formation, but provide general guidelines for tuning the stability of colloid mixtures, a topic relevant for soft matter physics and industrial applications.

  10. High dynamic range fusion for enhanced vision

    NASA Astrophysics Data System (ADS)

    Liu, Yuchi; Li, Yipeng; Dai, Qionghai

    2012-06-01

    Fusing multispectral images, Enhanced Vision (EV) has been proven helpful to improve pilot's Situation Awareness (SA) under Degraded Vision Environment (DVE), such as low visibility or adverse observation conditions, which caused by fog, dust, weak light, backlighting, etc. Numerous methods are applied to enhance and fuse optical and infrared (IR) images for visual details to provide pilot with enough information as far as possible. However, most existing optical and IR imaging devices, for their inherent defects, fail to acquire wide span of light and only generate Low Dynamic Range images (LDR, Dynamic Range: range between the lightest and darkest areas), which causes the loss of useful details. Normal display devices can't reveal HDR details as well. The proposed paper introduces and expands High Dynamic Range (HDR) technologies to fuse optical and IR images, which has rarely been involved in the study of HDR Imaging to our knowledge, for Enhanced Vision to better pilot's Situation Awareness. Two major problems should be discussed. (1) The way to generate fused image with HDR information under DVE. (2) The method to effectively display fused HDR image with normal LDR monitors. Aiming at application environment, HDR fusion scheme is proposed and relevant methods are explored. The experimental results prove that our scheme is effective and would be beneficial to enhancing pilot's Situation Awareness under DVE.

  11. Dynamic and Thermodynamic Stability of Black Holes and Black Branes

    NASA Astrophysics Data System (ADS)

    Wald, Robert M.

    I describe recent work with Stefan Hollands that establishes a new criterion for the dynamical stability of black holes in D ge 4 spacetime dimensions in general relativity with respect to axisymmetric perturbations: Dynamical stability is equivalent to the positivity of the canonical energy, E, on a subspace of linearized solutions that have vanishing linearized ADM mass, momentum, and angular momentum at infinity and satisfy certain gauge conditions at the horizon. We further show that E is related to the second order variations of mass, angular momentum, and horizon area by fancyscript{E} = δ ^2 M - sum _i \\varOmega _i δ ^2 J_i - (kappa /8π ) δ ^2 A, thereby establishing a close connection between dynamical stability and thermodynamic stability. Thermodynamic instability of a family of black holes need not imply dynamical instability because the perturbations towards other members of the family will not, in general, have vanishing linearized ADM mass and/or angular momentum. However, we prove that all black branes corresponding to thermodynamically unstable black holes are dynamically unstable, as conjectured by Gubser and Mitra. We also prove that positivity of E is equivalent to the satisfaction of a "local Penrose inequality," thus showing that satisfaction of this local Penrose inequality is necessary and sufficient for dynamical stability.

  12. Patterned Si thin film electrodes for enhancing structural stability.

    PubMed

    Cho, Gyu-Bong; Noh, Jung-Pil; Sung, Ho-Jin; Lee, Sang-Hun; Im, Yeon-Min; Ahn, Hyo-Jun; Kim, Ki-Won

    2012-01-01

    A patterned film (electrode) with lozenge-shaped Si tiles could be successfully fabricated by masking with an expanded metal foil during film deposition. Its electrochemical properties and structural stability during the charge-discharge process were examined and compared with those of a continuous (conventional) film electrode. The patterned electrode exhibited a remarkably improved cycleability (75% capacity retention after 120 cycles) and an enhanced structural stability compared to the continuous electrode. The good electrochemical performance of the patterned electrode was attributed to the space between Si tiles that acted as a buffer against the volume change of the Si electrode. PMID:22221620

  13. Patterned Si thin film electrodes for enhancing structural stability

    NASA Astrophysics Data System (ADS)

    Cho, Gyu-Bong; Noh, Jung-Pil; Sung, Ho-Jin; Lee, Sang-Hun; Im, Yeon-Min; Ahn, Hyo-Jun; Kim, Ki-Won

    2012-01-01

    A patterned film (electrode) with lozenge-shaped Si tiles could be successfully fabricated by masking with an expanded metal foil during film deposition. Its electrochemical properties and structural stability during the charge-discharge process were examined and compared with those of a continuous (conventional) film electrode. The patterned electrode exhibited a remarkably improved cycleability (75% capacity retention after 120 cycles) and an enhanced structural stability compared to the continuous electrode. The good electrochemical performance of the patterned electrode was attributed to the space between Si tiles that acted as a buffer against the volume change of the Si electrode.

  14. Dynamic stability of repulsive-force maglev suspension systems

    SciTech Connect

    Cai, Y.; Rote, D.M.; Mulcahy, T.M.; Wang, Z.

    1996-11-01

    This report summarizes the research performed on maglev vehicle dynamic stability at Argonne National Laboratory during the past few years. It also documents both measured and calculated magnetic-force data. Because dynamic instability is not acceptable for any commercial maglev system, it is important to consider this phenomenon in the development of all maglev systems. This report presents dynamic stability experiments on maglev systems and compares the results with predictions calculated by a nonlinear-dynamics computer code. Instabilities of an electrodynamic-suspension system type vehicle model were obtained by experimental observation and computer simulation of a five-degree-of-freedom maglev vehicle moving on a guideway that consists of a pair of L-shaped aluminum conductors attached to a rotating wheel. The experimental and theoretical analyses developed in this study identify basic stability characteristics and future research needs of maglev systems.

  15. Summary of methods for calculating dynamic lateral stability and response and for estimating aerodynamic stability derivatives

    NASA Technical Reports Server (NTRS)

    Campbell, John P; Mckinney, Marion O

    1952-01-01

    A summary of methods for making dynamic lateral stability and response calculations and for estimating the aerodynamic stability derivatives required for use in these calculations is presented. The processes of performing calculations of the time histories of lateral motions, of the period and damping of these motions, and of the lateral stability boundaries are presented as a series of simple straightforward steps. Existing methods for estimating the stability derivatives are summarized and, in some cases, simple new empirical formulas are presented. Detailed estimation methods are presented for low-subsonic-speed conditions but only a brief discussion and a list of references are given for transonic and supersonic speed conditions.

  16. Enhancing stability of industrial turbines using adjustable partial arc bearings

    NASA Astrophysics Data System (ADS)

    Chasalevris, Athanasios; Dohnal, Fadi

    2016-09-01

    The paper presents the principal of operation, the simulation and the characteristics of two partial-arc journal bearings of variable geometry and adjustable/controllable stiffness and damping properties. The proposed journals are supposed to consist of a scheme that enables the periodical variation of bearing properties. Recent achievements of suppressing rotor vibrations using plain circular journal bearings of variable geometry motivate the further extension of the principle to bearings of applicable geometry for industrial turbines. The paper describes the application of a partial-arc journal bearing to enhance stability of high speed industrial turbines. The proposed partial-arc bearings with adjustable/controllable properties enhance stability and they introduce stable margins in speeds much higher than the 1st critical.

  17. Biochemical stabilization enhances red blood cell recovery and stability following cryopreservation.

    PubMed

    Wagner, Christopher T; Martowicz, Melissa L; Livesey, Stephen A; Connor, Jerome

    2002-10-01

    Glycerolized red blood cells (RBC) are approved for long-term cryopreservation. However, the need to remove the glycerol cryoprotectant prior to transfusion has limited the usefulness of this cryopreservation method. This report describes using non-cryoprotectant biochemical stabilization techniques to substitute for the standard glycerol cryoprotectant. The glycerolized RBC method was compared to a newly developed LC-V method that combines transfusable cryoprotectants (hydroxyethyl starch and dextran) and specific non-cryoprotectant biochemical stabilizers (nicotinamide, nifedipine, and flurbiprofen). Results demonstrate that the biochemical stabilizers significantly reduce cryopreservation-induced hemolysis compared to cryopreservation in their absence and that thaw hemolysis levels approach those of standard 40% (w/v) glycerolized RBC (3.1+/-0.2% for 40% glycerol compared to 8.7+/-0.9% for the LC-V protocol). Furthermore, LC-V cryopreserved RBC exhibit a significantly enhanced post-thaw stability compared to glycerolized RBC as determined by osmotic fragility index (0.557+/-0.034 for 40% glycerol compared to 0.478+/-0.016 for the LC-V protocol). Analysis of biochemically stabilized RBC proteins revealed a transient translocation of carbonic anhydrase to the membrane fraction. However, the enhanced RBC recovery and stability could not be attributed to this event. Finally, DSC analysis demonstrated that the biochemical stabilizers of the LC-V process were not functioning as surrogate cryoprotectants in that they did not affect the quantity or quality of ice formed. Overall, this work demonstrates that cryopreservation-induced RBC damage may be corrected or prevented through specific biochemical stabilization and represents a significant step toward a directly transfusable cryopreserved RBC product.

  18. Subsonic Dynamic Stability Tests of a Sample Return Entry Vehicle

    NASA Technical Reports Server (NTRS)

    Fremaux, C. Michael; Johnson, R. Keith

    2006-01-01

    An investigation has been conducted in the NASA Langley 20-Foot Vertical Spin Tunnel (VST) to determine the subsonic dynamic stability characteristics of a proposed atmospheric entry vehicle for sample return missions. In particular, the effects of changes in aft-body geometry on stability were examined. Freeflying tests of a dynamically scaled model with various geometric features were conducted, including cases in which the model was perturbed to measure dynamic response. Both perturbed and non-perturbed runs were recorded as motion time histories using the VST optical data acquisition system and reduced for post-test analysis. In addition, preliminary results from a static force and moment test of a similar model in the Langley 12-Foot Low Speed Tunnel are presented. Results indicate that the configuration is dynamically stable for the baseline geometry, but exhibits degraded dynamic behavior for the geometry modifications tested.

  19. Enhanced catalyst stability for cyclic co methanation operations

    DOEpatents

    Risch, Alan P.; Rabo, Jule A.

    1983-01-01

    Carbon monoxide-containing gas streams are passed over a catalyst to deposit a surface layer of active surface carbon thereon essentially without the formation of inactive coke. The active carbon is thereafter reacted with steam or hydrogen to form methane. Enhanced catalyst stability for long term, cyclic operation is obtained by the incorporation of an alkali or alkaline earth dopant in a silica binding agent added to the catalyst-support additive composition.

  20. Enhanced Enzyme Kinetic Stability by Increasing Rigidity within the Active Site*

    PubMed Central

    Xie, Yuan; An, Jiao; Yang, Guangyu; Wu, Geng; Zhang, Yong; Cui, Li; Feng, Yan

    2014-01-01

    Enzyme stability is an important issue for protein engineers. Understanding how rigidity in the active site affects protein kinetic stability will provide new insight into enzyme stabilization. In this study, we demonstrated enhanced kinetic stability of Candida antarctica lipase B (CalB) by mutating the structurally flexible residues within the active site. Six residues within 10 Å of the catalytic Ser105 residue with a high B factor were selected for iterative saturation mutagenesis. After screening 2200 colonies, we obtained the D223G/L278M mutant, which exhibited a 13-fold increase in half-life at 48 °C and a 12 °C higher T5015, the temperature at which enzyme activity is reduced to 50% after a 15-min heat treatment. Further characterization showed that global unfolding resistance against both thermal and chemical denaturation also improved. Analysis of the crystal structures of wild-type CalB and the D223G/L278M mutant revealed that the latter formed an extra main chain hydrogen bond network with seven structurally coupled residues within the flexible α10 helix that are primarily involved in forming the active site. Further investigation of the relative B factor profile and molecular dynamics simulation confirmed that the enhanced rigidity decreased fluctuation of the active site residues at high temperature. These results indicate that enhancing the rigidity of the flexible segment within the active site may provide an efficient method for improving enzyme kinetic stability. PMID:24448805

  1. Dynamic Regulation of Schwann Cell Enhancers after Peripheral Nerve Injury*

    PubMed Central

    Hung, Holly A.; Sun, Guannan; Keles, Sunduz; Svaren, John

    2015-01-01

    Myelination of the peripheral nervous system is required for axonal function and long term stability. After peripheral nerve injury, Schwann cells transition from axon myelination to a demyelinated state that supports neuronal survival and ultimately remyelination of axons. Reprogramming of gene expression patterns during development and injury responses is shaped by the actions of distal regulatory elements that integrate the actions of multiple transcription factors. We used ChIP-seq to measure changes in histone H3K27 acetylation, a mark of active enhancers, to identify enhancers in myelinating rat peripheral nerve and their dynamics after demyelinating nerve injury. Analysis of injury-induced enhancers identified enriched motifs for c-Jun, a transcription factor required for Schwann cells to support nerve regeneration. We identify a c-Jun-bound enhancer in the gene for Runx2, a transcription factor induced after nerve injury, and we show that Runx2 is required for activation of other induced genes. In contrast, enhancers that lose H3K27ac after nerve injury are enriched for binding sites of the Sox10 and early growth response 2 (Egr2/Krox20) transcription factors, which are critical determinants of Schwann cell differentiation. Egr2 expression is lost after nerve injury, and many Egr2-binding sites lose H3K27ac after nerve injury. However, the majority of Egr2-bound enhancers retain H3K27ac, indicating that other transcription factors maintain active enhancer status after nerve injury. The global epigenomic changes in H3K27ac deposition pinpoint dynamic changes in enhancers that mediate the effects of transcription factors that control Schwann cell myelination and peripheral nervous system responses to nerve injury. PMID:25614629

  2. Structural dynamics, stability, and control of helicopters

    NASA Technical Reports Server (NTRS)

    Meirovitch, L.; Kraige, L. G.; Hale, A. L.

    1976-01-01

    The dynamic synthesis of a helicopter is reported. The method of approach is a variation of the component mode synthesis in the sense that it regards the aircraft as an assemblage of interconnected substructures. The equations of motion are derived in general form by means of the Lagrangian formulation in conjunction with an orderly kinematical procedure that takes into account the superposition of motion of various substructures, thus circumventing constraint problems.

  3. Dispersive Elements for Enhanced Laser Gyroscopy and Cavity Stabilization

    NASA Technical Reports Server (NTRS)

    Smith, David D.; Chang, Hongrok; Diels, J. C.

    2007-01-01

    We analyze the effect of a highly dispersive element placed inside a modulated optical cavity on the frequency and amplitude of the modulation to determine the conditions for cavity self-stabilization and enhanced gyroscopic sensitivity. We find an enhancement in the sensitivity of a laser gyroscope to rotation for normal dispersion, while anomalous dispersion can be used to self-stabilize an optical cavity. Our results indicate that atomic media, even coherent superpositions in multilevel atoms, are of limited use for these applications, because the amplitude and phase filters work against one another, i.e., decreasing the modulation frequency increases its amplitude and vice-versa. On the other hand, for optical resonators the dispersion reversal associated with critical coupling enables the amplitude and phase filters to work together. We find that for over-coupled resonators, the absorption and normal dispersion on-resonance increase the contrast and frequency of the beat-note, respectively, resulting in a substantial enhancement of the gyroscopic response. Under-coupled resonators can be used to stabilize the frequency of a laser cavity, but result in a concomitant increase in amplitude fluctuations. As a more ideal solution we propose the use of a variety of coupled-resonator-induced transparency that is accompanied by anomalous dispersion.

  4. Effects of asymmetry on the dynamic stability of aircraft

    NASA Technical Reports Server (NTRS)

    Fantino, R. E.; Parsons, E. K.; Powell, J. D.; Shevell, R. S.

    1975-01-01

    The oblique wing concept for transonic aircraft was proposed to reduce drag. The dynamic stability of the aircraft was investigated by analytically determining the stability derivatives at angles of skew ranging from 0 and 45 deg and using these stability derivatives in a linear analysis of the coupled aircraft behavior. The stability derivatives were obtained using a lifting line aerodynamic theory and found to give reasonable agreement with derivatives developed in a previous study for the same aircraft. In the dynamic analysis, no instability or large changes occurred in the root locations for skew angles varying from 0 to 45 deg with the exception of roll convergence. The damping in roll, however, decreased by an order of magnitude. Rolling was a prominent feature of all the oscillatory mode shapes at high skew angles.

  5. Dynamic stabilization of a coupled ultracold atom-molecule system.

    PubMed

    Li, Sheng-Chang; Ye, Chong

    2015-12-01

    We numerically demonstrate the dynamic stabilization of a strongly interacting many-body bosonic system which can be realized by coupled ultracold atom-molecule gases. The system is initialized to an unstable equilibrium state corresponding to a saddle point in the classical phase space, where subsequent free evolution gives rise to atom-molecule conversion. To control and stabilize the system, periodic modulation is applied that suddenly shifts the relative phase between the atomic and the molecular modes and limits their further interconversion. The stability diagram for the range of modulation amplitudes and periods that stabilize the dynamics is given. The validity of the phase diagram obtained from the time-average calculation is discussed by using the orbit tracking method, and the difference in contrast with the maximum absolute deviation analysis is shown as well. A brief quantum analysis shows that quantum fluctuations can put serious limitations on the applicability of the mean-field results. PMID:26764672

  6. Dynamic stabilization of a coupled ultracold atom-molecule system

    NASA Astrophysics Data System (ADS)

    Li, Sheng-Chang; Ye, Chong

    2015-12-01

    We numerically demonstrate the dynamic stabilization of a strongly interacting many-body bosonic system which can be realized by coupled ultracold atom-molecule gases. The system is initialized to an unstable equilibrium state corresponding to a saddle point in the classical phase space, where subsequent free evolution gives rise to atom-molecule conversion. To control and stabilize the system, periodic modulation is applied that suddenly shifts the relative phase between the atomic and the molecular modes and limits their further interconversion. The stability diagram for the range of modulation amplitudes and periods that stabilize the dynamics is given. The validity of the phase diagram obtained from the time-average calculation is discussed by using the orbit tracking method, and the difference in contrast with the maximum absolute deviation analysis is shown as well. A brief quantum analysis shows that quantum fluctuations can put serious limitations on the applicability of the mean-field results.

  7. Dynamic Stabilization of Expressed Proteins in Engineered Diatom Biosilica Matrices.

    PubMed

    Xiong, Yijia; Ford, Nicole R; Hecht, Karen A; Roesijadi, Guritno; Squier, Thomas C

    2016-05-18

    Self-assembly of recombinant proteins within the biosilica of living diatoms represents a means to construct functional materials in a reproducible and scalable manner that will enable applications that harness the inherent specificities of proteins to sense and respond to environmental cues. Here we describe the use of a silaffin-derived lysine-rich 39-amino-acid targeting sequence (Sil3T8) that directs a single chain fragment variable (scFv) antibody or an enhanced green fluorescent protein (EGFP) to assemble within the biosilica frustule, resulting in abundance of >200 000 proteins per frustule. Using either a fluorescent ligand bound to the scFv or the intrinsic fluorescence of EGFP, we monitored protein conformational dynamics, accessibility to external quenchers, binding affinity, and conformational stability. Like proteins in solution, proteins within isolated frustules undergo isotropic rotational motion, but with 2-fold increases in rotational correlation times that are indicative of weak macromolecular associations within the biosilica. Solvent accessibilities and high-affinity (pM) binding are comparable to those in solution. In contrast to solution conditions, scFv antibodies within the biosilica matrix retain their binding affinity in the presence of chaotropic agents (i.e., 8 M urea). Together, these results argue that dramatic increases in protein conformational stability within the biosilica matrices arise through molecular crowding, acting to retain native protein folds and associated functionality with the potential to allow the utility of engineered proteins under a range of harsh environmental conditions associated with environmental sensing and industrial catalytic transformations.

  8. Enhanced enzyme stability through site-directed covalent immobilization.

    PubMed

    Wu, Jeffrey Chun Yu; Hutchings, Christopher Hayden; Lindsay, Mark Jeffrey; Werner, Christopher James; Bundy, Bradley Charles

    2015-01-10

    Breakthroughs in enzyme immobilization have enabled increased enzyme recovery and reusability, leading to significant decreases in the cost of enzyme use and fueling biocatalysis growth. However, current enzyme immobilization techniques suffer from leaching, enzyme stability, and recoverability and reusability issues. Moreover, these techniques lack the ability to control the orientation of the immobilized enzymes. To determine the impact of orientation on covalently immobilized enzyme activity and stability, we apply our PRECISE (Protein Residue-Explicit Covalent Immobilization for Stability Enhancement) system to a model enzyme, T4 lysozyme. The PRECISE system uses non-canonical amino acid incorporation and the Huisgen 1,3-dipolar cycloaddition "click" reaction to enable directed enzyme immobilization at rationally chosen residues throughout an enzyme. Unlike previous site-specific systems, the PRECISE system is a truly covalent immobilization method. Utilizing this system, enzymes immobilized at proximate and distant locations from the active site were tested for activity and stability under denaturing conditions. Our results demonstrate that orientation control of covalently immobilized enzymes can provide activity and stability benefits exceeding that of traditional random covalent immobilization techniques. PRECISE immobilized enzymes were 50 and 73% more active than randomly immobilized enzymes after harsh freeze-thaw and chemical denaturant treatments.

  9. Nanodomain stabilization dynamics in plasma membranes of biological cells

    NASA Astrophysics Data System (ADS)

    Das, Tamal; Maiti, Tapas K.; Chakraborty, Suman

    2011-02-01

    We discover that a synergistically amplifying role of stabilizing membrane proteins and continuous lipid recycling can explain the physics governing the stability, polydispersity, and dynamics of lipid raft domains in plasma membranes of biological cells. We establish the conjecture using a generalized order parameter based on theoretical formalism, endorsed by detailed scaling arguments and domain mapping. Quantitative agreements with morphological distributions of raft complexes, as obtained from Förster resonance energy transfer based visualization, support the present theoretical conjecture.

  10. Solar Dynamic Power System Stability Analysis and Control

    NASA Technical Reports Server (NTRS)

    Momoh, James A.; Wang, Yanchun

    1996-01-01

    The objective of this research is to conduct dynamic analysis, control design, and control performance test of solar power system. Solar power system consists of generation system and distribution network system. A bench mark system is used in this research, which includes a generator with excitation system and governor, an ac/dc converter, six DDCU's and forty-eight loads. A detailed model is used for modeling generator. Excitation system is represented by a third order model. DDCU is represented by a seventh order system. The load is modeled by the combination of constant power and constant impedance. Eigen-analysis and eigen-sensitivity analysis are used for system dynamic analysis. The effects of excitation system, governor, ac/dc converter control, and the type of load on system stability are discussed. In order to improve system transient stability, nonlinear ac/dc converter control is introduced. The direct linearization method is used for control design. The dynamic analysis results show that these controls affect system stability in different ways. The parameter coordination of controllers are recommended based on the dynamic analysis. It is concluded from the present studies that system stability is improved by the coordination of control parameters and the nonlinear ac/dc converter control stabilize system oscillation caused by the load change and system fault efficiently.

  11. Pedicle Screw-Based Posterior Dynamic Stabilization: Literature Review

    PubMed Central

    Sengupta, Dilip K.; Herkowitz, Harry N.

    2012-01-01

    Posterior dynamic stabilization (PDS) indicates motion preservation devices that are aimed for surgical treatment of activity related mechanical low back pain. A large number of such devices have been introduced during the last 2 decades, without biomechanical design rationale, or clinical evidence of efficacy to address back pain. Implant failure is the commonest complication, which has resulted in withdrawal of some of the PDS devices from the market. In this paper the authors presented the current understanding of clinical instability of lumbar motions segment, proposed a classification, and described the clinical experience of the pedicle screw-based posterior dynamic stabilization devices. PMID:23227349

  12. Stability limits and dynamics of nonaxisymmetric liquid bridges

    NASA Technical Reports Server (NTRS)

    Alexander, J. Iwan D.; Resnik, Andy; Kaukler, William F.

    1993-01-01

    This program of theoretical and experimental ground-based and low gravity research is focussed on the understanding of the dynamics and stability limits of nonaxisymmetric liquid bridges. There are three basic objectives to the proposed work: (1) to determine the stability limits of nonaxisymmetric liquid bridges held between non-coaxially aligned disks; (2) to examine the dynamics of nonaxisymmetric bridges and nonaxisymmetric oscillations of initially axisymmetric bridges (some of these experiments require a low gravity environment and the ground-based research will culminate in a definitive flight experiment); and (3) to experimentally investigate the vibration sensitivity of liquid bridges under terrestrial and low gravity conditions.

  13. Control augmented structural synthesis with dynamic stability constraints

    NASA Technical Reports Server (NTRS)

    Thomas, H. L.; Schmit, L. A., Jr.

    1989-01-01

    Dynamic stability constraints are included in a computer program that simultaneously synthesizes a structure and its control system. Two measures of stability, the real part of the system complex eigenvalues and the damping ratio, are examined. The procedure for calculating the sensitivities of the two measures of stability to changes in the structure and its control system is explained. The sensitivities are used to formulate an approximate problem that is solved at each design iteration. The effects of structural damping and noncollated controllers on the synthesis process are discussed.

  14. Impacts of dispersal on rapid adaptation and dynamic stability of Daphnia in fluctuating environments.

    PubMed

    Steiner, Christopher F; Stockwell, Richard D; Tadros, Monica; Shaman, Laith; Patel, Komal; Khraizat, Laila

    2016-03-16

    Prior ecological research has shown that spatial processes can enhance the temporal stability of populations in fluctuating environments. Less explored is the effect of dispersal on rapid adaptation and its concomitant impact on population dynamics. For asexually reproducing populations, theory predicts that dispersal in fluctuating environments can facilitate asynchrony among clones and enhance stability by reducing temporal variability of total population abundance. This effect is predicted when clones exhibit heritable variation in environmental optima and when fluctuations occur asynchronously among patches. We tested this in the field using artificial ponds and metapopulations composed of a diverse assemblage of Daphnia pulex clones. We directly manipulated dispersal presence/absence and environmental fluctuations in the form of nutrient pulses. Consistent with predictions, dispersal enhanced temporal asynchrony among clones in the presence of nutrient pulses; this in turn stabilized population dynamics. This effect only emerged when patches experienced spatially asynchronous nutrient pulses (dispersal had no effect when patches were synchronously pulsed). Clonal asynchrony was driven by strong positive selection for a single clone that exhibited a performance advantage under conditions of low resource availability. Our work highlights the importance of dispersal as a driver of eco-evolutionary dynamics and population stability in variable environments.

  15. Enhanced photo-stability, thermal-stability and aqueous-stability of indocyanine green in polymeric nanoparticulate systems.

    PubMed

    Saxena, Vishal; Sadoqi, Mostafa; Shao, Jun

    2004-03-19

    Photo-degradation, thermal-degradation and aqueous-instability of indocyanine green (ICG) limits its application as a fluorescence contrast agent for imaging purposes. Thus, the objective of this study is to develop polymeric nanoparticles entrapping ICG and to establish its effectiveness in providing photo-stability, thermal stability and aqueous stability to ICG. Nanoparticles entrapping ICG were engineered, characterized and the degradation kinetics of ICG in the nanoparticles was investigated in aqueous media. The entrapment of ICG in the nanoparticles causes a shift in its wavelength of peak fluorescence and a decrease in its peak fluorescence intensity. The degradation of ICG in aqueous nanoparticle suspension followed first-order kinetics for the time period studied. ICG entrapment in the nanoparticles enhanced aqueous-stability of ICG (half-life, t(1/2) was 72.2+/-6.1 h for ICG in the nanoparticles as compared to 16.8+/-1.5 h for free ICG solution), photo-stability of ICG (t(1/2) was 73.7+/-7.5 h for ICG in the nanoparticles as compared to 14.4+/-2.4 h for free ICG solution when exposed to room light from two 32 W normal fluorescent tubes) and thermal-stability of ICG (t(1/2) of ICG at 42 degrees C was 62.4+/-1.7 h for ICG in the nanoparticles as compared to 10.1+/-0.6 h for free ICG solution).

  16. Computational Methods for Dynamic Stability and Control Derivatives

    NASA Technical Reports Server (NTRS)

    Green, Lawrence L.; Spence, Angela M.; Murphy, Patrick C.

    2004-01-01

    Force and moment measurements from an F-16XL during forced pitch oscillation tests result in dynamic stability derivatives, which are measured in combinations. Initial computational simulations of the motions and combined derivatives are attempted via a low-order, time-dependent panel method computational fluid dynamics code. The code dynamics are shown to be highly questionable for this application and the chosen configuration. However, three methods to computationally separate such combined dynamic stability derivatives are proposed. One of the separation techniques is demonstrated on the measured forced pitch oscillation data. Extensions of the separation techniques to yawing and rolling motions are discussed. In addition, the possibility of considering the angles of attack and sideslip state vector elements as distributed quantities, rather than point quantities, is introduced.

  17. Computational Methods for Dynamic Stability and Control Derivatives

    NASA Technical Reports Server (NTRS)

    Green, Lawrence L.; Spence, Angela M.; Murphy, Patrick C.

    2003-01-01

    Force and moment measurements from an F-16XL during forced pitch oscillation tests result in dynamic stability derivatives, which are measured in combinations. Initial computational simulations of the motions and combined derivatives are attempted via a low-order, time-dependent panel method computational fluid dynamics code. The code dynamics are shown to be highly questionable for this application and the chosen configuration. However, three methods to computationally separate such combined dynamic stability derivatives are proposed. One of the separation techniques is demonstrated on the measured forced pitch oscillation data. Extensions of the separation techniques to yawing and rolling motions are discussed. In addition, the possibility of considering the angles of attack and sideslip state vector elements as distributed quantities, rather than point quantities, is introduced.

  18. Enhancement of thermal stability in microwave applicators by mismatching and detuning

    SciTech Connect

    Nelson, E.M.

    1996-07-01

    Many microwave applicator systems experiencing thermal runaway can be stabilized by mismatching and/or detuning the system. The stability of the systems is discussed qualitatively and a conservative guide for adjusting microwave applicators for enhanced stability is described.

  19. Enhanced thermal stability of phosphate capped magnetite nanoparticles

    SciTech Connect

    Muthukumaran, T.; Philip, John

    2014-06-14

    We have studied the effect of phosphate capping on the high temperature thermal stability and magnetic properties of magnetite (Fe{sub 3}O{sub 4}) nanoparticles synthesized through a single-step co-precipitation method. The prepared magnetic nanoparticles are characterized using various techniques. When annealed in air, the phosphate capped nanoparticle undergoes a magnetic to non-magnetic phase transition at a temperature of 689 °C as compared to 580 °C in the uncoated nanoparticle of similar size. The observed high temperature phase stability of phosphate capped nanoparticle is attributed to the formation of a phosphocarbonaceous shell over the nanoparticles, which acts as a covalently attached protective layer and improves the thermal stability of the core material by increasing the activation energy. The phosphocarbonaceous shell prevents the intrusion of heat, oxygen, volatiles, and mass into the magnetic core. At higher temperatures, the coalescence of nanoparticles occurs along with the restructuring of the phosphocarbonaceous shell into a vitreous semisolid layer on the nanoparticles, which is confirmed from the small angle X-ray scattering, Fourier transform infra red spectroscopy, and transmission electron microscopy measurements. The probable mechanism for the enhancement of thermal stability of phosphocarbonaceous capped nanoparticles is discussed.

  20. Structural insight into the physical stability of amorphous Simvastatin dispersed in pHPMA: enhanced dynamics and local clustering as evidenced by solid-state NMR and Raman spectroscopy.

    PubMed

    Urbanova, Martina; Sturcova, Adriana; Kredatusova, Jana; Brus, Jiri

    2015-01-30

    New drug formulations are sought for poorly water-soluble substances because there is a risk of compromised bioavailability if such substances are administered orally. Such active pharmaceutical ingredients can be reformulated as solid dispersions with suitable water-soluble polymers. In this contribution, formulation of a novel and physically stable dispersion of Simvastatin in poly(2-hydroxypropyl) methacrylamide (pHPMA) is demonstrated. Due to the limited water sorption of pHPMA and a high Tg, the prepared dispersion is more suited for oral administration and storage compared with neat amorphous Simvastatin. Surprisingly, the rate of global reorientation and the internal motion of Simvastatin molecules were enhanced and exhibited dynamical heterogeneities when incorporated into the pHPMA matrix. As revealed by solid-state nuclear magnetic resonance combined with Raman spectroscopy exploiting the fluorescence phenomenon the mobility of the ester and lactone components increased considerably, whereas the naphthalene ring remained rigid. Furthermore, the solid dispersion was found to be nano-heterogeneous with nanometer-sized Simvastatin domains. The presence of these clusters had no impact on the dynamics of the rigid pHPMA chains. Thus, the diffusion of Simvastatin molecules through the glassy pHPMA walls and the subsequent transformation of the clusters into larger crystallites were prevented. No crystallization was detected for more than two years.

  1. Constraints on dynamic stability during forward, backward and lateral locomotion in skilled football players.

    PubMed

    Mehdizadeh, Sina; Arshi, Ahmed Reza; Davids, Keith

    2016-01-01

    The aim of this study was to investigate effects of speed and plane of motion on stability during locomotion in skilled football players. Ten male national-level football players participated in this study to run forward, backward and in lateral directions on a treadmill at 80%, 100% and 120% of their preferred running speeds. The coordinate data of passive reflective markers attached to body segments were recorded using motion capture systems. Time series data obtained from the ankle marker were used for further analyses. The largest finite-time Lyapunov exponent and maximum Floquet multiplier were adopted to quantify local and orbital dynamic stabilities, respectively. Results showed that speed did not significantly change local and orbital dynamic stabilities in any of running patterns. However, both local and orbital dynamic stability were significantly higher in the secondary plane of progression. Data revealed that in running, unlike walking, stability in the direction perpendicular to the direction of running is significantly higher, implying that less active control is required in the secondary plane of progression. The results of this study could be useful in sports training and rehabilitation programmes where development of fundamental exercise programmes that challenge both speed and the ability to maintain stability might produce a tangible enhancement of athletic skill level.

  2. Dynamic flight stability of a hovering model dragonfly.

    PubMed

    Liang, Bin; Sun, Mao

    2014-05-01

    The longitudinal dynamic flight stability of a model dragonfly at hovering flight is studied, using the method of computational fluid dynamics to compute the stability derivatives and the techniques of eigenvalue and eigenvector analysis for solving the equations of motion. Three natural modes of motion are identified for the hovering flight: one unstable oscillatory mode, one stable fast subsidence mode and one stable slow subsidence mode. The flight is dynamically unstable owing to the unstable oscillatory mode. The instability is caused by a pitch-moment derivative with respect to horizontal velocity. The damping force and moment derivatives (with respect to horizontal and vertical velocities and pitch-rotational velocity, respectively) weaken the instability considerably. The aerodynamic interaction between the forewing and the hindwing does not have significant effect on the stability properties. The dragonfly has similar stability derivatives, hence stability properties, to that of a one-wing-pair insect at normal hovering, but there are differences in how the derivatives are produced because of the highly inclined stroke plane of the dragonfly.

  3. Vesicle Stability and Dynamics: An Undergraduate Biochemistry Laboratory

    ERIC Educational Resources Information Center

    Del Bianco, Cristina; Torino, Domenica; Mansy, Sheref S.

    2014-01-01

    A laboratory exercise is described that helps students learn about lipid self-assembly by making vesicles under different solution conditions. Concepts covering the chemical properties of different lipids, the dynamics of lipids, and vesicle stability are explored. Further, the described protocol is easy and cheap to implement. One to two…

  4. Dynamic Stability Instrumentation System (DSIS). Volume 3; User Manual

    NASA Technical Reports Server (NTRS)

    Daniels, Taumi S.; Boyden, Richmond P.; Dress, David A.; Jordan, Thomas L.

    1996-01-01

    The paper is an operating manual for the Dynamic Stability Instrumentation System in specific NASA Langley wind tunnels. The instrumentation system performs either a synchronous demodulation or a Fast Fourier Transform on dynamic balance strain gage signals, and ultimately computes aerodynamic coefficients. The dynamic balance converts sting motor rotation into pitch or yaw plane or roll axis oscillation, with timing information provided by a shaft encoder. Additional instruments control model attitude and balance temperature and monitor sting vibrations. Other instruments perform self-calibration and diagnostics. Procedures for conducting calibrations and wind-off and wind-on tests are listed.

  5. Enhancement of charge ordering by dynamic electron-phonon interaction

    NASA Astrophysics Data System (ADS)

    Singer, Andrej; Fullerton, Eric; Shpyrko, Oleg

    Symmetry breaking and emergence of order is one of the most fascinating phenomena in condensed matter physics and leads to a plethora of intriguing ground states such as in antiferromagnets, Mott insulators, superconductors, and density-wave systems. Exploiting non-equilibrium dynamics of matter following ultrafast external excitation can provide even more striking routes to symmetry-lowered, ordered states, for instance, by accessing hidden equilibrium states in the free-energy landscape or dynamic stabilization of non-equilibrium states. This is remarkable because ultrafast excitation typically creates disorder, reduces the order parameter, and raises the symmetry. Here, we demonstrate for the case of antiferromagnetic chromium that moderate photo-excitation can transiently enhance the charge-density-wave (CDW) order by up to 30% above its equilibrium value, while strong excitation leads to an oscillating, large-amplitude CDW state that persists above the equilibrium transition temperature. Both effects result from dynamic electron-phonon interaction, which provides an efficient mechanism to selectively transform a broad excitation of the electronic order into a well defined, long-lived coherent lattice vibration. This mechanism may be exploited to transiently enhance the order parameter in other systems with coupled electronic and lattice orders. The data was collected at the x-ray free electron laser LCLS at SLAC.

  6. Dynamic Stability of Uncertain Laminated Beams Under Subtangential Loads

    NASA Technical Reports Server (NTRS)

    Goyal, Vijay K.; Kapania, Rakesh K.; Adelman, Howard (Technical Monitor); Horta, Lucas (Technical Monitor)

    2002-01-01

    Because of the inherent complexity of fiber-reinforced laminated composites, it can be challenging to manufacture composite structures according to their exact design specifications, resulting in unwanted material and geometric uncertainties. In this research, we focus on the deterministic and probabilistic stability analysis of laminated structures subject to subtangential loading, a combination of conservative and nonconservative tangential loads, using the dynamic criterion. Thus a shear-deformable laminated beam element, including warping effects, is derived to study the deterministic and probabilistic response of laminated beams. This twenty-one degrees of freedom element can be used for solving both static and dynamic problems. In the first-order shear deformable model used here we have employed a more accurate method to obtain the transverse shear correction factor. The dynamic version of the principle of virtual work for laminated composites is expressed in its nondimensional form and the element tangent stiffness and mass matrices are obtained using analytical integration The stability is studied by giving the structure a small disturbance about an equilibrium configuration, and observing if the resulting response remains small. In order to study the dynamic behavior by including uncertainties into the problem, three models were developed: Exact Monte Carlo Simulation, Sensitivity Based Monte Carlo Simulation, and Probabilistic FEA. These methods were integrated into the developed finite element analysis. Also, perturbation and sensitivity analysis have been used to study nonconservative problems, as well as to study the stability analysis, using the dynamic criterion.

  7. Dynamic nuclear polarization surface enhanced NMR spectroscopy.

    PubMed

    Rossini, Aaron J; Zagdoun, Alexandre; Lelli, Moreno; Lesage, Anne; Copéret, Christophe; Emsley, Lyndon

    2013-09-17

    Many of the functions and applications of advanced materials result from their interfacial structures and properties. However, the difficulty in characterizing the surface structure of these materials at an atomic level can often slow their further development. Solid-state NMR can probe surface structure and complement established surface science techniques, but its low sensitivity often limits its application. Many materials have low surface areas and/or low concentrations of active/surface sites. Dynamic nuclear polarization (DNP) is one intriguing method to enhance the sensitivity of solid-state NMR experiments by several orders of magnitude. In a DNP experiment, the large polarization of unpaired electrons is transferred to surrounding nuclei, which provides a maximum theoretical DNP enhancement of ∼658 for (1)H NMR. In this Account, we discuss the application of DNP to enhance surface NMR signals, an approach known as DNP surface enhanced NMR spectroscopy (DNP SENS). Enabling DNP for these systems requires bringing an exogeneous radical solution into contact with surfaces without diluting the sample. We proposed the incipient wetness impregnation technique (IWI), a well-known method in materials science, to impregnate porous and particulate materials with just enough radical containing solution to fill the porous volume. IWI offers several advantages: it is extremely simple, provides a uniform wetting of the surface, and does not increase the sample volume or substantially reduce the concentration of the sample. This Account describes the basic principles behind DNP SENS through results obtained for mesoporous and nanoparticulate samples impregnated with radical solutions. We also discuss the quantification of the overall sensitivity enhancements obtained with DNP SENS and compare that with ordinary room temperature NMR spectroscopy. We then review the development of radicals and solvents that give the best possible enhancements today. With the best

  8. Dynamic response and stability analysis of flexible, multibody systems. [spacecraft

    NASA Technical Reports Server (NTRS)

    Bodley, C. S.; Park, A. C.; Devers, A. D.; Frisch, H. P.

    1977-01-01

    A general version of Lagrange's equations, including auxiliary nonholonomic, rheonomic conditions of constraint, is used in the dynamic simulation and stability analysis of interconnected flexible bodies. Modeling of the nonlinear flexible/rigid dynamic coupling effects, the interaction forces/torques, and the elastic deformation effects is discussed. A digital computer program is developed to obtain time-domain solution for the nonlinear response of systems represented as a collection of individual bodies, numerical linearization of system-governing equations, time-domain solution for the perturbation response about a nominal state, and a frequency-domain stability analysis corresponding to the linearization. The digital simulation code is employed to study the dynamic behavior of a typical satellite and a spacecraft with deployable experiment booms.

  9. Stability of complex Langevin dynamics in effective models

    NASA Astrophysics Data System (ADS)

    Aarts, Gert; James, Frank A.; Pawlowski, Jan M.; Seiler, Erhard; Sexty, Dénes; Stamatescu, Ion-Olimpiu

    2013-03-01

    The sign problem at nonzero chemical potential prohibits the use of importance sampling in lattice simulations. Since complex Langevin dynamics does not rely on importance sampling, it provides a potential solution. Recently it was shown that complex Langevin dynamics fails in the disordered phase in the case of the three-dimensional XY model, while it appears to work in the entire phase diagram in the case of the three-dimensional SU(3) spin model. Here we analyse this difference and argue that it is due to the presence of the nontrivial Haar measure in the SU(3) case, which has a stabilizing effect on the complexified dynamics. The freedom to modify and stabilize the complex Langevin process is discussed in some detail.

  10. Structural and dynamic properties that govern the stability of an engineered fibronectin type III domain.

    PubMed

    Porebski, Benjamin T; Nickson, Adrian A; Hoke, David E; Hunter, Morag R; Zhu, Liguang; McGowan, Sheena; Webb, Geoffrey I; Buckle, Ashley M

    2015-03-01

    Consensus protein design is a rapid and reliable technique for the improvement of protein stability, which relies on the use of homologous protein sequences. To enhance the stability of a fibronectin type III (FN3) domain, consensus design was employed using an alignment of 2123 sequences. The resulting FN3 domain, FN3con, has unprecedented stability, with a melting temperature >100°C, a ΔG(D-N) of 15.5 kcal mol(-1) and a greatly reduced unfolding rate compared with wild-type. To determine the underlying molecular basis for stability, an X-ray crystal structure of FN3con was determined to 2.0 Å and compared with other FN3 domains of varying stabilities. The structure of FN3con reveals significantly increased salt bridge interactions that are cooperatively networked, and a highly optimized hydrophobic core. Molecular dynamics simulations of FN3con and comparison structures show the cooperative power of electrostatic and hydrophobic networks in improving FN3con stability. Taken together, our data reveal that FN3con stability does not result from a single mechanism, but rather the combination of several features and the removal of non-conserved, unfavorable interactions. The large number of sequences employed in this study has most likely enhanced the robustness of the consensus design, which is now possible due to the increased sequence availability in the post-genomic era. These studies increase our knowledge of the molecular mechanisms that govern stability and demonstrate the rising potential for enhancing stability via the consensus method.

  11. Structural and dynamic properties that govern the stability of an engineered fibronectin type III domain

    PubMed Central

    Porebski, Benjamin T.; Nickson, Adrian A.; Hoke, David E.; Hunter, Morag R.; Zhu, Liguang; McGowan, Sheena; Webb, Geoffrey I.; Buckle, Ashley M.

    2015-01-01

    Consensus protein design is a rapid and reliable technique for the improvement of protein stability, which relies on the use of homologous protein sequences. To enhance the stability of a fibronectin type III (FN3) domain, consensus design was employed using an alignment of 2123 sequences. The resulting FN3 domain, FN3con, has unprecedented stability, with a melting temperature >100°C, a ΔGD−N of 15.5 kcal mol−1 and a greatly reduced unfolding rate compared with wild-type. To determine the underlying molecular basis for stability, an X-ray crystal structure of FN3con was determined to 2.0 Å and compared with other FN3 domains of varying stabilities. The structure of FN3con reveals significantly increased salt bridge interactions that are cooperatively networked, and a highly optimized hydrophobic core. Molecular dynamics simulations of FN3con and comparison structures show the cooperative power of electrostatic and hydrophobic networks in improving FN3con stability. Taken together, our data reveal that FN3con stability does not result from a single mechanism, but rather the combination of several features and the removal of non-conserved, unfavorable interactions. The large number of sequences employed in this study has most likely enhanced the robustness of the consensus design, which is now possible due to the increased sequence availability in the post-genomic era. These studies increase our knowledge of the molecular mechanisms that govern stability and demonstrate the rising potential for enhancing stability via the consensus method. PMID:25691761

  12. Dramatic pressure-driven enhancement of bulk skyrmion stability.

    PubMed

    Levatić, I; Popčević, P; Šurija, V; Kruchkov, A; Berger, H; Magrez, A; White, J S; Rønnow, H M; Živković, I

    2016-01-01

    The recent discovery of magnetic skyrmion lattices initiated a surge of interest in the scientific community. Several novel phenomena have been shown to emerge from the interaction of conducting electrons with the skyrmion lattice, such as a topological Hall-effect and a spin-transfer torque at ultra-low current densities. In the insulating compound Cu2OSeO3, magneto-electric coupling enables control of the skyrmion lattice via electric fields, promising a dissipation-less route towards novel spintronic devices. One of the outstanding fundamental issues is related to the thermodynamic stability of the skyrmion lattice. To date, the skyrmion lattice in bulk materials has been found only in a narrow temperature region just below the order-disorder transition. If this narrow stability is unavoidable, it would severely limit applications. Here we present the discovery that applying just moderate pressure on Cu2OSeO3 substantially increases the absolute size of the skyrmion pocket. This insight demonstrates directly that tuning the electronic structure can lead to a significant enhancement of the skyrmion lattice stability. We interpret the discovery by extending the previously employed Ginzburg-Landau approach and conclude that change in the anisotropy is the main driver for control of the size of the skyrmion pocket. PMID:26892190

  13. Dramatic pressure-driven enhancement of bulk skyrmion stability

    PubMed Central

    Levatić, I.; Popčević, P.; Šurija, V.; Kruchkov, A.; Berger, H.; Magrez, A.; White, J. S.; Rønnow, H. M.; Živković, I.

    2016-01-01

    The recent discovery of magnetic skyrmion lattices initiated a surge of interest in the scientific community. Several novel phenomena have been shown to emerge from the interaction of conducting electrons with the skyrmion lattice, such as a topological Hall-effect and a spin-transfer torque at ultra-low current densities. In the insulating compound Cu2OSeO3, magneto-electric coupling enables control of the skyrmion lattice via electric fields, promising a dissipation-less route towards novel spintronic devices. One of the outstanding fundamental issues is related to the thermodynamic stability of the skyrmion lattice. To date, the skyrmion lattice in bulk materials has been found only in a narrow temperature region just below the order-disorder transition. If this narrow stability is unavoidable, it would severely limit applications. Here we present the discovery that applying just moderate pressure on Cu2OSeO3 substantially increases the absolute size of the skyrmion pocket. This insight demonstrates directly that tuning the electronic structure can lead to a significant enhancement of the skyrmion lattice stability. We interpret the discovery by extending the previously employed Ginzburg-Landau approach and conclude that change in the anisotropy is the main driver for control of the size of the skyrmion pocket. PMID:26892190

  14. Method for enhancing stability in multi-beam microscopy

    NASA Astrophysics Data System (ADS)

    Huang, Yujia; Wang, Yifan; Kuang, Cuifang; Liu, Xu

    2016-10-01

    A method based on close loop control of four degrees of freedom (4DF) is proposed to enhance angular and translational stability of beams in multi-beam microscopy including STED, RESOLFT and CARS, etc. Deviations of multi-beams can be measured and corrected by our module, which is composed of four degrees of freedom position sensitive detectors (4DF PSD) and two actuator mirrors (AM) with motor and piezo servos. An output crosslink matrix obtained by a self-learning process is used to control four actuators to compensate for 4DF independently in beam deviations. We realize a standard deviation within about 2 µm at the entrance pupil plane (a spatial optical path of 180 cm for the whole system) using a compact stabilization system, which is equivalent to around 3 nm at the sample plane under the 100×  objective lens with a focal length of 2 mm, corresponding to an improvement of stability by an order of magnitude. Our method can react fast in real time and compensate for large disturbances caused by air agitation or temperature variation.

  15. Glucocorticoids enhance stability of human growth hormone mRNA.

    PubMed Central

    Paek, I; Axel, R

    1987-01-01

    We have studied the control of expression of the human growth hormone (hGH) gene introduced into the chromosomes of mouse fibroblasts. Cell lines transformed with the hGH gene expressed low levels of intact hGH mRNA and secreted hGH protein into the medium. Although the level of expression of hGH mRNA was low, the gene remained responsive to induction by glucocorticoid hormones. To localize the sequences responsible for induction and to determine the mechanism by which these cis-acting sequences enhance gene expression, we have constructed a series of fusion genes between the hGH gene and the herpes simplex virus (HSV) thymidine kinase (tk) gene. We have demonstrated that a fusion gene in which hGH cDNA is flanked at its 5' terminus by an HSV tk promoter and is flanked at its 3' terminus by 3' HSV tk DNA remains inducible by glucocorticoids. Our studies indicate that the hGH exons contain sequences which are responsible for glucocorticoid hormone induction. Pulse-chase experiments, in vitro nuclear transcription, and approach to steady-state measurements indicate that the mechanisms responsible for induction of the hGH cDNA fusion gene operate posttranscriptionally to enhance the stability of hGH mRNA. Moreover, this increased stability was associated with an increase in the length of the 3' poly(A) tail on hGH mRNA. Images PMID:3037323

  16. Dynamical behavior and Jacobi stability analysis of wound strings

    NASA Astrophysics Data System (ADS)

    Lake, Matthew J.; Harko, Tiberiu

    2016-06-01

    We numerically solve the equations of motion (EOM) for two models of circular cosmic string loops with windings in a simply connected internal space. Since the windings cannot be topologically stabilized, stability must be achieved (if at all) dynamically. As toy models for realistic compactifications, we consider windings on a small section of mathbb {R}^2, which is valid as an approximation to any simply connected internal manifold if the winding radius is sufficiently small, and windings on an S^2 of constant radius mathcal {R}. We then use Kosambi-Cartan-Chern (KCC) theory to analyze the Jacobi stability of the string equations and determine bounds on the physical parameters that ensure dynamical stability of the windings. We find that, for the same initial conditions, the curvature and topology of the internal space have nontrivial effects on the microscopic behavior of the string in the higher dimensions, but that the macroscopic behavior is remarkably insensitive to the details of the motion in the compact space. This suggests that higher-dimensional signatures may be extremely difficult to detect in the effective (3+1)-dimensional dynamics of strings compactified on an internal space, even if configurations with nontrivial windings persist over long time periods.

  17. Summary of Methods for Calculating Dynamic Lateral Stability and Response and for Estimating Lateral Stability Derivatives

    NASA Technical Reports Server (NTRS)

    Campbell, John P; Mckinney, Marion O

    1951-01-01

    A summary of methods for making dynamic lateral stability and response calculations and for estimating the aerodynamic stability derivatives required for use in these calculations is presented. The processes of performing calculations of the time histories of lateral motions, of the period and damping of these motions, and of the lateral stability boundaries are presented as a series of simple straightforward steps. Existing methods for estimating the stability derivatives are summarized and, in some cases, simple new empirical formulas are presented. Reference is also made to reports presenting experimental data that should be useful in making estimates of the derivatives. Detailed estimating methods are presented for low-subsonic-speed conditions but only a brief discussion and a list of references are given for transonic- and supersonic-speed conditions.

  18. On the dynamics of turbulent transport near marginal stability

    SciTech Connect

    Diamond, P.H. |; Hahm, T.S.

    1995-03-01

    A general methodology for describing the dynamics of transport near marginal stability is formulated. Marginal stability is a special case of the more general phenomenon of self-organized criticality. Simple, one field models of the dynamics of tokamak plasma self-organized criticality have been constructed, and include relevant features such as sheared mean flow and transport bifurcations. In such models, slow mode (i.e. large scale, low frequency transport events) correlation times determine the behavior of transport dynamics near marginal stability. To illustrate this, impulse response scaling exponents (z) and turbulent diffusivities (D) have been calculated for the minimal (Burgers) and sheared flow models. For the minimal model, z = 1 (indicating ballastic propagation) and D {approximately}(S{sub 0}{sup 2}){sup 1/3}, where S{sub 0}{sup 2} is the noise strength. With an identically structured noise spectrum and flow with shearing rate exceeding the ambient decorrelation rate for the largest scale transport events, diffusion is recovered with z = 2 and D {approximately} (S{sub 0}{sup 2}){sup 3/5}. This indicates a qualitative change in the dynamics, as well as a reduction in losses. These results are consistent with recent findings from {rho} scaling scans. Several tokamak transport experiments are suggested.

  19. Stability Limits and Dynamics of Nonaxisymmetric Liquid Bridges

    NASA Technical Reports Server (NTRS)

    Alexander, J. Iwan D.

    1998-01-01

    Theoretical and experimental investigation of the stability of nonaxisymmetric and nonaxisymmetric bridges contained between equal and unequal radii disks as a function of Bond and Weber number with emphasis on the transition from unstable axisymmetric to stable nonaxisymmetric shapes. Numerical analysis of the stability of nonaxisymmetric bridges for various orientations of the gravity vector for equal and unequal disks. Experimental and theoretical investigation of large (nonaxisymmetric) oscillations and breaking of liquid bridges. This project involves both experimental and theoretical work. Static and dynamic experiments are conducted in a Plateau tank which makes a range of static Bond numbers accessible.

  20. Fluid Dynamic and Stability Analysis of a Thin Liquid Sheet

    NASA Technical Reports Server (NTRS)

    McMaster, Matthew S.

    1992-01-01

    Interest in thin sheet flows has recently been renewed due to their potential application in space radiators. Theoretical and experimental studies of the fluid dynamics and stability of thin liquid sheet flows have been carried out in this thesis. A computer program was developed to determine the cross-sectional shape of the edge cylinder given the cross-sectional area of the edge cylinder. A stability analysis was performed on a non-planer liquid sheet. A study was conducted to determine the effects of air resistance on the sheet.

  1. Stabilization of computational procedures for constrained dynamical systems

    NASA Technical Reports Server (NTRS)

    Park, K. C.; Chiou, J. C.

    1988-01-01

    A new stabilization method of treating constraints in multibody dynamical systems is presented. By tailoring a penalty form of the constraint equations, the method achieves stabilization without artificial damping and yields a companion matrix differential equation for the constraint forces; hence, the constraint forces are obtained by integrating the companion differential equation for the constraint forces in time. A principal feature of the method is that the errors committed in each constraint condition decay with its corresponding characteristic time scale associated with its constraint force. Numerical experiments indicate that the method yields a marked improvement over existing techniques.

  2. Dynamics and Adaptive Control for Stability Recovery of Damaged Aircraft

    NASA Technical Reports Server (NTRS)

    Nguyen, Nhan; Krishnakumar, Kalmanje; Kaneshige, John; Nespeca, Pascal

    2006-01-01

    This paper presents a recent study of a damaged generic transport model as part of a NASA research project to investigate adaptive control methods for stability recovery of damaged aircraft operating in off-nominal flight conditions under damage and or failures. Aerodynamic modeling of damage effects is performed using an aerodynamic code to assess changes in the stability and control derivatives of a generic transport aircraft. Certain types of damage such as damage to one of the wings or horizontal stabilizers can cause the aircraft to become asymmetric, thus resulting in a coupling between the longitudinal and lateral motions. Flight dynamics for a general asymmetric aircraft is derived to account for changes in the center of gravity that can compromise the stability of the damaged aircraft. An iterative trim analysis for the translational motion is developed to refine the trim procedure by accounting for the effects of the control surface deflection. A hybrid direct-indirect neural network, adaptive flight control is proposed as an adaptive law for stabilizing the rotational motion of the damaged aircraft. The indirect adaptation is designed to estimate the plant dynamics of the damaged aircraft in conjunction with the direct adaptation that computes the control augmentation. Two approaches are presented 1) an adaptive law derived from the Lyapunov stability theory to ensure that the signals are bounded, and 2) a recursive least-square method for parameter identification. A hardware-in-the-loop simulation is conducted and demonstrates the effectiveness of the direct neural network adaptive flight control in the stability recovery of the damaged aircraft. A preliminary simulation of the hybrid adaptive flight control has been performed and initial data have shown the effectiveness of the proposed hybrid approach. Future work will include further investigations and high-fidelity simulations of the proposed hybrid adaptive Bight control approach.

  3. Numerical stability in multifluid gas dynamics with implicit drag forces

    NASA Astrophysics Data System (ADS)

    Ramshaw, J. D.; Chang, C. H.

    2015-10-01

    The numerical stability of a conventional explicit numerical scheme for solving the inviscid multifluid dynamical equations describing a multicomponent gas mixture is investigated both analytically and computationally. Although these equations do not explicitly contain diffusion terms, it is well known that they reduce to a single-fluid diffusional description when the drag coefficients in the species momentum equations are large. The question then arises as to whether their numerical solution is subject to a diffusional stability restriction on the time step in addition to the usual Courant sound-speed stability condition. An analytical stability analysis is performed for the special case of a quiescent binary gas mixture with equal sound speeds and temperatures. It is found that the Courant condition is always sufficient to ensure stability, so that no additional diffusional stability restriction arises for any value of the drag coefficient, however large. This result is confirmed by one-dimensional computational results for binary and ternary mixtures with unequal sound speeds, which remain stable even when the time step exceeds the usual diffusional limit by factors of order 100.

  4. Lipid Cross-Linking of Nanolipoprotein Particles Substantially Enhances Serum Stability and Cellular Uptake.

    PubMed

    Gilmore, Sean F; Blanchette, Craig D; Scharadin, Tiffany M; Hura, Greg L; Rasley, Amy; Corzett, Michele; Pan, Chong-Xian; Fischer, Nicholas O; Henderson, Paul T

    2016-08-17

    Nanolipoprotein particles (NLPs) consist of a discoidal phospholipid lipid bilayer confined by an apolipoprotein belt. NLPs are a promising platform for a variety of biomedical applications due to their biocompatibility, size, definable composition, and amphipathic characteristics. However, poor serum stability hampers the use of NLPs for in vivo applications such as drug formulation. In this study, NLP stability was enhanced upon the incorporation and subsequent UV-mediated intermolecular cross-linking of photoactive DiynePC phospholipids in the lipid bilayer, forming cross-linked nanoparticles (X-NLPs). Both the concentration of DiynePC in the bilayer and UV exposure time significantly affected the resulting X-NLP stability in 100% serum, as assessed by size exclusion chromatography (SEC) of fluorescently labeled particles. Cross-linking did not significantly impact the size of X-NLPs as determined by dynamic light scattering and SEC. X-NLPs had essentially no degradation over 48 h in 100% serum, which is a drastic improvement compared to non-cross-linked NLPs (50% degradation by ∼10 min). X-NLPs had greater uptake into the human ATCC 5637 bladder cancer cell line compared to non-cross-linked particles, indicating their potential utility for targeted drug delivery. X-NLPs also exhibited enhanced stability following intravenous administration in mice. These results collectively support the potential utility of X-NLPs for a variety of in vivo applications. PMID:27411034

  5. Distributed Multi-Agent-Based Protection Scheme for Transient Stability Enhancement in Power Systems

    NASA Astrophysics Data System (ADS)

    Rahman, M. S.; Mahmud, M. A.; Pota, H. R.; Hossain, M. J.; Orchi, T. F.

    2015-04-01

    This paper presents a new distributed agent-based scheme to enhance the transient stability of power systems by maintaining phase angle cohesiveness of interconnected generators through proper relay coordination with critical clearing time (CCT) information. In this distributed multi-agent infrastructure, intelligent agents represent various physical device models to provide dynamic information and energy flow among different physical processes of power systems. The agents can communicate with each other in a distributed manner with a final aim to control circuit breakers (CBs) with CCT information as this is the key issue for maintaining and enhancing the transient stability of power systems. The performance of the proposed scheme is evaluated on a standard IEEE 39-bus New England benchmark system under different large disturbances such as three-phase short-circuit faults and changes in loads within the systems. From the simulation results, it is found that the proposed scheme significantly enhances the transient stability of power systems as compared to a conventional scheme of static CB operation.

  6. Stability Enhancement of Polymeric Sensing Films Using Fillers

    NASA Technical Reports Server (NTRS)

    Lin, Brian; Shevade, Abhijit; Ryan, Margaret Amy; Kisor, Adam; Yen, Shiao-Pin; Manatt, Kenneth; Homer, Margie; Fleurial, Jean-Pierre

    2006-01-01

    Experiments have shown the stability enhancement of polymeric sensing films on mixing the polymer with colloidal filler particles (submicron-sized) of carbon black, silver, titanium dioxide, and fumed silicon dioxide. The polymer films are candidates for potential use as sensing media in micro/nano chemical sensor devices. The need for stability enhancement of polymer sensing films arises because such films have been found to exhibit unpredictable changes in sensing activity over time, which could result in a possible failure of the sensor device. The changes in the physical properties of a polymer sensing film caused by the sorption of a target molecule can be measured by any of several established transduction techniques: electrochemical, optical, calorimetric, or piezoelectric, for example. The transduction technique used in the current polymer stability experiments is based on piezoelectric principles using a quartz-crystal microbalance (QCM). The surface of the QCM is coated with the polymer, and the mass uptake by the polymer film causes a change in the oscillating frequency of the quartz crystal. The polymer used for the current study is ethyl cellulose. The polymer/ polymer composite solutions were prepared in 1,3 dioxolane solvent. The filler concentration was fixed at 10 weight percent for the composites. The polymer or polymer composite solutions were cast on the quartz crystal having a fundamental frequency of about 6 MHz. The coated crystal was subjected to a multistage drying process to remove all measurable traces of the solvent. In each experiment, the frequency of oscillation was measured while the QCM was exposed to clean, dry, flowing air for about 30 minutes, then to air containing a known concentration of isopropanol for about 30 minutes, then again to clean dry air for about 30 minutes, and so forth. This cycle of measurements for varying isopropanol concentrations was repeated at intervals for several months. The figure depicts some of the

  7. Conditional random matrix ensembles and the stability of dynamical systems

    NASA Astrophysics Data System (ADS)

    Kirk, Paul; Rolando, Delphine M. Y.; MacLean, Adam L.; Stumpf, Michael P. H.

    2015-08-01

    Random matrix theory (RMT) has found applications throughout physics and applied mathematics, in subject areas as diverse as communications networks, population dynamics, neuroscience, and models of the banking system. Many of these analyses exploit elegant analytical results, particularly the circular law and its extensions. In order to apply these results, assumptions must be made about the distribution of matrix elements. Here we demonstrate that the choice of matrix distribution is crucial. In particular, adopting an unrealistic matrix distribution for the sake of analytical tractability is liable to lead to misleading conclusions. We focus on the application of RMT to the long-standing, and at times fractious, ‘diversity-stability debate’, which is concerned with establishing whether large complex systems are likely to be stable. Early work (and subsequent elaborations) brought RMT to bear on the debate by modelling the entries of a system’s Jacobian matrix as independent and identically distributed (i.i.d.) random variables. These analyses were successful in yielding general results that were not tied to any specific system, but relied upon a restrictive i.i.d. assumption. Other studies took an opposing approach, seeking to elucidate general principles of stability through the analysis of specific systems. Here we develop a statistical framework that reconciles these two contrasting approaches. We use a range of illustrative dynamical systems examples to demonstrate that: (i) stability probability cannot be summarily deduced from any single property of the system (e.g. its diversity); and (ii) our assessment of stability depends on adequately capturing the details of the systems analysed. Failing to condition on the structure of dynamical systems will skew our analysis and can, even for very small systems, result in an unnecessarily pessimistic diagnosis of their stability.

  8. Facet joint changes after application of lumbar nonfusion dynamic stabilization.

    PubMed

    Lee, Soo Eon; Jahng, Tae-Ahn; Kim, Hyun Jib

    2016-01-01

    OBJECTIVE The long-term effects on adjacent-segment pathology after nonfusion dynamic stabilization is unclear, and, in particular, changes at the adjacent facet joints have not been reported in a clinical study. This study aims to compare changes in the adjacent facet joints after lumbar spinal surgery. METHODS Patients who underwent monosegmental surgery at L4-5 with nonfusion dynamic stabilization using the Dynesys system (Dynesys group) or transforaminal lumbar interbody fusion with pedicle screw fixation (fusion group) were retrospectively compared. Facet joint degeneration was evaluated at each segment using the CT grading system. RESULTS The Dynesys group included 15 patients, while the fusion group included 22 patients. The preoperative facet joint degeneration CT grades were not different between the 2 groups. Compared with the preoperative CT grades, 1 side of the facet joints at L3-4 and L4-5 had significantly more degeneration in the Dynesys group. In the fusion group, significant facet joint degeneration developed on both sides at L2-3, L3-4, and L5-S1. The subjective back and leg pain scores were not different between the 2 groups during follow-up, but functional outcome based on the Oswestry Disability Index improved less in the fusion group than in the Dynesys group. CONCLUSIONS Nonfusion dynamic stabilization using the Dynesys system had a greater preventative effect on facet joint degeneration in comparison with that obtained using fusion surgery. The Dynesys system, however, resulted in facet joint degeneration at the instrumented segments and above. An improved physiological nonfusion dynamic stabilization system for lumbar spinal surgery should be developed.

  9. Dynamic stabilization for degenerative spondylolisthesis and lumbar spinal instability.

    PubMed

    Ohtonari, Tatsuya; Nishihara, Nobuharu; Suwa, Katsuyasu; Ota, Taisei; Koyama, Tsunemaro

    2014-01-01

    Lumbar interbody fusion is a widely accepted surgical procedure for patients with lumbar degenerative spondylolisthesis and lumbar spinal instability in the active age group. However, in elderly patients, it is often questionable whether it is truly necessary to construct rigid fixation for a short period of time. In recent years, we have been occasionally performing posterior dynamic stabilization in elderly patients with such lumbar disorders. Posterior dynamic stabilization was performed in 12 patients (6 women, 70.9 ± 5.6 years old at the time of operation) with lumbar degenerative spondylolisthesis in whom % slip was less than 20% or instability associated with lumbar disc herniation between March 2011 and March 2013. Movement occurs through the connector linked to the pedicle screw. In practice, 9 pairs of D connector system where the rod moves in the perpendicular direction alone and 8 pairs of Dynamic connector system where the connector linked to the pedicle screw rotates in the sagittal direction were installed. The observation period was 77-479 days, and the mean recovery rate of lumbar Japanese Orthopedic Association (JOA) score was 65.6 ± 20.8%. There was progression of slippage due to slight loosening in a case with lumbar degenerative spondylolisthesis, but this did not lead to exacerbation of the symptoms. Although follow-up was short, there were no symptomatic adjacent vertebral and disc disorders during this period. Posterior dynamic stabilization may diminish the development of adjacent vertebral or disc disorders due to lumbar interbody fusion, especially in elderly patients, and it may be a useful procedure that facilitates decompression and ensures a certain degree of spinal stabilization.

  10. Dynamic remedial action scheme using online transient stability analysis

    NASA Astrophysics Data System (ADS)

    Shrestha, Arun

    Economic pressure and environmental factors have forced the modern power systems to operate closer to their stability limits. However, maintaining transient stability is a fundamental requirement for the operation of interconnected power systems. In North America, power systems are planned and operated to withstand the loss of any single or multiple elements without violating North American Electric Reliability Corporation (NERC) system performance criteria. For a contingency resulting in the loss of multiple elements (Category C), emergency transient stability controls may be necessary to stabilize the power system. Emergency control is designed to sense abnormal conditions and subsequently take pre-determined remedial actions to prevent instability. Commonly known as either Remedial Action Schemes (RAS) or as Special/System Protection Schemes (SPS), these emergency control approaches have been extensively adopted by utilities. RAS are designed to address specific problems, e.g. to increase power transfer, to provide reactive support, to address generator instability, to limit thermal overloads, etc. Possible remedial actions include generator tripping, load shedding, capacitor and reactor switching, static VAR control, etc. Among various RAS types, generation shedding is the most effective and widely used emergency control means for maintaining system stability. In this dissertation, an optimal power flow (OPF)-based generation-shedding RAS is proposed. This scheme uses online transient stability calculation and generator cost function to determine appropriate remedial actions. For transient stability calculation, SIngle Machine Equivalent (SIME) technique is used, which reduces the multimachine power system model to a One-Machine Infinite Bus (OMIB) equivalent and identifies critical machines. Unlike conventional RAS, which are designed using offline simulations, online stability calculations make the proposed RAS dynamic and adapting to any power system

  11. Dynamic stability and phase resetting during biped gait

    NASA Astrophysics Data System (ADS)

    Nomura, Taishin; Kawa, Kazuyoshi; Suzuki, Yasuyuki; Nakanishi, Masao; Yamasaki, Taiga

    2009-06-01

    Dynamic stability during periodic biped gait in humans and in a humanoid robot is considered. Here gait systems of human neuromusculoskeletal system and a humanoid are simply modeled while keeping their mechanical properties plausible. We prescribe periodic gait trajectories in terms of joint angles of the models as a function of time. The equations of motion of the models are then constrained by one of the prescribed gait trajectories to obtain types of periodically forced nonlinear dynamical systems. Simulated gait of the models may or may not fall down during gait, since the constraints are made only for joint angles of limbs but not for the motion of the body trunk. The equations of motion can exhibit a limit cycle solution (or an oscillatory solution that can be considered as a limit cycle practically) for each selected gait trajectory, if an initial condition is set appropriately. We analyze the stability of the limit cycle in terms of Poincaré maps and the basin of attraction of the limit cycle in order to examine how the stability depends on the prescribed trajectory. Moreover, the phase resetting of gait rhythm in response to external force perturbation is modeled. Since we always prescribe a gait trajectory in this study, reacting gait trajectories during the phase resetting are also prescribed. We show that an optimally prescribed reacting gait trajectory with an appropriate amount of the phase resetting can increase the gait stability. Neural mechanisms for generation and modulation of the gait trajectories are discussed.

  12. Core stabilization exercises enhance lactate clearance following high-intensity exercise.

    PubMed

    Navalta, James W; Hrncir, Stephen P

    2007-11-01

    Dynamic activities such as running, cycling, and swimming have been shown to effectively reduce lactate in the postexercise period. It is unknown whether core stabilization exercises performed following an intense bout would exhibit a similar effect. Therefore, this study was designed to assess the extent of the lactate response with core stabilization exercises following high-intensity anaerobic exercise. Subjects (N = 12) reported twice for testing, and on both occasions baseline lactate was obtained after 5 minutes of seated rest. Subjects then performed a 30-second Wingate anaerobic cycle test, immediately followed by a blood lactate sample. In the 5-minute postexercise period, subjects either rested quietly or performed core stabilization exercises. A final blood lactate sample was obtained following the 5-minute intervention period. Analysis revealed a significant interaction (p = 0.05). Lactate values were similar at rest (core = 1.4 +/- 0.1, rest = 1.7 +/- 0.2 mmol x L(-1)) and immediately after exercise (core = 4.9 +/- 0.6, rest = 5.4 +/- 0.4 mmol x L(-1)). However, core stabilization exercises performed during the 5-minute postexercise period reduced lactate values when compared to rest (5.9 +/- 0.6 vs. 7.6 +/- 0.8 mmol x L(-1)). The results of this study show that performing core stabilization exercises during a recovery period significantly reduces lactate values. The reduction in lactate may be due to removal via increased blood flow or enhanced uptake into the core musculature. Incorporation of core stability exercises into a cool-down period following muscular work may result in benefits to both lactate clearance as well as enhanced postural control.

  13. Dynamics, stability, and statistics on lattices and networks

    NASA Astrophysics Data System (ADS)

    Livi, Roberto

    2014-07-01

    These lectures aim at surveying some dynamical models that have been widely explored in the recent scientific literature as case studies of complex dynamical evolution, emerging from the spatio-temporal organization of several coupled dynamical variables. The first message is that a suitable mathematical description of such models needs tools and concepts borrowed from the general theory of dynamical systems and from out-of-equilibrium statistical mechanics. The second message is that the overall scenario is definitely reacher than the standard problems in these fields. For instance, systems exhibiting complex unpredictable evolution do not necessarily exhibit deterministic chaotic behavior (i.e., Lyapunov chaos) as it happens for dynamical models made of a few degrees of freedom. In fact, a very large number of spatially organized dynamical variables may yield unpredictable evolution even in the absence of Lyapunov instability. Such a mechanism may emerge from the combination of spatial extension and nonlinearity. Moreover, spatial extension allows one to introduce naturally disorder, or heterogeneity of the interactions as important ingredients for complex evolution. It is worth to point out that the models discussed in these lectures share such features, despite they have been inspired by quite different physical and biological problems. Along these lectures we describe also some of the technical tools employed for the study of such models, e.g., Lyapunov stability analysis, unpredictability indicators for "stable chaos," hydrodynamic description of transport in low spatial dimension, spectral decomposition of stochastic dynamics on directed networks, etc.

  14. Dynamics, stability, and statistics on lattices and networks

    SciTech Connect

    Livi, Roberto

    2014-07-15

    These lectures aim at surveying some dynamical models that have been widely explored in the recent scientific literature as case studies of complex dynamical evolution, emerging from the spatio-temporal organization of several coupled dynamical variables. The first message is that a suitable mathematical description of such models needs tools and concepts borrowed from the general theory of dynamical systems and from out-of-equilibrium statistical mechanics. The second message is that the overall scenario is definitely reacher than the standard problems in these fields. For instance, systems exhibiting complex unpredictable evolution do not necessarily exhibit deterministic chaotic behavior (i.e., Lyapunov chaos) as it happens for dynamical models made of a few degrees of freedom. In fact, a very large number of spatially organized dynamical variables may yield unpredictable evolution even in the absence of Lyapunov instability. Such a mechanism may emerge from the combination of spatial extension and nonlinearity. Moreover, spatial extension allows one to introduce naturally disorder, or heterogeneity of the interactions as important ingredients for complex evolution. It is worth to point out that the models discussed in these lectures share such features, despite they have been inspired by quite different physical and biological problems. Along these lectures we describe also some of the technical tools employed for the study of such models, e.g., Lyapunov stability analysis, unpredictability indicators for “stable chaos,” hydrodynamic description of transport in low spatial dimension, spectral decomposition of stochastic dynamics on directed networks, etc.

  15. Low dose tunicamycin enhances atherosclerotic plaque stability by inducing autophagy.

    PubMed

    Ma, Meijuan; Song, Liqiang; Yan, Hao; Liu, Min; Zhang, Le; Ma, Ying; Yuan, Jian; Hu, Jianhua; Ji, Zhaole; Zhang, Rongqing; Li, Congye; Wang, Haichang; Tao, Ling; Zhang, Yingmei; Li, Yan

    2016-01-15

    After decades of indolent progression, atherosclerosis may cause unheralded events, such as myocardial infarction, acute coronary syndrome and stroke due to sudden rupture of atherosclerotic plaques, and pharmacologically modulating plaque stability would reduce the risk of cardiovascular diseases. Endoplasmic reticulum stress (ERS) is responsible for the vulnerability of plaques. However, the underlying mechanism has not been fully elucidated. In this work, ApoE(-/-) mice underwent perivascular carotid collar placement surgeries or sham operations were given higher (3.0mg/kg) and lower (0.3mg/kg) doses of tunicamycin (TM), and plaque stability was evaluated. It was shown that lower TM-treated animals exhibited reduced plaque areas and necrotic cores as well as fibrous cap thickness accompanied by a lower percentage of infiltrates and foam cells than the sham-operated and higher TM treated animals. Lower TM had a profound inhibitory effect on plasma inflammatory response and lipid profile in atherosclerotic ApoE(-/-) mice. In addition, we found that the ApoE(-/-) mice presented higher autophagy activity in response to lower TM administration while apoptosis was reduced. An in vitro study in murine macrophages revealed that lower TM could markedly reduce lipid uptake and accumulation and cell apoptosis while significantly upregulated the expression of Atg7. However, higher TM had adverse effects. Finally, mild induction of ERS by lower TM inhibits AKT-TSC-mTOR cascades to increase cellular autophagy. However, high TM failed to enhance autophagy and equilibrate elevated CHOP-mediated cell death in spite of the inhibition of AKT-TSC-mTOR signaling. In conclusion, lower TM stabilized plaques by activating autophagy through AKT-TSC-mTOR signaling. PMID:26616221

  16. Low dose tunicamycin enhances atherosclerotic plaque stability by inducing autophagy.

    PubMed

    Ma, Meijuan; Song, Liqiang; Yan, Hao; Liu, Min; Zhang, Le; Ma, Ying; Yuan, Jian; Hu, Jianhua; Ji, Zhaole; Zhang, Rongqing; Li, Congye; Wang, Haichang; Tao, Ling; Zhang, Yingmei; Li, Yan

    2016-01-15

    After decades of indolent progression, atherosclerosis may cause unheralded events, such as myocardial infarction, acute coronary syndrome and stroke due to sudden rupture of atherosclerotic plaques, and pharmacologically modulating plaque stability would reduce the risk of cardiovascular diseases. Endoplasmic reticulum stress (ERS) is responsible for the vulnerability of plaques. However, the underlying mechanism has not been fully elucidated. In this work, ApoE(-/-) mice underwent perivascular carotid collar placement surgeries or sham operations were given higher (3.0mg/kg) and lower (0.3mg/kg) doses of tunicamycin (TM), and plaque stability was evaluated. It was shown that lower TM-treated animals exhibited reduced plaque areas and necrotic cores as well as fibrous cap thickness accompanied by a lower percentage of infiltrates and foam cells than the sham-operated and higher TM treated animals. Lower TM had a profound inhibitory effect on plasma inflammatory response and lipid profile in atherosclerotic ApoE(-/-) mice. In addition, we found that the ApoE(-/-) mice presented higher autophagy activity in response to lower TM administration while apoptosis was reduced. An in vitro study in murine macrophages revealed that lower TM could markedly reduce lipid uptake and accumulation and cell apoptosis while significantly upregulated the expression of Atg7. However, higher TM had adverse effects. Finally, mild induction of ERS by lower TM inhibits AKT-TSC-mTOR cascades to increase cellular autophagy. However, high TM failed to enhance autophagy and equilibrate elevated CHOP-mediated cell death in spite of the inhibition of AKT-TSC-mTOR signaling. In conclusion, lower TM stabilized plaques by activating autophagy through AKT-TSC-mTOR signaling.

  17. Lower Protein Stability Does Not Necessarily Increase Local Dynamics.

    PubMed

    McClelland, Levi J; Bowler, Bruce E

    2016-05-17

    Overall protein stability is thought to have an important impact on the millisecond time scale dynamics modulating enzyme function. In order to better understand the effects of overall stability on the substructure dynamics of mitochondrial cytochrome c, we test the effect of a destabilizing L85A mutation on the kinetics and equilibrium thermodynamics of the alkaline conformational transition. The alkaline conformational transition replaces the Met80 ligand of the heme with a lysine residue from Ω-loop D, the heme crevice loop, consisting of residues 70-85. Residues 67-87 are the most conserved portion of the sequence of mitochondrial cytochrome c, suggesting that this region is of prime importance for function. Mutations to Ω-loop D affect the stability of the heme crevice directly, modulating the pKapp of the alkaline transition. Two variants of yeast iso-1-cytochrome c, WT*/L85A and WT*/K73H/L85A, were prepared for these studies. Guanidine-HCl unfolding monitored by circular dichroism and pH titrations at 695 nm, respectively, were used to study the thermodynamics of global and local unfolding of these variants. The kinetics of the alkaline transition were measured by pH-jump stopped-flow methods. Gated electron transfer techniques using bis(2,2',2″-terpyridine)cobalt(II) as a reducing reagent were implemented to measure the heme crevice dynamics for the WT*/K73H/L85A variant. Contrary to the expectation that dynamics around the heme crevice would be faster for the less stable WT*/K73H/L85A variant, based on the behavior of psychrophilic versus mesophilic enzymes, they were similar to those for a variant without the L85A mutation. In fact, below pH 7, the dynamics of the WT*/K73H/L85A variant were slower. PMID:27104373

  18. Metaconcrete: Engineered aggregates for enhanced dynamic performance

    NASA Astrophysics Data System (ADS)

    Mitchell, Stephanie J.

    This work presents the development and investigation of a new type of concrete for the attenuation of waves induced by dynamic excitation. Recent progress in the field of metamaterials science has led to a range of novel composites which display unusual properties when interacting with electromagnetic, acoustic, and elastic waves. A new structural metamaterial with enhanced properties for dynamic loading applications is presented, which is named metaconcrete. In this new composite material the standard stone and gravel aggregates of regular concrete are replaced with spherical engineered inclusions. Each metaconcrete aggregate has a layered structure, consisting of a heavy core and a thin compliant outer coating. This structure allows for resonance at or near the eigenfrequencies of the inclusions, and the aggregates can be tuned so that resonant oscillations will be activated by particular frequencies of an applied dynamic loading. The activation of resonance within the aggregates causes the overall system to exhibit negative effective mass, which leads to attenuation of the applied wave motion. To investigate the behavior of metaconcrete slabs under a variety of different loading conditions a finite element slab model containing a periodic array of aggregates is utilized. The frequency dependent nature of metaconcrete is investigated by considering the transmission of wave energy through a slab, which indicates the presence of large attenuation bands near the resonant frequencies of the aggregates. Applying a blast wave loading to both an elastic slab and a slab model that incorporates the fracture characteristics of the mortar matrix reveals that a significant portion of the supplied energy can be absorbed by aggregates which are activated by the chosen blast wave profile. The transfer of energy from the mortar matrix to the metaconcrete aggregates leads to a significant reduction in the maximum longitudinal stress, greatly improving the ability of the material

  19. Dynamic flight stability of a bumblebee in forward flight

    NASA Astrophysics Data System (ADS)

    Xiong, Yan; Sun, Mao

    2008-02-01

    The longitudinal dynamic flight stability of a bumblebee in forward flight is studied. The method of computational fluid dynamics is used to compute the aerodynamic derivatives and the techniques of eigenvalue and eigenvector analysis are employed for solving the equations of motion. The primary findings are as the following. The forward flight of the bumblebee is not dynamically stable due to the existence of one (or two) unstable or approximately neutrally stable natural modes of motion. At hovering to medium flight speed [flight speed u e = (0-3.5) m s-1; advance ratio J = 0-0.44], the flight is weakly unstable or approximately neutrally stable; at high speed ( u e = 4.5 m s-1; J = 0.57), the flight becomes strongly unstable (initial disturbance double its value in only 3.5 wingbeats).

  20. Dynamic-stability experiments in LMFBR steam-generator tubes

    SciTech Connect

    France, D.M.; Carlson, R.D.; Chiang, T.; Roy, R.

    1983-01-01

    A variety of instabilities have been recognized in two-phase flows. Parallel channel two-phase flows are particularly sensitive to static instability and dynamic instability of the density wave type. Sodium-heated steam generators, for Liquid Metal Fast Breeder Reactor (LMFBR) electric power plants, fall into this category, since they are typically comprised of 10/sup 2/ to 10/sup 3/ water tubes. The purpose of this study was to experimentally determine the threshold of dynamic instability in sodium-heated boiling-water tubes using a full scale LMFBR tube and prototypic system parameters. A series of 72 dynamic stability experiments were performed in the Steam Generator Test Facility (SGTF) at Argonne National Laboratory.

  1. Enhanced Raman sensitivity using an actively stabilized external resonator

    NASA Astrophysics Data System (ADS)

    Taylor, David J.; Glugla, Manfred; Penzhorn, Ralf-Dieter

    2001-04-01

    An enhancement up to 250-fold in laser Raman signals for real-time gas analysis has been achieved within an actively stabilized external resonator (ASER), whose length is actively matched to the single-frequency excitation laser using the Pound-Drever technique. With the Raman cell present, enhancements up to 50-fold are achieved, and the resulting detection limit for hydrogen in ambient-pressure gas mixtures is about ten parts-per-million in a 1 min analysis period at unity signal-to-noise ratio. Based upon the recent development of a fiber-pumped Nd:YVO4 laser with single-frequency output exceeding 5 W at 532 nm, this highly sensitive instrument is applied to detection of tritiated gases, wherein the compactness and low heat of this laser head permit placing the entire optical system, including laser head, charge coupled Raman detector, and ASER, within the glove box necessary for secondary containment of tritium, thereby accomplishing a robust, highly sensitive Raman analytical system for hazardous substances.

  2. Mental training enhances attentional stability: neural and behavioral evidence.

    PubMed

    Lutz, Antoine; Slagter, Heleen A; Rawlings, Nancy B; Francis, Andrew D; Greischar, Lawrence L; Davidson, Richard J

    2009-10-21

    The capacity to stabilize the content of attention over time varies among individuals, and its impairment is a hallmark of several mental illnesses. Impairments in sustained attention in patients with attention disorders have been associated with increased trial-to-trial variability in reaction time and event-related potential deficits during attention tasks. At present, it is unclear whether the ability to sustain attention and its underlying brain circuitry are transformable through training. Here, we show, with dichotic listening task performance and electroencephalography, that training attention, as cultivated by meditation, can improve the ability to sustain attention. Three months of intensive meditation training reduced variability in attentional processing of target tones, as indicated by both enhanced theta-band phase consistency of oscillatory neural responses over anterior brain areas and reduced reaction time variability. Furthermore, those individuals who showed the greatest increase in neural response consistency showed the largest decrease in behavioral response variability. Notably, we also observed reduced variability in neural processing, in particular in low-frequency bands, regardless of whether the deviant tone was attended or unattended. Focused attention meditation may thus affect both distracter and target processing, perhaps by enhancing entrainment of neuronal oscillations to sensory input rhythms, a mechanism important for controlling the content of attention. These novel findings highlight the mechanisms underlying focused attention meditation and support the notion that mental training can significantly affect attention and brain function.

  3. Plasma deposited stability enhancement coating for amorphous ketoprofen.

    PubMed

    Bosselmann, Stephanie; Owens, Donald E; Kennedy, Rachel L; Herpin, Matthew J; Williams, Robert O

    2011-05-01

    A hydrophobic fluorocarbon coating deposited onto amorphous ketoprofen via pulsed plasma-enhanced chemical vapor deposition (PPECVD) significantly prolonged the onset of recrystallization compared to uncoated drug. Rapid freezing (RF) employed to produce amorphous ketoprofen was followed by PPECVD of perfluorohexane. The effect of coating thickness on the recrystallization and dissolution behavior of ketoprofen was investigated. Samples were stored in open containers at 40°C and 75% relative humidity, and the onset of recrystallization was monitored by DSC. An increase in coating thickness provided enhanced stability against recrystallization for up to 6 months at accelerated storage conditions (longest time of observation) when compared to three days for uncoated ketoprofen. Results from XPS analysis demonstrated that an increase in coating thickness was associated with improved surface coverage thus enabling superior protection. Dissolution testing showed that at least 80% of ketoprofen was released in buffer pH 6.8 from all coated samples. Overall, an increase in coating thickness resulted in a more complete drug release due to decreased adhesion of the coating to the substrate.

  4. Dynamic flight stability in the desert locust Schistocerca gregaria.

    PubMed

    Taylor, Graham K; Thomas, Adrian L R

    2003-08-01

    Here we provide the first formal quantitative analysis of dynamic stability in a flying animal. By measuring the longitudinal static stability derivatives and mass distribution of desert locusts Schistocerca gregaria, we find that their static stability and static control responses are insufficient to provide asymptotic longitudinal dynamic stability unless they are sensitive to pitch attitude (measured with respect to an inertial or earth-fixed frame) as well as aerodynamic incidence (measured relative to the direction of flight). We find no evidence for a 'constant-lift reaction', previously supposed to keep lift production constant over a range of body angles, and show that such a reaction would be inconsequential because locusts can potentially correct for pitch disturbances within a single wingbeat. The static stability derivatives identify three natural longitudinal modes of motion: one stable subsidence mode, one unstable divergence mode, and one stable oscillatory mode (which is present with or without pitch attitude control). The latter is identified with the short period mode of aircraft, and shown to consist of rapid pitch oscillations with negligible changes in forward speed. The frequency of the short period mode (approx. 10 Hz) is only half the wingbeat frequency (approx. 22 Hz), so the mode would become coupled with the flapping cycle without adequate damping. Pitch rate damping is shown to be highly effective for this purpose - especially at the small scales associated with insect flight - and may be essential in stabilising locust flight. Although having a short period mode frequency close to the wingbeat frequency risks coupling, it is essential for control inputs made at the level of a single wingbeat to be effective. This is identified as a general constraint on flight control in flying animals.

  5. Flexible Launch Vehicle Stability Analysis Using Steady and Unsteady Computational Fluid Dynamics

    NASA Technical Reports Server (NTRS)

    Bartels, Robert E.

    2012-01-01

    Launch vehicles frequently experience a reduced stability margin through the transonic Mach number range. This reduced stability margin can be caused by the aerodynamic undamping one of the lower-frequency flexible or rigid body modes. Analysis of the behavior of a flexible vehicle is routinely performed with quasi-steady aerodynamic line loads derived from steady rigid aerodynamics. However, a quasi-steady aeroelastic stability analysis can be unconservative at the critical Mach numbers, where experiment or unsteady computational aeroelastic analysis show a reduced or even negative aerodynamic damping.Amethod of enhancing the quasi-steady aeroelastic stability analysis of a launch vehicle with unsteady aerodynamics is developed that uses unsteady computational fluid dynamics to compute the response of selected lower-frequency modes. The response is contained in a time history of the vehicle line loads. A proper orthogonal decomposition of the unsteady aerodynamic line-load response is used to reduce the scale of data volume and system identification is used to derive the aerodynamic stiffness, damping, and mass matrices. The results are compared with the damping and frequency computed from unsteady computational aeroelasticity and from a quasi-steady analysis. The results show that incorporating unsteady aerodynamics in this way brings the enhanced quasi-steady aeroelastic stability analysis into close agreement with the unsteady computational aeroelastic results.

  6. Dynamic stability of spine using stability-based optimization and muscle spindle reflex.

    PubMed

    Zeinali-Davarani, Shahrokh; Hemami, Hooshang; Barin, Kamran; Shirazi-Adl, Aboulfazl; Parnianpour, Mohamad

    2008-02-01

    A computational method for simulation of 3-D movement of the trunk under the control of 48 anatomically oriented muscle actions was developed. Neural excitation of muscles was set based on inverse dynamics approach along with the stability-based optimization. The effect of muscle spindle reflex response on the trunk movement stability was evaluated upon the application of a perturbation moment. The method was used to simulate the trunk movement from the upright standing to 60 degrees of flexion. Incorporation of the stability condition as an additional constraint in the optimization resulted in an increase in antagonistic activities demonstrating that the antagonistic co-activation acts to increase the trunk stability in response to self-induced postural internal perturbation. In presence of a 30 Nm flexion perturbation moment, muscle spindles decreased the induced deviation of the position and velocity profiles from the desired ones. The stability-generated co-activation decreased the reflexive response of muscle spindles to the perturbation demonstrating that the rise in muscle co-activation can ameliorate the corruption of afferent neural sensory system at the expense of higher loading of the spine.

  7. Assessment of current criteria for dynamic stability of container vessels

    NASA Astrophysics Data System (ADS)

    Stanca, C.; Ancuta, C.; Acomi, N.; Andrei, C.

    2016-08-01

    Container vessels sailing through heavy weather are exposed to a significant variation of stability due to specific shape of the hull combined with the action of the waves. Even if the weather forecast is transmitted to vessels, the way of acting it is a matter of officers’ experience. The Maritime Safety Committee, under the International Maritime Organization, has approved the Guidance to the master for avoiding dangerous situations in adverse weather and sea conditions. Adverse weather conditions include wind induced waves or heavy swell. The development of dangerous phenomena such as surf-riding and broaching to, syncronious and parametric rollings is a result of a these adverse conditions which has to be encountered by the vessels. Understanding the dynamic stability of the vessel in the waves and ship's behaviour based on mathematical and physical rules is a difficult task, any effort in order to assess these components are salutary. To avoid excessive acceleration and forces which can damage the hull of the vessel, lashing and integrity of containers, course and speed may need to be changed for the vessel's motion in heavy seas. Specific software have been developed as aids for evaluating the response of the vessel in heavy seas according to parameters variations. The paper aims at assessing of current criteria for dynamic stability of a container vessel model ship in order to determine the ways for avoiding dangerous conditions. The results should be regarded as a supporting tool during the decision making process.

  8. Dynamical stability of Minkowski space in higher order gravity

    NASA Astrophysics Data System (ADS)

    Tretyakov, Petr V.

    2015-06-01

    We discuss the Minkowski stability problem in modified gravity by using dynamical system approach. The method to investigate dynamical stability of Minkowski space is proposed. This method was applied for some modified gravity theories, such as f(R) gravity, f(R)+αR□R gravity and scalar-tensor gravity models with non-minimal kinetic coupling. It was shown that in the case of f(R) gravity Minkowski solution is asymptotically stable in ghost-free (f‧ > 0) and tachyon-free (f″ > 0) theories in expanding Universe with respect to isotropic and basic anisotropic perturbations. In the case of higher order gravity with αR□R correction conditions of Minkowski stability with respect to isotropic perturbations are significantly different: f‧(0) < 0, f″(0) < 0 and 3f‧(0) + f″(0)2/α > 0. And in the case of scalar-tensor gravity with non-minimal kinetic coupling Minkowski solution is asymptotically stable in expanding Universe with respect to isotropic perturbations of metric. Moreover, the developed method may be used for finding additional restrictions on parameters of different modified gravity theories.

  9. Origin of Shear Stability and Compressive Ductility Enhancement of Metallic Glasses by Metal Coating

    PubMed Central

    Sun, B. A.; Chen, S. H.; Lu, Y. M.; Zhu, Z. G.; Zhao, Y. L.; Yang, Y.; Chan, K. C.; Liu, C. T.

    2016-01-01

    Metallic glasses (MGs) are notorious for the poor macroscopic ductility and to overcome the weakness various intrinsic and extrinsic strategies have been proposed in past decades. Among them, the metal coating is regarded as a flexible and facile approach, yet the physical origin is poorly understood due to the complex nature of shear banding process. Here, we studied the origin of ductile enhancement in the Cu-coating both experimentally and theoretically. By examining serrated shear events and their stability of MGs, we revealed that the thin coating layer plays a key role in stopping the final catastrophic failure of MGs by slowing down shear band dynamics and thus retarding its attainment to a critical instable state. The mechanical analysis on interplay between the coating layer and shear banding process showed the enhanced shear stability mainly comes from the lateral tension of coating layer induced by the surface shear step and the bonding between the coating layer and MGs rather than the layer thickness is found to play a key role in contributing to the shear stability. PMID:27271435

  10. Origin of Shear Stability and Compressive Ductility Enhancement of Metallic Glasses by Metal Coating.

    PubMed

    Sun, B A; Chen, S H; Lu, Y M; Zhu, Z G; Zhao, Y L; Yang, Y; Chan, K C; Liu, C T

    2016-01-01

    Metallic glasses (MGs) are notorious for the poor macroscopic ductility and to overcome the weakness various intrinsic and extrinsic strategies have been proposed in past decades. Among them, the metal coating is regarded as a flexible and facile approach, yet the physical origin is poorly understood due to the complex nature of shear banding process. Here, we studied the origin of ductile enhancement in the Cu-coating both experimentally and theoretically. By examining serrated shear events and their stability of MGs, we revealed that the thin coating layer plays a key role in stopping the final catastrophic failure of MGs by slowing down shear band dynamics and thus retarding its attainment to a critical instable state. The mechanical analysis on interplay between the coating layer and shear banding process showed the enhanced shear stability mainly comes from the lateral tension of coating layer induced by the surface shear step and the bonding between the coating layer and MGs rather than the layer thickness is found to play a key role in contributing to the shear stability. PMID:27271435

  11. Origin of Shear Stability and Compressive Ductility Enhancement of Metallic Glasses by Metal Coating

    NASA Astrophysics Data System (ADS)

    Sun, B. A.; Chen, S. H.; Lu, Y. M.; Zhu, Z. G.; Zhao, Y. L.; Yang, Y.; Chan, K. C.; Liu, C. T.

    2016-06-01

    Metallic glasses (MGs) are notorious for the poor macroscopic ductility and to overcome the weakness various intrinsic and extrinsic strategies have been proposed in past decades. Among them, the metal coating is regarded as a flexible and facile approach, yet the physical origin is poorly understood due to the complex nature of shear banding process. Here, we studied the origin of ductile enhancement in the Cu-coating both experimentally and theoretically. By examining serrated shear events and their stability of MGs, we revealed that the thin coating layer plays a key role in stopping the final catastrophic failure of MGs by slowing down shear band dynamics and thus retarding its attainment to a critical instable state. The mechanical analysis on interplay between the coating layer and shear banding process showed the enhanced shear stability mainly comes from the lateral tension of coating layer induced by the surface shear step and the bonding between the coating layer and MGs rather than the layer thickness is found to play a key role in contributing to the shear stability.

  12. Strategy Switching in the Stabilization of Unstable Dynamics

    PubMed Central

    Zenzeri, Jacopo; De Santis, Dalia; Morasso, Pietro

    2014-01-01

    In order to understand mechanisms of strategy switching in the stabilization of unstable dynamics, this work investigates how human subjects learn to become skilled users of an underactuated bimanual tool in an unstable environment. The tool, which consists of a mass and two hand-held non-linear springs, is affected by a saddle-like force-field. The non-linearity of the springs allows the users to determine size and orientation of the tool stiffness ellipse, by using different patterns of bimanual coordination: minimal stiffness occurs when the two spring terminals are aligned and stiffness size grows by stretching them apart. Tool parameters were set such that minimal stiffness is insufficient to provide stable equilibrium whereas asymptotic stability can be achieved with sufficient stretching, although at the expense of greater effort. As a consequence, tool users have two possible strategies for stabilizing the mass in different regions of the workspace: 1) high stiffness feedforward strategy, aiming at asymptotic stability and 2) low stiffness positional feedback strategy aiming at bounded stability. The tool was simulated by a bimanual haptic robot with direct torque control of the motors. In a previous study we analyzed the behavior of naïve users and we found that they spontaneously clustered into two groups of approximately equal size. In this study we trained subjects to become expert users of both strategies in a discrete reaching task. Then we tested generalization capabilities and mechanism of strategy-switching by means of stabilization tasks which consist of tracking moving targets in the workspace. The uniqueness of the experimental setup is that it addresses the general problem of strategy-switching in an unstable environment, suggesting that complex behaviors cannot be explained in terms of a global optimization criterion but rather require the ability to switch between different sub-optimal mechanisms. PMID:24921254

  13. Symmetry-enhanced performance of dynamical decoupling

    SciTech Connect

    Pasini, S.; Uhrig, G. S.

    2011-10-15

    We consider a system with general decoherence and a quadratic dynamical decoupling sequence (QDD) for the coherence control of a qubit coupled to a bath of spins. We investigate the influence of the geometry and of the initial conditions of the bath on the performance of the sequence. The overall performance is quantified by a distance norm d. It is expected that d scales with {tau}, the total duration of the sequence, as {tau}{sup min{l_brace}N{sub x},N{sub z}{r_brace}+1}, where N{sub x} and N{sub z} are the number of pulses of the outer and of the inner sequence, respectively. We show both numerically and analytically that the state of the bath can boost the performance of QDD under certain conditions: The scaling of QDD for a given number of pulses can be enhanced by a factor of 2 if the bath is prepared in a highly symmetric state and if the system Hamiltonian is SU(2) invariant.

  14. A study of helicopter stability and control including blade dynamics

    NASA Technical Reports Server (NTRS)

    Zhao, Xin; Curtiss, H. C., Jr.

    1988-01-01

    A linearized model of rotorcraft dynamics has been developed through the use of symbolic automatic equation generating techniques. The dynamic model has been formulated in a unique way such that it can be used to analyze a variety of rotor/body coupling problems including a rotor mounted on a flexible shaft with a number of modes as well as free-flight stability and control characteristics. Direct comparison of the time response to longitudinal, lateral and directional control inputs at various trim conditions shows that the linear model yields good to very good correlation with flight test. In particular it is shown that a dynamic inflow model is essential to obtain good time response correlation, especially for the hover trim condition. It also is shown that the main rotor wake interaction with the tail rotor and fixed tail surfaces is a significant contributor to the response at translational flight trim conditions. A relatively simple model for the downwash and sidewash at the tail surfaces based on flat vortex wake theory is shown to produce good agreement. Then, the influence of rotor flap and lag dynamics on automatic control systems feedback gain limitations is investigated with the model. It is shown that the blade dynamics, especially lagging dynamics, can severly limit the useable values of the feedback gain for simple feedback control and that multivariable optimal control theory is a powerful tool to design high gain augmentation control system. The frequency-shaped optimal control design can offer much better flight dynamic characteristics and a stable margin for the feedback system without need to model the lagging dynamics.

  15. Enhanced stability and activity of an antimicrobial peptide in conjugation with silver nanoparticle.

    PubMed

    Pal, Indrani; Brahmkhatri, Varsha P; Bera, Swapna; Bhattacharyya, Dipita; Quirishi, Yasrib; Bhunia, Anirban; Atreya, Hanudatta S

    2016-12-01

    The conjugation of nanoparticles with antimicrobial peptides (AMP) is emerging as a promising route to achieve superior antimicrobial activity. However, the nature of peptide-nanoparticle interactions in these systems remains unclear. This study describes a system consisting of a cysteine containing antimicrobial peptide conjugated with silver nanoparticles, in which the two components exhibit a dynamic interaction resulting in a significantly enhanced stability and biological activity compared to that of the individual components. This was investigated using NMR spectroscopy in conjunction with other biophysical techniques. Using fluorescence assisted cell sorting and membrane mimics we carried out a quantitative comparison of the activity of the AMP-nanoparticle system and the free peptide. Taken together, the study provides new insights into nanoparticle-AMP interactions at a molecular level and brings out the factors that will be useful for consideration while designing new conjugates with enhanced functionality. PMID:27585423

  16. Kinematic variability, fractal dynamics and local dynamic stability of treadmill walking

    PubMed Central

    2011-01-01

    Background Motorized treadmills are widely used in research or in clinical therapy. Small kinematics, kinetics and energetics changes induced by Treadmill Walking (TW) as compared to Overground Walking (OW) have been reported in literature. The purpose of the present study was to characterize the differences between OW and TW in terms of stride-to-stride variability. Classical (Standard Deviation, SD) and non-linear (fractal dynamics, local dynamic stability) methods were used. In addition, the correlations between the different variability indexes were analyzed. Methods Twenty healthy subjects performed 10 min TW and OW in a random sequence. A triaxial accelerometer recorded trunk accelerations. Kinematic variability was computed as the average SD (MeanSD) of acceleration patterns among standardized strides. Fractal dynamics (scaling exponent α) was assessed by Detrended Fluctuation Analysis (DFA) of stride intervals. Short-term and long-term dynamic stability were estimated by computing the maximal Lyapunov exponents of acceleration signals. Results TW did not modify kinematic gait variability as compared to OW (multivariate T2, p = 0.87). Conversely, TW significantly modified fractal dynamics (t-test, p = 0.01), and both short and long term local dynamic stability (T2 p = 0.0002). No relationship was observed between variability indexes with the exception of significant negative correlation between MeanSD and dynamic stability in TW (3 × 6 canonical correlation, r = 0.94). Conclusions Treadmill induced a less correlated pattern in the stride intervals and increased gait stability, but did not modify kinematic variability in healthy subjects. This could be due to changes in perceptual information induced by treadmill walking that would affect locomotor control of the gait and hence specifically alter non-linear dependencies among consecutive strides. Consequently, the type of walking (i.e. treadmill or overground) is important to consider in each protocol

  17. Non-linear dynamics of human locomotion: effects of rhythmic auditory cueing on local dynamic stability

    PubMed Central

    Terrier, Philippe; Dériaz, Olivier

    2013-01-01

    It has been observed that times series of gait parameters [stride length (SL), stride time (ST), and stride speed (SS)], exhibit long-term persistence and fractal-like properties. Synchronizing steps with rhythmic auditory stimuli modifies the persistent fluctuation pattern to anti-persistence. Another non-linear method estimates the degree of resilience of gait control to small perturbations, i.e., the local dynamic stability (LDS). The method makes use of the maximal Lyapunov exponent, which estimates how fast a non-linear system embedded in a reconstructed state space (attractor) diverges after an infinitesimal perturbation. We propose to use an instrumented treadmill to simultaneously measure basic gait parameters (time series of SL, ST, and SS from which the statistical persistence among consecutive strides can be assessed), and the trajectory of the center of pressure (from which the LDS can be estimated). In 20 healthy participants, the response to rhythmic auditory cueing (RAC) of LDS and of statistical persistence [assessed with detrended fluctuation analysis (DFA)] was compared. By analyzing the divergence curves, we observed that long-term LDS (computed as the reverse of the average logarithmic rate of divergence between the 4th and the 10th strides downstream from nearest neighbors in the reconstructed attractor) was strongly enhanced (relative change +73%). That is likely the indication of a more dampened dynamics. The change in short-term LDS (divergence over one step) was smaller (+3%). DFA results (scaling exponents) confirmed an anti-persistent pattern in ST, SL, and SS. Long-term LDS (but not short-term LDS) and scaling exponents exhibited a significant correlation between them (r = 0.7). Both phenomena probably result from the more conscious/voluntary gait control that is required by RAC. We suggest that LDS and statistical persistence should be used to evaluate the efficiency of cueing therapy in patients with neurological gait disorders. PMID

  18. Dynamic and thermodynamic stability of relativistic, perfect fluid stars

    NASA Astrophysics Data System (ADS)

    Green, Stephen R.; Schiffrin, Joshua S.; Wald, Robert M.

    2014-02-01

    We consider perfect fluid bodies (‘stars’) in general relativity, with the local state of the fluid specified by its 4-velocity, ua, its ‘particle number density’, n, and its ‘entropy per particle’, s. A star is said to be in dynamic equilibrium if it is a stationary, axisymmetric solution to the Einstein-fluid equations with circular flow. A star is said to be in thermodynamic equilibrium if it is in dynamic equilibrium and its total entropy, S, is an extremum for all variations of initial data that satisfy the Einstein constraint equations and have fixed total mass, M, particle number, N, and angular momentum, J. We prove that for a star in dynamic equilibrium, the necessary and sufficient condition for thermodynamic equilibrium is constancy of angular velocity, Ω, redshifted temperature, \\widetilde{T}, and redshifted chemical potential, \\widetilde{\\mu }. A star in dynamic equilibrium is said to be linearly dynamically stable if all physical, gauge invariant quantities associated with linear perturbations of the star remain bounded in time; it is said to be mode stable if there are no exponentially growing solutions that are not pure gauge. A star in thermodynamic equilibrium is said to be linearly thermodynamically stable if δ2S < 0 for all variations at fixed M, N, and J; equivalently, a star in thermodynamic equilibrium is linearly thermodynamically stable if \\delta ^2 M - \\widetilde{T} \\delta ^2 S -\\widetilde{\\mu } \\delta ^2 N - \\Omega \\delta ^2 J > 0 for all variations that, to first order, satisfy δM = δN = δJ = 0 (and, hence, δS = 0). Friedman previously identified positivity of canonical energy, {E}, as a criterion for dynamic stability and argued that all rotating stars are dynamically unstable to sufficiently non-axisymmetric perturbations (the CFS instability), so our main focus is on axisymmetric stability (although we develop our formalism and prove many results for non-axisymmetric perturbations as well). We show that

  19. Lagrangian, Eulerian, and Dynamically Accessible Stability of MHD flows

    NASA Astrophysics Data System (ADS)

    Andreussi, Tommaso; Morrison, Philip; Pegoraro, Francesco

    2012-10-01

    Stability conditions of magnetized plasma flows are obtained by exploiting the Hamiltonian structure of the magnetohydrodynamics (MHD) equations and, in particular, by using three kinds of energy principles. First, the Lagrangian energy principle of Ref. [1] is introduced and sufficient stability conditions are presented. Next, plasma flows are described in terms of Eulerian variables and the noncanonical Hamiltonian formulation of MHD [2] is exploited. For symmetric equilibria, the energy-Casimir principle of Ref. [3] is expanded to second order and sufficient conditions for stability to symmetric perturbation are obtained. Then, dynamically accessible variations, i.e. variations that explicitly preserve the invariants of the system, are introduced and the respective energy principle is considered. As in Ref. [4], general criteria for stability are obtained. A comparison between the three different approaches is finally presented. [4pt] [1] E.A. Frieman and M. Rotenberg, Rev. Mod. Phys., 32 898 (1960).[0pt] [2] P.J. Morrison, J.M. Greene, Phys. Rev. Lett., 45 790 (1980).[0pt] [3] T. Andreussi, P.J. Morrison, F. Pegoraro, Phys. Plasmas, 19 052102 (2012).[0pt] [4] E. Hameiri, Phys. Plasmas, 10 2643 (2003).

  20. On Hamiltonian Magnetohydrodynamics: Lagrangian, Eulerian and Dynamically Accessible Stability

    NASA Astrophysics Data System (ADS)

    Andreussi, Tommaso; Morrison, Philip J.; Pegoraro, Francesco

    2013-10-01

    Stability conditions of magnetized plasma flows are obtained by exploiting the Hamiltonian structure of the magnetohydrodynamics (MHD) equations by using three kinds of energy principles. First, the Lagrangian variable energy principle is described and sufficient stability conditions are presented. Next, plasma flows are described in terms of Eulerian variables and the noncanonical Hamiltonian formulation of MHD is exploited. For symmetric equilibria, the energy-Casimir principle is expanded to second order and sufficient conditions for stability to symmetric perturbation are obtained. Then, dynamically accessible variations, i.e. variations that explicitly preserve invariants of the system, are introduced and the respective energy principle is considered. General criteria for stability are obtained, along with comparisons between the three different approaches. En route to our results we describe a time-dependent relabeling transformation, which to our knowledge has not heretofore been given, that will be needed in the Lagrangian variable framework in connection with the approach considered in E. A. Frieman, M. Rotenberg, Rev. Mod. Phys. 32, 898 (1960).

  1. Enhancement of stability of aqueous suspension of alumina nanoparticles by femtosecond laser irradiation

    SciTech Connect

    Seo, Youngsang; Ha, Jeonghong; Kim, Dongsik; Choi, Tae-Youl; Jeong, Dae-Yong; Lee, Seung Yong

    2015-09-21

    In this work, we report substantially enhanced colloidal stability of aqueous nanoparticle suspensions by ultrashort laser pulse irradiation. A Ti:Sapphire femtosecond laser (wavelength: 800 nm; pulse duration: 50 fs at full width at half maximum) was used to modify the electrochemical properties of nanoparticle suspensions at laser fluences below the particle ablation threshold. The colloidal stability of the suspension was evaluated by zeta potential and dynamic light scattering (DLS). The DLS results along with the images from transmission electron microscopy revealed that the laser irradiation caused no distinct morphological change to the individual alumina particles, but a substantial portion of the clustered particles was fragmented by the laser pulses, decreasing the apparent size of the suspended particles. Also, X-ray photoelectron spectroscopy analysis indicates that the laser irradiation modified the surface chemistry of the alumina particles. The stabilizing capability of the proposed technique was turned out to be better than that of conventional ultrasonic treatments. The stability of the laser-treated sample with no added surfactant was maintained for up to 30 days, without requiring an additional homogenizing process such as magnetic stirring.

  2. Dynamical Stability and Habitability of Extra-Solar Planets

    NASA Astrophysics Data System (ADS)

    Pilat-Lohinger, Elke

    2012-04-01

    Observations of about 60 binary star systems hosting exoplanets indicate the necessity of stability studies of planetary motion in such multi-stellar systems. For wide binary systems with separations between hundreds and thousands of AU, the results from single-star systems may be applicable but, in tight double stars systems, we have to take the stellar interactions into account which influences the planetary motion significantly. This review discusses the different types of planetary motion in double stars and the stability of the planets for different binary configurations. An application to the most famous tight binary system (γ Cephei) is also shown. Finally, we analyze the habitability from the dynamical point of view in such systems, where we discuss the motion of terrestrial-like planets in the so-called habitable zone.

  3. Dynamic stability of periodic shells with moving loads

    NASA Astrophysics Data System (ADS)

    Ruzzene, M.; Baz, A.

    2006-10-01

    A moving load causes the radial displacements of an axi-symmetric shell to be several times higher than that produced by the static application of the same load. The travel velocity of the moving load affects the amplitude of the radial response and a critical velocity above which the shell response becomes unstable can be identified. A finite element model (FEM) is developed to analyze the dynamic response of axi-symmetric shells subjected to axially moving loads. The model accounts for the effect of periodically placing stiffening rings along the shell, on the dynamic response and stability characteristics of the shell. Shape functions obtained from the steady-state solution of the equation of motion for a uniform shell are utilized in the development of the FEM. The model is formulated in a reference frame moving with the load in order to enable study of the shell stability using wave propagation and attenuation criteria. Hence, the critical velocity can be identified as the minimum velocity allowing the propagation of applied perturbations. Such stability boundaries are conveniently identified through a transfer matrix formulation. The model is used to determine the critical velocities of the moving load for various arrangements and geometry of the stiffening rings. The obtained results indicate that stiffening the shell generally increases the critical velocity and generates a pattern of alternating stable and unstable regions. The presented analysis provides a viable means for designing a wide variety of stable dynamic systems operating with fast moving loads such as crane booms, robotic arms and gun barrels.

  4. Dynamic stability of periodic shells with moving loads

    NASA Astrophysics Data System (ADS)

    Ruzzene, Massimo; Baz, Amr M.

    2001-08-01

    A moving load causes the radial displacements of an axi- symmetric shell to be several times higher than that produced by the static application of the same load. The travel velocity of the moving load affects the amplitude of the radial response and a critical velocity above which the shell response becomes unstable can be identified. A finite element model (FEM) is developed to analyze the dynamic response of axi-symmetric shells subjected to axially moving loads. The model accounts for the effect of periodically placing stiffening rings along the shell, on the dynamic response and stability characteristics of the shell. Shape functions obtained from the steady-state solution of the equation of motion for a uniform shell are utilized in the development of the FEM. The model is formulated in a reference frame moving with the load in order to enable studying the shell stability using wave propagation and attenuation criteria. Hence, the critical velocity can be identified as the minimum velocity allowing the propagation of applied perturbations. Such stability boundaries are conveniently identified through a transfer mis formulation. The model is used to determine the critical velocities of the moving load for various arrangements and geometry of the stiffening rings. The obtained results indicate that stiffening the shell generally increases the critical velocity and generates a pattern of alternating stable and unstable regions. The presented analysis provides a viable means for designing a wide variety of stable dynamic systems operating with fast moving loads such as crane booms, robotic arms and gun barrels.

  5. The addition of body armor diminishes dynamic postural stability in military soldiers.

    PubMed

    Sell, Timothy C; Pederson, Jonathan J; Abt, John P; Nagai, Takashi; Deluzio, Jennifer; Wirt, Michael D; McCord, Larry J; Lephart, Scott M

    2013-01-01

    Poor postural stability has been identified as a risk factor for lower extremity musculoskeletal injury. The additional weight of body armor carried by Soldiers alters static postural stability and may predispose Soldiers to lower extremity musculoskeletal injuries. However, static postural stability tasks poorly replicate the dynamic military environment, which places considerable stress on the postural control system during tactical training and combat. Therefore, the purpose of this study was to examine the effects of body armor on dynamic postural stability during single-leg jump landings. Thirty-six 101st Airborne Division (Air Assault) Soldiers performed single-leg jump landings in the anterior direction with and without wearing body armor. The dynamic postural stability index and the individual stability indices (medial-lateral stability index, anterior-posterior stability index, and vertical stability index) were calculated for each condition. Paired sample t-tests were performed to determine differences between conditions. Significant differences existed for the medial-lateral stability index, anterior-posterior stability index, vertical stability index, and dynamic postural stability index (p < 0.05). The addition of body armor resulted in diminished dynamic postural stability, which may result in increased lower extremity injuries. Training programs should address the altered dynamic postural stability while wearing body armor in attempts to promote adaptations that will result in safer performance during dynamic tasks.

  6. Nonequilibrium dynamics in lattice ecosystems: Chaotic stability and dissipative structures

    NASA Astrophysics Data System (ADS)

    Solé, Ricard V.; Bascompte, Jordi; Valls, Joaquim

    1992-07-01

    A generalized coupled map lattice (CML) model of ecosystem dynamics is presented. We consider the spatiotemporal behavior of a prey-predator map, a model of host-parasitoid interactions, and two-species competition. The latter model can show phase separation of domains (Turing-like structures) even when chaos is present. We also use this CML model to explore the time evolution and structural properties of ecological networks built with a set of N competing species. The May-Wigner criterion is applied as a measure of stability, and some regularities in the stable networks observed are discussed.

  7. Nonlinear flight dynamics and stability of hovering model insects.

    PubMed

    Liang, Bin; Sun, Mao

    2013-08-01

    Current analyses on insect dynamic flight stability are based on linear theory and limited to small disturbance motions. However, insects' aerial environment is filled with swirling eddies and wind gusts, and large disturbances are common. Here, we numerically solve the equations of motion coupled with the Navier-Stokes equations to simulate the large disturbance motions and analyse the nonlinear flight dynamics of hovering model insects. We consider two representative model insects, a model hawkmoth (large size, low wingbeat frequency) and a model dronefly (small size, high wingbeat frequency). For small and large initial disturbances, the disturbance motion grows with time, and the insects tumble and never return to the equilibrium state; the hovering flight is inherently (passively) unstable. The instability is caused by a pitch moment produced by forward/backward motion and/or a roll moment produced by side motion of the insect.

  8. Nonlinear flight dynamics and stability of hovering model insects

    PubMed Central

    Liang, Bin; Sun, Mao

    2013-01-01

    Current analyses on insect dynamic flight stability are based on linear theory and limited to small disturbance motions. However, insects' aerial environment is filled with swirling eddies and wind gusts, and large disturbances are common. Here, we numerically solve the equations of motion coupled with the Navier–Stokes equations to simulate the large disturbance motions and analyse the nonlinear flight dynamics of hovering model insects. We consider two representative model insects, a model hawkmoth (large size, low wingbeat frequency) and a model dronefly (small size, high wingbeat frequency). For small and large initial disturbances, the disturbance motion grows with time, and the insects tumble and never return to the equilibrium state; the hovering flight is inherently (passively) unstable. The instability is caused by a pitch moment produced by forward/backward motion and/or a roll moment produced by side motion of the insect. PMID:23697714

  9. Enhanced photoacoustic stability of gold nanorods by silica matrix confinement.

    PubMed

    Chen, Leng-Chun; Wei, Chen-Wei; Souris, Jeffrey S; Cheng, Shih-Hsun; Chen, Chin-Tu; Yang, Chung-Shi; Li, Pai-Chi; Lo, Leu-Wei

    2010-01-01

    Photoacoustic tomography (PAT) has garnered much attention for its high contrast and excellent spatial resolution of perfused tissues. Gold nanorods (GNRs) have been employed to further enhance the imaging contrast of PAT. However, the photon fluences typically needed for PA wave induction often also result in GNR shape changes that significantly reduce the efficiency of acoustic wave generation. In this work, we propose, synthesize, and evaluate amorphous silica-coated gold nanorods (GNR-Si) in an effort to improve contrast agent stability and ameliorate efficiency loss during photoacoustic (PA) wave induction. TEM and optical absorption spectra measurements of GNR and GNR-Si show that encasing GNRs within amorphous silica provides substantial protection of nanorod conformation from thermal deformation. PA signals generated by GNR-Si demonstrate considerably greater resistance to degradation of signal intensity with repetitive pulsing than do uncoated GNRs, thereby enabling much longer, high-contrast imaging sessions than previously possible. The prolongation of high-contrast imaging, and biocompatibility and easy surface functionalization for targeting ligands afforded by amorphous silica, suggest GNR-Si to be potentially significant for the clinical translation of PAT. PMID:20210456

  10. Magnetic vortex state stability, reversal and dynamics in restricted geometries.

    PubMed

    Guslienko, K Yu

    2008-06-01

    Magnetic vortices are typically the ground states in geometrically confined ferromagnets with small magnetocrystalline anisotropy. In this article I review static and dynamic properties of the magnetic vortex state in small particles with nanoscale thickness and sub-micron and micron lateral sizes (magnetic dots). Magnetic dots made of soft magnetic material shaped as flat circular and elliptic cylinders are considered. Such mesoscopic dots undergo magnetization reversal through successive nucleation, displacement and annihilation of magnetic vortices. The reversal process depends on the stability of different possible zero-field magnetization configurations with respect to the dot geometrical parameters and application of an external magnetic field. The interdot magnetostatic interaction plays an important role in magnetization reversal for dot arrays with a small dot-to-dot distance, leading to decreases in the vortex nucleation and annihilation fields. Magnetic vortices reveal rich, non-trivial dynamical properties due to existance of the vortex core bearing topological charges. The vortex ground state magnetization distribution leads to a considerable modification of the nature of spin excitations in comparison to those in the uniformly magnetized state. A magnetic vortex confined in a magnetically soft ferromagnet with micron-sized lateral dimensions possesses a characteristic dynamic excitation known as a translational mode that corresponds to spiral-like precession of the vortex core around its equilibrium position. The translation motions of coupled vortices are considered. There are, above the vortex translation mode eigenfrequencies, several dynamic magnetization eigenmodes localized outside the vortex core whose frequencies are determined principally by dynamic demagnetizing fields appearing due to restricted dot geometry. The vortex excitation modes are classified as translation modes and radially or azimuthally symmetric spin waves over the vortex

  11. Fast Dynamic Simulation-Based Small Signal Stability Assessment and Control

    SciTech Connect

    Acharya, Naresh; Baone, Chaitanya; Veda, Santosh; Dai, Jing; Chaudhuri, Nilanjan; Leonardi, Bruno; Sanches-Gasca, Juan; Diao, Ruisheng; Wu, Di; Huang, Zhenyu; Zhang, Yu; Jin, Shuangshuang; Zheng, Bin; Chen, Yousu

    2014-12-31

    Power grid planning and operation decisions are made based on simulation of the dynamic behavior of the system. Enabling substantial energy savings while increasing the reliability of the aging North American power grid through improved utilization of existing transmission assets hinges on the adoption of wide-area measurement systems (WAMS) for power system stabilization. However, adoption of WAMS alone will not suffice if the power system is to reach its full entitlement in stability and reliability. It is necessary to enhance predictability with "faster than real-time" dynamic simulations that will enable the dynamic stability margins, proactive real-time control, and improve grid resiliency to fast time-scale phenomena such as cascading network failures. Present-day dynamic simulations are performed only during offline planning studies, considering only worst case conditions such as summer peak, winter peak days, etc. With widespread deployment of renewable generation, controllable loads, energy storage devices and plug-in hybrid electric vehicles expected in the near future and greater integration of cyber infrastructure (communications, computation and control), monitoring and controlling the dynamic performance of the grid in real-time would become increasingly important. The state-of-the-art dynamic simulation tools have limited computational speed and are not suitable for real-time applications, given the large set of contingency conditions to be evaluated. These tools are optimized for best performance of single-processor computers, but the simulation is still several times slower than real-time due to its computational complexity. With recent significant advances in numerical methods and computational hardware, the expectations have been rising towards more efficient and faster techniques to be implemented in power system simulators. This is a natural expectation, given that the core solution algorithms of most commercial simulators were developed

  12. The dynamical stability of W Ursae Majoris-type systems

    NASA Astrophysics Data System (ADS)

    Li, Lifang; Zhang, Fenghui

    2006-07-01

    Theoretical study indicates that a contact binary system would merge into a rapidly rotating single star due to tidal instability when the spin angular momentum of the system is more than a third of its orbital angular momentum. Assuming that W Ursae Majoris (W UMa) contact binary systems rigorously comply with the Roche geometry and the dynamical stability limit is at a contact degree of about 70 per cent, we obtain that W UMa systems might suffer Darwin's instability when their mass ratios are in a region of about 0.076-0.078 and merge into the fast-rotating stars. This suggests that the W UMa systems with mass ratio q <= 0.076 cannot be observed. Meanwhile, we find that the observed W UMa systems with a mass ratio of about 0.077, corresponding to a contact degree of about 86 per cent would suffer tidal instability and merge into the single fast-rotating stars. This suggests that the dynamical stability limit for the observed W UMa systems is higher than the theoretical value, implying that the observed systems have probably suffered the loss of angular momentum due to gravitational wave radiation (GR) or magnetic stellar wind (MSW).

  13. Dynamic stability of a human standing on a balance board.

    PubMed

    Chagdes, James R; Rietdyk, Shirley; Jeffrey, M Haddad; Howard, N Zelaznik; Raman, Arvind

    2013-10-18

    The neuromuscular system used to stabilize upright posture in humans is a nonlinear dynamical system with time delays. The analysis of this system is important for improving balance and for early diagnosis of neuromuscular disease. In this work, we study the dynamic coupling between the neuromuscular system and a balance board-an unstable platform often used to improve balance in young athletes, and older or neurologically impaired patients. Using a simple inverted pendulum model of human posture on a balance board, we describe a surprisingly broad range of divergent and oscillatory CoP/CoM responses associated with instabilities of the upright equilibrium. The analysis predicts that a variety of sudden changes in the stability of upright postural equilibrium occurs with slow continuous deterioration in balance board stiffness, neuromuscular gain, and time delay associated with the changes in proprioceptive/vestibular/visual-neuromuscular feedback. The analysis also provides deeper insight into changes in the control of posture that enable stable upright posture on otherwise unstable platforms.

  14. Global asymptotic stability of dynamic dissipative compensators for multibody flexible space structures

    NASA Technical Reports Server (NTRS)

    Kelkar, Atul G.; Joshi, Suresh M.; Alberts, Thomas E.

    1993-01-01

    The stability characteristics of dynamic dissipative compensators are investigated for multibody flexible space structures having nonlinear dynamics. The problem addressed is that of proving asymptotic stability of dynamic dissipative compensators. The stability proof uses the Liapunov approach and exploits the inherent passivity of such systems. For such systems these compensators are shown to be robust to parametric uncertainties and unmodeled dynamics. The results are applicable to a large class of structures such as flexible space structures with articulated flexible appendages.

  15. Stability Limits and Dynamics of Nonaxisymmetric Liquid Bridges

    NASA Technical Reports Server (NTRS)

    Alexander, J. Iwan D.; Slobozhanin, Lev A.; Resnick, Andrew H.; Ramus, Jean-Francois; Delafontaine, Sylvie

    1999-01-01

    Liquid bridges have been the focus of numerous theoretical and experimental investigations since the early work by Plateau more than a century ago. More recently, motivated by interest in their physical behavior and their occurrence in a variety of technological situations, there has been a resurgence of interest in the static and dynamic behavior of liquid bridges. Furthermore, opportunities to carry out experiments in the near weightless environment of a low-Earth-orbit spacecraft have also led to a number of low-gravity experiments involving large liquid bridges. In this paper, we present selected results from our work concerning the stability of nonaxisymmetric liquid bridges, the bifurcation of weightless bridges in the neighborhood of the maximum volume stability limit, isorotating axisymmetric bridges contained between equidimensional disks, and bridges contained between unequal disks. For the latter, we discuss both theoretical and experimental results. Finally, we present results concerning the stability of axisymmetric equilibrium configurations for a capillary liquid partly contained in a closed circular cylinder.

  16. Effects of visual deprivation on gait dynamic stability.

    PubMed

    Iosa, Marco; Fusco, Augusto; Morone, Giovanni; Paolucci, Stefano

    2012-01-01

    Vision can improve bipedal upright stability during standing and affect spatiotemporal parameters during walking. However, little is known about the effects of visual deprivation on gait dynamic stability. We have tested 28 subjects during walking under two different visual conditions, full vision (FV) and no vision (NV), measuring their upper body accelerations. Lower accelerations were found in NV for the reduced walking speed. However, the normalized accelerations were higher in the NV than in the FV condition, both in anteroposterior (1.05 ± 0.21 versus 0.88 ± 0.16, P = 0.001) and laterolateral (0.99 ± 0.26 versus 0.78 ± 0.19, P < 0.001) directions. Vision also affected the gait anteroposterior harmony (P = 0.026) and, interacting with the environment, also the latero-lateral one (P = 0.017). Directly (as main factor of the ANOVA) or indirectly (by means of significant interactions with other factors), vision affected all the measured parameters. In conclusion, participants showed an environment-dependent reduction of upper body stability and harmony when deprived by visual feedback.

  17. Enhancing enzyme stability by construction of polymer-enzyme conjugate micelles for decontamination of organophosphate agents.

    PubMed

    Suthiwangcharoen, Nisaraporn; Nagarajan, Ramanathan

    2014-04-14

    Enhancing the stability of enzymes under different working environments is essential if the potential of enzyme-based applications is to be realized for nanomedicine, sensing and molecular diagnostics, and chemical and biological decontamination. In this study, we focus on the enzyme, organophosphorus hydrolase (OPH), which has shown great promise for the nontoxic and noncorrosive decontamination of organophosphate agents (OPs) as well as for therapeutics as a catalytic bioscavanger against nerve gas poisoning. We describe a facile approach to stabilize OPH using covalent conjugation with the amphiphilic block copolymer, Pluronic F127, leading to the formation of F127-OPH conjugate micelles, with the OPH on the micelle corona. SDS-PAGE and MALDI-TOF confirmed the successful conjugation, and transmission electron microscopy (TEM) and dynamic light scattering (DLS) revealed ∼100 nm size micelles. The conjugates showed significantly enhanced stability and higher activity compared to the unconjugated OPH when tested (i) in aqueous solutions at room temperature, (ii) in aqueous solutions at higher temperatures, (iii) after multiple freeze/thaw treatments, (iv) after lyophilization, and (v) in the presence of organic solvents. The F127-OPH conjugates also decontaminated paraoxon (introduced as a chemical agent simulant) on a polystyrene film surface and on a CARC (Chemical Agent Resistant Coating) test panel more rapidly and to a larger extent compared to free OPH. We speculate that, in the F127-OPH conjugates (both in the micellar form as well as in the unaggregated conjugate), the polypropylene oxide block of the copolymer interacts with the surface of the OPH and this confinement of the OPH reduces the potential for enzyme denaturation and provides robustness to OPH at different working environments. The use of such polymer-enzyme conjugate micelles with improved enzyme stability opens up new opportunities for numerous civilian and Warfighter applications.

  18. Stabilization and dynamics of edge flames in narrow channels

    NASA Astrophysics Data System (ADS)

    Bieri, Joanna A.

    The dynamics of edge flames in narrow channels is studied, first within the context of a reactive diffusive (or constant density) model and then in a variable density model which allows for the consideration of thermal expansion effects. Fuel and oxidizer, separated upstream by a thin plate of finite length, flow into a channel with a prescribed upstream velocity. At the end of the plate, the fuel and oxidizer mix and, when ignited, an edge flame is sustained at some distance from the tip of the plate. Typically, the flame, which is stabilized by heat conduction back to the cold plate, has a tribrachial structure. It consists of a leading edge, made up of lean and rich premixed segments, and an attached diffusion flame trailing behind. The flame can also have a hook-like shape, when one of the premixed branches is missing. This often happens for conditions away from stoichiometry and when the mass diffusivities of the fuel and oxidizer are unequal. Earlier work has determined the behavior of an edge flame in a mixing layer that develops downstream of a splitter plate with no boundaries in the lateral direction. This is relevant to the stabilization and liftoff of jet diffusion flames. The confined case has other possible applications, such as flames in mini-combustor systems, that have been recently tested experimentally. The objective in this work is to determine the effect that confinement has on the edge standoff distance, on the flame shape and on the flame stability. In particular, we examine the influence of channel width, wall temperature, and the effects of differential diffusion. We determine conditions under which the edge flame is stabilized near the tip of the splitter plate, is held near the tip but oscillates back and forth, or is blown-off. We consider a wide range of channel widths and boundary conditions at the walls.

  19. Stability and Load Sharing Characteristics of a Posterior Dynamic Stabilization Device

    PubMed Central

    Cook, Daniel J.; Yeager, Matthew S.; Thampi, Shankar S.; Whiting, Donald M.

    2015-01-01

    Background Lumbar interbody fusion is a common treatment for a variety of spinal pathologies. It has been hypothesized that insufficient mechanical loading of the interbody graft can prevent proper fusion of the joint. The purpose of this study was to evaluate the mechanical stability and anterior column loading sharing characteristics of a posterior dynamic system compared to titanium rods in an anterior lumbar interbody fusion (ALIF) model. Methods Range of motion, interpedicular kinematics and interbody graft loading were measured in human cadaveric lumbar segments tested under a pure moment flexibility testing protocol. Results Both systems provided significant fixation compared to the intact condition and to an interbody spacer alone in flexion extension and lateral bending. No significant differences in fixation were detected between the devices. A significant decrease in graft loading was detected in flexion for the titanium rod treatment compared to spacer alone. No significant differences in graft loading were detected between the spacer alone and posterior dynamic system or between the posterior dynamic system and the titanium rod. Conclusions The results of this study indicate that the posterior dynamic system provides similar fixation compared to that of a titanium rod, however, studies designed to evaluate the efficacy of fixation in a cadaver model may not be sufficiently powered to establish differences in load sharing using the techniques described here. PMID:26131403

  20. Enhanced stability and antibacterial efficacy of a traditional Chinese medicine-mediated silver nanoparticle delivery system.

    PubMed

    Sun, Wenjie; Qu, Ding; Ma, Yihua; Chen, Yan; Liu, Congyan; Zhou, Jing

    2014-01-01

    Silver nanoparticles (AgNPs) are widely used as antibacterial products in various fields. Recent studies have suggested that AgNPs need an appropriate stabilizer to improve their stability. Some antibacterial traditional Chinese medicines (TCMs) contain various reductive components, which can not only stabilize AgNPs but also enhance their antimicrobial activity. In this study, we developed a series of novel AgNPs using a TCM extract as a stabilizer, reducing agent, and antimicrobial agent (TCM-AgNPs). A storage stability investigation of the TCM-AgNPs suggested a significant improvement when compared with bare AgNPs. Further, conjugation of TCMs onto the AgNP surface resulted in stronger antimicrobial potency on antibacterial evaluation using Pseudomonas aeruginosa, Staphylococcus epidermidis, and Staphylococcus aureus with minimum inhibitory concentration 50% (MIC50) ratios (and minimum bactericidal concentration 90% [MBC90] ratios) of AgNPs to respective TCM-AgNPs as assessment indices. Among these, P. cuspidatum Sieb. et-conjugated AgNPs (P.C.-AgNPs) had the advantage of a combination of TCMs and AgNPs and was studied in detail with regard to its synthesis and characterization. The extraction time, reaction temperature, and concentrations of AgNO3 and Polygonum cuspidatum Sieb. et extract were critical factors in the preparation of P.C.-AgNPs. Further, the results of X-ray diffraction and Fourier transform infrared spectroscopy indicated successful preparation of P.C.-AgNPs. In representative studies, P.C.-AgNPs showed a well-defined spherical shape, a homogeneous small particle size (36.78 nm), a narrow polydispersity index (0.105), and a highly negative zeta potential (-23.6 mV) on transmission electron microscopy and dynamic light scattering. These results indicate that TCM-AgNPs have a potential role as antibacterial agents in the clinic setting. PMID:25473286

  1. Dynamics and stability of spinning flexible space tether systems

    NASA Astrophysics Data System (ADS)

    Tyc, George

    This dissertation focuses on a detailed dynamical investigation of a previously unexplored tether configuration that involves a spinning two-body tethered system with flexible appendages on each end-body where the spin axis is nominally aligned along the tether. The original motivation for this work came after the flight of the first Canadian sub-orbital tether mission OEDIPUS-A in 1989 which employed this spinning tethered configuration. To everyone's surprise, one of the end-bodies was observed to exhibit a rapid divergence of its nutation angle. It was clear after this flight that there were some fundamental mechanisms associated with the interaction between the tether and the end-body that were not fully understood at that time. Hence, a Tether Dynamics Experiment (TDE) was formed and became a formal part of the scientific agenda for the follow-on mission OEDIPUS-C which flew in 1995. This dissertation describes the work that was conducted as part of the TDE and involves: theoretical investigations into the dynamics of this spinning tethered flexible body system; ground testing to validate the models and establish the tether properties; application of the models to develop a stabilization approach for OEDIPUS-C, and comparisons between theory and flight data from both OEDIPUS-A and OEDIPUS-C. Nonlinear equations of motion are developed for a spinning tethered system where the tether could be either spinning with the end-bodies or attached to small de-spun platforms on the end-bodies. Since the tether used for the OEDIPUS missions is not a string, as is often assumed, but rather a wire that has some bending stiffness, albeit small, the tether bending was also taken into account in the formulation. Two sets of ground tests are described that were used to validate the stability conditions and gain confidence in the mathematical models. One set involved hanging a body by a tether and spinning at different speeds to investigate the end-body stability. The other set

  2. Dynamics and stability of divacancy defects in graphene

    NASA Astrophysics Data System (ADS)

    Kim, Youngkuk; Ihm, Jisoon; Yoon, Euijoon; Lee, Gun-Do

    2011-08-01

    A divacancy (DV) is one of the most abundant and most important defects in irradiated graphene, which modifies electronic and chemical properties of graphene. In this paper, we present ab initio calculations to study the dynamics and stability of DVs in graphene. Divacancies in graphene have various reconstructed structures, such as triple pentagon-triple heptagon (555-777) and pentagon-octagon-pentagon (5-8-5) patterns. A direct observation of the structural transformations between these reconstructions was recorded in transmission electron microscope images reported by Girit in ScienceSCIEAS0036-807510.1126/science.1166999 323, 1705 (2009). We clarify the atomic structures of DVs observed in the experiment and investigate the atomic processes and energetics for the observed dynamical motions in great detail. It is found that a series of Stone-Wales-type transformations are responsible for the migration and structural transformations of DVs and that a pentagon-heptagon-heptagon-pentagon (5-7-7-5) defect appearing as an intermediate structure during the dynamical process plays an important role in the transformations of DVs.

  3. Effect of oculo-motor and gaze stability exercises on postural stability and dynamic visual acuity in healthy young adults.

    PubMed

    Morimoto, Hiroyuki; Asai, Yuji; Johnson, Eric G; Lohman, Everett B; Khoo, Keiko; Mizutani, Yoko; Mizutani, Takehiko

    2011-04-01

    The purpose of this study was to investigate the effectiveness of oculo-motor exercises and gaze stability exercises on postural stability and dynamic visual acuity (DVA) in healthy young adults. Subjects were randomly divided into experimental (n=28) and control groups (n=13). The experimental group performed oculo-motor exercises and gaze stability exercise for three weeks and the control group did not. Pre and post postural stability during quiet standing, standing with active head rotation, and DVA were measured on both groups. Significant differences were found in postural stability during standing with active head rotation and DVA in the experimental group (p<0.05). No significant differences were found in postural stability or DVA in the control group. Improvements in postural stability and DVA after three weeks of oculo-motor exercises and gaze stability exercises suggest that this specific type of vestibular and ocular system exercises may be beneficial for healthy young adults.

  4. Carotenoid incorporation into microsomes: yields, stability and membrane dynamics.

    PubMed

    Socaciu, C; Jessel, R; Diehl, H A

    2000-12-01

    The carotenoids beta-carotene (BC), lycopene (LYC), lutein (LUT), zeaxanthin (ZEA), canthaxanthin (CTX) and astaxanthin (ASTA) have been incorporated into pig liver microsomes. Effective incorporation concentrations in the range of about 1-6 nmol/mg microsomal protein were obtained. A stability test at room temperature revealed that after 3 h BC and LYC had decayed totally whereas, gradually, CTX (46%), LUT (21%), ASTA (17%) and ZEA (5%) decayed. Biophysical parameters of the microsomal membrane were changed hardly by the incorporation of carotenoids. A small rigidification may occur. Membrane anisotropy seems to offer only a small tolerance for incorporation of carotenoids and seems to limit the achievable incorporation concentrations of the carotenoids into microsomes. Microsomes instead of liposomes should be preferred as a membrane model to study mutual effects of carotenoids and membrane dynamics.

  5. Dynamics and Stability and Control Characteristics of the X-37

    NASA Technical Reports Server (NTRS)

    Chaudhary, Ashwani; Nguyen, Viet; Tran, Hoi; Poladian, David; Falangas, Eric; Turner, Susan G. (Technical Monitor)

    2001-01-01

    This paper presents the stability and control analysis and the control design results for the Boeing/NASA/AFRL X-37. The X-37 is a flight demonstrator vehicle that will go into space and after its mission, autonomously reenter and land on a conventional runway. This paper studies the dynamics and control of the X-37 from atmospheric reentry through landing. A nominal trajectory that lands on the Edwards Air Force Base Lakebed is considered for all the analysis and design. The X-37's longitudinal and lateral/directional bare-airframe characteristics are presented. The level of maneuvering control power is assessed. Vehicle trim with multiple surfaces is discussed. Special challenges where the wings loose roll effectiveness are discussed and solutions are presented. Aerodynamic uncertainties and flexibility modeling issues are presented. Control design results and robustness analysis methods are presented. Results are provided for the Entry, Terminal Area Energy Management (TAEM), and Approach and Land phases.

  6. Dynamical stability of a many-body Kapitza pendulum

    SciTech Connect

    Citro, Roberta; Dalla Torre, Emanuele G.; D’Alessio, Luca; Polkovnikov, Anatoli; Babadi, Mehrtash; Oka, Takashi; Demler, Eugene

    2015-09-15

    We consider a many-body generalization of the Kapitza pendulum: the periodically-driven sine–Gordon model. We show that this interacting system is dynamically stable to periodic drives with finite frequency and amplitude. This finding is in contrast to the common belief that periodically-driven unbounded interacting systems should always tend to an absorbing infinite-temperature state. The transition to an unstable absorbing state is described by a change in the sign of the kinetic term in the Floquet Hamiltonian and controlled by the short-wavelength degrees of freedom. We investigate the stability phase diagram through an analytic high-frequency expansion, a self-consistent variational approach, and a numeric semiclassical calculation. Classical and quantum experiments are proposed to verify the validity of our results.

  7. U32: Vehicle Stability and Dynamics: Longer Combination Vehicles

    SciTech Connect

    Petrolino, Joseph; Spezia, Tony; Arant, Michael; Broshears, Eric; Chitwood, Caleb; Colbert, Jameson; Hathaway, Richard; Keil, Mitch; LaClair, Tim J; Pape, Doug; Patterson, Jim; Pittro, Collin

    2011-01-01

    This study investigated the safety and stability of longer combination vehicles (LCVs), in particular a triple trailer combination behind a commercial tractor, which has more complicated dynamics than the more common tractor in combination with a single semitrailer. The goal was to measure and model the behavior of LCVs in simple maneuvers. Example maneuvers tested and modeled were single and double lane changes, a gradual lane change, and a constant radius curve. In addition to test track data collection and a brief highway test, two computer models of LCVs were developed. One model is based on TruckSim , a lumped parameter model widely used for single semitrailer combinations. The other model was built in Adams software, which more explicitly models the geometry of the components of the vehicle, in terms of compliant structural members. Among other results, the models were able to duplicate the experimentally measured rearward amplification behavior that is characteristic of multi-unit combination vehicles.

  8. Statistical precision and sensitivity of measures of dynamic gait stability.

    PubMed

    Bruijn, Sjoerd M; van Dieën, Jaap H; Meijer, Onno G; Beek, Peter J

    2009-04-15

    Recently, two methods for quantifying a system's dynamic stability have been applied to human locomotion: local stability (quantified by finite time maximum Lyapunov exponents, lambda(S-stride) and lambda(L-stride)) and orbital stability (quantified as maximum Floquet multipliers, MaxFm). Thus far, however, it has remained unclear how many data points are required to obtain precise estimates of these measures during walking, and to what extent these estimates are sensitive to changes in walking behaviour. To resolve these issues, we collected long data series of healthy subjects (n=9) walking on a treadmill in three conditions (normal walking at 0.83 m/s (3 km/h) and 1.38 m/s (5 km/h), and walking at 1.38 m/s (5 km/h) while performing a Stroop dual task). Data series from 0.83 and 1.38 m/s trials were submitted to a bootstrap procedure and paired t-tests for samples of different data series lengths were performed between 0.83 and 1.38 m/s and between 1.38 m/s with and without Stroop task. Longer data series led to more precise estimates for lambda(S-stride), lambda(L-stride), and MaxFm. All variables showed an effect of data series length. Thus, when estimating and comparing these variables across conditions, data series covering an equal number of strides should be analysed. lambda(S-stride), lambda(L-stride), and MaxFm were sensitive to the change in walking speed while only lambda(S-stride) and MaxFm were sensitive enough to capture the modulations of walking induced by the Stroop task. Still, these modulations could only be detected when using a substantial number of strides (>150). PMID:19135478

  9. The dynamics of CRM attitude change: Attitude stability

    NASA Technical Reports Server (NTRS)

    Gregorich, Steven E.

    1993-01-01

    Special training seminars in cockpit resource management (CRM) are designed to enhance crew effectiveness in multicrew air-transport cockpits. In terms of CRM, crew effectiveness is defined by teamwork rather than technical proficiency. These seminars are designed to promote factual learning, alter aviator attitudes, and motivate aviators to make use of what they have learned. However, measures of attitude change resulting from CRM seminars have been the most common seminar evaluation technique. The current investigation explores a broader range of attitude change parameters with specific emphasis on the stability of change between recurrent visits to the training center. This allows for a comparison of training program strengths in terms of seminar ability to effect lasting change.

  10. Dynamical Stability of the F Ring Core and Moonlet Belt

    NASA Astrophysics Data System (ADS)

    Whizin, A.; Colwell, J.; Cuzzi, J. N.

    2011-12-01

    The stability of the F ring core has yet to be adequately established. We further work similar to Scargle, J. & Cuzzi, J., et al. (1993, Dynamical Evolution of Saturn's Rings, BAAS 25, 1103) through the orbital evolution of test particles in the F ring region in order to explore how Prometheus and Pandora control the position and perhaps even the fate of this unique ring. The F ring was once thought to be shepherded (Goldreich & Tremaine ARAA 1982, 20:249-83) but now it is clearer that it exhibits signs of chaos (Scargle et al., 1993, Winter, O. C., et al., 2007, MNRAS, 380, L54, and Winter, O.C., et al., 2010, A&A, 523, A67). Our work also sheds light on the evolution of the ~1km sized embedded moonlets ('clumps') which wreak havoc on the ring through encounters with Prometheus, creating gaps in the ring ('streaks')(Murray, C. D., et al., 2008, Nature, 453, 7196, 739-744). We present results pertaining to the stability of the F ring core, using a three-pronged approach consisting of N-body numerical simulations, analytical modeling, and detection and analysis of chaotic orbits with Lyapunov Residuals. Our results find narrow regions that are substantially more stable near the Bosh et al. (2002, Icarus 157, 57-75) core location, which we argue may explain the current location of the F ring.

  11. On the Dynamic Stability of Cool Supergiant Atmospheres

    NASA Astrophysics Data System (ADS)

    Lobel, A.

    2001-09-01

    We have developed a new formalism to compute the thermodynamic coefficient Γ1 in the theory of stellar and atmospheric stability. We generalize the classical derivation of the first adiabatic index, which is based on the assumption of thermal ionization and equilibrium between gas and radiation temperature, toward an expression that incorporates photoionization due to radiation with a temperature Trad different from the local kinetic gas temperature. Our formalism considers the important non-LTE conditions in the extended atmospheres of supergiant stars. An application to the Kurucz grid of cool supergiant atmospheres demonstrates that models with Trad~=Teff between 6500 and 7500 K become most unstable against dynamic perturbations, according to Ledoux' stability integral <Γ1>. This results from Γ1 and <Γ1> acquiring very low values, below 4/3, throughout the entire stellar atmosphere, which causes very high gas compression ratios around these effective temperatures. Based on detailed non-LTE calculations, we discuss atmospheric instability of pulsating massive yellow supergiants, such as the hypergiant ρ Cas (Ia+), which exist in the extension of the Cepheid instability strip, near the Eddington luminosity limit.

  12. Blowoff dynamics of bluff body stabilized turbulent premixed flames

    SciTech Connect

    Chaudhuri, Swetaprovo; Kostka, Stanislav; Renfro, Michael W.; Cetegen, Baki M.

    2010-04-15

    This article concerns the flame dynamics of a bluff body stabilized turbulent premixed flame as it approaches lean blowoff. Time resolved chemiluminescence imaging along with simultaneous particle image velocimetry and OH planar laser-induced fluorescence were utilized in an axisymmetric bluff body stabilized, propane-air flame to determine the sequence of events leading to blowoff and provide a quantitative analysis of the experimental results. It was found that as lean blowoff is approached by reduction of equivalence ratio, flame speed decreases and the flame shape progressively changes from a conical to a columnar shape. For a stably burning conical flame away from blowoff, the flame front envelopes the shear layer vortices. Near blowoff, the columnar flame front and shear layer vortices overlap to induce high local stretch rates that exceed the extinction stretch rates instantaneously and in the mean, resulting in local flame extinction along the shear layers. Following shear layer extinction, fresh reactants can pass through the shear layers to react within the recirculation zone with all other parts of the flame extinguished. This flame kernel within the recirculation zone may survive for a few milliseconds and can reignite the shear layers such that the entire flame is reestablished for a short period. This extinction and reignition event can happen several times before final blowoff which occurs when the flame kernel fails to reignite the shear layers and ultimately leads to total flame extinguishment. (author)

  13. Enrichment Ratio and Aggregate Stability Dynamics in Intensely Managed Landscapes

    NASA Astrophysics Data System (ADS)

    Wacha, K.; Papanicolaou, T.; Filley, T. R.; Hou, T.; Abban, B. K.; Wilson, C. G.; Boys, J.

    2015-12-01

    Challenges in understanding the soil carbon dynamics within intensely managed landscapes (IMLs), found throughout much the US Midwest, is highly complex due to the presence of heterogeneous landscape features and properties, as well as a mosaic of physical and biogeochemical processes occurring at different time scales. In addition, rainfall events exacerbate the effects of tillage by the impact of raindrops, which break down aggregates that encase carbon and dislodge and entrain soil particles and aggregates along the downslope. The redistribution of soil and carbon can have huge implications on biogeochemical cycling and overall carbon budgeting. In this study, we provide some rare field data on the mechanisms impacting aggregate stability, enrichment ratio values to estimate fluxes of carbon, as well as lignin chemistry to see influences on oxidation/mineralization rates. Rainfall simulation experiments were conducted within agricultural fields. Experiments were performed on the midslope (eroding) and toeslope (depositional) sections of representative hillslopes, under a variety of land managements, including row crop (conventional and conservation) and restored grasslands. Sensors were utilized to capture the evolution of soil moisture, temperature, microbial respiration pulses, and discharge rates to identify pseudo-steady state conditions. Samples collected at the weir outlet were tested for sediment concentrations and size fractions, as well as carbon and lignin fluxes. Preliminary findings show that conservation management practices have higher aggregate stability and decreased mass fluxes of carbon in the downslope than conventional tillage techniques.

  14. Mechanism study on stability enhancement of adefovir dipivoxil by cocrystallization: Degradation kinetics and structure-stability correlation.

    PubMed

    Lin, Rui-Zhen; Sun, Peng-Jie; Tao, Qian; Yao, Jia; Chen, Jia-Mei; Lu, Tong-Bu

    2016-03-31

    The purpose of this study is to determine the mechanism by which cocrystallization can enhance the stability of adefovir dipivoxil (AD), a diester prodrug of adefovir with known chemical stability problem. Three multi-component crystals of AD with biologically safe coformers, including gallic acid cocrystal hydrate (1:1:1), salicylate salt (1:1), and maleate salt (1:1) were prepared and characterized by thermal analysis, infrared spectroscopy, powder and single crystal X-ray diffraction. DVS measurements and stability tests were applied to evaluate the stability. The new crystalline phases exhibit improved stability compared to pure drug in the order AD gallic acid cocrystal>AD maleate>AD salicylate>AD form I. Degradation kinetics and structure-stability correlation studies demonstrate that the stability enhancement mechanism by cocrystallization involves (1) inhibition of hydrolysis of AD by replacement of drug-drug homosynthons by stronger drug-coformer heterosynthons at adenine fragments; (2) suppression of dimerization of AD by separation of adenine fragments by inserting coformers in crystal lattices; (3) further reducing rates of hydrolysis by forming hydrogen bonds with hydrate water at phosphoryl fragments. This study has important implications for use of cocrystallization approach to some easily degradable drugs in pharmaceutical. PMID:26462447

  15. Enhancing the stability of the synchronization of multivariable coupled oscillators

    NASA Astrophysics Data System (ADS)

    Sevilla-Escoboza, R.; Gutiérrez, R.; Huerta-Cuellar, G.; Boccaletti, S.; Gómez-Gardeñes, J.; Arenas, A.; Buldú, J. M.

    2015-09-01

    Synchronization processes in populations of identical networked oscillators are the focus of intense studies in physical, biological, technological, and social systems. Here we analyze the stability of the synchronization of a network of oscillators coupled through different variables. Under the assumption of an equal topology of connections for all variables, the master stability function formalism allows assessing and quantifying the stability properties of the synchronization manifold when the coupling is transferred from one variable to another. We report on the existence of an optimal coupling transference that maximizes the stability of the synchronous state in a network of Rössler-like oscillators. Finally, we design an experimental implementation (using nonlinear electronic circuits) which grounds the robustness of the theoretical predictions against parameter mismatches, as well as against intrinsic noise of the system.

  16. Enhancement of ferroelectric polarization stability by interface engineering.

    PubMed

    Lu, H; Liu, X; Burton, J D; Bark, C-W; Wang, Y; Zhang, Y; Kim, D J; Stamm, A; Lukashev, P; Felker, D A; Folkman, C M; Gao, P; Rzchowski, M S; Pan, X Q; Eom, C-B; Tsymbal, E Y; Gruverman, A

    2012-03-01

    By using theoretical predictions based on first-principle calculations, we explore an interface engineering approach to stabilize polarization states in ferroelectric heterostructures with a thickness of just several nanometers. PMID:22278910

  17. Enhancing the stability of the synchronization of multivariable coupled oscillators.

    PubMed

    Sevilla-Escoboza, R; Gutiérrez, R; Huerta-Cuellar, G; Boccaletti, S; Gómez-Gardeñes, J; Arenas, A; Buldú, J M

    2015-09-01

    Synchronization processes in populations of identical networked oscillators are the focus of intense studies in physical, biological, technological, and social systems. Here we analyze the stability of the synchronization of a network of oscillators coupled through different variables. Under the assumption of an equal topology of connections for all variables, the master stability function formalism allows assessing and quantifying the stability properties of the synchronization manifold when the coupling is transferred from one variable to another. We report on the existence of an optimal coupling transference that maximizes the stability of the synchronous state in a network of Rössler-like oscillators. Finally, we design an experimental implementation (using nonlinear electronic circuits) which grounds the robustness of the theoretical predictions against parameter mismatches, as well as against intrinsic noise of the system.

  18. Ethanol enhances collective dynamics of lipid membranes

    SciTech Connect

    Kaye, Martin D.; Schmalzl, Karin; Conti Nibali, Valeria; Tarek, Mounir; Rheinstaedter, Maikel C.

    2011-05-15

    From inelastic neutron-scattering experiments and all atom molecular dynamics simulations we present evidence for a low-energy dynamical mode in the fluid phase of a 1,2-dimyristoyl-sn-glycero-3-phoshatidylcholine (DMPC) bilayer immersed in a 5% water/ethanol solution. In addition to the well-known phonon that shows a liquidlike dispersion with energies up to 4.5 meV, we observe an additional mode at smaller energies of 0.8 meV, which shows little or no dispersion. Both modes show transverse properties and might be related to molecular motion perpendicular to the bilayer.

  19. Dynamics of microresonator frequency comb generation: models and stability

    NASA Astrophysics Data System (ADS)

    Hansson, Tobias; Wabnitz, Stefan

    2016-06-01

    Microresonator frequency combs hold promise for enabling a new class of light sources that are simultaneously both broadband and coherent, and that could allow for a profusion of potential applications. In this article, we review various theoretical models for describing the temporal dynamics and formation of optical frequency combs. These models form the basis for performing numerical simulations that can be used in order to better understand the comb generation process, for example helping to identify the universal combcharacteristics and their different associated physical phenomena. Moreover, models allow for the study, design and optimization of comb properties prior to the fabrication of actual devices. We consider and derive theoretical formalisms based on the Ikeda map, the modal expansion approach, and the Lugiato-Lefever equation. We further discuss the generation of frequency combs in silicon resonators featuring multiphoton absorption and free-carrier effects. Additionally, we review comb stability properties and consider the role of modulational instability as well as of parametric instabilities due to the boundary conditions of the cavity. These instability mechanisms are the basis for comprehending the process of frequency comb formation, for identifying the different dynamical regimes and the associated dependence on the comb parameters. Finally, we also discuss the phenomena of continuous wave bi- and multistability and its relation to the observation of mode-locked cavity solitons.

  20. Applications of Computational Methods for Dynamic Stability and Control Derivatives

    NASA Technical Reports Server (NTRS)

    Green, Lawrence L.; Spence, Angela M.

    2004-01-01

    Initial steps in the application o f a low-order panel method computational fluid dynamic (CFD) code to the calculation of aircraft dynamic stability and control (S&C) derivatives are documented. Several capabilities, unique to CFD but not unique to this particular demonstration, are identified and demonstrated in this paper. These unique capabilities complement conventional S&C techniques and they include the ability to: 1) perform maneuvers without the flow-kinematic restrictions and support interference commonly associated with experimental S&C facilities, 2) easily simulate advanced S&C testing techniques, 3) compute exact S&C derivatives with uncertainty propagation bounds, and 4) alter the flow physics associated with a particular testing technique from those observed in a wind or water tunnel test in order to isolate effects. Also presented are discussions about some computational issues associated with the simulation of S&C tests and selected results from numerous surface grid resolution studies performed during the course of the study.

  1. Enhancing synchronization stability in a multi-area power grid.

    PubMed

    Wang, Bing; Suzuki, Hideyuki; Aihara, Kazuyuki

    2016-01-01

    Maintaining a synchronous state of generators is of central importance to the normal operation of power grids, in which many networks are generally interconnected. In order to understand the condition under which the stability can be optimized, it is important to relate network stability with feedback control strategies as well as network structure. Here, we present a stability analysis on a multi-area power grid by relating it with several control strategies and topological design of network structure. We clarify the minimal feedback gain in the self-feedback control, and build the optimal communication network for the local and global control strategies. Finally, we consider relationship between the interconnection pattern and the synchronization stability; by optimizing the network interlinks, the obtained network shows better synchronization stability than the original network does, in particular, at a high power demand. Our analysis shows that interlinks between spatially distant nodes will improve the synchronization stability. The results seem unfeasible to be implemented in real systems but provide a potential guide for the design of stable power systems. PMID:27225708

  2. Enhancing synchronization stability in a multi-area power grid

    PubMed Central

    Wang, Bing; Suzuki, Hideyuki; Aihara, Kazuyuki

    2016-01-01

    Maintaining a synchronous state of generators is of central importance to the normal operation of power grids, in which many networks are generally interconnected. In order to understand the condition under which the stability can be optimized, it is important to relate network stability with feedback control strategies as well as network structure. Here, we present a stability analysis on a multi-area power grid by relating it with several control strategies and topological design of network structure. We clarify the minimal feedback gain in the self-feedback control, and build the optimal communication network for the local and global control strategies. Finally, we consider relationship between the interconnection pattern and the synchronization stability; by optimizing the network interlinks, the obtained network shows better synchronization stability than the original network does, in particular, at a high power demand. Our analysis shows that interlinks between spatially distant nodes will improve the synchronization stability. The results seem unfeasible to be implemented in real systems but provide a potential guide for the design of stable power systems. PMID:27225708

  3. Enhancing synchronization stability in a multi-area power grid

    NASA Astrophysics Data System (ADS)

    Wang, Bing; Suzuki, Hideyuki; Aihara, Kazuyuki

    2016-05-01

    Maintaining a synchronous state of generators is of central importance to the normal operation of power grids, in which many networks are generally interconnected. In order to understand the condition under which the stability can be optimized, it is important to relate network stability with feedback control strategies as well as network structure. Here, we present a stability analysis on a multi-area power grid by relating it with several control strategies and topological design of network structure. We clarify the minimal feedback gain in the self-feedback control, and build the optimal communication network for the local and global control strategies. Finally, we consider relationship between the interconnection pattern and the synchronization stability; by optimizing the network interlinks, the obtained network shows better synchronization stability than the original network does, in particular, at a high power demand. Our analysis shows that interlinks between spatially distant nodes will improve the synchronization stability. The results seem unfeasible to be implemented in real systems but provide a potential guide for the design of stable power systems.

  4. Dynamic stability of sequential stimulus representations in adapting neuronal networks

    PubMed Central

    Duarte, Renato C. F.; Morrison, Abigail

    2014-01-01

    The ability to acquire and maintain appropriate representations of time-varying, sequential stimulus events is a fundamental feature of neocortical circuits and a necessary first step toward more specialized information processing. The dynamical properties of such representations depend on the current state of the circuit, which is determined primarily by the ongoing, internally generated activity, setting the ground state from which input-specific transformations emerge. Here, we begin by demonstrating that timing-dependent synaptic plasticity mechanisms have an important role to play in the active maintenance of an ongoing dynamics characterized by asynchronous and irregular firing, closely resembling cortical activity in vivo. Incoming stimuli, acting as perturbations of the local balance of excitation and inhibition, require fast adaptive responses to prevent the development of unstable activity regimes, such as those characterized by a high degree of population-wide synchrony. We establish a link between such pathological network activity, which is circumvented by the action of plasticity, and a reduced computational capacity. Additionally, we demonstrate that the action of plasticity shapes and stabilizes the transient network states exhibited in the presence of sequentially presented stimulus events, allowing the development of adequate and discernible stimulus representations. The main feature responsible for the increased discriminability of stimulus-driven population responses in plastic networks is shown to be the decorrelating action of inhibitory plasticity and the consequent maintenance of the asynchronous irregular dynamic regime both for ongoing activity and stimulus-driven responses, whereas excitatory plasticity is shown to play only a marginal role. PMID:25374534

  5. Alterations of Nonconserved Residues Affect Protein Stability and Folding Dynamics through Charge-Charge Interactions.

    PubMed

    Tripathi, Swarnendu; Garcìa, Angel E; Makhatadze, George I

    2015-10-15

    Charge-charge interactions play an important role in thermal stability of proteins. We employed an all-atom, native-topology-based model with non-native electrostatics to explore the interplay between folding dynamics and stability of TNfn3 (the third fibronectin type III domain from tenascin-C). Our study elucidates the role of charge-charge interactions in modulating the folding energy landscape. In particular, we found that incorporation of explicit charge-charge interactions in the WT TNfn3 induces energetic frustration due to the presence of residual structure in the unfolded state. Moreover, optimization of the surface charge-charge interactions by altering the evolutionarily nonconserved residues not only increases the thermal stability (in agreement with previous experimental study) but also reduces the formation of residual structure and hence minimizes the energetic frustration along the folding route. We concluded that charge-charge interaction in the rationally designed TNfn3 plays an important role not only in enhancing the stability but also in assisting folding. PMID:26413861

  6. Dynamic Growth and Shrinkage Govern the pH Dependence of RecA Filament Stability

    PubMed Central

    Kim, Sung Hyun; Park, Jeehae; Joo, Chirlmin; Kim, Doseok; Ha, Taekjip

    2015-01-01

    RecA proteins form a long stable filament on a single-stranded DNA and catalyze strand exchange reaction. The stability of RecA filament changes dramatically with pH, yet its detailed mechanism is not known. Here, using a single molecule assay, we determined the binding and dissociation rates of RecA monomers at the filament ends at various pH. The pH-induced rate changes were moderate but occurred in opposite directions for binding and dissociation, resulting in a substantial increase in filament stability in lower pH. The highly charged residues in C-terminal domain do not contribute to the pH dependent stability. The stability enhancement of RecA filament in low pH may help the cell to cope with acidic stress by fine-tuning of the binding and dissociation rates without losing the highly dynamic nature of the filament required for strand exchange. PMID:25608006

  7. Robust transmission stabilization and dynamic switching in broadband hybrid waveguide systems with nonlinear gain and loss

    NASA Astrophysics Data System (ADS)

    Nguyen, Quan M.; Peleg, Avner; Tran, Thinh P.

    2015-01-01

    We develop a method for transmission stabilization and robust dynamic switching for colliding optical soliton sequences in broadband waveguide systems with nonlinear gain and loss. The method is based on employing hybrid waveguides, consisting of spans with linear gain and cubic loss, and spans with linear loss, cubic gain, and quintic loss. We show that the amplitude dynamics is described by a hybrid Lotka-Volterra (LV) model, and use the model to determine the physical parameter values required for enhanced transmission stabilization and switching. Numerical simulations with coupled nonlinear Schrödinger equations confirm the predictions of the LV model, and show complete suppression of radiative instability and pulse distortion. This enables stable transmission over distances larger by an order of magnitude compared with uniform waveguides with linear gain and cubic loss. Moreover, multiple on-off and off-on dynamic switching events are demonstrated over a wide range of soliton amplitudes, showing the superiority of hybrid waveguides compared with static switching in uniform waveguides.

  8. Exercise of mechanisms of dynamic stability improves the stability state after an unexpected gait perturbation in elderly.

    PubMed

    Bierbaum, Stefanie; Peper, Andreas; Arampatzis, Adamantios

    2013-10-01

    Unexpected changes during gait challenge elderly individuals to a greater degree than young adults. However, the adaptive potential of elderly seems to be retained, and therefore, the training of the mechanisms of dynamic stability as well as muscle strength training may improve the dynamic stability after unexpected perturbations. Thirty-eight subjects (65-75 years) participated in the study, divided into two experimental groups (stability training group, ST, n = 14 and mixed training group, MT, n = 14) and a control group (CG, n = 10). Both experimental groups performed exercises which focused on the mechanisms of dynamic stability. Additionally, the MT group executed a training to improve muscle strength. Session volume and duration were equal for both groups (14 weeks, twice a week, ~1.5 h per session). Pre- and post-intervention, subjects performed a gait protocol with an induced unexpected perturbation. Post-intervention, the margin of stability was significantly increased after the unexpected perturbation in the ST group, indicating an improvement in stability state (pre, -30.3 ± 5.9 cm; post, -24.1 ± 5.2 cm). Further, both intervention groups increased their base of support after the intervention to regain balance after gait perturbation, whereas only the ST group showed a statistically significant improvement (STpre, 90.9 ± 6.6 cm, STpost, 98.2 ± 8.5 cm; MTpre, 91.4 ± 6.2 cm; MTpost, 97.9 ± 12.7 cm). The CG showed no differences between pre- and post-measurements. The exercise of the mechanisms of dynamic stability led to a better application of these mechanisms after an unexpected perturbation during gait. We suggest that the repeated exercise of the mechanisms of dynamic stability contributes to significant improvements in postural stability. Additional strength training for healthy elderly individuals, however, shows no further effect on the ability to recover balance after unexpected perturbations during gait.

  9. Structural basis for the enhanced stability of highly fluorinated proteins

    PubMed Central

    Buer, Benjamin C.; Meagher, Jennifer L.; Stuckey, Jeanne A.; Marsh, E. Neil G.

    2012-01-01

    Noncanonical amino acids have proved extremely useful for modifying the properties of proteins. Among them, extensively fluorinated (fluorous) amino acids seem particularly effective in increasing protein stability; however, in the absence of structural data, the basis of this stabilizing effect remains poorly understood. To address this problem, we solved X-ray structures for three small proteins with hydrophobic cores that are packed with either fluorocarbon or hydrocarbon side chains and compared their stabilities. Although larger, the fluorinated residues are accommodated within the protein with minimal structural perturbation, because they closely match the shape of the hydrocarbon side chains that they replace. Thus, stability increases seem to be better explained by increases in buried hydrophobic surface area that accompany fluorination than by specific fluorous interactions between fluorinated side chains. This finding is illustrated by the design of a highly fluorinated protein that, by compensating for the larger volume and surface area of the fluorinated side chains, exhibits similar stability to its nonfluorinated counterpart. These structure-based observations should inform efforts to rationally modulate protein function using noncanonical amino acids. PMID:22411812

  10. Transient Dynamics of Electric Power Systems: Direct Stability Assessment and Chaotic Motions

    NASA Astrophysics Data System (ADS)

    Chu, Chia-Chi

    A power system is continuously experiencing disturbances. Analyzing, predicting, and controlling transient dynamics, which describe transient behaviors of the power system following disturbances, is a major concern in the planning and operation of a power utility. Important conclusions and decisions are made based on the result of system transient behaviors. As today's power network becomes highly interconnected and much more complex, it has become essential to enhance the fundamental understanding of transient dynamics, and to develop fast and reliable computational algorithms. In this thesis, we emphasize mathematical rigor rather than physical insight. Nonlinear dynamical system theory is applied to study two fundamental topics: direct stability assessment and chaotic motions. Conventionally, power system stability is determined by calculating the time-domain transient behaviors for a given disturbance. In contrast, direct methods identify whether or not the system will remain stable once the disturbance is removed by comparing the corresponding energy value of the post-fault system to a calculated threshold value. Direct methods not only avoid the time-consuming numerical integration of the time domain approach, but also provide a quantitative measure of the degree of system stability. We present a general framework for the theoretical foundations of direct methods. Canonical representations of network-reduction models as well as network-preserving models are proposed to facilitate the analysis and the construction of energy functions of various power system models. An advanced and practical method, called the boundary of stability region based controlling unstable equilibrium point method (BCU method), of computing the controlling unstable equilibrium point is proposed along with its theoretical foundation. Numerical solution algorithms capable of supporting on-line applications of direct methods are provided. Further possible improvements and enhancements are

  11. Metaconcrete: designed aggregates to enhance dynamic performance

    NASA Astrophysics Data System (ADS)

    Mitchell, Stephanie J.; Pandolfi, Anna; Ortiz, Michael

    2014-04-01

    We propose a new type of concrete for the attenuation of elastic waves induced by dynamic excitation. In this metamaterial, which we call metaconcrete, the stone, sand, and gravel aggregates of standard concrete are replaced with spherical inclusions consisting of a heavy metal core coated with a soft outer layer. These engineered aggregates can be tuned so that particular frequencies of a propagating blast wave will activate resonant oscillations of the heavy mass within the inclusions. The resonant behavior causes the system to exhibit negative effective mass, and this interaction between the wave motion and the resonant aggregates results in the attenuation of the applied dynamic loading. We introduce the concept of negative mass by deriving the effective momentum mass for the system and we define the geometrical and material parameters for the design of resonant aggregates. We develop finite element models for the analysis of metaconcrete behavior, defining a section of slab containing a periodic arrangement of inclusions. By computing the energy histories for the system when subject to a blast load, we show that there is a transfer of energy between the inclusions and the surrounding mortar. The inclusions are able to absorb a significant portion of the applied energy, resulting in a reduction in the amount of stress carried by the mortar phase and greatly improving the ability of the material to resist damage under explosive dynamic loading.

  12. Enhanced stability of hillslopes and channel beds to mass failure

    NASA Astrophysics Data System (ADS)

    Prancevic, Jeff; Lamb, Michael; Palucis, Marisa; Venditti, Jeremy

    2016-04-01

    The stability of inclined, unconsolidated sediments subjected to groundwater flow on hillslopes and steep channel beds is important for both landscape evolution and natural hazards. Force-balance models have been used for seven decades to predict the stability of slopes, but they generally underpredict the degree of saturation required to destabilize the sediment. Researchers often appeal to heightened stabilizing forces from root and mineral cohesion, and friction acting on the margins of the failure to explain this underprediction. Surprisingly, infinite-slope stability models in their simplest form have never been tested under controlled laboratory conditions. To address this gap in data, we perform a set of controlled laboratory experiments with slope-parallel seepage in the simplest possible configuration. We performed 47 experiments in a 5 m laboratory flume with 4 grain sizes (D50 = 0.7, 2, 5, and 15 mm) and a wide range in bed angles (20° to 43°), spanning both Darcian and turbulent subsurface flow regimes. Our experiments show that granular slopes were more stable than predicted by simple force balance models in experiments that lack root or mineral cohesion. Despite the smooth plastic walls and the long aspect ratio of our flume, we calculate wall and toe friction to be important. Including these additional resistance terms in the model reduces the model misfit with our experimental results. However, there is considerable remaining misfit (up to 50% underestimation of the saturation level required for failure). We investigate two explanations of this heightened stability: 1) standard frictional resistance terms are underestimated, and 2) seepage stresses are overestimated. Both explanations require that we modify the models used to predict slope stability.

  13. Unsteady numerical simulations of the stability and dynamics of flames

    NASA Technical Reports Server (NTRS)

    Kailasanath, K.; Patnaik, G.; Oran, E. S.

    1995-01-01

    In this report we describe the research performed at the Naval Research Laboratory in support of the NASA Microgravity Science and Applications Program over the past three years (from Feb. 1992) with emphasis on the work performed since the last microgravity combustion workshop. The primary objective of our research is to develop an understanding of the differences in the structure, stability, dynamics and extinction of flames in earth gravity and in microgravity environments. Numerical simulations, in which the various physical and chemical processes can be independently controlled, can significantly advance our understanding of these differences. Therefore, our approach is to use detailed time-dependent, multi-dimensional, multispecies numerical models to perform carefully designed computational experiments. The basic issues we have addressed, a general description of the numerical approach, and a summary of the results are described in this report. More detailed discussions are available in the papers published which are referenced herein. Some of the basic issues we have addressed recently are (1) the relative importance of wall losses and gravity on the extinguishment of downward-propagating flames; (2) the role of hydrodynamic instabilities in the formation of cellular flames; (3) effects of gravity on burner-stabilized flames, and (4) effects of radiative losses and chemical-kinetics on flames near flammability limits. We have also expanded our efforts to include hydrocarbon flames in addition to hydrogen flames and to perform simulations in support of other on-going efforts in the microgravity combustion sciences program. Modeling hydrocarbon flames typically involves a larger number of species and a much larger number of reactions when compared to hydrogen. In addition, more complex radiation models may also be needed. In order to efficiently compute such complex flames recent developments in parallel computing have been utilized to develop a state

  14. Active electrostatic control of liquid bridge dynamics and stability.

    PubMed

    Thiessen, David B; Wei, Wei; Marston, Philip L

    2004-11-01

    Stabilization of cylindrical liquid bridges beyond the Rayleigh-Plateau limit has been demonstrated in both Plateau-tank experiments and in short-duration low gravity on NASA KC-135 aircraft using an active electrostatic control method. The method controls the (2,0) capillary mode using an optical modal-amplitude detector and mode-coupled electrostatic feedback stress. The application of mode-coupled stresses to a liquid bridge is also a very useful way to study mode dynamics. A pure (2,0)-mode oscillation can be excited by periodic forcing and then the forcing can be turned off to allow for a free decay from which the frequency and damping of the mode is measured. This can be done in the presence or absence of feedback control. Mode-coupled feedback stress applied in proportion to modal amplitude with appropriate gain leads to stiffening of the mode allowing for stabilization beyond the Rayleigh-Plateau limit. If the opposite sign of gain is applied the mode frequency is reduced. It has also been demonstrated that, by applying feedback in proportion to the modal velocity, the damping of the mode can be increased or decreased depending on the velocity gain. Thus, both the mode frequency and damping can be independently controlled at the same time and this has been demonstrated in Plateau-tank experiments. The International Space Station (ISS) has its own modes of oscillation, some of which are in a low frequency range comparable to the (2,0)-mode frequency of typical liquid bridges. In the event that a vibration mode of the ISS were close to the frequency of a capillary mode it would be possible, with active electrostatic control, to shift the capillary-mode frequency away from that of the disturbance and simultaneously add artificial damping to further reduce the effect of the g-jitter. In principle, this method could be applied to any fluid configuration with a free surface.

  15. α-SNAP Enhances SNARE Zippering by Stabilizing the SNARE Four-Helix Bundle.

    PubMed

    Ma, Lu; Kang, Yuhao; Jiao, Junyi; Rebane, Aleksander A; Cha, Hyo Keun; Xi, Zhiqun; Qu, Hong; Zhang, Yongli

    2016-04-19

    Intracellular membrane fusion is mediated by dynamic assembly and disassembly of soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein (SNAP) receptors (SNAREs). α-SNAP guides NSF to disassemble SNARE complexes after membrane fusion. Recent experiments showed that α-SNAP also dramatically enhances SNARE assembly and membrane fusion. How α-SNAP is involved in these opposing activities is not known. Here, we examine the effect of α-SNAP on the stepwise assembly of the synaptic SNARE complex using optical tweezers. We found that α-SNAP destabilized the linker domain (LD) of the SNARE complex but stabilized its C-terminal domain (CTD) through a conformational selection mechanism. In contrast, α-SNAP minimally affected assembly of the SNARE N-terminal domain (NTD), indicating that α-SNAP barely bound the partially assembled trans-SNARE complex. Thus, α-SNAP recognizes the folded CTD for SNARE disassembly with NSF and subtly modulates membrane fusion by altering the stabilities of the SNARE CTD and LD.

  16. Dynamic Stability and Gravitational Balancing of Multiple Extended Bodies

    NASA Technical Reports Server (NTRS)

    Quadrelli, Marco

    2008-01-01

    Feasibility of a non-invasive compensation scheme was analyzed for precise positioning of a massive extended body in free fall using gravitational forces influenced by surrounding source masses in close proximity. The N-body problem of classical mechanics is a paradigm used to gain insight into the physics of the equivalent N-body problem subject to control forces. The analysis addressed how a number of control masses move around the proof mass so that the proof mass position can be accurately and remotely compensated when exogenous disturbances are acting on it, while its sensitivity to gravitational waves remains unaffected. Past methods to correct the dynamics of the proof mass have considered active electrostatic or capacitive methods, but the possibility of stray capacitances on the surfaces of the proof mass have prompted the investigation of other alternatives, such as the method presented in this paper. While more rigorous analyses of the problem should be carried out, the data show that, by means of a combined feedback and feed-forward control approach, the control masses succeeded in driving the proof mass along the specified trajectory, which implies that the proof mass can, in principle, be balanced via gravitational forces only while external perturbations are acting on it. This concept involves the dynamic stability of a group of massive objects interacting gravitationally under active control, and can apply to drag-free control of spacecraft during missions, to successor gravitational wave space borne sensors, or to any application requiring flying objects to be precisely controlled in position and attitude relative to another body via gravitational interactions only.

  17. Dynamic contrast-enhanced ultrasound for quantification of tissue perfusion.

    PubMed

    Fröhlich, Eckhart; Muller, Reinhold; Cui, Xin-Wu; Schreiber-Dietrich, Dagmar; Dietrich, Christoph F

    2015-02-01

    Dynamic contrast-enhanced ultrasound (US) imaging, a technique that uses microbubble contrast agents with diagnostic US, has recently been technically summarized and reviewed by a European Federation of Societies for Ultrasound in Medicine and Biology position paper. However, the practical applications of this imaging technique were not included. This article reviews and discusses the published literature on the clinical use of dynamic contrast-enhanced US. This review finds that dynamic contrast-enhanced US imaging is the most sensitive cross-sectional real-time method for measuring the perfusion of parenchymatous organs noninvasively. It can measure parenchymal perfusion and therefore can differentiate between benign and malignant tumors. The most important routine clinical role of dynamic contrast-enhanced US is the prediction of tumor responses to chemotherapy within a very short time, shorter than using Response Evaluation Criteria in Solid Tumors criteria. Other applications found include quantifying the hepatic transit time, diabetic kidneys, transplant grafts, and Crohn disease. In addition, the problems involved in using dynamic contrast-enhanced US are discussed.

  18. Bayesian model of dynamic image stabilization in the visual system.

    PubMed

    Burak, Yoram; Rokni, Uri; Meister, Markus; Sompolinsky, Haim

    2010-11-01

    Humans can resolve the fine details of visual stimuli although the image projected on the retina is constantly drifting relative to the photoreceptor array. Here we demonstrate that the brain must take this drift into account when performing high acuity visual tasks. Further, we propose a decoding strategy for interpreting the spikes emitted by the retina, which takes into account the ambiguity caused by retinal noise and the unknown trajectory of the projected image on the retina. A main difficulty, addressed in our proposal, is the exponentially large number of possible stimuli, which renders the ideal Bayesian solution to the problem computationally intractable. In contrast, the strategy that we propose suggests a realistic implementation in the visual cortex. The implementation involves two populations of cells, one that tracks the position of the image and another that represents a stabilized estimate of the image itself. Spikes from the retina are dynamically routed to the two populations and are interpreted in a probabilistic manner. We consider the architecture of neural circuitry that could implement this strategy and its performance under measured statistics of human fixational eye motion. A salient prediction is that in high acuity tasks, fixed features within the visual scene are beneficial because they provide information about the drifting position of the image. Therefore, complete elimination of peripheral features in the visual scene should degrade performance on high acuity tasks involving very small stimuli.

  19. Optimal mistuning for enhanced aeroelastic stability of transonic fans

    NASA Technical Reports Server (NTRS)

    Hall, K. C.; Crawley, E. F.

    1983-01-01

    An inverse design procedure was developed for the design of a mistuned rotor. The design requirements are that the stability margin of the eigenvalues of the aeroelastic system be greater than or equal to some minimum stability margin, and that the mass added to each blade be positive. The objective was to achieve these requirements with a minimal amount of mistuning. Hence, the problem was posed as a constrained optimization problem. The constrained minimization problem was solved by the technique of mathematical programming via augmented Lagrangians. The unconstrained minimization phase of this technique was solved by the variable metric method. The bladed disk was modelled as being composed of a rigid disk mounted on a rigid shaft. Each of the blades were modelled with a single tosional degree of freedom.

  20. Dynamic contrast-enhanced MRI of ocular melanoma.

    PubMed

    Jiang, Xuyuan; Asbach, Patrick; Willerding, Gregor; Dulce, Miriam; Xu, Ke; Taupitz, Matthias; Hamm, Bernd; Erb-Eigner, Katharina

    2015-04-01

    Dynamic contrast-enhanced MRI is used for the assessment of microvasculature in several tumours. We aimed to assess the contrast signal enhancement characteristics of ocular melanoma. Forty patients with ocular melanoma were prospectively investigated with ocular MRI including dynamic contrast-enhanced sequences over a 13-month period. A region-of-interest analysis of the images was carried out to calculate signal enhancement characteristics after a contrast injection. Clinical follow-up data such as extraocular spread and development of liver metastasis were compared with the signal enhancement characteristics of the ocular melanoma. In 39 patients (98%), the ocular melanomas showed an early strong signal enhancement after contrast injection, resulting in a mean time of maximum enhancement of 49 s. Clinical follow-up was available in 28 patients (70%) and indicated that the peak signal intensity was significantly increased (P=0.039) in patients who developed extraocular spread or liver metastasis at a later stage. Ocular melanoma shows signal enhancement characteristics of hypervascular neoplasms. This study provides baseline curve pattern data that may be useful for assessing changes in vascularity, for example during therapy response. Furthermore, the study showed that a strong signal enhancement of the ocular melanoma might be linked to a less favourable prognosis.

  1. Stability Enhancement of Lean, Premixed Flames by Flameholder Heating

    NASA Astrophysics Data System (ADS)

    Hermanson, James C.; Demmons, Nathaniel

    2001-11-01

    The effects of flameholder heating on the stability and emissions of lean, premixed, turbulent flames were examined experimentally. The flames were stabilized by an axial, cylindrical bluff-body flameholder 6.4 mm in diameter made of copper or stainless steel. In some cases, the stainless flameholder was heated electrically. The flame was at atmospheric pressure. The premixed ethylene/air mixture upstream of the flameholder was unheated and had an equivalence ratio of 0.37 to 0.87. The cold gas flow velocities ranged from 5.0 to 10.5 m/s to give Reynolds numbers at the flameholder tip from 3,250 to 6,700. The impact of flameholder heating on the lean-blow off limit was determined visually. Heating the flameholder to yield a local mixture temperature of 190 C resulted in a decrease in the equivalence ratio at lean blow-off of approximately 20%. This decrease in equivalence ratio resulted in up to a 26% decrease in exhaust-plane NOx emissions and a 51 K reduction in the exhaust-plane gas temperature. These reductions were consistent with the lower equivalence ratios attainable by the localized mixture preheating. At the same time, the exhaust concentrations of CO and unburned hydrocarbons increased by a factor of approximately two. A smaller increase in lean flame stability was seen for the unheated stainless flameholder versus the copper flameholder.

  2. Method for enhancing stability of high explosives, for purposes of transport or storage, and the stabilized high explosives

    DOEpatents

    Nutt, Gerald L.

    1991-01-01

    The stability of porous solid high explosives, for purposes of transport or storage, is enhanced by reducing the sensitivity to shock initiation of a reaction that leads to detonation. The pores of the explosive down to a certain size are filled under pressure with a stable, low melt temperature material in liquid form, and the combined material is cooled so the pore filling material solidifies. The stability can be increased to progressively higher levels by filling smaller pores. The pore filling material can be removed, at least partially, by reheating above its melt temperature and drained off so that the explosive is once more suitable for detonation.

  3. Synthesis and Characterization of Processable Polyimides with Enhanced Thermal Stability

    NASA Technical Reports Server (NTRS)

    Harris, Frank W.

    1999-01-01

    The following is a summary report of the research carried out under NASA Grant NAG-1-448. The work was divided into four major areas: 1) Enhanced polyimide processing through the use of reactive plasticizers 2) Development of processable polyhenylquinoxalines 3) Synthesis and characterization of perfluorovinylether-terminated imide oligomers and 4) Fluorosilicones containing perfuorocyclobutane rings.

  4. Microwave axial free-electron laser with enhanced phase stability

    SciTech Connect

    Carlsten, B.; Fazio, M.; Haynes, W.

    1995-12-31

    Free-electron laser (FEL) amplifiers have demonstrated high efficiencies and high output power at microwave wavelengths. However, measurements and simulations have indicated that the present level of phase stability for these devices is not sufficient for driving linear accelerators. Fluctuations in the diode voltage, which is needed to accelerate the electron beam, are the largest cause of the shifts in the phase of the output power. Pulse-power technology cannot keep the voltage fluctuations less than 1/4%. However, we have found a scheme that will make the output phase much less sensitive to these fluctuations by exploiting the traveling wave nature of the FEL interaction. In this paper we study the phase stability issue by analyzing the dispersion relation for an axial FEL, in which the rf field is transversely wiggled and the electron trajectories are purely longitudinal. The advantage of using the axial FEL interaction instead of the common transverse FEL interaction is that (1) the dispersion relation is not additionally complicated by how the transverse electron motion depends on the diode voltage and (2) such a device is simpler and less expensive to construct than a transverse-coupling FEL because there is no wiggler. The axial FEL interaction is with a fast wave and does involve axial bunching of the electron beam, so the results found for this device also apply to transverse-coupling FELs. By examination of the dispersion relation it is found that the effect of the phase dependency on the beam`s velocity can be cancelled by the effect of the phase dependency on the beam`s plasma wave, for an annular electron beam. By changing the annulus radius, exact cancellation can be found for a variety of beam voltages and currents in the ranges of 0.5-1.0 MV and 1-5 kA. This cancellation leads to first-order phase stability, which is not possible for standing-wave devices, such as klystrons.

  5. Microwave axial free-electron laser with enhanced phase stability

    SciTech Connect

    Carlsten, B.E.; Fortgang, C.M.; Fazio, M.V.; Haynes, W.B.; May, L.M.; Potter, J.M.

    1995-09-01

    Free-electron lasers (FELs) amplifiers have demonstrated high efficiencies and high output power at microwave wavelengths. However, measurements and simulations have indicated that the present level of phase stability for these devices is not sufficient for driving linear accelerators. Fluctuations in the diode voltage, which is needed to accelerate the electron beam, are the largest cause of the shifts in the phase of the output power. Present-day pulse-power technology cannot keep the voltage fluctuations less than 1/4%. However, we have found a scheme that win make the output phase much less sensitive to these fluctuations by exploiting the traveling-wave nature of the FEL interaction. In this paper we study the phase stability issue by analyzing the dispersion relation for an axial FEL, in which the rf field is transversely wiggled and the electron trajectories are purely longitudinal. The advantage of using the axial FEL interaction instead of the common transverse FEL interaction is that the dispersion relation is not additionally complicated by how the transverse electron motion depends on the diode voltage and such a device is simpler and less expensive to construct than a transverse-coupling FEL because there is no wiggler. By examination of the dispersion relation it is found that the effect of the phase dependency on the beam`s velocity can be cancelled by the effect of the phase dependency on the beam`s plasma wave, for an annular electron beam. This cancellation leads to first-order phase stability, which is not possible for standing-wave devices, such as klystrons. Detailed particle-in-cell simulations are included to demonstrate the transverse wiggling of the rf mode and the axial FEL interaction.

  6. Electrified film on a porous inclined plane: Dynamics and stability

    NASA Astrophysics Data System (ADS)

    Uma, B.; Usha, R.

    2010-07-01

    The time evolution of a thin conducting liquid film flowing down a porous inclined substrate is investigated when an electric field acts normal to the substrate. It is assumed that the flow through the porous medium is governed by Darcy’s law together with Beavers-Joseph condition. Under the assumption of small permeability relative to the thickness of the overlying fluid layer, the flow is decoupled from the filtration flow through the porous medium. A slip condition at the bottom is used to incorporate the effects of the permeability of the substrate. From the set of exact averaged equations derived using integral boundary method for the film thickness and for the flow rate, a nonlinear evolution equation for the film thickness is derived through a long-wave approximation. A linear stability analysis of the base flow is performed and the critical Reynolds number is obtained. The results reveal that the substrate porosity in general destabilizes the liquid film flow and the presence of the electric field enhances this destabilizing effect. A weakly nonlinear stability analysis divulges the existence of supercritical stable and subcritical unstable zones in the wave number/Reynolds number parameter space and the results demonstrate how the neutral curves change as the intensity of the electric filed or the permeability of the porous medium is varied. The numerical solution of the nonlinear evolution equation in a periodic domain reveals that the base flow yields to surface structures that are either time independent waves of permanent form that propagate or time-dependent modes that oscillate slightly in the amplitude. Further, it is observed that the shape and amplitude of long-time waveforms are influenced by the permeability of the porous medium as well as by the applied electric field. The results reveal that the destabilization induced by the electric field in an otherwise stable film over a porous medium is exhibited in the form of traveling waves of finite

  7. Electrified film on a porous inclined plane: dynamics and stability.

    PubMed

    Uma, B; Usha, R

    2010-07-01

    The time evolution of a thin conducting liquid film flowing down a porous inclined substrate is investigated when an electric field acts normal to the substrate. It is assumed that the flow through the porous medium is governed by Darcy's law together with Beavers-Joseph condition. Under the assumption of small permeability relative to the thickness of the overlying fluid layer, the flow is decoupled from the filtration flow through the porous medium. A slip condition at the bottom is used to incorporate the effects of the permeability of the substrate. From the set of exact averaged equations derived using integral boundary method for the film thickness and for the flow rate, a nonlinear evolution equation for the film thickness is derived through a long-wave approximation. A linear stability analysis of the base flow is performed and the critical Reynolds number is obtained. The results reveal that the substrate porosity in general destabilizes the liquid film flow and the presence of the electric field enhances this destabilizing effect. A weakly nonlinear stability analysis divulges the existence of supercritical stable and subcritical unstable zones in the wave number/Reynolds number parameter space and the results demonstrate how the neutral curves change as the intensity of the electric filed or the permeability of the porous medium is varied. The numerical solution of the nonlinear evolution equation in a periodic domain reveals that the base flow yields to surface structures that are either time independent waves of permanent form that propagate or time-dependent modes that oscillate slightly in the amplitude. Further, it is observed that the shape and amplitude of long-time waveforms are influenced by the permeability of the porous medium as well as by the applied electric field. The results reveal that the destabilization induced by the electric field in an otherwise stable film over a porous medium is exhibited in the form of traveling waves of finite

  8. Tuneable enhancement of the salt and thermal stability of polymeric micelles by cyclized amphiphiles

    PubMed Central

    Honda, Satoshi; Yamamoto, Takuya; Tezuka, Yasuyuki

    2013-01-01

    Cyclic molecules provide better stability for their aggregates. Typically in nature, the unique cyclic cell membrane lipids allow thermophilic archaea to inhabit extreme conditions. By mimicking the biological design, the robustness of self-assembled synthetic nanostructures is expected to be improved. Here we report topology effects by cyclized polymeric amphiphiles against their linear counterparts, demonstrating a drastic enhancement in the thermal, as well as salt stability of self-assembled micelles. Furthermore, through coassembly of the linear and cyclic amphiphiles, the stability was successfully tuned for a wide range of temperatures and salt concentrations. The enhanced thermal/salt stability was exploited in a halogen exchange reaction to stimulate the catalytic activity. The mechanism for the enhancement was also investigated. These topology effects by the cyclic amphiphiles offer unprecedented opportunities in polymer materials design unattainable by traditional means. PMID:23481382

  9. Enhanced Thermal Stability of Polylactide by Terminal Conjugation Groups

    NASA Astrophysics Data System (ADS)

    Tran, Hang Thi; Matsusaki, Michiya; Akashi, Mitsuru; Vu, Ngo Dinh

    2016-05-01

    Various acids such as aliphatic or carbocyclic fatty or aromatic acids were successfully conjugated into the ending hydroxyl group of poly( l-lactide) (PLLA). The chemical structures of various acid-PLLAs were confirmed by Fourier transform infrared and proton nuclear magnetic resonance analysis. The crystallinity and solubility of the original PLLA were maintained after the terminal conjugation of various acids. The thermal properties were significantly improved, especially the 10% weight-loss temperature that showed an increase of over 80°C for conjugation of aliphatic or aromatic acids as compared to that of the corresponding original PLLA. In addition, more than 60 wt.% of the aliphatic acid-PLLAs was pyrolyzed, and aromatic acid-PLLAs degraded only about 10 wt.% for 150 min, although the original PLLA was pyrolyzed completely at 250°C for 7 min. The thermal stability of PLLA was controlled by the conjugation of aliphatic or aromatic acids into a chain end. These acid-PLLAs may be useful as materials with high thermal stability for various application fields.

  10. Atmospheric accelerations and the stability of dynamic supergiant atmospheres.

    NASA Astrophysics Data System (ADS)

    Nieuwenhuijzen, H.; de Jager, C.

    1995-10-01

    The goal of this paper is to study instability regions in the HR diagram, through a calculation of the atmospheric accelerations for spherically symmetric stars, in dynamic equilibrium, without using detailed atmospheric models. The input data are five primary data, viz.: the stellar luminosity L, the effective temperature T_eff_, the mass M, the rate of mass loss ˙(M), and the microturbulent velocity component ζmu_, while we assume the temperature for a reference atmospheric layer, an assumption that appears not to be critical. An iterative solution of the momentum equation, simultaneous with some other equations, yields values for the various accelerations acting on a stellar atmosphere and their algebraic sum g_eff_', the predicted effective acceleration. In the first part of the paper we compare this latter quantity with the g_eff_-value derived observationally from spectral studies of nine program stars and we find overall fair agreement. This supports the method as well as the values of the five input data. In part 2 we determine g'_eff_ in same way for the whole upper part of the Hertzsprung-Russell diagram by using statistical primary data on the mass (based on evolutionary calculations), on mass-loss and on microturbulence (shock-strengths). We find as a fairly general rule that, as stars move along their evolutionary track, and for time scales longer than the dynamic time scale of the atmosphere, the atmosphere continuously adapts to the new (L,T_eff_)-values and essentially remains stable. Current practice of determining the stability limit of stellar atmospheres by extrapolating hydrostatic models to the Eddington limit is not justified by this study. There is one exception: we find a small area around T_eff_=8300K and log(L/Lsun_)=5.7, where no solution is possible for evolved stars on their blueward evolutionary track; the stars in this area have in any case effective accelerations <1mm/s^2^: the "Yellow Evolutionary Void". In the third part we

  11. Stability Limits and Dynamics of Nonaxisymmetric Liquid Bridges

    NASA Technical Reports Server (NTRS)

    Alexander, J. Iwan D.

    1996-01-01

    Theoretical and experimental investigation of the stability of nonaxisymmetric and axisymmetric bridges contained between equal and unequal radii disks as a function of Bond and Weber number with emphasis on the transition from unstable axisymmetric to stable nonaxisymmetric shapes. Numerical analysis of the stability of nonaxisymmetric bridges between unequal disks for various orientations of the gravity vector Experimental and numerical investigation of bridge stability (nonaxisymmetric and axisymmetric), large amplitude (nonaxisymmetric) oscillations and breaking.

  12. Dynamics of single-species population growth: stability or chaos

    SciTech Connect

    Mueller, L.D.; Ayala, F.J.

    1981-01-01

    We have examined stability at the carrying capacity for 25 genetically different populations of Drosophila melanogaster. In spite of their genetic heterogeneity, 20 of the populations yield stable equilibria and none have eigenvalues significantly greater than one. Computer simulations demonstrate how selection at the individual level may account for population stability (and, hence, that group selection is not necessary for the evolution of stability). Recent theoretical studies on density-dependent selection in random environments provide predictions consistent with our empirical findings.

  13. Dynamics and stability of mechanical systems with follower forces

    NASA Technical Reports Server (NTRS)

    Herrmann, G.

    1971-01-01

    A monograph on problems of stability of equilibrium of mechanical systems with follower forces is presented. Concepts of stability and criteria of stability are reviewed briefly, together with means of analytical specification of follower forces. Nondissipative systems with two degrees of freedom are discussed, and destabilizing effects due to various types of dissipative forces both in discrete and continuous systems, are treated. The analyses are accompanied by some quantative experiments and observations on demonstrational laboratory models.

  14. Dynamic enhancement of the exchange bias training effect

    NASA Astrophysics Data System (ADS)

    Sahoo, Sarbeswar; Berger, Andreas; Polisetty, Srinivas; Binek, Christian

    2007-03-01

    Exchange bias in coupled magnetic films and its accompanying training effect are fundamental interface phenomena which impact spintronic applications. Training is referred to as a gradual change of the bias field, which evolves upon cycling the soft layer through consecutive hysteresis loops. We report on its dynamic enhancement in exchange coupled bilayers of soft and hard ferromagnetic materials. Dynamic effects are induced with increasing sweep rate of the applied magnetic field from quasi-static to the fully dynamic range. A dynamically generalized theory based on triggered and partially truncated relaxation is in excellent agreement with the data. Remarkable universality of our theoretical approach is evidenced when applying the approach to the dynamic training effect of a conventional exchange bias system involving an antiferromagnetic pinning layer.

  15. The importance of steady and dynamic inflow on the stability of rotor-body systems

    NASA Technical Reports Server (NTRS)

    Peters, David A.

    1988-01-01

    The induced flow field of a rotor responds in a dynamic fashion to oscillations in rotor lift. This was long known to affect the stability and control derivatives of the rotor. More recently, however, it was also shown that this dynamic inflow also affects rotor and rotor-body aeroelastic stability. Thus, both the steady and unsteady inflow have pronounced effects on air resonance. Recent theoretical developments were made in the modeling of dynamic inflow, and these were verified experimentally. Thus, there is now a simple, verified dynamic inflow model for use in dynamic analyses.

  16. Synthesis and characterization of processable polyimides with enhanced thermal stability

    NASA Technical Reports Server (NTRS)

    Harris, Frank W.

    1987-01-01

    Many of the emerging applications of polymers on space vehicles require materials with outstanding thermal stability. These polymers must also be readily processable in order to facilitate their use. The syntheses and polymerization of a cardo dianhydride were investigated. This monomer was prepared via the reaction of N-methyl 4-nitrophthalimide with a cardo diol. Polyimides containing oxyalkylene linkages were studied. The effects of two additional structural modifications on the polymers' properties were investigated. The effects of carrying out the preparation of poly(amic acid)s under non-equilibrium conditions were examined. Approaches that were investigated included the in-situ neutralization of the generated amic acid and its in-situ esterification.

  17. Soy protein polymers: Enhancing the water stability property

    NASA Astrophysics Data System (ADS)

    Srinivasan, Gowrishankar

    Soy protein based plastics have been processed in the past by researchers for various short-term applications; however a common issue is the high water sensitivity of these plastics. This work concentrates on resolving this water sensitivity issue of soy protein polymers by employing chemical and mechanical interaction at the molecular level during extrusion. The primary chemical interactions employed were anhydride chemistries such as maleic anhydride (MA), phthalic anhydride (PTA), and butylated hydroxyanisole (BHA). These were respectively used in conjunction with glycerol as a plasticizer to produce relatively water stable soy protein based plastics. Formulations with varying additive levels of the chemistries were extruded and injection molded to form the samples for characterization. The additive levels of anhydrides were varied between 3-10% tw/tw (total mass). Results indicated that phthalic anhydride formulations resulted in highest water stability. Plastic formulations with concentration up to 10% phthalic anhydride were observed to have water absorption as low as 21.5% after 24 hrs of exposure to water with respect to 250% for the control formulation. Fourier transform infrared spectroscopy (FTIR) was utilized to characterize and confirm the fundamental mechanisms of water stability achieved by phthalic and maleic anhydride chemistries. In addition, the anhydride formulations were modified by inclusion of cotton fibers and pretreated cotton powder in order to improve mechanical properties. The incorporation of cotton fibers improved the dry strength by 18%, but did not significantly improve the wet state strength of the plastics. It was also observed that the butylated-hydroxy anisole (BHA) formulation exhibited high extension values in the dry state and had inferior water absorption properties in comparison with anhydride formulations.

  18. Stability of sticky particle dynamics and related scalar conservation laws

    NASA Astrophysics Data System (ADS)

    Moutsinga, Octave

    2009-06-01

    We show the stability of the sticky particle forward flow (x, s, t) [↦]{phi} (x, s, Pt, ut) w.r.t. perturbations of the initial mass distribution P0 and velocity function u0. Then, we deduce the stability of related scalar conservation laws and pressureless gas system.

  19. Enhanced weathering strategies for stabilizing climate and averting ocean acidification

    NASA Astrophysics Data System (ADS)

    Taylor, Lyla L.; Quirk, Joe; Thorley, Rachel M. S.; Kharecha, Pushker A.; Hansen, James; Ridgwell, Andy; Lomas, Mark R.; Banwart, Steve A.; Beerling, David J.

    2016-04-01

    Chemical breakdown of rocks, weathering, is an important but very slow part of the carbon cycle that ultimately leads to CO2 being locked up in carbonates on the ocean floor. Artificial acceleration of this carbon sink via distribution of pulverized silicate rocks across terrestrial landscapes may help offset anthropogenic CO2 emissions. We show that idealized enhanced weathering scenarios over less than a third of tropical land could cause significant drawdown of atmospheric CO2 and ameliorate ocean acidification by 2100. Global carbon cycle modelling driven by ensemble Representative Concentration Pathway (RCP) projections of twenty-first-century climate change (RCP8.5, business-as-usual; RCP4.5, medium-level mitigation) indicates that enhanced weathering could lower atmospheric CO2 by 30-300 ppm by 2100, depending mainly on silicate rock application rate (1 kg or 5 kg m-2 yr-1) and composition. At the higher application rate, end-of-century ocean acidification is reversed under RCP4.5 and reduced by about two-thirds under RCP8.5. Additionally, surface ocean aragonite saturation state, a key control on coral calcification rates, is maintained above 3.5 throughout the low latitudes, thereby helping maintain the viability of tropical coral reef ecosystems. However, we highlight major issues of cost, social acceptability, and potential unanticipated consequences that will limit utilization and emphasize the need for urgent efforts to phase down fossil fuel emissions.

  20. Enhanced Weathering Strategies for Stabilizing Climate and Averting Ocean Acidification

    NASA Technical Reports Server (NTRS)

    Taylor, Lyla L.; Quirk, Joe; Thorley, Rachel M. S.; Kharecha, Pushker A.; Hansen, James; Ridgwell, Andy; Lomas, Mark R.; Banwart, Steve A.; Beerling, David J.

    2015-01-01

    Chemical breakdown of rocks, weathering, is an important but very slow part of the carbon cycle that ultimately leads to CO2 being locked up in carbonates on the ocean floor. Artificial acceleration of this carbon sink via distribution of pulverized silicate rocks across terrestrial landscapes may help offset anthropogenic CO2 emissions. We show that idealized enhanced weathering scenarios over less than a third of tropical land could cause significant drawdown of atmospheric CO2 and ameliorate ocean acidification by 2100. Global carbon cycle modelling driven by ensemble Representative Concentration Pathway (RCP) projections of twenty-first-century climate change (RCP8.5, business-as-usual; RCP4.5, medium-level mitigation) indicates that enhanced weathering could lower atmospheric CO2 by 30-300 ppm by 2100, depending mainly on silicate rock application rate (1 kg or 5 kg m(exp -2) yr (exp -1)) and composition. At the higher application rate, end-of-century ocean acidification is reversed under RCP4.5 and reduced by about two-thirds under RCP8.5. Additionally, surface ocean aragonite saturation state, a key control on coral calcification rates, is maintained above 3.5 throughout the low latitudes, thereby helping maintain the viability of tropical coral reef ecosystems. However, we highlight major issues of cost, social acceptability, and potential unanticipated consequences that will limit utilization and emphasize the need for urgent efforts to phase down fossil fuel emissions.

  1. Optimal placement of unified power flow controllers to improve dynamic voltage stability using power system variable based voltage stability indices.

    PubMed

    Albatsh, Fadi M; Ahmad, Shameem; Mekhilef, Saad; Mokhlis, Hazlie; Hassan, M A

    2015-01-01

    This study examines a new approach to selecting the locations of unified power flow controllers (UPFCs) in power system networks based on a dynamic analysis of voltage stability. Power system voltage stability indices (VSIs) including the line stability index (LQP), the voltage collapse proximity indicator (VCPI), and the line stability index (Lmn) are employed to identify the most suitable locations in the system for UPFCs. In this study, the locations of the UPFCs are identified by dynamically varying the loads across all of the load buses to represent actual power system conditions. Simulations were conducted in a power system computer-aided design (PSCAD) software using the IEEE 14-bus and 39- bus benchmark power system models. The simulation results demonstrate the effectiveness of the proposed method. When the UPFCs are placed in the locations obtained with the new approach, the voltage stability improves. A comparison of the steady-state VSIs resulting from the UPFCs placed in the locations obtained with the new approach and with particle swarm optimization (PSO) and differential evolution (DE), which are static methods, is presented. In all cases, the UPFC locations given by the proposed approach result in better voltage stability than those obtained with the other approaches.

  2. Optimal placement of unified power flow controllers to improve dynamic voltage stability using power system variable based voltage stability indices.

    PubMed

    Albatsh, Fadi M; Ahmad, Shameem; Mekhilef, Saad; Mokhlis, Hazlie; Hassan, M A

    2015-01-01

    This study examines a new approach to selecting the locations of unified power flow controllers (UPFCs) in power system networks based on a dynamic analysis of voltage stability. Power system voltage stability indices (VSIs) including the line stability index (LQP), the voltage collapse proximity indicator (VCPI), and the line stability index (Lmn) are employed to identify the most suitable locations in the system for UPFCs. In this study, the locations of the UPFCs are identified by dynamically varying the loads across all of the load buses to represent actual power system conditions. Simulations were conducted in a power system computer-aided design (PSCAD) software using the IEEE 14-bus and 39- bus benchmark power system models. The simulation results demonstrate the effectiveness of the proposed method. When the UPFCs are placed in the locations obtained with the new approach, the voltage stability improves. A comparison of the steady-state VSIs resulting from the UPFCs placed in the locations obtained with the new approach and with particle swarm optimization (PSO) and differential evolution (DE), which are static methods, is presented. In all cases, the UPFC locations given by the proposed approach result in better voltage stability than those obtained with the other approaches. PMID:25874560

  3. Optimal Placement of Unified Power Flow Controllers to Improve Dynamic Voltage Stability Using Power System Variable Based Voltage Stability Indices

    PubMed Central

    Albatsh, Fadi M.; Ahmad, Shameem; Mekhilef, Saad; Mokhlis, Hazlie; Hassan, M. A.

    2015-01-01

    This study examines a new approach to selecting the locations of unified power flow controllers (UPFCs) in power system networks based on a dynamic analysis of voltage stability. Power system voltage stability indices (VSIs) including the line stability index (LQP), the voltage collapse proximity indicator (VCPI), and the line stability index (Lmn) are employed to identify the most suitable locations in the system for UPFCs. In this study, the locations of the UPFCs are identified by dynamically varying the loads across all of the load buses to represent actual power system conditions. Simulations were conducted in a power system computer-aided design (PSCAD) software using the IEEE 14-bus and 39- bus benchmark power system models. The simulation results demonstrate the effectiveness of the proposed method. When the UPFCs are placed in the locations obtained with the new approach, the voltage stability improves. A comparison of the steady-state VSIs resulting from the UPFCs placed in the locations obtained with the new approach and with particle swarm optimization (PSO) and differential evolution (DE), which are static methods, is presented. In all cases, the UPFC locations given by the proposed approach result in better voltage stability than those obtained with the other approaches. PMID:25874560

  4. New technique for enhancement of high dynamic range infrared images

    NASA Astrophysics Data System (ADS)

    Liu, Yu; Wang, Xin-sai; Xu, Hualiang; He, Ming; Li, Mingming

    2012-10-01

    A Bilateral Filter (BF) and Multi-scale Retinex (MSR) based infrared image enhancement algorithm is proposed in this paper. It's known that the MSR algorithm derived from vision theory can achieve dynamic range compression and tonal rendition effectively but suffers from `halo' phenomena caused by the existence of "sharp" edges in infrared images. Research shows that bilateral filter has the property of separating image details from strong edges. Therefore, we process detail components containing strong edges in MSR algorithm with bilateral filter to achieve dynamic range compression, detail enhancement and avoid `halo' artifacts at the same time. The performance of proposed algorithm is then validated by experiments with three real infrared images and compared with other two infrared images enhancement algorithms.

  5. Glycosylation of the enhanced aromatic sequon is similarly stabilizing in three distinct reverse turn contexts.

    PubMed

    Price, Joshua L; Powers, David L; Powers, Evan T; Kelly, Jeffery W

    2011-08-23

    Cotranslational N-glycosylation can accelerate protein folding, slow protein unfolding, and increase protein stability, but the molecular basis for these energetic effects is incompletely understood. N-glycosylation of proteins at naïve sites could be a useful strategy for stabilizing proteins in therapeutic and research applications, but without engineering guidelines, often results in unpredictable changes to protein energetics. We recently introduced the enhanced aromatic sequon as a family of portable structural motifs that are stabilized upon glycosylation in specific reverse turn contexts: a five-residue type I β-turn harboring a G1 β-bulge (using a Phe-Yyy-Asn-Xxx-Thr sequon) and a type II β-turn within a six-residue loop (using a Phe-Yyy-Zzz-Asn-Xxx-Thr sequon) [Culyba EK, et al. (2011) Science 331:571-575]. Here we show that glycosylating a new enhanced aromatic sequon, Phe-Asn-Xxx-Thr, in a type I' β-turn stabilizes the Pin 1 WW domain. Comparing the energetic effects of glycosylating these three enhanced aromatic sequons in the same host WW domain revealed that the glycosylation-mediated stabilization is greatest for the enhanced aromatic sequon complementary to the type I β-turn with a G1 β-bulge. However, the portion of the stabilization from the tripartite interaction between Phe, Asn(GlcNAc), and Thr is similar for each enhanced aromatic sequon in its respective reverse turn context. Adding the Phe-Asn-Xxx-Thr motif (in a type I' β-turn) to the enhanced aromatic sequon family doubles the number of proteins that can be stabilized by glycosylation without having to alter the native reverse turn type. PMID:21825145

  6. Enhanced hydrolytic stability of dental composites by use of fluoroalkyltrimethoxysilanes.

    PubMed

    Nihei, T; Kurata, S; Kondo, Y; Umemoto, K; Yoshino, N; Teranaka, T

    2002-07-01

    The hydrolytic stability of a group of experimental composite materials was evaluated. Seven distinct composites were formed by the mixing of a resin monomer mixture with silica filler that had been pre-treated with one of 7 different ethanol solutions. In one case, the filler was treated with an ethanol solution that contained only 3-methacryloyloxypropyltrimethoxysilane. In 5 cases, it was treated with solution containing a mixture of 3-methacryloyloxypropyltrimethoxysilane and one of the following hydrophobic fluoroalkyltrimethoxysilanes: trifluoropropyl-, nonafluorohexyl-, tridecafluorooctyl-, heptadecafluorodecyl-, and henicosafluorododecyl-trimethoxysilane. The tensile strength, after being immersed in water for 1800 days, of 2 of the experimental composites, whose pre-treatment regimen had included a fluoroalkyltrimethoxysilane, was significantly higher than that of the composite whose pre-treatment regimen had not included a fluoroalkyltrimethoxysilane. Moreover, there was no significant difference between the tensile strength of fresh samples of these 2 composites and the tensile strength of identically produced samples that had remained under water for 1800 days or that had been subjected to 30,000 cycles of thermal stress.

  7. Enhanced stability of skyrmions in magnets with broken mirror symmetry

    NASA Astrophysics Data System (ADS)

    Rowland, James; Banerjee, Sumilan; Randeria, Mohit

    Most previous work on skyrmion phases in chiral magnets with Dzyaloshinkii Moriya interactions (DMI) focuses on the case of broken bulk inversion symmetry. The skyrmion crystal is then stable only in a limited range of parameter space with easy-axis anisotropy. In this talk I will describe the effects of including broken mirror or surface inversion symmetry which leads to a Rashba DMI, in addition to the Dresselhaus DMI arising from broken bulk inversion. I will show that increasing Rashba DMI leads to a progressively larger domain of stability for skyrmions, especially in the easy-plane anisotropy regime. In the latter regime the topological charge density shows an unusual internal structure, and isolated skyrmions cannot be embedded in a ferromagnetic background. Thus the homotopy group π2 (S2) method of classifying skyrmions fails. I will discuss a Chern number classification of these non-trivial skyrmions using maps from the 2-torus (the unit cell for skyrmion crystals) to the 2-sphere in spin space. Finally, I will discuss the elliptic cone phase, a new state that emerges for easy-axis anisotropy and broken mirror symmetry. We acknowledge support by the National Science Foundation by the NSF Graduate Research Fellowship Program Grant No. DGE-1343012 (JR), by an NSF Grant DMR-1410364 (MR), and by the CEM, an NSF MRSEC, under Grant DMR-1420451.

  8. Enhancement of stability of various nZVI suspensions used in groundwater remediation with environmentally friendly organic stabilizers

    NASA Astrophysics Data System (ADS)

    Schmid, Doris; Wagner, Stephan; Velimirović, Milica; Laumann, Susanne; Micić, Vesna; Hofmann, Thilo

    2014-05-01

    The use of nanoscale zero-valent iron (nZVI) particles for in situ remediation of polluted soil and groundwater has been shown as one of the most promising techniques [1]. The success of this technology depends on the mobility, reactivity, and longevity of nZVI particles. The mobility of nZVI particles depends on the properties of the single particles, stability of the particle suspension, and the aquifer material [1,2]. In order to enhance the mobility of nZVI, the mobility-decisive properties of the nZVI particles in suspension such as concentration, size distribution, surface charge, and sedimentation rate have to be investigated and optimized. Previous studies showed that pristine nZVI particles aggregate rapidly in water, reducing the particles radius of influence after injection [3]. In order to prevent aggregation and sedimentation of the nZVI particles, and consequently improve the stability of nZVI suspension and therefore the mobility of the nZVI particles, surface stabilizers can be used to provide electrostatic repulsion and steric or electrosteric stabilization [3,4]. The objective of this lab-scale study is to investigate the potential for enhancing the stability of different nZVI suspensions by means of environmentally friendly organic stabilizers, including carboxymethyl cellulose, pectin, alginate, xanthan, and guar gum. The different nZVI particles used included pristine and polyacrylic acid-coated nZVI particles provided in suspension (Nanofer 25 and Nanofer 25S, respectively, NANOIRON s.r.o., Czech Republic), air-stable nZVI particles (Nanofer Star, (NANOIRON s.r.o., Czech Republic), and milled iron flakes (UVR-FIA, Germany). In order to study the enhancement of nZVI stability (1 g L-1 total iron) different concentrations of organic stabilizers (1-20 wt.%) were applied in these nZVI suspensions. Each nZVI suspension was freshly prepared and treated for 10 minutes with Ultra-Turrax (15 000 rpm) and 10 minutes ultrasonic bath prior to

  9. Animal flight dynamics I. Stability in gliding flight.

    PubMed

    Thomas, A L; Taylor, G K

    2001-10-01

    Stability is as essential to flying as lift itself, but previous discussions of how flying animals maintain stability have been limited in both number and scope. By developing the pitching moment equations for gliding animals and by discussing potential sources of roll and yaw stability, we consider the various sources of static stability used by gliding animals. We find that gliding animals differ markedly from aircraft in how they maintain stability. In particular, the pendulum stability provided when the centre of gravity lies below the wings is a much more important source of stability in flying animals than in most conventional aircraft. Drag-based stability also appears to be important for many gliding animals, whereas in aircraft, drag is usually kept to a minimum. One unexpected consequence of these differences is that the golden measure of static pitching stability in aircraft--the static margin--can only strictly be applied to flying animals if the equilibrium angle of attack is specified. We also derive several rules of thumb by which stable fliers can be identified. Stable fliers are expected to exhibit one or more of the following features: (1) Wings that are swept forward in slow flight. (2) Wings that are twisted down at the tips when swept back (wash-out) and twisted up at the tips when swept forwards (wash-in). (3) Additional lifting surfaces (canard, hindwings or a tail) inclined nose-up to the main wing if they lie forward of it, and nose-down if they lie behind it (longitudinal dihedral). Each of these predictions is directional--the opposite is expected to apply in unstable animals. In addition, animals with reduced stability are expected to display direct flight patterns in turbulent conditions, in contrast to the erratic flight patterns predicted for stable animals, in which large restoring forces are generated. Using these predictions, we find that flying animals possess a far higher degree of inherent stability than has generally been

  10. Enhanced subliminal emotional responses to dynamic facial expressions.

    PubMed

    Sato, Wataru; Kubota, Yasutaka; Toichi, Motomi

    2014-01-01

    Emotional processing without conscious awareness plays an important role in human social interaction. Several behavioral studies reported that subliminal presentation of photographs of emotional facial expressions induces unconscious emotional processing. However, it was difficult to elicit strong and robust effects using this method. We hypothesized that dynamic presentations of facial expressions would enhance subliminal emotional effects and tested this hypothesis with two experiments. Fearful or happy facial expressions were presented dynamically or statically in either the left or the right visual field for 20 (Experiment 1) and 30 (Experiment 2) ms. Nonsense target ideographs were then presented, and participants reported their preference for them. The results consistently showed that dynamic presentations of emotional facial expressions induced more evident emotional biases toward subsequent targets than did static ones. These results indicate that dynamic presentations of emotional facial expressions induce more evident unconscious emotional processing. PMID:25250001

  11. Enhanced subliminal emotional responses to dynamic facial expressions

    PubMed Central

    Sato, Wataru; Kubota, Yasutaka; Toichi, Motomi

    2014-01-01

    Emotional processing without conscious awareness plays an important role in human social interaction. Several behavioral studies reported that subliminal presentation of photographs of emotional facial expressions induces unconscious emotional processing. However, it was difficult to elicit strong and robust effects using this method. We hypothesized that dynamic presentations of facial expressions would enhance subliminal emotional effects and tested this hypothesis with two experiments. Fearful or happy facial expressions were presented dynamically or statically in either the left or the right visual field for 20 (Experiment 1) and 30 (Experiment 2) ms. Nonsense target ideographs were then presented, and participants reported their preference for them. The results consistently showed that dynamic presentations of emotional facial expressions induced more evident emotional biases toward subsequent targets than did static ones. These results indicate that dynamic presentations of emotional facial expressions induce more evident unconscious emotional processing. PMID:25250001

  12. Overview of Orion Crew Module and Launch Abort Vehicle Dynamic Stability

    NASA Technical Reports Server (NTRS)

    Owens, Donald B.; Aibicjpm. Vamessa V.

    2011-01-01

    With the retirement of the Space Shuttle, NASA is designing a new spacecraft, called Orion, to fly astronauts to low earth orbit and beyond. Characterization of the dynamic stability of the Orion spacecraft is important for the design of the spacecraft and trajectory construction. Dynamic stability affects the stability and control of the Orion Crew Module during re-entry, especially below Mach = 2.0 and including flight under the drogues. The Launch Abort Vehicle is affected by dynamic stability as well, especially during the re-orientation and heatshield forward segments of the flight. The dynamic stability was assessed using the forced oscillation technique, free-to-oscillate, ballistic range, and sub-scale free-flight tests. All of the test techniques demonstrated that in heatshield-forward flight the Crew Module and Launch Abort Vehicle are dynamically unstable in a significant portion of their flight trajectory. This paper will provide a brief overview of the Orion dynamic aero program and a high-level summary of the dynamic stability characteristics of the Orion spacecraft.

  13. Enhanced Immunogenicity of Stabilized Trimeric Soluble Influenza Hemagglutinin

    PubMed Central

    Weldon, William C.; Wang, Bao-Zhong; Martin, Maria P.; Koutsonanos, Dimitrios G.; Skountzou, Ioanna; Compans, Richard W.

    2010-01-01

    Background The recent swine-origin H1N1 pandemic illustrates the need to develop improved procedures for rapid production of influenza vaccines. One alternative to the current egg-based manufacture of influenza vaccine is to produce a hemagglutinin (HA) subunit vaccine using a recombinant expression system with the potential for high protein yields, ease of cloning new antigenic variants, and an established safety record in humans. Methodology/Principal Findings We generated a soluble HA (sHA), derived from the H3N2 virus A/Aichi/2/68, modified at the C-terminus with a GCN4pII trimerization repeat to stabilize the native trimeric structure of HA. When expressed in the baculovirus system, the modified sHA formed native trimers. In contrast, the unmodified sHA was found to present epitopes recognized by a low-pH conformation specific monoclonal antibody. We found that mice primed and boosted with 3 µg of trimeric sHA in the absence of adjuvants had significantly higher IgG and HAI titers than mice that received the unmodified sHA. This correlated with an increased survival and reduced body weight loss following lethal challenge with mouse-adapted A/Aichi/2/68 virus. In addition, mice receiving a single vaccination of the trimeric sHA in the absence of adjuvants had improved survival and body weight loss compared to mice vaccinated with the unmodified sHA. Conclusions/Significance Our data indicate that the recombinant trimeric sHA presents native trimeric epitopes while the unmodified sHA presents epitopes not exposed in the native HA molecule. The epitopes presented in the unmodified sHA constitute a “silent face” which may skew the antibody response to epitopes not accessible in live virus at neutral pH. The results demonstrate that the trimeric sHA is a more effective influenza vaccine candidate and emphasize the importance of structure-based antigen design in improving recombinant HA vaccines. PMID:20824188

  14. Static and dynamic stability analysis of the space shuttle vehicle-orbiter

    NASA Technical Reports Server (NTRS)

    Chyu, W. J.; Cavin, R. K.; Erickson, L. L.

    1978-01-01

    The longitudinal static and dynamic stability of a Space Shuttle Vehicle-Orbiter (SSV Orbiter) model is analyzed using the FLEXSTAB computer program. Nonlinear effects are accounted for by application of a correction technique in the FLEXSTAB system; the technique incorporates experimental force and pressure data into the linear aerodynamic theory. A flexible Orbiter model is treated in the static stability analysis for the flight conditions of Mach number 0.9 for rectilinear flight (1 g) and for a pull-up maneuver (2.5 g) at an altitude of 15.24 km. Static stability parameters and structural deformations of the Orbiter are calculated at trim conditions for the dynamic stability analysis, and the characteristics of damping in pitch are investigated for a Mach number range of 0.3 to 1.2. The calculated results for both the static and dynamic stabilities are compared with the available experimental data.

  15. Fast Dynamics and Stabilization of Proteins: Binary Glasses of Trehalose and Glycerol

    PubMed Central

    Cicerone, Marcus T.; Soles, Christopher L.

    2004-01-01

    We present elastic and inelastic incoherent neutron scattering data from a series of trehalose glasses diluted with glycerol. A strong correlation with recently published protein stability data in the same series of glasses illustrates that the dynamics at Q ≥ 0.71 Å−1 and ω > 200 MHz are important to stabilization of horseradish peroxidase and yeast alcohol dehydrogenase in these glasses. To the best of our knowledge, this is the first direct evidence that enzyme stability in a room temperature glass depends upon suppressing these short-length scale, high-frequency dynamics within the glass. We briefly discuss the coupling of protein motions to the local dynamics of the glass. Also, we show that Tg alone is not a good indicator for the protein stability in this series of glasses; the glass that confers the maximum room-temperature stability does not have the highest Tg. PMID:15189880

  16. Stability and attractivity in optimistic value for dynamical systems with uncertainty

    NASA Astrophysics Data System (ADS)

    Tao, Nana; Zhu, Yuanguo

    2016-05-01

    Stability analysis is an important aspect to investigate the qualitative analysis of solutions of dynamical systems with uncertainty. And the optimistic value of uncertain variable is a critical value for handing optimization problems under uncertain environments. In this paper, we introduce two concepts of stability and attractivity in optimistic value for dynamical systems with uncertainty. Then, we present a sufficient condition of stability and a sufficient and necessary condition of attractivity for linear dynamical systems with uncertainty. Furthermore, we discuss the relationship between stability in measure (in mean, in distribution) and stability in optimistic value, and the relationship between attractivity in measure (in mean, in distribution) and attractivity in optimistic value. Last, a population model is considered.

  17. Fall Risk Assessments Based on Postural and Dynamic Stability Using Inertial Measurement Unit

    PubMed Central

    Zhang, Xiaoyue; Lockhart, Thurmon E

    2012-01-01

    Objectives Slip and fall accidents in the workplace are one of the top causes of work related fatalities and injuries. Previous studies have indicated that fall risk was related to postural and dynamic stability. However, the usage of this theoretical relationship was limited by laboratory based measuring instruments. The current study proposed a new method for stability assessment by use of inertial measurement units (IMUs). Methods Accelerations at different body parts were recorded by the IMUs. Postural and local dynamic stability was assessed from these measures and compared with that computed from the traditional method. Results The results demonstrated: 1) significant differences between fall prone and healthy groups in IMU assessed dynamic stability; and 2) better power of discrimination with multi stability index assessed by IMUs. Conclusion The findings can be utilized in the design of a portable screening or monitoring tool for fall risk assessment in various industrial settings. PMID:23019531

  18. Improvement of bias stability for a micromachined gyroscope based on dynamic electrical balancing of coupling stiffness

    NASA Astrophysics Data System (ADS)

    Su, Jianbin; Xiao, Dingbang; Wu, Xuezhong; Hou, Zhanqiang; Chen, Zhihua

    2013-07-01

    We present a dynamic electrical balancing of coupling stiffness for improving the bias stability of micromachined gyroscopes, which embeds the coupling stiffness in a closed-loop system to make the micromachined gyroscope possess more robust bias stability by suppressing the variation of coupling stiffness. The effect of the dynamic electrical balancing control is theoretically analyzed and implemented using a silicon micromachined gyroscope as an example case. It has been experimentally shown that, comparing with open loop detection, the proposed method increased the stability of the amplitude of the mechanical quadrature signal by 38 times, and therefore improved the bias stability by 5.2 times from 89 to 17 deg/h, and the temperature stability of scale factor by 2.7 times from 622 to 231 ppm/°C. Experimental results effectively indicated the theoretical model of dynamic electrical balancing of coupling stiffness.

  19. Attitude dynamic of spin-stabilized satellites with flexible appendages

    NASA Technical Reports Server (NTRS)

    Renard, M. L.

    1973-01-01

    Equations of motion and computer programs have been developed for analyzing the motion of a spin-stabilized spacecraft having long, flexible appendages. Stability charts were derived, or can be redrawn with the desired accuracy for any particular set of design parameters. Simulation graphs of variables of interest are readily obtainable on line using program FLEXAT. Finally, applications to actual satellites, such as UK-4 and IMP-1 have been considered.

  20. Marginally subcritical dynamics explain enhanced stimulus discriminability under attention

    PubMed Central

    Tomen, Nergis; Rotermund, David; Ernst, Udo

    2014-01-01

    Recent experimental and theoretical work has established the hypothesis that cortical neurons operate close to a critical state which describes a phase transition from chaotic to ordered dynamics. Critical dynamics are suggested to optimize several aspects of neuronal information processing. However, although critical dynamics have been demonstrated in recordings of spontaneously active cortical neurons, little is known about how these dynamics are affected by task-dependent changes in neuronal activity when the cortex is engaged in stimulus processing. Here we explore this question in the context of cortical information processing modulated by selective visual attention. In particular, we focus on recent findings that local field potentials (LFPs) in macaque area V4 demonstrate an increase in γ-band synchrony and a simultaneous enhancement of object representation with attention. We reproduce these results using a model of integrate-and-fire neurons where attention increases synchrony by enhancing the efficacy of recurrent interactions. In the phase space spanned by excitatory and inhibitory coupling strengths, we identify critical points and regions of enhanced discriminability. Furthermore, we quantify encoding capacity using information entropy. We find a rapid enhancement of stimulus discriminability with the emergence of synchrony in the network. Strikingly, only a narrow region in the phase space, at the transition from subcritical to supercritical dynamics, supports the experimentally observed discriminability increase. At the supercritical border of this transition region, information entropy decreases drastically as synchrony sets in. At the subcritical border, entropy is maximized under the assumption of a coarse observation scale. Our results suggest that cortical networks operate at such near-critical states, allowing minimal attentional modulations of network excitability to substantially augment stimulus representation in the LFPs. PMID:25202240

  1. Marginally subcritical dynamics explain enhanced stimulus discriminability under attention.

    PubMed

    Tomen, Nergis; Rotermund, David; Ernst, Udo

    2014-01-01

    Recent experimental and theoretical work has established the hypothesis that cortical neurons operate close to a critical state which describes a phase transition from chaotic to ordered dynamics. Critical dynamics are suggested to optimize several aspects of neuronal information processing. However, although critical dynamics have been demonstrated in recordings of spontaneously active cortical neurons, little is known about how these dynamics are affected by task-dependent changes in neuronal activity when the cortex is engaged in stimulus processing. Here we explore this question in the context of cortical information processing modulated by selective visual attention. In particular, we focus on recent findings that local field potentials (LFPs) in macaque area V4 demonstrate an increase in γ-band synchrony and a simultaneous enhancement of object representation with attention. We reproduce these results using a model of integrate-and-fire neurons where attention increases synchrony by enhancing the efficacy of recurrent interactions. In the phase space spanned by excitatory and inhibitory coupling strengths, we identify critical points and regions of enhanced discriminability. Furthermore, we quantify encoding capacity using information entropy. We find a rapid enhancement of stimulus discriminability with the emergence of synchrony in the network. Strikingly, only a narrow region in the phase space, at the transition from subcritical to supercritical dynamics, supports the experimentally observed discriminability increase. At the supercritical border of this transition region, information entropy decreases drastically as synchrony sets in. At the subcritical border, entropy is maximized under the assumption of a coarse observation scale. Our results suggest that cortical networks operate at such near-critical states, allowing minimal attentional modulations of network excitability to substantially augment stimulus representation in the LFPs.

  2. Enhanced Physical Stability of Amorphous Drug Formulations via Dry Polymer Coating.

    PubMed

    Capece, Maxx; Davé, Rajesh

    2015-06-01

    Although amorphous solid drug formulations may be advantageous for enhancing the bioavailability of poorly soluble active pharmaceutical ingredients, they exhibit poor physical stability and undergo recrystallization. To address this limitation, this study investigates stability issues associated with amorphous solids through analysis of the crystallization behavior for acetaminophen (APAP), known as a fast crystallizer, using a modified form of the Avrami equation that kinetically models both surface and bulk crystallization. It is found that surface-enhanced crystallization, occurring faster at the free surface than in the bulk, is the major impediment to the stability of amorphous APAP. It is hypothesized that a novel use of a dry-polymer-coating process referred to as mechanical-dry-polymer-coating may be used to inhibit surface crystallization and enhance stability. The proposed process, which is examined, simultaneously mills and coats amorphous solids with polymer, while avoiding solvents or solutions, which may otherwise cause stability or crystallization issues during coating. It is shown that solid dispersions of APAP (64% loading) with a small particle size (28 μm) could be prepared and coated with the polymer, carnauba wax, in a vibratory ball mill. The resulting amorphous solid was found to have excellent stability as a result of inhibition of surface crystallization. PMID:25902736

  3. Enhanced Physical Stability of Amorphous Drug Formulations via Dry Polymer Coating.

    PubMed

    Capece, Maxx; Davé, Rajesh

    2015-06-01

    Although amorphous solid drug formulations may be advantageous for enhancing the bioavailability of poorly soluble active pharmaceutical ingredients, they exhibit poor physical stability and undergo recrystallization. To address this limitation, this study investigates stability issues associated with amorphous solids through analysis of the crystallization behavior for acetaminophen (APAP), known as a fast crystallizer, using a modified form of the Avrami equation that kinetically models both surface and bulk crystallization. It is found that surface-enhanced crystallization, occurring faster at the free surface than in the bulk, is the major impediment to the stability of amorphous APAP. It is hypothesized that a novel use of a dry-polymer-coating process referred to as mechanical-dry-polymer-coating may be used to inhibit surface crystallization and enhance stability. The proposed process, which is examined, simultaneously mills and coats amorphous solids with polymer, while avoiding solvents or solutions, which may otherwise cause stability or crystallization issues during coating. It is shown that solid dispersions of APAP (64% loading) with a small particle size (28 μm) could be prepared and coated with the polymer, carnauba wax, in a vibratory ball mill. The resulting amorphous solid was found to have excellent stability as a result of inhibition of surface crystallization.

  4. Dynamic stabilization of Rayleigh-Taylor instability: Experiments with Newtonian fluids as surrogates for ablation fronts

    SciTech Connect

    Rodriguez Prieto, G.; Piriz, A. R.; Lopez Cela, J. J.; Tahir, N. A.

    2013-01-15

    A previous theory on dynamic stabilization of Rayleigh-Taylor instability at interfaces between Newtonian fluids is reformulated in order to make evident the analogy of this problem with the related one on dynamic stabilization of ablation fronts in the framework of inertial confinement fusion. Explicit analytical expressions are obtained for the boundaries of the dynamically stable region which turns out to be completely analogue to the stability charts obtained for the case of ablation fronts. These results allow proposing experiments with Newtonian fluids as surrogates for studying the case of ablation fronts. Experiments with Newtonian fluids are presented which demonstrate the validity of the theoretical approach and encourage to pursue experimental research on ablation fronts to settle the feasibility of dynamic stabilization in the inertial confinement fusion scenario.

  5. Effects of slipping-like perturbation intensity on the dynamical stability.

    PubMed

    Aprigliano, Federica; Martelli, Dario; Tropea, Peppino; Micera, Silvestro; Monaco, Vito

    2015-01-01

    Falls are a major cause of morbidity and death in elderly people. Understanding how subjects maintain stability while walking or while being exposed to perturbations is important in order to prevent falls. Here, five healthy subjects were asked to manage unexpected slipping-like perturbations of increasing intensities (i.e., soft, medium and strong) in order to investigate the effects of the perturbation intensity on the biomechanical behavior and on the dynamical stability, described by the Margin of Stability. The lower limb kinematic (i.e., hip, knee and ankle joints angles) was computed before and after the onset of the perturbation. The compensatory time and the Margin of Stability were calculated after the onset of the perturbation. As expected, results showed that the perturbation altered the subjects' kinematic and the modulation of the perturbation intensity was reflected in the dynamical stability: the stronger was the perturbation, the lower was the Margin of Stability describing a lower balance recovery.

  6. Concert halls with strong lateral reflections enhance musical dynamics.

    PubMed

    Pätynen, Jukka; Tervo, Sakari; Robinson, Philip W; Lokki, Tapio

    2014-03-25

    One of the most thrilling cultural experiences is to hear live symphony-orchestra music build up from a whispering passage to a monumental fortissimo. The impact of such a crescendo has been thought to depend only on the musicians' skill, but here we show that interactions between the concert-hall acoustics and listeners' hearing also play a major role in musical dynamics. These interactions contribute to the shoebox-type concert hall's established success, but little prior research has been devoted to dynamic expression in this three-part transmission chain as a complete system. More forceful orchestral playing disproportionately excites high frequency harmonics more than those near the note's fundamental. This effect results in not only more sound energy, but also a different tone color. The concert hall transmits this sound, and the room geometry defines from which directions acoustic reflections arrive at the listener. Binaural directional hearing emphasizes high frequencies more when sound arrives from the sides of the head rather than from the median plane. Simultaneously, these same frequencies are emphasized by higher orchestral-playing dynamics. When the room geometry provides reflections from these directions, the perceived dynamic range is enhanced. Current room-acoustic evaluation methods assume linear behavior and thus neglect this effect. The hypothesis presented here is that the auditory excitation by reflections is emphasized with an orchestra forte most in concert halls with strong lateral reflections. The enhanced dynamic range provides an explanation for the success of rectangularly shaped concert-hall geometry.

  7. An Action Dependent Heuristic Dynamic Programming-controlled Superconducting Magnetic Energy Storage for Transient Stability Augmentation

    NASA Astrophysics Data System (ADS)

    Wang, Xinpu; Yang, Jun; Zhang, Xiaodong; Yu, Xiaopeng

    To enhance the stability of power system, the active power and reactive power can be absorbed from or released to Superconducting magnetic energy storage (SMES) unit according to system power requirements. This paper proposes a control strategy based on action dependent heuristic dynamic programing (ADHDP) which can control SMES to improve the stability of electric power system with on-line learning ability. Based on back propagation (BP) neural network, ADHDP approximates the optimal control solution of nonlinear system through iteration step by step. This on-line learning ability improves its performance by learning from its own mistakes through reinforcement signal from external environment, so that it can adjust the neural network weights according to the back propagation error to achieve optimal control performance. To investigate the effectiveness of the proposed control strategy, simulation tests are carried out in Matlab/Simulink. And a conventional Proportional-Integral (PI) controlled method is used to compare the performance of ADHDP. Simulation results show that the proposed controller demonstrates superior damping performance on power system oscillation caused by three-phase fault and wind power fluctuation over the PI controller.

  8. Dynamic hydroxymethylation of deoxyribonucleic acid marks differentiation-associated enhancers.

    PubMed

    Sérandour, Aurélien A; Avner, Stéphane; Oger, Frédérik; Bizot, Maud; Percevault, Frédéric; Lucchetti-Miganeh, Céline; Palierne, Gaëlle; Gheeraert, Céline; Barloy-Hubler, Frédérique; Péron, Christine Le; Madigou, Thierry; Durand, Emmanuelle; Froguel, Philippe; Staels, Bart; Lefebvre, Philippe; Métivier, Raphaël; Eeckhoute, Jérôme; Salbert, Gilles

    2012-09-01

    Enhancers are developmentally controlled transcriptional regulatory regions whose activities are modulated through histone modifications or histone variant deposition. In this study, we show by genome-wide mapping that the newly discovered deoxyribonucleic acid (DNA) modification 5-hydroxymethylcytosine (5hmC) is dynamically associated with transcription factor binding to distal regulatory sites during neural differentiation of mouse P19 cells and during adipocyte differentiation of mouse 3T3-L1 cells. Functional annotation reveals that regions gaining 5hmC are associated with genes expressed either in neural tissues when P19 cells undergo neural differentiation or in adipose tissue when 3T3-L1 cells undergo adipocyte differentiation. Furthermore, distal regions gaining 5hmC together with H3K4me2 and H3K27ac in P19 cells behave as differentiation-dependent transcriptional enhancers. Identified regions are enriched in motifs for transcription factors regulating specific cell fates such as Meis1 in P19 cells and PPARγ in 3T3-L1 cells. Accordingly, a fraction of hydroxymethylated Meis1 sites were associated with a dynamic engagement of the 5-methylcytosine hydroxylase Tet1. In addition, kinetic studies of cytosine hydroxymethylation of selected enhancers indicated that DNA hydroxymethylation is an early event of enhancer activation. Hence, acquisition of 5hmC in cell-specific distal regulatory regions may represent a major event of enhancer progression toward an active state and participate in selective activation of tissue-specific genes.

  9. Dynamic hydroxymethylation of deoxyribonucleic acid marks differentiation-associated enhancers

    PubMed Central

    Sérandour, Aurélien A.; Avner, Stéphane; Oger, Frédérik; Bizot, Maud; Percevault, Frédéric; Lucchetti-Miganeh, Céline; Palierne, Gaëlle; Gheeraert, Céline; Barloy-Hubler, Frédérique; Péron, Christine Le; Madigou, Thierry; Durand, Emmanuelle; Froguel, Philippe; Staels, Bart; Lefebvre, Philippe; Métivier, Raphaël; Eeckhoute, Jérôme; Salbert, Gilles

    2012-01-01

    Enhancers are developmentally controlled transcriptional regulatory regions whose activities are modulated through histone modifications or histone variant deposition. In this study, we show by genome-wide mapping that the newly discovered deoxyribonucleic acid (DNA) modification 5-hydroxymethylcytosine (5hmC) is dynamically associated with transcription factor binding to distal regulatory sites during neural differentiation of mouse P19 cells and during adipocyte differentiation of mouse 3T3-L1 cells. Functional annotation reveals that regions gaining 5hmC are associated with genes expressed either in neural tissues when P19 cells undergo neural differentiation or in adipose tissue when 3T3-L1 cells undergo adipocyte differentiation. Furthermore, distal regions gaining 5hmC together with H3K4me2 and H3K27ac in P19 cells behave as differentiation-dependent transcriptional enhancers. Identified regions are enriched in motifs for transcription factors regulating specific cell fates such as Meis1 in P19 cells and PPARγ in 3T3-L1 cells. Accordingly, a fraction of hydroxymethylated Meis1 sites were associated with a dynamic engagement of the 5-methylcytosine hydroxylase Tet1. In addition, kinetic studies of cytosine hydroxymethylation of selected enhancers indicated that DNA hydroxymethylation is an early event of enhancer activation. Hence, acquisition of 5hmC in cell-specific distal regulatory regions may represent a major event of enhancer progression toward an active state and participate in selective activation of tissue-specific genes. PMID:22730288

  10. Power system dynamic security enhancement using artificial neural networks and energy margin

    SciTech Connect

    Momoh, J.A.; Effiong, C.B.

    1996-11-01

    A framework for dynamic security enhancement based on area-wise preventive control is proposed. The power system is partitioned into areas for stability evaluation using the transient energy margin. Area vulnerability is evaluated based on the sensitivity of the energy margin w.r.t. controls in the given areas of the system. The areas of the system which contribute significantly to instability are labeled critical or weak areas and preventive control is applied in those areas of the system. The final control application is achieved by the use of artificial neural network (ANN) to compute the control inputs.

  11. Dynamic Stability Optimization of Laminated Composite Plates under Combined Boundary Loading

    NASA Astrophysics Data System (ADS)

    Shafei, Erfan; Kabir, Mohammad Zaman

    2011-12-01

    Dynamic stability and design optimization of laminated simply supported plates under planar conservative boundary loads are investigated in current study. Examples can be found in internal connecting elements of spacecraft and aerospace structures subjected to edge axial and shear loads. Designation of such elements is function of layup configuration, plate aspect ratio, loading combinations, and layup thickness. An optimum design aims maximum stability load satisfying a predefined stable vibration frequency. The interaction between compound loading and layup angle parameter affects the order of merging vibration modes and may stabilize the dynamic response. Laminated plates are assumed to be angle-plies symmetric to mid-plane surface. Dynamic equilibrium PDE has been solved using kernel integral transformation for modal frequency values and eigenvalue-based orthogonal functions for critical stability loads. The dictating dynamic stability mode is shown to be controlled by geometric stiffness distributions of composite plates. Solution of presented design optimization problem has been done using analytical approach combined with interior penalty multiplier algorithm. The results are verified by FEA approach and stability zones of original and optimized plates are stated as final data. Presented method can help designers to stabilize the dynamic response of composite plates by selecting an optimized layup orientation and thickness for prescribed design circumstances.

  12. Difference in static and dynamic stability between flexible flatfeet and neutral feet.

    PubMed

    Kim, Jeong-Ah; Lim, One-Bin; Yi, Chung-Hwi

    2015-02-01

    Different postural stability may be a contributor to secondary injuries in individuals with flexible flatfeet (FF) compared to those with neutral feet (NF). However, the differences between static and dynamic stability of FF and NF have not been examined. This study compared the static and dynamic stability of subjects with FF and NF and investigated the relationship between static and dynamic stability. Twenty-eight subjects (14 each in the FF and NF groups) performed three tasks (single leg standing with eyes open, with eyes closed, and the Y balance test). We quantified the center of pressure (COP) speed and Y balance test score (Y score) within the tasks. COP speed was significantly greater in the FF group than in the NF group under both conditions (eyes open and closed) and directions (anteroposterior and mediolateral). Y scores did not differ significantly between the two groups. No significant relationship was observed between the COP speed and Y score in either group. These results show that individuals with FF have different static stabilities, but not dynamic stabilities, compared with those with NF. This might indicate the absence of a relationship between static and dynamic stabilities.

  13. Investigation of biomechanical behavior of lumbar vertebral segments with dynamic stabilization device using finite element approach

    NASA Astrophysics Data System (ADS)

    Deoghare, Ashish B.; Kashyap, Siddharth; Padole, Pramod M.

    2013-03-01

    Degenerative disc disease is a major source of lower back pain and significantly alters the biomechanics of the lumbar spine. Dynamic stabilization device is a remedial technique which uses flexible materials to stabilize the affected lumbar region while preserving the natural anatomy of the spine. The main objective of this research work is to investigate the stiffness variation of dynamic stabilization device under various loading conditions under compression, axial rotation and flexion. Three dimensional model of the two segment lumbar spine is developed using computed tomography (CT) scan images. The lumbar structure developed is analyzed in ANSYS workbench. Two types of dynamic stabilization are considered: one with stabilizing device as pedicle instrumentation and second with stabilization device inserted around the inter-vertebral disc. Analysis suggests that proper positioning of the dynamic stabilization device is of paramount significance prior to the surgery. Inserting the device in the posterior region indicates the adverse effects as it shows increase in the deformation of the inter-vertebral disc. Analysis executed by positioning stabilizing device around the inter-vertebral disc yields better result for various stiffness values under compression and other loadings. [Figure not available: see fulltext.

  14. Motivational Dynamics in Language Learning: Change, Stability, and Context

    ERIC Educational Resources Information Center

    Waninge, Freerkien; Dörnyei, Zoltán; De Bot, Kees

    2014-01-01

    Motivation as a variable in L2 development is no longer seen as the stable individual difference factor it was once believed to be: Influenced by process-oriented models and principles, and especially by the growing understanding of how complex dynamic systems work, researchers have been focusing increasingly on the dynamic and changeable nature…

  15. Dynamic knee stability estimated by finite helical axis methods during functional performance approximately twenty years after anterior cruciate ligament injury.

    PubMed

    Grip, Helena; Tengman, Eva; Häger, Charlotte K

    2015-07-16

    Finite helical axis (FHA) measures of the knee joint during weight-bearing tasks may capture dynamic knee stability following Anterior Cruciate Ligament (ACL) injury. The aim was to investigate dynamic knee stability during two-leg squat (TLS) and one-leg side hop (SH) in a long-term follow-up of ACL injury, and to examine correlations with knee laxity (KT-1000), osteoarthritis (OA, Kellgren-Lawrence) and knee function (Lysholm score). Participants were injured 17-28 years ago and then treated with surgery (n=33, ACLR) or physiotherapy only (n=37, ACLPT) and healthy-knee controls (n=33) were tested. Movements were registered with an optical motion capture system. We computed three FHA inclination angles, its' Anterior-Posterior (A-P) position, and an index quantifying directional changes (DI), during stepwise knee flexion intervals of ∼15°. Injured knees were less stable compared to healthy controls' and to contralateral non-injured knees, regardless of treatment: the A-P intersection was more anterior (indicating a more anterior positioning of tibia relative to femur) positively correlating with high laxity/low knee function, and during SH, the FHA was more inclined relative to the flexion-extension axis, possibly due to reduced rotational stability. During the TLS, A-P intersection was more anterior in the non-injured knee than the injured, and DI was higher, probably related to higher load on the non-injured knee. ACLR had less anterior A-P intersection than ACLPT, suggesting that surgery enhanced stability, although rotational stability may remain reduced. More anterior A-P intersection and greater inclination between the FHA and the knee flexion-extension axis best revealed reduced dynamic stability ∼23 years post-injury.

  16. Dynamic knee stability estimated by finite helical axis methods during functional performance approximately twenty years after anterior cruciate ligament injury.

    PubMed

    Grip, Helena; Tengman, Eva; Häger, Charlotte K

    2015-07-16

    Finite helical axis (FHA) measures of the knee joint during weight-bearing tasks may capture dynamic knee stability following Anterior Cruciate Ligament (ACL) injury. The aim was to investigate dynamic knee stability during two-leg squat (TLS) and one-leg side hop (SH) in a long-term follow-up of ACL injury, and to examine correlations with knee laxity (KT-1000), osteoarthritis (OA, Kellgren-Lawrence) and knee function (Lysholm score). Participants were injured 17-28 years ago and then treated with surgery (n=33, ACLR) or physiotherapy only (n=37, ACLPT) and healthy-knee controls (n=33) were tested. Movements were registered with an optical motion capture system. We computed three FHA inclination angles, its' Anterior-Posterior (A-P) position, and an index quantifying directional changes (DI), during stepwise knee flexion intervals of ∼15°. Injured knees were less stable compared to healthy controls' and to contralateral non-injured knees, regardless of treatment: the A-P intersection was more anterior (indicating a more anterior positioning of tibia relative to femur) positively correlating with high laxity/low knee function, and during SH, the FHA was more inclined relative to the flexion-extension axis, possibly due to reduced rotational stability. During the TLS, A-P intersection was more anterior in the non-injured knee than the injured, and DI was higher, probably related to higher load on the non-injured knee. ACLR had less anterior A-P intersection than ACLPT, suggesting that surgery enhanced stability, although rotational stability may remain reduced. More anterior A-P intersection and greater inclination between the FHA and the knee flexion-extension axis best revealed reduced dynamic stability ∼23 years post-injury. PMID:25935685

  17. Nanocaged enzymes with enhanced catalytic activity and increased stability against protease digestion.

    PubMed

    Zhao, Zhao; Fu, Jinglin; Dhakal, Soma; Johnson-Buck, Alexander; Liu, Minghui; Zhang, Ting; Woodbury, Neal W; Liu, Yan; Walter, Nils G; Yan, Hao

    2016-02-10

    Cells routinely compartmentalize enzymes for enhanced efficiency of their metabolic pathways. Here we report a general approach to construct DNA nanocaged enzymes for enhancing catalytic activity and stability. Nanocaged enzymes are realized by self-assembly into DNA nanocages with well-controlled stoichiometry and architecture that enabled a systematic study of the impact of both encapsulation and proximal polyanionic surfaces on a set of common metabolic enzymes. Activity assays at both bulk and single-molecule levels demonstrate increased substrate turnover numbers for DNA nanocage-encapsulated enzymes. Unexpectedly, we observe a significant inverse correlation between the size of a protein and its activity enhancement. This effect is consistent with a model wherein distal polyanionic surfaces of the nanocage enhance the stability of active enzyme conformations through the action of a strongly bound hydration layer. We further show that DNA nanocages protect encapsulated enzymes against proteases, demonstrating their practical utility in functional biomaterials and biotechnology.

  18. Nanocaged enzymes with enhanced catalytic activity and increased stability against protease digestion

    PubMed Central

    Zhao, Zhao; Fu, Jinglin; Dhakal, Soma; Johnson-Buck, Alexander; Liu, Minghui; Zhang, Ting; Woodbury, Neal W.; Liu, Yan; Walter, Nils G.; Yan, Hao

    2016-01-01

    Cells routinely compartmentalize enzymes for enhanced efficiency of their metabolic pathways. Here we report a general approach to construct DNA nanocaged enzymes for enhancing catalytic activity and stability. Nanocaged enzymes are realized by self-assembly into DNA nanocages with well-controlled stoichiometry and architecture that enabled a systematic study of the impact of both encapsulation and proximal polyanionic surfaces on a set of common metabolic enzymes. Activity assays at both bulk and single-molecule levels demonstrate increased substrate turnover numbers for DNA nanocage-encapsulated enzymes. Unexpectedly, we observe a significant inverse correlation between the size of a protein and its activity enhancement. This effect is consistent with a model wherein distal polyanionic surfaces of the nanocage enhance the stability of active enzyme conformations through the action of a strongly bound hydration layer. We further show that DNA nanocages protect encapsulated enzymes against proteases, demonstrating their practical utility in functional biomaterials and biotechnology. PMID:26861509

  19. Nanocaged enzymes with enhanced catalytic activity and increased stability against protease digestion

    NASA Astrophysics Data System (ADS)

    Zhao, Zhao; Fu, Jinglin; Dhakal, Soma; Johnson-Buck, Alexander; Liu, Minghui; Zhang, Ting; Woodbury, Neal W.; Liu, Yan; Walter, Nils G.; Yan, Hao

    2016-02-01

    Cells routinely compartmentalize enzymes for enhanced efficiency of their metabolic pathways. Here we report a general approach to construct DNA nanocaged enzymes for enhancing catalytic activity and stability. Nanocaged enzymes are realized by self-assembly into DNA nanocages with well-controlled stoichiometry and architecture that enabled a systematic study of the impact of both encapsulation and proximal polyanionic surfaces on a set of common metabolic enzymes. Activity assays at both bulk and single-molecule levels demonstrate increased substrate turnover numbers for DNA nanocage-encapsulated enzymes. Unexpectedly, we observe a significant inverse correlation between the size of a protein and its activity enhancement. This effect is consistent with a model wherein distal polyanionic surfaces of the nanocage enhance the stability of active enzyme conformations through the action of a strongly bound hydration layer. We further show that DNA nanocages protect encapsulated enzymes against proteases, demonstrating their practical utility in functional biomaterials and biotechnology.

  20. Dynamics of a climbing surfactant-laden film II: stability.

    PubMed

    Mavromoustaki, A; Matar, O K; Craster, R V

    2012-04-01

    The linear and nonlinear stability of a spreading film of constant flux and a drop of constant volume, discussed in [1], are examined here. A linear stability analysis (LSA) is carried out to investigate the stability to spanwise perturbations, by linearisation of the two-dimensional (2-D) evolution equations derived in [1] for the film thickness and surfactant concentration fields. The latter correspond to convective-diffusion equations for the surfactant, existing in the form of monomers (present at the free surface and in the bulk) and micelles (present in the bulk). The results of the LSA indicate that the thinning region, present upstream of the leading front in the constant flux case, and the leading ridge in the constant volume case, are unstable to spanwise perturbations. Numerical simulations of the 2-D system of equations demonstrate that the above-mentioned regions exhibit finger formation; the effect of selected system parameters on the fingering patterns is discussed.

  1. Nonlinear dynamics near the stability margin in rotating pipe flow

    NASA Technical Reports Server (NTRS)

    Yang, Z.; Leibovich, S.

    1991-01-01

    The nonlinear evolution of marginally unstable wave packets in rotating pipe flow is studied. These flows depend on two control parameters, which may be taken to be the axial Reynolds number R and a Rossby number, q. Marginal stability is realized on a curve in the (R, q)-plane, and the entire marginal stability boundary is explored. As the flow passes through any point on the marginal stability curve, it undergoes a supercritical Hopf bifurcation and the steady base flow is replaced by a traveling wave. The envelope of the wave system is governed by a complex Ginzburg-Landau equation. The Ginzburg-Landau equation admits Stokes waves, which correspond to standing modulations of the linear traveling wavetrain, as well as traveling wave modulations of the linear wavetrain. Bands of wavenumbers are identified in which the nonlinear modulated waves are subject to a sideband instability.

  2. Stability and dynamical properties of Cooper-Shepard-Sodano compactons

    SciTech Connect

    Mihaila, Bogdan; Cardenas, Andres; Cooper, Fred; Saxena, Avadh

    2010-12-15

    Extending a Pade approximant method used for studying compactons in the Rosenau-Hyman (RH) equation, we study the numerical stability of single compactons of the Cooper-Shepard-Sodano (CSS) equation and their pairwise interactions. The CSS equation has a conserved Hamiltonian which has allowed various approaches for studying analytically the nonlinear stability of the solutions. We study three different compacton solutions and find they are numerically stable. Similar to the collisions between RH compactons, the CSS compactons re-emerge with same coherent shape when scattered. The time evolution of the small-amplitude ripple resulting after scattering depends on the values of the parameters l and p characterizing the corresponding CSS equation. The simulation of the CSS compacton scattering requires a much smaller artificial viscosity to obtain numerical stability than in the case of RH compacton propagation.

  3. Studies of the Stability and Dynamics of Levitated Drops

    NASA Technical Reports Server (NTRS)

    Anikumar, A.; Lee, Chun Ping; Wang, T. G.

    1996-01-01

    This is a review of our experimental and theoretical studies relating to equilibrium and stability of liquid drops, typically of low viscosity, levitated in air by a sound field. The major emphasis here is on the physical principles and understanding behind the stability of levitated drops. A comparison with experimental data is also given, along with some fascinating pictures from high-speed photography. One of the aspects we shall deal with is how a drop can suddenly burst in an intense sound field; a phenomenon which can find applications in atomization technology. Also, we are currently investigating the phenomenon of suppression of coalescence between drops levitated in intense acoustic fields.

  4. Walking in simulated Martian gravity: influence of the portable life support system's design on dynamic stability.

    PubMed

    Scott-Pandorf, Melissa M; O'Connor, Daniel P; Layne, Charles S; Josić, Kresimir; Kurz, Max J

    2009-09-01

    With human exploration of the moon and Mars on the horizon, research considerations for space suit redesign have surfaced. The portable life support system (PLSS) used in conjunction with the space suit during the Apollo missions may have influenced the dynamic balance of the gait pattern. This investigation explored potential issues with the PLSS design that may arise during the Mars exploration. A better understanding of how the location of the PLSS load influences the dynamic stability of the gait pattern may provide insight, such that space missions may have more productive missions with a smaller risk of injury and damaging equipment while falling. We explored the influence the PLSS load position had on the dynamic stability of the walking pattern. While walking, participants wore a device built to simulate possible PLSS load configurations. Floquet and Lyapunov analysis techniques were used to quantify the dynamic stability of the gait pattern. The dynamic stability of the gait pattern was influenced by the position of load. PLSS loads that are placed high and forward on the torso resulted in less dynamically stable walking patterns than loads placed evenly and low on the torso. Furthermore, the kinematic results demonstrated that all joints of the lower extremity may be important for adjusting to different load placements and maintaining dynamic stability. Space scientists and engineers may want to consider PLSS designs that distribute loads evenly and low, and space suit designs that will not limit the sagittal plane range of motion at the lower extremity joints.

  5. Enhanced control of saddle steady states of dynamical systems.

    PubMed

    Tamaševičius, Arūnas; Tamaševičiūtė, Elena; Mykolaitis, Gytis; Bumelienė, Skaidra

    2013-09-01

    An adaptive feedback technique for stabilizing a priori unknown saddle steady states of dynamical systems is described. The method is based on an unstable low-pass filter combined with a stable low-pass filter. The cutoff frequencies of both filters can be set relatively high. This allows considerable increase in the rate of convergence to the steady state. We demonstrate numerically and experimentally that the technique is robust to the influence of unknown external forces, which change the position of the steady state in the phase space. Experiments have been performed using electrical circuits imitating the damped Duffing-Holmes and chaotic Lindberg systems. PMID:24125322

  6. The shape, stability and dynamics of elastic surfaces

    NASA Astrophysics Data System (ADS)

    Mahadevan, L.

    2008-03-01

    Bending a thin sheet is easier than stretching it, an observation which has its roots in geometry. We will use this fact to explain some unusual problems in biology, physics and geology. At the everyday scale, I will discuss the morphology of avascular algal blades, the dynamics of defects in an elastic ribbon, and the dynamics of prey capture by certain carnivorous plants. At the geological scale, I will try to explain the shape of island arcs on our planet. Finally, time permitting, I will discuss how we might extend these ideas to the macromolecular scale, to derive a mechanical model for the dynamic instability of a growing microtubule.

  7. The Effects on Dynamic Lateral Stability and Control of Large Artificial Variations in the Rotary Stability Derivatives

    NASA Technical Reports Server (NTRS)

    Schade, Robert O; Hassell, James L , Jr

    1953-01-01

    This report presents the results of an investigation conducted in the Langley free-flight tunnel to determine the effects of large artificial variations of several rotary lateral-stability derivatives on the dynamic lateral stability and control characteristics of a 45 degree sweptback-wing airplane model. Calculations of the period and damping of the lateral motions and of the response to roll and yaw disturbances were made for correlation with the experimental results. The calculated results were in qualitative agreement with the experimental results in predicting the general trends in flight characteristics produced by large changes in the stability derivatives, but in some cases the theory with the assumption of zero lag was not in good quantitative agreement with the experimental results.

  8. A method for dynamic nuclear polarization enhancement of membrane proteins.

    PubMed

    Smith, Adam N; Caporini, Marc A; Fanucci, Gail E; Long, Joanna R

    2015-01-26

    Dynamic nuclear polarization (DNP) magic-angle spinning (MAS) solid-state NMR (ssNMR) spectroscopy has the potential to enhance NMR signals by orders of magnitude and to enable NMR characterization of proteins which are inherently dilute, such as membrane proteins. In this work spin-labeled lipid molecules (SL-lipids), when used as polarizing agents, lead to large and relatively homogeneous DNP enhancements throughout the lipid bilayer and to an embedded lung surfactant mimetic peptide, KL4 . Specifically, DNP MAS ssNMR experiments at 600 MHz/395 GHz on KL4 reconstituted in liposomes containing SL-lipids reveal DNP enhancement values over two times larger for KL4 compared to liposome suspensions containing the biradical TOTAPOL. These findings suggest an alternative sample preparation strategy for DNP MAS ssNMR studies of lipid membranes and integral membrane proteins. PMID:25504310

  9. Robust adaptive dynamic programming and feedback stabilization of nonlinear systems.

    PubMed

    Jiang, Yu; Jiang, Zhong-Ping

    2014-05-01

    This paper studies the robust optimal control design for a class of uncertain nonlinear systems from a perspective of robust adaptive dynamic programming (RADP). The objective is to fill up a gap in the past literature of adaptive dynamic programming (ADP) where dynamic uncertainties or unmodeled dynamics are not addressed. A key strategy is to integrate tools from modern nonlinear control theory, such as the robust redesign and the backstepping techniques as well as the nonlinear small-gain theorem, with the theory of ADP. The proposed RADP methodology can be viewed as an extension of ADP to uncertain nonlinear systems. Practical learning algorithms are developed in this paper, and have been applied to the controller design problems for a jet engine and a one-machine power system. PMID:24808035

  10. Dynamic Stability of a #D Tensegrity Structure Carrying a Top Mass: Simulations and Experiments

    NASA Astrophysics Data System (ADS)

    Michielsen, Joris; Fey, Rob H. B.; Nijmeijer, Henk

    2012-07-01

    The static and dynamic stability of a 3D tensegrity structure carrying a top mass is investigated both theoretically and experimentally by studying static and linear dynamic responses, (nonlinear) frequency-amplitude plots, and Poincaré maps. A good correspondence between numerical and experimental results is obtained for the eigenfrequencies, FRFs, and frequency-amplitude plots.

  11. Dynamic stability during level walking and obstacle crossing in persons with facioscapulohumeral muscular dystrophy.

    PubMed

    Rijken, N H M; van Engelen, B G M; Geurts, A C H; Weerdesteyn, V

    2015-09-01

    Patients with FSHD suffer from progressive skeletal muscle weakness, which is associated with an elevated fall risk. To obtain insight into fall mechanisms in this patient group, we aimed to assess dynamic stability during level walking and obstacle crossing in patients at different disease stages. Ten patients with at least some lower extremity weakness were included, of whom six were classified as moderately affected and four as mildly affected. Ten healthy controls were also included. Level walking at comfortable speed was assessed, as well as crossing a 10 cm high wooden obstacle. We assessed forward and lateral dynamic stability, as well as spatiotemporal and kinematics variables. During level walking, the moderately affected group demonstrated a lower walking speed, which was accompanied by longer step times and smaller step lengths, yet dynamic stability was unaffected. When crossing the obstacle, however, the moderately affected patients demonstrated reduced forward stability margins during the trailing step, which was accompanied by an increased toe clearance and greater trunk and hip flexion. This suggests that during level walking, the patients effectively utilized compensatory strategies for maintaining dynamic stability, but that the moderately affected group lacked the capacity to fully compensate for the greater stability demands imposed by obstacle crossing, rendering them unable to maintain optimal stability levels. The present results highlight the difficulties that FSHD patients experience in performing this common activity of daily living and may help explain their propensity to fall in the forward direction.

  12. Local dynamic stability of spine muscle activation and stiffness patterns during repetitive lifting.

    PubMed

    Graham, Ryan B; Brown, Stephen H M

    2014-12-01

    To facilitate stable trunk kinematics, humans must generate appropriate motor patterns to effectively control muscle force and stiffness and respond to biomechanical perturbations and/or neuromuscular control errors. Thus, it is important to understand physiological variables such as muscle force and stiffness, and how these relate to the downstream production of stable spine and trunk movements. This study was designed to assess the local dynamic stability of spine muscle activation and rotational stiffness patterns using Lyapunov analyses, and relationships to the local dynamic stability of resulting spine kinematics, during repetitive lifting and lowering at varying combinations of lifting load and rate. With an increase in the load lifted at a constant rate there was a trend for decreased local dynamic stability of spine muscle activations and the muscular contributions to spine rotational stiffness; although the only significant change was for the full state space muscle activation stability (p < 0.05). With an increase in lifting rate with a constant load there was a significant decrease in the local dynamic stability of spine muscle activations and the muscular contributions to spine rotational stiffness (p ≤ 0.001 for all measures). These novel findings suggest that the stability of motor inputs and the muscular contributions to spine rotational stiffness can be altered by external task demands (load and lifting rate), and therefore are important variables to consider when assessing the stability of the resulting kinematics.

  13. Dynamic stability during level walking and obstacle crossing in persons with facioscapulohumeral muscular dystrophy.

    PubMed

    Rijken, N H M; van Engelen, B G M; Geurts, A C H; Weerdesteyn, V

    2015-09-01

    Patients with FSHD suffer from progressive skeletal muscle weakness, which is associated with an elevated fall risk. To obtain insight into fall mechanisms in this patient group, we aimed to assess dynamic stability during level walking and obstacle crossing in patients at different disease stages. Ten patients with at least some lower extremity weakness were included, of whom six were classified as moderately affected and four as mildly affected. Ten healthy controls were also included. Level walking at comfortable speed was assessed, as well as crossing a 10 cm high wooden obstacle. We assessed forward and lateral dynamic stability, as well as spatiotemporal and kinematics variables. During level walking, the moderately affected group demonstrated a lower walking speed, which was accompanied by longer step times and smaller step lengths, yet dynamic stability was unaffected. When crossing the obstacle, however, the moderately affected patients demonstrated reduced forward stability margins during the trailing step, which was accompanied by an increased toe clearance and greater trunk and hip flexion. This suggests that during level walking, the patients effectively utilized compensatory strategies for maintaining dynamic stability, but that the moderately affected group lacked the capacity to fully compensate for the greater stability demands imposed by obstacle crossing, rendering them unable to maintain optimal stability levels. The present results highlight the difficulties that FSHD patients experience in performing this common activity of daily living and may help explain their propensity to fall in the forward direction. PMID:26130572

  14. A review of dynamic stability of repulsive-force maglev suspension systems

    SciTech Connect

    Cai, Y.; Rote, D.M.

    1998-07-01

    Vehicle dynamics and the need to satisfy ride quality requirements have long been recognized as crucial to the commercial success of passenger-carrying transportation systems. Design concepts for maglev systems are no exception. Early maglev investigators and designers were well aware of the importance of ride quality and took care to ensure that their designs would meet acceptable ride quality standards. In contrast, the dynamic stability of electrodynamic suspension (EDS) systems, which has obvious implications for system safety and cost as well as for ride quality, has not received nearly as much attention. Because of the well-known under-damped nature of EDS suspension systems and the observation of instabilities in laboratory-scale model systems, it is prudent to develop a better understanding of vehicle stability characteristics. The work reported in this was undertaken with the intention of summarizing information that has been accumulated worldwide and that is relevant to dynamic stability of repulsive-force maglev suspension systems, assimilating that information, and gaining an understanding of the factors that influence that stability. Included in the paper is a discussion and comparison of results acquired from some representative tests of large-scale vehicles on linear test tracks, together with analytical and laboratory-scale investigations of stability and dynamics of EDS systems. This paper will also summarize the R and D activities at Argonne National Laboratory (ANL) since 1991 to study the nature of the forces that are operative in an EDS system and the dynamic stability of such systems.

  15. Filopodial dynamics and growth cone stabilization in Drosophila visual circuit development.

    PubMed

    Özel, Mehmet Neset; Langen, Marion; Hassan, Bassem A; Hiesinger, P Robin

    2015-10-29

    Filopodial dynamics are thought to control growth cone guidance, but the types and roles of growth cone dynamics underlying neural circuit assembly in a living brain are largely unknown. To address this issue, we have developed long-term, continuous, fast and high-resolution imaging of growth cone dynamics from axon growth to synapse formation in cultured Drosophila brains. Using R7 photoreceptor neurons as a model we show that >90% of the growth cone filopodia exhibit fast, stochastic dynamics that persist despite ongoing stepwise layer formation. Correspondingly, R7 growth cones stabilize early and change their final position by passive dislocation. N-Cadherin controls both fast filopodial dynamics and growth cone stabilization. Surprisingly, loss of N-Cadherin causes no primary targeting defects, but destabilizes R7 growth cones to jump between correct and incorrect layers. Hence, growth cone dynamics can influence wiring specificity without a direct role in target recognition and implement simple rules during circuit assembly.

  16. Deciphering the Dynamics of Non-Covalent Interactions Affecting Thermal Stability of a Protein: Molecular Dynamics Study on Point Mutant of Thermus thermophilus Isopropylmalate Dehydrogenase.

    PubMed

    Sharma, Reetu; Sastry, G Narahari

    2015-01-01

    Thermus thermophilius isopropylmalate dehydrogenase catalyzes oxidative decarboxylation and dehydrogenation of isopropylmalate. Substitution of leucine to alanine at position 172 enhances the thermal stability among the known point mutants. Exploring the dynamic properties of non-covalent interactions such as saltbridges, hydrogen bonds and hydrophobic interactions to explain thermal stability of a protein is interesting in its own right. In this study dynamic changes in the non-covalent interactions are studied to decipher the deterministic features of thermal stability of a protein considering a case study of a point mutant in Thermus thermophilus isopropylmalate dehydrogenase. A total of four molecular dynamic simulations of 0.2 μs were carried out on wild type and mutant's functional dimers at 300 K and 337 K. Higher thermal stability of the mutant as compared to wild type is revealed by root mean square deviation, root mean square fluctuations and Cα-Cα distance with an increase in temperature from 300 K to 337 K. Most of the regions of wild type fluctuate higher than the corresponding regions of mutant with an increase in temperature. Cα-Cα distance analysis suggests that long distance networks are significantly affected in wild type as compared to the mutant. Short lived contacts are higher in wild type, while long lived contacts are lost at 337 K. The mutant forms less hydrogen bonds with water as compared to wild type at 337 K. In contrast to wild type, the mutant shows significant increase in unique saltbridges, hydrogen bonds and hydrophobic contacts at 337 K. The current study indicates that there is a strong inter-dependence of thermal stability on the way in which non-covalent interactions reorganize, and it is rewarding to explore this connection in single mutant studies. PMID:26657745

  17. Deciphering the Dynamics of Non-Covalent Interactions Affecting Thermal Stability of a Protein: Molecular Dynamics Study on Point Mutant of Thermus thermophilus Isopropylmalate Dehydrogenase.

    PubMed

    Sharma, Reetu; Sastry, G Narahari

    2015-01-01

    Thermus thermophilius isopropylmalate dehydrogenase catalyzes oxidative decarboxylation and dehydrogenation of isopropylmalate. Substitution of leucine to alanine at position 172 enhances the thermal stability among the known point mutants. Exploring the dynamic properties of non-covalent interactions such as saltbridges, hydrogen bonds and hydrophobic interactions to explain thermal stability of a protein is interesting in its own right. In this study dynamic changes in the non-covalent interactions are studied to decipher the deterministic features of thermal stability of a protein considering a case study of a point mutant in Thermus thermophilus isopropylmalate dehydrogenase. A total of four molecular dynamic simulations of 0.2 μs were carried out on wild type and mutant's functional dimers at 300 K and 337 K. Higher thermal stability of the mutant as compared to wild type is revealed by root mean square deviation, root mean square fluctuations and Cα-Cα distance with an increase in temperature from 300 K to 337 K. Most of the regions of wild type fluctuate higher than the corresponding regions of mutant with an increase in temperature. Cα-Cα distance analysis suggests that long distance networks are significantly affected in wild type as compared to the mutant. Short lived contacts are higher in wild type, while long lived contacts are lost at 337 K. The mutant forms less hydrogen bonds with water as compared to wild type at 337 K. In contrast to wild type, the mutant shows significant increase in unique saltbridges, hydrogen bonds and hydrophobic contacts at 337 K. The current study indicates that there is a strong inter-dependence of thermal stability on the way in which non-covalent interactions reorganize, and it is rewarding to explore this connection in single mutant studies.

  18. Deciphering the Dynamics of Non-Covalent Interactions Affecting Thermal Stability of a Protein: Molecular Dynamics Study on Point Mutant of Thermus thermophilus Isopropylmalate Dehydrogenase

    PubMed Central

    Sharma, Reetu; Sastry, G. Narahari

    2015-01-01

    Thermus thermophilius isopropylmalate dehydrogenase catalyzes oxidative decarboxylation and dehydrogenation of isopropylmalate. Substitution of leucine to alanine at position 172 enhances the thermal stability among the known point mutants. Exploring the dynamic properties of non-covalent interactions such as saltbridges, hydrogen bonds and hydrophobic interactions to explain thermal stability of a protein is interesting in its own right. In this study dynamic changes in the non-covalent interactions are studied to decipher the deterministic features of thermal stability of a protein considering a case study of a point mutant in Thermus thermophilus isopropylmalate dehydrogenase. A total of four molecular dynamic simulations of 0.2 μs were carried out on wild type and mutant’s functional dimers at 300 K and 337 K. Higher thermal stability of the mutant as compared to wild type is revealed by root mean square deviation, root mean square fluctuations and Cα-Cα distance with an increase in temperature from 300 K to 337 K. Most of the regions of wild type fluctuate higher than the corresponding regions of mutant with an increase in temperature. Cα-Cα distance analysis suggests that long distance networks are significantly affected in wild type as compared to the mutant. Short lived contacts are higher in wild type, while long lived contacts are lost at 337 K. The mutant forms less hydrogen bonds with water as compared to wild type at 337 K. In contrast to wild type, the mutant shows significant increase in unique saltbridges, hydrogen bonds and hydrophobic contacts at 337 K. The current study indicates that there is a strong inter-dependence of thermal stability on the way in which non-covalent interactions reorganize, and it is rewarding to explore this connection in single mutant studies. PMID:26657745

  19. Microtubule Dynamicity Is More Important than Stability in Memory Formation: an In Vivo Study.

    PubMed

    Atarod, Deyhim; Eskandari-Sedighi, Ghazaleh; Pazhoohi, Farid; Karimian, Seyed Morteza; Khajeloo, Mojtaba; Riazi, Gholam Hossein

    2015-06-01

    It has been shown that microtubule (MT) activity and dynamics can have huge impacts on synaptic plasticity and memory formation. This is mainly due to various functions of MTs in neurons; MTs are involved in dendritic spine formation, axonal transportation, neuronal polarity, and receptor trafficking. Recent studies from our group and other labs have suggested the possible role of brain MT dynamicity and activity in memory; however, there is a need for more detailed studies regarding this aspect. In this study, we have tried to evaluate the importance of microtubule dynamicity rather than stability in memory formation in vivo. In order to investigate the role of MT stability in memory formation, we treated mice with paclitaxel-a classic microtubule-stabilizing agent. We then studied the behavior of treated animals using Morris water maze (MWM) test. To measure the effect of injected paclitaxel on MT polymerization kinetics, we conducted polymerization assays on brain extracts of the same paclitaxel-treated animals. Our results show that paclitaxel treatment affects animals' memory in a negative way and treated animals behave poorly in MWM compared to control group. In addition, our kinetics studies show that MT stability is significantly increased in brain extracts from paclitaxel-treated mice, but MT dynamics is reduced. Thus, we suggest that dynamicity is a very important feature of MT protein structures, and regarding memory formation, dynamicity is more important than stability and high activity.

  20. Clinical evaluation of a lumbar interspinous dynamic stabilization device (the Wallis system) with a 13-year mean follow-up.

    PubMed

    Sénégas, Jacques; Vital, Jean-Marc; Pointillart, Vincent; Mangione, Paolo

    2009-07-01

    The authors determined current health status of patients who had been included in a long-term survivorship analysis of a lumbar dynamic stabilizer. Among 133 living patients, 107 (average age at surgery, 44.2 +/- 9.9 years) completed health questionnaires. All patients had initially been scheduled for decompression and fusion for canal stenosis, herniated disc, or both. In 20 patients, the implant was removed, and fusion was performed. The other 87 still had the dynamic stabilizer. Satisfaction, Oswestry disability index, visual analog scales for back and leg pain, short-form (SF-36) quality-of-life physical composite score, physical function, and social function were significantly better (p < or = 0.05) in the patients who still had the dynamic stabilization device. SF-36 scores of the fused subgroup were no worse than those reported elsewhere in patients who had primary pedicle-screw enhanced lumbar fusion. This anatomy-sparing device provided a good 13-year clinical outcome and obviated arthrodesis in 80% of patients.

  1. Enhancing the stability and antibiofilm activity of DspB by immobilization on carboxymethyl chitosan nanoparticles.

    PubMed

    Tan, Yulong; Ma, Su; Liu, Chenguang; Yu, Wengong; Han, Feng

    2015-09-01

    A β-N-acetyl-glucosaminidase (DspB) from Aggregatibacter actinomycetemcomitans CU1000 has been proved to inhibit and detach the biofilms formed by Staphylococcus epidermidis, Staphylococcus aureus and A. actinomycetemcomitans. However, the application of this enzyme is limited by its poor stability. In the present study, a β-N-acetyl-glucosaminidase encoding gene, dspB, was cloned from A. actinomycetemcomitans HK1651 and expressed in Escherichia coli. The recombinant DspB was loaded on hydrogel nanoparticles, which was prepared by using linoleic acid (LA) modified carboxymethyl chitosan (CMCS) after sonication. The nanoparticles were almost saturated by DspB at 0.3 mg/ml, which gave a loading capacity of 76.7%. The immobilization enhanced thermal stability, storage stability and reusability of DspB significantly. Moreover, it also increased antibiofilm activity due to the dual mechanism, including the improvement of the enzyme stability and the antibiofilm activity of CMCS nanoparticles. PMID:26302845

  2. Stability and dynamics of crystals and glasses of motorized particles

    PubMed Central

    Shen, Tongye; Wolynes, Peter G.

    2004-01-01

    Many of the large structures of the cell, such as the cytoskeleton, are assembled and maintained far from equilibrium. We study the stabilities of various structures for a simple model of such a far-from-equilibrium organized assembly in which spherical particles move under the influence of attached motors. From the variational solutions of the many-body master equation for Brownian motion with motorized kicking we obtain a closed equation for the order parameter of localization. Thus, we obtain the transition criterion for localization and stability limits for the crystalline phase and frozen amorphous structures of motorized particles. The theory also allows an estimate of nonequilibrium effective temperatures characterizing the response and fluctuations of motorized asemblies. PMID:15173584

  3. The effect of walking speed on local dynamic stability is sensitive to calculation methods.

    PubMed

    Stenum, Jan; Bruijn, Sjoerd M; Jensen, Bente R

    2014-11-28

    Local dynamic stability has been assessed by the short-term local divergence exponent (λS), which quantifies the average rate of logarithmic divergence of infinitesimally close trajectories in state space. Both increased and decreased local dynamic stability at faster walking speeds have been reported. This might pertain to methodological differences in calculating λS. Therefore, the aim was to test if different calculation methods would induce different effects of walking speed on local dynamic stability. Ten young healthy participants walked on a treadmill at five speeds (60%, 80%, 100%, 120% and 140% of preferred walking speed) for 3min each, while upper body accelerations in three directions were sampled. From these time-series, λS was calculated by three different methods using: (a) a fixed time interval and expressed as logarithmic divergence per stride-time (λS-a), (b) a fixed number of strides and expressed as logarithmic divergence per time (λS-b) and (c) a fixed number of strides and expressed as logarithmic divergence per stride-time (λS-c). Mean preferred walking speed was 1.16±0.09m/s. There was only a minor effect of walking speed on λS-a. λS-b increased with increasing walking speed indicating decreased local dynamic stability at faster walking speeds, whereas λS-c decreased with increasing walking speed indicating increased local dynamic stability at faster walking speeds. Thus, the effect of walking speed on calculated local dynamic stability was significantly different between methods used to calculate local dynamic stability. Therefore, inferences and comparisons of studies employing λS should be made with careful consideration of the calculation method.

  4. Phase stability and dynamics of entangled polymer-nanoparticle composites

    SciTech Connect

    Mangal, Rahul; Srivastava, Samanvaya; Archer, Lynden A.

    2015-06-10

    Nanoparticle–polymer composites, or polymer–nanoparticle composites (PNCs), exhibit unusual mechanical and dynamical features when the particle size approaches the random coil dimensions of the host polymer. Here, we harness favourable enthalpic interactions between particle-tethered and free, host polymer chains to create model PNCs, in which spherical nanoparticles are uniformly dispersed in high molecular weight entangled polymers. Investigation of the mechanical properties of these model PNCs reveals that the nanoparticles have profound effects on the host polymer motions on all timescales. On short timescales, nanoparticles slow-down local dynamics of the host polymer segments and lower the glass transition temperature. On intermediate timescales, where polymer chain motion is typically constrained by entanglements with surrounding molecules, nanoparticles provide additional constraints, which lead to an early onset of entangled polymer dynamics. Finally, on long timescales, nanoparticles produce an apparent speeding up of relaxation of their polymer host.

  5. Synthesis and Characterisation of Biocompatible Polymer-Conjugated Magnetic Beads for Enhancement Stability of Urease.

    PubMed

    Doğaç, Yasemin Ispirli; Teke, Mustafa

    2016-04-01

    We reported natural polymer-conjugated magnetic featured urease systems for removal of urea effectively. The optimum temperature (20-60 °C), optimum pH (3.0-10.0), kinetic parameters, thermal stability (4-70 °C), pH stability (4.0-9.0), operational stability (0-250 min), reusability (18 times) and storage stability (24 weeks) were studied for characterisation of the urease-encapsulated biocompatible polymer-conjugated magnetic beads. Also, the surface groups and chemical structure of the magnetic beads were determined by using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). The all urease-encapsulated magnetic beads protected their stability of 30-45 % relative activity at 70 °C. A significant increase was observed at their pH stability compared with the free urease for both acidic and alkaline medium. Besides this, their repeatability activity were approximately 100 % during 4(th) run. They showed residual activity of 50 % after 16 weeks. The importance of this work is enhancement stability of immobilised urease by biocompatible polymer-conjugated magnetic beads for the industrial application based on removal of urea.

  6. Intracellular Ca(2+) dynamics and the stability of ventricular tachycardia.

    PubMed Central

    Chudin, E; Goldhaber, J; Garfinkel, A; Weiss, J; Kogan, B

    1999-01-01

    Ventricular fibrillation (VF), the major cause of sudden cardiac death, is typically preceded by ventricular tachycardia (VT), but the mechanisms underlying the transition from VT to VF are poorly understood. Intracellular Ca(2+) overload occurs during rapid heart rates typical of VT and is also known to promote arrhythmias. We therefore studied the role of intracellular Ca(2+) dynamics in the transition from VT to VF, using a combined experimental and mathematical modeling approach. Our results show that 1) rapid pacing of rabbit ventricular myocytes at 35 degrees C led to increased intracellular Ca(2+) levels and complex patterns of action potential (AP) configuration and the intracellular Ca(2+) transients; 2) the complex patterns of the Ca(2+) transient arose directly from the dynamics of intracellular Ca(2+) cycling, and were not merely passive responses to beat-to-beat alterations in AP; 3) the complex Ca(2+) dynamics were simulated in a modified version of the Luo-Rudy (LR) ventricular action potential with improved intracellular Ca(2+) dynamics, and showed good agreement with the experimental findings in isolated myocytes; and 4) when incorporated into simulated two-dimensional cardiac tissue, this action potential model produced a form of spiral wave breakup from VT to a VF-like state in which intracellular Ca(2+) dynamics played a key role through its influence on Ca(2+)-sensitive membrane currents such as I(Ca), I(NaCa), and I(ns(Ca)). To the extent that spiral wave breakup is useful as a model for the transition from VT to VF, these findings suggest that intracellular Ca(2+) dynamics may play an important role in the destabilization of VT and its degeneration into VF. PMID:10585917

  7. Concert halls with strong lateral reflections enhance musical dynamics

    PubMed Central

    Pätynen, Jukka; Tervo, Sakari; Robinson, Philip W.; Lokki, Tapio

    2014-01-01

    One of the most thrilling cultural experiences is to hear live symphony-orchestra music build up from a whispering passage to a monumental fortissimo. The impact of such a crescendo has been thought to depend only on the musicians’ skill, but here we show that interactions between the concert-hall acoustics and listeners’ hearing also play a major role in musical dynamics. These interactions contribute to the shoebox-type concert hall’s established success, but little prior research has been devoted to dynamic expression in this three-part transmission chain as a complete system. More forceful orchestral playing disproportionately excites high frequency harmonics more than those near the note’s fundamental. This effect results in not only more sound energy, but also a different tone color. The concert hall transmits this sound, and the room geometry defines from which directions acoustic reflections arrive at the listener. Binaural directional hearing emphasizes high frequencies more when sound arrives from the sides of the head rather than from the median plane. Simultaneously, these same frequencies are emphasized by higher orchestral-playing dynamics. When the room geometry provides reflections from these directions, the perceived dynamic range is enhanced. Current room-acoustic evaluation methods assume linear behavior and thus neglect this effect. The hypothesis presented here is that the auditory excitation by reflections is emphasized with an orchestra forte most in concert halls with strong lateral reflections. The enhanced dynamic range provides an explanation for the success of rectangularly shaped concert-hall geometry. PMID:24591584

  8. Surface effects on dynamic stability and loading during outdoor running using wireless trunk accelerometry.

    PubMed

    Schütte, Kurt H; Aeles, Jeroen; De Beéck, Tim Op; van der Zwaard, Babette C; Venter, Rachel; Vanwanseele, Benedicte

    2016-07-01

    Despite frequently declared benefits of using wireless accelerometers to assess running gait in real-world settings, available research is limited. The purpose of this study was to investigate outdoor surface effects on dynamic stability and dynamic loading during running using tri-axial trunk accelerometry. Twenty eight runners (11 highly-trained, 17 recreational) performed outdoor running on three outdoor training surfaces (concrete road, synthetic track and woodchip trail) at self-selected comfortable running speeds. Dynamic postural stability (tri-axial acceleration root mean square (RMS) ratio, step and stride regularity, sample entropy), dynamic loading (impact and breaking peak amplitudes and median frequencies), as well as spatio-temporal running gait measures (step frequency, stance time) were derived from trunk accelerations sampled at 1024Hz. Results from generalized estimating equations (GEE) analysis showed that compared to concrete road, woodchip trail had several significant effects on dynamic stability (higher AP ratio of acceleration RMS, lower ML inter-step and inter-stride regularity), on dynamic loading (downward shift in vertical and AP median frequency), and reduced step frequency (p<0.05). Surface effects were unaffected when both running level and running speed were added as potential confounders. Results suggest that woodchip trails disrupt aspects of dynamic stability and loading that are detectable using a single trunk accelerometer. These results provide further insight into how runners adapt their locomotor biomechanics on outdoor surfaces in situ.

  9. Microtubule dynamics control HGF-induced lung endothelial barrier enhancement.

    PubMed

    Tian, Xinyong; Tian, Yufeng; Moldobaeva, Nurgul; Sarich, Nicolene; Birukova, Anna A

    2014-01-01

    Microtubules (MT) play a vital role in many cellular functions, but their role in peripheral actin cytoskeletal dynamics which is essential for control of endothelial barrier and monolayer integrity is less understood. We have previously described the enhancement of lung endothelial cell (EC) barrier by hepatocyte growth factor (HGF) which was associated with Rac1-mediated remodeling of actin cytoskeleton. This study investigated involvement of MT-dependent mechanisms in the HGF-induced enhancement of EC barrier. HGF-induced Rac1 activation was accompanied by phosphorylation of stathmin, a regulator of MT dynamics. HGF also stimulated MT peripheral growth monitored by time lapse imaging and tracking analysis of EB-1-decorated MT growing tips, and increased the pool of acetylated tubulin. These effects were abolished by EC pretreatment with HGF receptor inhibitor, downregulation of Rac1 pathway, or by expression of a stathmin-S63A phosphorylation deficient mutant. Expression of stathmin-S63A abolished the HGF protective effects against thrombin-induced activation of RhoA cascade, permeability increase, and EC barrier dysfunction. These results demonstrate a novel MT-dependent mechanism of HGF-induced EC barrier regulation via Rac1/PAK1/stathmin-dependent control of MT dynamics. PMID:25198505

  10. Protein kinesis: The dynamics of protein trafficking and stability

    SciTech Connect

    1995-12-31

    The purpose of this conference is to provide a multidisciplinary forum for exchange of state-of-the-art information on protein kinesis. This volume contains abstracts of papers in the following areas: protein folding and modification in the endoplasmic reticulum; protein trafficking; protein translocation and folding; protein degradation; polarity; nuclear trafficking; membrane dynamics; and protein import into organelles.

  11. Quantum dynamical simulations of local field enhancement in metal nanoparticles.

    PubMed

    Negre, Christian F A; Perassi, Eduardo M; Coronado, Eduardo A; Sánchez, Cristián G

    2013-03-27

    Field enhancements (Γ) around small Ag nanoparticles (NPs) are calculated using a quantum dynamical simulation formalism and the results are compared with electrodynamic simulations using the discrete dipole approximation (DDA) in order to address the important issue of the intrinsic atomistic structure of NPs. Quite remarkably, in both quantum and classical approaches the highest values of Γ are located in the same regions around single NPs. However, by introducing a complete atomistic description of the metallic NPs in optical simulations, a different pattern of the Γ distribution is obtained. Knowing the correct pattern of the Γ distribution around NPs is crucial for understanding the spectroscopic features of molecules inside hot spots. The enhancement produced by surface plasmon coupling is studied by using both approaches in NP dimers for different inter-particle distances. The results show that the trend of the variation of Γ versus inter-particle distance is different for classical and quantum simulations. This difference is explained in terms of a charge transfer mechanism that cannot be obtained with classical electrodynamics. Finally, time dependent distribution of the enhancement factor is simulated by introducing a time dependent field perturbation into the Hamiltonian, allowing an assessment of the localized surface plasmon resonance quantum dynamics.

  12. Enhancing Intrinsic Stability of Hybrid Perovskite Solar Cell by Strong, yet Balanced, Electronic Coupling

    NASA Astrophysics Data System (ADS)

    El-Mellouhi, Fedwa; Bentria, El Tayeb; Rashkeev, Sergey N.; Kais, Sabre; Alharbi, Fahhad H.

    2016-07-01

    In the past few years, the meteoric development of hybrid organic–inorganic perovskite solar cells (PSC) astonished the community. The efficiency has already reached the level needed for commercialization; however, the instability hinders its deployment on the market. Here, we report a mechanism to chemically stabilize PSC absorbers. We propose to replace the widely used methylammonium cation (CH3NH3+) by alternative molecular cations allowing an enhanced electronic coupling between the cation and the PbI6 octahedra while maintaining the band gap energy within the suitable range for solar cells. The mechanism exploits establishing a balance between the electronegativity of the materials’ constituents and the resulting ionic electrostatic interactions. The calculations demonstrate the concept of enhancing the electronic coupling, and hence the stability, by exploring the stabilizing features of CH3PH3+, CH3SH2+, and SH3+ cations, among several other possible candidates. Chemical stability enhancement hence results from a strong, yet balanced, electronic coupling between the cation and the halides in the octahedron. This shall unlock the hindering instability problem for PSCs and allow them to hit the market as a serious low-cost competitor to silicon based solar cell technologies.

  13. Enhancing Intrinsic Stability of Hybrid Perovskite Solar Cell by Strong, yet Balanced, Electronic Coupling.

    PubMed

    El-Mellouhi, Fedwa; Bentria, El Tayeb; Rashkeev, Sergey N; Kais, Sabre; Alharbi, Fahhad H

    2016-01-01

    In the past few years, the meteoric development of hybrid organic-inorganic perovskite solar cells (PSC) astonished the community. The efficiency has already reached the level needed for commercialization; however, the instability hinders its deployment on the market. Here, we report a mechanism to chemically stabilize PSC absorbers. We propose to replace the widely used methylammonium cation (CH3NH3(+)) by alternative molecular cations allowing an enhanced electronic coupling between the cation and the PbI6 octahedra while maintaining the band gap energy within the suitable range for solar cells. The mechanism exploits establishing a balance between the electronegativity of the materials' constituents and the resulting ionic electrostatic interactions. The calculations demonstrate the concept of enhancing the electronic coupling, and hence the stability, by exploring the stabilizing features of CH3PH3(+), CH3SH2(+), and SH3(+) cations, among several other possible candidates. Chemical stability enhancement hence results from a strong, yet balanced, electronic coupling between the cation and the halides in the octahedron. This shall unlock the hindering instability problem for PSCs and allow them to hit the market as a serious low-cost competitor to silicon based solar cell technologies. PMID:27457130

  14. VMCast: A VM-Assisted Stability Enhancing Solution for Tree-Based Overlay Multicast.

    PubMed

    Gu, Weidong; Zhang, Xinchang; Gong, Bin; Zhang, Wei; Wang, Lu

    2015-01-01

    Tree-based overlay multicast is an effective group communication method for media streaming applications. However, a group member's departure causes all of its descendants to be disconnected from the multicast tree for some time, which results in poor performance. The above problem is difficult to be addressed because overlay multicast tree is intrinsically instable. In this paper, we proposed a novel stability enhancing solution, VMCast, for tree-based overlay multicast. This solution uses two types of on-demand cloud virtual machines (VMs), i.e., multicast VMs (MVMs) and compensation VMs (CVMs). MVMs are used to disseminate the multicast data, whereas CVMs are used to offer streaming compensation. The used VMs in the same cloud datacenter constitute a VM cluster. Each VM cluster is responsible for a service domain (VMSD), and each group member belongs to a specific VMSD. The data source delivers the multicast data to MVMs through a reliable path, and MVMs further disseminate the data to group members along domain overlay multicast trees. The above approach structurally improves the stability of the overlay multicast tree. We further utilized CVM-based streaming compensation to enhance the stability of the data distribution in the VMSDs. VMCast can be used as an extension to existing tree-based overlay multicast solutions, to provide better services for media streaming applications. We applied VMCast to two application instances (i.e., HMTP and HCcast). The results show that it can obviously enhance the stability of the data distribution.

  15. VMCast: A VM-Assisted Stability Enhancing Solution for Tree-Based Overlay Multicast

    PubMed Central

    Gu, Weidong; Zhang, Xinchang; Gong, Bin; Zhang, Wei; Wang, Lu

    2015-01-01

    Tree-based overlay multicast is an effective group communication method for media streaming applications. However, a group member’s departure causes all of its descendants to be disconnected from the multicast tree for some time, which results in poor performance. The above problem is difficult to be addressed because overlay multicast tree is intrinsically instable. In this paper, we proposed a novel stability enhancing solution, VMCast, for tree-based overlay multicast. This solution uses two types of on-demand cloud virtual machines (VMs), i.e., multicast VMs (MVMs) and compensation VMs (CVMs). MVMs are used to disseminate the multicast data, whereas CVMs are used to offer streaming compensation. The used VMs in the same cloud datacenter constitute a VM cluster. Each VM cluster is responsible for a service domain (VMSD), and each group member belongs to a specific VMSD. The data source delivers the multicast data to MVMs through a reliable path, and MVMs further disseminate the data to group members along domain overlay multicast trees. The above approach structurally improves the stability of the overlay multicast tree. We further utilized CVM-based streaming compensation to enhance the stability of the data distribution in the VMSDs. VMCast can be used as an extension to existing tree-based overlay multicast solutions, to provide better services for media streaming applications. We applied VMCast to two application instances (i.e., HMTP and HCcast). The results show that it can obviously enhance the stability of the data distribution. PMID:26562152

  16. Enhancing Intrinsic Stability of Hybrid Perovskite Solar Cell by Strong, yet Balanced, Electronic Coupling

    PubMed Central

    El-Mellouhi, Fedwa; Bentria, El Tayeb; Rashkeev, Sergey N.; Kais, Sabre; Alharbi, Fahhad H.

    2016-01-01

    In the past few years, the meteoric development of hybrid organic–inorganic perovskite solar cells (PSC) astonished the community. The efficiency has already reached the level needed for commercialization; however, the instability hinders its deployment on the market. Here, we report a mechanism to chemically stabilize PSC absorbers. We propose to replace the widely used methylammonium cation (CH3NH3+) by alternative molecular cations allowing an enhanced electronic coupling between the cation and the PbI6 octahedra while maintaining the band gap energy within the suitable range for solar cells. The mechanism exploits establishing a balance between the electronegativity of the materials’ constituents and the resulting ionic electrostatic interactions. The calculations demonstrate the concept of enhancing the electronic coupling, and hence the stability, by exploring the stabilizing features of CH3PH3+, CH3SH2+, and SH3+ cations, among several other possible candidates. Chemical stability enhancement hence results from a strong, yet balanced, electronic coupling between the cation and the halides in the octahedron. This shall unlock the hindering instability problem for PSCs and allow them to hit the market as a serious low-cost competitor to silicon based solar cell technologies. PMID:27457130

  17. VMCast: A VM-Assisted Stability Enhancing Solution for Tree-Based Overlay Multicast.

    PubMed

    Gu, Weidong; Zhang, Xinchang; Gong, Bin; Zhang, Wei; Wang, Lu

    2015-01-01

    Tree-based overlay multicast is an effective group communication method for media streaming applications. However, a group member's departure causes all of its descendants to be disconnected from the multicast tree for some time, which results in poor performance. The above problem is difficult to be addressed because overlay multicast tree is intrinsically instable. In this paper, we proposed a novel stability enhancing solution, VMCast, for tree-based overlay multicast. This solution uses two types of on-demand cloud virtual machines (VMs), i.e., multicast VMs (MVMs) and compensation VMs (CVMs). MVMs are used to disseminate the multicast data, whereas CVMs are used to offer streaming compensation. The used VMs in the same cloud datacenter constitute a VM cluster. Each VM cluster is responsible for a service domain (VMSD), and each group member belongs to a specific VMSD. The data source delivers the multicast data to MVMs through a reliable path, and MVMs further disseminate the data to group members along domain overlay multicast trees. The above approach structurally improves the stability of the overlay multicast tree. We further utilized CVM-based streaming compensation to enhance the stability of the data distribution in the VMSDs. VMCast can be used as an extension to existing tree-based overlay multicast solutions, to provide better services for media streaming applications. We applied VMCast to two application instances (i.e., HMTP and HCcast). The results show that it can obviously enhance the stability of the data distribution. PMID:26562152

  18. Enhancement of colour stability of anthocyanins in model beverages by gum arabic addition.

    PubMed

    Chung, Cheryl; Rojanasasithara, Thananunt; Mutilangi, William; McClements, David Julian

    2016-06-15

    This study investigated the potential of gum arabic to improve the stability of anthocyanins that are used in commercial beverages as natural colourants. The degradation of purple carrot anthocyanin in model beverage systems (pH 3.0) containing L-ascorbic acid proceeded with a first-order reaction rate during storage (40 °C for 5 days in light). The addition of gum arabic (0.05-5.0%) significantly enhanced the colour stability of anthocyanin, with the most stable systems observed at intermediate levels (1.5%). A further increase in concentration (>1.5%) reduced its efficacy due to a change in the conformation of the gum arabic molecules that hindered their exposure to the anthocyanins. Fluorescence quenching measurements showed that the anthocyanin could have interacted with the glycoprotein fractions of the gum arabic through hydrogen bonding, resulting in enhanced stability. Overall, this study provides valuable information about enhancing the stability of anthocyanins in beverage systems using natural ingredients.

  19. Stability of numerical integration techniques for transient rotor dynamics

    NASA Technical Reports Server (NTRS)

    Kascak, A. F.

    1977-01-01

    A finite element model of a rotor bearing system was analyzed to determine the stability limits of the forward, backward, and centered Euler; Runge-Kutta; Milne; and Adams numerical integration techniques. The analysis concludes that the highest frequency mode determines the maximum time step for a stable solution. Thus, the number of mass elements should be minimized. Increasing the damping can sometimes cause numerical instability. For a uniform shaft, with 10 mass elements, operating at approximately the first critical speed, the maximum time step for the Runge-Kutta, Milne, and Adams methods is that which corresponds to approximately 1 degree of shaft movement. This is independent of rotor dimensions.

  20. Nyquist and Bode stability criteria to assess changes in dynamic knee stability in healthy and anterior cruciate ligament reconstructed individuals during walking.

    PubMed

    Morgan, Kristin D; Zheng, Yanbing; Bush, Heather; Noehren, Brian

    2016-06-14

    Anterior cruciate ligament (ACL) injuries are one of the most frequently injured knee ligaments. Despite reconstruction, many individuals report difficulty returning to high level activities that require greater dynamic stability. Since few methods have been tested to assess dynamic stability post ACL reconstruction (ACLR), the purpose of this study was to evaluate between and within dynamic knee stability in control and ACLR individuals using Nyquist and Bode stability criteria. Sixteen control and sixteen post ACLR individuals performed a walking protocol. Nyquist and Bode stability criteria were implemented to classify and quantify individual step-to-step sagittal plane dynamic knee stability from the gait waveforms at initial contact, 15% and 30% of stance based on the resulting gain and phase margins. An ANOVA compared differences in phase margins between the control and ACLR limbs and found that the ACLR limbs were overall significantly more unstable than the non-reconstructed and control limbs (p=0.001). The results indicated that the ACLR individuals who exhibited stable steps adopted a more compensatory strategy aimed to stabilize the knee. These methods of evaluating dynamic knee stability may help clinicians to assess dynamic knee stability progression throughout rehabilitation and help assess return-to-sport with minimal risk to the individual.

  1. The Effects of Balance Training on Static and Dynamic Postural Stability Indices After Acute ACL Reconstruction

    PubMed Central

    Akbari, Asghar; Ghiasi, Fateme; Mir, Mohsen; Hosseinifar, Mohammad

    2016-01-01

    Background: Proprioception and postural stability play an important role in knee movements. However, there are controversies about the overall recovery time of proprioception following knee surgery and onset of balance and neuromuscular training after ACL reconstruction. Therefore, it is necessary to evaluate the effect of balance training in early stage of knee rehabilitation after anterior cruciate ligament (ACL) reconstruction. The purpose of this study was to evaluate the effect of balance exercises on postural stability indices in subjects with anterior cruciate ligament (ACL) reconstruction. Methods: The study was a controlled randomized trial study. Twenty four patients who had ACL reconstructed (balance training group) and twenty four healthy adults without any knee injury (control group) were recruited in the study. The balance exercises group performed balance exercises for 2 weeks. Before and after the interventions, overall, anteroposterior, and mediolateral stability indices were measured with a Biodex Balance System in bilateral and unilateral stance positions with the eyes open and closed. T-tests were used for statistical analysis (p<0.05). Results: Results showed that amount of static stability indices did not change after training and there were not significant differences in static stability indices before and after balance training (p>0.05). Although amount of dynamic stability indices decreased, there were not significant differences in dynamic stability indices before and after balance training (p>0.05). Amount of dynamic stability indices were decreased in balance training group, however, there were not significant differences between groups (p>0.05). Conclusion: These results support that balance exercise could partially improved dynamic stability indices in early stage of ACL reconstruction rehabilitation. The results of this study suggest that balance exercises should be part of the rehabilitation program following ACL reconstruction. PMID

  2. Steady-State Computation of Constant Rotational Rate Dynamic Stability Derivatives

    NASA Technical Reports Server (NTRS)

    Park, Michael A.; Green, Lawrence L.

    2000-01-01

    Dynamic stability derivatives are essential to predicting the open and closed loop performance, stability, and controllability of aircraft. Computational determination of constant-rate dynamic stability derivatives (derivatives of aircraft forces and moments with respect to constant rotational rates) is currently performed indirectly with finite differencing of multiple time-accurate computational fluid dynamics solutions. Typical time-accurate solutions require excessive amounts of computational time to complete. Formulating Navier-Stokes (N-S) equations in a rotating noninertial reference frame and applying an automatic differentiation tool to the modified code has the potential for directly computing these derivatives with a single, much faster steady-state calculation. The ability to rapidly determine static and dynamic stability derivatives by computational methods can benefit multidisciplinary design methodologies and reduce dependency on wind tunnel measurements. The CFL3D thin-layer N-S computational fluid dynamics code was modified for this study to allow calculations on complex three-dimensional configurations with constant rotation rate components in all three axes. These CFL3D modifications also have direct application to rotorcraft and turbomachinery analyses. The modified CFL3D steady-state calculation is a new capability that showed excellent agreement with results calculated by a similar formulation. The application of automatic differentiation to CFL3D allows the static stability and body-axis rate derivatives to be calculated quickly and exactly.

  3. Stability and damping in a dynamical model of hillslope hydrology

    NASA Astrophysics Data System (ADS)

    Brandes, David; Duffy, Christopher J.; Cusumano, Joseph P.

    1998-12-01

    A stability analysis is performed on the two-state variable, integral-balance model of hillslope hydrology developed by Duffy [1996]. The motivation for the research is to develop a physically based, low-dimensional representation of inflow/outflow behavior within a hillslope-stream setting. Stability criteria are developed for the model equilibria and are evaluated using the results of numerical solutions of Richards' equation for a convex-concave hillslope geometry. We show that for homogeneous hillslopes of three widely varying soil types the single moisture equilibrium is classified as a stable node for low precipitation rates and a stable spiral for wet conditions. The spiral equilibrium indicates that the hillslope system is lightly damped, and transient oscillations of the state variables are expected for high precipitation rates. The timescale of these oscillations is of the order of several days to weeks for the model hillslopes examined. Furthermore, we demonstrate that the model contains a Hopf bifurcation from a stable static equilibrium to a stable limit cycle. The amplitude, phase, and frequency of the limit cycle are determined analytically using second-order averaging. However, this behavior is shown to be nonphysical for the particular homogeneous soils and hillslope geometry investigated. Implications of lightly damped behavior in the hillslope system include moisture oscillations in the field under wet conditions and difficulty in numerical solution of Richards' equation.

  4. Enhanced planar hall sensitivity with better thermal stability by introducing interfacial modification of Au spacer

    NASA Astrophysics Data System (ADS)

    Li, Xu-Jing; Feng, Chun; Chen, Xi; Zhang, Jing-Yan; Liu, Yi-Wei; Jiang, Shao-Long; Liu, Yang; Li, Ming-Hua; Yu, Guang-Hua

    2015-05-01

    This paper reports an enhancement of planar Hall sensitivity in NiFe/Au/IrMn multilayers by introducing interfacial modification. The improvement of the sensitivity derives from the increase of resistivity change (Δρ), which is attributed to strengthened spin-asymmetry of polarized electrons in NiFe layer induced by strong spin-orbit scattering of Au layer. Furthermore, the NiFe/Au/IrMn structure based sensor exhibits good thermal stability. The high sensitivity together with good thermal stability makes the NiFe/Au/IrMn structure based sensor very promising for bio-detections.

  5. Development of a Stirling System Dynamic Model With Enhanced Thermodynamics

    NASA Technical Reports Server (NTRS)

    Regan, Timothy F.; Lewandowski, Edward J.

    2005-01-01

    The Stirling Convertor System Dynamic Model developed at NASA Glenn Research Center is a software model developed from first principles that includes the mechanical and mounting dynamics, the thermodynamics, the linear alternator, and the controller of a free-piston Stirling power convertor, along with the end user load. As such it represents the first detailed modeling tool for fully integrated Stirling convertor-based power systems. The thermodynamics of the model were originally a form of the isothermal Stirling cycle. In some situations it may be desirable to improve the accuracy of the Stirling cycle portion of the model. An option under consideration is to enhance the SDM thermodynamics by coupling the model with Gedeon Associates Sage simulation code. The result will be a model that gives a more accurate prediction of the performance and dynamics of the free-piston Stirling convertor. A method of integrating the Sage simulation code with the System Dynamic Model is described. Results of SDM and Sage simulation are compared to test data. Model parameter estimation and model validation are discussed.

  6. Dynamic Flux Tubes Form Reservoirs of Stability in Neuronal Circuits

    NASA Astrophysics Data System (ADS)

    Monteforte, Michael; Wolf, Fred

    2012-10-01

    Neurons in cerebral cortical circuits interact by sending and receiving electrical impulses called spikes. The ongoing spiking activity of cortical circuits is fundamental to many cognitive functions including sensory processing, working memory, and decision making. London et al. [Sensitivity to Perturbations In Vivo Implies High Noise and Suggests Rate Coding in Cortex, Nature (London)NATUAS0028-0836 466, 123 (2010).10.1038/nature09086] recently argued that even a single additional spike can cause a cascade of extra spikes that rapidly decorrelate the microstate of the network. Here, we show theoretically in a minimal model of cortical neuronal circuits that single-spike perturbations trigger only a very weak rate response. Nevertheless, single-spike perturbations are found to rapidly decorrelate the microstate of the network, although the dynamics is stable with respect to small perturbations. The coexistence of stable and unstable dynamics results from a system of exponentially separating dynamic flux tubes around stable trajectories in the network’s phase space. The radius of these flux tubes appears to decrease algebraically with neuron number N and connectivity K, which implies that the entropy of the circuit’s repertoire of state sequences scales as Nln⁡(KN).

  7. Flexible body dynamic stability for high performance aircraft

    NASA Technical Reports Server (NTRS)

    Goforth, E. A.; Youssef, H. M.; Apelian, C. V.; Schroeder, S. C.

    1991-01-01

    Dynamic equations which include the effects of unsteady aerodynamic forces and a flexible body structure were developed for a free flying high performance fighter aircraft. The linear and angular deformations are assumed to be small in the body reference frame, allowing the equations to be linearized in the deformation variables. Equations for total body dynamics and flexible body dynamics are formulated using the hybrid coordinate method and integrated in a state space format. A detailed finite element model of a generic high performance fighter aircraft is used to generate the mass and stiffness matrices. Unsteady aerodynamics are represented by a rational function approximation of the doublet lattice matrices. The equations simplify for the case of constant angular rate of the body reference frame, allowing the effect of roll rate to be studied by computing the eigenvalues of the system. It is found that the rigid body modes of the aircraft are greatly affected by introducing a constant roll rate, while the effect on the flexible modes is minimal for this configuration.

  8. Biodiversity simultaneously enhances the production and stability of community biomass, but the effects are independent.

    PubMed

    Cardinale, Bradley J; Gross, Kevin; Fritschie, Keith; Flombaum, Pedro; Fox, Jeremy W; Rixen, Christian; van Ruijven, Jasper; Reich, Peter B; Scherer-Lorenzen, Michael; Wilsey, Brian J

    2013-08-01

    To predict the ecological consequences of biodiversity loss, researchers have spent much time and effort quantifying how biological variation affects the magnitude and stability of ecological processes that underlie the functioning of ecosystems. Here we add to this work by looking at how biodiversity jointly impacts two aspects of ecosystem functioning at once: (1) the production of biomass at any single point in time (biomass/area or biomass/ volume), and (2) the stability of biomass production through time (the CV of changes in total community biomass through time). While it is often assumed that biodiversity simultaneously enhances both of these aspects of ecosystem functioning, the joint distribution of data describing how species richness regulates productivity and stability has yet to be quantified. Furthermore, analyses have yet to examine how diversity effects on production covary with diversity effects on stability. To overcome these two gaps, we reanalyzed the data from 34 experiments that have manipulated the richness of terrestrial plants or aquatic algae and measured how this aspect of biodiversity affects community biomass at multiple time points. Our reanalysis confirms that biodiversity does indeed simultaneously enhance both the production and stability of biomass in experimental systems, and this is broadly true for terrestrial and aquatic primary producers. However, the strength of diversity effects on biomass production is independent of diversity effects on temporal stability. The independence of effect sizes leads to two important conclusions. First, while it may be generally true that biodiversity enhances both productivity and stability, it is also true that the highest levels of productivity in a diverse community are not associated with the highest levels of stability. Thus, on average, diversity does not maximize the various aspects of ecosystem functioning we might wish to achieve in conservation and management. Second, knowing how

  9. Dynamics of poloidal flows in enhanced reverse shear bifurcation

    SciTech Connect

    Srinivasan, R.; Avinash, K.

    2005-07-15

    A simple reduced enhanced reverse shear (RERS) model is constructed to study the dynamics of poloidal flows during the ERS transition. This model predicts that a reversal of poloidal flow shear occurs just prior to the transition, as seen in experiment [R. E. Bell et al., Phys. Rev. Lett. 81, 1429 (1998)]. This transition front propagates until the radial location where the safety factor (q) is minimum and becomes locked there due to insufficient input power to overcome the threshold requirement for the bifurcation. This study also reveals that there can be many routes to ERS transition depending upon various tunable parameters.

  10. Combined analytical and numerical approaches in Dynamic Stability analyses of engineering systems

    NASA Astrophysics Data System (ADS)

    Náprstek, Jiří

    2015-03-01

    Dynamic Stability is a widely studied area that has attracted many researchers from various disciplines. Although Dynamic Stability is usually associated with mechanics, theoretical physics or other natural and technical disciplines, it is also relevant to social, economic, and philosophical areas of our lives. Therefore, it is useful to occasionally highlight the general aspects of this amazing area, to present some relevant examples and to evaluate its position among the various branches of Rational Mechanics. From this perspective, the aim of this study is to present a brief review concerning the Dynamic Stability problem, its basic definitions and principles, important phenomena, research motivations and applications in engineering. The relationships with relevant systems that are prone to stability loss (encountered in other areas such as physics, other natural sciences and engineering) are also noted. The theoretical background, which is applicable to many disciplines, is presented. In this paper, the most frequently used Dynamic Stability analysis methods are presented in relation to individual dynamic systems that are widely discussed in various engineering branches. In particular, the Lyapunov function and exponent procedures, Routh-Hurwitz, Liénard, and other theorems are outlined together with demonstrations. The possibilities for analytical and numerical procedures are mentioned together with possible feedback from experimental research and testing. The strengths and shortcomings of these approaches are evaluated together with examples of their effective complementing of each other. The systems that are widely encountered in engineering are presented in the form of mathematical models. The analyses of their Dynamic Stability and post-critical behaviour are also presented. The stability limits, bifurcation points, quasi-periodic response processes and chaotic regimes are discussed. The limit cycle existence and stability are examined together with their

  11. Dynamic contrast-enhanced diffuse optical tomography (DCE-DOT): experimental validation with a dynamic phantom

    PubMed Central

    Unlu, Mehmet Burcin; Lin, Yuting; Gulsen, Gultekin

    2010-01-01

    Dynamic contrast-enhanced diffuse optical tomography (DCE-DOT) can provide spatially resolved enhancement kinetics of an optical contrast agent. We undertook a systematic phantom study to evaluate the effects of the geometrical parameters such as the depth and size of the inclusion as well as the optical parameters of the background on the recovered enhancement kinetics of the most commonly used optical contrast agent, indocyanine green (ICG). For this purpose a computer-controlled dynamic phantom was constructed. An ICG–intralipid–water mixture was circulated through the inclusions while the DCE-DOT measurements were acquired with a temporal resolution of 16 s. The same dynamic study was repeated using inclusions of different sizes located at different depths. In addition to this, the effect of non-scattering regions was investigated by placing a second inclusion filled with water in the background. The phantom studies confirmed that although the peak enhancement varied substantially for each case, the recovered injection and dilution rates obtained from the percentage enhancement maps agreed within 15% independent of not only the depth and the size of the inclusion but also the presence of a non-scattering region in the background. Although no internal structural information was used in these phantom studies, it may be necessary to use it for small objects buried deep in tissue. However, the different contrast mechanisms of optical and other imaging modalities as well as imperfect co-registration between both modalities may lead to potential errors in the structural a priori. Therefore, the effect of erroneous selection of structural priors was investigated as the final step. Again, the injection and dilution rates obtained from the percentage enhancement maps were also immune to the systematic errors introduced by erroneous selection of the structural priors, e.g. choosing the diameter of the inclusion 20% smaller increased the peak enhancement 60% but

  12. Fabrication of amorphous curcumin nanosuspensions using β-lactoglobulin to enhance solubility, stability, and bioavailability.

    PubMed

    Aditya, N P; Yang, Hanjoo; Kim, Saehoon; Ko, Sanghoon

    2015-03-01

    Curcumin has low aqueous stability and solubility in its native form. It also has a low bioavailability which presents a major barrier to its use in fortifying food products. The aim of this work was to reduce the size of curcumin crystals to the nanoscale and subsequently stabilize them in an amorphous form. To this end, amorphous curcumin nanosuspensions were fabricated using the antisolvent precipitation method with β-lactoglobulin (β-lg) as a stabilizer. The resulting amorphous curcumin nanosuspensions were in the size range of 150-175 nm with unimodal size distribution. The curcumin particles were amorphous and were molecularly dispersed within the β-lg as confirmed by differential scanning calorimetry (DSC) and X-ray diffraction (XRD) studies. The solubility of the amorphous curcumin nanosuspension was enhanced ∼35-fold due to the reduced size and lower crystallinity. Among the formulations, the amorphous curcumin nanosuspensions stabilized with β-lg and prepared at pH 3.4 (β-lg-cur 3.4), showed maximum aqueous stability which was >90% after 30 days. An in vitro study using Caco-2 cell lines showed a significant increase in curcumin bioavailability after stabilization with β-lg.

  13. Effect of dual task type on gait and dynamic stability during stair negotiation at different inclinations.

    PubMed

    Madehkhaksar, Forough; Egges, Arjan

    2016-01-01

    Stair gait is a common daily activity with great potential risk for falls. Stairs have varying inclinations and people may perform other tasks concurrently with stair gait. This study investigated dual-task interference in the context of complex gait tasks, such as stair gait at different inclinations, a topic about which little is understood. We examined how secondary cognitive and manual tasks interfere with stair gait when a person concurrently performed tasks at different levels of complexity. Gait kinematic data and secondary task performance measures were obtained from fifteen healthy young males while ascending and descending a four-step staircase at three inclinations (17.7°, 29.4°, and 41.5°) as well as level walking. They performed a cognitive task, 'backward digit recall', a manual task, 'carrying a cup of water' and a combination of the two tasks. Gait performance and dynamic stability were assessed by gait speed and whole body center of mass (COM) range of motion in the medial-lateral direction, respectively. No significant effect of the gait task on the cognitive task performance was observed. In contrast, stair walking adversely affected the performance of the manual task compared to level walking. Overall, more difficult postural and secondary tasks resulted in a decrease in gait speed and variation in COM displacement within normal range. Results suggest that COM displacement and gait alterations might be adopted to enhance the stability, and optimize the secondary task performance while walking under challenging circumstances. Our findings are useful for balance and gait evaluation, and for future falls prediction.

  14. Enhanced dynamic electron paramagnetic resonance imaging of in vivo physiology

    NASA Astrophysics Data System (ADS)

    Redler, Gage

    It is well established that low oxygen concentration (hypoxia) in tumors strongly affects their malignant state and resistance to therapy. The importance of tumor oxygenation status has led to increased interest in the development of robust oxygen imaging modalities. One such method is electron paramagnetic resonance imaging (EPRI). EPRI has provided a non-invasive, quantitative imaging modality with sensitivity deep in tissues, capable of investigating static oxygen concentration (pO2) in vivo and has helped to corroborate the correlation between chronic states of hypoxia and tumor malignancy. However, when studying the complicated physiology of a living animal, the situation tends to be inherently dynamic. It has been found that in certain tumor regions there may exist steady states of hypoxia, or chronic hypoxia, whereas in other regions there may exist transient states of hypoxia, or acute hypoxia. It has been postulated that the negative prognostic implications associated with hypoxic tumors may be amplified for acutely hypoxic tumors. However, controversial data and a current lack in methods with the capability to noninvasively image tumor pO2 in vivo with sufficient spatial, temporal, and pO 2 resolution preclude definitive conclusions on the relationships between the different forms of hypoxia and the differences in their clinical implications. A particularly promising oxygen imaging modality that can help to study both chronic and acute hypoxia and elucidate important physiological and clinical differences is rapid Dynamic EPRI. The focus of this work is the development of methods enabling Dynamic EPRI of in vivo physiology as well as its potential applications. This work describes methods which enhance various aspects of EPRI in order to establish a more robust Dynamic EPRI capable of noninvasively studying and quantifying acute hypoxia in vivo. These enhancements are achieved through improvements that span from methods for the acquisition of individual

  15. Population dynamics and the ecological stability of obligate pollination mutualisms

    USGS Publications Warehouse

    Holland, J. Nathaniel; DeAngelis, Donald L.

    2001-01-01

    Mutualistic interactions almost always produce both costs and benefits for each of the interacting species. It is the difference between gross benefits and costs that determines the net benefit and the per-capita effect on each of the interacting populations. For example, the net benefit of obligate pollinators, such as yucca and senita moths, to plants is determined by the difference between the number of ovules fertilized from moth pollination and the number of ovules eaten by the pollinator's larvae. It is clear that if pollinator populations are large, then, because many eggs are laid, costs to plants are large, whereas, if pollinator populations are small, gross benefits are low due to lack of pollination. Even though the size and dynamics of the pollinator population are likely to be crucial, their importance has been neglected in the investigation of mechanisms, such as selective fruit abortion, that can limit costs and increase net benefits. Here, we suggest that both the population size and dynamics of pollinators are important in determining the net benefits to plants, and that fruit abortion can significantly affect these. We develop a model of mutualism between populations of plants and their pollinating seed-predators to explore the ecological consequences of fruit abortion on pollinator population dynamics and the net effect on plants. We demonstrate that the benefit to a plant population is unimodal as a function of pollinator abundance, relative to the abundance of flowers. Both selective abortion of fruit with eggs and random abortion of fruit, without reference to whether they have eggs or not, can limit pollinator population size. This can increase the net benefits to the plant population by limiting the number of eggs laid, if the pollination rate remains high. However, fruit abortion can possibly destabilize the pollinator population, with negative consequences for the plant population.

  16. Bluff-body stabilized flame dynamics of lean premixed syngas combustion

    NASA Astrophysics Data System (ADS)

    Im, Hong G.; Kim, Yu Jeong; Lee, Bok Jik; Kaust Team

    2015-11-01

    Recently, syngas combustion has been actively investigated for the potential application to integrated gasification combined cycle (IGCC) systems. While lean premixed combustion is attractive for both reduced emission and enhanced efficiency, flame instability becomes often an issue. Bluff-bodies have been adopted as effective flame holders for practical application of premixed flames. In the present study, high-fidelity direct numerical simulations are conducted to investigate the dynamics of lean premixed syngas flames stabilized on a bluff-body, in particular at the near blow-off regime of the flame. A two-dimensional domain of 4 mm height and 20 mm length with a flame holder of a 1 mm-by-1 mm square geometry is used. For a syngas mixture with the equivalence ratio of 0.5 and the CO:H2 ratio of 1, several distinct flame modes are identified as the inflow velocity approaches to the blowoff limit. The sequences of extinction pathway and combustion characteristics are discussed.

  17. Scapholunate stabilization with dynamic extensor carpi radialis longus tendon transfer.

    PubMed

    Peterson, Steven L; Freeland, Alan E

    2010-12-01

    Dynamic extensor carpi radialis longus tendon transfer to the distal pole of the scaphoid acts synchronously and synergistically with wrist motion to restore the slider crank mechanism of the scaphoid after scapholunate interosseous ligament (SLIL) injury. The procedure is designed to simulate a hypothetical dorsal radioscaphoid ligament that more closely approximates the normal viscoelastic forces acting on the scaphoid throughout all phases of wrist motion than does the static checkrein effect and motion limitations of capsulodesis or tenodesis. Extensor carpi radialis longus transfer may be independently sufficient to support normal or near-normal scapholunate and midcarpal kinematics and prevent further injury propagation in patients with partial SLIL tears and dynamic scapholunate instability. Extensor carpi radialis longus transfer alone may improve carpal congruity in patients with static scapholunate instability, but SLIL and dorsal lunate ligament repair or reconstruction is essential for favorable durable outcomes. Extensor carpi radialis longus transfer offers a simple and reasonable alternative to capsulodesis or tenodesis to support these ligament repairs or reconstructions, does not require intercarpal fixation, and allows rehabilitation to proceed expeditiously at approximately 1 month after surgery. PMID:21134618

  18. Bacterial dynamics in steady-state biofilters: beyond functional stability.

    PubMed

    Cabrol, Léa; Malhautier, Luc; Poly, Franck; Lepeuple, Anne-Sophie; Fanlo, Jean-Louis

    2012-01-01

    The spatial and temporal dynamics of microbial community structure and function were surveyed in duplicated woodchip-biofilters operated under constant conditions for 231 days. The contaminated gaseous stream for treatment was representative of composting emissions, included ammonia, dimethyl disulfide and a mixture of five oxygenated volatile organic compounds. The community structure and diversity were investigated by denaturing gradient gel electrophoresis on 16S rRNA gene fragments. During the first 42 days, microbial acclimatization revealed the influence of operating conditions and contaminant loading on the biofiltration community structure and diversity, as well as the limited impact of inoculum compared to the greater persistence of the endogenous woodchip community. During long-term operation, a high and stable removal efficiency was maintained despite a highly dynamic microbial community, suggesting the probable functional redundancy of the community. Most of the contaminant removal occurred in the first compartment, near the gas inlet, where the microbial diversity was the highest. The stratification of the microbial structures along the filter bed was statistically correlated to the longitudinal distribution of environmental conditions (selective pressure imposed by contaminant concentrations) and function (contaminant elimination capacity), highlighting the central role of the bacterial community. The reproducibility of microbial succession in replicates suggests that the community changes were presumably driven by a deterministic process.

  19. Dynamic characteristics and seismic stability of expanded polystyrene geofoam embankments

    NASA Astrophysics Data System (ADS)

    Amini, Zahra A.

    Expanded Polystyrene (EPS) geofoam has become a preferred material in various construction applications due to its light weight. Application of EPS accelerates the projects particularly on soft soils. The focus of this research is on the application of the EPS in embankments and its behavior mainly under harmonic vibration. The goal of this study was to investigate dynamic characteristics of freestanding vertical EPS geofoam embankment and address potential seismic issues that result from the distinguished dynamic behavior of such systems due to the layered and discrete block structure. A series of experimental studies on EPS 19 and a commercially available adhesive was conducted. Two-dimensional numerical analyses were performed to replicate the response of EPS geofoam embankment to horizontal and vertical harmonic motions. The results of the analyses have shown that for some acceleration amplitude levels interlayer sliding is expected to occur in EPS geofoam embankments almost immediately after the start of the base excitation; however, as a highly efficient energy dissipation mechanism sliding ceases rapidly. Shear keys and adhesive may be used to prevent interlayer sliding if they cover the proper extent of area of the embankment. EPS blocks placed in the corners of the embankment and at the edges of the segment prohibited from sliding may experience high stress concentrations. The embankment may show horizontal sway and rocking once sliding is prevented.

  20. Zwitterionic gel encapsulation promotes protein stability, enhances pharmacokinetics, and reduces immunogenicity

    PubMed Central

    Zhang, Peng; Sun, Fang; Tsao, Caroline; Liu, Sijun; Jain, Priyesh; Sinclair, Andrew; Hung, Hsiang-Chieh; Bai, Tao; Wu, Kan; Jiang, Shaoyi

    2015-01-01

    Advances in protein therapy are hindered by the poor stability, inadequate pharmacokinetic (PK) profiles, and immunogenicity of many therapeutic proteins. Polyethylene glycol conjugation (PEGylation) is the most successful strategy to date to overcome these shortcomings, and more than 10 PEGylated proteins have been brought to market. However, anti-PEG antibodies induced by treatment raise serious concerns about the future of PEGylated therapeutics. Here, we demonstrate a zwitterionic polymer network encapsulation technology that effectively enhances protein stability and PK while mitigating the immune response. Uricase modified with a comprehensive zwitterionic polycarboxybetaine (PCB) network exhibited exceptional stability and a greatly prolonged circulation half-life. More importantly, the PK behavior was unchanged, and neither anti-uricase nor anti-PCB antibodies were detected after three weekly injections in a rat model. This technology is applicable to a variety of proteins and unlocks the possibility of adopting highly immunogenic proteins for therapeutic or protective applications. PMID:26371311

  1. Transient stability enhancement of electric power generating systems by 120-degree phase rotation

    DOEpatents

    Cresap, Richard L.; Taylor, Carson W.; Kreipe, Michael J.

    1982-01-01

    A method and system for enhancing the transient stability of an intertied three-phase electric power generating system. A set of power exporting generators (10) is connected to a set of power importing generators (20). When a transient cannot be controlled by conventional stability controls, and imminent loss of synchronism is detected (such as when the equivalent rotor angle difference between the two generator sets exceeds a predetermined value, such as 150 degrees), the intertie is disconnected by circuit breakers. Then a switch (30) having a 120-degree phase rotation, or a circuit breaker having a 120-degree phase rotation is placed in the intertie. The intertie is then reconnected. This results in a 120-degree reduction in the equivalent rotor angle difference between the two generator sets, making the system more stable and allowing more time for the conventional controls to stabilize the transient.

  2. Enhanced stability of black phosphorus field-effect transistors with SiO2 passivation

    NASA Astrophysics Data System (ADS)

    Wan, Bensong; Yang, Bingchao; Wang, Yue; Zhang, Junying; Zeng, Zhongming; Liu, Zhongyuan; Wang, Wenhong

    2015-10-01

    Few-layer black phosphorus (BP) has attracted much attention due to its high mobility and suitable band gap for potential applic5ations in optoelectronics and flexible devices. However, its instability under ambient conditions limits its practical applications. Our investigations indicate that by passivation of the mechanically exfoliated BP flakes with a SiO2 layer, the fabricated BP field-effect transistors (FETs) exhibit greatly enhanced environmental stability. Compared to the unpassivated BP devices, which show a fast drop of on/off current ratio by a factor of 10 after one week of ambient exposure, the SiO2-passivated BP devices display a high retained on/off current ratio of over 600 after one week of exposure, just a little lower than the initial value of 810. Our investigations provide an effective route to passivate the few-layer BPs for enhancement of their environmental stability.

  3. Enhanced stability of black phosphorus field-effect transistors with SiO₂ passivation.

    PubMed

    Wan, Bensong; Yang, Bingchao; Wang, Yue; Zhang, Junying; Zeng, Zhongming; Liu, Zhongyuan; Wang, Wenhong

    2015-10-30

    Few-layer black phosphorus (BP) has attracted much attention due to its high mobility and suitable band gap for potential applic5ations in optoelectronics and flexible devices. However, its instability under ambient conditions limits its practical applications. Our investigations indicate that by passivation of the mechanically exfoliated BP flakes with a SiO2 layer, the fabricated BP field-effect transistors (FETs) exhibit greatly enhanced environmental stability. Compared to the unpassivated BP devices, which show a fast drop of on/off current ratio by a factor of 10 after one week of ambient exposure, the SiO2-passivated BP devices display a high retained on/off current ratio of over 600 after one week of exposure, just a little lower than the initial value of 810. Our investigations provide an effective route to passivate the few-layer BPs for enhancement of their environmental stability.

  4. Dynamics, stability, and control analyses of flapping wing micro-air vehicles

    NASA Astrophysics Data System (ADS)

    Orlowski, Christopher T.; Girard, Anouck R.

    2012-05-01

    The paper presents an overview of the various analyses of flight dynamics, stability, and control of flapping wing micro-air vehicles available in the literature. The potential benefits of flapping wing micro-air vehicles for civil, military, and search and rescue operations are numerous. The majority of the flight dynamics research involves the standard aircraft (6DOF) equations of motion, although a growth is evident in examining the multibody flight dynamics models of flapping wing micro-air vehicles. The stability of flapping wing micro-air vehicles is largely studied in the vicinity of hover and forward flight. The majority of stability studies focus on linear, time-invariant stability in the vicinity of reference flight conditions, such as hover or forward flight. The consistent result is that flapping wing micro-air vehicles are unstable in an open loop setting. The unstable result is based on linear and nonlinear stability analyses. Control has been demonstrated for hovering and forward flight through various methods, both linear and nonlinear in nature. The entirety of reported research into the stability and control of flapping wing micro-air vehicles has neglected the mass effects of the wings on the position and orientation of the central body. Successful control of a flapping wing micro-air vehicle, with the wings' mass effects included, is still an open research area.

  5. The Comprehensive Biomechanics and Load-Sharing of Semirigid PEEK and Semirigid Posterior Dynamic Stabilization Systems

    PubMed Central

    Sengupta, D. K.; Bucklen, Brandon; McAfee, Paul C.; Nichols, Jeff; Angara, Raghavendra; Khalil, Saif

    2013-01-01

    Alternatives to conventional rigid fusion have been proposed for several conditions related to degenerative disc disease when nonoperative treatment has failed. Semirigid fixation, in the form of dynamic stabilization or PEEK rods, is expected to provide compression under loading as well as an intermediate level of stabilization. This study systematically examines both the load-sharing characteristics and kinematics of these two devices compared to the standard of internal rigid fixators. Load-sharing was studied by using digital pressure films inserted between an artificially machined disc and two loading fixtures. Rigid rods, PEEK rods, and the dynamic stabilization system were inserted posteriorly for stabilization. The kinematics were quantified on ten, human, cadaver lumbosacral spines (L3-S1) which were tested under a pure bending moment, in flexion-extension, lateral bending, and axial rotation. The magnitude of load transmission through the anterior column was significantly greater with the dynamic device compared to PEEK rods and rigid rods. The contact pressures were distributed more uniformly, throughout the disc with the dynamic stabilization devices, and had smaller maximum point-loading (pressures) on any particular point within the disc. Kinematically, the motion was reduced by both semirigid devices similarly in all directions, with slight rigidity imparted by a lateral interbody device. PMID:23984077

  6. Guidelines for Computing Longitudinal Dynamic Stability Characteristics of a Subsonic Transport

    NASA Technical Reports Server (NTRS)

    Thompson, Joseph R.; Frank, Neal T.; Murphy, Patrick C.

    2010-01-01

    A systematic study is presented to guide the selection of a numerical solution strategy for URANS computation of a subsonic transport configuration undergoing simulated forced oscillation about its pitch axis. Forced oscillation is central to the prevalent wind tunnel methodology for quantifying aircraft dynamic stability derivatives from force and moment coefficients, which is the ultimate goal for the computational simulations. Extensive computations are performed that lead in key insights of the critical numerical parameters affecting solution convergence. A preliminary linear harmonic analysis is included to demonstrate the potential of extracting dynamic stability derivatives from computational solutions.

  7. Cavity Self-Stabilization and Enhancement of Laser Gyroscopes by (Coupled) Optical Resonators

    NASA Technical Reports Server (NTRS)

    Smith, David D.

    2006-01-01

    We analyze the effect of a highly dispersive element placed inside a modulated optical cavity on the frequency and amplitude of the modulation to determine the conditions for cavity self-stabilization and enhanced gyroscopic sensitivity. Hence, we model cavity rotation or instability by an arbitrary AM/FM modulation, and the dispersive element as a phase and amplitude filter. We find that anomalous dispersion may be used to self-stabilize a laser cavity, provided the magnitude of the group index of refraction is smaller than the phase index of refraction in the cavity. The optimal stabilization is found to occur when the group index is zero. Group indices with magnitudes larger than the phase index (both normal and anomalous dispersion) are found to enhance the sensitivity of a laser gyroscope to rotation. Furthermore, our results indicate that atomic media, even coherent superpositions in multilevel atoms, are not useful for these applications, because the amplitude and phase filters work against one another, i.e., decreasing the modulation frequency increases its amplitude and vice versa, with one exception: negative group indices whose magnitudes are larger than the phase index result in negative, but enhanced, beat frequencies. On the other hand, for optical resonators the dispersion reversal associated with critical coupling enables the amplitude and phase filters to work together under a greater variety of circumstances than for atomic media. We find that for single over-coupled resonators, or in the case of under-coupled coupled-resonator-induced absorption, the absorption and normal dispersion on-resonance increase the contrast and frequency of the beat-note, respectively, resulting in a substantial enhancement of the gyroscopic response. Moreover, for cavity self-stabilization, we propose the use of a variety of coupled-resonator induced transparency that is accompanied by anomalous dispersion.

  8. Chemical derivatization to enhance chemical/oxidative stability of resorcinol-formaldehyde resin

    SciTech Connect

    Hubler, T.

    1996-10-01

    The purpose of this work is to develop modified resorcinol-formaldehyde (R-F) resin with enhanced chemical/oxidative stability in conditions typically encountered in the remediation of radioactive waste tanks. R-F resin is a regenerable organic ion-exchanger developed at Savannah River Technology Center that is being considered for use in the selective removal of radioactive cesium from alkaline waste tank supernates at both the Hanford and Savannah River sites.

  9. Biological soil crusts exhibit a dynamic response to seasonal rain and release from grazing with implications for soil stability

    USGS Publications Warehouse

    Jimenez, Aguilar A.; Huber-Sannwald, E.; Belnap, J.; Smart, D.R.; Arredondo, Moreno J.T.

    2009-01-01

    In Northern Mexico, long-term grazing has substantially degraded semiarid landscapes. In semiarid systems, ecological and hydrological processes are strongly coupled by patchy plant distribution and biological soil crust (BSC) cover in plant-free interspaces. In this study, we asked: 1) how responsive are BSC cover/composition to a drying/wetting cycle and two-year grazing removal, and 2) what are the implications for soil erosion? We characterized BSC morphotypes and their influence on soil stability under grazed/non-grazed conditions during a dry and wet season. Light- and dark-colored cyanobacteria were dominant at the plant tussock and community level. Cover changes in these two groups differed after a rainy season and in response to grazing removal. Lichens with continuous thalli were more vulnerable to grazing than those with semi-continuous/discontinuous thalli after the dry season. Microsites around tussocks facilitated BSC colonization compared to interspaces. Lichen and cyanobacteria morphotypes differentially enhanced resistance to soil erosion; consequently, surface soil stability depends on the spatial distribution of BSC morphotypes, suggesting soil stability may be as dynamic as changes in the type of BSC cover. Longer-term spatially detailed studies are necessary to elicit spatiotemporal dynamics of BSC communities and their functional role in biotically and abiotically variable environments. ?? 2009 Elsevier Ltd.

  10. Dynamics of dc bus networks and their stabilization by decentralized delayed feedback.

    PubMed

    Konishi, Keiji; Sugitani, Yoshiki; Hara, Naoyuki

    2015-01-01

    The present paper deals with the dynamics of bus networks, which consist of several identical dc bus systems connected by resistors. It is analytically guaranteed that the stability of a stand-alone dc bus system is equivalent to that of the networks, independent of the number of bus systems and the network topology. In addition, we show that a decentralized delayed-feedback control can stabilize an unstable operating point embedded within the networks. Moreover, this stabilization does not depend on the number of bus systems or the network topology. A systematic procedure for designing the controller is presented. Finally, the validity of the analytical results is confirmed through numerical examples.

  11. Dynamics of dc bus networks and their stabilization by decentralized delayed feedback

    NASA Astrophysics Data System (ADS)

    Konishi, Keiji; Sugitani, Yoshiki; Hara, Naoyuki

    2015-01-01

    The present paper deals with the dynamics of bus networks, which consist of several identical dc bus systems connected by resistors. It is analytically guaranteed that the stability of a stand-alone dc bus system is equivalent to that of the networks, independent of the number of bus systems and the network topology. In addition, we show that a decentralized delayed-feedback control can stabilize an unstable operating point embedded within the networks. Moreover, this stabilization does not depend on the number of bus systems or the network topology. A systematic procedure for designing the controller is presented. Finally, the validity of the analytical results is confirmed through numerical examples.

  12. Navier-Stokes Simulation of the Canard-Wing-Body Longitudinal Dynamic Stability Characteristics

    NASA Technical Reports Server (NTRS)

    Tu, Eugene L.; VanDalsem, William R. (Technical Monitor)

    1996-01-01

    Many modern aircraft are canard-configured for aircraft control and improved aerodynamic performance. Canards can often enhance aircraft cruise performance, maneuverability and agility. For close-coupled canard configurations, the aerodynamic interaction between the canard and wing significantly changes the flow characteristics of the wing. In unsteady flow, such changes in the flow structure and performance of wings can be quite pronounced. Accurate modeling of the unsteady aerodynamics is essential for potential CFD design and analysis of such configurations. A time-accurate numerical simulation is performed to study the unsteady aerodynamic interaction between a canard and wing with emphasis on the effects of the canard on the configuration's dynamic response characteristics. The thin-layer Reynolds-averaged Navier-Stokes Equations with various turbulence models are used in this study. Computations are made on a generic, analytically-defined, close-coupled canard-wing-body configuration which has been the subject of numerous previously published experimental studies during the 1970's to mid-80's. More recently, a series of steady-flow simulations has been performed and published by the author. In the current study, the configuration is given prescribed ramp and oscillatory motions in order to predict characteristics such as the damping-in-pitch and oscillatory longitudinal stability parameters. The current computations are made at high-subsonic and transonic Mach numbers, moderate angles-of- attack from -4 to 20 degrees, and at various pitch rates and reduced frequencies. Comparisons of pressures and integrated force quantities (e.g. lift, drag, pitching moment and selected dynamic parameters) are made with other published computational results and available experimental data. Results showing the unsteady effects of the canard on surface pressures, integrated forces, canard-wing vortex interaction and vortex breakdown will be presented.

  13. Chemisorption of oxygen onto activated carbon can enhance the stability of biological perchlorate reduction in fixed bed biofilm reactors.

    PubMed

    Choi, Young Chul; Li, Xu; Raskin, Lutgarde; Morgenroth, Eberhard

    2008-07-01

    Fixed bed biofilm reactors with granular activated carbon (GAC) or glass beads as support media were used to evaluate the influence of short-term (12h) and long-term (23 days) increases of influent dissolved oxygen (DO) concentrations on biological perchlorate removal. The goal was to evaluate the extent by which chemisorption of oxygen to GAC can enhance the stability of biological perchlorate reduction. Baseline influent concentrations were 50 microg/L of perchlorate, 2 mg/L of acetate as C, and 1mg/L of DO. Perchlorate removal in the glass bead reactor seized immediately after increasing influent DO concentrations from 1 to 4 mg/L since glass beads have no sorptive capacity. In the biologically active carbon (BAC) reactor, chemisorption of oxygen to GAC removed a substantial fraction of the influent DO, and perchlorate removal was maintained during short-term increases of influent DO levels up to 8 mg/L. During long-term exposure to influent DO concentrations of 8.5mg/L, effluent perchlorate and DO concentrations increased slowly. Subsequent exposure of the BAC reactor bed to low DO concentrations partially regenerated the capacity for oxygen chemisorption. Microbial analyses indicated similar microbial communities in both reactors, which confirmed that the differences in reactor performance during dynamic loading conditions could be attributed to the sorptive properties of GAC. Using a sorptive biofilm support medium can enhance biological perchlorate removal under dynamic loading conditions.

  14. STABILITY AND DYNAMICS OF SPATIO-TEMPORAL STRUCTURES

    SciTech Connect

    Hermann Riecke

    2005-10-21

    This document constitutes the final report for the grant. It provides a complete list of publications and presentations that arose from the project as well as a brief description of the highlights of the research results. The research funded by this grant has provided insights into the spontaneous formation of structures of increasing complexity in systems driven far from thermodynamic equilibrium. A classic example of such a system is thermally driven convection in a horizontal fluid layer. Highlights of the research are: (1) explanation of the localized traveling wave pulses observed in binary-mixture convection, (2) explanation of the localized waves in electroconvection, (3) introduction of a new diagnostics for spatially and temporally chaotic states, which is based on the statistics of defect trajectories, (4) prediction of complex states in thermally driven convection in rotating systems. Additional contributions provided insight into the localization mechanism for oscillons, the prediction of a new localization mechanism for traveling waves based on a resonant periodic forcing, and an analysis of the stability of quasi-periodic patterns.

  15. Verifying Stability of Dynamic Soft-Computing Systems

    NASA Technical Reports Server (NTRS)

    Wen, Wu; Napolitano, Marcello; Callahan, John

    1997-01-01

    Soft computing is a general term for algorithms that learn from human knowledge and mimic human skills. Example of such algorithms are fuzzy inference systems and neural networks. Many applications, especially in control engineering, have demonstrated their appropriateness in building intelligent systems that are flexible and robust. Although recent research have shown that certain class of neuro-fuzzy controllers can be proven bounded and stable, they are implementation dependent and difficult to apply to the design and validation process. Many practitioners adopt the trial and error approach for system validation or resort to exhaustive testing using prototypes. In this paper, we describe our on-going research towards establishing necessary theoretic foundation as well as building practical tools for the verification and validation of soft-computing systems. A unified model for general neuro-fuzzy system is adopted. Classic non-linear system control theory and recent results of its applications to neuro-fuzzy systems are incorporated and applied to the unified model. It is hoped that general tools can be developed to help the designer to visualize and manipulate the regions of stability and boundedness, much the same way Bode plots and Root locus plots have helped conventional control design and validation.

  16. Recent Advances in Heliogyro Solar Sail Structural Dynamics, Stability, and Control Research

    NASA Technical Reports Server (NTRS)

    Wilkie, W. Keats; Warren, Jerry E.; Horta, Lucas G.; Lyle, Karen H.; Juang, Jer-Nan; Gibbs, S. Chad; Dowell, Earl H.; Guerrant, Daniel V.; Lawrence, Dale

    2015-01-01

    Results from recent NASA sponsored research on the structural dynamics, stability, and control characteristics of heliogyro solar sails are summarized. Specific areas under investigation include coupled nonlinear finite element analysis of heliogyro membrane blade with solar radiation pressure effects, system identification of spinning membrane structures, and solarelastic stability analysis of heliogyro solar sails, including stability during blade deployment. Recent results from terrestrial 1-g blade dynamics and control experiments on "rope ladder" membrane blade analogs, and small-scale in vacuo system identification experiments with hanging and spinning high-aspect ratio membranes will also be presented. A low-cost, rideshare payload heliogyro technology demonstration mission concept is used as a mission context for these heliogyro structural dynamics and solarelasticity investigations, and is also described. Blade torsional dynamic response and control are also shown to be significantly improved through the use of edge stiffening structural features or inclusion of modest tip masses to increase centrifugal stiffening of the blade structure. An output-only system identification procedure suitable for on-orbit blade dynamics investigations is also developed and validated using ground tests of spinning sub-scale heliogyro blade models. Overall, analytical and experimental investigations to date indicate no intractable stability or control issues for the heliogyro solar sail concept.

  17. Protection enhances community and habitat stability: evidence from a mediterranean marine protected area.

    PubMed

    Fraschetti, Simonetta; Guarnieri, Giuseppe; Bevilacqua, Stanislao; Terlizzi, Antonio; Boero, Ferdinando

    2013-01-01

    Rare evidences support that Marine Protected Areas (MPAs) enhance the stability of marine habitats and assemblages. Based on nine years of observation (2001-2009) inside and outside a well managed MPA, we assessed the potential of conservation and management actions to modify patterns of spatial and/or temporal variability of Posidonia oceanica meadows, the lower midlittoral and the shallow infralittoral rock assemblages. Significant differences in both temporal variations and spatial patterns were observed between protected and unprotected locations. A lower temporal variability in the protected vs. unprotected assemblages was found in the shallow infralittoral, demonstrating that, at least at local scale, protection can enhance community stability. Macrobenthos with long-lived and relatively slow-growing invertebrates and structurally complex algal forms were homogeneously distributed in space and went through little fluctuations in time. In contrast, a mosaic of disturbed patches featured unprotected locations, with small-scale shifts from macroalgal stands to barrens, and harsh temporal variations between the two states. Opposite patterns of spatial and temporal variability were found for the midlittoral assemblages. Despite an overall clear pattern of seagrass regression through time, protected meadows showed a significantly higher shoot density than unprotected ones, suggesting a higher resistance to local human activities. Our results support the assumption that the exclusion/management of human activities within MPAs enhance the stability of the structural components of protected marine systems, reverting or arresting threat-induced trajectories of change. PMID:24349135

  18. Protection enhances community and habitat stability: evidence from a mediterranean marine protected area.

    PubMed

    Fraschetti, Simonetta; Guarnieri, Giuseppe; Bevilacqua, Stanislao; Terlizzi, Antonio; Boero, Ferdinando

    2013-01-01

    Rare evidences support that Marine Protected Areas (MPAs) enhance the stability of marine habitats and assemblages. Based on nine years of observation (2001-2009) inside and outside a well managed MPA, we assessed the potential of conservation and management actions to modify patterns of spatial and/or temporal variability of Posidonia oceanica meadows, the lower midlittoral and the shallow infralittoral rock assemblages. Significant differences in both temporal variations and spatial patterns were observed between protected and unprotected locations. A lower temporal variability in the protected vs. unprotected assemblages was found in the shallow infralittoral, demonstrating that, at least at local scale, protection can enhance community stability. Macrobenthos with long-lived and relatively slow-growing invertebrates and structurally complex algal forms were homogeneously distributed in space and went through little fluctuations in time. In contrast, a mosaic of disturbed patches featured unprotected locations, with small-scale shifts from macroalgal stands to barrens, and harsh temporal variations between the two states. Opposite patterns of spatial and temporal variability were found for the midlittoral assemblages. Despite an overall clear pattern of seagrass regression through time, protected meadows showed a significantly higher shoot density than unprotected ones, suggesting a higher resistance to local human activities. Our results support the assumption that the exclusion/management of human activities within MPAs enhance the stability of the structural components of protected marine systems, reverting or arresting threat-induced trajectories of change.

  19. Enhancing enzyme stability and metabolic functional ability of β-galactosidase through functionalized polymer nanofiber immobilization.

    PubMed

    Misson, Mailin; Jin, Bo; Chen, Binghui; Zhang, Hu

    2015-10-01

    A functionalized polystyrene nanofiber (PSNF) immobilized β-galactosidase assembly (PSNF-Gal) was synthesized as a nanobiocatalyst aiming to enhance the biocatalyst stability and functional ability. The PSNF fabricated by electrospinning was functionalized through a chemical oxidation method for enzyme binding. The bioengineering performance of the enzyme carriers was further evaluated for bioconversion of lactose to galacto-oligosaccharides (GOS). The modified PSNF-Gal demonstrated distinguished performances to preserve the same activity as the free β-galactosidase at the optimum pH of 7.0, and to enhance the enzyme stability of PSNF-Gal in an alkaline condition up to pH 10. The PSNF assembly demonstrated improved thermal stability from 37 to 60 °C. The nanobiocatalyst was able to retain 30 % of its initial activity after ninth operation cycles comparing to four cycles with the unmodified counterpart. In contrast with free β-galactosidase, the modified PSNF-Gal enhanced the GOS yield from 14 to 28 %. These findings show the chemically modified PSNF-based nanobiocatalyst may be pertinent for various enzyme-catalysed bioprocessing applications.

  20. Protection Enhances Community and Habitat Stability: Evidence from a Mediterranean Marine Protected Area

    PubMed Central

    Fraschetti, Simonetta; Guarnieri, Giuseppe; Bevilacqua, Stanislao; Terlizzi, Antonio; Boero, Ferdinando

    2013-01-01

    Rare evidences support that Marine Protected Areas (MPAs) enhance the stability of marine habitats and assemblages. Based on nine years of observation (2001–2009) inside and outside a well managed MPA, we assessed the potential of conservation and management actions to modify patterns of spatial and/or temporal variability of Posidonia oceanica meadows, the lower midlittoral and the shallow infralittoral rock assemblages. Significant differences in both temporal variations and spatial patterns were observed between protected and unprotected locations. A lower temporal variability in the protected vs. unprotected assemblages was found in the shallow infralittoral, demonstrating that, at least at local scale, protection can enhance community stability. Macrobenthos with long-lived and relatively slow-growing invertebrates and structurally complex algal forms were homogeneously distributed in space and went through little fluctuations in time. In contrast, a mosaic of disturbed patches featured unprotected locations, with small-scale shifts from macroalgal stands to barrens, and harsh temporal variations between the two states. Opposite patterns of spatial and temporal variability were found for the midlittoral assemblages. Despite an overall clear pattern of seagrass regression through time, protected meadows showed a significantly higher shoot density than unprotected ones, suggesting a higher resistance to local human activities. Our results support the assumption that the exclusion/management of human activities within MPAs enhance the stability of the structural components of protected marine systems, reverting or arresting threat-induced trajectories of change. PMID:24349135

  1. Effects of ligand binding on the mechanical stability of protein GB1 studied by steered molecular dynamics simulation.

    PubMed

    Su, Ji-Guo; Zhao, Shu-Xin; Wang, Xiao-Feng; Li, Chun-Hua; Li, Jing-Yuan

    2016-08-01

    Regulation of the mechanical properties of proteins plays an important role in many biological processes, and sheds light on the design of biomaterials comprised of protein. At present, strategies to regulate protein mechanical stability focus mainly on direct modulation of the force-bearing region of the protein. Interestingly, the mechanical stability of GB1 can be significantly enhanced by the binding of Fc fragments of human IgG antibody, where the binding site is distant from the force-bearing region of the protein. The mechanism of this long-range allosteric control of protein mechanics is still elusive. In this work, the impact of ligand binding on the mechanical stability of GB1 was investigated using steered molecular dynamics simulation, and a mechanism underlying the enhanced protein mechanical stability is proposed. We found that the external force causes deformation of both force-bearing region and ligand binding site. In other words, there is a long-range coupling between these two regions. The binding of ligand restricts the distortion of the binding site and reduces the deformation of the force-bearing region through a long-range allosteric communication, which thus improves the overall mechanical stability of the protein. The simulation results are very consistent with previous experimental observations. Our studies thus provide atomic-level insights into the mechanical unfolding process of GB1, and explain the impact of ligand binding on the mechanical properties of the protein through long-range allosteric regulation, which should facilitate effective modulation of protein mechanical properties.

  2. Effects of ligand binding on the mechanical stability of protein GB1 studied by steered molecular dynamics simulation.

    PubMed

    Su, Ji-Guo; Zhao, Shu-Xin; Wang, Xiao-Feng; Li, Chun-Hua; Li, Jing-Yuan

    2016-08-01

    Regulation of the mechanical properties of proteins plays an important role in many biological processes, and sheds light on the design of biomaterials comprised of protein. At present, strategies to regulate protein mechanical stability focus mainly on direct modulation of the force-bearing region of the protein. Interestingly, the mechanical stability of GB1 can be significantly enhanced by the binding of Fc fragments of human IgG antibody, where the binding site is distant from the force-bearing region of the protein. The mechanism of this long-range allosteric control of protein mechanics is still elusive. In this work, the impact of ligand binding on the mechanical stability of GB1 was investigated using steered molecular dynamics simulation, and a mechanism underlying the enhanced protein mechanical stability is proposed. We found that the external force causes deformation of both force-bearing region and ligand binding site. In other words, there is a long-range coupling between these two regions. The binding of ligand restricts the distortion of the binding site and reduces the deformation of the force-bearing region through a long-range allosteric communication, which thus improves the overall mechanical stability of the protein. The simulation results are very consistent with previous experimental observations. Our studies thus provide atomic-level insights into the mechanical unfolding process of GB1, and explain the impact of ligand binding on the mechanical properties of the protein through long-range allosteric regulation, which should facilitate effective modulation of protein mechanical properties. PMID:27444879

  3. Protein Stability and Dynamics Modulation: The Case of Human Frataxin

    PubMed Central

    Gallo, Mariana; Salvay, Andres G.; Ferreiro, Diego U.; Santos, Javier

    2012-01-01

    Frataxin (FXN) is an α/β protein that plays an essential role in iron homeostasis. Apparently, the function of human FXN (hFXN) depends on the cooperative formation of crucial interactions between helix α1, helix α2, and the C-terminal region (CTR) of the protein. In this work we quantitatively explore these relationships using a purified recombinant fragment hFXN90–195. This variant shows the hydrodynamic behavior expected for a monomeric globular domain. Circular dichroism, fluorescence, and NMR spectroscopies show that hFXN90–195 presents native-like secondary and tertiary structure. However, chemical and temperature induced denaturation show that CTR truncation significantly destabilizes the overall hFXN fold. Accordingly, limited proteolysis experiments suggest that the native-state dynamics of hFXN90–195 and hFXN90–210 are indeed different, being the former form much more sensitive to the protease at specific sites. The overall folding dynamics of hFXN fold was further explored with structure-based protein folding simulations. These suggest that the native ensemble of hFXN can be decomposed in at least two substates, one with consolidation of the CTR and the other without consolidation of the CTR. Explicit-solvent all atom simulations identify some of the proteolytic target sites as flexible regions of the protein. We propose that the local unfolding of CTR may be a critical step for the global unfolding of hFXN, and that modulation of the CTR interactions may strongly affect hFXN physiological function. PMID:23049850

  4. Dynamics and stability of directional jumps in the desert locust

    PubMed Central

    Gvirsman, Omer

    2016-01-01

    Locusts are known for their ability to jump large distances to avoid predation. The jump also serves to launch the adult locust into the air in order to initiate flight. Various aspects of this important behavior have been studied extensively, from muscle physiology and biomechanics, to the energy storage systems involved in powering the jump, and more. Less well understood are the mechanisms participating in control of the jump trajectory. Here we utilise video monitoring and careful analysis of experimental directional jumps by adult desert locusts, together with dynamic computer simulation, in order to understand how the locusts control the direction and elevation of the jump, the residual angular velocities resulting from the jump and the timing of flapping-flight initiation. Our study confirms and expands early findings regarding the instrumental role of the initial body position and orientation. Both real-jump video analysis and simulations based on our expanded dynamical model demonstrate that the initial body coordinates of position (relative to the hind-legs ground-contact points) are dominant in predicting the jumps’ azimuth and elevation angles. We also report a strong linear correlation between the jumps’ pitch-angular-velocity and flight initiation timing, such that head downwards rotations lead to earlier wing opening. In addition to offering important insights into the bio-mechanical principles of locust jumping and flight initiation, the findings from this study will be used in designing future prototypes of a bio-inspired miniature jumping robot that will be employed in animal behaviour studies and environmental monitoring applications. PMID:27703846

  5. Dynamic contrast-enhanced 3D photoacoustic imaging

    NASA Astrophysics Data System (ADS)

    Wong, Philip; Kosik, Ivan; Carson, Jeffrey J. L.

    2013-03-01

    Photoacoustic imaging (PAI) is a hybrid imaging modality that integrates the strengths from both optical imaging and acoustic imaging while simultaneously overcoming many of their respective weaknesses. In previous work, we reported on a real-time 3D PAI system comprised of a 32-element hemispherical array of transducers. Using the system, we demonstrated the ability to capture photoacoustic data, reconstruct a 3D photoacoustic image, and display select slices of the 3D image every 1.4 s, where each 3D image resulted from a single laser pulse. The present study aimed to exploit the rapid imaging speed of an upgraded 3D PAI system by evaluating its ability to perform dynamic contrast-enhanced imaging. The contrast dynamics can provide rich datasets that contain insight into perfusion, pharmacokinetics and physiology. We captured a series of 3D PA images of a flow phantom before and during injection of piglet and rabbit blood. Principal component analysis was utilized to classify the data according to its spatiotemporal information. The results suggested that this technique can be used to separate a sequence of 3D PA images into a series of images representative of main features according to spatiotemporal flow dynamics.

  6. Encapsulation of biophenolic phytochemical EGCG within lipid nanoparticles enhances its stability and cytotoxicity against cancer.

    PubMed

    Radhakrishnan, Rasika; Kulhari, Hitesh; Pooja, Deep; Gudem, Sagarika; Bhargava, Suresh; Shukla, Ravi; Sistla, Ramakrishna

    2016-06-01

    Epigallocatechin gallate (EGCG), a green tea polyphenolic catechin, has been known to possess a variety of beneficial biological activities. The in-vitro anti-cancer activity of EGCG is well documented. However, the use of EGCG in modern therapeutics is limited due to its poor bioavailability and limited stability at physiological pH. In this study, we have investigated the stability profiles of EGCG in aqueous solutions using UV-vis spectroscopy. Stability results showed very low stability profile of EGCG at physiological pH with rapid degradation under alkaline conditions. Therefore, we have encapsulated EGCG in solid lipid nanoparticles to increase its stability and evaluated for anticancer activity. The lipid core of nanoparticles not only provides an additional structural reinforcement to the nanoparticle assembly, but also makes it biologically compatible, thereby enabling a stealth vehicle for efficient drug delivery. EGCG loaded nanoparticles (EGCG-SLN) were characterized using dynamic light scattering, Fourier transform infrared spectroscopy and differential scanning calorimetry. EGCG and EGCG-SLN were evaluated for their anticancer activities by cellular proliferation. The cytotoxicity of EGCG-SLN was found to be 8.1 times higher against MDA-MB 231 human breast cancer cells and 3.8 times higher against DU-145 human prostate cancer cells than that of the pure EGCG. PMID:27234272

  7. Fluid dynamics at transition regions of enhanced heat transfer channels

    NASA Astrophysics Data System (ADS)

    Case, Jennifer C.; Pohlman, Nicholas A.

    2012-11-01

    Helical wire coil inserts are used to enhance heat transfer in high heat flux cooling channels. Past research using temperature probes has sufficiently proven that wire coils increase heat transfer by factors of three to five through the disruption of the boundary layer in the channels. The coils are passive devices that are inexpensive to manufacture and easily integrate into existing heat exchangers given the limited pressure drop they produce. Most of the fluid mechanics research in flow over helical coils has focused on the dynamics and vortex structure in fully developed regions rather than the short transition region where the enhanced heat transfer is often expected. Understanding how the development of the flow occurs over the axial length of the cooling channel will determine minimum dimensions necessary for enhanced heat transfer. Results of particle-shadow velocimetry (PSV) measurements report on the flow velocities and turbulence that occurs in the transition regions at the beginning of wire coil inserts. The ability to relate parameters such as flow rate, wire diameter, coil pitch, and the total tube length will increase fundamental knowledge and will allow for more efficient heat exchanger designs. Funding provided by NIU's Undergraduate Special Opportunities in Artistry & Research grant program.

  8. Rewiring dynamical networks with prescribed degree distribution for enhancing synchronizability

    NASA Astrophysics Data System (ADS)

    Dadashi, Majid; Barjasteh, Iman; Jalili, Mahdi

    2010-12-01

    In this paper, we present an algorithm for enhancing synchronizability of dynamical networks with prescribed degree distribution. The algorithm takes an unweighted and undirected network as input and outputs a network with the same node-degree distribution and enhanced synchronization properties. The rewirings are based on the properties of the Laplacian of the connection graph, i.e., the eigenvectors corresponding to the second smallest and the largest eigenvalues of the Laplacian. A term proportional to the eigenvectors is adopted to choose potential edges for rewiring, provided that the node-degree distribution is preserved. The algorithm can be implemented on networks of any sizes as long as their eigenvalues and eigenvectors can be calculated with standard algorithms. The effectiveness of the proposed algorithm in enhancing the network synchronizability is revealed by numerical simulation on a number of sample networks including scale-free, Watts-Strogatz, and Erdős-Rényi graphs. Furthermore, a number of network's structural parameters such as node betweenness centrality, edge betweenness centrality, average path length, clustering coefficient, and degree assortativity are tracked as a function of optimization steps.

  9. Use of computational fluid dynamics in the design of dynamic contrast enhanced imaging phantoms

    NASA Astrophysics Data System (ADS)

    Hariharan, Prasanna; Freed, Melanie; Myers, Matthew R.

    2013-09-01

    Phantoms for dynamic contrast enhanced (DCE) imaging modalities such as DCE computed tomography (DCE-CT) and DCE magnetic resonance imaging (DCE-MRI) are valuable tools for evaluating and comparing imaging systems. It is important for the contrast-agent distribution within the phantom to possess a time dependence that replicates a curve observed clinically, known as the ‘tumor-enhancement curve’. It is also important for the concentration field within the lesion to be as uniform as possible. This study demonstrates how computational fluid dynamics (CFD) can be applied to achieve these goals within design constraints. The distribution of the contrast agent within the simulated phantoms was investigated in relation to the influence of three factors of the phantom design. First, the interaction between the inlets and the uniformity of the contrast agent within the phantom was modeled. Second, pumps were programmed using a variety of schemes and the resultant dynamic uptake curves were compared to tumor-enhancement curves obtained from clinical data. Third, the effectiveness of pulsing the inlet flow rate to produce faster equilibration of the contrast-agent distribution was quantified. The models employed a spherical lesion and design constraints (lesion diameter, inlet-tube size and orientation, contrast-agent flow rates and fluid properties) taken from a recently published DCE-MRI phantom study. For DCE-MRI in breast cancer detection, where the target tumor-enhancement curve varies on the scale of hundreds of seconds, optimizing the number of inlet tubes and their orientation was found to be adequate for attaining concentration uniformity and reproducing the target tumor-enhancement curve. For DCE-CT in liver tumor detection, where the tumor-enhancement curve varies on a scale of tens of seconds, the use of an iterated inlet condition (programmed into the pump) enabled the phantom to reproduce the target tumor-enhancement curve within a few per cent beyond about

  10. Facile Synthesis of Phosphatidyl Saccharides for Preparation of Anionic Nanoliposomes with Enhanced Stability

    PubMed Central

    Song, Shuang; Cheong, Ling-Zhi; Falkeborg, Mia; Liu, Lei; Dong, Mingdong; Jensen, Henrik Max; Bertelsen, Kresten; Thorsen, Michael; Tan, Tianwei; Xu, Xuebing; Guo, Zheng

    2013-01-01

    Physical stability during storage and against processing such as dehyration/rehydration are the cornerstone in designing delivery vehicles. In this work, mono-, di- and tri-saccharides were enzymatically conjugated to phosphatidyl group through a facile approach namely phospholipase D (PLD) mediated transphosphatidylation in a biphasic reaction system. The purified products were structurally identified and the connectivities of carbohydrate to phosphatidyl moiety precisely mapped by 1H, 31P, 13C NMR pulse sequences and LC-ESI-FTMS. The synthetic phosphatidyl saccharides were employed as the sole biomimetic component for preparation of nanoliposomes. It was found that the critical micelle concentration (CMC) of phosphatidyl saccharides increases as more bulky sugar moiety (mono- to tri-) is introduced. Phosphatidyl di-saccharide had the largest membrane curvature. In comparison to the zwitterionic phosphatidylcholine liposome, all phosphatidyl saccharides liposomes are anionic and demonstrated significantly enhanced stability during storage. According to the confocal laser scan microscopy (CLSM) and atom force microscopy (AFM) analyses, the nanoliposomes formed by the synthetic phosphatidyl saccharides also show excellent stability against dehydration/rehydration process in which most of the liposomal structures remained intact. The abundance hydroxyl groups in the saccharide moieties might provide sufficient H-bondings for stabilization. This work demonstrated the synthesized phosphatidyl saccharides are capable of functioning as enzymatically liable materials which can form stable nanoliposomes without addition of stabilizing excipients. PMID:24069243

  11. Co-composting solid biowastes with alkaline materials to enhance carbon stabilization and revegetation potential.

    PubMed

    Chowdhury, Saikat; Bolan, Nanthi S; Seshadri, Balaji; Kunhikrishnan, Anitha; Wijesekara, Hasintha; Xu, Yilu; Yang, Jianjun; Kim, Geon-Ha; Sparks, Donald; Rumpel, Cornelia

    2016-04-01

    Co-composting biowastes such as manures and biosolids can be used to stabilize carbon (C) without impacting the quality of these biowastes. This study investigated the effect of co-composting biowastes with alkaline materials on C stabilization and monitored the fertilization and revegetation values of these co-composts. The stabilization of C in biowastes (poultry manure and biosolids) was examined by their composting in the presence of various alkaline amendments (lime, fluidized bed boiler ash, flue gas desulphurization gypsum, and red mud) for 6 months in a controlled environment. The effects of co-composting on the biowastes' properties were assessed for different physical C fractions, microbial biomass C, priming effect, potentially mineralizable nitrogen, bioavailable phosphorus, and revegetation of an urban landfill soil. Co-composting biowastes with alkaline materials increased C stabilization, attributed to interaction with alkaline materials, thereby protecting it from microbial decomposition. The co-composted biowastes also increased the fertility of the landfill soil, thereby enhancing its revegetation potential. Stabilization of biowastes using alkaline materials through co-composting maintains their fertilization value in terms of improving plant growth. The co-composted biowastes also contribute to long-term soil C sequestration and reduction of bioavailability of heavy metals. PMID:26381784

  12. Flash Nanoprecipitation: Prediction and Enhancement of Particle Stability via Drug Structure

    PubMed Central

    2015-01-01

    Flash nanoprecipitation (FNP) can generate hydrophobic drug nanoparticles in ∼100 nm with a much higher drug loading (e.g., > 40 wt %) than traditional nanocarriers (e.g., < 20 wt %). This paper studies the effects of drug molecules on nanoparticle stability made via FNP and demonstrates that chemically bonding a drug compound (e.g., paclitaxel) with a cleavable hydrophobic moiety of organosilicate (e.g., triethoxysilicate) is able to enhance the particle size stability. A nonionic amphiphilic diblock copolymer, poly(lactic-co-glycolic acid)-block-poly(ethylene glycol) (PLGA-b-PEG), is used as a model surfactant to provide steric stabilization. The experiments here show that the lower the drug solubility in the aqueous medium, the more stable the particles in terms of Ostwald ripening, which are consistent with the prediction by the LSW theory. The initial particle size distribution is sufficiently narrow and of insignificance to Ostwald ripening. To correlate the particle stability with hydrophobicity, this study introduces the n-octanol/water partition coefficient (LogP), a hydrophobicity indication, into the FNP technique. A comparison of various drugs and their analogues shows that LogP of a drug is a better hydrophobicity indication than the solubility parameter (δ) and correlates well with the particle stability. Empirically, with ACDLogP > ∼12, nanoparticles have good stability; with ∼2 < ACDLogP < ∼9, nanoparticles show fast Ostwald ripening and interparticle recrystallization; with ACDLogP < ∼2, the drug is very likely difficult to form nanoparticles. This rule creates a quick way to predict particle stability for a randomly selected drug structure and helps to enable a fast preclinical drug screen. PMID:24484077

  13. Decreased aperture surface energy enhances electrical, mechanical, and temporal stability of suspended lipid membranes

    PubMed Central

    Bright, Leonard K.; Baker, Christopher A.; Agasid, Mark T.; Ma, Lin; Aspinwall, Craig A.

    2013-01-01

    The development of next-generation transmembrane protein-based biosensors relies heavily on the use of black lipid membranes (BLMs); however, electrical, mechanical, and temporal instability of BLMs pose a limiting challenge to biosensor development. In this work, micron-sized glass apertures were modified with silanes of different chain length and fluorine composition, including 3-cyanopropyldimethychlorosilane (CPDCS), ethyldimethylchlorosilane (EDCS), n-octyldimethylchlorosilane (ODCS), (tridecafluoro 1, 1, 2, 2-tetrahydrooctyl)dimethylchlorosilane (PFDCS) or (heptadecafluoro-1,1,2,2-tetrahydrodecyl)dimethylchlorosilane (PFDDCS) to explore the effect of substrate surface energy on BLM stability. Low energy silane-modified surfaces promoted enhanced lipid-substrate interactions that facilitate the formation of low-leakage, stable BLMs. The surface energies of silane-modified substrates were 30 ± 3, 16 ± 1, 14 ± 2, 11 ± 1 and 7.1 ± 2 mJ m−2 for CDCS, EDCS, ODCS, PFDCS and PFDDCS, respectively. Decreased surface energy directly correlated to improved electrical, mechanical, and temporal BLM stability. Amphiphobic perfluorinated surface modifiers yielded superior performance compared to traditional hydrocarbon modifiers in terms of stability and BLM formation, with only marginal effects on BLM membrane permeability. Leakage currents obtained for PFDCS and PFDDCS BLMs were elevated only 10-30%, though PFDDCS modification yielded > 5-fold increase in electrical stability as indicated by breakdown voltage (> 2000 mV vs. 418 ± 73 mV), and > 25-fold increase in mechanical stability as indicated by air-water transfers (> 50 vs. 2 ± 0.2) when compared to previously reported CPDCS modification. Importantly, the dramatically improved membrane stabilities were achieved with no deleterious effects on reconstituted ion channel function as evidenced by α-hemolysin activity. Thus, this approach provides a simple, low cost and broadly applicable alternative for BLM

  14. Flash nanoprecipitation: prediction and enhancement of particle stability via drug structure.

    PubMed

    Zhu, Zhengxi

    2014-03-01

    Flash nanoprecipitation (FNP) can generate hydrophobic drug nanoparticles in ∼ 100 nm with a much higher drug loading (e.g., > 40 wt %) than traditional nanocarriers (e.g., < 20 wt %). This paper studies the effects of drug molecules on nanoparticle stability made via FNP and demonstrates that chemically bonding a drug compound (e.g., paclitaxel) with a cleavable hydrophobic moiety of organosilicate (e.g., triethoxysilicate) is able to enhance the particle size stability. A nonionic amphiphilic diblock copolymer, poly(lactic-co-glycolic acid)-block-poly(ethylene glycol) (PLGA-b-PEG), is used as a model surfactant to provide steric stabilization. The experiments here show that the lower the drug solubility in the aqueous medium, the more stable the particles in terms of Ostwald ripening, which are consistent with the prediction by the LSW theory. The initial particle size distribution is sufficiently narrow and of insignificance to Ostwald ripening. To correlate the particle stability with hydrophobicity, this study introduces the n-octanol/water partition coefficient (LogP), a hydrophobicity indication, into the FNP technique. A comparison of various drugs and their analogues shows that LogP of a drug is a better hydrophobicity indication than the solubility parameter (δ) and correlates well with the particle stability. Empirically, with ACDLogP > ∼ 12, nanoparticles have good stability; with ∼ 2 < ACDLogP < ∼ 9, nanoparticles show fast Ostwald ripening and interparticle recrystallization; with ACDLogP < ∼ 2, the drug is very likely difficult to form nanoparticles. This rule creates a quick way to predict particle stability for a randomly selected drug structure and helps to enable a fast preclinical drug screen.

  15. Flash nanoprecipitation: prediction and enhancement of particle stability via drug structure.

    PubMed

    Zhu, Zhengxi

    2014-03-01

    Flash nanoprecipitation (FNP) can generate hydrophobic drug nanoparticles in ∼ 100 nm with a much higher drug loading (e.g., > 40 wt %) than traditional nanocarriers (e.g., < 20 wt %). This paper studies the effects of drug molecules on nanoparticle stability made via FNP and demonstrates that chemically bonding a drug compound (e.g., paclitaxel) with a cleavable hydrophobic moiety of organosilicate (e.g., triethoxysilicate) is able to enhance the particle size stability. A nonionic amphiphilic diblock copolymer, poly(lactic-co-glycolic acid)-block-poly(ethylene glycol) (PLGA-b-PEG), is used as a model surfactant to provide steric stabilization. The experiments here show that the lower the drug solubility in the aqueous medium, the more stable the particles in terms of Ostwald ripening, which are consistent with the prediction by the LSW theory. The initial particle size distribution is sufficiently narrow and of insignificance to Ostwald ripening. To correlate the particle stability with hydrophobicity, this study introduces the n-octanol/water partition coefficient (LogP), a hydrophobicity indication, into the FNP technique. A comparison of various drugs and their analogues shows that LogP of a drug is a better hydrophobicity indication than the solubility parameter (δ) and correlates well with the particle stability. Empirically, with ACDLogP > ∼ 12, nanoparticles have good stability; with ∼ 2 < ACDLogP < ∼ 9, nanoparticles show fast Ostwald ripening and interparticle recrystallization; with ACDLogP < ∼ 2, the drug is very likely difficult to form nanoparticles. This rule creates a quick way to predict particle stability for a randomly selected drug structure and helps to enable a fast preclinical drug screen. PMID:24484077

  16. Dynamical stability and assembly cooperativity of β-sheet amyloid oligomers--effect of polarization.

    PubMed

    Li, Yang; Ji, Changge; Xu, Weixin; Zhang, John Z H

    2012-11-15

    The soluble intermediate oligomers of amyloidogenic proteins are suspected to be more cytotoxic than the mature fibrils in neurodegenerative disorders. Here, the dynamic stability and assembly cooperativity of a model oligomer of human islet amyloid polypeptide (hIAPP) segments were explored by means of all-atom molecular dynamics (MD) simulations under different force fields including AMBER99SB, OPLS, and polarized protein-specific charge (PPC) model. Simulation results show that the dynamic stability of β-sheet oligomers is seriously impacted by electrostatic polarization. Without inclusion of polarization (simulation under standard AMBER and OPLS force field), the β-sheet oligomers are dynamically unstable during MD simulation. For comparison, simulation results under PPC give significantly more stable dynamical structures of the oligomers. Furthermore, calculation of electrostatic interaction energy between the neighboring β strands with an approximate polarizable method produces energetic evidence for cooperative assembly of β-strand oligomers. This result supports a picture of downhill-like cooperative assembly of β strands during fibrillation process. The present study demonstrates the critical role of polarization in dynamic stability and assembly cooperativity of β-sheet-rich amyloid oligomers.

  17. Network Firewall Dynamics and the Subsaturation Stabilization of HIV

    PubMed Central

    Khan, Bilal; Dombrowski, Kirk; Saad, Mohamed; McLean, Katherine; Friedman, Samuel

    2014-01-01

    In 2001, Friedman et al. conjectured the existence of a “firewall effect” in which individuals who are infected with HIV, but remain in a state of low infectiousness, serve to prevent the virus from spreading. To evaluate this historical conjecture, we develop a new graph-theoretic measure that quantifies the extent to which Friedman's firewall hypothesis(FH)holds in a risk network. We compute this new measure across simulated trajectories of a stochastic discrete dynamical system that models a social network of 25,000 individuals engaging in risk acts over a period of 15 years. The model's parameters are based on analyses of data collected in prior studies of the real-world risk networks of people who inject drugs (PWID) in New York City. Analysis of system trajectories reveals the structural mechanisms by which individuals with mature HIV infections tend to partition the network into homogeneous clusters (with respect to infection status) and how uninfected clusters remain relatively stable (with respect to infection status) over long stretches of time. We confirm the spontaneous emergence of network firewalls in the system and reveal their structural role in the nonspreading of HIV. PMID:25083120

  18. Network Firewall Dynamics and the Subsaturation Stabilization of HIV.

    PubMed

    Khan, Bilal; Dombrowski, Kirk; Saad, Mohamed; McLean, Katherine; Friedman, Samuel

    2013-01-01

    In 2001, Friedman et al. conjectured the existence of a "firewall effect" in which individuals who are infected with HIV, but remain in a state of low infectiousness, serve to prevent the virus from spreading. To evaluate this historical conjecture, we develop a new graph-theoretic measure that quantifies the extent to which Friedman's firewall hypothesis(FH)holds in a risk network. We compute this new measure across simulated trajectories of a stochastic discrete dynamical system that models a social network of 25,000 individuals engaging in risk acts over a period of 15 years. The model's parameters are based on analyses of data collected in prior studies of the real-world risk networks of people who inject drugs (PWID) in New York City. Analysis of system trajectories reveals the structural mechanisms by which individuals with mature HIV infections tend to partition the network into homogeneous clusters (with respect to infection status) and how uninfected clusters remain relatively stable (with respect to infection status) over long stretches of time. We confirm the spontaneous emergence of network firewalls in the system and reveal their structural role in the nonspreading of HIV. PMID:25083120

  19. Dynamics and Kinetics Study of "In-Water" Chemical Reactions by Enhanced Sampling of Reactive Trajectories.

    PubMed

    Zhang, Jun; Yang, Y Isaac; Yang, Lijiang; Gao, Yi Qin

    2015-11-12

    High potential energy barriers and engagement of solvent coordinates set challenges for in silico studies of chemical reactions, and one is quite commonly limited to study reactions along predefined reaction coordinate(s). A systematic protocol, QM/MM MD simulations using enhanced sampling of reactive trajectories (ESoRT), is established to quantitatively study chemical transitions in complex systems. A number of trajectories for Claisen rearrangement in water and toluene were collected and analyzed, respectively. Evidence was found that the bond making and breaking during this reaction are concerted processes in solutions, preferentially through a chairlike configuration. Water plays an important dynamic role that helps stabilize the transition sate, and the dipole-dipole interaction between water and the solute also lowers the transition barrier. The calculated rate coefficient is consistent with the experimental measurement. Compared with water, the reaction pathway in toluene is "narrower" and the reaction rate is slower by almost three orders of magnitude due to the absence of proper interactions to stabilize the transition state. This study suggests that the "in-water" nature of the Claisen rearrangement in aqueous solution influences its thermodynamics, kinetics, as well as dynamics.

  20. Stability and lattice dynamics of SiO2 cristobalite

    NASA Astrophysics Data System (ADS)

    Coh, Sinisa; Vanderbilt, David

    2008-03-01

    Among the phases of SiO2 are alpha and beta cristobalite. Despite early indications that the higher-temperature beta phase might be cubic (Fd3m), it is now accepted that it is in fact tetragonal (I42d), and that the experiments suggesting a cubic structure were averaging spatially or dynamically over tetragonal domains. Recently, Zhang and Scott (J. Phys. Cond.Matt. 19, 275201) suggested that the lower-temperature alpha phase, widely accepted to be tetragonal (P41212), might be an artifact in a similar way. With this motivation we investigate the energy landscape in the vicinity of cristobalite phases using first-principles calculations. We use the ABINIT implementation of density-functional theory in a plane-wave pseudopotential framework. We find that both the P41212 alpha and I42d beta phases are local minima, thus reinforcing that the identification of the alpha phase as belonging to the P41212 structure. We compute the frequencies of phonon modes at high-symmetry k-points in both structures and compare with experiment. We also identify a minimum-energy path connecting the alpha and beta phases through an intermediate orthorhombic phase (P212121), and find a surprisingly low barrier of ˜5,eV per formula unit. We note that a simple rigid-unit mode picture gives a good rough description of these energetics, and we map out the minimum-energy path in the space of rigid unit rotations in a physically insightful way.

  1. Effect of pH and penetration enhancers on cysteamine stability and trans-corneal transport.

    PubMed

    Pescina, Silvia; Carra, Federica; Padula, Cristina; Santi, Patrizia; Nicoli, Sara

    2016-10-01

    Ocular cystinosis is a rare metabolic disorder characterized by the presence of insoluble cystine crystals inside the corneal stroma, with consequent photophobia, keratopathies and frequent corneal erosions. The current therapy consists in the lifetime ophthalmic administration of cysteamine, drug characterized by extremely high hydrophilicity, low molecular weight (77g/mol), and easy oxidization to disulfide. Ocular delivery of cysteamine is very challenging, for its poor permeability and stability in solution. The purpose of the present paper was to study the impact of formulation pH and composition on (1) the trans-corneal delivery and (2) the stability in solution of cysteamine, with particular focus on the use of alpha-cyclodextrin (α-CD), benzalkonium chloride (BAC) and disodium edetate (EDTA). Permeation experiments were performed ex vivo through freshly excised porcine cornea; stability was evaluated for six months at -20°, +4° and +25°C; irritation potential was evaluated using HET-CAM assay. The results showed that cysteamine trans-corneal diffusion is strictly dependent on both pH (7.4 preferred to 4.2) and buffering capacity, that negatively impact on the permeation; EDTA did not enhance the trans-corneal diffusion of cysteamine neither at pH 7.4 nor at pH 4.2, while benzalkonium chloride (BAC), antimicrobial agent present within commercial eye-drops, significantly enhanced it. Notably, α-CD was able to promote the trans-corneal diffusion of cysteamine and, at a 5.5%, a 4-fold higher penetration compared to the BAC-containing formulation was obtained. EDTA and acidic pH demonstrated to be essential for cysteamine stability. The formulation obtained by combining α-CD and EDTA was characterized by significant permeation, good stability profile, and no irritation potential, even if the tolerability should be further confirmed by in vivo test. PMID:27395395

  2. Enhanced Performance and Stability in Polymer Photovoltaic Cells Using Ultraviolet-Treated PEDOT:PSS

    NASA Astrophysics Data System (ADS)

    Xu, Xue-Jian; Yang, Li-Ying; Tian, Hui; Qin, Wen-Jing; Yin, Shou-Gen; Zhang, Fengling

    2013-07-01

    We investigate the effects of ultraviolet (UV) irradiation treatment with varying irradiation intensities for different treatment times of poly(3, 4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) film on the performance and stability of polymer solar cells (PSCs) based on regioregular poly(3-hexylthiophene) (P3HT) and methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM) blend. Ultraviolet-visible transmission spectra, x-ray photoelectron spectroscopy, contact angle measurement, atomic force microscopy and the Kelvin probe method are conducted to characterize the UV-treated PEDOT:PSS film. The results demonstrate that UV treatment can improve the power conversion efficiency (PCE) and stability of PSCs effectively. The best performance is achieved under 1200 μW/cm2 UV treatment for 50 min. Compared to the control device, the optimized device exhibits enhanced performance with a Voc of 0.59 V, Jsc of 12.3 mA/cm2, fill factor of 51%, and PCE of 3.64%, increased by 3.5%, 33%, 8.7% and 50%, respectively. The stability of the PSCs is enhanced by 2.5 times simply through the UV treatment on the PEDOT:PSS buffer layer. The improvement in the device performance and stability is attributed to the improvement in the wettability property and the increase in the work function of the PEDOT:PSS film by UV treatment, while the impact of UV treatment on the transparency of the PEDOT:PSS film is negligible. The strategy of using UV treatment to improve device performance and stability is attractive due to its simplicity, cost-effectiveness, and because it is suitable for large-scale commercial production.

  3. Perturbation analysis of 6DoF flight dynamics and passive dynamic stability of hovering fruit fly Drosophila melanogaster.

    PubMed

    Gao, Na; Aono, Hikaru; Liu, Hao

    2011-02-01

    Insects exhibit exquisite control of their flapping flight, capable of performing precise stability and steering maneuverability. Here we develop an integrated computational model to investigate flight dynamics of insect hovering based on coupling the equations of 6 degree of freedom (6DoF) motion with the Navier-Stokes (NS) equations. Unsteady aerodynamics is resolved by using a biology-inspired dynamic flight simulator that integrates models of realistic wing-body morphology and kinematics, and a NS solver. We further develop a dynamic model to solve the rigid body equations of 6DoF motion by using a 4th-order Runge-Kutta method. In this model, instantaneous forces and moments based on the NS-solutions are represented in terms of Fourier series. With this model, we perform a systematic simulation-based analysis on the passive dynamic stability of a hovering fruit fly, Drosophila melanogaster, with a specific focus on responses of state variables to six one-directional perturbation conditions during latency period. Our results reveal that the flight dynamics of fruit fly hovering does not have a straightforward dynamic stability in a conventional sense that perturbations damp out in a manner of monotonous convergence. However, it is found to exist a transient interval containing an initial converging response observed for all the six perturbation variables and a terminal instability that at least one state variable subsequently tends to diverge after several wing beat cycles. Furthermore, our results illustrate that a fruit fly does have sufficient time to apply some active mediation to sustain a steady hovering before losing body attitudes. PMID:21093456

  4. Stability and dynamical properties of material flow systems on random networks

    NASA Astrophysics Data System (ADS)

    Anand, K.; Galla, T.

    2009-04-01

    The theory of complex networks and of disordered systems is used to study the stability and dynamical properties of a simple model of material flow networks defined on random graphs. In particular we address instabilities that are characteristic of flow networks in economic, ecological and biological systems. Based on results from random matrix theory, we work out the phase diagram of such systems defined on extensively connected random graphs, and study in detail how the choice of control policies and the network structure affects stability. We also present results for more complex topologies of the underlying graph, focussing on finitely connected Erdös-Réyni graphs, Small-World Networks and Barabási-Albert scale-free networks. Results indicate that variability of input-output matrix elements, and random structures of the underlying graph tend to make the system less stable, while fast price dynamics or strong responsiveness to stock accumulation promote stability.

  5. Stability and dynamics of serpentinite layer in subduction zone

    NASA Astrophysics Data System (ADS)

    Hilairet, Nadege; Reynard, Bruno

    2009-02-01

    The hydrous phyllosilicate serpentines have a strong influence on subduction zone dynamics because of their high water content and low strength at shallow and intermediate depths. In the absence of data, Newtonian rheology of serpentinites has been assumed in numerical models yet experimental data show that serpentine rheology is best described by a power law rheology recently determined in subduction zone conditions [Hilairet, N., et al., 2007. High-pressure creep of serpentine, interseismic deformation, and initiation of subduction. Science, 318(5858): 1910-1913]. Using a simple 1D model of a serpentinized channel and - as opposed to previous models - in this power law rheology, we examine the influence of channel thickness, temperature and subduction angle on serpentine flow driven by density contrast (serpentinization degree) with the surroundings. At temperatures of 200-500 °C relevant to intermediate depths a fully serpentinized channel is unlikely to be thicker than 2-3 km. For channel thicknesses of 2 km upward velocities are comparable to those using a constant viscosity of 10 18 Pa s. The velocity profile using power law rheology shows shear zones at the edges of the channel and a low strain rate region at its centre consistent with the frequent observation of weakly deformed HP-rocks. Upward velocities estimated for channels 1 to 3 km thick are comparable to the serpentinization rates for maximum estimates of fluid velocities within shear zones in the literature. Competition between the upward flow and serpentinization may lead to intermittent behavior with alternating growth periods and thinning by exhumation. At shallower levels the thickness allowed for a channel may be up to ~ 8-10 km if the rheology has a higher dependence on stress. We therefore propose that the exhumation of HP oceanic units in serpentinite channels is organized in two levels, the deepest and fastest motion being driven by density contrast with the surrounding mantle and the

  6. Robustness, stability and efficiency of phage lambda genetic switch: dynamical structure analysis.

    PubMed

    Zhu, X-M; Yin, L; Hood, L; Ao, P

    2004-12-01

    Based on the dynamical structure theory for complex networks recently developed by one of us and on the physical-chemical models for gene regulation, developed by Shea and Ackers in the 1980's, we formulate a direct and concise mathematical framework for the genetic switch controlling phage lambda life cycles, which naturally includes the stochastic effect. The dynamical structure theory states that the dynamics of a complex network is determined by its four elementary components: The dissipation (analogous to degradation), the stochastic force, the driving force determined by a potential, and the transverse force. The potential may be interpreted as a landscape for the phage development in terms of attractive basins, saddle points, peaks and valleys. The dissipation gives rise to the adaptivity of the phage in the landscape defined by the potential: The phage always has the tendency to approach the bottom of the nearby attractive basin. The transverse force tends to keep the network on the equal-potential contour of the landscape. The stochastic fluctuation gives the phage the ability to search around the potential landscape by passing through saddle points. With molecular parameters in our model fixed primarily by the experimental data on wild-type phage and supplemented by data on one mutant, our calculated results on mutants agree quantitatively with the available experimental observations on other mutants for protein number, lysogenization frequency, and a lysis frequency in lysogen culture. The calculation reproduces the observed robustness of the phage lambda genetic switch. This is the first mathematical description that successfully represents such a wide variety of major experimental phenomena. Specifically, we find: (1) The explanation for both the stability and the efficiency of phage lambda genetic switch is the exponential dependence of saddle point crossing rate on potential barrier height, a result of the stochastic motion in a landscape; and (2

  7. Enhanced Performance of Plasmid DNA Polyplexes Stabilized by a Combination of Core Hydrophobicity and Surface PEGylation

    PubMed Central

    Adolph, Elizabeth J.; Nelson, Christopher E.; Werfel, Thomas A.; Guo, Ruijing; Davidson, Jeffrey M.; Duvall, Craig L.

    2014-01-01

    Nonviral gene therapy has high potential for safely promoting tissue restoration and for treating various genetic diseases. One current limitation is that conventional transfection reagents such as polyethylenimine (PEI) form electrostatically stabilized plasmid DNA (pDNA) polyplexes with poor colloidal stability. In this study, a library of poly(ethylene glycol-b-(dimethylaminoethyl methacrylate-co-butyl methacrylate)) [poly(EG-b-(DMAEMA-co-BMA))] polymers were synthesized and screened for improved colloidal stability and nucleic acid transfection following lyophilization. When added to pDNA in the appropriate pH buffer, the DMAEMA moieties initiate formation of electrostatic polyplexes that are internally stabilized by hydrophobic interactions of the core BMA blocks and sterically stabilized against aggregation by a PEG corona. The BMA content was varied from 0% to 60% in the second polymer block in order to optimally tune the balance of electrostatic and hydrophobic interactions in the polyplex core, and polymers with 40 and 50 mol% BMA achieved the highest transfection efficiency. Diblock copolymers were more stable than PEI in physiologic buffers. Consequently, diblock copolymer polyplexes aggregated more slowly and followed a reaction-limited colloidal aggregation model, while fast aggregation of PEI polyplexes was governed by a diffusion-limited model. Polymers with 40% BMA did not aggregate significantly after lyophilization and produced up to 20-fold higher transfection efficiency than PEI polyplexes both before and after lyophilization. Furthermore, poly(EG-b-(DMAEMA-co-BMA)) polyplexes exhibited pH-dependent membrane disruption in a red blood cell hemolysis assay and endosomal escape as observed by confocal microscopy.Lyophilized polyplexes made with the lead candidate diblock copolymer (40% BMA) also successfully transfected cells in vitro following incorporation into gas-foamed polymeric scaffolds. In summary, the enhanced colloidal stability

  8. Validation of enhanced stabilization of municipal solid waste under controlled leachate recirculation using FTIR and XRD.

    PubMed

    Sethi, Sapna; Kothiyal, N C; Nema, Arvind K

    2012-07-01

    Leachate recirculation at neutral PH accompanied with buffer/nutrients addition has been used successfully in earlier stabilization of municipal solid waste in bioreactor landfills. In the present study, efforts were made to enhance the stabilization rate of municipal solid waste (MSW) and organic solid waste (OSW) in simulated landfill bioreactors by controlling the pH of recirculated leachate towards slightly alkaline side in absence of additional buffer and nutrients addition. Enhanced stabilization in waste samples was monitored with the help of analytical tools like Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Diffraction (XRD). Predominance of bands assigned to inorganic compounds and comparatively lower intensities of bands for organic compounds in the FTIR spectra of waste samples degraded with leachate recirculation under controlled pH confirmed higher rate of biodegradation and mineralization of waste than the samples degraded without controlled leachate recirculation. XRD spectra also confirmed to a greater extent of mineralization in the waste samples degraded under leachate recirculation with controlled pH. Comparison of XRD spectra of two types of wastes pointed out higher degree of mineralization in organic solid waste as compared to municipal solid waste. PMID:24749191

  9. Intestine-Specific Delivery of Hydrophobic Bioactives from Oxidized Starch Microspheres with an Enhanced Stability.

    PubMed

    Wang, Shanshan; Chen, Yuying; Liang, Hao; Chen, Yiming; Shi, Mengxuan; Wu, Jiande; Liu, Xianwu; Li, Zuseng; Liu, Bin; Yuan, Qipeng; Li, Yuan

    2015-10-01

    An intestine-specific delivery system for hydrophobic bioactives with improved stability was developed. It consists of oxidized potato starch polymers, where the carboxyl groups were physically cross-linked via ferric ions. The model hydrophobic ingredients (β-carotene) were incorporated inside the starch microspheres via a double-emulsion method. Confocal laser scanning microscopy images showed that β-carotene were distributed homogeneously in the inner oil phase of the starch microspheres. The negative value of the ζ-potential of microspheres increased with increasing pH and decreasing ionic strength. In vitro release experiments showed that the microspheres were stable at acidic stomach conditions (pH < 2), whereas at neutral intestinal conditions (pH 7.0), they rupture to release the loaded β-carotene. The 1,1-diphenyl-2-picrylhydrazyl radical, 2,2-diphenyl-1-(2,4,6-trinitriphenyl), scavenging activity results suggested that microsphere-encapsulated β-carotene had an improved activity after thermal treatment at 80 °C. The storage stability of encapsulated β-carotene at room temperature was also enhanced. The starch microspheres showed potential as intestine-specific carriers with an enhanced stability.

  10. Chemical stability of plasmon-active silver tips for tip-enhanced Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Kalbacova, Jana; Rodriguez, Raul D.; Desale, Vivek; Schneider, Maximilian; Amin, Ihsan; Jordan, Rainer; Zahn, Dietrich R. T.

    2015-01-01

    Silver nanostructures are used in tip- and surface-enhanced Raman spectroscopy due to their high electric field enhancement over almost the entire visible spectral range. However, the low chemical stability of silver, compared to other noble metals, promotes silver sulfide and sulfate formation which decreases its plasmonic activity. This is why silver tips are usually prepared on the same day of the experiments or are disregarded in favour of gold that is chemically more stable. Since silver degradation cannot be avoided, we hypothesized that a protection layer may be able to minimize or control degradation. In this contribution, we report the successful preparation of 4-biphenylthiol and 4'-nitro-4-biphenylthiol self-assembled monolayers on silver tips in order to protect them against tarnishing and to investigate the effect on the life-time of the plasmonic activity. The electrochemically etched wire surface was probed via Raman spectroscopy and scanning electron microscopy. The best long term stability and resistance against corrosion was shown by a monolayer of 4-biphenylthiol formed from dimethylformamide which did not display any degradation of the metallic tip during the observed period. Here, we demonstrate an easy and straightforward approach towards increasing the chemical stability of silver TERS-active probes.

  11. Dual enhancement of electroluminescence efficiency and operational stability by rapid upconversion of triplet excitons in OLEDs

    PubMed Central

    Furukawa, Taro; Nakanotani, Hajime; Inoue, Munetomo; Adachi, Chihaya

    2015-01-01

    Recently, triplet harvesting via a thermally activated delayed fluorescence (TADF) process has been established as a realistic route for obtaining ultimate internal electroluminescence (EL) quantum efficiency in organic light-emitting diodes (OLEDs). However, the possibility that the rather long transient lifetime of the triplet excited states would reduce operational stability due to an increased chance for unwarranted chemical reactions has been a concern. Herein, we demonstrate dual enhancement of EL efficiency and operational stability in OLEDs by employing a TADF molecule as an assistant dopant and a fluorescent molecule as an end emitter. The proper combination of assistant dopant and emitter molecules realized a “one-way” rapid Förster energy transfer of singlet excitons from TADF molecules to fluorescent emitters, reducing the number of cycles of intersystem crossing (ISC) and reverse ISC in the TADF molecules and resulting in a significant enhancement of operational stability compared to OLEDs with a TADF molecule as the end emitter. In addition, we found that the presence of this rapid energy transfer significantly suppresses singlet-triplet annihilation. Using this finely-tuned rapid triplet-exciton upconversion scheme, OLED performance and lifetime was greatly improved. PMID:25673259

  12. Silica Cladding of Ag Nanoparticles for High Stability and Surface-Enhanced Raman Spectroscopy Performance

    NASA Astrophysics Data System (ADS)

    Zhao, Miaomiao; Guo, Hao; Liu, Wenyao; Tang, Jun; Wang, Lei; Zhang, Binzhen; Xue, Chenyang; Liu, Jun; Zhang, Wendong

    2016-09-01

    For high-precision biochemical sensing, surface-enhanced Raman spectroscopy (SERS) has been demonstrated to be a highly sensitive spectroscopic analytical method and Ag is considered to be the best material for SERS performance. Due to the high surface activity of Ag nanoparticles, the high stability of Ag nanostructures, especially in moist environments, is one of the key issues that need to be solved. A method for silica (SiO2) cladding of Ag nanoparticles (NPs) is demonstrated here for high sensitivity and long-term stability when putted in aqueous solution. The chemically inert, transparent, hydrophilic, and bio-compatible SiO2 surface acts as the protection layer for the Ag nanoparticles, which can also enhance the Raman intensity to a certain extent. In our study, the Ag@SiO2 core-shell substrate can detect crystal violet solutions with molar concentrations down to 10-12 M. After 24 h of immersion, the reduction in Raman scattering intensity is about 85 % for sole Ag NP films, compared to 12 % for the Ag coated with a 10-nm SiO2 layer. This thickness was found to be optimum for Ag@SiO2 core-shell substrates with long-term stability and high SERS activity.

  13. Validation of enhanced stabilization of municipal solid waste under controlled leachate recirculation using FTIR and XRD.

    PubMed

    Sethi, Sapna; Kothiyal, N C; Nema, Arvind K

    2012-07-01

    Leachate recirculation at neutral PH accompanied with buffer/nutrients addition has been used successfully in earlier stabilization of municipal solid waste in bioreactor landfills. In the present study, efforts were made to enhance the stabilization rate of municipal solid waste (MSW) and organic solid waste (OSW) in simulated landfill bioreactors by controlling the pH of recirculated leachate towards slightly alkaline side in absence of additional buffer and nutrients addition. Enhanced stabilization in waste samples was monitored with the help of analytical tools like Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Diffraction (XRD). Predominance of bands assigned to inorganic compounds and comparatively lower intensities of bands for organic compounds in the FTIR spectra of waste samples degraded with leachate recirculation under controlled pH confirmed higher rate of biodegradation and mineralization of waste than the samples degraded without controlled leachate recirculation. XRD spectra also confirmed to a greater extent of mineralization in the waste samples degraded under leachate recirculation with controlled pH. Comparison of XRD spectra of two types of wastes pointed out higher degree of mineralization in organic solid waste as compared to municipal solid waste.

  14. Silica Cladding of Ag Nanoparticles for High Stability and Surface-Enhanced Raman Spectroscopy Performance.

    PubMed

    Zhao, Miaomiao; Guo, Hao; Liu, Wenyao; Tang, Jun; Wang, Lei; Zhang, Binzhen; Xue, Chenyang; Liu, Jun; Zhang, Wendong

    2016-12-01

    For high-precision biochemical sensing, surface-enhanced Raman spectroscopy (SERS) has been demonstrated to be a highly sensitive spectroscopic analytical method and Ag is considered to be the best material for SERS performance. Due to the high surface activity of Ag nanoparticles, the high stability of Ag nanostructures, especially in moist environments, is one of the key issues that need to be solved. A method for silica (SiO2) cladding of Ag nanoparticles (NPs) is demonstrated here for high sensitivity and long-term stability when putted in aqueous solution. The chemically inert, transparent, hydrophilic, and bio-compatible SiO2 surface acts as the protection layer for the Ag nanoparticles, which can also enhance the Raman intensity to a certain extent. In our study, the Ag@SiO2 core-shell substrate can detect crystal violet solutions with molar concentrations down to 10(-12) M. After 24 h of immersion, the reduction in Raman scattering intensity is about 85 % for sole Ag NP films, compared to 12 % for the Ag coated with a 10-nm SiO2 layer. This thickness was found to be optimum for Ag@SiO2 core-shell substrates with long-term stability and high SERS activity. PMID:27637895

  15. TCTP regulates spindle microtubule dynamics by stabilizing polar microtubules during mouse oocyte meiosis.

    PubMed

    Jeon, Hyuk-Joon; You, Seung Yeop; Park, Yong Seok; Chang, Jong Wook; Kim, Jae-Sung; Oh, Jeong Su

    2016-04-01

    Dynamic changes in spindle structure and function are essential for maintaining genomic integrity during the cell cycle. Spindle dynamics are highly dependent on several microtubule-associated proteins that coordinate the dynamic behavior of microtubules, including microtubule assembly, stability and organization. Here, we show that translationally controlled tumor protein (TCTP) is a novel microtubule-associated protein that regulates spindle dynamics during meiotic maturation. TCTP was expressed and widely distributed in the cytoplasm with strong enrichment at the spindle microtubules during meiosis. TCTP was found to be phosphorylated during meiotic maturation, and was exclusively localized to the spindle poles. Knockdown of TCTP impaired spindle organization without affecting chromosome alignment. These spindle defects were mostly due to the destabilization of the polar microtubules. However, the stability of kinetochore microtubules attached to chromosomes was not affected by TCTP knockdown. Overexpression of a nonphosphorylable mutant of TCTP disturbed meiotic maturation, stabilizing the spindle microtubules. In addition, Plk1 was decreased by TCTP knockdown. Taken together, our results demonstrate that TCTP is a microtubule-associating protein required to regulate spindle microtubule dynamics during meiotic maturation in mouse oocytes.

  16. Enhancement of the robustness on dynamic speckle laser numerical analysis

    NASA Astrophysics Data System (ADS)

    Cardoso, R. R.; Braga, R. A.

    2014-12-01

    When a dynamic process occurs in a material under laser illumination the phenomenon that appears is named dynamic laser speckle, or biospeckle laser (BSL) if we have a biological material. The work with biological material and its dispersion of light brings considerable complexity, and the way we can deal with that complex outputs is based on a sophisticated analysis of the images associated to statistical approaches. One of the most known numerical analysis of the BSL has been applied in many applications, and it is named Inertia Moment, however its outputs have great coefficients of variation, most of the time attributed to the variability of the biological material. A change in the inertia moment method was done and the Absolute Value of the Differences (AVD) was presented as an alternative to reduce the variations and to follow a broader range of frequencies than before. However, it was not enough concerning with the variability of the outputs. This study aimed to improve the BSL technique in order to enhance the robustness of the numerical method known as Inertia Moment (IM) and improve the absolute value of the differences reducing even more its coefficient of variation by means of changes in the normalization provided in both methods. The new normalization was tested in simulated data, as well as in real data. The results showed the improvements of the methods, IM and AVD, with the reduction of the coefficients of variation of the activity in the outputs, increasing the robustness of the analysis.

  17. Uncertainty estimation in dynamic contrast-enhanced MRI.

    PubMed

    Garpebring, Anders; Brynolfsson, Patrik; Yu, Jun; Wirestam, Ronnie; Johansson, Adam; Asklund, Thomas; Karlsson, Mikael

    2013-04-01

    Using dynamic contrast-enhanced MRI (DCE-MRI), it is possible to estimate pharmacokinetic (PK) parameters that convey information about physiological properties, e.g., in tumors. In DCE-MRI, errors propagate in a nontrivial way to the PK parameters. We propose a method based on multivariate linear error propagation to calculate uncertainty maps for the PK parameters. Uncertainties in the PK parameters were investigated for the modified Kety model. The method was evaluated with Monte Carlo simulations and exemplified with in vivo brain tumor data. PK parameter uncertainties due to noise in dynamic data were accurately estimated. Noise with standard deviation up to 15% in the baseline signal and the baseline T1 map gave estimated uncertainties in good agreement with the Monte Carlo simulations. Good agreement was also found for up to 15% errors in the arterial input function amplitude. The method was less accurate for errors in the bolus arrival time with disagreements of 23%, 32%, and 29% for K(trans) , ve , and vp , respectively, when the standard deviation of the bolus arrival time error was 5.3 s. In conclusion, the proposed method provides efficient means for calculation of uncertainty maps, and it was applicable to a wide range of sources of uncertainty.

  18. Cross-linking oppositely charged oil-in-water emulsions to enhance heteroaggregate stability.

    PubMed

    Maier, Christiane; Oechsle, Anja M; Weiss, Jochen

    2015-11-01

    The formation and subsequent enzymatic and chemical cross-linking of heteroaggregates from oppositely charged oil-in-water (O/W) emulsions was investigated. For this purpose, 10% (w/w) oil-in-water emulsions (d43<1 μm) were prepared at pH 4 using a positively charged emulsifier (Nα-lauroyl-L-arginine ethyl ester (LAE), cold water fish gelatin, or whey protein isolate) or a negatively charged one (sugar beet pectin or Quillaja saponins). The oppositely charged emulsions were then combined at a volume ratio of 1:1 and treated with laccase or glutaraldehyde in order to further stabilize the electrostatically attached aggregates by covalently cross-linking the oppositely charged membranes. Emulsions and heteroaggregates were characterized by their rheological properties, their surface charge, particle size distribution, and microstructure using dynamic and static light scattering as well as confocal laser scanning microscopy. Prior to cross-linking, the emulsifiers' stabilization mechanism were found to greatly influence the formation of heteroaggregates. Laccase treatment (1.34 mU/mL) increased aggregate expansion by ca. 30% for the combined emulsions stabilized by Quillaja saponins/whey protein isolate, while combined Quillaja saponins/fish gelatin stabilized emulsions remained unaffected. When combined emulsions were treated with 50mM glutaraldehyde, aggregate size significantly increased 2- and 3-fold, respectively. Thus, our study provides novel insights into the enzymatic and chemical cross-linking of heteroaggregates composed of oppositely charged O/W emulsions.

  19. Cross-linking oppositely charged oil-in-water emulsions to enhance heteroaggregate stability.

    PubMed

    Maier, Christiane; Oechsle, Anja M; Weiss, Jochen

    2015-11-01

    The formation and subsequent enzymatic and chemical cross-linking of heteroaggregates from oppositely charged oil-in-water (O/W) emulsions was investigated. For this purpose, 10% (w/w) oil-in-water emulsions (d43<1 μm) were prepared at pH 4 using a positively charged emulsifier (Nα-lauroyl-L-arginine ethyl ester (LAE), cold water fish gelatin, or whey protein isolate) or a negatively charged one (sugar beet pectin or Quillaja saponins). The oppositely charged emulsions were then combined at a volume ratio of 1:1 and treated with laccase or glutaraldehyde in order to further stabilize the electrostatically attached aggregates by covalently cross-linking the oppositely charged membranes. Emulsions and heteroaggregates were characterized by their rheological properties, their surface charge, particle size distribution, and microstructure using dynamic and static light scattering as well as confocal laser scanning microscopy. Prior to cross-linking, the emulsifiers' stabilization mechanism were found to greatly influence the formation of heteroaggregates. Laccase treatment (1.34 mU/mL) increased aggregate expansion by ca. 30% for the combined emulsions stabilized by Quillaja saponins/whey protein isolate, while combined Quillaja saponins/fish gelatin stabilized emulsions remained unaffected. When combined emulsions were treated with 50mM glutaraldehyde, aggregate size significantly increased 2- and 3-fold, respectively. Thus, our study provides novel insights into the enzymatic and chemical cross-linking of heteroaggregates composed of oppositely charged O/W emulsions. PMID:26298085

  20. Variable prey development time suppresses predator-prey cycles and enhances stability.

    PubMed

    Cronin, James T; Reeve, John D; Xu, Dashun; Xiao, Mingqing; Stevens, Heidi N

    2016-03-01

    Although theoretical models have demonstrated that predator-prey population dynamics can depend critically on age (stage) structure and the duration and variability in development times of different life stages, experimental support for this theory is non-existent. We conducted an experiment with a host-parasitoid system to test the prediction that increased variability in the development time of the vulnerable host stage can promote interaction stability. Host-parasitoid microcosms were subjected to two treatments: Normal and High variance in the duration of the vulnerable host stage. In control and Normal-variance microcosms, hosts and parasitoids exhibited distinct population cycles. In contrast, insect abundances were 18-24% less variable in High- than Normal-variance microcosms. More significantly, periodicity in host-parasitoid population dynamics disappeared in the High-variance microcosms. Simulation models confirmed that stability in High-variance microcosms was sufficient to prevent extinction. We conclude that developmental variability is critical to predator-prey population dynamics and could be exploited in pest-management programs.

  1. Aeromechanical stability analysis of a multirotor vehicle with application to hybrid heavy lift helicopter dynamics

    NASA Technical Reports Server (NTRS)

    Venkatesan, C.; Friedmann, P. P.

    1984-01-01

    The Hybrid Heavy Lift Helicopter (HHLH) is a potential candidate vehicle aimed at providing heavy lift capability at low cost. This vehicle consists of a buoyant envelope attached to a supporting structure. Four rotor systems are also attached to the supporting structure. Nonlinear equations of motion capable of modeling the dynamics of this multi-rotor/support frame/vehicle system have been developed and used to study the fundamental aeromechanical stability characteristics of this class of vehicles. The mechanism of coupling between the blades, supporting structure and rigid body modes is identified and the effect of buoyancy ratio (buoyant lift/total weight) on the vehicle dynamics is studied. It is shown that dynamics effects have a major role in the design of such vehicles. The analytical model developed is also useful for studying the aeromechanical stability of single rotor and tandem rotor coupled rotor/fuselage systems.

  2. Enhanced stability of low fouling zwitterionic polymer brushes in seawater with diblock architecture.

    PubMed

    Quintana, Robert; Gosa, Maria; Jańczewski, Dominik; Kutnyanszky, Edit; Vancso, G Julius

    2013-08-27

    The successful implementation of zwitterionic polymeric brushes as antifouling materials for marine applications is conditioned by the stability of the polymer chain and the brush-anchoring segment in seawater. Here we demonstrate that robust, antifouling, hydrophilic polysulfobetaine-based brushes with diblock architecture can be fabricated by atom-transfer radical polymerization (ATRP) using initiator-modified surfaces. Sequential living-type polymerization of hydrophobic styrene or methyl methacrylate and commercially available hydrophilic sulfobetaine methacrylamide (SBMAm) monomer is employed. Stability enhancement is accomplished by protecting the siloxane anchoring bond of brushes on the substrate, grafted from silicon oxide surfaces. The degradation of unprotected PSBMAm brushes is clearly evident after a 3 month immersion challenge in sterilized artificial seawater. Ellipsometry and atomic force microscopy (AFM) measurements are used to follow changes in coating thickness and surface morphology. Comparative stability results indicate that surface-tethered poly(methyl methacrylate) and polystyrene hydrophobic blocks substantially improve the stability of zwitterionic brushes in an artificial marine environment. In addition, differences between the hydration of zwitterionic brushes in fresh and salt water are discussed to provide a better understanding of hydration and degradation processes with the benefit of improved design of polyzwitterionic coatings. PMID:23876125

  3. Enhanced stability of uncemented canine femoral components by bone ingrowth into the porous coatings.

    PubMed

    Jasty, M; Bragdon, C R; Zalenski, E; O'Connor, D; Page, A; Harris, W H

    1997-01-01

    The following questions were answered in this study: (1) What is the initial stability of proximally porous-coated canine femoral components? (2) Does bone ingrowth occur under these conditions? (3) Is the stability enhanced by tissue ingrowth in vivo? The stability of proximally porous-coated femoral components of canine total hip arthroplasties after 6 months to 2 years of in vivo service in dogs was measured in vitro using displacement transducers under loads simulating canine midstance. This was compared with the stability of identical components under the same loading conditions immediately after implantation in vitro in the contralateral femurs. The femurs were then sectioned and bone ingrowth into the porous coatings was quantified. The results showed that immediately after implantation the implants can move as much as 50 microns, but that the bone ingrowth into porous coatings of canine femoral components can occur even under such conditions. These data also suggested that the relative motion existing at the time of insertion can be reduced to very small amounts (< 10 microns) by bone ingrowth. PMID:9021510

  4. The role of glycerol and phosphatidylcholine in solubilizing and enhancing insulin stability in reverse hexagonal mesophases.

    PubMed

    Amar-Yuli, Idit; Azulay, Doron; Mishraki, Tehila; Aserin, Abraham; Garti, Nissim

    2011-12-15

    The potential of reverse hexagonal mesophases based on monoolein (GMO) and glycerol (as cosolvent) to facilitate the solubilization of proteins, such as insulin was explored. H(II) mesophases composed of GMO/decane/water were compared to GMO/decane/glycerol/water and GMO/phosphatidylcholine (PC)/decane/glycerol/water systems. The stability of insulin was tested, applying external physical modifications such as low pH and heat treatment (up to 70°C), in which insulin is known to form ordered amyloid-like aggregates (that are associated with several neurodegenerative diseases) with a characteristic cross β-pleated sheet structure. The impact of insulin confinement within these carriers on its stability, unfolding, and aggregation pathways was studied by combining SAXS, FTIR, and AFM techniques. These techniques provided a better insight into the molecular level of the "component interplay" in solubilizing and stabilizing insulin and its conformational modifications that dictate its final aggregate morphology. PC enlarged the water channels while glycerol shrank them, yet both facilitated insulin solubilization within the channels. The presence of glycerol within the mesophase water channels led to the formation of stronger hydrogen bonds with the hosting medium that enhanced the thermal stability of the protein and remarkably affected the unfolding process even after heat treatment (at 70°C for 60 min).

  5. Enhanced Hydrolytic Stability of Siliceous Surfaces Modified with Pendant Dipodal Silanes

    PubMed Central

    Arkles, Barry; Pan, Youlin; Larson, Gerald L; Singh, Mani

    2014-01-01

    Dipodal silanes possess two silicon atoms that can covalently bond to a surface. They offer a distinct advantage over conventional silanes commonly used for surface modification in terms of maintaining the integrity of surface coatings, adhesive primers, and composites in aqueous environments. New nonfunctional and functional dipodal silanes with structures containing “pendant” rather than “bridged” organofunctionality are introduced. The stability of surfaces in aqueous environments prepared from dipodal silanes with hydrophobic alkyl functionality is compared to the stability of similar surfaces prepared from the conventional silanes. In strongly acidic and brine environments, surfaces modified with dipodal silanes demonstrate markedly improved resistance to hydrolysis compared to surfaces prepared from conventional silanes. Pendant dipodal silanes exhibit greater stability than bridged dipodal silanes. The apparent equilibrium constant for the formation of silanol species by the hydrolysis of a disiloxane bond was determined as Kc=[SiOH]2/[Si-O-Si][H2O]=6±1×10−5 and is helpful in understanding the enhanced hydrolytic stability of surfaces modified with dipodal silanes. PMID:25043315

  6. Enhancing stability of poly(1,3-cyclohexadiene)-based materials by bromination and dehydrobromination

    SciTech Connect

    Huang, Tianzi; Wang, Xiaojun; Malmgren, Thomas W; Mays, Jimmy

    2012-01-01

    In order to improve their thermal stability, poly(1,3-cyclohexadiene) (PCHD) homopolymer, diblock copolymer of PCHD with styrene (PCHD-b-PS), and crosslinked PCHD membranes were dehydrogenated by addition of bromine to the polymer in solution, followed by dehydrobromination using an isothermal treatment at elevated temperature. The brominated PCHD materials thus obtained were characterized via FT-IR and thermogravimetric analysis (TGA) before and after dehydrobromination. Dehydrobromination was performed inside a TGA instrument, allowing insight into thermal stability of the analytes to be obtained. The dehydrobrominated PCHD samples were characterized using elemental analysis, and it was found the dehydrogenation of PCHD to polyphenylene was not complete. Nevertheless, some aromatization did occur, and the thermal stability of the treated polymer was greatly enhanced as compared to its PCHD precursor. Such materials may thus be of interest as high carbon content, graphene-like films. Crosslinked PCHD membranes and PCHD-b-PS diblock copolymers were treated via the same bromination/pyrolysis process, which resulted in markedly improved thermal stabilities for these materials as well.

  7. Thermal stability enhancement of modified carboxymethyl cellulose films using SnO2 nanoparticles.

    PubMed

    Baniasad, Arezou; Ghorbani, Mohsen

    2016-05-01

    In this study, in-situ and ex-situ hydrothermal synthesis procedures were applied to synthesize novel CMC/porous SnO2 nanocomposites from rice husk extracted carboxymethyl cellulose (CMC) biopolymer. In addition, the effects of SnO2 nanoparticles on thermal stability of the prepared nanocomposite were specifically studied. Products were investigated in terms of morphology, particle size, chemical structure, crystallinity and thermal stability by using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA), respectively. Presence of characteristic bands in the FTIR spectra of samples confirmed the successful formation of CMC and CMC/SnO2 nanocomposites. In addition, FESEM images revealed four different morphologies of porous SnO2 nanoparticles including nanospheres, microcubes, nanoflowers and olive-like nanoparticles with hollow cores which were formed on CMC. These nanoparticles possessed d-spacing values of 3.35Å. Thermal stability measurements revealed that introduction of SnO2 nanoparticles in the structure of CMC enhanced stability of CMC to 85%.

  8. The frequency response of dynamic friction: Enhanced rate-and-state models

    NASA Astrophysics Data System (ADS)

    Cabboi, A.; Putelat, T.; Woodhouse, J.

    2016-07-01

    The prediction and control of friction-induced vibration requires a sufficiently accurate constitutive law for dynamic friction at the sliding interface: for linearised stability analysis, this requirement takes the form of a frictional frequency response function. Systematic measurements of this frictional frequency response function are presented for small samples of nylon and polycarbonate sliding against a glass disc. Previous efforts to explain such measurements from a theoretical model have failed, but an enhanced rate-and-state model is presented which is shown to match the measurements remarkably well. The tested parameter space covers a range of normal forces (10-50 N), of sliding speeds (1-10 mm/s) and frequencies (100-2000 Hz). The key new ingredient in the model is the inclusion of contact stiffness to take into account elastic deformations near the interface. A systematic methodology is presented to discriminate among possible variants of the model, and then to identify the model parameter values.

  9. Dynamic stability of running: The effects of speed and leg amputations on the maximal Lyapunov exponent

    SciTech Connect

    Look, Nicole; Arellano, Christopher J.; Grabowski, Alena M.; Kram, Rodger; McDermott, William J.; Bradley, Elizabeth

    2013-12-15

    In this paper, we study dynamic stability during running, focusing on the effects of speed, and the use of a leg prosthesis. We compute and compare the maximal Lyapunov exponents of kinematic time-series data from subjects with and without unilateral transtibial amputations running at a wide range of speeds. We find that the dynamics of the affected leg with the running-specific prosthesis are less stable than the dynamics of the unaffected leg and also less stable than the biological legs of the non-amputee runners. Surprisingly, we find that the center-of-mass dynamics of runners with two intact biological legs are slightly less stable than those of runners with amputations. Our results suggest that while leg asymmetries may be associated with instability, runners may compensate for this effect by increased control of their center-of-mass dynamics.

  10. Dynamic stability of running: The effects of speed and leg amputations on the maximal Lyapunov exponent

    NASA Astrophysics Data System (ADS)

    Look, Nicole; Arellano, Christopher J.; Grabowski, Alena M.; McDermott, William J.; Kram, Rodger; Bradley, Elizabeth

    2013-12-01

    In this paper, we study dynamic stability during running, focusing on the effects of speed, and the use of a leg prosthesis. We compute and compare the maximal Lyapunov exponents of kinematic time-series data from subjects with and without unilateral transtibial amputations running at a wide range of speeds. We find that the dynamics of the affected leg with the running-specific prosthesis are less stable than the dynamics of the unaffected leg and also less stable than the biological legs of the non-amputee runners. Surprisingly, we find that the center-of-mass dynamics of runners with two intact biological legs are slightly less stable than those of runners with amputations. Our results suggest that while leg asymmetries may be associated with instability, runners may compensate for this effect by increased control of their center-of-mass dynamics.

  11. Stability enhancement and fuel economy of the 4-wheel-drive hybrid electric vehicles by optimal tyre force distribution

    NASA Astrophysics Data System (ADS)

    Goodarzi, Avesta; Mohammadi, Masoud

    2014-04-01

    In this paper, vehicle stability control and fuel economy for a 4-wheel-drive hybrid vehicle are investigated. The integrated controller is designed within three layers. The first layer determines the total yaw moment and total lateral force made by using an optimal controller method to follow the desired dynamic behaviour of a vehicle. The second layer determines optimum tyre force distribution in order to optimise tyre usage and find out how the tyres should share longitudinal and lateral forces to achieve a target vehicle response under the assumption that all four wheels can be independently steered, driven, and braked. In the third layer, the active steering, wheel slip, and electrical motor torque controllers are designed. In the front axle, internal combustion engine (ICE) is coupled to an electric motor (EM). The control strategy has to determine the power distribution between ICE and EM to minimise fuel consumption and allowing the vehicle to be charge sustaining. Finally, simulations performed in MATLAB/SIMULINK environment show that the proposed structure could enhance the vehicle stability and fuel economy in different manoeuvres.

  12. Anomalously enhanced hydration of aqueous electrolyte solution in hydrophobic carbon nanotubes to maintain stability.

    PubMed

    Ohba, Tomonori

    2014-02-24

    An understanding of the structure and behavior of electrolyte solutions in nanoenvironements is crucial not only for a wide variety of applications, but also for the development of physical, chemical, and biological processes. We demonstrate the structure and stability of electrolyte in carbon nanotubes using hybrid reverse Monte Carlo simulations of X-ray diffraction patterns. Hydrogen bonds between water are adequately formed in carbon nanotubes, although some hydrogen bonds are restricted by the interfaces of carbon nanotubes. The hydrogen bonding network of water in electrolyte in the carbon nanotubes is further weakened. On the other hand, formation of the ion hydration shell is significantly enhanced in the electrolyte in the carbon nanotubes in comparison to ion hydration in bulk electrolyte. The significant hydrogen bond and hydration shell formation are a result of gaining stability in the hydrophobic nanoenvironment.

  13. Engineering bright solitons to enhance the stability of two-component Bose-Einstein condensates

    NASA Astrophysics Data System (ADS)

    Radha, R.; Vinayagam, P. S.; Sudharsan, J. B.; Liu, Wu-Ming; Malomed, Boris A.

    2015-12-01

    We consider a system of coupled Gross-Pitaevskii (GP) equations describing a binary quasi-one-dimensional Bose-Einstein condensate (BEC) with intrinsic time-dependent attractive interactions, placed in a time-dependent expulsive parabolic potential, in a special case when the system is integrable (a deformed Manakov's system). Since the nonlinearity in the integrable system which represents binary attractive interactions exponentially decays with time, solitons are also subject to decay. Nevertheless, it is shown that the robustness of bright solitons can be enhanced in this system, making their respective lifetime longer, by matching the time dependence of the interaction strength (adjusted with the help of the Feshbach-resonance management) to the time modulation of the strength of the parabolic potential. The analytical results, and their stability, are corroborated by numerical simulations. In particular, we demonstrate that the addition of random noise does not impact the stability of the solitons.

  14. Enhancing the thermal stability of inulin fructotransferase with high hydrostatic pressure.

    PubMed

    Li, Yungao; Miao, Ming; Liu, Miao; Chen, Xiangyin; Jiang, Bo; Feng, Biao

    2015-03-01

    The thermal stability of inulin fructotransferase (IFTase) subjected to high hydrostatic pressure (HHP) was studied. The value of inactivation rate of IFTase in the range of 70-80°C decreased under the pressure of 100 or 200 MPa, indicating that the thermostability of IFTase under high temperature was enhanced by HHP. Far-UV CD and fluorescence spectra showed that HHP impeded the unfolding of the conformation of IFTase under high temperature, reflecting the antagonistic effect between temperature and pressure on IFTase. The new intramolecular disulfide bonds in IFTase were formed under a combination of HHP and high temperature. These bonds might be related to the stabilization of IFTase at high temperature. All the above results suggested that HHP had the protective effect on IFTase against high temperature.

  15. Fullerene mixtures enhance the thermal stability of a non-crystalline polymer solar cell blend

    NASA Astrophysics Data System (ADS)

    Lindqvist, Camilla; Bergqvist, Jonas; Bäcke, Olof; Gustafsson, Stefan; Wang, Ergang; Olsson, Eva; Inganäs, Olle; Andersson, Mats R.; Müller, Christian

    2014-04-01

    Printing of polymer:fullerene solar cells at high speed requires annealing at temperatures up to 140 °C. However, bulk-heterojunction blends that comprise a non-crystalline donor polymer often suffer from insufficient thermal stability and hence rapidly coarsen upon annealing above the glass transition temperature of the blend. In addition, micrometer-sized fullerene crystals grow, which are detrimental for the solar cell performance. In this manuscript, we present a strategy to limit fullerene crystallization, which is based on the use of fullerene mixtures of the two most common derivatives, PC61BM and PC71BM, as the acceptor material. Blends of this fullerene mixture and a non-crystalline thiophene-quinoxaline copolymer display considerably enhanced thermal stability and largely retain their photovoltaic performance upon annealing at elevated temperatures as high as 170 °C.

  16. Enhancing Stability of Perovskite Solar Cells to Moisture by the Facile Hydrophobic Passivation.

    PubMed

    Hwang, Insung; Jeong, Inyoung; Lee, Jinwoo; Ko, Min Jae; Yong, Kijung

    2015-08-12

    In this study, a novel and facile passivation process for a perovskite solar cell is reported. Poor stability in ambient atmosphere, which is the most critical demerit of a perovskite solar cell, is overcome by a simple passivation process using a hydrophobic polymer layer. Teflon, the hydrophobic polymer, is deposited on the top of a perovskite solar cell by a spin-coating method. With the hydrophobic passivation, the perovskite solar cell shows negligible degradation after a 30 day storage in ambient atmosphere. Suppressed degradation of the perovskite film is proved in various ways: X-ray diffraction, light absorption spectrum, and quartz crystal microbalance. This simple but effective passivation process suggests new kind of approach to enhance stability of perovskite solar cells to moisture.

  17. Aeroelastic Tailoring for Stability Augmentation and Performance Enhancements of Tiltrotor Aircraft

    NASA Technical Reports Server (NTRS)

    Nixon, Mark W.; Piatak, David J.; Corso, Lawrence M.; Popelka, David A.

    1999-01-01

    The requirements for increased speed and productivity for tiltrotors has spawned several investigations associated with proprotor aeroelastic stability augmentation and aerodynamic performance enhancements. Included among these investigations is a focus on passive aeroelastic tailoring concepts which exploit the anisotropic capabilities of fiber composite materials. Researchers at Langley Research Center and Bell Helicopter have devoted considerable effort to assess the potential for using these materials to obtain aeroelastic responses which are beneficial to the important stability and performance considerations of tiltrotors. Both experimental and analytical studies have been completed to examine aeroelastic tailoring concepts for the tiltrotor, applied either to the wing or to the rotor blades. This paper reviews some of the results obtained in these aeroelastic tailoring investigations and discusses the relative merits associated with these approaches.

  18. Screening of polysaccharides for preparation of α-amylase conjugate to enhance stability and storage life.

    PubMed

    Jadhav, Swati B; Singhal, Rekha S

    2013-02-15

    Nine polysaccharides differing in structure and chemical nature were screened for their ability to conjugate with α-amylase by covalent binding for enhancing the thermal and pH stability of α-amylase. Among these polysaccharides, agar, dextran, pectin and xanthan showed better results but dextran stood out among all the polysaccharide for providing both thermal and pH stability to α-amylase. α-Amylase conjugated with agar, dextran, pectin and xanthan showed antimicrobial property with added preservative (0.2% sodium benzoate) in liquid formulation of α-amylase challenged with Bacillus subtilis and Escherichia coli. Dextran was the only polysaccharide which showed significant reduction of microbial growth of challenged organisms and aerobic flora without any preservative added. Aerobic flora could flourish well in the liquid α-amylase, but low temperature (4 °C), dextran, and preservative showed synergistic effect in efficiently increasing the storage life of liquid α-amylase.

  19. Enhanced stability of steep channel beds to mass failure and debris flow initiation

    NASA Astrophysics Data System (ADS)

    Prancevic, J.; Lamb, M. P.; Ayoub, F.; Venditti, J. G.

    2015-12-01

    Debris flows dominate bedrock erosion and sediment transport in very steep mountain channels, and are often initiated from failure of channel-bed alluvium during storms. While several theoretical models exist to predict mass failures, few have been tested because observations of in-channel bed failures are extremely limited. To fill this gap in our understanding, we performed laboratory flume experiments to identify the conditions necessary to initiate bed failures in non-cohesive sediment of different sizes (D = 0.7 mm to 15 mm) on steep channel-bed slopes (S = 0.45 to 0.93) and in the presence of water flow. In beds composed of sand, failures occurred under sub-saturated conditions on steep bed slopes (S > 0.5) and under super-saturated conditions at lower slopes. In beds of gravel, however, failures occurred only under super-saturated conditions at all tested slopes, even those approaching the dry angle of repose. Consistent with theoretical models, mass failures under super-saturated conditions initiated along a failure plane approximately one grain-diameter below the bed surface, whereas the failure plane was located near the base of the bed under sub-saturated conditions. However, all experimental beds were more stable than predicted by 1-D infinite-slope stability models. In partially saturated sand, enhanced stability appears to result from suction stress. Enhanced stability in gravel may result from turbulent energy losses in pores or increased granular friction for failures that are shallow with respect to grain size. These grain-size dependent effects are not currently included in stability models for non-cohesive sediment, and they may help to explain better the timing and location of debris flow occurrence.

  20. Noise‐enhanced postural stability in subjects with functional ankle instability

    PubMed Central

    Ross, Scott E

    2007-01-01

    Objective To examine the effects of stochastic resonance (SR) stimulation on the postural stability of subjects with functional ankle instability (FAI). Design Experimental research design. Setting Sports medicine research laboratory. Participants 12 subjects with FAI who reported a history of recurrent ankle sprains and “giving way” sensations at the ankle. Interventions Subjects performed 20 s single‐leg balance tests under SR stimulation at 0.05 mA and 0.01 mA and under control conditions. Testing order was randomised. Stimulators that delivered subsensory stimulation to ankle muscles and ligaments were worn. Subjects were blinded to the test conditions, as SR stimulation was subsensory and stimulators were turned off during the control condition. Main outcome measures Anterior/posterior and medial/lateral centre‐of‐pressure velocities (COPVs) were combined to form a resultant vector (COPV‐R). The COPV‐R differences between the optimal SR stimulation and control conditions were analysed. Optimal SR stimulation was defined as the SR stimulation input intensity level (0.05 mA or 0.01 mA) that produced the greatest percentage improvement in postural stability compared with the control condition. Slower velocities indicated enhanced postural stability. Results The optimal input intensity was 0.05 mA for nine subjects and 0.01 mA for the other three. The optimal SR stimulation significantly (p<0.05) improved COPV‐R compared with the control condition (6.60 (1.06) vs 7.20 (1.03) cm/s; mean (SD)). Conclusion SR stimulation may enhance signal detection of sensorimotor signals associated with postural stability. This result has clinical relevance as improvements in postural instability associated with FAI may decrease ankle sprain injury. PMID:17550917

  1. Apoferritin Nanoparticle: A Novel and Biocompatible Carrier for Enzyme Immobilization with Enhanced Activity and Stability

    SciTech Connect

    Zhang, Youyu; Tang, Zhiwen; Wang, Jun; Wu, Hong J.; Lin, Chiann Tso; Lin, Yuehe

    2011-11-01

    Apoferritin is a nanostructured material with a uniform size and spherical structure, and it has excellent bio-compatibility. In this work, we report the use of apoferritin as a novel and biocompatible carrier for stabilizing enzymes and their activities. We used glucose oxidase (GOx) as a model enzyme. GOx was immobilized on the surface of the apoferritin through a green synthetic approach taking advantage of bioaffinity binding between streptavidin and biotin. As a result, a glucose oxidase-biotin/streptavidin/biotin-apoferritin conjugate (Apo-GOx) was prepared using streptavidin as a bridge. The synthesized Apo-GOx was characterized with transmission electron microscopy, ultraviolet, and fluorescence spectroscopy. The activity and stability of GOx on the surface of the apoferritin were studied in different environments, such as temperature, chemicals, and pH, in comparison with the biotinylated GOx (B-GOx). The results showed that the activity of GOx on the apoferritin surface was significantly enhanced. The thermal and chemical stability of the GOx on the apoferritin was also greatly improved compared to free B-GOx in a solution. It was found that the activity of the GOx on the apoferritin only lost 30% in comparison to a 70% loss of free B-GOx after a 2 h incubation at 50oC. There was almost no decrease in activity for the GOx on the apoferritin as compared to an 80% activity decrease for free B-GOx after 30 min incubation in a 5 M urea solution. Glucose detection was used as a model application for the enzyme immobilization method developed in this work. The GOx immobilized apoferritin nanoparticles exhibited high sensitivity for glucose detection with a detection limit of 3 nM glucose. This work offers a novel approach for immobilizing enzymes with enhanced stability and activity, and this method may find a number of applications, such as in enzyme catalysis, DNA assays and immunoassays.

  2. Glyceryl monooleate cubic phase gel as chemical stability enhancer of cefazolin and cefuroxime.

    PubMed

    Sadhale, Y; Shah, J C

    1998-11-01

    The primary objective of this study was to determine the ability of the glyceryl monooleate (GMO) cubic phase gel to protect drugs from chemical instability reactions such as hydrolysis and oxidation. Stability was assessed on cefazolin incorporated in cubic phase gel and in solution at two different concentrations (200 and 50 micrograms/g), at 22, 37, and 50 degrees C. Degradation profiles, plotting percent cefazolin remaining on a logarithmic scale versus time, were constructed and the degradation rate constants calculated from the slopes. At both concentrations, degradation of cefazolin was found to be slower in the cubic phase gel than in solution at 22 and 37 degrees C, but not at 50 degrees C. The degradation rate constants were 3- to 18-fold lower in the gel than in solution at low concentration of cefazolin. At 22 and 37 degrees C, the kinetics of degradation at high concentration of cefazolin was not first-order but showed a lag phase followed by an exponential loss of cefazolin, typical of oxidation. The potential oxidation of the thioether moiety of cefazolin was confirmed by its 18-fold higher stability in the presence of ethylenediaminetetraacetic acid (EDTA) and nitrogen in solution. Cefuroxime, a cephalosporin which degrades solely via beta-lactam hydrolysis, degraded twice as fast in solution as it did in the gel. The enhanced stability of cefazolin and cefuroxime in the GMO cubic phase gel shows its potential as a chemical stability enhancer and this is the first report to demonstrate oxidation, in addition to beta-lactam hydrolysis, as a mechanism for degradation of cefazolin.

  3. Correction: Enhanced photocatalytic activity of a self-stabilized synthetic flavin anchored on a TiO2 surface.

    PubMed

    Pandiri, Manjula; Shaham-Waldmann, Nurit; Hossain, Mohammad S; Foss, Frank W; Rajeshwar, Krishnan; Paz, Yaron

    2016-09-14

    Correction for 'Enhanced photocatalytic activity of a self-stabilized synthetic flavin anchored on a TiO2 surface' by Manjula Pandiri et al., Phys. Chem. Chem. Phys., 2016, 18, 18575-18583. PMID:27509005

  4. Rapid Small-Signal Stability Assessment and Enhancement Following Changes in Topology

    SciTech Connect

    Saric, AT; Stankovic, AM

    2015-05-01

    The paper proposes a scalable and tractable algorithm for dynamic topology optimization of power systems involving changes in branch on/off status, while respecting small-signal stability (SSS) constraints. A procedure for fast updates of the system matrices (in descriptor form) and without additional full matrix inversions is proposed. To additionally reduce the computation time, only critical eigenvalues (right-most or those in a specified damping ratio and frequency range) are calculated. A quadratic optimization approach is proposed for optimized generation re-dispatch to satisfy SSS constraints. The approach is applied to two (medium- and large-scale) real-world test power systems.

  5. Viscoelastic creep induced by repetitive spine flexion and its relationship to dynamic spine stability.

    PubMed

    Howarth, Samuel J; Kingston, David C; Brown, Stephen H M; Graham, Ryan B

    2013-08-01

    Repetitive trunk flexion elicits passive tissue creep, which has been hypothesized to compromise spine stability. The current investigation determined if increased spine flexion angle at the onset of flexion relaxation (FR) in the lumbar extensor musculature was associated with altered dynamic stability of spine kinematics. Twelve male participants performed 125 consecutive cycles of full forward trunk flexion. Spine kinematics and lumbar erector spinae (LES) electromyographic (EMG) activity were obtained throughout the repetitive trunk flexion trial. Dynamic stability was evaluated with maximum finite-time Lyapunov exponents over five sequential blocks of 25cycles. Spine flexion angle at FR onset, and peak LES EMG activity were determined at baseline and every 25th cycle. Spine flexion angle at FR increased on average by 1.7° after baseline with significant increases of 1.7° and 2.4° at the 50th and 100th cycles. Maximum finite-time Lyapunov exponents demonstrated a transient, non-statistically significant, increase between cycles 26 and 50 followed by a recovery to baseline over the remainder of the repetitive trunk flexion cycles. Recovery of dynamic stability may be the consequence of increased active spine stiffness demonstrated by the non-significant increase in peak LES EMG that occurred as the repetitive trunk flexion progressed.

  6. The Effects of Experimentally Induced Low Back Pain on Spine Rotational Stiffness and Local Dynamic Stability.

    PubMed

    Ross, Gwyneth B; Mavor, Matthew; Brown, Stephen H M; Graham, Ryan B

    2015-09-01

    Local dynamic stability, quantified using the maximum finite-time Lyapunov exponent (λ max), and the muscular contributions to spine rotational stiffness can provide pertinent information regarding the neuromuscular control of the spine during movement tasks. The primary goal of the present study was to assess if experimental capsaicin-induced low back pain (LBP) affects spine stability and the neuromuscular control of repetitive trunk movements in a group of healthy participants with no history of LBP. Fourteen healthy males were recruited for this investigation. Each participant was asked to complete three trials (baseline, in pain, and recovery) of 35 cycles of a repetitive trunk flexion/extension task at a rate of 0.25 Hz. Local dynamic stability and the muscular contributions to lumbar spine rotational stiffness were significantly impaired during the LBP trial compared to the baseline trial (p < 0.05); however, there was a trend for these measures to recover after a 1 h rest. This study provides evidence that capsaicin can effectively induce LBP, thereby altering spine rotational stiffness and local dynamic stability. Future research should directly compare the effects capsaicin-induced LBP and intramuscular/intraligamentous induced LBP on these same variables.

  7. The effects of core stabilization exercise on dynamic balance and gait function in stroke patients.

    PubMed

    Chung, Eun-Jung; Kim, Jung-Hee; Lee, Byoung-Hee

    2013-07-01

    [Purpose] The purpose of this study was to determine the effects of core stabilization exercise on dynamic balance and gait function in stroke patients. [Subjects] The subjects were 16 stroke patients, who were randomly divided into two groups: a core stabilization exercise group of eight subjects and control group of eight subjects. [Methods] Subjects in both groups received general training five times per week. Subjects in the core stabilization exercise group practiced an additional core stabilization exercise program, which was performed for 30 minutes, three times per week, during a period of four weeks. All subjects were evaluated for dynamic balance (Timed Up and Go test, TUG) and gait parameters (velocity, cadence, step length, and stride length). [Results] Following intervention, the core exercise group showed a significant change in TUG, velocity, and cadence. The only significant difference observed between the core group and control group was in velocity. [Conclusion] The results of this study suggest the feasibility and suitability of core stabilization exercise for stroke patients.

  8. Filopodial dynamics and growth cone stabilization in Drosophila visual circuit development

    PubMed Central

    Özel, Mehmet Neset; Langen, Marion; Hassan, Bassem A; Hiesinger, P Robin

    2015-01-01

    Filopodial dynamics are thought to control growth cone guidance, but the types and roles of growth cone dynamics underlying neural circuit assembly in a living brain are largely unknown. To address this issue, we have developed long-term, continuous, fast and high-resolution imaging of growth cone dynamics from axon growth to synapse formation in cultured Drosophila brains. Using R7 photoreceptor neurons as a model we show that >90% of the growth cone filopodia exhibit fast, stochastic dynamics that persist despite ongoing stepwise layer formation. Correspondingly, R7 growth cones stabilize early and change their final position by passive dislocation. N-Cadherin controls both fast filopodial dynamics and growth cone stabilization. Surprisingly, loss of N-Cadherin causes no primary targeting defects, but destabilizes R7 growth cones to jump between correct and incorrect layers. Hence, growth cone dynamics can influence wiring specificity without a direct role in target recognition and implement simple rules during circuit assembly. DOI: http://dx.doi.org/10.7554/eLife.10721.001 PMID:26512889

  9. X-ray source assembly having enhanced output stability, and fluid stream analysis applications thereof

    DOEpatents

    Radley, Ian; Bievenue, Thomas J.; Burdett Jr., John H.; Gallagher, Brian W.; Shakshober, Stuart M.; Chen, Zewu; Moore, Michael D.

    2007-04-24

    An x-ray source assembly (2700) and method of operation are provided having enhanced output stability. The assembly includes an anode (2125) having a source spot upon which electrons (2120) impinge and a control system (2715/2720) for controlling position of the anode source spot relative to an output structure. The control system can maintain the anode source spot location relative to the output structure (2710) notwithstanding a change in one or more operating conditions of the x-ray source assembly. One aspect of the disclosed invention is most amenable to the analysis of sulfur in petroleum-based fuels.

  10. X-ray source assembly having enhanced output stability, and fluid stream analysis applications thereof

    DOEpatents

    Radley, Ian; Bievenue, Thomas J.; Burdett, John H.; Gallagher, Brian W.; Shakshober, Stuart M.; Chen, Zewu; Moore, Michael D.

    2008-06-08

    An x-ray source assembly and method of operation are provided having enhanced output stability. The assembly includes an anode having a source spot upon which electrons impinge and a control system for controlling position of the anode source spot relative to an output structure. The control system can maintain the anode source spot location relative to the output structure notwithstanding a change in one or more operating conditions of the x-ray source assembly. One aspect of the disclosed invention is most amenable to the analysis of sulfur in petroleum-based fuels.

  11. Fluorous metal-organic frameworks with enhanced stability and high H2/CO2 storage capacities.

    PubMed

    Zhang, Da-Shuai; Chang, Ze; Li, Yi-Fan; Jiang, Zhong-Yi; Xuan, Zhi-Hong; Zhang, Ying-Hui; Li, Jian-Rong; Chen, Qiang; Hu, Tong-Liang; Bu, Xian-He

    2013-11-22

    A new class of metal-organic frameworks (MOFs) has been synthesized by ligand-functionalization strategy. Systematic studies of their adsorption properties were performed at low and high pressure. Importantly, when fluorine was introduced into the framework via the functionalization, both the framework stabilities and adsorption capacities towards H2/CO2 were enhanced significantly. This consequence can be well interpreted by theoretical studies of these MOFs structures. In addition, one of these MOFs TKL-107 was used to fabricate mixed matrix membranes, which exhibit great potential for the application of CO2 separation.

  12. Fluorous Metal-Organic Frameworks with Enhanced Stability and High H2/CO2 Storage Capacities

    PubMed Central

    Zhang, Da-Shuai; Chang, Ze; Li, Yi-Fan; Jiang, Zhong-Yi; Xuan, Zhi-Hong; Zhang, Ying-Hui; Li, Jian-Rong; Chen, Qiang; Hu, Tong-Liang; Bu, Xian-He

    2013-01-01

    A new class of metal-organic frameworks (MOFs) has been synthesized by ligand-functionalization strategy. Systematic studies of their adsorption properties were performed at low and high pressure. Importantly, when fluorine was introduced into the framework via the functionalization, both the framework stabilities and adsorption capacities towards H2/CO2 were enhanced significantly. This consequence can be well interpreted by theoretical studies of these MOFs structures. In addition, one of these MOFs TKL-107 was used to fabricate mixed matrix membranes, which exhibit great potential for the application of CO2 separation. PMID:24264725

  13. Enhancement of thermal stability of porous bodies comprised of stainless steel or an alloy

    DOEpatents

    Bischoff, Brian L.; Sutton, Theodore G.; Judkins, Roddie R.; Armstrong, Timothy R.; Adcock, Kenneth D.

    2010-11-09

    A method for treating a porous item constructed of metal powder, such as a powder made of Series 400 stainless steel, involves a step of preheating the porous item to a temperature of between about 700 and 900.degree. C. degrees in an oxidizing atmosphere and then sintering the body in an inert or reducing atmosphere at a temperature which is slightly below the melting temperature of the metal which comprises the porous item. The thermal stability of the resulting item is enhanced by this method so that the item retains its porosity and metallic characteristics, such as ductility, at higher (e.g. near-melting) temperatures.

  14. Local Dynamic Stability Assessment of Motion Impaired Elderly Using Electronic Textile Pants.

    PubMed

    Liu, Jian; Lockhart, Thurmon E; Jones, Mark; Martin, Tom

    2008-10-01

    A clear association has been demonstrated between gait stability and falls in the elderly. Integration of wearable computing and human dynamic stability measures into home automation systems may help differentiate fall-prone individuals in a residential environment. The objective of the current study was to evaluate the capability of a pair of electronic textile (e-textile) pants system to assess local dynamic stability and to differentiate motion-impaired elderly from their healthy counterparts. A pair of e-textile pants comprised of numerous e-TAGs at locations corresponding to lower extremity joints was developed to collect acceleration, angular velocity and piezoelectric data. Four motion-impaired elderly together with nine healthy individuals (both young and old) participated in treadmill walking with a motion capture system simultaneously collecting kinematic data. Local dynamic stability, characterized by maximum Lyapunov exponent, was computed based on vertical acceleration and angular velocity at lower extremity joints for the measurements from both e-textile and motion capture systems. Results indicated that the motion-impaired elderly had significantly higher maximum Lyapunov exponents (computed from vertical acceleration data) than healthy individuals at the right ankle and hip joints. In addition, maximum Lyapunov exponents assessed by the motion capture system were found to be significantly higher than those assessed by the e-textile system. Despite the difference between these measurement techniques, attaching accelerometers at the ankle and hip joints was shown to be an effective sensor configuration. It was concluded that the e-textile pants system, via dynamic stability assessment, has the potential to identify motion-impaired elderly.

  15. Structure, dynamics, and stability of beta-cyclodextrin inclusion complexes of aspartame and neotame.

    PubMed

    Garbow, J R; Likos, J J; Schroeder, S A

    2001-04-01

    Studies of the high-intensity sweetener aspartame show that its stability is significantly enhanced in the presence of beta-cyclodextrin (beta-CyD). At a 5:1 beta-CyD/aspartame molar ratio, the stability of aspartame is 42% greater in 4 mM phosphate buffer (pH 3.1) compared to solutions prepared without beta-CyD. Solution-state (1)H NMR experiments demonstrate the formation of 1:1 beta-CyD/aspartame complexes, stabilized by the interaction of the phenyl-ring protons of aspartame with the H3 and H5 protons of beta-CyD. Inclusion complex formation clearly accounts for the observed stability enhancement of aspartame in solution. The formation of inclusion complexes in solution is also demonstrated for beta-CyD and neotame, a structural derivative of aspartame containing an N-substituted 3,3-dimethylbutyl group. These complexes are stabilized by the interaction of beta-CyD with both phenyl-ring and dimethylbutyl protons. Solid-state NMR experiments provide additional characterization, clearly demonstrating the formation of inclusion complexes in lyophilized solids prepared from solutions of beta-CyD and either aspartame or neotame.

  16. Stability analysis of a multibody system model for coupled slosh-vehicle dynamics

    NASA Astrophysics Data System (ADS)

    Nichkawde, Chetan; Harish, P. M.; Ananthkrishnan, N.

    2004-08-01

    The coupled slosh-vehicle dynamics of a rigid body in planar atmospheric flight carrying a sloshing liquid is considered as a multibody system with the sloshing motion modelled as a simple pendulum. The coupled, non-linear equations for the four-degree-of-freedom multibody system are derived using the method of Lagrangian dynamics. Careful non-dimensionalization reveals two crucial parameters that determine the extent of coupling between the rigid body and slosh modes, and also two important frequency parameters. Using a two-parameter continuation method, critical combinations of these four parameters for which the coupled slosh-vehicle dynamics can become unstable are computed. Results are displayed in the form of neutral stability curves (stability boundaries) in parameter space, and an analytical expression incorporating the four parameters that represents the neutral stability curves is obtained. Reduced-order linearized models and key transfer functions are derived in an effort to understand the instability phenomenon. Physically, the sloshing motion is seen to induce a static instability, sometimes called tumbling, in the vehicle pitch dynamics, depending on the slosh mass fraction and the location of the slosh pendulum hinge point above the rigid vehicle center of mass.

  17. Treatment of a patient with posterior cortical atrophy (PCA) with chiropractic manipulation and Dynamic Neuromuscular Stabilization (DNS): A case report

    PubMed Central

    Francio, Vinicius T.; Boesch, Ron; Tunning, Michael

    2015-01-01

    Objective: Posterior cortical atrophy (PCA) is a rare progressive neurodegenerative syndrome which unusual symptoms include deficits of balance, bodily orientation, chronic pain syndrome and dysfunctional motor patterns. Current research provides minimal guidance on support, education and recommended evidence-based patient care. This case reports the utilization of chiropractic spinal manipulation, dynamic neuromuscular stabilization (DNS), and other adjunctive procedures along with medical treatment of PCA. Clinical features: A 54-year-old male presented to a chiropractic clinic with non-specific back pain associated with visual disturbances, slight memory loss, and inappropriate cognitive motor control. After physical examination, brain MRI and PET scan, the diagnosis of PCA was recognized. Intervention and Outcome: Chiropractic spinal manipulation and dynamic neuromuscular stabilization were utilized as adjunctive care to conservative pharmacological treatment of PCA. Outcome measurements showed a 60% improvement in the patient’s perception of health with restored functional neuromuscular pattern, improvements in locomotion, posture, pain control, mood, tolerance to activities of daily living (ADLs) and overall satisfactory progress in quality of life. Yet, no changes on memory loss progression, visual space orientation, and speech were observed. Conclusion: PCA is a progressive and debilitating condition. Because of poor awareness of PCA by physicians, patients usually receive incomplete care. Additional efforts must be centered on the musculoskeletal features of PCA, aiming enhancement in quality of life and functional improvements (FI). Adjunctive rehabilitative treatment is considered essential for individuals with cognitive and motor disturbances, and manual medicine procedures may be consider a viable option. PMID:25729084

  18. Dynamic stability of a doubly quantized vortex in a three-dimensional condensate

    SciTech Connect

    Lundh, Emil; Nilsen, Halvor M.

    2006-12-15

    The Bogoliubov equations are solved for a three-dimensional Bose-Einstein condensate containing a doubly quantized vortex, trapped in a harmonic potential. Complex frequencies, signifying dynamical instability, are found for certain ranges of parameter values. The existence of alternating windows of stability and instability, respectively, is explained qualitatively and quantitatively using variational calculus and direct numerical solutions. It is seen that the windows of stability disappear in the limit of a cigar-shaped condensate, which is consistent with recent experimental results on the lifetime of a doubly quantized vortex in that regime.

  19. Dynamics and stability of Bose-Einstein solitons in tilted optical lattices

    SciTech Connect

    Diaz, E.; Dominguez-Adame, F.; Gaul, C.; Lima, R. P. A.; Mueller, C. A.

    2010-05-15

    Bloch oscillations of Bose-Einstein condensates realize sensitive matter-wave interferometers. We investigate the dynamics and stability of bright-soliton wave packets in one-dimensional tilted optical lattices with a modulated mean-field interaction g(t). By means of a time-reversal argument, we prove the stability of Bloch oscillations of breathing solitons that would be quasistatically unstable. Floquet theory shows that these breathing solitons can be more stable against certain experimental perturbations than rigid solitons or even noninteracting wave packets.

  20. An atomic magnetometer with autonomous frequency stabilization and large dynamic range

    SciTech Connect

    Pradhan, S. E-mail: pradhans75@gmail.com; Poornima,; Dasgupta, K.; Mishra, S.; Behera, R.

    2015-06-15

    The operation of a highly sensitive atomic magnetometer using elliptically polarized resonant light is demonstrated. It is based on measurement of zero magnetic field resonance in degenerate two level systems using polarimetric detection. The transmitted light through the polarimeter is used for laser frequency stabilization, whereas reflected light is used for magnetic field measurement. Thus, the experimental geometry allows autonomous frequency stabilization of the laser frequency leading to compact operation of the overall device and has a preliminary sensitivity of <10 pT/Hz{sup 1/2} @ 1 Hz. Additionally, the dynamic range of the device is improved by feedback controlling the bias magnetic field without compromising on its sensitivity.

  1. Classical linear-control analysis applied to business-cycle dynamics and stability

    NASA Technical Reports Server (NTRS)

    Wingrove, R. C.

    1983-01-01

    Linear control analysis is applied as an aid in understanding the fluctuations of business cycles in the past, and to examine monetary policies that might improve stabilization. The analysis shows how different policies change the frequency and damping of the economic system dynamics, and how they modify the amplitude of the fluctuations that are caused by random disturbances. Examples are used to show how policy feedbacks and policy lags can be incorporated, and how different monetary strategies for stabilization can be analytically compared. Representative numerical results are used to illustrate the main points.

  2. Dynamic stability of fcc crystals under isotropic loading from first principles.

    PubMed

    Rehák, Petr; Cerný, Miroslav; Pokluda, Jaroslav

    2012-05-30

    Lattice dynamics and stability of four fcc crystals (Al, Ir, Pt and Au) under isotropic (hydrostatic) tensile loading are studied from first principles using the linear response method and the harmonic approximation. The results reveal that, contrary to former expectations, strengths of all the studied crystals are limited by instabilities related to soft phonons with finite or vanishing wavevectors. The critical strains associated with such instabilities are remarkably lower than those related to the volumetric instability. On the other hand, the corresponding reduction of the tensile strength is by 20% at the most. An analysis of elastic stability conditions is also performed and the results obtained by means of both approaches are compared.

  3. An atomic magnetometer with autonomous frequency stabilization and large dynamic range.

    PubMed

    Pradhan, S; Mishra, S; Behera, R; Poornima; Dasgupta, K

    2015-06-01

    The operation of a highly sensitive atomic magnetometer using elliptically polarized resonant light is demonstrated. It is based on measurement of zero magnetic field resonance in degenerate two level systems using polarimetric detection. The transmitted light through the polarimeter is used for laser frequency stabilization, whereas reflected light is used for magnetic field measurement. Thus, the experimental geometry allows autonomous frequency stabilization of the laser frequency leading to compact operation of the overall device and has a preliminary sensitivity of <10 pT/Hz(1/2) @ 1 Hz. Additionally, the dynamic range of the device is improved by feedback controlling the bias magnetic field without compromising on its sensitivity. PMID:26133825

  4. An atomic magnetometer with autonomous frequency stabilization and large dynamic range.

    PubMed

    Pradhan, S; Mishra, S; Behera, R; Poornima; Dasgupta, K

    2015-06-01

    The operation of a highly sensitive atomic magnetometer using elliptically polarized resonant light is demonstrated. It is based on measurement of zero magnetic field resonance in degenerate two level systems using polarimetric detection. The transmitted light through the polarimeter is used for laser frequency stabilization, whereas reflected light is used for magnetic field measurement. Thus, the experimental geometry allows autonomous frequency stabilization of the laser frequency leading to compact operation of the overall device and has a preliminary sensitivity of <10 pT/Hz(1/2) @ 1 Hz. Additionally, the dynamic range of the device is improved by feedback controlling the bias magnetic field without compromising on its sensitivity.

  5. Contributors to Enhanced CO2 Electroreduction Activity and Stability in a Nanostructured Au Electrocatalyst.

    PubMed

    Kim, Haeri; Jeon, Hyo Sang; Jee, Michael Shincheon; Nursanto, Eduardus Budi; Singh, Jitendra Pal; Chae, Keunhwa; Hwang, Yun Jeong; Min, Byoung Koun

    2016-08-23

    The formation of a nanostructure is a popular strategy for catalyst applications because it can generate new surfaces that can significantly improve the catalytic activity and durability of the catalysts. However, the increase in the surface area resulting from nanostructuring does not fully explain the substantial improvement in the catalytic properties of the CO2 electroreduction reaction, and the underlying mechanisms have not yet been fully understood. Here, based on a combination of extended X-ray absorption fine structure analysis, X-ray photoelectron spectroscopy, and Kelvin probe force microscopy, we observed a contracted Au-Au bond length and low work function with the nanostructured Au surface that had enhanced catalytic activity for electrochemical CO2 reduction. The results may improve the understanding of the enhanced stability of the nanostructured Au electrode based on the resistance of cation adhesion during the CO2 reduction reaction. PMID:27466025

  6. Stabilization and relative phase effects in a dichromatically driven diatomic Morse molecule: interpretation based on nonlinear classical dynamics.

    PubMed

    Constantoudis, Vassilios; Nicolaides, Cleanthes A

    2005-02-22

    The dissociation dynamics of a dichromatically laser-driven diatomic Morse molecule vibrating in the ground state is investigated by applying tools of the nonlinear theory of classical Hamiltonian systems. Emphasis is placed on the role of the relative phase of the two fields, phi. First, it is found that, just like in quantum mechanics, there is dependence of the dissociation probability on phi. Then, it is demonstrated that addition of the second laser leads to suppression of probability (stabilization), when the intensity of the first laser is kept constant just above or below the single laser dissociation threshold. This "chemical bond hardening" diminishes as phi increases. These effects are investigated and interpreted in terms of modifications in phase space topology. Variations of phi as well as of the intensity of the second laser may cause (i) appearance/disappearance of the stability island corresponding to the common resonance with the lowest energy and (ii) deformation and movement of the region of Kolmogorov-Arnold-Moser tori that survive from the undriven system. The latter is the main origin in phase space of stabilization and phi dependence. Finally, it is shown that the use of short laser pulses enhances both effects.

  7. Peristaltic pulse dynamic compression of the lower extremity enhances flexibility.

    PubMed

    Sands, William A; Murray, Melonie B; Murray, Steven R; McNeal, Jeni R; Mizuguchi, Satoshi; Sato, Kimitake; Stone, Michael H

    2014-04-01

    This study investigated the effects of peristaltic pulse dynamic compression (PPDC) on range-of-motion (ROM) changes in forward splits. Serious stretching usually involves discomfort and large time investments. Tissue structural changes and stretch tolerance have heretofore been considered the primary mechanisms of enhanced ROM. The PPDC treatment was computer controlled. Circumferential and segmented inflation pressures were induced by feet to hip leggings. Nine subjects, experienced in stretching and a forward split position, volunteered. The subjects were familiarized with the protocol and randomly assigned to an initial condition: experimental (PPDC), or control (CONT). The study involved a crossover design. Second conditions were tested within 1-5 days. All tests were 2 trials of right and left forward splits. Split flexibility was assessed by measuring the height of the anterior superior iliac spine of the rear leg from the floor. Pelvic posture was controlled by rear leg position. The PPDC treatment was 15 minutes of seated PPDC. The control condition was the same except that leggings were not inflated. Pressures of 5 cells in the leggings were set at factory defaults, 70 mm Hg sequentially. Difference score results indicated statistically significant (p ≤ 0.05) differences by condition and the condition by leg interaction. The rapid acute changes in ROM (PPDC: right 25.3%, left 33.3%; CONT: right 12.2%, left 1.0%) support the premise that changes in ROM were dependent on mechanisms other than tissue structural changes and/or stretch tolerance. PPDC provides a means of rapidly enhancing acute ROM requiring less discomfort and time.

  8. Geometrical Effects in Plasma Stability and Dynamics of Coherent Structures in the Divertor

    SciTech Connect

    Ryutov, D D; Cohen, R H

    2007-05-16

    Plasma dynamics in the divertor region is strongly affected by a variety of phenomena associated with the magnetic field geometry and the shape of the divertor plates. One of the most universal effects is the squeezing of a normal cross-section of a thin magnetic flux-tube on its way from the divertor plate to the main SOL. It leads to decoupling of the most unstable perturbations in the divertor legs from those in the main SOL. For perturbations on either side of the X-point, this effect can be cast as a boundary condition at some 'control surface' situated near the X-point. We discuss several boundary conditions proposed thus far and assess the influence of the magnetic field geometry on them. Another set of geometrical effects is related to the transformation of a flux-tube that occurs when it is displaced in such a way that its central magnetic field line coincides with some other field line, and the magnetic field is not perturbed. These flute-like displacements are of a particular interest for the low-beta edge plasmas. It turns out that this transformation may also lead to a considerable deformation of a flux-tube cross-section; in addition, the distance between plasma particles occupying the flux-tube may change significantly even if there is no parallel plasma motion. We present expressions describing aforementioned transformations for the general tokamak geometry and simplify them for the divertor region (using the proximity of the X-point). We also discuss the effects associated with the shape of the plasma-limiting surfaces, both those designed to intercept the plasma (like divertor plates and limiters) and those that can be hit in some 'abnormal' events, e.g., in the course of a radial motion of an isolated plasma filament. The orientation of the limiting surface with respect to the magnetic field affects the plasma dynamics via the sheath boundary conditions. One can enhance or suppress plasma instabilities in the divertor legs by tilting the divertor

  9. Enhancing stability of octahedral PtNi nanoparticles for oxygen reduction reaction by halide treatment

    NASA Astrophysics Data System (ADS)

    Choi, Juhyuk; Lee, Youhan; Kim, Jihan; Lee, Hyunjoo

    2016-03-01

    Because a reduction in the amount of Pt catalysts is essential for the commercialization of fuel cells, various approaches have been tested to maximize the mass activity of Pt-based catalysts. Among these, the most successful results so far were obtained using shaped PtNi alloy nanoparticles, preferably with PtNi(111) facets. However, these nanoparticles typically suffer from much lower activity after the durability tests due to the leaching out of the surface Ni during the oxygen reduction reaction (ORR), which leads to the disappearance of the activity-enhancing effect caused by electronic structure modification. Here, we showed that halide treatment of the octahedral PtNi nanoparticles could significantly enhance their durability. Halides are adsorbed on surface Ni more strongly than on surface Pt, and the surface halides are found to preserve the surface Ni that induces the ORR activity enhancement. Especially, Br can preserve the surface Ni effectively. Durability testing by repeating cyclic voltammetry 10,000 times in the 0.6-1.1 V range showed that the mass activity decreased by 52.6% for the as-prepared PtNi octahedral nanoparticles, whereas the mass activity decreased by only 15.0% for the Br-treated PtNi nanoparticles. The simple treatment significantly enhanced the long-term stability of the highly active PtNi alloy nano-octahedra.

  10. Lasic -Cavity-enhanced molecular iodine laser frequency stabilization for space projects

    NASA Astrophysics Data System (ADS)

    Turazza, Oscar; Acef, O.; Auger, G.; Halloin, H.; Duburck, F.; Plagnol, E.; Holleville, D.; Dimarcq, N.; Binetruy, P.; Brillet, A.; Lemonde, P.; Devismes, E.; Prat, P.; Lours, M.; Tuckey, P.; Argence, B.

    We present work in progress at SYRTE, APC and ARTEMIS aiming at stabilizing the frequency of a Nd:YAG laser using saturated absorption spectroscopy of molecular iodine 127I2. The novel design of the LASIC project allows for robustness and compacity while achieving high-performance phase noise suppression. The project is a follow-up of the laser stabilization work started at Artemis and continued at APC. The use of a low-finesse bow-tie optical cavity around the iodine absorber, combined with an adapted high-frequency modulation of the laser phase -NICE-OHMS technique-yields shot-noise limited saturated absorption signals with cavity-enhanced signal-to-noise ratios. Residual fractional frequency instability in terms of Allan Std. Deviation is expected below 10-14 @1s integration time and down to 10-15 over several hours. The compact iodine / cavity design, and performance well above LISA requirements make this project an interesting candidate for the space-based Gravitational Waves detector. We discuss the scientific background and outline of this project within the LISA framework, as well as its potential impact on other stringent technical requirements of the LISA project (e.g. U.S.O. clock-stability, arm-length measurements. . . ). We also present other possible applications for space projects involving interferometry, laser ranging or onboard ultrastable oscillators.

  11. Using detrended fluctuation analysis (DFA) to analyze whether vibratory insoles enhance balance stability for elderly fallers.

    PubMed

    Wang, Chien-Chih; Yang, Wen-Hung

    2012-01-01

    Falls are a common and devastating problem among elderly people. In a previous study, vibratory insoles were developed to improve postural stability for elderly fallers. To verify the effects of vibratory insoles, a two-stage experiment was conducted to collect center of pressure (COP) signals from 26 elderly fallers and 16 healthy young subjects while standing still. The DFA is used to analyze the behavior of different time-series data obtained from the trajectory of COP. Postural stability was compared by the DFA scaling exponent between a control condition (before using vibratory insoles) and a vibration condition (after using vibratory insoles). For elderly fallers, DFA scaling exponents 95% confidence interval were [1.434, 1.547] and [1.329, 1.451] under control and vibration conditions in the anteroposterior (AP) direction, respectively. The experimental results revealed that temporary stimuli of appropriate amplitude produced by vibration insoles enhanced postural stability in elderly fallers and was more obvious in the AP direction.

  12. Enhanced capacity and stability for the separation of cesium in electrically switched ion exchange

    SciTech Connect

    Tawfic, A.F.; Dickson, S.E.; Kim, Y.; Mekky, W.

    2015-03-15

    Electrically switched ion exchange (ESIX) can be used to separate ionic contaminants from industrial wastewater, including that generated by the nuclear industry. The ESIX method involves sequential application of reduction and oxidation potentials to an ion exchange film to induce the respective loading and unloading of cesium. This technology is superior to conventional methods (e.g electrodialysis reversal or reverse osmosis) as it requires very little energy for ionic separation. In previous studies, ESIX films have demonstrated relatively low ion exchange capacities and limited film stabilities over repeated potential applications. In this study, the methodology for the deposition of electro-active films (nickel hexacyanoferrate) on nickel electrodes was modified to improve the ion exchange capacity for cesium removal using ESIX. Cyclic voltammetry was used to investigate the ion exchange capacity and stability. Scanning electron microscopy (SEM) was used to characterize the modified film surfaces. Additionally, the films were examined for the separation of cesium ions. This modified film preparation technique enhanced the ion exchange capacity and improves the film stability compared to previous methods for the deposition of ESIX films. (authors)

  13. Enhanced Stability of Skyrmions in Two-Dimensional Chiral Magnets with Rashba Spin-Orbit Coupling

    NASA Astrophysics Data System (ADS)

    Banerjee, Sumilan; Rowland, James; Erten, Onur; Randeria, Mohit

    2014-07-01

    Recent developments have led to an explosion of activity on skyrmions in three-dimensional (3D) chiral magnets. Experiments have directly probed these topological spin textures, revealed their nontrivial properties, and led to suggestions for novel applications. However, in 3D the skyrmion crystal phase is observed only in a narrow region of the temperature-field phase diagram. We show here, using a general analysis based on symmetry, that skyrmions are much more readily stabilized in two-dimensional (2D) systems with Rashba spin-orbit coupling. This enhanced stability arises from the competition between field and easy-plane magnetic anisotropy and results in a nontrivial structure in the topological charge density in the core of the skyrmions. We further show that, in a variety of microscopic models for magnetic exchange, the required easy-plane anisotropy naturally arises from the same spin-orbit coupling that is responsible for the chiral Dzyaloshinskii-Moriya interactions. Our results are of particular interest for 2D materials like thin films, surfaces, and oxide interfaces, where broken surface-inversion symmetry and Rashba spin-orbit coupling naturally lead to chiral exchange and easy-plane compass anisotropy. Our theory gives a clear direction for experimental studies of 2D magnetic materials to stabilize skyrmions over a large range of magnetic fields down to T=0.

  14. A computational study on the enhanced stabilization of aminophenol derivatives by internal hydrogen bonding

    NASA Astrophysics Data System (ADS)

    Gomes, José R. B.; Ribeiro da Silva, Manuel A. V.

    2006-05-01

    The stabilization of aminophenol derivatives and their radicals due to internal hydrogen bonding has been analyzed by means of density functional theory and by topological electron density analysis. The calculations have been carried out at the B3LYP level of theory, using several basis sets, and by means of the CBS-4M composite approach. A strong O-H⋯NH 2 hydrogen bond is found to stabilize the aminophenol with the lone-pair of the nitrogen atom co-planar with the aromatic ring, contrasting with the optimized structure found for aniline. The effect of electron donors and electron acceptors on the strength of the internal hydrogen bond is also analyzed. For one of the species studied, 2,6-diaminophenol, the computed O-H bond dissociation enthalpy is only 300 kJ/mol, the lowest value found so far for phenol and other compounds containing the O-H bond, almost 25 kJ/mol lower than those found experimentally for pyrogallol and for vitamin E. The explanation for such a small value comes from the enhanced stabilization of the corresponding radical species by internal hydrogen bonding, combined with a decrease of the steric effects caused by rotation of the amino groups.

  15. Improving the durability of a drag-reducing nanocoating by enhancing its mechanical stability.

    PubMed

    Cheng, Mengjiao; Zhang, Songsong; Dong, Hongyu; Han, Shihui; Wei, Hao; Shi, Feng

    2015-02-25

    The durability of superhydrophobic surface is a major problem to restrict industrial application of superhydrophobic materials from laboratory research, which can be attributed to a more general issue of mechanical stability for superhydrophobic coatings. Therefore, in order to handle this issue, we have fabricated a mechanically stable drag-reducing coating composed of elastic polydimethylsiloxane (PDMS) and hydrophobic copper particles on model ships, which can resist mechanical abrasion and has displayed a durable drag-reducing effect. In comparison with normal Au superhydrophobic coatings, the as-prepared PDMS/copper coatings showed durable drag reduction performance with a similar drag-reducing rate before (26%) and after (24%) mechanical abrasion. The mechanism for the enhanced mechanical stability and maintained drag reduction of the superhydrophobic surfaces was investigated through characterizations of surface morphology, surface wettability, and water adhesive force evaluation before and after abrasion. This is the first demonstration to realize the application of durable drag reduction by improving the mechanical stability of superhydrophobic coatings. We do believe that superhydrophobic surfaces with good resistance to mechanical abrasion or scratching may draw wide attention and gain significant applications with durable drag-reducing properties.

  16. Shaped Apertures in Photoresist Films Enhance the Lifetime and Mechanical Stability of Suspended Lipid Bilayers

    PubMed Central

    Kalsi, Sumit; Powl, Andrew M.; Wallace, B.A.; Morgan, Hywel; de Planque, Maurits R.R.

    2014-01-01

    Planar lipid bilayers suspended in apertures provide a controlled environment for ion channel studies. However, short lifetimes and poor mechanical stability of suspended bilayers limit the experimental throughput of bilayer electrophysiology experiments. Although bilayers are more stable in smaller apertures, ion channel incorporation through vesicle fusion with the suspended bilayer becomes increasingly difficult. In an alternative bilayer stabilization approach, we have developed shaped apertures in SU8 photoresist that have tapered sidewalls and a minimum diameter between 60 and 100 μm. Bilayers formed at the thin tip of these shaped apertures, either with the painting or the folding method, display drastically increased lifetimes, typically >20 h, and mechanical stability, being able to withstand extensive perturbation of the buffer solution. Single-channel electrical recordings of the peptide alamethicin and of the proteoliposome-delivered potassium channel KcsA demonstrate channel conductance with low noise, made possible by the small capacitance of the 50 μm thick SU8 septum, which is only thinned around the aperture, and unimpeded proteoliposome fusion, enabled by the large aperture diameter. We anticipate that these shaped apertures with micrometer edge thickness can substantially enhance the throughput of channel characterization by bilayer lipid membrane electrophysiology, especially in combination with automated parallel bilayer platforms. PMID:24739164

  17. Iridium-Tin oxide solid-solution nanocatalysts with enhanced activity and stability for oxygen evolution

    NASA Astrophysics Data System (ADS)

    Li, Guangfu; Yu, Hongmei; Yang, Donglei; Chi, Jun; Wang, Xunying; Sun, Shucheng; Shao, Zhigang; Yi, Baolian

    2016-09-01

    Addressing major challenges from the material cost, efficiency and stability, it is highly desirable to develop high-performance catalysts for oxygen evolution reaction (OER). Herein we explore a facile surfactant-assisted approach for fabricating Irsbnd Sn (Ir/Sn = 0.6/0.4, by mol.) nano-oxide catalysts with good morphology control. Direct proofs from XRD and X-ray photoelectron spectra indicate hydrophilic triblock polymer (TBP, like Pluronic® F108) surfactant can boost the formation of stable solid-solution structure. With the TBP hydrophilic and block-length increase, the fabricated Irsbnd Sn oxides undergoing the rod-to-sphere transition obtain the relatively lower crystallization, decreased crystallite size, Ir-enriched surface and incremental available active sites, all of which can bolster the OER activity and stability. Meanwhile, it is observed that the coupled Ir oxidative etching takes a crucial role in determining the material structure and performance. Compared with commercial Ir black, half-cell tests confirm F108-assistant catalysts with over 40 wt% Ir loading reduction show 2-fold activity enhancement as well as significant stability improvement. The lowest cell voltage using 0.88 mg cm-2 Ir loading is only 1.621 V at 1000 mA cm-2 and 80 °C with a concomitant energy efficiency of 75.8% which is beyond the DOE 2017 efficiency target of 74%.

  18. ITO/ATO bilayer transparent electrodes with enhanced light scattering, thermal stability and electrical conductance

    NASA Astrophysics Data System (ADS)

    Guillén, C.; Montero, J.; Herrero, J.

    2016-10-01

    Transparent electrodes based on In2O3:Sn (ITO) and SnO2:Sb (ATO) thin films have been deposited by sputtering at room temperature on soda lime glass (SLG) substrates. The preparation conditions were adjusted to obtain 250 nm-thick ITO layers with high conductivity and textured ATO coatings with various thicknesses from 80 to 200 nm. These ITO and ATO films have been combined to enhance the optical scattering and the electrical conductivity of the bilayer electrodes. Besides, a suitable ATO coating can prevent the oxidation of the ITO underlayer, thus increasing the stability of the overall electrical performance. With this purpose the structure, morphology, optical and electrical properties have been analysed comparatively for SLG/ITO, SLG/ATO and SLG/ITO/ATO samples after heating in air at 500 °C, studying the influence of the ATO layer thickness on the light scattering and thermal stability of the electrodes. In this way, a minimum sheet resistance of 8 Ω/sq has been achieved with a 120 nm-thick ATO film deposited on the 250 nm-thick ITO layer; such stacked electrode has visible transmittance near 80% and average haze HT = 10%, showing superior stability, light scattering and electrical performance than the isolated ITO and ATO films.

  19. Self aligning electron beam gun having enhanced thermal and mechanical stability

    DOEpatents

    Scarpetti, Jr., Raymond D.; Parkison, Clarence D.; Switzer, Vernon A.; Lee, Young J.; Sawyer, William C.

    1995-01-01

    A compact, high power electron gun having enhanced thermal and mechanical stability which incorporates a mechanically coupled, self aligning structure for the anode and cathode. The enhanced stability, and reduced need for realignment of the cathode to the anode and downstream optics during operation are achieved by use of a common support structure for the cathode and anode which requires no adjustment screws or spacers. The electron gun of the present invention also incorporates a modular design for the cathode, in which the electron emitter, its support structure, and the hardware required to attach the emitter assembly to the rest of the gun are a single element. This modular design makes replacement of the emitter simpler and requires no realignment after a new emitter has been installed. Compactness and a reduction in the possibility of high voltage breakdown are achieved by shielding the "triple point" where the electrode, insulator, and vacuum meet. The use of electric discharge machining (EDM) for fabricating the emitter allows for the accurate machining of the emitter into intricate shapes without encountering the normal stresses developed by standard emitter fabrication techniques.

  20. Self aligning electron beam gun having enhanced thermal and mechanical stability

    DOEpatents

    Scarpetti, R.D. Jr.; Parkison, C.D.; Switzer, V.A.; Lee, Y.J.; Sawyer, W.C.

    1995-05-16

    A compact, high power electron gun is disclosed having enhanced thermal and mechanical stability which incorporates a mechanically coupled, self aligning structure for the anode and cathode. The enhanced stability, and reduced need for realignment of the cathode to the anode and downstream optics during operation are achieved by use of a common support structure for the cathode and anode which requires no adjustment screws or spacers. The electron gun of the present invention also incorporates a modular design for the cathode, in which the electron emitter, its support structure, and the hardware required to attach the emitter assembly to the rest of the gun are a single element. This modular design makes replacement of the emitter simpler and requires no realignment after a new emitter has been installed. Compactness and a reduction in the possibility of high voltage breakdown are achieved by shielding the ``triple point`` where the electrode, insulator, and vacuum meet. The use of electric discharge machining (EDM) for fabricating the emitter allows for the accurate machining of the emitter into intricate shapes without encountering the normal stresses developed by standard emitter fabrication techniques. 12 Figs.