Exploring Protein Stability by Comparative Molecular Dynamics Simulations of Homologous Hyperthermophilic, Mesophilic, and Psychrophilic Proteins.

PubMed

Khan, Sara; Farooq, Umar; Kurnikova, Maria

2016-11-28

In the present studies, we analyzed the influence of temperature on the stability and dynamics of the α subunit of tryptophan synthase (TRPS) from hyperthermophilic, mesophilic, and psychrophilic homologues at different temperatures by molecular dynamics simulations. Employing different indicators such as root-mean-square deviations, root-mean-square fluctuations, principal component analysis, and free energy landscapes, this study manifests the diverse behavior of these homologues with changes in temperature. Especially, an enhancement in the collective motions, classified as representative motions, is observed at high temperature. Similarly, the criterion for the selection of electrostatic interactions in terms of their life span (duty cycle) has indeed helped in identifying the short- and long-lived electrostatic interactions and how they affect the protein's overall stability at different temperatures. Rigidity and flexibility patterns of the homologous proteins are examined using FIRST software along with the calculation of duty cycles with various threshold limits at different temperatures. Rigid cluster decomposition in TRPS of psychrophilic, mesophilic, and hyperthermophilic origin identifies the flexible and rigid regions in the protein. Early loss of rigidity is observed in mesophilic TRPS via loss of contact between the major fragments of the protein compared with the other homologues. In spite of the high similarity of their three-dimensional structures, the overall responses of the three proteins to varying temperatures are significantly different.

Watt steam governor stability

NASA Astrophysics Data System (ADS)

Denny, Mark

2002-05-01

The physics of the fly-ball governor, introduced to regulate the speed of steam engines, is here analysed anew. The original analysis is generalized to arbitrary governor geometry. The well-known stability criterion for the linearized system breaks down for large excursions from equilibrium; we show approximately how this criterion changes.

The stability of the epitaxially introduced metastable metallic structures of thin layers and multilayers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cadeville, M.C.

Among the very large number of metallic thin films, sandwiches and multilayers which have been elaborated by epitaxy on various single crystalline substrates during the last decade, few new structures are reported. Limiting to the case of 3d metals, one finds with a great confidence bcc Cobalt, possibly bee Nickel and a non-compact hexagonal (hp) iron. Moreover structures existing at high temperature under ambient pressure are epitaxially stabilized at room temperature (RT) like fcc Cobalt, fcc Iron, fcc and bcc Manganese. The hcp iron which is stable under high pressure at RT would not be epitaxially stabilized at ambient pressuremore » conversely to first findings. The critical thickness of the metastable phase is generally limited to some monolayers in thin films, being slightly increased in sandwiches or multilayers, even if the phenomenological wetting criterion to build superlattices is not satisfied. No increased magnetic moment has been found up to now in the expanded lattices, contrary to band structure calculation predictions. 56 refs.« less

Scandia-and-Yttria-Stabilized Zirconia for Thermal Barriers

NASA Technical Reports Server (NTRS)

Mess, Derek

2003-01-01

yttria in suitable proportions has shown promise of being a superior thermal- barrier coating (TBC) material, relative to zirconia stabilized with yttria only. More specifically, a range of compositions in the zirconia/scandia/yttria material system has been found to afford increased resistance to deleterious phase transformations at temperatures high enough to cause deterioration of yttria-stabilized zirconia. Yttria-stabilized zirconia TBCs have been applied to metallic substrates in gas turbine and jet engines to protect the substrates against high operating temperatures. These coatings have porous and microcracked structures, which can accommodate strains induced by thermal-expansion mismatch and thermal shock. The longevity of such a coating depends upon yttria as a stabilizing additive that helps to maintain the zirconia in an yttria-rich, socalled non-transformable tetragonal crystallographic phase, thus preventing transformation to the monoclinic phase with an associated deleterious volume change. However, at a temperature greater than about 1,200 C, there is sufficient atomic mobility that the equilibrium, transformable zirconia phase is formed. Upon subsequent cooling, this phase transforms to the monoclinic phase, with an associated volume change that adversely affects the integrity of the coating. Recently, scandia was identified as a stabilizer that could be used instead of, or in addition to, yttria. Of particular interest are scandia-and-yttria-stabilized zirconia (SYSZ) compositions of about 6 mole percent scandia and 1 mole percent yttria, which have been found to exhibit remarkable phase stability at a temperature of 1,400 C in simple aging tests. Unfortunately, scandia is expensive, so that the problem becomes one of determining whether there are compositions with smaller proportions of scandia that afford the required high-temperature stability. In an attempt to solve this problem, experiments were performed on specimens made with reduced proportions of scandia. The criterion used to judge these specimens was whether they retained the non-transformable tetragonal phase after a severe heat treatment of 140 hours at 1,400 C.

Establishment of an equivalence acceptance criterion for accelerated stability studies.

PubMed

Burdick, Richard K; Sidor, Leslie

2013-01-01

In this article, the use of statistical equivalence testing for providing evidence of process comparability in an accelerated stability study is advocated over the use of a test of differences. The objective of such a study is to demonstrate comparability by showing that the stability profiles under nonrecommended storage conditions of two processes are equivalent. Because it is difficult at accelerated conditions to find a direct link to product specifications, and hence product safety and efficacy, an equivalence acceptance criterion is proposed that is based on the statistical concept of effect size. As with all statistical tests of equivalence, it is important to collect input from appropriate subject-matter experts when defining the acceptance criterion.

The stability analysis of magnetohydrodynamic equilibria - Comparing the thermodynamic approach with the energy principle

NASA Technical Reports Server (NTRS)

Brinkmann, R. P.

1989-01-01

This paper is a contribution to the stability analysis of current-carrying plasmas, i.e., plasma systems that are forced by external mchanisms to carry a nonrelaxing electrical current. Under restriction to translationally invariant configurations, the thermodynamic stability criterion for a multicomponent plasma is rederived within the framework of nonideal MHD. The chosen dynamics neglects scalar resistivity, but allows for other types of dissipation effects both in Ohm's law and in the equation of motion. In the second section of the paper, the thermodynamic stability criterion is compared with the ideal MHD based energy principle of Bernstein et al. With the help of Schwarz's inequality, it is shown that the former criterion is always more 'pessimistic' than the latter, i.e., that thermodynamic stability implies stability according to the MHD principle, but not vice versa. This reuslt confirms the physical plausible idea that dissipational effects tend to weaken the stability properties of current-carrying plasma equilibria by breaking the constraints of ideal MHD and allowing for possibly destabilizing effects such as magnetic field line reconfiguration.

Steady-state solutions of a diffusive energy-balance climate model and their stability

NASA Technical Reports Server (NTRS)

Ghil, M.

1975-01-01

A diffusive energy-balance climate model, governed by a nonlinear parabolic partial differential equation, was studied. Three positive steady-state solutions of this equation are found; they correspond to three possible climates of our planet: an interglacial (nearly identical to the present climate), a glacial, and a completely ice-covered earth. Models similar to the main one are considered, and the number of their steady states was determined. All the models have albedo continuously varying with latitude and temperature, and entirely diffusive horizontal heat transfer. The stability under small perturbations of the main model's climates was investigated. A stability criterion is derived, and its application shows that the present climate and the deep freeze are stable, whereas the model's glacial is unstable. The dependence was examined of the number of steady states and of their stability on the average solar radiation.

Thermal instability in gravitationally stratified plasmas: implications for multiphase structure in clusters and galaxy haloes

NASA Astrophysics Data System (ADS)

McCourt, Michael; Sharma, Prateek; Quataert, Eliot; Parrish, Ian J.

2012-02-01

We study the interplay among cooling, heating, conduction and magnetic fields in gravitationally stratified plasmas using simplified, plane-parallel numerical simulations. Since the physical heating mechanism remains uncertain in massive haloes such as groups or clusters, we adopt a simple, phenomenological prescription which enforces global thermal equilibrium and prevents a cooling flow. The plasma remains susceptible to local thermal instability, however, and cooling drives an inward flow of material. For physically plausible heating mechanisms in clusters, the thermal stability of the plasma is independent of its convective stability. We find that the ratio of the cooling time-scale to the dynamical time-scale tcool/tff controls the non-linear evolution and saturation of the thermal instability: when tcool/tff≲ 1, the plasma develops extended multiphase structure, whereas when tcool/tff≳ 1 it does not. (In a companion paper, we show that the criterion for thermal instability in a more realistic, spherical potential is somewhat less stringent, tcool/tff≲ 10.) When thermal conduction is anisotropic with respect to the magnetic field, the criterion for multiphase gas is essentially independent of the thermal conductivity of the plasma. Our criterion for local thermal instability to produce multiphase structure is an extension of the cold versus hot accretion modes in galaxy formation that applies at all radii in hot haloes, not just to the virial shock. We show that this criterion is consistent with data on multiphase gas in galaxy groups and clusters; in addition, when tcool/tff≳ 1, the net cooling rate to low temperatures and the mass flux to small radii are suppressed enough relative to models without heating to be qualitatively consistent with star formation rates and X-ray line emission in groups and clusters.

A solid criterion based on strict LMI without invoking equality constraint for stabilization of continuous singular systems.

PubMed

Zhang, Xuefeng; Chen, YangQuan

2017-11-01

The paper considers the stabilization issue of linear continuous singular systems by dealing with strict linear matrix inequalities (LMIs) without invoking equality constraint and proposes a complete and effective solved LMIs formulation. The criterion is necessary and sufficient condition and can be directly solved the feasible solutions with LMI toolbox and is much more tractable and reliable in numerical simulation than existing results, which involve positive semi-definite LMIs with equality constraints. The most important property of the criterion proposed in the paper is that it can overcome the drawbacks of the invalidity caused by the singularity of Ω=PE T +SQ for stabilization of singular systems. Two counterexamples are presented to avoid the disadvantages of the existing condition of stabilization of continuous singular systems. Copyright © 2017 ISA. Published by Elsevier Ltd. All rights reserved.

Periodic gaits for the CMU ambler

NASA Technical Reports Server (NTRS)

Mahalingam, Swaminathan; Dwivedi, Suren N.

1989-01-01

The configuration of the Carnegie Mellon University Ambler, a six legged autonomous walking vehicle for exploring Mars, enables the recovery of a trailing leg past the leading leg to reduce the energy expenditure in terrain interactions. Gaits developed for this unprecedented configuration are described. A stability criterion was developed which ensures stability of the vehicle in the event of failure of any one of the supporting legs. Periodic gaits developed for the Ambler utilize the Ambler's unique abilities, and continuously satisfy the stability criterion.

Periodic gaits for the CMU Ambler

NASA Astrophysics Data System (ADS)

Dwivedi, Suren N.; Mahalingam, Swaminathan

1992-02-01

The configuration of the Carnegie-Mellon University Ambler, a six-legged autonomous walking vehicle for exploring Mars, enables the recovery of a trailing leg past the leading leg to reduce the energy expenditure in terrain interactions. In this article, gaits developed for this unprecedented configuration are described. A stability criterion has been developed that ensures stability of the vehicle in the event of failure of any one of the supporting legs. Periodic gaits developed for the Ambler utilize the Ambler's unique abilities and continuously satisfy the stability criterion.

Diffusion modelling of metamorphic layered coronas with stability criterion and consideration of affinity

NASA Astrophysics Data System (ADS)

Ashworth, J. R.; Sheplev, V. S.

1997-09-01

Layered coronas between two reactant minerals can, in many cases, be attributed to diffusion-controlled growth with local equilibrium. This paper clarifies and unifies the previous approaches of various authors to the simplest form of modelling, which uses no assumed values for thermochemical quantities. A realistic overall reaction must be estimated from measured overall proportions of minerals and their major element compositions. Modelling is not restricted to a particular number of components S, relative to the number of phases Φ. IfΦ > S + 1, the overall reaction is a combination of simultaneous reactions. The stepwise method, solving for the local reaction at each boundary in turn, is extended to allow for recurrence of a mineral (its presence in two parts of the layer structure separated by a gap). The equations are also given in matrix form. A thermodynamic stability criterion is derived, determining which layer sequence is truly stable if several are computable from the same inputs. A layer structure satisfying the stability criterion has greater growth rate (and greater rate of entropy production) than the other computable layer sequences. This criterion of greatest entropy production is distinct from Prigogine's theorem of minimum entropy production, which distinguishes the stationary or quasi-stationary state from other states of the same layer sequence. The criterion leads to modification of previous results for coronas comprising hornblende, spinel, and orthopyroxene between olivine (Ol) and plagioclase (Pl). The outcome supports the previous inference that Si, and particularly Al, commonly behave as immobile relative to other cation-forming major elements. The affinity (-ΔG) of a corona-forming reaction is estimated, using previous estimates of diffusion coefficient and the duration t of reaction, together with a new model quantity (-ΔG) *. For an example of the Ol + Pl reaction, a rough calculation gives (-ΔG) > 1.7RT (per mole of P1 consumed, based on a 24-oxygen formula for Pl). At 600-700°C, this represents (-ΔG) > 10kJ mol -1 and departure from equilibrium temperature by at least ˜ 100°C. The lower end of this range is petrologically reasonable and, for t < 100Ma, corresponds to a Fick's-law diffusion coefficient for Al, DAl > 10 -25m 2s -1, larger than expected for lattice diffusion but consistent with fluid-absent grain-boundary diffusion and small concentration gradients.

Automatic location of disruption times in JET

NASA Astrophysics Data System (ADS)

Moreno, R.; Vega, J.; Murari, A.

2014-11-01

The loss of stability and confinement in tokamak plasmas can induce critical events known as disruptions. Disruptions produce strong electromagnetic forces and thermal loads which can damage fundamental components of the devices. Determining the disruption time is extremely important for various disruption studies: theoretical models, physics-driven models, or disruption predictors. In JET, during the experimental campaigns with the JET-C (Carbon Fiber Composite) wall, a common criterion to determine the disruption time consisted of locating the time of the thermal quench. However, with the metallic ITER-like wall (JET-ILW), this criterion is usually not valid. Several thermal quenches may occur previous to the current quench but the temperature recovers. Therefore, a new criterion has to be defined. A possibility is to use the start of the current quench as disruption time. This work describes the implementation of an automatic data processing method to estimate the disruption time according to this new definition. This automatic determination allows both reducing human efforts to locate the disruption times and standardizing the estimates (with the benefit of being less vulnerable to human errors).

Stability Assessment as a Criterion of Stabilization of the Movement Trajectory of Mobile Crane Working Elements

NASA Astrophysics Data System (ADS)

Kacalak, W.; Budniak, Z.; Majewski, M.

2018-02-01

The article presents a stability assessment method of the mobile crane handling system based on the safety indicator values that were accepted as the trajectory optimization criterion. With the use of the mathematical model built and the model built in the integrated CAD/CAE environment, analyses were conducted of the displacements of the mass centre of the crane system, reactions of the outrigger system, stabilizing and overturning torques that act on the crane as well as the safety indicator values for the given movement trajectories of the crane working elements.

Effects of Hall current and electrical resistivity on the stability of gravitating anisotropic quantum plasma

NASA Astrophysics Data System (ADS)

Bhakta, S.; Prajapati, R. P.

2018-02-01

The effects of Hall current and finite electrical resistivity are studied on the stability of uniformly rotating and self-gravitating anisotropic quantum plasma. The generalized Ohm's law modified by Hall current and electrical resistivity is used along with the quantum magnetohydrodynamic fluid equations. The general dispersion relation is derived using normal mode analysis and discussed in the parallel and perpendicular propagations. In the parallel propagation, the Jeans instability criterion, expression of critical Jeans wavenumber, and Jeans length are found to be independent of non-ideal effects and uniform rotation but in perpendicular propagation only rotation affects the Jeans instability criterion. The unstable gravitating mode modified by Bohm potential and the stable Alfven mode modified by non-ideal effects are obtained separately. The criterion of firehose instability remains unaffected due to the presence of non-ideal effects. In the perpendicular propagation, finite electrical resistivity and quantum pressure anisotropy modify the dispersion relation, whereas no effect of Hall current was observed in the dispersion characteristics. The Hall current, finite electrical resistivity, rotation, and quantum corrections stabilize the growth rate. The stability of the dynamical system is analyzed using the Routh-Hurwitz criterion.

Stochastic stability assessment of a semi-free piston engine generator concept

NASA Astrophysics Data System (ADS)

Kigezi, T. N.; Gonzalez Anaya, J. A.; Dunne, J. F.

2016-09-01

Small engines, as power generators with low-noise and vibration characteristics, are needed in two niche application areas: as electric vehicle range extenders and as domestic micro Combined Heat and Power systems. A recent semi-free piston design known as the AMOCATIC generator fully meets this requirement. The engine potentially allows for high energy conversion efficiencies at resonance derived from having a mass and spring assembly. As with free-piston engines in general, stability and control of piston motion has been cited as the prime challenge limiting the technology's widespread application. Using physical principles, we derive in this paper two important results: an energy balance criterion and a related general stability criterion for a semi-free piston engine. Control is achieved by systematically designing a Proportional Integral (PI) controller using a control-oriented engine model for which a specific stability condition is stated. All results are presented in closed form throughout the paper. Simulation results under stochastic pressure conditions show that the proposed energy balance, stability criterion, and PI controller, operate as predicted to yield stable engine operation at fixed compression ratio.

Prediction of Fracture Initiation in Hot Compression of Burn-Resistant Ti-35V-15Cr-0.3Si-0.1C Alloy

NASA Astrophysics Data System (ADS)

Zhang, Saifei; Zeng, Weidong; Zhou, Dadi; Lai, Yunjin

2015-11-01

An important concern in hot working of metals is whether the desired deformation can be accomplished without fracture of the material. This paper builds a fracture prediction model to predict fracture initiation in hot compression of a burn-resistant beta-stabilized titanium alloy Ti-35V-15Cr-0.3Si-0.1C using a combined approach of upsetting experiments, theoretical failure criteria and finite element (FE) simulation techniques. A series of isothermal compression experiments on cylindrical specimens were conducted in temperature range of 900-1150 °C, strain rate of 0.01-10 s-1 first to obtain fracture samples and primary reduction data. Based on that, a comparison of eight commonly used theoretical failure criteria was made and Oh criterion was selected and coded into a subroutine. FE simulation of upsetting experiments on cylindrical specimens was then performed to determine the fracture threshold values of Oh criterion. By building a correlation between threshold values and the deforming parameters (temperature and strain rate, or Zener-Hollomon parameter), a new fracture prediction model based on Oh criterion was established. The new model shows an exponential decay relationship between threshold values and Zener-Hollomon parameter (Z), and the relative error of the model is less than 15%. This model was then applied successfully in the cogging of Ti-35V-15Cr-0.3Si-0.1C billet.

Majority of Solar Wind Intervals Support Ion-Driven Instabilities

NASA Astrophysics Data System (ADS)

Klein, K. G.; Alterman, B. L.; Stevens, M. L.; Vech, D.; Kasper, J. C.

2018-05-01

We perform a statistical assessment of solar wind stability at 1 AU against ion sources of free energy using Nyquist's instability criterion. In contrast to typically employed threshold models which consider a single free-energy source, this method includes the effects of proton and He2 + temperature anisotropy with respect to the background magnetic field as well as relative drifts between the proton core, proton beam, and He2 + components on stability. Of 309 randomly selected spectra from the Wind spacecraft, 53.7% are unstable when the ion components are modeled as drifting bi-Maxwellians; only 4.5% of the spectra are unstable to long-wavelength instabilities. A majority of the instabilities occur for spectra where a proton beam is resolved. Nearly all observed instabilities have growth rates γ slower than instrumental and ion-kinetic-scale timescales. Unstable spectra are associated with relatively large He2 + drift speeds and/or a departure of the core proton temperature from isotropy; other parametric dependencies of unstable spectra are also identified.

Majority of Solar Wind Intervals Support Ion-Driven Instabilities.

PubMed

Klein, K G; Alterman, B L; Stevens, M L; Vech, D; Kasper, J C

2018-05-18

We perform a statistical assessment of solar wind stability at 1 AU against ion sources of free energy using Nyquist's instability criterion. In contrast to typically employed threshold models which consider a single free-energy source, this method includes the effects of proton and He^{2+} temperature anisotropy with respect to the background magnetic field as well as relative drifts between the proton core, proton beam, and He^{2+} components on stability. Of 309 randomly selected spectra from the Wind spacecraft, 53.7% are unstable when the ion components are modeled as drifting bi-Maxwellians; only 4.5% of the spectra are unstable to long-wavelength instabilities. A majority of the instabilities occur for spectra where a proton beam is resolved. Nearly all observed instabilities have growth rates γ slower than instrumental and ion-kinetic-scale timescales. Unstable spectra are associated with relatively large He^{2+} drift speeds and/or a departure of the core proton temperature from isotropy; other parametric dependencies of unstable spectra are also identified.

Dynamics of an HBV/HCV infection model with intracellular delay and cell proliferation

NASA Astrophysics Data System (ADS)

Zhang, Fengqin; Li, Jianquan; Zheng, Chongwu; Wang, Lin

2017-01-01

A new mathematical model of hepatitis B/C virus (HBV/HCV) infection which incorporates the proliferation of healthy hepatocyte cells and the latent period of infected hepatocyte cells is proposed and studied. The dynamics is analyzed via Pontryagin's method and a newly proposed alternative geometric stability switch criterion. Sharp conditions ensuring stability of the infection persistent equilibrium are derived by applying Pontryagin's method. Using the intracellular delay as the bifurcation parameter and applying an alternative geometric stability switch criterion, we show that the HBV/HCV infection model undergoes stability switches. Furthermore, numerical simulations illustrate that the intracellular delay can induce complex dynamics such as persistence bubbles and chaos.

Urey prize lecture: On the diversity of plausible planetary systems

NASA Technical Reports Server (NTRS)

Lissauer, J. J.

1995-01-01

Models of planet formation and of the orbital stability of planetary systems are used to predict the variety of planetary and satellite systems that may be present within our galaxy. A new approximate global criterion for orbital stability of planetary systems based on an extension of the local resonance overlap criterion is proposed. This criterion implies that at least some of Uranus' small inner moons are significantly less massive than predicted by estimates based on Voyager volumes and densities assumed to equal that of Miranda. Simple calculations (neglecting planetary gravity) suggest that giant planets which acrete substantial amounts of gas while their envelopes are extremely distended ultimately rotate rapidly in the prgrade direction.

Convective instabilities in SN 1987A

NASA Technical Reports Server (NTRS)

Benz, Willy; Thielemann, Friedrich-Karl

1990-01-01

Following Bandiera (1984), it is shown that the relevant criterion to determine the stability of a blast wave, propagating through the layers of a massive star in a supernova explosion, is the Schwarzschild (or Ledoux) criterion rather than the Rayleigh-Taylor criterion. Both criteria coincide only in the incompressible limit. Results of a linear stability analysis are presented for a one-dimensional (spherical) explosion in a realistic model for the progenitor of SN 1987A. When applying the Schwarzschild criterion, unstable regions get extended considerably. Convection is found to develop behind the shock, with a characteristic growth rate corresponding to a time scale much smaller than the shock traversal time. This ensures that efficient mixing will take place. Since the entire ejected mass is found to be convectively unstable, Ni can be transported outward, even into the hydrogen envelope, while hydrogen can be mixed deep into the helium core.

Continuous control of chaos based on the stability criterion.

PubMed

Yu, Hong Jie; Liu, Yan Zhu; Peng, Jian Hua

2004-06-01

A method of chaos control based on stability criterion is proposed in the present paper. This method can stabilize chaotic systems onto a desired periodic orbit by a small time-continuous perturbation nonlinear feedback. This method does not require linearization of the system around the stabilized orbit and only an approximate location of the desired periodic orbit is required which can be automatically detected in the control process. The control can be started at any moment by choosing appropriate perturbation restriction condition. It seems that more flexibility and convenience are the main advantages of this method. The discussions on control of attitude motion of a spacecraft, Rössler system, and two coupled Duffing oscillators are given as numerical examples.

Discrete time modeling and stability analysis of TCP Vegas

NASA Astrophysics Data System (ADS)

You, Byungyong; Koo, Kyungmo; Lee, Jin S.

2007-12-01

This paper presents an analysis method for TCP Vegas network model with single link and single source. Some papers showed global stability of several network models, but those models are not a dual problem where dynamics both exist in sources and links such as TCP Vegas. Other papers studied TCP Vegas as a dual problem, but it did not fully derive an asymptotic stability region. Therefore we analyze TCP Vegas with Jury's criterion which is necessary and sufficient condition. So we use state space model in discrete time and by using Jury's criterion, we could find an asymptotic stability region of TCP Vegas network model. This result is verified by ns-2 simulation. And by comparing with other results, we could know our method performed well.

Stability and instability of axisymmetric droplets in thermocapillary-driven thin films

NASA Astrophysics Data System (ADS)

Nicolaou, Zachary G.

2018-03-01

The stability of compactly supported, axisymmetric droplet states is considered for driven thin viscous films evolving on two-dimensional surfaces. Stability is assessed using Lyapunov energy methods afforded by the Cahn-Hilliard variational form of the governing equation. For general driving forces, a criterion on the gradient of profiles at the boundary of their support (their contact slope) is shown to be a necessary condition for stability. Additional necessary and sufficient conditions for stability are established for a specific driving force corresponding to a thermocapillary-driven film. It is found that only droplets of sufficiently short height that satisfy the contact slope criterion are stable. This destabilization of droplets with increasing height is characterized as a saddle-node bifurcation between a branch of tall, unstable droplets and a branch of short, stable droplets.

Modeling and Simulation of Swirl Stabilized Turbulent Non-Premixed Flames

NASA Astrophysics Data System (ADS)

Badillo-Rios, Salvador; Karagozian, Ann

2017-11-01

Flame stabilization is an important design criterion for many combustion chambers, especially at lean conditions and/or high power output, where insufficient stabilization can result in dangerous oscillations and noisy or damaged combustors. At high flow rates, swirling flow can offer a suitable stabilization mechanism, although understanding the dynamics of swirl-stabilized turbulent flames remains a significant challenge. Utilizing the General Equation and Mesh Solver (GEMS) code, which solves the Navier-Stokes equations along with the energy equation and five species equations, 2D axisymmetric and full 3D parametric studies and simulations are performed to guide the design and development of an experimental swirl combustor configuration and to study the effects of swirl on statistically stationary combustion. Results show that as the momentum of air is directed into the inner air inlet rather than the outer inlet of the swirl combustor, the central recirculating region becomes stronger and more unsteady, improving mixing and burning efficiency in that region. A high temperature region is found to occur as a result of burning of the trapped fuel from the central toroidal vortex. The effects of other parameters on flowfield and flame-stabilization dynamics are explored. Supported by ERC, Inc. (PS150006) and AFOSR (Dr. Chiping Li).

Energy Criterion for the Spectral Stability of Discrete Breathers.

PubMed

Kevrekidis, Panayotis G; Cuevas-Maraver, Jesús; Pelinovsky, Dmitry E

2016-08-26

Discrete breathers are ubiquitous structures in nonlinear anharmonic models ranging from the prototypical example of the Fermi-Pasta-Ulam model to Klein-Gordon nonlinear lattices, among many others. We propose a general criterion for the emergence of instabilities of discrete breathers analogous to the well-established Vakhitov-Kolokolov criterion for solitary waves. The criterion involves the change of monotonicity of the discrete breather's energy as a function of the breather frequency. Our analysis suggests and numerical results corroborate that breathers with increasing (decreasing) energy-frequency dependence are generically unstable in soft (hard) nonlinear potentials.

New R-SiC extends service life in kiln furniture

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sonntag, A.

1997-11-01

Silicon carbide kiln furniture systems are an essential part of modern high-temperature technology. SiC ceramics have exceptional high-temperature stability and thermal shock resistance., They show no plastic deformation (creep) under mechanical load and maintain their geometry after each high-temperature cycle. Therefore, various new kiln systems with light and open setting patterns can be realized where more fired goods can be produced with less kiln furniture ballast and within shorter firing cycles. The fast-firing technology of porcelain is an opportunity for new SiC kiln furniture ceramics. The new SiC ceramic systems available include: (1) recrystallized SiC (R-SiC); (2) silicon-infiltrated reaction-bonded SiCmore » (SiSiC); and (3) nitride-bonded SiC (NSiC). The new SiC ceramics have an important production criterion in common. They show practically no shrinkage during production. This is important for the manufacture of large shapes, such as beams, rollers and setter plates, as well as tailored geometries that allow light and open kiln furniture construction. Because of the extraordinarily high thermal shock resistance, high strength and high-temperature creep stability of these SiC ceramics, delicate and precise kiln furniture configurations have been introduced. One application is the fast firing of tableware with automatic setting robots.« less

Stability analysis of a run-of-river diversion hydropower plant with surge tank and spillway in the head pond.

PubMed

Sarasúa, José Ignacio; Elías, Paz; Martínez-Lucas, Guillermo; Pérez-Díaz, Juan Ignacio; Wilhelmi, José Román; Sánchez, José Ángel

2014-01-01

Run-of-river hydropower plants usually lack significant storage capacity; therefore, the more adequate control strategy would consist of keeping a constant water level at the intake pond in order to harness the maximum amount of energy from the river flow or to reduce the surface flooded in the head pond. In this paper, a standard PI control system of a run-of-river diversion hydropower plant with surge tank and a spillway in the head pond that evacuates part of the river flow plant is studied. A stability analysis based on the Routh-Hurwitz criterion is carried out and a practical criterion for tuning the gains of the PI controller is proposed. Conclusions about the head pond and surge tank areas are drawn from the stability analysis. Finally, this criterion is applied to a real hydropower plant in design state; the importance of considering the spillway dimensions and turbine characteristic curves for adequate tuning of the controller gains is highlighted.

Stability Analysis of a Run-of-River Diversion Hydropower Plant with Surge Tank and Spillway in the Head Pond

PubMed Central

Sarasúa, José Ignacio; Elías, Paz; Wilhelmi, José Román; Sánchez, José Ángel

2014-01-01

Run-of-river hydropower plants usually lack significant storage capacity; therefore, the more adequate control strategy would consist of keeping a constant water level at the intake pond in order to harness the maximum amount of energy from the river flow or to reduce the surface flooded in the head pond. In this paper, a standard PI control system of a run-of-river diversion hydropower plant with surge tank and a spillway in the head pond that evacuates part of the river flow plant is studied. A stability analysis based on the Routh-Hurwitz criterion is carried out and a practical criterion for tuning the gains of the PI controller is proposed. Conclusions about the head pond and surge tank areas are drawn from the stability analysis. Finally, this criterion is applied to a real hydropower plant in design state; the importance of considering the spillway dimensions and turbine characteristic curves for adequate tuning of the controller gains is highlighted. PMID:25405237

Stability of the iterative solutions of integral equations as one phase freezing criterion.

PubMed

Fantoni, R; Pastore, G

2003-10-01

A recently proposed connection between the threshold for the stability of the iterative solution of integral equations for the pair correlation functions of a classical fluid and the structural instability of the corresponding real fluid is carefully analyzed. Direct calculation of the Lyapunov exponent of the standard iterative solution of hypernetted chain and Percus-Yevick integral equations for the one-dimensional (1D) hard rods fluid shows the same behavior observed in 3D systems. Since no phase transition is allowed in such 1D system, our analysis shows that the proposed one phase criterion, at least in this case, fails. We argue that the observed proximity between the numerical and the structural instability in 3D originates from the enhanced structure present in the fluid but, in view of the arbitrary dependence on the iteration scheme, it seems uneasy to relate the numerical stability analysis to a robust one-phase criterion for predicting a thermodynamic phase transition.

Neutrality and evolvability of designed protein sequences

NASA Astrophysics Data System (ADS)

Bhattacherjee, Arnab; Biswas, Parbati

2010-07-01

The effect of foldability on protein’s evolvability is analyzed by a two-prong approach consisting of a self-consistent mean-field theory and Monte Carlo simulations. Theory and simulation models representing protein sequences with binary patterning of amino acid residues compatible with a particular foldability criteria are used. This generalized foldability criterion is derived using the high temperature cumulant expansion approximating the free energy of folding. The effect of cumulative point mutations on these designed proteins is studied under neutral condition. The robustness, protein’s ability to tolerate random point mutations is determined with a selective pressure of stability (ΔΔG) for the theory designed sequences, which are found to be more robust than that of Monte Carlo and mean-field-biased Monte Carlo generated sequences. The results show that this foldability criterion selects viable protein sequences more effectively compared to the Monte Carlo method, which has a marked effect on how the selective pressure shapes the evolutionary sequence space. These observations may impact de novo sequence design and its applications in protein engineering.

Improved Multi-Axial, Temperature and Time Dependent (MATT) Failure Model

NASA Technical Reports Server (NTRS)

Richardson, D. E.; Anderson, G. L.; Macon, D. J.

2002-01-01

An extensive effort has recently been completed by the Space Shuttle's Reusable Solid Rocket Motor (RSRM) nozzle program to completely characterize the effects of multi-axial loading, temperature and time on the failure characteristics of three filled epoxy adhesives (TIGA 321, EA913NA, EA946). As part of this effort, a single general failure criterion was developed that accounted for these effects simultaneously. This model was named the Multi- Axial, Temperature, and Time Dependent or MATT failure criterion. Due to the intricate nature of the failure criterion, some parameters were required to be calculated using complex equations or numerical methods. This paper documents some simple but accurate modifications to the failure criterion to allow for calculations of failure conditions without complex equations or numerical techniques.

Investigation of thermocapillary convection in a three-liquid-layer system

NASA Astrophysics Data System (ADS)

Géoris, Ph.; Hennenberg, M.; Lebon, G.; Legros, J. C.

1999-06-01

This paper presents the first experimental results on Marangoni Bénard instability in a symmetrical three-layer system. A pure thermocapillary phenomenon has been observed by performing the experiment in a microgravity environment where buoyancy forces can be neglected. This configuration enables the hydrodynamic stability of two identical liquid liquid interfaces subjected to a normal gradient of temperature to be studied. The flow is driven by one interface only and obeys the criterion based on the heat diffusivity ratio proposed by Scriven & Sternling (1959) and Smith (1966). The measured critical temperature difference for the onset of convection is compared to the value obtained from two-dimensional numerical simulations. The results of the simulations are in reasonable agreement with the velocimetry and the thermal experimental data for moderate supercriticality. Numerically and experimentally, the convective pattern exhibits a transition between different convective regimes for similar temperature gradients. Their common detailed features are discussed.

[Thermodynamics of drug polymorphism: domains and stability hierarchy by pressure temperature diagram. Application to the tetramorphism of fananserine].

PubMed

Toscani, S

2002-05-01

In this communication, an application of classical thermodynamics to crystalline solid state polymorphism is shown to allow stability p, T domains and stability hierarchy among crystalline phases of a polymorph to be defined by constructing the unary p, T phase diagram. The three topological rules upon which this construction is founded are presented; the first one is a straight consequence of the least vapour pressure criterion by Ostwald. Calculation of triple point co-ordinates and of two-phase equilibrium curves is based upon using both thermodynamic and crystallographic data obtained at ordinary pressure. Clapeyron equation allows the slopes of the straight lines representing equilibria between condensed phases to be calculated and, hence, triple points situated at high or negative pressure to be determined. On the other hand, the hierarchy among the thermodynamic stability degrees of the crystalline varieties may be inferred from the location of the sublimation curves, by merely acknowledging inequalities among vapour pressures at each temperature on the whole T-range. These building-up processes are pointed out by outlining the achievement of a phase diagram related to the tetramorphism of fananserine, an anxiolytic drug. Three out four crystalline forms, namely phases II, III and IV, possess their own stability domain, although those belonging to phases II and III are limited at high pressure by that of phase IV. Conversely, phase I is overall metastable and exhibits a whole monotropic behaviour.

Calculation of cracking under pulsed heat loads in tungsten manufactured according to ITER specifications

NASA Astrophysics Data System (ADS)

Arakcheev, A. S.; Skovorodin, D. I.; Burdakov, A. V.; Shoshin, A. A.; Polosatkin, S. V.; Vasilyev, A. A.; Postupaev, V. V.; Vyacheslavov, L. N.; Kasatov, A. A.; Huber, A.; Mertens, Ph; Wirtz, M.; Linsmeier, Ch; Kreter, A.; Löwenhoff, Th; Begrambekov, L.; Grunin, A.; Sadovskiy, Ya

2015-12-01

A mathematical model of surface cracking under pulsed heat load was developed. The model correctly describes a smooth brittle-ductile transition. The elastic deformation is described in a thin-heated-layer approximation. The plastic deformation is described with the Hollomon equation. The time dependence of the deformation and stresses is described for one heating-cooling cycle for a material without initial plastic deformation. The model can be applied to tungsten manufactured according to ITER specifications. The model shows that the stability of stress-relieved tungsten deteriorates when the base temperature increases. This proved to be a result of the close ultimate tensile and yield strengths. For a heat load of arbitrary magnitude a stability criterion was obtained in the form of condition on the relation of the ultimate tensile and yield strengths.

Test of the Hill Stability Criterion against Chaos Indicators

NASA Astrophysics Data System (ADS)

Satyal, Suman; Quarles, Billy; Hinse, Tobias

2012-10-01

The efficacy of Hill Stability (HS) criterion is tested against other known chaos indicators such as Maximum Lyapunov Exponents (MLE) and Mean Exponential Growth of Nearby Orbits (MEGNO) maps. First, orbits of four observationally verified binary star systems: γ Cephei, Gliese-86, HD41004, and HD196885 are integrated using standard integration packages (MERCURY, SWIFTER, NBI, C/C++). The HS which measures orbital perturbation of a planet around the primary star due to the secondary star is calculated for each system. The LEs spectra are generated to measure the divergence/convergence rate of stable manifolds and the MEGNO maps are generated by using the variational equations of the system during the integration process. These maps allow to accurately differentiate between stable and unstable dynamical systems. Then the results obtained from the analysis of HS, MLE, and MEGNO maps are checked for their dynamical variations and resemblance. The HS of most of the planets seems to be stable, quasi-periodic for at least ten million years. The MLE and the MEGNO maps also indicate the local quasi-periodicity and global stability in relatively short integration period. The HS criterion is found to be a comparably efficient tool to measure the stability of planetary orbits.

Discrete-time BAM neural networks with variable delays

NASA Astrophysics Data System (ADS)

Liu, Xin-Ge; Tang, Mei-Lan; Martin, Ralph; Liu, Xin-Bi

2007-07-01

This Letter deals with the global exponential stability of discrete-time bidirectional associative memory (BAM) neural networks with variable delays. Using a Lyapunov functional, and linear matrix inequality techniques (LMI), we derive a new delay-dependent exponential stability criterion for BAM neural networks with variable delays. As this criterion has no extra constraints on the variable delay functions, it can be applied to quite general BAM neural networks with a broad range of time delay functions. It is also easy to use in practice. An example is provided to illustrate the theoretical development.

Effect of composition gradient on magnetothermal instability modified by shear and rotation

NASA Astrophysics Data System (ADS)

Gupta, Himanshu; Chaudhuri, Anya; Sadhukhan, Shubhadeep; Chakraborty, Sagar

2018-02-01

We model the intracluster medium as a weakly collisional plasma that is a binary mixture of the hydrogen and the helium ions, along with free electrons. When, owing to the helium sedimentation, the gradient of the mean-molecular weight (or equivalently, composition or helium ions' concentration) of the plasma is not negligible, it can have appreciable influence on the stability criteria of the thermal convective instabilities, e.g. the heat-flux-buoyancy instability and the magnetothermal instability (MTI). These instabilities are consequences of the anisotropic heat conduction occurring preferentially along the magnetic field lines. In this paper, without ignoring the magnetic tension, we first present the mathematical criterion for the onset of composition gradient modified MTI. Subsequently, we relax the commonly adopted equilibrium state in which the plasma is at rest, and assume that the plasma is in a sheared state which may be due to differential rotation. We discuss how the concentration gradient affects the coupling between the Kelvin-Helmholtz instability and the MTI in rendering the plasma unstable or stable. We derive exact stability criterion by working with the sharp boundary case in which the physical variables - temperature, mean-molecular weight, density and magnetic field - change discontinuously from one constant value to another on crossing the boundary. Finally, we perform the linear stability analysis for the case of the differentially rotating plasma that is thermally and compositionally stratified as well. By assuming axisymmetric perturbations, we find the corresponding dispersion relation and the explicit mathematical expression determining the onset of the modified MTI.

Failure Criterion For Isotropic Time Dependent Materials Which Accounts for Multi-Axial Loading

NASA Technical Reports Server (NTRS)

Richardson, D. E.; Anderson, G. L.; Macon, D. J.

2003-01-01

The Space Shuttle's Reusable Solid Rocket Motor (RSRM) nozzle program has recently conducted testing to characterize the effects of multi-axial loading, temperature and time on the failure characteristics of TIGA321, EA913NA, EA946 (three filled epoxy adhesives). From the test data a "Multi-Axial, Temperature, and Time Dependent" or MATT failure criterion was developed. It is shown that this criterion simplifies, for constant load and constant load rate conditions, into a form that can be easily used for stress analysis. Failure for TIGA321 and EA913NA are characterized below their glass transition temperature. Failure for EA946 is characterized for conditions that pass through its glass transition. The MATT failure criterion is shown to be accurate for a wide range of conditions for these adhesives.

Stability of large-scale systems with stable and unstable subsystems.

NASA Technical Reports Server (NTRS)

Grujic, Lj. T.; Siljak, D. D.

1972-01-01

The purpose of this paper is to develop new methods for constructing vector Liapunov functions and broaden the application of Liapunov's theory to stability analysis of large-scale dynamic systems. The application, so far limited by the assumption that the large-scale systems are composed of exponentially stable subsystems, is extended via the general concept of comparison functions to systems which can be decomposed into asymptotically stable subsystems. Asymptotic stability of the composite system is tested by a simple algebraic criterion. With minor technical adjustments, the same criterion can be used to determine connective asymptotic stability of large-scale systems subject to structural perturbations. By redefining the constraints imposed on the interconnections among the subsystems, the considered class of systems is broadened in an essential way to include composite systems with unstable subsystems. In this way, the theory is brought substantially closer to reality since stability of all subsystems is no longer a necessary assumption in establishing stability of the overall composite system.

Relativistic stellar stability: Preferred-frame effects

NASA Technical Reports Server (NTRS)

Ni, W.

1973-01-01

Possible preferred-frame effects on stellar stability were examined and no new instabilities were found. In particular, it is shown that: (1) Although terms linear in the preferred-frame velocity w (time-odd terms, analogous to viscosity and energy generation) change the shapes of the normal modes, their symmetry properties prevent them from changing the characteristic frequencies. Thus, no new vibrational or secular instabilities can occur. (2) Terms quadratic in w do not change either the shapes of the normal modes or the characteristic frequencies for radial pulsations. Thus, they have no influence on radial stability. (3) Terms quadratic in w do change both the normal modes and the characteristic frequencies of nonradial pulsations; but in the limit of a neutral mode these changes vanish. Hence, there is no modification of the criterion for convective stability, i.e., the standard Schwarzschild criterion remains valid.

SABRE: a method for assessing the stability of gene modules in complex tissues and subject populations.

PubMed

Shannon, Casey P; Chen, Virginia; Takhar, Mandeep; Hollander, Zsuzsanna; Balshaw, Robert; McManus, Bruce M; Tebbutt, Scott J; Sin, Don D; Ng, Raymond T

2016-11-14

Gene network inference (GNI) algorithms can be used to identify sets of coordinately expressed genes, termed network modules from whole transcriptome gene expression data. The identification of such modules has become a popular approach to systems biology, with important applications in translational research. Although diverse computational and statistical approaches have been devised to identify such modules, their performance behavior is still not fully understood, particularly in complex human tissues. Given human heterogeneity, one important question is how the outputs of these computational methods are sensitive to the input sample set, or stability. A related question is how this sensitivity depends on the size of the sample set. We describe here the SABRE (Similarity Across Bootstrap RE-sampling) procedure for assessing the stability of gene network modules using a re-sampling strategy, introduce a novel criterion for identifying stable modules, and demonstrate the utility of this approach in a clinically-relevant cohort, using two different gene network module discovery algorithms. The stability of modules increased as sample size increased and stable modules were more likely to be replicated in larger sets of samples. Random modules derived from permutated gene expression data were consistently unstable, as assessed by SABRE, and provide a useful baseline value for our proposed stability criterion. Gene module sets identified by different algorithms varied with respect to their stability, as assessed by SABRE. Finally, stable modules were more readily annotated in various curated gene set databases. The SABRE procedure and proposed stability criterion may provide guidance when designing systems biology studies in complex human disease and tissues.

Intervention criterion and control research for active front steering with consideration of road adhesion

NASA Astrophysics Data System (ADS)

Wu, Xiaojian; Zhou, Bing; Wen, Guilin; Long, Lefei; Cui, Qingjia

2018-04-01

A multi-objective active front steering (AFS) control system considering the road adhesion constraint on vehicle stability is developed using the sliding mode control (SMC) method. First, an identification function combined with the relationship between the yaw rate and the steering angle is developed to determine whether the tyre state is linear or nonlinear. On this basis, an intervention criterion for the AFS system is proposed to improve vehicle handling and stability in emergent conditions. A sideslip angle stability domain enveloped by the upper, lower, left, and right boundaries, as well as the constraint of road adhesion coefficient, is constructed based on the ? phase-plane method. A dynamic weighting coefficient to coordinate the control of yaw rate and sideslip angle, and a control strategy that considers changing control objectives based on the desired yaw rate, the desired sideslip angle, and their proportional weights, are proposed for the SMC controller. Because road adhesion has a significant effect on vehicle stability and to meet the control algorithm's requirement of real-time access to vehicle states, a unscented Kalman filter-based state observer is proposed to estimate the adhesion coefficient and the required states. Finally, simulations are performed using high and low road adhesion conditions in a Matlab/Simulink environment, and the results show that the proposed AFS control system promptly intervenes according to the intervention criterion, effectively improving vehicle handling and stability.

New explicit global asymptotic stability criteria for higher order difference equations

NASA Astrophysics Data System (ADS)

El-Morshedy, Hassan A.

2007-12-01

New explicit sufficient conditions for the asymptotic stability of the zero solution of higher order difference equations are obtained. These criteria can be applied to autonomous and nonautonomous equations. The celebrated Clark asymptotic stability criterion is improved. Also, applications to models from mathematical biology and macroeconomics are given.

Sex differences in human cardiovascular stress responses: mathematical and physiological approaches

NASA Astrophysics Data System (ADS)

Anishchenko, Tatijana G.; Igosheva, N. B.; Saparin, P. I.

1993-06-01

A new quantitative electrocardiogram characteristic is introduced as a distribution entropy, normalized by the signal energy. A perspective of this parameter application as a diagnostic criterion is proved by series of test experiments. By way of comparison with traditional medico-biological characteristics the higher sensitivity and stability of this criterion is proved.

Slope stability analysis using limit equilibrium method in nonlinear criterion.

PubMed

Lin, Hang; Zhong, Wenwen; Xiong, Wei; Tang, Wenyu

2014-01-01

In slope stability analysis, the limit equilibrium method is usually used to calculate the safety factor of slope based on Mohr-Coulomb criterion. However, Mohr-Coulomb criterion is restricted to the description of rock mass. To overcome its shortcomings, this paper combined Hoek-Brown criterion and limit equilibrium method and proposed an equation for calculating the safety factor of slope with limit equilibrium method in Hoek-Brown criterion through equivalent cohesive strength and the friction angle. Moreover, this paper investigates the impact of Hoek-Brown parameters on the safety factor of slope, which reveals that there is linear relation between equivalent cohesive strength and weakening factor D. However, there are nonlinear relations between equivalent cohesive strength and Geological Strength Index (GSI), the uniaxial compressive strength of intact rock σ ci , and the parameter of intact rock m i . There is nonlinear relation between the friction angle and all Hoek-Brown parameters. With the increase of D, the safety factor of slope F decreases linearly; with the increase of GSI, F increases nonlinearly; when σ ci is relatively small, the relation between F and σ ci is nonlinear, but when σ ci is relatively large, the relation is linear; with the increase of m i , F decreases first and then increases.

Slope Stability Analysis Using Limit Equilibrium Method in Nonlinear Criterion

PubMed Central

Lin, Hang; Zhong, Wenwen; Xiong, Wei; Tang, Wenyu

2014-01-01

In slope stability analysis, the limit equilibrium method is usually used to calculate the safety factor of slope based on Mohr-Coulomb criterion. However, Mohr-Coulomb criterion is restricted to the description of rock mass. To overcome its shortcomings, this paper combined Hoek-Brown criterion and limit equilibrium method and proposed an equation for calculating the safety factor of slope with limit equilibrium method in Hoek-Brown criterion through equivalent cohesive strength and the friction angle. Moreover, this paper investigates the impact of Hoek-Brown parameters on the safety factor of slope, which reveals that there is linear relation between equivalent cohesive strength and weakening factor D. However, there are nonlinear relations between equivalent cohesive strength and Geological Strength Index (GSI), the uniaxial compressive strength of intact rock σ ci, and the parameter of intact rock m i. There is nonlinear relation between the friction angle and all Hoek-Brown parameters. With the increase of D, the safety factor of slope F decreases linearly; with the increase of GSI, F increases nonlinearly; when σ ci is relatively small, the relation between F and σ ci is nonlinear, but when σ ci is relatively large, the relation is linear; with the increase of m i, F decreases first and then increases. PMID:25147838

Adaptive tracking control for a class of stochastic switched systems

NASA Astrophysics Data System (ADS)

Zhang, Hui; Xia, Yuanqing

2018-02-01

The problem of adaptive tracking is considered for a class of stochastic switched systems, in this paper. As preliminaries, the criterion of global asymptotical practical stability in probability is first presented by the aid of common Lyapunov function method. Based on the Lyapunov stability criterion, adaptive backstepping controllers are designed to guarantee that the closed-loop system has a unique global solution, which is globally asymptotically practically stable in probability, and the tracking error in the fourth moment converges to an arbitrarily small neighbourhood of zero. Simulation examples are given to demonstrate the efficiency of the proposed schemes.

An analytic expression for the sheath criterion in magnetized plasmas with multi-charged ion species

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hatami, M. M., E-mail: m-hatami@kntu.ac.ir

2015-04-15

The generalized Bohm criterion in magnetized multi-component plasmas consisting of multi-charged positive and negative ion species and electrons is analytically investigated by using the hydrodynamic model. It is assumed that the electrons and negative ion density distributions are the Boltzmann distribution with different temperatures and the positive ions enter into the sheath region obliquely. Our results show that the positive and negative ion temperatures, the orientation of the applied magnetic field and the charge number of positive and negative ions strongly affect the Bohm criterion in these multi-component plasmas. To determine the validity of our derived generalized Bohm criterion, itmore » reduced to some familiar physical condition and it is shown that monotonically reduction of the positive ion density distribution leading to the sheath formation occurs only when entrance velocity of ion into the sheath satisfies the obtained Bohm criterion. Also, as a practical application of the obtained Bohm criterion, effects of the ionic temperature and concentration as well as magnetic field on the behavior of the charged particle density distributions and so the sheath thickness of a magnetized plasma consisting of electrons and singly charged positive and negative ion species are studied numerically.« less

Corrections to the Eckhaus' stability criterion for one-dimensional stationary structures

NASA Astrophysics Data System (ADS)

Malomed, B. A.; Staroselsky, I. E.; Konstantinov, A. B.

1989-01-01

Two amendments to the well-known Eckhaus' stability criterion for small-amplitude non-linear structures generated by weak instability of a spatially uniform state of a non-equilibrium one-dimensional system against small perturbations with finite wavelengths are obtained. Firstly, we evaluate small corrections to the main Eckhaus' term which, on the contrary so that term, do not have a universal form. Comparison of those non-universal corrections with experimental or numerical results gives a possibility to select a more relevant form of an effective nonlinear evolution equation. In particular, the comparison with such results for convective rolls and Taylor vortices gives arguments in favor of the Swift-Hohenberg equation. Secondly, we derive an analog of the Eckhaus criterion for systems degenerate in the sense that in an expansion of their non-linear parts in powers of dynamical variables, the second and third degree terms are absent.

Vehicle lift-off modelling and a new rollover detection criterion

NASA Astrophysics Data System (ADS)

Mashadi, Behrooz; Mostaghimi, Hamid

2017-05-01

The modelling and development of a general criterion for the prediction of rollover threshold is the main purpose of this work. Vehicle dynamics models after the wheels lift-off and when the vehicle moves on the two wheels are derived and the governing equations are used to develop the rollover threshold. These models include the properties of the suspension and steering systems. In order to study the stability of motion, the steady-state solutions of the equations of motion are carried out. Based on the stability analyses, a new relation is obtained for the rollover threshold in terms of measurable response parameters. The presented criterion predicts the best time for the prevention of the vehicle rollover by applying a correcting moment. It is shown that the introduced threshold of vehicle rollover is a proper state of vehicle motion that is best for stabilising the vehicle with a low energy requirement.

Development of a job stressor scale for nurses caring for patients with intractable neurological diseases.

PubMed

Ando, Yukako; Kataoka, Tsuyoshi; Okamura, Hitoshi; Tanaka, Katsutoshi; Kobayashi, Toshio

2013-12-01

The purpose of this research is to verify the reliability and validity of a job stressor scale for nurses caring for patients with intractable neurological diseases. A mail survey was conducted using a self-report questionnaire. The subjects were 263 nurses and assistant nurses working in wards specializing in intractable neurological diseases. The response rate was 71.9% (valid response rate, 66.2%). With regard to reliability, internal consistency and stability were assessed. Internal consistency was examined via Cronbach's alpha. For stability, the test-retest method was performed and stability was examined via intraclass correlation coefficients. With regard to validity, factor validity, criterion-related validity, and content validity were assessed. Exploratory factor analysis was used for factor validity. For criterion-related validity, an existing scale was used as an external criterion; concurrent validity was examined via Spearman's rank correlation coefficients. As a result of analysis, there were 26 items in the scale created with an eight factor structure. Cronbach's a for the 26 items was 0.90; with the exception of two factors, alpha for all of the individual sub-factors was high at 0.7 or higher. The intraclass correlation coefficient for the 26 items was 0.89 (p < 0.001). With regard to criterion-related validity, concurrent validity was confirmed and the correlation coefficient with an external criterion was 0.73 (p < 0.001). For content validity, subjects who responded that "The questionnaire represents a stressor well or to a degree" accounted for 81% of the total responses. Reliability and validity were confirmed, so the scale created in the current research is a usable scale.

Research of facial feature extraction based on MMC

NASA Astrophysics Data System (ADS)

Xue, Donglin; Zhao, Jiufen; Tang, Qinhong; Shi, Shaokun

2017-07-01

Based on the maximum margin criterion (MMC), a new algorithm of statistically uncorrelated optimal discriminant vectors and a new algorithm of orthogonal optimal discriminant vectors for feature extraction were proposed. The purpose of the maximum margin criterion is to maximize the inter-class scatter while simultaneously minimizing the intra-class scatter after the projection. Compared with original MMC method and principal component analysis (PCA) method, the proposed methods are better in terms of reducing or eliminating the statistically correlation between features and improving recognition rate. The experiment results on Olivetti Research Laboratory (ORL) face database shows that the new feature extraction method of statistically uncorrelated maximum margin criterion (SUMMC) are better in terms of recognition rate and stability. Besides, the relations between maximum margin criterion and Fisher criterion for feature extraction were revealed.

Verification of the Multi-Axial, Temperature and Time Dependent (MATT) Failure Criterion

NASA Technical Reports Server (NTRS)

Richardson, David E.; Macon, David J.

2005-01-01

An extensive test and analytical effort has been completed by the Space Shuttle's Reusable Solid Rocket Motor (KSKM) nozzle program to characterize the failure behavior of two epoxy adhesives (TIGA 321 and EA946). As part of this effort, a general failure model, the "Multi-Axial, Temperature, and Time Dependent" or MATT failure criterion was developed. In the initial development of this failure criterion, tests were conducted to provide validation of the theory under a wide range of test conditions. The purpose of this paper is to present additional verification of the MATT failure criterion, under new loading conditions for the adhesives TIGA 321 and EA946. In many cases, the loading conditions involve an extrapolation from the conditions under which the material models were originally developed. Testing was conducted using three loading conditions: multi-axial tension, torsional shear, and non-uniform tension in a bondline condition. Tests were conducted at constant and cyclic loading rates ranging over four orders of magnitude. Tests were conducted under environmental conditions of primary interest to the RSRM program. The temperature range was not extreme, but the loading ranges were extreme (varying by four orders of magnitude). It should be noted that the testing was conducted at temperatures below the glass transition temperature of the TIGA 321 adhesive. However for the EA946, the testing was conducted at temperatures that bracketed the glass transition temperature.

Numerical stability of the error diffusion concept

NASA Astrophysics Data System (ADS)

Weissbach, Severin; Wyrowski, Frank

1992-10-01

The error diffusion algorithm is an easy implementable mean to handle nonlinearities in signal processing, e.g. in picture binarization and coding of diffractive elements. The numerical stability of the algorithm depends on the choice of the diffusion weights. A criterion for the stability of the algorithm is presented and evaluated for some examples.

Analysis of the coupled electron-ripplon oscillations resonance spectra in the Wigner solid at different temperatures and modeling of the excitation process

NASA Astrophysics Data System (ADS)

Syvokon, V. E.; Sharapova, I. V.

2018-05-01

The spectrum of coupled electron-ripplon oscillations in a Wigner crystal on the surface of superfluid helium at various temperatures and excitation voltages, leading to spectrum distortion, was studied experimentally. It was shown that at all temperatures, increasing excitation voltage leads to the appearance of non-axisymmetric vibrational modes, which indicates distortions of the crystal lattice. The possibility of excitation of the non-axisymmetric modes in a cell was demonstrated by modeling electronic crystal oscillations using the molecular dynamics method. At several fixed frequencies, the amplitudes of the response of the electronic crystal to external excitation were measured as a function of the magnitude of excitation voltage, and jumps were detected at certain critical voltages. Using the Lindemann criterion, a correlation was found between the critical stress and stability limit of the crystal lattice. It was concluded that when the critical voltage is reached, dynamic melting of the electronic crystal occurs.

On the hydrothermal stability of Cu/SSZ-13 SCR catalysts

DOE PAGES

Gao, Feng; Szanyi, Janos

2018-05-07

Cu/SSZ-13 SCR catalysts have been extensively studied in the past decade or so. Hydrothermal stability of these catalysts has been identified as the most important criterion for application. In this perspective, we describe recent atomic-level understanding of their hydrothermal stability. In particular, electron paramagnetic resonance (EPR) is shown to rather accurately quantify isolated Cu(II) ions and CuO clusters in fresh and aged catalysts to demonstrate the remarkable hydrothermal stability for Cu 2+ ions located in 6-membered ring windows, and the conversion of [Cu(OH)] + ions in Chabazite cages to CuO clusters. The hydrothermal stability difference of the two isolated Cu(II)more » ions is confirmed with DFT simulations and the conversion of [Cu(OH)] + to CuO is proposed to involve formation, migration and condensation of Cu(OH) 2 intermediates. The structural destructive role of CuO clusters is attributed to mesopore formation from their migration, which more severely damages the catalysts than dealumination. Lastly, perspectives are given on new strategies for low-temperature NO x removal, rational design and refinement of Cu/SSZ-13, and development of new Cu/zeolite SCR catalysts with even better performance than the state-of-the-art Cu/SSZ-13.« less

On the hydrothermal stability of Cu/SSZ-13 SCR catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Feng; Szanyi, Janos

Cu/SSZ-13 SCR catalysts have been extensively studied in the past decade or so. Hydrothermal stability of these catalysts has been identified as the most important criterion for application. In this perspective, we describe recent atomic-level understanding of their hydrothermal stability. In particular, electron paramagnetic resonance (EPR) is shown to rather accurately quantify isolated Cu(II) ions and CuO clusters in fresh and aged catalysts to demonstrate the remarkable hydrothermal stability for Cu 2+ ions located in 6-membered ring windows, and the conversion of [Cu(OH)] + ions in Chabazite cages to CuO clusters. The hydrothermal stability difference of the two isolated Cu(II)more » ions is confirmed with DFT simulations and the conversion of [Cu(OH)] + to CuO is proposed to involve formation, migration and condensation of Cu(OH) 2 intermediates. The structural destructive role of CuO clusters is attributed to mesopore formation from their migration, which more severely damages the catalysts than dealumination. Lastly, perspectives are given on new strategies for low-temperature NO x removal, rational design and refinement of Cu/SSZ-13, and development of new Cu/zeolite SCR catalysts with even better performance than the state-of-the-art Cu/SSZ-13.« less

Static stability and thermal wind in an atmosphere of variable composition Applications to Mars

NASA Technical Reports Server (NTRS)

Hess, S. L.

1979-01-01

Radiometric measurements of the temperature of the south polar cap of Mars in winter have yielded values significantly below the expected 148 K. One proposed explanation for this result is a substantial reduction in the CO2 content of the atmosphere and a lowering of the mean molecule weight near the surface. The meteorological consequences of this explanation are explored by deriving a criterion for vertical static stability and a thermal wind law for an atmosphere of variable composition. The atmosphere proves to be statically unstable unless the anomaly in the CO2 mixing ratio extends to heights of tens of kilometers. The effect of varying molecular weight exceeds the effect of temperature gradient, producing shears with height of reversed sign. The shears are baroclinically unstable, and this instability would eradicate the latitudinal gradient of molecular weight. This inconsistency can be resolved by invoking a reasonable elevation of the central polar cap and by imposing an adequate zonal wind. It is concluded that if the explanation requiring a change in atmospheric composition is correct, it must be accompanied by other special circumstances to make it meteorologically consistent.

Generalization of von Neumann analysis for a model of two discrete half-spaces: The acoustic case

USGS Publications Warehouse

Haney, M.M.

2007-01-01

Evaluating the performance of finite-difference algorithms typically uses a technique known as von Neumann analysis. For a given algorithm, application of the technique yields both a dispersion relation valid for the discrete time-space grid and a mathematical condition for stability. In practice, a major shortcoming of conventional von Neumann analysis is that it can be applied only to an idealized numerical model - that of an infinite, homogeneous whole space. Experience has shown that numerical instabilities often arise in finite-difference simulations of wave propagation at interfaces with strong material contrasts. These interface instabilities occur even though the conventional von Neumann stability criterion may be satisfied at each point of the numerical model. To address this issue, I generalize von Neumann analysis for a model of two half-spaces. I perform the analysis for the case of acoustic wave propagation using a standard staggered-grid finite-difference numerical scheme. By deriving expressions for the discrete reflection and transmission coefficients, I study under what conditions the discrete reflection and transmission coefficients become unbounded. I find that instabilities encountered in numerical modeling near interfaces with strong material contrasts are linked to these cases and develop a modified stability criterion that takes into account the resulting instabilities. I test and verify the stability criterion by executing a finite-difference algorithm under conditions predicted to be stable and unstable. ?? 2007 Society of Exploration Geophysicists.

[On the problems of the evolutionary optimization of life history. II. To justification of optimization criterion for nonlinear Leslie model].

PubMed

Pasekov, V P

2013-03-01

The paper considers the problems in the adaptive evolution of life-history traits for individuals in the nonlinear Leslie model of age-structured population. The possibility to predict adaptation results as the values of organism's traits (properties) that provide for the maximum of a certain function of traits (optimization criterion) is studied. An ideal criterion of this type is Darwinian fitness as a characteristic of success of an individual's life history. Criticism of the optimization approach is associated with the fact that it does not take into account the changes in the environmental conditions (in a broad sense) caused by evolution, thereby leading to losses in the adequacy of the criterion. In addition, the justification for this criterion under stationary conditions is not usually rigorous. It has been suggested to overcome these objections in terms of the adaptive dynamics theory using the concept of invasive fitness. The reasons are given that favor the application of the average number of offspring for an individual, R(L), as an optimization criterion in the nonlinear Leslie model. According to the theory of quantitative genetics, the selection for fertility (that is, for a set of correlated quantitative traits determined by both multiple loci and the environment) leads to an increase in R(L). In terms of adaptive dynamics, the maximum R(L) corresponds to the evolutionary stability and, in certain cases, convergent stability of the values for traits. The search for evolutionarily stable values on the background of limited resources for reproduction is a problem of linear programming.

Uncooled thermal imaging and image analysis

NASA Astrophysics Data System (ADS)

Wang, Shiyun; Chang, Benkang; Yu, Chunyu; Zhang, Junju; Sun, Lianjun

2006-09-01

Thermal imager can transfer difference of temperature to difference of electric signal level, so can be application to medical treatment such as estimation of blood flow speed and vessel 1ocation [1], assess pain [2] and so on. With the technology of un-cooled focal plane array (UFPA) is grown up more and more, some simple medical function can be completed with un-cooled thermal imager, for example, quick warning for fever heat with SARS. It is required that performance of imaging is stabilization and spatial and temperature resolution is high enough. In all performance parameters, noise equivalent temperature difference (NETD) is often used as the criterion of universal performance. 320 x 240 α-Si micro-bolometer UFPA has been applied widely presently for its steady performance and sensitive responsibility. In this paper, NETD of UFPA and the relation between NETD and temperature are researched. several vital parameters that can affect NETD are listed and an universal formula is presented. Last, the images from the kind of thermal imager are analyzed based on the purpose of detection persons with fever heat. An applied thermal image intensification method is introduced.

L to H mode transition: Parametric dependencies of the temperature threshold

DOE PAGES

Bourdelle, C.; Chone, L.; Fedorczak, N.; ...

2015-06-15

The L to H mode transition occurs at a critical power which depends on various parameters, such as the magnetic field, the density, etc. Experimental evidence on various tokamaks (JET, ASDEX-Upgrade, DIII-D, Alcator C-Mod) points towards the existence of a critical temperature characterizing the transition. This criterion for the L-H transition is local and is therefore easier to be compared to theoretical approaches. In order to shed light on the mechanisms of the transition, simple theoretical ideas are used to derive a temperature threshold (T th). They are based on the stabilization of the underlying turbulence by a mean radialmore » electric field shear. The nature of the turbulence varies as the collisionality decreases, from resistive ballooning modes to ion temperature gradient and trapped electron modes. The obtained parametric dependencies of the derived T th are tested versus magnetic field, density, effective charge. Furthermore, various robust experimental observations are reproduced, in particular T th increases with magnetic field B and increases with density below the density roll-over observed on the power threshold.« less

Blade row dynamic digital compressor program. Volume 1: J85 clean inlet flow and parallel compressor models

NASA Technical Reports Server (NTRS)

Tesch, W. A.; Steenken, W. G.

1976-01-01

The results are presented of a one-dimensional dynamic digital blade row compressor model study of a J85-13 engine operating with uniform and with circumferentially distorted inlet flow. Details of the geometry and the derived blade row characteristics used to simulate the clean inlet performance are given. A stability criterion based upon the self developing unsteady internal flows near surge provided an accurate determination of the clean inlet surge line. The basic model was modified to include an arbitrary extent multi-sector parallel compressor configuration for investigating 180 deg 1/rev total pressure, total temperature, and combined total pressure and total temperature distortions. The combined distortions included opposed, coincident, and 90 deg overlapped patterns. The predicted losses in surge pressure ratio matched the measured data trends at all speeds and gave accurate predictions at high corrected speeds where the slope of the speed lines approached the vertical.

Mechanism for stabilization of the molten globule state of papain by sodium n-alkyl sulfates: spectroscopic and calorimetric approaches.

PubMed

Chamani, J; Heshmati, M

2008-06-01

Papain exists in a molten globule (MG) state at pH 2 and in this state protein tends to aggregate in the presence of lower concentrations of guanidine hydrochloride (GuHCl). Such aggregation is prevented if low concentrations of sodium n-alkyl sulfates are also present in the buffer; in addition, stabilization of the protein is also induced. The guanidine hydrochloride and temperature-induced unfolding of papain, in the presence of n-alkyl sulfates, indicate stabilization of the protein as seen from the higher transition midpoints when monitored by fluorescence, circular dichroism, and differential scanning calorimetry. However, a similar phenomenon is not seen under neutral conditions in the presence of n-alkyl sulfate concentrations. The effect of n-alkyl sulfates on the structure of the MG state of papain was utilized to investigate the contribution of hydrophobic interaction to the stability of the MG state. The Td values of the MG states of papain in the presence of n-alkyl sulfates at different concentrations showed substantial variation. The enhancement of Td values at the stability criterion of MG states corresponded with increasing chain length of the cited n-alkyl sulfates. The present results suggest that the hydrophobic interactions play important roles in stabilizing and preventing the aggregation of the MG state of papain.

An Efficient Method for Studying the Stability and Dynamics of the Rotational Motions of Celestial Bodies

NASA Astrophysics Data System (ADS)

Pavlov, A. I.; Maciejewski, A. J.

2003-08-01

We use the alternative MEGNO (Mean Exponential Growth of Nearby Orbits) technique developed by Cincotta and Simo to study the stability of orbital-rotational motions for plane oscillations and three-dimensional rotations. We present a detailed numerical-analytical study of a rigid body in the case where the proper rotation of the body is synchronized with its orbital motion as 3: 2 (Mercurian-type synchronism). For plane rotations, the loss of stability of the periodic solution that corresponds to a 3: 2 resonance is shown to be soft, which should be taken into account to estimate the upper limit for the ellipticity of Mercury. In studying stable and chaotic translational-rotational motions, we point out that the MEGNO criterion can be effectively used. This criterion gives a clear picture of the resonant structures and allows the calculations to be conveniently presented in the form of the corresponding MEGNO stability maps for multidimensional systems. We developed an appropriate software package.

Effect of ripples on the finite temperature elastic properties of hexagonal boron nitride using strain-fluctuation method

NASA Astrophysics Data System (ADS)

Thomas, Siby; Ajith, K. M.; Valsakumar, M. C.

2017-11-01

This work intents to put forth the results of a classical molecular dynamics study to investigate the temperature dependent elastic constants of monolayer hexagonal boron nitride (h-BN) between 100 and 1000 K for the first time using strain fluctuation method. The temperature dependence of out-of-plane fluctuations (ripples) is quantified and is explained using continuum theory of membranes. At low temperatures, negative in-plane thermal expansion is observed and at high temperatures, a transition to positive thermal expansion has been observed due to the presence of thermally excited ripples. The decrease of Young's modulus, bulk modulus, shear modulus and Poisson's ratio with increase in temperature has been analyzed. The thermal rippling in h-BN leads to strong anharmonic behaviour that causes large deviation from the isotropic elasticity. A detailed study shows that the strong thermal rippling in large systems is also responsible for the softening of elastic constants in h-BN. From the determined values of elastic constants and elastic moduli, it has been elucidated that 2D h-BN sheets meet the Born's mechanical stability criterion in the investigated temperature range. The variation of longitudinal and shear velocities with temperature is also calculated from the computed values of elastic constants and elastic moduli.

A machine learns to predict the stability of circumbinary planets

NASA Astrophysics Data System (ADS)

Lam, Christopher; Kipping, David

2018-06-01

Long-period circumbinary planets appear to be as common as those orbiting single stars and have been found to frequently have orbital radii just beyond the critical distance for dynamical stability. Assessing the stability is typically done either through N-body simulations or using the classic stability criterion first considered by Dvorak and later developed by Holman and Wiegert: a second-order polynomial calibrated to broadly match numerical simulations. However, the polynomial is unable to capture islands of instability introduced by mean motion resonances, causing the accuracy of the criterion to approach that of a random coin-toss when close to the boundary. We show how a deep neural network (DNN) trained on N-body simulations generated with REBOUND is able to significantly improve stability predictions for circumbinary planets on initially coplanar, circular orbits. Specifically, we find that the accuracy of our DNN never drops below 86 per cent, even when tightly surrounding the boundary of instability, and is fast enough to be practical for on-the-fly calls during likelihood evaluations typical of modern Bayesian inference. Our binary classifier DNN is made publicly available at https://github.com/CoolWorlds/orbital-stability.

Unifying perspective: Solitary traveling waves as discrete breathers in Hamiltonian lattices and energy criteria for their stability

NASA Astrophysics Data System (ADS)

Cuevas-Maraver, Jesús; Kevrekidis, Panayotis G.; Vainchtein, Anna; Xu, Haitao

2017-09-01

In this work, we provide two complementary perspectives for the (spectral) stability of solitary traveling waves in Hamiltonian nonlinear dynamical lattices, of which the Fermi-Pasta-Ulam and the Toda lattice are prototypical examples. One is as an eigenvalue problem for a stationary solution in a cotraveling frame, while the other is as a periodic orbit modulo shifts. We connect the eigenvalues of the former with the Floquet multipliers of the latter and using this formulation derive an energy-based spectral stability criterion. It states that a sufficient (but not necessary) condition for a change in the wave stability occurs when the functional dependence of the energy (Hamiltonian) H of the model on the wave velocity c changes its monotonicity. Moreover, near the critical velocity where the change of stability occurs, we provide an explicit leading-order computation of the unstable eigenvalues, based on the second derivative of the Hamiltonian H''(c0) evaluated at the critical velocity c0. We corroborate this conclusion with a series of analytically and numerically tractable examples and discuss its parallels with a recent energy-based criterion for the stability of discrete breathers.

Dilatancy Criteria for Salt Cavern Design: A Comparison Between Stress- and Strain-Based Approaches

NASA Astrophysics Data System (ADS)

Labaune, P.; Rouabhi, A.; Tijani, M.; Blanco-Martín, L.; You, T.

2018-02-01

This paper presents a new approach for salt cavern design, based on the use of the onset of dilatancy as a design threshold. In the proposed approach, a rheological model that includes dilatancy at the constitutive level is developed, and a strain-based dilatancy criterion is defined. As compared to classical design methods that consist in simulating cavern behavior through creep laws (fitted on long-term tests) and then using a criterion (derived from short-terms tests or experience) to determine the stability of the excavation, the proposed approach is consistent both with short- and long-term conditions. The new strain-based dilatancy criterion is compared to a stress-based dilatancy criterion through numerical simulations of salt caverns under cyclic loading conditions. The dilatancy zones predicted by the strain-based criterion are larger than the ones predicted by the stress-based criteria, which is conservative yet constructive for design purposes.

Sharp conditions for global stability of Lotka-Volterra systems with distributed delays

NASA Astrophysics Data System (ADS)

Faria, Teresa

We give a criterion for the global attractivity of a positive equilibrium of n-dimensional non-autonomous Lotka-Volterra systems with distributed delays. For a class of autonomous Lotka-Volterra systems, we show that such a criterion is sharp, in the sense that it provides necessary and sufficient conditions for the global asymptotic stability independently of the choice of the delay functions. The global attractivity of positive equilibria is established by imposing a diagonal dominance of the instantaneous negative feedback terms, and relies on auxiliary results showing the boundedness of all positive solutions. The paper improves and generalizes known results in the literature, namely by considering systems with distributed delays rather than discrete delays.

Improved result on stability analysis of discrete stochastic neural networks with time delay

NASA Astrophysics Data System (ADS)

Wu, Zhengguang; Su, Hongye; Chu, Jian; Zhou, Wuneng

2009-04-01

This Letter investigates the problem of exponential stability for discrete stochastic time-delay neural networks. By defining a novel Lyapunov functional, an improved delay-dependent exponential stability criterion is established in terms of linear matrix inequality (LMI) approach. Meanwhile, the computational complexity of the newly established stability condition is reduced because less variables are involved. Numerical example is given to illustrate the effectiveness and the benefits of the proposed method.

Physical stability of API/polymer-blend amorphous solid dispersions.

PubMed

Lehmkemper, Kristin; Kyeremateng, Samuel O; Bartels, Mareike; Degenhardt, Matthias; Sadowski, Gabriele

2018-03-01

The preparation of amorphous solid dispersions (ASDs) is a well-established strategy for formulating active pharmaceutical ingredients by embedding them in excipients, usually amorphous polymers. Different polymers can be combined for designing ASDs with desired properties like an optimized dissolution behavior. One important criterion for the development of ASD compositions is the physical stability. In this work, the physical stability of API/polymer-blend ASDs was investigated by thermodynamic modeling and stability studies. Amorphous naproxen (NAP) and acetaminophen (APAP) were embedded in blends of hydroxypropyl methylcellulose acetate succinate (HPMCAS) and either poly(vinylpyrrolidone) (PVP) or poly(vinylpyrrolidone-co-vinyl acetate) (PVPVA64). Parameters for modeling the API solubility in the blends and the glass-transition temperature curves of the water-free systems with Perturbed-Chain Statistical Associating Fluid Theory and Kwei equation, respectively, were correlated to experimental data. The phase behavior for standardized storage conditions (0%, 60% and 75% relative humidity (RH)) was predicted and compared to six months-long stability studies. According to modeling and experimental results, the physical stability was reduced with increasing HPMCAS content and increasing RH. This trend was observed for all investigated systems, with both APIs (NAP and APAP) and both polymer blends (PVP/HPMCAS and PVPVA64/HPMCAS). PC-SAFT and the Kwei equation turned out to be suitable tools for modeling and predicting the physical stability of the investigated API/polymer-blends ASDs. Copyright © 2017 Elsevier B.V. All rights reserved.

Real-time flutter boundary prediction based on time series models

NASA Astrophysics Data System (ADS)

Gu, Wenjing; Zhou, Li

2018-03-01

For the purpose of predicting the flutter boundary in real time during flutter flight tests, two time series models accompanied with corresponding stability criterion are adopted in this paper. The first method simplifies a long nonstationary response signal as many contiguous intervals and each is considered to be stationary. The traditional AR model is then established to represent each interval of signal sequence. While the second employs a time-varying AR model to characterize actual measured signals in flutter test with progression variable speed (FTPVS). To predict the flutter boundary, stability parameters are formulated by the identified AR coefficients combined with Jury's stability criterion. The behavior of the parameters is examined using both simulated and wind-tunnel experiment data. The results demonstrate that both methods show significant effectiveness in predicting the flutter boundary at lower speed level. A comparison between the two methods is also given in this paper.

Linear Stability of Binary Alloy Solidification for Unsteady Growth Rates

NASA Technical Reports Server (NTRS)

Mazuruk, K.; Volz, M. P.

2010-01-01

An extension of the Mullins and Sekerka (MS) linear stability analysis to the unsteady growth rate case is considered for dilute binary alloys. In particular, the stability of the planar interface during the initial solidification transient is studied in detail numerically. The rapid solidification case, when the system is traversing through the unstable region defined by the MS criterion, has also been treated. It has been observed that the onset of instability is quite accurately defined by the "quasi-stationary MS criterion", when the growth rate and other process parameters are taken as constants at a particular time of the growth process. A singular behavior of the governing equations for the perturbed quantities at the constitutional supercooling demarcation line has been observed. However, when the solidification process, during its transient, crosses this demarcation line, a planar interface is stable according to the linear analysis performed.

Local fragmentation of thin disks in Eddington-inspired gravity

NASA Astrophysics Data System (ADS)

Roshan, Mahmood; Kazemi, Ali; De Martino, Ivan

2018-06-01

We find the generalized version of the Toomre's criterion for the stability of a rotating thin disk in the context of Eddington inspired Born-Infeld (EiBI) gravity which possesses one free parameter χ. To do so we use the weak field limit of the theory and find the dispersion relation for the propagation of matter density waves on the surface of a self-gravitating and differentially rotating disk. Finally we find a new version of Toomre's stability criterion for thin disks. We show that EiBI gravity with negative χ destabilizes all the rotating thin disks. On the other hand EiBI with positive χ substantially can suppress the local fragmentation, and has stabilizing effects against axi-symmetric perturbations. More specifically, we show that only an annulus remains unstable on the surface of the disk. The width of the annulus directly depends on the magnitude of χ.

Analytical stability criteria for the Caledonian Symmetric Four and Five Body Problems

NASA Astrophysics Data System (ADS)

Steves, Bonnie; Shoaib Afridi, Mohammad; Sweatman, Winston

2017-06-01

Analytical studies of the stability of three or more body gravitational systems are difficult because of the greater number of variables involved with the increasing number of bodies and the limitation of 10 integrals that exist in the gravitational n-body problem. Utilisation of symmetries or the neglecting of the masses of some of the bodies compared to others can simplify the dynamical problem and enable global analytical stability solutions to be derived. These symmetric and restricted few body systems with their analytical stability criterion can then provide useful information on the stability of the general few body system when near symmetry or the restricted situation. Even with symmetrical reductions, analytical stability derivations for four and five body problems are rare. In this paper, we develop an analytical stability criterion for the Caledonian Symmetric Five Body Problem (CS5BP) , a dynamically symmetrical planar problem with two pairs of equal masses and a fifth mass located at the centre of mass. Sundman’s inequality is applied to derive boundary surfaces to the allowed real motion of the system. This enables the derivation of a stability criterion valid for all time for the hierarchical stability of the CS5BP and its subset the Caledonian Symmetric Four Body Problem (CSFBP), where the central mass is taken to be equal to zero. We show that the hierarchical stability depends solely on the Szebehely constant C0, which is a function of the total energy H and angular momentum c. The critical value Ccrit at which the system becomes hierarchically stable for all time depends only on the two mass ratios of the symmetric five body system. We then explore the effect on the stability of the whole system of adding an increasing massive central body. It is shown both analytically and numerically that all CS5BPs and CSFBPs of different mass ratios are hierarchically stable if C0 > 0.0659 and C0 > 0.0465, respectively. The Caledonian Symmetric Four and Five Body gravitational models are relevant to the study of the stability and evolution of symmetric quadruple/quintuple stellar clusters and symmetric exoplanetary systems of two planets orbiting a binary/triplet of stars.

Correlation of DCPI with deformation under proof roller loading to assess soft subgrade stabilization criterion : addendum to NCDOT final report 2011-05, entitled : "Field verification of undercut criteria and alternatives for subgrade stabilization in th

DOT National Transportation Integrated Search

2016-11-21

Work presented herein is an addendum to the final report for NCDOT Project 2011-05 entitled : Field Verification of Undercut Criteria and Alternatives for Subgrade Stabilization in the : Piedmont Area. The objective of the addendum work is to p...

Molecular Based Temperature and Strain Rate Dependent Yield Criterion for Anisotropic Elastomeric Thin Films

NASA Technical Reports Server (NTRS)

Bosi, F.; Pellegrino, S.

2017-01-01

A molecular formulation of the onset of plasticity is proposed to assess temperature and strain rate effects in anisotropic semi-crystalline rubbery films. The presented plane stress criterion is based on the strain rate-temperature superposition principle and the cooperative theory of yielding, where some parameters are assumed to be material constants, while others are considered to depend on specific modes of deformation. An orthotropic yield function is developed for a linear low density polyethylene thin film. Uniaxial and biaxial inflation experiments were carried out to determine the yield stress of the membrane via a strain recovery method. It is shown that the 3% offset method predicts the uniaxial elastoplastic transition with good accuracy. Both the tensile yield points along the two principal directions of the film and the biaxial yield stresses are found to obey the superposition principle. The proposed yield criterion is compared against experimental measurements, showing excellent agreement over a wide range of deformation rates and temperatures.

Mechanical and Thermal Properties of Praseodymium Monopnictides: AN Ultrasonic Study

NASA Astrophysics Data System (ADS)

Bhalla, Vyoma; Kumar, Raj; Tripathy, Chinmayee; Singh, Devraj

2013-09-01

We have computed ultrasonic attenuation, acoustic coupling constants and ultrasonic velocities of praseodymium monopnictides PrX(X: N, P, As, Sb and Bi) along the <100>, <110>, <111> in the temperature range 100-500 K using higher order elastic constants. The higher order elastic constants are evaluated using Coulomb and Born-Mayer potential with two basic parameters viz. nearest-neighbor distance and hardness parameter in the temperature range of 0-500 K. Several other mechanical and thermal parameters like bulk modulus, shear modulus, Young's modulus, Poisson ratio, anisotropic ratio, tetragonal moduli, Breazeale's nonlinearity parameter and Debye temperature are also calculated. In the present study, the fracture/toughness (B/G) ratio is less than 1.75 which implies that PrX compounds are brittle in nature at room temperature. The chosen material fulfilled Born criterion of mechanical stability. We also found the deviation of Cauchy's relation at higher temperatures. PrN is most stable material as it has highest valued higher order elastic constants as well as the ultrasonic velocity. Further, the lattice thermal conductivity using modified approach of Slack and Berman is determined at room temperature. The ultrasonic attenuation due to phonon-phonon interaction and thermoelastic relaxation mechanisms have been computed using modified Mason's approach. The results with other well-known physical properties are useful for industrial applications.

Canonical fluid thermodynamics. [variational principles of stability for compressible adiabatic flow

NASA Technical Reports Server (NTRS)

Schmid, L. A.

1974-01-01

The space-time integral of the thermodynamic pressure plays in a certain sense the role of the thermodynamic potential for compressible adiabatic flow. The stability criterion can be converted into a variational minimum principle by requiring the molar free-enthalpy and temperature to be generalized velocities. In the fluid context, the definition of proper-time differentiation involves the fluid velocity expressed in terms of three particle identity parameters. The pressure function is then converted into a functional which is the Lagrangian density of the variational principle. Being also a minimum principle, the variational principle provides a means for comparing the relative stability of different flows. For boundary conditions with a high degree of symmetry, as in the case of a uniformly expanding spherical gas box, the most stable flow is a rectilinear flow for which the world-trajectory of each particle is a straight line. Since the behavior of the interior of a freely expanding cosmic cloud may be expected to be similar to that of the fluid in the spherical box of gas, this suggests that the cosmic principle is a consequence of the laws of thermodynamics, rather than just an ad hoc postulate.

The Absolute Stability Analysis in Fuzzy Control Systems with Parametric Uncertainties and Reference Inputs

NASA Astrophysics Data System (ADS)

Wu, Bing-Fei; Ma, Li-Shan; Perng, Jau-Woei

This study analyzes the absolute stability in P and PD type fuzzy logic control systems with both certain and uncertain linear plants. Stability analysis includes the reference input, actuator gain and interval plant parameters. For certain linear plants, the stability (i.e. the stable equilibriums of error) in P and PD types is analyzed with the Popov or linearization methods under various reference inputs and actuator gains. The steady state errors of fuzzy control systems are also addressed in the parameter plane. The parametric robust Popov criterion for parametric absolute stability based on Lur'e systems is also applied to the stability analysis of P type fuzzy control systems with uncertain plants. The PD type fuzzy logic controller in our approach is a single-input fuzzy logic controller and is transformed into the P type for analysis. In our work, the absolute stability analysis of fuzzy control systems is given with respect to a non-zero reference input and an uncertain linear plant with the parametric robust Popov criterion unlike previous works. Moreover, a fuzzy current controlled RC circuit is designed with PSPICE models. Both numerical and PSPICE simulations are provided to verify the analytical results. Furthermore, the oscillation mechanism in fuzzy control systems is specified with various equilibrium points of view in the simulation example. Finally, the comparisons are also given to show the effectiveness of the analysis method.

Formation of H2-He substellar bodies in cold conditions. Gravitational stability of binary mixtures in a phase transition

NASA Astrophysics Data System (ADS)

Füglistaler, A.; Pfenniger, D.

2016-06-01

Context. Molecular clouds typically consist of 3/4 H2, 1/4 He and traces of heavier elements. In an earlier work we showed that at very low temperatures and high densities, H2 can be in a phase transition leading to the formation of ice clumps as large as comets or even planets. However, He has very different chemical properties and no phase transition is expected before H2 in dense interstellar medium conditions. The gravitational stability of fluid mixtures has been studied before, but these studies did not include a phase transition. Aims: We study the gravitational stability of binary fluid mixtures with special emphasis on when one component is in a phase transition. The numerical results are aimed at applications in molecular cloud conditions, but the theoretical results are more general. Methods: First, we study the gravitational stability of van der Waals fluid mixtures using linearized analysis and examine virial equilibrium conditions using the Lennard-Jones intermolecular potential. Then, combining the Lennard-Jones and gravitational potentials, the non-linear dynamics of fluid mixtures are studied via computer simulations using the molecular dynamics code LAMMPS. Results: Along with the classical, ideal-gas Jeans instability criterion, a fluid mixture is always gravitationally unstable if it is in a phase transition because compression does not increase pressure. However, the condensed phase fraction increases. In unstable situations the species can separate: in some conditions He precipitates faster than H2, while in other conditions the converse occurs. Also, for an initial gas phase collapse the geometry is essential. Contrary to spherical or filamentary collapses, sheet-like collapses starting below 15 K easily reach H2 condensation conditions because then they are fastest and both the increase of heating and opacity are limited. Conclusions: Depending on density, temperature and mass, either rocky H2 planetoids, or gaseous He planetoids form. H2 planetoids are favoured by high density, low temperature and low mass, while He planetoids need more mass and can form at temperature well above the critical value.

Contributions to study of the stability of the electric welding arc under the action of acoustic pressure

NASA Technical Reports Server (NTRS)

Petru, S.

1974-01-01

During the treatment of an electric welding arc with ultrasonic oscillations, an improvement was found in overall source-arc stability. Theoretical explanations are provided for this phenomenon and formulas of equivalence between the classical arc and the treated arc are derived, taking stability as their criterion. A knowledge of this phenomenon can be useful in extending the applications of ultrasounds to different forms of electric arcs.

Complex symmetric matrices with strongly stable iterates

NASA Technical Reports Server (NTRS)

Tadmor, E.

1985-01-01

Complex-valued symmetric matrices are studied. A simple expression for the spectral norm of such matrices is obtained, by utilizing a unitarily congruent invariant form. A sharp criterion is provided for identifying those symmetric matrices whose spectral norm is not exceeding one: such strongly stable matrices are usually sought in connection with convergent difference approximations to partial differential equations. As an example, the derived criterion is applied to conclude the strong stability of a Lax-Wendroff scheme.

A passivity criterion for sampled-data bilateral teleoperation systems.

PubMed

Jazayeri, Ali; Tavakoli, Mahdi

2013-01-01

A teleoperation system consists of a teleoperator, a human operator, and a remote environment. Conditions involving system and controller parameters that ensure the teleoperator passivity can serve as control design guidelines to attain maximum teleoperation transparency while maintaining system stability. In this paper, sufficient conditions for teleoperator passivity are derived for when position error-based controllers are implemented in discrete-time. This new analysis is necessary because discretization causes energy leaks and does not necessarily preserve the passivity of the system. The proposed criterion for sampled-data teleoperator passivity imposes lower bounds on the teleoperator's robots dampings, an upper bound on the sampling time, and bounds on the control gains. The criterion is verified through simulations and experiments.

Rheological investigation of body cream and body lotion in actual application conditions

NASA Astrophysics Data System (ADS)

Kwak, Min-Sun; Ahn, Hye-Jin; Song, Ki-Won

2015-08-01

The objective of the present study is to systematically evaluate and compare the rheological behaviors of body cream and body lotion in actual usage situations. Using a strain-controlled rheometer, the steady shear flow properties of commercially available body cream and body lotion were measured over a wide range of shear rates, and the linear viscoelastic properties of these two materials in small amplitude oscillatory shear flow fields were measured over a broad range of angular frequencies. The temperature dependency of the linear viscoelastic behaviors was additionally investigated over a temperature range most relevant to usual human life. The main findings obtained from this study are summarized as follows: (1) Body cream and body lotion exhibit a finite magnitude of yield stress. This feature is directly related to the primary (initial) skin feel that consumers usually experience during actual usage. (2) Body cream and body lotion exhibit a pronounced shear-thinning behavior. This feature is closely connected with the spreadability when cosmetics are applied onto the human skin. (3) The linear viscoelastic behaviors of body cream and body lotion are dominated by an elastic nature. These solid-like properties become a criterion to assess the selfstorage stability of cosmetic products. (4) A modified form of the Cox-Merz rule provides a good ability to predict the relationship between steady shear flow and dynamic viscoelastic properties for body cream and body lotion. (5) The storage modulus and loss modulus of body cream show a qualitatively similar tendency to gradually decrease with an increase in temperature. In the case of body lotion, with an increase in temperature, the storage modulus is progressively decreased while the loss modulus is slightly increased and then decreased. This information gives us a criterion to judge how the characteristics of cosmetic products are changed by the usual human environments.

Microsegregation during directional solidification

NASA Technical Reports Server (NTRS)

Coriell, S. R.; Mcfadden, G. B.

1984-01-01

During the directional solidification of alloys, solute inhomogeneities transverse to the growth direction arise due to morphological instabilities (leading to cellular or dendritic growth) and/or due to convection in the melt. In the absence of convection, the conditions for the onset of morphological instability are given by the linear stability analysis of Mullins and Sekerka. For ordinary solidification rates, the predictions of linear stability analysis are similar to the constitutional supercooling criterion. However, at very rapid solidification rates, linear stability analysis predicts a vast increase in stabilization in comparison to constitutional supercooling.

Ion-cyclotron-frequency stabilization of internal kink mode and sawtooth oscillations in tokamaks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Litwin, C.

It is proposed that the ponderomotive force due to applied ion-cyclotron resonance-frequency waves can stabilize the internal kink mode in tokamaks. The sufficient stability criterion is derived and the necessary power estimated. It is concluded that at the rf power level, present in the Joint European Torus experiment, the ponderomotive force effects are significant and may be responsible for the modification of the sawtooth activity observed in recent experiments.

The transition prediction toolkit: LST, SIT, PSE, DNS, and LES

NASA Technical Reports Server (NTRS)

Zang, Thomas A.; Chang, Chau-Lyan; Ng, Lian L.

1992-01-01

The e(sup N) method for predicting transition onset is an amplitude ratio criterion that is on the verge of full maturation for three-dimensional, compressible, real gas flows. Many of the components for a more sophisticated, absolute amplitude criterion are now emerging: receptivity theory, secondary instability theory, parabolized stability equations approaches, direct numerical simulation and large-eddy simulation. This paper will provide a description of each of these new theoretical tools and provide indications of their current status.

Critical fictive temperature for plasticity in metallic glasses

PubMed Central

Kumar, Golden; Neibecker, Pascal; Liu, Yan Hui; Schroers, Jan

2013-01-01

A long-sought goal in metallic glasses is to impart ductility without conceding their strength and elastic limit. The rational design of tough metallic glasses, however, remains challenging because of the inability of existing theories to capture the correlation between plasticity, composition and processing for a wide range of glass-forming alloys. Here we propose a phenomenological criterion based on a critical fictive temperature, Tfc, which can rationalize the effect of composition, cooling rate and annealing on room-temperature plasticity of metallic glasses. Such criterion helps in understanding the widespread mechanical behaviour of metallic glasses and reveals alloy-specific preparation conditions to circumvent brittleness. PMID:23443564

Disorder-induced amorphization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lam, N.Q.; Okamoto, P.R.; Li, Mo

1997-03-01

Many crystalline materials undergo a crystalline-to-amorphous (c-a) phase transition when subjected to energetic particle irradiation at low temperatures. By focusing on the mean-square static atomic displacement as a generic measure of chemical and topological disorder, we are led quite naturally to a generalized version of the Lindemann melting criterion as a conceptual framework for a unified thermodynamic approach to solid-state amorphizing transformations. In its simplest form, the generalized Lindemann criterion assumes that the sum of the static and dynamic mean-square atomic displacements is constant along the polymorphous melting curve so that c-a transformations can be understood simply as melting ofmore » a critically-disordered crystal at temperatures below the glass transition temperature where the supercooled liquid can persist indefinitely in a configurationally-frozen state. Evidence in support of the generalized Lindemann melting criterion for amorphization is provided by a large variety of experimental observations and by molecular dynamics simulations of heat-induced melting and of defect-induced amorphization of intermetallic compounds.« less

The elastic stability, bifurcation and ideal strength of gold under hydrostatic stress: an ab initio calculation.

PubMed

Wang, Hao; Li, Mo

2009-11-11

In this paper, we employ an ab initio density functional theory calculation to investigate the elastic stability of face-centered cubic Au under hydrostatic deformation. We identify the elastic stiffness constant B(ijkl) as the coefficient in the stress-strain relation for an arbitrary deformed state, and use it to test the stability condition. We show that this criterion bears the same physics as that proposed earlier by Frenkel and Orowan and agrees with the Born-Hill criterion. The results from those two approaches agree well with each other. We show that the stability limit, or instability, of the perfect Au crystal under hydrostatic expansion is not associated with the bulk stiffness modulus as predicted in the previous work; rather it is caused by a shear instability associated with the vanishing rhombohedral shear stiffness modulus. The deviation of the deformation mode from the primary hydrostatic loading path signals a bifurcation or symmetry breaking in the ideal crystal. The corresponding ideal hydrostatic strength for Au is 19.2 GPa at the Lagrangian expansion strain of ∼0.06. In the case of compression, Au remains stable over the entire pressure range in our calculation.

Variational approach to stability boundary for the Taylor-Goldstein equation

NASA Astrophysics Data System (ADS)

Hirota, Makoto; Morrison, Philip J.

2015-11-01

Linear stability of inviscid stratified shear flow is studied by developing an efficient method for finding neutral (i.e., marginally stable) solutions of the Taylor-Goldstein equation. The classical Miles-Howard criterion states that stratified shear flow is stable if the local Richardson number JR is greater than 1/4 everywhere. In this work, the case of JR > 0 everywhere is considered by assuming strictly monotonic and smooth profiles of the ambient shear flow and density. It is shown that singular neutral modes that are embedded in the continuous spectrum can be found by solving one-parameter families of self-adjoint eigenvalue problems. The unstable ranges of wavenumber are searched for accurately and efficiently by adopting this method in a numerical algorithm. Because the problems are self-adjoint, the variational method can be applied to ascertain the existence of singular neutral modes. For certain shear flow and density profiles, linear stability can be proven by showing the non-existence of a singular neutral mode. New sufficient conditions, extensions of the Rayleigh-Fjortoft stability criterion for unstratified shear flows, are derived in this manner. This work was supported by JSPS Strategic Young Researcher Overseas Visits Program for Accelerating Brain Circulation # 55053270.

Equal-area criterion in power systems revisited

NASA Astrophysics Data System (ADS)

Sun, Yong; Ma, Jinpeng; Kurths, Jürgen; Zhan, Meng

2018-02-01

The classic equal-area criterion (EAC) is of key importance in power system analysis, and provides a powerful, pictorial and quantitative means of analysing transient stability (i.e. the system's ability to maintain stable operation when subjected to a large disturbance). Based on the traditional EAC, it is common sense in engineering that there is a critical cleaning time (CCT); namely, a power system is stable (unstable) if a fault is cleared before (after) this CCT. We regard this form of CCT as bipartite. In this paper, we revisit the EAC theory and, surprisingly, find different kinds of transient stability behaviour. Based on these analyses, we discover that the bipartite CCT is only one type among four major types, and, actually, the forms of CCT can be diversified. In particular, under some circumstances, a system may have no CCT or show a periodic CCT. Our theoretical analysis is verified by numerical simulations in a single-machine-infinite-bus system and also in multi-machine systems. Thus, our study provides a panoramic framework for diverse transient stability behaviour in power systems and also may have a significant impact on applications of multi-stability in various other systems, such as neuroscience, climatology or photonics.

Wavelength selection in injection-driven Hele-Shaw flows: A maximum amplitude criterion

NASA Astrophysics Data System (ADS)

Dias, Eduardo; Miranda, Jose

2013-11-01

As in most interfacial flow problems, the standard theoretical procedure to establish wavelength selection in the viscous fingering instability is to maximize the linear growth rate. However, there are important discrepancies between previous theoretical predictions and existing experimental data. In this work we perform a linear stability analysis of the radial Hele-Shaw flow system that takes into account the combined action of viscous normal stresses and wetting effects. Most importantly, we introduce an alternative selection criterion for which the selected wavelength is determined by the maximum of the interfacial perturbation amplitude. The effectiveness of such a criterion is substantiated by the significantly improved agreement between theory and experiments. We thank CNPq (Brazilian Sponsor) for financial support.

Mechanical Stability Criterion, Triple-Phase Condition, and Pressure Differences of Matter Condensed in a Porous Matrix.

PubMed

Setzer, Max J.

2001-03-01

In contrast to the triple-point condition of bulk material, condensed matter in porous media can coexist stably as liquid, solid, and vapor over a wide temperature range. The necessary conditions are found by a thermodynamic approach starting with the potential which reflects the grand canonical distribution and is characterized by heat and matter exchange. The other parameters are volume and surface. Therefore, it is designated the free mechanical potential. General expressions for mechanical stability are given. On condensation and melting the nonwetting phases vanish. These are thermodynamically stable phase transitions. For the opposing effects evaporation and fusion, an energy barrier must be transgressed either by nucleation or by intrusion as discussed here. These are metastable states. Phase transitions are the conditions which limit the triple-phase region. Within this region high negative pressures are generated in the unfrozen liquid independent of the pore size where it exists. The findings are applied to water in the disperse matrix of hardened cement paste. They are the basis for "micro ice lens pumping". Copyright 2001 Academic Press.

Thermodynamic and kinetic considerations of nucleation and stabilization of acoustic cavitation bubbles in water.

PubMed

Bapat, Pratap S; Pandit, Aniruddha B

2008-01-01

Qualitative explanation for a homogeneous nucleation of acoustic cavitation bubbles in the incompressible liquid water with simple phenomenological approach has been provided via the concept of the desorbtion of the dissolved gas and the vaporization of local liquid molecules. The liquid medium has been viewed as an ensemble of lattice structures. Validity of the lattice structure approach against the Brownian motion of molecules in the liquid state has been discussed. Criterion based on probability for nucleus formation has been defined for the vaporization of local liquid molecules. Energy need for the enthalpy of vaporization has been considered as an energy criterion for the formation of a vaporous nucleus. Sound energy, thermal energy of the liquid bulk (Joule-Thomson effect) and free energy of activation, which is associated with water molecules in the liquid state (Brownian motion) as per the modified Eyring's kinetic theory of liquid are considered as possible sources for the enthalpy of vaporization of water molecules forming a single unit lattice. The classical nucleation theory has then been considered for expressing further growth of the vaporous nucleus against the surface energy barrier. Effect of liquid property (temperature), and effect of an acoustic parameter (frequency) on an acoustic cavitation threshold pressure have been discussed. Kinetics of nucleation has been considered.

Orthotropic elasto-plastic behavior of AS4/APC-2 thermoplastic composite in compression

NASA Technical Reports Server (NTRS)

Sun, C. T.; Rui, Y.

1989-01-01

Uniaxial compression tests were performed on off-axis coupon specimens of unidirectional AS4/APC-2 thermoplastic composite at various temperatures. The elasto-plastic and strength properties of AS4/APC-2 composite were characterized with respect to temperature variation by using a one-parameter orthotropic plasticity model and a one-parameter failure criterion. Experimental results show that the orthotropic plastic behavior can be characterized quite well using the plasticity model, and the matrix-dominant compressive strengths can be predicted very accurately by the one-parameter failure criterion.

A measurable Lawson criterion and hydro-equivalent curves for inertial confinement fusion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, C. D.; Betti, R.

2008-01-01

This article demonstrates how the ignition condition (Lawson criterion) for inertial confinement fusion (ICF) can be cast in a form depending on the only two parameters of the compressed fuel assembly that can be measured with methods already in existence: the hot spot ion temperature and the total areal density.

Techniques for Liquid Rocket Combustion Spontaneous Stability and Rough Combustion Assessments

NASA Technical Reports Server (NTRS)

Kenny, R. J.; Giacomoni, C.; Casiano, M. J.; Fischbach, S. R.

2016-01-01

This work presents techniques for liquid rocket engine combustion stability assessments with respect to spontaneous stability and rough combustion. Techniques covering empirical parameter extraction, which were established in prior works, are applied for three additional programs: the F-1 Gas Generator (F1GG) component test program, the RS-84 preburner component test program, and the Marshall Integrated Test Rig (MITR) program. Stability assessment parameters from these programs are compared against prior established spontaneous stability metrics and updates are identified. Also, a procedure for comparing measured with predicted mode shapes is presented, based on an extension of the Modal Assurance Criterion (MAC).

Orthotropic elastic-plastic behavior of AS4/APC-2 thermoplastic composite at elevated temperatures

NASA Technical Reports Server (NTRS)

Sun, C. T.; Yoon, K. J.

1989-01-01

Inelastic and strength properties of AS4/APC-2 composites were characterized with respect to temperature variation by using a one parameter orthotropic plasticity model and a one parameter failure criterion. Simple uniaxial off-axis tension tests were performed on coupon specimens of unidirectional AS4/APC-2 thermoplastic composite at various temperatures. To avoid the complication caused by the extension-shear coupling effect in off-axis testing, new tabs were designed and used on the test specimens. The experimental results showed that the nonlinear behavior of constitutive relations and the strength can be characterized quite well using the one parameter plasticity model and the failure criterion, respectively.

Diagonal recurrent neural network based adaptive control of nonlinear dynamical systems using lyapunov stability criterion.

PubMed

Kumar, Rajesh; Srivastava, Smriti; Gupta, J R P

2017-03-01

In this paper adaptive control of nonlinear dynamical systems using diagonal recurrent neural network (DRNN) is proposed. The structure of DRNN is a modification of fully connected recurrent neural network (FCRNN). Presence of self-recurrent neurons in the hidden layer of DRNN gives it an ability to capture the dynamic behaviour of the nonlinear plant under consideration (to be controlled). To ensure stability, update rules are developed using lyapunov stability criterion. These rules are then used for adjusting the various parameters of DRNN. The responses of plants obtained with DRNN are compared with those obtained when multi-layer feed forward neural network (MLFFNN) is used as a controller. Also, in example 4, FCRNN is also investigated and compared with DRNN and MLFFNN. Robustness of the proposed control scheme is also tested against parameter variations and disturbance signals. Four simulation examples including one-link robotic manipulator and inverted pendulum are considered on which the proposed controller is applied. The results so obtained show the superiority of DRNN over MLFFNN as a controller. Copyright © 2017 ISA. Published by Elsevier Ltd. All rights reserved.

The effect of suspended particles on Jean's criterion for gravitational instability

NASA Technical Reports Server (NTRS)

Wollkind, David J.; Yates, Kemble R.

1990-01-01

The effect that the proper inclusion of suspended particles has on Jeans' criterion for the self-gravitational instability of an unbounded nonrotating adiabatic gas cloud is examined by formulating the appropriate model system, introducing particular physically plausible equations of state and constitutive relations, performing a linear stability analysis of a uniformly expanding exact solution to these governing equations, and exploiting the fact that there exists a natural small material parameter for this problem given by N sub 1/n sub 1, the ratio of the initial number density for the particles to that for the gas. The main result of this investigation is the derivation of an altered criterion which can substantially reduce Jeans' original critical wavelength for instability. It is then shown that the existing discrepancy between Jeans' theoretical prediction using and actual observational data relevant to the Andromeda nebula M31 can be accounted for by this new criterion of assuming suspended particles of a reasonable grain size and distribution to be present.

Associative memory in an analog iterated-map neural network

NASA Astrophysics Data System (ADS)

Marcus, C. M.; Waugh, F. R.; Westervelt, R. M.

1990-03-01

The behavior of an analog neural network with parallel dynamics is studied analytically and numerically for two associative-memory learning algorithms, the Hebb rule and the pseudoinverse rule. Phase diagrams in the parameter space of analog gain β and storage ratio α are presented. For both learning rules, the networks have large ``recall'' phases in which retrieval states exist and convergence to a fixed point is guaranteed by a global stability criterion. We also demonstrate numerically that using a reduced analog gain increases the probability of recall starting from a random initial state. This phenomenon is comparable to thermal annealing used to escape local minima but has the advantage of being deterministic, and therefore easily implemented in electronic hardware. Similarities and differences between analog neural networks and networks with two-state neurons at finite temperature are also discussed.

Canonical fluid thermodynamics

NASA Technical Reports Server (NTRS)

Schmid, L. A.

1972-01-01

The space-time integral of the thermodynamic pressure plays the role of the thermodynamic potential for compressible, adiabatic flow in the sense that the pressure integral for stable flow is less than for all slightly different flows. This stability criterion can be converted into a variational minimum principle by requiring the molar free-enthalpy and the temperature, which are the arguments of the pressure function, to be generalized velocities, that is, the proper-time derivatives of scalar spare-time functions which are generalized coordinates in the canonical formalism. In a fluid context, proper-time differentiation must be expressed in terms of three independent quantities that specify the fluid velocity. This can be done in several ways, all of which lead to different variants (canonical transformations) of the same constraint-free action integral whose Euler-Lagrange equations are just the well-known equations of motion for adiabatic compressible flow.

Cascade control of superheated steam temperature with neuro-PID controller.

PubMed

Zhang, Jianhua; Zhang, Fenfang; Ren, Mifeng; Hou, Guolian; Fang, Fang

2012-11-01

In this paper, an improved cascade control methodology for superheated processes is developed, in which the primary PID controller is implemented by neural networks trained by minimizing error entropy criterion. The entropy of the tracking error can be estimated recursively by utilizing receding horizon window technique. The measurable disturbances in superheated processes are input to the neuro-PID controller besides the sequences of tracking error in outer loop control system, hence, feedback control is combined with feedforward control in the proposed neuro-PID controller. The convergent condition of the neural networks is analyzed. The implementation procedures of the proposed cascade control approach are summarized. Compared with the neuro-PID controller using minimizing squared error criterion, the proposed neuro-PID controller using minimizing error entropy criterion may decrease fluctuations of the superheated steam temperature. A simulation example shows the advantages of the proposed method. Copyright © 2012 ISA. Published by Elsevier Ltd. All rights reserved.

THERMAL COMFORT IN RELATION TO MEAN SKIN TEMPERATURE,

DTIC Science & Technology

Nude men were exposed to a range of ambient temperatures and were brought to a condition of thermal comfort by adjustment of the incident radiation...was evident that mean skin temperature, per se, was not a dependable criterion of thermal comfort . (Author)

Symbolic computation of the Birkhoff normal form in the problem of stability of the triangular libration points

NASA Astrophysics Data System (ADS)

Shevchenko, I. I.

2008-05-01

The problem of stability of the triangular libration points in the planar circular restricted three-body problem is considered. A software package, intended for normalization of autonomous Hamiltonian systems by means of computer algebra, is designed so that normalization problems of high analytical complexity could be solved. It is used to obtain the Birkhoff normal form of the Hamiltonian in the given problem. The normalization is carried out up to the 6th order of expansion of the Hamiltonian in the coordinates and momenta. Analytical expressions for the coefficients of the normal form of the 6th order are derived. Though intermediary expressions occupy gigabytes of the computer memory, the obtained coefficients of the normal form are compact enough for presentation in typographic format. The analogue of the Deprit formula for the stability criterion is derived in the 6th order of normalization. The obtained floating-point numerical values for the normal form coefficients and the stability criterion confirm the results by Markeev (1969) and Coppola and Rand (1989), while the obtained analytical and exact numeric expressions confirm the results by Meyer and Schmidt (1986) and Schmidt (1989). The given computational problem is solved without constructing a specialized algebraic processor, i.e., the designed computer algebra package has a broad field of applicability.

Testing the Hip Abductor Muscle Strength of Older Persons Using a Handheld Dynamometer.

PubMed

Awwad, Daniel H; Buckley, Jonathan D; Thomson, Rebecca L; O'Connor, Matthew; Carbone, Tania A; Chehade, Mellick J

2017-09-01

To investigate the reliability of a clinically applicable method of dynamometry to assess and monitor hip abductor muscle strength in older persons. Bilateral isometric hip abductor muscle strength measured with a handheld dynamometer, patients supine with the contralateral hip positioned directly against a wall for stabilization. Reliability determined by comparing intra-assessor and inter-assessor results and comparison to a criterion standard (stabilized dynamometer with patients in the standing position). UniSA Nutritional Physiology Research Centre. Twenty-one patients older than 65 years were recruited from the Royal Adelaide Hospital. Intraclass correlation coefficients (ICCs), bias, and limits of agreement calculated to determine reliability. Intra-assessor and inter-assessor ICCs were high (0.94 and 0.92-0.94, respectively). There was no intra-assessor bias and narrow limits of agreement (±2.4%). There was a small inter-assessor bias but narrow limits of agreement (0.6%-0.9% and ± 2.3%, respectively). There was a wide variation comparing results to the criterion standard (±5.0%-5.2% limits of agreement), highlighting problems attributed to difficulties that the test population had with the standing position used in the criterion standard test. Testing older persons' hip abductor muscle strength while in the supine position with optimal pelvic stabilization using a handheld dynamometer is highly reliable. While further studies must be done to assess patients with specific pathologies, this test has potential application to monitor and evaluate the effects of surgical interventions and/or rehabilitation protocols for a variety of conditions affecting hip abductor function such as hip fractures and arthritis.

Interface stability in a slowly rotating low-gravity tank Theory

NASA Technical Reports Server (NTRS)

Gans, R. F.; Leslie, F. W.

1986-01-01

The equilibrium configuration of a bubble in a rotating liquid confined by flat axial boundaries (baffles) is found. The maximum baffle spacing assuring bubble confinement is bounded from above by the natural length of a bubble in an infinite medium under the same conditions. Effects of nonzero contact angle are minimal. The problem of dynamic stability is posed. It can be solved in the limit of rapid rotation, for which the bubble is a long cylinder. Instability is to axisymmetric perturbations; nonaxisymmetric perturbations are stable. The stability criterion agrees with earlier results.

A simple criterion for determining the dynamical stability of three-body systems

NASA Technical Reports Server (NTRS)

Black, D. C.

1982-01-01

Coplanar, prograde three-body systems (TBS) are discussed, emphasizing the specification of general criteria for determining whether such systems are dynamically stable. It is shown that the Graziani-Black (1981) criteria provide a quantitatively accurate characterization of the onset of dynamic instability for values of the dimensionless mass ranging from one millionth to one million. Harrington's (1977) general criterion and the Graziani-Black criterion are compared with results from analytic work that spans a 12-orders-of-magnitude variation in the mass ratios of the TBS components. Comparison of the Graziani-Black criteria with data for eight well-studied triple-star systems indicates that the observed lower limit for the ratio of periastron distance of the tertiary orbit to the semimajor axis of the binary orbit is due to dynamical instability rather than to cosmogonic processes.

On the Absolutely Continuous Spectrum of Stark Operators

NASA Astrophysics Data System (ADS)

Perelman, Galina

The stability of the absolutely continuous spectrum of the one-dimensional Stark operator under perturbations of the potential is discussed. The focus is on proving this stability under minimal assumptions on smoothness of the perturbation. A general criterion is presented together with some applications. These include the case of periodic perturbations where we show that any perturbation vL1()∩H-1/2() preserves the a.c. spectrum.

A feedback control model for network flow with multiple pure time delays

NASA Technical Reports Server (NTRS)

Press, J.

1972-01-01

A control model describing a network flow hindered by multiple pure time (or transport) delays is formulated. Feedbacks connect each desired output with a single control sector situated at the origin. The dynamic formulation invokes the use of differential difference equations. This causes the characteristic equation of the model to consist of transcendental functions instead of a common algebraic polynomial. A general graphical criterion is developed to evaluate the stability of such a problem. A digital computer simulation confirms the validity of such criterion. An optimal decision making process with multiple delays is presented.

Finite-Time Adaptive Control for a Class of Nonlinear Systems With Nonstrict Feedback Structure.

PubMed

Sun, Yumei; Chen, Bing; Lin, Chong; Wang, Honghong

2017-09-18

This paper focuses on finite-time adaptive neural tracking control for nonlinear systems in nonstrict feedback form. A semiglobal finite-time practical stability criterion is first proposed. Correspondingly, the finite-time adaptive neural control strategy is given by using this criterion. Unlike the existing results on adaptive neural/fuzzy control, the proposed adaptive neural controller guarantees that the tracking error converges to a sufficiently small domain around the origin in finite time, and other closed-loop signals are bounded. At last, two examples are used to test the validity of our results.

Dimensioning Principles in Potash and Salt: Stability and Integrity

NASA Astrophysics Data System (ADS)

Minkley, W.; Mühlbauer, J.; Lüdeling, C.

2016-11-01

The paper describes the principal geomechanical approaches to mine dimensioning in salt and potash mining, focusing on stability of the mining system and integrity of the hydraulic barrier. Several common dimensioning are subjected to a comparative analysis. We identify geomechanical discontinuum models as essential physical ingredients for examining the collapse of working fields in potash mining. The basic mechanisms rely on the softening behaviour of salt rocks and the interfaces. A visco-elasto-plastic material model with strain softening, dilatancy and creep describes the time-dependent softening behaviour of the salt pillars, while a shear model with velocity-dependent adhesive friction with shear displacement-dependent softening is used for bedding planes and discontinuities. Pillar stability critically depends on the shear conditions of the bedding planes to the overlying and underlying beds, which provide the necessary confining pressure for the pillar core, but can fail dynamically, leading to large-scale field collapses. We further discuss the integrity conditions for the hydraulic barrier, most notably the minimal stress criterion, the violation of which leads to pressure-driven percolation as the mechanism of fluid transport and hence barrier failure. We present a number of examples where violation of the minimal stress criterion has led to mine floodings.

Nonparallel linear stability analysis of unconfined vortices

NASA Astrophysics Data System (ADS)

Herrada, M. A.; Barrero, A.

2004-10-01

Parabolized stability equations [F. P. Bertolotti, Th. Herbert, and P. R. Spalart, J. Fluid. Mech. 242, 441 (1992)] have been used to study the stability of a family of swirling jets at high Reynolds numbers whose velocity and pressure fields decay far from the axis as rm-2 and r2(m-2), respectively [M. Pérez-Saborid, M. A. Herrada, A. Gómez-Barea, and A. Barrero, J. Fluid. Mech. 471, 51 (2002)]; r is the radial distance and m is a real number in the interval 0

Metallic phases from disordered (2+1)-dimensional quantum electrodynamics

DOE PAGES

Goswami, Pallab; Goldman, Hart; Raghu, S.

2017-06-15

Metallic phases have been observed in several disordered two-dimensional (2D) systems, including thin films near superconductor-insulator transitions and quantum Hall systems near plateau transitions. The existence of 2D metallic phases at zero temperature generally requires an interplay of disorder and interaction effects. Consequently, experimental observations of 2D metallic behavior have largely defied explanation. We formulate a general stability criterion for strongly interacting, massless Dirac fermions against disorder, which describe metallic ground states with vanishing density of states. We show that (2+1)-dimensional quantum electrodynamics (QED 3) with a large, even number of fermion flavors remains metallic in the presence of weakmore » scalar potential disorder due to the dynamic screening of disorder by gauge fluctuations. In conclusion, we also show that QED 3 with weak mass disorder exhibits a stable, dirty metallic phase in which both interactions and disorder play important roles.« less

Synthesis, growth and characterization of 3-nitroacetanilide—A new organic nonlinear optical crystal by Bridgman technique

NASA Astrophysics Data System (ADS)

Lenin, M.; Ramasamy, P.

2008-10-01

Single crystals of 3-nitroacetanilide, an organic nonlinear optical material has been grown by the Bridgman-Stockbarger method. The single crystal X-ray diffraction (XRD) data revealed the noncentrosymmetric crystal structure, which is an essential criterion for second harmonic generation. The crystalline nature of the grown crystals was confirmed using powder XRD techniques. The functional group of the compound is identified by FTIR spectrum. The thermal stability and its tendency to grow as single crystal in solution and in melt have been identified for the new title compound. The UV-vis spectrum of mNAA shows the lower optical cut off at 400 nm and was transparent in the visible region. The second harmonic generation efficiency was found using Kurtz powder technique. The dielectric constant and dielectric loss of the crystal were measured as a function of frequency and temperature, and the results are discussed.

Optimal region of latching activity in an adaptive Potts model for networks of neurons

NASA Astrophysics Data System (ADS)

Abdollah-nia, Mohammad-Farshad; Saeedghalati, Mohammadkarim; Abbassian, Abdolhossein

2012-02-01

In statistical mechanics, the Potts model is a model for interacting spins with more than two discrete states. Neural networks which exhibit features of learning and associative memory can also be modeled by a system of Potts spins. A spontaneous behavior of hopping from one discrete attractor state to another (referred to as latching) has been proposed to be associated with higher cognitive functions. Here we propose a model in which both the stochastic dynamics of Potts models and an adaptive potential function are present. A latching dynamics is observed in a limited region of the noise(temperature)-adaptation parameter space. We hence suggest noise as a fundamental factor in such alternations alongside adaptation. From a dynamical systems point of view, the noise-adaptation alternations may be the underlying mechanism for multi-stability in attractor-based models. An optimality criterion for realistic models is finally inferred.

Metallic phases from disordered (2+1)-dimensional quantum electrodynamics

NASA Astrophysics Data System (ADS)

Goswami, Pallab; Goldman, Hart; Raghu, S.

2017-06-01

Metallic phases have been observed in several disordered two-dimensional (2D) systems, including thin films near superconductor-insulator transitions and quantum Hall systems near plateau transitions. The existence of 2D metallic phases at zero temperature generally requires an interplay of disorder and interaction effects. Consequently, experimental observations of 2D metallic behavior have largely defied explanation. We formulate a general stability criterion for strongly interacting, massless Dirac fermions against disorder, which describe metallic ground states with vanishing density of states. We show that (2+1)-dimensional quantum electrodynamics (QED3) with a large, even number of fermion flavors remains metallic in the presence of weak scalar potential disorder due to the dynamic screening of disorder by gauge fluctuations. We also show that QED3 with weak mass disorder exhibits a stable, dirty metallic phase in which both interactions and disorder play important roles.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goswami, Pallab; Goldman, Hart; Raghu, S.

Metallic phases have been observed in several disordered two-dimensional (2D) systems, including thin films near superconductor-insulator transitions and quantum Hall systems near plateau transitions. The existence of 2D metallic phases at zero temperature generally requires an interplay of disorder and interaction effects. Consequently, experimental observations of 2D metallic behavior have largely defied explanation. We formulate a general stability criterion for strongly interacting, massless Dirac fermions against disorder, which describe metallic ground states with vanishing density of states. We show that (2+1)-dimensional quantum electrodynamics (QED 3) with a large, even number of fermion flavors remains metallic in the presence of weakmore » scalar potential disorder due to the dynamic screening of disorder by gauge fluctuations. In conclusion, we also show that QED 3 with weak mass disorder exhibits a stable, dirty metallic phase in which both interactions and disorder play important roles.« less

Suicide-related behaviors and anxiety in children and adolescents: a review.

PubMed

Hill, Ryan M; Castellanos, Daniel; Pettit, Jeremy W

2011-11-01

This paper reviews empirical evidence of the association between suicide-related behaviors and anxiety among children and adolescents. It begins with a review of suicide-related behaviors and anxiety, discusses methodological issues related to measurement, and reviews empirical findings published since the last review of this topic in 1988. Evidence is summarized on four criteria necessary to establish anxiety as a causal risk factor for suicide-related behaviors among children and adolescents. There is consistent evidence for a significant association between anxiety and suicide-related behaviors (Criterion 1). Evidence that the influence of anxiety on suicide-related behaviors is not due to a third variable (Criterion 2) is mixed and hindered by methodological limitations. The literature is also unclear as to whether anxiety temporally precedes suicide-related behaviors (Criterion 3). Finally, this review found no evidence to support or refute anxiety's stability independent of and across instances of suicide-related behaviors (Criterion 4). Theoretical and clinical implications of these findings and directions for future research are discussed. Copyright © 2011 Elsevier Ltd. All rights reserved.

Applications of ENF criterion in forensic audio, video, computer and telecommunication analysis.

PubMed

Grigoras, Catalin

2007-04-11

This article reports on the electric network frequency criterion as a means of assessing the integrity of digital audio/video evidence and forensic IT and telecommunication analysis. A brief description is given to different ENF types and phenomena that determine ENF variations. In most situations, to reach a non-authenticity opinion, the visual inspection of spectrograms and comparison with an ENF database are enough. A more detailed investigation, in the time domain, requires short time windows measurements and analyses. The stability of the ENF over geographical distances has been established by comparison of synchronized recordings made at different locations on the same network. Real cases are presented, in which the ENF criterion was used to investigate audio and video files created with secret surveillance systems, a digitized audio/video recording and a TV broadcasted reportage. By applying the ENF Criterion in forensic audio/video analysis, one can determine whether and where a digital recording has been edited, establish whether it was made at the time claimed, and identify the time and date of the registering operation.

On the stability of the internal kink mode in the banana regime

NASA Astrophysics Data System (ADS)

Fogaccia, G.; Romanelli, F.

1995-01-01

The stability of the internal kink mode is investigated taking into account the kinetic response associated to the trapped thermal ions. Ion-ion collisions and diamagnetic effects in the layer are also considered. A significant stabilizing contribution is obtained, even at low-β values, on the mode, which might be stable, on present experiments, even though predicted unstable according to the Bussac criterion [Bussac et al., Phys. Rev. Lett. 35, 1638 (1975)]. In addition, a trapped-ion instability is found, characterized by mode frequency of the order of the trapped-ion bounce-averaged magnetic drift frequency.

Effect of a strong-current ion ring on spheromak stability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Litwin, C.; Sudan, R.N.

The stability of a spheromak with an energetic ion ring, carrying a current comparable to the plasma current, to the tilt mode is considered. For small departures from sphericity a perturbative approach is applied to an appropriate energy principle in order to calculate the lowest nontrivial kinetic contribution of the ion ring. An analytic stability criterion is obtained. It is seen that the prolate configuration becomes more stable while the oblate one is less stable than in the absence of the ring. The prolomak becomes stable when the ring kinetic energy exceeds the magnetic energy within the separatrix.

Coexistence of collapse and stable spatiotemporal solitons in multimode fibers

NASA Astrophysics Data System (ADS)

Shtyrina, Olga V.; Fedoruk, Mikhail P.; Kivshar, Yuri S.; Turitsyn, Sergei K.

2018-01-01

We analyze spatiotemporal solitons in multimode optical fibers and demonstrate the existence of stable solitons, in a sharp contrast to earlier predictions of collapse of multidimensional solitons in three-dimensional media. We discuss the coexistence of blow-up solutions and collapse stabilization by a low-dimensional external potential in graded-index media, and also predict the existence of stable higher-order nonlinear waves such as dipole-mode spatiotemporal solitons. To support the main conclusions of our numerical studies we employ a variational approach and derive analytically the stability criterion for input powers for the collapse stabilization.

General instability criterion of laminar velocity distributions

NASA Technical Reports Server (NTRS)

Tollmien, W

1936-01-01

The present paper describes the results of a stability investigation on symmetrical velocity profiles in a channel and of boundary-layer profiles. The effect of friction was assumed to be vanishing and did not occur in the stability consideration so far as it had been resorted to for preparatory asymptotic considerations. Proceeding on very general premises as regards the form of the velocity distribution, a proof was deduced of the elementary theorem that velocity profiles with inflection points are unstable.

A Unifying Mathematical Framework for Genetic Robustness, Environmental Robustness, Network Robustness and their Trade-off on Phenotype Robustness in Biological Networks Part I: Gene Regulatory Networks in Systems and Evolutionary Biology

PubMed Central

Chen, Bor-Sen; Lin, Ying-Po

2013-01-01

Robust stabilization and environmental disturbance attenuation are ubiquitous systematic properties observed in biological systems at different levels. The underlying principles for robust stabilization and environmental disturbance attenuation are universal to both complex biological systems and sophisticated engineering systems. In many biological networks, network robustness should be enough to confer intrinsic robustness in order to tolerate intrinsic parameter fluctuations, genetic robustness for buffering genetic variations, and environmental robustness for resisting environmental disturbances. With this, the phenotypic stability of biological network can be maintained, thus guaranteeing phenotype robustness. This paper presents a survey on biological systems and then develops a unifying mathematical framework for investigating the principles of both robust stabilization and environmental disturbance attenuation in systems and evolutionary biology. Further, from the unifying mathematical framework, it was discovered that the phenotype robustness criterion for biological networks at different levels relies upon intrinsic robustness + genetic robustness + environmental robustness ≦ network robustness. When this is true, the phenotype robustness can be maintained in spite of intrinsic parameter fluctuations, genetic variations, and environmental disturbances. Therefore, the trade-offs between intrinsic robustness, genetic robustness, environmental robustness, and network robustness in systems and evolutionary biology can also be investigated through their corresponding phenotype robustness criterion from the systematic point of view. PMID:23515240

A Unifying Mathematical Framework for Genetic Robustness, Environmental Robustness, Network Robustness and their Trade-off on Phenotype Robustness in Biological Networks Part I: Gene Regulatory Networks in Systems and Evolutionary Biology.

PubMed

Chen, Bor-Sen; Lin, Ying-Po

2013-01-01

Robust stabilization and environmental disturbance attenuation are ubiquitous systematic properties observed in biological systems at different levels. The underlying principles for robust stabilization and environmental disturbance attenuation are universal to both complex biological systems and sophisticated engineering systems. In many biological networks, network robustness should be enough to confer intrinsic robustness in order to tolerate intrinsic parameter fluctuations, genetic robustness for buffering genetic variations, and environmental robustness for resisting environmental disturbances. With this, the phenotypic stability of biological network can be maintained, thus guaranteeing phenotype robustness. This paper presents a survey on biological systems and then develops a unifying mathematical framework for investigating the principles of both robust stabilization and environmental disturbance attenuation in systems and evolutionary biology. Further, from the unifying mathematical framework, it was discovered that the phenotype robustness criterion for biological networks at different levels relies upon intrinsic robustness + genetic robustness + environmental robustness ≦ network robustness. When this is true, the phenotype robustness can be maintained in spite of intrinsic parameter fluctuations, genetic variations, and environmental disturbances. Therefore, the trade-offs between intrinsic robustness, genetic robustness, environmental robustness, and network robustness in systems and evolutionary biology can also be investigated through their corresponding phenotype robustness criterion from the systematic point of view.

An axial temperature profile curvature criterion for the engineering of convex crystal growth interfaces in Bridgman systems

NASA Astrophysics Data System (ADS)

Peterson, Jeffrey H.; Derby, Jeffrey J.

2017-06-01

A unifying idea is presented for the engineering of convex melt-solid interface shapes in Bridgman crystal growth systems. Previous approaches to interface control are discussed with particular attention paid to the idea of a "booster" heater. Proceeding from the idea that a booster heater promotes a converging heat flux geometry and from the energy conservation equation, we show that a convex interface shape will naturally result when the interface is located in regions of the furnace where the axial thermal profile exhibits negative curvature, i.e., where d2 T / dz2 < 0 . This criterion is effective in explaining prior literature results on interface control and promising for the evaluation of new furnace designs. We posit that the negative curvature criterion may be applicable to the characterization of growth systems via temperature measurements in an empty furnace, providing insight about the potential for achieving a convex interface shape, without growing a crystal or conducting simulations.

An investigation of the effects of pitch-roll (de)-coupling on helicopter handling qualities

NASA Technical Reports Server (NTRS)

Ockier, C. J.; Pausder, H. J.; Blanken, C. L.

1995-01-01

An investigation of the effects of pitch-roll coupling on helicopter handling qualities was performed by the US Army and DLR, using a NASA ground-based and a DLR inflight simulator. Over 90 different coupling configurations were evaluated using a roll-axis tracking task. The results show that although the current ADS-33C coupling criterion discriminates against those types of coupling typical of conventionally controlled helicopters, it not always suited for the prediction of handling qualities of helicopters with modern control systems. Based on the observation that high frequency inputs during tracking are used to alleviate coupling, a frequency domain pitch-roll coupling criterion that uses the average coupling ratio between the bandwidth and neutral stability frequency is formulated. This criterion provides a more comprehensive coverage with respect to the different types of coupling and shows excellent consistency.

Effects of friction dampers on aerodynamically unstable rotor stages

NASA Technical Reports Server (NTRS)

Griffin, J. H.; Sinha, A.

1983-01-01

Attention is given to the physical concepts and mathematical techniques useful in the analysis of the stabilizing effect of friction on aerodynamically unstable rotor stages. Results are presented for three-, four-, and five-bladed disks. In the present multidegree-of-freedom model of an aerodynamically unstable rotor stage, a harmonic steady state solution due to the friction dampers may be either a stability limit, a stable cycle limit, or neither. A criterion is established in the form of an energy function which determines whether the solution is a stability limit. In the event that the initial displacement and velocity exeed those associated with the steady state solution corresponding to a stability limit, the reponse becomes unbounded.

Stability and chaotification of vibration isolation floating raft systems with time-delayed feedback control.

PubMed

Li, Y L; Xu, D L; Fu, Y M; Zhou, J X

2011-09-01

This paper presents a systematic study on the stability of a two-dimensional vibration isolation floating raft system with a time-delayed feedback control. Based on the generalized Sturm criterion, the critical control gain for the delay-independent stability region and critical time delays for the stability switches are derived. The critical conditions can provide a theoretical guidance of chaotification design for line spectra reduction. Numerical simulations verify the correctness of the approach. Bifurcation analyses reveal that chaotification is more likely to occur in unstable region defined by these critical conditions, and the stiffness of the floating raft and mass ratio are the sensitive parameters to reduce critical control gain.

Boundedness and global robust stability analysis of delayed complex-valued neural networks with interval parameter uncertainties.

PubMed

Song, Qiankun; Yu, Qinqin; Zhao, Zhenjiang; Liu, Yurong; Alsaadi, Fuad E

2018-07-01

In this paper, the boundedness and robust stability for a class of delayed complex-valued neural networks with interval parameter uncertainties are investigated. By using Homomorphic mapping theorem, Lyapunov method and inequality techniques, sufficient condition to guarantee the boundedness of networks and the existence, uniqueness and global robust stability of equilibrium point is derived for the considered uncertain neural networks. The obtained robust stability criterion is expressed in complex-valued LMI, which can be calculated numerically using YALMIP with solver of SDPT3 in MATLAB. An example with simulations is supplied to show the applicability and advantages of the acquired result. Copyright © 2018 Elsevier Ltd. All rights reserved.

Asymptotic stability and instability of large-scale systems. [using vector Liapunov functions

NASA Technical Reports Server (NTRS)

Grujic, L. T.; Siljak, D. D.

1973-01-01

The purpose of this paper is to develop new methods for constructing vector Lyapunov functions and broaden the application of Lyapunov's theory to stability analysis of large-scale dynamic systems. The application, so far limited by the assumption that the large-scale systems are composed of exponentially stable subsystems, is extended via the general concept of comparison functions to systems which can be decomposed into asymptotically stable subsystems. Asymptotic stability of the composite system is tested by a simple algebraic criterion. By redefining interconnection functions among the subsystems according to interconnection matrices, the same mathematical machinery can be used to determine connective asymptotic stability of large-scale systems under arbitrary structural perturbations.

Forming limit strains for non-linear strain path of AA6014 aluminium sheet deformed at room temperature

NASA Astrophysics Data System (ADS)

Bressan, José Divo; Liewald, Mathias; Drotleff, Klaus

2017-10-01

Forming limit strain curves of conventional aluminium alloy AA6014 sheets after loading with non-linear strain paths are presented and compared with D-Bressan macroscopic model of sheet metal rupture by critical shear stress criterion. AA6014 exhibits good formability at room temperature and, thus, is mainly employed in car body external parts by manufacturing at room temperature. According to Weber et al., experimental bi-linear strain paths were carried out in specimens with 1mm thickness by pre-stretching in uniaxial and biaxial directions up to 5%, 10% and 20% strain levels before performing Nakajima testing experiments to obtain the forming limit strain curves, FLCs. In addition, FLCs of AA6014 were predicted by employing D-Bressan critical shear stress criterion for bi-linear strain path and comparisons with the experimental FLCs were analyzed and discussed. In order to obtain the material coefficients of plastic anisotropy, strain and strain rate hardening behavior and calibrate the D-Bressan model, tensile tests, two different strain rate on specimens cut at 0°, 45° and 90° to the rolling direction and also bulge test were carried out at room temperature. The correlation of experimental bi-linear strain path FLCs is reasonably good with the predicted limit strains from D-Bressan model, assuming equivalent pre-strain calculated by Hill 1979 yield criterion.

Flutter of Hybrid Laminated Flat Panels with Simply Supported Edges in Supersonic Flow

NASA Astrophysics Data System (ADS)

Barai, A.; Durvasula, S.

1994-01-01

Flutter of hybrid laminated flat panels in supersonic flow is studied by using first order shear deformation theory in conjunction with the assumed mode method. Both the quasi-static approximation and piston theory are used for aerodynamic force calculations at supersonic speeds. The flutter stability boundaries are determined by using the frequency coalescence criterion with the quasi-static approximation and Movchan-Krumhaar's criterion with the piston theory aerodynamics. Numerical calculations are presented for hybrid laminates consisting of graphite, Kevlar and glass fibres in an epoxy matrix. The effects of hybridization, shear deformation, ply orientation and aspect ratio are studied. The critical dynamic pressure parameter of a hybrid laminate lies between the values for laminates made with all plies of higher stiffness and with all plies of lower stiffness, respectively. The role of aerodynamic damping is found to be particularly important in determining the aeroelastic stability boundaries of laminated composite panels. Shear flexibility reduces the critical dynamic pressure parameter, but the reduction is insignificant for thin panels.

Bulk hydrodynamic stability and turbulent saturation in compressing hot spots

NASA Astrophysics Data System (ADS)

Davidovits, Seth; Fisch, Nathaniel J.

2018-04-01

For hot spots compressed at constant velocity, we give a hydrodynamic stability criterion that describes the expected energy behavior of non-radial hydrodynamic motion for different classes of trajectories (in ρR — T space). For a given compression velocity, this criterion depends on ρR, T, and d T /d (ρR ) (the trajectory slope) and applies point-wise so that the expected behavior can be determined instantaneously along the trajectory. Among the classes of trajectories are those where the hydromotion is guaranteed to decrease and those where the hydromotion is bounded by a saturated value. We calculate this saturated value and find the compression velocities for which hydromotion may be a substantial fraction of hot-spot energy at burn time. The Lindl (Phys. Plasmas 2, 3933 (1995)] "attractor" trajectory is shown to experience non-radial hydrodynamic energy that grows towards this saturated state. Comparing the saturation value with the available detailed 3D simulation results, we find that the fluctuating velocities in these simulations reach substantial fractions of the saturated value.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaothekar, Sachin, E-mail: sackaothekar@gmail.com

I have studied the effects of finite electron inertia, finite ion Larmor radius (FLR) corrections, and radiative heat-loss function on the thermal instability of an infinite homogeneous, viscous plasma incorporating the effect of thermal conductivity for star formation in interstellar medium (ISM). A general dispersion relation is derived using the normal mode analysis method with the help of relevant linearized perturbation equations of the problem. The wave propagation is discussed for longitudinal and transverse directions to the external magnetic field and the conditions of modified thermal instabilities and stabilities are discussed in different cases. We find that the thermal instabilitymore » criterion is get modified into radiative instability criterion by inclusion of radiative heat-loss functions with thermal conductivity. The viscosity of medium removes the effect of FLR corrections from the condition of radiative instability. Numerical calculation shows stabilizing effect of heat-loss function, viscosity and FLR corrections, and destabilizing effect of finite electron inertia on the thermal instability. Results carried out in this paper shows that stars are formed in interstellar medium mainly due to thermal instability.« less

Crack stability and branching at interfaces

NASA Astrophysics Data System (ADS)

Thomson, Robb

1995-11-01

The various events that occur at a crack on an interface are explored, and described in terms of a simple graphical construction called the crack stability diagram. For simple Griffith cleavage in a homogeneous material, the stability diagram is a sector of a circle in the space of stress intensity factors, KI/KII. The Griffith circle is limited in both positive and negative KII directions by nonblunting dislocation emission on the cleavage plane. For a branching plane inclined at an angle to the original cleavage plane, both cleavage and emission (which blunts the crack) can be described as a balance between an elastic driving force and a lattice resistance for the event. We use an analytic expression obtained by Cotterell and Rice for cleavage, and show that it is an excellent approximation, but show that the lattice resistance includes a cornering resistance, in addition to the standard surface energy in the final cleavage criterion. Our discussion of the lattaice resistance is derived from simulations in two-dimensional hexagonal lattices with UBER force laws with a variety of shapes. Both branching cleavage and blunting emission can be described in terms of a stability diagram in the space of the remote stress intensity factors, and the competition between events on the initial cleavage plane and those on the branching plane can be described by overlays of the two appropriate stability diagrams. The popular criterion that kII=0 on the branching plane is explored for lattices and found to fail significantly, because the lattice stabilizes cleavage by the anisotropy of the surface energy. Also, in the lattice, dislocation emission must must always be considered as an alternative competing event to branching.

Failure criterion for materials with spatially correlated mechanical properties

NASA Astrophysics Data System (ADS)

Faillettaz, J.; Or, D.

2015-03-01

The role of spatially correlated mechanical elements in the failure behavior of heterogeneous materials represented by fiber bundle models (FBMs) was evaluated systematically for different load redistribution rules. Increasing the range of spatial correlation for FBMs with local load sharing is marked by a transition from ductilelike failure characteristics into brittlelike failure. The study identified a global failure criterion based on macroscopic properties (external load and cumulative damage) that is independent of spatial correlation or load redistribution rules. This general metric could be applied to assess the mechanical stability of complex and heterogeneous systems and thus provide an important component for early warning of a class of geophysical ruptures.

Corrigendum

NASA Astrophysics Data System (ADS)

Faghihi, M.; Scheffel, J.

1988-12-01

A minor correction, having no major influence on our results, is reported here. The coefficients in the equations of state (16) and (17) should read The set of equations (13)-(20) now comprise the correct, linearized and Fourierdecomposed double adiabatic equations in cylindrical geometry. In addition, there is a printing error in (15): a factor bz should multiply the last term of the left-hand side. Our results are only slightly modified, and the discussion remains unchanged. We wish, however, to point out that the correct stability criterion for isotropic pressure, (26), should be This is the double adiabatic counterpart to the m ╪ 0 Kadomtsev criterion of ideal MHD.

Characterization of elastic-plastic properties of AS4/APC-2 thermoplastic composite

NASA Technical Reports Server (NTRS)

Sun, C. T.; Yoon, K. J.

1988-01-01

Elastic and inelastic properties of AS4/APC-2 composites were characterized with respect to temperature variation by using a one-parameter orthotropic plasticity model and a one parameter failure criterion. Simple uniaxial off-axis tension tests were performed on coupon specimens of unidirectional AS4/APC-2 thermoplastic composite at various temperatures. To avoid the complication caused by the extension-shear coupling effect in off-axis testing, new tabs were designed and used on the test specimens. The experimental results showed that the nonlinear behavior of constitutive relations and the failure strengths can be characterized quite well using the one parameter plasticity model and the failure criterion, respectively.

Unsteady Motions in Combustion Chambers for Propulsion Systems

DTIC Science & Technology

2006-12-01

Internal Heat Conduction on the Propagation of Acoustic 5-10 Waves 5.4 Energy and Intensity Associated with Acoustic Waves 5-13 5.5 The Growth or... Heat Source and Motion of the Boundary 6-16 6.6 Rayleigh’s Criterion and Linear Stability 6-18 6.7 Some Results for Linear Stability in Three...7.11.1 Pulsing Solid Propellant Rockets 7-45 7.12 Dependence of Wall Heat Transfer on the Amplitude of Oscillations 7-52 7.13 One Way to Analyze

Nonlinear propagation of electromagnetic waves in negative-refraction-index composite materials.

PubMed

Kourakis, I; Shukla, P K

2005-07-01

We investigate the nonlinear propagation of electromagnetic waves in left-handed materials. For this purpose, we consider a set of coupled nonlinear Schrödinger (CNLS) equations, which govern the dynamics of coupled electric and magnetic field envelopes. The CNLS equations are used to obtain a nonlinear dispersion, which depicts the modulational stability profile of the coupled plane-wave solutions in left-handed materials. An exact (in)stability criterion for modulational interactions is derived, and analytical expressions for the instability growth rate are obtained.

Effect of Pressure Anisotropy on the m = 1 Small Wavelength Modes in Z-Pinches

NASA Astrophysics Data System (ADS)

Faghihi, M.

1987-05-01

A generalization of Freidberg's perpendicular MHD model is used to investigate the effect of pressure anisotropy on the small wavelength internal kink (m = 1) mode instability in a Z-Pinch. A normal mode analysis of perturbed motion of an incompressible, collisionless and cylindrical plasma is performed. The stability criterion is (rΣB2)' <= 0, where Σ = 1 - (P|| - P⊥)/B2. It cannot be fulfilled without violation of the fire hose stability condition Σ >= 0.

The influence of continuous historical velocity difference information on micro-cooperative driving stability

NASA Astrophysics Data System (ADS)

Yang, Liang-Yi; Sun, Di-Hua; Zhao, Min; Cheng, Sen-Lin; Zhang, Geng; Liu, Hui

2018-03-01

In this paper, a new micro-cooperative driving car-following model is proposed to investigate the effect of continuous historical velocity difference information on traffic stability. The linear stability criterion of the new model is derived with linear stability theory and the results show that the unstable region in the headway-sensitivity space will be shrunk by taking the continuous historical velocity difference information into account. Through nonlinear analysis, the mKdV equation is derived to describe the traffic evolution behavior of the new model near the critical point. Via numerical simulations, the theoretical analysis results are verified and the results indicate that the continuous historical velocity difference information can enhance the stability of traffic flow in the micro-cooperative driving process.

Meteorological Measurements from Satellite Platforms. [stability and control of flexible stochastic satellites

NASA Technical Reports Server (NTRS)

Suomi, V. E.

1975-01-01

The stability of stochastic satellites and the stability and control of flexible satellites were investigated. The effects of random environmental torques and noises in the moments of inertia of spinning and three-axes stabilized satellites were first compared analytically by four methods and by analog simulations. Among the analytical methods, it was shown that the Fokker-Planck formulation yields predictions which most coincide with the simulation results. It was then shown that the required stability criterion of a satellite is quite different from that obtained by a deterministic approach, under the assumption that the environmental and control torques experienced by the satellite are random. Finally, it was demonstrated that, by monitoring the deformations of the flexible elements of a satellite, the effectiveness of the satellite control system can be increased considerably.

Accurate chromatic control and color rendering optimization in LED lighting systems using junction temperature feedback

NASA Astrophysics Data System (ADS)

Sisto, Marco Michele; Gauvin, Jonny

2014-09-01

Accurate color control of LED lighting systems is a challenging task: noticeable chromaticity shifts are commonly observed in mixed-color and phosphor converted LEDs due to intensity dimming. Furthermore, the emitted color varies with the LED temperature. We present a novel color control method for tri-chromatic and tetra-chromatic LEDs, which enable to set and maintain the LED emission at a target color, or combination of correlated color temperature (CCT) and intensity. The LED color point is maintained over variations in the LED junctions' temperatures and intensity dimming levels. The method does not require color feedback sensors, so to minimize system complexity and cost, but relies on estimation of the LED junctions' temperatures from the junction voltages. If operated with tetra-chromatic LEDs, the method allows meeting an additional optimization criterion: for example, the maximization of a color rendering metric like the Color Rendering Index (CRI) or the Color Quality Scale (CQS), thus providing a high quality and clarity of colors on the surface illuminated by the LED. We demonstrate the control of a RGBW LED at target D65 white point with CIELAB color difference metric triangle;a,bE < 1 for simultaneous variations of flux from approximately 30 lm to 100 lm and LED heat sink temperature from 25°C to 58°C. In the same conditions, we demonstrate a CCT error <1%. Furthermore, the method allows varying the LED CCT from 5500K to 8000K while maintaining luminance within 1% of target. Further work is ongoing to evaluate the stability of the method over LED aging.

A commentary on the Atlantic meridional overturning circulation stability in climate models

NASA Astrophysics Data System (ADS)

Gent, Peter R.

2018-02-01

The stability of the Atlantic meridional overturning circulation (AMOC) in ocean models depends quite strongly on the model formulation, especially the vertical mixing, and whether it is coupled to an atmosphere model. A hysteresis loop in AMOC strength with respect to freshwater forcing has been found in several intermediate complexity climate models and in one fully coupled climate model that has very coarse resolution. Over 40% of modern climate models are in a bistable AMOC state according to the very frequently used simple stability criterion which is based solely on the sign of the AMOC freshwater transport across 33° S. In a recent freshwater hosing experiment in a climate model with an eddy-permitting ocean component, the change in the gyre freshwater transport across 33° S is larger than the AMOC freshwater transport change. This casts very strong doubt on the usefulness of this simple AMOC stability criterion. If a climate model uses large surface flux adjustments, then these adjustments can interfere with the atmosphere-ocean feedbacks, and strongly change the AMOC stability properties. AMOC can be shut off for many hundreds of years in modern fully coupled climate models if the hosing or carbon dioxide forcing is strong enough. However, in one climate model the AMOC recovers after between 1000 and 1400 years. Recent 1% increasing carbon dioxide runs and RCP8.5 future scenario runs have shown that the AMOC reduction is smaller using an eddy-resolving ocean component than in the comparable standard 1° ocean climate models.

Effects of Agitation and Storage Temperature on Measurements of Hydration Status.

PubMed

Adams, Heather M; Eberman, Lindsey E; Yeargin, Susan W; Niemann, Andrew J; Mata, Heather L; Dziedzicki, David J

2015-12-01

Hypohydration can have significant implications on normal physiological functions of the body. This study aimed to determine the impact of agitation, storage temperature, and storage time on urine osmolality compared to the criterion control. We used a descriptive diagnostic validity test design. To investigate agitation, we recruited 75 healthy individuals (males = 41, females = 34; mean age = 22 ± 5 years; mean self-reported height = 172 ± 23 cm and mass = 77 ± 17 kg) who provided one or more samples (total = 81). The independent variables were agitation (vortex, hand shaken, no agitation) and temperature (room temperature, freezer, and refrigerator) type. Participants completed informed consent, a health questionnaire and were asked to provide a urine sample, which was split and labeled according to agitation type or storage temperature. Urine osmolality was used to determine hydration status at two time points (within 2 hours [control], 48 hours). We used t-tests to determine the difference between each condition and the control and calculated percent error for each condition. No significant differences for no agitation (t79 = -0.079, P = 0.937), hand shaken (t79 = 1.395, P = 0.167) or vortex mixed (t79 = -0.753, P = 0.453) were identified when compared to the criterion control. No significant differences for room temperature (t82 = -0.720, P = 0.474), refrigerator (t82 = -2.697, P = 0.008) or freezer (t82 = 2.576, P = 0.012) were identified when compared to the criterion control. Our findings suggest agitation of urine specimen is not necessary and samples do not require refrigeration or freezing if assessed within 48 hours. Analysis within two hours of collection is not necessary and samples can be stored for up to 48 hours without impacting the hydration status of the sample.

Muscle Fiber Orientation Angle Dependence of the Tensile Fracture Behavior of Frozen Fish Muscle

NASA Astrophysics Data System (ADS)

Hagura, Yoshio; Okamoto, Kiyoshi; Suzuki, Kanichi; Kubota, Kiyoshi

We have proposed a new cutting method for frozen fish named "cryo-cutting". This method applied tensile fracture force or bending fracture force to the frozen fish at appropriate low temperatures. In this paper, to clarify cryo-cutting mechanism, we analyzed tensile fracture behavior of the frozen fish muscle. In the analysis, the frozen fish muscle was considered unidirectionally fiber-reinforced composite material which consisted of fiber (muscle fiber) and matrix (connective tissue). Fracture criteria (maximum stress criterion, Tsai-Hill criterion) for the unidirectionally fiber-reinforced composite material were used. The following results were obtained: (1) By using Tsai-Hill criterion, muscle fiber orientation angle dependence of the tensile fracture stress could be calculated. (2) By using the maximum stress theory jointly with Tsai-Hill criterion, muscle fiber orientation angle dependence of the fracture mode of the frozen fish muscle could be estimated.

Construction of edge cracks pre-criterion model based on hot rolling experiment and simulation of AZ31 magnesium alloy

NASA Astrophysics Data System (ADS)

Ning, Fangkun; Jia, Weitao; Hou, Jian; Chen, Xingrui; Le, Qichi

2018-05-01

Various fracture criteria, especially Johnson and Cook (J-C) model and (normalized) Cockcroft and Latham (C-L) criterion were contrasted and discussed. Based on normalized C-L criterion, adopted in this paper, FE simulation was carried out and hot rolling experiments under temperature range of 200 °C–350 °C, rolling reduction rate of 25%–40% and rolling speed from 7–21 r/min was implemented. The microstructure was observed by optical microscope and damage values of simulation results were contrasted with the length of cracks on diverse parameters. The results show that the plate generated less edge cracks and the microstructure emerged slight shear bands and fine dynamic recrystallization grains rolled at 350 °C, 40% reduction and 14 r/min. The edge cracks pre-criterion model was obtained combined with Zener-Hollomon equation and deformation activation energy.

Critical role of electron heat flux on Bohm criterion

DOE PAGES

Tang, Xianzhu; Guo, Zehua

2016-12-05

Bohm criterion, originally derived for an isothermal-electron and cold-ion plasma, is often used as a rule of thumb for more general plasmas. Here, we establish a more precise determination of the Bohm criterion that are quantitatively useful for understanding and modeling collisional plasmas that still have collisional mean-free-path much greater than plasma Debye length. Specifically, it is shown that electron heat flux, rather than the isothermal electron assumption, is what sets the Bohm speed to bemore » $$\\sqrt{k_B(T_e||+3T_i||)/m_i}$$ with T e,i∥ the electron and ion parallel temperature at the sheath entrance and m i the ion mass.« less

Critical role of electron heat flux on Bohm criterion

NASA Astrophysics Data System (ADS)

Tang, Xian-Zhu; Guo, Zehua

2016-12-01

Bohm criterion, originally derived for an isothermal-electron and cold-ion plasma, is often used as a rule of thumb for more general plasmas. Here, we establish a more precise determination of the Bohm criterion that are quantitatively useful for understanding and modeling collisional plasmas that still have collisional mean-free-path much greater than plasma Debye length. Specifically, it is shown that electron heat flux, rather than the isothermal electron assumption, is what sets the Bohm speed to be √{ k B ( T e ∥ + 3 T i ∥ ) / m i } with T e , i ∥ the electron and ion parallel temperature at the sheath entrance and mi the ion mass.

Stability of wave processes in a rotating electrically conducting fluid

NASA Astrophysics Data System (ADS)

Peregudin, S. I.; Peregudina, E. S.; Kholodova, S. E.

2018-05-01

The paper puts forward a mathematical model of dynamics of spatial large-scale motions in a rotating layer of electrically conducting incompressible perfect fluid of variable depth with due account of dissipative effects. The resulting boundary-value problem is reduced to a vector system of partial differential equations for any values of the Reynolds number. Theoretical analysis of the so-obtained analytical solution reveals the effect of the magnetic field diffusion on the stability of the wave mode — namely, with the removed external magnetic field, the diffusion of the magnetic field promotes its damping. Besides, a criterion of stability of a wave mode is obtained.

Global stability results for a generalized Lotka-Volterra system with distributed delays. Applications to predator-prey and to epidemic systems.

PubMed

Beretta, E; Capasso, V; Rinaldi, F

1988-01-01

The paper contains an extension of the general ODE system proposed in previous papers by the same authors, to include distributed time delays in the interaction terms. The new system describes a large class of Lotka-Volterra like population models and epidemic models with continuous time delays. Sufficient conditions for the boundedness of solutions and for the global asymptotic stability of nontrivial equilibrium solutions are given. A detailed analysis of the epidemic system is given with respect to the conditions for global stability. For a relevant subclass of these systems an existence criterion for steady states is also given.

Evaluation of the relevance of the glassy state as stability criterion for freeze-dried bacteria by application of the Arrhenius and WLF model.

PubMed

Aschenbrenner, Mathias; Kulozik, Ulrich; Foerst, Petra

2012-12-01

The aim of this work was to describe the temperature dependence of microbial inactivation for several storage conditions and protective systems (lactose, trehalose and dextran) in relation to the physical state of the sample, i.e. the glassy or non-glassy state. The resulting inactivation rates k were described by applying two models, Arrhenius and Williams-Landel-Ferry (WLF), in order to evaluate the relevance of diffusional limitation as a protective mechanism. The application of the Arrhenius model revealed a significant decrease in activation energy E(a) for storage conditions close to T(g). This finding is an indication that the protective effect of a surrounding glassy matrix can, at least, partly be ascribed to its inherent restricted diffusion and mobility. The application of the WLF model revealed that the temperature dependence of microbial inactivation above T(g) is significantly weaker than predicted by the universal coefficients. Thus, it can be concluded that microbial inactivation is not directly linked with the mechanical relaxation behavior of the surrounding matrix as it was reported for viscosity and crystallization phenomena in case of disaccharide systems. Copyright © 2012. Published by Elsevier Inc.

Stability of a family of uniform vortices related to vortex configurations before merging

NASA Astrophysics Data System (ADS)

Luzzatto-Fegiz, P.; Williamson, C. H. K.

2006-11-01

Motivated by the merger of two corotating vortices, Cerretelli & Williamson (JFM 2003) discovered a family of uniform vorticity patches representing the continuation of two corotating vortices into a single ``dumbbell'' shape. This branch of solutions passes through a bifurcation from the Kirchhoff ellipses (discovered by Kamm 1987 and Saffman 1988) and ends into a cat's eye shape. By using a more accurate method for equilibrium shape calculation, we find some differences in the equilibrium shapes to those discovered by Cerretelli & Williamson, particularly near the topological change (from a two-vortex to a single vortex shape). We implement the approach of Dritschel (1985), and show that all the simply connected shapes are unstable to a three-fold perturbation, while a regime of the two-vortex shapes nearing the topological change is unstable to a two-fold antisymmetric perturbation. The stability of two patches has been source of debate in the literature. Saffman & Szeto (1980) predicted exchange of stability at an extremum in energy and angular momentum; on the other hand, Dritschel (1985) found that conditions for instability from linear analysis did not match those coming from the energy criterion. In the present work, we find precise agreement between results from linear analysis and energy criterion, in accordance with the more recent work of Kamm (1987) and Dritschel (1995).

Volume of larvae Is the most important single predictor of mass temperatures in the forensically important Calliphorid, Chrysomya megacephala (Diptera: Calliphoridae)

USGS Publications Warehouse

Gruner, S. V.; Slone, D.H.; Capinera, J.L.; Turco, M. P.

2017-01-01

Calliphorid species form larval aggregations that are capable of generating heat above ambient temperature. We wanted to determine the relationship between volume, number of larvae, and different combinations of instars on larval mass heat generation. We compared different numbers of Chrysomya megacephala (F.) larvae (40, 100, 250, 600, and 2,000), and different combinations of instars (∼50/50 first and second instars, 100% second instars, ∼50/50 second and third instars, and 100% third instars) at two different ambient temperatures (20 and 30 °C). We compared 13 candidate multiple regression models that were fitted to the data; the models were then scored and ranked with Akaike information criterion and Bayesian information criterion. The results indicate that although instar, age, treatment temperature, elapsed time, and number of larvae in a mass were significant, larval volume was the best predictor of larval mass temperatures. The volume of a larval mass may need to be taken into consideration for determination of a postmortem interval.

Optimal low symmetric dissipation Carnot engines and refrigerators

NASA Astrophysics Data System (ADS)

de Tomás, C.; Hernández, A. Calvo; Roco, J. M. M.

2012-01-01

A unified optimization criterion for Carnot engines and refrigerators is proposed. It consists of maximizing the product of the heat absorbed by the working system times the efficiency per unit time of the device, either the engine or the refrigerator. This criterion can be applied to both low symmetric dissipation Carnot engines and refrigerators. For engines the criterion coincides with the maximum power criterion and then the Curzon-Ahlborn efficiency ηCA=1-Tc/Th is recovered, where Th and Tc are the temperatures of the hot and cold reservoirs, respectively [Esposito, Kawai, Lindenberg, and Van den Broeck, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.105.150603 105, 150603 (2010)]. For refrigerators the criterion provides the counterpart of Curzon-Ahlborn efficiency for refrigerators ɛCA=[1/(1-(Tc/Th)]-1, first derived by Yan and Chen for the particular case of an endoreversible Carnot-type refrigerator with linear (Newtonian) finite heat transfer laws [Yan and Chen, J. Phys. D: Appl. Phys.JPAPBE0022-372710.1088/0022-3727/23/2/002 23, 136 (1990)].

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.

Introduction to the theory and application of a unified Bohm criterion for arbitrary-ion-temperature collision-free plasmas with finite Debye lengths

NASA Astrophysics Data System (ADS)

Kos, L.; Jelić, N.; Kuhn, S.; Tskhakaya, D. D.

2018-04-01

At present, identifying and characterizing the common plasma-sheath edge (PSE) in the conventional fluid approach leads to intrinsic oversimplifications, while the kinetic one results in unusable over-generalizations. In addition, none of these approaches can be justified in realistic plasmas, i.e., those which are characterized by non-negligible Debye lengths and a well-defined non-negligible ion temperature. In an attempt to resolve this problem, we propose a new formulation of the Bohm criterion [D. Bohm, The Characteristics of Electrical Discharges in Magnetic Fields (McGraw-Hill, New York, 1949)], which is here expressed in terms of fluid, kinetic, and electrostatic-pressure contributions. This "unified" Bohm criterion consists of a set of two equations for calculating the ion directional energy (i.e., the mean directional velocity) and the plasma potential at the common PSE, and is valid for arbitrary ion-to-electron temperature ratios. It turns out to be exact at any point of the quasi-neutral plasma provided that the ion differential polytropic coefficient function (DPCF) of Kuhn et al. [Phys. Plasmas 13, 013503 (2006)] is employed, with the advantage that the DPCF is an easily measurable fluid quantity. Moreover, our unified Bohm criterion holds in plasmas with finite Debye lengths, for which the famous kinetic criterion formulated by Harrison and Thompson [Proc. Phys. Soc. 74, 145 (1959)] fails. Unlike the kinetic criterion in the case of negligible Debye length, the kinetic contribution to the unified Bohm criterion, arising due to the presence of negative and zero velocities in the ion velocity distribution function, can be calculated separately from the fluid term. This kinetic contribution disappears identically at the PSE, yielding strict equality of the ion directional velocity there and the ion sound speed, provided that the latter is formulated in terms of the present definition of DPCFs. The numerical values of these velocities are found for the Tonks-Langmuir collision-free, plane-parallel discharge model [Phys. Rev. 34, 876 (1929)], however, with the ion-source temperature extended here from the original (zero) value to arbitrary high ones. In addition, it turns out, that the charge-density derivative (in the potential "space") with respect to the potential exhibits two characteristic points, i.e., potentials, namely the points of inflection and maximum of that derivative (in the potential space), which stay "fixed" at their respective potentials independent of the Debye length until it is kept fairly small. Plasma quasi-neutrality appears well satisfied up to the first characteristic point/potential, so we identify that one as the plasma edge (PE). Adopting the convention that the sheath is a region characterized by considerable electrostatic pressure (energy density), we identify the second characteristic point/potential as the sheath edge (SE). Between these points, the charge density increases from zero to a finite value. Thus, the interval between the PE and SE, with the "fixed" width (in the potential "space") of about one third of the electron temperature, will be named the plasma-sheath transition (PST). Outside the PST, the electrostatic-pressure term and its derivatives turn out to be nearly identical with each other, independent of the particular values of the ion temperature and Debye length. In contrast, an increase in Debye lengths from zero to finite values causes the location of the sonic point/potential (laying inside the PST) to shift from the PE (for vanishing Debye length) towards the SE, while at the same time, the absolute value of the corresponding ion-sound velocity slightly decreases. These shifts turn out to be manageable with employing the mathematical concept of the plasma-to-sheath transition (different from, but related to our natural PST concept), resulting in approximate, but sufficiently reliable semi-analytic expressions, which are functions of the ion temperature and Debye length.

Dynamic stability of spinning pretwisted beams subjected to axial random forces

NASA Astrophysics Data System (ADS)

Young, T. H.; Gau, C. Y.

2003-11-01

This paper studies the dynamic stability of a pretwisted cantilever beam spinning along its longitudinal axis and subjected to an axial random force at the free end. The axial force is assumed as the sum of a constant force and a random process with a zero mean. Due to this axial force, the beam may experience parametric random instability. In this work, the finite element method is first applied to yield discretized system equations. The stochastic averaging method is then adopted to obtain Ito's equations for the response amplitudes of the system. Finally the mean-square stability criterion is utilized to determine the stability condition of the system. Numerical results show that the stability boundary of the system converges as the first three modes are taken into calculation. Before the convergence is reached, the stability condition predicted is not conservative enough.

Stability analysis of neural networks with time-varying delay: Enhanced stability criteria and conservatism comparisons

NASA Astrophysics Data System (ADS)

Lin, Wen-Juan; He, Yong; Zhang, Chuan-Ke; Wu, Min

2018-01-01

This paper is concerned with the stability analysis of neural networks with a time-varying delay. To assess system stability accurately, the conservatism reduction of stability criteria has attracted many efforts, among which estimating integral terms as exact as possible is a key issue. At first, this paper develops a new relaxed integral inequality to reduce the estimation gap of popular Wirtinger-based inequality (WBI). Then, for showing the advantages of the proposed inequality over several existing inequalities that also improve the WBI, four stability criteria are derived through different inequalities and the same Lyapunov-Krasovskii functional (LKF), and the conservatism comparison of them is analyzed theoretically. Moreover, an improved criterion is established by combining the proposed inequality and an augmented LKF with delay-product-type terms. Finally, several numerical examples are used to demonstrate the advantages of the proposed method.

Occurrence and distribution of fecal indicator bacteria, and physical and chemical indicators of water quality in streams receiving discharge from Dallas/Fort Worth International Airport and vicinity, North-Central Texas, 2008

USGS Publications Warehouse

Harwell, Glenn R.; Mobley, Craig A.

2009-01-01

This report, done by the U.S. Geological Survey in cooperation with Dallas/Fort Worth International (DFW) Airport in 2008, describes the occurrence and distribution of fecal indicator bacteria (fecal coliform and Escherichia [E.] coli), and the physical and chemical indicators of water quality (relative to Texas Surface Water Quality Standards), in streams receiving discharge from DFW Airport and vicinity. At sampling sites in the lower West Fork Trinity River watershed during low-flow conditions, geometric mean E. coli counts for five of the eight West Fork Trinity River watershed sampling sites exceeded the Texas Commission on Environmental Quality E. coli criterion, thus not fully supporting contact recreation. Two of the five sites with geometric means that exceeded the contact recreation criterion are airport discharge sites, which here means that the major fraction of discharge at those sites is from DFW Airport. At sampling sites in the Elm Fork Trinity River watershed during low-flow conditions, geometric mean E. coli counts exceeded the geometric mean contact recreation criterion for seven (four airport, three non-airport) of 13 sampling sites. Under low-flow conditions in the lower West Fork Trinity River watershed, E. coli counts for airport discharge sites were significantly different from (lower than) E. coli counts for non-airport sites. Under low-flow conditions in the Elm Fork Trinity River watershed, there was no significant difference between E. coli counts for airport sites and non-airport sites. During stormflow conditions, fecal indicator bacteria counts at the most downstream (integrator) sites in each watershed were considerably higher than counts at those two sites during low-flow conditions. When stormflow sample counts are included with low-flow sample counts to compute a geometric mean for each site, classification changes from fully supporting to not fully supporting contact recreation on the basis of the geometric mean contact recreation criterion. All water temperature measurements at sampling sites in the lower West Fork Trinity River watershed were less than the maximum criterion for water temperature for the lower West Fork Trinity segment. Of the measurements at sampling sites in the Elm Fork Trinity River watershed, 95 percent were less than the maximum criterion for water temperature for the Elm Fork Trinity River segment. All dissolved oxygen concentrations were greater than the minimum criterion for stream segments classified as exceptional aquatic life use. Nearly all pH measurements were within the pH criterion range for the classified segments in both watersheds, except for those at one airport site. For sampling sites in the lower West Fork Trinity River watershed, all annual average dissolved solids concentrations were less than the maximum criterion for the lower West Fork Trinity segment. For sampling sites in the Elm Fork Trinity River, nine of the 13 sites (six airport, three non-airport) had annual averages that exceeded the maximum criterion for that segment. For ammonia, 23 samples from 12 different sites had concentrations that exceeded the screening level for ammonia. Of these 12 sites, only one non-airport site had more than the required number of exceedances to indicate a screening level concern. Stormflow total suspended solids concentrations were significantly higher than low-flow concentrations at the two integrator sites. For sampling sites in the lower West Fork Trinity River watershed, all annual average chloride concentrations were less than the maximum annual average chloride concentration criterion for that segment. For the 13 sampling sites in the Elm Fork Trinity River watershed, one non-airport site had an annual average concentration that exceeded the maximum annual average chloride concentration criterion for that segment.

Mechanisms of deformation and fracture in high temperature low cycle fatigue of Rene 80 and IN 100

NASA Technical Reports Server (NTRS)

Romanoski, G. R., Jr.

1982-01-01

Specimens tested for the AGARD strain range partitioning program were investigated. Rene 80 and IN 100 were tested in air and in vacuum; at 871 C, 925 C, and 1000 C; and in the coated and uncoated condition. The specimens exhibited a multiplicity of high-temperature low-cycle fatigue damage. Observations of the various forms of damage were consistent with material and testing conditions and were generally in agreement with previous studies. In every case observations support a contention that failure occurs at a particular combination of crack length and maximum stress. A failure criterion which is applicable in the regime of testing studied is presented. The predictive capabilities of this criterion are straight forward.

Flow and fracture behavior of NiAl in relation to the brittle-to-ductile transition temperature

NASA Technical Reports Server (NTRS)

Noebe, R. D.; Bowman, R. R.; Cullers, C. L.; Raj, S. V.

1991-01-01

NiAl has only three independent slip systems operating at low and intermediate temperatures whereas five independent deformation mechanisms are required to satisfy the von Mises criterion for general plasticity in polycrystalline materials. Yet, it is generally recognized that polycrystalline NiAl can be deformed extensively in compression at room temperature and that limited tensile ductility can be obtained in extruded materials. In order to determine whether these results are in conflict with the von Mises criterion, tension and compression tests were conducted on powder-extruded, binary NiAl between 300 and 1300 K. The results indicate that below the brittle-to-ductile transition temperature (BDTT) the failure mechanism in NiAl involves the initiation and propagation of cracks at the grain boundaries which is consistent with the von Mises analysis. Furthermore, evaluation of the flow behavior of NiAl indicates that the transition from brittle to ductile behavior with increasing temperature coincides with the onset of recovery mechanisms such as dislocation climb. The increase in ductility above the BDTT is therefore attributed to the climb of the 001 line type dislocations which in combination with dislocation glide enable grain boundary compatibility to be maintained at the higher temperatures.

High-throughput density functional calculations to optimize properties and interfacial chemistry of piezoelectric materials

NASA Astrophysics Data System (ADS)

Barr, Jordan A.; Lin, Fang-Yin; Ashton, Michael; Hennig, Richard G.; Sinnott, Susan B.

2018-02-01

High-throughput density functional theory calculations are conducted to search through 1572 A B O3 compounds to find a potential replacement material for lead zirconate titanate (PZT) that exhibits the same excellent piezoelectric properties as PZT and lacks both its use of the toxic element lead (Pb) and the formation of secondary alloy phases with platinum (Pt) electrodes. The first screening criterion employed a search through the Materials Project database to find A -B combinations that do not form ternary compounds with Pt. The second screening criterion aimed to eliminate potential candidates through first-principles calculations of their electronic structure, in which compounds with a band gap of 0.25 eV or higher were retained. Third, thermodynamic stability calculations were used to compare the candidates in a Pt environment to compounds already calculated to be stable within the Materials Project. Formation energies below or equal to 100 meV/atom were considered to be thermodynamically stable. The fourth screening criterion employed lattice misfit to identify those candidate perovskites that have low misfit with the Pt electrode and high misfit of potential secondary phases that can be formed when Pt alloys with the different A and B components. To aid in the final analysis, dynamic stability calculations were used to determine those perovskites that have dynamic instabilities that favor the ferroelectric distortion. Analysis of the data finds three perovskites warranting further investigation: CsNb O3 , RbNb O3 , and CsTa O3 .

CORRELATION OF THE GLASS TRANSITION TEMPERATURE OF PLASTICIZED PVC USING A LATTICE FLUID MODEL

EPA Science Inventory

A model has been developed to describe the composition dependence of the glass transition temperature (Tg) of polyvinyl chloride (PVC) + plasticizer mixtures. The model is based on Sanchez-Lacombe equation of state and the Gibbs-Di Marzio criterion, which states that th...

Phase Transitions on Random Lattices: How Random is Topological Disorder?

NASA Astrophysics Data System (ADS)

Barghathi, Hatem; Vojta, Thomas

2015-03-01

We study the effects of topological (connectivity) disorder on phase transitions. We identify a broad class of random lattices whose disorder fluctuations decay much faster with increasing length scale than those of generic random systems, yielding a wandering exponent of ω = (d - 1) / (2 d) in d dimensions. The stability of clean critical points is thus governed by the criterion (d + 1) ν > 2 rather than the usual Harris criterion dν > 2 , making topological disorder less relevant than generic randomness. The Imry-Ma criterion is also modified, allowing first-order transitions to survive in all dimensions d > 1 . These results explain a host of puzzling violations of the original criteria for equilibrium and nonequilibrium phase transitions on random lattices. We discuss applications, and we illustrate our theory by computer simulations of random Voronoi and other lattices. This work was supported by the NSF under Grant Nos. DMR-1205803 and PHYS-1066293. We acknowledge the hospitality of the Aspen Center for Physics.

The psychometric properties of the Portuguese version of the Personality Inventory for DSM-5.

PubMed

Pires, Rute; Sousa Ferreira, Ana; Guedes, David

2017-10-01

The DSM-5 Section III proposes a hybrid dimensional-categorical model of conceptualizing personality and its disorders that includes assessment of impairments in personality functioning (criterion A) and maladaptive personality traits (criterion B). The Personality Inventory for the DSM-5 is a new dimensional tool, composed of 220 items organized into 25 facets that delineate five higher order domains of clinically relevant personality differences, and was developed to operationalize the DSM-5 model of pathological personality traits. The current studies address the internal consistency (study 1), the test-retest reliability (study 2) and the criterion validity (studies 3 and 4) of the Portuguese version of the PID-5 in samples of native speaking psychology students. Results indicated good internal consistency reliabilities and good temporal stability reliabilities for the majority of the PID-5 traits. The correlational pattern of the PID-5 traits with two measures of personality was in accordance with theoretical expectations and showed its concurrent validity. © 2017 Scandinavian Psychological Associations and John Wiley & Sons Ltd.

Proteome Evolution of Deep-Sea Hydrothermal Vent Alvinellid Polychaetes Supports the Ancestry of Thermophily and Subsequent Adaptation to Cold in Some Lineages

PubMed Central

Fontanillas, Eric; Galzitskaya, Oxana V.; Lecompte, Odile; Lobanov, Mikhail Y.; Tanguy, Arnaud; Mary, Jean; Girguis, Peter R.; Hourdez, Stéphane

2017-01-01

Temperature, perhaps more than any other environmental factor, is likely to influence the evolution of all organisms. It is also a very interesting factor to understand how genomes are shaped by selection over evolutionary timescales, as it potentially affects the whole genome. Among thermophilic prokaryotes, temperature affects both codon usage and protein composition to increase the stability of the transcriptional/translational machinery, and the resulting proteins need to be functional at high temperatures. Among eukaryotes less is known about genome evolution, and the tube-dwelling worms of the family Alvinellidae represent an excellent opportunity to test hypotheses about the emergence of thermophily in ectothermic metazoans. The Alvinellidae are a group of worms that experience varying thermal regimes, presumably having evolved into these niches over evolutionary times. Here we analyzed 423 putative orthologous loci derived from 6 alvinellid species including the thermophilic Alvinella pompejana and Paralvinella sulfincola. This comparative approach allowed us to assess amino acid composition, codon usage, divergence, direction of residue changes and the strength of selection along the alvinellid phylogeny, and to design a new eukaryotic thermophilic criterion based on significant differences in the residue composition of proteins. Contrary to expectations, the alvinellid ancestor of all present-day species seems to have been thermophilic, a trait subsequently maintained by purifying selection in lineages that still inhabit higher temperature environments. In contrast, lineages currently living in colder habitats likely evolved under selective relaxation, with some degree of positive selection for low-temperature adaptation at the protein level. PMID:28082607

HEATING 7. 1 user's manual

DOE Office of Scientific and Technical Information (OSTI.GOV)

Childs, K.W.

1991-07-01

HEATING is a FORTRAN program designed to solve steady-state and/or transient heat conduction problems in one-, two-, or three- dimensional Cartesian, cylindrical, or spherical coordinates. A model may include multiple materials, and the thermal conductivity, density, and specific heat of each material may be both time- and temperature-dependent. The thermal conductivity may be anisotropic. Materials may undergo change of phase. Thermal properties of materials may be input or may be extracted from a material properties library. Heating generation rates may be dependent on time, temperature, and position, and boundary temperatures may be time- and position-dependent. The boundary conditions, which maymore » be surface-to-boundary or surface-to-surface, may be specified temperatures or any combination of prescribed heat flux, forced convection, natural convection, and radiation. The boundary condition parameters may be time- and/or temperature-dependent. General graybody radiation problems may be modeled with user-defined factors for radiant exchange. The mesh spacing may be variable along each axis. HEATING is variably dimensioned and utilizes free-form input. Three steady-state solution techniques are available: point-successive-overrelaxation iterative method with extrapolation, direct-solution (for one-dimensional or two-dimensional problems), and conjugate gradient. Transient problems may be solved using one of several finite-difference schemes: Crank-Nicolson implicit, Classical Implicit Procedure (CIP), Classical Explicit Procedure (CEP), or Levy explicit method (which for some circumstances allows a time step greater than the CEP stability criterion). The solution of the system of equations arising from the implicit techniques is accomplished by point-successive-overrelaxation iteration and includes procedures to estimate the optimum acceleration parameter.« less

Thermal Stability of Nanocrystalline Alloys by Solute Additions and A Thermodynamic Modeling

NASA Astrophysics Data System (ADS)

Saber, Mostafa

Nanocrystalline alloys show superior properties due to their exceptional microstructure. Thermal stability of these materials is a critical aspect. It is well known that grain boundaries in nanocrystalline microstructures cause a significant increase in the total free energy of the system. A driving force provided to reduce this excess free energy can cause grain growth. The presence of a solute addition within a nanocrystalline alloy can lead to the thermal stability. Kinetic and thermodynamic stabilization are the two basic mechanisms with which stability of a nanoscale grain size can be achieved at high temperatures. The basis of this thesis is to study the effect of solute addition on thermal stability of nanocrystalline alloys. The objective is to determine the effect of Zr addition on the thermal stability of mechanically alloyed nanocrysatillne Fe-Cr and Fe-Ni alloys. In Fe-Cr-Zr alloy system, nanoscale grain size stabilization was maintained up to 900 °C by adding 2 at% Zr. Kinetic pinning by intermetallic particles in the nanoscale range was identified as a primary mechanism of thermal stabilization. In addition to the grain size strengthening, intermetallic particles also contribute to strengthening mechanisms. The analysis of microhardness, XRD data, and measured grain sizes from TEM micrographs suggested that both thermodynamic and kinetic mechanisms are possible mechanisms. It was found that alpha → gamma phase transformation in Fe-Cr-Zr system does not influence the grain size stabilization. In the Fe-Ni-Zr alloy system, it was shown that the grain growth in Fe-8Ni-1Zr alloy is much less than that of pure Fe and Fe-8Ni alloy at elevated temperatures. The microstructure of the ternary Fe-8Ni-1Zr alloy remains in the nanoscale range up to 700 °C. Using an in-situ TEM study, it was determined that drastic grain growth occurs when the alpha → gamma phase transformation occurs. Accordingly, there can be a synergistic relationship between grain growth and alpha → gamma phase transformation in Fe-Ni-Zr alloys. In addition to the experimental study of thermal stabilization of nanocrystalline Fe-Cr-Zr or Fe-Ni-Zr alloys, the thesis presented here developed a new predictive model, applicable to strongly segregating solutes, for thermodynamic stabilization of binary alloys. This model can serve as a benchmark for selecting solute and evaluating the possible contribution of stabilization. Following a regular solution model, both the chemical and elastic strain energy contributions are combined to obtain the mixing enthalpy. The total Gibbs free energy of mixing is then minimized with respect to simultaneous variations in the grain boundary volume fraction and the solute concentration in the grain boundary and the grain interior. The Lagrange multiplier method was used to obtained numerical solutions. Application are given for the temperature dependence of the grain size and the grain boundary solute excess for selected binary system where experimental results imply that thermodynamic stabilization could be operative. This thesis also extends the binary model to a new model for thermodynamic stabilization of ternary nanocrystalline alloys. It is applicable to strongly segregating size-misfit solutes and uses input data available in the literature. In a same manner as the binary model, this model is based on a regular solution approach such that the chemical and elastic strain energy contributions are incorporated into the mixing enthalpy DeltaHmix, and the mixing entropy DeltaSmix is obtained using the ideal solution approximation. The Gibbs mixing free energy Delta Gmix is then minimized with respect to simultaneous variations in grain growth and solute segregation parameters. The Lagrange multiplier method is similarly used to obtain numerical solutions for the minimum Delta Gmix. The temperature dependence of the nanocrystalline grain size and interfacial solute excess can be obtained for selected ternary systems. As an example, model predictions are compared to experimental results for Fe-Cr-Zr and Fe-Ni-Zr alloy systems. Consistency between the experimental results and the present model predictions provide a more rigorous criterion for investigating thermal stabilization. However, other possible contributions for grain growth stabilization should still be considered.

Effect of anharmonicity on the phonon density of states and specific heat of a monoatomic, one-dimensional crystal lattice

NASA Astrophysics Data System (ADS)

Mukherjee, Krishnendu; Hossain, S. Minhaz

2008-12-01

We analyze the lattice equation of motion involving terms up to third order in lattice displacement. The phenomenological arguments suggest that the force constant D1 of the quadratic term must always be positive and the force constant B1 of the cubic term may take either positive or negative value. The criterion for stability of the lattice provides constraint on the relative magnitudes of the three force constants. We solve the equation of motion using root mean-square spatial fluctuation approximation and obtain the seminonperturbative dispersion relation both for positive and negative B1 . The nature of phonon density of states curves for positive B1 show some close resemblance with the experimental observations. At very low temperature, the specific heat of this system to leading order in large positive B1 varies as square root of temperature and it obeys Debye’s T law in one dimension for small negative B1 . At very high temperature, the specific heat may fall below or above its classical value depending on the relative magnitudes of B1 and D1 for B1>0 and it always falls above its classical value for B1<0 . The lattice model with positive B1 emerges as a good candidate for description of a monoatomic crystal.

A stage structure pest management model with impulsive state feedback control

NASA Astrophysics Data System (ADS)

Pang, Guoping; Chen, Lansun; Xu, Weijian; Fu, Gang

2015-06-01

A stage structure pest management model with impulsive state feedback control is investigated. We get the sufficient condition for the existence of the order-1 periodic solution by differential equation geometry theory and successor function. Further, we obtain a new judgement method for the stability of the order-1 periodic solution of the semi-continuous systems by referencing the stability analysis for limit cycles of continuous systems, which is different from the previous method of analog of Poincarè criterion. Finally, we analyze numerically the theoretical results obtained.

Stability analysis of Caisson Cofferdam Based on Strength Reduction Method

NASA Astrophysics Data System (ADS)

Xu, B. B.; Zhang, N. S.

2018-05-01

The working mechanism of the caisson cofferdam depends on the self-weight of the structure and internal filling to ensure its skid resistance and overturn resistance stability. Using the strength reduction method, the safety factor of the caisson cofferdam can be obtained. The potential slide surface can be searched automatically without constraining the range of the arc center. According to the results, the slippage surface goes through the bottom of the caisson. Based on the judgement criterion of the strength reduction method, the final safety factor is about 1.65.

Effect of hinge-moment parameters on elevator stick forces in rapid maneuvers

NASA Technical Reports Server (NTRS)

Jones, Robert T; Greenberg, Harry

1944-01-01

The importance of the stick force per unit normal acceleration as a criterion of longitudinal stability and the critical dependence of this gradient on elevator hinge-moment parameters have been shown in previous reports. The present report continues the investigation with special reference to transient effects for maneuvers of short duration.

A Note on the Incremental Validity of Aggregate Predictors.

ERIC Educational Resources Information Center

Day, H. D.; Marshall, David

Three computer simulations were conducted to show that very high aggregate predictive validity coefficients can occur when the across-case variability in absolute score stability occurring in both the predictor and criterion matrices is quite small. In light of the increase in internal consistency reliability achieved by the method of aggregation…

An "Instantaneous" Estimate of a Lifetime's Cognitive Change

ERIC Educational Resources Information Center

Deary, Ian J.; Whalley, Lawrence J.; Crawford, John R.

2004-01-01

Change in cognitive functioning is an important aspect of human aging and a key outcome in many medical conditions. However, cognitive change can rarely be measured directly, since prior cognitive data do not exist for most people. We examined the criterion validity and one-year stability of the difference between National Adult Reading Test…

Within-Semester Stability and Adjustment Correlates of the Multidimensional Perfectionism Scale.

ERIC Educational Resources Information Center

Rice, Kenneth G.; Dellwo, Jacqueline P.

2001-01-01

Subscale scores from R.O. Frost, P. Marten, C. Lahart, and R. Rosenblate's (1990) Mulitdimensional Perfectionism Scale were found to be moderately stable over a 10-week period. Associations between perfectionism and self-esteem, depression, and academic integration yielded mixed support for the criterion-related validity of the scores from this…

Jeans instability in collisional strongly coupled dusty plasma with radiative condensation and polarization force

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prajapati, R. P., E-mail: prajapati-iter@yahoo.co.in; Bhakta, S.; Chhajlani, R. K.

2016-05-15

The influence of dust-neutral collisions, polarization force, and electron radiative condensation is analysed on the Jeans (gravitational) instability of partially ionized strongly coupled dusty plasma (SCDP) using linear perturbation (normal mode) analysis. The Boltzmann distributed ions, dynamics of inertialess electrons, charged dust and neutral particles are considered. Using the plane wave solutions, a general dispersion relation is derived which is modified due to the presence of dust-neutral collisions, strong coupling effect, polarization force, electron radiative condensation, and Jeans dust/neutral frequencies. In the long wavelength perturbations, the Jeans instability criterion depends upon strong coupling effect, polarization interaction parameter, and thermal loss,more » but it is independent of dust-neutral collision frequency. The stability of the considered configuration is analysed using the Routh–Hurwitz criterion. The growth rates of Jeans instability are illustrated, and stabilizing influence of viscoelasticity and dust-neutral collision frequency while destabilizing effect of electron radiative condensation, polarization force, and Jeans dust-neutral frequency ratio is observed. This work is applied to understand the gravitational collapse of SCDP with dust-neutral collisions.« less

Improving the Critic Learning for Event-Based Nonlinear $H_{\\infty }$ Control Design.

PubMed

Wang, Ding; He, Haibo; Liu, Derong

2017-10-01

In this paper, we aim at improving the critic learning criterion to cope with the event-based nonlinear H ∞ state feedback control design. First of all, the H ∞ control problem is regarded as a two-player zero-sum game and the adaptive critic mechanism is used to achieve the minimax optimization under event-based environment. Then, based on an improved updating rule, the event-based optimal control law and the time-based worst-case disturbance law are obtained approximately by training a single critic neural network. The initial stabilizing control is no longer required during the implementation process of the new algorithm. Next, the closed-loop system is formulated as an impulsive model and its stability issue is handled by incorporating the improved learning criterion. The infamous Zeno behavior of the present event-based design is also avoided through theoretical analysis on the lower bound of the minimal intersample time. Finally, the applications to an aircraft dynamics and a robot arm plant are carried out to verify the efficient performance of the present novel design method.

Stability of bulk Ba2YCu3O(7-x) in a variety of environments

NASA Technical Reports Server (NTRS)

Gaier, James R.; Hepp, Aloysius F.; Curtis, Henry B.; Schupp, Donald A.; Hambourger, Paul D.; Blue, James W.

1988-01-01

Small bars of ceramic Ba2YCu3O(7-x) were fabricated and subjected to environments similar to those that might be encountered during some NASA missions. These conditions include ambient conditions, high humidity, vacuum, and high fluences of electrons and protrons. The normal state resistivity or critical current density (J sub c) were monitored during these tests to assess the stability of the material. When normal state resistivity is used as a criterion, the ambient stability of these samples was relatively good, exhibiting only a 2 percent degradation over a 3 month period. The humidity stability was shown to be very poor, and to be a steep function of temperature. Samples stored at 50 C for 40 min increased in normal state resistivity by four orders of magnitude. Kinetic analysis indicates that the degradation reaction is second order with water vapor concentration. It is suspected that humidity degradation also accounts for the ambient instability. The samples were stable to vacuum over a period of at least 3 months. Degradation of J sub c in a 1 MeV electron fluence of 9.7 x 10 to the 14th e(-)/sq cm was determined to be no more than about 2 percent. Degradation of J sub c in a 8.7 x 10 to the 14th p(+)/sq cm of 42 MeV protons was found to be grain size dependent. Samples with smaller grain size and initial J sub c of about 240 A/sq cm showed no degradation. while that with larger grain size and an initial J sub c of about 30 A/sq cm degraded to 37 percent of its original value.

Stability testing and analysis of a PMAD dc test bed for the Space Station Freedom

NASA Technical Reports Server (NTRS)

Button, Robert M.; Brush, Andrew S.

1992-01-01

The Power Management and Distribution (PMAD) dc Test Bed at the NASA Lewis Research Center is introduced. Its usefulness to the Space Station Freedom Electrical Power (EPS) development and design are discussed in context of verifying system stability. Stability criteria developed by Middlebrook and Cuk are discussed as they apply to constant power dc to dc converters exhibiting negative input impedance at low frequencies. The utility-type Secondary Subsystem is presented and each component is described. The instrumentation used to measure input and output impedance under load is defined. Test results obtained from input and output impedance measurements of test bed components are presented. It is shown that the PMAD dc Test Bed Secondary Subsystem meets the Middlebrook stability criterion for certain loading conditions.

Stability Testing and Analysis of a PMAD DC Test Bed for the Space Station Freedom

NASA Technical Reports Server (NTRS)

Button, Robert M.; Brush, Andrew S.

1992-01-01

The Power Management and Distribution (PMAD) DC Test Bed at the NASA Lewis Research Center is introduced. Its usefulness to the Space Station Freedom Electrical Power (EPS) development and design are discussed in context of verifying system stability. Stability criteria developed by Middlebrook and Cuk are discussed as they apply to constant power DC to DC converters exhibiting negative input impedance at low frequencies. The utility-type Secondary Subsystem is presented and each component is described. The instrumentation used to measure input and output impedance under load is defined. Test results obtained from input and output impedance measurements of test bed components are presented. It is shown that the PMAD DC Test Bed Secondary Subsystem meets the Middlebrook stability criterion for certain loading conditions.

AC losses and stability on large cable-in-conduit superconductors

NASA Astrophysics Data System (ADS)

Bruzzone, Pierluigi

1998-12-01

The cable-in-conduit superconductors are preferred for applications where the AC losses and stability are a major concern, e.g., fusion magnets and SMES. A review of coupling currents loss results for both NbTi and Nb 3Sn cable-in-conduit conductors (CICC) is presented and the AC loss relevant features are listed, with special emphasis for the role of the interstrand resistance and strand coating. The transient stability approach for CICCs is discussed and the analytical models are quoted as well as the relevant experimental database. The likely spectrum of transient disturbance in CICC is reviewed and the need to account for interstrand current sharing in the design is outlined. Eventually a practical criterion for the interstrand resistance is proposed to link the stability and AC loss design.

Regions of stability of asteroids

NASA Technical Reports Server (NTRS)

Szebehely, V.; Lundberg, J.; Vicente, R.

1983-01-01

Using Hill's modified stability criterion, regions of orbital elements are established for conditions of stability. The model of the three-dimensional restricted problem of three bodies is used with the sun and Jupiter as the primaries. Four different cases are studied: direct and retrograde, outside and inside asteroidal orbits. The directions of the asteroidal orbits refer to the synodical reference frame and the positions refer to Jupiter's orbit. The orbital parameters of the asteroids are the semi-major axis (a), the eccentricity (e), and the inclination from Jupiter's orbital plane (i). The argument of the perihelion and the longitude of the ascending node are fixed at Omega = omega = 90 deg and the time of perihelion passage is T = 0 for all orbits.

State fusion entropy for continuous and site-specific analysis of landslide stability changing regularities

NASA Astrophysics Data System (ADS)

Liu, Yong; Qin, Zhimeng; Hu, Baodan; Feng, Shuai

2018-04-01

Stability analysis is of great significance to landslide hazard prevention, especially the dynamic stability. However, many existing stability analysis methods are difficult to analyse the continuous landslide stability and its changing regularities in a uniform criterion due to the unique landslide geological conditions. Based on the relationship between displacement monitoring data, deformation states and landslide stability, a state fusion entropy method is herein proposed to derive landslide instability through a comprehensive multi-attribute entropy analysis of deformation states, which are defined by a proposed joint clustering method combining K-means and a cloud model. Taking Xintan landslide as the detailed case study, cumulative state fusion entropy presents an obvious increasing trend after the landslide entered accelerative deformation stage and historical maxima match highly with landslide macroscopic deformation behaviours in key time nodes. Reasonable results are also obtained in its application to several other landslides in the Three Gorges Reservoir in China. Combined with field survey, state fusion entropy may serve for assessing landslide stability and judging landslide evolutionary stages.

Development and psychometric testing of the Cancer Knowledge Scale for Elders.

PubMed

Su, Ching-Ching; Chen, Yuh-Min; Kuo, Bo-Jein

2009-03-01

To develop the Cancer Knowledge Scale for Elders and test its validity and reliability. The number of elders suffering from cancer is increasing. To facilitate cancer prevention behaviours among elders, they shall be educated about cancer-related knowledge. Prior to designing a programme that would respond to the special needs of elders, understanding the cancer-related knowledge within this population was necessary. However, extensive review of the literature revealed a lack of appropriate instruments for measuring cancer-related knowledge. A valid and reliable cancer knowledge scale for elders is necessary. A non-experimental methodological design was used to test the psychometric properties of the Cancer Knowledge Scale for Elders. Item analysis was first performed to screen out items that had low corrected item-total correlation coefficients. Construct validity was examined with a principle component method of exploratory factor analysis. Cancer-related health behaviour was used as the criterion variable to evaluate criterion-related validity. Internal consistency reliability was assessed by the KR-20. Stability was determined by two-week test-retest reliability. The factor analysis yielded a four-factor solution accounting for 49.5% of the variance. For criterion-related validity, cancer knowledge was positively correlated with cancer-related health behaviour (r = 0.78, p < 0.001). The KR-20 coefficients of each factor were 0.85, 0.76, 0.79 and 0.67 and 0.87 for the total scale. Test-retest reliability over a two-week period was 0.83 (p < 0.001). This study provides evidence for content validity, construct validity, criterion-related validity, internal consistency and stability of the Cancer Knowledge Scale for Elders. The results show that this scale is an easy-to-use instrument for elders and has adequate validity and reliability. The scale can be used as an assessment instrument when implementing cancer education programmes for elders. It can also be used to evaluate the effects of education programmes.

Mixtures of bosonic and fermionic atoms in optical lattices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Albus, Alexander; Dipartimento di Fisica, Universita di Salerno, Via S. Allende, I-84081 Baronissi; Illuminati, Fabrizio

2003-08-01

We discuss the theory of mixtures of bosonic and fermionic atoms in periodic potentials at zero temperature. We derive a general Bose-Fermi Hubbard Hamiltonian in a one-dimensional optical lattice with a superimposed harmonic trapping potential. We study the conditions for linear stability of the mixture and derive a mean-field criterion for the onset of a bosonic superfluid transition. We investigate the ground-state properties of the mixture in the Gutzwiller formulation of mean-field theory, and present numerical studies of finite systems. The bosonic and fermionic density distributions and the onset of quantum phase transitions to demixing and to a bosonic Mott-insulatormore » are studied as a function of the lattice potential strength. The existence is predicted of a disordered phase for mixtures loaded in very deep lattices. Such a disordered phase possessing many degenerate or quasidegenerate ground states is related to a breaking of the mirror symmetry in the lattice.« less

Information hidden in the velocity distribution of ions and the exact kinetic Bohm criterion

NASA Astrophysics Data System (ADS)

Tsankov, Tsanko V.; Czarnetzki, Uwe

2017-05-01

Non-equilibrium distribution functions of electrons and ions play an important role in plasma physics. A prominent example is the kinetic Bohm criterion. Since its first introduction it has been controversial for theoretical reasons and due to the lack of experimental data, in particular on the ion distribution function. Here we resolve the theoretical as well as the experimental difficulties by an exact solution of the kinetic Boltzmann equation including charge exchange collisions and ionization. This also allows for the first time non-invasive measurement of spatially resolved ion velocity distributions, absolute values of the ion and electron densities, temperatures, and mean energies as well as the electric field and the plasma potential in the entire plasma. The non-invasive access to the spatially resolved distribution functions of electrons and ions is applied to the problem of the kinetic Bohm criterion. Theoretically a so far missing term in the criterion is derived and shown to be of key importance. With the new term the validity of the kinetic criterion at high collisionality and its agreement with the fluid picture are restored. All findings are supported by experimental data, theory and a numerical model with excellent agreement throughout.

Fatigue Life Prediction of Fiber-Reinforced Ceramic-Matrix Composites with Different Fiber Preforms at Room and Elevated Temperatures

PubMed Central

Li, Longbiao

2016-01-01

In this paper, the fatigue life of fiber-reinforced ceramic-matrix composites (CMCs) with different fiber preforms, i.e., unidirectional, cross-ply, 2D (two dimensional), 2.5D and 3D CMCs at room and elevated temperatures in air and oxidative environments, has been predicted using the micromechanics approach. An effective coefficient of the fiber volume fraction along the loading direction (ECFL) was introduced to describe the fiber architecture of preforms. The statistical matrix multicracking model and fracture mechanics interface debonding criterion were used to determine the matrix crack spacing and interface debonded length. Under cyclic fatigue loading, the fiber broken fraction was determined by combining the interface wear model and fiber statistical failure model at room temperature, and interface/fiber oxidation model, interface wear model and fiber statistical failure model at elevated temperatures, based on the assumption that the fiber strength is subjected to two-parameter Weibull distribution and the load carried by broken and intact fibers satisfies the Global Load Sharing (GLS) criterion. When the broken fiber fraction approaches the critical value, the composites fatigue fracture. PMID:28773332

Duality and the universality class of the three-state Potts antiferromagnet on plane quadrangulations.

PubMed

Lv, Jian-Ping; Deng, Youjin; Jacobsen, Jesper Lykke; Salas, Jesús; Sokal, Alan D

2018-04-01

We provide a criterion based on graph duality to predict whether the three-state Potts antiferromagnet on a plane quadrangulation has a zero- or finite-temperature critical point, and its universality class. The former case occurs for quadrangulations of self-dual type, and the zero-temperature critical point has central charge c=1. The latter case occurs for quadrangulations of non-self-dual type, and the critical point belongs to the universality class of the three-state Potts ferromagnet. We have tested this criterion against high-precision computations on four lattices of each type, with very good agreement. We have also found that the Wang-Swendsen-Kotecký algorithm has no critical slowing-down in the former case, and critical slowing-down in the latter.

Characteristics of Electronegative Plasma Sheath with q-Nonextensive Electron Distribution

NASA Astrophysics Data System (ADS)

Borgohain, D. R.; Saharia, K.

2018-01-01

The characteristics of sheath in a plasma system containing q-nonextensive electrons, cold fluid ions, and Boltzmann-distributed negative ions are investigated. A modified Bohm sheath criterion is derived by using the Sagdeev pseudopotential technique. It is found that the proposed Bohm velocity depends on the degree of nonextensivity ( q), negative ion temperature to nonextensive electron temperature ratio (σ), and negative ion density ( B). Using the modified Bohm sheath criterion, the sheath characteristics, such as the spatial distribution of the potential, positive ion velocity, and density profile, have been numerically investigated, which clearly shows the effect of negative ions, as well as the nonextensive distribution of electrons. It is found that, as the nonextensivity parameter and the electronegativity increases, the electrostatic sheath potential increases sharply and the sheath width decreases.

Duality and the universality class of the three-state Potts antiferromagnet on plane quadrangulations

NASA Astrophysics Data System (ADS)

Lv, Jian-Ping; Deng, Youjin; Jacobsen, Jesper Lykke; Salas, Jesús; Sokal, Alan D.

2018-04-01

We provide a criterion based on graph duality to predict whether the three-state Potts antiferromagnet on a plane quadrangulation has a zero- or finite-temperature critical point, and its universality class. The former case occurs for quadrangulations of self-dual type, and the zero-temperature critical point has central charge c =1 . The latter case occurs for quadrangulations of non-self-dual type, and the critical point belongs to the universality class of the three-state Potts ferromagnet. We have tested this criterion against high-precision computations on four lattices of each type, with very good agreement. We have also found that the Wang-Swendsen-Kotecký algorithm has no critical slowing-down in the former case, and critical slowing-down in the latter.

New true-triaxial rock strength criteria considering intrinsic material characteristics

NASA Astrophysics Data System (ADS)

Zhang, Qiang; Li, Cheng; Quan, Xiaowei; Wang, Yanning; Yu, Liyuan; Jiang, Binsong

2018-02-01

A reasonable strength criterion should reflect the hydrostatic pressure effect, minimum principal stress effect, and intermediate principal stress effect. The former two effects can be described by the meridian curves, and the last one mainly depends on the Lode angle dependence function. Among three conventional strength criteria, i.e. Mohr-Coulomb (MC), Hoek-Brown (HB), and Exponent (EP) criteria, the difference between generalized compression and extension strength of EP criterion experience a firstly increase then decrease process, and tends to be zero when hydrostatic pressure is big enough. This is in accordance with intrinsic rock strength characterization. Moreover, the critical hydrostatic pressure I_c corresponding to the maximum difference of between generalized compression and extension strength can be easily adjusted by minimum principal stress influence parameter K. So, the exponent function is a more reasonable meridian curves, which well reflects the hydrostatic pressure effect and is employed to describe the generalized compression and extension strength. Meanwhile, three Lode angle dependence functions of L_{{MN}}, L_{{WW}}, and L_{{YMH}}, which unconditionally satisfy the convexity and differential requirements, are employed to represent the intermediate principal stress effect. Realizing the actual strength surface should be located between the generalized compression and extension surface, new true-triaxial criteria are proposed by combining the two states of EP criterion by Lode angle dependence function with a same lode angle. The proposed new true-triaxial criteria have the same strength parameters as EP criterion. Finally, 14 groups of triaxial test data are employed to validate the proposed criteria. The results show that the three new true-triaxial exponent criteria, especially the Exponent Willam-Warnke criterion (EPWW) criterion, give much lower misfits, which illustrates that the EP criterion and L_{{WW}} have more reasonable meridian and deviatoric function form, respectively. The proposed new true-triaxial strength criteria can provide theoretical foundation for stability analysis and optimization of support design of rock engineering.

Fully three-dimensional ideal magnetohydrodynamic stability analysis of low- n modes and Mercier modes in stellarators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fu, G.Y.; Cooper, W.A.; Gruber, R.

1992-06-01

The TERPSICHORE three-dimensional linear ideal magnetohydrodynamic (MHD) stability code ({ital Theory} {ital of} {ital Fusion} {ital Plasmas}, Proceedings of the Joint Varenna--Lausanne International Workshop, Chexbres, Switzerland, 1988 (Editrice Compositori, Bologna, Italy, 1989), p. 93; {ital Controlled} {ital Fusion} {ital and} {ital Plasma} {ital Heating}, Proceedings of the 17th European Conference, Amsterdam, The Netherlands (European Physical Society, Petit-Lancy, Switzerland, 1990), Vol. 14B, Part II, p. 931; {ital Theory} {ital of} {ital Fusion} {ital Plasmas}, Proceedings of the Joint Varenna--Lausanne International Workshop, Valla Monastero, Varenna, Italy, 1990 (Editrice Compositori, Bologna, Italy, 1990), p. 655) has been extended to the full MHD equations.more » The new code is used to calculate the physical growth rates of nonlocal low-{ital n} modes for {ital l}=2 torsatron configurations. A comprehensive investigation of the relation between the Mercier modes and the low-{ital n} modes has been performed. The unstable localized low-{ital n} modes are found to be correlated with the Mercier criterion. Finite growth rates of the low-{ital n} modes correspond to finite values of the Mercier criterion parameter. Near the Mercier marginal stability boundary, the low-{ital n} modes tend to be weakly unstable with very small growth rates. However, the stability of global-type low-{ital n} modes is found to be decorrelated from that of Mercier modes. The low-{ital n} modes with global radial structures can be more stable or more unstable than Mercier modes.« less

The Processing of High Temperature Ceramic Superconducting Devices. Volume 1.

DTIC Science & Technology

1992-01-31

assuming frequency squared dependence) for ease of comparison with other measurements. At the low power levels the surface resistance is I 200 micro ...transition temperature is 106K, where the measured resistivity becomes zero. The noimal state resistivity at the transition temperature, 100 micro -ohms...our films at temperatures down t o 4K. A four-point measurement is used, and the criterion of 1 micro -volt per millimeter is usedI to determine

Shape selection criterion for cellular array during constrained growth of binary alloys - Need for low gravity experiment

NASA Technical Reports Server (NTRS)

Tewari, Surendra N.; Trivedi, Rohit

1991-01-01

Development of steady-state periodic cellular array is one of the critical problems in the study of nonlinear pattern formation during directional solidification of binary alloys. The criterion which establishes the values of cell tip radius and spacing under given growth condition is not known. Theoretical models, such as marginal stability and microscopic solvability, have been developed for purely diffusive regime. However, the experimental conditions where cellular structures are stable are precisely the ones where the convection effects are predominant. Thus, the critical data for meaningful evaluation of cellular array growth models can only be obtained by partial directional solidification and quenching experiments carried out in the low gravity environment of space.

The Reliability, Validity, and Evaluation of the Objective Structured Clinical Examination in Podiatry (Chiropody).

ERIC Educational Resources Information Center

Woodburn, Jim; Sutcliffe, Nick

1996-01-01

The Objective Structured Clinical Examination (OSCE), initially developed for undergraduate medical education, has been adapted for assessment of clinical skills in podiatry students. A 12-month pilot study found the test had relatively low levels of reliability, high construct and criterion validity, and good stability of performance over time.…

A method to achieve comparable thermal states of car brakes during braking on the road and on a high-speed roll-stand

NASA Astrophysics Data System (ADS)

Wolff, Andrzej

2010-01-01

The temperature of a brake friction surface influences significantly the braking effectiveness. The paper describes a heat transfer process in car brakes. Using a developed program of finite element method, the temperature distributions in brake rotors (disc and drum brake) of a light truck have been calculated. As a preliminary consistency criterion of the brake thermal state in road and roll-stand braking conditions, a balance of the energy cumulated in the brake rotor has been taken into account. As the most reliable consistency criterion an equality of average temperatures of the friction surface has been assumed. The presented method allows to achieve on a roll-stand the analogical thermal states of automotive brakes, which are observed during braking in road conditions. Basing on this method, it is possible to calculate the braking time and force for a high-speed roll-stand. In contrast to the previous papers of the author, new calculation results have been presented.

Test system stability and natural variability of a Lemna gibba L. bioassay.

PubMed

Scherr, Claudia; Simon, Meinhard; Spranger, Jörg; Baumgartner, Stephan

2008-09-04

In ecotoxicological and environmental studies Lemna spp. are used as test organisms due to their small size, rapid predominantly vegetative reproduction, easy handling and high sensitivity to various chemicals. However, there is not much information available concerning spatial and temporal stability of experimental set-ups used for Lemna bioassays, though this is essential for interpretation and reliability of results. We therefore investigated stability and natural variability of a Lemna gibba bioassay assessing area-related and frond number-related growth rates under controlled laboratory conditions over about one year. Lemna gibba L. was grown in beakers with Steinberg medium for one week. Area-related and frond number-related growth rates (r(area) and r(num)) were determined with a non-destructive image processing system. To assess inter-experimental stability, 35 independent experiments were performed with 10 beakers each in the course of one year. We observed changes in growth rates by a factor of two over time. These did not correlate well with temperature or relative humidity in the growth chamber. In order to assess intra-experimental stability, we analysed six systematic negative control experiments (nontoxicant tests) with 96 replicate beakers each. Evaluation showed that the chosen experimental set-up was stable and did not produce false positive results. The coefficient of variation was lower for r(area) (2.99%) than for r(num) (4.27%). It is hypothesised that the variations in growth rates over time under controlled conditions are partly due to endogenic periodicities in Lemna gibba. The relevance of these variations for toxicity investigations should be investigated more closely. Area-related growth rate seems to be more precise as non-destructive calculation parameter than number-related growth rate. Furthermore, we propose two new validity criteria for Lemna gibba bioassays: variability of average specific and section-by-section segmented growth rate, complementary to average specific growth rate as the only validity criterion existing in guidelines for duckweed bioassays.

Test System Stability and Natural Variability of a Lemna Gibba L. Bioassay

PubMed Central

Scherr, Claudia; Simon, Meinhard; Spranger, Jörg; Baumgartner, Stephan

2008-01-01

Background In ecotoxicological and environmental studies Lemna spp. are used as test organisms due to their small size, rapid predominantly vegetative reproduction, easy handling and high sensitivity to various chemicals. However, there is not much information available concerning spatial and temporal stability of experimental set-ups used for Lemna bioassays, though this is essential for interpretation and reliability of results. We therefore investigated stability and natural variability of a Lemna gibba bioassay assessing area-related and frond number-related growth rates under controlled laboratory conditions over about one year. Methology/Principal Findings Lemna gibba L. was grown in beakers with Steinberg medium for one week. Area-related and frond number-related growth rates (r(area) and r(num)) were determined with a non-destructive image processing system. To assess inter-experimental stability, 35 independent experiments were performed with 10 beakers each in the course of one year. We observed changes in growth rates by a factor of two over time. These did not correlate well with temperature or relative humidity in the growth chamber. In order to assess intra-experimental stability, we analysed six systematic negative control experiments (nontoxicant tests) with 96 replicate beakers each. Evaluation showed that the chosen experimental set-up was stable and did not produce false positive results. The coefficient of variation was lower for r(area) (2.99%) than for r(num) (4.27%). Conclusions/Significance It is hypothesised that the variations in growth rates over time under controlled conditions are partly due to endogenic periodicities in Lemna gibba. The relevance of these variations for toxicity investigations should be investigated more closely. Area-related growth rate seems to be more precise as non-destructive calculation parameter than number-related growth rate. Furthermore, we propose two new validity criteria for Lemna gibba bioassays: variability of average specific and section-by-section segmented growth rate, complementary to average specific growth rate as the only validity criterion existing in guidelines for duckweed bioassays. PMID:18769541

Issues with Strong Compression of Plasma Target by Stabilized Imploding Liner

NASA Astrophysics Data System (ADS)

Turchi, Peter; Frese, Sherry; Frese, Michael

2017-10-01

Strong compression (10:1 in radius) of an FRC by imploding liquid metal liners, stabilized against Rayleigh-Taylor modes, using different scalings for loss based on Bohm vs 100X classical diffusion rates, predict useful compressions with implosion times half the initial energy lifetime. The elongation (length-to-diameter ratio) near peak compression needed to satisfy empirical stability criterion and also retain alpha-particles is about ten. The present paper extends these considerations to issues of the initial FRC, including stability conditions (S*/E) and allowable angular speeds. Furthermore, efficient recovery of the implosion energy and alpha-particle work, in order to reduce the necessary nuclear gain for an economical power reactor, is seen as an important element of the stabilized liner implosion concept for fusion. We describe recent progress in design and construction of the high energy-density prototype of a Stabilized Liner Compressor (SLC) leading to repetitive laboratory experiments to develop the plasma target. Supported by ARPA-E ALPHA Program.

A general method to determine the stability of compressible flows

NASA Technical Reports Server (NTRS)

Guenther, R. A.; Chang, I. D.

1982-01-01

Several problems were studied using two completely different approaches. The initial method was to use the standard linearized perturbation theory by finding the value of the individual small disturbance quantities based on the equations of motion. These were serially eliminated from the equations of motion to derive a single equation that governs the stability of fluid dynamic system. These equations could not be reduced unless the steady state variable depends only on one coordinate. The stability equation based on one dependent variable was found and was examined to determine the stability of a compressible swirling jet. The second method applied a Lagrangian approach to the problem. Since the equations developed were based on different assumptions, the condition of stability was compared only for the Rayleigh problem of a swirling flow, both examples reduce to the Rayleigh criterion. This technique allows including the viscous shear terms which is not possible in the first method. The same problem was then examined to see what effect shear has on stability.

Finite-time stability and synchronization of memristor-based fractional-order fuzzy cellular neural networks

NASA Astrophysics Data System (ADS)

Zheng, Mingwen; Li, Lixiang; Peng, Haipeng; Xiao, Jinghua; Yang, Yixian; Zhang, Yanping; Zhao, Hui

2018-06-01

This paper mainly studies the finite-time stability and synchronization problems of memristor-based fractional-order fuzzy cellular neural network (MFFCNN). Firstly, we discuss the existence and uniqueness of the Filippov solution of the MFFCNN according to the Banach fixed point theorem and give a sufficient condition for the existence and uniqueness of the solution. Secondly, a sufficient condition to ensure the finite-time stability of the MFFCNN is obtained based on the definition of finite-time stability of the MFFCNN and Gronwall-Bellman inequality. Thirdly, by designing a simple linear feedback controller, the finite-time synchronization criterion for drive-response MFFCNN systems is derived according to the definition of finite-time synchronization. These sufficient conditions are easy to verify. Finally, two examples are given to show the effectiveness of the proposed results.

A Clue to the Extent of Convective Mixing Inside Massive Stars: The Surface Hydrogen Abundances of Luminous Blue Variables and Hydrogen-Poor Wolf-Rayet Stars

NASA Technical Reports Server (NTRS)

Stothers, Richard B.; Chin, Chao-wen

1999-01-01

Interior layers of stars that have been exposed by surface mass loss reveal aspects of their chemical and convective histories that are otherwise inaccessible to observation. It must be significant that the surface hydrogen abundances of luminous blue variables (LBVs) show a remarkable uniformity, specifically X(sub surf) = 0.3 - 0.4, while those of hydrogen-poor Wolf-Rayet (WN) stars fall, almost without exception, below these values, ranging down to X(sub surf) = 0. According to our stellar model calculations, most LBVs are post-red-supergiant objects in a late blue phase of dynamical instability, and most hydrogen-poor WN stars are their immediate descendants. If this is so, stellar models constructed with the Schwarzschild (temperature-gradient) criterion for convection account well for the observed hydrogen abundances, whereas models built with the Ledoux (density-gradient) criterion fail. At the brightest luminosities, the observed hydrogen abundances of LBVs are too large to be explained by any of our highly evolved stellar models, but these LBVs may occupy transient blue loops that exist during an earlier phase of dynamical instability when the star first becomes a yellow supergiant. Independent evidence concerning the criterion for convection, which is based mostly on traditional color distributions of less massive supergiants on the Hertzsprung-Russell diagram, tends to favor the Ledoux criterion. It is quite possible that the true criterion for convection changes over from something like the Ledoux criterion to something like the Schwarzschild criterion as the stellar mass increases.

Effect of Climate Change on Water Temperature and ...

EPA Pesticide Factsheets

There is increasing evidence that our planet is warming and this warming is also resulting in rising sea levels. Estuaries which are located at the interface between land and ocean are impacted by these changes. We used CE-QUAL-W2 water quality model to predict changes in water temperature as a function of increasing air temperatures and rising sea level for the Yaquina Estuary, Oregon (USA). Annual average air temperature in the Yaquina watershed is expected to increase about 0.3 deg C per decade by 2040-2069. An air temperature increase of 3 deg C in the Yaquina watershed is likely to result in estuarine water temperature increasing by 0.7 to 1.6 deg C. Largest water temperature increases are expected in the upper portion of the estuary, while sea level rise may ameliorate some of the warming in the lower portion of the estuary. Smallest changes in water temperature are predicted to occur in the summer, and maximum changes during the winter and spring. Increases in air temperature may result in an increase in the number of days per year that the 7-day maximum average temperature exceeds 18 deg C (criterion for protection of rearing and migration of salmonids and trout) as well as other water quality concerns. In the upstream portion of the estuary, a 4 deg C increase in air temperature is predicted to cause an increase of 40 days not meeting the temperature criterion, while in the lower estuary the increase will depend upon rate of sea level rise (rang

Implementation of model predictive control for resistive wall mode stabilization on EXTRAP T2R

NASA Astrophysics Data System (ADS)

Setiadi, A. C.; Brunsell, P. R.; Frassinetti, L.

2015-10-01

A model predictive control (MPC) method for stabilization of the resistive wall mode (RWM) in the EXTRAP T2R reversed-field pinch is presented. The system identification technique is used to obtain a linearized empirical model of EXTRAP T2R. MPC employs the model for prediction and computes optimal control inputs that satisfy performance criterion. The use of a linearized form of the model allows for compact formulation of MPC, implemented on a millisecond timescale, that can be used for real-time control. The design allows the user to arbitrarily suppress any selected Fourier mode. The experimental results from EXTRAP T2R show that the designed and implemented MPC successfully stabilizes the RWM.

The near optimality of the stabilizing control in a weakly nonlinear system with state-dependent coefficients

NASA Astrophysics Data System (ADS)

Dmitriev, Mikhail G.; Makarov, Dmitry A.

2016-08-01

We carried out analysis of near optimality of one computationally effective nonlinear stabilizing control built for weakly nonlinear systems with coefficients depending on the state and the formal small parameter. First investigation of that problem was made in [M. G. Dmitriev, and D. A. Makarov, "The suboptimality of stabilizing regulator in a quasi-linear system with state-depended coefficients," in 2016 International Siberian Conference on Control and Communications (SIBCON) Proceedings, National Research University, Moscow, 2016]. In this paper, another optimal control and gain matrix representations were used and theoretical results analogous to cited work above were obtained. Also as in the cited work above the form of quality criterion on which this close-loop control is optimal was constructed.

Characteristics pertaining to a stiffness cross-coupled Jeffcott model

NASA Technical Reports Server (NTRS)

Spanyer, K. L.

1985-01-01

Rotordynamic studies of complex systems utilizing multiple degree-of-freedom analysis have been performed to understand response, loads, and stability. In order to understand the fundamental nature of rotordynamic response, the Jeffcott rotor model has received wide attention. The purpose of this paper is to provide a generic rotordynamic analysis of a stiffness cross-coupled Jeffcott rotor model to illustrate characteristics of a second order stiffness-coupled linear system. The particular characteristics investigated were forced response, force vector diagrams, response orbits, and stability. Numerical results were achieved through a fourth order Runge-Kutta method for solving differential equations and the Routh Hurwitz stability criterion. The numerical results were verified to an exact mathematical solution for the steady state response.

Stability analysis and compensation of a boost regulator with two-loop control

NASA Technical Reports Server (NTRS)

Wester, G. W.

1974-01-01

A useful stability measure has been demonstrated by Wester (1973) for switching regulators with a single feedback loop by applying the Nyquist criterion to the approximate loop gain determined by a time-averaging technique. This approach is extended and applied to the characterization, stability analysis, and compensation design of a switching regulator with two-loop control. The role and relative significance of each control loop is clarified on the basis of a description of circuit operation, and the major and minor loops are identified. In view of the inapplicability of linear feedback theory, describing functions of the feedback loops and power stage are derived, using small-signal analysis. Several phenomena revealed from an analysis of the major loop gain are discussed.

Mean intensity of the vortex Bessel-Gaussian beam in turbulent atmosphere

NASA Astrophysics Data System (ADS)

Lukin, Igor P.

2017-11-01

In this work the question of stability of the vortex Bessel-Gaussian optical beams formed in turbulent atmosphere is theoretically considered. The detailed analysis of features of spatial structure of distribution of mean intensity of vortex Bessel-Gaussian optical beams in turbulent atmosphere are analyzed. The quantitative criterion of possibility of formation of vortex Bessel-Gaussian optical beams in turbulent atmosphere is derived. It is shown that stability of the form of a vortex Bessel-Gaussian optical beam during propagation in turbulent atmosphere increases with increase of value of a topological charge of this optical beam.

Diurnal flight behavior of Ichneumonoidea (Insecta: Hymenoptera) related to environmental factors in a tropical dry forest.

PubMed

González-Moreno, A; Bordera, S; Leirana-Alcocer, J; Delfín-González, H

2012-06-01

The biology and behavior of insects are strongly influenced by environmental conditions such as temperature and precipitation. Because some of these factors present a within day variation, they may be causing variations on insect diurnal flight activity, but scant information exists on the issue. The aim of this work was to describe the patterns on diurnal variation of the abundance of Ichneumonoidea and their relation with relative humidity, temperature, light intensity, and wind speed. The study site was a tropical dry forest at Ría Lagartos Biosphere Reserve, Mexico; where correlations between environmental factors (relative humidity, temperature, light, and wind speed) and abundance of Ichneumonidae and Braconidae (Hymenoptera: Ichneumonoidea) were estimated. The best regression model for explaining abundance variation was selected using the second order Akaike Information Criterion. The optimum values of temperature, humidity, and light for flight activity of both families were also estimated. Ichneumonid and braconid abundances were significantly correlated to relative humidity, temperature, and light intensity; ichneumonid also showed significant correlations to wind speed. The second order Akaike Information Criterion suggests that in tropical dry conditions, relative humidity is more important that temperature for Ichneumonoidea diurnal activity. Ichneumonid wasps selected toward intermediate values of relative humidity, temperature and the lowest wind speeds; while Braconidae selected for low values of relative humidity. For light intensity, braconids presented a positive selection for moderately high values.

A new criterion for predicting rolling-element fatigue lives of through-hardened steels

NASA Technical Reports Server (NTRS)

Chevalier, J. L.; Zaretsky, E. V.; Parker, R. J.

1972-01-01

A carbide factor was derived based upon a statistical analysis which related rolling-element fatigue life to the total number of residual carbide particles per unit area, median residual carbide size, and percent residual carbide area. An equation was experimentally determined which predicts material hardness as a function of temperature. The limiting temperatures of all of the materials studied were dependent on initial room temperature hardness and tempering temperature. An equation was derived combining the effects of material hardness, carbide factor, and bearing temperature to predict rolling-element bearing life.

An investigation of the effects of pitch-roll (de)coupling on helicopter handling qualities

NASA Technical Reports Server (NTRS)

Blanken, C. L.; Pausder, H. J.; Ockier, C. J.

1995-01-01

An extensive investigation of the effects of pitch-roll coupling on helicopter handling qualities was performed by the U.S. Army and Deutsche Forschungsanstalt fur Luft- und Raumfahrt (DLR), using a NASA ground-based and a DLR in-flight simulator. Over 90 different coupling configurations were evaluated using a high gain roll-axis tracking task. The results show that although the current ADS-33C coupling criterion discriminates against those types of coupling typical of conventionally controlled helicopters, it is not always suited for the prediction of handling qualities of helicopters with modern control systems. Based on the observation that high frequency inputs during tracking are used to alleviate coupling, a frequency domain pitch-roll coupling criterion that uses the average coupling ratio between the bandwidth and neutral stability frequency is formulated. This criterion provides a more comprehensive coverage with respect to the different types of coupling, shows excellent consistency, and has the additional benefit that compliance testing data are obtained from the bandwidth/phase delay tests, so that no additional flight testing is needed.

Validity of field expedient devices to assess core temperature during exercise in the cold.

PubMed

Bagley, James R; Judelson, Daniel A; Spiering, Barry A; Beam, William C; Bartolini, J Albert; Washburn, Brian V; Carney, Keven R; Muñoz, Colleen X; Yeargin, Susan W; Casa, Douglas J

2011-12-01

Exposure to cold environments affects human performance and physiological function. Major medical organizations recommend rectal temperature (TREC) to evaluate core body temperature (TcORE) during exercise in the cold; however, other field expedient devices claim to measure TCORE. The purpose of this study was to determine if field expedient devices provide valid measures of TcRE during rest and exercise in the cold. Participants included 13 men and 12 women (age = 24 +/- 3 yr, height = 170.7 +/- 10.6 cm, mass = 73.4 +/- 16.7 kg, body fat = 18 +/- 7%) who reported being healthy and at least recreationally active. During 150 min of cold exposure, subjects sequentially rested for 30 min, cycled for 90 min (heart rate = 120-140 bpm), and rested for an additional 30 min. Investigators compared aural (T(AUR)), expensive axillary (T(AXLe)), inexpensive axillary (T(AXLi)), forehead (T(FOR)), gastrointestinal (T(GI)), expensive oral (T(ORLe)), inexpensive oral (T(ORLi)), and temporal (T(TEM)) temperatures to T(REc) every 15 min. Researchers used mean difference between each device and T(REC) (i.e., mean bias) as the primary criterion for validity. T(AUR), T(AXLe), T(AXLi), T(FOR), TORLe, T(ORLi), and TTEM provided significantly lower measures compared to T(REC) and fell below our validity criterion. T(GI) significantly exceeded T(REC) at three of eleven time points, but no significant difference existed between mean T(REC) and T(GI) across time. Only T(GI) achieved our validity criterion and compared favorably to T(REC). T(GI) offers a valid measurement with which to assess T(CORE) during rest and exercise in the cold; athletic trainers, mountain rescuers, and military medical personnel should avoid other field expedient devices in similar conditions.

Experimental investigation of shaping disturbance observer design for motion control of precision mechatronic stages with resonances

NASA Astrophysics Data System (ADS)

Yang, Jin; Hu, Chuxiong; Zhu, Yu; Wang, Ze; Zhang, Ming

2017-08-01

In this paper, shaping disturbance observer (SDOB) is investigated for precision mechatronic stages with middle-frequency zero/pole type resonance to achieve good motion control performance in practical manufacturing situations. Compared with traditional standard disturbance observer (DOB), in SDOB a pole-zero cancellation based shaping filter is cascaded to the mechatronic stage plant to meet the challenge of motion control performance deterioration caused by actual resonance. Noting that pole-zero cancellation is inevitably imperfect and the controller may even consequently become unstable in practice, frequency domain stability analysis is conducted to find out how each parameter of the shaping filter affects the control stability. Moreover, the robust design criterion of the shaping filter, and the design procedure of SDOB, are both proposed to guide the actual design and facilitate practical implementation. The SDOB with the proposed design criterion is applied to a linear motor driven stage and a voice motor driven stage, respectively. Experimental results consistently validate the effectiveness nature of the proposed SDOB scheme in practical mechatronics motion applications. The proposed SDOB design actually could be an effective unit in the controller design for motion stages of mechanical manufacture equipments.

Long-term effects of executive process training in young and old adults.

PubMed

Sandberg, Petra; Stigsdotter Neely, Anna

2016-10-01

Prior studies have examined the magnitude of training and transfer effects after process-based training in early and late adulthood. However, little is known about how long-lasting these effects are. Here we investigate the degree of stability of training gains and transfer effects in younger and older adults 18 months after completion of executive process training, tapping updating, inhibition, and shifting. From the original sample, 24 out of 30 older participants, and 19 out of 29 young adults, returned for follow-up assessment at which the criterion and transfer tests from pre- and post-test were re-administered. The results demonstrated stability of training gains in the updating criterion task (Letter Memory Running Span), and in a near transfer updating task (Number Memory Running Span) for both age groups. The young adults improved performance in two complex working memory tasks immediately after training. These transfer effects did not survive across time. Our results provide evidence that executive process training has its greatest effect on transfer tasks with a substantial process overlap with the trained tasks: only those effects are maintained over an 18 month period in both early and late adulthood.

Subgrade stabilization alternatives to lime and cement.

DOT National Transportation Integrated Search

2010-04-15

This project involved four distinct research activities, (1) the influence of temperature on lime-stabilized soils, (2) the influence of temperature on cement-stabilized soils (3) temperature modeling of stabilized subgrade and (4) use of calcium chl...

The free growth criterion for grain initiation in TiB 2 inoculated γ-titanium aluminide based alloys

NASA Astrophysics Data System (ADS)

Gosslar, D.; Günther, R.

2014-02-01

γ-titanium aluminide (γ-TiAl) based alloys enable for the design of light-weight and high-temperature resistant engine components. This work centers on a numerical study of the condition for grain initiation during solidification of TiB2 inoculated γ-TiAl based alloys. Grain initiation is treated according to the so-called free growth criterion. This means that the free growth barrier for grain initiation is determined by the maximum interfacial mean curvature between a nucleus and the melt. The strategy presented in this paper relies on iteratively increasing the volume of a nucleus, which partially wets a hexagonal TiB2 crystal, minimizing the interfacial energy and calculating the corresponding interfacial curvature. The hereby obtained maximum curvature yields a scaling relation between the size of TiB2 crystals and the free growth barrier. Comparison to a prototypical TiB2 crystal in an as cast γ-TiAl based alloy allowed then to predict the free growth barrier prevailing under experimental conditions. The validity of the free growth criterion is discussed by an interfacial energy criterion.

Thermo-solutal growth of an anisotropic dendrite with six-fold symmetry

NASA Astrophysics Data System (ADS)

Alexandrov, D. V.; Galenko, P. K.

2018-03-01

A stable growth of dendritic crystal with the six-fold crystalline anisotropy is analyzed in a binary nonisothermal mixture. A selection criterion representing a relationship between the dendrite tip velocity and its tip diameter is derived on the basis of morphological stability analysis and solvability theory. A complete set of nonlinear equations, consisting of the selection criterion and undercooling balance condition, which determines implicit dependencies of the dendrite tip velocity and tip diameter as functions of the total undercooling, is formulated. Exact analytical solutions of these nonlinear equations are found in a parametric form. Asymptotic solutions describing the crystal growth at small Péclet numbers are determined. Theoretical predictions are compared with experimental data obtained for ice dendrites growing in binary water-ethylenglycol solutions as well as in pure water.

Unraveling protein stabilization mechanisms: vitrification and water replacement in a glass transition temperature controlled system.

PubMed

Grasmeijer, N; Stankovic, M; de Waard, H; Frijlink, H W; Hinrichs, W L J

2013-04-01

The aim of this study was to elucidate the role of the two main mechanisms used to explain the stabilization of proteins by sugar glasses during drying and subsequent storage: the vitrification and the water replacement theory. Although in literature protein stability is often attributed to either vitrification or water replacement, both mechanisms could play a role and they should be considered simultaneously. A model protein, alkaline phosphatase, was incorporated in either inulin or trehalose by spray drying. To study the storage stability at different glass transition temperatures, a buffer which acts as a plasticizer, ammediol, was incorporated in the sugar glasses. At low glass transition temperatures (<50°C), the enzymatic activity of the protein strongly decreased during storage at 60°C. Protein stability increased when the glass transition temperature was raised considerably above the storage temperature. This increased stability could be attributed to vitrification. A further increase of the glass transition temperature did not further improve stability. In conclusion, vitrification plays a dominant role in stabilization at glass transition temperatures up to 10 to 20°C above storage temperature, depending on whether trehalose or inulin is used. On the other hand, the water replacement mechanism predominantly determines stability at higher glass transition temperatures. Copyright © 2013 Elsevier B.V. All rights reserved.

Co-treatment of fruit and vegetable waste in sludge digesters. An analysis of the relationship among bio-methane generation, process stability and digestate phytotoxicity.

PubMed

Di Maria, Francesco; Sordi, Alessio; Cirulli, Giuseppe; Gigliotti, Giovanni; Massaccesi, Luisa; Cucina, Mirko

2014-09-01

The co-digestion of a variable amount of fruit and vegetable waste in a waste mixed sludge digester was investigated using a pilot scale apparatus. The organic loading rate (OLR) was increased from 1.46 kg VS/m(3) day to 2.8 kg VS/m(3) day. The hydraulic retention time was reduced from 14 days to about 10 days. Specific bio-methane production increased from about 90 NL/kg VS to the maximum value of about 430 NL/kg VS when OLR was increased from 1.46 kg VS/m(3) day to 2.1 kg VS/m(3) day. A higher OLR caused an excessive reduction in the hydraulic retention time, enhancing microorganism wash out. Process stability evaluated by the total volatile fatty acids concentration (mg/l) to the alkalinity buffer capacity (eq. mg/l CaCO3) ratio (i.e. FOS/TAC) criterion was <0.1 indicating high stability for OLR <2.46 kg VS/m(3 )day. For higher OLR, FOS/TAC increased rapidly. Residual phytotoxicty of the digestate evaluated by the germination index (GI) (%) was quite constant for OLR<2.46 kg VS/m(3)day, which is lower than the 60% limit, indicating an acceptable toxicity level for crops. For OLR>2.46 kg VS/m(3) day, GI decreased rapidly. This corresponding trend between FOS/TAC and GI was further investigated by the definition of the GI ratio (GIR) parameter. Comparison between GIR and FOS/TAC suggests that GI could be a suitable criterion for evaluating process stability. Copyright © 2014 Elsevier Ltd. All rights reserved.

Equilibrium properties of simple metal thin films in the self-compressed stabilized jellium model.

PubMed

Mahmoodi, T; Payami, M

2009-07-01

In this work, we have applied the self-compressed stabilized jellium model to predict the equilibrium properties of isolated thin Al, Na and Cs slabs. To make a direct correspondence to atomic slabs, we have considered only those L values that correspond to n-layered atomic slabs with 2≤n≤20, for surface indices (100), (110), and (111). The calculations are based on the density functional theory and self-consistent solution of the Kohn-Sham equations in the local density approximation. Our results show that firstly, the quantum size effects are significant for slabs with sizes smaller than or near to the Fermi wavelength of the valence electrons λ(F), and secondly, some slabs expand while others contract with respect to the bulk spacings. Based on the results, we propose a criterion for realization of significant quantum size effects that lead to expansion of some thin slabs. For more justification of the criterion, we have tested it on Li slabs for 2≤n≤6. We have compared our Al results with those obtained from using all-electron or pseudo-potential first-principles calculations. This comparison shows excellent agreements for Al(100) work functions, and qualitatively good agreements for the other work functions and surface energies. These agreements justify the way we have used the self-compressed stabilized jellium model for the correct description of the properties of simple metal slab systems. On the other hand, our results for the work functions and surface energies of large- n slabs are in good agreement with those obtained from applying the stabilized jellium model for semi-infinite systems. In addition, we have performed the slab calculations in the presence of surface corrugation for selected Al slabs and have shown that the results are worsened.

Synchronization of two homodromy rotors installed on a double vibro-body in a coupling vibration system.

PubMed

Fang, Pan; Hou, Yongjun; Nan, Yanghai

2015-01-01

A new mechanism is proposed to implement synchronization of the two unbalanced rotors in a vibration system, which consists of a double vibro-body, two induction motors and spring foundations. The coupling relationship between the vibro-bodies is ascertained with the Laplace transformation method for the dynamics equation of the system obtained with the Lagrange's equation. An analytical approach, the average method of modified small parameters, is employed to study the synchronization characteristics between the two unbalanced rotors, which is converted into that of existence and the stability of zero solutions for the non-dimensional differential equations of the angular velocity disturbance parameters. By assuming the disturbance parameters that infinitely approach to zero, the synchronization condition for the two rotors is obtained. It indicated that the absolute value of the residual torque between the two motors should be equal to or less than the maximum of their coupling torques. Meanwhile, the stability criterion of synchronization is derived with the Routh-Hurwitz method, and the region of the stable phase difference is confirmed. At last, computer simulations are preformed to verify the correctness of the approximate solution of the theoretical computation for the stable phase difference between the two unbalanced rotors, and the results of theoretical computation is in accordance with that of computer simulations. To sum up, only the parameters of the vibration system satisfy the synchronization condition and the stability criterion of the synchronization, the two unbalanced rotors can implement the synchronization operation.

Synchronization of Two Homodromy Rotors Installed on a Double Vibro-Body in a Coupling Vibration System

PubMed Central

Fang, Pan; Hou, Yongjun; Nan, Yanghai

2015-01-01

A new mechanism is proposed to implement synchronization of the two unbalanced rotors in a vibration system, which consists of a double vibro-body, two induction motors and spring foundations. The coupling relationship between the vibro-bodies is ascertained with the Laplace transformation method for the dynamics equation of the system obtained with the Lagrange’s equation. An analytical approach, the average method of modified small parameters, is employed to study the synchronization characteristics between the two unbalanced rotors, which is converted into that of existence and the stability of zero solutions for the non-dimensional differential equations of the angular velocity disturbance parameters. By assuming the disturbance parameters that infinitely approach to zero, the synchronization condition for the two rotors is obtained. It indicated that the absolute value of the residual torque between the two motors should be equal to or less than the maximum of their coupling torques. Meanwhile, the stability criterion of synchronization is derived with the Routh-Hurwitz method, and the region of the stable phase difference is confirmed. At last, computer simulations are preformed to verify the correctness of the approximate solution of the theoretical computation for the stable phase difference between the two unbalanced rotors, and the results of theoretical computation is in accordance with that of computer simulations. To sum up, only the parameters of the vibration system satisfy the synchronization condition and the stability criterion of the synchronization, the two unbalanced rotors can implement the synchronization operation. PMID:25993472

Validity and reliability of temperature measurement by heat flow thermistors, flexible thermocouple probes and thermistors in a stirred water bath.

PubMed

Versey, Nathan G; Gore, Christopher J; Halson, Shona L; Plowman, Jamie S; Dawson, Brian T

2011-09-01

We determined the validity and reliability of heat flow thermistors, flexible thermocouple probes and general purpose thermistors compared with a calibrated reference thermometer in a stirred water bath. Validity (bias) was defined as the difference between the observed and criterion values, and reliability as the repeatability (standard deviation or typical error) of measurement. Data were logged every 5 s for 10 min at water temperatures of 14, 26 and 38 °C for ten heat flow thermistors and 24 general purpose thermistors, and at 35, 38 and 41 °C for eight flexible thermocouple probes. Statistical analyses were conducted using spreadsheets for validity and reliability, where an acceptable bias was set at ±0.1 °C. None of the heat flow thermistors, 17% of the flexible thermocouple probes and 71% of the general purpose thermistors met the validity criterion for temperature. The inter-probe reliabilities were 0.03 °C for heat flow thermistors, 0.04 °C for flexible thermocouple probes and 0.09 °C for general purpose thermistors. The within trial intra-probe reliability of all three temperature probes was 0.01 °C. The results suggest that these temperature sensors should be calibrated individually before use at relevant temperatures and the raw data corrected using individual linear regression equations.

Stability analysis of a reinforced carbon carbon shell

NASA Technical Reports Server (NTRS)

Agan, W. E.; Jordan, B. M.

1977-01-01

This paper presents the development of a stability analysis for the nose cap of the NASA Space Shuttle Orbiter. Stability is evaluated by the differential stiffness analysis of the NASTRAN finite-element computer code, addressing those nonstandard characteristics in the nose cap such as nonuniform curvature, asymmetrical and nonuniform loads, support fixity, and various combinations of membrane and bending stresses. A full-sized nose cap, thinner than production, was statically tested and stability analyzed. The failing load level correlated to within 30%. The region and mode of buckling that occurred during test was accurately predicted by analysis. The criterion for predicting instability is based on the behavior of the nonlinear deflections. The deflections are nonlinear elastic in that the stresses are well within the elastic range of the material, but the geometry-load relationship produces nonlinear deflections. The load-deflection relationship is well defined by differential stiffness analysis up to the zero-slope portion of the curve, the point of neutral stability or where the shell 'snaps through' just prior to general instability.

Exploiting structure: Introduction and motivation

NASA Technical Reports Server (NTRS)

Xu, Zhong Ling

1993-01-01

Research activities performed during the period of 29 June 1993 through 31 Aug. 1993 are summarized. The Robust Stability of Systems where transfer function or characteristic polynomial are multilinear affine functions of parameters of interest in two directions, Algorithmic and Theoretical, was developed. In the algorithmic direction, a new approach that reduces the computational burden of checking the robust stability of the system with multilinear uncertainty is found. This technique is called 'Stability by linear process.' In fact, the 'Stability by linear process' described gives an algorithm. In analysis, we obtained a robustness criterion for the family of polynomials with coefficients of multilinear affine function in the coefficient space and obtained the result for the robust stability of diamond families of polynomials with complex coefficients also. We obtained the limited results for SPR design and we provide a framework for solving ACS. Finally, copies of the outline of our results are provided in the appendix. Also, there is an administration issue in the appendix.

A quiet tunnel investigation of hypersonic boundary-layer stability over a cooled, flared cone

NASA Technical Reports Server (NTRS)

Blanchard, Alan E.; Selby, Gregory V.; Wilkinson, Stephen P.

1996-01-01

A flared-cone model under adiabatic and cooled-wall conditions was placed in a calibrated, low-disturbance Mach 6 flow and the stability of the boundary layer was investigated using a prototype constant-voltage anemometer. The results were compared with linear-stability theory predictions and good agreement was found in the prediction of second-mode frequencies and growth. In addition, the same 'N = 10' criterion used to predict boundary-layer transition in subsonic, transonic, and supersonic flows under low freestream noise conditions was found to be applicable for the hypersonic flow regime as well. Under cooled-wall conditions, a unique set of spectral data was acquired that documents the linear, nonlinear, and breakdown regions associated with the transition of hypersonic flow under low-noise conditions.

Ballooning instabilities in tokamaks with sheared toroidal flows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Waelbroeck, F.L.; Chen, L.

1990-11-01

The stability of ballooning modes in the presence of sheared toroidal flows is investigated. The eigenmodes are shown to be related by a Fourier transformation to the non-exponentially growing Floquet solutions found by Cooper. It is further shown that the problem cannot be reduced further than to a two dimensional partial differential equation. Next, the generalized ballooning equation is solved analytically for a circular tokamak equilibrium with sonic flows, but with a small rotation shear compared to the sound speed. With this ordering, the centrifugal forces are comparable to the pressure gradient forces driving the instability, but coupling of themore » mode with the sound wave is avoided. A new stability criterion is derived which explicitly demonstrates that flow shear is stabilizing at constant centrifugal force gradient. 34 refs.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sakaguchi, Hidetsugu; Malomed, Boris A.

We study ordinary solitons and gap solitons (GS's) in the framework of the one-dimensional Gross-Pitaevskii equation (GPE) with a combination of both linear and nonlinear lattice potentials. The main points of the analysis are the effects of (in)commensurability between the lattices, the development of analytical methods, viz., the variational approximation (VA) for narrow ordinary solitons and various forms of the averaging method for broad solitons of both types, and also the study of the mobility of the solitons. Under the direct commensurability (equal periods of the lattices, L{sub lin}=L{sub nonlin}), the family of ordinary solitons is similar to its counterpartmore » in the GPE without external potentials. In the case of the subharmonic commensurability with L{sub lin}=(1/2)L{sub nonlin}, or incommensurability, there is an existence threshold for the ordinary solitons and the scaling relation between their amplitude and width is different from that in the absence of the potentials. GS families demonstrate a bistability unless the direct commensurability takes place. Specific scaling relations are found for them as well. Ordinary solitons can be readily set in motion by kicking. GS's are also mobile and feature inelastic collisions. The analytical approximations are shown to be quite accurate, predicting correct scaling relations for the soliton families in different cases. The stability of the ordinary solitons is fully determined by the Vakhitov-Kolokolov (VK) criterion (i.e., a negative slope in the dependence between the solitons's chemical potential mu and norm N). The stability of GS families obeys an inverted ('anti-VK') criterion dmu/dN>0, which is explained by the approximation based on the averaging method. The present system provides for the unique possibility to check the anti-VK criterion, as mu(N) dependencies for GS's feature turning points except in the case of direct commensurability.« less

Behavior of collisional sheath in electronegative plasma with q-nonextensive electron distribution

NASA Astrophysics Data System (ADS)

Borgohain, Dima Rani; Saharia, K.

2018-03-01

Electronegative plasma sheath is addressed in a collisional unmagnetized plasma consisting of q-nonextensive electrons, Boltzmann distributed negative ions and cold fluid positive ions. Considering the positive ion-neutral collisions and ignoring the effects of ionization and collisions between negative species and positive ions (neutrals), a modified Bohm sheath criterion and hence floating potential are derived by using multifluid model. Using the modified Bohm sheath criterion, the sheath characteristics such as spatial profiles of density, potential and net space charge density have been numerically investigated. It is found that increasing values of q-nonextensivity, electronegativity and collisionality lead to a decrease of the sheath thickness and an increase of the sheath potential and the net space charge density. With increasing values of the electron temperature to negative ion temperature ratio, the sheath thickness increases and the sheath potential as well as the net space charge density in the sheath region decreases.

Rapid thermal process by RF heating of nano-graphene layer/silicon substrate structure: Heat explosion theory approach

NASA Astrophysics Data System (ADS)

Sinder, M.; Pelleg, J.; Meerovich, V.; Sokolovsky, V.

2018-03-01

RF heating kinetics of a nano-graphene layer/silicon substrate structure is analyzed theoretically as a function of the thickness and sheet resistance of the graphene layer, the dimensions and thermal parameters of the structure, as well as of cooling conditions and of the amplitude and frequency of the applied RF magnetic field. It is shown that two regimes of the heating can be realized. The first one is characterized by heating of the structure up to a finite temperature determined by equilibrium between the dissipated loss power caused by induced eddy-currents and the heat transfer to environment. The second regime corresponds to a fast unlimited temperature increase (heat explosion). The criterions of realization of these regimes are presented in the analytical form. Using the criterions and literature data, it is shown the possibility of the heat explosion regime for a graphene layer/silicon substrate structure at RF heating.

Two-dimensional thermal modeling of power monolithic microwave integrated circuits (MMIC's)

NASA Technical Reports Server (NTRS)

Fan, Mark S.; Christou, Aris; Pecht, Michael G.

1992-01-01

Numerical simulations of the two-dimensional temperature distributions for a typical GaAs MMIC circuit are conducted, aiming at understanding the heat conduction process of the circuit chip and providing temperature information for device reliability analysis. The method used is to solve the two-dimensional heat conduction equation with a control-volume-based finite difference scheme. In particular, the effects of the power dissipation and the ambient temperature are examined, and the criterion for the worst operating environment is discussed in terms of the allowed highest device junction temperature.

ASRDI oxygen technology survey. Volume 4: Low temperature measurement

NASA Technical Reports Server (NTRS)

Sparks, L. L.

1974-01-01

Information is presented on temperature measurement between the triple point and critical point of liquid oxygen. The criterion selected is that all transducers which may reasonably be employed in the liquid oxygen (LO2) temperature range are considered. The temperature range for each transducer is the appropriate full range for the particular thermometer. The discussion of each thermometer or type of thermometer includes the following information: (1) useful temperature range, (2) general and particular methods of construction and the advantages of each type, (3) specifications (accuracy, reproducibility, response time, etc.), (4) associated instrumentation, (5) calibrations and procedures, and (6) analytical representations.

The Three-Dimensional (3D) Numerical Stability Analysis of Hyttemalmen Open-Pit

NASA Astrophysics Data System (ADS)

Cała, Marek; Kowalski, Michał; Stopkowicz, Agnieszka

2014-10-01

The purpose of this paper was to perform the 3D numerical calculations allowing slope stability analysis of Hyttemalmen open pit (location Kirkenes, Finnmark Province, Norway). After a ramp rock slide, which took place in December 2010, as well as some other small-scale rock slope stability problems, it proved necessary to perform a serious stability analyses. The Hyttemalmen open pit was designed with a depth up to 100 m, a bench height of 24 m and a ramp width of 10 m. The rock formation in the iron mining district of Kirkenes is called the Bjornevaten Group. This is the most structurally complicated area connected with tectonic process such as folding, faults and metamorphosis. The Bjornevaten Group is a volcano-sedimentary sequence. Rock slope stability depends on the mechanical properties of the rock, hydro-geological conditions, slope topography, joint set systems and seismic activity. However, rock slope stability is mainly connected with joint sets. Joints, or general discontinuities, are regarded as weak planes within rock which have strength reducing consequences with regard to rock strength. Discontinuities within the rock mass lead to very low tensile strength. Several simulations were performed utilising the RocLab (2007) software to estimate the gneiss cohesion for slopes of different height. The RocLab code is dedicated to estimate rock mass strength using the Hoek-Brown failure criterion. Utilising both the GSI index and the Hoek-Brown strength criterion the equivalent Mohr-Coulomb parameters (cohesion and angle of internal friction) can be calculated. The results of 3D numerical calculations (with FLA3D code) show that it is necessary to redesign the slope-bench system in the Hyttemalmen open pit. Changing slope inclination for lower stages is recommended. The minimum factor of safety should be equal 1.3. At the final planned stage of excavation, the factor of safety drops to 1.06 with failure surface ranging through all of the slopes. In the case of a slope angle 70° for lower stages, FS = 1.26, which is not enough to provide slope stability. Another series of calculations were therefore performed taking water table lowering into consideration, which increases the global safety factor. It was finally evaluated, that for a water table level of 72 m the factor of safety equals 1.3, which is enough to assure global open-pit stability.

An Empirical Examination of the Permanence of Performance and Response Patterns Generated by a CRM-Reading Produced by Expert Judgment.

ERIC Educational Resources Information Center

Hess, Richard Wayne

Stability of performance on a criterion referenced reading test was examined for 413 students in grades one through six. The test, which measures 367 behavioral reading objectives, was administered twice to each student, with an interval of at least three weeks between the first and second administrations. Three statistical indices of permanence…

Development of a Smart Diagnostics Platform for Early-Stage Screening of Breast Cancer

DTIC Science & Technology

2007-04-01

Kawaguchi, H.; Fujimoto, K. A Novel Preparation of Nonsymmetrical Microspheres Using the Langmuir Blodgett Technique. Langmuir 2000, 16, 7882–7886. 64...performance liquid chromatography, gas chromatography, mass spectrometry, and enzyme-linked immunosorbent assay. All of these methods require...important criterion for selection of suitable signal transduction systems. A 10 manuscript describing the stability has been published in Langmuir in 2007

Theoretical flow regime diagrams for the AGCE

NASA Technical Reports Server (NTRS)

Fowlis, W. W.; Miller, T. L.; Roberts, G. O.; Kopecky, K. J.

1984-01-01

The major criterion for the design of the Atmospheric General Circulation Experiment is that it be possible to realize strong baroclinic instability in the apparatus. A spherical annulus configuration which allows only steady basic state flows was chosen for the first set of stability analyses. Baroclinic instability was found for this configuration and few results suggest a regime diagram very different from the cylindrical annulus regime diagram.

RR-MR transition of a Type V shock interaction in inviscid double-wedge flow with high-temperature gas effects

NASA Astrophysics Data System (ADS)

Xiong, W.; Li, J.; Zhu, Y.; Luo, X.

2018-07-01

The transition between regular reflection (RR) and Mach reflection (MR) of a Type V shock-shock interaction on a double-wedge geometry with non-equilibrium high-temperature gas effects is investigated theoretically and numerically. A modified shock polar method that involves thermochemical non-equilibrium processes is applied to calculate the theoretical critical angles of transition based on the detachment criterion and the von Neumann criterion. Two-dimensional inviscid numerical simulations are performed correspondingly to reveal the interactive wave patterns, the transition processes, and the critical transition angles. The theoretical and numerical results of the critical transition angles are compared, which shows evident disagreement, indicating that the transition mechanism between RR and MR of a Type V shock interaction is beyond the admissible scope of the classical theory. Numerical results show that the collisions of triple points of the Type V interaction cause the transition instead. Compared with the frozen counterpart, it is found that the high-temperature gas effects lead to a larger critical transition angle and a larger hysteresis interval.

Research study for effects of case flexibility on bearing loads and rotor stability

NASA Technical Reports Server (NTRS)

Fenwick, J. R.; Tarn, R. B.

1984-01-01

Methods to evaluate the effect of casing flexibility on rotor stability and component loads were developed. Recent Rocketdyne turbomachinery was surveyed to determine typical properties and frequencies versus running speed. A small generic rotor was run with a flexible case with parametric variations in casing properties for comparison with a rotor attached to rigid supports. A program for the IBM personal computer for interactive evaluation of rotors and casings is developed. The Root locus method is extended for use in rotor dynamics for symmetrical systems by transforming all motion and coupling into a single plane and using a 90 degree criterion when plotting loci.

On thermonuclear ignition criterion at the National Ignition Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, Baolian; Kwan, Thomas J. T.; Wang, Yi-Ming

2014-10-15

Sustained thermonuclear fusion at the National Ignition Facility remains elusive. Although recent experiments approached or exceeded the anticipated ignition thresholds, the nuclear performance of the laser-driven capsules was well below predictions in terms of energy and neutron production. Such discrepancies between expectations and reality motivate a reassessment of the physics of ignition. We have developed a predictive analytical model from fundamental physics principles. Based on the model, we obtained a general thermonuclear ignition criterion in terms of the areal density and temperature of the hot fuel. This newly derived ignition threshold and its alternative forms explicitly show the minimum requirementsmore » of the hot fuel pressure, mass, areal density, and burn fraction for achieving ignition. Comparison of our criterion with existing theories, simulations, and the experimental data shows that our ignition threshold is more stringent than those in the existing literature and that our results are consistent with the experiments.« less

Hot-air forming of Al-Mg-Cr alloy and prediction of failure based on Zener-Holloman parameter

NASA Astrophysics Data System (ADS)

Kim, W. J.; Kim, W. Y.; Kim, H. K.

2010-12-01

The microstructure of an Al-Mg-Cr alloy tube fabricated through indirect extrusion at 673 K showed elongated grains with a mean size of ˜26 μm. The strain rate-stress relationship at high temperatures (753 K to 793 K) revealed that dislocation climb creep was the rate-controlling deformation mechanism. The hot-air forming process was successful at a pressure of 70 bar. The Zener-Hollomon parameter based failure criterion was 3602+, and was used to explain the failure behavior of a deforming body. The forming and fracture behavior of the Al-Mg-Cr alloy tube was analyzed with the aid of finite element (FE) simulation, into which the failure criterion was incorporated. Comparison of the simulation and the experimental results indicated that the proposed fracture criterion was useful in predicting the fracture behavior of aluminum tube deforming by means of gas pressure.

Adequacy of the Ultra-Short-Term HRV to Assess Adaptive Processes in Youth Female Basketball Players.

PubMed

Nakamura, Fabio Y; Pereira, Lucas A; Cal Abad, Cesar C; Cruz, Igor F; Flatt, Andrew A; Esco, Michael R; Loturco, Irineu

2017-02-01

Heart rate variability has been widely used to monitor athletes' cardiac autonomic control changes induced by training and competition, and recently shorter recording times have been sought to improve its practicality. The aim of this study was to test the agreement between the (ultra-short-term) natural log of the root-mean-square difference of successive normal RR intervals (lnRMSSD - measured in only 1 min post-1 min stabilization) and the criterion lnRMSSD (measured in the last 5 min out of 10 min of recording) in young female basketball players. Furthermore, the correlation between training induced delta change in the ultra-short-term lnRMSSD and the criterion lnRMSSD was calculated. Seventeen players were assessed at rest pre- and post-eight weeks of training. Trivial effect sizes (-0.03 in the pre- and 0.10 in the post- treatment) were found in the comparison between the ultra-short-term lnRMSSD (3.29 ± 0.45 and 3.49 ± 0.35 ms, in the pre- and post-, respectively) and the criterion lnRMSSD (3.30 ± 0.40 and 3.45 ± 0.41 ms, in the pre- and post-, respectively) (intraclass correlation coefficient = 0.95 and 0.93). In both cases, the response to training was significant, with Pearson's correlation of 0.82 between the delta changes of the ultra-short-term lnRMSSD and the criterion lnRMSSD. In conclusion, the lnRMSSD can be calculated within only 2 min of data acquisition (the 1 st min discarded) in young female basketball players, with the ultra-short-term measure presenting similar sensitivity to training effects as the standard criterion measure.

Adequacy of the Ultra-Short-Term HRV to Assess Adaptive Processes in Youth Female Basketball Players

PubMed Central

Nakamura, Fabio Y; Pereira, Lucas A; Cal Abad, Cesar C; Cruz, Igor F; Flatt, Andrew A; Esco, Michael R; Loturco, Irineu

2017-01-01

Abstract Heart rate variability has been widely used to monitor athletes’ cardiac autonomic control changes induced by training and competition, and recently shorter recording times have been sought to improve its practicality. The aim of this study was to test the agreement between the (ultra-short-term) natural log of the root-mean-square difference of successive normal RR intervals (lnRMSSD - measured in only 1 min post-1 min stabilization) and the criterion lnRMSSD (measured in the last 5 min out of 10 min of recording) in young female basketball players. Furthermore, the correlation between training induced delta change in the ultra-short-term lnRMSSD and the criterion lnRMSSD was calculated. Seventeen players were assessed at rest pre- and post-eight weeks of training. Trivial effect sizes (-0.03 in the pre- and 0.10 in the post- treatment) were found in the comparison between the ultra-short-term lnRMSSD (3.29 ± 0.45 and 3.49 ± 0.35 ms, in the pre- and post-, respectively) and the criterion lnRMSSD (3.30 ± 0.40 and 3.45 ± 0.41 ms, in the pre- and post-, respectively) (intraclass correlation coefficient = 0.95 and 0.93). In both cases, the response to training was significant, with Pearson’s correlation of 0.82 between the delta changes of the ultra-short-term lnRMSSD and the criterion lnRMSSD. In conclusion, the lnRMSSD can be calculated within only 2 min of data acquisition (the 1st min discarded) in young female basketball players, with the ultra-short-term measure presenting similar sensitivity to training effects as the standard criterion measure. PMID:28469745

Risk analysis of gravity dam instability using credibility theory Monte Carlo simulation model.

PubMed

Xin, Cao; Chongshi, Gu

2016-01-01

Risk analysis of gravity dam stability involves complicated uncertainty in many design parameters and measured data. Stability failure risk ratio described jointly by probability and possibility has deficiency in characterization of influence of fuzzy factors and representation of the likelihood of risk occurrence in practical engineering. In this article, credibility theory is applied into stability failure risk analysis of gravity dam. Stability of gravity dam is viewed as a hybrid event considering both fuzziness and randomness of failure criterion, design parameters and measured data. Credibility distribution function is conducted as a novel way to represent uncertainty of influence factors of gravity dam stability. And combining with Monte Carlo simulation, corresponding calculation method and procedure are proposed. Based on a dam section, a detailed application of the modeling approach on risk calculation of both dam foundation and double sliding surfaces is provided. The results show that, the present method is feasible to be applied on analysis of stability failure risk for gravity dams. The risk assessment obtained can reflect influence of both sorts of uncertainty, and is suitable as an index value.

Magnetodynamic stability of a fluid cylinder under the Lundquist force-free magnetic field

NASA Astrophysics Data System (ADS)

Radwan, Ahmed E.; Halawa, Mohamed A.

1990-04-01

The magnetodynamic (in)stability of a conducting fluid cylinder subject to the capillarity and electromagnetic forces has been developed. The cylinder is pervaded by a uniform magnetic field but embedded in the Lundquist force-free varying field that allows for flowing a current surrounding the fluid. A general eigenvalue relation is derived based on a study of the equilibrium and perturbed states. The stability criterion is discussed analytically in general terms. The surface tension is destabilizing for small axisymmetric mode and stable for all others. The principle of the exchange of stability is allowed for the present problem due to the non-uniform behavior of the force-free field. Each of the axial and transverse force-free fields separately exerts a stabilizing influence in the most dangerous mode but the combined contribution of them is strongly destabilizing. Whether the model is acted upon the electromagnetic force (with the Lundquist field) the stability restrictions or/and the capillarity force are identified. Several reported works can be recovered as limiting cases with appropriate simplifications.

Cold weather paving requirements for bituminous concrete.

DOT National Transportation Integrated Search

1973-01-01

Cold weather paving specifications were developed from work by Corlew and Dickson, who used a computer solution to predict the cooling rate of bituminous concrete. Virginia had used a minimum atmospheric temperature as a criterion; however, it was ev...

The "critical limits for crystallinity" in nanoparticles of the elements: A combined thermodynamic and crystallographic critique

NASA Astrophysics Data System (ADS)

Pelegrina, J. L.; Guillermet, A. Fernández

2018-03-01

The theme of the present work is the procedure for evaluating the minimum size for the stability of a crystalline particle with respect to the same group of atoms but in the amorphous state. A key goal of the study is the critical analysis of an extensively quoted paper by F.G. Shi [J. Mater. Res. 9 (1994) 1307-1313], who presented a criterion for evaluating a "crystallinity distance" (h) through its relation with the "critical diameter" (dC) of a particle, i.e., the diameter below which no particles with the crystalline structure are expected to exist at finite temperatures. Key assumptions of Shi's model are a direct proportionality relation between h and dC , and a prescription for estimating h from crystallographic information. In the present work the accuracy of the Shi model is assessed with particular reference to nanoparticles of the elements. To this end, an alternative way to obtain h, that better realizes Shi's idea of this quantity as "the height of a monolayer of atoms on the bulk crystal surface", is explored. Moreover, a thermodynamic calculation of dC , which involves a description of the bulk- and the surface contributions to the crystalline/amorphous relative phase stability for nanoparticles, is performed. It is shown that the Shi equation does not account for the key features of the h vs. dC relation established in the current work. Consequently, it is concluded that the parameter h obtained only from information about the structure of the crystalline phase, does not provide an accurate route to estimate the quantity dC . In fact, a key result of the current study is that dC crucially depends on the relation between bulk- and surface contributions to the crystalline/amorphous relative thermodynamic stability.

Reducing the Ideal Shear Strengths of ZrB2 by High Efficient Alloying Elements (Ag, Au, Pd and Pt)

NASA Astrophysics Data System (ADS)

Dai, Fu-Zhi; Zhou, Yanchun

2017-02-01

Activating the plasticity of ZrB2 is a promising approach to improve its key properties for applications in hypersonic vehicles, including high temperature strength and thermal shock resistance. The present work demonstrates that ideal shear strength of ZrB2, which is a good indicator of the critical stress for dislocation nucleation, can be significantly reduced by dissolving of appropriate alloying elements. Analyzing on the bonding nature of ZrB2 reveals that choosing alloying elements with low energy valence electrons will prevent electron transferring from alloying element to the electron deficient B-B π orbits, which will reduce the local stability of the region surrounding the alloying element. Under the criterion, elements with d electrons tending to be full-filled (Ag, Au, Pd and Pt, the full-filled state is associated with low energy level) are selected as promising candidates with their prominent efficiency in reducing ideal shear strengths verified by first-principles calculations. The results provide useful guidelines for further designs of ZrB2 based materials, especially for improving their mechanical properties.

Reducing the Ideal Shear Strengths of ZrB2 by High Efficient Alloying Elements (Ag, Au, Pd and Pt)

PubMed Central

Dai, Fu-Zhi; Zhou, Yanchun

2017-01-01

Activating the plasticity of ZrB2 is a promising approach to improve its key properties for applications in hypersonic vehicles, including high temperature strength and thermal shock resistance. The present work demonstrates that ideal shear strength of ZrB2, which is a good indicator of the critical stress for dislocation nucleation, can be significantly reduced by dissolving of appropriate alloying elements. Analyzing on the bonding nature of ZrB2 reveals that choosing alloying elements with low energy valence electrons will prevent electron transferring from alloying element to the electron deficient B-B π orbits, which will reduce the local stability of the region surrounding the alloying element. Under the criterion, elements with d electrons tending to be full-filled (Ag, Au, Pd and Pt, the full-filled state is associated with low energy level) are selected as promising candidates with their prominent efficiency in reducing ideal shear strengths verified by first-principles calculations. The results provide useful guidelines for further designs of ZrB2 based materials, especially for improving their mechanical properties. PMID:28233838

Reducing the Ideal Shear Strengths of ZrB2 by High Efficient Alloying Elements (Ag, Au, Pd and Pt).

PubMed

Dai, Fu-Zhi; Zhou, Yanchun

2017-02-24

Activating the plasticity of ZrB 2 is a promising approach to improve its key properties for applications in hypersonic vehicles, including high temperature strength and thermal shock resistance. The present work demonstrates that ideal shear strength of ZrB 2 , which is a good indicator of the critical stress for dislocation nucleation, can be significantly reduced by dissolving of appropriate alloying elements. Analyzing on the bonding nature of ZrB 2 reveals that choosing alloying elements with low energy valence electrons will prevent electron transferring from alloying element to the electron deficient B-B π orbits, which will reduce the local stability of the region surrounding the alloying element. Under the criterion, elements with d electrons tending to be full-filled (Ag, Au, Pd and Pt, the full-filled state is associated with low energy level) are selected as promising candidates with their prominent efficiency in reducing ideal shear strengths verified by first-principles calculations. The results provide useful guidelines for further designs of ZrB 2 based materials, especially for improving their mechanical properties.

Stochastic subspace identification for operational modal analysis of an arch bridge

NASA Astrophysics Data System (ADS)

Loh, Chin-Hsiung; Chen, Ming-Che; Chao, Shu-Hsien

2012-04-01

In this paer the application of output-only system identification technique, known as Stochastic Subspace Identification (SSI) algorithms, for civil infrastructures is carried out. The ability of covariance driven stochastic subspace identification (SSI-COV) was proved through the analysis of the ambient data of an arch bridge under operational condition. A newly developed signal processing technique, Singular Spectrum analysis (SSA), capable to smooth noisy signals, is adopted for pre-processing the recorded data before the SSI. The conjunction of SSA and SSICOV provides a useful criterion for the system order determination. With the aim of estimating accurate modal parameters of the structure in off-line analysis, a stabilization diagram is constructed by plotting the identified poles of the system with increasing the size of data Hankel matrix. Identification task of a real structure, Guandu Bridge, is carried out to identify the system natural frequencies and mode shapes. The uncertainty of the identified model parameters from output-only measurement of the bridge under operation condition, such as temperature and traffic loading conditions, is discussed.

Electric flux tube in a magnetic plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liao Jinfeng; Shuryak, Edward

2008-06-15

In this paper we study a methodical problem related to the magnetic scenario recently suggested and initiated by Liao and Shuryak [Phys. Rev. C 75, 054907 (2007)] to understand the strongly coupled quark-gluon plasma (sQGP): the electric flux tube in a monopole plasma. A macroscopic approach, in which we interpolate between a Bose condensed (dual superconductor) medium and a classical gas medium, is developed first. Then we work out a microscopic approach based on detailed quantum mechanical calculations of the monopole scattering on the electric flux tube, evaluating induced currents for all partial waves. As expected, the flux tube losesmore » its stability when particles can penetrate it: We make this condition precise by calculating the critical value for the product of the flux tube size times the particle momentum, above which the flux tube dissolves. Lattice static potentials indicate that flux tubes seem to dissolve at T>T{sub dissolution}{approx_equal}1.3T{sub c}. Using our criterion one gets an estimate of the magnetic density n{approx_equal}4.4-6.6 fm{sup -3} at this temperature.« less

Analysis of neighborhood behavior in lead optimization and array design.

PubMed

Papadatos, George; Cooper, Anthony W J; Kadirkamanathan, Visakan; Macdonald, Simon J F; McLay, Iain M; Pickett, Stephen D; Pritchard, John M; Willett, Peter; Gillet, Valerie J

2009-02-01

Neighborhood behavior describes the extent to which small structural changes defined by a molecular descriptor are likely to lead to small property changes. This study evaluates two methods for the quantification of neighborhood behavior: the optimal diagonal method of Patterson et al. and the optimality criterion method of Horvath and Jeandenans. The methods are evaluated using twelve different types of fingerprint (both 2D and 3D) with screening data derived from several lead optimization projects at GlaxoSmithKline. The principal focus of the work is the design of chemical arrays during lead optimization, and the study hence considers not only biological activity but also important drug properties such as metabolic stability, permeability, and lipophilicity. Evidence is provided to suggest that the optimality criterion method may provide a better quantitative description of neighborhood behavior than the optimal diagonal method.

Validity of Devices That Assess Body Temperature During Outdoor Exercise in the Heat

PubMed Central

Casa, Douglas J; Becker, Shannon M; Ganio, Matthew S; Brown, Christopher M; Yeargin, Susan W; Roti, Melissa W; Siegler, Jason; Blowers, Julie A; Glaviano, Neal R; Huggins, Robert A; Armstrong, Lawrence E; Maresh, Carl M

2007-01-01

Context: Rectal temperature is recommended by the National Athletic Trainers' Association as the criterion standard for recognizing exertional heat stroke, but other body sites commonly are used to measure temperature. Few authors have assessed the validity of the thermometers that measure body temperature at these sites in athletic settings. Objective: To assess the validity of commonly used temperature devices at various body sites during outdoor exercise in the heat. Design: Observational field study. Setting: Outdoor athletic facilities. Patients or Other Participants: Fifteen men and 10 women (age = 26.5 ± 5.3 years, height = 174.3 ± 11.1 cm, mass = 72.73 ± 15.95 kg, body fat = 16.2 ± 5.5%). Intervention(s): We simultaneously tested inexpensive and expensive devices orally and in the axillary region, along with measures of aural, gastrointestinal, forehead, temporal, and rectal temperatures. Temporal temperature was measured according to the instruction manual and a modified method observed in medical tents at local road races. We also measured forehead temperatures directly on the athletic field (other measures occurred in a covered pavilion) where solar radiation was greater. Rectal temperature was the criterion standard used to assess the validity of all other devices. Subjects' temperatures were measured before exercise, every 60 minutes during 180 minutes of exercise, and every 20 minutes for 60 minutes of postexercise recovery. Temperature devices were considered invalid if the mean bias (average difference between rectal temperature and device temperature) was greater than ±0.27°C (±0.5°F). Main Outcome Measure(s): Temperature from each device at each site and time point. Results: Mean bias for the following temperatures was greater than the allowed limit of ±0.27°C (±0.5°F): temperature obtained via expensive oral device (−1.20°C [−2.17°F]), inexpensive oral device (−1.67°C [−3.00°F]), expensive axillary device (−2.58°C [−4.65°F]), inexpensive axillary device (−2.07°C [−3.73°F]), aural method (−1.00°C [−1.80°F]), temporal method according to instruction manual (−1.46°C [−2.64°F]), modified temporal method (−1.36°C [−2.44°F]), and forehead temperature on the athletic field (0.60°C [1.08°F]). Mean bias for gastrointestinal temperature (−0.19°C [−0.34°F]) and forehead temperature in the pavillion (−0.14°C [−0.25°F]) was less than the allowed limit of ±0.27°C (±0.5°F). Forehead temperature depended on the setting in which it was measured and showed greater variation than other temperatures. Conclusions: Compared with rectal temperature (the criterion standard), gastrointestinal temperature was the only measurement that accurately assessed core body temperature. Oral, axillary, aural, temporal, and field forehead temperatures were significantly different from rectal temperature and, therefore, are considered invalid for assessing hyperthermia in individuals exercising outdoors in the heat. PMID:18059987

Composition dependent structural and optical properties of PbF₂-TeO₂-B₂O₃-Eu₂O₃ glasses.

PubMed

Wagh, Akshatha; Raviprakash, Y; Upadhyaya, Vyasa; Kamath, Sudha D

2015-12-05

Boric oxide based quaternary glasses in the system PbF2-TeO2-B2O3-Eu2O3 have been prepared by melt quenching technique. Density, molar volume, FTIR, UV-Vis techniques were used to probe the structural modifications with incorporation of europium ions in the glass network. An increase in glass density & decrease in molar volume (Vm) values proved the structural changes occurring in coordination of boron atom [conversion of BO3 units to BO4]. This resulted in the increase of the compaction of the prepared glasses with increase in Eu2O3 contents. The amorphous natures of the samples were ascertained by XRD and metallization criterion (M) studies. XPS study showed the values of core-level binding energy [O1s, Eu3d, Eu4d, Te3d, Te4d, Pd4f, Pb5d, O1s, and F1s] of (PbF2-TeO2-B2O3-Eu2O3) the glass matrix. The frequency and temperature dependence of dielectric properties of present glasses were investigated in the frequency range of 1 Hz-10 MHz and temperature range of 313-773K. The study of dielectric measurements proved good insulating and thermal stability of the prepared glasses. At room temperature, dielectric loss [tanδ] values were negligibly small for prepared glasses and increased with increase in temperature. FTIR spectroscopy results were in good agreement with optical band energy gap, density, molar volume and hardness values revealing network modifications caused by europium ions in the glass structure. Copyright © 2015 Elsevier B.V. All rights reserved.

Hierarchical Type Stability Criteria for Delayed Neural Networks via Canonical Bessel-Legendre Inequalities.

PubMed

Zhang, Xian-Ming; Han, Qing-Long; Zeng, Zhigang

2018-05-01

This paper is concerned with global asymptotic stability of delayed neural networks. Notice that a Bessel-Legendre inequality plays a key role in deriving less conservative stability criteria for delayed neural networks. However, this inequality is in the form of Legendre polynomials and the integral interval is fixed on . As a result, the application scope of the Bessel-Legendre inequality is limited. This paper aims to develop the Bessel-Legendre inequality method so that less conservative stability criteria are expected. First, by introducing a canonical orthogonal polynomial sequel, a canonical Bessel-Legendre inequality and its affine version are established, which are not explicitly in the form of Legendre polynomials. Moreover, the integral interval is shifted to a general one . Second, by introducing a proper augmented Lyapunov-Krasovskii functional, which is tailored for the canonical Bessel-Legendre inequality, some sufficient conditions on global asymptotic stability are formulated for neural networks with constant delays and neural networks with time-varying delays, respectively. These conditions are proven to have a hierarchical feature: the higher level of hierarchy, the less conservatism of the stability criterion. Finally, three numerical examples are given to illustrate the efficiency of the proposed stability criteria.

Multiscale implementation of infinite-swap replica exchange molecular dynamics.

PubMed

Yu, Tang-Qing; Lu, Jianfeng; Abrams, Cameron F; Vanden-Eijnden, Eric

2016-10-18

Replica exchange molecular dynamics (REMD) is a popular method to accelerate conformational sampling of complex molecular systems. The idea is to run several replicas of the system in parallel at different temperatures that are swapped periodically. These swaps are typically attempted every few MD steps and accepted or rejected according to a Metropolis-Hastings criterion. This guarantees that the joint distribution of the composite system of replicas is the normalized sum of the symmetrized product of the canonical distributions of these replicas at the different temperatures. Here we propose a different implementation of REMD in which (i) the swaps obey a continuous-time Markov jump process implemented via Gillespie's stochastic simulation algorithm (SSA), which also samples exactly the aforementioned joint distribution and has the advantage of being rejection free, and (ii) this REMD-SSA is combined with the heterogeneous multiscale method to accelerate the rate of the swaps and reach the so-called infinite-swap limit that is known to optimize sampling efficiency. The method is easy to implement and can be trivially parallelized. Here we illustrate its accuracy and efficiency on the examples of alanine dipeptide in vacuum and C-terminal β-hairpin of protein G in explicit solvent. In this latter example, our results indicate that the landscape of the protein is a triple funnel with two folded structures and one misfolded structure that are stabilized by H-bonds.

Viscosity and viscoelasticity of two-phase systems having diffuse interfaces

NASA Technical Reports Server (NTRS)

Hopper, R. W.

1976-01-01

The equilibrium stability criterion for diffuse interfaces in a two-component solution with a miscibility gap requires that the interdiffusion flux vanish. If the system is continuously deformed, convective fluxes disrupt the equilibrium in the interface regions and induce a counter diffusive flux, which is dissipative and contributes to the apparent viscosity of the mixture. Chemical free energy is recoverably stored, causing viscoelastic phenomena. Both effects are significant.

Mesoscale Modeling of Dynamic Compression of Boron Carbide Polycrystals

DTIC Science & Technology

2013-05-01

reported later. Recrystallization has not been reported in the literature and is precluded by the model, meaning : 0 →1 is irreversible. Following...average HEL, above which a measurable strength loss is evident (Vogler et al., 2004), though amorphization has not been definitively proven to cause... definition (A.7) is exact when ı2 E→ 0 (Clayton, 2012). This criterion agrees exactly with that for classical stability under hydrostatic loading

Matter-wave two-dimensional solitons in crossed linear and nonlinear optical lattices

NASA Astrophysics Data System (ADS)

da Luz, H. L. F.; Abdullaev, F. Kh.; Gammal, A.; Salerno, M.; Tomio, Lauro

2010-10-01

The existence of multidimensional matter-wave solitons in a crossed optical lattice (OL) with a linear optical lattice (LOL) in the x direction and a nonlinear optical lattice (NOL) in the y direction, where the NOL can be generated by a periodic spatial modulation of the scattering length using an optically induced Feshbach resonance is demonstrated. In particular, we show that such crossed LOLs and NOLs allow for stabilizing two-dimensional solitons against decay or collapse for both attractive and repulsive interactions. The solutions for the soliton stability are investigated analytically, by using a multi-Gaussian variational approach, with the Vakhitov-Kolokolov necessary criterion for stability; and numerically, by using the relaxation method and direct numerical time integrations of the Gross-Pitaevskii equation. Very good agreement of the results corresponding to both treatments is observed.

Stabilization for sampled-data neural-network-based control systems.

PubMed

Zhu, Xun-Lin; Wang, Youyi

2011-02-01

This paper studies the problem of stabilization for sampled-data neural-network-based control systems with an optimal guaranteed cost. Unlike previous works, the resulting closed-loop system with variable uncertain sampling cannot simply be regarded as an ordinary continuous-time system with a fast-varying delay in the state. By defining a novel piecewise Lyapunov functional and using a convex combination technique, the characteristic of sampled-data systems is captured. A new delay-dependent stabilization criterion is established in terms of linear matrix inequalities such that the maximal sampling interval and the minimal guaranteed cost control performance can be obtained. It is shown that the newly proposed approach can lead to less conservative and less complex results than the existing ones. Application examples are given to illustrate the effectiveness and the benefits of the proposed method.

Is pervasive developmental disorder not otherwise specified less stable than autistic disorder? A meta-analysis.

PubMed

Rondeau, Emélie; Klein, Leslie S; Masse, André; Bodeau, Nicolas; Cohen, David; Guilé, Jean-Marc

2011-09-01

We reviewed the stability of the diagnosis of pervasive developmental disorder not otherwise specified (PDD-NOS). A Medline search found eight studies reiterating a diagnostic assessment for PDD-NOS. The pooled group included 322 autistic disorder (AD) and 122 PDD-NOS cases. We used percentage of individuals with same diagnose at Times 1 and 2 as response criterion. The pooled Relative Risk was 1.95 (p < 0.001) showing that AD diagnostic stability was higher than PDD-NOS. When diagnosed before 36 months PDD-NOS bore a 3-year stability rate of 35%. Examining the developmental trajectories showed that PDD-NOS corresponded to a group of heterogeneous pathological conditions including prodromic forms of later AD, remitted or less severe forms of AD, and developmental delays in interaction and communication.

Polymer Stabilization of Liquid-Crystal Blue Phase II toward Photonic Crystals.

PubMed

Jo, Seong-Yong; Jeon, Sung-Wook; Kim, Byeong-Cheon; Bae, Jae-Hyun; Araoka, Fumito; Choi, Suk-Won

2017-03-15

The temperature ranges where a pure simple-cubic blue phase (BPII) emerges are quite narrow compared to the body-centered-cubic BP (BPI) such that the polymer stabilization of BPII is much more difficult. Hence, a polymer-stabilized BPII possessing a wide temperature range has been scarcely reported. Here, we fabricate a polymer-stabilized BPII over a temperature range of 50 °C including room temperature. The fabricated polymer-stabilized BPII is confirmed via polarized optical microscopy, Bragg reflection, and Kossel diagram observations. Furthermore, we demonstrate reflective BP liquid-crystal devices utilizing the reflectance-voltage performance as a potential application of the polymer-stabilized BPII. Our work demonstrates the possibility of practical application of the polymer-stabilized BPII to photonic crystals.

Nursing Intensive-Care Satisfaction Scale [NICSS]: Development and validation of a patient-centred instrument.

PubMed

Romero-García, Marta; de la Cueva-Ariza, Laura; Benito-Aracil, Llucia; Lluch-Canut, Teresa; Trujols-Albet, Joan; Martínez-Momblan, Maria Antonia; Juvé-Udina, Maria-Eulàlia; Delgado-Hito, Pilar

2018-06-01

The aim of this study was to develop and validate the Nursing Intensive-Care Satisfaction Scale to measures satisfaction with nursing care from the critical care patient's perspective. Instruments that measure satisfaction with nursing cares have been designed and validated without taking the patient's perspective into consideration. Despite the benefits and advances in measuring satisfaction with nursing care, none instrument is specifically designed to assess satisfaction in intensive care units. Instrument development. The population were all discharged patients (January 2013 - January 2015) from three Intensive Care Units of a third level hospital (N = 200). All assessment instruments were given to discharged patients and 48 hours later, to analyse the temporal stability, only the questionnaire was given again. The validation process of the scale included the analysis of internal consistency, temporal stability; validity of construct through a confirmatory factor analysis; and criterion validity. Reliability was 0.95. The intraclass correlation coefficient for the total scale was 0.83 indicating a good temporal stability. Construct validity showed an acceptable fit and factorial structure with four factors, in accordance with the theoretical model, being Consequences factor the best correlated with other factors. Criterion validity, presented a correlation between low and high (range: 0.42-0.68). The scale has been designed and validated incorporating the perspective of critical care patients. Thanks to its reliability and validity, this questionnaire can be used both in research and in clinical practice. The scale offers a possibility to assess and develop interventions to improve patient satisfaction with nursing care. © 2018 John Wiley & Sons Ltd.

Kinematic evaluation of the classical ballet step "plié".

PubMed

Gontijo, Kaanda Nabilla Souza; Candotti, Cláudia Tarragô; Feijó, Grace Dos Santos; Ribeiro, Lais Paixão; Loss, Jefferson Fagundes

2015-06-01

Lack of alignment between the lowerlimb structures, such as the hips, knees, and longitudinal arches of the feet, has been described as an important predisposing factor in musculoskeletal injury among classical ballet dancers. However, no studies were found that analyzed basic ballet movements with quantification of objective criteria of the movements. The purposes of this study were: 1. to establish a methodology to quantify, using kinematic evaluation, the technical criteria that guide the correct execution of all phases of the plié (simultaneous flexion of the hips, knees, and ankle joints); and 2. to explore whether experienced ballet dancers respect those criteria when performing the plié. The technical criteria considered were the following: 1. midfoot stability; 2. pelvic positioning in a neutral alignment; 3. pelvic stability, represented by pelvic angle variation; and 4. vertical alignment of the knee joint with the second toe of the ipsilateral foot. Twenty dancers from Porto Alegre, Brazil, with 18 years of uninterrupted ballet training, were filmed while performing plié using four synchronized cameras. The descriptive statistical analysis involved calculating the median, minimum, and maximum of each of the technical criteria. Results showed that for criterion 1, the 20 dancers showed great stabilization of the midfoot; for criteria 2 and 3, 18 dancers displayed pelvic instability tending toward retroversion throughout execution of the plié; and for criterion 4, 13 dancers presented with medial misalignment of the knees at all phases of the plié. Using these criteria, it was possible to characterize the plié from a kinematic point of view.

The H2/CH4 ratio during serpentinization cannot reliably identify biological signatures

NASA Astrophysics Data System (ADS)

Huang, Ruifang; Sun, Weidong; Liu, Jinzhong; Ding, Xing; Peng, Shaobang; Zhan, Wenhuan

2016-09-01

Serpentinization potentially contributes to the origin and evolution of life during early history of the Earth. Serpentinization produces molecular hydrogen (H2) that can be utilized by microorganisms to gain metabolic energy. Methane can be formed through reactions between molecular hydrogen and oxidized carbon (e.g., carbon dioxide) or through biotic processes. A simple criterion, the H2/CH4 ratio, has been proposed to differentiate abiotic from biotic methane, with values approximately larger than 40 for abiotic methane and values of <40 for biotic methane. The definition of the criterion was based on two serpentinization experiments at 200 °C and 0.3 kbar. However, it is not clear whether the criterion is applicable at a wider range of temperatures. In this study, we performed sixteen experiments at 311-500 °C and 3.0 kbar using natural ground peridotite. Our results demonstrate that the H2/CH4 ratios strongly depend on temperature. At 311 °C and 3.0 kbar, the H2/CH4 ratios ranged from 58 to 2,120, much greater than the critical value of 40. By contrast, at 400-500 °C, the H2/CH4 ratios were much lower, ranging from 0.1 to 8.2. The results of this study suggest that the H2/CH4 ratios cannot reliably discriminate abiotic from biotic methane.

The H2/CH4 ratio during serpentinization cannot reliably identify biological signatures.

PubMed

Huang, Ruifang; Sun, Weidong; Liu, Jinzhong; Ding, Xing; Peng, Shaobang; Zhan, Wenhuan

2016-09-26

Serpentinization potentially contributes to the origin and evolution of life during early history of the Earth. Serpentinization produces molecular hydrogen (H 2 ) that can be utilized by microorganisms to gain metabolic energy. Methane can be formed through reactions between molecular hydrogen and oxidized carbon (e.g., carbon dioxide) or through biotic processes. A simple criterion, the H 2 /CH 4 ratio, has been proposed to differentiate abiotic from biotic methane, with values approximately larger than 40 for abiotic methane and values of <40 for biotic methane. The definition of the criterion was based on two serpentinization experiments at 200 °C and 0.3 kbar. However, it is not clear whether the criterion is applicable at a wider range of temperatures. In this study, we performed sixteen experiments at 311-500 °C and 3.0 kbar using natural ground peridotite. Our results demonstrate that the H 2 /CH 4 ratios strongly depend on temperature. At 311 °C and 3.0 kbar, the H 2 /CH 4 ratios ranged from 58 to 2,120, much greater than the critical value of 40. By contrast, at 400-500 °C, the H 2 /CH 4 ratios were much lower, ranging from 0.1 to 8.2. The results of this study suggest that the H 2 /CH 4 ratios cannot reliably discriminate abiotic from biotic methane.

Fabrication of long-term stable superoleophobic surface based on copper oxide/cobalt oxide with micro-nanoscale hierarchical roughness

NASA Astrophysics Data System (ADS)

Barthwal, Sumit; Lim, Si-Hyung

2015-02-01

We have demonstrated a simple and cost-effective technique for the large-area fabrication of a superoleophobic surface using copper as a substrate. The whole process included three simple steps: First, the copper substrate was oxidized under hot alkaline conditions to fabricate flower-like copper oxide microspheres by heating at a particular temperature for an interval of time. Second, the copper-oxide-covered copper substrate was further heated in a solution of cobalt nitrate and ammonium nitrate in the presence of an ammonia solution to fabricate cobalt oxide nanostructures. We applied this second step to increase the surface roughness because it is an important criterion for improved superoleophobicity. Finally, to reduce the surface energy of the fabricated structures, the surfaces were chemically modified with perfluorooctyltrichlorosilane. Contact-angle measurements indicate that the micro-nano binary (MNB) hierarchical structures fabricated on the copper substrate became super-repellent toward a broad range of liquids with surface tension in the range of 21.5-72 mN/m. In an attempt to significantly improve the superoleophobic property of the surface, we also examined and compared the role of nanostructures in MNB hierarchical structures with only micro-fabricated surfaces. The fabricated MNB hierarchical structures also displays thermal stability and excellent long-term stability after exposure in air for more than 9 months. Our method might provide a general route toward the preparation of novel hierarchical films on metal substrates for various industrial applications.

Noise performance of frequency modulation Kelvin force microscopy

PubMed Central

Deresmes, Dominique; Mélin, Thierry

2014-01-01

Summary Noise performance of a phase-locked loop (PLL) based frequency modulation Kelvin force microscope (FM-KFM) is assessed. Noise propagation is modeled step by step throughout the setup using both exact closed loop noise gains and an approximation known as “noise gain” from operational amplifier (OpAmp) design that offers the advantage of decoupling the noise performance study from considerations of stability and ideal loop response. The bandwidth can be chosen depending on how much noise is acceptable and it is shown that stability is not an issue up to a limit that will be discussed. With thermal and detector noise as the only sources, both approaches yield PLL frequency noise expressions equal to the theoretical value for self-oscillating circuits and in agreement with measurement, demonstrating that the PLL components neither modify nor contribute noise. Kelvin output noise is then investigated by modeling the surrounding bias feedback loop. A design rule is proposed that allows choosing the AC modulation frequency for optimized sharing of the PLL bandwidth between Kelvin and topography loops. A crossover criterion determines as a function of bandwidth, temperature and probe parameters whether thermal or detector noise is the dominating noise source. Probe merit factors for both cases are then established, suggesting how to tackle noise performance by probe design. Typical merit factors of common probe types are compared. This comprehensive study is an encouraging step toward a more integral performance assessment and a remedy against focusing on single aspects and optimizing around randomly chosen key values. PMID:24455457

The Onset of Double Diffusive Convection in a Viscoelastic Fluid-Saturated Porous Layer with Non-Equilibrium Model

PubMed Central

Yang, Zhixin; Wang, Shaowei; Zhao, Moli; Li, Shucai; Zhang, Qiangyong

2013-01-01

The onset of double diffusive convection in a viscoelastic fluid-saturated porous layer is studied when the fluid and solid phase are not in local thermal equilibrium. The modified Darcy model is used for the momentum equation and a two-field model is used for energy equation each representing the fluid and solid phases separately. The effect of thermal non-equilibrium on the onset of double diffusive convection is discussed. The critical Rayleigh number and the corresponding wave number for the exchange of stability and over-stability are obtained, and the onset criterion for stationary and oscillatory convection is derived analytically and discussed numerically. PMID:24312193

The onset of double diffusive convection in a viscoelastic fluid-saturated porous layer with non-equilibrium model.

PubMed

Yang, Zhixin; Wang, Shaowei; Zhao, Moli; Li, Shucai; Zhang, Qiangyong

2013-01-01

The onset of double diffusive convection in a viscoelastic fluid-saturated porous layer is studied when the fluid and solid phase are not in local thermal equilibrium. The modified Darcy model is used for the momentum equation and a two-field model is used for energy equation each representing the fluid and solid phases separately. The effect of thermal non-equilibrium on the onset of double diffusive convection is discussed. The critical Rayleigh number and the corresponding wave number for the exchange of stability and over-stability are obtained, and the onset criterion for stationary and oscillatory convection is derived analytically and discussed numerically.

Calculation of strained BaTiO3 with different exchange correlation functionals examined with criterion by Ginzburg-Landau theory, uncovering expressions by crystallographic parameters

NASA Astrophysics Data System (ADS)

Watanabe, Yukio

2018-05-01

In the calculations of tetragonal BaTiO3, some exchange-correlation (XC) energy functionals such as local density approximation (LDA) have shown good agreement with experiments at room temperature (RT), e.g., spontaneous polarization (PS), and superiority compared with other XC functionals. This is due to the error compensation of the RT effect and, hence, will be ineffective in the heavily strained case such as domain boundaries. Here, ferroelectrics under large strain at RT are approximated as those at 0 K because the strain effect surpasses the RT effects. To find effective XC energy functionals for strained BaTiO3, we propose a new comparison, i.e., a criterion. This criterion is the properties at 0 K given by the Ginzburg-Landau (GL) theory because GL theory is a thermodynamic description of experiments working under the same symmetry-constraints as ab initio calculations. With this criterion, we examine LDA, generalized gradient approximations (GGA), meta-GGA, meta-GGA + local correlation potential (U), and hybrid functionals, which reveals the high accuracy of some XC functionals superior to XC functionals that have been regarded as accurate. This result is examined directly by the calculations of homogenously strained tetragonal BaTiO3, confirming the validity of the new criterion. In addition, the data points of theoretical PS vs. certain crystallographic parameters calculated with different XC functionals are found to lie on a single curve, despite their wide variations. Regarding these theoretical data points as corresponding to the experimental results, analytical expressions of the local PS using crystallographic parameters are uncovered. These expressions show the primary origin of BaTiO3 ferroelectricity as oxygen displacements. Elastic compliance and electrostrictive coefficients are estimated. For the comparison of strained results, we show that the effective critical temperature TC under strain <-0.01 is >1000 K from an approximate method combining ab initio results with GL theory. In addition, in a definite manner, the present results show much more enhanced ferroelectricity at large strain than the previous reports.

Durability Characterization of Advanced Polymeric Composites at Cryogenic Temperatures

NASA Technical Reports Server (NTRS)

Gates, T. S.

2001-01-01

The next generation of reusable launch vehicles will require technology development in several key areas. Of these key areas, the development of polymeric composite cryogenic fuel tanks promises to present one of the most difficult technical challenges. It is envisioned that a polymer matrix composite (PMC) tank would be a large shell structure capable of containing cryogenic fuels and carrying a range of structural loads. The criteria that will be imposed on such a design include reduced weight, conformal geometry, and impermeability. It is this last criterion, impermeability, that will provide the focus of this paper. The essence of the impermeability criterion is that the tank remains leak free throughout its design lifetime. To address this criterion, one of the first steps is to conduct a complete durability assessment of the PMC materials. At Langley Research Center, a durability assessment of promising new polyimide-based PMCs is underway. This durability program has focused on designing a set of critical laboratory experiments that will determine fundamental material properties under combined thermal-mechanical loading at cryogenic temperatures. The test program provides measurements of lamina and laminate properties, including strength, stiffness, and fracture toughness. The performance of the PMC materials is monitored as a function of exposure conditions and aging time. Residual properties after exposure are measured at cryogenic temperatures and provide quantitative values of residual strength and stiffness. Primary degradation mechanisms and the associated damage modes are measured with both destructive and nondestructive techniques. In addition to mechanical properties, a range of physical properties, such as weight, glass transition, and crack density, are measured and correlated with the test conditions. This paper will report on the progress of this research program and present critical results and illustrative examples of current findings.

An Experimental Investigation of Wall-Cooling Effects on Hypersonic Boundary-Layer Stability in a Quiet Wind Tunnel

NASA Technical Reports Server (NTRS)

Blanchard, Alan E.; Selby, Gregory V.

1996-01-01

One of the primary reasons for developing quiet tunnels is for the investigation of high-speed boundary-layer stability and transition phenomena without the transition-promoting effects of acoustic radiation from tunnel walls. In this experiment, a flared-cone model under adiabatic- and cooled-wall conditions was placed in a calibrated, 'quiet' Mach 6 flow and the stability of the boundary layer was investigated using a prototype constant-voltage anemometer. The results were compared with linear-stability theory predictions and good agreement was found in the prediction of second-mode frequencies and growth. In addition, the same 'N=10' criterion used to predict boundary-layer transition in subsonic, transonic, and supersonic flows was found to be applicable for the hypersonic flow regime as well. Under cooled-wall conditions, a unique set of continuous spectra data was acquired that documents the linear, nonlinear, and breakdown regions associated with the transition of hypersonic flow under low-noise conditions.

Theoretical prediction of the energy stability of graphene nanoblisters

NASA Astrophysics Data System (ADS)

Glukhova, O. E.; Slepchenkov, M. M.; Barkov, P. V.

2018-04-01

The paper presents the results of a theoretical prediction of the energy stability of graphene nanoblisters with various geometrical parameters. As a criterion for the evaluation of the stability of investigated carbon objects we propose to consider the value of local stress of the nanoblister atomic grid. Numerical evaluation of stresses experienced by atoms of the graphene blister framework was carried out by means of an original method for calculation of local stresses that is based on energy approach. Atomistic models of graphene nanoblisters corresponding to the natural experiment data were built for the first time in this work. New physical regularities of the influence of topology on the thermodynamic stability of nanoblisters were established as a result of the analysis of the numerical experiment data. We built the distribution of local stresses for graphene blister structures, whose atomic grid contains a variety of structural defects. We have shown how the concentration and location of defects affect the picture of the distribution of the maximum stresses experienced by the atoms of the nanoblisters.

Characterizing gravitational instability in turbulent multicomponent galactic discs

NASA Astrophysics Data System (ADS)

Agertz, Oscar; Romeo, Alessandro B.; Grisdale, Kearn

2015-05-01

Gravitational instabilities play an important role in galaxy evolution and in shaping the interstellar medium (ISM). The ISM is observed to be highly turbulent, meaning that observables like the gas surface density and velocity dispersion depend on the size of the region over which they are measured. In this work, we investigate, using simulations of Milky Way-like disc galaxies with a resolution of ˜ 9 pc, the nature of turbulence in the ISM and how this affects the gravitational stability of galaxies. By accounting for the measured average turbulent scalings of the density and velocity fields in the stability analysis, we can more robustly characterize the average level of stability of the galaxies as a function of scale, and in a straightforward manner identify scales prone to fragmentation. Furthermore, we find that the stability of a disc with feedback-driven turbulence can be well described by a `Toomre-like' Q stability criterion on all scales, whereas the classical Q can formally lose its meaning on small scales if violent disc instabilities occur in models lacking pressure support from stellar feedback.

Stabilization of a locally minimal forest

NASA Astrophysics Data System (ADS)

Ivanov, A. O.; Mel'nikova, A. E.; Tuzhilin, A. A.

2014-03-01

The method of partial stabilization of locally minimal networks, which was invented by Ivanov and Tuzhilin to construct examples of shortest trees with given topology, is developed. According to this method, boundary vertices of degree 2 are not added to all edges of the original locally minimal tree, but only to some of them. The problem of partial stabilization of locally minimal trees in a finite-dimensional Euclidean space is solved completely in the paper, that is, without any restrictions imposed on the number of edges remaining free of subdivision. A criterion for the realizability of such stabilization is established. In addition, the general problem of searching for the shortest forest connecting a finite family of boundary compact sets in an arbitrary metric space is formalized; it is shown that such forests exist for any family of compact sets if and only if for any finite subset of the ambient space there exists a shortest tree connecting it. The theory developed here allows us to establish further generalizations of the stabilization theorem both for arbitrary metric spaces and for metric spaces with some special properties. Bibliography: 10 titles.

Event-based cluster synchronization of coupled genetic regulatory networks

NASA Astrophysics Data System (ADS)

Yue, Dandan; Guan, Zhi-Hong; Li, Tao; Liao, Rui-Quan; Liu, Feng; Lai, Qiang

2017-09-01

In this paper, the cluster synchronization of coupled genetic regulatory networks with a directed topology is studied by using the event-based strategy and pinning control. An event-triggered condition with a threshold consisting of the neighbors' discrete states at their own event time instants and a state-independent exponential decay function is proposed. The intra-cluster states information and extra-cluster states information are involved in the threshold in different ways. By using the Lyapunov function approach and the theories of matrices and inequalities, we establish the cluster synchronization criterion. It is shown that both the avoidance of continuous transmission of information and the exclusion of the Zeno behavior are ensured under the presented triggering condition. Explicit conditions on the parameters in the threshold are obtained for synchronization. The stability criterion of a single GRN is also given under the reduced triggering condition. Numerical examples are provided to validate the theoretical results.

Psychometric characteristics and dimensionality of a Persian version of Rosenberg Self-esteem Scale.

PubMed

Shapurian, R; Hojat, M; Nayerahmadi, H

1987-08-01

The Rosenberg Self-esteem scale was translated into Persian and 12 Iranian bilingual judges confirmed the soundness of translation. The psychometric properties of the Persian version of Rosenberg Self-esteem Scale were studied in two samples of Iranian college students separately. Sample I consisted of 232 Iranian students in American universities, and Sample II comprised 305 Iranian students in Iranian universities. Criterion measures of loneliness, depression, anxiety, neuroticism, psychoticism, misanthropy, locus of control, tendency to dissimulate, and measures of relationship with parents, peers, and academic achievement were obtained. Item-total score correlations and alpha reliabilities supported the internal consistency of the scale. Test-retest reliabilities indicated the stability of the scores, and correlations between scores of the scale, and criterion measures supported the concurrent validity of the Rosenberg scale. Factor analysis of the Rosenberg scores confirmed the unidimensionality of the scale.

Modularity and hierarchical organization of action programs in children's acquisition of graphic skills.

PubMed

Manoel, Edison de J; Dantas, Luiz; Gimenez, Roberto; de Oliveira, Dalton Lustosa

2011-10-01

The organization of actions is based on modules in memory as a result of practice, easing the demand of performing more complex actions. If this modularization occurs, the elements of the module must remain invariant in new tasks. To test this hypothesis, 35 children, age 10 yr., practiced a graphic criterion task on a digital tablet and completed a complex graphic task enclosing the previous one. Total movement and pause times to draw the figure indicated skill acquisition. A module was identified by the variability of relative timing, pause time, and sequencing. Total movement to perform the criterion task did not increase significantly when it was embedded in the more complex task. Modularity was evidenced by the stability of relative timing and pause time and sequencing. The spatial position of new elements did not perturb the module, so the grammar of action may still have been forming.

Magnetic Transport Barriers in the DIII-D Tokamak

NASA Astrophysics Data System (ADS)

Kessler, J.; Volpe, F.; Evans, T. E.; Ali, H.; Punjabi, A.

2009-11-01

Large overlapping magnetic islands generate chaotic fields. However, a previous work [1] showed that second or third order perturbations of special topology and strength can also generate magnetic diffusion ``barriers" in the middle of stochastic regions. In the present study, we numerically assess their experimental feasibility at DIII-D. For this, realistic I- and C-coils perturbations are superimposed on the equilibrium field and puncture plots are generated with a field-line tracer. A criterion is defined for the automatic recognition of barriers and successfully tested on earlier symplectic maps in magnetic coordinates. The criterion is systematically applied to the new puncture plots in search for dependencies, e.g. upon the edge safety factor q95, which might be relevant to edge localized mode (ELM) stability, as well as to assess the robustness of barriers against fluctuations of the plasma parameters and coil currents. 8pt [1] H. Ali and A. Punjabi, Plasma Phys. Control. Fusion 49, 1565 (2007).

Comparison of two non-convex mixed-integer nonlinear programming algorithms applied to autoregressive moving average model structure and parameter estimation

NASA Astrophysics Data System (ADS)

Uilhoorn, F. E.

2016-10-01

In this article, the stochastic modelling approach proposed by Box and Jenkins is treated as a mixed-integer nonlinear programming (MINLP) problem solved with a mesh adaptive direct search and a real-coded genetic class of algorithms. The aim is to estimate the real-valued parameters and non-negative integer, correlated structure of stationary autoregressive moving average (ARMA) processes. The maximum likelihood function of the stationary ARMA process is embedded in Akaike's information criterion and the Bayesian information criterion, whereas the estimation procedure is based on Kalman filter recursions. The constraints imposed on the objective function enforce stability and invertibility. The best ARMA model is regarded as the global minimum of the non-convex MINLP problem. The robustness and computational performance of the MINLP solvers are compared with brute-force enumeration. Numerical experiments are done for existing time series and one new data set.

Comparison of temporal to pulmonary artery temperature in febrile patients.

PubMed

Furlong, Donna; Carroll, Diane L; Finn, Cynthia; Gay, Diane; Gryglik, Christine; Donahue, Vivian

2015-01-01

As a routine part of clinical care, temperature measurement is a key indicator of illness. With the criterion standard of temperature measurement from the pulmonary artery catheter thermistor (PAT), which insertion of PAT carries significant risk to the patient, a noninvasive method that is accurate and precise is needed. The purpose of this study was to measure the precision and accuracy of 2 commonly used methods of collecting body temperature: PAT considered the criterion standard and the temporal artery thermometer (TAT) in those patients with a temperature greater than 100.4°F. This is a repeated-measures design with each patient with a PAT in the intensive care unit acting as their own control to investigate the difference in PAT readings and readings from TAT in the core mode. Accuracy and precision were analyzed. There were 60 subjects, 41 males and 19 females, with mean age of 60.8 years, and 97% (n = 58) were post-cardiac surgery. There was a statistically significant difference between PAT and TAT (101.0°F [SD, 0.5°F] vs 100.5°F [SD, 0.8°F]; bias, -0.49°F; P < .001). Differences in temperature between the 2 methods were clinically significant (ie, >0.9°F different) in 15 of 60 cases (25%). No TAT measurements were 0.9 F greater than the corresponding PAT measurement (0%; 95% confidence interval, 0%-6%). These data demonstrate the accuracy of TAT when compared with PAT in those with temperatures of 100.4°F or greater. This study demonstrates that TAT set to core mode is accurate with a 0.5°F lower temperature than PAT. There was 25% in variability in precision of TAT.

A Semi-analytic Criterion for the Spontaneous Initiation of Carbon Detonations in White Dwarfs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garg, Uma; Chang, Philip, E-mail: umagarg@uwm.edu, E-mail: chang65@uwm.edu

Despite over 40 years of active research, the nature of the white dwarf progenitors of SNe Ia remains unclear. However, in the last decade, various progenitor scenarios have highlighted the need for detonations to be the primary mechanism by which these white dwarfs are consumed, but it is unclear how these detonations are triggered. In this paper we study how detonations are spontaneously initiated due to temperature inhomogeneities, e.g., hotspots, in burning nuclear fuel in a simplified physical scenario. Following the earlier work by Zel’Dovich, we describe the physics of detonation initiation in terms of the comparison between the spontaneousmore » wave speed and the Chapman–Jouguet speed. We develop an analytic expression for the spontaneous wave speed and utilize it to determine a semi-analytic criterion for the minimum size of a hotspot with a linear temperature gradient between a peak and base temperature for which detonations in burning carbon–oxygen material can occur. Our results suggest that spontaneous detonations may easily form under a diverse range of conditions, likely allowing a number of progenitor scenarios to initiate detonations that burn up the star.« less

Tribological Behavior and the Mild–Severe Wear Transition of Mg97Zn1Y2 Alloy with a LPSO Structure Phase

PubMed Central

Sun, Wei; Xuan, Xihua; Li, Liang; An, Jian

2018-01-01

Dry friction and wear tests were performed on as-cast Mg97Zn1Y2 alloy using a pin-on-disc configuration. Coefficients of friction and wear rates were measured as a function of applied load at sliding speeds of 0.2, 0.8 and 3.0 m/s. The wear mechanisms were identified in the mild and severe wear regimes by means of morphological observation and composition analysis of worn surfaces using scanning electron microscope (SEM) and energy dispersive X-ray spectrometer (EDS). Analyses of microstructure and hardness changes in subsurfaces verified the microstructure transformation from the deformed to the dynamically recrystallized, and properties changed from the strain hardening to dynamic crystallization (DRX) softening before and after the mild–severe wear transition. The mild–severe wear transition can be determined by a proposed contact surface DRX temperature criterion, from which the critical DRX temperatures at different sliding speeds are calculated using DRX dynamics; hence transition loads can also be calculated using a transition load model. The calculated transition loads are in good agreement with the measured ones, demonstrating the validity and applicability of the contact surface DRX temperature criterion. PMID:29584692

A Semi-analytic Criterion for the Spontaneous Initiation of Carbon Detonations in White Dwarfs

NASA Astrophysics Data System (ADS)

Garg, Uma; Chang, Philip

2017-02-01

Despite over 40 years of active research, the nature of the white dwarf progenitors of SNe Ia remains unclear. However, in the last decade, various progenitor scenarios have highlighted the need for detonations to be the primary mechanism by which these white dwarfs are consumed, but it is unclear how these detonations are triggered. In this paper we study how detonations are spontaneously initiated due to temperature inhomogeneities, e.g., hotspots, in burning nuclear fuel in a simplified physical scenario. Following the earlier work by Zel’Dovich, we describe the physics of detonation initiation in terms of the comparison between the spontaneous wave speed and the Chapman-Jouguet speed. We develop an analytic expression for the spontaneous wave speed and utilize it to determine a semi-analytic criterion for the minimum size of a hotspot with a linear temperature gradient between a peak and base temperature for which detonations in burning carbon-oxygen material can occur. Our results suggest that spontaneous detonations may easily form under a diverse range of conditions, likely allowing a number of progenitor scenarios to initiate detonations that burn up the star.

Is Oral Temperature an Accurate Measurement of Deep Body Temperature? A Systematic Review

PubMed Central

Mazerolle, Stephanie M.; Ganio, Matthew S.; Casa, Douglas J.; Vingren, Jakob; Klau, Jennifer

2011-01-01

Context: Oral temperature might not be a valid method to assess core body temperature. However, many clinicians, including athletic trainers, use it rather than criterion standard methods, such as rectal thermometry. Objective: To critically evaluate original research addressing the validity of using oral temperature as a measurement of core body temperature during periods of rest and changing core temperature. Data Sources: In July 2010, we searched the electronic databases PubMed, Scopus, Cumulative Index to Nursing and Allied Health Literature (CINAHL), SPORTDiscus, Academic Search Premier, and the Cochrane Library for the following concepts: core body temperature, oral, and thermometers. Controlled vocabulary was used, when available, as well as key words and variations of those key words. The search was limited to articles focusing on temperature readings and studies involving human participants. Data Synthesis: Original research was reviewed using the Physiotherapy Evidence Database (PEDro). Sixteen studies met the inclusion criteria and subsequently were evaluated by 2 independent reviewers. All 16 were included in the review because they met the minimal PEDro score of 4 points (of 10 possible points), with all but 2 scoring 5 points. A critical review of these studies indicated a disparity between oral and criterion standard temperature methods (eg, rectal and esophageal) specifically as the temperature increased. The difference was −0.50°C ± 0.31°C at rest and −0.58°C ± 0.75°C during a nonsteady state. Conclusions: Evidence suggests that, regardless of whether the assessment is recorded at rest or during periods of changing core temperature, oral temperature is an unsuitable diagnostic tool for determining body temperature because many measures demonstrated differences greater than the predetermined validity threshold of 0.27°C (0.5°F). In addition, the differences were greatest at the highest rectal temperatures. Oral temperature cannot accurately reflect core body temperature, probably because it is influenced by factors such as ambient air temperature, probe placement, and ingestion of fluids. Any reliance on oral temperature in an emergency, such as exertional heat stroke, might grossly underestimate temperature and delay proper diagnosis and treatment. PMID:22488144

Is oral temperature an accurate measurement of deep body temperature? A systematic review.

PubMed

Mazerolle, Stephanie M; Ganio, Matthew S; Casa, Douglas J; Vingren, Jakob; Klau, Jennifer

2011-01-01

Oral temperature might not be a valid method to assess core body temperature. However, many clinicians, including athletic trainers, use it rather than criterion standard methods, such as rectal thermometry. To critically evaluate original research addressing the validity of using oral temperature as a measurement of core body temperature during periods of rest and changing core temperature. In July 2010, we searched the electronic databases PubMed, Scopus, Cumulative Index to Nursing and Allied Health Literature (CINAHL), SPORTDiscus, Academic Search Premier, and the Cochrane Library for the following concepts: core body temperature, oral, and thermometers. Controlled vocabulary was used, when available, as well as key words and variations of those key words. The search was limited to articles focusing on temperature readings and studies involving human participants. Original research was reviewed using the Physiotherapy Evidence Database (PEDro). Sixteen studies met the inclusion criteria and subsequently were evaluated by 2 independent reviewers. All 16 were included in the review because they met the minimal PEDro score of 4 points (of 10 possible points), with all but 2 scoring 5 points. A critical review of these studies indicated a disparity between oral and criterion standard temperature methods (eg, rectal and esophageal) specifically as the temperature increased. The difference was -0.50°C ± 0.31°C at rest and -0.58°C ± 0.75°C during a nonsteady state. Evidence suggests that, regardless of whether the assessment is recorded at rest or during periods of changing core temperature, oral temperature is an unsuitable diagnostic tool for determining body temperature because many measures demonstrated differences greater than the predetermined validity threshold of 0.27°C (0.5°F). In addition, the differences were greatest at the highest rectal temperatures. Oral temperature cannot accurately reflect core body temperature, probably because it is influenced by factors such as ambient air temperature, probe placement, and ingestion of fluids. Any reliance on oral temperature in an emergency, such as exertional heat stroke, might grossly underestimate temperature and delay proper diagnosis and treatment.

Dynamical freeze-out criterion in a hydrodynamical description of Au + Au collisions at √{sNN}=200 GeV and Pb + Pb collisions at √{sNN}=2760 GeV

NASA Astrophysics Data System (ADS)

Ahmad, Saeed; Holopainen, Hannu; Huovinen, Pasi

2017-05-01

In hydrodynamical modeling of ultrarelativistic heavy-ion collisions, the freeze-out is typically assumed to take place at a surface of constant temperature or energy density. A more physical approach is to assume that freeze-out takes place at a surface of constant Knudsen number. We evaluate the Knudsen number as a ratio of the expansion rate of the system to the pion-scattering rate and apply the constant Knudsen number freeze-out criterion to the ideal hydrodynamical description of heavy-ion collisions at the Relativistic Heavy Ion Collider at BNL (√{sNN}=200 GeV) and the Large Hadron Collider (√{sNN}=2760 GeV) energies. We see that once the numerical values of freeze-out temperature and freeze-out Knudsen number are chosen to produce similar pT distributions, the elliptic and triangular anisotropies are similar too, in both event-by-event and averaged initial state calculations.

Synthesis of high-temperature viscosity stabilizer used in drilling fluid

NASA Astrophysics Data System (ADS)

Zhang, Yanna; Luo, Huaidong; Shi, Libao; Huang, Hongjun

2018-02-01

Abstract For a well performance drilling fluid, when it operates in deep wells under high temperature, the most important property required is the thermal stability. The drilling fluid properties under high temperature can be controlled by proper selection of viscosity stabilizer, which can capture oxygen to protect polymer agent in the drilling fluid. In this paper a viscosity stabilizer PB-854 is described, which was synthesized by 4-phenoxybutyl bromide, paraformaldehyde, and phloroglucinol using etherification method and condensation reaction. We studied the effect of catalyst dosage, temperature, time, and stirring rate on the synthetic yield. Under this condition: molar ratio of 2-tert-Butylphenol, paraformaldehyde and phloroglucinol of 2:1:2.5, reacting temperature of 100 °C, stirring rate of 100 r min-1, and mass content of catalyst of 15 %, char yield of 5-bromine-3-tert-butyl salicylaldehyde reached 86 %. Under this condition: molar ratio of 5-bromine-3-tert-butyl salicylaldehyde and phloroglucinol of 4, reacting temperature of 60 °C, reacting time of 30 min, volume content of sulphuric acid of 80 %, char yield of the target product viscosity stabilizer PB-854 is 86%. Finally, in this paper, infrared spectroscopy is adopted to analyse the structure of the synthetic product PB-854.The improvement in the stability of drilling fluid was further shown after adding the viscosity stabilizer in the common polymer drilling fluid under high temperature conditions of 120 °C ˜ 180 °C. The results show significant change in terms of fluid stability in the presence of this new stabilizer as it provides better stability.

Divergence instability of pipes conveying fluid with uncertain flow velocity

NASA Astrophysics Data System (ADS)

Rahmati, Mehdi; Mirdamadi, Hamid Reza; Goli, Sareh

2018-02-01

This article deals with investigation of probabilistic stability of pipes conveying fluid with stochastic flow velocity in time domain. As a matter of fact, this study has focused on the randomness effects of flow velocity on stability of pipes conveying fluid while most of research efforts have only focused on the influences of deterministic parameters on the system stability. The Euler-Bernoulli beam and plug flow theory are employed to model pipe structure and internal flow, respectively. In addition, flow velocity is considered as a stationary random process with Gaussian distribution. Afterwards, the stochastic averaging method and Routh's stability criterion are used so as to investigate the stability conditions of system. Consequently, the effects of boundary conditions, viscoelastic damping, mass ratio, and elastic foundation on the stability regions are discussed. Results delineate that the critical mean flow velocity decreases by increasing power spectral density (PSD) of the random velocity. Moreover, by increasing PSD from zero, the type effects of boundary condition and presence of elastic foundation are diminished, while the influences of viscoelastic damping and mass ratio could increase. Finally, to have a more applicable study, regression analysis is utilized to develop design equations and facilitate further analyses for design purposes.

The evolution of the intergalactic medium and the origin of the galaxy luminosity function

NASA Technical Reports Server (NTRS)

Valls-Gabaud, David; Blanchard, Alain; Mamon, Gary

1993-01-01

The coupling of the Press and Schechter prescription with the CDM scenario and the Hoyle-Rees-Ostriker cooling criterion leads to a galaxy formation scenario in which galaxies are overproduced by a large factor. Although star formation might be suppressed in the smaller halos, a large amount of energy per galactic mass is needed to account for the present number density of galaxies. The evolution of the intergalactic medium (IGM) provides a simple criterion to prevent galaxy formation without requiring feedback, since halos with small virial temperatures are not able to retain the infalling hot gas of the IGM. If the ionizing background has decreased since z is approximately 1 - 2, then this criterion explains the slope of the luminosity function at the faint end. In addition, this scenario predicts two populations of dwarf galaxies, well differentiated in age, gas content, stellar populations, and clustering properties, which can be identified with dE and dIm galaxies.

Stability: Conservation laws, Painlevé analysis and exact solutions for S-KP equation in coupled dusty plasma

NASA Astrophysics Data System (ADS)

EL-Kalaawy, O. H.; Moawad, S. M.; Wael, Shrouk

The propagation of nonlinear waves in unmagnetized strongly coupled dusty plasma with Boltzmann distributed electrons, iso-nonthermal distributed ions and negatively charged dust grains is considered. The basic set of fluid equations is reduced to the Schamel Kadomtsev-Petviashvili (S-KP) equation by using the reductive perturbation method. The variational principle and conservation laws of S-KP equation are obtained. It is shown that the S-KP equation is non-integrable using Painlevé analysis. A set of new exact solutions are obtained by auto-Bäcklund transformations. The stability analysis is discussed for the existence of dust acoustic solitary waves (DASWs) and it is found that the physical parameters have strong effects on the stability criterion. In additional to, the electric field and the true Mach number of this solution are investigated. Finally, we will study the physical meanings of solutions.

Improved Stability and Stabilization Results for Stochastic Synchronization of Continuous-Time Semi-Markovian Jump Neural Networks With Time-Varying Delay.

PubMed

Wei, Yanling; Park, Ju H; Karimi, Hamid Reza; Tian, Yu-Chu; Jung, Hoyoul; Yanling Wei; Park, Ju H; Karimi, Hamid Reza; Yu-Chu Tian; Hoyoul Jung; Tian, Yu-Chu; Wei, Yanling; Jung, Hoyoul; Karimi, Hamid Reza; Park, Ju H

2018-06-01

Continuous-time semi-Markovian jump neural networks (semi-MJNNs) are those MJNNs whose transition rates are not constant but depend on the random sojourn time. Addressing stochastic synchronization of semi-MJNNs with time-varying delay, an improved stochastic stability criterion is derived in this paper to guarantee stochastic synchronization of the response systems with the drive systems. This is achieved through constructing a semi-Markovian Lyapunov-Krasovskii functional together as well as making use of a novel integral inequality and the characteristics of cumulative distribution functions. Then, with a linearization procedure, controller synthesis is carried out for stochastic synchronization of the drive-response systems. The desired state-feedback controller gains can be determined by solving a linear matrix inequality-based optimization problem. Simulation studies are carried out to demonstrate the effectiveness and less conservatism of the presented approach.

Local stability of galactic discs in modified dynamics

NASA Astrophysics Data System (ADS)

Shenavar, Hossein; Ghafourian, Neda

2018-04-01

The local stability of stellar and fluid discs, under a new modified dynamical model, is surveyed by using WKB approximation. The exact form of the modified Toomre criterion is derived for both types of systems and it is shown that the new model is, in all situations, more locally stable than Newtonian model. In addition, it has been proved that the central surface density of the galaxies plays an important role in the local stability in the sense that low surface brightness (LSB) galaxies are more stable than high surface brightness (HSBs). Furthermore, the growth rate in the new model is found to be lower than the Newtonian one. We found that, according to this model, the local instability is related to the ratio of surface density of the disc to a critical surface density Σcrit. We provide observational evidence to support this result based on star formation rate in HSBs and LSBs.

Relativistic stellar stability: An empirical approach

NASA Technical Reports Server (NTRS)

Ni, W.

1972-01-01

The PPN formalism which encompasses the post-Newtonian limit of nearly every metric theory of gravity is used to analyze stellar stability. This analysis enables one to infer, for any given gravitation theory, the extent to which post-Newtonian effects induce instabilities in white dwarfs, in neutron stars, and in supermassive stars. It also reveals the extent to which our current empirical knowledge of post-Newtonian gravity (based on solar-system experiments) actually guarantees that relativistic instabilities exist. In particular, it shows that: (1) for conservative theories of gravity, current solar-system experiments guarantee that the critical adiabatic index, for the stability of stars against radial pulsations exceeds the Newtonian value of 4/3 and (2) for nonconservative theories, current experiments do not permit any firm conclusion about the sign of the critical adiabatic index, and (3) in the PPN approximation to every metric theory, the standard Schwarzschild criterion for convection is valid.

Stabilization of Au Monatomic-High Islands on the (2 ×2 )-Nad Reconstructed Surface of Wurtzite AlN(0001)

NASA Astrophysics Data System (ADS)

Eydoux, Benoit; Baris, Bulent; Khoussa, Hassan; Guillermet, Olivier; Gauthier, Sébastien; Bouju, Xavier; Martrou, David

2017-10-01

Noncontact atomic force microscopy images show that gold grows on the (2 ×2 )-Nad reconstructed polar (0001) surface of AlN insulating films, in the form of large monatomic islands. High-resolution images and in situ reflection high-energy electron diffraction spectra reveal two moiré patterns from which an atomic model can be built. Density functional theory calculations confirm this model and give insight into the mechanisms that lead to the stabilization of the monolayer. Gold adsorption is accompanied, first, by a global vertical charge transfer from the AlN substrate that fulfills the electrostatic stability criterion for a polar material, and second, by lateral charge transfers that are driven by the local chemical properties of the (2 ×2 )-Nad reconstruction. These results present alternative strategies to grow metal electrodes onto nitride compounds with a better controlled interface, a crucial issue for applications.

Climate variability decreases species richness and community stability in a temperate grassland.

PubMed

Zhang, Yunhai; Loreau, Michel; He, Nianpeng; Wang, Junbang; Pan, Qingmin; Bai, Yongfei; Han, Xingguo

2018-06-26

Climate change involves modifications in both the mean and the variability of temperature and precipitation. According to global warming projections, both the magnitude and the frequency of extreme weather events are increasing, thereby increasing climate variability. The previous studies have reported that climate warming tends to decrease biodiversity and the temporal stability of community primary productivity (i.e., community stability), but the effects of the variability of temperature and precipitation on biodiversity, community stability, and their relationship have not been clearly explored. We used a long-term (from 1982 to 2014) field data set from a temperate grassland in northern China to explore the effects of the variability of mean temperature and total precipitation on species richness, community stability, and their relationship. Results showed that species richness promoted community stability through increases in asynchronous dynamics across species (i.e., species asynchrony). Both species richness and species asynchrony were positively associated with the residuals of community stability after controlling for its dependence on the variability of mean temperature and total precipitation. Furthermore, the variability of mean temperature reduced species richness, while the variability of total precipitation decreased species asynchrony and community stability. Overall, the present study revealed that species richness and species asynchrony promoted community stability, but increased climate variability may erode these positive effects and thereby threaten community stability.

Assessment of released heavy metals from electrical and electronic equipment (EEE) existing in shipwrecks through laboratory-scale simulation reactor.

PubMed

Hahladakis, John N; Stylianos, Michailakis; Gidarakos, Evangelos

2013-04-15

In a passenger ship, the existence of EEE is obvious. In time, under shipwreck's conditions, all these materials will undergo an accelerated severe corrosion, due to salt water, releasing, consequently, heavy metals and other hazardous substances in the aquatic environment. In this study, a laboratory-scale reactor was manufactured in order to simulate the conditions under which the "Sea Diamond" shipwreck lies (14 bars of pressure and 16°C of temperature) and remotely observe and assess any heavy metal release that would occur, from part of the EEE present in the ship, into the sea. Ten metals were examined and the results showed that zinc, mercury and copper were abundant in the water samples taken from the reactor and in significantly higher concentrations compared to the US EPA CMC (criterion maximum concentration) criterion. Moreover, nickel and lead were found in concentrations higher than the CCC (criterion constant concentration) criterion set by the US EPA for clean seawater. The rest of the elements were measured in concentrations within the permissible limits. It is therefore of environmental benefit to salvage the wreck and recycle all the WEEE found in it. Copyright © 2013 Elsevier B.V. All rights reserved.

Cold stability of microtubules in wood-forming tissues of conifers during seasons of active and dormant cambium.

PubMed

Begum, Shahanara; Shibagaki, Masaki; Furusawa, Osamu; Nakaba, Satoshi; Yamagishi, Yusuke; Yoshimoto, Joto; Jin, Hyun-O; Sano, Yuzou; Funada, Ryo

2012-01-01

The cold stability of microtubules during seasons of active and dormant cambium was analyzed in the conifers Abies firma, Abies sachalinensis and Larix leptolepis by immunofluorescence microscopy. Samples were fixed at room temperature and at a low temperature of 2-3°C to examine the effects of low temperature on the stability of microtubules. Microtubules were visible in cambium, xylem cells and phloem cells after fixation at room temperature during seasons of active and dormant cambium. By contrast, fixation at low temperature depolymerized microtubules in cambial cells, differentiating tracheids, differentiating xylem ray parenchyma and phloem ray parenchyma cells during the active season. However, similar fixation did not depolymerize microtubules during cambial dormancy in winter. Our results indicate that the stability of microtubules in cambial cells and cambial derivatives at low temperature differs between seasons of active and dormant cambium. Moreover, the change in the stability of microtubules that we observed at low temperature might be closely related to seasonal changes in the cold tolerance of conifers. In addition, low-temperature fixation depolymerized microtubules in cambial cells and differentiating cells that had thin primary cell walls, while such low-temperature fixation did not depolymerize microtubules in differentiating secondary xylem ray parenchyma cells and tracheids that had thick secondary cell walls. The stability of microtubules at low temperature appears to depend on the structure of the cell wall, namely, primary or secondary. Therefore, we propose that the secondary cell wall might be responsible for the cold stability of microtubules in differentiating secondary xylem cells of conifers.

Thermomechanical Methodology for Stabilizing Shape Memory Alloy (SMA) Response

NASA Technical Reports Server (NTRS)

Padula, II, Santo A (Inventor)

2013-01-01

Methods and apparatuses for stabilizing the strain-temperature response for a shape memory alloy are provided. To perform stabilization of a second sample of the shape memory alloy, a first sample of the shape memory alloy is selected for isobaric treatment and the second sample is selected for isothermal treatment. When applying the isobaric treatment to the first sample, a constant stress is applied to the first sample. Temperature is also cycled from a minimum temperature to a maximum temperature until a strain on the first sample stabilizes. Once the strain on the first sample stabilizes, the isothermal treatment is performed on the second sample. During isothermal treatment, different levels of stress on the second sample are applied until a strain on the second sample matches the stabilized strain on the first sample.

Thermomechanical Methodology for Stabilizing Shape Memory Alloy (SMA) Response

NASA Technical Reports Server (NTRS)

Padula, Santo A., II (Inventor)

2016-01-01

Methods and apparatuses for stabilizing the strain-temperature response for a shape memory alloy are provided. To perform stabilization of a second sample of the shape memory alloy, a first sample of the shape memory alloy is selected for isobaric treatment and the second sample is selected for isothermal treatment. When applying the isobaric treatment to the first sample, a constant stress is applied to the first sample. Temperature is also cycled from a minimum temperature to a maximum temperature until a strain on the first sample stabilizes. Once the strain on the first sample stabilizes, the isothermal treatment is performed on the second sample. During isothermal treatment, different levels of stress on the second sample are applied until a strain on the second sample matches the stabilized strain on the first sample.

The Lyapunov-Krasovskii theorem and a sufficient criterion for local stability of isochronal synchronization in networks of delay-coupled oscillators

NASA Astrophysics Data System (ADS)

Grzybowski, J. M. V.; Macau, E. E. N.; Yoneyama, T.

2017-05-01

This paper presents a self-contained framework for the stability assessment of isochronal synchronization in networks of chaotic and limit-cycle oscillators. The results were based on the Lyapunov-Krasovskii theorem and they establish a sufficient condition for local synchronization stability of as a function of the system and network parameters. With this in mind, a network of mutually delay-coupled oscillators subject to direct self-coupling is considered and then the resulting error equations are block-diagonalized for the purpose of studying their stability. These error equations are evaluated by means of analytical stability results derived from the Lyapunov-Krasovskii theorem. The proposed approach is shown to be a feasible option for the investigation of local stability of isochronal synchronization for a variety of oscillators coupled through linear functions of the state variables under a given undirected graph structure. This ultimately permits the systematic identification of stability regions within the high-dimensionality of the network parameter space. Examples of applications of the results to a number of networks of delay-coupled chaotic and limit-cycle oscillators are provided, such as Lorenz, Rössler, Cubic Chua's circuit, Van der Pol oscillator and the Hindmarsh-Rose neuron.

Performance and stability analysis of gas-injection enhanced natural circulation in heavy-liquid-metal-cooled systems

NASA Astrophysics Data System (ADS)

Yoo, Yeon-Jong

The purpose of this study is to investigate the performance and stability of the gas-injection enhanced natural circulation in heavy-liquid-metal-cooled systems. The target system is STAR-LM, which is a 400-MWt-class advanced lead-cooled fast reactor under development by Argonne National Laboratory and Oregon State University. The primary loop of STAR-LM relies on natural circulation to eliminate main circulation pumps for enhancement of passive safety. To significantly increase the natural circulation flow rate for the incorporation of potential future power uprates, the injection of noncondensable gas into the coolant above the core is envisioned ("gas lift pump"). Reliance upon gas-injection enhanced natural circulation raises the concern of flow instability due to the relatively high temperature change in the reactor core and the two-phase flow condition in the riser. For this study, the one-dimensional flow field equations were applied to each flow section and the mixture models of two-phase flow, i.e., both the homogeneous and drift-flux equilibrium models were used in the two-phase region of the riser. For the stability analysis, the linear perturbation technique based on the frequency-domain approach was used by employing the Nyquist stability criterion and a numerical root search method. It has been shown that the thermal power of the STAR-LM natural circulation system could be increased from 400 up to 1152 MW with gas injection under the limiting void fraction of 0.30 and limiting coolant velocity of 2.0 m/s from the steady-state performance analysis. As the result of the linear stability analysis, it has turned out that the STAR-LM natural circulation system would be stable even with gas injection. In addition, through the parametric study, it has been found that the thermal inertia effects of solid structures such as fuel rod and heat exchanger tube should be considered in the stability analysis model. The results of this study will be a part of the optimized stable design of the gas-injection enhanced natural circulation of STAR-LM with substantially improved power level and economical competitiveness. Furthermore, combined with the parametric study, this research could contribute a guideline for the design of other similar heavy-liquid-metal-cooled natural circulation systems with gas injection.

Developing a tool to measure satisfaction among health professionals in sub-Saharan Africa

PubMed Central

2013-01-01

Background In sub-Saharan Africa, lack of motivation and job dissatisfaction have been cited as causes of poor healthcare quality and outcomes. Measurement of health workers’ satisfaction adapted to sub-Saharan African working conditions and cultures is a challenge. The objective of this study was to develop a valid and reliable instrument to measure satisfaction among health professionals in the sub-Saharan African context. Methods A survey was conducted in Senegal and Mali in 2011 among 962 care providers (doctors, midwives, nurses and technicians) practicing in 46 hospitals (capital, regional and district). The participation rate was very high: 97% (937/962). After exploratory factor analysis (EFA), construct validity was assessed through confirmatory factor analysis (CFA). The discriminant validity of our subscales was evaluated by comparing the average variance extracted (AVE) for each of the constructs with the squared interconstruct correlation (SIC), and finally for criterion validity, each subscale was tested with two hypotheses. Two dimensions of reliability were assessed: internal consistency with Cronbach’s alpha subscales and stability over time using a test-retest process. Results Eight dimensions of satisfaction encompassing 24 items were identified and validated using a process that combined psychometric analyses and expert opinions: continuing education, salary and benefits, management style, tasks, work environment, workload, moral satisfaction and job stability. All eight dimensions demonstrated significant discriminant validity. The final model showed good performance, with a root mean square error of approximation (RMSEA) of 0.0508 (90% CI: 0.0448 to 0.0569) and a comparative fit index (CFI) of 0.9415. The concurrent criterion validity of the eight dimensions was good. Reliability was assessed based on internal consistency, which was good for all dimensions but one (moral satisfaction < 0.70). Test-retest showed satisfactory temporal stability (intra class coefficient range: 0.60 to 0.91). Conclusions Job satisfaction is a complex construct; this study provides a multidimensional instrument whose content, construct and criterion validities were verified to ensure its suitability for the sub-Saharan African context. When using these subscales in further studies, the variability of the reliability of the subscales should be taken in to account for calculating the sample sizes. The instrument will be useful in evaluative studies which will help guide interventions aimed at improving both the quality of care and its effectiveness. PMID:23826720

Thermo-solutal and kinetic modes of stable dendritic growth with different symmetries of crystalline anisotropy in the presence of convection

NASA Astrophysics Data System (ADS)

Alexandrov, Dmitri V.; Galenko, Peter K.; Toropova, Lyubov V.

2018-01-01

Motivated by important applications in materials science and geophysics, we consider the steady-state growth of anisotropic needle-like dendrites in undercooled binary mixtures with a forced convective flow. We analyse the stable mode of dendritic evolution in the case of small anisotropies of growth kinetics and surface energy for arbitrary Péclet numbers and n-fold symmetry of dendritic crystals. On the basis of solvability and stability theories, we formulate a selection criterion giving a stable combination between dendrite tip diameter and tip velocity. A set of nonlinear equations consisting of the solvability criterion and undercooling balance is solved analytically for the tip velocity V and tip diameter ρ of dendrites with n-fold symmetry in the absence of convective flow. The case of convective heat and mass transfer mechanisms in a binary mixture occurring as a result of intensive flows in the liquid phase is detailed. A selection criterion that describes such solidification conditions is derived. The theory under consideration comprises previously considered theoretical approaches and results as limiting cases. This article is part of the theme issue `From atomistic interfaces to dendritic patterns'. This article is part of the theme issue `From atomistic interfaces to dendritic patterns'.

The nature of stable insomnia phenotypes.

PubMed

Pillai, Vivek; Roth, Thomas; Drake, Christopher L

2015-01-01

We examined the 1-y stability of four insomnia symptom profiles: sleep onset insomnia; sleep maintenance insomnia; combined onset and maintenance insomnia; and neither criterion (i.e., insomnia cases that do not meet quantitative thresholds for onset or maintenance problems). Insomnia cases that exhibited the same symptom profile over a 1-y period were considered to be phenotypes, and were compared in terms of clinical and demographic characteristics. Longitudinal. Urban, community-based. Nine hundred fifty-four adults with Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition based current insomnia (46.6 ± 12.6 y; 69.4% female). None. At baseline, participants were divided into four symptom profile groups based on quantitative criteria. Follow-up assessment 1 y later revealed that approximately 60% of participants retained the same symptom profile, and were hence judged to be phenotypes. Stability varied significantly by phenotype, such that sleep onset insomnia (SOI) was the least stable (42%), whereas combined insomnia (CI) was the most stable (69%). Baseline symptom groups (cross-sectionally defined) differed significantly across various clinical indices, including daytime impairment, depression, and anxiety. Importantly, however, a comparison of stable phenotypes (longitudinally defined) did not reveal any differences in impairment or comorbid psychopathology. Another interesting finding was that whereas all other insomnia phenotypes showed evidence of an elevated wake drive both at night and during the day, the 'neither criterion' phenotype did not; this latter phenotype exhibited significantly higher daytime sleepiness despite subthreshold onset and maintenance difficulties. By adopting a stringent, stability-based definition, this study offers timely and important data on the longitudinal trajectory of specific insomnia phenotypes. With the exception of daytime sleepiness, few clinical differences are apparent across stable phenotypes. © 2014 Associated Professional Sleep Societies, LLC.

Preservative activity of lavender hydrosols in moisturizing body gels.

PubMed

Kunicka-Styczyńska, A; Śmigielski, K; Prusinowska, R; Rajkowska, K; Kuśmider, B; Sikora, M

2015-01-01

The study was undertaken to verify the antimicrobial activity of Lavandula angustifolia hydrosols in moisturizing body gels. The inhibition efficacy of four lavender hydrosols (obtained from fresh or dry herbs or flowers) was tested against Staphylococcus aureus ATCC 6538, Escherichia coli ATCC 1627, Candida sp. ŁOCK 0008 and Aspergillus niger ATCC 16404 in compliance with the standards of the European Pharmacopoeia Commission. Although the tested hydrosols did not express any remarkable antimicrobial action when tested via the macrodilution method, they show preservative activity in cosmetic preparations. Criterion A for fungi was fulfilled for the cosmetic formulation containing dried flower hydrosol (reduction of the inoculum by two logarithmic units within 14 days with no increase up to the 28th day) and Criterion B for bacteria E. coli and Staph. aureus (reduction of the inoculum by three logarithmic units within 14 days with no increase up to the 28th day). The fresh herb lavender hydrosol in the cosmetic formulation was regarded as the second one effectively satisfying Criterion B for bacteria, but its activity against fungi was below the acceptance value set out in the official regulations. Lavender hydrosols used as a replacement for water phase in cosmetics may contribute to maintaining microbiological stability of cosmetic formulations. The presented research proved antimicrobial activity of hydrosols obtained from fresh or dried Lavandula angustifolia herbs or flowers in moisturizing body gel. The study shows the usefulness of lavender hydrosols as a natural, ecologically friendly component of cosmetics with potential preservative activity in formulations. Hydrosols are commonly regarded as waste in the production of essential oils. The use of lavender hydrosols in the cosmetic industry as a replacement for water phase in cosmetics may not only result in expenses reduction for chemical stabilizers and preservatives but also in substantial decrease in sewage disposal. © 2014 The Society for Applied Microbiology.

Stability limits of unsteady open capillary channel flow

NASA Astrophysics Data System (ADS)

Grah, Aleksander; Haake, Dennis; Rosendahl, Uwe; Klatte, J.?Rg; Dreyer, Michael E.

This paper is concerned with steady and unsteady flow rate limitations in open capillary channels under low-gravity conditions. Capillary channels are widely used in Space technology for liquid transportation and positioning, e.g. in fuel tanks and life support systems. The channel observed in this work consists of two parallel plates bounded by free liquid surfaces along the open sides. The capillary forces of the free surfaces prevent leaking of the liquid and gas ingestion into the flow.In the case of steady stable flow the capillary pressure balances the differential pressure between the liquid and the surrounding constant-pressure gas phase. Increasing the flow rate in small steps causes a decrease of the liquid pressure. A maximum steady flow rate is achieved when the flow rate exceeds a certain limit leading to a collapse of the free surfaces due to the choking effect. In the case of unsteady flow additional dynamic effects take place due to flow rate transition and liquid acceleration. The maximum flow rate is smaller than in the case of steady flow. On the other hand, the choking effect does not necessarily cause surface collapse and stable temporarily choked flow is possible under certain circumstances.To determine the limiting volumetric flow rate and stable flow dynamic properties, a new stability theory for both steady and unsteady flow is introduced. Subcritical and supercritical (choked) flow regimes are defined. Stability criteria are formulated for each flow type. The steady (subcritical) criterion corresponds to the speed index defined by the limiting longitudinal small-amplitude wave speed, similar to the Mach number. The unsteady (supercritical) criterion for choked flow is defined by a new characteristic number, the dynamic index. It is based on pressure balances and reaches unity at the stability limit.The unsteady model based on the Bernoulli equation and the mass balance equation is solved numerically for perfectly wetting incompressible liquids. The unsteady model and the stability theory are verified by comparison to results of a sounding rocket experiment (TEXUS 41) on capillary channel flows launched in December 2005 from ESRANGE in north Sweden. For a clear overview of subcritical, supercritical, and unstable flow, parametric studies and stability diagrams are shown and compared to experimental observations.

Temperature compensation via cooperative stability in protein degradation

NASA Astrophysics Data System (ADS)

Peng, Yuanyuan; Hasegawa, Yoshihiko; Noman, Nasimul; Iba, Hitoshi

2015-08-01

Temperature compensation is a notable property of circadian oscillators that indicates the insensitivity of the oscillator system's period to temperature changes; the underlying mechanism, however, is still unclear. We investigated the influence of protein dimerization and cooperative stability in protein degradation on the temperature compensation ability of two oscillators. Here, cooperative stability means that high-order oligomers are more stable than their monomeric counterparts. The period of an oscillator is affected by the parameters of the dynamic system, which in turn are influenced by temperature. We adopted the Repressilator and the Atkinson oscillator to analyze the temperature sensitivity of their periods. Phase sensitivity analysis was employed to evaluate the period variations of different models induced by perturbations to the parameters. Furthermore, we used experimental data provided by other studies to determine the reasonable range of parameter temperature sensitivity. We then applied the linear programming method to the oscillatory systems to analyze the effects of protein dimerization and cooperative stability on the temperature sensitivity of their periods, which reflects the ability of temperature compensation in circadian rhythms. Our study explains the temperature compensation mechanism for circadian clocks. Compared with the no-dimer mathematical model and linear model for protein degradation, our theoretical results show that the nonlinear protein degradation caused by cooperative stability is more beneficial for realizing temperature compensation of the circadian clock.

The dynamics of a delayed predator-prey model with state dependent feedback control

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, Anuraj; Gakkhar, Sunita

2011-11-30

A delayed prey-predator model with state-dependent impulses is investigated. The sufficient conditions of existence and stability of semi-trivial solution and positive period-1 solution are obtained by using the Poincare map and analogue of the Poincare Criterion. The qualitative analysis shows that the positive period-one solution bifurcates from the semi-trivial solution through a fold bifurcation. The complex dynamics including chaos is obtained and numerical simulations substantiate the analytical results.

Criterion 6, indicator 33 : recovery or recycling of forest products as a percentage of total forest products consumption

Treesearch

Ken Skog; James Howard; Rebecca Westby

2011-01-01

This indicator shows the trend in recovering wood and paper for reuse in products in the United States. This reuse can hold down the need to harvest wood to meet U.S. consumption needs. The paper recycling rate (utilization rate in producing new paper) increased from 22% to 38% between 1970 and 1996, but then stabilized at 37% to 38% between 1996 and 2006. This rate...

An entropy regularization method applied to the identification of wave distribution function for an ELF hiss event

NASA Astrophysics Data System (ADS)

Prot, Olivier; SantolíK, OndřEj; Trotignon, Jean-Gabriel; Deferaudy, Hervé

2006-06-01

An entropy regularization algorithm (ERA) has been developed to compute the wave-energy density from electromagnetic field measurements. It is based on the wave distribution function (WDF) concept. To assess its suitability and efficiency, the algorithm is applied to experimental data that has already been analyzed using other inversion techniques. The FREJA satellite data that is used consists of six spectral matrices corresponding to six time-frequency points of an ELF hiss-event spectrogram. The WDF analysis is performed on these six points and the results are compared with those obtained previously. A statistical stability analysis confirms the stability of the solutions. The WDF computation is fast and without any prespecified parameters. The regularization parameter has been chosen in accordance with the Morozov's discrepancy principle. The Generalized Cross Validation and L-curve criterions are then tentatively used to provide a fully data-driven method. However, these criterions fail to determine a suitable value of the regularization parameter. Although the entropy regularization leads to solutions that agree fairly well with those already published, some differences are observed, and these are discussed in detail. The main advantage of the ERA is to return the WDF that exhibits the largest entropy and to avoid the use of a priori models, which sometimes seem to be more accurate but without any justification.

Appearance motives to tan and not tan: evidence for validity and reliability of a new scale.

PubMed

Cafri, Guy; Thompson, J Kevin; Roehrig, Megan; Rojas, Ariz; Sperry, Steffanie; Jacobsen, Paul B; Hillhouse, Joel

2008-04-01

Risk for skin cancer is increased by UV exposure and decreased by sun protection. Appearance reasons to tan and not tan have consistently been shown to be related to intentions and behaviors to UV exposure and protection. This study was designed to determine the factor structure of appearance motives to tan and not tan, evaluate the extent to which this factor structure is gender invariant, test for mean differences in the identified factors, and evaluate internal consistency, temporal stability, and criterion-related validity. Five-hundred eighty-nine females and 335 male college students were used to test confirmatory factor analysis models within and across gender groups, estimate latent mean differences, and use the correlation coefficient and Cronbach's alpha to further evaluate the reliability and validity of the identified factors. A measurement invariant (i.e., factor-loading invariant) model was identified with three higher-order factors: sociocultural influences to tan (lower order factors: media, friends, family, significant others), appearance reasons to tan (general, acne, body shape), and appearance reasons not to tan (skin aging, immediate skin damage). Females had significantly higher means than males on all higher-order factors. All subscales had evidence of internal consistency, temporal stability, and criterion-related validity. This study offers a framework and measurement instrument that has evidence of validity and reliability for evaluating appearance-based motives to tan and not tan.

A neural-network-based exponential H∞ synchronisation for chaotic secure communication via improved genetic algorithm

NASA Astrophysics Data System (ADS)

Hsiao, Feng-Hsiag

2016-10-01

In this study, a novel approach via improved genetic algorithm (IGA)-based fuzzy observer is proposed to realise exponential optimal H∞ synchronisation and secure communication in multiple time-delay chaotic (MTDC) systems. First, an original message is inserted into the MTDC system. Then, a neural-network (NN) model is employed to approximate the MTDC system. Next, a linear differential inclusion (LDI) state-space representation is established for the dynamics of the NN model. Based on this LDI state-space representation, this study proposes a delay-dependent exponential stability criterion derived in terms of Lyapunov's direct method, thus ensuring that the trajectories of the slave system approach those of the master system. Subsequently, the stability condition of this criterion is reformulated into a linear matrix inequality (LMI). Due to GA's random global optimisation search capabilities, the lower and upper bounds of the search space can be set so that the GA will seek better fuzzy observer feedback gains, accelerating feedback gain-based synchronisation via the LMI-based approach. IGA, which exhibits better performance than traditional GA, is used to synthesise a fuzzy observer to not only realise the exponential synchronisation, but also achieve optimal H∞ performance by minimizing the disturbance attenuation level and recovering the transmitted message. Finally, a numerical example with simulations is given in order to demonstrate the effectiveness of our approach.

Renormalization group flow of the Higgs potential

NASA Astrophysics Data System (ADS)

Gies, Holger; Sondenheimer, René

2018-01-01

We summarize results for local and global properties of the effective potential for the Higgs boson obtained from the functional renormalization group, which allows one to describe the effective potential as a function of both scalar field amplitude and renormalization group scale. This sheds light onto the limitations of standard estimates which rely on the identification of the two scales and helps in clarifying the origin of a possible property of meta-stability of the Higgs potential. We demonstrate that the inclusion of higher-dimensional operators induced by an underlying theory at a high scale (GUT or Planck scale) can relax the conventional lower bound on the Higgs mass derived from the criterion of absolute stability. This article is part of the Theo Murphy meeting issue `Higgs cosmology'.

A measurable Lawson criterion and hydro-equivalent curves for inertial confinement fusion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, C. D.; Betti, R.; Departments of Mechanical Engineering and Physics and Astronomy, University of Rochester, Rochester, New York 14623

2008-10-15

It is shown that the ignition condition (Lawson criterion) for inertial confinement fusion (ICF) can be cast in a form dependent on the only two parameters of the compressed fuel assembly that can be measured with existing techniques: the hot spot ion temperature (T{sub i}{sup h}) and the total areal density ({rho}R{sub tot}), which includes the cold shell contribution. A marginal ignition curve is derived in the {rho}R{sub tot}, T{sub i}{sup h} plane and current implosion experiments are compared with the ignition curve. On this plane, hydrodynamic equivalent curves show how a given implosion would perform with respect to themore » ignition condition when scaled up in the laser-driver energy. For 3<{sub n}<6 keV, an approximate form of the ignition condition (typical of laser-driven ICF) is {sub n}{sup 2.6}{center_dot}<{rho}R{sub tot}>{sub n}>50 keV{sup 2.6}{center_dot} g/cm{sup 2}, where <{rho}R{sub tot}>{sub n} and {sub n} are the burn-averaged total areal density and hot spot ion temperature, respectively. Both quantities are calculated without accounting for the alpha-particle energy deposition. Such a criterion can be used to determine how surrogate D{sub 2} and subignited DT target implosions perform with respect to the one-dimensional ignition threshold.« less

The H2/CH4 ratio during serpentinization cannot reliably identify biological signatures

PubMed Central

Huang, Ruifang; Sun, Weidong; Liu, Jinzhong; Ding, Xing; Peng, Shaobang; Zhan, Wenhuan

2016-01-01

Serpentinization potentially contributes to the origin and evolution of life during early history of the Earth. Serpentinization produces molecular hydrogen (H2) that can be utilized by microorganisms to gain metabolic energy. Methane can be formed through reactions between molecular hydrogen and oxidized carbon (e.g., carbon dioxide) or through biotic processes. A simple criterion, the H2/CH4 ratio, has been proposed to differentiate abiotic from biotic methane, with values approximately larger than 40 for abiotic methane and values of <40 for biotic methane. The definition of the criterion was based on two serpentinization experiments at 200 °C and 0.3 kbar. However, it is not clear whether the criterion is applicable at a wider range of temperatures. In this study, we performed sixteen experiments at 311–500 °C and 3.0 kbar using natural ground peridotite. Our results demonstrate that the H2/CH4 ratios strongly depend on temperature. At 311 °C and 3.0 kbar, the H2/CH4 ratios ranged from 58 to 2,120, much greater than the critical value of 40. By contrast, at 400–500 °C, the H2/CH4 ratios were much lower, ranging from 0.1 to 8.2. The results of this study suggest that the H2/CH4 ratios cannot reliably discriminate abiotic from biotic methane. PMID:27666288

[Study on the stability of tetrandrine microsphere].

PubMed

Cheng, Guohu; Luo, Jiabo

2005-05-01

To study the stability of Tetrandrine Microsphere. Higher speed test and room temperature test were adopted to investigate the indexes, such as properties of appearance, amount of medicine loaded, seal rate, seepage rate, microbial stability, etc. Through the test of six months, properties of appearance, amount of medicine loaded, seal rate, seepage rate, microbial stability have not obviously change. But after testing for 6 months with higher temperature, the seal rate was reduced, and the seepage rate was increased. Tetrandrine microsphere is steady under the room temperature condition, but is unstable to hot, and ought to keep in conformity with low-temperature.

Effects of temperature and relative humidity on the stability of paper-immobilized antibodies.

PubMed

Wang, Jingyun; Yiu, Brian; Obermeyer, Jaclyn; Filipe, Carlos D M; Brennan, John D; Pelton, Robert

2012-02-13

The stability of a paper-immobilized antibody was investigated over a range of temperatures (40-140 °C) and relative humidities (RH, 30-90%) using both unmodified filter paper and the same paper impregnated with polyamide-epichlorohydrin (PAE) as supports. Antibody stability decreased with increasing temperature, as expected, but also decreased with increasing RH. At 40 °C, the half-life was more than 10 days, with little dependence on RH. However, at 80 °C, the half-life varied from ~3 days at low RH to less than half an hour at 90% RH, demonstrating that hydration of the antibody promotes unfolding. Antibody stability was not influenced by the PAE paper surface treatment. This work shows that antibodies are good candidates for development of bioactive paper as they have sufficient stability at high temperature to withstand printing and other roll-to-roll processing steps, and sufficient low temperature stability to allow long-term storage of bioactive paper materials.

Nanostructure templating using low temperature atomic layer deposition

DOEpatents

Grubbs, Robert K [Albuquerque, NM; Bogart, Gregory R [Corrales, NM; Rogers, John A [Champaign, IL

2011-12-20

Methods are described for making nanostructures that are mechanically, chemically and thermally stable at desired elevated temperatures, from nanostructure templates having a stability temperature that is less than the desired elevated temperature. The methods comprise depositing by atomic layer deposition (ALD) structural layers that are stable at the desired elevated temperatures, onto a template employing a graded temperature deposition scheme. At least one structural layer is deposited at an initial temperature that is less than or equal to the stability temperature of the template, and subsequent depositions made at incrementally increased deposition temperatures until the desired elevated temperature stability is achieved. Nanostructure templates include three dimensional (3D) polymeric templates having features on the order of 100 nm fabricated by proximity field nanopatterning (PnP) methods.

Evaluation of the Weather Research and Forecasting (WRF) Model over Portugal: Case study

NASA Astrophysics Data System (ADS)

Rodrigues, Mónica; Rocha, Alfredo; Monteiro, Ana

2013-04-01

Established in 1756 the Demarcated Douro Region, became the first viticulturist region to be delimited and regulated under worldwide scale. The region has an area of 250000 hectares, from which 45000 are occupied by continuous vineyards (IVDP, 2010). It stretches along the Douro river valleys and its main streams, from the region of Mesão Frio, about 100 kilometers east from Porto town where this river discharges till attaining the frontier with Spain in the east border. Due to its stretching and extension in the W-E direction accompanying the Douro Valley, it is not strange that the region is not homogeneous having, therefore, three sub-regions: Baixo Corgo, Cima Corgo and Douro Superior. The Baixo Corgo the most western region is the "birthplace" of the viticulturalist region. The main purpose of this work is to evaluate and test the quality of a criterion developed to determine the occurrence of frost. This criterion is to be used latter by numerical weather forecasts (WRF-ARW) and put into practice in 16 meteorological stations in the Demarcated Douro Region. Firstly, the criterion was developed to calculate the occurrence of frost based on the meteorological data observed in those 16 stations. Time series of temperatures and precipitation were used for a period of approximately 20 years. It was verified that the meteorological conditions associated to days with frost (SG) and without frost (CG) are different in each station. Afterwards, the model was validated, especially in what concerns the simulation of the daily minimal temperature. Correcting functions were applied to the data of the model, having considerably diminished the errors of simulation. Then the criterion of frost estimate was applied do the output of the model for a period of 2 frost seasons. The results show that WRF simulates successfully the appearance of frost episodes and so can be used in the frost forecasting.

A hedging point strategy--balancing effluent quality, economy and robustness in the control of wastewater treatment plants.

PubMed

Ingildsen, P; Olsson, G; Yuan, Z

2002-01-01

An operational space map is an efficient tool to compare a large number of operational strategies to find an optimal choice of setpoints based on a multicriterion. Typically, such a multicriterion includes a weighted sum of cost of operation and effluent quality. Due to the relative high cost of aeration such a definition of optimality result in a relatively high fraction of the effluent total nitrogen in the form of ammonium. Such a strategy may however introduce a risk into operation because a low degree of ammonium removal leads to a low amount of nitrifiers. This in turn leads to a reduced ability to reject event disturbances, such as large variations in the ammonium load, drop in temperature, the presence of toxic/inhibitory compounds in the influent etc. Hedging is a risk minimisation tool, with the aim to "reduce one's risk of loss on a bet or speculation by compensating transactions on the other side" (The Concise Oxford Dictionary (1995)). In wastewater treatment plant operation hedging can be applied by choosing a higher level of ammonium removal to increase the amount of nitrifiers. This is a sensible way to introduce disturbance rejection ability into the multi criterion. In practice, this is done by deciding upon an internal effluent ammonium criterion. In some countries such as Germany, a separate criterion already applies to the level of ammonium in the effluent. However, in most countries the effluent criterion applies to total nitrogen only. In these cases, an internal effluent ammonium criterion should be selected in order to secure proper disturbance rejection ability.

Low temperature stabilization process for production of carbon fiber having structural order

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rios, Orlando; McGuire, Michael Alan; More, Karren Leslie

A method for producing a carbon fiber, the method comprising: (i) subjecting a continuous carbon fiber precursor having a polymeric matrix in which strength-enhancing particles are incorporated to a stabilization process during which the carbon fiber precursor is heated to within a temperature range ranging from the glass transition temperature to no less than 20.degree. C. below the glass transition temperature of the polymeric matrix, wherein the maximum temperature employed in the stabilization process is below 400.degree. C., for a processing time within said temperature range of at least 1 hour in the presence of oxygen and in the presencemore » of a magnetic field of at least 1 Tesla, while said carbon fiber precursor is held under an applied axial tension; and (ii) subjecting the stabilized carbon fiber precursor, following step (i), to a carbonization process. The stabilized carbon fiber precursor, resulting carbon fiber, and articles made thereof are also described.« less

Correlation of high-temperature stability of alpha-chymotrypsin with 'salting-in' properties of solution.

PubMed

Levitsky VYu; Panova, A A; Mozhaev, V V

1994-01-15

A correlation between the stability of alpha-chymotrypsin against irreversible thermal inactivation at high temperatures (long-term stability) and the coefficient of Setchenov equation as a measure of salting-in/out efficiency of solutes in the Hofmeister series has been found. An increase in the concentration of salting-in solutes (KSCN, urea, guanidinium chloride, formamide) leads to a many-fold decrease of the inactivation rate of the enzyme. In contrast, addition of salting-out solutes has a small effect on the long-term stability of alpha-chymotrypsin at high temperatures. The effects of solutes are additive with respect to their salting-in/out capacities; the stabilizing action of the solutes is determined by the calculated Setchenov coefficient of solution. The correlation is explained by a solute-driven shift of the conformational equilibrium between the 'low-temperature' native and the 'high-temperature' denatured forms of the enzyme within the range of the kinetic scheme put forward in the preceding paper in this journal: irreversible inactivation of the high-temperature form proceeds much more slowly compared with the low-temperature form.

EXPERIMENTAL MEASUREMENT AND INTERPRETATION OF VOLT-AMPERE CURVES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gingrich, J.E.; Warner, C.; Weeks, C.C.

1962-07-01

Cylindrical and parallel-plane cesium vapor thermionic converters were used for obtaining volt-ampere curves for systematic variations of emitter, collector, and cesium reservoir temperatures, with electrode spacings ranging from a few to many mean free paths, and with space charge conditions varying from electron-rich to ion-rich. The resulting curves exhibit much variety. The saturation currents agree well with the data of Houston and Aamodt for the space charge neutralized, few-mean-free-path cases. Apparent'' saturation currents for space charge limited cases were observed and were always less than the currents predicted by Houston and Aamodt. Several discontinuities in slope were observed in themore » reverse current portion of the curves and these have tentatively been identified with volume ionization of atoms in both the ground and excited states. Similar processes may be important for obtaining the ignited mode. The methods used to measure static and dynamic volt-ampere curves are described. The use of a controlled-current load has yielded a negative resistance'' region in the curves which show the ignited mode. The curves obtained with poor current control do not show this phenomenon. Extinction is considered from the standpoint of Kaufmann' s criterion for stability. (auth)« less

Dislocation mechanism based model for stage II fatigue crack propagation rate

NASA Technical Reports Server (NTRS)

Mazumdar, P. K.

1986-01-01

Repeated plastic deformation, which of course depends on dislocation mechanism, at or near the crack tip leads to the fatigue crack propagation. By involving the theory of thermally activated flow and the cumulative plastic strain criterion, an effort is made here to model the stage II fatigue crack propagation rate in terms of the dislocation mechanism. The model, therefore, provides capability to ascertain: (1) the dislocation mechanism (and hence the near crack tip microstructures) assisting the crack growth, (2) the relative resistance of dislocation mechanisms to the crack growth, and (3) the fracture surface characteristics and its interpretation in terms of the dislocation mechanism. The local microstructure predicted for the room temperature crack growth in copper by this model is in good agreement with the experimental results taken from the literature. With regard to the relative stability of such dislocation mechanisms as the cross-slip and the dislocation intersection, the model suggests an enhancement of crack growth rate with an ease of cross-slip which in general promotes dislocation cell formation and is common in material which has high stacking fault energy (produces wavy slips). Cross-slip apparently enhances crack growth rate by promoting slip irreversibility and fracture surface brittleness to a greater degree.

Bilateral Comparison Between NIM and NMC Over the Temperature Range from 83.8058 K to 692.677 K

NASA Astrophysics Data System (ADS)

Sun, Jianping; Ye, Shaochun; Kho, Haoyuan; Zhang, Jintao; Wang, Li

2015-08-01

A bilateral comparison of local realization of the International Temperature Scale of 1990 between the National Institute of Metrology (NIM) and National Metrology Centre (NMC) was carried out over the temperature range from 83.8058 K to 692.677 K. It involved six fixed points including the argon triple point, the mercury triple point, the triple point of water, the melting point of gallium, the freezing point of tin, and the freezing point of zinc. In 2009, NMC asked NIM to participate in a bilateral comparison to link the NMC results to the Consultative Committee for Thermometry Key Comparison 3 (CCT-K3) and facilitate the NMC's calibration and measurement capabilities submission. This comparison was agreed by NIM and Asia Pacific Metrology Programme in 2009, and registered in the Key Comparison Database in 2010 as CCT-K3.2. NMC supplied two fused silica sheath standard platinum resistance thermometers (SPRTs) as traveling standards. One of them was used at the Ga, Sn, and Zn fixed points, while the other one was used at the Ar and Hg fixed points. NMC measured them before and after NIM measured them. During the comparison, a criterion for the SPRT was set as the stability at the triple point of water to be less than 0.3 mK. The results for both laboratories are summarized. A proposal for linking the NMC's comparison results to CCT-K3 is presented. The difference between NMC and NIM and the difference between NMC and the CCT-K3 average reference value using NIM as a link are reported with expanded uncertainties at each measured fixed point.

A comprehensive model to determine the effects of temperature and species fluctuations on reaction rates in turbulent reacting flows

NASA Technical Reports Server (NTRS)

Foy, E.; Ronan, G.; Chinitz, W.

1982-01-01

A principal element to be derived from modeling turbulent reacting flows is an expression for the reaction rates of the various species involved in any particular combustion process under consideration. A temperature-derived most-likely probability density function (pdf) was used to describe the effects of temperature fluctuations on the Arrhenius reaction rate constant. A most-likely bivariate pdf described the effects of temperature and species concentrations fluctuations on the reaction rate. A criterion is developed for the use of an "appropriate" temperature pdf. The formulation of models to calculate the mean turbulent Arrhenius reaction rate constant and the mean turbulent reaction rate is considered and the results of calculations using these models are presented.

Bionic Control of Cheetah Bounding with a Segmented Spine.

PubMed

Wang, Chunlei; Wang, Shigang

2016-01-01

A cheetah model is built to mimic real cheetah and its mechanical and dimensional parameters are derived from the real cheetah. In particular, two joints in spine and four joints in a leg are used to realize the motion of segmented spine and segmented legs which are the key properties of the cheetah bounding. For actuating and stabilizing the bounding gait of cheetah, we present a bioinspired controller based on the state-machine. The controller mainly mimics the function of the cerebellum to plan the locomotion and keep the body balance. The haptic sensor and proprioception system are used to detect the trigger of the phase transition. Besides, the vestibular modulation could perceive the pitching angle of the trunk. At last, the cerebellum acts as the CPU to operate the information from the biological sensors. In addition, the calculated results are transmitted to the low-level controller to actuate and stabilize the cheetah bounding. Moreover, the delay feedback control method is employed to plan the motion of the leg joints to stabilize the pitching motion of trunk with the stability criterion. Finally, the cyclic cheetah bounding with biological properties is realized. Meanwhile, the stability and dynamic properties of the cheetah bounding gait are analyzed elaborately.

Structural stability of DNA origami nanostructures in the presence of chaotropic agents

NASA Astrophysics Data System (ADS)

Ramakrishnan, Saminathan; Krainer, Georg; Grundmeier, Guido; Schlierf, Michael; Keller, Adrian

2016-05-01

DNA origami represent powerful platforms for single-molecule investigations of biomolecular processes. The required structural integrity of the DNA origami may, however, pose significant limitations regarding their applicability, for instance in protein folding studies that require strongly denaturing conditions. Here, we therefore report a detailed study on the stability of 2D DNA origami triangles in the presence of the strong chaotropic denaturing agents urea and guanidinium chloride (GdmCl) and its dependence on concentration and temperature. At room temperature, the DNA origami triangles are stable up to at least 24 h in both denaturants at concentrations as high as 6 M. At elevated temperatures, however, structural stability is governed by variations in the melting temperature of the individual staple strands. Therefore, the global melting temperature of the DNA origami does not represent an accurate measure of their structural stability. Although GdmCl has a stronger effect on the global melting temperature, its attack results in less structural damage than observed for urea under equivalent conditions. This enhanced structural stability most likely originates from the ionic nature of GdmCl. By rational design of the arrangement and lengths of the individual staple strands used for the folding of a particular shape, however, the structural stability of DNA origami may be enhanced even further to meet individual experimental requirements. Overall, their high stability renders DNA origami promising platforms for biomolecular studies in the presence of chaotropic agents, including single-molecule protein folding or structural switching.DNA origami represent powerful platforms for single-molecule investigations of biomolecular processes. The required structural integrity of the DNA origami may, however, pose significant limitations regarding their applicability, for instance in protein folding studies that require strongly denaturing conditions. Here, we therefore report a detailed study on the stability of 2D DNA origami triangles in the presence of the strong chaotropic denaturing agents urea and guanidinium chloride (GdmCl) and its dependence on concentration and temperature. At room temperature, the DNA origami triangles are stable up to at least 24 h in both denaturants at concentrations as high as 6 M. At elevated temperatures, however, structural stability is governed by variations in the melting temperature of the individual staple strands. Therefore, the global melting temperature of the DNA origami does not represent an accurate measure of their structural stability. Although GdmCl has a stronger effect on the global melting temperature, its attack results in less structural damage than observed for urea under equivalent conditions. This enhanced structural stability most likely originates from the ionic nature of GdmCl. By rational design of the arrangement and lengths of the individual staple strands used for the folding of a particular shape, however, the structural stability of DNA origami may be enhanced even further to meet individual experimental requirements. Overall, their high stability renders DNA origami promising platforms for biomolecular studies in the presence of chaotropic agents, including single-molecule protein folding or structural switching. Electronic supplementary information (ESI) available: Melting curves without baseline subtraction, AFM images of DNA origami after 24 h incubation, calculated melting temperatures of all staple strands. See DOI: 10.1039/c6nr00835f

Geomechanical Evaluation of Thermal Impact of Injected CO 2 Temperature on a Geological Reservoir: Application to the FutureGen 2.0 Site

DOE PAGES

Bonneville, Alain; USA, Richland Washington; Nguyen, Ba Nghiep; ...

2014-12-31

The impact of temperature variations of injected CO 2 on the mechanical integrity of a reservoir is a problem rarely addressed in the design of a CO 2 storage site. The geomechanical simulation of the FutureGen 2.0 storage site presented here takes into account the complete modeling of heat exchange between the environment and CO 2 during its transport in the pipeline and injection well before reaching the reservoir, as well as its interaction with the reservoir host rock. An ad-hoc program was developed to model CO 2 transport from the power plant to the reservoir and an approach couplingmore » PNNL STOMP-CO 2 multiphase flow simulator and ABAQUS® has been developed for the reservoir model which is fully three-dimensional with four horizontal wells and variable layer thickness. The Mohr-Coulomb fracture criterion has been employed, where hydraulic fracture was predicted to occur at an integration point if the fluid pressure at the point exceeded the least compressive principal stress. Evaluation of the results shows that the fracture criterion has not been verified at any node and time step for the CO 2 temperature range predicted at the top of the injection zone.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

White, M.K.

Corrosion data have been obtained for tub is exposed for 1500--2000 hours in a proof-of-concept magnetohydrodynamics (MHD) power generation test facility to conditions representative of superheater and intermediate temperature air heater (ITAH) components. The tubes, coated with K{sub 2}SO{sub 4}-rich deposits, were corroded more than in most pulverized coal fired superheater service, but much less than the highly aggressive liquid phase attack encountered in conventional plants with certain coals and temperatures. Results indicated that, with parabolic corrosion kinetics, type 310 and 253MA stainless steels should be usable to 1400F at hot end of ITAH. At final superheater temperatures, 2.25 andmore » 5 Cr steels were indicated to have parabolic corrosion rates generally below a 0.5 mm/yr criterion, based on corrosion scale thickness. However, unknown amounts of scale loss from spallation made this determination uncertain. Stainless steels 304H, 316H, and 321H had parabolic rates variably above the criterion, but may be servicable under less cyclic conditions. Corrosion rates derived from scale thickness and intergranular corrosion depth measurements are reported, along with scale morphologies and compositions. Implications of results on commercial MHD utilization of the alloys are discussed, as well as the indicated need for more corrosion resistant alloys or coatings under the most severe exposure conditions.« less

Stabilizing Nanocrystalline Oxide Nanofibers at Elevated Temperatures by Coating Nanoscale Surface Amorphous Films.

PubMed

Yao, Lei; Pan, Wei; Luo, Jian; Zhao, Xiaohui; Cheng, Jing; Nishijima, Hiroki

2018-01-10

Nanocrystalline materials often exhibit extraordinary mechanical and physical properties but their applications at elevated temperatures are impaired by the rapid grain growth. Moreover, the grain growth in nanocrystalline oxide nanofibers at high temperatures can occur at hundreds of degrees lower than that would occur in corresponding bulk nanocrystalline materials, which would eventually break the fibers. Herein, by characterizing a model system of scandia-stabilized zirconia using hot-stage in situ scanning transmission electron microscopy, we discover that the enhanced grain growth in nanofibers is initiated at the surface. Subsequently, we demonstrate that coating the fibers with nanometer-thick amorphous alumina layer can enhance their temperature stability by nearly 400 °C via suppressing the surface-initiated grain growth. Such a strategy can be effectively applied to other oxide nanofibers, such as samarium-doped ceria, yttrium-stabilized zirconia, and lanthanum molybdate. The nanocoatings also increase the flexibility of the oxide nanofibers and stabilize the high-temperature phases that have 10 times higher ionic conductivity. This study provides new insights into the surface-initiated grain growth in nanocrystalline oxide nanofibers and develops a facile yet innovative strategy to improve the high-temperature stability of nanofibers for a broad range of applications.

Collisionless kinetic theory of oblique tearing instabilities

DOE PAGES

Baalrud, S. D.; Bhattacharjee, A.; Daughton, W.

2018-02-15

The linear dispersion relation for collisionless kinetic tearing instabilities is calculated for the Harris equilibrium. In contrast to the conventional 2D geometry, which considers only modes at the center of the current sheet, modes can span the current sheet in 3D. Modes at each resonant surface have a unique angle with respect to the guide field direction. Both kinetic simulations and numerical eigenmode solutions of the linearized Vlasov-Maxwell equations have recently revealed that standard analytic theories vastly overestimate the growth rate of oblique modes. In this paper, we find that this stabilization is associated with the density-gradient-driven diamagnetic drift. Themore » analytic theories miss this drift stabilization because the inner tearing layer broadens at oblique angles sufficiently far that the assumption of scale separation between the inner and outer regions of boundary-layer theory breaks down. The dispersion relation obtained by numerically solving a single second order differential equation is found to approximately capture the drift stabilization predicted by solutions of the full integro-differential eigenvalue problem. Finally, a simple analytic estimate for the stability criterion is provided.« less

Collisionless kinetic theory of oblique tearing instabilities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baalrud, S. D.; Bhattacharjee, A.; Daughton, W.

The linear dispersion relation for collisionless kinetic tearing instabilities is calculated for the Harris equilibrium. In contrast to the conventional 2D geometry, which considers only modes at the center of the current sheet, modes can span the current sheet in 3D. Modes at each resonant surface have a unique angle with respect to the guide field direction. Both kinetic simulations and numerical eigenmode solutions of the linearized Vlasov-Maxwell equations have recently revealed that standard analytic theories vastly overestimate the growth rate of oblique modes. In this paper, we find that this stabilization is associated with the density-gradient-driven diamagnetic drift. Themore » analytic theories miss this drift stabilization because the inner tearing layer broadens at oblique angles sufficiently far that the assumption of scale separation between the inner and outer regions of boundary-layer theory breaks down. The dispersion relation obtained by numerically solving a single second order differential equation is found to approximately capture the drift stabilization predicted by solutions of the full integro-differential eigenvalue problem. Finally, a simple analytic estimate for the stability criterion is provided.« less

An application of the LC-LSTM framework to the self-esteem instability case.

PubMed

Alessandri, Guido; Vecchione, Michele; Donnellan, Brent M; Tisak, John

2013-10-01

The present research evaluates the stability of self-esteem as assessed by a daily version of the Rosenberg (Society and the adolescent self-image, Princeton University Press, Princeton, 1965) general self-esteem scale (RGSE). The scale was administered to 391 undergraduates for five consecutive days. The longitudinal data were analyzed using the integrated LC-LSTM framework that allowed us to evaluate: (1) the measurement invariance of the RGSE, (2) its stability and change across the 5-day assessment period, (3) the amount of variance attributable to stable and transitory latent factors, and (4) the criterion-related validity of these factors. Results provided evidence for measurement invariance, mean-level stability, and rank-order stability of daily self-esteem. Latent state-trait analyses revealed that variances in scores of the RGSE can be decomposed into six components: stable self-esteem (40 %), ephemeral (or temporal-state) variance (36 %), stable negative method variance (9 %), stable positive method variance (4 %), specific variance (1 %) and random error variance (10 %). Moreover, latent factors associated with daily self-esteem were associated with measures of depression, implicit self-esteem, and grade point average.

Collisionless kinetic theory of oblique tearing instabilities

NASA Astrophysics Data System (ADS)

Baalrud, S. D.; Bhattacharjee, A.; Daughton, W.

2018-02-01

The linear dispersion relation for collisionless kinetic tearing instabilities is calculated for the Harris equilibrium. In contrast to the conventional 2D geometry, which considers only modes at the center of the current sheet, modes can span the current sheet in 3D. Modes at each resonant surface have a unique angle with respect to the guide field direction. Both kinetic simulations and numerical eigenmode solutions of the linearized Vlasov-Maxwell equations have recently revealed that standard analytic theories vastly overestimate the growth rate of oblique modes. We find that this stabilization is associated with the density-gradient-driven diamagnetic drift. The analytic theories miss this drift stabilization because the inner tearing layer broadens at oblique angles sufficiently far that the assumption of scale separation between the inner and outer regions of boundary-layer theory breaks down. The dispersion relation obtained by numerically solving a single second order differential equation is found to approximately capture the drift stabilization predicted by solutions of the full integro-differential eigenvalue problem. A simple analytic estimate for the stability criterion is provided.

Motion stability of the magnetic levitation and suspension with YBa2Cu3O7-x high-Tc superconducting bulks and NdFeB magnets

NASA Astrophysics Data System (ADS)

Li, Jipeng; Zheng, Jun; Huang, Huan; Li, Yanxing; Li, Haitao; Deng, Zigang

2017-10-01

The flux pinning effect of YBa2Cu3O7-x high temperature superconducting (HTS) bulk can achieve self-stable levitation over a permanent magnet or magnet array. Devices based on this phenomenon have been widely developed. However, the self-stable flux pinning effect is not unconditional, under disturbances, for example. To disclose the roots of this amazing self-stable levitation phenomenon in theory, mathematical and mechanical calculations using Lyapunov's stability theorem and the Hurwitz criterion were performed under the conditions of magnetic levitation and suspension of HTS bulk near permanent magnets in Halbach array. It is found that the whole dynamical system, in the case of levitation, has only one equilibrium solution, and the singular point is a stable focus. In the general case of suspension, the system has two singular points: one is a stable focus, and the other is an unstable saddle. With the variation of suspension force, the two first-order singular points mentioned earlier will get closer and closer, and finally degenerate to a high-order singular point, which means the stable region gets smaller and smaller, and finally vanishes. According to the center manifold theorem, the high-order singular point is unstable. With the interaction force varying, the HTS suspension dynamical system undergoes a saddle-node bifurcation. Moreover, a deficient damping can also decrease the stable region. These findings, together with existing experiments, could enlighten the improvement of HTS devices with strong anti-interference ability.

Constraints on oceanic methane emissions west of Svalbard from atmospheric in situ measurements and Lagrangian transport modeling

NASA Astrophysics Data System (ADS)

Pisso, Ignacio; Myhre, Cathrine Lund; Platt, Stephen Matthew; Eckhardt, Sabine; Hermansen, Ove; Schmidbauer, Norbert; Mienert, Jurgen; Vadakkepuliyambatta, Sunil; Bauguitte, Stephane; Pitt, Joseph; Allen, Grant; Bower, Keith; O'Shea, Sebastian; Gallagher, Martin; Percival, Carl; Pyle, John; Cain, Michelle; Stohl, Andreas

2017-04-01

Methane stored in seabed reservoirs such as methane hydrates can reach the atmosphere in the form of bubbles or dissolved in water. Hydrates could destabilize with rising temperature further increasing greenhouse gas emissions in a warming climate. To assess the impact of oceanic emissions from the area west of Svalbard, where methane hydrates are abundant, we used measurements collected with a research aircraft (FAAM) and a ship (Helmer Hansen) during the Summer 2014, and for Zeppelin Observatory for the full year. We present a model-supported analysis of the atmospheric CH4 mixing ratios measured by the different platforms. To address uncertainty about where CH4 emissions actually occur, we explored three scenarios: areas with known seeps, a hydrate stability model and an ocean depth criterion. We then used a budget analysis and a Lagrangian particle dispersion model to compare measurements taken upwind and downwind of the potential CH4 emission areas. We found small differences between the CH4 mixing ratios measured upwind and downwind of the potential emission areas during the campaign. By taking into account measurement and sampling uncertainties and by determining the sensitivity of the measured mixing ratios to potential oceanic emissions, we provide upper limits for the CH4 fluxes. The CH4 flux during the campaign was small, with an upper limit of 2.5 nmol / m s in the stability model scenario. The Zeppelin Observatory data for 2014 suggests CH4 fluxes from the Svalbard continental platform below 0.2 Tg/yr . All estimates are in the lower range of values previously reported.

Optimal design of gas adsorption refrigerators for cryogenic cooling

NASA Technical Reports Server (NTRS)

Chan, C. K.

1983-01-01

The design of gas adsorption refrigerators used for cryogenic cooling in the temperature range of 4K to 120K was examined. The functional relationships among the power requirement for the refrigerator, the system mass, the cycle time and the operating conditions were derived. It was found that the precool temperature, the temperature dependent heat capacities and thermal conductivities, and pressure and temperature variations in the compressors have important impacts on the cooling performance. Optimal designs based on a minimum power criterion were performed for four different gas adsorption refrigerators and a multistage system. It is concluded that the estimates of the power required and the system mass are within manageable limits in various spacecraft environments.

Prediction of the bending behavior after pre-strain of an aluminum alloy

NASA Astrophysics Data System (ADS)

Pradeau, A.; Thuillier, S.; Yoon, J. W.

2016-10-01

The present work is focused on the modeling of sheet metal mechanical behavior up to rupture, including anisotropy and hardening. The mechanical behavior of an AA6016 alloy was characterized at room temperature in tension, simple shear and hydraulic bulging. The initial anisotropy was described with the Yld2004-18p yield criterion coupled to a mixed hardening law. Concerning rupture, an uncoupled phenomenological criterion of Mohr-Coulomb type will be used. For the material parameter identification, an inverse methodology was used with the objective of reducing the gap between experimental and numerical data. Finally, validation of the results was performed on bending tests with different amplitudes of tension pre-strain in order to reach or not rupture in the bent area.

Matrix cracking in laminated composites under monotonic and cyclic loadings

NASA Technical Reports Server (NTRS)

Allen, David H.; Lee, Jong-Won

1991-01-01

An analytical model based on the internal state variable (ISV) concept and the strain energy method is proposed for characterizing the monotonic and cyclic response of laminated composites containing matrix cracks. A modified constitution is formulated for angle-ply laminates under general in-plane mechanical loading and constant temperature change. A monotonic matrix cracking criterion is developed for predicting the crack density in cross-ply laminates as a function of the applied laminate axial stress. An initial formulation for a cyclic matrix cracking criterion for cross-ply laminates is also discussed. For the monotonic loading case, a number of experimental data and well-known models are compared with the present study for validating the practical applicability of the ISV approach.

Linearized blade row compression component model. Stability and frequency response analysis of a J85-3 compressor

NASA Technical Reports Server (NTRS)

Tesch, W. A.; Moszee, R. H.; Steenken, W. G.

1976-01-01

NASA developed stability and frequency response analysis techniques were applied to a dynamic blade row compression component stability model to provide a more economic approach to surge line and frequency response determination than that provided by time-dependent methods. This blade row model was linearized and the Jacobian matrix was formed. The clean-inlet-flow stability characteristics of the compressors of two J85-13 engines were predicted by applying the alternate Routh-Hurwitz stability criterion to the Jacobian matrix. The predicted surge line agreed with the clean-inlet-flow surge line predicted by the time-dependent method to a high degree except for one engine at 94% corrected speed. No satisfactory explanation of this discrepancy was found. The frequency response of the linearized system was determined by evaluating its Laplace transfer function. The results of the linearized-frequency-response analysis agree with the time-dependent results when the time-dependent inlet total-pressure and exit-flow function amplitude boundary conditions are less than 1 percent and 3 percent, respectively. The stability analysis technique was extended to a two-sector parallel compressor model with and without interstage crossflow and predictions were carried out for total-pressure distortion extents of 180 deg, 90 deg, 60 deg, and 30 deg.

An experimental study of the Rayleigh-Taylor instability critical wave length

NASA Astrophysics Data System (ADS)

Kong, Xujing; Wang, Youchun; Zhang, Shufei; Xu, Hongkun

1992-06-01

A physical model has been constructed to represent the condensate film pattern on a horizontal downward-facing surface with fins, which is based on visual observation in experiment. The results of analysis using this model confirms the validity of the critical wave length formula obtained from Rayleigh-Taylor stability analysis. This formula may be used as a criterion to design horizontal downward-facing surfaces with fins that can best destabilize the condensate film, thus enhancing condensation heat transfer.

Evaluation of Solidification/Stabilization for Treating Contaminates Soils from the Frontier Hard Chrome Site

DTIC Science & Technology

1992-05-01

replicates were ɘ.020 mg/L. The chromium present was in the trivalent form. 139. Vendor 2. The replicate total chromium TCLP concentrations in the...criterion. The chromium present in the leachates was in the trivalent form, shown by concentrations of Cr(VI) of ɘ.020, ɘ.020, and 0.042 mg/L. 142...concentrations of total chromium were 4.7, 3.7, and 4.1 mg/L. Chromium is present in the trivalent form. The total chromium concentrations were below

Localized temperature stability of low temperature cofired ceramics

DOEpatents

Dai, Steven Xunhu

2013-11-26

The present invention is directed to low temperature cofired ceramic modules having localized temperature stability by incorporating temperature coefficient of resonant frequency compensating materials locally into a multilayer LTCC module. Chemical interactions can be minimized and physical compatibility between the compensating materials and the host LTCC dielectrics can be achieved. The invention enables embedded resonators with nearly temperature-independent resonance frequency.

Likelihood of Alfvénic instability bifurcation in experiments

NASA Astrophysics Data System (ADS)

Duarte, Vinicius; Gorelenkov, Nikolai; Schneller, Mirjam; Fredrickson, Eric; Berk, Herbert; Canal, Gustavo; Heidbrink, William; Kaye, Stanley; Podesta, Mario; van Zeeland, Michael; Wang, Weixing

2017-10-01

We apply a criterion for the likely nature of fast ion redistribution in tokamaks to be in the convective or diffusive nonlinear regimes. The criterion, which is shown to be rather sensitive to the relative strength of collisional or micro-turbulent scattering and drag processes, ultimately translates into a condition for the applicability of reduced quasilinear modeling for realistic tokamak eigenmodes scenarios. The criterion is tested and validated against different machines, where the chirping mode behavior is shown to be in accord with the model. It has been found that the anomalous fast ion transport is a likely mediator of the bifurcation between the fixed-frequency mode behavior and rapid chirping in tokamaks. In addition, micro-turbulence appears to resolve the disparity with respect to the ubiquitous chirping observation in spherical tokamaks and its rarer occurrence in conventional tokamaks. In NSTX, the tendency for chirping is further studied in terms of the beam beta and the plasma rotation shear. For more accurate quantitative assessment, numerical simulations of the effects of electrostatic ion temperature gradient turbulence on chirping are presently being pursued using the GTS code.

Empirical extensions of the lasso penalty to reduce the false discovery rate in high-dimensional Cox regression models.

PubMed

Ternès, Nils; Rotolo, Federico; Michiels, Stefan

2016-07-10

Correct selection of prognostic biomarkers among multiple candidates is becoming increasingly challenging as the dimensionality of biological data becomes higher. Therefore, minimizing the false discovery rate (FDR) is of primary importance, while a low false negative rate (FNR) is a complementary measure. The lasso is a popular selection method in Cox regression, but its results depend heavily on the penalty parameter λ. Usually, λ is chosen using maximum cross-validated log-likelihood (max-cvl). However, this method has often a very high FDR. We review methods for a more conservative choice of λ. We propose an empirical extension of the cvl by adding a penalization term, which trades off between the goodness-of-fit and the parsimony of the model, leading to the selection of fewer biomarkers and, as we show, to the reduction of the FDR without large increase in FNR. We conducted a simulation study considering null and moderately sparse alternative scenarios and compared our approach with the standard lasso and 10 other competitors: Akaike information criterion (AIC), corrected AIC, Bayesian information criterion (BIC), extended BIC, Hannan and Quinn information criterion (HQIC), risk information criterion (RIC), one-standard-error rule, adaptive lasso, stability selection, and percentile lasso. Our extension achieved the best compromise across all the scenarios between a reduction of the FDR and a limited raise of the FNR, followed by the AIC, the RIC, and the adaptive lasso, which performed well in some settings. We illustrate the methods using gene expression data of 523 breast cancer patients. In conclusion, we propose to apply our extension to the lasso whenever a stringent FDR with a limited FNR is targeted. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

Fault Diagnosis Based on Chemical Sensor Data with an Active Deep Neural Network

PubMed Central

Jiang, Peng; Hu, Zhixin; Liu, Jun; Yu, Shanen; Wu, Feng

2016-01-01

Big sensor data provide significant potential for chemical fault diagnosis, which involves the baseline values of security, stability and reliability in chemical processes. A deep neural network (DNN) with novel active learning for inducing chemical fault diagnosis is presented in this study. It is a method using large amount of chemical sensor data, which is a combination of deep learning and active learning criterion to target the difficulty of consecutive fault diagnosis. DNN with deep architectures, instead of shallow ones, could be developed through deep learning to learn a suitable feature representation from raw sensor data in an unsupervised manner using stacked denoising auto-encoder (SDAE) and work through a layer-by-layer successive learning process. The features are added to the top Softmax regression layer to construct the discriminative fault characteristics for diagnosis in a supervised manner. Considering the expensive and time consuming labeling of sensor data in chemical applications, in contrast to the available methods, we employ a novel active learning criterion for the particularity of chemical processes, which is a combination of Best vs. Second Best criterion (BvSB) and a Lowest False Positive criterion (LFP), for further fine-tuning of diagnosis model in an active manner rather than passive manner. That is, we allow models to rank the most informative sensor data to be labeled for updating the DNN parameters during the interaction phase. The effectiveness of the proposed method is validated in two well-known industrial datasets. Results indicate that the proposed method can obtain superior diagnosis accuracy and provide significant performance improvement in accuracy and false positive rate with less labeled chemical sensor data by further active learning compared with existing methods. PMID:27754386

Fault Diagnosis Based on Chemical Sensor Data with an Active Deep Neural Network.

PubMed

Jiang, Peng; Hu, Zhixin; Liu, Jun; Yu, Shanen; Wu, Feng

2016-10-13

Big sensor data provide significant potential for chemical fault diagnosis, which involves the baseline values of security, stability and reliability in chemical processes. A deep neural network (DNN) with novel active learning for inducing chemical fault diagnosis is presented in this study. It is a method using large amount of chemical sensor data, which is a combination of deep learning and active learning criterion to target the difficulty of consecutive fault diagnosis. DNN with deep architectures, instead of shallow ones, could be developed through deep learning to learn a suitable feature representation from raw sensor data in an unsupervised manner using stacked denoising auto-encoder (SDAE) and work through a layer-by-layer successive learning process. The features are added to the top Softmax regression layer to construct the discriminative fault characteristics for diagnosis in a supervised manner. Considering the expensive and time consuming labeling of sensor data in chemical applications, in contrast to the available methods, we employ a novel active learning criterion for the particularity of chemical processes, which is a combination of Best vs. Second Best criterion (BvSB) and a Lowest False Positive criterion (LFP), for further fine-tuning of diagnosis model in an active manner rather than passive manner. That is, we allow models to rank the most informative sensor data to be labeled for updating the DNN parameters during the interaction phase. The effectiveness of the proposed method is validated in two well-known industrial datasets. Results indicate that the proposed method can obtain superior diagnosis accuracy and provide significant performance improvement in accuracy and false positive rate with less labeled chemical sensor data by further active learning compared with existing methods.

Adaptive fuzzy controller for thermal comfort inside the air-conditioned automobile chamber

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tong, L.; Yu, B.; Chen, Z.

1999-07-01

In order to meet the passengers' demand for thermal comfort, the adaptive fuzzy logic control design methodology is applied for the automobile airconditioner system. In accordance with the theory of air flow and heat transfer, the air temperature field inside the airconditioned automobile chamber is simulated by a set of simplified half-empirical formula. Then, instead of PMV (Predicted Mean Vote) criterion, RIV (Real Individual Vote) criterion is adopted as the base of the control for passengers' thermal comfort. The proposed controller is applied to the air temperature regulation at the individual passenger position. The control procedure is based on partitioningmore » the state space of the system into cell-groups and fuzzily quantificating the state space into these cells. When the system model has some parameter perturbation, the controller can also adjust its control parameters to compensate for the perturbation and maintain the good performance. The learning procedure shows its ideal effect in both computer simulation and experiments. The final results demonstrate the ideal performance of this adaptive fuzzy controller.« less

SULTAN measurement and qualification: ITER-US-LLNL-NMARTOVETSKY- 092008

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martovetsky, N N

2006-09-21

Measuring the characteristics of full scale ITER CICC at SULTAN is the critical qualification test. If volt-ampere characteristic (VAC) or volt-temperature characteristic (VTC) are distorted, the criterion of 10 uV/m may not be a valid criterion to judge the conductor performance. Only measurements with a clear absence or low signals from the current distribution should be considered as quantitatively representative, although in some obvious circumstances one can judge if a conductor will meet or fail ITER requirements. SULTAN full scale ITER CICC testing should be done with all measures taken to ensure uniform current redistribution. A full removal of Crmore » plating in the joint area and complete solder filling of the joints (with provision of the central channel for helium flow) should be mandatory for DC qualification samples for ITER. Also, T and I should be increased slowly that an equilibrium could be established for accurate measurement of Tcs, Ic and N. It is also desirable to go up in down in current and/or temperature (within stable range) to make sure that the equilibrium is reached.« less

Stability of peptides in high-temperature aqueous solutions

NASA Astrophysics Data System (ADS)

Shock, Everett L.

1992-09-01

Estimated standard molal thermodynamic properties of aqueous dipeptides and their constituent amino acids indicate that temperature increases correspond to increased stability of peptide bonds relative to hydrolysis reactions. Pressure increases cause slight decreases in peptide bond stability, which are generally offset by greater stability caused by temperature increases along geothermal gradients. These calculations suggest that peptides, polypeptides, and proteins may survive hydrothermal alteration of organic matter depending on the rates of the hydrolysis reactions. Extremely thermophilic organisms may be able to take advantage of the decreased energy required to form peptide bonds in order to maintain structural proteins and enzymes at elevated temperatures and pressures. As the rates of hydrolysis reactions increase with increasing temperature, formation of peptide bonds may become a facile process in hydrothermal systems and deep in sedimentary basins.

The relationship between dental implant stability and trabecular bone structure using cone-beam computed tomography

PubMed Central

2016-01-01

Purpose The objective of this study was to investigate the relationships between primary implant stability as measured by impact response frequency and the structural parameters of trabecular bone using cone-beam computed tomography(CBCT), excluding the effect of cortical bone thickness. Methods We measured the impact response of a dental implant placed into swine bone specimens composed of only trabecular bone without the cortical bone layer using an inductive sensor. The peak frequency of the impact response spectrum was determined as an implant stability criterion (SPF). The 3D microstructural parameters were calculated from CT images of the bone specimens obtained using both micro-CT and CBCT. Results SPF had significant positive correlations with trabecular bone structural parameters (BV/TV, BV, BS, BSD, Tb.Th, Tb.N, FD, and BS/BV) (P<0.01) while SPF demonstrated significant negative correlations with other microstructural parameters (Tb.Sp, Tb.Pf, and SMI) using micro-CT and CBCT (P<0.01). Conclusions There was an increase in implant stability prediction by combining BV/TV and SMI in the stepwise forward regression analysis. Bone with high volume density and low surface density shows high implant stability. Well-connected thick bone with small marrow spaces also shows high implant stability. The combination of bone density and architectural parameters measured using CBCT can predict the implant stability more accurately than the density alone in clinical diagnoses. PMID:27127692

Rational rates of uniform decay for strong solutions to a fluid-structure PDE system

NASA Astrophysics Data System (ADS)

Avalos, George; Bucci, Francesca

2015-06-01

In this work we investigate the uniform stability properties of solutions to a well-established partial differential equation (PDE) model for a fluid-structure interaction. The PDE system under consideration comprises a Stokes flow which evolves within a three-dimensional cavity; moreover, a Kirchhoff plate equation is invoked to describe the displacements along a (fixed) portion - say, Ω - of the cavity wall. Contact between the respective fluid and structure dynamics occurs on the boundary interface Ω. The main result in the paper is as follows: the solutions to the composite PDE system, corresponding to smooth initial data, decay at the rate of O (1 / t). Our method of proof hinges upon the appropriate invocation of a relatively recent resolvent criterion for polynomial decays of C0-semigroups. While the characterization provided by said criterion originates in the context of operator theory and functional analysis, the work entailed here is wholly within the realm of PDE.

A Manual Control Test for the Detection and Deterrence of Impaired Drivers

NASA Technical Reports Server (NTRS)

Stein, A. C.; Allen, R. W.; Jex, H. R.

1984-01-01

A brief manual control test and a decision strategy were developed, laboratory tested, and field validated which provide a means for detecting human operator impairment from alcohol or other drugs. The test requires the operator to stabilize progressively unstable controlled element dynamics. Control theory and experimental data verify that the human operator's control ability on this task is constrained by basic cybernetic characteristics, and that task performance is reliably affected by impairment effects on these characteristics. Assessment of human operator control ability is determined by a statistically based decision strategy. The operator is allowed several chances to exceed a preset pass criterion. Procedures are described for setting the pass criterion based on individual ability and a desired unimpaired failure rate. These procedures were field tested with apparatus installed in automobiles that were designed to discourage drunk drivers from operating their vehicles. This test program demonstrated that the control task and detection strategy could be applied in a practical setting to screen human operators for impairment in their basic cybernetic skills.

The Italian version of the Inventory of Interpersonal Problems Personality Disorders Scales (IIP-47): psychometric properties and clinical usefulness as a screening measure.

PubMed

Ubbiali, Alessandro; Chiorri, Carlo; Donati, Deborah

2011-08-01

The Inventory of Interpersonal Problems-47 (IIP-47) is a brief and valid self-report measure for screening Personality Disorders (PDs). This study examined internal consistency, factor structure, criterion validity, temporal stability, and operating characteristics of the Italian version of the IIP-47 in two independent samples: PD subjects (n = 120) and nonclinical subjects (n = 475). Alpha coefficients ranged from .70 to .90. Multiple-Group Confirmatory Factor Analyses showed that the five-correlated-factor model reported in literature had the highest measurement invariance across the two groups. Criterion validity was supported by correlations among IIP-47 scale scores and scores on established measures of personality dimensions and pathology. Test-retest indices ranged from .71 to .95. PD subjects scored significantly higher than nonclinical subjects on all IIP-47 scales and cut-off scores for different levels of specificity and sensibility are reported. It is concluded that the psychometric properties of the original IIP-47 were preserved in its Italian version.

Stability of volcanic conduits: insights from magma ascent modelling and possible consequences on eruptive dynamics

NASA Astrophysics Data System (ADS)

Aravena, Alvaro; de'Michieli Vitturi, Mattia; Cioni, Raffaello; Neri, Augusto

2017-04-01

Geological evidences of changes in volcanic conduit geometry (i.e. erosive processes) are common in the volcanic record, as revealed by the occurrence of lithic fragments in most pyroclastic deposits. However, the controlling factors of conduit enlargement mechanisms are still partially unclear, as well as the influence of conduit geometry in the eruptive dynamics. Despite physical models have been systematically used for studying volcanic conduits, their mechanical stability has been poorly addressed. In order to study the mechanical stability of volcanic conduits during explosive eruptions, we present a 1D steady-state model which considers the main processes experimented by ascending magmas, such as crystallization, drag forces, fragmentation, outgassing and degassing; and the application of the Mogi-Coulomb collapse criterion, using a set of constitutive equations for studying typical cases of rhyolitic and trachytic explosive volcanism. From our results emerge that conduit stability is mainly controlled by magma rheology and conduit dimensions. Indeed, in order to be stable, feeding conduits of rhyolitic eruptions need larger radii respect to their trachytic counterparts, which is manifested in the higher eruption rates usually observed in rhyolitic explosive eruptions, as confirmed by a small compilation of global data. Additionally, for both magma compositions, we estimated a minimum magma flux for developing stable conduits (˜3ṡ106 kg/s for trachytic magmas and ˜8ṡ107 kg/s for rhyolitic magmas), which is consistent with the unsteady character commonly observed in low-mass flux events (e.g. sub-Plinian eruptions), which would be produced by episodic collapse events of the volcanic conduit, opposite to the mainly stationary high-mass flux events (e.g. Plinian eruptions), characterized by stable conduits. For a given magma composition, a minimum radius for reaching stable conditions can be computed, as a function of inlet overpressure and water content. Under the assumption that magma chamber conditions during a typical volcanic eruption follow a depressurizing trend, a continuous conduit widening process is expected. This process could explain the pervasive and continuous presence of lithic fragments in most pyroclastic deposits, even with stationary properties and conditions of the magma source (e.g. water content, temperature, composition).

Transition temperature and fracture mode of as-castand austempered ductile iron.

PubMed

Rajnovic, D; Eric, O; Sidjanin, L

2008-12-01

The ductile to brittle transition temperature is a very important criterion that is used for selection of materials in some applications, especially in low-temperature conditions. For that reason, in this paper transition temperature of as-cast and austempered copper and copper-nickel alloyed ductile iron (DI) in the temperature interval from -196 to +150 degrees C have been investigated. The microstructures of DIs and ADIs were examined by light microscope, whereas the fractured surfaces were observed by scanning electron microscope. The ADI materials have higher impact energies compared with DIs in an as-cast condition. In addition, the transition curves for ADIs are shifted towards lower temperatures. The fracture mode of Dls is influenced by a dominantly pearlitic matrix, exhibiting mostly brittle fracture through all temperatures of testing. By contrast, with decrease of temperature, the fracture mode for ADI materials changes gradually from fully ductile to fully brittle.

Formability analysis of aluminum alloy sheets at elevated temperatures with numerical simulation based on the M-K method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bagheriasl, Reza; Ghavam, Kamyar; Worswick, Michael

2011-05-04

The effect of temperature on formability of aluminum alloy sheet is studied by developing the Forming Limit Diagrams, FLD, for aluminum alloy 3000-series using the Marciniak and Kuczynski technique by numerical simulation. The numerical model is conducted in LS-DYNA and incorporates the Barlat's YLD2000 anisotropic yield function and the temperature dependant Bergstrom hardening law. Three different temperatures; room temperature, 250 deg. C and 300 deg. C, are studied. For each temperature case, various loading conditions are applied to the M-K defect model. The effect of the material anisotropy is considered by varying the defect angle. A simplified failure criterion ismore » used to predict the onset of necking. Minor and major strains are obtained from the simulations and plotted for each temperature level. It is demonstrated that temperature improves the forming limit of aluminum 3000-series alloy sheet.« less

Renormalization group flow of the Higgs potential.

PubMed

Gies, Holger; Sondenheimer, René

2018-03-06

We summarize results for local and global properties of the effective potential for the Higgs boson obtained from the functional renormalization group, which allows one to describe the effective potential as a function of both scalar field amplitude and renormalization group scale. This sheds light onto the limitations of standard estimates which rely on the identification of the two scales and helps in clarifying the origin of a possible property of meta-stability of the Higgs potential. We demonstrate that the inclusion of higher-dimensional operators induced by an underlying theory at a high scale (GUT or Planck scale) can relax the conventional lower bound on the Higgs mass derived from the criterion of absolute stability.This article is part of the Theo Murphy meeting issue 'Higgs cosmology'. © 2018 The Author(s).

Global stability and optimal control of epidemic spreading on multiplex networks with nonlinear mutual interaction

NASA Astrophysics Data System (ADS)

Jia, Nan; Ding, Li; Liu, Yu-Jing; Hu, Ping

2018-07-01

In this paper, we consider two interacting pathogens spreading on multiplex networks. Each pathogen spreads only on its single layer, and different layers have the same individuals but different network topology. A state-dependent infectious rate is proposed to describe the nonlinear mutual interaction during the propagation of two pathogens. Then a novel epidemic spreading model incorporating treatment control strategy is established. We investigate the global asymptotic stability of the equilibrium points by using Dulac's criterion, Poincaré-Bendixson theorem and Lyapunov method. Furthermore, we discuss an optimal strategy to minimize the total number of the infected individuals and the cost associated with treatment control for both spreading of two pathogens. Finally, numerical simulations are presented to show the validity and efficiency of our results.

Effect of rotation on gravitational instability of optically thick magnetized quantum plasma in the presence of radiation

NASA Astrophysics Data System (ADS)

Kumar, A.; Pensia, R. K.

2018-05-01

This paper deals with the effect of rotation on the gravitational instability of optically thick magnetized quantum plasma in the presence of radiation. By using linearized perturbation equations of the problem, general dispersion relation is obtained which is reduced for longitudinal and transverse modes of propagation. For each mode, the problem is analyzed for two cases, when the direction of axis of rotation is parallel or perpendicular to the direction of magnetic field. Rotation parameter is found to modify the Jeans criterion of instability and expression for Jeans wavelength for transverse mode, when the axis of rotation is along the direction of magnetic field and it has stabilizing effect on the system. Magnetic field, radiation pressure and quantum correction also found to have stabilizing effect.

Solid oxide fuel cell operable over wide temperature range

DOEpatents

Baozhen, Li; Ruka, Roswell J.; Singhal, Subhash C.

2001-01-01

Solid oxide fuel cells having improved low-temperature operation are disclosed. In one embodiment, an interfacial layer of terbia-stabilized zirconia is located between the air electrode and electrolyte of the solid oxide fuel cell. The interfacial layer provides a barrier which controls interaction between the air electrode and electrolyte. The interfacial layer also reduces polarization loss through the reduction of the air electrode/electrolyte interfacial electrical resistance. In another embodiment, the solid oxide fuel cell comprises a scandia-stabilized zirconia electrolyte having high electrical conductivity. The scandia-stabilized zirconia electrolyte may be provided as a very thin layer in order to reduce resistance. The scandia-stabilized electrolyte is preferably used in combination with the terbia-stabilized interfacial layer. The solid oxide fuel cells are operable over wider temperature ranges and wider temperature gradients in comparison with conventional fuel cells.

Statistical evaluation of accelerated stability data obtained at a single temperature. I. Effect of experimental errors in evaluation of stability data obtained.

PubMed

Yoshioka, S; Aso, Y; Takeda, Y

1990-06-01

Accelerated stability data obtained at a single temperature is statistically evaluated, and the utility of such data for assessment of stability is discussed focussing on the chemical stability of solution-state dosage forms. The probability that the drug content of a product is observed to be within the lower specification limit in the accelerated test is interpreted graphically. This probability depends on experimental errors in the assay and temperature control, as well as the true degradation rate and activation energy. Therefore, the observation that the drug content meets the specification in the accelerated testing can provide only limited information on the shelf-life of the drug, without the knowledge of the activation energy and the accuracy and precision of the assay and temperature control.

Fatigue acceptance test limit criterion for larger diameter rolled thread fasteners

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kephart, A.R.

1997-05-01

This document describes a fatigue lifetime acceptance test criterion by which studs having rolled threads, larger than 1.0 inches in diameter, can be assured to meet minimum quality attributes associated with a controlled rolling process. This criterion is derived from a stress dependent, room temperature air fatigue database for test studs having a 0.625 inch diameter threads of Alloys X-750 HTH and direct aged 625. Anticipated fatigue lives of larger threads are based on thread root elastic stress concentration factors which increase with increasing thread diameters. Over the thread size range of interest, a 30% increase in notch stress ismore » equivalent to a factor of five (5X) reduction in fatigue life. The resulting diameter dependent fatigue acceptance criterion is normalized to the aerospace rolled thread acceptance standards for a 1.0 inch diameter, 0.125 inch pitch, Unified National thread with a controlled Root radius (UNR). Testing was conducted at a stress of 50% of the minimum specified material ultimate strength, 80 Ksi, and at a stress ratio (R) of 0.10. Limited test data for fastener diameters of 1.00 to 2.25 inches are compared to the acceptance criterion. Sensitivity of fatigue life of threads to test nut geometry variables was also shown to be dependent on notch stress conditions. Bearing surface concavity of the compression nuts and thread flank contact mismatch conditions can significantly affect the fastener fatigue life. Without improved controls these conditions could potentially provide misleading acceptance data. Alternate test nut geometry features are described and implemented in the rolled thread stud specification, MIL-DTL-24789(SH), to mitigate the potential effects on fatigue acceptance data.« less

On the spatial stability of a liquid jet in the presence of vapor cavities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lü, Ming; Ning, Zhi, E-mail: zhining@bjtu.edu.cn; Lu, Mei

2013-11-15

A dispersion equation describing the effect of temperature differences on the stability of three-dimensional cylindrical liquid jets in the presence of vapor cavities is presented by the use of linear stability analysis. The mathematical model and its solving method are verified by comparing them with the data in the literature, and then the effect of temperature differences between jet and surrounding gas on the spatial stability of liquid jet is investigated. Some conclusions can be drawn from the results of this investigation: (1) the temperature difference destabilizes the liquid jet when the jet liquid is cooler than the surrounding gas,more » (2) the smallest atomized droplet without taking into account the effect of temperature differences is significantly larger than that when the effect of temperature differences is taken into account, (3) the effect of temperature differences on the stability of liquid jet has little relationship with azimuthal wave modes, (4) cavitation destabilizes the liquid jet when the value of the bubble volume fraction is not greater than 0.1 (0 ≤ α ≤ 0.1), and the temperature difference can weaken this effect of cavitation on the stability of liquid jet, and (5) cavitation is responsible for generating smaller droplets, the effect of cavitation on the critical wave number with and without taking into account the effect of temperature differences is quite different, and temperature difference is likely to fully restrain the effect of cavitation on the critical wave number; however, cavitation is again responsible for generating smaller droplets despite the effect of temperature differences when the bubble volume fraction α = 0.1. These findings may explain some observations of practical atomizer performance.« less

Low-temperature technique for thick film resist stabilization and curing

NASA Astrophysics Data System (ADS)

Minter, Jason P.; Wong, Selmer S.; Marlowe, Trey; Ross, Matthew F.; Narcy, Mark E.; Livesay, William R.

1999-06-01

For a range of thick film photoresist applications, including MeV ion implant processing, thin film head manufacturing, and microelectromechanical systems processing, there is a need for a low-temperature method for resist stabilization and curing. Traditional methods of stabilizing or curing resist films have relied on thermal cycling, which may not be desirable due to device temperature limitations or thermally-induced distortion of the resist features.

A Topology Control Strategy with Reliability Assurance for Satellite Cluster Networks in Earth Observation

PubMed Central

Chen, Qing; Zhang, Jinxiu; Hu, Ze

2017-01-01

This article investigates the dynamic topology control problem of satellite cluster networks (SCNs) in Earth observation (EO) missions by applying a novel metric of stability for inter-satellite links (ISLs). The properties of the periodicity and predictability of satellites’ relative position are involved in the link cost metric which is to give a selection criterion for choosing the most reliable data routing paths. Also, a cooperative work model with reliability is proposed for the situation of emergency EO missions. Based on the link cost metric and the proposed reliability model, a reliability assurance topology control algorithm and its corresponding dynamic topology control (RAT) strategy are established to maximize the stability of data transmission in the SCNs. The SCNs scenario is tested through some numeric simulations of the topology stability of average topology lifetime and average packet loss rate. Simulation results show that the proposed reliable strategy applied in SCNs significantly improves the data transmission performance and prolongs the average topology lifetime. PMID:28241474

A Topology Control Strategy with Reliability Assurance for Satellite Cluster Networks in Earth Observation.

PubMed

Chen, Qing; Zhang, Jinxiu; Hu, Ze

2017-02-23

This article investigates the dynamic topology control problemof satellite cluster networks (SCNs) in Earth observation (EO) missions by applying a novel metric of stability for inter-satellite links (ISLs). The properties of the periodicity and predictability of satellites' relative position are involved in the link cost metric which is to give a selection criterion for choosing the most reliable data routing paths. Also, a cooperative work model with reliability is proposed for the situation of emergency EO missions. Based on the link cost metric and the proposed reliability model, a reliability assurance topology control algorithm and its corresponding dynamic topology control (RAT) strategy are established to maximize the stability of data transmission in the SCNs. The SCNs scenario is tested through some numeric simulations of the topology stability of average topology lifetime and average packet loss rate. Simulation results show that the proposed reliable strategy applied in SCNs significantly improves the data transmission performance and prolongs the average topology lifetime.

Stability of Bifurcating Stationary Solutions of the Artificial Compressible System

NASA Astrophysics Data System (ADS)

Teramoto, Yuka

2018-02-01

The artificial compressible system gives a compressible approximation of the incompressible Navier-Stokes system. The latter system is obtained from the former one in the zero limit of the artificial Mach number ɛ which is a singular limit. The sets of stationary solutions of both systems coincide with each other. It is known that if a stationary solution of the incompressible system is asymptotically stable and the velocity field of the stationary solution satisfies an energy-type stability criterion, then it is also stable as a solution of the artificial compressible one for sufficiently small ɛ . In general, the range of ɛ shrinks when the spectrum of the linearized operator for the incompressible system approaches to the imaginary axis. This can happen when a stationary bifurcation occurs. It is proved that when a stationary bifurcation from a simple eigenvalue occurs, the range of ɛ can be taken uniformly near the bifurcation point to conclude the stability of the bifurcating solution as a solution of the artificial compressible system.

Stability analysis for discrete-time stochastic memristive neural networks with both leakage and probabilistic delays.

PubMed

Liu, Hongjian; Wang, Zidong; Shen, Bo; Huang, Tingwen; Alsaadi, Fuad E

2018-06-01

This paper is concerned with the globally exponential stability problem for a class of discrete-time stochastic memristive neural networks (DSMNNs) with both leakage delays as well as probabilistic time-varying delays. For the probabilistic delays, a sequence of Bernoulli distributed random variables is utilized to determine within which intervals the time-varying delays fall at certain time instant. The sector-bounded activation function is considered in the addressed DSMNN. By taking into account the state-dependent characteristics of the network parameters and choosing an appropriate Lyapunov-Krasovskii functional, some sufficient conditions are established under which the underlying DSMNN is globally exponentially stable in the mean square. The derived conditions are made dependent on both the leakage and the probabilistic delays, and are therefore less conservative than the traditional delay-independent criteria. A simulation example is given to show the effectiveness of the proposed stability criterion. Copyright © 2018 Elsevier Ltd. All rights reserved.

Investigation of numerical simulation on all-optical flip-flop stability maps of 1550nm vertical-cavity surface-emitting laser

NASA Astrophysics Data System (ADS)

Li, Jun; Xia, Qing; Wang, Xiaofa

2017-10-01

Based on the extended spin-flip model, the all-optical flip-flop stability maps of the 1550nm vertical-cavity surface-emitting laser have been studied. Theoretical results show that excellent agreement is found between theoretical and the reported experimental results in polarization switching point current which is equal to 1.95 times threshold. Furthermore, the polarization bistable region is wide which is from 1.05 to 1.95 times threshold. A new method is presented that uses power difference between two linear polarization modes as the judging criterion of trigger degree and stability maps of all-optical flip-flop operation under different injection parameters are obtained. By alternately injecting set and reset pulse with appropriate parameters, the mutual conversion switching between two polarization modes is realized, the feasibility of all-optical flip-flop operation is checked theoretically. The results show certain guiding significance on the experimental study on all optical buffer technology.

Suppression of OsMADS7 in rice endosperm stabilizes amylose content under high temperature stress.

PubMed

Zhang, Hua; Xu, Heng; Feng, Mengjie; Zhu, Ying

2018-01-01

High temperature significantly alters the amylose content of rice, resulting in mature grains with poor eating quality. However, only few genes and/or quantitative trait loci involved in this process have been isolated and the molecular mechanisms of this effect remain unclear. Here, we describe a floral organ identity gene, OsMADS7, involved in stabilizing rice amylose content at high temperature. OsMADS7 is greatly induced by high temperature at the early filling stage. Constitutive suppression of OsMADS7 stabilizes amylose content under high temperature stress but results in low spikelet fertility. However, rice plants with both stable amylose content at high temperature and normal spikelet fertility can be obtained by specifically suppressing OsMADS7 in endosperm. GBSSI is the major enzyme responsible for amylose biosynthesis. A low filling rate and high expression of GBSSI were detected in OsMADS7 RNAi plants at high temperature, which may be correlated with stabilized amylose content in these transgenic seeds under high temperature. Thus, specific suppression of OsMADS7 in endosperm could improve the stability of rice amylose content at high temperature, and such transgenic materials may be a valuable genetic resource for breeding rice with elite thermal resilience. © 2017 The Authors. Plant Biotechnology Journal published by Society for Experimental Biology and The Association of Applied Biologists and John Wiley & Sons Ltd.

Temperature stabilization in dispersed flows of frameless heat removal systems in space

NASA Astrophysics Data System (ADS)

Safronov, A. A.; Filatov, N. I.; Koroteev, A. A.; Bondareva, N. V.

2017-11-01

The temperature profile stabilization is studied at radiation cooling of a dispersed veil of droplet coolers-radiators. The stabilization is shown to be nonmonotonic. The influence of the studied process regularities on the characteristics of the radiating systems is analyzed.

Topical formulations with superoxide dismutase: influence of formulation composition on physical stability and enzymatic activity.

PubMed

Di Mambro, Valéria M; Borin, Maria F; Fonseca, Maria J V

2003-04-24

Three different topical formulations were supplemented with superoxide dismutase (SOD) and evaluated concerning physical and chemical stabilities in order to determine the most stable formulation that would maintain SOD activity. Physical stability was evaluated by storing the formulation at room temperature, and at 37 and 45 degrees C for 28 days. Samples were collected at 7-day intervals for assessment of rheological behavior. Chemical stability was evaluated by the measurement of enzymatic activity in formulations stored at room temperature and at 45 degrees C for 75 days. The formulations showed a pseudoplastic behavior, with a flow index of less than 1. There was no significant difference in the initial values of flow index, hysteresis loop or minimum apparent viscosity. The simple emulsion and the one stabilized with hydroxyethylcellulose showed decreased viscosity by the 21st day and with higher temperature, but no significant changes concerning the presence of SOD. Although there were no significant changes concerning storage time or temperature, the formulation stabilized with hydroxyethylcellulose showed a marked loss of SOD activity. The addition of SOD to the formulations studied did not affect their physical stability. Simple emulsions or emulsions stabilized with carboxypolymethylene seem to be better bases for enzyme addition than emulsion stabilized with hydroxyethylcellulose.

Propellant vaporization as a criterion for rocket-engine design : experimental effect of fuel temperature on liquid-oxygen - heptane performance

NASA Technical Reports Server (NTRS)

Heidmann, M F

1957-01-01

Characteristic exhaust velocity of a 200-pound-thrust rocket engine was evaluated for fuel temperatures of -90 degrees, and 200 degrees f with a spray formed by two impinging heptane jets reacting in a highly atomized oxygen atmosphere. Tests covered a range of mixture ratios and chamber lengths. The characteristic exhaust-velocity efficiency increased 2 percent for a 290 degree f increase in fuel temperature. This increase in performance can be compared with that obtained by increasing chamber length by about 1/2 inch. The result agrees with the fuel-temperature effect predicted from an analysis based on droplet evaporation theory. Mixture ratio markedly affected characteristic exhaust velocity efficiency, but total flow rate and fuel temperature did not.

The Psychometric Parameters of the Farsi Form of the Arabic Scale of Death Anxiety

PubMed Central

Abdel-Khalek, Ahmed M.; Lester, David

2017-01-01

The aim of this study was to describe the psychometric properties of the Farsi Form of the Arabic Scale of Death Anxiety (ASDA). The original scale was first translated into Farsi by language experts using the back translation procedure and then administered to a total of 252 Iranian college students and 52 psychiatric outpatients from psychiatric and psychological clinics. The one-week test-retest reliability of the Farsi version in a sample of college students was 0.78, indicating good temporal stability and corroborating the trait-like nature of scores. Cronbach's α was 0.90 for the college students and 0.92 for the psychiatric outpatients, indicating high internal consistency. Scale scores correlated 0.46 with Death Obsession Scale scores, 0.56 with Death Depression Scale scores, 0.41 with Death Anxiety Scale scores, and 0.40 with Wish to be Dead Scale scores, indicating good construct and criterion-related validity. A principal component analysis with a Varimax rotation yielded four factors in the sample of Iranian college students, indicating a lack of homogeneity in the content of the scale. Male students obtained a significant higher mean score than did females. It was concluded that the Farsi ASDA had good internal consistency, temporal stability, criterion-related validity, and a factor structure reflecting important features of death anxiety. In general, the Farsi ASDA could be recommended for use in research on death anxiety among Iranian college students and psychiatric outpatients. PMID:28698887

The Psychometric Parameters of the Farsi Form of the Arabic Scale of Death Anxiety.

PubMed

Dadfar, Mahboubeh; Abdel-Khalek, Ahmed M; Lester, David; Atef Vahid, Mohammad Kazem

2017-01-01

The aim of this study was to describe the psychometric properties of the Farsi Form of the Arabic Scale of Death Anxiety (ASDA). The original scale was first translated into Farsi by language experts using the back translation procedure and then administered to a total of 252 Iranian college students and 52 psychiatric outpatients from psychiatric and psychological clinics. The one-week test-retest reliability of the Farsi version in a sample of college students was 0.78, indicating good temporal stability and corroborating the trait-like nature of scores. Cronbach's α was 0.90 for the college students and 0.92 for the psychiatric outpatients, indicating high internal consistency. Scale scores correlated 0.46 with Death Obsession Scale scores, 0.56 with Death Depression Scale scores, 0.41 with Death Anxiety Scale scores, and 0.40 with Wish to be Dead Scale scores, indicating good construct and criterion-related validity. A principal component analysis with a Varimax rotation yielded four factors in the sample of Iranian college students, indicating a lack of homogeneity in the content of the scale. Male students obtained a significant higher mean score than did females. It was concluded that the Farsi ASDA had good internal consistency, temporal stability, criterion-related validity, and a factor structure reflecting important features of death anxiety. In general, the Farsi ASDA could be recommended for use in research on death anxiety among Iranian college students and psychiatric outpatients.

Structural stability of DNA origami nanostructures in the presence of chaotropic agents.

PubMed

Ramakrishnan, Saminathan; Krainer, Georg; Grundmeier, Guido; Schlierf, Michael; Keller, Adrian

2016-05-21

DNA origami represent powerful platforms for single-molecule investigations of biomolecular processes. The required structural integrity of the DNA origami may, however, pose significant limitations regarding their applicability, for instance in protein folding studies that require strongly denaturing conditions. Here, we therefore report a detailed study on the stability of 2D DNA origami triangles in the presence of the strong chaotropic denaturing agents urea and guanidinium chloride (GdmCl) and its dependence on concentration and temperature. At room temperature, the DNA origami triangles are stable up to at least 24 h in both denaturants at concentrations as high as 6 M. At elevated temperatures, however, structural stability is governed by variations in the melting temperature of the individual staple strands. Therefore, the global melting temperature of the DNA origami does not represent an accurate measure of their structural stability. Although GdmCl has a stronger effect on the global melting temperature, its attack results in less structural damage than observed for urea under equivalent conditions. This enhanced structural stability most likely originates from the ionic nature of GdmCl. By rational design of the arrangement and lengths of the individual staple strands used for the folding of a particular shape, however, the structural stability of DNA origami may be enhanced even further to meet individual experimental requirements. Overall, their high stability renders DNA origami promising platforms for biomolecular studies in the presence of chaotropic agents, including single-molecule protein folding or structural switching.

Stability of rhombohedral phases in vanadium at high-pressure and high-temperature: first-principles investigations

NASA Astrophysics Data System (ADS)

Wang, Yi X.; Wu, Q.; Chen, Xiang R.; Geng, Hua Y.

2016-09-01

The pressure-induced transition of vanadium from BCC to rhombohedral structures is unique and intriguing among transition metals. In this work, the stability of these phases is revisited by using density functional theory. At finite temperatures, a novel transition of rhombohedral phases back to BCC phase induced by thermal electrons is discovered. This reentrant transition is found not driven by phonons, instead it is the electronic entropy that stabilizes the latter phase, which is totally out of expectation. Parallel to this transition, we find a peculiar and strong increase of the shear modulus C44 with increasing temperature. It is counter-intuitive in the sense that it suggests an unusual harding mechanism of vanadium by temperature. With these stability analyses, the high-pressure and finite-temperature phase diagram of vanadium is proposed. Furthermore, the dependence of the stability of RH phases on the Fermi energy and chemical environment is investigated. The results demonstrate that the position of the Fermi level has a significant impact on the phase stability, and follows the band-filling argument. Besides the Fermi surface nesting, we find that the localization/delocalization of the d orbitals also contributes to the instability of rhombohedral distortions in vanadium.

Pickering emulsions stabilized by paraffin wax and Laponite clay particles.

PubMed

Li, Caifu; Liu, Qian; Mei, Zhen; Wang, Jun; Xu, Jian; Sun, Dejun

2009-08-01

Emulsions containing wax in dispersed droplets stabilized by disc-like Laponite clay particles are prepared. Properties of the emulsions prepared at different temperatures are examined using stability, microscopy and droplet-size analysis. At low temperature, the wax crystals in the oil droplets can protrude through the interface, leading to droplet coalescence. But at higher temperatures, the droplet size decreases with wax concentration. Considering the viscosity of the oil phase and the interfacial tension, we conclude that the wax is liquid-like during the high temperature emulsification process, but during cooling wax crystals appear around the oil/water interface and stabilize the droplets. The oil/water ratio has minimal effect on the emulsions between ratios of 3:7 and 7:3. The Laponite is believed to stabilize the emulsions by increasing the viscosity of the continuous phase and also by adsorbing at the oil/water interface, thus providing a physical barrier to coalescence.

Fracture Behavior of Boron Aluminum Composites at Room and Elevated Temperatures.

DTIC Science & Technology

1985-04-01

listed in Table I. TABLE I: LIST OF FRACTURE MODELS REVIEWED Authors Ref. Abbrv. Criterion Hole Slits M.E. Waddoups J.R. Eisenmann 3 WEK LEFM V/ SB.E...Laminates: Predictions and Experiemtns - A Review", NASA CR , 1985, (to be published). 3. M.E. Waddoups, J.R. Eisenmann and B.E. Kaminski

Mechanisms of Stability of Robust Chaperones from Hyperthermophiles

DTIC Science & Technology

2009-02-03

basis for high temperature stability is still under active study. Activity and stability of enzymes at high temperature is an obvious and critically...important adaptation for the survival of thermophiles at the extremes of their temperature ranges. One of the novel aspects of our project is that we...with optimal growth at 100°C, with homologous proteins from Methanococcus jannaschii, an 88°C extreme thermophile . We have previously shown that

International Conference on Materials and Mechanisms of Superconductivity -- High Temperature Superconductors

DTIC Science & Technology

1989-10-01

wide range of Selds and temperatures.’ is the symmetrized two-dimensional strain matrix, A The .L der?.nn criterion assumes wave vector -inde- and A are...plificatioG, especially if fluctuations are important. A then (assuming 2 1 + A >> ) more accurate theory would use wave vector dependent k8 T elastic...with this siri’ M respect to B, H and Ha; the three latter approach; e.g., a possible anisotropy in the vectors are almost the same in"’’e and basal

The Analysis and Modeling of Phase Stability and Multiphase Designs in High Temperature Refractory Metal-Silicon-Boron Alloys

DTIC Science & Technology

2009-01-27

high temperature mechanical properties , it was confirmed that the three phase eutectic structure exhibited exceptionally high strength and creep...microstructurc constituent, offer an attractive property balance of high melting temperature, oxidation resistance and useful high temperature mechanical ...design of new multiphase high-temperature alloys with balanced environmental and mechanical properties . 15. SUBJECT TERMS Phase Stability, Alloying

Hierarchical functional organization of formal biological systems: a dynamical approach. II. The concept of non-symmetry leads to a criterion of evolution deduced from an optimum principle of the (O-FBS) sub-system.

PubMed

Chauvet, G A

1993-03-29

In paper I a theory of functional organization in terms of functional interactions was proposed for a formal biological system (FBS). A functional interaction was defined as the product emitted by a structural unit, i.e. an assembly of molecules, cells, tissues or organs, which acts on another. We have shown that a self-association hypothesis could be an explanation for the source of these functional interactions because it is consistent with increased stability of the system after association. The construction of the set of interactions provides the topology of the biological system, called (O-FBS), in contrast to the (D-FBS) which describes the dynamics of the processes associated with the functional interactions. In this paper, an optimum principle is established, due to the non-symmetry of functional interactions, which could explain the stability of an FBS, and a criterion of evolution for the hierarchical topological organization of a FBS during development is deduced from that principle. The combinatorics of the (O-FBS) leads to the topological stability of the related graph. It is shown that this problem can be expressed as the re-distribution of sources and sinks, when one of them is suppressed, given the constraint of the invariance of the physiological function. Such an optimum principle could be called a 'principle of increase in functional order by hierarchy'. The first step is the formulation of a 'potential' for the functional organization, which describes the ability of the system to combine functional interactions, such that the principle of vital coherence (paper I) is satisfied. This function measures the number of potential functional interactions. The second step is to discover the maximum of this function. Biological systems in such a state of maximum organization are shown to satisfy particular dynamics, which can be experimentally verified: either the number of sinks decreases, or this number increases, in a monotonic way. The class of systems considered here is assumed to satisfy such an extremum hypothesis. The third step is a study of the variation of the degree of organization (paper I), i.e. the number of structural units when the biological system is growing. We establish an optimum principle for a new function called 'orgatropy'. By adding a criterion of specialization to the system we show the emergence of a level of organization with a re-organization of the system.(ABSTRACT TRUNCATED AT 400 WORDS)

WGM Temperature Tracker

NASA Technical Reports Server (NTRS)

Strekalov, Dmitry V.

2012-01-01

This software implements digital control of a WGM (whispering-gallerymode) resonator temperature based on the dual-mode approach. It comprises one acquisition (dual-channel) and three control modules. The interaction of the proportional-integral loops is designed in the original way, preventing the loops from fighting. The data processing is organized in parallel with the acquisition, which allows the computational overhead time to be suppressed or often completely avoided. WGM resonators potentially provide excellent optical references for metrology, clocks, spectroscopy, and other applications. However, extremely accurate (below micro-Kelvin) temperature stabilization is required. This software allows one specifically advantageous method of such stabilization to be implemented, which is immune to a variety of effects that mask the temperature variation. WGM Temperature Tracker 2.3 (see figure) is a LabVIEW code developed for dual-mode temperature stabilization of WGM resonators. It has allowed for the temperature stabilization at the level of 200 nK with one-second integration time, and 6 nK with 10,000-second integration time, with the above room-temperature set point. This software, in conjunction with the appropriate hardware, can be used as a noncryogenic temperature sensor/ controller with sub-micro-Kelvin sensitivity, which at the time of this reporting considerably outperforms the state of the art.

Temperature-stabilized, narrowband tunable fiber-Bragg gratings for matched-filter receiver

NASA Astrophysics Data System (ADS)

Roth, Jeffrey M.; Kummer, Joseph W.; Minch, Jeffrey R.; Malinsky, Bryan G.; Scalesse, Vincent; Walther, Frederick G.

2017-02-01

We report on a 1550-nm matched filter based on a pair of fiber Bragg gratings (FBGs) that is actively stabilized over temperature. The filter is constructed of a cascaded pair of athermally-packaged FBGs. The tandem FBG pair produces an aggregate 3-dB bandwidth of 3.9-GHz that is closely matched to a return-to-zero, 2.880-GHz differential-phase-shift-keyed optical waveform. The FBGs comprising the filter are controlled in wavelength using a custom-designed, pulse-width modulation (PWM) heater controller. The controllers allow tuning of the FBGs over temperature to compensate and cancel out native temperature dependence of the athermal FBG (AFBG) package. Two heaters are bonded to each FBG device, one on each end. One heater is a static offset that biases the FBG wavelength positively. The second heater is a PWM controller that actively moves the FBG wavelength negatively. A temperature sensor measures the FBGs' temperature, and a feed-forward control loop adjusts the PWM signal to hold the wavelength within a desired range. This stabilization technique reduces the device's native temperature dependence from approximately 0.65 pm/°C to 0.06 pm/°C, improving the temperature stability by tenfold, while retaining some control for poten- tial long-term drifts. The technique demonstrates that the FBGs can be held to +/-1.5 pm (+/-188 MHz) of the target wavelength over a 0 to +50°C temperature range. The temperature-stabilized FBGs are integrated into a low-noise, optical pre-amplifier that operates over a wide temperature range for a laser communication system.

Task II: Three-dimensional Rotating Stall Inception and Effects of Rotating Tip Clearance Asymmetry in Axial Compressors

NASA Technical Reports Server (NTRS)

Suder, Kenneth (Technical Monitor); Tan, Choon-Sooi

2003-01-01

The effects of two types of flow non-uniformity on stall inception behavior were assessed with linearized stability analyses of two compressor flow models. Response to rotating tip clearance asymmetries induced by a whirling rotor shaft or rotor height variations were investigated with a two-dimensional flow model. A 3-D compressor model was also developed to study the stability of both full-span and part-span rotating stall modes in annular geometries with radial flow variations. The studies focussed on (1) understanding what compressor designs were sensitive to these types of circumferential and spanwise flow non-uniformities, and (2) situations where 2-D stability theories were inadequate because of 3-D flow effects. Rotating tip clearance non-uniformity caused the greatest performance loss for shafts whirling at the rotating stall frequency. A whirling shaft displacement of 1 percent chord caused the stalling mass flow to rise by as much as 10 percent and the peak pressure rise to decrease by 6 percent. These changes were an order of magnitude larger than for equivalent-sized stationary or rotor-locked clearance asymmetries. Spanwise flow non-uniformity always destabilized the compressor, so that 2-D models over-predicted that stall margin compared to 3-D theory. The difference increased for compressors with larger spanwise variations of characteristic slope and reduced characteristic curvature near the peak. Differences between 2-D and 3-D stall point predictions were generally unacceptable (2 - 4 percent of flow coefficient) for single-stage configurations, but were less than 1 percent for multistage compressors. 2-D analyses predicted the wrong stall mode for specific cases of radial inlet flow distortion, mismatching and annulus area contraction, where higher-order radial modes led to stall. The stability behavior of flows with circumferential or radial non-uniformity was unified through a single stability criterion. The stall point for both cases was set by the integral around the annulus of the pressure rise characteristic slope, weighted by the amplitude of the mode shape. For the case of steady circumferential variations, this criterion reduced to the integrated mean slope (IMS) condition associated with steady inlet distortions. The rotating tip clearance asymmetry model was also used to demonstrate the feasibility of actively controlling the shaft position to suppress rotating stall. In axisymmetric mean flow, this method only stabilized the first harmonic mode, increasing the operating range until surge or higher harmonic modes became unstable.

Changes in extremely hot days under stabilized 1.5 and 2.0 °C global warming scenarios as simulated by the HAPPI multi-model ensemble

NASA Astrophysics Data System (ADS)

Wehner, Michael; Stone, Dáithí; Mitchell, Dann; Shiogama, Hideo; Fischer, Erich; Graff, Lise S.; Kharin, Viatcheslav V.; Lierhammer, Ludwig; Sanderson, Benjamin; Krishnan, Harinarayan

2018-03-01

The half a degree additional warming, prognosis and projected impacts (HAPPI) experimental protocol provides a multi-model database to compare the effects of stabilizing anthropogenic global warming of 1.5 °C over preindustrial levels to 2.0 °C over these levels. The HAPPI experiment is based upon large ensembles of global atmospheric models forced by sea surface temperature and sea ice concentrations plausible for these stabilization levels. This paper examines changes in extremes of high temperatures averaged over three consecutive days. Changes in this measure of extreme temperature are also compared to changes in hot season temperatures. We find that over land this measure of extreme high temperature increases from about 0.5 to 1.5 °C over present-day values in the 1.5 °C stabilization scenario, depending on location and model. We further find an additional 0.25 to 1.0 °C increase in extreme high temperatures over land in the 2.0 °C stabilization scenario. Results from the HAPPI models are consistent with similar results from the one available fully coupled climate model. However, a complicating factor in interpreting extreme temperature changes across the HAPPI models is their diversity of aerosol forcing changes.

An alphavirus temperature-sensitive capsid mutant reveals stages of nucleocapsid assembly

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, Yan, E-mail: yzheng15@students.kgi.edu; Kielian, Margaret, E-mail: margaret.kielian@einstein.yu.edu

2015-10-15

Alphaviruses have a nucleocapsid core composed of the RNA genome surrounded by an icosahedral lattice of capsid protein. An insertion after position 186 in the capsid protein produced a strongly temperature-sensitive growth phenotype. Even when the structural proteins were synthesized at the permissive temperature (28 °C), subsequent incubation of the cells at the non-permissive temperature (37 °C) dramatically decreased mutant capsid protein stability and particle assembly. Electron microscopy confirmed the presence of cytoplasmic nucleocapsids in mutant-infected cells cultured at the permissive temperature, but these nucleocapsids were not stable to sucrose gradient separation. In contrast, nucleocapsids isolated from mutant virus particlesmore » had similar stability to that of wildtype virus. Our data support a model in which cytoplasmic nucleocapsids go through a maturation step during packaging into virus particles. The insertion site lies in the interface between capsid proteins in the assembled nucleocapsid, suggesting the region where such a stabilizing transition occurs. - Highlights: • We characterize an alphavirus capsid insertion mutation. • These capsid mutants are highly temperature sensitive for growth. • The insertion affects nucleocapsid stability. • Results suggest that the nucleocapsid is stabilized during virus budding.« less

Effects of temperature distribution on boundary layer stability for a circular cone at Mach 10

NASA Astrophysics Data System (ADS)

Rigney, Jeffrey M.

A CFD analysis was conducted on a circular cone at 3 degrees angle of attack at Mach 10 using US3D and STABL 3D to determine the effect of wall temperature on the stability characteristics that lead to laminar-to-turbulent transition. Wall temperature distributions were manipulated while all other flow inputs and geometric qualities were held constant. Laminar-to-turbulent transition was analyzed for isothermal and adiabatic wall conditions, a simulated short-duration wind tunnel case, and several hot-nose temperature distributions. For this study, stability characteristics include maximum N-factor growth and the corresponding frequency range, disturbance spatial amplification rate and the corresponding modal frequency, and stability neutral point location. STABL 3D analysis indicates that temperature distributions typical of those in short-duration hypersonic wind tunnels do not result in any significant difference on the stability characteristics, as compared to an isothermal wall boundary condition. Hypothetical distributions of much greater temperatures at and past the nose tip do show a trend of dampening of second-mode disturbances, most notably on the leeward ray. The most pronounced differences existed between the isothermal and adiabatic cases.

[Research on the identification method of LTE condition in the laser-induced plasma].

PubMed

Fan, Juan-juan; Huang, Dan; Wang, Xin; Zhang, Lei; Ma, Wei-guang; Dong, Lei; Yin, Wang-bao; Jia, Suo-tang

2014-12-01

Because of the poor accuracy of the commonly used Boltzmann plot method and double-line method, the Boltzmann-Maxwell distribution combined with the Saha-Eggert formula is proposed to improve the measurement accuracy of the plasma temperature; the simple algorithm for determining the linewidth of the emission line was established according to the relationship between the area and the peak value of the Gaussian formula, and the plasma electron density was calculated through the Stark broadening of the spectral lines; the method for identifying the plasma local thermal equilibrium (LTE) condition was established based on the McWhirter criterion. The experimental results show that with the increase in laser energy, the plasma temperature and electron density increase linearly; when the laser energy changes within 127~510 mJ, the plasma electron density changes in the range of 1.30532X10(17)~1.87322X10(17) cm(-3), the plasma temperature changes in the range of 12586~12957 K, and all the plasma generated in this experiment meets the LTE condition threshold according to the McWhirter criterion. For element Al, there exist relatively few observable lines at the same ionization state in the spectral region of the spectrometer, thus it is unable to use the Boltzmann plane method to calculate temperature. One hundred sets of Al plasma spectra were used for temperature measurement by employing the Saha-Boltzmann method and the relative standard deviation (RSD) value is 0.4%, and compared with 1.3% of the double line method, the accuracy has been substantially increased. The methods proposed can be used for rapid plasma temperature and electron density calculation, the LTE condition identification, and are valuable in studies such as free calibration, spectral effectiveness analysis, spectral temperature correction, the best collection location determination, LTE condition distribution in plasma, and so on.

Dynamic compressive behavior of Pr-Nd alloy at high strain rates and temperatures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang Huanran; Cai Canyuan; Chen Danian

2012-07-01

Based on compressive tests, static on 810 material test system and dynamic on the first compressive loading in split Hopkinson pressure bar (SHPB) tests for Pr-Nd alloy cylinder specimens at high strain rates and temperatures, this study determined a J-C type [G. R. Johnson and W. H. Cook, in Proceedings of Seventh International Symposium on Ballistics (The Hague, The Netherlands, 1983), pp. 541-547] compressive constitutive equation of Pr-Nd alloy. It was recorded by a high speed camera that the Pr-Nd alloy cylinder specimens fractured during the first compressive loading in SHPB tests at high strain rates and temperatures. From highmore » speed camera images, the critical strains of the dynamic shearing instability for Pr-Nd alloy in SHPB tests were determined, which were consistent with that estimated by using Batra and Wei's dynamic shearing instability criterion [R. C. Batra and Z. G. Wei, Int. J. Impact Eng. 34, 448 (2007)] and the determined compressive constitutive equation of Pr-Nd alloy. The transmitted and reflected pulses of SHPB tests for Pr-Nd alloy cylinder specimens computed with the determined compressive constitutive equation of Pr-Nd alloy and Batra and Wei's dynamic shearing instability criterion could be consistent with the experimental data. The fractured Pr-Nd alloy cylinder specimens of compressive tests were investigated by using 3D supper depth digital microscope and scanning electron microscope.« less

Stability of matter-wave solitons in optical lattices

NASA Astrophysics Data System (ADS)

Ali, Sk. Golam; Roy, S. K.; Talukdar, B.

2010-08-01

We consider localized states of both single- and two-component Bose-Einstein condensates (BECs) confined in a potential resulting from the superposition of linear and nonlinear optical lattices and make use of Vakhitov-Kolokolov criterion to investigate the effect of nonlinear lattice on the stability of the soliton solutions in the linear optical lattice (LOL). For the single-component case we show that a weak nonlinear lattice has very little effect on the stability of such solitons while sufficiently strong nonlinear optical lattice (NOL) squeezes them to produce narrow bound states. For two-component condensates we find that when the strength of the NOL (γ1) is less than that of the LOL (V0) a relatively weak intra-atomic interaction (IAI) has little effect on the stability of the component solitons. This is true for both attractive and repulsive IAI. A strong attractive IAI, however, squeezes the BEC solitons while a similar repulsive IAI makes the component solitons wider. For γ1 > V0, only a strong attractive IAI squeezes the BEC solitons but the squeezing effect is less prominent than that found for γ1 < V0. We make useful checks on the results of our semianalytical stability analysis by solving the appropriate Gross-Pitaevskii equations numerically.

The stability of water- and fat-soluble vitamin in dentifrices according to pH level and storage type.

PubMed

Park, Jung-Eun; Kim, Ki-Eun; Choi, Yong-Jun; Park, Yong-Duk; Kwon, Ha-Jeong

2016-02-01

The purpose of this study is to evaluate the vitamin stabilities in dentifrices by analyzing various vitamins according to the level and storage temperature. The stabilities of water- and fat-soluble vitamins were investigated in buffer solution at different pH values (4, 7, 8, 10 and 11) for 14 days and in dentifrices at different pH (7 and 10) for 5 months at two temperature conditions (room and refrigeration temperature) by analyzing the remaining amounts using HPLC methods. In the buffer solution, the stability of vitamins B1 , B6 and C was increased as the pH values increased. Vitamins E and K showed poor stability at pH 4, and vitamin B3 showed poor stability at pH 11. In dentifrices, the storage temperature highly influenced vitamin stability, especially vitamins C and E, but the stabilities of vitamins B1 and C according to pH values did not correspond to the buffer solution tests. Vitamin B group was relatively stable in dentifrices, but vitamin C completely disappeared after 5 months. Vitamin K showed the least initial preservation rates. Vitamins were not detected in commercial dentifrices for adults and detected amounts were less than the advertised contents in dentifrices for children. Copyright © 2015 John Wiley & Sons, Ltd.

Ab Initio Simulations of Temperature Dependent Phase Stability and Martensitic Transitions in NiTi

NASA Technical Reports Server (NTRS)

Haskins, Justin B.; Thompson, Alexander E.; Lawson, John W.

2016-01-01

For NiTi based alloys, the shape memory effect is governed by a transition from a low-temperature martensite phase to a high-temperature austenite phase. Despite considerable experimental and computational work, basic questions regarding the stability of the phases and the martensitic phase transition remain unclear even for the simple case of binary, equiatomic NiTi. We perform ab initio molecular dynamics simulations to describe the temperature-dependent behavior of NiTi and resolve several of these outstanding issues. Structural correlation functions and finite temperature phonon spectra are evaluated to determine phase stability. In particular, we show that finite temperature, entropic effects stabilize the experimentally observed martensite (B19') and austenite (B2) phases while destabilizing the theoretically predicted (B33) phase. Free energy computations based on ab initio thermodynamic integration confirm these results and permit estimates of the transition temperature between the phases. In addition to the martensitic phase transition, we predict a new transition between the B33 and B19' phases. The role of defects in suppressing these phase transformations is discussed.

A surface acoustic wave ICP sensor with good temperature stability.

PubMed

Zhang, Bing; Hu, Hong; Ye, Aipeng; Zhang, Peng

2017-07-20

Intracranial pressure (ICP) monitoring is very important for assessing and monitoring hydrocephalus, head trauma and hypertension patients, which could lead to elevated ICP or even devastating neurological damage. The mortality rate due to these diseases could be reduced through ICP monitoring, because precautions can be taken against the brain damage. This paper presents a surface acoustic wave (SAW) pressure sensor to realize ICP monitoring, which is capable of wireless and passive transmission with antenna attached. In order to improve the temperature stability of the sensor, two methods were adopted. First, the ST cut quartz was chosen as the sensor substrate due to its good temperature stability. Then, a differential temperature compensation method was proposed to reduce the effects of temperature. Two resonators were designed based on coupling of mode (COM) theory and the prototype was fabricated and verified using a system established for testing pressure and temperature. The experiment result shows that the sensor has a linearity of 2.63% and hysteresis of 1.77%. The temperature stability of the sensor has been greatly improved by using the differential compensation method, which validates the effectiveness of the proposed method.

Linear stability of compressible Taylor-Couette flow

NASA Technical Reports Server (NTRS)

Kao, Kai-Hsiung; Chow, Chuen-Yen

1992-01-01

A temporal stability analysis of compressible Taylor-Couette flow is presented. The viscous flow studied in this paper is contained between two concentric cylinders of infinite length, which are rotating with different angular velocities and are kept at different surface temperatures. The effects of differential rotation and temperature difference on the stability of Taylor-Couette flow are contrasted for a range of Mach numbers ranging from incompressible to Mach 3.0. The relative motion of the cylinders dramatically affects the characteristics of the Couette flow at the onset of instability. The flow is stabilized or destabilized depending upon the temperature ratio and speeds of the two cylinders. Independent of Mach number and temperature ratio, increasing Reynolds number generally promotes a destabilizing effect, indicating the inviscid nature of the Taylor-Couette flow.

Ignition criterion for heterogeneous energetic materials based on hotspot size-temperature threshold

NASA Astrophysics Data System (ADS)

Barua, A.; Kim, S.; Horie, Y.; Zhou, M.

2013-02-01

A criterion for the ignition of granular explosives (GXs) and polymer-bonded explosives (PBXs) under shock and non-shock loading is developed. The formulation is based on integration of a quantification of the distributions of the sizes and locations of hotspots in loading events using a cohesive finite element method (CFEM) developed recently and the characterization by Tarver et al. [C. M. Tarver et al., "Critical conditions for impact- and shock-induced hot spots in solid explosives," J. Phys. Chem. 100, 5794-5799 (1996)] of the critical size-temperature threshold of hotspots required for chemical ignition of solid explosives. The criterion, along with the CFEM capability to quantify the thermal-mechanical behavior of GXs and PBXs, allows the critical impact velocity for ignition, time to ignition, and critical input energy at ignition to be determined as functions of material composition, microstructure, and loading conditions. The applicability of the relation between the critical input energy (E) and impact velocity of James [H. R. James, "An extension to the critical energy criterion used to predict shock initiation thresholds," Propellants, Explos., Pyrotech. 21, 8-13 (1996)] for shock loading is examined, leading to a modified interpretation, which is sensitive to microstructure and loading condition. As an application, numerical studies are undertaken to evaluate the ignition threshold of granular high melting point eXplosive, octahydro-1,3,5,7-tetranitro-1,2,3,5-tetrazocine (HMX) and HMX/Estane PBX under loading with impact velocities up to 350 ms-1 and strain rates up to 105 s-1. Results show that, for the GX, the time to criticality (tc) is strongly influenced by initial porosity, but is insensitive to grain size. Analyses also lead to a quantification of the differences between the responses of the GXs and PBXs in terms of critical impact velocity for ignition, time to ignition, and critical input energy at ignition. Since the framework permits explicit tracking of the influences of microstructure, loading, and mechanical constraints, the calculations also show the effects of stress wave reflection and confinement condition on the ignition behaviors of GXs and PBXs.

[Evaluation of the influence of humidity and temperature on the drug stability by initial average rate experiment].

PubMed

He, Ning; Sun, Hechun; Dai, Miaomiao

2014-05-01

To evaluate the influence of temperature and humidity on the drug stability by initial average rate experiment, and to obtained the kinetic parameters. The effect of concentration error, drug degradation extent, humidity and temperature numbers, humidity and temperature range, and average humidity and temperature on the accuracy and precision of kinetic parameters in the initial average rate experiment was explored. The stability of vitamin C, as a solid state model, was investigated by an initial average rate experiment. Under the same experimental conditions, the kinetic parameters obtained from this proposed method were comparable to those from classical isothermal experiment at constant humidity. The estimates were more accurate and precise by controlling the extent of drug degradation, changing humidity and temperature range, or by setting the average temperature closer to room temperature. Compared with isothermal experiments at constant humidity, our proposed method saves time, labor, and materials.

Viscoelastic Taylor-Couette instability as analog of the magnetorotational instability.

PubMed

Bai, Yang; Crumeyrolle, Olivier; Mutabazi, Innocent

2015-09-01

A linear stability analysis and an experimental study of a viscoelastic Taylor-Couette flow corotating in the Keplerian ratio allow us to elucidate the analogy between the viscoelastic instability and the magnetorotational instability (MRI). A generalized Rayleigh criterion allows us to determine the potentially unstable zone to pure-elasticity-driven perturbations. Experiments with a viscoelastic polymer solution yield four modes: one pure-elasticity mode and three elastorotational instability (ERI) modes that represent the MRI-analog modes. The destabilization by the polymer viscosity is evidenced for the ERI modes.

Phase-locking of magnetic islands diagnosed by ECE-imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tobias, Benjamin; Grierson, Brian A.; Muscatello, Christopher M.

2014-08-13

Millimeter-wave imaging diagnostics identify phase-locking and the satisfaction of 3-wave coupling selection criteria amongst multiple magnetic island chains by providing a localized, internal measurement of the 2D power spectral density, S(ω, k pol). In high-confinement tokamak discharges, these interactions impact both plasma rotation and tearing stability. Here, nonlinear coupling amongst neoclassical tearing modes (NTMs) of different n-number, with islands not satisfying the poloidal mode number selection criterion {m, m ', m - m ' }, contributes to a reduction in core rotation and flow shear in the vicinity of the modes.

Stability and Metastability of Trapless Bose-Einstein Condensates and Quantum Liquids

NASA Astrophysics Data System (ADS)

Zloshchastiev, Konstantin G.

2017-07-01

Various kinds of Bose-Einstein condensates are considered, which evolve without any geometric constraints or external trap potentials including gravitational. For studies of their collective oscillations and stability, including the metastability and macroscopic tunneling phenomena, both the variational approach and the Vakhitov-Kolokolov (VK) criterion are employed; calculations are done for condensates of an arbitrary spatial dimension. It is determined that that the trapless condensate described by the logarithmic wave equation is essentially stable, regardless of its dimensionality, while the trapless condensates described by wave equations of a polynomial type with respect to the wavefunction, such as the Gross-Pitaevskii (cubic), cubic-quintic, and so on, are at best metastable. This means that trapless "polynomial" condensates are unstable against spontaneous delocalization caused by fluctuations of their width, density and energy, leading to a finite lifetime.

The effect of low velocity impact in the strength characteristics of composite materials laminates

NASA Technical Reports Server (NTRS)

Liebowitz, H.

1983-01-01

The nonlinear vibration response of a double cantilevered beam subjected to pulse loading over a central sector is studied. The initial response is generated in detail to ascertain the energetics of the response. The total energy is used as a gauge of the stability and accuracy of the solution. It is shown that to obtain accurate and stable initial solutions an extremely high spatial and time resolution is required. This requirement was only evident through an examination of the energy of the system. It is proposed, therefore, to use the total energy of the system as a necessary stability and accuracy criterion for the nonlinear response of conservative systems. The results also demonstrate that even for moderate nonlinearities, the effects of membrane forces have a significant influence on the system.

Antiwindup analysis and design approaches for MIMO systems

NASA Technical Reports Server (NTRS)

Marcopoli, Vincent R.; Phillips, Stephen M.

1994-01-01

Performance degradation of multiple-input multiple-output (MIMO) control systems having limited actuators is often handled by augmenting the controller with an antiwindup mechanism, which attempts to maintain system performance when limits are encountered. The goals of this paper are: (1) To develop a method to analyze antiwindup systems to determine precisely what stability and performance degradation is incurred under limited conditions. It is shown that by reformulating limited actuator commands as resulting from multiplicative perturbations to the corresponding controller requests, mu-analysis tools can be utilized to obtain quantitative measures of stability and performance degradation. (2) To propose a linear, time invariant (LTI) criterion on which to base the antiwindup design. These analysis and design methods are illustrated through the evaluation of two competing antiwindup schemes augmenting the controller of a Short Take-Off and Vertical Landing (STOVL) aircraft in transition flight.

Antiwindup analysis and design approaches for MIMO systems

NASA Technical Reports Server (NTRS)

Marcopoli, Vincent R.; Phillips, Stephen M.

1993-01-01

Performance degradation of multiple-input multiple-output (MIMO) control systems having limited actuators is often handled by augmenting the controller with an antiwindup mechanism, which attempts to maintain system performance when limits are encountered. The goals of this paper are: 1) to develop a method to analyze antiwindup systems to determine precisely what stability and performance degradation is incurred under limited conditions. It is shown that by reformulating limited actuator commands as resulting from multiplicative perturbations to the corresponding controller requests, mu-analysis tools can be utilized to obtain quantitative measures of stability and performance degradation. 2) To propose a linear, time invariant (LTI) criterion on which to base the antiwindup design. These analysis and design methods are illustrated through the evaluation of two competing antiwindup schemes augmenting the controller of a Short Take-Off and Vertical Landing (STOVL) aircraft in transition flight.

TOPICAL REVIEW: Protein stability and enzyme activity at extreme biological temperatures

NASA Astrophysics Data System (ADS)

Feller, Georges

2010-08-01

Psychrophilic microorganisms thrive in permanently cold environments, even at subzero temperatures. To maintain metabolic rates compatible with sustained life, they have improved the dynamics of their protein structures, thereby enabling appropriate molecular motions required for biological activity at low temperatures. As a consequence of this structural flexibility, psychrophilic proteins are unstable and heat-labile. In the upper range of biological temperatures, thermophiles and hyperthermophiles grow at temperatures > 100 °C and synthesize ultra-stable proteins. However, thermophilic enzymes are nearly inactive at room temperature as a result of their compactness and rigidity. At the molecular level, both types of extremophilic proteins have adapted the same structural factors, but in opposite directions, to address either activity at low temperatures or stability in hot environments. A model based on folding funnels is proposed accounting for the stability-activity relationships in extremophilic proteins.

Thermal Stability of Zone Melting p-Type (Bi, Sb)2Te3 Ingots and Comparison with the Corresponding Powder Metallurgy Samples

NASA Astrophysics Data System (ADS)

Jiang, Chengpeng; Fan, Xi'an; Hu, Jie; Feng, Bo; Xiang, Qiusheng; Li, Guangqiang; Li, Yawei; He, Zhu

2018-04-01

During the past few decades, Bi2Te3-based alloys have been investigated extensively because of their promising application in the area of low temperature waste heat thermoelectric power generation. However, their thermal stability must be evaluated to explore the appropriate service temperature. In this work, the thermal stability of zone melting p-type (Bi, Sb)2Te3-based ingots was investigated under different annealing treatment conditions. The effect of service temperature on the thermoelectric properties and hardness of the samples was also discussed in detail. The results showed that the grain size, density, dimension size and mass remained nearly unchanged when the service temperature was below 523 K, which suggested that the geometry size of zone melting p-type (Bi, Sb)2Te3-based materials was stable below 523 K. The power factor and Vickers hardness of the ingots also changed little and maintained good thermal stability. Unfortunately, the thermal conductivity increased with increasing annealing temperature, which resulted in an obvious decrease of the zT value. In addition, the thermal stabilities of the zone melting p-type (Bi, Sb)2Te3-based materials and the corresponding powder metallurgy samples were also compared. All evidence implied that the thermal stabilities of the zone-melted (ZMed) p-type (Bi, Sb)2Te3 ingots in terms of crystal structure, geometry size, power factor (PF) and hardness were better than those of the corresponding powder metallurgy samples. However, their thermal stabilities in terms of zT values were similar under different annealing temperatures.

Maximum likelihood identification and optimal input design for identifying aircraft stability and control derivatives

NASA Technical Reports Server (NTRS)

Stepner, D. E.; Mehra, R. K.

1973-01-01

A new method of extracting aircraft stability and control derivatives from flight test data is developed based on the maximum likelihood cirterion. It is shown that this new method is capable of processing data from both linear and nonlinear models, both with and without process noise and includes output error and equation error methods as special cases. The first application of this method to flight test data is reported for lateral maneuvers of the HL-10 and M2/F3 lifting bodies, including the extraction of stability and control derivatives in the presence of wind gusts. All the problems encountered in this identification study are discussed. Several different methods (including a priori weighting, parameter fixing and constrained parameter values) for dealing with identifiability and uniqueness problems are introduced and the results given. The method for the design of optimal inputs for identifying the parameters of linear dynamic systems is also given. The criterion used for the optimization is the sensitivity of the system output to the unknown parameters. Several simple examples are first given and then the results of an extensive stability and control dervative identification simulation for a C-8 aircraft are detailed.

Phase stability and electronic structure of UMo2Al20: A first-principles study

NASA Astrophysics Data System (ADS)

Liu, Peng-Chuang; Xian, Ya-Jiang; Wang, Xin; Zhang, Yu-Ting; Zhang, Peng-Cheng

2017-09-01

In this paper, the phase stability of UMo2Al20 was explored using cluster formula in combination with first-principles calculations. Cluster formula analysis uncovered that the compound was composed of two principal clusters, i.e. [Mo-Al12] and [U-Al16]. The electronic interactions between U, Mo and Al atoms in this compound were discussed using elastic property, Bader charges and energy-resolved local bonding analysis, as well as the electronic interactions between Mo and Al atoms in [Mo-Al12] cluster and between U and Al atoms in [U-Al16] cluster. It revealed that UMo2Al20 satisfied the mechanical stability criterion for cubic system, and exhibited near ionic bonding character with weak bonding directionality. The calculations within both standard DFT and HSE frameworks demonstrated that U and Al atoms acted as an electron donor while Mo atoms acted as electron acceptor. The intrinsic stability of UMo2Al20 mainly stemmed from the bonding states of Mo-Al bonds and Al-Al bonds in [Mo-Al12] cluster. These calculations provide a further insight on the CeCr2Al20-type ternary compounds.

Closed-form analytical solutions of high-temperature heat pipe startup and frozen startup limitation

NASA Technical Reports Server (NTRS)

Cao, Y.; Faghri, A.

1992-01-01

Previous numerical and experimental studies indicate that the high-temperature heat pipe startup process is characterized by a moving hot zone with relatively sharp fronts. Based on the above observation, a flat-front model for an approximate analytical solution is proposed. A closed-form solution related to the temperature distribution in the hot zone and the hot zone length as a function of time are obtained. The analytical results agree well with the corresponding experimental data, and provide a quick prediction method for the heat pipe startup performance. Finally, a heat pipe limitation related to the frozen startup process is identified, and an explicit criterion for the high-temperature heat pipe startup is derived. The frozen startup limit identified in this paper provides a fundamental guidance for high-temperature heat pipe design.

Stability of Tranexamic Acid after 12-Week Storage at Temperatures from -20 deg C to 50 deg C

DTIC Science & Technology

2013-07-01

PRELIMINARY REPORTS STABILITY OF TRANEXAMIC ACID AFTER 12-WEEK STORAGE AT TEMPERATURES FROM –20◦C TO 50◦C Rodolfo de Guzman, Jr., MT, I. Amy...Polykratis, BS, Jill L. Sondeen, PhD, Daniel N. Darlington, PhD, Andrew P. Cap, MD, PhD, Michael A. Dubick, PhD ABSTRACT Background. Tranexamic acid (TXA) is... tranexamic acid ; temperature stability; HPLC; thromboelastography; storage PREHOSPITAL EMERGENCY CARE 2013;17:394–400 BACKGROUND Hemorrhage is the leading

14 CFR 29.1047 - Takeoff cooling test procedures.

Code of Federal Regulations, 2010 CFR

2010-01-01

... minutes after the occurence of the highest temperature recorded. (5) The cooling test must be conducted at... takeoff and subsequent climb as follows: (1) Each temperature must be stabilized while hovering in ground...; and (iii) The maximum weight. (2) After the temperatures have stabilized, a climb must be started at...

14 CFR 29.1047 - Takeoff cooling test procedures.

Code of Federal Regulations, 2014 CFR

2014-01-01

... minutes after the occurance of the highest temperature recorded. (5) The cooling test must be conducted at... takeoff and subsequent climb as follows: (1) Each temperature must be stabilized while hovering in ground...; and (iii) The maximum weight. (2) After the temperatures have stabilized, a climb must be started at...

14 CFR 29.1047 - Takeoff cooling test procedures.

Code of Federal Regulations, 2013 CFR

2013-01-01

... minutes after the occurance of the highest temperature recorded. (5) The cooling test must be conducted at... takeoff and subsequent climb as follows: (1) Each temperature must be stabilized while hovering in ground...; and (iii) The maximum weight. (2) After the temperatures have stabilized, a climb must be started at...

14 CFR 29.1047 - Takeoff cooling test procedures.

Code of Federal Regulations, 2011 CFR

2011-01-01

... minutes after the occurence of the highest temperature recorded. (5) The cooling test must be conducted at... takeoff and subsequent climb as follows: (1) Each temperature must be stabilized while hovering in ground...; and (iii) The maximum weight. (2) After the temperatures have stabilized, a climb must be started at...

14 CFR 29.1047 - Takeoff cooling test procedures.

Code of Federal Regulations, 2012 CFR

2012-01-01

... minutes after the occurence of the highest temperature recorded. (5) The cooling test must be conducted at... takeoff and subsequent climb as follows: (1) Each temperature must be stabilized while hovering in ground...; and (iii) The maximum weight. (2) After the temperatures have stabilized, a climb must be started at...

Exact analytical solution to a transient conjugate heat-transfer problem

NASA Technical Reports Server (NTRS)

Sucec, J.

1973-01-01

An exact analytical solution is found for laminar, constant-property, slug flow over a thin plate which is also convectively cooled from below. The solution is found by means of two successive Laplace transformations when a transient in the plate and the fluid is initiated by a step change in the fluid inlet temperature. The exact solution yields the transient fluid temperature, surface heat flux, and surface temperature distributions. The results of the exact transient solution for the surface heat flux are compared to the quasi-steady values, and a criterion for the validity of the quasi-steady results is found. Also the effect of the plate coupling parameter on the surface heat flux are investigated.

Stability of rhombohedral phases in vanadium at high-pressure and high-temperature: first-principles investigations

PubMed Central

Wang, Yi X.; Wu, Q.; Chen, Xiang R.; Geng, Hua Y.

2016-01-01

The pressure-induced transition of vanadium from BCC to rhombohedral structures is unique and intriguing among transition metals. In this work, the stability of these phases is revisited by using density functional theory. At finite temperatures, a novel transition of rhombohedral phases back to BCC phase induced by thermal electrons is discovered. This reentrant transition is found not driven by phonons, instead it is the electronic entropy that stabilizes the latter phase, which is totally out of expectation. Parallel to this transition, we find a peculiar and strong increase of the shear modulus C44 with increasing temperature. It is counter-intuitive in the sense that it suggests an unusual harding mechanism of vanadium by temperature. With these stability analyses, the high-pressure and finite-temperature phase diagram of vanadium is proposed. Furthermore, the dependence of the stability of RH phases on the Fermi energy and chemical environment is investigated. The results demonstrate that the position of the Fermi level has a significant impact on the phase stability, and follows the band-filling argument. Besides the Fermi surface nesting, we find that the localization/delocalization of the d orbitals also contributes to the instability of rhombohedral distortions in vanadium. PMID:27581551

Stability of compressible Taylor-Couette flow

NASA Technical Reports Server (NTRS)

Kao, Kai-Hsiung; Chow, Chuen-Yen

1991-01-01

Compressible stability equations are solved using the spectral collocation method in an attempt to study the effects of temperature difference and compressibility on the stability of Taylor-Couette flow. It is found that the Chebyshev collocation spectral method yields highly accurate results using fewer grid points for solving stability problems. Comparisons are made between the result obtained by assuming small Mach number with a uniform temperature distribution and that based on fully incompressible analysis.

High Reynolds Number Thermal Stability Experiments

NASA Technical Reports Server (NTRS)

Emens, Jessica M.; Brown, Sarah P.; Frederick Robert A., Jr.; Wood, A. John

2004-01-01

This work represents preliminary thermal stability results for liquid hydrocarbon fuels. High Reynolds Number Thermal Stability experiments with Jet A and RP-1 resulted in a quantitative measurement of the thermal stability. Each fuel flowed through a heated capillary tube that held the outlet temperature at 290 C. An optical pyrometer measured the surface temperature of the tube at 12 locations as a function of time. The High Reynolds Number Thermal Stability number was then determined using standards published by the American Society for Testing and Materials. The results for Jet A showed lower thermal stability than similar tests conducted at another facility. The RP-1 results are the first reported using this technique. Because the temperature rise on the capillary tube during testing for the RP-1 fuels was not significant, a new standard for the testing conditions should be developed for these types of fuels.

Effect of Temperature and Time on Fecal Hemoglobin Stability in 5 Fecal Immunochemical Test Methods and One Guaiac Method.

PubMed

Catomeris, Peter; Baxter, Nancy N; Boss, Sheila C; Paszat, Lawrence F; Rabeneck, Linda; Randell, Edward; Serenity, Mardie L; Sutradhar, Rinku; Tinmouth, Jill

2018-01-01

- Although promising for colorectal cancer screening, hemoglobin (Hb) stability remains a concern with fecal immunochemical tests. This study implemented a novel, standardized method to compare Hb stability across various fecal immunochemical tests. The method can be used to inform decisions when selecting a kit for use in colorectal cancer screening. In so doing, this work addressed a critical need for standardization in this field. - To compare the stability of Hb across 5 different immunochemical kits and one guaiac kit. - The stability of Hb was analyzed in collection devices inoculated with Hb-spiked feces and (1) stored at various temperatures (frozen, refrigerated, ambient, and elevated) for more than 60 days; (2) after undergoing 3 controlled, freeze-thaw cycles; and (3) after being transported by courier or postal services in uncontrolled temperature conditions from 3 locations in Ontario, Canada, to a central testing center. - The stability of Hb varied with time and temperature and by kit. Lower Hb recoveries occurred with increasing temperature and increasing time from sample collection to testing. Refrigeration provided the best stability, although results varied across kits (eg, from 4.2 days to >60 days before a prespecified threshold [<70% probability of the test results remaining positive] was reached). Freeze-thaw stability varied across kits and cycles (Hb recoveries: NS Plus [Alfresa Pharma, Chuo-ku, Osaka, Japan], 91.7% to 95.4%; OC Diana [Eiken Chemical, Taito-ku, Tokyo, Japan], 57.6% to 74.9%). Agreement regarding Hb levels before and after transportation varied across kits (from 57% to 100%). - Important differences in Hb stability were found across the included fecal immunochemical tests. These findings should inform practice-based and population-based colorectal cancer screening.

A novel kinetic modeling method for the stabilization phase of the composting process for biodegradation of solid wastes.

PubMed

Ebrahimzadeh, Reza; Ghazanfari Moghaddam, Ahmad; Sarcheshmehpour, Mehdi; Mortezapour, Hamid

2017-12-01

Biomass degradation kinetics of the composting process for kitchen waste, pruned elm tree branches and sheep manure were studied to model changes in volatile solids (VS) over time. Three experimental reactors containing raw mixtures with a carbon to nitrogen (C/N) ratio of 27:1 and a moisture content of 65% were prepared. During the composting process two of the reactors used forced air and the third used natural aeration. The composting stabilization phases in all reactors were completed in 30 days. During this period, composting indexes such as temperature, moisture content and VS changes were recorded. Elementary reactions were used for kinetics modeling of the degradation process. Results showed that the numerical values of rate constant ( k) for zero-order ranged from 0.86 to 1.03 VS×day -1 , for first-order models it ranged from 0.01 to 0.02 day -1 , for second-order the range was from 1.36×10 -5 to 1.78×10 -5 VS -1 ×day -1 and for n-order the rate constant ranged from 0.031 to 0.095 VS (1-n) ×day -1 . The resulting models were validated by comparing statistical parameters. Evaluation of the models showed that, in the aerated reactors, the n-order models (less than 1) successfully estimated the VS changes. In the non-aeration reactor, for the second-order model good agreement was achieved between the simulated and actual quantities of VS. Also, half-life time provided a useful criterion for the estimation of expected time for completion of different phases of composting.

Collective Modes of Dust Helical Clusters

NASA Astrophysics Data System (ADS)

Tsytovich, V. N.; Gousein-Zade, N. G.; Morfill, G. E.

2005-10-01

The helical structures are the simplest 3D crystal-like cylindrical structures with radius R being a system of 2D clusters equally separated along the cylindrical axis with a relative rotation on constant angle φ0. For mean free path for grain charging much larger than the separation of the grains, the total energy of grain interaction is a sum of all pair grain interactions. The helical structures have been found experimentally for ions in laser traps in cylindrical gas discharges at very low temperatures (in both case as ``warms''). The equilibrium criterion and the criteria of stability including the absence of saddle points show that in the plane ρ, φ the bifurcation points are often present with new branches appearing (stable and unstable). Numerical MD simulations show that for cylindrical symmetry any random distributions of grains is developing into helical structures. The theory of collective modes of helical structures is developed for arbitrary grain interactions. The dispersion relation for frequencies of the collective modes for different branches of helical structures is derived and solved numerically for interaction including different type of screened grain potentials including the grain attraction. The dispersion relation in the first Brillouin zone for the square of the frequency ω2 is shown to be a be-cubic equation and gives the square of frequency ω2 > 0 for stable modes and the square of the growth rates for the unstable modes ω2 < 0. Modes for helical structures in parabolic external confining potential well perpendicular to cylindrical axis are found. Stabile self-confined structures without external confinement are discovered in presence of both non-collective and collective grain attractions.

Constraints on oceanic methane emissions west of Svalbard from atmospheric in situ measurements and Lagrangian transport modeling.

PubMed

Pisso, I; Myhre, C Lund; Platt, S M; Eckhardt, S; Hermansen, O; Schmidbauer, N; Mienert, J; Vadakkepuliyambatta, S; Bauguitte, S; Pitt, J; Allen, G; Bower, K N; O'Shea, S; Gallagher, M W; Percival, C J; Pyle, J; Cain, M; Stohl, A

2016-12-16

Methane stored in seabed reservoirs such as methane hydrates can reach the atmosphere in the form of bubbles or dissolved in water. Hydrates could destabilize with rising temperature further increasing greenhouse gas emissions in a warming climate. To assess the impact of oceanic emissions from the area west of Svalbard, where methane hydrates are abundant, we used measurements collected with a research aircraft (Facility for Airborne Atmospheric Measurements) and a ship (Helmer Hansen) during the Summer 2014 and for Zeppelin Observatory for the full year. We present a model-supported analysis of the atmospheric CH 4 mixing ratios measured by the different platforms. To address uncertainty about where CH 4 emissions actually occur, we explored three scenarios: areas with known seeps, a hydrate stability model, and an ocean depth criterion. We then used a budget analysis and a Lagrangian particle dispersion model to compare measurements taken upwind and downwind of the potential CH 4 emission areas. We found small differences between the CH 4 mixing ratios measured upwind and downwind of the potential emission areas during the campaign. By taking into account measurement and sampling uncertainties and by determining the sensitivity of the measured mixing ratios to potential oceanic emissions, we provide upper limits for the CH 4 fluxes. The CH 4 flux during the campaign was small, with an upper limit of 2.5 nmol m -2  s -1 in the stability model scenario. The Zeppelin Observatory data for 2014 suggest CH 4 fluxes from the Svalbard continental platform below 0.2 Tg yr -1 . All estimates are in the lower range of values previously reported.

Constraints on oceanic methane emissions west of Svalbard from atmospheric in situ measurements and Lagrangian transport modeling

PubMed Central

Myhre, C. Lund; Platt, S. M.; Eckhardt, S.; Hermansen, O.; Schmidbauer, N.; Mienert, J.; Vadakkepuliyambatta, S.; Bauguitte, S.; Pitt, J.; Allen, G.; Bower, K. N.; O'Shea, S.; Gallagher, M. W.; Percival, C. J.; Pyle, J.; Cain, M.; Stohl, A.

2016-01-01

Abstract Methane stored in seabed reservoirs such as methane hydrates can reach the atmosphere in the form of bubbles or dissolved in water. Hydrates could destabilize with rising temperature further increasing greenhouse gas emissions in a warming climate. To assess the impact of oceanic emissions from the area west of Svalbard, where methane hydrates are abundant, we used measurements collected with a research aircraft (Facility for Airborne Atmospheric Measurements) and a ship (Helmer Hansen) during the Summer 2014 and for Zeppelin Observatory for the full year. We present a model‐supported analysis of the atmospheric CH4 mixing ratios measured by the different platforms. To address uncertainty about where CH4 emissions actually occur, we explored three scenarios: areas with known seeps, a hydrate stability model, and an ocean depth criterion. We then used a budget analysis and a Lagrangian particle dispersion model to compare measurements taken upwind and downwind of the potential CH4 emission areas. We found small differences between the CH4 mixing ratios measured upwind and downwind of the potential emission areas during the campaign. By taking into account measurement and sampling uncertainties and by determining the sensitivity of the measured mixing ratios to potential oceanic emissions, we provide upper limits for the CH4 fluxes. The CH4 flux during the campaign was small, with an upper limit of 2.5 nmol m−2 s−1 in the stability model scenario. The Zeppelin Observatory data for 2014 suggest CH4 fluxes from the Svalbard continental platform below 0.2 Tg yr−1. All estimates are in the lower range of values previously reported. PMID:28261536

Constraints on oceanic methane emissions west of Svalbard from atmospheric in situ measurements and Lagrangian transport modeling

NASA Astrophysics Data System (ADS)

Pisso, I.; Myhre, C. Lund; Platt, S. M.; Eckhardt, S.; Hermansen, O.; Schmidbauer, N.; Mienert, J.; Vadakkepuliyambatta, S.; Bauguitte, S.; Pitt, J.; Allen, G.; Bower, K. N.; O'Shea, S.; Gallagher, M. W.; Percival, C. J.; Pyle, J.; Cain, M.; Stohl, A.

2016-12-01

Methane stored in seabed reservoirs such as methane hydrates can reach the atmosphere in the form of bubbles or dissolved in water. Hydrates could destabilize with rising temperature further increasing greenhouse gas emissions in a warming climate. To assess the impact of oceanic emissions from the area west of Svalbard, where methane hydrates are abundant, we used measurements collected with a research aircraft (Facility for Airborne Atmospheric Measurements) and a ship (Helmer Hansen) during the Summer 2014 and for Zeppelin Observatory for the full year. We present a model-supported analysis of the atmospheric CH4 mixing ratios measured by the different platforms. To address uncertainty about where CH4 emissions actually occur, we explored three scenarios: areas with known seeps, a hydrate stability model, and an ocean depth criterion. We then used a budget analysis and a Lagrangian particle dispersion model to compare measurements taken upwind and downwind of the potential CH4 emission areas. We found small differences between the CH4 mixing ratios measured upwind and downwind of the potential emission areas during the campaign. By taking into account measurement and sampling uncertainties and by determining the sensitivity of the measured mixing ratios to potential oceanic emissions, we provide upper limits for the CH4 fluxes. The CH4 flux during the campaign was small, with an upper limit of 2.5 nmol m-2 s-1 in the stability model scenario. The Zeppelin Observatory data for 2014 suggest CH4 fluxes from the Svalbard continental platform below 0.2 Tg yr-1. All estimates are in the lower range of values previously reported.

Effect of temperature on microbial growth rate-mathematical analysis: the Arrhenius and Eyring-Polanyi connections.

PubMed

Huang, Lihan; Hwang, Andy; Phillips, John

2011-10-01

The objective of this work is to develop a mathematical model for evaluating the effect of temperature on the rate of microbial growth. The new mathematical model is derived by combination and modification of the Arrhenius equation and the Eyring-Polanyi transition theory. The new model, suitable for both suboptimal and the entire growth temperature ranges, was validated using a collection of 23 selected temperature-growth rate curves belonging to 5 groups of microorganisms, including Pseudomonas spp., Listeria monocytogenes, Salmonella spp., Clostridium perfringens, and Escherichia coli, from the published literature. The curve fitting is accomplished by nonlinear regression using the Levenberg-Marquardt algorithm. The resulting estimated growth rate (μ) values are highly correlated to the data collected from the literature (R(2) = 0.985, slope = 1.0, intercept = 0.0). The bias factor (B(f) ) of the new model is very close to 1.0, while the accuracy factor (A(f) ) ranges from 1.0 to 1.22 for most data sets. The new model is compared favorably with the Ratkowsky square root model and the Eyring equation. Even with more parameters, the Akaike information criterion, Bayesian information criterion, and mean square errors of the new model are not statistically different from the square root model and the Eyring equation, suggesting that the model can be used to describe the inherent relationship between temperature and microbial growth rates. The results of this work show that the new growth rate model is suitable for describing the effect of temperature on microbial growth rate. Practical Application:  Temperature is one of the most significant factors affecting the growth of microorganisms in foods. This study attempts to develop and validate a mathematical model to describe the temperature dependence of microbial growth rate. The findings show that the new model is accurate and can be used to describe the effect of temperature on microbial growth rate in foods. Journal of Food Science © 2011 Institute of Food Technologists® No claim to original US government works.

A Low-cost Environmental Control System for Precise Radial Velocity Spectrometers

NASA Astrophysics Data System (ADS)

Sliski, David H.; Blake, Cullen H.; Halverson, Samuel

2017-12-01

We present an environmental control system (ECS) designed to achieve milliKelvin (mK) level temperature stability for small-scale astronomical instruments. This ECS is inexpensive and is primarily built from commercially available components. The primary application for our ECS is the high-precision Doppler spectrometer MINERVA-Red, where the thermal variations of the optical components within the instrument represent a major source of systematic error. We demonstrate ±2 mK temperature stability within a 0.5 m3 thermal enclosure using resistive heaters in conjunction with a commercially available PID controller and off-the-shelf thermal sensors. The enclosure is maintained above ambient temperature, enabling rapid cooling through heat dissipation into the surrounding environment. We demonstrate peak-to-valley (PV) temperature stability of better than 5 mK within the MINERVA-Red vacuum chamber, which is located inside the thermal enclosure, despite large temperature swings in the ambient laboratory environment. During periods of stable laboratory conditions, the PV variations within the vacuum chamber are less than 3 mK. This temperature stability is comparable to the best stability demonstrated for Doppler spectrometers currently achieving m s-1 radial velocity precision. We discuss the challenges of using commercially available thermoelectrically cooled CCD cameras in a temperature-stabilized environment, and demonstrate that the effects of variable heat output from the CCD camera body can be mitigated using PID-controlled chilled water systems. The ECS presented here could potentially provide the stable operating environment required for future compact “astrophotonic” precise radial velocity (PRV) spectrometers to achieve high Doppler measurement precision with a modest budget.

Borehole Stability in High-Temperature Formations

NASA Astrophysics Data System (ADS)

Yan, Chuanliang; Deng, Jingen; Yu, Baohua; Li, Wenliang; Chen, Zijian; Hu, Lianbo; Li, Yang

2014-11-01

In oil and gas drilling or geothermal well drilling, the temperature difference between the drilling fluid and formation will lead to an apparent temperature change around the borehole, which will influence the stress state around the borehole and tend to cause borehole instability in high geothermal gradient formations. The thermal effect is usually not considered as a factor in most of the conventional borehole stability models. In this research, in order to solve the borehole instability in high-temperature formations, a calculation model of the temperature field around the borehole during drilling is established. The effects of drilling fluid circulation, drilling fluid density, and mud displacement on the temperature field are analyzed. Besides these effects, the effect of temperature change on the stress around the borehole is analyzed based on thermoelasticity theory. In addition, the relationships between temperature and strength of four types of rocks are respectively established based on experimental results, and thermal expansion coefficients are also tested. On this basis, a borehole stability model is established considering thermal effects and the effect of temperature change on borehole stability is also analyzed. The results show that the fracture pressure and collapse pressure will both increase as the temperature of borehole rises, and vice versa. The fracture pressure is more sensitive to temperature. Temperature has different effects on collapse pressures due to different lithological characters; however, the variation of fracture pressure is unrelated to lithology. The research results can provide a reference for the design of drilling fluid density in high-temperature wells.

Effect of thermal aging on stability of transformer oil based temperature sensitive magnetic fluids

NASA Astrophysics Data System (ADS)

Kaur, Navjot; Chudasama, Bhupendra

2018-04-01

Synthesizing stable temperature sensitive magnetic fluids with tunable magnetic properties that can be used as coolant in transformers is of great interest, however not exploited commercially due to the lack of its stability at elevated temperatures in bulk quantities. The task is quite challenging as the performance parameters of magnetic fluids are strongly influenced by thermal aging. In this article, we report the effect of thermal aging on colloidal stability and magnetic properties of Mn1-xZnxFe2O4 magnetic fluids prepared in industrial grade transformer oil. As-synthesized magnetic fluids possess good dispersion stability and tunable magnetic properties. Effect of accelerated thermal aging on the dispersion stability and magnetic properties have been evaluated by photon correlation spectroscopy and vibration sample magnetometry, respectively. Magnetic fluids are stable under accelerated aging at elevated temperatures (from 50 °C to 125 °C), which is critical for their efficient performance in high power transformers.

The effect of Ti-B on stabilization of Cu-Zn-Al martensite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stipcich, M.; Romero, R.

1998-10-05

The application of shape memory effect in devices requires, in many cases, stable and reliable transformation temperatures. However, as a consequence of diffusional processes, in Cu-based shape memory alloys, reverse transformation temperature significantly rises after aging at temperatures above room temperature. This generally unwanted behavior is usually referred to as the stabilization of martensite. Numerous investigations have been carried out on this subject as reviewed by Ahlers and Chandrasekaran et al. Within the Cu-based alloys the Cu-Zn-Al are claimed to be more prone to stabilization than Cu-Al-Ni on aging. It has been proposed that in the Cu-Zn-Al the stabilization ismore » due to the interchange of Cu and Zn atoms assisted by vacancies, changing, consequently, the long range order inherited from the {beta} phase. In the present work, the authors investigate the stabilization behavior of polycrystalline samples of stress induced Cu-Zn-Al and Cu-Zn-Al-B martensite.« less

LOX/Hydrocarbon Combustion Instability Investigation

NASA Technical Reports Server (NTRS)

Jensen, R. J.; Dodson, H. C.; Claflin, S. E.

1989-01-01

The LOX/Hydrocarbon Combustion Instability Investigation Program was structured to determine if the use of light hydrocarbon combustion fuels with liquid oxygen (LOX) produces combustion performance and stability behavior similar to the LOX/hydrogen propellant combination. In particular methane was investigated to determine if that fuel can be rated for combustion instability using the same techniques as previously used for LOX/hydrogen. These techniques included fuel temperature ramping and stability bomb tests. The hot fire program probed the combustion behavior of methane from ambient to subambient temperatures. Very interesting results were obtained from this program that have potential importance to future LOX/methane development programs. A very thorough and carefully reasoned documentation of the experimental data obtained is contained. The hot fire test logic and the associated tests are discussed. Subscale performance and stability rating testing was accomplished using 40,000 lb. thrust class hardware. Stability rating tests used both bombs and fuel temperature ramping techniques. The test program was successful in generating data for the evaluation of the methane stability characteristics relative to hydrogen and to anchor stability models. Data correlations, performance analysis, stability analyses, and key stability margin enhancement parameters are discussed.

Long-term stability and properties of zirconia ceramics for heavy duty diesel engine components

NASA Technical Reports Server (NTRS)

Larsen, D. C.; Adams, J. W.

1985-01-01

Physical, mechanical, and thermal properties of commercially available transformation-toughened zirconia are measured. Behavior is related to the material microstructure and phase assemblage. The stability of the materials is assessed after long-term exposure appropriate for diesel engine application. Properties measured included flexure strength, elastic modulus, fracture toughness, creep, thermal shock, thermal expansion, internal friction, and thermal diffusivity. Stability is assessed by measuring the residual property after 1000 hr/1000C static exposure. Additionally static fatigue and thermal fatigue testing is performed. Both yttria-stabilized and magnesia-stabilized materials are compared and contrasted. The major limitations of these materials are short term loss of properties with increasing temperature as the metastable tetragonal phase becomes more stable. Fine grain yttria-stabilized material (TZP) is higher strength and has a more stable microstructure with respect to overaging phenomena. The long-term limitation of Y-TZP is excessive creep deformation. Magnesia-stabilized PSZ has relatively poor stability at elevated temperature. Overaging, decomposition, and/or destabilization effects are observed. The major limitation of Mg-PSZ is controlling unwanted phase changes at elevated temperature.

Formation and evolution of quasi-interchange convection cell on the HL-2A tokamak

NASA Astrophysics Data System (ADS)

Shi, P. W.; Chen, W.; Shi, Z. B.; Duan, X. R.; Zhong, W. L.; Jiang, M.; Yang, Z. C.; Yu, L. M.; Wen, J.; Liang, A. S.; Yu, D. L.; Liu, Y.; Yang, Q. W.

2018-06-01

Formation and evolution of quasi-interchange convection cell have been observed for the first time by an electron cyclotron emission imaging (ECEI) system on the HL-2A tokamak. The instability with mode numbers of m/n = -1/-1 and a frequency of 2-4 kHz propagates in the electron diamagnetic drift direction. The mode downgrades the inner stored energy WE and enhances the divertor Hα signal, which indicates a degradation of plasma confinement. The ECEI reveals that the colder core temperature fluctuation distorts to a crescent shape, while a bubble originates from hot fluctuation gradually and draws into the concave side of the crescent. A finger-like structure can be observed during the convection process, and it presents a typical feature of the quasi-interchange model. The radial structure of the interchange mode obtained from electron cyclotron emission is quite narrow at the high field side but relatively wider at the low field side. Further analysis suggests that the discharge parameters are favorable for the excitation of interchange mode, and the stability criterion is violated in the core region. Moreover, the experimental frequency agrees with that given by the linear dispersion relation of interchange instability. The large grow rate suggests that the mode grows on a very short time scale.

Tunable Noncollinear Antiferromagnetic Resistive Memory through Oxide Superlattice Design

NASA Astrophysics Data System (ADS)

Hoffman, Jason D.; Wu, Stephen M.; Kirby, Brian J.; Bhattacharya, Anand

2018-04-01

Antiferromagnets (AFMs) have recently gathered a large amount of attention as a potential replacement for ferromagnets (FMs) in spintronic devices due to their lack of stray magnetic fields, invisibility to external magnetic probes, and faster magnetization dynamics. Their development into a practical technology, however, has been hampered by the small number of materials where the antiferromagnetic state can be both controlled and read out. We show that by relaxing the strict criterion on pure antiferromagnetism, we can engineer an alternative class of magnetic materials that overcome these limitations. This is accomplished by stabilizing a noncollinear magnetic phase in LaNiO3 /La2 /3Sr1 /3MnO3 superlattices. This state can be continuously tuned between AFM and FM coupling through varying the superlattice spacing, strain, applied magnetic field, or temperature. By using this alternative "knob" to tune magnetic ordering, we take a nanoscale materials-by-design approach to engineering ferromagneticlike controllability into antiferromagnetic synthetic magnetic structures. This approach can be used to trade-off between the favorable and unfavorable properties of FMs and AFMs when designing realistic resistive antiferromagnetic memories. We demonstrate a memory device in one such superlattice, where the magnetic state of the noncollinear antiferromagnet is reversibly switched between different orientations using a small magnetic field and read out in real time with anisotropic magnetoresistance measurements.

Corrigendum to “High-fidelity micro-scale modeling of the thermo-visco-plastic behavior of carbon fiber polymer matrix composites” [Compos Struct 134 (2015) 132–141

DOE PAGES

Bai, Xiaoming; Bessa, Miguel A.; Melro, Antonio R.; ...

2016-10-01

The authors would like to inform that one of the modifications proposed in the article “High-fidelity micro-scale modeling of the thermo-visco-plastic behavior of carbon fiber polymer matrix composites” [1] was found to be unnecessary: the paraboloid yield criterion is sufficient to describe the shear behavior of the epoxy matrix considered (Epoxy 3501-6). The authors recently noted that the experimental work [2] used to validate the pure matrix response considered engineering shear strain instead of its tensorial counter-part, which caused the apparent inconsistency with the paraboloid yield criterion. A recently proposed temperature dependency law for glassy polymers is evaluated herein, thusmore » better agreement with the experimental results for this epoxy is observed.« less

Corrigendum to “High-fidelity micro-scale modeling of the thermo-visco-plastic behavior of carbon fiber polymer matrix composites” [Compos Struct 134 (2015) 132–141

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bai, Xiaoming; Bessa, Miguel A.; Melro, Antonio R.

The authors would like to inform that one of the modifications proposed in the article “High-fidelity micro-scale modeling of the thermo-visco-plastic behavior of carbon fiber polymer matrix composites” [1] was found to be unnecessary: the paraboloid yield criterion is sufficient to describe the shear behavior of the epoxy matrix considered (Epoxy 3501-6). The authors recently noted that the experimental work [2] used to validate the pure matrix response considered engineering shear strain instead of its tensorial counter-part, which caused the apparent inconsistency with the paraboloid yield criterion. A recently proposed temperature dependency law for glassy polymers is evaluated herein, thusmore » better agreement with the experimental results for this epoxy is observed.« less

Stability studies of oxytetracycline in methanol solution

NASA Astrophysics Data System (ADS)

Wang, Wei; Wu, Nan; Yang, Jinghui; Zeng, Ming; Xu, Chenshan; Li, Lun; Zhang, Meng; Li, Liting

2018-02-01

As one kind of typical tetracycline antibiotics, antibiotic residues of oxytetracycline have been frequently detected in many environmental media. In this study, the stability of oxytetracycline in methanol solution was investigated by high-performance liquid chromatography combined with UV-vis (HPLC-UV). The results show that the stability of oxytetracycline in methanol solution is highly related to its initial concentration and the preserved temperature. Under low temperature condition, the solution was more stable than under room temperature preservation. Under the same temperature preservation condition, high concentrations of stock solutions are more stable than low concentrations. The study provides a foundation for preserving the oxytetracycline-methanol solution.

Optimization of extraction of novel pectinase enzyme discovered in red pitaya (Hylocereus polyrhizus) peel.

PubMed

Zohdi, Nor Khanani; Amid, Mehrnoush

2013-11-20

Plant peels could be a potential source of novel pectinases for use in various industrial applications due to their broad substrate specificity with high stability under extreme conditions. Therefore, the extraction conditions of a novel pectinase enzyme from pitaya peel was optimized in this study. The effect of extraction variables, namely buffer to sample ratio (2:1 to 8:1, X₁), extraction temperature (-15 to +25 °C, X₂) and buffer pH (4.0 to 12.0, X₃) on specific activity, temperature stability, storage stability and surfactant agent stability of pectinase from pitaya peel was investigated. The study demonstrated that the optimum conditions for the extraction of pectinase from pitaya sources could improve the enzymatic characteristics of the enzyme and protect its activity and stability during the extraction procedure. The optimum extraction conditions cause the pectinase to achieve high specific activity (15.31 U/mg), temperature stability (78%), storage stability (88%) and surfactant agent stability (83%). The most desirable conditions to achieve the highest activity and stability of pectinase enzyme from pitaya peel were the use of 5:1 buffer to sample ratio at 5 °C and pH 8.0.

Effect of fly ash on properties of crushed brick and reclaimed asphalt in pavement base/subbase applications.

PubMed

Mohammadinia, Alireza; Arulrajah, Arul; Horpibulsuk, Suksun; Chinkulkijniwat, Avirut

2017-01-05

Fly Ash (FA), an abundant by-product with no carbon footprint, is a potential stabilizer for enhancing the physical and geotechnical properties of pavement aggregates. In this research, FA was used in different ratios to stabilize crushed brick (CB) and reclaimed asphalt pavement (RAP) for pavement base/subbase applications. The FA stabilization of CB and RAP was targeted to improve the strength and durability of these recycled materials for pavement base/subbase applications. The Unconfined Compressive Strength (UCS) and resilient modulus (M R ) development of the stabilized CB and RAP aggregates was studied under room temperature and at an elevated temperatures of 40°C, and results compared with unbound CB and RAP. Analysis of atomic silica content showed that when the amount of silica and alumina crystalline was increased, the soil structure matrix deteriorated, resulting in strength reduction. The results of UCS and M R testing of FA stabilized CB and RAP aggregates indicated that FA was a viable binder for the stabilization of recycled CB and RAP. CB and RAP stabilized with 15% FA showed the highest UCS results at both room temperature and at 40°C. Higher temperature curing was also found to result in higher strengths. Copyright © 2016 Elsevier B.V. All rights reserved.

Effect of parallel electric fields on the ponderomotive stabilization of MHD instabilities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Litwin, C.; Hershkowitz, N.

The contribution of the wave electric field component E/sub parallel/, parallel to the magnetic field, to the ponderomotive stabilization of curvature driven instabilities is evaluated and compared to the transverse component contribution. For the experimental density range, in which the stability is primarily determined by the m = 1 magnetosonic wave, this contribution is found to be the dominant and stabilizing when the electron temperature is neglected. For sufficiently high electron temperatures the dominant fast wave is found to be axially evanescent. In the same limit, E/sub parallel/ becomes radially oscillating. It is concluded that the increased electron temperature nearmore » the plasma surface reduces the magnitude of ponderomotive effects.« less

Design of DC-contact RF MEMS switch with temperature stability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Junfeng; Nanjing Electronic Devices Institute, Nanjing, 210016; Li, Zhiqun, E-mail: zhiqunli@seu.edu.cn

In order to improve the temperature stability of DC-contact RF MEMS switch, a thermal buckle-beam structure is implemented. The stability of the switch pull-in voltage versus temperature is not only improved, but also the impact of stress and stress gradient on the drive voltage is suppressed. Test results show that the switch pull-in voltage is less sensitive to temperature between -20 °C and 100 °C. The variable rate of pull-in voltage to temperature is about -120 mV/°C. The RF performance of the switch is stable, and the isolation is almost independent of temperature. After being annealed at 280 °C formore » 12 hours, our switch samples, which are suitable for packaging, have less than 1.5% change in the rate of pull-in voltage.« less

Optimization of ultrasound-assisted extraction of pectinase enzyme from guava (Psidium guajava) peel: Enzyme recovery, specific activity, temperature, and storage stability.

PubMed

Amid, Mehrnoush; Murshid, Fara Syazana; Manap, Mohd Yazid; Islam Sarker, Zaidul

2016-01-01

This study aimed to investigate the effects of the ultrasound-assisted extraction conditions on the yield, specific activity, temperature, and storage stability of the pectinase enzyme from guava peel. The ultrasound variables studied were sonication time (10-30 min), ultrasound temperature (30-50 °C), pH (2.0-8.0), and solvent-to-sample ratio (2:1 mL/g to 6:1 mL/g). The main goal was to optimize the ultrasound-assisted extraction conditions to maximize the recovery of pectinase from guava peel with the most desirable enzyme-specific activity and stability. Under the optimum conditions, a high yield (96.2%), good specific activity (18.2 U/mg), temperature stability (88.3%), and storage stability (90.3%) of the extracted enzyme were achieved. The optimal conditions were 20 min sonication time, 40 °C temperature, at pH 5.0, using a 4:1 mL/g solvent-to-sample ratio. The study demonstrated that optimization of ultrasound-assisted process conditions for the enzyme extraction could improve the enzymatic characteristics and yield of the enzyme.

Adaptive detection of noise signal according to Neumann-Pearson criterion

NASA Astrophysics Data System (ADS)

Padiryakov, Y. A.

1985-03-01

Optimum detection according to the Neumann-Pearson criterion is considered in the case of a random Gaussian noise signal, stationary during measurement, and a stationary random Gaussian background interference. Detection is based on two samples, their statistics characterized by estimates of their spectral densities, it being a priori known that sample A from the signal channel is either the sum of signal and interference or interference alone and sample B from the reference interference channel is an interference with the same spectral density as that of the interference in sample A for both hypotheses. The probability of correct detection is maximized on the average, first in the 2N-dimensional space of signal spectral density and interference spectral density readings, by fixing the probability of false alarm at each point so as to stabilize it at a constant level against variation of the interference spectral density. Deterministic decision rules are established. The algorithm is then reduced to equivalent detection in the N-dimensional space of the ratio of sample A readings to sample B readings.

Towards a Probabilistic Preliminary Design Criterion for Buckling Critical Composite Shells

NASA Technical Reports Server (NTRS)

Arbocz, Johann; Hilburger, Mark W.

2003-01-01

A probability-based analysis method for predicting buckling loads of compression-loaded laminated-composite shells is presented, and its potential as a basis for a new shell-stability design criterion is demonstrated and discussed. In particular, a database containing information about specimen geometry, material properties, and measured initial geometric imperfections for a selected group of laminated-composite cylindrical shells is used to calculate new buckling-load "knockdown factors". These knockdown factors are shown to be substantially improved, and hence much less conservative than the corresponding deterministic knockdown factors that are presently used by industry. The probability integral associated with the analysis is evaluated by using two methods; that is, by using the exact Monte Carlo method and by using an approximate First-Order Second- Moment method. A comparison of the results from these two methods indicates that the First-Order Second-Moment method yields results that are conservative for the shells considered. Furthermore, the results show that the improved, reliability-based knockdown factor presented always yields a safe estimate of the buckling load for the shells examined.

Reliability assessment of an OVH HV power line truss transmission tower subjected to seismic loading

NASA Astrophysics Data System (ADS)

Winkelmann, Karol; Jakubowska, Patrycja; Soltysik, Barbara

2017-03-01

The study focuses on the reliability of a transmission tower OS24 ON150 + 10, an element of an OVH HV power line, under seismic loading. In order to describe the seismic force, the real-life recording of the horizontal component of the El Centro earthquake was adopted. The amplitude and the period of this excitation are assumed random, their variation is described by Weibull distribution. The possible space state of the phenomenon is given in the form of a structural response surface (RSM methodology), approximated by an ANOVA table with directional sampling (DS) points. Four design limit states are considered: stress limit criterion for a natural load combination, criterion for an accidental combination (one-sided cable snap), vertical and horizontal translation criteria. According to these cases the HLRF reliability index β is used for structural safety assessment. The RSM approach is well suited for the analysis - it is numerically efficient, not excessively time consuming, indicating a high confidence level. Given the problem conditions, the seismic excitation is shown the sufficient trigger to the loss of load-bearing capacity or stability of the tower.

The origin of and conditions for clustering in fluids with competing interactions

NASA Astrophysics Data System (ADS)

Jadrich, Ryan; Bollinger, Jonathan; Truskett, Thomas

2015-03-01

Fluids with competing short-range attractions and long-range repulsions exhibit a rich phase behavior characterized by intermediate range order (IRO), as quantified via the static structure factor. This phase behavior includes cluster formation depending upon density-controlled packing effects and the magnitude and range of the attractive and repulsive interactions. Such model systems mimic (to zeroth order) screened, charge-stabilized, aqueous colloidal dispersions of, e.g., proteins. We employ molecular dynamics simulations and integral equation theory to elucidate a more fundamental microscopic explanation for IRO-driven clustering. A simple criterion is identified that indicates when dynamic, amorphous clustering emerges in a polydisperse system, namely when the Ornstein-Zernike thermal correlation length in the system exceeds the repulsive potential tail range. Remarkably, this criterion also appears tightly correlated to crystalline cluster formation in a monodisperse system. Our new gauge is compared to another phenomenological condition for clustering which is when the IRO peak magnitude exceeds ~ 2.7. Ramifications of crystalline versus amorphous clustering are discussed and potential ways of using our new measure in experiment are put forward.

Explore Stochastic Instabilities of Periodic Points by Transition Path Theory

NASA Astrophysics Data System (ADS)

Cao, Yu; Lin, Ling; Zhou, Xiang

2016-06-01

We consider the noise-induced transitions from a linearly stable periodic orbit consisting of T periodic points in randomly perturbed discrete logistic map. Traditional large deviation theory and asymptotic analysis at small noise limit cannot distinguish the quantitative difference in noise-induced stochastic instabilities among the T periodic points. To attack this problem, we generalize the transition path theory to the discrete-time continuous-space stochastic process. In our first criterion to quantify the relative instability among T periodic points, we use the distribution of the last passage location related to the transitions from the whole periodic orbit to a prescribed disjoint set. This distribution is related to individual contributions to the transition rate from each periodic points. The second criterion is based on the competency of the transition paths associated with each periodic point. Both criteria utilize the reactive probability current in the transition path theory. Our numerical results for the logistic map reveal the transition mechanism of escaping from the stable periodic orbit and identify which periodic point is more prone to lose stability so as to make successful transitions under random perturbations.

Research of HCR Gearing Properties from Warm Scuffing Damage Point of View

NASA Astrophysics Data System (ADS)

Kuzmanović, Siniša; Rackov, Milan; Vereš, Miroslav; Krajčovič, Adam

2014-12-01

The issue of design and dimensioning of HCR gearing, particularly of the gearings with an internal engagement, it nowadays, especially in the design of hybrid cars drives, highly topical. This kind of gearing has many advantages in operation, but at the same time it is more complicated in stage of its design and load capacity calculation. Authors in this contribution present some results of temperature scuffing research of internal and external HCR gearing. There are given the equations for calculation of warm scuffing resistance of both external and internal HCR gearing derived according to the integral temperature criterion.

A comprehensive model to determine the effects of temperature and species fluctuations on reactions in turbulent reacting flows

NASA Technical Reports Server (NTRS)

Antaki, P. J.

1981-01-01

The joint probability distribution function (pdf), which is a modification of the bivariate Gaussian pdf, is discussed and results are presented for a global reaction model using the joint pdf. An alternative joint pdf is discussed. A criterion which permits the selection of temperature pdf's in different regions of turbulent, reacting flow fields is developed. Two principal approaches to the determination of reaction rates in computer programs containing detailed chemical kinetics are outlined. These models represent a practical solution to the modeling of species reaction rates in turbulent, reacting flows.

A nonlinear viscoelastic constitutive equation - Yield predictions in multiaxial deformations

NASA Technical Reports Server (NTRS)

Shay, R. M., Jr.; Caruthers, J. M.

1987-01-01

Yield stress predictions of a nonlinear viscoelastic constitutive equation for amorphous polymer solids have been obtained and are compared with the phenomenological von Mises yield criterion. Linear viscoelasticity theory has been extended to include finite strains and a material timescale that depends on the instantaneous temperature, volume, and pressure. Results are presented for yield and the correct temperature and strain-rate dependence in a variety of multiaxial deformations. The present nonlinear viscoelastic constitutive equation can be formulated in terms of either a Cauchy or second Piola-Kirchhoff stress tensor, and in terms of either atmospheric or hydrostatic pressure.

Smart polyaniline nanoparticles with thermal and photothermal sensitivity

NASA Astrophysics Data System (ADS)

Bongiovanni Abel, Silvestre; Molina, María A.; Rivarola, Claudia R.; Kogan, Marcelo J.; Barbero, Cesar A.

2014-12-01

Conductive polyaniline nanoparticles (PANI NPs) are synthesized by oxidation of aniline with persulfate in acid media, in the presence of polymeric stabilizers: polyvinilpyrrolidone (PVP), poly(N-isopropylacrylamide) (PNIPAM), and hydroxylpropylcellulose (HPC). It is observed that the size of the nanoparticles obtained depends on the polymeric stabilizer used, suggesting a mechanism where the aggregation of polyaniline molecules is arrested by adsorption of the polymeric stabilizer. Indeed, polymerization in the presence of a mixture of two polymers having different stabilizing capacity (PVP and PNIPAM) allows tuning of the size of the nanoparticles. Stabilization with biocompatible PVP, HPC and PNIPAM allows use of the nanoparticle dispersions in biological applications. The nanoparticles stabilized by thermosensitive polymers (PNIPAM and HPC) aggregate when the temperature exceeds the phase transition (coil to globule) temperature of each stabilizer (Tpt = 32 °C for PNIPAM or Tpt = 42 °C for HPC). This result suggests that an extended coil form of the polymeric stabilizer is necessary to avoid aggregation. The dispersions are reversibly restored when the temperature is lowered below Tpt. In that way, the effect could be used to separate the nanoparticles from soluble contaminants. On the other hand, the PANI NPs stabilized with PVP are unaffected by the temperature change. UV-visible spectroscopy measurements show that the nanoparticle dispersion changes their spectra with the pH of the external solution, suggesting that small molecules can easily penetrate the stabilizer shell. Near infrared radiation is absorbed by PANI NPs causing an increase of their temperature which induces the collapse of the thermosensitive polymer shell and aggregation of the NPs. The effect reveals that it is possible to locally heat the nanoparticles, a phenomenon that can be used to destroy tumor cells in cancer therapy or to dissolve protein aggregates of neurodegenerative diseases (e.g. Alzheimer). Moreover, the long range control of aggregation can be used to modulate the nanoparticle residence inside biological tissues.

Interfacial material for solid oxide fuel cell

DOEpatents

Baozhen, Li; Ruka, Roswell J.; Singhal, Subhash C.

1999-01-01

Solid oxide fuel cells having improved low-temperature operation are disclosed. In one embodiment, an interfacial layer of terbia-stabilized zirconia is located between the air electrode and electrolyte of the solid oxide fuel cell. The interfacial layer provides a barrier which controls interaction between the air electrode and electrolyte. The interfacial layer also reduces polarization loss through the reduction of the air electrode/electrolyte interfacial electrical resistance. In another embodiment, the solid oxide fuel cell comprises a scandia-stabilized zirconia electrolyte having high electrical conductivity. The scandia-stabilized zirconia electrolyte may be provided as a very thin layer in order to reduce resistance. The scandia-stabilized electrolyte is preferably used in combination with the terbia-stabilized interfacial layer. The solid oxide fuel cells are operable over wider temperature ranges and wider temperature gradients in comparison with conventional fuel cells.

Temperature-dependent spectroscopic evidences of curcumin in aqueous medium: a mechanistic study of its solubility and stability.

PubMed

Jagannathan, Ramya; Abraham, Priya Mary; Poddar, Pankaj

2012-12-20

In curcumin, keto-enol-enolate equilibrium of the heptadiene-dione moiety determines its physiochemical and antioxidant properties. However, its poor solubility in water at neutral pH and room temperature decreases its bioavailability. Potential therapeutic applications have triggered an interest in manipulating the solubility of curcumin in water as its stability and solubility in water remains poorly understood. Here, the mechanism behind its solubility at various temperatures and the influence of interplay of temperature, intramolecular H-bonding, and intermolecular forces is reported, which leads to aggregation-disaggregation at various temperatures. Remarkable change is observed in temperature-dependent electronic transition behavior of curcumin, however, the absorption spectra after cooling and heating cycles remain unchanged, hinting much better thermal stability of curcumin in water than previously thought. This study indicates that it is perhaps the breaking of intramolecular hydrogen bonding which leads to exposure of polar groups and hence responsible for the dissolution of curcumin at higher temperature. The formation of intermolecular aggregates might be responsible behind a better room temperature stability of the molecules after cooling its aqueous suspension from 90 to 25 °C. These curcumin solubility studies have great application in biological research with reference to bioavailability and to understand target oriented mode of action of curcumin.

SNAP 10A ESTIMATED ELECTRICAL CHARACTERISTICS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cooper, J.C.

1961-06-01

The electrical power characteristics of a SNAP 10A converter are estimated for given fractions of power degradation. Graphs are included showing the power characteristics for instantaneous transients from stabilized operation at the maximum efficiency point, and after system temperature stabilization at the operating point. Open-circuit emf's of the converter are estimated for instantaneous and temperature-stabilized cases. (D.L.C.)

What Have We Learned From Decades of CRT, And Where Do We Go From Here?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burnham, A K; Souers, P C; Gagliardi, F J

2006-09-11

The Chemical Reactivity Test, or CRT, has been the workhorse for determining short-to-medium term compatibility and thermal stability for energetic materials since the mid 1960s. The concept behind the CRT is quite simple. 0.25 g of material is heated in a 17 cm{sup 3} vessel for 22 hours at 80, 100, or 120 C, and the yield of gaseous products are analyzed by gas chromatography to determine its thermal stability. The instrumentation is shown in Figure 1, and the vessel configuration is shown in Figure 2. For compatibility purposes, two materials, normally 0.25 g of each, are analyzed as amore » mixture. Recently, data from the past 4 decades have been compiled in an Excel spreadsheet and inspected for reliability and internal consistency. The resulting processed data will be added this year to the LLNL HE Reference Guide. Also recently, we have begun to assess the suitability of the CRT to answer new compatibility issues, especially in view of more modern instrumentation now available commercially. One issue that needs to be addressed is the definition of thermal stability and compatibility from the CRT. Prokosch and Garcia (and the associated MIL-STD-1751A) state that the criterion for thermal stability is a gas yield of less than 4 cm{sup 3}/g for a single material for 22 hours at 120 C. The gases from energetic materials of interest ordinarily have an average molecular weight of about 36 g/mol, so this represents decomposition of 0.5-1.0% of the sample. This is a reasonable value, and a relatively unstable energetic material such as PETN has no problem passing. PBX 9404, which yields 1.5 to 2.0 cm{sup 3}/g historically, is used as a periodic check standard. This is interesting in itself, since the nitrocellulose in the 9404 is unstable and probably has partially decomposed over the decades. However, it is not clear whether this aging of the standard would lead to more or less gas, since the initial gaseous degradation products are captured by the DPA stabilizer. Clearly this is an issue that needs reconsideration. The criterion for compatibility is less clearly correct. Although some LLNL reports say that generation of gas in excess of the materials by themselves is an indication of incompatibility, LLNL reports invariably say that materials are compatible if they generate less than 1 cm{sup 3}/g of gas. There are two problems with this criterion. First, it is not stated whether the gas yield is per gram of energetic material or mixture. Second, a material that generates >2 cm{sup 3}/g by itself could never pass the compatibility tests as stated, because even a mixture of equal masses of that material with a completely inert material would generate >1 cm{sup 3}/g of gas per mixture. Furthermore, Prokosch states that a yield equal to or less than from the materials individually means that no reaction has occurred. Clearly, less gas can not be generated unless some type of interaction has occurred. An obvious example would be mixing CaO with a CO{sub 2}-generating energetic material. In the absence of any direct action of the CaO on the energetic material, the CO{sub 2} product would be captured by the CaO, thereby decreasing the gas yield and liberating considerable heat. In a large, closed volume, this could tip the balance to thermal runaway.« less

Accurate prediction of vaccine stability under real storage conditions and during temperature excursions.

PubMed

Clénet, Didier

2018-04-01

Due to their thermosensitivity, most vaccines must be kept refrigerated from production to use. To successfully carry out global immunization programs, ensuring the stability of vaccines is crucial. In this context, two important issues are critical, namely: (i) predicting vaccine stability and (ii) preventing product damage due to excessive temperature excursions outside of the recommended storage conditions (cold chain break). We applied a combination of advanced kinetics and statistical analyses on vaccine forced degradation data to accurately describe the loss of antigenicity for a multivalent freeze-dried inactivated virus vaccine containing three variants. The screening of large amounts of kinetic models combined with a statistical model selection approach resulted in the identification of two-step kinetic models. Predictions based on kinetic analysis and experimental stability data were in agreement, with approximately five percentage points difference from real values for long-term stability storage conditions, after excursions of temperature and during experimental shipments of freeze-dried products. Results showed that modeling a few months of forced degradation can be used to predict various time and temperature profiles endured by vaccines, i.e. long-term stability, short time excursions outside the labeled storage conditions or shipments at ambient temperature, with high accuracy. Pharmaceutical applications of the presented kinetics-based approach are discussed. Copyright © 2018 The Author. Published by Elsevier B.V. All rights reserved.

Effect of stabilization temperature during pyrolysis process of P84 co-polyimide-based tubular carbon membrane for H2/N2 and He/N2 separations

NASA Astrophysics Data System (ADS)

Sazali, N.; Salleh, W. N. W.; Ismail, A. F.; Ismail, N. H.; Aziz, F.; Yusof, N.; Hasbullah, H.

2018-04-01

In this study, the effect of stabilization temperature on the performance of tubular carbon membrane was being investigated. P84 co-polyimide-based tubular carbon membrane will be fabricated through the dip-coating technique. The tubular carbon membrane performance can be controlled by manipulating the pyrolysis conditions which was conducted at different stabilization temperatures of 250, 300, 350, 400, and 450°C under N2 environment (200 ml/min). The prepared membranes were characterized by using scanning electron microscopy (SEM), x-ray diffraction (XRD), and pure gas permeation system. The pure gas of H2, He, and N2 were used to determine the permeation properties of the carbon membrane. The P84 co-polyimide-based tubular carbon membrane stabilized at 300°C demonstrated an excellent permeation property with H2, He, and N2 gas permeance of 1134.51±2.87, 1287.22±2.86 and 2.98±1.28GPU, respectively. The highest H2/N2 and He/N2 selectivity of 380.71±2.34 and 431.95±2.61 was obtained when the stabilization temperature of 450°C was applied. It is concluded that the stabilization temperatures have protrusive effect on the carbon membrane properties specifically their pore structure, and eventually their gas separation properties.

Lock-in in forced vibration of a circular cylinder

NASA Astrophysics Data System (ADS)

Kumar, Samvit; Navrose, Mittal, Sanjay

2016-11-01

The phenomenon of lock-in/synchronization in uniform flow past an oscillating cylinder is investigated via a stabilized finite element method at Re = 100. Computations are carried out for various amplitudes and frequencies of cylinder oscillation to accurately obtain the boundary of the lock-in regime. Results from earlier studies show a significant scatter in the lock-in boundary. The scatter might be an outcome of the difference in data collection or the use of a different criterion for identifying lock-in. A new criterion for lock-in is proposed, wherein the following two conditions are to be satisfied. (i) The most dominant frequency in the power spectrum of lift coefficient matches the frequency of cylinder oscillation (fy) and (ii) other peaks in the power spectrum, if any, are present only at super-harmonics of fy. Utilizing this criterion, three flow regimes are identified on the frequency-amplitude plane: lock-in, transition, and no lock-in. The behaviour of the wake is also investigated by examining the power spectra of the velocity traces at various locations downstream of the cylinder. Wake-lock-in is observed during lock-in. A wake-transition regime is identified wherein the near wake, up to a certain streamwise location, is in a lock-in state while the downstream region is in a desynchronized state. For a fixed fy, the location beyond which the wake is desynchronized moves downstream as the amplitude of oscillation is increased. The proposed criterion for lock-in addresses the wide scatter in the boundary of the lock-in regime among earlier studies. Energy transfer from the fluid to the structure, per cycle of cylinder oscillation, is computed from the data for forced vibration. The data is utilized to generate iso-energy transfer contours in the frequency-amplitude plane. The free vibration response with zero structural damping is found to be in very good agreement with the contour corresponding to zero energy transfer.

[Reliability and validity of warning signs checklist for screening psychological, behavioral and developmental problems of children].

PubMed

Huang, X N; Zhang, Y; Feng, W W; Wang, H S; Cao, B; Zhang, B; Yang, Y F; Wang, H M; Zheng, Y; Jin, X M; Jia, M X; Zou, X B; Zhao, C X; Robert, J; Jing, Jin

2017-06-02

Objective: To evaluate the reliability and validity of warning signs checklist developed by the National Health and Family Planning Commission of the People's Republic of China (NHFPC), so as to determine the screening effectiveness of warning signs on developmental problems of early childhood. Method: Stratified random sampling method was used to assess the reliability and validity of checklist of warning sign and 2 110 children 0 to 6 years of age(1 513 low-risk subjects and 597 high-risk subjects) were recruited from 11 provinces of China. The reliability evaluation for the warning signs included the test-retest reliability and interrater reliability. With the use of Age and Stage Questionnaire (ASQ) and Gesell Development Diagnosis Scale (GESELL) as the criterion scales, criterion validity was assessed by determining the correlation and consistency between the screening results of warning signs and the criterion scales. Result: In terms of the warning signs, the screening positive rates at different ages ranged from 10.8%(21/141) to 26.2%(51/137). The median (interquartile) testing time for each subject was 1(0.6) minute. Both the test-retest reliability and interrater reliability of warning signs reached 0.7 or above, indicating that the stability was good. In terms of validity assessment, there was remarkable consistency between ASQ and warning signs, with the Kappa value of 0.63. With the use of GESELL as criterion, it was determined that the sensitivity of warning signs in children with suspected developmental delay was 82.2%, and the specificity was 77.7%. The overall Youden index was 0.6. Conclusion: The reliability and validity of warning signs checklist for screening early childhood developmental problems have met the basic requirements of psychological screening scales, with the characteristics of short testing time and easy operation. Thus, this warning signs checklist can be used for screening psychological and behavioral problems of early childhood, especially in community settings.

Design optimization of natural laminar flow bodies in compressible flow

NASA Technical Reports Server (NTRS)

Dodbele, Simha S.

1992-01-01

An optimization method has been developed to design axisymmetric body shapes such as fuselages, nacelles, and external fuel tanks with increased transition Reynolds numbers in subsonic compressible flow. The new design method involves a constraint minimization procedure coupled with analysis of the inviscid and viscous flow regions and linear stability analysis of the compressible boundary-layer. In order to reduce the computer time, Granville's transition criterion is used to predict boundary-layer transition and to calculate the gradients of the objective function, and linear stability theory coupled with the e(exp n)-method is used to calculate the objective function at the end of each design iteration. Use of a method to design an axisymmetric body with extensive natural laminar flow is illustrated through the design of a tiptank of a business jet. For the original tiptank, boundary layer transition is predicted to occur at a transition Reynolds number of 6.04 x 10(exp 6). For the designed body shape, a transition Reynolds number of 7.22 x 10(exp 6) is predicted using compressible linear stability theory coupled with the e(exp n)-method.

Stability of Poisson Equilibria and Hamiltonian Relative Equilibria by Energy Methods

NASA Astrophysics Data System (ADS)

Patrick, George W.; Roberts, Mark; Wulff, Claudia

2004-12-01

We develop a general stability theory for equilibrium points of Poisson dynamical systems and relative equilibria of Hamiltonian systems with symmetries, including several generalisations of the Energy-Casimir and Energy-Momentum Methods. Using a topological generalisation of Lyapunov’s result that an extremal critical point of a conserved quantity is stable, we show that a Poisson equilibrium is stable if it is an isolated point in the intersection of a level set of a conserved function with a subset of the phase space that is related to the topology of the symplectic leaf space at that point. This criterion is applied to generalise the energy-momentum method to Hamiltonian systems which are invariant under non-compact symmetry groups for which the coadjoint orbit space is not Hausdorff. We also show that a G-stable relative equilibrium satisfies the stronger condition of being A-stable, where A is a specific group-theoretically defined subset of G which contains the momentum isotropy subgroup of the relative equilibrium. The results are illustrated by an application to the stability of a rigid body in an ideal irrotational fluid.

Critical evaluation of the unsteady aerodynamics approach to dynamic stability at high angles of attack

NASA Technical Reports Server (NTRS)

Hui, W. H.

1985-01-01

Bifurcation theory is used to analyze the nonlinear dynamic stability characteristics of an aircraft subject to single-degree-of-freedom. The requisite moment of the aerodynamic forces in the equations of motion is shown to be representable in a form equivalent to the response to finite amplitude oscillations. It is shown how this information can be deduced from the case of infinitesimal-amplitude oscillations. The bifurcation theory analysis reveals that when the bifurcation parameter is increased beyond a critical value at which the aerodynamic damping vanishes, new solutions representing finite amplitude periodic motions bifurcate from the previously stable steady motion. The sign of a simple criterion, cast in terms of aerodynamic properties, determines whether the bifurcating solutions are stable or unstable. For the pitching motion of flat-plate airfoils flying at supersonic/hypersonic speed and for oscillation of flaps at transonic speed, the bifurcation is subcritical, implying either the exchanges of stability between steady and periodic motion are accompanied by hysteresis phenomena, or that potentially large aperiodic departures from steady motion may develop.

Concurrent Increases and Decreases in Local Stability and Conformational Heterogeneity in Cu, Zn Superoxide Dismutase Variants Revealed by Temperature-Dependence of Amide Chemical Shifts.

PubMed

Doyle, Colleen M; Rumfeldt, Jessica A; Broom, Helen R; Sekhar, Ashok; Kay, Lewis E; Meiering, Elizabeth M

2016-03-08

The chemical shifts of backbone amide protons in proteins are sensitive reporters of local structural stability and conformational heterogeneity, which can be determined from their readily measured linear and nonlinear temperature-dependences, respectively. Here we report analyses of amide proton temperature-dependences for native dimeric Cu, Zn superoxide dismutase (holo pWT SOD1) and structurally diverse mutant SOD1s associated with amyotrophic lateral sclerosis (ALS). Holo pWT SOD1 loses structure with temperature first at its periphery and, while having extremely high global stability, nevertheless exhibits extensive conformational heterogeneity, with ∼1 in 5 residues showing evidence for population of low energy alternative states. The holo G93A and E100G ALS mutants have moderately decreased global stability, whereas V148I is slightly stabilized. Comparison of the holo mutants as well as the marginally stable immature monomeric unmetalated and disulfide-reduced (apo(2SH)) pWT with holo pWT shows that changes in the local structural stability of individual amides vary greatly, with average changes corresponding to differences in global protein stability measured by differential scanning calorimetry. Mutants also exhibit altered conformational heterogeneity compared to pWT. Strikingly, substantial increases as well as decreases in local stability and conformational heterogeneity occur, in particular upon maturation and for G93A. Thus, the temperature-dependence of amide shifts for SOD1 variants is a rich source of information on the location and extent of perturbation of structure upon covalent changes and ligand binding. The implications for potential mechanisms of toxic misfolding of SOD1 in disease and for general aspects of protein energetics, including entropy-enthalpy compensation, are discussed.

The denaturation and degradation of stable enzymes at high temperatures.

PubMed Central

Daniel, R M; Dines, M; Petach, H H

1996-01-01

Now that enzymes are available that are stable above 100 degrees C it is possible to investigate conformational stability at this temperature, and also the effect of high-temperature degradative reactions in functioning enzymes and the inter-relationship between degradation and denaturation. The conformational stability of proteins depends upon stabilizing forces arising from a large number of weak interactions, which are opposed by an almost equally large destabilizing force due mostly to conformational entropy. The difference between these, the net free energy of stabilization, is relatively small, equivalent to a few interactions. The enhanced stability of very stable proteins can be achieved by an additional stabilizing force which is again equivalent to only a few stabilizing interactions. There is currently no strong evidence that any particular interaction (e.g. hydrogen bonds, hydrophobic interactions) plays a more important role in proteins that are stable at 100 degrees C than in those stable at 50 degrees C, or that the structures of very stable proteins are systematically different from those of less stable proteins. The major degradative mechanisms are deamidation of asparagine and glutamine, and succinamide formation at aspartate and glutamate leading to peptide bond hydrolysis. In addition to being temperature-dependent, these reactions are strongly dependent upon the conformational freedom of the susceptible amino acid residues. Evidence is accumulating which suggests that even at 100 degrees C deamidation and succinamide formation proceed slowly or not at all in conformationally intact (native) enzymes. Whether this is the case at higher temperatures is not yet clear, so it is not known whether denaturation of degradation will set the upper limit of stability for enzymes. PMID:8694749

Transport and geotechnical properties of porous media with applications to retorted oil shale. Volume 4. Appendix D. Temperature and toe erosion effects on spent oil shale embankment stability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, N.Y.; Wu, T.H.

1986-01-01

To evaluate the engineering property of spent shale at elevated temperatures, high temperature triaxial cells were designed and manufactured. The cells were then used in the test program designed to provide the physical and engineering properties of spent shale (TOSCO-II) at elevated temperatures. A series of consolidated drained triaxial tests were conducted at high temperatures. Duncan-Chang hyperbolic model was adopted to simulate the laboratory stress versus strain behavior of spent shale at various temperatures. This model provides very good fit to the laboratory stress-strain-volumetric strain characteristics of spent shale at various temperatures. The parameters of this model were then formulatedmore » as functions of temperatures and the Duncan-Chang model was implemented in a finite element analysis computer code for predicting the stress-deformation behavior of large spent shale embankments. Modified Bishop method was also used in analyzing the stability of spent shale embankments. The stability of three different spent shale embankments at three different temperatures were investigated in the study. Additionally the stability of embankments with different degrees of toe erosion was also studied. Results of this study indicated that (1) the stress-strain-strength properties of soils are affected by temperature variation; (2) the stress-strain-strength behavior of spent shale can be simulated by Duncan-Chang hyperbolic model, (3) the factor of safety of embankment slope decreases with rising temperatures; (4) the embankment deformation increases with rising temperatures; and (5) the toe erosion induced by floods causes the embankment slope to become less stable. It is strongly recommended, to extend this study to investigate the effect of internal seepage on the stability of large spent shale embankment. 68 refs., 53 figs., 16 tabs.« less

Clay facial masks: physicochemical stability at different storage temperatures.

PubMed

Zague, Vivian; de Almeida Silva, Diego; Baby, André Rolim; Kaneko, Telma Mary; Velasco, Maria Valéria Robles

2007-01-01

Clay facial masks--formulations that contain a high percentage of solids dispersed in a liquid vehicle--have become of special interest due to specific properties presented by clays, such as particle size, cooling index, high adsorption capacity, and plasticity. Although most of the physicochemical properties of clay dispersions have been studied, specific aspects concerning the physicochemical stability of clay mask products remain unclear. This work aimed at investigating the accelerated physicochemical stability of clay mask formulations stored at different temperatures. Formulations were subjected to centrifuge testing and to thermal treatment for 15 days, during which temperature was varied from -5.0 degrees to 45.0 degrees C. The apparent viscosity and visual aspect (homogeneity) of all formulations were affected by temperature variation, whereas color, odor, and pH value remained unaltered. These results, besides the estimation of physicochemical stability under aging, can be useful in determining the best storage conditions for clay-based formulations.

Thermophysical properties of liquid Ni around the melting temperature from molecular dynamics simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rozas, R. E.; Department of Physics, University of Bío-Bío, Av. Collao 1202, P.O. Box 5C, Concepción; Demiraǧ, A. D.

Thermophysical properties of liquid nickel (Ni) around the melting temperature are investigated by means of classical molecular dynamics (MD) simulation, using three different embedded atom method potentials to model the interactions between the Ni atoms. Melting temperature, enthalpy, static structure factor, self-diffusion coefficient, shear viscosity, and thermal diffusivity are compared to recent experimental results. Using ab initio MD simulation, we also determine the static structure factor and the mean-squared displacement at the experimental melting point. For most of the properties, excellent agreement is found between experiment and simulation, provided the comparison relative to the corresponding melting temperature. We discuss themore » validity of the Hansen-Verlet criterion for the static structure factor as well as the Stokes-Einstein relation between self-diffusion coefficient and shear viscosity. The thermal diffusivity is extracted from the autocorrelation function of a wavenumber-dependent temperature fluctuation variable.« less