Science.gov

Sample records for exchange rate dynamics

  1. Fluctuation Dynamics of Exchange Rates on Indian Financial Market

    NASA Astrophysics Data System (ADS)

    Sarkar, A.; Barat, P.

    Here we investigate the scaling behavior and the complexity of the average daily exchange rate returns of the Indian Rupee against four foreign currencies namely US Dollar, Euro, Great Britain Pound and Japanese Yen. Our analysis revealed that the average daily exchange rate return of the Indian Rupee against the US Dollar exhibits a persistent scaling behavior and follow Levy stable distribution. On the contrary the average daily exchange rate returns of the other three foreign currencies show randomness and follow Gaussian distribution. Moreover, it is seen that the complexity of the average daily exchange rate return of the Indian Rupee against US Dollar is less than the other three exchange rate returns.

  2. Currency Exchange Rates.

    ERIC Educational Resources Information Center

    Siler, Carl R.

    This curriculum unit of the Muncie (Indiana) Southside High School is to simulate the dynamics of foreign currency exchange rates from the perspectives of: (1) a major U.S. corporation, ABB Power T & D Company, Inc., of Muncie, Indiana, a manufacturer of large power transformers for the domestic and foreign markets; and (2) individual consumers…

  3. The long-run dynamic relationship between exchange rate and its attention index: Based on DCCA and TOP method

    NASA Astrophysics Data System (ADS)

    Wang, Xuan; Guo, Kun; Lu, Xiaolin

    2016-07-01

    The behavior information of financial market plays a more and more important role in modern economic system. The behavior information reflected in INTERNET search data has already been used in short-term prediction for exchange rate, stock market return, house price and so on. However, the long-run relationship between behavior information and financial market fluctuation has not been studied systematically. Further, most traditional statistic methods and econometric models could not catch the dynamic and non-linear relationship. An attention index of CNY/USD exchange rate is constructed based on search data from 360 search engine of China in this paper. Then the DCCA and Thermal Optimal Path methods are used to explore the long-run dynamic relationship between CNY/USD exchange rate and the corresponding attention index. The results show that the significant interdependency exists and the change of exchange rate is 1-2 days lag behind the attention index.

  4. Dynamics of ventilation, heart rate, and gas exchange: sinusoidal and impulse work loads in man.

    PubMed

    Bakker, H K; Struikenkamp, R S; De Vries, G A

    1980-02-01

    Dynamic characteristics of ventilation, heart rate, and gas exchange in response to sinusoidally varying work loads were analyzed in four male subjects, exercising in the upright position on a bicycle ergometer. Mean work-load and sinusoidal amplitude were about 1.5 and 0.9 W/kg, fat-free mass), respectively. Seven different frequencies were used, the periods ranging from 12 to 0.75 min. To further investigate the linearity of the variables under study, 10-s impulse loads were also applied to three of the four subjects. Harmonic analysis of the sine-wave data and comparison of the sine-wave fundamental responses with the impulse frequency responses showed that only O2 uptake behaves in a linear fashion. Ventilation and CO2 production showed quasi- to nonlinear behaviors, whereas the responses of heart rate and alveolar partial pressures were clearly dependent on the type of forcing used. By means of mathematical parameter identification techniques, it was found that the individual frequency responses of O2 uptake could be almost completely described by a four-parameter transfer function with parameter values showing second-order underdamped to critically damped dynamics.

  5. Phase transition of dynamical herd behaviors for Yen Dollar exchange rates

    NASA Astrophysics Data System (ADS)

    Yoon, Seong-Min; Choi, J. S.; Kim, Y.; Kim, Kyungsik

    2006-01-01

    We study the herd behavior and the phase transition for the yen-dollar exchange rate in the Japanese financial market. It is obtained that the probability distribution of returns satisfies the power-law behavior P(R)≃R with scaling exponents β=3.11, 2.81, and 2.29 at time intervals τ=1min, 30min, and 1 h. The crash region in which the probability density increases with the increasing return appears, when the herding parameter h satisfies h⩾2.33 for the case of τ<30min. We especially obtain that no crash occurs τ>30min and that the probability distribution of price returns occurs in the phase transition at τ=30min.

  6. Nonadiabatic exchange dynamics during adiabatic frequency sweeps

    NASA Astrophysics Data System (ADS)

    Barbara, Thomas M.

    2016-04-01

    A Bloch equation analysis that includes relaxation and exchange effects during an adiabatic frequency swept pulse is presented. For a large class of sweeps, relaxation can be incorporated using simple first order perturbation theory. For anisochronous exchange, new expressions are derived for exchange augmented rotating frame relaxation. For isochronous exchange between sites with distinct relaxation rate constants outside the extreme narrowing limit, simple criteria for adiabatic exchange are derived and demonstrate that frequency sweeps commonly in use may not be adiabatic with regard to exchange unless the exchange rates are much larger than the relaxation rates. Otherwise, accurate assessment of the sensitivity to exchange dynamics will require numerical integration of the rate equations. Examples of this situation are given for experimentally relevant parameters believed to hold for in-vivo tissue. These results are of significance in the study of exchange induced contrast in magnetic resonance imaging.

  7. The Dynamics of Multilateral Exchange

    NASA Astrophysics Data System (ADS)

    Hausken, Kjell; Moxnes, John F.

    The article formulates a dynamic mathematical model where arbitrarily many players produce, consume, exchange, loan, and deposit arbitrarily many goods over time to maximize utility. Consuming goods constitutes a benefit, and producing, exporting, and loaning away goods constitute a cost. Utilities are benefits minus costs, which depend on the exchange ratios and bargaining functions. Three-way exchange occurs when one player acquires, through exchange, one good from another player with the sole purpose of using this good to exchange against the desired good from a third player. Such a triple handshake is not merely a set of double handshakes since the player assigns no interest to the first good in his benefit function. Cognitive and organization costs increase dramatically for higher order exchanges. An exchange theory accounting for media of exchange follows from simple generalization of two-way exchange. The examples of r-way exchange are the triangle trade between Africa, the USA, and England in the 17th and 18th centuries, the hypothetical hypercycle involving RNAs as players and enzymes as goods, and reaction-diffusion processes. The emergence of exchange, and the role of trading agents are discussed. We simulate an example where two-way exchange gives zero production and zero utility, while three-way exchange causes considerable production and positive utility. Maximum utility for each player is reached when exchanges of the same order as the number of players in society are allowed. The article merges micro theory and macro theory within the social, natural, and physical sciences.

  8. Communication: Rigorous quantum dynamics of O + O{sub 2} exchange reactions on an ab initio potential energy surface substantiate the negative temperature dependence of rate coefficients

    SciTech Connect

    Li, Yaqin; Sun, Zhigang E-mail: dawesr@mst.edu; Jiang, Bin; Guo, Hua E-mail: dawesr@mst.edu; Xie, Daiqian; Dawes, Richard E-mail: dawesr@mst.edu

    2014-08-28

    The kinetics and dynamics of several O + O{sub 2} isotope exchange reactions have been investigated on a recently determined accurate global O{sub 3} potential energy surface using a time-dependent wave packet method. The agreement between calculated and measured rate coefficients is significantly improved over previous work. More importantly, the experimentally observed negative temperature dependence of the rate coefficients is for the first time rigorously reproduced theoretically. This negative temperature dependence can be attributed to the absence in the new potential energy surface of a submerged “reef” structure, which was present in all previous potential energy surfaces. In addition, contributions of rotational excited states of the diatomic reactant further accentuate the negative temperature dependence.

  9. Rate of disappearance of labeled carbon dioxide from the lungs of humans during breath holding: a method for studying the dynamics of pulmonary CO2 exchange

    PubMed Central

    Hyde, Richard W.; Puy, Ricardo J. M.; Raub, William F.; Forster, Robert E.

    1968-01-01

    The dynamics of CO2 exchange in the lungs of man was studied by observing the rate of disappearance of a stable isotope of CO2 (13CO2) from the alveolar gas during breath holding. Over 50% of the inspired isotope disappeared within the first 3 sec followed by a moderately rapid logarithmic decline in which one-half of the remaining 13CO2 disappeared every 10 sec. The large initial disappearance of 13CO2 indicated that alveolar 13CO2 equilibrated in less than 3 sec with the CO2 stored in the pulmonary tissues and capillary blood. The volume of CO2 in the pulmonary tissues calculated from this initial disappearance was 200 ml or 0.33 ml of CO2 per milliliter of pulmonary tissue volume. The alveolar to end-capillary gradient for 13CO2 was calculated by comparing the simultaneous disappearance rates of 13CO2 and acetylene. At rest and during exercise this gradient for 13CO2 was either very small or not discernible, and diffusing capacity for CO2 (DLCO2) exceeded 200 ml/(min × mm Hg). After the administration of a carbonic anhydrase inhibitor the rate of disappearance of 13CO2 decreased markedly. DLCO2 fell to 42 ml/(min × mm Hg) and at least 70% of the exchange of 13CO2 with the CO2 stores in the pulmonary tissues and blood was blocked by the inhibitor. These changes were attributed to impairment of exchange of 13CO2 with the bicarbonate in the pulmonary tissues and blood. The pH of the pulmonary tissues (Vtis) was determined by a method based on the premise that the CO2 space in the pulmonary tissues blocked by the inhibitor represented total bicarbonate content. At an alveolar PCO2 of 40 mm Hg pH of Vtis equalled 6.97 ± 0.09. PMID:5658586

  10. Heat exchangers: Selection, rating, and thermal design

    SciTech Connect

    Kakac, S.; Liu, H.

    1998-01-01

    This book takes a systematic approach to the subject, focusing on the selection, design, rating, and operational challenges of various types of heat exchangers. Written by well-known authors in the field of heat transfer, this book covers all the most commonly used types of heat exchangers, including condensers and evaporators. The text begins with the classification of the different types of heat exchangers and discusses methods for their sizing and rating. Single phase forced convection correlations in ducts and pressure drop and pumping power analysis are also covered. A chapter is devoted to the special problem of fouling. Thermal design methods and processes, including designs for condensers and evaporators, complete this thorough introduction to the subject. The appendix provides information on the thermophysical properties of fluids, including the new refrigerants. Every topic features worked examples to illustrate the methods and procedures presented, and additional problems are included at the end of each chapter, with examples to be used as a student design project. An instructor's manual is available, including complete solutions to selected problems in the text. The contents include: classification of heat exchangers; basic design methods of heat exchangers; forced convection correlations for single-phase side of heat exchangers; heat exchanger pressure drop and pumping power; fouling of heat exchangers; double-pipe heat exchangers; design correlations for condensers and evaporators; shell-and-tube heat exchangers; compact heat exchangers; gasketed-plate heat exchangers; and condensers and evaporators.

  11. Evaluation of methods for determining air exchange rate in a naturally ventilated dairy cattle building with large openings using computational fluid dynamics (CFD)

    NASA Astrophysics Data System (ADS)

    Wu, Wentao; Zhai, John; Zhang, Guoqiang; Nielsen, Peter V.

    2012-12-01

    Naturally ventilated dairy cattle buildings are a major source of ammonia and greenhouse gas emissions. Accurate estimation in gas emissions constitutes the first step towards reducing the negative impact of emissions on the local environment. The greatest uncertainty in the emission estimation from a naturally ventilated livestock building with large openings is the determination of the air exchange rate (AER) and the choice of the gas sampling positions for representative outlet gas concentration. To reduce the uncertainties in the emission estimation, the performances of three techniques - integrating volume flow rates (VFR), tracer gas decay (TGD) and constant tracer gas (CTG) for determination of ventilation rates were assessed in this paper by Computational fluid dynamics (CFD). In the developed CFD model, the animal occupied zone (AOZ) was treated as porous media and the resistance coefficient of porous zone was derived by pressure drops across AOZ using a sub-CFD model. The results showed that AERs predicted by VFR and TGD were in good agreement with each other within a large range of wind speeds. The large difference in AER estimation using CTG and VFR indicates that the mean CO2 concentration of the entire room may not represent the concentration at the air exit. It may be not suitable to calculate AER using mean concentration of internal sampling positions. When wind became stronger, the accuracy of CTG decreased. The gas sampling positions should be close to the openings or even in the openings; the gas sampling positions should be located adjacent to the openings or even in the openings. To reduce the uncertain introduced by wind direction, all the openings especially of different azimuths should possess sampling tubes. The maximum gas concentrations in the different openings could be the optimum value to represent the concentration in the exit air.

  12. Brazilian exchange rate complexity: Financial crisis effects

    NASA Astrophysics Data System (ADS)

    Piqueira, José Roberto C.; Mortoza, Letícia Pelluci D.

    2012-04-01

    With the financial market globalization, foreign investments became vital for the economies, mainly in emerging countries. In the last decades, Brazilian exchange rates appeared as a good indicator to measure either investors' confidence or risk aversion. Here, some events of global or national financial crisis are analyzed, trying to understand how they influenced the "dollar-real" rate evolution. The theoretical tool to be used is the López-Mancini-Calbet (LMC) complexity measure that, applied to real exchange rate data, has shown good fitness between critical events and measured patterns.

  13. World currency exchange rate cross-correlations

    NASA Astrophysics Data System (ADS)

    Droå¼dż, S.; Górski, A. Z.; Kwapień, J.

    2007-08-01

    World currency network constitutes one of the most complex structures that is associated with the contemporary civilization. On a way towards quantifying its characteristics we study the cross correlations in changes of the daily foreign exchange rates within the basket of 60 currencies in the period December 1998 May 2005. Such a dynamics turns out to predominantly involve one outstanding eigenvalue of the correlation matrix. The magnitude of this eigenvalue depends however crucially on which currency is used as a base currency for the remaining ones. Most prominent it looks from the perspective of a peripheral currency. This largest eigenvalue is seen to systematically decrease and thus the structure of correlations becomes more heterogeneous, when more significant currencies are used as reference. An extreme case in this later respect is the USD in the period considered. Besides providing further insight into subtle nature of complexity, these observations point to a formal procedure that in general can be used for practical purposes of measuring the relative currencies significance on various time horizons.

  14. A theory of exchange rate modeling

    SciTech Connect

    Alekseev, A.A.

    1995-09-01

    The article examines exchange rate modeling for two cases: (a) when the trading partners have mutual interests and (b) when the trading partners have antogonistic interests. Exchange rates in world markets are determined by supply and demand for the currency of each state, and states may control the exchange rate of their currency by changing the interest rate, the volume of credit, and product prices in both domestic and export markets. Abstracting from issues of production and technology in different countries and also ignoring various trade, institutional, and other barriers, we consider in this article only the effect of export and import prices on the exchange rate, we propose a new criterion of external trade activity: each trading partner earns a profit which is proportional to the volume of benefits enjoyed by the other partner. We consider a trading cycle that consists of four stages: (a) purchase of goods in the domestic market with the object of selling them abroad; (b) sale of the goods in foreign markets; (c) purchase of goods abroad with the object of selling them in the domestic market; (d) sale of the goods domestically.

  15. Large Devaluations and the Real Exchange Rate

    ERIC Educational Resources Information Center

    Burstein, Ariel; Eichenbaum, Martin; Rebelo, Sergio

    2005-01-01

    In this paper we argue that the primary force behind the large drop in real exchange rates that occurs after large devaluations is the slow adjustment in the prices of nontradable goods and services. Our empirical analysis uses data from five large devaluation episodes: Argentina (2002), Brazil (1999), Korea (1997), Mexico (1994), and Thailand…

  16. Amide proton exchange of a dynamic loop in cell extracts.

    PubMed

    Smith, Austin E; Sarkar, Mohona; Young, Gregory B; Pielak, Gary J

    2013-10-01

    Intrinsic rates of exchange are essential parameters for obtaining protein stabilities from amide (1) H exchange data. To understand the influence of the intracellular environment on stability, one must know the effect of the cytoplasm on these rates. We probed exchange rates in buffer and in Escherichia coli lysates for the dynamic loop in the small globular protein chymotrypsin inhibitor 2 using a modified form of the nuclear magnetic resonance experiment, SOLEXSY. No significant changes were observed, even in 100 g dry weight L(-1) lysate. Our results suggest that intrinsic rates from studies conducted in buffers are applicable to studies conducted under cellular conditions.

  17. Water exchange dynamics around H3O+ and OH- ions

    NASA Astrophysics Data System (ADS)

    Roy, Santanu; Dang, Liem X.

    2015-05-01

    In this letter, we report the first computer simulation of the dynamics of water exchanging between the first and second solvation shells of H3O+. Employing different rate theories for chemical reactions such as the transition state theory, the Grote-Hynes theory, the reactive flux method, and the Impey-Madden-McDonald method, we calculate the solvent exchange rates from molecular dynamics simulations that account for explicit polarization effects. In addition, we also study water exchanges around OH- and find that the corresponding time scale is much smaller than that for H3O+.

  18. Solvent exchange in liquid methanol and rate theory

    NASA Astrophysics Data System (ADS)

    Dang, Liem X.; Schenter, Gregory K.

    2016-01-01

    To enhance our understanding of the solvent exchange mechanism in liquid methanol, we report a systematic study using molecular dynamics simulations. We use transition state theory, the Impey-Madden-McDonald method, the reactive flux method, and Grote-Hynes theory to compute the rate constants for this process. Solvent coupling was found to dominate, resulting in a significantly small transmission coefficient. We predict a positive activation volume for methanol exchange. The essential features of the dynamics as well as the pressure dependence are recovered from a Generalized Langevin Equation description of the dynamics. We find that the response to anharmonicity can be decomposed into two time regimes, one corresponding to short time response (<0.1 ps) and long time response (>5 ps). An effective characterization of the process is obtained from launching dynamics from the planar hypersurface corresponding to Grote-Hynes theory, resulting in improved numerical convergence of correlation functions.

  19. Foreign exchange rate entropy evolution during financial crises

    NASA Astrophysics Data System (ADS)

    Stosic, Darko; Stosic, Dusan; Ludermir, Teresa; de Oliveira, Wilson; Stosic, Tatijana

    2016-05-01

    This paper examines the effects of financial crises on foreign exchange (FX) markets, where entropy evolution is measured for different exchange rates, using the time-dependent block entropy method. Empirical results suggest that financial crises are associated with significant increase of exchange rate entropy, reflecting instability in FX market dynamics. In accordance with phenomenological expectations, it is found that FX markets with large liquidity and large trading volume are more inert - they recover quicker from a crisis than markets with small liquidity and small trading volume. Moreover, our numerical analysis shows that periods of economic uncertainty are preceded by periods of low entropy values, which may serve as a tool for anticipating the onset of financial crises.

  20. Marriage exchanges, seed exchanges, and the dynamics of manioc diversity

    PubMed Central

    Delêtre, Marc; McKey, Doyle B.; Hodkinson, Trevor R.

    2011-01-01

    The conservation of crop genetic resources requires understanding the different variables—cultural, social, and economic—that impinge on crop diversity. In small-scale farming systems, seed exchanges represent a key mechanism in the dynamics of crop genetic diversity, and analyzing the rules that structure social networks of seed exchange between farmer communities can help decipher patterns of crop genetic diversity. Using a combination of ethnobotanical and molecular genetic approaches, we investigated the relationships between regional patterns of manioc genetic diversity in Gabon and local networks of seed exchange. Spatially explicit Bayesian clustering methods showed that geographical discontinuities of manioc genetic diversity mirror major ethnolinguistic boundaries, with a southern matrilineal domain characterized by high levels of varietal diversity and a northern patrilineal domain characterized by low varietal diversity. Borrowing concepts from anthropology—kinship, bridewealth, and filiation—we analyzed the relationships between marriage exchanges and seed exchange networks in patrilineal and matrilineal societies. We demonstrate that, by defining marriage prohibitions, kinship systems structure social networks of exchange between farmer communities and influence the movement of seeds in metapopulations, shaping crop diversity at local and regional levels. PMID:22042843

  1. Dynamic enhancement of the exchange bias training effect

    NASA Astrophysics Data System (ADS)

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

    2007-03-01

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

  2. On exchange rate misalignments in the Eurozone's peripheral countries

    NASA Astrophysics Data System (ADS)

    Grochová, Ladislava; Plecitá, Klára

    2013-10-01

    In this paper we model equilibrium exchange rates for the Eurozone's countries on the basis of the Behavioural Equilibrium Exchange Rate approach, which assumes, that equilibrium exchange rates are in the long run affected by economic fundamentals. To assess the degree of exchange rate misalignment for the Eurozone's peripheral countries - Portugal, Ireland, Greece and Spain - the gap between the actual and the modelled equilibrium exchange rate value is calculated. Our results show that Spain, Portugal and Ireland had their real exchange rates in equilibrium when they joined the Eurozone; however their real exchange rates have been persistently overvalued since the beginning of the 2000s. Greece, on the other hand, has experienced diminishing undervaluation at the beginning of its membership in the Eurozone and since 2009 has exhibited an overvalued real exchange rate.

  3. Solvent Exchange in Liquid Methanol and Rate Theory

    SciTech Connect

    Dang, Liem X.; Schenter, Gregory K.

    2016-01-01

    To enhance our understanding of the solvent exchange mechanism in liquid methanol, we report a systematic study of this process using molecular dynamics simulations. We use transition state theory, the Impey-Madden-McDonald method, the reactive flux method, and Grote-Hynes theory to compute the rate constants for this process. Solvent coupling was found to dominate, resulting in a significantly small transmission coefficient. We predict a positive activation volume for the methanol exchange process. The essential features of the dynamics of the system as well as the pressure dependence are recovered from a Generalized Langevin Equation description of the dynamics. We find that the dynamics and response to anharmonicity can be decomposed into two time regimes, one corresponding to short time response (< 0.1 ps) and long time response (> 5 ps). An effective characterization of the process results from launching dynamics from the planar hypersurface corresponding to Grote-Hynes theory. This results in improved numerical convergence of correlation functions. This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. The calculations were carried out using computer resources provided by the Office of Basic Energy Sciences.

  4. Pion double charge exchange and hadron dynamics

    SciTech Connect

    Johnson, M.B.

    1991-01-01

    This paper will review theoretical results to show how pion double charge exchange is contributing to our understanding of hadron dynamics in nuclei. The exploitation of the nucleus as a filter is shown to be essential in facilitating the comparison between theory and experiment. 23 refs., 3 figs., 2 tabs.

  5. Measuring a hidden coordinate: Rate-exchange kinetics from 3D correlation functions

    NASA Astrophysics Data System (ADS)

    Berg, Mark A.; Darvin, Jason R.

    2016-08-01

    Nonexponential kinetics imply the existence of at least one slow variable other than the observable, that is, the system has a "hidden" coordinate. We develop a simple, but general, model that allows multidimensional correlation functions to be calculated for these systems. Homogeneous and heterogeneous mechanisms are both included, and slow exchange of the rates is allowed. This model shows that 2D and 3D correlation functions of the observable measure the distribution and kinetics of the hidden coordinate controlling the rate exchange. Both the mean exchange time and the shape of the exchange relaxation are measurable. However, complications arise because higher correlation functions are sums of multiple "pathways," each of which measures different dynamics. Only one 3D pathway involves exchange dynamics. Care must be used to extract exchange dynamics without contamination from other processes.

  6. Exchange of Standardized Flight Dynamics Data

    NASA Technical Reports Server (NTRS)

    Martin-Mur, Tomas J.; Berry, David; Flores-Amaya, Felipe; Folliard, J.; Kiehling, R.; Ogawa, M.; Pallaschke, S.

    2004-01-01

    Spacecraft operations require the knowledge of the vehicle trajectory and attitude and also that of other spacecraft or natural bodies. This knowledge is normally provided by the Flight Dynamics teams of the different space organizations and, as very often spacecraft operations involve more than one organization, this information needs to be exchanged between Agencies. This is why the Navigation Working Group within the CCSDS (Consultative Committee for Space Data Systems), has been instituted with the task of establishing standards for the exchange of Flight Dynamics data. This exchange encompasses trajectory data, attitude data, and tracking data. The Navigation Working Group includes regular members and observers representing the participating Space Agencies. Currently the group includes representatives from CNES, DLR, ESA, NASA and JAXA. This Working Group meets twice per year in order to devise standardized language, methods, and formats for the description and exchange of Navigation data. Early versions of some of these standards have been used to support mutual tracking of ESA and NASA interplanetary spacecraft, especially during the arrival of the 2003 missions to Mars. This paper provides a summary of the activities carried out by the group, briefly outlines the current and envisioned standards, describes the tests and operational activities that have been performed using the standards, and lists and discusses the lessons learned from these activities.

  7. Molecular Exchange Dynamics in Block Copolymer Micelles

    NASA Astrophysics Data System (ADS)

    Bates, Frank; Lu, Jie; Choi, Soohyung; Lodge, Timothy

    2012-02-01

    Poly(styrene-b-ethylene propylene) (PS-PEP) diblock copolymers were mixed with squalane (C30H62) at 1% by weight resulting in the formation of spherical micelles. The structure and dynamics of molecular exchange were characterized by synchrotron small-angle x-ray scattering (SAXS) and time resolved small-angle neutron scattering (TR-SANS), respectively, between 100 C and 160 C. TR-SANS measurements were performed with solutions initially containing deuterium labeled micelle cores and normal cores dispersed in a contrast matched squalane. Monitoring the reduction in scattering intensity as a function of time at various temperatures revealed molecular exchange dynamics highly sensitive to the core molecular weight and molecular weight distribution. Time-temperature superposition of data acquired at different temperatures produced a single master curve for all the mixtures. Experiments conducted with isotopically labeled micelle cores, each formed from two different but relatively mondisperse PS blocks, confirmed a simple dynamical model based on first order kinetics and core Rouse single chain relaxation. These findings demonstrate a dramatic transition to nonergodicity with increasing micelle core molecular weight and confirm the origins of the logarithmic exchange kinetics in such systems.

  8. Is dynamic rating the answer?

    SciTech Connect

    1996-10-01

    Capacity of transmission line to move power is very dependent on weather conditions. If all transmission lines could be instrumented so that the dispatchers know their capacity at all times, much uncertainty about network capacity would be eliminated. The problem is high cost; dynamic line-rating systems are likely to be in widespread use in the near future. Dynamic rating is very useful for dealing with contingency, when dispatchers need to know the maximum capacity of equipment and how many minutes they have before action must be taken.

  9. Towards Smart Grid Dynamic Ratings

    NASA Astrophysics Data System (ADS)

    Cheema, Jamal; Clark, Adrian; Kilimnik, Justin; Pavlovski, Chris; Redman, David; Vu, Maria

    2011-08-01

    The energy distribution industry is giving greater attention to smart grid solutions as a means for increasing the capabilities, efficiency and reliability of the electrical power network. The smart grid makes use of intelligent monitoring and control devices throughout the distribution network to report on electrical properties such as voltage, current and power, as well as raising network alarms and events. A further aspect of the smart grid embodies the dynamic rating of electrical assets of the network. This fundamentally involves a rating of the load current capacity of electrical assets including feeders, transformers and switches. The mainstream approach to rate assets is to apply the vendor plate rating, which often under utilizes assets, or in some cases over utilizes when environmental conditions reduce the effective rated capacity, potentially reducing lifetime. Using active intelligence we have developed a rating system that rates assets in real time based upon several events. This allows for a far more efficient and reliable electrical grid that is able to extend further the life and reliability of the electrical network. In this paper we describe our architecture, the observations made during development and live deployment of the solution into operation. We also illustrate how this solution blends with the smart grid by proposing a dynamic rating system for the smart grid.

  10. Noninvasive detection of gas exchange rate by near infrared spectroscopy

    NASA Astrophysics Data System (ADS)

    Xu, Guodong; Mao, Zongzhen; Wang, Bangde

    2008-12-01

    In order to study the relationship among the oxygen concentration in skeletal muscle tissues and the heart rate (HR), oxygen uptake (VO2), respiratory exchange ratio (RER) during incremental running exercises on a treadmill, a near-infrared spectroscopy muscle oxygen monitor system is employed to measure the relative change in muscle oxygenation, with the heart rate, oxygen uptake, production of carbon dioxide (VCO2) and respiratory exchange ratio are recorded synchronously. The results indicate parameters mentioned above present regular changes during the incremental exercise. High correlations are discovered between relative change of oxy-hemoglobin concentration and heart rate, oxygen uptake, respiratory exchange ratio at the significance level (P=0.01). This research might introduce a new measurement technology and/or a novel biological monitoring parameter to the evaluation of physical function status, control the training intensity, estimation of the effectiveness of exercise. Keywords: near-infrared spectroscopy; muscle oxygen concentration; heart rate; oxygen uptake; respiratory exchange ratio.

  11. Statistical Analysis of the Exchange Rate of Bitcoin.

    PubMed

    Chu, Jeffrey; Nadarajah, Saralees; Chan, Stephen

    2015-01-01

    Bitcoin, the first electronic payment system, is becoming a popular currency. We provide a statistical analysis of the log-returns of the exchange rate of Bitcoin versus the United States Dollar. Fifteen of the most popular parametric distributions in finance are fitted to the log-returns. The generalized hyperbolic distribution is shown to give the best fit. Predictions are given for future values of the exchange rate. PMID:26222702

  12. Statistical Analysis of the Exchange Rate of Bitcoin

    PubMed Central

    Chu, Jeffrey; Nadarajah, Saralees; Chan, Stephen

    2015-01-01

    Bitcoin, the first electronic payment system, is becoming a popular currency. We provide a statistical analysis of the log-returns of the exchange rate of Bitcoin versus the United States Dollar. Fifteen of the most popular parametric distributions in finance are fitted to the log-returns. The generalized hyperbolic distribution is shown to give the best fit. Predictions are given for future values of the exchange rate. PMID:26222702

  13. Statistical Analysis of the Exchange Rate of Bitcoin.

    PubMed

    Chu, Jeffrey; Nadarajah, Saralees; Chan, Stephen

    2015-01-01

    Bitcoin, the first electronic payment system, is becoming a popular currency. We provide a statistical analysis of the log-returns of the exchange rate of Bitcoin versus the United States Dollar. Fifteen of the most popular parametric distributions in finance are fitted to the log-returns. The generalized hyperbolic distribution is shown to give the best fit. Predictions are given for future values of the exchange rate.

  14. Kinetic isotope effects for fast deuterium and proton exchange rates

    PubMed Central

    Mammoli, Daniele; Kadeřávek, Pavel; Pelupessy, Philippe; Bodenhausen, Geoffrey

    2016-01-01

    By monitoring the effect of deuterium decoupling on the decay of transverse 15N magnetization in D–15N spin pairs during multiple-refocusing echo sequences, we have determined fast D–D exchange rates k D and compared them with fast H–H exchange rates k H in tryptophan to determine the kinetic isotope effect as a function of pH and temperature. PMID:27009684

  15. Exchange Rate Volatility and Trade Equation in Indonesia

    NASA Astrophysics Data System (ADS)

    Pasasa, Linus; Fechter, Nadine; Bustaman, Yosman

    2010-12-01

    This paper examines the characteristics of short-term and long-term fluctuations/volatility of Indonesia exchange rate and investigates whether this volatility has affected Indonesia's exports flows. In particular the paper investigates the impact of exchange rate volatility on aggregate Indonesia exports flows to the United State and also on imports. The Augmented Dickey-Fuller Test was employed on quarterly data for the period January 2000 to December 2008 to test for stationarity on the variables of interest. Estimates of the long-term influence of exchange rate volatility on the trade flows are obtained using the Johansen Cointegration Test. The results suggest that a significant long-term relationship linking exchange rate volatility and the trade volume between Indonesia and the United States exists. A negative long-term relationship between exchange rate fluctuations and the export volume sent from Indonesia to the US is obtained. On the other hand, exchange rate volatility exerts a positive long-term effect upon the import volume.

  16. Dynamic Analysis of Capture Devices for Momentum Exchange with Tethers

    NASA Technical Reports Server (NTRS)

    Canfield, Stephen

    2002-01-01

    One of the significant challenges in developing a momentum exchange / electrodynamic reboost tether system is in the analysis and design of the capture device and its effects on the overall dynamics of the system. The goal of this work is to develop appropriate tether momentum exchange models that can simulate and evaluate the requirements of such a system, and be used to create specifications on the design of a capture device. This report briefly describes dynamic model development, simulation of the momentum exchange process, evaluation of dynamic effects of errors in the momentum exchange process, and the development of guidelines in selecting dynamic properties in the design of a capture device.

  17. Modeling inflation rates and exchange rates in Ghana: application of multivariate GARCH models.

    PubMed

    Nortey, Ezekiel Nn; Ngoh, Delali D; Doku-Amponsah, Kwabena; Ofori-Boateng, Kenneth

    2015-01-01

    This paper was aimed at investigating the volatility and conditional relationship among inflation rates, exchange rates and interest rates as well as to construct a model using multivariate GARCH DCC and BEKK models using Ghana data from January 1990 to December 2013. The study revealed that the cumulative depreciation of the cedi to the US dollar from 1990 to 2013 is 7,010.2% and the yearly weighted depreciation of the cedi to the US dollar for the period is 20.4%. There was evidence that, the fact that inflation rate was stable, does not mean that exchange rates and interest rates are expected to be stable. Rather, when the cedi performs well on the forex, inflation rates and interest rates react positively and become stable in the long run. The BEKK model is robust to modelling and forecasting volatility of inflation rates, exchange rates and interest rates. The DCC model is robust to model the conditional and unconditional correlation among inflation rates, exchange rates and interest rates. The BEKK model, which forecasted high exchange rate volatility for the year 2014, is very robust for modelling the exchange rates in Ghana. The mean equation of the DCC model is also robust to forecast inflation rates in Ghana. PMID:25741459

  18. Modeling inflation rates and exchange rates in Ghana: application of multivariate GARCH models.

    PubMed

    Nortey, Ezekiel Nn; Ngoh, Delali D; Doku-Amponsah, Kwabena; Ofori-Boateng, Kenneth

    2015-01-01

    This paper was aimed at investigating the volatility and conditional relationship among inflation rates, exchange rates and interest rates as well as to construct a model using multivariate GARCH DCC and BEKK models using Ghana data from January 1990 to December 2013. The study revealed that the cumulative depreciation of the cedi to the US dollar from 1990 to 2013 is 7,010.2% and the yearly weighted depreciation of the cedi to the US dollar for the period is 20.4%. There was evidence that, the fact that inflation rate was stable, does not mean that exchange rates and interest rates are expected to be stable. Rather, when the cedi performs well on the forex, inflation rates and interest rates react positively and become stable in the long run. The BEKK model is robust to modelling and forecasting volatility of inflation rates, exchange rates and interest rates. The DCC model is robust to model the conditional and unconditional correlation among inflation rates, exchange rates and interest rates. The BEKK model, which forecasted high exchange rate volatility for the year 2014, is very robust for modelling the exchange rates in Ghana. The mean equation of the DCC model is also robust to forecast inflation rates in Ghana.

  19. Football and exchange rates: empirical support for behavioral economics.

    PubMed

    Eker, Gulin; Berument, Hakan; Dogan, Burak

    2007-10-01

    Recently, economic theory has been expanded to incorporate emotions, which have been assumed to play an important role in financial decisions. The present study illustrates this by showing a connection between the sports performance of popular national football teams (Besiktas, Fenerbahce, and Galatasaray) and performance of the Turkish economy. Specifically, a significant positive association was found between the success of three major professional Turkish football teams and the exchange rate of the Turkish lira against the U.S. dollar. The effect of the football success of several Turkish football teams on the exchange rate of the Turkish lira was examined using the simultaneous multiple regression model with predictor measures of wins, losses, and ties for different combinations of teams to predict the depreciation rate of the Turkish lira between the years 1987 and 2003. Wins by Turkish football teams against foreign (non-Turkish) rivals increased with exchange rate depreciation of the Turkish lira against the U.S. dollar.

  20. Football and exchange rates: empirical support for behavioral economics.

    PubMed

    Eker, Gulin; Berument, Hakan; Dogan, Burak

    2007-10-01

    Recently, economic theory has been expanded to incorporate emotions, which have been assumed to play an important role in financial decisions. The present study illustrates this by showing a connection between the sports performance of popular national football teams (Besiktas, Fenerbahce, and Galatasaray) and performance of the Turkish economy. Specifically, a significant positive association was found between the success of three major professional Turkish football teams and the exchange rate of the Turkish lira against the U.S. dollar. The effect of the football success of several Turkish football teams on the exchange rate of the Turkish lira was examined using the simultaneous multiple regression model with predictor measures of wins, losses, and ties for different combinations of teams to predict the depreciation rate of the Turkish lira between the years 1987 and 2003. Wins by Turkish football teams against foreign (non-Turkish) rivals increased with exchange rate depreciation of the Turkish lira against the U.S. dollar. PMID:18175508

  1. A Role Play on Export Decisions and the Exchange Rate.

    ERIC Educational Resources Information Center

    Cotterell, Ann

    1987-01-01

    Explains that the goal of this exercise is to encourage an understanding of the effects of exchange rate changes and the use of forward rates. Provides a role play that involves students working in groups to decide whether to export a consignment of golf trollies to Italy and shortbread to Canada. (BSR)

  2. The rate of oxygen isotope exchange between nitrate and water

    NASA Astrophysics Data System (ADS)

    Kaneko, Masanori; Poulson, Simon R.

    2013-10-01

    The oxygen isotope exchange rate between nitrate and water was measured at a temperature of 50-80 °C and pH -0.6 to 1.1. Oxygen isotope exchange is a first-order reaction, with the exchange rate being strongly affected by both reaction temperature and pH, with increased rates of isotope exchange at higher temperatures and lower pH values. The rate of oxygen isotope exchange under natural conditions is extremely slow, with an estimated half-life for isotope exchange of 5.5 × 109 years at 25 °C and pH 7. The extremely slow rate of oxygen isotope exchange between nitrate and water under typical environmental conditions illustrates that nitrate-δ18O signatures (and also nitrate δ17O and Δ17O signatures) associated with various nitrate sources, as well as isotope compositions produced by biogeochemical processes, will be preserved. Hence, it is valid to use the value of nitrate-δ18O to investigate the sources and biogeochemical behavior of nitrate, in a similar manner to the use of sulfate-δ18O signatures to study the sources and biogeochemical behavior of sulfate. Equilibrium oxygen isotope fractionation factors have been determined, although quantification of the nitrate-water equilibrium fractionation factor is not possible due to the presence of nitrate as both protonated (i.e. HNO3) and unprotonated forms (i.e. NO3-) under the experimental conditions, and the difficulty in accurately calculating nitrate speciation in low pH, high ionic strength solutions.

  3. Extreme-value dependence: An application to exchange rate markets

    NASA Astrophysics Data System (ADS)

    Fernandez, Viviana

    2007-04-01

    Extreme value theory (EVT) focuses on modeling the tail behavior of a loss distribution using only extreme values rather than the whole data set. For a sample of 10 countries with dirty/free float regimes, we investigate whether paired currencies exhibit a pattern of asymptotic dependence. That is, whether an extremely large appreciation or depreciation in the nominal exchange rate of one country might transmit to another. In general, after controlling for volatility clustering and inertia in returns, we do not find evidence of extreme-value dependence between paired exchange rates. However, for asymptotic-independent paired returns, we find that tail dependency of exchange rates is stronger under large appreciations than under large depreciations.

  4. Evidence of multifractality from CEE exchange rates against Euro

    NASA Astrophysics Data System (ADS)

    Caraiani, Petre; Haven, Emmanuel

    2015-02-01

    The multifractal spectrum of a time series can be ascertained with a number of techniques, some based on wavelets, others based on the much newer (multifractal) detrended fluctuation analysis (MF-DFA). We test for the presence of multifractality in daily data on selected exchange rates from Central and Eastern European economies against EURO. The approach is based on a slight modification of the MF-DFA analysis in that local trends are not allowed to be polynomially fitted but rather are estimated through a sifting process which is established through a so called Empirical Mode Decomposition (EMD) algorithm. We assess the drivers of the multifractal spectrum strength, like temporal correlations or distributions based on surrogate data. Another topic discussed is whether the entrance in the exchange rate mechanism ERM II influenced the multifractality of the exchange rates.

  5. Residue-specific NH exchange rates studied by NMR diffusion experiments

    NASA Astrophysics Data System (ADS)

    Brand, Torsten; Cabrita, Eurico J.; Morris, Gareth A.; Günther, Robert; Hofmann, Hans-Jörg; Berger, Stefan

    2007-07-01

    We present a novel approach to the investigation of rapid (>2 s -1) NH exchange rates in proteins, based on residue-specific diffusion measurements. 1H, 15N-DOSY-HSQC spectra are recorded in order to observe resolved amide proton signals for most residues of the protein. Human ubiquitin was used to demonstrate the proposed method. Exchange rates are derived directly from the decay data of the diffusion experiment by applying a model deduced from the assumption of a two-site exchange with water and the "pure" diffusion coefficients of water and protein. The "pure" diffusion coefficient of the protein is determined in an experiment with selective excitation of the amide protons in order to suppress the influence of magnetization transfer from water to amide protons on the decay data. For rapidly exchanging residues a comparison of our results with the exchange rates obtained in a MEXICO experiment showed good agreement. Molecular dynamics (MD) and quantum mechanical calculations were performed to find molecular parameters correlating with the exchangeability of the NH protons. The RMS fluctuations of the amide protons, obtained from the MD simulations, together with the NH coupling constants provide a bilinear model which shows a good correlation with the experimental NH exchange rates.

  6. The American Foreign Exchange Option in Time-Dependent One-Dimensional Diffusion Model for Exchange Rate

    SciTech Connect

    Rehman, Nasir Shashiashvili, Malkhaz

    2009-06-15

    The classical Garman-Kohlhagen model for the currency exchange assumes that the domestic and foreign currency risk-free interest rates are constant and the exchange rate follows a log-normal diffusion process.In this paper we consider the general case, when exchange rate evolves according to arbitrary one-dimensional diffusion process with local volatility that is the function of time and the current exchange rate and where the domestic and foreign currency risk-free interest rates may be arbitrary continuous functions of time. First non-trivial problem we encounter in time-dependent case is the continuity in time argument of the value function of the American put option and the regularity properties of the optimal exercise boundary. We establish these properties based on systematic use of the monotonicity in volatility for the value functions of the American as well as European options with convex payoffs together with the Dynamic Programming Principle and we obtain certain type of comparison result for the value functions and corresponding exercise boundaries for the American puts with different strikes, maturities and volatilities.Starting from the latter fact that the optimal exercise boundary curve is left continuous with right-hand limits we give a mathematically rigorous and transparent derivation of the significant early exercise premium representation for the value function of the American foreign exchange put option as the sum of the European put option value function and the early exercise premium.The proof essentially relies on the particular property of the stochastic integral with respect to arbitrary continuous semimartingale over the predictable subsets of its zeros. We derive from the latter the nonlinear integral equation for the optimal exercise boundary which can be studied by numerical methods.

  7. Extensions to the Dynamic Aerospace Vehicle Exchange Markup Language

    NASA Technical Reports Server (NTRS)

    Brian, Geoffrey J.; Jackson, E. Bruce

    2011-01-01

    The Dynamic Aerospace Vehicle Exchange Markup Language (DAVE-ML) is a syntactical language for exchanging flight vehicle dynamic model data. It provides a framework for encoding entire flight vehicle dynamic model data packages for exchange and/or long-term archiving. Version 2.0.1 of DAVE-ML provides much of the functionality envisioned for exchanging aerospace vehicle data; however, it is limited in only supporting scalar time-independent data. Additional functionality is required to support vector and matrix data, abstracting sub-system models, detailing dynamics system models (both discrete and continuous), and defining a dynamic data format (such as time sequenced data) for validation of dynamics system models and vehicle simulation packages. Extensions to DAVE-ML have been proposed to manage data as vectors and n-dimensional matrices, and record dynamic data in a compatible form. These capabilities will improve the clarity of data being exchanged, simplify the naming of parameters, and permit static and dynamic data to be stored using a common syntax within a single file; thereby enhancing the framework provided by DAVE-ML for exchanging entire flight vehicle dynamic simulation models.

  8. 14 CFR 65.43 - Rating privileges and exchange.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... (CONTINUED) AIRMEN CERTIFICATION: AIRMEN OTHER THAN FLIGHT CREWMEMBERS Air Traffic Control Tower Operators... tower. However, if he does not do so before August 31, 1971, he may not thereafter exercise the privileges of his senior rating at the control tower concerned until he makes the exchange. (b) The holder...

  9. 14 CFR 65.43 - Rating privileges and exchange.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... (CONTINUED) AIRMEN CERTIFICATION: AIRMEN OTHER THAN FLIGHT CREWMEMBERS Air Traffic Control Tower Operators... tower. However, if he does not do so before August 31, 1971, he may not thereafter exercise the privileges of his senior rating at the control tower concerned until he makes the exchange. (b) The holder...

  10. 14 CFR 65.43 - Rating privileges and exchange.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... (CONTINUED) AIRMEN CERTIFICATION: AIRMEN OTHER THAN FLIGHT CREWMEMBERS Air Traffic Control Tower Operators... tower. However, if he does not do so before August 31, 1971, he may not thereafter exercise the privileges of his senior rating at the control tower concerned until he makes the exchange. (b) The holder...

  11. Covariation of synaptonemal complex length and mammalian meiotic exchange rates.

    PubMed

    Lynn, Audrey; Koehler, Kara E; Judis, LuAnn; Chan, Ernest R; Cherry, Jonathan P; Schwartz, Stuart; Seftel, Allen; Hunt, Patricia A; Hassold, Terry J

    2002-06-21

    Analysis of recombination between loci (linkage analysis) has been a cornerstone of human genetic research, enabling investigators to localize and, ultimately, identify genetic loci. However, despite these efforts little is known about patterns of meiotic exchange in human germ cells or the mechanisms that control these patterns. Using recently developed immunofluorescence methodology to examine exchanges in human spermatocytes, we have identified remarkable variation in the rate of recombination within and among individuals. Subsequent analyses indicate that, in humans and mice, this variation is linked to differences in the length of the synaptonemal complex. Thus, at least in mammals, a physical structure, the synaptonemal complex, reflects genetic rather than physical distance.

  12. Does implied volatility of currency futures option imply volatility of exchange rates?

    NASA Astrophysics Data System (ADS)

    Wang, Alan T.

    2007-02-01

    By investigating currency futures options, this paper provides an alternative economic implication for the result reported by Stein [Overreactions in the options market, Journal of Finance 44 (1989) 1011-1023] that long-maturity options tend to overreact to changes in the implied volatility of short-maturity options. When a GARCH process is assumed for exchange rates, a continuous-time relationship is developed. We provide evidence that implied volatilities may not be the simple average of future expected volatilities. By comparing the term-structure relationship of implied volatilities with the process of the underlying exchange rates, we find that long-maturity options are more consistent with the exchange rates process. In sum, short-maturity options overreact to the dynamics of underlying assets rather than long-maturity options overreacting to short-maturity options.

  13. Hybrid empirical mode decomposition- ARIMA for forecasting exchange rates

    NASA Astrophysics Data System (ADS)

    Abadan, Siti Sarah; Shabri, Ani; Ismail, Shuhaida

    2015-02-01

    This paper studied the forecasting of monthly Malaysian Ringgit (MYR)/ United State Dollar (USD) exchange rates using the hybrid of two methods which are the empirical model decomposition (EMD) and the autoregressive integrated moving average (ARIMA). MYR is pegged to USD during the Asian financial crisis causing the exchange rates are fixed to 3.800 from 2nd of September 1998 until 21st of July 2005. Thus, the chosen data in this paper is the post-July 2005 data, starting from August 2005 to July 2010. The comparative study using root mean square error (RMSE) and mean absolute error (MAE) showed that the EMD-ARIMA outperformed the single-ARIMA and the random walk benchmark model.

  14. Selection, Evaluation, And Rating of Compact Heat exchangers

    SciTech Connect

    Carlson, Matt

    2014-10-07

    SEARCH determines and optimizes the design of a compact heat exchanger for specified process conditions. The user specifies process boundary conditions including the fluid state and flow rate and SEARCH will determine the optimum flow arrangement, channel geometry, and mechanical design for the unit. Fluids are modeled using NUST Refprop or tabulated values. A variety of thermal-hydraulic correlations are available including user-defined equations to accurately capture the heat transfer and pressure drop behavior of the process flows.

  15. Complex dynamical behaviors of daily data series in stock exchange

    NASA Astrophysics Data System (ADS)

    Wang, Hongchun; Chen, Guanrong; Lü, Jinhu

    2004-12-01

    It is well known that many economic data series show chaotic behaviors. In this Letter, we further investigate the complex dynamical behaviors of the daily data series, including opening quotation, closing quotation, maximum price, minimum price, and total exchange quantum, in Shenzhen stock exchange and Shanghai stock exchange, which are two representative stock exchanges in mainland China. The maximum Lyapunov exponents, correlation dimensions, and frequency spectra are calculated for these time series. Our results indicate that some daily data series of stock exchanges display low-dimensional chaotic behaviors, and some other daily data series do not show any chaotic behavior. Moreover, we introduce a weighted one-rank local-region approach for predicting short-term daily data series of stock exchange.

  16. 26 CFR 1.989(b)-1 - Definition of weighted average exchange rate.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 26 Internal Revenue 10 2010-04-01 2010-04-01 false Definition of weighted average exchange rate. 1... average exchange rate. For purposes of section 989(b)(3) and (4), the term “weighted average exchange rate” means the simple average of the daily exchange rates (determined by reference to a qualified source...

  17. Oil Prices and Interest Rates: Do They Determine the Exchange Rate?

    ERIC Educational Resources Information Center

    Law, I. A.; Old, J. L.

    1986-01-01

    Argues that the relationship between the British pound sterling, interest rates, and oil prices has been overemphasized by economic commentators because they ignored a basic economic theory about the determination of the exchange rate. Provides an example and suggestions for follow up instruction. (Author/JDH)

  18. Oxygen ionization rates at Mars and Venus - Relative contributions of impact ionization and charge exchange

    NASA Technical Reports Server (NTRS)

    Zhang, M. H. G.; Luhmann, J. G.; Nagy, A. F.; Spreiter, J. R.; Stahara, S. S.

    1993-01-01

    Oxygen ion production rates above the ionopauses of Venus and Mars are calculated for photoionization, charge exchange, and solar wind electron impact ionization processes. The latter two require the use of the Spreiter and Stahara (1980) gas dynamic model to estimate magnetosheath velocities, densities, and temperatures. The results indicate that impact ionization is the dominant mechanism for the production of O(+) ions at both Venus and Mars. This finding might explain both the high ion escape rates measured by Phobos 2 and the greater mass loading rate inferred for Venus from the bow shock positions.

  19. Oxygen ionization rates at Mars and Venus - Relative contributions of impact ionization and charge exchange

    NASA Astrophysics Data System (ADS)

    Zhang, M. H. G.; Luhmann, J. G.; Nagy, A. F.; Spreiter, J. R.; Stahara, S. S.

    1993-02-01

    Oxygen ion production rates above the ionopauses of Venus and Mars are calculated for photoionization, charge exchange, and solar wind electron impact ionization processes. The latter two require the use of the Spreiter and Stahara (1980) gas dynamic model to estimate magnetosheath velocities, densities, and temperatures. The results indicate that impact ionization is the dominant mechanism for the production of O(+) ions at both Venus and Mars. This finding might explain both the high ion escape rates measured by Phobos 2 and the greater mass loading rate inferred for Venus from the bow shock positions.

  20. The groundwater exchange rate of the southern Baltic coastal lowland

    NASA Astrophysics Data System (ADS)

    Burzyński, K.; Sadurski, A.

    1990-11-01

    The groundwater of the southern Baltic lowlands usually occurs in particular hydrogeological conditions. The lowland is mostly covered by peats several metres in thickness. Peatbog water is isolated from deeper aquifers and has different chemical composition. Salty, relic groundwater of marine origin from the Atlantic period of the Holocene (Littorina transgression) may have survived in the deeper coastal aquifers in places of sluggish flow. The results of mathematical modelling of groundwater circulation show that the flow rate and local directions of groundwater change during the year, depending on the rate of groundwater recharge by precipitation. We present here an unsteady flow model, which makes it possible to predict the water table fluctuations during a year at any point of the area studied. The calculation of the groundwater exchange rate did not confirm the presence of any places of very sluggish groundwater flow, where salty, young relic water might have survived.

  1. Peptide-Column Interactions and Their Influence on Back Exchange Rates in Hydrogen/Deuterium Exchange-MS

    NASA Astrophysics Data System (ADS)

    Sheff, Joey G.; Rey, Martial; Schriemer, David C.

    2013-07-01

    Hydrogen/deuterium exchange (HDX) methods generate useful information on protein structure and dynamics, ideally at the individual residue level. Most MS-based HDX methods involve a rapid proteolytic digestion followed by LC/MS analysis, with exchange kinetics monitored at the peptide level. Localizing specific sites of HDX is usually restricted to a resolution the size of the host peptide because gas-phase processes can scramble deuterium throughout the peptide. Subtractive methods may improve resolution, where deuterium levels of overlapping and nested peptides are used in a subtractive manner to localize exchange to smaller segments. In this study, we explore the underlying assumption of the subtractive method, namely, that the measured back exchange kinetics of a given residue is independent of its host peptide. Using a series of deuterated peptides, we show that secondary structure can be partially retained under quenched conditions, and that interactions between peptides and reversed-phase LC columns may both accelerate and decelerate residue HDX, depending upon peptide sequence and length. Secondary structure is induced through column interactions in peptides with a solution-phase propensity for structure, which has the effect of slowing HDX rates relative to predicted random coil values. Conversely, column interactions can orient random-coil peptide conformers to accelerate HDX, the degree to which correlates with peptide charge in solution, and which can be reversed by using stronger ion pairing reagents. The dependency of these effects on sequence and length suggest that subtractive methods for improving structural resolution in HDX-MS will not offer a straightforward solution for increasing exchange site resolution.

  2. Selection, Evaluation, And Rating of Compact Heat exchangers

    2014-10-07

    SEARCH determines and optimizes the design of a compact heat exchanger for specified process conditions. The user specifies process boundary conditions including the fluid state and flow rate and SEARCH will determine the optimum flow arrangement, channel geometry, and mechanical design for the unit. Fluids are modeled using NUST Refprop or tabulated values. A variety of thermal-hydraulic correlations are available including user-defined equations to accurately capture the heat transfer and pressure drop behavior of themore » process flows.« less

  3. Air exchange rates from atmospheric CO2 daily cycle

    PubMed Central

    Carrilho, João Dias; Mateus, Mário; Batterman, Stuart; da Silva, Manuel Gameiro

    2015-01-01

    We propose a new approach for measuring ventilation air exchange rates (AERs). The method belongs to the class of tracer gas techniques, but is formulated in the light of systems theory and signal processing. Unlike conventional CO2 based methods that assume the outdoor ambient CO2 concentration is constant, the proposed method recognizes that photosynthesis and respiration cycle of plants and processes associated with fuel combustion produce daily, quasi-periodic, variations in the ambient CO2 concentrations. These daily variations, which are within the detection range of existing monitoring equipment, are utilized for estimating ventilation rates without the need of a source of CO2 in the building. Using a naturally-ventilated residential apartment, AERs obtained using the new method compared favorably (within 10%) to those obtained using the conventional CO2 decay fitting technique. The new method has the advantages that no tracer gas injection is needed, and high time resolution results are obtained. PMID:26236090

  4. Mutation rate evolution in replicator dynamics.

    PubMed

    Allen, Benjamin; Rosenbloom, Daniel I Scholes

    2012-11-01

    The mutation rate of an organism is itself evolvable. In stable environments, if faithful replication is costless, theory predicts that mutation rates will evolve to zero. However, positive mutation rates can evolve in novel or fluctuating environments, as analytical and empirical studies have shown. Previous work on this question has focused on environments that fluctuate independently of the evolving population. Here we consider fluctuations that arise from frequency-dependent selection in the evolving population itself. We investigate how the dynamics of competing traits can induce selective pressure on the rates of mutation between these traits. To address this question, we introduce a theoretical framework combining replicator dynamics and adaptive dynamics. We suppose that changes in mutation rates are rare, compared to changes in the traits under direct selection, so that the expected evolutionary trajectories of mutation rates can be obtained from analysis of pairwise competition between strains of different rates. Depending on the nature of frequency-dependent trait dynamics, we demonstrate three possible outcomes of this competition. First, if trait frequencies are at a mutation-selection equilibrium, lower mutation rates can displace higher ones. Second, if trait dynamics converge to a heteroclinic cycle-arising, for example, from "rock-paper-scissors" interactions-mutator strains succeed against non-mutators. Third, in cases where selection alone maintains all traits at positive frequencies, zero and nonzero mutation rates can coexist indefinitely. Our second result suggests that relatively high mutation rates may be observed for traits subject to cyclical frequency-dependent dynamics.

  5. 12 CFR Appendix A to Subpart A of... - Minimum Capital Components for Interest Rate and Foreign Exchange Rate Contracts

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... and Foreign Exchange Rate Contracts A Appendix A to Subpart A of Part 1750 Banks and Banking OFFICE OF... CAPITAL Minimum Capital Pt. 1750, Subpt. A, App. A Appendix A to Subpart A of Part 1750—Minimum Capital... sheet interest rate and foreign exchange rate contracts: a. Interest Rate Contracts i. Single...

  6. 12 CFR Appendix A to Subpart A of... - Minimum Capital Components for Interest Rate and Foreign Exchange Rate Contracts

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... and Foreign Exchange Rate Contracts A Appendix A to Subpart A of Part 1750 Banks and Banking OFFICE OF... CAPITAL Minimum Capital Pt. 1750, Subpt. A, App. A Appendix A to Subpart A of Part 1750—Minimum Capital... sheet interest rate and foreign exchange rate contracts: a. Interest Rate Contracts i. Single...

  7. 12 CFR Appendix A to Subpart A of... - Minimum Capital Components for Interest Rate and Foreign Exchange Rate Contracts

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... and Foreign Exchange Rate Contracts A Appendix A to Subpart A of Part 1750 Banks and Banking OFFICE OF... CAPITAL Minimum Capital Pt. 1750, Subpt. A, App. A Appendix A to Subpart A of Part 1750—Minimum Capital... sheet interest rate and foreign exchange rate contracts: a. Interest Rate Contracts i. Single...

  8. 12 CFR Appendix A to Subpart A of... - Minimum Capital Components for Interest Rate and Foreign Exchange Rate Contracts

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... and Foreign Exchange Rate Contracts A Appendix A to Subpart A of Part 1750 Banks and Banking OFFICE OF... CAPITAL Minimum Capital Pt. 1750, Subpt. A, App. A Appendix A to Subpart A of Part 1750—Minimum Capital... sheet interest rate and foreign exchange rate contracts: a. Interest Rate Contracts i. Single...

  9. 12 CFR Appendix A to Subpart A of... - Minimum Capital Components for Interest Rate and Foreign Exchange Rate Contracts

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... and Foreign Exchange Rate Contracts A Appendix A to Subpart A of Part 1750 Banks and Banking OFFICE OF... CAPITAL Minimum Capital Pt. 1750, Subpt. A, App. A Appendix A to Subpart A of Part 1750—Minimum Capital... sheet interest rate and foreign exchange rate contracts: a. Interest Rate Contracts i. Single...

  10. Return Rates for Needle Exchange Programs: A Common Criticism Answered

    PubMed Central

    Ksobiech, Kate

    2004-01-01

    This study searched the available needle exchange program (NEP) literature for return rate data. A total of 26 articles were found. The overall worldwide return rate was 90%, although this ranged from a low of 15% to a high of 112%. U.S. NEP return rates were gathered from only eight studies, indicating a clear need for more data, although U.S. return rates were comparable to those from NEPs outside of the U.S. One underlying assumption made by opponents of NEPs is that IDUs will not return needles to the distribution site, thereby potentially increasing the risk of health problems to the surrounding community from exposure to contaminated needles. This study's results suggest that NEPs are relatively successful in taking in used needles, although it is generally unclear where the needles were originally acquired, and if IDUs return their own needles, or are returning needles for a social network. Ways for AIDS Service Organizations to capitalize on these brief encounters with IDUs, as well as public policy implications of the findings, are discussed. PMID:15169545

  11. Glucans monomer-exchange dynamics as an open chemical network

    SciTech Connect

    Rao, Riccardo Esposito, Massimiliano; Lacoste, David

    2015-12-28

    We describe the oligosaccharides-exchange dynamics performed by the so-called D-enzymes on polysaccharides. To mimic physiological conditions, we treat this process as an open chemical network by assuming some of the polymer concentrations fixed (chemostatting). We show that three different long-time behaviors may ensue: equilibrium states, nonequilibrium steady states, and continuous growth states. We dynamically and thermodynamically characterize these states and emphasize the crucial role of conservation laws in identifying the chemostatting conditions inducing them.

  12. Dependence and risk assessment for oil prices and exchange rate portfolios: A wavelet based approach

    NASA Astrophysics Data System (ADS)

    Aloui, Chaker; Jammazi, Rania

    2015-10-01

    In this article, we propose a wavelet-based approach to accommodate the stylized facts and complex structure of financial data, caused by frequent and abrupt changes of markets and noises. Specifically, we show how the combination of both continuous and discrete wavelet transforms with traditional financial models helps improve portfolio's market risk assessment. In the empirical stage, three wavelet-based models (wavelet-EGARCH with dynamic conditional correlations, wavelet-copula, and wavelet-extreme value) are considered and applied to crude oil price and US dollar exchange rate data. Our findings show that the wavelet-based approach provides an effective and powerful tool for detecting extreme moments and improving the accuracy of VaR and Expected Shortfall estimates of oil-exchange rate portfolios after noise is removed from the original data.

  13. Transitional steady states of exchange dynamics between finite quantum systems.

    PubMed

    Jeon, Euijin; Yi, Juyeon; Kim, Yong Woon

    2016-08-01

    We examine energy and particle exchange between finite-sized quantum systems and find a new form of nonequilibrium state. The exchange rate undergoes stepwise evolution in time, and its magnitude and sign dramatically change according to system size differences. The origin lies in interference effects contributed by multiply scattered waves at system boundaries. Although such characteristics are utterly different from those of true steady state for infinite systems, Onsager's reciprocal relation remains universally valid. PMID:27627275

  14. Transitional steady states of exchange dynamics between finite quantum systems

    NASA Astrophysics Data System (ADS)

    Jeon, Euijin; Yi, Juyeon; Kim, Yong Woon

    2016-08-01

    We examine energy and particle exchange between finite-sized quantum systems and find a new form of nonequilibrium state. The exchange rate undergoes stepwise evolution in time, and its magnitude and sign dramatically change according to system size differences. The origin lies in interference effects contributed by multiply scattered waves at system boundaries. Although such characteristics are utterly different from those of true steady state for infinite systems, Onsager's reciprocal relation remains universally valid.

  15. Dithioacetal Exchange: A New Reversible Reaction for Dynamic Combinatorial Chemistry.

    PubMed

    Orrillo, A Gastón; Escalante, Andrea M; Furlan, Ricardo L E

    2016-05-10

    Reversibility of dithioacetal bond formation is reported under acidic mild conditions. Its utility for dynamic combinatorial chemistry was explored by combining it with orthogonal disulfide exchange. In such a setup, thiols are positioned at the intersection of both chemistries, constituting a connecting node between temporally separated networks. PMID:26990904

  16. The Dynamics of Social Interaction in Telecollaborative Tandem Exchanges

    ERIC Educational Resources Information Center

    Janssen Sanchez, Brianna

    2015-01-01

    Using both quantitative and qualitative methods of inquiry, this dissertation study undertakes an exploration of the dynamics of the social interaction in discourse co-constructed by pairs of college students in telecollaborative tandem exchanges. Two groups of participants, Mexican learners of English as a foreign language and American learners…

  17. Combined Steady-State and Dynamic Heat Exchanger Experiment

    ERIC Educational Resources Information Center

    Luyben, William L.; Tuzla, Kemal; Bader, Paul N.

    2009-01-01

    This paper describes a heat-transfer experiment that combines steady-state analysis and dynamic control. A process-water stream is circulated through two tube-in-shell heat exchangers in series. In the first, the process water is heated by steam. In the second, it is cooled by cooling water. The equipment is pilot-plant size: heat-transfer areas…

  18. Dithioacetal Exchange: A New Reversible Reaction for Dynamic Combinatorial Chemistry.

    PubMed

    Orrillo, A Gastón; Escalante, Andrea M; Furlan, Ricardo L E

    2016-05-10

    Reversibility of dithioacetal bond formation is reported under acidic mild conditions. Its utility for dynamic combinatorial chemistry was explored by combining it with orthogonal disulfide exchange. In such a setup, thiols are positioned at the intersection of both chemistries, constituting a connecting node between temporally separated networks.

  19. Flight Dynamic Model Exchange using XML

    NASA Technical Reports Server (NTRS)

    Jackson, E. Bruce; Hildreth, Bruce L.

    2002-01-01

    The AIAA Modeling and Simulation Technical Committee has worked for several years to develop a standard by which the information needed to develop physics-based models of aircraft can be specified. The purpose of this standard is to provide a well-defined set of information, definitions, data tables and axis systems so that cooperating organizations can transfer a model from one simulation facility to another with maximum efficiency. This paper proposes using an application of the eXtensible Markup Language (XML) to implement the AIAA simulation standard. The motivation and justification for using a standard such as XML is discussed. Necessary data elements to be supported are outlined. An example of an aerodynamic model as an XML file is given. This example includes definition of independent and dependent variables for function tables, definition of key variables used to define the model, and axis systems used. The final steps necessary for implementation of the standard are presented. Software to take an XML-defined model and import/export it to/from a given simulation facility is discussed, but not demonstrated. That would be the next step in final implementation of standards for physics-based aircraft dynamic models.

  20. Computational Studies of Water-Exchange Rates around Aqueous Mg2+ and Be2+

    SciTech Connect

    Dang, Liem X.

    2014-12-18

    The water-exchange mechanisms occurring around aqueous divalent Mg2+ and Be2+ ions were studied using molecular dynamics simulations and rate theory methods. Properties associated with the water-exchange process, such as ion-water potentials of mean force, time-dependent transmission coefficients, and rate constants, were examined along with transition rate theory and the reactive flux method, which includes the role of solvent friction. The effects of pressure on water-exchange rates and activation volumes also were studied. The simulated activation volume values and mechanism were different for Mg2+ and Be2+ because of the nature of their solvation shells. We found the agreement with experiments was improved up on solvent effects were taken into account. The Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences (BES), of the U.S. Department of Energy (DOE) funded this work. Battelle operates Pacific Northwest National Laboratory for DOE. The calculations were carried out using computer resources provided by BES.

  1. Tuning the dynamic exchange interaction in ferromagnet/semiconductor heterostructures

    NASA Astrophysics Data System (ADS)

    Ou, Yu-Sheng; Chiu, Yi-Hsin; Harmon, N. J.; Odenthal, Patrick; Sheffield, Matthew; Chilcote, Michael; Kawakami, R. K.; Flatté, M. E.; Johnston-Halperin, E.

    2015-09-01

    We investigate the impact of tunnel barrier thickness on electron spin dynamics in Fe/MgO/GaAs heterostructures using spin-resolved optical pump-probe spectroscopy. Comparison of the Larmor frequency between thick and thin MgO barriers reveals a four-fold variation in exchange coupling strength, and investigation of the inhomogeneous dephasing time, T2*, argues that inhomogeneity in the local effective hyperfine field dominates free-carrier spin relaxation across the entire range of barrier thickness. These results provide additional evidence to support the theory of hyperfine-dominated spin relaxation in GaAs at low temperature and in the presence of an externally applied magnetic field. Further, this work lays the foundation for engineering both the exchange coupling and the free carrier spin dynamics in ferromagnet/semiconductor heterostructures, allowing for the exploration of dissipation and transport in the regime of dynamically-driven spin pumping.

  2. Nondiffusive mechanisms enhance protein uptake rates in ion exchange particles

    PubMed Central

    Dziennik, S. R.; Belcher, E. B.; Barker, G. A.; DeBergalis, M. J.; Fernandez, S. E.; Lenhoff, A. M.

    2003-01-01

    Scanning confocal fluorescence microscopy and multiphoton fluorescence microscopy were used to image the uptake of the protein lysozyme into individual ion exchange chromatography particles in a packed bed in real time. Self-sharpening concentration fronts penetrating into the particles were observed at low salt concentrations in all of the adsorbents studied, but persisted to 100 mM ionic strength only in some materials. In other adsorbents, diffuse profiles were seen at these higher salt concentrations, with the transition region exhibiting a pronounced fluorescence peak at the front at intermediate salt concentrations. These patterns in the uptake profiles are accompanied by significant increases in protein uptake rates that are also seen macroscopically in batch uptake experiments. The fluorescence peak appears to be a concentration overshoot that may develop, in part, from an electrokinetic contribution to transport that also enhances the uptake rate. Further evidence for an electrokinetic origin is that the effect is correlated with high adsorbent surface charge densities. Predictions of a mathematical model incorporating the electrokinetic effect are in qualitative agreement with the observations. These findings indicate that mechanisms other than diffusion contribute to protein transport in oppositely charged porous materials and may be exploited to achieve rapid uptake in process chromatography. PMID:12522150

  3. Dynamic exchange of myosin molecules between thick filaments.

    PubMed

    Saad, A D; Pardee, J D; Fischman, D A

    1986-12-01

    To examine thick filament assembly and myosin exchange, a fluorescence energy transfer assay has been established. Assembly-competent myosin molecules labeled with the sulfhydryl-specific fluorochromes 5-(2-[(iodoacetyl)-amino]ethyl)aminonaphthalene-1-sulfonic acids (IAEDANS) or 5-iodoacetamidofluorescein (IAF) were prepared. Using IAEDANS-labeled myosin as fluorescence donor and IAF-labeled myosin as acceptor, thick filament formation was followed by the decrease in donor fluorescence at 0.1 M KCl/10 mM potassium phosphate, pH 6.9. The critical concentration of myosin--i.e., that concentration that remained unassembled at equilibrium with fully formed filaments--was 40 nM. In FET and 125I-labeled myosin incorporation assays, extensive exchange of myosin between thick filaments was observed. The presence of a critical concentration and the measurements of extensive exchange suggest a dynamic equilibrium between fully polymerized myosin and a small pool of soluble myosin.

  4. Australian Universities' Strategic Goals of Student Exchange and Participation Rates in Outbound Exchange Programmes

    ERIC Educational Resources Information Center

    Daly, Amanda; Barker, Michelle

    2010-01-01

    International student exchange programmes are acknowledged as one aspect of a broader suite of internationalisation strategies aimed at enhancing students' intercultural understanding and competence. The decision to participate in an exchange programme is dependent on both individual and contextual factors such as student exchange policies and…

  5. Effect of experimental wood addition on hyporheic exchange and thermal dynamics in a losing meadow stream

    NASA Astrophysics Data System (ADS)

    Sawyer, Audrey H.; Cardenas, M. Bayani

    2012-10-01

    Stream restoration structures such as large wood can enhance shallow river-groundwater exchange, or hyporheic exchange, and alter temperature dynamics in restored reaches. We added and then removed channel-spanning logs in a second-order mountain meadow stream to test short-term impacts on hyporheic exchange, streambed temperatures, and surface water temperatures. Based on vertical seepage measurements and numerical simulations of hyporheic fluid and heat flow, large wood addition increased hyporheic exchange and altered streambed temperatures. In this losing stream, meter-scale hyporheic exchange cells formed beneath large wood. Upwelling pore water downstream of logs stabilized diel temperature cycles across <8% of the streambed, creating localized but potentially valuable thermal refuge. Exchange rates were <0.1% of channel discharge—too small to impact the range of diel temperature signals in surface water. However, the lag between downstream and upstream diel temperature signals was slightly greater with large wood, which may indicate that surface storage zones rather than hyporheic storage zones increased thermal retardation. Losing conditions limited the spatial extent and rates of hyporheic exchange near large wood. Impacts of large wood reintroduction on hyporheic exchange depend on ambient groundwater discharge or recharge, streambed permeability, channel Froude number, large wood blockage ratio, and large wood spacing. In many streams, large wood reintroduction may increase hyporheic habitat volume and complexity but may not increase exchange rates enough to alter surface water temperature or chemistry. Surface storage zones such as eddies and pools can still influence heat and solute retention in the channel.

  6. Acidity and hydrogen exchange dynamics of iron(II)-bound nitroxyl in aqueous solution.

    PubMed

    Gao, Yin; Toubaei, Abouzar; Kong, Xianqi; Wu, Gang

    2014-10-20

    Nitroxyl-iron(II) (HNO-Fe(II)) complexes are often unstable in aqueous solution, thus making them very difficult to study. Consequently, many fundamental chemical properties of Fe(II)-bound HNO have remained unknown. Using a comprehensive multinuclear ((1)H, (15)N, (17)O) NMR approach, the acidity of the Fe(II)-bound HNO in [Fe(CN)5(HNO)](3-) was investigated and its pK(a) value was determined to be greater than 11. Additionally, HNO undergoes rapid hydrogen exchange with water in aqueous solution and this exchange process is catalyzed by both acid and base. The hydrogen exchange dynamics for the Fe(II)-bound HNO have been characterized and the obtained benchmark values, when combined with the literature data on proteins, reveal that the rate of hydrogen exchange for the Fe(II)-bound HNO in the interior of globin proteins is reduced by a factor of 10(6). PMID:25205463

  7. Multifractality and value-at-risk forecasting of exchange rates

    NASA Astrophysics Data System (ADS)

    Batten, Jonathan A.; Kinateder, Harald; Wagner, Niklas

    2014-05-01

    This paper addresses market risk prediction for high frequency foreign exchange rates under nonlinear risk scaling behaviour. We use a modified version of the multifractal model of asset returns (MMAR) where trading time is represented by the series of volume ticks. Our dataset consists of 138,418 5-min round-the-clock observations of EUR/USD spot quotes and trading ticks during the period January 5, 2006 to December 31, 2007. Considering fat-tails, long-range dependence as well as scale inconsistency with the MMAR, we derive out-of-sample value-at-risk (VaR) forecasts and compare our approach to historical simulation as well as a benchmark GARCH(1,1) location-scale VaR model. Our findings underline that the multifractal properties in EUR/USD returns in fact have notable risk management implications. The MMAR approach is a parsimonious model which produces admissible VaR forecasts at the 12-h forecast horizon. For the daily horizon, the MMAR outperforms both alternatives based on conditional as well as unconditional coverage statistics.

  8. Metabolic rate, respiratory exchange ratio, and apneas during meditation.

    PubMed

    Kesterson, J; Clinch, N F

    1989-03-01

    We tested the hypothesis that a drop in metabolic rate (MR) causes the apneas observed in some subjects during transcendental meditation (TM). We measured O2 consumption (VO2) and CO2 production (VCO2) in three groups of experienced meditators and one group of nonmeditating controls. Measurements were made before, during, and after TM for the meditators and before, during, and after eyes-closed relaxation for the nonmeditating controls. The three groups of meditators consisted of 1) those showing little change in the frequency of ventilation (f) with meditation, 2) those showing a marked decline in f, and 3) those showing numerous apneas and a marked fall in f. There were significant trial effects but no group or interaction effects for the decline in VO2. Thus we concluded that a drop in MR is not the cause of the apneas. However, there were significant trial and interaction effects for the changes in VCO2 and the respiratory exchange ratio (R), with a significant drop in R for the meditators but not for the controls. We report additional evidence and speculate that the drop in R is a consequence of mild hypoventilation.

  9. Glucans monomer-exchange dynamics as an open chemical network.

    PubMed

    Rao, Riccardo; Lacoste, David; Esposito, Massimiliano

    2015-12-28

    We describe the oligosaccharides-exchange dynamics performed by the so-called D-enzymes on polysaccharides. To mimic physiological conditions, we treat this process as an open chemical network by assuming some of the polymer concentrations fixed (chemostatting). We show that three different long-time behaviors may ensue: equilibrium states, nonequilibrium steady states, and continuous growth states. We dynamically and thermodynamically characterize these states and emphasize the crucial role of conservation laws in identifying the chemostatting conditions inducing them. PMID:26723707

  10. Dynamic Line Rating: Research and Policy Evaluation

    SciTech Connect

    Jake P. Gentle; Kurt S. Myers; Michael R. West

    2014-07-01

    Dynamic Line Rating (DLR) is a smart grid technology that allows the rating of electrical conductors to be increased based on local weather conditions. Overhead lines are conventionally given a conservative rating based on worst case scenarios. We demonstrate that observing the conditions in real time leads to additional capacity and safer operation. This paper provides a report of a pioneering scheme in the United States of America in which DLR has been applied. Thereby, we demonstrate that observing the local weather conditions in real time leads to additional capacity and safer operation. Secondly, we discuss limitations involved. In doing so, we arrive at novel insights which will inform and improve future DLR projects. Third, we provide a policy background and discussion to clarify the technology’s potential and identifies barriers to the imminent adoption of dynamic line rating systems. We provide suggestions for regulatory bodies about possible improvements in policy to encourage adoption of this beneficial technology.

  11. G-register exchange dynamics in guanine quadruplexes

    PubMed Central

    Harkness, Robert W.; Mittermaier, Anthony K.

    2016-01-01

    G-quadruplexes (GQs) are 4-stranded DNA structures formed by tracts of stacked, Hoogsteen-hydrogen bonded guanosines. GQs are found in gene promoters and telomeres where they regulate gene transcription and telomere elongation. Though GQ structures are well-characterized, many aspects of their conformational dynamics are poorly understood. For example, when there are surplus guanosines in some of the tracts, they can slide with respect to one another, a process we term G-register (GR) exchange. These motions could in principle entropically stabilize the folded state, crucially benefitting GQs as their stabilities are closely tied to biological function. We have developed a method for characterizing GR exchange where each isomer in the wild-type conformational ensemble is trapped by mutation and thermal denaturation data for the set of trapped mutants and wild-type are analyzed simultaneously. This yields GR isomer populations as a function of temperature, quantifies conformational entropy and sheds light on correlated sliding motions of the G-tracts. We measured entropic stabilizations from GR exchange up to 14.3 ± 1.6 J mol−1 K−1, with melting temperature increases up to 7.3 ± 1.6°C. Furthermore, bioinformatic analysis suggests a majority of putative human GQ sequences are capable of GR exchange, pointing to the generality of this phenomenon. PMID:27060139

  12. Design and simulation of heat exchangers using Aspen HYSYS, and Aspen exchanger design and rating for paddy drying application

    NASA Astrophysics Data System (ADS)

    Janaun, J.; Kamin, N. H.; Wong, K. H.; Tham, H. J.; Kong, V. V.; Farajpourlar, M.

    2016-06-01

    Air heating unit is one of the most important parts in paddy drying to ensure the efficiency of a drying process. In addition, an optimized air heating unit does not only promise a good paddy quality, but also save more for the operating cost. This study determined the suitable and best specifications heating unit to heat air for paddy drying in the LAMB dryer. In this study, Aspen HYSYS v7.3 was used to obtain the minimum flow rate of hot water needed. The resulting data obtained from Aspen HYSYS v7.3 were used in Aspen Exchanger Design and Rating (EDR) to generate heat exchanger design and costs. The designs include shell and tubes and plate heat exchanger. The heat exchanger was designed in order to produce various drying temperatures of 40, 50, 60 and 70°C of air with different flow rate, 300, 2500 and 5000 LPM. The optimum condition for the heat exchanger were found to be plate heat exchanger with 0.6 mm plate thickness, 198.75 mm plate width, 554.8 mm plate length and 11 numbers of plates operating at 5000 LPM air flow rate.

  13. DYNACLIPS (DYNAmic CLIPS): A dynamic knowledge exchange tool for intelligent agents

    NASA Technical Reports Server (NTRS)

    Cengeloglu, Yilmaz; Khajenoori, Soheil; Linton, Darrell

    1994-01-01

    In a dynamic environment, intelligent agents must be responsive to unanticipated conditions. When such conditions occur, an intelligent agent may have to stop a previously planned and scheduled course of actions and replan, reschedule, start new activities and initiate a new problem solving process to successfully respond to the new conditions. Problems occur when an intelligent agent does not have enough knowledge to properly respond to the new situation. DYNACLIPS is an implementation of a framework for dynamic knowledge exchange among intelligent agents. Each intelligent agent is a CLIPS shell and runs a separate process under SunOS operating system. Intelligent agents can exchange facts, rules, and CLIPS commands at run time. Knowledge exchange among intelligent agents at run times does not effect execution of either sender and receiver intelligent agent. Intelligent agents can keep the knowledge temporarily or permanently. In other words, knowledge exchange among intelligent agents would allow for a form of learning to be accomplished.

  14. Water exchange dynamics around H₃O⁺ and OH⁻ ions

    SciTech Connect

    Roy, Santanu; Dang, Liem X.

    2015-05-01

    Proton transfer in water and other solvents is a complicated process and an active research area. Conformational changes of water hydrating a proton can have a significant influence on proton dynamics. A hydrated proton leads to H₃O⁺ that forms three hydrogen bonds with neighboring water molecules. In this letter, we report the first computer simulation of the dynamics of water exchanging between the first and second solvation shells of H₃O⁺. Employing different rate theories for chemical reactions such as the transition state theory, the Grote-Hynes theory, the reactive flux method, and the Impey-Madden-McDonald method, we calculate the solvent exchange rates from molecular dynamics simulations that account for explicit polarization effects. In addition, we also study water exchanges around OH⁻ and find that the corresponding time scale (~50 picoseconds [ps]) is much smaller than that for H₃O⁺ (~100 ps). Results from all the rate theories are computed and compared. This work was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. The calculations were carried out using computer resources provided by the Office of Basic Energy Sciences.

  15. Dynamic communities in multichannel data: An application to the foreign exchange market during the 2007-2008 credit crisis

    NASA Astrophysics Data System (ADS)

    Fenn, Daniel J.; Porter, Mason A.; McDonald, Mark; Williams, Stacy; Johnson, Neil F.; Jones, Nick S.

    2009-09-01

    We study the cluster dynamics of multichannel (multivariate) time series by representing their correlations as time-dependent networks and investigating the evolution of network communities. We employ a node-centric approach that allows us to track the effects of the community evolution on the functional roles of individual nodes without having to track entire communities. As an example, we consider a foreign exchange market network in which each node represents an exchange rate and each edge represents a time-dependent correlation between the rates. We study the period 2005-2008, which includes the recent credit and liquidity crisis. Using community detection, we find that exchange rates that are strongly attached to their community are persistently grouped with the same set of rates, whereas exchange rates that are important for the transfer of information tend to be positioned on the edges of communities. Our analysis successfully uncovers major trading changes that occurred in the market during the credit crisis.

  16. Dynamics of Chain Exchange in Block Copolymer Micelles

    NASA Astrophysics Data System (ADS)

    Lodge, Timothy

    Block copolymer micelles are rarely at equilibrium. The primary reason is the large number of repeat units in the insoluble block, Ncore, which makes the thermodynamic penalty for extracting a single chain (``unimer exchange'') substantial. As a consequence, the critical micelle concentration (CMC) is rarely accessed experimentally; however, in the proximity of a critical micelle temperature (CMT), equilibration is possible. We have been using time-resolved small angle neutron scattering (TR-SANS) to obtain a detailed picture of the mechanisms and time scales for chain exchange, at or near equilibrium. Our model system is poly(styrene)-block-poly(ethylene-alt-propylene)) (PS-PEP), in the PEP-selective solvent squalane (C30H62) . Equivalent micelles with either normal (hPS) or perdeuterated (dPS) cores are initially mixed in a blend of isotopically substituted squalane, designed to contrast-match a 50:50 hPS:dPS core. Samples are then annealed at a target temperature, and chain exchange is revealed quantitatively by the temporal decay in scattered intensity. The rate of exchange as function of concentration, temperature, Ncore, Ncorona, and chain architecture (diblock versus triblock) will be discussed.

  17. Quantitative chemical exchange saturation transfer with hyperpolarized nuclei (qHyper-CEST): Sensing xenon-host exchange dynamics and binding affinities by NMR

    SciTech Connect

    Kunth, M. Witte, C.; Schröder, L.

    2014-11-21

    The reversible binding of xenon to host molecules has found numerous applications in nuclear magnetic resonance studies. Quantitative characterization of the Xe exchange dynamics is important to understand and optimize the physico-chemical behavior of such Xe hosts, but is often challenging to achieve at low host concentrations. We have investigated a sensitive quantification technique based on chemical exchange saturation transfer with hyperpolarized nuclei, qHyper-CEST. Using simulated signals we demonstrated that qHyper-CEST yielded accurate and precise results and was robust in the presence of large amounts of noise (10%). This is of particular importance for samples with completely unknown exchange rates. Using these findings we experimentally determined the following exchange parameters for the Xe host cryptophane-A monoacid in dimethyl sulfoxide in one type of experiment: the ratio of bound and free Xe, the Xe exchange rate, the resonance frequencies of free and bound Xe, the Xe host occupancy, and the Xe binding constant. Taken together, qHyper-CEST facilitates sensitive quantification of the Xe exchange dynamics and binding to hydrophobic cavities and has the potential to analyze many different host systems or binding sites. This makes qHyper-CEST an indispensable tool for the efficient design of highly specific biosensors.

  18. Biased Brownian dynamics for rate constant calculation.

    PubMed

    Zou, G; Skeel, R D; Subramaniam, S

    2000-08-01

    An enhanced sampling method-biased Brownian dynamics-is developed for the calculation of diffusion-limited biomolecular association reaction rates with high energy or entropy barriers. Biased Brownian dynamics introduces a biasing force in addition to the electrostatic force between the reactants, and it associates a probability weight with each trajectory. A simulation loses weight when movement is along the biasing force and gains weight when movement is against the biasing force. The sampling of trajectories is then biased, but the sampling is unbiased when the trajectory outcomes are multiplied by their weights. With a suitable choice of the biasing force, more reacted trajectories are sampled. As a consequence, the variance of the estimate is reduced. In our test case, biased Brownian dynamics gives a sevenfold improvement in central processing unit (CPU) time with the choice of a simple centripetal biasing force.

  19. Biased Brownian dynamics for rate constant calculation.

    PubMed

    Zou, G; Skeel, R D; Subramaniam, S

    2000-08-01

    An enhanced sampling method-biased Brownian dynamics-is developed for the calculation of diffusion-limited biomolecular association reaction rates with high energy or entropy barriers. Biased Brownian dynamics introduces a biasing force in addition to the electrostatic force between the reactants, and it associates a probability weight with each trajectory. A simulation loses weight when movement is along the biasing force and gains weight when movement is against the biasing force. The sampling of trajectories is then biased, but the sampling is unbiased when the trajectory outcomes are multiplied by their weights. With a suitable choice of the biasing force, more reacted trajectories are sampled. As a consequence, the variance of the estimate is reduced. In our test case, biased Brownian dynamics gives a sevenfold improvement in central processing unit (CPU) time with the choice of a simple centripetal biasing force. PMID:10919998

  20. Review of Air Exchange Rate Models for Air Pollution Exposure Assessments

    EPA Science Inventory

    A critical aspect of air pollution exposure assessments is estimation of the air exchange rate (AER) for various buildings, where people spend their time. The AER, which is rate the exchange of indoor air with outdoor air, is an important determinant for entry of outdoor air pol...

  1. Heterogeneous effects of oil shocks on exchange rates: evidence from a quantile regression approach.

    PubMed

    Su, Xianfang; Zhu, Huiming; You, Wanhai; Ren, Yinghua

    2016-01-01

    The determinants of exchange rates have attracted considerable attention among researchers over the past several decades. Most studies, however, ignore the possibility that the impact of oil shocks on exchange rates could vary across the exchange rate returns distribution. We employ a quantile regression approach to address this issue. Our results indicate that the effect of oil shocks on exchange rates is heterogeneous across quantiles. A large US depreciation or appreciation tends to heighten the effects of oil shocks on exchange rate returns. Positive oil demand shocks lead to appreciation pressures in oil-exporting countries and this result is robust across lower and upper return distributions. These results offer rich and useful information for investors and decision-makers. PMID:27516925

  2. Heterogeneous effects of oil shocks on exchange rates: evidence from a quantile regression approach.

    PubMed

    Su, Xianfang; Zhu, Huiming; You, Wanhai; Ren, Yinghua

    2016-01-01

    The determinants of exchange rates have attracted considerable attention among researchers over the past several decades. Most studies, however, ignore the possibility that the impact of oil shocks on exchange rates could vary across the exchange rate returns distribution. We employ a quantile regression approach to address this issue. Our results indicate that the effect of oil shocks on exchange rates is heterogeneous across quantiles. A large US depreciation or appreciation tends to heighten the effects of oil shocks on exchange rate returns. Positive oil demand shocks lead to appreciation pressures in oil-exporting countries and this result is robust across lower and upper return distributions. These results offer rich and useful information for investors and decision-makers.

  3. TIREX: Replica-exchange molecular dynamics using TINKER

    NASA Astrophysics Data System (ADS)

    Penev, Evgeni S.; Lampoudi, Sotiria; Shea, Joan-Emma

    2009-10-01

    We present a driver program for performing replica-exchange molecular dynamics simulations with the TINKER package. Parallelization is based on the Message Passing Interface, with every replica assigned to a separate process. The algorithm is not communication intensive, which makes the program suitable for running even on loosely coupled cluster systems. Particular attention is paid to the practical aspects of analyzing the program output. Program summaryProgram title: TiReX Catalogue identifier: AEEK_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEEK_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 43 385 No. of bytes in distributed program, including test data, etc.: 502 262 Distribution format: tar.gz Programming language: Fortran 90/95 Computer: Most UNIX machines Operating system: Linux Has the code been vectorized or parallelized?: parallelized with MPI Classification: 16.13 External routines: TINKER version 4.2 or 5.0, built as a library Nature of problem: Replica-exchange molecular dynamics. Solution method: Each replica is assigned to a separate process; temperatures are swapped between replicas at regular time intervals. Running time: The sample run may take up to a few minutes.

  4. The simultaneous measurement of low rates of CO2 and O2 exchange in biological systems.

    PubMed

    Willms, J R; Dowling, A N; Dong, Z M; Hunt, S; Shelp, B J; Layzell, D B

    1997-12-15

    An instrument for measuring low rates of biological O2 exchange using an open-flow gas analysis system is described. A novel differential O2 sensor that is capable of measuring as little as 0.4 Pa O2 against a back-ground of ambient air (20,900 Pa O2), yet has a dynamic range of +/- 2000 Pa O2 (i.e., +/- ca. 2% O2) is described. Baseline drift was typically less than 0.025 Pa min-1. The differential O2 sensor was incorporated into a respiratory quotient/photosynthetic quotient analyzer that contained other environmental sensors for atmospheric pressure, absolute O2 and CO2 concentration, temperature of the differential O2 sensor block, and differential pressure between reference and sample streams. Protocols for how these sensors can be used to calibrate the differential O2 sensor and to improve its stability with time are described. Together, the differential O2 sensor, the environmental sensors, and the simple calibration techniques allow for simultaneous, noninvasive, and accurate measurements of O2 and CO2 exchange in tissues with metabolic rates as low as about 0.1 mumol O2 or CO2 h-1. Example data are provided in which O2 differentials of 3 to 41 Pa O2 were measured in an open-flow system. PMID:9417789

  5. Extinction rate fragility in population dynamics.

    PubMed

    Khasin, M; Dykman, M I

    2009-08-01

    Population extinction is of central interest for population dynamics. It may occur from a large rare fluctuation. We find that, in contrast to related large-fluctuation effects like noise-induced interstate switching, quite generally extinction rates in multipopulation systems display fragility, where the height of the effective barrier to be overcome in the fluctuation depends on the system parameters nonanalytically. We show that one of the best-known models of epidemiology, the susceptible-infectious-susceptible model, is fragile to total population fluctuations.

  6. Wealth distribution of simple exchange models coupled with extremal dynamics

    NASA Astrophysics Data System (ADS)

    Bagatella-Flores, N.; Rodríguez-Achach, M.; Coronel-Brizio, H. F.; Hernández-Montoya, A. R.

    2015-01-01

    Punctuated Equilibrium (PE) states that after long periods of evolutionary quiescence, species evolution can take place in short time intervals, where sudden differentiation makes new species emerge and some species extinct. In this paper, we introduce and study the effect of punctuated equilibrium on two different asset exchange models: the yard sale model (YS, winner gets a random fraction of a poorer player's wealth) and the theft and fraud model (TF, winner gets a random fraction of the loser's wealth). The resulting wealth distribution is characterized using the Gini index. In order to do this, we consider PE as a perturbation with probability ρ of being applied. We compare the resulting values of the Gini index at different increasing values of ρ in both models. We found that in the case of the TF model, the Gini index reduces as the perturbation ρ increases, not showing dependence with the agents number. While for YS we observe a phase transition which happens around ρc = 0.79. For perturbations ρ <ρc the Gini index reaches the value of one as time increases (an extreme wealth condensation state), whereas for perturbations greater than or equal to ρc the Gini index becomes different to one, avoiding the system reaches this extreme state. We show that both simple exchange models coupled with PE dynamics give more realistic results. In particular for YS, we observe a power low decay of wealth distribution.

  7. Dynamic Group Diffie-Hellman Key Exchange under standard assumptions

    SciTech Connect

    Bresson, Emmanuel; Chevassut, Olivier; Pointcheval, David

    2002-02-14

    Authenticated Diffie-Hellman key exchange allows two principals communicating over a public network, and each holding public-private keys, to agree on a shared secret value. In this paper we study the natural extension of this cryptographic problem to a group of principals. We begin from existing formal security models and refine them to incorporate major missing details (e.g., strong-corruption and concurrent sessions). Within this model we define the execution of a protocol for authenticated dynamic group Diffie-Hellman and show that it is provably secure under the decisional Diffie-Hellman assumption. Our security result holds in the standard model and thus provides better security guarantees than previously published results in the random oracle model.

  8. Seasonal soil VOC exchange rates in a Mediterranean holm oak forest and their responses to drought conditions

    NASA Astrophysics Data System (ADS)

    Asensio, Dolores; Peñuelas, Josep; Ogaya, Romà; Llusià, Joan

    Available information on soil volatile organic compound (VOC) exchange, emissions and uptake, is very scarce. We here describe the amounts and seasonality of soil VOC exchange during a year in a natural Mediterranean holm oak forest growing in Southern Catalonia. We investigated changes in soil VOC dynamics in drought conditions by decreasing the soil moisture to 30% of ambient conditions by artificially excluding rainfall and water runoff, and predicted the response of VOC exchange to the drought forecasted in the Mediterranean region for the next decades by GCM and ecophysiological models. The annual average of the total (detected) soil VOC and total monoterpene exchange rates were 3.2±3.2 and -0.4±0.3 μg m -2 h -1, respectively, in control plots. These values represent 0.003% of the total C emitted by soil at the study site as CO 2 whereas the annual mean of soil monoterpene exchange represents 0.0004% of total C. Total soil VOC exchange rates in control plots showed seasonal variations following changes in soil moisture and phenology. Maximum values were found in spring (17±8 μg m -2 h -1). Although there was no significant global effect of drought treatment on the total soil VOC exchange rates, annual average of total VOC exchange rates in drought plots resulted in an uptake rate (-0.5±1.8 μg m -2 h -1) instead of positive net emission rates. Larger soil VOC and monoterpene exchanges were measured in drought plots than in control plots in summer, which might be mostly attributable to autotrophic (roots) metabolism. The results show that the diversity and magnitude of monoterpene and VOC soil emissions are low compared with plant emissions, that they are driven by soil moisture, that they represent a very small part of the soil-released carbon and that they may be strongly reduced or even reversed into net uptakes by the predicted decreases of soil water availability in the next decades. In all cases, it seems that VOC fluxes in soil might have greater

  9. TIME-VARYING DYNAMICAL STAR FORMATION RATE

    SciTech Connect

    Lee, Eve J.; Chang, Philip; Murray, Norman

    2015-02-10

    We present numerical evidence of dynamic star formation in which the accreted stellar mass grows superlinearly with time, roughly as t {sup 2}. We perform simulations of star formation in self-gravitating hydrodynamic and magnetohydrodynamic turbulence that is continuously driven. By turning the self-gravity of the gas in the simulations on or off, we demonstrate that self-gravity is the dominant physical effect setting the mass accretion rate at early times before feedback effects take over, contrary to theories of turbulence-regulated star formation. We find that gravitational collapse steepens the density profile around stars, generating the power-law tail on what is otherwise a lognormal density probability distribution function. Furthermore, we find turbulent velocity profiles to flatten inside collapsing regions, altering the size-line width relation. This local flattening reflects enhancements of turbulent velocity on small scales, as verified by changes to the velocity power spectra. Our results indicate that gas self-gravity dynamically alters both density and velocity structures in clouds, giving rise to a time-varying star formation rate. We find that a substantial fraction of the gas that forms stars arrives via low-density flows, as opposed to accreting through high-density filaments.

  10. Automatable Measurement of Gas Exchange Rate in Streams: Oxygen-Carbon Method

    NASA Astrophysics Data System (ADS)

    Pennington, R.; Haggerty, R.; Argerich, A.; Wondzell, S. M.

    2015-12-01

    Gas exchange rates between streams and the atmosphere are critically important to measurement of in-stream ecologic processes, as well as fate and transport of hazardous pollutants such as mercury and PCBs. Methods to estimate gas exchange rates include empirical relations to hydraulics, and direct injection of a tracer gas such as propane or SF6. Empirical relations are inconsistent and inaccurate, particularly for lower order, high-roughness streams. Gas injections are labor-intensive, and measured gas exchange rates are difficult to extrapolate in time since they change with discharge and stream geometry. We propose a novel method for calculation of gas exchange rates utilizing O2, pCO2, pH, and temperature data. Measurements, which can be automated using data loggers and probes, are made on the upstream and downstream end of the study reach. Gas exchange rates are then calculated from a solution to the transport equations for oxygen and dissolved inorganic carbon. Field tests in steep, low order, high roughness streams of the HJ Andrews Experimental Forest indicate the method to be viable along stream reaches with high downstream gas concentration gradients and high rates of gas transfer velocity. Automated and continuous collection of oxygen and carbonate chemistry data is increasingly common, thus the method may be used to estimate gas exchange rates through time, and is well suited for interactivity with databases.

  11. The evolutionary synchronization of the exchange rate system in ASEAN+6

    NASA Astrophysics Data System (ADS)

    Feng, Xiaobing; Hu, Haibo; Wang, Xiaofan

    2010-12-01

    Although there are extensive researches on the behavior of the world currency network, the complexity of the Asian regional currency system is not well understood regardless of its importance. Using daily exchange rates this paper examines exchange rate co-movements in the region before and after the China exchange rate reform. It was found that the correlation between Asian currencies and the US Dollar, the previous regional key currency has become weaker and intra-Asia interactions have increased. Cross sample entropy and cross entropy approaches are also applied to examine the synchrony behavior among the Asian currencies. The study also shows that the Asian exchange rate markets featured are neither stochastic nor efficient. These findings may shed some light on the in-depth understanding of collective behaviors in a regional currency network; they will also lay a theoretical foundation for further policy formulation in Asian currency integration.

  12. Gas exchange rates of potato stands for bioregenerative life support

    NASA Astrophysics Data System (ADS)

    Wheeler, Raymond M.; Stutte, Gary W.; Mackowiak, Cheryl L.; Yorio, Neil C.; Sager, John C.; Knott, William M.

    Plants can provide a means for removing carbon dioxide (CO2) while generating oxygen (O2) and clean water for life support systems in space. To study this, 20 m2 stands of potato (Solanum tuberosum L.) plants were grown in a large (113 m3 vol.), atmospherically closed chamber. Photosynthetic uptake of CO2 by the stands was detected about 10 DAP (days after planting), after which photosynthetic rates rose rapidly as stand ground cover and total light interception increased. Photosynthetic rates peaked ca. 50 DAP near 45 μmol CO2 m-2 s-1 under 865 μmol m-2 s-1 PPF (average photosynthetic photon flux), and near 35 μmol CO2 m-2 s-1 under 655 μmol m-2 s-1 PPF. Short term changes in PPF caused a linear response in stand photosynthetic rates up to 1100 μmol m-2 s-1 PPF, with a light compensation point of 185 μmol m-2 s-1 PPF. Comparisons of stand photosynthetic rates at different CO2 concentrations showed a classic C3 response, with saturation occurring near 1200 μmol mol-1 CO2 and compensation near 100 μmol mol-1 CO2. In one study, the photoperiod was changed from 12 h light/12 h dark to continuous light at 58 DAP. This caused a decrease in net photosynthetic rates within 48 h and eventual damage (scorching) of upper canopy leaves, suggesting the abrupt change stressed the plants and/or caused feedback effects on photosynthesis. Dark period (night) respiration rates increased during early growth as standing biomass increased and peaked near 9 μmol CO2 m-2 s-1 ca. 50 DAP, after which rates declined gradually with age. Stand transpiration showed a rapid rise with canopy ground cover and peaked ca. 50 DAP near 8.9 L m-2 d-1 under 860 μmol m-2 s-1 PPF and near 6.3 L m-2 d-1 under 650 μmol m-2 s-1 PPF. Based on the best photosynthetic rates from these studies, approximately 25 m2 of potato plants under continuous cultivation would be required to support the CO2 removal and O2 requirements for one person.

  13. PEE-PEO block copolymer exchange rate between micelles is detergent and temperature activated

    NASA Astrophysics Data System (ADS)

    Schantz, Allen; Saboe, Patrick; Lee, Hee-Young; Sines, Ian; Butler, Paul; Bishop, Kyle; Maranas, Janna; Kumar, Manish

    We examine the kinetics of polymer chain exchange between polymer/detergent micelles, a system relevant to the synthesis of protein-containing biomimetic membranes. Although chain exchange between polymer aggregates in water is too slow to observe, adding detergent allows us to determine chain exchange rates using time-resolved small-angle neutron scattering (TR-SANS). We examine a membrane-protein-relevant, vesicle-forming ultra-short polymer, Poly(ethyl ethylene)20-Poly(ethylene oxide)18 (PEE20-PEO18). PEE20-PEO18 is solubilized in mixed micelles with the membrane-protein-compatible non-ionic detergent octyl- β -D-glucoside (OG). We show that OG activates block copolymer exchange, and obtain rate constants at two detergent concentrations above the CMC (critical micellar concentration) of OG. We find that chain exchange increases two orders of magnitude when temperature increases from 308 to 338 K, and that even a 1 mg/mL increase in OG concentration leads to a noticeable increase in exchange rate. We also calculate the activation energy for chain exchange and find that it is much higher than for lipid exchange. These findings explain the need for high detergent concentration and/or temperature to synthesize densely packed polymer/protein membranes.

  14. Trade balance instability and the optimal exchange rate regime: The case of OPEC countries

    SciTech Connect

    Aljerrah, M.A.

    1993-01-01

    The OPEC members have experienced wide fluctuations in their trade balances. This can be attributed to several factors: (1) heavy dependence of national income and export earnings on a single primary export-oil; (2) instability of price and world demand for oil; and (3) the exchange rate regime practiced in recent years. An exchange rate policy can be used to minimize the fluctuations in trade balance, given the changes in exchange rates of major international currencies. The purpose of this study is two fold; first, examine the effects of fluctuations in trade balance on the OPEC economies, and second, propose appropriate exchange rate regime for selected OPEC members. The study is divided into two parts. The first part demonstrates the impact of trade balance changes on national income and other macroeconomic variables using a Keynesian framework. The second part involves using conventional trade models to search for the appropriate exchange rate regime to minimize the fluctuations in trade balance of each selective country. The study's findings are: first, fluctuations in trade balances had negative effects on the economics of Algeria, Kuwait, Libya, Saudi Arabia, and the United Arab Emirates. Second, the current exchange rate regime of no sample country is optimal in minimizing trade balance fluctuations. Third, in contrast to expectations, U.S. dollar peg did not stabilize the trade balance of any OPEC member. Finally, the results show that the sample OPEC economies could have enjoyed faster - though with different degree - economic growth if they had pegged their currencies to the derived optimal exchange rate regime. These optimal exchange rate regimes are: the SDR for Algeria and the United Arab Emirates, the purchasing power parity for Libya and Saudi Arabia, and the real Yen for Kuwait.

  15. Exchange and redistribution dynamics of the cytoskeleton of the active zone molecule bassoon.

    PubMed

    Tsuriel, Shlomo; Fisher, Arava; Wittenmayer, Nina; Dresbach, Thomas; Garner, Craig C; Ziv, Noam E

    2009-01-14

    Presynaptic sites typically appear as varicosities (boutons) distributed along axons. Ultrastructurally, presynaptic boutons lack obvious physical barriers that separate them from the axon proper, yet activity-related and constitutive dynamics continuously promote the "reshuffling" of presynaptic components and even their dispersal into flanking axonal segments. How presynaptic sites manage to maintain their organization and individual characteristics over long durations is thus unclear. Conceivably, presynaptic tenacity might depend on the active zone (AZ), an electron-dense specialization of the presynaptic membrane, and particularly on the cytoskeletal matrix associated with the AZ (CAZ) that could act as a relatively stable "core scaffold" that conserves and dictates presynaptic organization. At present, however, little is known on the molecular dynamics of CAZ molecules, and thus, the factual basis for this hypothesis remains unclear. To examine the stability of the CAZ, we studied the molecular dynamics of the major CAZ molecule Bassoon in cultured hippocampal neurons. Fluorescence recovery after photobleaching and photoactivation experiments revealed that exchange rates of green fluorescent protein and photoactivatable green fluorescent protein-tagged Bassoon at individual presynaptic sites are very low (tau > 8 h). Exchange rates varied between boutons and were only slightly accelerated by stimulation. Interestingly, photoactivation experiments revealed that Bassoon lost from one synapse was occasionally assimilated into neighboring presynaptic sites. Our findings indicate that Bassoon is engaged in relatively stable associations within the CAZ and thus support the notion that the CAZ or some of its components might constitute a relatively stable presynaptic core scaffold.

  16. MDMS: Molecular Dynamics Meta-Simulator for evaluating exchange type sampling methods.

    PubMed

    Smith, Daniel B; Okur, Asim; Brooks, Bernard

    2012-08-30

    Replica exchange methods have become popular tools to explore conformational space for small proteins. For larger biological systems, even with enhanced sampling methods, exploring the free energy landscape remains computationally challenging. This problem has led to the development of many improved replica exchange methods. Unfortunately, testing these methods remains expensive. We propose a Molecular Dynamics Meta-Simulator (MDMS) based on transition state theory to simulate a replica exchange simulation, eliminating the need to run explicit dynamics between exchange attempts. MDMS simulations allow for rapid testing of new replica exchange based methods, greatly reducing the amount of time needed for new method development.

  17. Multifractal analysis of managed and independent float exchange rates

    NASA Astrophysics Data System (ADS)

    Stošić, Darko; Stošić, Dusan; Stošić, Tatijana; Stanley, H. Eugene

    2015-06-01

    We investigate multifractal properties of daily price changes in currency rates using the multifractal detrended fluctuation analysis (MF-DFA). We analyze managed and independent floating currency rates in eight countries, and determine the changes in multifractal spectrum when transitioning between the two regimes. We find that after the transition from managed to independent float regime the changes in multifractal spectrum (position of maximum and width) indicate an increase in market efficiency. The observed changes are more pronounced for developed countries that have a well established trading market. After shuffling the series, we find that the multifractality is due to both probability density function and long term correlations for managed float regime, while for independent float regime multifractality is in most cases caused by broad probability density function.

  18. Rate theory of solvent exchange and kinetics of Li+ - BF4-/PF6- ion pairs in acetonitrile

    NASA Astrophysics Data System (ADS)

    Dang, Liem X.; Chang, Tsun-Mei

    2016-09-01

    In this paper, we describe our efforts to apply rate theories in studies of solvent exchange around Li+ and the kinetics of ion pairings in lithium-ion batteries (LIBs). We report one of the first computer simulations of the exchange dynamics around solvated Li+ in acetonitrile (ACN), which is a common solvent used in LIBs. We also provide details of the ion-pairing kinetics of Li+-[BF4] and Li+-[PF6] in ACN. Using our polarizable force-field models and employing classical rate theories of chemical reactions, we examine the ACN exchange process between the first and second solvation shells around Li+. We calculate exchange rates using transition state theory and weighted them with the transmission coefficients determined by the reactive flux, Impey, Madden, and McDonald approaches, and Grote-Hynes theory. We found the relaxation times changed from 180 ps to 4600 ps and from 30 ps to 280 ps for Li+-[BF4] and Li+-[PF6] ion pairs, respectively. These results confirm that the solvent response to the kinetics of ion pairing is significant. Our results also show that, in addition to affecting the free energy of solvation into ACN, the anion type also should significantly influence the kinetics of ion pairing. These results will increase our understanding of the thermodynamic and kinetic properties of LIB systems.

  19. Rate theory of solvent exchange and kinetics of Li(+) - BF4 (-)/PF6 (-) ion pairs in acetonitrile.

    PubMed

    Dang, Liem X; Chang, Tsun-Mei

    2016-09-01

    In this paper, we describe our efforts to apply rate theories in studies of solvent exchange around Li(+) and the kinetics of ion pairings in lithium-ion batteries (LIBs). We report one of the first computer simulations of the exchange dynamics around solvated Li(+) in acetonitrile (ACN), which is a common solvent used in LIBs. We also provide details of the ion-pairing kinetics of Li(+)-[BF4] and Li(+)-[PF6] in ACN. Using our polarizable force-field models and employing classical rate theories of chemical reactions, we examine the ACN exchange process between the first and second solvation shells around Li(+). We calculate exchange rates using transition state theory and weighted them with the transmission coefficients determined by the reactive flux, Impey, Madden, and McDonald approaches, and Grote-Hynes theory. We found the relaxation times changed from 180 ps to 4600 ps and from 30 ps to 280 ps for Li(+)-[BF4] and Li(+)-[PF6] ion pairs, respectively. These results confirm that the solvent response to the kinetics of ion pairing is significant. Our results also show that, in addition to affecting the free energy of solvation into ACN, the anion type also should significantly influence the kinetics of ion pairing. These results will increase our understanding of the thermodynamic and kinetic properties of LIB systems.

  20. Rate theory of solvent exchange and kinetics of Li(+) - BF4 (-)/PF6 (-) ion pairs in acetonitrile.

    PubMed

    Dang, Liem X; Chang, Tsun-Mei

    2016-09-01

    In this paper, we describe our efforts to apply rate theories in studies of solvent exchange around Li(+) and the kinetics of ion pairings in lithium-ion batteries (LIBs). We report one of the first computer simulations of the exchange dynamics around solvated Li(+) in acetonitrile (ACN), which is a common solvent used in LIBs. We also provide details of the ion-pairing kinetics of Li(+)-[BF4] and Li(+)-[PF6] in ACN. Using our polarizable force-field models and employing classical rate theories of chemical reactions, we examine the ACN exchange process between the first and second solvation shells around Li(+). We calculate exchange rates using transition state theory and weighted them with the transmission coefficients determined by the reactive flux, Impey, Madden, and McDonald approaches, and Grote-Hynes theory. We found the relaxation times changed from 180 ps to 4600 ps and from 30 ps to 280 ps for Li(+)-[BF4] and Li(+)-[PF6] ion pairs, respectively. These results confirm that the solvent response to the kinetics of ion pairing is significant. Our results also show that, in addition to affecting the free energy of solvation into ACN, the anion type also should significantly influence the kinetics of ion pairing. These results will increase our understanding of the thermodynamic and kinetic properties of LIB systems. PMID:27608999

  1. Forecasting of magnitude and duration of currency crises based on the analysis of distortions of fractal scaling in exchange rate fluctuations

    NASA Astrophysics Data System (ADS)

    Uritskaya, Olga Y.

    2005-05-01

    Results of fractal stability analysis of daily exchange rate fluctuations of more than 30 floating currencies for a 10-year period are presented. It is shown for the first time that small- and large-scale dynamical instabilities of national monetary systems correlate with deviations of the detrended fluctuation analysis (DFA) exponent from the value 1.5 predicted by the efficient market hypothesis. The observed dependence is used for classification of long-term stability of floating exchange rates as well as for revealing various forms of distortion of stable currency dynamics prior to large-scale crises. A normal range of DFA exponents consistent with crisis-free long-term exchange rate fluctuations is determined, and several typical scenarios of unstable currency dynamics with DFA exponents fluctuating beyond the normal range are identified. It is shown that monetary crashes are usually preceded by prolonged periods of abnormal (decreased or increased) DFA exponent, with the after-crash exponent tending to the value 1.5 indicating a more reliable exchange rate dynamics. Statistically significant regression relations (R=0.99, p<0.01) between duration and magnitude of currency crises and the degree of distortion of monofractal patterns of exchange rate dynamics are found. It is demonstrated that the parameters of these relations characterizing small- and large-scale crises are nearly equal, which implies a common instability mechanism underlying these events. The obtained dependences have been used as a basic ingredient of a forecasting technique which provided correct in-sample predictions of monetary crisis magnitude and duration over various time scales. The developed technique can be recommended for real-time monitoring of dynamical stability of floating exchange rate systems and creating advanced early-warning-system models for currency crisis prevention.

  2. Experimental studies of alunite: II. Rates of alunite-water alkali and isotope exchange

    USGS Publications Warehouse

    Stoffregen, R.E.; Rye, R.O.; Wasserman, M.D.

    1994-01-01

    Rates of alkali exchange between alunite and water have been measured in hydrothermal experiments of 1 hour to 259 days duration at 150 to 400??C. Examination of run products by scanning electron microscope indicates that the reaction takes place by dissolution-reprecipitation. This exchange is modeled with an empirical rate equation which assumes a linear decrease in mineral surface area with percent exchange (f) and a linear dependence of the rate on the square root of the affinity for the alkali exchange reaction. This equation provides a good fit of the experimental data for f = 17% to 90% and yields log rate constants which range from -6.25 moles alkali m-2s-1 at 400??C to - 11.7 moles alkali m-2s-1 at 200??C. The variation in these rates with temperature is given by the equation log k* = -8.17(1000/T(K)) + 5.54 (r2 = 0.987) which yields an activation energy of 37.4 ?? 1.5 kcal/mol. For comparison, data from O'Neil and Taylor (1967) and Merigoux (1968) modeled with a pseudo-second-order rate expression give an activation energy of 36.1 ?? 2.9 kcal/mol for alkali-feldspar water Na-K exchange. In the absence of coupled alkali exchange, oxygen isotope exchange between alunite and water also occurs by dissolution-reprecipitation but rates are one to three orders of magnitude lower than those for alkali exchange. In fine-grained alunites, significant D-H exchange occurs by hydrogen diffusion at temperatures as low as 100??C. Computed hydrogen diffusion coefficients range from -15.7 to -17.3 cm2s-1 and suggest that the activation energy for hydrogen diffusion may be as low as 6 kcal/mol. These experiments indicate that rates of alkali exchange in the relatively coarse-grained alunites typical of hydrothermal ore deposits are insignificant, and support the reliability of K-Ar age data from such samples. However, the fine-grained alunites typical of low temperature settings may be susceptible to limited alkali exchange at surficial conditions which could cause

  3. Dynamics of compressible air flow in ducts with heat exchange

    NASA Astrophysics Data System (ADS)

    Abdulhadi, M.

    1986-12-01

    An investigation into the effect of heat addition on subsonic flow of an air stream in a constant-area duct preceded by a convergent nozzle is carried out. A nozzle flow apparatus with a heat exchanger encasing the constant-area duct has been built for this purpose. Hot water is provided from an electric boiler where the flow rate and the in-flow hot water temperature could be controlled. It is confirmed experimentally, as predicted analytically, that heat transfer to the gas decreases its local static pressure along the duct axis, and that this decrease is associated with an increase in Mach number toward M = 1 at the exit (thermal choking). In the case of subsonic flow, the additional entropy generated by the heat interaction exceeding the amount that produces thermal choking can only be accommodated by moving to a new Rayleigh line, at a decreased flow rate which lowers the inlet Mach number. The good correlation between the experimental results and the analytical derivations illustrates that the experimental arrangement has potential for further experiments and investigations.

  4. Computational fluid dynamics modeling of proton exchange membrane fuel cells

    SciTech Connect

    UM,SUKKEE; WANG,C.Y.; CHEN,KEN S.

    2000-02-11

    A transient, multi-dimensional model has been developed to simulate proton exchange membrane (PEM) fuel cells. The model accounts simultaneously for electrochemical kinetics, current distribution, hydrodynamics and multi-component transport. A single set of conservation equations valid for flow channels, gas-diffusion electrodes, catalyst layers and the membrane region are developed and numerically solved using a finite-volume-based computational fluid dynamics (CFD) technique. The numerical model is validated against published experimental data with good agreement. Subsequently, the model is applied to explore hydrogen dilution effects in the anode feed. The predicted polarization cubes under hydrogen dilution conditions are found to be in qualitative agreement with recent experiments reported in the literature. The detailed two-dimensional electrochemical and flow/transport simulations further reveal that in the presence of hydrogen dilution in the fuel stream, hydrogen is depleted at the reaction surface resulting in substantial kinetic polarization and hence a lower current density that is limited by hydrogen transport from the fuel stream to the reaction site.

  5. Antipersistent dynamics in kinetic models of wealth exchange

    NASA Astrophysics Data System (ADS)

    Goswami, Sanchari; Chatterjee, Arnab; Sen, Parongama

    2011-11-01

    We investigate the detailed dynamics of gains and losses made by agents in some kinetic models of wealth exchange. An earlier work suggested that a walk in an abstract gain-loss space can be conceived for the agents. For models in which agents do not save, or save with uniform saving propensity, the walk has diffusive behavior. For the case in which the saving propensity λ is distributed randomly (0≤λ<1), the resultant walk showed a ballistic nature (except at a particular value of λ*≈0.47). Here we consider several other features of the walk with random λ. While some macroscopic properties of this walk are comparable to a biased random walk, at microscopic level, there are gross differences. The difference turns out to be due to an antipersistent tendency toward making a gain (loss) immediately after making a loss (gain). This correlation is in fact present in kinetic models without saving or with uniform saving as well, such that the corresponding walks are not identical to ordinary random walks. In the distributed saving case, antipersistence occurs with a simultaneous overall bias.

  6. Optimization of replica exchange molecular dynamics by fast mimicking.

    PubMed

    Hritz, Jozef; Oostenbrink, Chris

    2007-11-28

    We present an approach to mimic replica exchange molecular dynamics simulations (REMD) on a microsecond time scale within a few minutes rather than the years, which would be required for real REMD. The speed of mimicked REMD makes it a useful tool for "testing" the efficiency of different settings for REMD and then to select those settings, that give the highest efficiency. We present an optimization approach with the example of Hamiltonian REMD using soft-core interactions on two model systems, GTP and 8-Br-GTP. The optimization process using REMD mimicking is very fast. Optimization of Hamiltonian-REMD settings of GTP in explicit water took us less than one week. In our study we focus not only on finding the optimal distances between neighboring replicas, but also on finding the proper placement of the highest level of softness. In addition we suggest different REMD simulation settings at this softness level. We allow several replicas to be simulated at the same Hamiltonian simultaneously and reduce the frequency of switching attempts between them. This approach allows for more efficient conversions from one stable conformation to the other.

  7. Dynamics of double-diffusive lock-exchange gravity currents

    NASA Astrophysics Data System (ADS)

    Konopliv, Nathan; Meiburg, Eckart

    2015-11-01

    The dynamics of double-diffusive gravity currents exhibiting the fingering instability were examined using 2D simulations of a lock exchange initial configuration. Both the initial stability ratio and the diffusivity ratio were varied. It was found that although the spreading of the currents was governed by a balance of buoyancy and turbulent drag forces, currents with more intense fingering spread faster than those with less intense or no fingering. This was due to an increase in the buoyancy of the currents with stronger fingering, which had a stronger effect than the increased drag. The fingering also affected the thickness of the currents, with more fingering corresponding to thinner currents. The mechanism that caused the thinner currents was also responsible for the creation of secondary and tertiary currents after a long time in a simulation that had intense fingering. If no secondary or tertiary currents formed, the density of the current was governed by a balance of double-diffusive and diffusive fluxes. An energy budget analysis revealed that double diffusive currents released more potential energy, had more dissipation and converted a significant amount of internal energy into potential energy via the diffusion of heat and salinity.

  8. Three dimensional dynamics of a flexible Motorised Momentum Exchange Tether

    NASA Astrophysics Data System (ADS)

    Ismail, N. A.; Cartmell, M. P.

    2016-03-01

    This paper presents a new flexural model for the three dimensional dynamics of the Motorised Momentum Exchange Tether (MMET) concept. This study has uncovered the relationships between planar and nonplanar motions, and the effect of the coupling between these two parameters on pragmatic circular and elliptical orbits. The tether sub-spans are modelled as stiffened strings governed by partial differential equations of motion, with specific boundary conditions. The tether sub-spans are flexible and elastic, thereby allowing three dimensional displacements. The boundary conditions lead to a specific frequency equation and the eigenvalues from this provide the natural frequencies of the orbiting flexible motorised tether when static, accelerating in monotonic spin, and at terminal angular velocity. A rotation transformation matrix has been utilised to get the position vectors of the system's components in an assumed inertial frame. Spatio-temporal coordinates are transformed to modal coordinates before applying Lagrange's equations, and pre-selected linear modes are included to generate the equations of motion. The equations of motion contain inertial nonlinearities which are essentially of cubic order, and these show the potential for intricate intermodal coupling effects. A simulation of planar and non-planar motions has been undertaken and the differences in the modal responses, for both motions, and between the rigid body and flexible models are highlighted and discussed.

  9. Experiments probing the influence of air exchange rates on secondary organic aerosols derived from indoor chemistry

    NASA Astrophysics Data System (ADS)

    Weschler, Charles J.; Shields, Helen C.

    Reactions between ozone and terpenes have been shown to increase the concentrations of submicron particles in indoor settings. The present study was designed to examine the influence of air exchange rates on the concentrations of these secondary organic aerosols as well as on the evolution of their particle size distributions. The experiments were performed in a manipulated office setting containing a constant source of d-limonene and an ozone generator that was remotely turned "on" or "off" at 6 h intervals. The particle number concentrations were monitored using an optical particle counter with eight-channels ranging from 0.1-0.2 to>2.0 μm diameter. The air exchange rates during the experiments were either high (working hours) or low (non-working hours) and ranged from 1.6 to>12 h -1, with intermediate exchange rates. Given the emission rates of ozone and d-limonene used in these studies, at an air exchange rate of 1.6 h -1 particle number concentration in the 0.1-0.2 μm size-range peaked 1.2 h after the ozone generator was switched on. In the ensuing 4.8 h particle counts increased in successive size-ranges up to the 0.5-0.7 μm diameter range. At higher air exchange rates, the resulting concentrations of total particles and particle mass (calculated from particle counts) were smaller, and at exchange rates exceeding 12 h -1, no excess particle formation was detectable with the instrument used in this study. Particle size evolved through accretion and, in some cases, coagulation. There was evidence for coagulation among particles in the smallest size-range at low air exchange rates (high particle concentrations) but no evidence of coagulation was apparent at higher air exchange rates (lower particle concentrations). At higher air exchange rates the particle count or size distributions were shifted towards smaller particle diameters and less time was required to achieve the maximum concentration in each of the size-ranges where discernable particle growth

  10. Dynamic modeling of tube-support interaction in heat exchangers

    NASA Astrophysics Data System (ADS)

    Azizian, Reza

    Flow-induced forces in heat exchangers can cause excessive tube vibration and interaction with their supports. Long term interaction may develop fretting-wear and consequently lead to tube failures. An accurate prediction of the tube-support interaction behavior is important to quantify tube fretting-wear. Therefore, a detailed study of the related friction and impact forces is required for formulating a precise wear model. This study aimed to develop a friction model for accurate representations of various states of the friction process, including elastic, plastic and partial slipping states. In addition, the tube-support impact model is verified both numerically and experimentally. A hybrid spring-damper rate dependent friction model was developed to precisely simulate the friction process from zero velocity to the gross slip state. This was achieved by considering various physical phenomena during the friction process including the Stribeck effect, varying break-away force, bristle elastic, plastic and partial-slipping behaviors. The slipping time in the velocity-limited friction model was compared to the LuGre friction model. The inability of the velocity limited friction model to detect the sticking region was explained by the dependency of a limiting velocity criterion on the varying break-away force and the Stribeck effect. This confirmed the importance of having an adaptive limiting velocity for the velocity limited friction model. In addition, the stress distribution within the contact region was studied in detail to demarcate different regions within a contact area during the friction process. This analysis attributed a physical meaning to each component of the new hybrid friction model. The ability of the hybrid model to accurately reproduce stick-slip behavior was examined using the Ozaki and Hashiguchi friction model and the Baumberger et al. experimental tests. The result showed better estimation of the stick-slip behavior, both qualitatively and

  11. Temporal Dynamics of Social Exchange and the Development of Solidarity: "Testing the Waters" versus "Taking a Leap of Faith"

    ERIC Educational Resources Information Center

    Kuwabara, Ko; Sheldon, Oliver

    2012-01-01

    In their concerted efforts to unpack the microprocesses that transform repeated exchanges into an exchange relation, exchange theorists have paid little attention to how actors perceive changes and dynamics in exchanges over time. We help fill this gap by studying how temporal patterns of exchange affect the development of cohesion. Some exchange…

  12. Improving dynamic performance of proton-exchange membrane fuel cell system using time delay control

    NASA Astrophysics Data System (ADS)

    Kim, Young-Bae

    Transient behaviour is a key parameter for the vehicular application of proton-exchange membrane (PEM) fuel cell. The goal of this presentation is to construct better control technology to increase the dynamic performance of a PEM fuel cell. The PEM fuel cell model comprises a compressor, an injection pump, a humidifier, a cooler, inlet and outlet manifolds, and a membrane-electrode assembly. The model includes the dynamic states of current, voltage, relative humidity, stoichiometry of air and hydrogen, cathode and anode pressures, cathode and anode mass flow rates, and power. Anode recirculation is also included with the injection pump, as well as anode purging, for preventing anode flooding. A steady-state, isothermal analytical fuel cell model is constructed to analyze the mass transfer and water transportation in the membrane. In order to prevent the starvation of air and flooding in a PEM fuel cell, time delay control is suggested to regulate the optimum stoichiometry of oxygen and hydrogen, even when there are dynamical fluctuations of the required PEM fuel cell power. To prove the dynamical performance improvement of the present method, feed-forward control and Linear Quadratic Gaussian (LQG) control with a state estimator are compared. Matlab/Simulink simulation is performed to validate the proposed methodology to increase the dynamic performance of a PEM fuel cell system.

  13. Self-other rating agreement and leader-member exchange (LMX): a quasi-replication.

    PubMed

    Barbuto, John E; Wilmot, Michael P; Singh, Matthew; Story, Joana S P

    2012-04-01

    Data from a sample of 83 elected community leaders and 391 direct-report staff (resulting in 333 useable leader-member dyads) were reanalyzed to test relations between self-other rating agreement of servant leadership and member-reported leader-member exchange (LMX). Polynomial regression analysis indicated that the self-other rating agreement model was not statistically significant. Instead, all of the variance in member-reported LMX was accounted for by the others' ratings component alone.

  14. Exchange rate regimes, saving glut and the Feldstein Horioka puzzle: The East Asian experience

    NASA Astrophysics Data System (ADS)

    Kaya-Bahçe, Seçil; Özmen, Erdal

    2008-04-01

    This paper investigates whether the recent experience of the emerging East Asian countries with current account surpluses is consistent with the “saving glut” hypothesis and the Feldstein and Horioka puzzle. The evidence suggests that the saving retention coefficients declined substantially in most of the countries after an endogenous break date coinciding with a major exchange rate regime change with the 1997-1998 crisis. Exchange rate flexibility appears to be enhancing financial integration. The results are consistent with an “investment slump” explanation rather than the “saving glut” postulation.

  15. pH and urea dependence of amide hydrogen-deuterium exchange rates in the beta-trefoil protein hisactophilin.

    PubMed

    Houliston, R Scott; Liu, Chengsong; Singh, Laila M R; Meiering, Elizabeth M

    2002-01-29

    Amide hydrogen/deuterium exchange rates were measured as a function of pH and urea for 37 slowly exchanging amides in the beta-trefoil protein hisactophilin. The rank order of exchange rates is generally maintained under different solution conditions, and trends in the pH and urea dependence of exchange rates are correlated with the rank order of exchange rates. The observed trends are consistent with the expected behavior for exchange of different amides via global and/or local unfolding. Analysis of the pH dependence of exchange in terms of rate constants for structural opening and closing reveals a wide range of rates in different parts of the hisactophilin structure. The slowest exchanging amides have the slowest opening and closing rates. Many of the slowest exchanging amides are located in trefoil 2, but there are also some slow exchanging amides in trefoils 1 and 3. Slow exchangers tend to be near the interface between the beta-barrel and the beta-hairpin triplet portions of this single-domain structure. The pattern of exchange behaviour in hisactophilin is similar to that observed previously in interleukin-1 beta, indicating that exchange properties may be conserved among beta-trefoil proteins. Comparisons of opening and closing rates in hisactophilin with rates obtained for other proteins reveal clear trends for opening rates; however, trends in closing rates are less apparent, perhaps due to inaccuracies in the values used for intrinsic exchange rates in the data fitting. On the basis of the pH and urea dependence of exchange rates and optical measurements of stability and folding, EX2 is the main exchange mechanism in hisactophilin, but there is also evidence for varying levels of EX1 exchange at low and high pH and high urea concentrations. Equilibrium intermediates in which subglobal portions of structure are cooperatively disrupted are not apparent from analysis of the urea dependence of exchange rates. There is, however, a strong correlation between

  16. EXCHANGE

    SciTech Connect

    Boltz, J.C.

    1992-09-01

    EXCHANGE is published monthly by the Idaho National Engineering Laboratory (INEL), a multidisciplinary facility operated for the US Department of Energy (DOE). The purpose of EXCHANGE is to inform computer users about about recent changes and innovations in both the mainframe and personal computer environments and how these changes can affect work being performed at DOE facilities.

  17. Optimal asymptotic learning rate: Macroscopic versus microscopic dynamics

    NASA Astrophysics Data System (ADS)

    Leen, Todd K.; Schottky, Bernhard; Saad, David

    1999-01-01

    We investigate the asymptotic dynamics of on-line learning for neural networks, and provide an exact solution to the network dynamics at late times under various annealing schedules. The dynamics is solved using two different frameworks: the master equation and order parameter dynamics, which concentrate on microscopic and macroscopic parameters, respectively. The two approaches provide complementary descriptions of the dynamics. Optimal annealing rates and the corresponding prefactors are derived for soft committee machine networks with hidden layers of arbitrary size.

  18. Probing exchange kinetics and atomic resolution dynamics in high-molecular-weight complexes using dark-state exchange saturation transfer NMR spectroscopy.

    PubMed

    Fawzi, Nicolas L; Ying, Jinfa; Torchia, Dennis A; Clore, G Marius

    2012-07-19

    We present the protocol for the measurement and analysis of dark-state exchange saturation transfer (DEST), a novel solution NMR method for characterizing, at atomic resolution, the interaction between an NMR-'visible' free species and an NMR-'invisible' species transiently bound to a very high-molecular-weight (>1 MDa) macromolecular entity. The reduced rate of reorientational motion in the bound state that precludes characterization by traditional NMR methods permits the observation of DEST. (15)N-DEST profiles are measured on a sample comprising the dark state in exchange with an NMR-visible species; in addition, the difference (ΔR(2)) in (15)N transverse relaxation rates between this sample and a control sample comprising only the NMR-visible species is also obtained. The (15)N-DEST and ΔR(2) data for all residues are then fitted simultaneously to the McConnell equations for various exchange models describing the residue-specific dynamics in the bound state(s) and the interconversion rate constants. Although the length of the experiments depends strongly on sample conditions, approximately 1 week of NMR spectrometer time was sufficient for full characterization of samples of amyloid-β (Aβ) at concentrations of ~100 μM.

  19. Improving NO(x) cap-and-trade system with adjoint-based emission exchange rates.

    PubMed

    Mesbah, S Morteza; Hakami, Amir; Schott, Stephan

    2012-11-01

    Cap-and-trade programs have proven to be effective instruments for achieving environmental goals while incurring minimum cost. The nature of the pollutant, however, affects the design of these programs. NO(x), an ozone precursor, is a nonuniformly mixed pollutant with a short atmospheric lifetime. NO(x) cap-and-trade programs in the U.S. are successful in reducing total NO(x) emissions but may result in suboptimal environmental performance because location-specific ozone formation potentials are neglected. In this paper, the current NO(x) cap-and-trade system is contrasted to a hypothetical NO(x) trading policy with sensitivity-based exchange rates. Location-specific exchange rates, calculated through adjoint sensitivity analysis, are combined with constrained optimization for prediction of NO(x) emissions trading behavior and post-trade ozone concentrations. The current and proposed policies are examined in a case study for 218 coal-fired power plants that participated in the NO(x) Budget Trading Program in 2007. We find that better environmental performance at negligibly higher system-wide abatement cost can be achieved through inclusion of emission exchange rates. Exposure-based exchange rates result in better environmental performance than those based on concentrations. PMID:23050674

  20. A Classroom Experiment on Exchange Rate Determination with Purchasing Power Parity

    ERIC Educational Resources Information Center

    Mitchell, David T.; Rebelein, Robert P.; Schneider, Patricia H.; Simpson, Nicole B.; Fisher, Eric

    2009-01-01

    The authors developed a classroom experiment on exchange rate determination appropriate for undergraduate courses in macroeconomics and international economics. In the experiment, students represent citizens from different countries and need to obtain currency to purchase goods. By participating in an auction to buy currency, students gain a…

  1. Dynamic communities in multichannel data: an application to the foreign exchange market during the 2007-2008 credit crisis.

    PubMed

    Fenn, Daniel J; Porter, Mason A; McDonald, Mark; Williams, Stacy; Johnson, Neil F; Jones, Nick S

    2009-09-01

    We study the cluster dynamics of multichannel (multivariate) time series by representing their correlations as time-dependent networks and investigating the evolution of network communities. We employ a node-centric approach that allows us to track the effects of the community evolution on the functional roles of individual nodes without having to track entire communities. As an example, we consider a foreign exchange market network in which each node represents an exchange rate and each edge represents a time-dependent correlation between the rates. We study the period 2005-2008, which includes the recent credit and liquidity crisis. Using community detection, we find that exchange rates that are strongly attached to their community are persistently grouped with the same set of rates, whereas exchange rates that are important for the transfer of information tend to be positioned on the edges of communities. Our analysis successfully uncovers major trading changes that occurred in the market during the credit crisis. PMID:19791999

  2. Increase Effect of Available Transfer Capability by Dynamic Rating Application

    NASA Astrophysics Data System (ADS)

    Miura, Masaki; Satoh, Takuya; Iwamoto, Shinichi; Kurihara, Ikuo

    As the deregulated environment of power systems has been spread in the world, it is essential to operate power systems efficiently and economy. Under the environments, with the advance of communication technologies and sensors, the so-called dynamic rating is now to be realized. The dynamic rating is a method which determines accurate ratings by utilizing real-time information such as conductor temperatures, ambient temperatures and wind speeds. The dynamic rating is considered to increase the thermal capacities of overhead transmission lines and therefore take on importance in the deregulated electric power industry. The importance of the dynamic rating lies mainly in the area of Available Transfer Capability (ATC) improvement. In this paper, the validity of the proposed dynamic rating application is shown from the viewpoint of ATC, especially, ATC with thermal constraints. In addition, the possibilities of ATC estimations using sensitivities are verified on the purpose of reducing calculating time, considering the importance of real time simulation of ATC.

  3. A macro-physics model of depreciation rate in economic exchange

    NASA Astrophysics Data System (ADS)

    Marmont Lobo, Rui F.; de Sousa, Miguel Rocha

    2014-02-01

    This article aims at a new approach for a known fundamental result: barter or trade increases economic value. It successfully bridges the gap between the theory of value and the exchange process attached to the transition from endowments to the equilibrium in the core and contract curve. First, we summarise the theory of value; in Section 2, we present the Edgeworth (1881) box and an axiomatic approach and in Section 3, we apply our pure exchange model. Finally (in Section 4), using our open econo-physics pure barter (EPB) model, we derive an improvement in value, which means that pure barter leads to a decline in depreciation rate.

  4. Amplifying the sensitivity of zinc(II) responsive MRI contrast agents by altering water exchange rates.

    PubMed

    Yu, Jing; Martins, André F; Preihs, Christian; Clavijo Jordan, Veronica; Chirayil, Sara; Zhao, Piyu; Wu, Yunkou; Nasr, Khaled; Kiefer, Garry E; Sherry, A Dean

    2015-11-11

    Given the known water exchange rate limitations of a previously reported Zn(II)-sensitive MRI contrast agent, GdDOTA-diBPEN, new structural targets were rationally designed to increase the rate of water exchange to improve MRI detection sensitivity. These new sensors exhibit fine-tuned water exchange properties and, depending on the individual structure, demonstrate significantly improved longitudinal relaxivities (r1). Two sensors in particular demonstrate optimized parameters and, therefore, show exceptionally high longitudinal relaxivities of about 50 mM(-1) s(-1) upon binding to Zn(II) and human serum albumin (HSA). This value demonstrates a 3-fold increase in r1 compared to that displayed by the original sensor, GdDOTA-diBPEN. In addition, this study provides important insights into the interplay between structural modifications, water exchange rate, and kinetic stability properties of the sensors. The new high relaxivity agents were used to successfully image Zn(II) release from the mouse pancreas in vivo during glucose stimulated insulin secretion. PMID:26462412

  5. HTO washout model: on the relationship between exchange rate and washout coefficient

    SciTech Connect

    Golubev, A.; Balashov, Y.; Mavrin, S.; Golubeva, V.; Galeriu, D.

    2015-03-15

    Washout coefficient Λ is widely used as a parameter in washout models. These models describes overall HTO washout with rain by a first-order kinetic equation, while washout coefficient Λ depends on the type of rain event and rain intensity and empirical parameters a, b. The washout coefficient is a macroscopic parameter and we have considered in this paper its relationship with a microscopic rate K of HTO isotopic exchange in atmospheric humidity and drops of rainwater. We have shown that the empirical parameters a, b can be represented through the rain event characteristics using the relationships of molecular impact rate, rain intensity and specific rain water content while washout coefficient Λ can be represented through the exchange rate K, rain intensity, raindrop diameter and terminal raindrop velocity.

  6. Experimental Investigation of Heat transfer rate of Nano fluids using a Shell and Tube Heat exchanger

    NASA Astrophysics Data System (ADS)

    SIVA ESWARA RAO, M.; SREERAMULU, DOWLURU; ASIRI NAIDU, D.

    2016-09-01

    Nano fluids are used for increasing thermal properties in heat transfer equipment like heat exchangers, radiators etc. This paper investigates the heat transfer rate of Nano fluids using a shell and tube heat exchanger in single and multi tubes under turbulent flow condition by a forced convection mode. Alumina Nanoparticles are prepared by using Sol-Gel method. Heat transfer rate increases with decreasing particle size. In this experiment Alumina Nano particles of about 22 nm diameter used. Alumina Nano fluids are prepared with different concentrations of Alumina particles (0.13%, 0.27%, 0.4%, and 0.53%) with water as a base fluid using ultra-sonicator. Experiment have been conducted on shell and tube heat exchanger for the above concentrations on parallel and counter flow conditions by keeping constant inlet temperatures and mass flow rate. The result shows that the heat transfer rate is good compared to conventional fluids. The properties of Nano fluids and non-dimensional numbers have been calculated.

  7. Using a spectral approach to compare dynamic and static head driven hyporheic exchange

    NASA Astrophysics Data System (ADS)

    Wörman, Anders; Morén, Ida; Riml, Joakim

    2016-04-01

    Hyporheic exchange is an important process controlling the transportation and fate of solutes in natural streams. The exchange is driven by the hydraulic head gradients over the stream bottom and occurs on a wide range of spatial scales. The hydraulic head gradient is either dominated by the static head, originating from water surface elevation differences or it is dominated by the dynamic head that is created when the velocity head of the stream is transformed to pressure variations along an uneven bed surface. This article uses a power spectral approach to compare the exchange due to the static and dynamic head occurring over a range of spatial scales in the Tullstorps Brook. Prediction of hyporheic exchange is restrained by the complications of performing measurements of high quality and quantity in the field. In this study bottom elevation and water depth was measured with a levelling instrument every 2.56 - 16.83 m along a 500 m long reach of the Tullstorps Brook. The velocity head was calculated at the same sections based on the measured cross section area of the stream and the average discharge during the day when the measurements were done. Parallel to the head investigations a Rhodamine WT tracer test was performed in the reach and the parameters controlling hyporheic exchange was estimated through inverse modelling. These tracer test parameters were compared with theoretical parameters obtained from a spectral model. Hyporheic exchange is often modelled by assuming the head variations to be harmonic with a certain wavelength and amplitude. In the reality the head variation cannot be represented by a single harmonic function, but the representation of head geometry can be improved by superimposing a large number of harmonic functions. Here, to be able to include the whole range of harmonics, we used a power spectral approach to analyse the hydraulic head measurements from the field. The Fourier power spectrum of the data was calculated for the water

  8. Dynamic Patterns, Parameters, and Climatic Response of CO2 Exchange of Agricultural Crops: Monocotyledons VS. Dicotyledons

    NASA Astrophysics Data System (ADS)

    Gilmanov, T. G.; Wylie, B. K.; Howard, D. M.

    2012-12-01

    Net CO2 exchange data from long-term flux tower measurements in monocotyledonous (wheat, maize) and dicotyledonous (soybeans, alfalfa, peas, peanuts) crops were partitioned into photosynthesis (P) and respiration (R) using the light-soil temperature-VPD response method. Analysis of the resulting time series of P and R revealed patterns of temporal and phenological dynamics in these plant groups. We established differences in ranges and dynamic patterns of P and R as well as CO2 exchange parameters (quantum yield, photosynthetic capacity, respiration rate, light-use efficiency, curvature of the VPD response). Weekly P and R data combined with remotely sensed 7-day eMODIS NDVI allow identification of the quasi-linear relationships between P, R, and NDVI, as well as estimation of parameters of NDVI response (start of the growing season, duration of the linearity period, slope of NDVI response). While the linear-like patterns occur early in the season, later the flux response to NDVI becomes less pronounced, and for the whole season the flux-NDVI relationship assumes a hysteresis-like pattern. Introduction of VPD and soil moisture limitation as well as phenological controls (growing degree days) leads to more flexible models for P and R in relation to NDVI and on-site drivers. These models allow mapping of the cropland CO2 exchange at regional and larger scales (e.g., the Great Plains). Significant relationships of the crop GPP to the seasonally integrated NDVI were also established, providing an opportunity for mapping of crop productivity using geographically distributed historic NDVI data. On the other hand, long time series (6 to 12 years and longer) of weekly P and R data lead to models of annual photosynthesis and respiration in response to climatic factors that may be used for prognostic purposes. We developed a model of maize GPP on the Great Plains in relation to the sum of temperatures above 5 °C and the hydrologic year precipitation. The model describes 75

  9. Cooperation between bound waters and hydroxyls in controlling isotope-exchange rates

    NASA Astrophysics Data System (ADS)

    Panasci, Adele F.; McAlpin, J. Gregory; Ohlin, C. André; Christensen, Shauna; Fettinger, James C.; Britt, R. David; Rustad, James R.; Casey, William H.

    2012-02-01

    Mineral oxides differ from aqueous ions in that the bound water molecules are usually attached to different metal centers, or vicinal, and thus separated from one another. In contrast, for most monomeric ions used to establish kinetic reactivity trends, such as octahedral aquo ions (e.g., Al(H 2O) 63+), the bound waters are closely packed, or geminal. Because of this structural difference, the existing literature about ligand substitution in monomer ions may be a poor guide to the reactions of geochemical interest. To understand how coordination of the reactive functional groups might affect the rates of simple water-exchange reactions, we synthesized two structurally similar Rh(III) complexes, [Rh(phen) 2(H 2O) 2] 3+ [ 1] and [Rh(phen) 2(H 2O)Cl] 2+ [ 2] where (phen) = 1,10-phenanthroline. Complex [ 1] has two adjacent, geminal, bound waters in the inner-coordination sphere and [ 2] has a single bound water adjacent to a bound chloride ion. We employed Rh(III) as a trivalent metal rather than a more geochemically relevant metal like Fe(III) or Al(III) to slow the rate of reaction, which makes possible measurement of the rates of isotopic substitution by simple mass spectrometry. We prepared isotopically pure versions of the molecules, dissolved them into isotopically dissimilar water, and measured the rates of exchange from the extents of 18O and 16O exchange at the bound waters. The pH dependency of rates differ enormously between the two complexes. Pseudo-first-order rate coefficients at 298 K for water exchanges from the fully protonated molecules are close: k0298 = 5 × 10 -8(±0.5 × 10 -8) s -1 for [ 1] and k0298 = 2.5 × 10 -9(±1 × 10 -9) for [ 2]. Enthalpy and entropy activation parameters (Δ H‡ and Δ S‡) were measured to be 119(±3) kJ mol -1, and 14(±1) J mol -1 K -1, respectively for [ 1]. The corresponding parameters for the mono-aquo complex, [ 2], are 132(±3) kJ mol -1 and 41.5(±2) J mol -1 K -1. Rates increase by many orders of magnitude

  10. Utilizing MRI to measure the transcytolemmal water exchange rate for the rat brain

    NASA Astrophysics Data System (ADS)

    Quirk, James D.; Bretthorst, G. Larry; Neil, Jeffrey J.

    2001-05-01

    Understanding the exchange of water between the intra- and extracellular compartments of the brain is important both for understanding basic physiology and for the interpretation of numerous MRI results. However, due to experimental difficulties, this basic property has proven difficult to measure in vivo. In our experiments, we will track overall changes in the relaxation rate constant of water in the rat brain following the administration of gadoteridol, a relaxation agent, to the extracellular compartment. From these changes, we will utilize probability theory and Markov Chain Monte Carlo simulations to infer the compartment specific water exchange and relaxation rate constants. Due to the correlated nature of these parameters and our inability to independently observe them, intelligent model selection is critical. Through analysis of simulated data sets, we refine our choice of model and method of data collection to optimize applicability to the in vivo situation.

  11. Dynamic changes of the total pore area available for peritoneal exchange in children.

    PubMed

    Fischbach, M; Haraldsson, B

    2001-07-01

    The most important of the parameters that describe exchange across the peritoneal membrane is the total pore area over diffusion distance (A(0)/Deltax). It determines the rate of diffusion and mainly seems to reflect the number of capillaries available for exchange. In the present study, a simplified three-pore analysis was used to estimate A(0)/Deltax from peritoneal equilibration tests. Two groups of children (mean age, 9.5 yr) who were on chronic peritoneal dialysis underwent studies with peritoneal equilibration tests. In the first group of children, three levels of fill volumes were used in each patient. In the second group of patients, the effects of posture and dwell time were analyzed from four consecutive peritoneal dialysis samples obtained after 15, 30, 60, and 90 min. As the fill volume was raised from 800 to 1400 ml/m(2) BSA, the steady-state A(0)/Deltax increased significantly by 21%, i.e., from 19,900 +/- 1200 to 24,000 +/- 1450 cm(2)/cm per 1.73 m(2) (n = 8). A further increase to 2000 ml/m(2) did not result in any change of A(0)/Deltax. Moreover, steady-state A(0)/Deltax fell significantly when the patients were standing, 21,900 +/- 1400 compared with 29,400 +/- 1330 cm(2)/cm per 1.73m(2) (n = 6) obtained in the supine position. There was a transient (<30 min) increase in A(0)/Deltax initially during the dwell, probably reflecting vasodilation and recruitment of capillaries. It is concluded that factors such as the intraperitoneal fill volume, posture, and dwell time all dynamically affect the total pore area available for exchange.

  12. Charge Exchange and Ablation Rates of a Titanium Wire Plasma Corona

    SciTech Connect

    Terry, Robert E.

    2009-01-21

    Wire ablation rates are important features in any examination of precursors or transparent mode implosions of wire arrays. When ion temperatures in a Ti wire plasma corona exceed a few eV, the process of resonant charge exchange competes with elastic scattering. Ions pushed into the corona from an anode bias wire array can be expected to drive a fast neutral wind into the surrounding volume, while a cathode bias wire array would not show the strong neutral wind.

  13. Strategies for Optimizing Water-Exchange Rates of Lanthanide-Based Contrast Agents for Magnetic Resonance Imaging

    PubMed Central

    Siriwardena-Mahanama, Buddhima N.; Allen, Matthew J.

    2013-01-01

    This review describes recent advances in strategies for tuning the water-exchange rates of contrast agents for magnetic resonance imaging (MRI). Water-exchange rates play a critical role in determining the efficiency of contrast agents; consequently, optimization of water-exchange rates, among other parameters, is necessary to achieve high efficiencies. This need has resulted in extensive research efforts to modulate water-exchange rates by chemically altering the coordination environments of the metal complexes that function as contrast agents. The focus of this review is coordination-chemistry-based strategies used to tune the water-exchange rates of lanthanide(III)-based contrast agents for MRI. Emphasis will be given to results published in the 21st century, as well as implications of these strategies on the design of contrast agents. PMID:23921796

  14. Dynamical exchange-correlation potentials for the electron liquid

    NASA Astrophysics Data System (ADS)

    Qian, Zhixin; Vignale, Giovanni

    2002-03-01

    The imaginary parts of the exchange-correlation kernels f_xc^L,T(q=0, ω) in the linear density-density and transverse current-current response functions of a homogeneous electron liquid are calculated exactly at low frequency, to leading order in the Coulomb interaction. Combining these new results with the previously known high-frequency behaviors of Im f_xc^L,T(q=0, ω) and with the compressibility and the third frequency moment sum rules, we construct simple interpolation for Im f_xc^L,T(q=0, ω) in 3- and 2- dimensions. A novel feature of our interpolation formulas is that they explicitly take into account the two-plasmon component of the excitation spectrum: our longitudinal spectrum Im f_xc^L(q=0, ω) is thus intermediate between the Gross-Kohn interpolation, which ignores the two-plasmon contribution, and a recent approximate calculation by Nifosi, Conti, and Tosi, which probably overestimates it. Numerical results for both the real and imaginary parts of the exchange-correlation kernels at typical electron densities are presented, and compared with those obtained from previous approximations.

  15. Cluster fusion-fission dynamics in the Singapore stock exchange

    NASA Astrophysics Data System (ADS)

    Teh, Boon Kin; Cheong, Siew Ann

    2015-10-01

    In this paper, we investigate how the cross-correlations between stocks in the Singapore stock exchange (SGX) evolve over 2008 and 2009 within overlapping one-month time windows. In particular, we examine how these cross-correlations change before, during, and after the Sep-Oct 2008 Lehman Brothers Crisis. To do this, we extend the complete-linkage hierarchical clustering algorithm, to obtain robust clusters of stocks with stronger intracluster correlations, and weaker intercluster correlations. After we identify the robust clusters in all time windows, we visualize how these change in the form of a fusion-fission diagram. Such a diagram depicts graphically how the cluster sizes evolve, the exchange of stocks between clusters, as well as how strongly the clusters mix. From the fusion-fission diagram, we see a giant cluster growing and disintegrating in the SGX, up till the Lehman Brothers Crisis in September 2008 and the market crashes of October 2008. After the Lehman Brothers Crisis, clusters in the SGX remain small for few months before giant clusters emerge once again. In the aftermath of the crisis, we also find strong mixing of component stocks between clusters. As a result, the correlation between initially strongly-correlated pairs of stocks decay exponentially with average life time of about a month. These observations impact strongly how portfolios and trading strategies should be formulated.

  16. Quantitative chemical exchange saturation transfer (qCEST) MRI--RF spillover effect-corrected omega plot for simultaneous determination of labile proton fraction ratio and exchange rate.

    PubMed

    Sun, Phillip Zhe; Wang, Yu; Dai, ZhuoZhi; Xiao, Gang; Wu, Renhua

    2014-01-01

    Chemical exchange saturation transfer (CEST) MRI is sensitive to dilute proteins and peptides as well as microenvironmental properties. However, the complexity of the CEST MRI effect, which varies with the labile proton content, exchange rate and experimental conditions, underscores the need for developing quantitative CEST (qCEST) analysis. Towards this goal, it has been shown that omega plot is capable of quantifying paramagnetic CEST MRI. However, the use of the omega plot is somewhat limited for diamagnetic CEST (DIACEST) MRI because it is more susceptible to direct radio frequency (RF) saturation (spillover) owing to the relatively small chemical shift. Recently, it has been found that, for dilute DIACEST agents that undergo slow to intermediate chemical exchange, the spillover effect varies little with the labile proton ratio and exchange rate. Therefore, we postulated that the omega plot analysis can be improved if RF spillover effect could be estimated and taken into account. Specifically, simulation showed that both labile proton ratio and exchange rate derived using the spillover effect-corrected omega plot were in good agreement with simulated values. In addition, the modified omega plot was confirmed experimentally, and we showed that the derived labile proton ratio increased linearly with creatine concentration (p < 0.01), with little difference in their exchange rate (p = 0.32). In summary, our study extends the conventional omega plot for quantitative analysis of DIACEST MRI.

  17. Respiratory dynamics of discontinuous gas exchange in the tracheal system of the desert locust, Schistocerca gregaria.

    PubMed

    Groenewald, Berlizé; Hetz, Stefan K; Chown, Steven L; Terblanche, John S

    2012-07-01

    Gas exchange dynamics in insects is of fundamental importance to understanding evolved variation in breathing patterns, such as discontinuous gas exchange cycles (DGCs). Most insects do not rely solely on diffusion for the exchange of respiratory gases but may also make use of respiratory movements (active ventilation) to supplement gas exchange at rest. However, their temporal dynamics have not been widely investigated. Here, intratracheal pressure, V(CO2) and body movements of the desert locust Schistocerca gregaria were measured simultaneously during the DGC and revealed several important aspects of gas exchange dynamics. First, S. gregaria employs two different ventilatory strategies, one involving dorso-ventral contractions and the other longitudinal telescoping movements. Second, although a true spiracular closed (C)-phase of the DGC could be identified by means of subatmospheric intratracheal pressure recordings, some CO(2) continued to be released. Third, strong pumping actions do not necessarily lead to CO(2) release and could be used to ensure mixing of gases in the closed tracheal system, or enhance water vapour reabsorption into the haemolymph from fluid-filled tracheole tips by increasing the hydrostatic pressure or forcing fluid into the haemocoel. Finally, this work showed that the C-phase of the DGC can occur at any pressure. These results provide further insights into the mechanistic basis of insect gas exchange. PMID:22675191

  18. Coupled acoustic-gravity field for dynamic evaluation of ion exchange with a single resin bead.

    PubMed

    Kanazaki, Takahiro; Hirawa, Shungo; Harada, Makoto; Okada, Tetsuo

    2010-06-01

    A coupled acoustic-gravity field is efficient for entrapping a particle at the position determined by its acoustic properties rather than its size. This field has been applied to the dynamic observation of ion-exchange reactions occurring in a single resin bead. The replacement of counterions in an ion-exchange resin induces changes in its acoustic properties, such as density and compressibility. Therefore, we can visually trace the advancement of an ion-exchange reaction as a time change in the levitation position of a resin bead entrapped in the field. Cation-exchange reactions occurring in resin beads with diameters of 40-120 microm are typically completed within 100-200 s. Ion-exchange equilibrium or kinetics is often evaluated with off-line chemical analyses, which require a batch amount of ion exchangers. Measurements with a single resin particle allow us to evaluate ion-exchange dynamics and kinetics of ions including those that are difficult to measure by usual off-line analyses. The diffusion properties of ions in resins have been successfully evaluated from the time change in the levitation positions of resin beads. PMID:20462180

  19. Oral Pseudoephedrine Decreases the Rate of Trans-mucosal Nitrous Oxide Exchange for the Middle Ear

    PubMed Central

    Teixeira, Miriam S.; Alper, Cuneyt M.; Martin, Brian S; Cullen Doyle, Brendan M.; Doyle, William J.

    2015-01-01

    Objective Determine if oral pretreatment with a vasoconstrictor decreases the blood to middle-ear exchange-rate of the perfusion-limited gas, Nitrous Oxide (N2O). Study Design Randomized, double-blind, crossover study. Methods Ten adult subjects with and 10 without past middle-ear disease completed paired experimental sessions, identical but for oral pretreatment with either pseudoephedrine HCL or lactose placebo. At each session, subjects were fitted with a non-rebreathing mask and breathed room air for 20 minutes (acclimation period), 50% N2O:50% O2 for 20 minutes (experimental period) and 100% O2 for 10 minutes (recovery period). Throughout, heart-rate, blood-pressure and O2 saturation were monitored and bilateral middle-ear pressures were recorded by tympanometry every minute. The primary outcome was the slope of the middle-ear pressure-time function for the experimental period which estimates the volume N2O exchange-rate. Using repeated measures ANOVA, the effects of Group (disease history), Treatment (active vs. placebo) and Period (1 vs. 2) on the recorded vital signs, and of Group, Treatment and Ear (left/right) on the middle-ear pressure-time slope were evaluated for statistical significance. Results Statistically significant effects of Period on O2 saturation (Period 2>Period 1) and of Treatment on heart-rate (Active>Placebo) were documented. Only Treatment was statistically significant for the middle-ear pressure-time slope with a shallower slope characterizing the active treatment session. Conclusion The volume exchange-rate across the middle-ear mucosa of perfusion-limited gases can be modulated pharmacologically. Theoretically, similar drugs can be used to reduce the requisite Eustachian tube opening efficiency for adequate middle-ear pressure regulation. PMID:26152838

  20. Reduction of Large Dynamical Systems by Minimization of Evolution Rate

    NASA Technical Reports Server (NTRS)

    Girimaji, Sharath S.

    1999-01-01

    Reduction of a large system of equations to a lower-dimensional system of similar dynamics is investigated. For dynamical systems with disparate timescales, a criterion for determining redundant dimensions and a general reduction method based on the minimization of evolution rate are proposed.

  1. Dynamics of the force exchanged between membrane inclusions.

    PubMed

    Fournier, Jean-Baptiste

    2014-03-28

    We study the dynamical response of a fluid membrane to the sudden conformation change of active inclusions linearly coupled to the membrane curvature. The mutual force between two inclusions triggered simultaneously is shown to exhibit a transient maximum much larger than the equilibrium force. Even in the presence of tension, this dynamical interaction is long range over distances much larger than the correlation length. We derive the scaling laws describing these phenomena analytically, and we stress the importance of the damping due to intermonolayer friction. PMID:24724681

  2. Reversible Control of Nanoparticle Functionalization and Physicochemical Properties by Dynamic Covalent Exchange**

    PubMed Central

    della Sala, Flavio; Kay, Euan R

    2015-01-01

    Existing methods for the covalent functionalization of nanoparticles rely on kinetically controlled reactions, and largely lack the sophistication of the preeminent oligonucleotide-based noncovalent strategies. Here we report the application of dynamic covalent chemistry for the reversible modification of nanoparticle (NP) surface functionality, combining the benefits of non-biomolecular covalent chemistry with the favorable features of equilibrium processes. A homogeneous monolayer of nanoparticle-bound hydrazones can undergo quantitative dynamic covalent exchange. The pseudomolecular nature of the NP system allows for the in situ characterization of surface-bound species, and real-time tracking of the exchange reactions. Furthermore, dynamic covalent exchange offers a simple approach for reversibly switching—and subtly tuning—NP properties such as solvophilicity. PMID:25973468

  3. Simultaneous Disulfide and Boronic Acid Ester Exchange in Dynamic Combinatorial Libraries.

    PubMed

    Diemer, Sanna L; Kristensen, Morten; Rasmussen, Brian; Beeren, Sophie R; Pittelkow, Michael

    2015-09-10

    Dynamic combinatorial chemistry has emerged as a promising tool for the discovery of complex receptors in supramolecular chemistry. At the heart of dynamic combinatorial chemistry are the reversible reactions that enable the exchange of building blocks between library members in dynamic combinatorial libraries (DCLs) ensuring thermodynamic control over the system. If more than one reversible reaction operates in a single dynamic combinatorial library, the complexity of the system increases dramatically, and so does its possible applications. One can imagine two reversible reactions that operate simultaneously or two reversible reactions that operate independently. Both these scenarios have advantages and disadvantages. In this contribution, we show how disulfide exchange and boronic ester transesterification can function simultaneous in dynamic combinatorial libraries under appropriate conditions. We describe the detailed studies necessary to establish suitable reaction conditions and highlight the analytical techniques appropriate to study this type of system.

  4. The interactive effect of leader-member exchange and communication frequency on performance ratings.

    PubMed

    Kacmar, K Michele; Witt, L A; Zivnuska, Suzanne; Gully, Stanley M

    2003-08-01

    The authors tested the hypothesis that communication frequency moderates the relationship between leader-member exchange (LMX) and job-performance ratings. In a study of 188 private sector workers, they found that LMX was more strongly related to job-performance ratings among individuals reporting frequent communication with the supervisor than among those reporting infrequent communication. At high levels of LMX, workers reporting frequent communication with the supervisor received more favorable job-performance ratings than did workers reporting infrequent communication. In contrast, at low levels of LMX, workers reporting frequent communication with the supervisor received less favorable job-performance ratings than workers reporting infrequent communication. The authors conducted a 2nd study of 153 public sector workers to provide a constructive replication and found similar results.

  5. Photolithography and Fluorescence Correlation Spectroscopy used to examine the rates of exchange in reverse micelle systems

    NASA Astrophysics Data System (ADS)

    Norris, Zach; Mawson, Cara; Johnson, Kyron; Kessler, Sarah; Rebecca, Anne; Wolf, Nathan; Lim, Michael; Nucci, Nathaniel

    Reverse micelles are molecular complexes that encapsulate a nanoscale pool of water in a surfactant shell dissolved in non-polar solvent. These complexes have a wide range of applications, and in all cases, the degree to which reverse micelles (RM) exchange their contents is relevant for their use. Despite its importance, this aspect of RM behavior is poorly understood. Photolithography is employed here to create micro and nano scale fluidic systems in which mixing rates can be precisely measured using fluorescence correlation spectroscopy (FCS). Micro-channel patterns are etched using reactive ion etching process into a layer of silicon dioxide on crystalline silicon substrates. Solutions containing mixtures of reverse micelles, proteins, and fluorophores are placed into reservoirs in the patterns, while diffusion and exchange between RMs is monitored using a FCS system built from a modified confocal Raman spectrometer. Using this approach, the diffusion and exchange rates for RM systems are measured as a function of the components of the RM mixture. Funding provided by Rowan University.

  6. Dynamics of leaf gas exchange, chlorophyll fluorescence and stem diameter changes during freezing and thawing of Scots pine seedlings.

    PubMed

    Lindfors, Lauri; Hölttä, Teemu; Lintunen, Anna; Porcar-Castell, Albert; Nikinmaa, Eero; Juurola, Eija

    2015-12-01

    Boreal trees experience repeated freeze-thaw cycles annually. While freezing has been extensively studied in trees, the dynamic responses occurring during the freezing and thawing remain poorly understood. At freezing and thawing, rapid changes take place in the water relations of living cells in needles and in stem. While freezing is mostly limited to extracellular spaces, living cells dehydrate, shrink and their osmotic concentration increases. We studied how the freezing-thawing dynamics reflected on leaf gas exchange, chlorophyll fluorescence and xylem and living bark diameter changes of Scots pine (Pinus sylvestris L.) saplings in controlled experiments. Photosynthetic rate quickly declined following ice nucleation and extracellular freezing in xylem and needles, almost parallel to a rapid shrinking of xylem diameter, while that of living bark followed with a slightly longer delay. While xylem and living bark diameters responded well to decreasing temperature and water potential of ice, the relationship was less consistent in the case of increasing temperature. Xylem showed strong temporal swelling at thawing suggesting water movement from bark. After thawing xylem diameter recovered to a pre-freezing level but living bark remained shrunk. We found that freezing affected photosynthesis at multiple levels. The distinct dynamics of photosynthetic rate and stomatal conductance reveals that the decreased photosynthetic rate reflects impaired dark reactions rather than stomatal closure. Freezing also inhibited the capacity of the light reactions to dissipate excess energy as heat, via non-photochemical quenching, whereas photochemical quenching of excitation energy decreased gradually with temperature in agreement with the gas exchange data.

  7. Quantum dynamics of {sup 16}O + {sup 36}O{sub 2} and {sup 18}O + {sup 32}O{sub 2} exchange reactions

    SciTech Connect

    Rajagopala Rao, T.; Mahapatra, S.; Guillon, G.; Honvault, P.

    2015-05-07

    We present quantum dynamical investigations of {sup 16}O + {sup 36}O{sub 2} and {sup 18}O + {sup 32}O{sub 2} exchange reactions using a time-independent quantum mechanical method and an accurate global potential energy surface of ozone [Dawes et al., J. Chem. Phys. 135, 081102 (2011)]. Initial state-selected integral cross sections, rate constants, and Boltzmann averaged thermal rate constants are obtained and compared with earlier experimental and theoretical results. The computed thermal rate constants for the oxygen exchange reactions exhibit a negative temperature dependence, as found experimentally. They are in better agreement with the experiments than the previous studies on the same reactions.

  8. Thixoforming of Steel: New Tools Conception to Analyse Thermal Exchanges and Strain Rate Effects

    NASA Astrophysics Data System (ADS)

    Cezard, P.; Bigot, R.; Becker, E.; Mathieu, S.; Pierret, J. C.; Rassili, A.

    2007-04-01

    Through different papers, authors shown that the influence of thermal exchanges was a first order parameter on the semi-solid steel behaviour, and certainly for every semi-solid metallic materials. These thermal exchanges hide other parameters effect like, for example, the strain rate influence. This paper tries to determine the influence of these two parameters by using a new extrusion device on a hydraulic press. This new tools conception annihilated the influence of the decrease of the punch speed before stopping and permitted to have a constant speed during the experiment. This work also deals with the homogeneous flow during thixoforming of steel and shows the importance to couple initial temperature of the slug with punch speed. This paper presents different conditions which permitted to have a homogeneous flow by keeping a low load.

  9. Effects of the anion salt nature on the rate constants of the aqueous proton exchange reactions.

    PubMed

    Paredes, Jose M; Garzon, Andres; Crovetto, Luis; Orte, Angel; Lopez, Sergio G; Alvarez-Pez, Jose M

    2012-04-28

    The proton-transfer ground-state rate constants of the xanthenic dye 9-[1-(2-methyl-4-methoxyphenyl)]-6-hydroxy-3H-xanthen-3-one (TG-II), recovered by Fluorescence Lifetime Correlation Spectroscopy (FLCS), have proven to be useful to quantitatively reflect specific cation effects in aqueous solutions (J. M. Paredes, L. Crovetto, A. Orte, J. M. Alvarez-Pez and E. M. Talavera, Phys. Chem. Chem. Phys., 2011, 13, 1685-1694). Since these phenomena are more sensitive to anions than to cations, in this paper we have accounted for the influence of salts with the sodium cation in common, and the anion classified according to the empirical Hofmeister series, on the proton transfer rate constants of TG-II. We demonstrate that the presence of ions accelerates the rate of the ground-state proton-exchange reaction in the same order than ions that affect ion solvation in water. The combination of FLCS with a fluorophore undergoing proton transfer reactions in the ground state, along with the desirable feature of a pseudo-dark state when the dye is protonated, allows one unique direct determination of kinetic rate constants of the proton exchange chemical reaction. PMID:22421957

  10. Rate-dependent extensional "dynamic ligaments" using shear thickening fluids

    NASA Astrophysics Data System (ADS)

    Nenno, Paul T.; Wetzel, Eric D.

    2014-04-01

    A novel "dynamic ligament" smart material that exhibits a strongly rate-dependent response in extension is developed and characterized. The devices, based on elastomeric polymers and shear thickening fluids, exhibit low resistance to extension at rates below 10 mm/s, but when stretched at 100 mm/s or higher resist with up to 7 × higher force. A link between the shear thickening fluid's rheology and the dynamic ligament's tensile performance is presented to explain the rate-dependent response. Future recommendations for improving device performance are presented, along with a host of different potential application areas including safety equipment, adaptive braces, sporting goods, and military equipment.

  11. Time Dependency of Psychotherapeutic Exchanges: The Contribution of the Theory of Dynamic Systems in Analyzing Process

    PubMed Central

    Salvatore, Sergio; Tschacher, Wolfgang

    2012-01-01

    This paper provides a general framework for the use of Theory of Dynamic Systems (TDS) in the field of psychotherapy research. Psychotherapy is inherently dynamic, namely a function of time. Consequently, the improvement of construct validity and clinical relevance of psychotherapy process research require the development of models of investigation allowing dynamic mappings of clinical exchange. Thus, TDS becomes a significant theoretical and methodological reference. The paper focuses two topics. First, the main concepts of TDS are briefly introduced together with a basic typology of approaches developed within this domain. Second, we propose a repertoire of investigation strategies that can be used to capture the dynamic nature of clinical exchange. In this way we intend to highlight the feasibility and utility of strategies of analysis informed by TDS. PMID:22848205

  12. Microbial desalination cells packed with ion-exchange resin to enhance water desalination rate.

    PubMed

    Morel, Alexandre; Zuo, Kuichang; Xia, Xue; Wei, Jincheng; Luo, Xi; Liang, Peng; Huang, Xia

    2012-08-01

    A novel configuration of microbial desalination cell (MDC) packed with ion-exchange resin (R-MDC) was proposed to enhance water desalination rate. Compared with classic MDC (C-MDC), an obvious increase in desalination rate (DR) was obtained by R-MDC. With relatively low concentration (10-2 g/L NaCl) influents, the DR values of R-MDC were about 1.5-8 times those of C-MDC. Ion-exchange resins packed in the desalination chamber worked as conductor and thus counteracted the increase in ohmic resistance during treatment of low concentration salt water. Ohmic resistances of R-MDC stabilized at 3.0-4.7 Ω. By contrast, the ohmic resistances of C-MDC ranged from 5.5 to 12.7 Ω, which were 55-272% higher than those of R-MDC. Remarkable improvement in desalination rate helped improve charge efficiency for desalination in R-MDC. The results first showed the potential of R-MDC in the desalination of water with low salinity.

  13. Soil Net Nitrification Rates and Exchangeable Calcium in Ten Small Upland Watersheds of the Northeastern USA

    NASA Astrophysics Data System (ADS)

    Ross, D.; Bailey, S.; Shanley, J.; Fredriksen, G.; Jamison, A.

    2004-05-01

    Possible links have been suggested between soil nitrification rates, soil calcium concentrations and tree species composition (e.g. sugar maple). We are measuring soil nitrification rates and stream nitrate export in ten watersheds in Vermont, New Hampshire and New York. These include relatively Ca-poor sites at Cone Pond NH and Ca-rich sites at Sleepers River, VT. Our objectives are to determine the relationship between nitrification rates and watershed characteristics (e.g. vegetation, soils, topography), and to explore the link between these rates and watershed nitrate export. Net nitrification rates are highly variable both within and among the eight sites and are related to the soil C/N ratio and vegetation characteristics at some, but not all, sites. Our preliminary results show distinct differences in exchangeable Ca concentrations among watersheds. Although some locations are enriched in Ca and high in sugar maple density, we have not found a good overall relationship between Ca and net nitrification rates. High rates can be found in Ca-enriched sites that are also relatively high in pH.

  14. On Value at Risk for Foreign Exchange Rates --- the Copula Approach

    NASA Astrophysics Data System (ADS)

    Jaworski, P.

    2006-11-01

    The aim of this paper is to determine the Value at Risk (VaR) of the portfolio consisting of long positions in foreign currencies on an emerging market. Basing on empirical data we restrict ourselves to the case when the tail parts of distributions of logarithmic returns of these assets follow the power laws and the lower tail of associated copula C follows the power law of degree 1. We will illustrate the practical usefulness of this approach by the analysis of the exchange rates of EUR and CHF at the Polish forex market.

  15. The dynamics of sorption of sulfuric acid by weakly basic polyacrylic anion exchangers

    NASA Astrophysics Data System (ADS)

    Mamchenko, A. V.; Kushnir, T. V.

    2009-05-01

    The nonequilibrium dynamics of sorption of sulfuric acid by free base forms of Amberlite IRA-67 and Lewatite VP.OC.1072 weakly basic anion exchangers is studied. It is established that, in hydrodynamic regimes of filtration, which are typical of OH filters of the first stage of water-desalting plants, the limiting stage of sorption kinetics is inside diffusion. It is concluded that the process is correctly described by an asymptotic solution to the inside-diffusion model of sorption dynamics.

  16. NASA geometry data exchange specification for computational fluid dynamics (NASA IGES)

    NASA Technical Reports Server (NTRS)

    Blake, Matthew W.; Kerr, Patricia A.; Thorp, Scott A.; Jou, Jin J.

    1994-01-01

    This document specifies a subset of an existing product data exchange specification that is widely used in industry and government. The existing document is called the Initial Graphics Exchange Specification. This document, a subset of IGES, is intended for engineers analyzing product performance using tools such as computational fluid dynamics (CFD) software. This document specifies how to define mathematically and exchange the geometric model of an object. The geometry is represented utilizing nonuniform rational B-splines (NURBS) curves and surfaces. Only surface models are represented; no solid model representation is included. This specification does not include most of the other types of product information available in IGES (e.g., no material properties or surface finish properties) and does not provide all the specific file format details of IGES. The data exchange protocol specified in this document is fully conforming to the American National Standard (ANSI) IGES 5.2.

  17. Dynamic Models of Learning That Characterize Parent-Child Exchanges Predict Vocabulary Growth

    ERIC Educational Resources Information Center

    Ober, David R.; Beekman, John A.

    2016-01-01

    Cumulative vocabulary models for infants and toddlers were developed from models of learning that predict trajectories associated with low, average, and high vocabulary growth rates (14 to 46 months). It was hypothesized that models derived from rates of learning mirror the type of exchanges provided to infants and toddlers by parents and…

  18. Amide hydrogen exchange and internal dynamics in the chemotactic protein CheY from Escherichia coli.

    PubMed

    Lacroix, E; Bruix, M; López-Hernández, E; Serrano, L; Rico, M

    1997-08-22

    The backbone internal dynamics of the wild-type 129 amino acid alpha/beta parallel protein CheY and its double mutant F14N/P110G are analysed here by the hydrogen-exchange method. The F14N mutation is known to stabilise the protein and to accelerate refolding while P110G is destabilising and accelerates unfolding. We first assigned and characterised the double mutant by nuclear magnetic resonance (NMR), to try and discover any possible conformational change induced by the two mutations. The main difference between the two proteins is a favourable N-capping interaction of the newly introduced Asn14 side-chain at the beginning of the first alpha-helix (alpha-helix A). Second, we have measured the exchange rates in the wild-type and mutant CheY. In the first case the observed protection factors are slightly dispersed around an average value. According to their distribution in the structure, protein stability is highest on one face of the central beta-sheet, in the surroundings of the main hydrophobic core formed by side-chains of residues in beta-strands I, II and III and helices A and E. The mutations in the double mutant protein affect two distinct subdomains differently (from beta-strand I to III and from alpha-helix C to the end). In the second subdomain the number of protected protons is reduced with respect to those in the wild-type. This differential behaviour can be explained by a selective decrease in stability of the second folding subdomain produced by the P110G mutation and the opposite effect in the first subdomain, produced by the F14N mutation. alpha-Helix A, which is involved together with beta-strands I and III in the folding nucleus of CheY, shows the largest protection factors in both proteins.

  19. Dynamic exchanges between DOM and POM pools in coastal and inland aquatic ecosystems: A review.

    PubMed

    He, Wei; Chen, Meilian; Schlautman, Mark A; Hur, Jin

    2016-05-01

    Dynamic exchanges between dissolved organic matter (DOM) and particulate organic matter (POM) plays a critical role in organic carbon cycling in coastal and inland aquatic ecosystems, interactions with aquatic organisms, mobility and bioavailability of pollutants, among many other ecological and geochemical phenomena. Although DOM-POM exchange processes have been widely studied from different aspects, little to no effort has been made to date to provide a comprehensive, mechanistic, and micro-spatial schema for understanding various exchange processes occurring in different aquatic ecosystems in a unified way. The phenomena occurring between DOM and POM were explained here with the homogeneous and heterogeneous mechanisms. In the homogeneous mechanism, the participating components are only organic matter (OM) constituents themselves with aggregation and dissolution involved, whereas OM is associated with other components such as minerals and particulate colloids in the heterogeneous counterpart. Besides the generally concerned processes of aggregation/dissolution and adsorption/desorption, other ecological factors such as sunlight and organisms can also participate in DOM-POM exchanges through altering the chemical nature of OM. Despite the limitation of current analytical technologies, many unknown and/or unquantified processes need to be identified to unravel the complicated exchanges of OM between its dissolved and particulate states. Based on the review of several previous mathematical models, we proposed a unified conceptual model to describe all major dynamic exchange mechanisms on the basis of exergy theory. More knowledge of dynamic DOM-POM exchanges is warranted to overcome the potential problems arising from a simple division of OM into dissolved versus particulate states and to further develop more sophisticated mathematic models.

  20. Theoretical investigation on the mechanism and dynamics of oxo exchange of neptunyl(VI) hydroxide in aqueous solution.

    PubMed

    Yang, Xia; Chai, Zhifang; Wang, Dongqi

    2015-03-21

    Four types of reaction mechanisms for the oxo ligand exchange of monomeric and dimeric neptunyl(VI) hydroxide in aqueous solution were explored computationally using density functional theory (DFT) and ab initio classical molecular dynamics. The obtained results were compared with previous studies on the oxo exchange of uranyl hydroxide, as well as with experiments. It is found that the stable T-shaped [NpO3(OH)3](3-) intermediate is a key species for oxo exchange in the proton transfer in mononuclear Path I and binuclear Path IV, similar to the case of uranyl(VI) hydroxide. Path I is thought to be the preferred oxo exchange mechanism for neptunyl(VI) hydroxide in our calculations, due to the lower activation energy (22.7 and 13.1 kcal mol(-1) for ΔG(‡) and ΔH(‡), respectively) of the overall reaction. Path II via a cis-neptunyl structure assisted by a water molecule might be a competitive channel against Path I with a mononuclear mechanism, owing to a rapid dynamical process occurring in Path II. In Path IV with the binuclear mechanism, oxo exchange is accomplished via the interaction between [NpO2(OH)4](2-) and T-shaped [NpO3(OH)3](3-) with a low activation energy for the rate-determining step, however, the overall energy required to fulfill the reaction is slightly higher than that in mononuclear Path I, suggesting a possible binuclear process in the higher energy region. The chemical bonding evolution along the reaction pathways was discussed by using topological methodologies of the electron localization function (ELF).

  1. Slow process in confined polymer melts: Layer exchange dynamics at a polymer solid interface

    NASA Astrophysics Data System (ADS)

    Yelash, L.; Virnau, P.; Binder, K.; Paul, W.

    2010-11-01

    Employing Molecular Dynamics simulations of a chemically realistic model of 1,4-polybutadiene between graphite walls we show that the mass exchange between layers close to the walls is a slow process already in the melt state. For the glass transition of confined polymers this process competes with the slowing down due to packing effects and intramolecular rotation barriers.

  2. An Analytical Model for Estimating Water Exchange Rate in White Matter Using Diffusion MRI

    PubMed Central

    Davoodi-Bojd, Esmaeil; Chopp, Michael; Soltanian-Zadeh, Hamid; Wang, Shiyang; Ding, Guangliang; Jiang, Quan

    2014-01-01

    Substantial effort is being expended on using micro-structural modeling of the white matter, with the goal of relating diffusion weighted magnetic resonance imaging (DWMRI) to the underlying structure of the tissue, such as axonal density. However, one of the important parameters affecting diffusion is the water exchange rate between the intra- and extra-axonal space, which has not been fully investigated and is a crucial marker of brain injury such as multiple sclerosis (MS), stroke, and traumatic brain injury (TBI). To our knowledge, there is no diffusion analytical model which includes the Water eXchange Rate (WXR) without the requirement of short gradient pulse (SGP) approximation. We therefore propose a new analytical model by deriving the diffusion signal for a permeable cylinder, assuming a clinically feasible pulse gradient spin echo (PGSE) sequence. Simulations based on Markov Random Walk confirm that the exchange parameter included in our model has a linear correlation (R2>0.88) with the actual WXR. Moreover, increasing WXR causes the estimated values of diameter and volume fraction of the cylinders to increase and decrease, respectively, which is consistent with our findings from histology measurements in tissues near TBI regions. This model was also applied to the diffusion signal acquired from ex vivo brains of 14 male (10 TBI and 4 normal) rats using hybrid diffusion imaging. The estimated values of axon diameter and axonal volume fraction are in agreement with their corresponding histological measurements in normal brains, with 0.96 intra-class correlation coefficient value resulting from consistency analysis. Moreover, a significant increase (p = 0.001) in WXR and diameter and decrease in axonal volume fraction in the TBI boundary were detected in the TBI rats compared with the normal rats. PMID:24836290

  3. An analytical model for estimating water exchange rate in white matter using diffusion MRI.

    PubMed

    Davoodi-Bojd, Esmaeil; Chopp, Michael; Soltanian-Zadeh, Hamid; Wang, Shiyang; Ding, Guangliang; Jiang, Quan

    2014-01-01

    Substantial effort is being expended on using micro-structural modeling of the white matter, with the goal of relating diffusion weighted magnetic resonance imaging (DWMRI) to the underlying structure of the tissue, such as axonal density. However, one of the important parameters affecting diffusion is the water exchange rate between the intra- and extra-axonal space, which has not been fully investigated and is a crucial marker of brain injury such as multiple sclerosis (MS), stroke, and traumatic brain injury (TBI). To our knowledge, there is no diffusion analytical model which includes the Water eXchange Rate (WXR) without the requirement of short gradient pulse (SGP) approximation. We therefore propose a new analytical model by deriving the diffusion signal for a permeable cylinder, assuming a clinically feasible pulse gradient spin echo (PGSE) sequence. Simulations based on Markov Random Walk confirm that the exchange parameter included in our model has a linear correlation (R2>0.88) with the actual WXR. Moreover, increasing WXR causes the estimated values of diameter and volume fraction of the cylinders to increase and decrease, respectively, which is consistent with our findings from histology measurements in tissues near TBI regions. This model was also applied to the diffusion signal acquired from ex vivo brains of 14 male (10 TBI and 4 normal) rats using hybrid diffusion imaging. The estimated values of axon diameter and axonal volume fraction are in agreement with their corresponding histological measurements in normal brains, with 0.96 intra-class correlation coefficient value resulting from consistency analysis. Moreover, a significant increase (p = 0.001) in WXR and diameter and decrease in axonal volume fraction in the TBI boundary were detected in the TBI rats compared with the normal rats.

  4. Monitoring the Dynamics of Monomer Exchange Using Electrospray Mass Spectrometry: The Case of the Dimeric Glucosamine-6-Phosphate Synthase

    NASA Astrophysics Data System (ADS)

    Chevreux, Guillaume; Atmanene, Cédric; Lopez, Philippe; Ouazzani, Jamal; Van Dorsselaer, Alain; Badet, Bernard; Badet-Denisot, Marie-Ange; Sanglier-Cianférani, Sarah

    2011-03-01

    Escherichia coli glucosamine-6-phosphate synthase (GlmS) is a dimeric enzyme from the glutamine-dependent amidotransferases family, which catalyses the conversion of D-fructose-6-phosphate (Fru6P) and glutamine (Gln) into D-glucosamine-6-phosphate (GlcN6P) and glutamate, respectively. Extensive X-ray crystallography investigations have been reported, highlighting the importance of the dimeric association to form the sugar active site as well as significant conformational changes of the protein upon substrate and product binding. In the present work, an approach based on time-resolved noncovalent mass spectrometry has been developed to study the dynamics of GlmS subunit exchange. Using 14N versus 15N labeled proteins, the kinetics of GlmS subunit exchange was monitored with the wild-type enzyme in the presence of different substrates and products as well as with the protein bearing a key amino acid mutation specially designed to weaken the dimer interface. Determination of rate constants of subunit exchange revealed important modifications of the protein dynamics: while glutamine, glutamate, and K603A mutation accelerates subunit exchange, Fru6P and GlcN6P totally prevent it. These results are described in light of the available structural information, providing additional useful data for both the characterization of GlmS catalytic process and the design of new GlmS inhibitors. Finally, time-resolved noncovalent MS can be proposed as an additional biophysical technique for real-time monitoring of protein dynamics.

  5. Maximizing T2-exchange in Dy3+DOTA-(amide)X chelates: Fine-tuning the water molecule exchange rate for enhanced T2 contrast in MRI

    PubMed Central

    Soesbe, Todd C.; Ratnakar, S. James; Milne, Mark; Zhang, Shanrong; Do, Quyen N.; Kovacs, Zoltan; Sherry, A. Dean

    2014-01-01

    Purpose The water molecule exchange rates in a series of DyDOTA-(amide)X chelates were fine-tuned to maximize the effects of T2-exchange line broadening and improve T2 contrast. Methods Four DyDOTA-(amide)X chelates having a variable number of glycinate side-arms were prepared and characterized as T2-exchange agents. The non-exchanging DyTETA chelate was also used to measure the bulk water T2 reduction due solely to T2*. The total transverse relaxivity (r2tot) at 22, 37, and 52 °C for each chelate was measured in vitro at 9.4 T (400 MHz) by fitting plots of total T2−1 versus concentration. The water molecule exchange rates for each complex were measured by fitting 17O line-width versus temperature data taken at 9.4 T (54.3 MHz). Results The measured transverse relaxivities due to water molecule exchange (r2ex) and bound water lifetimes (τM) were in excellent agreement with Swift-Connick theory, with DyDOTA-(gly)3 giving the largest r2ex = 11.8 s−1 mM−1 at 37 °C. Conclusion By fine-tuning the water molecule exchange rate at 37 °C, the transverse relaxivity has been increased by 2 to 30 times compared to previously studied Dy3+-based chelates. Polymerization or dendrimerization of the optimal chelate could yield a highly sensitive, molecule-sized T2 contrast agent for improved molecular imaging applications. PMID:24390729

  6. Long range dependence in the high frequency USD/INR exchange rate

    NASA Astrophysics Data System (ADS)

    Kumar, Dilip

    2014-02-01

    Using high frequency data, this paper examines the long memory property in the unconditional and conditional volatility of the USD/INR exchange rate at different time scales using the Local Whittle (LW), the Exact Local Whittle (ELW) and the FIAPARCH models. Results indicate that the long memory property remains quite stable across different time scales for both unconditional and conditional volatility measures. Results from the non-overlapping moving window approach indicate that the extreme events (such as the subprime crisis and the European debt crisis) resulted in highly persistent behavior of the USD/INR exchange rate and thus lead to market inefficiency. This paper also examines the long memory property in the realized volatility based on different time scale data. Results indicate that the realized volatility measures based on different scales of the high frequency data exhibit a consistent and stable long memory property. However, the realized volatility measures based on daily data exhibit lower degree of long-range dependence. This study has implications for traders and investors (with different trading horizons) and can be helpful in predicting expected future volatility and in designing and implementing trading strategies at different time scales.

  7. Emergence of dynamical complexity related to human heart rate variability

    NASA Astrophysics Data System (ADS)

    Chang, Mei-Chu; Peng, C.-K.; Stanley, H. Eugene

    2014-12-01

    We apply the refined composite multiscale entropy (MSE) method to a one-dimensional directed small-world network composed of nodes whose states are binary and whose dynamics obey the majority rule. We find that the resulting fluctuating signal becomes dynamically complex. This dynamical complexity is caused (i) by the presence of both short-range connections and long-range shortcuts and (ii) by how well the system can adapt to the noisy environment. By tuning the adaptability of the environment and the long-range shortcuts we can increase or decrease the dynamical complexity, thereby modeling trends found in the MSE of a healthy human heart rate in different physiological states. When the shortcut and adaptability values increase, the complexity in the system dynamics becomes uncorrelated.

  8. Collective firm bankruptcies and phase transition in rating dynamics

    NASA Astrophysics Data System (ADS)

    Sieczka, P.; Hołyst, J. A.

    2009-10-01

    We present a simple model of firm rating evolution. We consider two sources of defaults: individual dynamics of economic development and Potts-like interactions between firms. We show that such a defined model leads to phase transition, which results in collective defaults. The existence of the collective phase depends on the mean interaction strength. For small interaction strength parameters, there are many independent bankruptcies of individual companies. For large parameters, there are giant collective defaults of firm clusters. In the case when the individual firm dynamics favors dumping of rating changes, there is an optimal strength of the firm's interactions from the systemic risk point of view. in here

  9. Dynamic heart rate estimation using principal component analysis.

    PubMed

    Yu, Yong-Poh; Raveendran, P; Lim, Chern-Loon; Kwan, Ban-Hoe

    2015-11-01

    In this paper, facial images from various video sequences are used to obtain a heart rate reading. In this study, a video camera is used to capture the facial images of eight subjects whose heart rates vary dynamically, between 81 and 153 BPM. Principal component analysis (PCA) is used to recover the blood volume pulses (BVP) which can be used for the heart rate estimation. An important consideration for accuracy of the dynamic heart rate estimation is to determine the shortest video duration that realizes it. This video duration is chosen when the six principal components (PC) are least correlated amongst them. When this is achieved, the first PC is used to obtain the heart rate. The results obtained from the proposed method are compared to the readings obtained from the Polar heart rate monitor. Experimental results show the proposed method is able to estimate the dynamic heart rate readings using less computational requirements when compared to the existing method. The mean absolute error and the standard deviation of the absolute errors between experimental readings and actual readings are 2.18 BPM and 1.71 BPM respectively.

  10. Dynamic heart rate estimation using principal component analysis

    PubMed Central

    Yu, Yong-Poh; Raveendran, P.; Lim, Chern-Loon; Kwan, Ban-Hoe

    2015-01-01

    In this paper, facial images from various video sequences are used to obtain a heart rate reading. In this study, a video camera is used to capture the facial images of eight subjects whose heart rates vary dynamically, between 81 and 153 BPM. Principal component analysis (PCA) is used to recover the blood volume pulses (BVP) which can be used for the heart rate estimation. An important consideration for accuracy of the dynamic heart rate estimation is to determine the shortest video duration that realizes it. This video duration is chosen when the six principal components (PC) are least correlated amongst them. When this is achieved, the first PC is used to obtain the heart rate. The results obtained from the proposed method are compared to the readings obtained from the Polar heart rate monitor. Experimental results show the proposed method is able to estimate the dynamic heart rate readings using less computational requirements when compared to the existing method. The mean absolute error and the standard deviation of the absolute errors between experimental readings and actual readings are 2.18 BPM and 1.71 BPM respectively. PMID:26601022

  11. Environmental variation, vegetation distribution, carbon dynamics and water/energy exchange at high latitudes

    USGS Publications Warehouse

    McGuire, A.D.; Wirth, C.; Apps, M.; Beringer, J.; Clein, J.; Epstein, H.; Kicklighter, D.W.; Bhatti, J.; Chapin, F. S.; De Groot, B.; Efremov, D.; Eugster, W.; Fukuda, M.; Gower, T.; Hinzman, L.; Huntley, B.; Jia, G.J.; Kasischke, E.; Melillo, J.; Romanovsky, V.; Shvidenko, A.; Vaganov, E.; Walker, D.

    2002-01-01

    The responses of high latitude ecosystems to global change involve complex interactions among environmental variables, vegetation distribution, carbon dynamics, and water and energy exchange. These responses may have important consequences for the earth system. In this study, we evaluated how vegetation distribution, carbon stocks and turnover, and water and energy exchange are related to environmental variation spanned by the network of the IGBP high latitude transects. While the most notable feature of the high latitude transects is that they generally span temperature gradients from southern to northern latitudes, there are substantial differences in temperature among the transects. Also, along each transect temperature co-varies with precipitation and photosynthetically active radiation, which are also variable among the transects. Both climate and disturbance interact to influence latitudinal patterns of vegetation and soil carbon storage among the transects, and vegetation distribution appears to interact with climate to determine exchanges of heat and moisture in high latitudes. Despite limitations imposed by the data we assembled, the analyses in this study have taken an important step toward clarifying the complexity of interactions among environmental variables, vegetation distribution, carbon stocks and turnover, and water and energy exchange in high latitude regions. This study reveals the need to conduct coordinated global change studies in high latitudes to further elucidate how interactions among climate, disturbance, and vegetation distribution influence carbon dynamics and water and energy exchange in high latitudes.

  12. Dynamic UltraFast 2D EXchange SpectroscopY (UF-EXSY) of hyperpolarized substrates

    PubMed Central

    Swisher, Christine Leon; Koelsch, Bertram; Sukumar, Subramianam; Sriram, Renuka; Santos, Romelyn Delos; Wang, Zhen Jane; Kurhanewicz, John; Vigneron, Daniel; Larson, Peder

    2015-01-01

    In this work, we present a new ultrafast method for acquiring dynamic 2D EXchange SpectroscopY (EXSY) within a single acquisition. This technique reconstructs two-dimensional EXSY spectra from one-dimensional spectra based on the phase accrual during echo times. The Ultrafast-EXSY acquisition overcomes long acquisition times typically needed to acquire 2D NMR data by utilizing sparsity and phase dependence to dramatically undersample in the indirect time dimension. This allows for the acquisition of the 2D spectrum within a single shot. We have validated this method in simulations and hyperpolarized enzyme assay experiments separating the dehydration of pyruvate and lactate-to-pyruvate conversion. In a renal cell carcinoma cell (RCC) line, bidirectional exchange was observed. This new technique revealed decreased conversion of lactate-to-pyruvate with high expression of monocarboxylate transporter 4 (MCT4), known to correlate with aggressive cancer phenotypes. We also showed feasibility of this technique in vivo in a RCC model where bidirectional exchange was observed for pyruvate–lactate, pyruvate–alanine, and pyruvate–hydrate and were resolved in time. Broadly, the technique is well suited to investigate the dynamics of multiple exchange pathways and applicable to hyperpolarized substrates where chemical exchange has shown great promise across a range of disciplines. PMID:26117655

  13. Improving the replica-exchange molecular-dynamics method for efficient sampling in the temperature space.

    PubMed

    Chen, Changjun; Xiao, Yi; Huang, Yanzhao

    2015-05-01

    Replica-exchange molecular dynamics (REMD) is a popular sampling method in the molecular simulation. By frequently exchanging the replicas at different temperatures, the molecule can jump out of the minima and sample efficiently in the conformational space. Although REMD has been shown to be practical in a lot of applications, it does have a critical limitation. All the replicas at all the temperatures must be simulated for a period between the replica-exchange steps. This may be problematic for the reaction with high free energy barriers. In that case, too many replicas are required in the simulation. To reduce the calculation quantity and improve its performance, in this paper we propose a modified REMD method. During the simulation, each replica at each temperature can stay in either the active or inactive state and only switch between the states at the exchange step. In the active state, the replica moves freely in the canonical ensemble by the normal molecular dynamics, and in the inactive state, the replica is frozen temporarily until the next exchange step. The number of the replicas in the active states (active replicas) depends on the number of CPUs in the computer. Using the additional inactive replicas, one can perform an REMD simulation in a wider temperature space. The practical applications show that the modified REMD method is reliable. With the same number of active replicas, this REMD method can produce a more reasonable free energy surface around the free energy minima than the standard REMD method. PMID:26066200

  14. Dynamic UltraFast 2D EXchange SpectroscopY (UF-EXSY) of hyperpolarized substrates

    NASA Astrophysics Data System (ADS)

    Leon Swisher, Christine; Koelsch, Bertram; Sukumar, Subramianam; Sriram, Renuka; Santos, Romelyn Delos; Wang, Zhen Jane; Kurhanewicz, John; Vigneron, Daniel; Larson, Peder

    2015-08-01

    In this work, we present a new ultrafast method for acquiring dynamic 2D EXchange SpectroscopY (EXSY) within a single acquisition. This technique reconstructs two-dimensional EXSY spectra from one-dimensional spectra based on the phase accrual during echo times. The Ultrafast-EXSY acquisition overcomes long acquisition times typically needed to acquire 2D NMR data by utilizing sparsity and phase dependence to dramatically undersample in the indirect time dimension. This allows for the acquisition of the 2D spectrum within a single shot. We have validated this method in simulations and hyperpolarized enzyme assay experiments separating the dehydration of pyruvate and lactate-to-pyruvate conversion. In a renal cell carcinoma cell (RCC) line, bidirectional exchange was observed. This new technique revealed decreased conversion of lactate-to-pyruvate with high expression of monocarboxylate transporter 4 (MCT4), known to correlate with aggressive cancer phenotypes. We also showed feasibility of this technique in vivo in a RCC model where bidirectional exchange was observed for pyruvate-lactate, pyruvate-alanine, and pyruvate-hydrate and were resolved in time. Broadly, the technique is well suited to investigate the dynamics of multiple exchange pathways and applicable to hyperpolarized substrates where chemical exchange has shown great promise across a range of disciplines.

  15. Transfer Rate Edited experiment for the selective detection of Chemical Exchange via Saturation Transfer (TRE-CEST)

    NASA Astrophysics Data System (ADS)

    Friedman, Joshua I.; Xia, Ding; Regatte, Ravinder R.; Jerschow, Alexej

    2015-07-01

    Chemical Exchange Saturation Transfer (CEST) magnetic resonance experiments have become valuable tools in magnetic resonance for the detection of low concentration solutes with far greater sensitivity than direct detection methods. Accurate measures of rates of chemical exchange provided by CEST are of particular interest to biomedical imaging communities where variations in chemical exchange can be related to subtle variations in biomarker concentration, temperature and pH within tissues using MRI. Despite their name, however, traditional CEST methods are not truly selective for chemical exchange and instead detect all forms of magnetization transfer including through-space NOE. This ambiguity crowds CEST spectra and greatly complicates subsequent data analysis. We have developed a Transfer Rate Edited CEST experiment (TRE-CEST) that uses two different types of solute labeling in order to selectively amplify signals of rapidly exchanging proton species while simultaneously suppressing 'slower' NOE-dominated magnetization transfer processes. This approach is demonstrated in the context of both NMR and MRI, where it is used to detect the labile amide protons of proteins undergoing chemical exchange (at rates ⩾ 30 s-1) while simultaneously eliminating signals originating from slower (∼5 s-1) NOE-mediated magnetization transfer processes. TRE-CEST greatly expands the utility of CEST experiments in complex systems, and in-vivo, in particular, where it is expected to improve the quantification of chemical exchange and magnetization transfer rates while enabling new forms of imaging contrast.

  16. Tungsten polyoxometalate molecules as active nodes for dynamic carrier exchange in hybrid molecular/semiconductor capacitors

    SciTech Connect

    Balliou, A.; Douvas, A. M.; Normand, P.; Argitis, P.; Glezos, N.; Tsikritzis, D.; Kennou, S.

    2014-10-14

    In this work we study the utilization of molecular transition metal oxides known as polyoxometalates (POMs), in particular the Keggin structure anions of the formula PW₁₂O₄₀³⁻, as active nodes for potential switching and/or fast writing memory applications. The active molecules are being integrated in hybrid Metal-Insulator/POM molecules-Semiconductor capacitors, which serve as prototypes allowing investigation of critical performance characteristics towards the design of more sophisticated devices. The charging ability as well as the electronic structure of the molecular layer is probed by means of electrical characterization, namely, capacitance-voltage and current-voltage measurements, as well as transient capacitance measurements, C (t), under step voltage polarization. It is argued that the transient current peaks observed are manifestations of dynamic carrier exchange between the gate electrode and specific molecular levels, while the transient C (t) curves under conditions of molecular charging can supply information for the rate of change of the charge that is being trapped and de-trapped within the molecular layer. Structural characterization via surface and cross sectional scanning electron microscopy as well as atomic force microscopy, spectroscopic ellipsometry, UV and Fourier-transform IR spectroscopies, UPS, and XPS contribute to the extraction of accurate electronic structure characteristics and open the path for the design of new devices with on-demand tuning of their interfacial properties via the controlled preparation of the POM layer.

  17. The evolutionary rate dynamically tracks changes in HIV-1 epidemics

    SciTech Connect

    Maljkovic-berry, Irina; Athreya, Gayathri; Daniels, Marcus; Bruno, William; Korber, Bette; Kuiken, Carla; Ribeiro, Ruy M

    2009-01-01

    Large-sequence datasets provide an opportunity to investigate the dynamics of pathogen epidemics. Thus, a fast method to estimate the evolutionary rate from large and numerous phylogenetic trees becomes necessary. Based on minimizing tip height variances, we optimize the root in a given phylogenetic tree to estimate the most homogenous evolutionary rate between samples from at least two different time points. Simulations showed that the method had no bias in the estimation of evolutionary rates and that it was robust to tree rooting and topological errors. We show that the evolutionary rates of HIV-1 subtype B and C epidemics have changed over time, with the rate of evolution inversely correlated to the rate of virus spread. For subtype B, the evolutionary rate slowed down and tracked the start of the HAART era in 1996. Subtype C in Ethiopia showed an increase in the evolutionary rate when the prevalence increase markedly slowed down in 1995. Thus, we show that the evolutionary rate of HIV-1 on the population level dynamically tracks epidemic events.

  18. Experience with dynamic reinforcement rates decreases resistance to extinction.

    PubMed

    Craig, Andrew R; Shahan, Timothy A

    2016-03-01

    The ability of organisms to detect reinforcer-rate changes in choice preparations is positively related to two factors: the magnitude of the change in rate and the frequency with which rates change. Gallistel (2012) suggested similar rate-detection processes are responsible for decreases in responding during operant extinction. Although effects of magnitude of change in reinforcer rate on resistance to extinction are well known (e.g., the partial-reinforcement-extinction effect), effects of frequency of changes in rate prior to extinction are unknown. Thus, the present experiments examined whether frequency of changes in baseline reinforcer rates impacts resistance to extinction. Pigeons pecked keys for variable-interval food under conditions where reinforcer rates were stable and where they changed within and between sessions. Overall reinforcer rates between conditions were controlled. In Experiment 1, resistance to extinction was lower following exposure to dynamic reinforcement schedules than to static schedules. Experiment 2 showed that resistance to presession feeding, a disruptor that should not involve change-detection processes, was unaffected by baseline-schedule dynamics. These findings are consistent with the suggestion that change detection contributes to extinction. We discuss implications of change-detection processes for extinction of simple and discriminated operant behavior and relate these processes to the behavioral-momentum based approach to understanding extinction. PMID:26813330

  19. On the use of a weak-coupling thermostat in replica-exchange molecular dynamics simulations.

    PubMed

    Lin, Zhixiong; van Gunsteren, Wilfred F

    2015-07-21

    In a molecular dynamics (MD) simulation, various thermostat algorithms, including Langevin dynamics (LD), Nosé-Hoover (NH), and weak-coupling (WC) thermostats, can be used to keep the simulation temperature constant. A canonical ensemble is generated by the use of LD and NH, while the nature of the ensemble produced by WC has not yet been identified. A few years ago, it was shown that when using a WC thermostat with particular values of the temperature coupling time for liquid water at ambient temperature and pressure, the distribution of the potential energy is less wide than the canonical one. This led to an artifact in temperature replica-exchange molecular dynamics (T-REMD) simulations in which the potential energy distributions appear not to be equal to the ones of standard MD simulations. In this paper, we re-investigate this problem. We show that this artifact is probably due to the ensemble generated by WC being incompatible with the T-REMD replica-exchange criterion, which assumes a canonical configurational ensemble. We also show, however, that this artifact can be reduced or even eliminated by particular choices of the temperature coupling time of WC and the replica-exchange time period of T-REMD, i.e., when the temperature coupling time is chosen very close to the MD time step or when the exchange time period is chosen large enough. An attempt to develop a T-REMD replica-exchange criterion which is likely to be more compatible with the WC configurational ensemble is reported. Furthermore, an exchange criterion which is compatible with a microcanonical ensemble is used in total energy REMD simulations.

  20. Is the surface oxygen exchange rate linked to bulk ion diffusivity in mixed conducting Ruddlesden–Popper phases?

    DOE PAGESBeta

    Tomkiewicz, Alex C.; Tamimi, Mazin A.; Huq, Ashfia; McIntosh, Steven

    2015-03-02

    There is a possible link between oxygen surface exchange rate and bulk oxygen anion diffusivity in mixed ionic and electronic conducting oxides; it is a topic of great interest and debate. While a large body of experimental evidence and theoretical analyses support a link, observed differences between bulk and surface composition of these materials are hard to reconcile with this observation. This is further compounded by potential problems with simultaneous measurement of both parameters. Here we utilize separate techniques, in situ neutron diffraction and pulsed isotopic surface exchange, to examine bulk ion mobility and surface oxygen exchange rates of threemore » Ruddlesden-Popper phases, general form An-1A2'BnO3n+1, An-1A2'BnX3n+1; LaSrCo0.5Fe0.5O4-δ (n = 1), La0.3Sr2.7CoFeO7-δ (n = 2) and LaSr3Co1.5Fe1.5O10-δ (n = 3). These measurements are complemented by surface composition determination via high sensitivity-low energy ion scattering. We observe a correlation between bulk ion mobility and surface exchange rate between materials. The surface exchange rates vary by more than one order of magnitude with high anion mobility in the bulk of an oxygen vacancy-rich n = 2 Ruddlesden-Popper material correlating with rapid oxygen exchange. Furthermore this is in contrast with the similar surface exchange rates which we may expect due to similar surface compositions across all three samples. This paper conclude that experimental limitations lead to inherent convolution of surface and bulk rates, and that surface exchange steps are not likely to be rate limiting in oxygen incorporation.« less

  1. Is the surface oxygen exchange rate linked to bulk ion diffusivity in mixed conducting Ruddlesden-Popper phases?

    PubMed

    Tomkiewicz, Alex C; Tamimi, Mazin A; Huq, Ashfia; McIntosh, Steven

    2015-01-01

    The possible link between oxygen surface exchange rate and bulk oxygen anion diffusivity in mixed ionic and electronic conducting oxides is a topic of great interest and debate. While a large body of experimental evidence and theoretical analyses support a link, observed differences between bulk and surface composition of these materials are hard to reconcile with this observation. This is further compounded by potential problems with simultaneous measurement of both parameters. Here we utilize separate techniques, in situ neutron diffraction and pulsed isotopic surface exchange, to examine bulk ion mobility and surface oxygen exchange rates of three Ruddlesden-Popper phases, general form A(n-1)A(2)'B(n)O(3n+1), A(n-1)A(2)'B(n)X(3n+1); LaSrCo(0.5)Fe(0.5)O(4-δ) (n = 1), La(0.3)Sr(2.7)CoFeO(7-δ) (n = 2) and LaSr3Co(1.5)Fe(1.5)O(10-δ) (n = 3). These measurements are complemented by surface composition determination via high sensitivity-low energy ion scattering. We observe a correlation between bulk ion mobility and surface exchange rate between materials. The surface exchange rates vary by more than one order of magnitude with high anion mobility in the bulk of an oxygen vacancy-rich n = 2 Ruddlesden-Popper material correlating with rapid oxygen exchange. This is in contrast with the similar surface exchange rates which we may expect due to similar surface compositions across all three samples. We conclude that experimental limitations lead to inherent convolution of surface and bulk rates, and that surface exchange steps are not likely to be rate limiting in oxygen incorporation.

  2. Metabolic analyzer. [for measuring metabolic rate and breathing dynamics of human beings

    NASA Technical Reports Server (NTRS)

    Rummel, J. A.; Perry, C. L. (Inventor)

    1974-01-01

    An apparatus is described for the measurement of metabolic rate and breathing dynamics in which inhaled and exhaled breath are sensed by sealed, piston-displacement type spirometers. These spirometers electrically measure the volume of inhaled and exhaled breath. A mass spectrometer analyzes simultaneously for oxygen, carbon dioxide, nitrogen and water vapor. Computation circuits are responsive to the outputs of the spirometers, mass spectrometer, temperature, pressure and timing signals and compute oxygen consumption, carbon dioxide production, minute volume and respiratory exchange ratio. A selective indicator provides for read-out of these data at predetermined cyclic intervals.

  3. Competition between abstraction and exchange channels in H + HCN reaction: Full-dimensional quantum dynamics

    SciTech Connect

    Jiang, Bin; Guo, Hua

    2013-12-14

    Dynamics of the title reaction is investigated on an ab initio based potential energy surface using a full-dimensional quantum wave packet method within the centrifugal sudden approximation. It is shown that the reaction between H and HCN leads to both the hydrogen exchange and hydrogen abstraction channels. The exchange channel has a lower threshold and larger cross section than the abstraction channel. It also has more oscillations due apparently to quantum resonances. Both channels are affected by long-lived resonances supported by potential wells. Comparison with experimental cross sections indicates underestimation of the abstraction barrier height.

  4. Competition between abstraction and exchange channels in H + HCN reaction: Full-dimensional quantum dynamics

    NASA Astrophysics Data System (ADS)

    Jiang, Bin; Guo, Hua

    2013-12-01

    Dynamics of the title reaction is investigated on an ab initio based potential energy surface using a full-dimensional quantum wave packet method within the centrifugal sudden approximation. It is shown that the reaction between H and HCN leads to both the hydrogen exchange and hydrogen abstraction channels. The exchange channel has a lower threshold and larger cross section than the abstraction channel. It also has more oscillations due apparently to quantum resonances. Both channels are affected by long-lived resonances supported by potential wells. Comparison with experimental cross sections indicates underestimation of the abstraction barrier height.

  5. Local dynamics of heart rate: detection and prognostic implications.

    PubMed

    Moss, Travis J; Lake, Douglas E; Moorman, J Randall

    2014-10-01

    The original observation that reduced heart rate variability (HRV) confers poor prognosis after myocardial infarction has been followed by many studies of heart rate dynamics. We tested the hypothesis that an entropy-based local dynamics measure gave prognostic information in ambulatory patients undergoing 24-h electrocardiography. In this context, entropy is the probability that short templates will find matches in the time series. We studied RR interval time series from 24-h Holter monitors of 1564 consecutive patients over age 39. We generated histograms of the count of templates as a function of the number of templates matches in short RR interval time series, and found characteristic appearance of histograms for atrial fibrillation, sinus rhythm with normal HRV, and sinus rhythm with reduced HRV and premature ventricular contractions (PVCs). We developed statistical models to detect the abnormal dynamic phenotype of reduced HRV with PVCs and fashioned a local dynamics score (LDs) that, after controlling for age, added more prognostic information than other standard risk factors and common HRV metrics, including, to our surprise, the PVC count and the HRV of normal-to-normal intervals. Addition of the LDs to a predictive model using standard risk factors significantly increased the ROC area and the net reclassification improvement was 27%. We conclude that abnormal local dynamics of heart rate confer adverse prognosis in patients undergoing 24-h ambulatory electrocardiography.

  6. THE RATE OF EXCHANGE OF TRITIATED WATER ACROSS THE HUMAN RED CELL MEMBRANE

    PubMed Central

    Paganelli, C. V.; Solomon, A. K.

    1957-01-01

    The flow method of reaction rate measurement has been adapted to the determination of the rate of diffusion of water into the human red cell. In seven experiments the half-time for diffusion exchange has been found to be 4.2 ± 1.1 msec., which is equivalent to a diffusion flow of 8.6 x 10–9 ml. H2O/(sec., red cell). This figure has been compared with the rate of water entrance under an osmotic pressure gradient, and has been found to be smaller by a factor of 2.5. The difference between these two rates of water entrance has been interpreted as indicating the presence of water-filled channels in the membrane. An estimate of the equivalent radius of these channels (on the assumption of uniform right cylindrical pores) leads to a value of 3.5 Å, which is viewed as an operational description of the resistance offered by the membrane to the passage of water. PMID:13475690

  7. Amide proton exchange rates of oxidized and reduced Saccharomyces cerevisiae iso-1-cytochrome c.

    PubMed Central

    Marmorino, J. L.; Auld, D. S.; Betz, S. F.; Doyle, D. F.; Young, G. B.; Pielak, G. J.

    1993-01-01

    Proton NMR spectroscopy was used to determine the rate constant, kobs, for exchange of labile protons in both oxidized (Fe(III)) and reduced (Fe(II)) iso-1-cytochrome c. We find that slowly exchanging backbone amide protons tend to lack solvent-accessible surface area, possess backbone hydrogen bonds, and are present in regions of regular secondary structure as well as in omega-loops. Furthermore, there is no correlation between kobs and the distance from a backbone amide nitrogen to the nearest solvent-accessible atom. These observations are consistent with the local unfolding model. Comparisons of the free energy change for denaturation, delta Gd, at 298 K to the free energy change for local unfolding, delta Gop, at 298 K for the oxidized protein suggest that certain conformations possessing higher free energy than the denatured state are detected at equilibrium. Reduction of the protein results in a general increase in delta Gop. Comparisons of delta Gd to delta Gop for the reduced protein show that the most open states of the reduced protein possess more structure than its chemically denatured form. This persistent structure in high-energy conformations of the reduced form appears to involve the axially coordinated heme. PMID:8268806

  8. Transfer Rate Edited experiment for the selective detection of Chemical Exchange via Saturation Transfer (TRE-CEST).

    PubMed

    Friedman, Joshua I; Xia, Ding; Regatte, Ravinder R; Jerschow, Alexej

    2015-07-01

    Chemical Exchange Saturation Transfer (CEST) magnetic resonance experiments have become valuable tools in magnetic resonance for the detection of low concentration solutes with far greater sensitivity than direct detection methods. Accurate measures of rates of chemical exchange provided by CEST are of particular interest to biomedical imaging communities where variations in chemical exchange can be related to subtle variations in biomarker concentration, temperature and pH within tissues using MRI. Despite their name, however, traditional CEST methods are not truly selective for chemical exchange and instead detect all forms of magnetization transfer including through-space NOE. This ambiguity crowds CEST spectra and greatly complicates subsequent data analysis. We have developed a Transfer Rate Edited CEST experiment (TRE-CEST) that uses two different types of solute labeling in order to selectively amplify signals of rapidly exchanging proton species while simultaneously suppressing 'slower' NOE-dominated magnetization transfer processes. This approach is demonstrated in the context of both NMR and MRI, where it is used to detect the labile amide protons of proteins undergoing chemical exchange (at rates⩾30s(-1)) while simultaneously eliminating signals originating from slower (∼5s(-1)) NOE-mediated magnetization transfer processes. TRE-CEST greatly expands the utility of CEST experiments in complex systems, and in-vivo, in particular, where it is expected to improve the quantification of chemical exchange and magnetization transfer rates while enabling new forms of imaging contrast. PMID:25996515

  9. Improved measurement of labile proton concentration-weighted chemical exchange rate (kws) with experimental factor-compensated and T1-normalized quantitative chemical exchange saturation transfer (CEST) MRI

    PubMed Central

    Wu, Renhua; Liu, Charng-Ming; Liu, Philip K; Sun, Phillip Zhe

    2012-01-01

    Chemical exchange saturation transfer (CEST) MRI enables measurement of dilute CEST agents and microenvironment properties such as pH and temperature, holding great promise for in vivo applications. However, because of confounding concomitant RF irradiation and relaxation effects, the CEST-weighted MRI contrast may not fully characterize the underlying CEST phenomenon. We postulated that the accuracy of quantitative CEST MRI could be improved if the experimental factors (labeling efficiency and RF spillover effect) were estimated and taken into account. Specifically, the experimental factor was evaluated as a function of exchange rate and CEST agent concentration ratio, which remained relatively constant for intermediate RF irradiation power levels. Hence, the experimental factors can be calculated based on the reasonably estimated exchange rate and labile proton concentration ratio, which significantly improved quantification. The simulation was confirmed with Creatine phantoms of serially varied concentration titrated to the same pH, whose reverse exchange rate (kws) was found to be linearly correlated with the concentration. In summary, the proposed solution provides simplified yet reasonably accurate quantification of the underlying CEST system, which may help guide the ongoing development of quantitative CEST MRI. PMID:22649044

  10. Organic matter remineralization and porewater exchange rates in permeable South Atlantic Bight continental shelf sediments

    NASA Astrophysics Data System (ADS)

    Jahnke, Richard; Richards, Mary; Nelson, James; Robertson, Charles; Rao, Alexandra; Jahnke, Deborah

    2005-08-01

    South Atlantic Bight (SAB) continental shelf sediments are characterized by high permeabilities, substantial benthic microalgal photosynthesis, and rapid tidally driven bottom currents. Primary productivity by benthic microalgae rivals water column production for much of the shelf area for most of the year and porewater exchange proceeds at rates of 2-100 (mean 34) times that of molecular diffusion. In this environment, traditional techniques of porewater diffusion calculations and benthic flux chamber incubations do not yield accurate estimates of integrated sedimentary reaction and metabolic rates. Between 1995 and 2001, porewater nutrient distributions have been determined on sediment cores recovered on 24 separate expeditions to the central shelf. Measurements demonstrate that standing stocks of porewater nutrients vary significantly seasonally. Replicate whole core incubations from 1999-2001 conducted over a seasonal cycle reveal that remineralization rates vary seasonally by more than a factor of 18, in response to changes in bottom temperature and possibly organic carbon input. These results suggest that changes in remineralization rate and not changes in porewater advective transport rate are the primary factor accounting for the observed seasonal differences in porewater nutrient inventories. Integrating the observed remineralization rates over the shelf area and throughout an annual cycle implies that approximately 3.8 Tg C, equivalent to 17% of the integrated mid-shelf water column production, is recycled annually in the sediments below the surface benthic microalgal layer of the South Atlantic Bight. Including respiration associated with the sediment surface photosynthetic community implies that the sediments account for approximately half of the total metabolic carbon turnover in this shelf system.

  11. Effects of flooding on ion exchange rates in an Upper Mississippi River floodplain forest impacted by herbivory, invasion, and restoration

    USGS Publications Warehouse

    Kreiling, Rebecca; DeJager, Nathan R.; Whitney Swanson,; Eric A. Strauss,; Meredith Thomsen,

    2015-01-01

    We examined effects of flooding on supply rates of 14 nutrients in floodplain areas invaded by Phalaris arundinacea (reed canarygrass), areas restored to young successional forests (browsed by white-tailed deer and unbrowsed), and remnant mature forests in the Upper Mississippi River floodplain. Plant Root Simulator ion-exchange probes were deployed for four separate 28-day periods. The first deployment occurred during flooded conditions, while the three subsequent deployments were conducted during progressively drier periods. Time after flooding corresponded with increases in NO3 −-N, K+ and Zn+2, decreases in H2PO4 −-P, Fe+3, Mn+2, and B(OH)4-B, a decrease followed by an increase in NH4 +-N, Ca+2, Mg+2 and Al+3, and an increase followed by a decrease for SO4 −2-S. Plant community type had weak to no effects on nutrient supply rates compared to the stronger effects of flooding duration. Our results suggest that seasonal dynamics in floodplain nutrient availability are similarly driven by flood pulses in different community types. However, reed canarygrass invasion has potential to increase availability of some nutrients, while restoration of forest cover may promote recovery of nutrient availability to that observed in reference mature forests.

  12. Two-component mixture model: Application to palm oil and exchange rate

    NASA Astrophysics Data System (ADS)

    Phoong, Seuk-Yen; Ismail, Mohd Tahir; Hamzah, Firdaus Mohamad

    2014-12-01

    Palm oil is a seed crop which is widely adopt for food and non-food products such as cookie, vegetable oil, cosmetics, household products and others. Palm oil is majority growth in Malaysia and Indonesia. However, the demand for palm oil is getting growth and rapidly running out over the years. This phenomenal cause illegal logging of trees and destroy the natural habitat. Hence, the present paper investigates the relationship between exchange rate and palm oil price in Malaysia by using Maximum Likelihood Estimation via Newton-Raphson algorithm to fit a two components mixture model. Besides, this paper proposes a mixture of normal distribution to accommodate with asymmetry characteristics and platykurtic time series data.

  13. Removal Dynamics of Immunoglobulin and Fibrinogen by Conventional Plasma Exchange, Selective Plasma Exchange, and a Combination of the Two.

    PubMed

    Miyamoto, Satoko; Ohkubo, Atsushi; Seshima, Hiroshi; Maeda, Takuma; Itagaki, Ayako; Kurashima, Naoki; Iimori, Soichiro; Naito, Shotaro; Sohara, Eisei; Rai, Tatemitsu; Uchida, Shinichi; Okado, Tomokazu

    2016-08-01

    While plasma exchange (PE) can eliminate plasma proteins, including all immunoglobulin (Ig) and coagulation factors, selective plasma exchange (SePE) can retain fibrinogen (Fbg). Here, we investigated the removal dynamics of Ig and Fbg in 53 patients with immunological disorders by PE, SePE, and a combination of the two. When the mean processed plasma volume (PPV) was 0.9 plasma volume (PV), the mean percent reductions of Ig and Fbg by PE were both approximately 62%-65%. When the mean PPV was 1.1 PV, the mean percent reductions by SePE were 53.1% for IgG, 30.1% for IgA, 3.6% for IgM, and 19.0% for Fbg, respectively. In the three plasmapheresis sessions performed on alternate days, we classified treatments into three categories: PE group (PE-PE-PE, N = 2), SePE group (SePE-SePE-SePE, N = 14), and PE/SePE group (PE-SePE-SePE, N = 4). The mean percent reductions of IgG, IgA, IgM, and Fbg were 82.0%, 80.4%, 87.3%, and 80.9%, respectively, for the PE group; 76.4%, 57.7%, 43.3%, and 35.9%, respectively, for the PE/SePE group; and 75.4%, 50.6%, 3.2%, and 29.3%, respectively, for the SePE group. Plasmapheresis modalities can be combined according to clinical conditions, for instance, to achieve both the unspecific removal of pathogens by PE and retention of coagulation factors, such as Fbg, by SePE. PMID:27523073

  14. Rates of diffusion in dynamical systems with random jumps

    NASA Astrophysics Data System (ADS)

    Kobre, Elisha J.

    2005-12-01

    This dissertation explores the diffusion properties of a large class of measures under a dynamical system on bigcup i=0infinity S1i with randomly occurring jumps that behave according to a particular probability distribution. The drift rate for the center of mass of the system is then defined and is shown to be well defined Lebesgue almost everywhere. Properties of the drift rate are then explored. In particular the drift rate is shown to be continuous as a function of the probability "jump" distribution and, in a special case, it is shown that the drift rate increases with the probability of jumping. Finally, a central limit theorem for fluctuations about the drift rate is proved. The results are obtained by modeling the system as a random map on a compact space, and using the ergodic properties of the random map.

  15. Generalized rate-equation analysis of excitation exchange between silicon nanoclusters and erbium ions

    SciTech Connect

    Kenyon, A. J.; Wojdak, M.; Ahmad, I.; Loh, W. H.; Oton, C. J.

    2008-01-15

    We discuss the use of rate equations to analyze the sensitization of erbium luminescence by silicon nanoclusters. In applying the general form of second-order coupled rate-equations to the Si nanocluster-erbium system, we find that the photoluminescence dynamics cannot be described using a simple rate equation model. Both rise and fall times exhibit a stretched exponential behavior, which we propose arises from a combination of a strongly distance-dependent nanocluster-erbium interaction, along with the finite size distribution and indirect band gap of the silicon nanoclusters. Furthermore, the low fraction of erbium ions that can be excited nonresonantly is a result of the small number of ions coupled to nanoclusters.

  16. Energy exchange analysis in droplet dynamics via the Navier–Stokes–Cahn–Hilliard model

    NASA Astrophysics Data System (ADS)

    Espath, L. F. R.; Sarmiento, A. F.; Vignal, P.; Varga, B. O. N.; Cortes, A. M. A.; Dalcin, L.; Calo, V. M.

    2016-06-01

    We develop the energy budget equation of the coupled Navier-Stokes-Cahn-Hilliard (NSCH) system. We use the NSCH equations to model the dynamics of liquid droplets in a liquid continuum. Buoyancy effects are accounted for through the Boussinesq assumption. We physically interpret each quantity involved in the energy exchange to further insight into the model. Highly resolved simulations involving density-driven flows and merging of droplets allow us to analyze these energy budgets. In particular, we focus on the energy exchanges when droplets merge, and describe flow features relevant to this phenomenon. By comparing our numerical simulations to analytical predictions and experimental results available in the literature, we conclude that modeling droplet dynamics within the framework of NSCH equations is a sensible approach worth further research.

  17. Exact-exchange time-dependent density-functional theory for static and dynamic polarizabilities

    SciTech Connect

    Hirata, So; Ivanov, Stanislav; Bartlett, Rodney J.; Grabowski, Ireneusz

    2005-03-01

    Time-dependent density-functional theory (TDDFT) employing the exact-exchange functional has been formulated on the basis of the optimized-effective-potential (OEP) method of Talman and Shadwick for second-order molecular properties and implemented into a Gaussian-basis-set, trial-vector algorithm. The only approximation involved, apart from the lack of correlation effects and the use of Gaussian-type basis functions, was the consistent use of the adiabatic approximation in the exchange kernel and in the linear response function. The static and dynamic polarizabilities and their anisotropy predicted by the TDDFT with exact exchange (TDOEP) agree accurately with the corresponding values from time-dependent Hartree-Fock theory, the exact-exchange counterpart in the wave function theory. The TDOEP is free from the nonphysical asymptotic decay of the exchange potential of most conventional density functionals or from any other manifestations of the incomplete cancellation of the self-interaction energy. The systematic overestimation of the absolute values and dispersion of polarizabilities that plagues most conventional TDDFT cannot be seen in the TDOEP.

  18. Dynamics of leaf gas exchange, chlorophyll fluorescence and stem diameter changes during freezing and thawing of Scots pine seedlings.

    PubMed

    Lindfors, Lauri; Hölttä, Teemu; Lintunen, Anna; Porcar-Castell, Albert; Nikinmaa, Eero; Juurola, Eija

    2015-12-01

    Boreal trees experience repeated freeze-thaw cycles annually. While freezing has been extensively studied in trees, the dynamic responses occurring during the freezing and thawing remain poorly understood. At freezing and thawing, rapid changes take place in the water relations of living cells in needles and in stem. While freezing is mostly limited to extracellular spaces, living cells dehydrate, shrink and their osmotic concentration increases. We studied how the freezing-thawing dynamics reflected on leaf gas exchange, chlorophyll fluorescence and xylem and living bark diameter changes of Scots pine (Pinus sylvestris L.) saplings in controlled experiments. Photosynthetic rate quickly declined following ice nucleation and extracellular freezing in xylem and needles, almost parallel to a rapid shrinking of xylem diameter, while that of living bark followed with a slightly longer delay. While xylem and living bark diameters responded well to decreasing temperature and water potential of ice, the relationship was less consistent in the case of increasing temperature. Xylem showed strong temporal swelling at thawing suggesting water movement from bark. After thawing xylem diameter recovered to a pre-freezing level but living bark remained shrunk. We found that freezing affected photosynthesis at multiple levels. The distinct dynamics of photosynthetic rate and stomatal conductance reveals that the decreased photosynthetic rate reflects impaired dark reactions rather than stomatal closure. Freezing also inhibited the capacity of the light reactions to dissipate excess energy as heat, via non-photochemical quenching, whereas photochemical quenching of excitation energy decreased gradually with temperature in agreement with the gas exchange data. PMID:26423334

  19. MuSTAR MD: multi-scale sampling using temperature accelerated and replica exchange molecular dynamics.

    PubMed

    Yamamori, Yu; Kitao, Akio

    2013-10-14

    A new and efficient conformational sampling method, MuSTAR MD (Multi-scale Sampling using Temperature Accelerated and Replica exchange Molecular Dynamics), is proposed to calculate the free energy landscape on a space spanned by a set of collective variables. This method is an extension of temperature accelerated molecular dynamics and can also be considered as a variation of replica-exchange umbrella sampling. In the MuSTAR MD, each replica contains an all-atom fine-grained model, at least one coarse-grained model, and a model defined by the collective variables that interacts with the other models in the same replica through coupling energy terms. The coarse-grained model is introduced to drive efficient sampling of large conformational space and the fine-grained model can serve to conduct more accurate conformational sampling. The collective variable model serves not only to mediate the coarse- and fine-grained models, but also to enhance sampling efficiency by temperature acceleration. We have applied this method to Ala-dipeptide and examined the sampling efficiency of MuSTAR MD in the free energy landscape calculation compared to that for replica exchange molecular dynamics, replica exchange umbrella sampling, temperature accelerated molecular dynamics, and conventional MD. The results clearly indicate the advantage of sampling a relatively high energy conformational space, which is not sufficiently sampled with other methods. This feature is important in the investigation of transition pathways that go across energy barriers. MuSTAR MD was also applied to Met-enkephalin as a test case in which two Gō-like models were employed as the coarse-grained model.

  20. On the accuracy of instantaneous gas exchange rates, energy expenditure, and respiratory quotient calculations obtained in indirect whole room calorimeter

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This paper analyzes the accuracy of metabolic rate calculations performed in the whole room indirect calorimeter using the molar balance equations. The equations are treated from the point of view of cause-effect relationship where the gaseous exchange rates representing the unknown causes need to b...

  1. Simultaneous determination of labile proton concentration and exchange rate utilizing optimal RF power: Radio frequency power (RFP) dependence of chemical exchange saturation transfer (CEST) MRI

    NASA Astrophysics Data System (ADS)

    Sun, Phillip Zhe

    2010-02-01

    Chemical exchange saturation transfer (CEST) MRI is increasingly used to probe mobile proteins and microenvironment properties, and shows great promise for tumor and stroke diagnosis. However, CEST MRI contrast mechanism is complex, depending not only on the CEST agent concentration, exchange and relaxation properties, but also varying with experimental conditions such as magnetic field strength and RF power. Hence, it remains somewhat difficult to quantify apparent CEST MRI contrast for properties such as pH, temperature and protein content. In particular, CEST MRI is susceptible to RF spillover effects in that RF irradiation may directly saturate the bulk water MR signal, leading to an optimal RF power at which the CEST contrast is maximal. Whereas RF spillover is generally considered an adverse effect, it is noted here that the optimal RF power strongly varies with exchange rate, although with negligible dependence on labile proton concentration. An empirical solution suggested that optimal RF power may serve as a sensitive parameter for simultaneously determining the labile proton content and exchange rate, hence, allowing improved characterization of the CEST system. The empirical solution was confirmed by numerical simulation, and experimental validation is needed to further evaluate the proposed technique.

  2. Kinetic bottlenecks to chemical exchange rates for deep-sea animals II: Carbon dioxide

    NASA Astrophysics Data System (ADS)

    Hofmann, A. F.; Peltzer, E. T.; Brewer, P. G.

    2012-11-01

    Increased ocean acidification from fossil fuel CO2 invasion, from temperature-driven changes in respiration, and from possible leakage from sub-seabed geologic CO2 disposal has aroused concern over the impacts of elevated CO2 concentrations on marine life. Discussion of these impacts has so far focused only on changes in the oceanic bulk fluid properties (ΔpH, Δ[∑CO2] etc.) as the critical variable and with a major focus on carbonate shell dissolution. Here we describe the rate problem for animals that must export CO2 at about the same rate at which O2 is consumed. We analyze the basic properties controlling CO2 export within the diffusive boundary layer around marine animals in an ocean changing in temperature (T) and CO2 concentration in order to compare the challenges posed by O2 uptake under stress with the equivalent problem of CO2 expulsion. The problem is more complex than that for a non-reactive gas since, as with gas exchange of CO2 at the air-sea interface, the influence of the ensemble of reactions within the CO2-HCO3--CO32- acid-base system needs to be considered. These reactions significantly facilitate CO2 efflux compared to O2 intake at equal temperature, pressure and flow rate under typical oceanic concentrations.The effect of these reactions can be described by an enhancement factor. For organisms, this means mechanically increasing flow over their surface to thin the boundary layer as is required to alleviate O2 stress seems not necessary to facilitate CO2 efflux. Nevertheless the elevated pCO2 cost most likely is non-zero. Regionally as with O2 the combination of T, P, and pH/pCO2 creates a zone of maximum CO2 stress at around 1000 m depth. But the net result is that, for the problem of gas exchange with the bulk ocean, the combination of an increasing T combined with declining O2 poses a greater challenge to marine life than does increasing CO2. The relationships developed here allow a more accurate prediction of the impacts on marine life

  3. Influence of molecular packing and phospholipid type on rates of cholesterol exchange

    SciTech Connect

    Lund-Katz, S.; Laboda, H.M.; McLean, L.R.; Phillips, M.C.

    1986-05-01

    The rate-limiting step for transfer of cholesterol molecules between membranes and lipoproteins is desorption from the donor lipid-water interface. Cholesterol-phospholipid (PL) interactions influence this process so that at 50/sup 0/C the halftimes for transfer of (/sup 14/C)cholesterol from liquid-crystal, small unilamellar vesicles (SUV) containing 10 mol % cholesterol in egg phosphatidylcholine (PC), dipalmitoyl PC and egg or brain sphingomyelin (SM) are about 0.5, 3 and 5 h, respectively. The molecular packing in these cholesterol-PC mixtures has been investigated using (/sup 13/C)NMR and monolayer techniques. The relaxation times of the 4-(/sup 13/C)cholesterol nucleus in SUV of the above PL are essentially the same suggesting that the fast and slow molecular motions of the cholesterol molecules are similar in all bilayers. Comparison of surface pressure-molecular area isotherms of mixed cholesterol-PL monolayers indicates that the relative condensations of average PL molecular areas by cholesterol increase in the order unsaturated PC < saturated PC < SM. It follows that tighter molecular packing in the lipid-water interface correlates with a slower rate of cholesterol exchange. Because SM are generally more saturated than PC, increasing the SM/PC ratio increases the residence time of cholesterol molecules in a given PL environment. Such an effect is observed in human LDL compared to HDL.

  4. Can Heart Rate Variability be used to Estimate Gas Exchange Threshold in Obese Adolescents?

    PubMed

    Vasconcellos, F; Seabra, A; Montenegro, R; Cunha, F; Bouskela, E; Farinatti, P

    2015-07-01

    This study investigated the agreement and reliability of oxygen uptake (V̇O2), V̇O2 reserve (V̇O2 R), heart rate (HR) and power output at intensities corresponding to the gas exchange threshold (GET) and heart rate variability threshold (HRVT) during maximal cardiopulmonary exercise testing (CPET) in obese and eutrophic adolescents. A further aim was to establish whether the HRVT was able to detect changes in cardio-respiratory fitness in obese adolescents after 3 months of recreational soccer practice. First, 25 obese and 10 eutrophic adolescents (ages 12-17) visited the laboratory twice to perform cycling CPET to test the reliability of CPET outcomes at GET and HRVT. Furthermore, the level of agreement between GET and HRVT was determined for a subgroup of 10 obese adolescents after performing a 3-month recreational soccer program. No significant difference was found for V̇O2, %V̇O2 R, HR and power output at the GET and HRVT (P>0.05), which were equally able to detect improvements in aerobic fitness after the soccer intervention. Correlations between GET and HRVT for V̇O2 and %V̇O2 R ranged from 0.89 to 0.95 (P<0.001) and test-retest reliability ranged from 0.59 to 0.82 (P<0.006). Overall, HRVT seems to be a reliable alternative for prescribing aerobic exercise intensity in obese adolescents.

  5. Influence of magnesium sulfate on HCO3/Cl transmembrane exchange rate in human erythrocytes.

    PubMed

    Chernyshova, Ekaterina S; Zaikina, Yulia S; Tsvetovskaya, Galina A; Strokotov, Dmitry I; Yurkin, Maxim A; Serebrennikova, Elena S; Volkov, Leonid; Maltsev, Valeri P; Chernyshev, Andrei V

    2016-03-21

    Magnesium sulfate (MgSO4) is widely used in medicine but molecular mechanisms of its protection through influence on erythrocytes are not fully understood and are considerably controversial. Using scanning flow cytometry, in this work for the first time we observed experimentally (both in situ and in vitro) a significant increase of HCO3(-)/Cl(-) transmembrane exchange rate of human erythrocytes in the presence of MgSO4 in blood. For a quantitative analysis of the obtained experimental data, we introduced and verified a molecular kinetic model, which describes activation of major anion exchanger Band 3 (or AE1) by its complexation with free intracellular Mg(2+) (taking into account Mg(2+) membrane transport and intracellular buffering). Fitting the model to our in vitro experimental data, we observed a good correspondence between theoretical and experimental kinetic curves that allowed us to evaluate the model parameters and to estimate for the first time the association constant of Mg(2+) with Band 3 as KB~0.07mM, which is in agreement with known values of the apparent Mg(2+) dissociation constant (from 0.01 to 0.1mM) that reflects experiments on enrichment of Mg(2+) at the inner erythrocyte membrane (Gunther, 2007). Results of this work partly clarify the molecular mechanisms of MgSO4 action in human erythrocytes. The method developed allows one to estimate quantitatively a perspective of MgSO4 treatment for a patient. It should be particularly helpful in prenatal medicine for early detection of pathologies associated with the risk of fetal hypoxia.

  6. Heart Rate and Energy Expenditure During Aqua Dynamics.

    PubMed

    Vickery, S R; Cureton, K J; Langstaff, J L

    1983-03-01

    In brief: The heart rate, oxygen uptake, and energy expenditure of three young women were measured during 20-minute low-gear, 30-minute middle-gear, and 60-minute high-gear aqua dynamics workouts. All three workouts were moderate in intensity, eliciting average heart rates of 132 to 143 beats min(-1) (70% to 77% HR max), average oxygen uptakes of 1.2 to 1.3 liters min(-1) (51% to 57% VO2 max), and average energy expenditures of 5.9 to 6.5 kcals min(-1) The findings indicate that aqua dynamics could be a beneficial conditioning program for people who have relatively low physical work capacity and enjoy swimming but cannot conveniently engage in lap swimming. PMID:27409547

  7. Heart rate dynamics preceding hemorrhage in the intensive care unit.

    PubMed

    Moss, Travis J; Clark, Matthew T; Lake, Douglas E; Moorman, J Randall; Calland, J Forrest

    2015-01-01

    Occult hemorrhage in surgical/trauma intensive care unit (STICU) patients is common and may lead to circulatory collapse. Continuous electrocardiography (ECG) monitoring may allow for early identification and treatment, and could improve outcomes. We studied 4,259 consecutive admissions to the STICU at the University of Virginia Health System. We collected ECG waveform data captured by bedside monitors and calculated linear and non-linear measures of the RR interbeat intervals. We tested the hypothesis that a transfusion requirement of 3 or more PRBC transfusions in a 24 hour period is preceded by dynamical changes in these heart rate measures and performed logistic regression modeling. We identified 308 hemorrhage events. A multivariate model including heart rate, standard deviation of the RR intervals, detrended fluctuation analysis, and local dynamics density had a C-statistic of 0.62. Earlier detection of hemorrhage might improve outcomes by allowing earlier resuscitation in STICU patients.

  8. A molecular dynamics study of bond exchange reactions in covalent adaptable networks.

    PubMed

    Yang, Hua; Yu, Kai; Mu, Xiaoming; Shi, Xinghua; Wei, Yujie; Guo, Yafang; Qi, H Jerry

    2015-08-21

    Covalent adaptable networks are polymers that can alter the arrangement of network connections by bond exchange reactions where an active unit attaches to an existing bond then kicks off its pre-existing peer to form a new bond. When the polymer is stretched, bond exchange reactions lead to stress relaxation and plastic deformation, or the so-called reforming. In addition, two pieces of polymers can be rejoined together without introducing additional monomers or chemicals on the interface, enabling welding and reprocessing. Although covalent adaptable networks have been researched extensively in the past, knowledge about the macromolecular level network alternations is limited. In this study, molecular dynamics simulations are used to investigate the macromolecular details of bond exchange reactions in a recently reported epoxy system. An algorithm for bond exchange reactions is first developed and applied to study a crosslinking network formed by epoxy resin DGEBA with the crosslinking agent tricarballylic acid. The trace of the active units is tracked to show the migration of these units within the network. Network properties, such as the distance between two neighboring crosslink sites, the chain angle, and the initial modulus, are examined after each iteration of the bond exchange reactions to provide detailed information about how material behaviors and macromolecular structure evolve. Stress relaxation simulations are also conducted. It is found that even though bond exchange reactions change the macroscopic shape of the network, microscopic network characteristic features, such as the distance between two neighboring crosslink sites and the chain angle, relax back to the unstretched isotropic state. Comparison with a recent scaling theory also shows good agreement.

  9. Numerical exploration of Kaldorian interregional macrodynamics: stability and the trade threshold for business cycles under fixed exchange rates.

    PubMed

    Asada, Toichiro; Douskos, Christos; Markellos, Panagiotis

    2011-01-01

    The stability of equilibrium and the possibility of generation of business cycles in a discrete interregional Kaldorian macrodynamic model with fixed exchange rates are explored using numerical methods. One of the aims is to illustrate the feasibility and effectiveness of the numerical approach for dynamical systems of moderately high dimensionality and several parameters. The model considered is five-dimensional with four parameters, the speeds of adjustment of the goods markets and the degrees of economic interactions between the regions through trade and capital movement. Using a grid search method for the determination of the region of stability of equilibrium in two-dimensional parameter subspaces, and coefficient criteria for the flip bifurcation - and Hopf bifurcation - curve, we determine the stability region in several parameter ranges and identify Hopf bifurcation curves when they exist. It is found that interregional cycles emerge only for sufficient interregional trade. The relevant threshold is predicted by the model at 14 - 16 % of trade transactions. By contrast, no minimum level of capital mobility exists in a global sense as a requirement for the emergence of interregional cycles; the main conclusion being, therefore, that cycles may occur for very low levels of capital mobility if trade is sufficient. Examples of bifurcation and Lyapunov exponent diagrams illustrating the occurrence of cycles or period doubling, and examples of the development of the occurring cycles, are given. Both supercritical and subcritical bifurcations are found to occur, the latter type indicating coexistence of a point and a cyclical attractor.

  10. IMPACT OF SMALL COLUMN ION EXCHANGE STREAMS ON DWPF GLASS FORMULATION MELT RATE STUDIES

    SciTech Connect

    Fox, K.; Miller, D.; Koopman, D.

    2011-04-26

    This study was undertaken to evaluate the potential impacts of the Small Column Ion Exchange (SCIX) streams - particularly the addition of Monosodium Titanate (MST) and Crystalline Silicotitanate (CST) - on the melt rate of simulated feed for the Defense Waste Processing Facility (DWPF). Additional MST was added to account for contributions from the Salt Waste Processing Facility (SWPF). The Savannah River National Laboratory (SRNL) Melt Rate Furnace (MRF) was used to evaluate four melter feed compositions: two with simulated SCIX and SWPF material and two without. The Slurry-fed Melt Rate Furnace (SMRF) was then used to compare two different feeds: one with and one without bounding concentrations of simulated SCIX and SWPF material. Analyses of the melter feed materials confirmed that they met their targeted compositions. Four feeds were tested in triplicate in the MRF. The linear melt rates were determined by using X-ray computed tomography to measure the height of the glass formed along the bottom of the beakers. The addition of the SCIX and SWPF material reduced the average measured melt rate by about 10% in MRF testing, although there was significant scatter in the data. Two feeds were tested in the SMRF. It was noted that the ground CST alone (ground CST with liquid in a bucket) was extremely difficult to resuspend during preparation of the feed with material from SCIX and SWPF. This feed was also more difficult to pump than the material without MST and CST due to settling occurring in the melter feed line, although the yield stress of both feeds was high relative to the DWPF design basis. Steady state feeding conditions were maintained for about five hours for each feed. There was a reduction in the feed and pour rates of approximately 15% when CST and MST were added to the feed, although there was significant scatter in the data. Analysis of samples collected from the SMRF pour stream showed that the composition of the glass changed as expected when MST and

  11. Central metal ion exchange in a coordination polymer based on lanthanide ions and di(2-ethylhexyl)phosphoric acid: exchange rate and tunable affinity.

    PubMed

    Tasaki-Handa, Yuiko; Abe, Yukie; Ooi, Kenta; Tanaka, Mikiya; Wakisaka, Akihiro

    2014-01-01

    In this paper the exchange of lanthanide(III) ions (Ln(3+)) between a solution and a coordination polymer (CP) of di(2-ethylhexyl)phosphoric acid (Hdehp), [Ln(dehp)3], is studied. Kinetic and selectivity studies suggest that a polymeric network of [Ln(dehp)3] has different characteristics than the corresponding monomeric complex. The reaction rate is remarkably slow and requires over 600 h to reach in nearly equilibrium, and this can be explained by the polymeric crystalline structure and high valency of Ln(3+). The affinity of the exchange reaction reaches a maximum with the Ln(3+) possessing an ionic radius 7% smaller than that of the central Ln(3+), therefore, the affinity of the [Ln(dehp)3] is tunable based on the choice of the central metal ion. Such unique affinity, which differs from the monomeric complex, can be explained by two factors: the coordination preference and steric strain caused by the polymeric structure. The latter likely becomes predominant for Ln(3+) exchange when the ionic radius of the ion in solution is smaller than the original Ln(3+) by more than 7%. Structural studies suggest that the incoming Ln(3+) forms a new phase though an exchange reaction, and this could plausibly cause the structural strain.

  12. Dynamics of nitrate limitation on gaseous nitrogen exchanges from pristine peatlands

    NASA Astrophysics Data System (ADS)

    Roobroeck, D.; Brüggemann, N.; Butterbach-Bahl, K.; Boeckx, P.

    2009-04-01

    The cycling of gaseous nitrogen species in peatland ecosystems and the functioning of driving forces on microbial denitrification rates are poorly accounted. Physico-chemical soil conditions and biotic interactions1 control the availability of nitrate for respiratory denitrification resulting in high spatial variability of gaseous nitrogen exchange rates in nutrient poor peat soils and complicating impact assessment of eutrophication. The responses of nitrous oxide (N2O) and dinitrogen (N2) fluxes to nitrate addition were compared between distinct contrasts in plant growth at a pristine, hummocky peatland. Allowing to determine the dynamics of nitrate limitation on gaseous nitrogen exchanges in accordance to covariance in soil anaerobiosis and resource competition. Two quantification techniques were applied parallel to soil core incubations in order to determine N2O and N2 fluxes. Helium atmosphere incubation was used for direct quantification of net N2O and N2 fluxes. Reducing the background N2 concentration in the soil atmosphere to approx. 20 ppm enabled highly sensitive measurement of N2 fluxes. On the other hand a 15N-N2O tracer technique was explored as a tool to demonstrate and quantify gross consumption rates of atmospheric N2O to N2 and recycling of gaseous N-losses by microbial fixation. The headspace N2O pool was increased with 0.03 ppm 15•15N-N2O rendering an enrichment of ± 9.8 atom% 15•15N-N2O. Triplicate soil core samples were taken from two contrasting soil habitat in a hummocky, Carex dominated fen located in the Biebrza National Park, NE Poland (53 °07′N; 23 °10′E). The hummocks had a gravimetric soil water content of 76.6 ± 2.2% and high root abundance, dissimilar to 83.4 ± 1.0% and little root prevalence in the hollows. Singular nitrate addition, comparable to the atmospheric NOY -deposition, was applied two days in advance of flux measurement. Actual net gaseous nitrogen fluxes and responses to nitrate addition were apparently

  13. Heart rate dynamics in different levels of Zen meditation.

    PubMed

    Peressutti, Caroline; Martín-González, Juan M; M García-Manso, Juan; Mesa, Denkô

    2010-11-01

    The dynamic interactions among physiological rhythms imbedded in the heart rate signal can give valuable insights into autonomic modulation in conditions of reduced outward attention. Therefore, in this study we analyzed the heart rate variability (HRV) in different levels of practice in Zen meditation (Zazen). Nineteen subjects with variable experience took part in this study. In four special cases we collected both HRV and respiration data. The time series were analyzed in frequency domain and also using the Continuous Wavelet Transform, which detects changes in the time domain and in the frequency domain simultaneously. The shifts in the respiratory modulation of heart rate, or respiratory sinus arrhythmia (RSA), reflect the different levels of practice among practitioners with variable experience in Zazen; in turn the modulation of the RSA may reflect changes in the breathing pattern as in the parasympathetic outflow related to the quality and focus of attention in each stage.

  14. Stochastic heart-rate model can reveal pathologic cardiac dynamics

    NASA Astrophysics Data System (ADS)

    Kuusela, Tom

    2004-03-01

    A simple one-dimensional Langevin-type stochastic difference equation can simulate the heart-rate fluctuations in a time scale from minutes to hours. The model consists of a deterministic nonlinear part and a stochastic part typical of Gaussian noise, and both parts can be directly determined from measured heart-rate data. Data from healthy subjects typically exhibit the deterministic part with two or more stable fixed points. Studies of 15 congestive heart-failure subjects reveal that the deterministic part of pathologic heart dynamics has no clear stable fixed points. Direct simulations of the stochastic model for normal and pathologic cases can produce statistical parameters similar to those of real subjects. Results directly indicate that pathologic situations simplify the heart-rate control system.

  15. Electron-Nuclear Dynamics of collision processes: Charge exchange and energy loss

    NASA Astrophysics Data System (ADS)

    Cabrera-Trujillo, Remigio; Sabin, John R.; Öhrn, Yngve; Deumens, Erik

    2004-03-01

    We present the Electron-Nuclear Dynamics (END) method for the study of time-dependent scattering processes. The END is a general approach for treating time-dependent problems which includes the dynamics of electrons and nuclei simultaneously by considering the full electron-nuclear coupling in the system and thus eliminates the necessity of constructing potential-energy surfaces. The theory approximates the time dependent Schrödinger equation starting from the time dependent variational principle by deriving a Hamiltonian dynamical system for time dependent nuclear and electronic wave function parameters. The wave function is described in a coherent state manifold, which leads to a system of Hamilton's equations of motion. Emphasis is put on electron exchange, differential cross section and energy loss (stopping cross section) of collision of ions, atoms and molecules involving H, He, C, N, O, and Ne atoms. We compare our results to available experimental data.

  16. Rowing Crew Coordination Dynamics at Increasing Stroke Rates

    PubMed Central

    2015-01-01

    In rowing, perfect synchronisation is important for optimal performance of a crew. Remarkably, a recent study on ergometers demonstrated that antiphase crew coordination might be mechanically more efficient by reducing the power lost to within-cycle velocity fluctuations of the boat. However, coupled oscillator dynamics predict the stability of the coordination to decrease with increasing stroke rate, which in case of antiphase may eventually yield breakdowns to in-phase. Therefore, this study examined the effects of increasing stroke rate on in- and antiphase crew coordination in rowing dyads. Eleven experienced dyads rowed on two mechanically coupled ergometers on slides, which allowed the ergometer system to move back and forth as one ‘boat’. The dyads performed a ramp trial in both in- and antiphase pattern, in which stroke rates gradually increased from 30 strokes per minute (spm) to as fast as possible in steps of 2 spm. Kinematics of rowers, handles and ergometers were captured. Two dyads showed a breakdown of antiphase into in-phase coordination at the first stroke rate of the ramp trial. The other nine dyads reached between 34–42 spm in antiphase but achieved higher rates in in-phase. As expected, the coordinative accuracy in antiphase was worse than in in-phase crew coordination, while, somewhat surprisingly, the coordinative variability did not differ between the patterns. Whereas crew coordination did not substantially deteriorate with increasing stroke rate, stroke rate did affect the velocity fluctuations of the ergometers: fluctuations were clearly larger in the in-phase pattern than in the antiphase pattern, and this difference significantly increased with stroke rate. Together, these results suggest that although antiphase rowing is less stable (i.e., less resistant to perturbation), potential on-water benefits of antiphase over in-phase rowing may actually increase with stroke rate. PMID:26185987

  17. Gas Exchange Rates for a First-Order Stream Determined With Deliberate and Natural Tracers

    NASA Astrophysics Data System (ADS)

    Wanninkhof, R.; Mulholland, P. J.; Elwood, J. W.

    1990-07-01

    Gas transfer velocities have been determined for a first-order stream by performing a 3-hour release of the volatile tracer sulfur hexafluoride, SF6, and the nonvolatile tracer tritiated water, 3H2O. The average gas transfer velocity for the 292-m reach was 29 cm/h which corresponds to a reaeration coefficient for oxygen at 25°C of 134 day-1. Groundwater inflow along the stream was corrected for by measuring the downstream dilution of the 3H2O spike. Downstream discharge increased from 0.5 L/s, 2 m downstream of the point of tracer release, to 19.3 L/s at a point 292 m downstream. As an alternative to using (radioactive) 3H2O, we investigated the possibility of using natural radon, 222Rn, as a groundwater tag and using the variation of SF6 and 222Rn along the stream to determine gas exchange rates and groundwater inflow. The method yielded an average transfer velocity of 21 cm/h and underestimated the groundwater inflow by a factor of 3. This large discrepancy is attributed to a doubling of stream discharge between the time the stream was sampled for radon and the tracer experiment and the limited number of radon samples.

  18. Measuring and modeling air exchange rates inside taxi cabs in Los Angeles, California

    NASA Astrophysics Data System (ADS)

    Shu, Shi; Yu, Nu; Wang, Yueyan; Zhu, Yifang

    2015-12-01

    Air exchange rates (AERs) have a direct impact on traffic-related air pollutant (TRAP) levels inside vehicles. Taxi drivers are occupationally exposed to TRAP on a daily basis, yet there is limited measurement of AERs in taxi cabs. To fill this gap, AERs were quantified in 22 representative Los Angeles taxi cabs including 10 Prius, 5 Crown Victoria, 3 Camry, 3 Caravan, and 1 Uplander under realistic driving (RD) conditions. To further study the impacts of window position and ventilation settings on taxi AERs, additional tests were conducted on 14 taxis with windows closed (WC) and on the other 8 taxis with not only windows closed but also medium fan speed (WC-MFS) under outdoor air mode. Under RD conditions, the AERs in all 22 cabs had a mean of 63 h-1 with a median of 38 h-1. Similar AERs were observed under WC condition when compared to those measured under RD condition. Under WC-MFS condition, AERs were significantly increased in all taxi cabs, when compared with those measured under RD condition. A General Estimating Equation (GEE) model was developed and the modeling results showed that vehicle model was a significant factor in determining the AERs in taxi cabs under RD condition. Driving speed and car age were positively associated with AERs but not statistically significant. Overall, AERs measured in taxi cabs were much higher than typical AERs people usually encounter in indoor environments such as homes, offices, and even regular passenger vehicles.

  19. Predicting residential air exchange rates from questionnaires and meteorology: model evaluation in central North Carolina.

    PubMed

    Breen, Michael S; Breen, Miyuki; Williams, Ronald W; Schultz, Bradley D

    2010-12-15

    A critical aspect of air pollution exposure models is the estimation of the air exchange rate (AER) of individual homes, where people spend most of their time. The AER, which is the airflow into and out of a building, is a primary mechanism for entry of outdoor air pollutants and removal of indoor source emissions. The mechanistic Lawrence Berkeley Laboratory (LBL) AER model was linked to a leakage area model to predict AER from questionnaires and meteorology. The LBL model was also extended to include natural ventilation (LBLX). Using literature-reported parameter values, AER predictions from LBL and LBLX models were compared to data from 642 daily AER measurements across 31 detached homes in central North Carolina, with corresponding questionnaires and meteorological observations. Data was collected on seven consecutive days during each of four consecutive seasons. For the individual model-predicted and measured AER, the median absolute difference was 43% (0.17 h(-1)) and 40% (0.17 h(-1)) for the LBL and LBLX models, respectively. Additionally, a literature-reported empirical scale factor (SF) AER model was evaluated, which showed a median absolute difference of 50% (0.25 h(-1)). The capability of the LBL, LBLX, and SF models could help reduce the AER uncertainty in air pollution exposure models used to develop exposure metrics for health studies.

  20. Intelligent Soft Computing on Forex: Exchange Rates Forecasting with Hybrid Radial Basis Neural Network.

    PubMed

    Falat, Lukas; Marcek, Dusan; Durisova, Maria

    2016-01-01

    This paper deals with application of quantitative soft computing prediction models into financial area as reliable and accurate prediction models can be very helpful in management decision-making process. The authors suggest a new hybrid neural network which is a combination of the standard RBF neural network, a genetic algorithm, and a moving average. The moving average is supposed to enhance the outputs of the network using the error part of the original neural network. Authors test the suggested model on high-frequency time series data of USD/CAD and examine the ability to forecast exchange rate values for the horizon of one day. To determine the forecasting efficiency, they perform a comparative statistical out-of-sample analysis of the tested model with autoregressive models and the standard neural network. They also incorporate genetic algorithm as an optimizing technique for adapting parameters of ANN which is then compared with standard backpropagation and backpropagation combined with K-means clustering algorithm. Finally, the authors find out that their suggested hybrid neural network is able to produce more accurate forecasts than the standard models and can be helpful in eliminating the risk of making the bad decision in decision-making process. PMID:26977450

  1. Measurement of air exchange rates in different indoor environments using continuous CO2 sensors.

    PubMed

    You, Yan; Niu, Can; Zhou, Jian; Liu, Yating; Bai, Zhipeng; Zhang, Jiefeng; He, Fei; Zhang, Nan

    2012-01-01

    A new air exchange rate (AER) monitoring method using continuous CO2 sensors was developed and validated through both laboratory experiments and field studies. Controlled laboratory simulation tests were conducted in a 1-m3 environmental chamber at different AERs (0.1-10.0 hr(-1)). AERs were determined using the decay method based on box model assumptions. Field tests were conducted in classrooms, dormitories, meeting rooms and apartments during 2-5 weekdays using CO2 sensors coupled with data loggers. Indoor temperature, relative humidity (RH), and CO2 concentrations were continuously monitored while outdoor parameters combined with on-site climate conditions were recorded. Statistical results indicated that good laboratory performance was achieved: duplicate precision was within 10%, and the measured AERs were 90%-120% of the real AERs. Average AERs were 1.22, 1.37, 1.10, 1.91 and 0.73 hr(-1) in dormitories, air-conditioned classrooms, classrooms with an air circulation cooling system, reading rooms, and meeting rooms, respectively. In an elderly particulate matter exposure study, all the homes had AER values ranging from 0.29 to 3.46 hr(-1) in fall, and 0.12 to 1.39 hr(-1) in winter with a median AER of 1.15.

  2. Intelligent Soft Computing on Forex: Exchange Rates Forecasting with Hybrid Radial Basis Neural Network.

    PubMed

    Falat, Lukas; Marcek, Dusan; Durisova, Maria

    2016-01-01

    This paper deals with application of quantitative soft computing prediction models into financial area as reliable and accurate prediction models can be very helpful in management decision-making process. The authors suggest a new hybrid neural network which is a combination of the standard RBF neural network, a genetic algorithm, and a moving average. The moving average is supposed to enhance the outputs of the network using the error part of the original neural network. Authors test the suggested model on high-frequency time series data of USD/CAD and examine the ability to forecast exchange rate values for the horizon of one day. To determine the forecasting efficiency, they perform a comparative statistical out-of-sample analysis of the tested model with autoregressive models and the standard neural network. They also incorporate genetic algorithm as an optimizing technique for adapting parameters of ANN which is then compared with standard backpropagation and backpropagation combined with K-means clustering algorithm. Finally, the authors find out that their suggested hybrid neural network is able to produce more accurate forecasts than the standard models and can be helpful in eliminating the risk of making the bad decision in decision-making process.

  3. Intelligent Soft Computing on Forex: Exchange Rates Forecasting with Hybrid Radial Basis Neural Network

    PubMed Central

    Marcek, Dusan; Durisova, Maria

    2016-01-01

    This paper deals with application of quantitative soft computing prediction models into financial area as reliable and accurate prediction models can be very helpful in management decision-making process. The authors suggest a new hybrid neural network which is a combination of the standard RBF neural network, a genetic algorithm, and a moving average. The moving average is supposed to enhance the outputs of the network using the error part of the original neural network. Authors test the suggested model on high-frequency time series data of USD/CAD and examine the ability to forecast exchange rate values for the horizon of one day. To determine the forecasting efficiency, they perform a comparative statistical out-of-sample analysis of the tested model with autoregressive models and the standard neural network. They also incorporate genetic algorithm as an optimizing technique for adapting parameters of ANN which is then compared with standard backpropagation and backpropagation combined with K-means clustering algorithm. Finally, the authors find out that their suggested hybrid neural network is able to produce more accurate forecasts than the standard models and can be helpful in eliminating the risk of making the bad decision in decision-making process. PMID:26977450

  4. Is the surface oxygen exchange rate linked to bulk ion diffusivity in mixed conducting Ruddlesden–Popper phases?

    SciTech Connect

    Tomkiewicz, Alex C.; Tamimi, Mazin A.; Huq, Ashfia; McIntosh, Steven

    2015-03-02

    There is a possible link between oxygen surface exchange rate and bulk oxygen anion diffusivity in mixed ionic and electronic conducting oxides; it is a topic of great interest and debate. While a large body of experimental evidence and theoretical analyses support a link, observed differences between bulk and surface composition of these materials are hard to reconcile with this observation. This is further compounded by potential problems with simultaneous measurement of both parameters. Here we utilize separate techniques, in situ neutron diffraction and pulsed isotopic surface exchange, to examine bulk ion mobility and surface oxygen exchange rates of three Ruddlesden-Popper phases, general form An-1A2'BnO3n+1, An-1A2'BnX3n+1; LaSrCo0.5Fe0.5O4-δ (n = 1), La0.3Sr2.7CoFeO7-δ (n = 2) and LaSr3Co1.5Fe1.5O10-δ (n = 3). These measurements are complemented by surface composition determination via high sensitivity-low energy ion scattering. We observe a correlation between bulk ion mobility and surface exchange rate between materials. The surface exchange rates vary by more than one order of magnitude with high anion mobility in the bulk of an oxygen vacancy-rich n = 2 Ruddlesden-Popper material correlating with rapid oxygen exchange. Furthermore this is in contrast with the similar surface exchange rates which we may expect due to similar surface compositions across all three samples. This paper conclude that experimental limitations lead to inherent convolution of surface and bulk rates, and that surface exchange steps are not likely to be rate limiting in oxygen incorporation.

  5. Determinants of protein elution rates from preparative ion-exchange adsorbents.

    PubMed

    Angelo, James M; Lenhoff, Abraham M

    2016-04-01

    The rate processes involved in elution in preparative chromatography can affect both peak resolution and hence selectivity as well as practical factors such as facility fit. These processes depend on the physical structure of the adsorbent particles, the amount of bound solute, the solution conditions for operation or some combination of these factors. Ion-exchange adsorbents modified with covalently attached or grafted polymer layers have become widely used in preparative chromatography. Their often easily accessible microstructures offer substantial binding capacities for biomolecules, but elution has sometimes been observed to be undesirably slow. In order to determine which physicochemical phenomena control elution behavior, commercially available cellulosic, dextran-grafted and unmodified agarose materials were characterized here by their elution profiles at various conditions, including different degrees of loading. Elution data were analyzed under the assumption of purely diffusion-limited control, including the role of pore structure properties such as porosity and tortuosity. In general, effective elution rates decreased with the reduction of accessible pore volume, but differences among different proteins indicated the roles of additional factors. Additional measurements and analysis, including the use of confocal laser scanning microscopy to observe elution within single chromatographic particles, indicated the importance of protein association within the particle during elution. The use of protein stabilizing agents was explored in systems presenting atypical elution behavior, and l-arginine and disaccharide excipients were shown to alleviate the effects for one protein, lysozyme, in the presence of sodium chloride. Incorporation of these excipients into eluent buffer gave rise to faster elution and significantly lower pool volumes in elution from polymer-modified adsorbents.

  6. THE EFFECT OF SALINITY ON RATES OF ELEMENTAL MERCURY AIR/WATER EXCHANGE

    EPA Science Inventory

    The U.S. EPA laboratory in Athens, Georgia i spursuing the goal of developing a model for describing toxicant vapor phase air/water exchange under all relevant environmental conditions. To date, the two-layer exchange model (suitable for low wind speed conditions) has been modif...

  7. 78 FR 69418 - Patient Protection and Affordable Care Act; Exchanges and Qualified Health Plans, Quality Rating...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-11-19

    ... Plans; Exchange Standards for Employers, 77 FR 18310 (Mar. 27, 2012) (to be codified at 45 CFR parts 155... Quality for Exchanges: http://www.gpo.gov/fdsys/pkg/FR-2012-11-27/pdf/2012-28473.pdf . Importance: the... Rule 78 FR 12834 (Feb. 25, 2013) (to be codified at 45 CFR parts 147, 155 and 156). The draft...

  8. Simulating the frontal instability of lock-exchange density currents with dissipative particle dynamics

    NASA Astrophysics Data System (ADS)

    Li, Yanggui; Geng, Xingguo; Wang, Heping; Zhuang, Xin; Ouyang, Jie

    2016-06-01

    The frontal instability of lock-exchange density currents is numerically investigated using dissipative particle dynamics (DPD) at the mesoscopic particle level. For modeling two-phase flow, the “color” repulsion model is adopted to describe binary fluids according to Rothman-Keller method. The present DPD simulation can reproduce the flow phenomena of lock-exchange density currents, including the lobe-and-cleft instability that appears at the head, as well as the formation of coherent billow structures at the interface behind the head due to the growth of Kelvin-Helmholtz instability. Furthermore, through the DPD simulation, some small-scale characteristics can be observed, which are difficult to be captured in macroscopic simulation and experiment.

  9. High-resolution determination of 147Pm in urine using dynamic ion-exchange chromatography.

    PubMed

    Elchuk, S; Lucy, C A; Burns, K I

    1992-10-15

    A procedure has been developed for measuring 147Pm in bioassay samples, based on the separation and preconcentration of 147Pm from the urine matrix by adsorption onto a conventional cation-exchange column with final separation and purification by HPLC using dynamic ion-exchange chromatography. The concentration of 147Pm is determined by collecting the appropriate HPLC fraction and measuring the 147Pm by liquid scintillation counting. The limit of detection is 0.1 Bq (3 fg) 147Pm based on a 500-mL sample of urine and a counting time of 30 min with a background of 100 cpm. Ten samples can be processed in 1.5-2 days.

  10. Communication: Engineered tunable decay rate and controllable dissipative dynamics

    SciTech Connect

    Lue Zhiguo; Zheng Hang

    2012-03-28

    We investigate the steering dissipative dynamics of a two-level system (qubit) by means of the modulation of an assisted tunneling degree of freedom which is described by a quantum-oscillator spin-boson model. Our results reveal that the decoherence rate of the qubit can be significantly suppressed and simultaneously its quality factor is enhanced. Moreover, the modulated dynamical susceptibility exhibits a multi-peak feature which is indicative of the underlying structure and measurable in experiment. Our findings demonstrate that the interplay between the combined degrees of freedom and the qubit is crucial for reducing the dissipation of qubit and expanding the coherent regime of quantum operation much large. The strategy might be used to fight against deterioration of quantum coherence in quantum information processing.

  11. Turning Rate Dynamics of Zebrafish Exposed to Ethanol

    NASA Astrophysics Data System (ADS)

    Mwaffo, Violet; Porfiri, Maurizio

    2015-06-01

    Zebrafish is emerging as a species of choice in alcohol-related pharmacological studies. In these studies, zebrafish are often exposed to acute ethanol treatments and their activity scored during behavioral assays. Computational modeling of zebrafish behavior is expected to positively impact these efforts by offering a predictive toolbox to plan hypothesis-driven studies, reduce the number of subjects, perform pilot trials, and refine behavioral screening. In this work, we demonstrate the use of the recently proposed jump persistent turning walker to model the turning rate dynamics of zebrafish exposed to acute ethanol administration. This modeling framework is based on a stochastic mean reverting jump process to capture the sudden and large changes in orientation of swimming zebrafish. The model is calibrated on an available experimental dataset of 40 subjects, tested at different ethanol concentrations. We demonstrate that model parameters are modulated by ethanol administration, whereby both the relaxation rate and jump frequency of the turning rate dynamics are influenced by ethanol concentration. This effort offers a first evidence for the possibility of complementing zebrafish pharmacological research with computational modeling of animal behavior.

  12. Ultrafast Study of Dynamic interfacial Exchange Coupling in Ferromagnet/Oxide/Semiconductor Heterostructures

    NASA Astrophysics Data System (ADS)

    Ou, Yu-Sheng; Chiu, Yi-Hsin; Harmon, Nicholas; Odenthal, Patrick; Sheffield, Matthew; Chilcote, Michael; Kawakami, Roland; Flatté, Michael; Johnston-Halperin, Ezekiel

    Time-resolved Kerr/Faraday rotation (TRKR/TRFR) is employed to study GaAs spin dynamics in the regime of strong and dynamic exchange coupling to an adjacent MgO/Fe layer. This study reveals a dramatic, resonant suppression in the inhomogeneous spin lifetime (T2*) in the GaAs layer. Further investigation of the magnetization dynamics of the neighboring Fe layer, also using TRKR/TRFR, reveals not only the expected Kittel-dispersion but also additional lower frequency modes with very short lifetime (65 ps) that are not easily observed with conventional ferromagnetic resonance (FMR) techniques. These results suggest the intriguing possibility of resonant dynamic spin transfer between the GaAs and Fe spin systems. We discuss the potential for this work to establish GaAs spin dynamics as an efficient detector of spin dissipation and transport in the regime of dynamically-driven spin injection in ferromagnet/semiconductor heterostructures. Center for Emergent Materials; U.S. Department of Energy.

  13. Dynamic Regulation of Histone Modifications in Xenopus Oocytes through Histone Exchange

    PubMed Central

    Stewart, M. David; Sommerville, John; Wong, Jiemin

    2006-01-01

    Histone H3 lysine 9 (H3K9) methylation has broad roles in transcriptional repression, gene silencing, maintenance of heterochromatin, and epigenetic inheritance of heterochromatin. Using Xenopus laevis oocytes, we have previously shown that targeting G9a, an H3K9 histone methyltransferase, to chromatin increases H3K9 methylation and consequently represses transcription. Here we report that treatment with trichostatin A induces histone acetylation and is sufficient to activate transcription repressed by G9a, and this activation is accompanied by a reduction in dimethyl H3K9 (H3K9me2). We tested the possibility that the reduction in H3K9me2 was due to the replacement of methylated H3 with unmethylated H3.3. Surprisingly, we found that both free H3 and H3.3 are continually exchanged with chromatin-associated histones. This dynamic exchange of chromatin-associated H3 with free H3/H3.3 was not affected by alterations in transcriptional activity, elongation, acetylation, H3K9 methylation, or DNA replication. In support of this continual histone exchange model, we show that maintenance of H3K9 methylation at a specific site requires the continual presence of an H3K9 histone methyltransferase. Upon dissociation of the methyltransferase, H3K9 methylation decreases. Taken together, our data suggest that chromatin-associated and non-chromatin-associated histones are continually exchanged in the Xenopus oocyte, creating a highly dynamic chromatin environment. PMID:16943430

  14. The Dynamic Hyporheic Zone: Variability of Groundwater-Surface Water Exchange at Multiple Temporal Scales

    NASA Astrophysics Data System (ADS)

    Binley, A. M.; Dudley-Southern, M. J.

    2014-12-01

    The pathways of exchange of surface water and groundwater can have a significant influence on the delivery of nutrient-rich groundwater to streams. Many studies have revealed how the spatial variability of physical properties (sediment permeability, bedform structures, etc.) at the interface of groundwater and surface water can impact on flow pathways and residence times of hyporheic exchange flow. Here we explore the temporal variability of flow pathways at this interface. We focus on observations made on a study reach of the River Leith, UK but also provide evidence of dynamic exchanges at a number of other study sites. Under baseflow conditions, the study reach of the River Leith shows a predominance of upwelling of groundwater to the river, and in some sections of the reach a significant groundwater discharge zone in evident. However, from observations of piezometric heads made over a two year study period, repeated reversal of flow direction was observed during storm events. By deploying novel miniature electrode sensors in the river bed we were able to monitor the migration of surface water during these events. Penetration of river water to depths of 30cm was observed during monitored events, which support the reported reversal of hydraulic gradients. We, therefore, observed event-driven hyporheic exchange flow. The duration and frequency of such events may have significant impact on the biogeochemistry of shallow river bed sediments within this reach. Furthermore, temporal variability of exchange is not limited to such events: changes in regional groundwater flow pathways over longer time scales may have a significant impact on the location of localised upwelling; at much shorter timescales we see evidence of diurnal fluctuations in hydraulic heads due to evapotranspiration processes. We report on similar observations at companion study sites and discuss implications on the management of water quality in these groundwater fed systems.

  15. Electron-Nuclear Dynamics of atomic and molecular collisions: Charge exchange and energy loss

    NASA Astrophysics Data System (ADS)

    Cabrera-Trujillo, Remigio; Sabin, John R.; Ohrn, Yngve; Deumens, Erik

    2004-05-01

    Processes like electron exchange (capture and loss), bond breaking, and chemical reactions are difficult to visualize and treat in a time-independent approach. In this work, we present the Electron-Nuclear Dynamics (END) method for the study of time-dependent scattering processes. The END is a general approach for treating time-dependent problems which includes the dynamics of electrons and nuclei simultaneously by considering the full electron-nuclear coupling in the system and thus eliminates the necessity of constructing potential-energy surfaces. The theory approximates the time dependent Schrödinger equation starting from the time dependent variational principle (TDVP) by deriving a Hamiltonian dynamical system for time dependent nuclear and electronic wave function parameters. The wave function is described in a coherent state manifold, which leads to a system of Hamilton's equations of motion. The resulting system of coupled, first order, ordinary differential equations approximates the Schrödinger equation. A detailed analysis of the END equations is given for the case of a single-determinantal state for the electrons and a classical treatment of the nuclei. Emphasis is put on electron exchange, differential cross section and energy loss (stopping cross section) of collision of ions, atoms and molecules involving H, He, C, N, O, and Ne atoms. We compare our results to available experimental data.

  16. Probing protein dynamics and function under native and mildly denaturing conditions with hydrogen exchange and mass spectrometry

    NASA Astrophysics Data System (ADS)

    Kaltashov, Igor A.

    2005-02-01

    A combination of hydrogen exchange and mass spectrometry emerged in recent years as a powerful experimental tool capable of probing both structural and dynamic features of proteins. Although its concept is very simple, the interpretation of experimental data is not always straightforward, as a combination of chemical reactions (isotope exchange) and dynamic processes within protein molecules give rise to convoluted exchange patterns. This paper provides a historical background of this technique, candid assessment of its current state and limitations and a discussion of promising recent developments that can result in tremendous improvements and a dramatic expansion of the scope of its applications.

  17. Circulating protein synthesis rates reveal skeletal muscle proteome dynamics

    PubMed Central

    Shankaran, Mahalakshmi; King, Chelsea L.; Angel, Thomas E.; Holmes, William E.; Li, Kelvin W.; Colangelo, Marc; Price, John C.; Turner, Scott M.; Bell, Christopher; Hamilton, Karyn L.; Miller, Benjamin F.; Hellerstein, Marc K.

    2015-01-01

    Here, we have described and validated a strategy for monitoring skeletal muscle protein synthesis rates in rodents and humans over days or weeks from blood samples. We based this approach on label incorporation into proteins that are synthesized specifically in skeletal muscle and escape into the circulation. Heavy water labeling combined with sensitive tandem mass spectrometric analysis allowed integrated synthesis rates of proteins in muscle tissue across the proteome to be measured over several weeks. Fractional synthesis rate (FSR) of plasma creatine kinase M-type (CK-M) and carbonic anhydrase 3 (CA-3) in the blood, more than 90% of which is derived from skeletal muscle, correlated closely with FSR of CK-M, CA-3, and other proteins of various ontologies in skeletal muscle tissue in both rodents and humans. Protein synthesis rates across the muscle proteome generally changed in a coordinate manner in response to a sprint interval exercise training regimen in humans and to denervation or clenbuterol treatment in rodents. FSR of plasma CK-M and CA-3 revealed changes and interindividual differences in muscle tissue proteome dynamics. In human subjects, sprint interval training primarily stimulated synthesis of structural and glycolytic proteins. Together, our results indicate that this approach provides a virtual biopsy, sensitively revealing individualized changes in proteome-wide synthesis rates in skeletal muscle without a muscle biopsy. Accordingly, this approach has potential applications for the diagnosis, management, and treatment of muscle disorders. PMID:26657858

  18. El Niño Southern Oscillation (ENSO) enhances CO2 exchange rates in freshwater Marsh ecosystems in the Florida everglades.

    PubMed

    Malone, Sparkle L; Staudhammer, Christina L; Oberbauer, Steven F; Olivas, Paulo; Ryan, Michael G; Schedlbauer, Jessica L; Loescher, Henry W; Starr, Gregory

    2014-01-01

    This research examines the relationships between El Niño Southern Oscillation (ENSO), water level, precipitation patterns and carbon dioxide (CO2) exchange rates in the freshwater wetland ecosystems of the Florida Everglades. Data was obtained over a 5-year study period (2009-2013) from two freshwater marsh sites located in Everglades National Park that differ in hydrology. At the short-hydroperiod site (Taylor Slough; TS) and the long-hydroperiod site (Shark River Slough; SRS) fluctuations in precipitation patterns occurred with changes in ENSO phase, suggesting that extreme ENSO phases alter Everglades hydrology which is known to have a substantial influence on ecosystem carbon dynamics. Variations in both ENSO phase and annual net CO2 exchange rates co-occurred with changes in wet and dry season length and intensity. Combined with site-specific seasonality in CO2 exchanges rates, El Niño and La Niña phases magnified season intensity and CO2 exchange rates at both sites. At TS, net CO2 uptake rates were higher in the dry season, whereas SRS had greater rates of carbon sequestration during the wet season. As La Niña phases were concurrent with drought years and extended dry seasons, TS became a greater sink for CO2 on an annual basis (-11 to -110 g CO2 m-2 yr-1) compared to El Niño and neutral years (-5 to -43.5 g CO2 m-2 yr-1). SRS was a small source for CO2 annually (1.81 to 80 g CO2 m-2 yr-1) except in one exceptionally wet year that was associated with an El Niño phase (-16 g CO2 m-2 yr-1). Considering that future climate predictions suggest a higher frequency and intensity in El Niño and La Niña phases, these results indicate that changes in extreme ENSO phases will significantly alter CO2 dynamics in the Florida Everglades.

  19. El Niño Southern Oscillation (ENSO) Enhances CO2 Exchange Rates in Freshwater Marsh Ecosystems in the Florida Everglades

    PubMed Central

    Malone, Sparkle L.; Staudhammer, Christina L.; Oberbauer, Steven F.; Olivas, Paulo; Ryan, Michael G.; Schedlbauer, Jessica L.; Loescher, Henry W.; Starr, Gregory

    2014-01-01

    This research examines the relationships between El Niño Southern Oscillation (ENSO), water level, precipitation patterns and carbon dioxide (CO2) exchange rates in the freshwater wetland ecosystems of the Florida Everglades. Data was obtained over a 5-year study period (2009–2013) from two freshwater marsh sites located in Everglades National Park that differ in hydrology. At the short-hydroperiod site (Taylor Slough; TS) and the long-hydroperiod site (Shark River Slough; SRS) fluctuations in precipitation patterns occurred with changes in ENSO phase, suggesting that extreme ENSO phases alter Everglades hydrology which is known to have a substantial influence on ecosystem carbon dynamics. Variations in both ENSO phase and annual net CO2 exchange rates co-occurred with changes in wet and dry season length and intensity. Combined with site-specific seasonality in CO2 exchanges rates, El Niño and La Niña phases magnified season intensity and CO2 exchange rates at both sites. At TS, net CO2 uptake rates were higher in the dry season, whereas SRS had greater rates of carbon sequestration during the wet season. As La Niña phases were concurrent with drought years and extended dry seasons, TS became a greater sink for CO2 on an annual basis (−11 to −110 g CO2 m−2 yr−1) compared to El Niño and neutral years (−5 to −43.5 g CO2 m−2 yr−1). SRS was a small source for CO2 annually (1.81 to 80 g CO2 m−2 yr−1) except in one exceptionally wet year that was associated with an El Niño phase (−16 g CO2 m−2 yr−1). Considering that future climate predictions suggest a higher frequency and intensity in El Niño and La Niña phases, these results indicate that changes in extreme ENSO phases will significantly alter CO2 dynamics in the Florida Everglades. PMID:25521299

  20. The impact of water exchange rate on the health and performance of rainbow trout Oncorhynchus mykiss in recirculation aquaculture systems

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Fish mortality in recirculating aquaculture systems (RAS) has been observed by the authors to increase when RAS are managed at low makeup water exchange rates with relatively high feed loading. The precise etiology of this elevated mortality was unknown, all typical water quality parameters were wit...

  1. Development and Evaluation of a New Air Exchange Rate Algorithm for the Stochastic Human Exposure and Dose Simulation Model

    EPA Science Inventory

    between-home and between-city variability in residential pollutant infiltration. This is likely a result of differences in home ventilation, or air exchange rates (AER). The Stochastic Human Exposure and Dose Simulation (SHEDS) model is a population exposure model that uses a pro...

  2. Feedbacks between Exchange-Rate Movements and Domestic Inflation: Vicious and Not So Virtuous Cycles, Old and New.

    ERIC Educational Resources Information Center

    Spaventa, Luigi

    1983-01-01

    Theories and models dealing with the vicious cycle between exchange rates and domestic inflation and the way in which this relationship has influenced the economic policies of European nations are reviewed. Attempts of European nations to avoid the cycle of depreciation and inflation are covered. New theories may be necessary. (IS)

  3. 76 FR 26549 - Removal of Certain References to Credit Ratings Under the Securities Exchange Act of 1934

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-05-06

    ..., Securities Act of 1933 (``Securities Act'') Release No. 9193 (Mar. 3, 2011), 76 FR 12896 (Mar. 9, 2011) and Security Ratings, Exchange Act Release No. 63874 (Feb. 9, 2011), 76 FR 8946 (Feb. 16, 2011). As is... Release No. 11497 (Jun. 26, 1975), 40 FR 29795 (Jul. 16, 1975) and 17 CFR 240.15c3-1. \\12\\ See...

  4. On the accuracy of instantaneous gas exchange rates, energy expenditure, and respiratory quotient calculations obtained in indirect whole room calorimetry

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The molar balance equations of indirect calorimetry are treated from the point of view of cause-effect relationship where the gaseous exchange rates representing the unknown causes heed to be inferred from a known noisy effect – gaseous concentrations. Two methods of such inversion are analyzed. Th...

  5. Dehumidification: Prediction of Condensate Flow Rate for Plate-Fin Tube Heat Exchangers Using the Latent j Factor

    SciTech Connect

    Baxter, V.D.; Chen, D.T.; Conklin, J.C.

    1999-03-15

    Condensate flow rate is an important factor in designing dehumidifiers or evaporators. In this paper, the latentj fimtor is used to analyze the dehumidification performance of two plate-fin tube heat exchangers. This latent j factor, analogous to the total j factor, is a flmction of the mass transfa coefllcient, the volumetric air flow rate, and the Schmidt number. This latent j factor did predict condensate flow rate more directly and accurately than any other sensiblej factor method. The Iatentj factor has been used in the present study because the sensible j factor correlations presented in the literature failed to predict the condensate flow rate at high Reynolds numbers. Results show that the latent j i%ctor em be simply correlated as a fhnction of the Reynolds number based on the tube outside diameter and number of rows of the heat exchanger.

  6. Dynamic XML-based exchange of relational data: application to the Human Brain Project.

    PubMed

    Tang, Zhengming; Kadiyska, Yana; Li, Hao; Suciu, Dan; Brinkley, James F

    2003-01-01

    This paper discusses an approach to exporting relational data in XML format for data exchange over the web. We describe the first real-world application of SilkRoute, a middleware program that dynamically converts existing relational data to a user-defined XML DTD. The application, called XBrain, wraps SilkRoute in a Java Server Pages framework, thus permitting a web-based XQuery interface to a legacy relational database. The application is demonstrated as a query interface to the University of Washington Brain Project's Language Map Experiment Management System, which is used to manage data about language organization in the brain.

  7. Numerical simulation of gas dynamics and heat exchange tasks in fuel assemblies of the nuclear reactors

    SciTech Connect

    Zhuchenko, S. V.

    2014-11-12

    This report presents a PC-based program for solution gas dynamics and heat exchange mathematical tasks in fuel assemblies of the fast-neutron nuclear reactors. A fuel assembly consisting of bulk heat-generating elements, which are integrated together by the system of supply and pressure manifolds, is examined. Spherical heat-generating microelements, which contain nuclear fuel, are pulled into the heat-generating elements. Gaseous coolant proceed from supply manifolds to heat-generating elements, where it withdraws the nuclear reaction heat and assembles in pressure manifolds.

  8. Gas exchange rates across the sediment-water and air-water interfaces in south San Francisco Bay

    USGS Publications Warehouse

    Hartman, Blayne; Hammond, Douglas E.

    1984-01-01

    Radon 222 concentrations in the water and sedimentary columns and radon exchange rates across the sediment-water and air-water interfaces have been measured in a section of south San Francisco Bay. Two independent methods have been used to determine sediment-water exchange rates, and the annual averages of these methods agree within the uncertainty of the determinations, about 20%. The annual average of benthic fluxes from shoal areas is nearly a factor of 2 greater than fluxes from the channel areas. Fluxes from the shoal and channel areas exceed those expected from simple molecular diffusion by factors of 4 and 2, respectively, apparently due to macrofaunal irrigation. Values of the gas transfer coefficient for radon exchange across the air-water interface were determined by constructing a radon mass balance for the water column and by direct measurement using floating chambers. The chamber method appears to yield results which are too high. Transfer coefficients computed using the mass balance method range from 0.4 m/day to 1.8 m/day, with a 6-year average of 1.0 m/day. Gas exchange is linearly dependent upon wind speed over a wind speed range of 3.2–6.4 m/s, but shows no dependence upon current velocity. Gas transfer coefficients predicted from an empirical relationship between gas exchange rates and wind speed observed in lakes and the oceans are within 30% of the coefficients determined from the radon mass balance and are considerably more accurate than coefficients predicted from theoretical gas exchange models.

  9. The Interactive Effects of Organizational Politics and Exchange Ideology on Manager Ratings of Retention.

    ERIC Educational Resources Information Center

    Andrews, Martha C.; Witt, L. A.; Kacmar, K. Michele

    2003-01-01

    For 178 employees, perceptions of organizational politics were negatively related to manager assessments of employees' likelihood of staying. This association was true only for employees with moderate to strong exchange ideology (beliefs regarding workplace reciprocity). (Contains 45 references.) (SK)

  10. Regional trends in soil acidification and exchangeable metal concentrations in relation to acid deposition rates.

    PubMed

    Stevens, Carly J; Dise, Nancy B; Gowing, David J

    2009-01-01

    The deposition of high levels of reactive nitrogen (N) and sulphur (S), or the legacy of that deposition, remain among the world's most important environmental problems. Although regional impacts of acid deposition in aquatic ecosystems have been well documented, quantitative evidence of wide-scale impacts on terrestrial ecosystems is not common. In this study we analysed surface and subsoil chemistry of 68 acid grassland sites across the UK along a gradient of acid deposition, and statistically related the concentrations of exchangeable soil metals (1 M KCl extraction) to a range of potential drivers. The deposition of N, S or acid deposition was the primary correlate for 8 of 13 exchangeable metals measured in the topsoil and 5 of 14 exchangeable metals in the subsoil. In particular, exchangeable aluminium and lead both show increased levels above a soil pH threshold of about 4.5, strongly related to the deposition flux of acid compounds.

  11. Quantification of fetal heart rate regularity using symbolic dynamics

    NASA Astrophysics Data System (ADS)

    van Leeuwen, P.; Cysarz, D.; Lange, S.; Geue, D.; Groenemeyer, D.

    2007-03-01

    Fetal heart rate complexity was examined on the basis of RR interval time series obtained in the second and third trimester of pregnancy. In each fetal RR interval time series, short term beat-to-beat heart rate changes were coded in 8bit binary sequences. Redundancies of the 28 different binary patterns were reduced by two different procedures. The complexity of these sequences was quantified using the approximate entropy (ApEn), resulting in discrete ApEn values which were used for classifying the sequences into 17 pattern sets. Also, the sequences were grouped into 20 pattern classes with respect to identity after rotation or inversion of the binary value. There was a specific, nonuniform distribution of the sequences in the pattern sets and this differed from the distribution found in surrogate data. In the course of gestation, the number of sequences increased in seven pattern sets, decreased in four and remained unchanged in six. Sequences that occurred less often over time, both regular and irregular, were characterized by patterns reflecting frequent beat-to-beat reversals in heart rate. They were also predominant in the surrogate data, suggesting that these patterns are associated with stochastic heart beat trains. Sequences that occurred more frequently over time were relatively rare in the surrogate data. Some of these sequences had a high degree of regularity and corresponded to prolonged heart rate accelerations or decelerations which may be associated with directed fetal activity or movement or baroreflex activity. Application of the pattern classes revealed that those sequences with a high degree of irregularity correspond to heart rate patterns resulting from complex physiological activity such as fetal breathing movements. The results suggest that the development of the autonomic nervous system and the emergence of fetal behavioral states lead to increases in not only irregular but also regular heart rate patterns. Using symbolic dynamics to

  12. Direct measurement of the self-exchange rate of stellacyanin by a novel e.p.r. method.

    PubMed Central

    Dahlin, S; Reinhammar, B; Wilson, M T

    1984-01-01

    A method for reconstituting the blue copper protein stellacyanin with the stable copper isotopes 63Cu and 65Cu is reported. Small differences in the e.p.r. spectra of the two isotopic forms of stellacyanin have been used to monitor the electron self-exchange reaction of stellacyanin by rapid-freeze e.p.r. methods. The self-exchange rate constant (k11) for stellacyanin has been determined as 1.2 X 10(5) M-1 X S-1 at 20 degrees C. This value is in close agreement with values obtained from less-direct methods. PMID:6324759

  13. Cryogenic sample exchange NMR probe for magic angle spinning dynamic nuclear polarization

    PubMed Central

    Barnes, Alexander B.; Mak-Jurkauskas, Melody L.; Matsuki, Yoh; Bajaj, Vikram S.; van der Wel, Patrick C. A.; DeRocher, Ronald; Bryant, Jeffrey; Sirigiri, Jagadishwar R.; Temkin, Richard J.; Lugtenburg, Johan; Herzfeld, Judith; Griffin, Robert G.

    2009-01-01

    We describe a cryogenic sample exchange system that dramatically improves the efficiency of magic angle spinning (MAS) dynamic nuclear polarization (DNP) experiments by reducing the time required to change samples and by improving long-term instrument stability. Changing samples in conventional cryogenic MAS DNP/NMR experiments involves warming the probe to room temperature, detaching all cryogenic, RF, and microwave connections, removing the probe from the magnet, replacing the sample, and reversing all the previous steps, with the entire cycle requiring a few hours. The sample exchange system described here — which relies on an eject pipe attached to the front of the MAS stator and a vacuum jacketed dewar with a bellowed hole — circumvents these procedures. To demonstrate the excellent sensitivity, resolution, and stability achieved with this quadruple resonance sample exchange probe, we have performed high precision distance measurements on the active site of the membrane protein bacteriorhodopsin. We also include a spectrum of the tripeptide N-f-MLF-OH at 100 K which shows 30 Hz linewidths. PMID:19356957

  14. A Model for Dynamic Simulation and Analysis of Tether Momentum Exchange

    NASA Technical Reports Server (NTRS)

    Canfield, Stephen; Johnson, David; Sorensen, Kirk; Welzyn, Ken; Rodgers, Stephen L. (Technical Monitor)

    2002-01-01

    Momentum-exchange/electrodynamic reboost (MXER) tether systems may enable high-energy missions to the Moon, Mars, and beyond by serving as an 'upper stage in space'. Existing rockets that use an MXER tether station could double their capability to launch communications satellites and help improve US competitiveness. A MXER tether station would boost spacecraft from low Earth orbit to a high-energy orbit quickly, like a high-thrust rocket. Then, using the same principles that make an electric motor work, it would slowly rebuild its orbital momentum by pushing against the Earth's magnetic field-without using any propellant. One of the significant challenges in developing a momentum-exchange/electrodynamic reboost tether systems is in the analysis and design of the capture mechanism and its effects on the overall dynamics of the system. This paper will present a model for a momentum-exchange tether system that can simulate and evaluate the performance and requirements of such a system.

  15. Redox dynamics in the Chesapeake Bay: The effect on sediment/water uranium exchange

    SciTech Connect

    Shaw, T.J.; Sholkovitz, E.R.; Klinkhammer, G. )

    1994-07-01

    The effect of seasonal variations in productivity and redox dynamics on the sediment/water exchange of uranium was investigated on a twelve cruise time series in the Chesapeake Bay. The deep waters of the bay undergo seasonal anoxia in response to high primary productivity and water column stratification from late spring to early fall. Dissolved oxygen was used to monitor sediment redox conditions. Dissolved [sup 238]U was measured in the water column and sediment porewaters to monitor water column/sediment exchange. Uranium incorporation in bay sediments results from two distinct processes: productivity-dependent scavenging from the water column and redox-dependent cycling of uranium between sediments and bottomwater. Uranium is removed from surface waters of the bay by scavenging with biodetritus during periods of high primary productivity. Bottomwater and sediment redox conditions determine whether this particle-bound uranium is buried or released to overlying water. Particulate uranium is released to bottomwaters and porewaters during the degradation of biodetritus and oxidation of authigenic uranium. Low oxygen in bottomwaters in the summer results in minimal exchange of uranium between the sediments and bottomwater, due to the stability of reduced U(IV). High bottomwater oxygen concentrations associated with bay turnover in the fall results in release of authigenic uranium by oxidation to the soluble (VI) form. Enrichment of uranium in fall bottomwater suggests that authigenic uranium is very labile when exposed to oxic environmental conditions. This process is enhanced by physical mixing when anoxic sediments are resuspended into the oxic bottomwaters.

  16. Search for Length Dependent Stable Structures of Polyglutamaine Proteins with Replica Exchange Molecular Dynamic

    NASA Astrophysics Data System (ADS)

    Kluber, Alexander; Hayre, Robert; Cox, Daniel

    2012-02-01

    Motivated by the need to find beta-structure aggregation nuclei for the polyQ diseases such as Huntington's, we have undertaken a search for length dependent structure in model polyglutamine proteins. We use the Onufriev-Bashford-Case (OBC) generalized Born implicit solvent GPU based AMBER11 molecular dynamics with the parm96 force field coupled with a replica exchange method to characterize monomeric strands of polyglutamine as a function of chain length and temperature. This force field and solvation method has been shown among other methods to accurately reproduce folded metastability in certain small peptides, and to yield accurately de novo folded structures in a millisecond time-scale protein. Using GPU molecular dynamics we can sample out into the microsecond range. Additionally, explicit solvent runs will be used to verify results from the implicit solvent runs. We will assess order using measures of secondary structure and hydrogen bond content.

  17. Dynamics of Exchange at Gas-Zeolite Interfaces 1: Pure Component n-Butane and Isobutane

    SciTech Connect

    CHANDROSS,MICHAEL E.; WEBB III,EDMUND B.; GREST,GARY S.; MARTIN,MARCUS G.; THOMPSON,AIDAN P.; ROTH,M.W.

    2000-07-13

    The authors present the results of molecular dynamics simulations of n-butane and isobutane in silicalite. They begin with a comparison of the bulk adsorption and diffusion properties for two different parameterizations of the interaction potential between the hydrocarbon species, both of which have been shown to reproduce experimental gas-liquid coexistence curves. They examine diffusion as a function of the loading of the zeolite, as well as the temperature dependence of the diffusion constant at loading and for infinite dilution. They continue with simulations in which interfaces are formed between single component gases and the zeolite. After reaching equilibrium, they examine the dynamics of exchange between the bulk gas and the zeolite. Finally, they calculate the permeability of the zeolite for n-butane and isobutane as a function of pressure. Their simulations are performed for a number of different gas temperatures and pressures, covering a wide range of state points.

  18. Dynamics of oxygen sorption from water by copper-containing fibrous porous redox ion-exchangers

    SciTech Connect

    Ul'eva, L.S.; Burinskii, S.V.; Grebennikov, S.F.

    1985-08-10

    A most important field of practical application of oxidation-reduction (redox) polymers is the sorption of dissolved oxygen from water in order to prevent corrosion of power equipment. Copper-containing redox polymers, which have fairly high capacity and good swelling characteristics were used. Values of the dynamic exchange capacity (DEC) for copper ions, the redox capacity (ROC) for the reducing metal, and the dynamic reduction capacity for oxygen are given. It can be seen from these data that fibrous porous reactive materials (FPRM) in which the mass fiber content is 60% have somewhat better characteristics. The authors conclude that despite the fibrous porous material's considerably lower coefficient of internal diffusion, it is superior to granular EI-21 in the length of the masstransfer zone and in the coefficient of utilization of capacity, in consequence of the low linear density of the fibers. Their mass transfer zone is shorter by a factor of about 5.

  19. Adaptive Partitioning QM/MM Dynamics Simulations for Substrate Uptake, Product Release, and Solvent Exchange.

    PubMed

    Duster, A; Garza, C; Lin, H

    2016-01-01

    Combined quantum mechanics/molecular mechanics (QM/MM) plays an important role in multiscale simulations of biological systems including enzymes. The adaptive-partitioning (AP) schemes surpass the conventional QM/MM methods in that they allow the on-the-fly, smooth exchange of particles between QM and MM subsystems in molecular dynamics simulations, leading to a seamless and dynamic integration of the QM and MM realms. Originally developed for simulating ion solvation in bulk solutions, the AP schemes have recently been extended to the treatment of proteins, fostering applications in the simulations of enzymes. The present contribution provides a detailed account of the AP schemes. We delineate the background of the algorithms and their parallel implementation, as well as offer practical advice and examples for their applications in the simulations of biological systems. PMID:27498644

  20. Dynamic Line Rating Oncor Electric Delivery Smart Grid Program

    SciTech Connect

    Johnson, Justin; Smith, Cale; Young, Mike; Donohoo, Ken; Owen, Ross; Clark, Eddit; Espejo, Raul; Aivaliotis, Sandy; Stelmak, Ron; Mohr, Ron; Barba, Cristian; Gonzalez, Guillermo; Malkin, Stuart; Dimitrova, Vessela; Ragsdale, Gary; Mitchem, Sean; Jeirath, Nakul; Loomis, Joe; Trevino, Gerardo; Syracuse, Steve; Hurst, Neil; Mereness, Matt; Johnson, Chad; Bivens, Carrie

    2013-05-04

    Electric transmission lines are the lifeline of the electric utility industry, delivering its product from source to consumer. This critical infrastructure is often constrained such that there is inadequate capacity on existing transmission lines to efficiently deliver the power to meet demand in certain areas or to transport energy from high-generation areas to high-consumption regions. When this happens, the cost of the energy rises; more costly sources of power are used to meet the demand or the system operates less reliably. These economic impacts are known as congestion, and they can amount to substantial dollars for any time frame of reference: hour, day or year. There are several solutions to the transmission constraint problem, including: construction of new generation, construction of new transmission facilities, rebuilding and reconductoring of existing transmission assets, and Dynamic Line Rating (DLR). All of these options except DLR are capital intensive, have long lead times and often experience strong public and regulatory opposition. The Smart Grid Demonstration Program (SGDP) project co-funded by the Department of Energy (DOE) and Oncor Electric Delivery Company developed and deployed the most extensive and advanced DLR installation to demonstrate that DLR technology is capable of resolving many transmission capacity constraint problems with a system that is reliable, safe and very cost competitive. The SGDP DLR deployment is the first application of DLR technology to feed transmission line real-time dynamic ratings directly into the system operation’s State Estimator and load dispatch program, which optimizes the matching of generation with load demand on a security, reliability and economic basis. The integrated Dynamic Line Rating (iDLR)1 collects transmission line parameters at remote locations on the lines, calculates the real-time line rating based on the equivalent conductor temperature, ambient temperature and influence of wind and solar

  1. RPMDRATE: Bimolecular chemical reaction rates from ring polymer molecular dynamics

    NASA Astrophysics Data System (ADS)

    Suleimanov, Yu. V.; Allen, J. W.; Green, W. H.

    2013-03-01

    We present RPMDRATE, a computer program for the calculation of gas phase bimolecular reaction rate coefficients using the ring polymer molecular dynamics (RPMD) method. The RPMD rate coefficient is calculated using the Bennett-Chandler method as a product of a static (centroid density quantum transition state theory (QTST) rate) and a dynamic (ring polymer transmission coefficient) factor. The computational procedure is general and can be used to treat bimolecular polyatomic reactions of any complexity in their full dimensionality. The program has been tested for the H+H2, H+CH4, OH+CH4 and H+C2H6 reactions. Catalogue identifier: AENW_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AENW_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: MIT license No. of lines in distributed program, including test data, etc.: 94512 No. of bytes in distributed program, including test data, etc.: 1395674 Distribution format: tar.gz Programming language: Fortran 90/95, Python (version 2.6.x or later, including any version of Python 3, is recommended). Computer: Not computer specific. Operating system: Any for which Python, Fortran 90/95 compiler and the required external routines are available. Has the code been vectorized or parallelized?: The program can efficiently utilize 4096+ processors, depending on problem and available computer. At low temperatures, 110 processors are reasonable for a typical umbrella integration run with an analytic potential energy function and gradients on the latest x86-64 machines.

  2. Modeling the dynamic operation of a small fin plate heat exchanger - parametric analysis

    NASA Astrophysics Data System (ADS)

    Motyliński, Konrad; Kupecki, Jakub

    2015-09-01

    Given its high efficiency, low emissions and multiple fuelling options, the solid oxide fuel cells (SOFC) offer a promising alternative for stationary power generators, especially while engaged in micro-combined heat and power (μ-CHP) units. Despite the fact that the fuel cells are a key component in such power systems, other auxiliaries of the system can play a critical role and therefore require a significant attention. Since SOFC uses a ceramic material as an electrolyte, the high operating temperature (typically of the order of 700-900 °C) is required to achieve sufficient performance. For that reason both the fuel and the oxidant have to be preheated before entering the SOFC stack. Hot gases exiting the fuel cell stack transport substantial amount of energy which has to be partly recovered for preheating streams entering the stack and for heating purposes. Effective thermal integration of the μ-CHP can be achieved only when proper technical measures are used. The ability of efficiently preheating the streams of oxidant and fuel relies on heat exchangers which are present in all possible configurations of power system with solid oxide fuel cells. In this work a compact, fin plate heat exchanger operating in the high temperature regime was under consideration. Dynamic model was proposed for investigation of its performance under the transitional states of the fuel cell system. Heat exchanger was simulated using commercial modeling software. The model includes key geometrical and functional parameters. The working conditions of the power unit with SOFC vary due to the several factors, such as load changes, heating and cooling procedures of the stack and others. These issues affect parameters of the incoming streams to the heat exchanger. The mathematical model of the heat exchanger is based on a set of equations which are simultaneously solved in the iterative process. It enables to define conditions in the outlets of both the hot and the cold sides

  3. Dynamics of intramolecular spin exchange interaction of a nitronyl nitroxide diradical in solution and on surfaces.

    PubMed

    Lloveras, V; Badetti, E; Veciana, J; Vidal-Gancedo, J

    2016-03-01

    In this paper we report the study of the dynamics of a thermally modulated intramolecular spin exchange interaction of a novel diradical nitronyl nitroxide-substituted disulfide in solution and when it is grafted on a gold surface. The structure of this diradical was designed to have flexible chains leading to intramolecular collisions and hence spin exchange interaction, and with an appropriate binding group to be grafted on the gold surface to study its behavior on the surface. In solution, this diradical shows a strong spin exchange interaction between both radicals which is modulated by temperature, but also gold nanoparticles (AuNPs) functionalized with this diradical permit investigation of such a phenomenon in surface-grafted radicals. The spin-labelled AuNP synthesis was optimized to obtain high coverage of spin labels to lead to high spin exchange interaction. The obtained AuNPs were studied by Electron Paramagnetic Resonance (EPR), UV-Vis, and IR spectroscopies, HR-TEM microscopy, Cyclic Voltammetry (CV), Energy Dispersive X-ray analysis (EDX) and Thermogravimetric Analysis (TGA). This inorganic-organic hybrid material also showed dipolar interactions between its radicals which were confirmed by the appearance in the EPR spectra of an |Δms| = 2 transition at half-field. This signal gives direct evidence of the presence of a high-spin state and permitted us to study the nature of the magnetic coupling between the spins which was found to be antiferromagnetic. Self-Assembled Monolayers (SAMs) of these radicals on the Au (111) substrate were also prepared and studied by contact angle, X-Ray Photoelectron Spectroscopy (XPS), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), Cyclic Voltammetry and EPR. The magnetic as well as the electrochemical properties of the hybrid surfaces were studied and compared with the properties of this diradical in solution. Analogies between the properties of AuNPs with high coverage of radicals and those of SAM were

  4. A canonical replica exchange molecular dynamics implementation with normal pressure in each replica

    NASA Astrophysics Data System (ADS)

    Peter, Emanuel K.; Pivkin, Igor V.; Shea, Joan-Emma

    2016-07-01

    In this paper, we present a new canonical replica exchange molecular dynamics (REMD) simulation method with normal pressure for all replicas (REMD-NV(p) T). This method is suitable for systems for which conventional constant NPT-setups are difficult to implement. In this implementation, each replica has an individual volume, with normal pressure maintained for each replica in the simulation. We derive a novel exchange term and validate this method on the structural properties of SPC/E water and dialanine (Ala2) in the bulk and in the presence of a graphene layer. Compared to conventional constant NPT-REMD and NVT-REMD simulations, we find that the structural properties of our new method are in good agreement with simulations in the NPT-ensemble at all temperatures. The structural properties of the systems considered are affected by high pressures at elevated temperatures in the constant NVT-ensemble, an effect that our method corrects for. Unprojected distributions reveal that essential motions of the peptide are affected by the presence of the barostat in the NPT implementation but that the dynamical eigenmodes of the NV(p)T method are in close quantitative agreement with the NVT-ensemble.

  5. A canonical replica exchange molecular dynamics implementation with normal pressure in each replica.

    PubMed

    Peter, Emanuel K; Pivkin, Igor V; Shea, Joan-Emma

    2016-07-28

    In this paper, we present a new canonical replica exchange molecular dynamics (REMD) simulation method with normal pressure for all replicas (REMD-NV(p) T). This method is suitable for systems for which conventional constant NPT-setups are difficult to implement. In this implementation, each replica has an individual volume, with normal pressure maintained for each replica in the simulation. We derive a novel exchange term and validate this method on the structural properties of SPC/E water and dialanine (Ala2) in the bulk and in the presence of a graphene layer. Compared to conventional constant NPT-REMD and NVT-REMD simulations, we find that the structural properties of our new method are in good agreement with simulations in the NPT-ensemble at all temperatures. The structural properties of the systems considered are affected by high pressures at elevated temperatures in the constant NVT-ensemble, an effect that our method corrects for. Unprojected distributions reveal that essential motions of the peptide are affected by the presence of the barostat in the NPT implementation but that the dynamical eigenmodes of the NV(p)T method are in close quantitative agreement with the NVT-ensemble. PMID:27475393

  6. Dynamics of suspended sediment exchange and transport in a degraded mangrove creek in Kenya.

    PubMed

    Kitheka, Johnson U; Ongwenyi, George S; Mavuti, Kenneth M

    2002-12-01

    This study focuses on sediment exchange dynamics in Mwache Creek, a shallow tidal mangrove wetland in Kenya. The surface area of the creek is 17 km2 at high water spring. The creek experiences semidiurnal tides with tidal ranges of 3.2 m and 1.4 m during spring and neap tides, respectively. The creek is ebb dominant in the frontwater zone main channel and is flood dominant in the backwater zone main channel. During rainy season, the creek receives freshwater and terrigenous sediments from the seasonal Mwache River. Heavy supply of terrigenous sediments during the El Niño of 1997-1998 led to the huge deposition of sediments (10(60 tonnes) in the wetland that caused massive destruction of the mangrove forest in the upper region. In this study, sea level, tidal discharges, tidal current velocities, salinity, total suspended sediment concentrations (TSSC) and particulate organic sediment concentrations (POSC) measured in stations established within the main channel and also within the mangrove forests, were used to determine the dynamics of sediment exchange between the frontwater and backwater zones of the main channel including also the exchange with mangrove forests. The results showed that during wet seasons, the high suspended sediment concentration associated with river discharge and tidal resuspension of fine channel-bed sediment accounts for the inflow of highly turbid water into the degraded mangrove forest. Despite the degradation of the mangrove forest, sediment outflow from the mangrove forest was considerably less than the inflow. This caused a net trapping of sediment in the wetland. The net import of the sediment dominated in spring tide during both wet and dry season and during neap tide in the wet season. However, as compared to heavily vegetated mangrove wetlands, the generally degraded Mwache Creek mangrove wetland sediment trapping efficiency is low as the average is about 30% for the highly degraded backwater zone mangrove forest and 65% in the

  7. Insights into the folding pathway of the Engrailed Homeodomain protein using replica exchange molecular dynamics simulations.

    PubMed

    Koulgi, Shruti; Sonavane, Uddhavesh; Joshi, Rajendra

    2010-11-01

    Protein folding studies were carried out by performing microsecond time scale simulations on the ultrafast/fast folding protein Engrailed Homeodomain (EnHD) from Drosophila melanogaster. It is a three-helix bundle protein consisting of 54 residues (PDB ID: 1ENH). The positions of the helices are 8-20 (Helix I), 26-36 (Helix II) and 40-53 (Helix III). The second and third helices together form a Helix-Turn-Helix (HTH) motif which belongs to the family of DNA binding proteins. The molecular dynamics (MD) simulations were performed using replica exchange molecular dynamics (REMD). REMD is a method that involves simulating a protein at different temperatures and performing exchanges at regular time intervals. These exchanges were accepted or rejected based on the Metropolis criterion. REMD was performed using the AMBER FF03 force field with the generalised Born solvation model for the temperature range 286-373 K involving 30 replicas. The extended conformation of the protein was used as the starting structure. A simulation of 600 ns per replica was performed resulting in an overall simulation time of 18 μs. The protein was seen to fold close to the native state with backbone root mean square deviation (RMSD) of 3.16 Å. In this low RMSD structure, the Helix I was partially formed with a backbone RMSD of 3.37 Å while HTH motif had an RMSD of 1.81 Å. Analysis suggests that EnHD folds to its native structure via an intermediate in which the HTH motif is formed. The secondary structure development occurs first followed by tertiary packing. The results were in good agreement with the experimental findings.

  8. Kinetic Analyses of Cation Exchange Rates in Synthetic Birnessite Measured by Time- Resolved Synchrotron X-ray Diffraction

    NASA Astrophysics Data System (ADS)

    Lopano, C. L.; Heaney, P. J.; Post, J. E.; Bandstra, J.; Brantley, S. L.

    2006-05-01

    -stage model produced the following rate equation: R = 0.081 ⋆ XNa ⋆ [K(aq)], where [K(aq)] is the molar concentration of the aqueous cation The two-stage model generated a rate equation of R = 0.146 ⋆ (1- (XK(dis) + XK(ord))) - 0.01153 ⋆ XK(dis), where X is mole fraction interlayer cation and R is the rate of exchange in terms sec-1. We assume a linear relationship between mole fraction and unit-cell volume based on Vegard's Law. Further kinetic analyses are in progress in order to determine the cation exchange rate dependence on concentration and to compare cation exchange rates for K-, Cs- and Ba- exchange.

  9. Structural dynamics of soluble chloride intracellular channel protein CLIC1 examined by amide hydrogen-deuterium exchange mass spectrometry.

    PubMed

    Stoychev, Stoyan H; Nathaniel, Christos; Fanucchi, Sylvia; Brock, Melissa; Li, Sheng; Asmus, Kyle; Woods, Virgil L; Dirr, Heini W

    2009-09-01

    Chloride intracellular channel protein 1 (CLIC1) functions as an anion channel in plasma and nuclear membranes when its soluble monomeric form converts to an integral-membrane form. The transmembrane region of CLIC1 is located in its thioredoxin-like domain 1, but the mechanism whereby the protein converts to its membrane conformation has yet to be determined. Since channel formation in membranes is enhanced at low pH (5 to 5.5), a condition that is found at the surface of membranes, the structural dynamics of soluble CLIC1 was studied at pH 7 and at pH 5.5 in the absence of membranes by amide hydrogen-deuterium exchange mass spectrometry (DXMS). Rapid hydrogen exchange data indicate that CLIC1 displays a similar core structure at these pH values. Domain 1 is less stable than the all-helical domain 2, and, while the structure of domain 1 remains intact, its conformational flexibility is further increased in an acidic environment (pH 5.5). In the absence of membrane, an acidic environment appears to prime the solution structure of CLIC1 by destabilizing domain 1 in order to lower the activation energy barrier for its conversion to the membrane-insertion conformation. The significantly enhanced H/D-exchange rates at pH 5.5 displayed by two segments (peptides 11-31 and 68-82) could be due to the protonation of acidic residues in salt bridges. One of these segments (peptide 11-31) includes part of the transmembrane region which, in the solution structure, consists of helix alpha1. This helix is intrinsically stable and is most likely retained in the membrane conformation. Strand beta2, another element of the transmembrane region, displays a propensity to form a helical structure and has putative N- and C-capping motifs, suggesting that it too most likely forms a helix in a lipid bilayer.

  10. Superior bit error rate and jitter due to improved switching field distribution in exchange spring magnetic recording media.

    PubMed

    Suess, D; Fuger, M; Abert, C; Bruckner, F; Vogler, C

    2016-06-01

    We report two effects that lead to a significant reduction of the switching field distribution in exchange spring media. The first effect relies on a subtle mechanism of the interplay between exchange coupling between soft and hard layers and anisotropy that allows significant reduction of the switching field distribution in exchange spring media. This effect reduces the switching field distribution by about 30% compared to single-phase media. A second effect is that due to the improved thermal stability of exchange spring media over single-phase media, the jitter due to thermal fluctuation is significantly smaller for exchange spring media than for single-phase media. The influence of this overall improved switching field distribution on the transition jitter in granular recording and the bit error rate in bit-patterned magnetic recording is discussed. The transition jitter in granular recording for a distribution of Khard values of 3% in the hard layer, taking into account thermal fluctuations during recording, is estimated to be a = 0.78 nm, which is similar to the best reported calculated jitter in optimized heat-assisted recording media.

  11. Superior bit error rate and jitter due to improved switching field distribution in exchange spring magnetic recording media

    PubMed Central

    Suess, D.; Fuger, M.; Abert, C.; Bruckner, F.; Vogler, C.

    2016-01-01

    We report two effects that lead to a significant reduction of the switching field distribution in exchange spring media. The first effect relies on a subtle mechanism of the interplay between exchange coupling between soft and hard layers and anisotropy that allows significant reduction of the switching field distribution in exchange spring media. This effect reduces the switching field distribution by about 30% compared to single-phase media. A second effect is that due to the improved thermal stability of exchange spring media over single-phase media, the jitter due to thermal fluctuation is significantly smaller for exchange spring media than for single-phase media. The influence of this overall improved switching field distribution on the transition jitter in granular recording and the bit error rate in bit-patterned magnetic recording is discussed. The transition jitter in granular recording for a distribution of Khard values of 3% in the hard layer, taking into account thermal fluctuations during recording, is estimated to be a = 0.78 nm, which is similar to the best reported calculated jitter in optimized heat-assisted recording media. PMID:27245287

  12. Measurement of air exchange rate of stationary vehicles and estimation of in-vehicle exposure.

    PubMed

    Park, J H; Spengler, J D; Yoon, D W; Dumyahn, T; Lee, K; Ozkaynak, H

    1998-01-01

    The air exchange rates or air changes per hour (ACH) were measured under 4 conditions in 3 stationary automobiles. The ACH ranged between 1.0 and 3.0 h-1 with windows closed and no mechanical ventilation, between 1.8 and 3.7 h-1 for windows closed with fan set on recirculation, between 13.3 and 26.1 h-1 for window open with no mechanical ventilation, and between 36.2 and 47.5 h-1 for window closed with the fan set on fresh air. ACHs for windows closed with no ventilation were higher for the older automobile than for the newer automobiles. With the windows closed and fan turned off, ACH was not influenced by wind speed (p > 0.05). When the window was open, ACH appeared to be greatly affected by wind speed (R2 = 0.86). These measurements are relevant to understanding exposures inside automobiles to sources such as dry-cleaned clothes, cigarettes and airbags. Therefore, to understand the in-vehicle exposure to these internal sources, perchloroethylene (PCE) emitted from dry-cleaned clothes and environmental tobacco smoke (ETS) inside a vehicle were modeled for simulated driving cycles. Airbag deployment was also modeled for estimating exposure level to alkaline particulate and carbon monoxide (CO). Average exposure to PCE inside a vehicle for 30 minutes period was high (approximately 780 micrograms/m3); however, this is only 6% of the two-week exposure that is influenced by the storage of dry cleaned clothing at home. On the other hand, the exposure levels of respirable suspended particulate (RSP) and formaldehyde due to ETS could reach 2.1 mg/m3 and 0.11 ppm, respectively, when a person smokes inside a driving car even with the window open. In modeling the in-vehicle concentrations following airbag deployment, the average CO level over 20 minutes would not appear to present problem (less than 28 ppm). The peak concentration of respirable particulate would have exceeded 140 mg/m3. Since most of the particle mass is composed of alkaline material, these high levels

  13. The effectiveness of China's RMB exchange rate reforms: An insight from multifractal detrended fluctuation analysis

    NASA Astrophysics Data System (ADS)

    Qin, Jing; Lu, Xinsheng; Zhou, Ying; Qu, Ling

    2015-03-01

    This paper examines the effectiveness of the RMB regime reforms on market efficiency improving for the mainland onshore market and Hong Kong offshore market. Based on multifractal detrended fluctuation analysis (MF-DFA), we study the multifractal properties as well as multifractality degree of RMB/USD and RMB/HKD exchange markets. Our empirical results show that, the first RMB regime reform undertaken on July 21, 2005 has a greater impact on RMB/USD exchange market in the short term, while the second RMB exchange reform undertaken on June 19, 2010 exerts the long-term influences on the efficiency of both RMB/USD and RMB/HKD markets. Further, RMB/HKD market is found to work more efficiently, although both mainland onshore market and Hong Kong offshore market have achieved a higher level of efficiency post reforms.

  14. Ionization dynamics of small water clusters: Proton transfer rate

    NASA Astrophysics Data System (ADS)

    Tachikawa, Hiroto; Takada, Tomoya

    2016-08-01

    The surfaces of icy planets and comets are composed of frozen water (H2O), carbon dioxide (CO2), and methane (CH4). These surfaces are irradiated by solar wind and cosmic rays from the interstellar space and they cause ionization of surface molecules. In this report, the effects of ionization of cold water clusters have been investigated using a direct ab initio molecular dynamics (AIMD) method to elucidate the rate of proton transfer (PT) in cations of small water clusters (H2O)n (n = 2-7). After ionization of the water clusters, PT occurred in all the cluster cations, and dissociation of the OH radical occurred for n = 4-7. The time of PT decreased with increasing the cluster size at n = 2-5 and reached a limiting value at n = 6 and 7. The mechanism of the PT process in ionized water clusters was discussed based on the theoretical results.

  15. Laser-enhanced dynamics in molecular rate processes

    NASA Technical Reports Server (NTRS)

    George, T. F.; Zimmerman, I. H.; Devries, P. L.; Yuan, J.-M.; Lam, K.-S.; Bellum, J. C.; Lee, H.-W.; Slutsky, M. S.

    1978-01-01

    The present discussion deals with some theoretical aspects associated with the description of molecular rate processes in the presence of intense laser radiation, where the radiation actually interacts with the molecular dynamics. Whereas for weak and even moderately intense radiation, the absorption and stimulated emission of photons by a molecular system can be described by perturbative methods, for intense radiation, perturbation theory is usually not adequate. Limiting the analysis to the gas phase, an attempt is made to describe nonperturbative approaches applicable to the description of such processes (in the presence of intense laser radiation) as electronic energy transfer in molecular (in particular atom-atom) collisions; collision-induced ionization and emission; and unimolecular dissociation.

  16. Material dynamics under extreme conditions of pressure and strain rate

    SciTech Connect

    Remington, B A; Allen, P; Bringa, E; Hawreliak, J; Ho, D; Lorenz, K T; Lorenzana, H; Meyers, M A; Pollaine, S W; Rosolankova, K; Sadik, B; Schneider, M S; Swift, D; Wark, J; Yaakobi, B

    2005-09-06

    Solid state experiments at extreme pressures (10-100 GPa) and strain rates ({approx}10{sup 6}-10{sup 8}s{sup -1}) are being developed on high-energy laser facilities, and offer the possibility for exploring new regimes of materials science. These extreme solid-state conditions can be accessed with either shock loading or with a quasi-isentropic ramped pressure drive. Velocity interferometer measurements establish the high pressure conditions. Constitutive models for solid-state strength under these conditions are tested by comparing 2D continuum simulations with experiments measuring perturbation growth due to the Rayleigh-Taylor instability in solid-state samples. Lattice compression, phase, and temperature are deduced from extended x-ray absorption fine structure (EXAFS) measurements, from which the shock-induced {alpha}-{omega} phase transition in Ti and the {alpha}-{var_epsilon} phase transition in Fe are inferred to occur on sub-nanosec time scales. Time resolved lattice response and phase can also be measured with dynamic x-ray diffraction measurements, where the elastic-plastic (1D-3D) lattice relaxation in shocked Cu is shown to occur promptly (< 1 ns). Subsequent large-scale molecular dynamics (MD) simulations elucidate the microscopic dynamics that underlie the 3D lattice relaxation. Deformation mechanisms are identified by examining the residual microstructure in recovered samples. The slip-twinning threshold in single-crystal Cu shocked along the [001] direction is shown to occur at shock strengths of {approx}20 GPa, whereas the corresponding transition for Cu shocked along the [134] direction occurs at higher shock strengths. This slip-twinning threshold also depends on the stacking fault energy (SFE), being lower for low SFE materials. Designs have been developed for achieving much higher pressures, P > 1000 GPa, in the solid state on the National Ignition Facility (NIF) laser.

  17. Heart rate estimation from facial photoplethysmography during dynamic illuminance changes.

    PubMed

    Dongseok Lee; Jeehoon Kim; Sungjun Kwon; Kwangsuk Park

    2015-08-01

    Camera-based remote photoplethysmography (rPPG) enables low-cost, non-contact cardiovascular activity monitoring. However, applying rPPG to practical use has some limitations caused from the artifacts by illuminance changes. During watching a video in a dark room, for example, watching a TV at night without illuminance, there is a high correlation between the brightness changes of a video and the illuminance variation on the skin of the viewer's face. In this study, we propose an artifact reduction method in rPPG, which is caused by the variation of the illuminance. The method subtracts the artifacts from the raw facial rPPG signal by applying multi-order curve fitting between the illuminance information from the facial rPPG signal and the brightness information from a video. On average, the results showed that signal-to-noise ratio (SNR) increased from -11.74 to -4.19 dB and from -15.27 to 7.99 dB for low-dynamic-brightness and high-dynamic-brightness video, respectively. In addition, the root-mean-square-error (RMSE) of estimated heart rate decreased from 11.00 to 1.82 bpm and from 9.88 to 4.65 bpm for the videos, respectively. PMID:26736863

  18. Heart rate estimation from facial photoplethysmography during dynamic illuminance changes.

    PubMed

    Dongseok Lee; Jeehoon Kim; Sungjun Kwon; Kwangsuk Park

    2015-08-01

    Camera-based remote photoplethysmography (rPPG) enables low-cost, non-contact cardiovascular activity monitoring. However, applying rPPG to practical use has some limitations caused from the artifacts by illuminance changes. During watching a video in a dark room, for example, watching a TV at night without illuminance, there is a high correlation between the brightness changes of a video and the illuminance variation on the skin of the viewer's face. In this study, we propose an artifact reduction method in rPPG, which is caused by the variation of the illuminance. The method subtracts the artifacts from the raw facial rPPG signal by applying multi-order curve fitting between the illuminance information from the facial rPPG signal and the brightness information from a video. On average, the results showed that signal-to-noise ratio (SNR) increased from -11.74 to -4.19 dB and from -15.27 to 7.99 dB for low-dynamic-brightness and high-dynamic-brightness video, respectively. In addition, the root-mean-square-error (RMSE) of estimated heart rate decreased from 11.00 to 1.82 bpm and from 9.88 to 4.65 bpm for the videos, respectively.

  19. Autonomic neural control of heart rate during dynamic exercise: revisited

    PubMed Central

    White, Daniel W; Raven, Peter B

    2014-01-01

    The accepted model of autonomic control of heart rate (HR) during dynamic exercise indicates that the initial increase is entirely attributable to the withdrawal of parasympathetic nervous system (PSNS) activity and that subsequent increases in HR are entirely attributable to increases in cardiac sympathetic activity. In the present review, we sought to re-evaluate the model of autonomic neural control of HR in humans during progressive increases in dynamic exercise workload. We analysed data from both new and previously published studies involving baroreflex stimulation and pharmacological blockade of the autonomic nervous system. Results indicate that the PSNS remains functionally active throughout exercise and that increases in HR from rest to maximal exercise result from an increasing workload-related transition from a 4 : 1 vagal–sympathetic balance to a 4 : 1 sympatho–vagal balance. Furthermore, the beat-to-beat autonomic reflex control of HR was found to be dependent on the ability of the PSNS to modulate the HR as it was progressively restrained by increasing workload-related sympathetic nerve activity. In conclusion: (i) increases in exercise workload-related HR are not caused by a total withdrawal of the PSNS followed by an increase in sympathetic tone; (ii) reciprocal antagonism is key to the transition from vagal to sympathetic dominance, and (iii) resetting of the arterial baroreflex causes immediate exercise-onset reflexive increases in HR, which are parasympathetically mediated, followed by slower increases in sympathetic tone as workloads are increased. PMID:24756637

  20. Comparative rates of exchange behind reflected shock waves. 2. /sup 15/No + C/sup 18/O vs. /sup 15/NO + N/sub 2/

    SciTech Connect

    Bopp, A.F.; Kern, R.D.; Niki, T.; Stack, G.M.

    1980-10-02

    The rates of isotopic exchange of nitric oxide with nitrogen and carbon monoxide were studied over the temperature range 2700-3800 K by analyzing the gas from the reflected shock zone at 20-..mu..s intervals with a time-of-flight mass spectrometer. Two mixtures containing 4% /sup 15/NO-4% N/sub 2/ in one and 4% /sup 15/NO-4% C/sup 18/O in the other were each diluted with a mixture of inert gases (Ne-Ar-Kr). The reacting gases were sampled dynamically in order to determine the time dependence of the products; i.e., m/e 29 and 30 for the first mixture and m/e 28 and 33 for the second mixture. The exchange of nitric oxide and carbon monoxide took place readily over the range investigated. The reaction profiles displayed nonlinear growth of the products with respect to reaction time. Computer simulation of the product profiles assuming an atomic mechanism revealed reasonable agreement with the experimental data. In contrast to /sup 15/NO + C/sup 18/O, the exchange of /sup 15/NO + N/sub 2/ did not occur to any measurable extent in accordance with the predictions of an atomic mechanism.

  1. Nucleation Rate Analysis of Methane Hydrate from Molecular Dynamics Simulations

    SciTech Connect

    Yuhara, Daisuke; Barnes, Brian C.; Suh, Donguk; Knott, Brandon C.; Beckham, Gregg T.; Yasuoka, Kenji; Wu, David T.; Amadeu K. Sum

    2015-01-06

    Clathrate hydrates are solid crystalline structures most commonly formed from solutions that have nucleated to form a mixed solid composed of water and gas. Understanding the mechanism of clathrate hydrate nucleation is essential to grasp the fundamental chemistry of these complex structures and their applications. Molecular dynamics (MD) simulation is an ideal method to study nucleation at the molecular level because the size of the critical nucleus and formation rate occur on the nano scale. Moreover, various analysis methods for nucleation have been developed through MD to analyze nucleation. In particular, the mean first-passage time (MFPT) and survival probability (SP) methods have proven to be effective in procuring the nucleation rate and critical nucleus size for monatomic systems. This study assesses the MFPT and SP methods, previously used for monatomic systems, when applied to analyzing clathrate hydrate nucleation. Because clathrate hydrate nucleation is relatively difficult to observe in MD simulations (due to its high free energy barrier), these methods have yet to be applied to clathrate hydrate systems. In this study, we have analyzed the nucleation rate and critical nucleus size of methane hydrate using MFPT and SP methods from data generated by MD simulations at 255 K and 50 MPa. MFPT was modified for clathrate hydrate from the original version by adding the maximum likelihood estimate and growth effect term. The nucleation rates were calculated by MFPT and SP methods and are within 5%; the critical nucleus size estimated by the MFPT method was 50% higher, than values obtained through other more rigorous but computationally expensive estimates. These methods can also be extended to the analysis of other clathrate hydrates.

  2. Nucleation Rate Analysis of Methane Hydrate from Molecular Dynamics Simulations

    DOE PAGESBeta

    Yuhara, Daisuke; Barnes, Brian C.; Suh, Donguk; Knott, Brandon C.; Beckham, Gregg T.; Yasuoka, Kenji; Wu, David T.; Amadeu K. Sum

    2015-01-06

    Clathrate hydrates are solid crystalline structures most commonly formed from solutions that have nucleated to form a mixed solid composed of water and gas. Understanding the mechanism of clathrate hydrate nucleation is essential to grasp the fundamental chemistry of these complex structures and their applications. Molecular dynamics (MD) simulation is an ideal method to study nucleation at the molecular level because the size of the critical nucleus and formation rate occur on the nano scale. Moreover, various analysis methods for nucleation have been developed through MD to analyze nucleation. In particular, the mean first-passage time (MFPT) and survival probability (SP)more » methods have proven to be effective in procuring the nucleation rate and critical nucleus size for monatomic systems. This study assesses the MFPT and SP methods, previously used for monatomic systems, when applied to analyzing clathrate hydrate nucleation. Because clathrate hydrate nucleation is relatively difficult to observe in MD simulations (due to its high free energy barrier), these methods have yet to be applied to clathrate hydrate systems. In this study, we have analyzed the nucleation rate and critical nucleus size of methane hydrate using MFPT and SP methods from data generated by MD simulations at 255 K and 50 MPa. MFPT was modified for clathrate hydrate from the original version by adding the maximum likelihood estimate and growth effect term. The nucleation rates were calculated by MFPT and SP methods and are within 5%; the critical nucleus size estimated by the MFPT method was 50% higher, than values obtained through other more rigorous but computationally expensive estimates. These methods can also be extended to the analysis of other clathrate hydrates.« less

  3. Rates of water exchange for two cobalt(II) heteropoly-oxotungstate compounds in aqueous solution

    SciTech Connect

    Ohlin, C. Andre; Harley, Stephen J.; McAlpin, J. Gregory; Hocking, Rosalie K.; Mercado, Brandon Q.; Johnson, Rene L.; Villa, Eric M.; Fidler, Mary Kate; Olmstead, Marilyn M.; Spiccia, Leone; Britt, R. David; Casey, William H.

    2011-03-17

    Polyoxometalate ions are used as ligands in water-oxidation processes related to solar energy production. An important step in these reactions is the association and dissociation of water from the catalytic sites, the rates of which are unknown. Here we report the exchange rates of water ligated to CoII atoms in two polyoxotungstate sandwich molecules using the 17O-NMR-based Swift–Connick method. The compounds were the [Co4(H2O)2(B-α-W9O34)2]-10 and the larger αββα-[Co4(H2O)2(P2W15O56)2]-16 ions, each with two water molecules bound trans to one another in a CoII sandwich between the tungstate ligands. The clusters, in both solid and solution state, were characterized by a range of methods, including NMR, EPR, FT-IR, UV-Vis, and EXAFS spectroscopy, ESI-MS, single-crystal X-ray crystallography, and potentiometry. For [Co4(H2O)2(B-α-PW9O34)2]-10 at pH 5.4, we estimate: k 298=1.5(5)±0.3×106 s-1, ΔH=39.8±0.4 kJ mol-1, ΔS=+7.1±1.2 J mol-1 K-1 and ΔV=5.6 ±1.6 cm3 mol-1. For the Wells–Dawson sandwich cluster (αββα-[Co4(H2O)2(P2W15O56)2]-16) at pH 5.54, we find: k298=1.6(2)±0.3×106 s-1, ΔH=27.6±0.4 kJ mol-1 ΔS=-33±1.3 J mol-1 K-1 and ΔV=2.2±1.4 cm3mol-1 at pH 5.2. The molecules are clearly stable and monospecific in slightly acidic solutions, but dissociate in strongly acidic solutions. This dissociation is detectable by EPR

  4. Effect of ionophores on the rate of intramolecular cation exchange in durosemiquinone ion pairs

    NASA Technical Reports Server (NTRS)

    Eastman, M. P.; Bruno, G. V.; Mcguyer, C. A.; Gutierrez, A. R.; Shannon, J. M.

    1979-01-01

    The effects of the ionophores 15-crown-5 (15C5), 18-crown-6 (18C6), dibenzo-18-crown-6 (DBC) and cryptand 222 (C222) on intramolecular cation exchange in ion pairs of the sodium salt of the durosemiquinone anion in benzene solution are investigated. Electron paramagnetic resonance spectra of the 18C6 and 15C5 complexes with durosemiquinone reduced by contact with a sodium mirror show an alternating line width which indicates that the sodium ion is being exchanged between equivalent sites near the oxygens of the semiquinone with activation energies of 8.7 and 6.0 kcal/mole and Arrhenius preexponential factors of 9 x 10 to the 12th/sec and 10 to the 12th/sec, respectively. Spectra obtained for the DBC complexes show no evidence of exchange, while those of C222 indicate rapid exchange. It is also noted that the hyperfine splitting constants measured do not change over the 50-K temperature interval studied.

  5. Completion Rates and Accuracy of Performance Under Fixed and Variable Token Exchange Periods.

    ERIC Educational Resources Information Center

    McLaughlin, T. F.; Malaby, J. E.

    This research investigated the effects of employing fixed, variable, and extended token exchange periods for back-ups on the completion and accuracy of daily assignments for a total fifth and sixth-grade class. The results indicated that, in general, a higher percentage of assignments was completed when the number of days between point exchanges…

  6. THE ROLE OF AQUEOUS THIN FILM EVAPORATIVE COOLING ON RATES OF ELEMENTAL MERCURY AIR-WATER EXCHANGE UNDER TEMPERATURE DISEQUILIBRIUM CONDITIONS

    EPA Science Inventory

    The technical conununity has only recently addressed the role of atmospheric temperature variations on rates of air-water vapor phase toxicant exchange. The technical literature has documented that: 1) day time rates of elemental mercury vapor phase air-water exchange can exceed ...

  7. Assessing the Dynamics of Bittorrent Swarms Topologies Using the Peer Exchange Protocol

    NASA Astrophysics Data System (ADS)

    Fauzie, Mohamad Dikshie; Thamrin, Achmad Husni; van Meter, Rodney; Murai, Jun

    Bittorrent is one of the most popular and successful applications in the current Internet. However, we still have little knowledge about the topology of real Bittorrent swarms, how dynamic the topology is, and how it affects overall behavior. This paper describes an experimental study of the overlay topologies of real-world Bittorrent networks, focusing on the activity of the nodes of its P2P topology and especially their dynamic relationships. Peer Exchange Protocol (PEX) messages are analyzed to infer topologies and their properties, capturing the variations of their behavior. Our measurements, verified using the Kolmogorov-Smirnov goodness of fit test and the likelihood ratio test and confirmed via simulation, show that a power-law with exponential cutoff is a more plausible model than a pure power-law distribution. We also found that the average clustering coefficient is very low, supporting this observation. Bittorrent swarms are far more dynamic than has been recognized previously, potentially impacting attempts to optimize the performance of the system as well as the accuracy of simulations and analyses.

  8. The loss rates of O{sup +} in the inner magnetosphere caused by both magnetic field line curvature scattering and charge exchange reactions

    SciTech Connect

    Ji, Y.; Shen, C.

    2014-03-15

    With consideration of magnetic field line curvature (FLC) pitch angle scattering and charge exchange reactions, the O{sup +} (>300 keV) in the inner magnetosphere loss rates are investigated by using an eigenfunction analysis. The FLC scattering provides a mechanism for the ring current O{sup +} to enter the loss cone and influence the loss rates caused by charge exchange reactions. Assuming that the pitch angle change is small for each scattering event, the diffusion equation including a charge exchange term is constructed and solved; the eigenvalues of the equation are identified. The resultant loss rates of O{sup +} are approximately equal to the linear superposition of the loss rate without considering the charge exchange reactions and the loss rate associated with charge exchange reactions alone. The loss time is consistent with the observations from the early recovery phases of magnetic storms.

  9. Conformational sampling enhancement of replica exchange molecular dynamics simulations using swarm particle intelligence

    SciTech Connect

    Kamberaj, Hiqmet

    2015-09-28

    In this paper, we present a new method based on swarm particle social intelligence for use in replica exchange molecular dynamics simulations. In this method, the replicas (representing the different system configurations) are allowed communicating with each other through the individual and social knowledge, in additional to considering them as a collection of real particles interacting through the Newtonian forces. The new method is based on the modification of the equations of motion in such way that the replicas are driven towards the global energy minimum. The method was tested for the Lennard-Jones clusters of N = 4,  5, and 6 atoms. Our results showed that the new method is more efficient than the conventional replica exchange method under the same practical conditions. In particular, the new method performed better on optimizing the distribution of the replicas among the thermostats with time and, in addition, ergodic convergence is observed to be faster. We also introduce a weighted histogram analysis method allowing analyzing the data from simulations by combining data from all of the replicas and rigorously removing the inserted bias.

  10. Identifying ligand binding sites and poses using GPU-accelerated Hamiltonian replica exchange molecular dynamics

    PubMed Central

    Wang, Kai; Yang, Yanzhi; Chodera, John D.; Shirts, Michael R.

    2014-01-01

    We present a method to identify small molecule ligand binding sites and orientations to a given protein crystal structure using GPU-accelerated Hamiltonian replica exchange molecular dynamics simulations. The Hamiltonians used vary from the physical end state of protein interacting with the ligand to a unphysical end state where the ligand does not interact with the protein. As replicas explore the space of Hamiltonians interpolating between these states the ligand can rapidly escape local minima and explore potential binding sites. Geometric restraints keep the ligands within the protein volume, and a potential energy pathway designed to increase phase space overlap between intermediates ensures good mixing. Because of the rigorous statistical mechanical nature of the Hamiltonian exchange framework, we can also extract binding free energy estimates at all putative binding sites, which agree well with free energies computed from occupation probabilities. We present results of this methodology on the T4 lysozyme L99A model system with four ligands, including one non-binder as a control. We find that our methodology identifies the crystallographic binding sites consistently and accurately for the small number of ligands considered here and gives free energies consistent with experiment. We are also able to analyze the contribution of individual binding sites on the overall binding affinity. Our methodology points to near term potential applications in early-stage drug discovery. PMID:24297454

  11. Fluid Analysis and Improved Structure of an ATEG Heat Exchanger Based on Computational Fluid Dynamics

    NASA Astrophysics Data System (ADS)

    Tang, Z. B.; Deng, Y. D.; Su, C. Q.; Yuan, X. H.

    2015-06-01

    In this study, a numerical model has been employed to analyze the internal flow field distribution in a heat exchanger applied for an automotive thermoelectric generator based on computational fluid dynamics. The model simulates the influence of factors relevant to the heat exchanger, including the automotive waste heat mass flow velocity, temperature, internal fins, and back pressure. The result is in good agreement with experimental test data. Sensitivity analysis of the inlet parameters shows that increase of the exhaust velocity, compared with the inlet temperature, makes little contribution (0.1 versus 0.19) to the heat transfer but results in a detrimental back pressure increase (0.69 versus 0.21). A configuration equipped with internal fins is proved to offer better thermal performance compared with that without fins. Finally, based on an attempt to improve the internal flow field, a more rational structure is obtained, offering a more homogeneous temperature distribution, higher average heat transfer coefficient, and lower back pressure.

  12. Conformational sampling enhancement of replica exchange molecular dynamics simulations using swarm particle intelligence

    NASA Astrophysics Data System (ADS)

    Kamberaj, Hiqmet

    2015-09-01

    In this paper, we present a new method based on swarm particle social intelligence for use in replica exchange molecular dynamics simulations. In this method, the replicas (representing the different system configurations) are allowed communicating with each other through the individual and social knowledge, in additional to considering them as a collection of real particles interacting through the Newtonian forces. The new method is based on the modification of the equations of motion in such way that the replicas are driven towards the global energy minimum. The method was tested for the Lennard-Jones clusters of N = 4, 5, and 6 atoms. Our results showed that the new method is more efficient than the conventional replica exchange method under the same practical conditions. In particular, the new method performed better on optimizing the distribution of the replicas among the thermostats with time and, in addition, ergodic convergence is observed to be faster. We also introduce a weighted histogram analysis method allowing analyzing the data from simulations by combining data from all of the replicas and rigorously removing the inserted bias.

  13. Dynamics of energy exchange in model samples subjected to elastic and electromagnetic impacts

    NASA Astrophysics Data System (ADS)

    Avagimov, A. A.; Zeigarnik, V. A.; Okunev, V. I.

    2011-10-01

    The effects of elastic and electromagnetic (EM) fields are studied as an additional factor of energy exchange in the process of the deformation of a heterogeneous medium. The threshold value of initiating energy, Ktr( kp), relative to the current relaxation process is quantitatively estimated. It is shown that the estimated energy impacts below the threshold can initiate relaxation of local structural stresses and, thus, reduce the risk of a macrofracture. In a seismically active region, a similar scenario of initiation of dynamic development is considered in the local zones of potential sources of earthquakes. The possibility to determine the location, the time, and the intensity of the initiating EM impact is considered. From the experiments, the coefficient of electromechanical conversion is calculated.

  14. Replica exchange molecular dynamics of the thermodynamics of fibril growth of Alzheimer's Aβ42 peptide

    NASA Astrophysics Data System (ADS)

    Han, Ming; Hansmann, Ulrich H. E.

    2011-08-01

    The growth of amyloid fibrils is studied by replica exchange molecular dynamics in an implicit solvent. Our data indicate that extremely long simulation times (at least a few hundred ns) are necessary to study the thermodynamics of fibril elongation in detail. However some aspects of the aggregation process are already accessible on the time scales available in the present study. A peak in the specific heat indicates a docking temperature of Tdock ≈ 320 K. Irreversible locking requires lower temperatures with the locking temperature estimated as Tlock ≈ 280 K. In our simulation the fibril grows from both sides with the C-terminal of the incoming monomer attaching to the C-terminal of the peptides in the fibril forming a β-sheet on the fibril edge. Our simulation indicates that the C-terminal is crucial for aggregation.

  15. Molecular Dynamics Simulation Study on Energy Exchange Between Vibration Modes of a Square Graphene Nanoflake Oscillator.

    PubMed

    Lee, Eunae; Kang, Jeong Won; Kim, Ki-Sub; Kwon, Oh-Kuen

    2016-02-01

    Superlubricity in nanoscale graphene structures has been of interest for developing graphene-based nanoelectromechanical systems, as well as for the study of basic mechanical properties. Here, we investigated the translational and rotational motions of a square graphene nanoflake with retracting motions by performing classical molecular dynamics simulations. Our results show that the kinetic energy of the translational motion was exchanged into the kinetic energy of the rotational motion. Thus, square graphene nanoflake oscillators have very low quality factors in translational motions. We discuss that square graphene nanoflakes have great potential to be a core component in nanoelectromechanical systems by detecting their motions with ultrahigh sensitivity to facilitate the development of sensor, memory, and quantum computing.

  16. Stability of single sheet GNNQQNY aggregates analyzed by replica exchange molecular dynamics: Antiparallel versus parallel association

    SciTech Connect

    Vitagliano, Luigi; Esposito, Luciana; Pedone, Carlo; De Simone, Alfonso

    2008-12-26

    Protein and peptide aggregation into amyloid plaques is associated with a large variety of neurodegenerative diseases. The definition of the molecular bases of these pathologies is hampered by the transient nature of pre-fibrillar small-oligomers that are considered the toxic species. The ability of the peptide GNNQQNY to form amyloid-like structures makes it a good model to investigate the complex processes involved into amyloid fiber formation. By employing full atomistic replica exchange molecular dynamics simulations, we constructed the free energy surface of small assemblies of GNNQQNY to gain novel insights into the fiber formation process. The calculations suggest that the peptide exhibits a remarkable tendency to form both parallel and antiparallel {beta}-sheets. The data show that GNNQQNY preference for parallel or antiparallel {beta}-sheets is governed by a subtle balance of factors including assemblies' size, sidechain-sidechain interactions and pH. The samplings analysis provides a rationale to the observed trends.

  17. Molecular Dynamics Simulation Study on Energy Exchange Between Vibration Modes of a Square Graphene Nanoflake Oscillator.

    PubMed

    Lee, Eunae; Kang, Jeong Won; Kim, Ki-Sub; Kwon, Oh-Kuen

    2016-02-01

    Superlubricity in nanoscale graphene structures has been of interest for developing graphene-based nanoelectromechanical systems, as well as for the study of basic mechanical properties. Here, we investigated the translational and rotational motions of a square graphene nanoflake with retracting motions by performing classical molecular dynamics simulations. Our results show that the kinetic energy of the translational motion was exchanged into the kinetic energy of the rotational motion. Thus, square graphene nanoflake oscillators have very low quality factors in translational motions. We discuss that square graphene nanoflakes have great potential to be a core component in nanoelectromechanical systems by detecting their motions with ultrahigh sensitivity to facilitate the development of sensor, memory, and quantum computing. PMID:27433628

  18. Replica exchange molecular dynamics optimization of tensor network states for quantum many-body systems.

    PubMed

    Liu, Wenyuan; Wang, Chao; Li, Yanbin; Lao, Yuyang; Han, Yongjian; Guo, Guang-Can; Zhao, Yong-Hua; He, Lixin

    2015-03-01

    Tensor network states (TNS) methods combined with the Monte Carlo (MC) technique have been proven a powerful algorithm for simulating quantum many-body systems. However, because the ground state energy is a highly non-linear function of the tensors, it is easy to get stuck in local minima when optimizing the TNS of the simulated physical systems. To overcome this difficulty, we introduce a replica-exchange molecular dynamics optimization algorithm to obtain the TNS ground state, based on the MC sampling technique, by mapping the energy function of the TNS to that of a classical mechanical system. The method is expected to effectively avoid local minima. We make benchmark tests on a 1D Hubbard model based on matrix product states (MPS) and a Heisenberg J1-J2 model on square lattice based on string bond states (SBS). The results show that the optimization method is robust and efficient compared to the existing results.

  19. Radon exchange dynamics in a karst system investigated by radon continuous measurements in water: first results.

    PubMed

    Peano, G; Vigna, B; Villavecchia, E; Agnesod, G

    2011-05-01

    In 2008 the underground Karst Laboratory of Bossea Cave started research on radon exchange dynamics between bedrock, cave waters (main collector and percolations) and indoor underground atmosphere. Radon air concentrations, normally high, increase more and more during the collector's floods. An explanation of this is a radon-water solubilisation process more effective in flood events, because of a greater rock-water contact surface. Radon is then carried by water into the cave and released into the air. To verify this, continuous measurements of radon concentration are needed not only in the air, but also in the waters of the cave. So a new device for continuous radon monitoring in water was tested, connected to the AlphaGuard radon monitor. For the first 6 months of 2010, for different sections of the cave, the correlations between radon in the air, radon in the waters and the collector's stream flow fluctuations were presented and discussed. PMID:21586541

  20. Beryllium fluoride exchange rate accelerated by Mg²⁺ as discovered by ¹⁹F NMR.

    PubMed

    Liu, Yixiang; Mao, Xi-an; Liu, Maili; Jiang, Ling

    2015-01-01

    Beryllium fluoride is widely used as a phosphoryl analogue in macromolecular studies, which are not only fluoride-sensitive but also magnesium-dependent. The beryllium fluorides are a mixture of different species including BeF3(-) and BeF4(2-) exchanging under thermodynamic equilibrium in neutral aqueous solutions. In the cases of mimicking phosphate group transfer, both beryllium fluoride and the magnesium ion are generally needed. However, the impact of magnesium on the bioactivity of beryllium fluoride is not clear. We have found by (19)F NMR spectroscopy that Mg(2+) can severely affect the chemical exchange kinetics between BeF3(-) and BeF4(2-). When the F(-) concentration is relatively low, the presence of 10.0 mM Mg(2+) can accelerate the exchange rate 3-4 fold. However, when the F(-) concentration is relatively high, the Mg(2+) effect on the chemical exchange vanishes. On the basis of these findings, we proposed a possible mechanism that BeF4(2-) and Mg(2+) form an ion pair that affects the distribution of beryllium fluoride species and thus the activity in the solution.

  1. Analysis of bubbles and crashes in the TRY/USD, TRY/EUR, TRY/JPY and TRY/CHF exchange rate within the scope of econophysics

    NASA Astrophysics Data System (ADS)

    Deviren, Bayram; Kocakaplan, Yusuf; Keskin, Mustafa; Balcılar, Mehmet; Özdemir, Zeynel Abidin; Ersoy, Ersan

    2014-09-01

    In this study, we analyze the Turkish Lira/US Dollar (TRY/USD), Turkish Lira/Euro (TRY/EUR), Turkish Lira/Japanese Yen (TRY/JPY) and Turkish Lira/Swiss Franc (TRY/CHF) exchange rates in the global financial crisis period to detect the bubbles and crashes in the TRY by using a mathematical methodology developed by Watanabe et al. (2007). The methodology defines the bubbles and crashes in financial market price fluctuations by considering an exponential fitting of the associated data. This methodology is applied to detect the bubbles and crashes in the TRY/USD, TRY/EUR, TRY/JPY and TRY/CHF exchange rates from January, 1, 2005 to December, 20, 2013. In this mathematical methodology, the whole period of bubbles and crashes can be determined purely from past data, and the start of bubbles and crashes can be identified even before its bursts. In this way, the periods of bubbles and crashes in the TRY/USD, TRY/EUR, TRY/JPY and TRY/CHF are determined, and the beginning and end points of these periods are detected. The results show that the crashes in the TRY/CHF exchange rate are commonly finished earlier than in the other exchange rates; hence it is probable that the crashes in the other exchange rates would be finished soon when the crashes in the TRY/CHF exchange rate ended. We also find that the periods of crashes in the TRY/EUR exchange rate take longer time than in the other exchange rates. This information can be used in risk management and/or speculative gain. The crashes' periods in the TRY/EUR and TRY/USD exchange rates are observed to be relatively longer than in the other exchange rates.

  2. 75% success rate after open debridement, exchange of tibial insert, and antibiotics in knee prosthetic joint infections

    PubMed Central

    Thórhallsdóttir, Valdís Gudrún; Robertsson, Otto; W-Dahl, Annette; Stefánsdóttir, Anna

    2015-01-01

    Background and purpose Prosthetic joint infection (PJI) is a leading cause of early revision after total knee arthroplasty (TKA). Open debridement with exchange of tibial insert allows treatment of infection with retention of fixed components. We investigated the success rate of this procedure in the treatment of knee PJIs in a nationwide material, and determined whether the results were affected by microbiology, antibiotic treatment, or timing of debridement. Patients and methods 145 primary TKAs revised for the first time, due to infection, with debridement and exchange of the tibial insert were identified in the Swedish Knee Arthroplasty Register (SKAR). Staphylococcus aureus was the most common pathogen (37%) followed by coagulase-negative staphylococci (CNS) (23%). Failure was defined as death before the end of antibiotic treatment, revision of major components due to infection, life-long antibiotic treatment, or chronic infection. Results The overall healing rate was 75%. The type of infecting pathogen did not statistically significantly affect outcome. Staphylococcal infections treated without a combination of antibiotics including rifampin had a higher failure rate than those treated with rifampin (RR = 4, 95% CI: 2–10). In the 16 cases with more than 3 weeks of symptoms before treatment, the healing rate was 62%, as compared to 77% in the other cases (p = 0.2). The few patients with a revision model of prosthesis at primary operation had a high failure rate (5 of 8). Interpretation Good results can be achieved by open debridement with exchange of tibial insert. It is important to use an antibiotic combination including rifampin in staphylococcal infections. PMID:25753311

  3. Interest rate change and Omori dynamics in the Stock Market

    NASA Astrophysics Data System (ADS)

    Petersen, Alexander; Wang, Fengzhong; Havlin, Shlomo; Stanley, H. Eugene

    2009-03-01

    I present the behavior of U.S. markets on the day of U.S. Federal Open Market Commission (FOMC) meetings from the perspective of Statistical Physics. The announcement of key U.S. Federal Reserve rate changes causes a small financial shock, where the dynamics before and after the announcement can be described by an Omori law. We find that markets respond sharply to the news in a complex way reminiscent of physical earthquakes described by the Omori law, which describes the power-law relaxation of aftershocks following a singular perturbation. We find Omori laws in both the volatility of the price (also known as the absolute returns) and the volume traded, using 1-minute resolution financial time series. These results suggest that the perturbative response of the stock market is the same for both financial news and financial crises. The intraday response can be measured by the Omori power-law exponent φ, which has opposite sign before and after the announcement. We estimate the magnitude of news by relating φ to the behavior of the U. S. Treasury Bill before and after FOMC announcements.

  4. Functionally dissociable influences on learning rate in a dynamic environment

    PubMed Central

    McGuire, Joseph T.; Nassar, Matthew R.; Gold, Joshua I.; Kable, Joseph W.

    2015-01-01

    Summary Maintaining accurate beliefs in a changing environment requires dynamically adapting the rate at which one learns from new experiences. Beliefs should be stable in the face of noisy data, but malleable in periods of change or uncertainty. Here we used computational modeling, psychophysics and fMRI to show that adaptive learning is not a unitary phenomenon in the brain. Rather, it can be decomposed into three computationally and neuroanatomically distinct factors that were evident in human subjects performing a spatial-prediction task: (1) surprise-driven belief updating, related to BOLD activity in visual cortex; (2) uncertainty-driven belief updating, related to anterior prefrontal and parietal activity; and (3) reward-driven belief updating, a context-inappropriate behavioral tendency related to activity in ventral striatum. These distinct factors converged in a core system governing adaptive learning. This system, which included dorsomedial frontal cortex, responded to all three factors and predicted belief updating both across trials and across individuals. PMID:25459409

  5. Heat Exchange Processes and Thermal Dynamics of a Glacier-Fed Stream

    NASA Astrophysics Data System (ADS)

    Khamis, K.; Hannah, D. M.; Brown, L. E.; Milner, A. M.

    2012-12-01

    Glacier-fed river thermal regimes vary markedly in space and time. However, knowledge is limited of fundamental processes controlling alpine stream temperature dynamics. The few studies have not sufficiently characterised above-stream micro-climate and have been limited to single melt seasons. To address the research gap, this study quantified heat exchanges at the water surface and bed of a glacier fed stream over two summers to improve understanding of factors and processes driving thermal dynamics. An automatic weather station and river gauge were set up on a stream 1.5 km from the Taillon Glacier, French Pyrénées. Hydro-meteorological observations were recorded at 15-min intervals between 16 June-2 September 2010 and 2011. Energy balance components were measured [net radiation (Q*); bed heat flux (Qbhf)] or estimated based on site-specific data [sensible heat transfer (Qh); latent heat (Qe); fluid friction (Qf)]. During 2010, snowline altitude was lower and glacier ablation occurred in late season. During 2010, the mean snowline altitude was lower and ablation of glacier ice occurred later in the season Mean water temperature was lower (-0.8°C), precipitation greater (+87mm) and daily discharge variation lower (-0.03 m3s-1) than 2011. The net heat budget was strongly positive in both summers, with the majority of energy exchanged at the air-water interface. Averaged over the seasons, Q* was the largest heat source (~80% of total flux); Qh (~13%) and Qf (~3%) were also sources. Qe displayed inter-annual variability; during 2010 (2011) it contributed 5.2% (0.03%) of the total heat budget due to windier, drier conditions that offset early season condensation gains with late season evaporative losses. Energy exchanges at the channel - river bed interface comprised <1% of the heat budget; Qbhf was a sink (source) during 2010 (2011). Daily flux totals were used to characterize sub-seasonal dynamics. Declines in net radiation receipt and total energy available to

  6. Simplified quantification of labile proton concentration-weighted chemical exchange rate (k(ws) ) with RF saturation time dependent ratiometric analysis (QUESTRA): normalization of relaxation and RF irradiation spillover effects for improved quantitative chemical exchange saturation transfer (CEST) MRI.

    PubMed

    Sun, Phillip Zhe

    2012-04-01

    Chemical exchange saturation transfer MRI is an emerging imaging technique capable of detecting dilute proteins/peptides and microenvironmental properties, with promising in vivo applications. However, chemical exchange saturation transfer MRI contrast is complex, varying not only with the labile proton concentration and exchange rate, but also with experimental conditions such as field strength and radiofrequency (RF) irradiation scheme. Furthermore, the optimal RF irradiation power depends on the exchange rate, which must be estimated in order to optimize the chemical exchange saturation transfer MRI experiments. Although methods including numerical fitting with modified Bloch-McConnell equations, quantification of exchange rate with RF saturation time and power (QUEST and QUESP), have been proposed to address this relationship, they require multiple-parameter non-linear fitting and accurate relaxation measurement. Our work extended the QUEST algorithm with ratiometric analysis (QUESTRA) that normalizes the magnetization transfer ratio at labile and reference frequencies, which effectively eliminates the confounding relaxation and RF spillover effects. Specifically, the QUESTRA contrast approaches its steady state mono-exponentially at a rate determined by the reverse exchange rate (k(ws) ), with little dependence on bulk water T(1) , T(2) , RF power and chemical shift. The proposed algorithm was confirmed numerically, and validated experimentally using a tissue-like phantom of serially titrated pH compartments.

  7. Influence of Hydration Level on Polymer and Water Dynamics in Alkaline Anion Exchange Fuel Cell Membranes

    NASA Astrophysics Data System (ADS)

    Tarver, Jacob; Kim, Jenny; Tyagi, Madhu; Soles, Christopher; Tsai, Tsung-Han; Coughlin, Bryan

    2015-03-01

    Triblock copolymers based on poly(chloromethylstyrene)-b-poly(ethylene)-b-poly(chloromethylstyrene) can be quaternized to different extents to yield anion exchange membranes for alkaline fuel cells. In the absence of moisture, these membranes demonstrate bilayer lamellar morphology. Upon high levels of hydration, however, in-situ small angle neutron scattering reveals the emergence of higher-order diffraction peaks. This phenomena has previously been observed in analogous diblock copolymer-based membranes and has been attributed to the induction of a multilayer lamellar morphology in which selective striping of water occurs in the center of the ion-rich domain. By conducting humidity-resolved quasielastic neutron scattering (QENS) measurements using deuterated water, we are able to isolate differences in the pico- to nanosecond timescale dynamics of the hydrogenated membrane upon hydration. QENS measurements in the presence of a hydrogenated water source subsequently permit deconvolution and isolation of the translational and rotational dynamics of water as a function of relative humidity, revealing spatial and temporal changes in polymer and water motion at high levels of hydration.

  8. Dynamics of intramolecular spin exchange interaction of a nitronyl nitroxide diradical in solution and on surfaces

    NASA Astrophysics Data System (ADS)

    Lloveras, V.; Badetti, E.; Veciana, J.; Vidal-Gancedo, J.

    2016-02-01

    In this paper we report the study of the dynamics of a thermally modulated intramolecular spin exchange interaction of a novel diradical nitronyl nitroxide-substituted disulfide in solution and when it is grafted on a gold surface. The structure of this diradical was designed to have flexible chains leading to intramolecular collisions and hence spin exchange interaction, and with an appropriate binding group to be grafted on the gold surface to study its behavior on the surface. In solution, this diradical shows a strong spin exchange interaction between both radicals which is modulated by temperature, but also gold nanoparticles (AuNPs) functionalized with this diradical permit investigation of such a phenomenon in surface-grafted radicals. The spin-labelled AuNP synthesis was optimized to obtain high coverage of spin labels to lead to high spin exchange interaction. The obtained AuNPs were studied by Electron Paramagnetic Resonance (EPR), UV-Vis, and IR spectroscopies, HR-TEM microscopy, Cyclic Voltammetry (CV), Energy Dispersive X-ray analysis (EDX) and Thermogravimetric Analysis (TGA). This inorganic-organic hybrid material also showed dipolar interactions between its radicals which were confirmed by the appearance in the EPR spectra of an |Δms| = 2 transition at half-field. This signal gives direct evidence of the presence of a high-spin state and permitted us to study the nature of the magnetic coupling between the spins which was found to be antiferromagnetic. Self-Assembled Monolayers (SAMs) of these radicals on the Au (111) substrate were also prepared and studied by contact angle, X-Ray Photoelectron Spectroscopy (XPS), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), Cyclic Voltammetry and EPR. The magnetic as well as the electrochemical properties of the hybrid surfaces were studied and compared with the properties of this diradical in solution. Analogies between the properties of AuNPs with high coverage of radicals and those of SAM were

  9. Measurements of soil and canopy exchange rates in the Amazon rain forest using Rn-222

    NASA Technical Reports Server (NTRS)

    Trumbore, S. E.; Keller, M.; Wofsy, S. C.; Da Costa, J. M.

    1990-01-01

    Measurements were taken of the emission of Rn-222 from Amazon forest rocks and soils and used as a tracer of ventilation of the forest canopy layer at night. It was determined that the greatest resistance to transfer of trace gases from the soil to the atmosphere lies in the soil air space. Profiles of Rn-222 and CO2 showed steepest concentration gradients in the layer between 0 and 3 m above soil surface. Aerodynamic resistances calculated for this layer from Rn-222 and CO2 varied from 1.6 to 18 s/cm, with greater resistance during the afternoon than at night. The resistance to exchange with air from the entire 41 m layer below the canopy averaged 4.8 s/cm during 13 nights of CO2 profiles. The calculated average time to flush the layer below 41 m is 5.5 hr, and it is concluded that this indicates that significant exchange occurs despite nocturnal stratification.

  10. Catalysis in a Cage: Condition-Dependent Speciation and Dynamics of Exchanged Cu Cations in SSZ-13 Zeolites.

    PubMed

    Paolucci, Christopher; Parekh, Atish A; Khurana, Ishant; Di Iorio, John R; Li, Hui; Albarracin Caballero, Jonatan D; Shih, Arthur J; Anggara, Trunojoyo; Delgass, W Nicholas; Miller, Jeffrey T; Ribeiro, Fabio H; Gounder, Rajamani; Schneider, William F

    2016-05-11

    The relationships among the macroscopic compositional parameters of a Cu-exchanged SSZ-13 zeolite catalyst, the types and numbers of Cu active sites, and activity for the selective catalytic reduction (SCR) of NOx with NH3 are established through experimental interrogation and computational analysis of materials across the catalyst composition space. Density functional theory, stochastic models, and experimental characterizations demonstrate that within the synthesis protocols applied here and across Si:Al ratios, the volumetric density of six-membered-rings (6MR) containing two Al (2Al sites) is consistent with a random Al siting in the SSZ-13 lattice subject to Löwenstein's rule. Further, exchanged Cu(II) ions first populate these 2Al sites before populating remaining unpaired, or 1Al, sites as Cu(II)OH. These sites are distinguished and enumerated ex situ through vibrational and X-ray absorption spectroscopies (XAS) and chemical titrations. In situ and operando XAS follow Cu oxidation state and coordination environment as a function of environmental conditions including low-temperature (473 K) SCR catalysis and are rationalized through first-principles thermodynamics and ab initio molecular dynamics. Experiment and theory together reveal that the Cu sites respond sensitively to exposure conditions, and in particular that Cu species are solvated and mobilized by NH3 under SCR conditions. While Cu sites are spectroscopically and chemically distinct away from these conditions, they exhibit similar turnover rates, apparent activation energies and apparent reaction orders at the SCR conditions, even on zeolite frameworks other than SSZ13. PMID:27070199

  11. Protein structural dynamics at the gas/water interface examined by hydrogen exchange mass spectrometry.

    PubMed

    Xiao, Yiming; Konermann, Lars

    2015-08-01

    Gas/water interfaces (such as air bubbles or foam) are detrimental to the stability of proteins, often causing aggregation. This represents a potential problem for industrial processes, for example, the production and handling of protein drugs. Proteins possess surfactant-like properties, resulting in a high affinity for gas/water interfaces. The tendency of previously buried nonpolar residues to maximize contact with the gas phase can cause significant structural distortion. Most earlier studies in this area employed spectroscopic tools that could only provide limited information. Here we use hydrogen/deuterium exchange (HDX) mass spectrometry (MS) for probing the conformational dynamics of the model protein myoglobin (Mb) in the presence of N(2) bubbles. HDX/MS relies on the principle that unfolded and/or highly dynamic regions undergo faster deuteration than tightly folded segments. In bubble-free solution Mb displays EX2 behavior, reflecting the occurrence of short-lived excursions to partially unfolded conformers. A dramatically different behavior is seen in the presence of N(2) bubbles; EX2 dynamics still take place, but in addition the protein shows EX1 behavior. The latter results from interconversion of the native state with conformers that are globally unfolded and long-lived. These unfolded species likely correspond to Mb that is adsorbed to the surface of gas bubbles. N(2) sparging also induces aggregation. To explain the observed behavior we propose a simple model, that is, "semi-unfolded" ↔ "native" ↔ "globally unfolded" → "aggregated". This model quantitatively reproduces the experimentally observed kinetics. To the best of our knowledge, the current study marks the first exploration of surface denaturation phenomena by HDX/MS. PMID:25761782

  12. Protein structural dynamics at the gas/water interface examined by hydrogen exchange mass spectrometry

    PubMed Central

    Xiao, Yiming; Konermann, Lars

    2015-01-01

    Gas/water interfaces (such as air bubbles or foam) are detrimental to the stability of proteins, often causing aggregation. This represents a potential problem for industrial processes, for example, the production and handling of protein drugs. Proteins possess surfactant-like properties, resulting in a high affinity for gas/water interfaces. The tendency of previously buried nonpolar residues to maximize contact with the gas phase can cause significant structural distortion. Most earlier studies in this area employed spectroscopic tools that could only provide limited information. Here we use hydrogen/deuterium exchange (HDX) mass spectrometry (MS) for probing the conformational dynamics of the model protein myoglobin (Mb) in the presence of N2 bubbles. HDX/MS relies on the principle that unfolded and/or highly dynamic regions undergo faster deuteration than tightly folded segments. In bubble-free solution Mb displays EX2 behavior, reflecting the occurrence of short-lived excursions to partially unfolded conformers. A dramatically different behavior is seen in the presence of N2 bubbles; EX2 dynamics still take place, but in addition the protein shows EX1 behavior. The latter results from interconversion of the native state with conformers that are globally unfolded and long-lived. These unfolded species likely correspond to Mb that is adsorbed to the surface of gas bubbles. N2 sparging also induces aggregation. To explain the observed behavior we propose a simple model, that is, “semi-unfolded” ↔ “native” ↔ “globally unfolded” → “aggregated”. This model quantitatively reproduces the experimentally observed kinetics. To the best of our knowledge, the current study marks the first exploration of surface denaturation phenomena by HDX/MS. PMID:25761782

  13. Replica Exchange Molecular Dynamics Study of Dimerization in Prion Protein: Multiple Modes of Interaction and Stabilization.

    PubMed

    Chamachi, Neharika G; Chakrabarty, Suman

    2016-08-01

    The pathological forms of prions are known to be a result of misfolding, oligomerization, and aggregation of the cellular prion. While the mechanism of misfolding and aggregation in prions has been widely studied using both experimental and computational tools, the structural and energetic characterization of the dimer form have not garnered as much attention. On one hand dimerization can be the first step toward a nucleation-like pathway to aggregation, whereas on the other hand it may also increase the conformational stability preventing self-aggregation. In this work, we have used extensive all-atom replica exchange molecular dynamics simulations of both monomer and dimer forms of a mouse prion protein to understand the structural, dynamic, and thermodynamic stability of dimeric prion as compared to the monomeric form. We show that prion proteins can dimerize spontaneously being stabilized by hydrophobic interactions as well as intermolecular hydrogen bonding and salt bridge formation. We have computed the conformational free energy landscapes for both monomer and dimer forms to compare the thermodynamic stability and misfolding pathways. We observe large conformational heterogeneity among the various modes of interactions between the monomers and the strong intermolecular interactions may lead to as high as 20% β-content. The hydrophobic regions in helix-2, surrounding coil regions, terminal regions along with the natively present β-sheet region appear to actively participate in prion-prion intermolecular interactions. Dimerization seems to considerably suppress the inherent dynamic instability observed in monomeric prions, particularly because the regions of structural frustration constitute the dimer interface. Further, we demonstrate an interesting reversible coupling between the Q160-G131 interaction (which leads to inhibition of β-sheet extension) and the G131-V161 H-bond formation. PMID:27390876

  14. Characterization of the internal dynamics and conformational space of zinc-bound amyloid β peptides by replica-exchange molecular dynamics simulations.

    PubMed

    Xu, Liang; Wang, Xiaojuan; Wang, Xicheng

    2013-07-01

    Amyloid β (Aβ) peptides and metal ions have been associated with the pathogenesis of Alzheimer's disease. The conformational space of Aβ fragments of different length with and without binding of metal ions has been extensively investigated by replica-exchange molecular dynamics (REMD) simulation. However, only trajectories extracted at relatively low temperatures have been used for this analysis. The capability of REMD simulations to characterize the internal dynamics of such intrinsically disordered proteins (IDPs) as Aβ has been overlooked. In this work, we use an approach recently developed by Xue and Skrynnikov (J Am Chem Soc 133:14614-14628, 2011) to calculate NMR observables, including (15)N relaxation rates and (15)N-(1)H nuclear Overhauser enhancement (NOE), from the high-temperature trajectory of REMD simulations for zinc-bound Aβ peptides. The time axis of the trajectory was rescaled to correct for the effect of the high temperature (408 K) compared with the experimental temperature (278 K). Near-quantitative agreement between simulated values and experimental results was obtained. When the structural properties and free-energy surfaces of zinc-bound Aβ(1-40) and Aβ(1-42) were compared at the physiological temperature 310 K it was found that zinc-bound Aβ(1-42) was more rigid than Aβ(1-40) at the C terminus, and its conformational transitions were also more preferred. The self-consistent results derived from trajectories at high and low temperatures demonstrate the capability of REMD simulations to capture the internal dynamics of IDPs.

  15. Dynamics of carbon dioxide exchange of a wheat community grown in a semi-closed environment

    NASA Technical Reports Server (NTRS)

    Corey, Kenneth A.

    1989-01-01

    A wheat (Triticum aestivum Yecora Rojo) community was grown in the semi-closed conditions of the NASA/KSC Biomass Production Chamber (BPC). Experiments were conducted to determine whole community carbon dioxide exchange rates as influenced by growth and development, carbon dioxide concentration, time within the photoperiod, irradiance, and temperature. Plants were grown at a population of about 1500 per sq meter using a 20 hour light/4 hour dark daily regime. Light was supplied by HPS vapor lamps and irradiance was maintained in the range of 590 to 675 mu mol per sq meter. The temperature regime was 20 C light/16 C dark and nutrients were supplied hydroponically as a thin film. Fractional interception of PPF by the community increased rapidly during growth reaching a maximum of 0.96, 24 days after planting. This time corresponded to canopy closure and maximum rates of net photosynthesis (NP). Net daily CO2 utilization rates were calculated to day 48 and a 4th order regression equation integrated to obtain total moles of CO2 fixed by the community. This procedure may be useful for monitoring and prediction of biomass yields in a closed ecology life support system (CELSS).

  16. Time variations of 222Rn concentration and air exchange rates in a Hungarian cave.

    PubMed

    Nagy, Hedvig Éva; Szabó, Zsuzsanna; Jordán, Gyozo; Szabó, Csaba; Horváth, Akos; Kiss, Attila

    2012-09-01

    A long-term radon concentration monitoring was carried out in the Pál-völgy cave, Budapest, Hungary, for 1.5 years. Our major goal was to determine the time dependence of the radon concentration in the cave to characterise the air exchange and define the most important environmental parameters that influence the radon concentration inside the cave. The radon concentration in the cave air was measured continuously by an AlphaGuard radon monitor, and meteorological parameters outside the cave were collected simultaneously. The air's radon concentration in the cave varied between 104 and 7776 Bq m(-3), the annual average value was 1884±85 Bq m(-3). The summer to winter radon concentration ratio was as high as 21.8. The outside air temperature showed the strongest correlation with the radon concentration in the cave, the correlation coefficient (R) was 0.76. PMID:22462600

  17. An evaluation of multiple-schedule variations to reduce high-rate requests in the picture exchange communication system.

    PubMed

    Landa, Robin; Hanley, Gregory P

    2016-06-01

    Using procedures similar to those of Tiger, Hanley, and Heal (2006), we compared two multiple-schedule variations (S+/S- and S+ only) to treat high-rate requests for edible items in the Picture Exchange Communication System (PECS). Two individuals with autism participated, after they showed persistent requests for edible items after PECS training. Stimulus control was achieved only with the multiple schedule that involved presentation of a discriminative stimulus during reinforcement components and its removal during extinction components (S+ only). Discriminated requests were maintained for the 1 participant who experienced schedule thinning. PMID:26814152

  18. Asymmetrical long-run dependence between oil price and US dollar exchange rate-Based on structural oil shocks

    NASA Astrophysics Data System (ADS)

    Jiang, Jiaqi; Gu, Rongbao

    2016-08-01

    The multifractal behavior in cross-correlation between oil prices and exchange rates is examined in this paper. We use the multifractal detrended cross-correlation analysis to investigate the general cross-correlations, and further show that these cross-correlations are asymmetric by multifractal asymmetric cross-correlation analysis. We recover the structural oil shocks and then use these indicators to characterize the asymmetries along with oil price trend itself. Our empirical results show that their asymmetric degrees vary significantly. The sign of oil supply shock leads to the most significant asymmetry among them.

  19. Confirmatory analysis of the AP1000 passive residual heat removal heat exchanger with 3-D computational fluid dynamic analysis

    SciTech Connect

    Schwall, James R.; Karim, Naeem U.; Thakkar, Jivan G.; Taylor, Creed; Schulz, Terry; Wright, Richard F.

    2006-07-01

    The AP1000 is an 1100 MWe advanced nuclear power plant that uses passive safety features to enhance plant safety and to provide significant and measurable improvements in plant simplification, reliability, investment protection and plant costs. The AP1000 received final design approval from the US-NRC in 2004. The AP1000 design is based on the AP600 design that received final design approval in 1999. Wherever possible, the AP1000 plant configuration and layout was kept the same as AP600 to take advantage of the maturity of the design and to minimize new design efforts. As a result, the two-loop configuration was maintained for AP1000, and the containment vessel diameter was kept the same. It was determined that this significant power up-rate was well within the capability of the passive safety features, and that the safety margins for AP1000 were greater than those of operating PWRs. A key feature of the passive core cooling system is the passive residual heat removal heat exchanger (PRHR HX) that provides decay heat removal for postulated LOCA and non-LOCA events. The PRHR HX is a C-tube heat exchanger located in the in-containment refueling water storage tank (IRWST) above the core promoting natural circulation heat removal between the reactor cooling system and the tank. Component testing was performed for the AP600 PRHR HX to determine the heat transfer characteristics and to develop correlations to be used for the AP1000 safety analysis codes. The data from these tests were confirmed by subsequent integral tests at three separate facilities including the ROSA facility in Japan. Owing to the importance of this component, an independent analysis has been performed using the ATHOS-based computational fluid dynamics computer code PRHRCFD. Two separate models of the PRHR HX and IRWST have been developed representing the ROSA test geometry and the AP1000 plant geometry. Confirmation of the ROSA test results were used to validate PRHRCFD, and the AP1000 plant model

  20. Dynamic analysis of heart rate may predict subsequent ventricular tachycardia after myocardial infarction

    NASA Technical Reports Server (NTRS)

    Makikallio, T. H.; Seppanen, T.; Airaksinen, K. E.; Koistinen, J.; Tulppo, M. P.; Peng, C. K.; Goldberger, A. L.; Huikuri, H. V.

    1997-01-01

    Dynamics analysis of RR interval behavior and traditional measures of heart rate variability were compared between postinfarction patients with and without vulnerability to ventricular tachyarrhythmias in a case-control study. Short-term fractal correlation of heart rate dynamics was better than traditional measures of heart rate variability in differentiating patients with and without life-threatening arrhythmias.

  1. Low air exchange rate causes high indoor radon concentration in energy-efficient buildings.

    PubMed

    Vasilyev, A V; Yarmoshenko, I V; Zhukovsky, M V

    2015-06-01

    Since 1995, requirements on energy-efficient building construction were established in Russian Building Codes. In the course of time, utilisation of such technologies became prevailing, especially in multi-storey building construction. According to the results of radon survey in buildings constructed meeting new requirements on energy efficiency, radon concentration exceeds the average level in early-constructed buildings. Preponderance of the diffusion mechanism of radon entry in modern multi-storey buildings has been experimentally established. The experimental technique of the assessment of ventilation rate in dwellings under real conditions was developed. Based on estimates of average ventilation rate, it was approved that measures to increase energy efficiency lead to reduction in ventilation rate and accumulation of higher radon concentrations indoors. Obtained ventilation rate values have to be considered as extremely low.

  2. Quantum dynamics of two-optical modes and a single mechanical mode optomechanical system: Selective energy exchange

    NASA Astrophysics Data System (ADS)

    Aggarwal, Neha; Bhattacherjee, Aranya B.

    2014-01-01

    We study the quantum dynamics of an optomechanical setup comprising two optical modes and one mechanical mode. We show that the same system can undergo a dynamical phase transition analogous to Dicke-Hepp-Lieb superradiant type phase transition. We found that the coupling between the momentum quadratures of the two optical fields gives rise to a new dynamical critical point. We show that selective energy exchange between any two modes is possible by coherent control of the coupling parameters. In addition we also demonstrate the occurrence of normal mode splitting (NMS) in the mechanical displacement spectrum.

  3. Exposing Differences in Monomer Exchange Rates of Multicomponent Supramolecular Polymers in Water.

    PubMed

    Baker, Matthew B; Gosens, Ronald P J; Albertazzi, Lorenzo; Matsumoto, Nicholas M; Palmans, Anja R A; Meijer, E W

    2016-02-01

    The formation of multicomponent and bioactive supramolecular polymers is a promising strategy for the formation of biomaterials that match the dynamic and responsive nature of biological systems. In order to fully realize the potential of this strategy, knowledge of the location and behavior of bioactive components within the system is crucial. By employing synthetic strategies to create multifunctional monomers, coupled with FRET and STORM techniques, we have investigated the formation and behavior of a bioactive and multicomponent supramolecular polymer. By creating a peptide-dye-monomer conjugate, we were able to measure high degrees of monomer incorporation and to visualize the equal distribution of monomers within the supramolecular polymer. Furthermore, by tracking the movement of monomers, we uncovered small differences in the dynamics of the bioactive monomers. PMID:26603687

  4. Effect of gas composition and gas utilisation on the dynamic response of a proton exchange membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Weydahl, Helge; Møller-Holst, Steffen; Børresen, Børre

    The transient response of a proton exchange membrane fuel cell (PEMFC) was measured for various cathode gas compositions and gas utilisations (fraction of supplied reactant gas which is consumed in the fuel cell reaction). For a PEMFC operated on pure hydrogen and oxygen, the cell voltage response to current steps was fast, with response times in the range 0.01-1 s, depending on the applied current. For a PEMFC supplied with air as cathode gas, an additional relaxation process related to oxygen transport caused a slower response (approximately 0.1-2 s depending on the applied current). Response curves up to approximately 0.01 s were apparently unaffected by gas composition and utilisation and were most likely dominated by capacitive discharge of the double layer and reaction with surplus oxygen residing in the cathode. The utilisation of hydrogen had only a minor effect on the response curves, while the utilisation of air severely influenced the PEMFC dynamics. Results suggested that air flow rates should be high to obtain rapid PEMFC response.

  5. Effect of low /sup 60/Co dose rates on sister chromatid exchange incidence in the benthic worm. Neanthes arenaceodentata

    SciTech Connect

    Harrison, F.L.; Rice, D.W. Jr.

    1981-10-13

    The usefulness of sister chromatid exchange (SCE) induction as a measure of low-level radiation effect was examined in a benthic marine worm, Neanthes arenaceodentata. Larvae were exposed to /sup 60/Co radiation for 12 to 24 h at total doses ranging from 0.5 to 309 R and at dose rates from 0.04 to 13 R/h. Animals exposed at intermediate dose rates (0.5, 0.6, 1.25, 2.0, and 2.5 R/h) had SCE frequencies per chromosome about twice that of those receiving no radiation (controls), whereas those exposed at the higher dose rates (7.0 and 13 R/h) had SCE frequencies lower than the controls. Animals exposed at the lower dose rates (0.04 and 0.1 R/h) had lower SCE frequencies than those exposed at intermediate dose rates (and higher SCE frequencies than controls). The length of chromosome pair number one differed among metaphase spreads and was used as an index of chromosome condensation in a given metaphase. Because there is a possibility that chromosome morphology may affect the ability to resolve SCEs, morphology will be monitored in future studies. A preliminary experiment was performed to assess the effects of 2.2 and 11.5 R/h for 24 h on growth and development. Larvae observed at 6 and 17 d after irradiation did not have significantly different numbers of abnormal larvae or survival rates.

  6. Helix bending in alamethicin: molecular dynamics simulations and amide hydrogen exchange in methanol.

    PubMed Central

    Gibbs, N; Sessions, R B; Williams, P B; Dempsey, C E

    1997-01-01

    Molecular dynamics simulations of alamethicin in methanol were carried out with either a regular alpha-helical conformation or the x-ray crystal structure as starting structures. The structures rapidly converged to a well-defined hydrogen-bonding pattern with mixed alpha-helical and 3(10)-helical hydrogen bonds, consistent with NMR structural characterization, and did not unfold throughout the 1-ns simulation, despite some sizable backbone fluctuations involving reversible breaking of helical hydrogen bonds. Bending of the helical structure around residues Aib10-Aib13 was associated with reversible flips of the peptide bonds involving G11 (Aib10-G11 or G11-L12 peptide bonds), yielding discrete structural states in which the Aib10 carbonyl or (rarely) the G11 carbonyl was oriented away from the peptide helix. These peptide bond reversals could be accommodated without greatly perturbing the adjacent helical structure, and intramolecular hydrogen bonding was generally maintained in bent states through the formation of new (non-alpha or 3[10]) hydrogen bonds with good geometries: G11 NH-V9 CO (inverse gamma turn), Aib13 NH-Aib8 CO (pi-helix) and, rarely, L12 NH- Q7 NH (pi-helix). These observations may reconcile potentially conflicting NMR structural information for alamethicin in methanol, in which evidence for conformational flexibility in the peptide sequence before P14 (G11-Aib13) contrasts with the stability of backbone amide NH groups to exchange with solvent. Similar reversible reorientation of the Thr11-Gly12 peptide bond of melittin is also observed in dynamics simulations in methanol (R. B. Sessions, N. Gibbs, and C. E. Dempsey, submitted). This phenomenon may have some role in the orientation of the peptide carbonyl in solvating the channel lumen in membrane ion channel states of these peptides. Images FIGURE 1 FIGURE 2 PMID:9168025

  7. River temperature processes under contrasting riparian land cover: linking microclimate, heat exchange and water thermal dynamics

    NASA Astrophysics Data System (ADS)

    Hannah, D. M.; Kantola, K.; Malcolm, I.

    2012-12-01

    River temperature influences strongly growth and survival in salmonid fish, which are often the target of river management strategies. Temperature is controlled by transfers of heat and water to/ from the river system, with land and water management modifying exchanges and consequently thermal regime. In the UK, fisheries managers are promoting riparian forest planting as a climate change adaption measure to reduce water temperature extremes. However, scientific understanding lags behind management and policy needs. Specifically, there is an urgent requirement to determine planting strategies that maximise expected benefits of riparian forest in terms of reduction in maximum water temperature. Scientific knowledge is necessary to underpin conceptual and deterministic models to inform management. To address this research gap, this paper analyses high resolution (15 minute) hydrometeorological data collected over a calendar year in the western Scottish Highlands (Loch Ard) to understand the controls and processes determining river temperature dynamics under open moorland (control), semi-natural woodland and commercial forest. The research programme aims: (1) to characterise spatial and temporal variability in riparian microclimate and stream water temperature regime across forest treatments; (2) to identify the hydrological, climatological and site-specific factors affecting stream temperature; (3) to estimate the energy balance at sites representative of each forest treatment and, thus, yield physical process understanding about dominant heat exchanges driving thermal variability; and (4) to use 1-3 to predict stream temperature sensitivity under different forestry and hydroclimatological scenarios. Results indicated that inter-treatment differences in mean and maximum daily water column temperature were ordered open > semi-natural > commercial during summer, but semi-natural > commercial > open during winter. Minimum water temperature was ordered commercial > semi

  8. Assessment of the Draft AIAA S-119 Flight Dynamic Model Exchange Standard

    NASA Technical Reports Server (NTRS)

    Jackson, E. Bruce; Murri, Daniel G.; Hill, Melissa A.; Jessick, Matthew V.; Penn, John M.; Hasan, David A.; Crues, Edwin Z.; Falck, Robert D.; McCarthy, Thomas G.; Vuong, Nghia; Zimmerman, Curtis

    2011-01-01

    An assessment of a draft AIAA standard for flight dynamics model exchange, ANSI/AIAA S-119-2011, was conducted on behalf of NASA by a team from the NASA Engineering and Safety Center. The assessment included adding the capability of importing standard models into real-time simulation facilities at several NASA Centers as well as into analysis simulation tools. All participants were successful at importing two example models into their respective simulation frameworks by using existing software libraries or by writing new import tools. Deficiencies in the libraries and format documentation were identified and fixed; suggestions for improvements to the standard were provided to the AIAA. An innovative tool to generate C code directly from such a model was developed. Performance of the software libraries compared favorably with compiled code. As a result of this assessment, several NASA Centers can now import standard models directly into their simulations. NASA is considering adopting the now-published S-119 standard as an internal recommended practice.

  9. Custom-tailored adsorbers: A molecular dynamics study on optimal design of ion exchange chromatography material.

    PubMed

    Lang, Katharina M H; Kittelmann, Jörg; Pilgram, Florian; Osberghaus, Anna; Hubbuch, Jürgen

    2015-09-25

    The performance of functionalized materials, e.g., ion exchange resins, depends on multiple resin characteristics, such as type of ligand, ligand density, the pore accessibility for a molecule, and backbone characteristics. Therefore, the screening and identification process for optimal resin characteristics for separation is very time and material consuming. Previous studies on the influence of resin characteristics have focused on an experimental approach and to a lesser extent on the mechanistic understanding of the adsorption mechanism. In this in silico study, a previously developed molecular dynamics (MD) tool is used, which simulates any given biomolecule on resins with varying ligand densities. We describe a set of simulations and experiments with four proteins and six resins varying in ligand density, and show that simulations and experiments correlate well in a wide range of ligand density. With this new approach simulations can be used as pre-experimental screening for optimal adsorber characteristics, reducing the actual number of screening experiments, which results in a faster and more knowledge-based development of custom-tailored adsorbers.

  10. Efficient Determination of Relative Entropy Using Combined Temperature and Hamiltonian Replica-Exchange Molecular Dynamics.

    PubMed

    Jo, Sunhwan; Chipot, Christophe; Roux, Benoît

    2015-05-12

    The performance and accuracy of different simulation schemes for estimating the entropy inferred from free energy calculations are tested. The results obtained from replica-exchange molecular dynamics (REMD) simulations based on a simplified toy model are compared to exact numerically derived ones to assess accuracy and convergence. It is observed that the error in entropy estimation decreases by at least an order of magnitude and the quantities of interest converge much faster when the simulations are coupled via a temperature REMD algorithm and the trajectories from different temperatures are combined. Simulations with the infinite-swapping method and its variants show some improvement over the traditional nearest-neighbor REMD algorithms, but they are more computationally expensive. To test the methodologies further, the free energy profile for the reversible association of two methane molecules in explicit water was calculated and decomposed into its entropic and enthalpic contributions. Finally, a strategy based on umbrella sampling computations carried out via simultaneous temperature and Hamiltonian REMD simulations is shown to yield the most accurate entropy estimation. The entropy profile between the two methane molecules displays the characteristic signature of a hydrophobic interaction.

  11. Replica exchange molecular dynamics simulations of an α/β-type small acid soluble protein (SASP).

    PubMed

    Ojeda-May, P; Pu, Jingzhi

    2013-12-31

    Small acid soluble proteins (SASPs) of α/β-type play a major role in the resistance of spore DNAs to external assaults. It has been found that α/β-type SASP exhibits intrinsic disorder on isolation, but it acquires a defined native state upon binding to DNA. This disorder to order transition is not yet understood. Other questions related to the role of the thermodynamics and structure of the individual protein in the complex formation remain elusive. Characterization of the unbound state of α/β-type SASP in experiments could be a challenging problem because of the heterogeneous nature of the ensemble. Here, computer simulations can help gain more insights into the unbound state of α/β-type SASP. In the present work, by using replica exchange molecular dynamics (REMD), we simulated an α/β-type SASP on isolation with an implicit solvent. We found that α/β-type SASP undergoes a continuous phase transition with a small free energy barrier, a common feature of intrinsically disordered proteins (IDPs). Additionally, we detected the presence of residual α-helical structures at local level and a high degree of plasticity in the chain which can contribute to the fast disorder to order transition by reducing the fly-casting mechanism.

  12. Spatiotemporally‐Resolved Air Exchange Rate as a Modifier of Acute Air Pollution‐Related Morbidity in AtlantaMorbidity in Atlanta

    EPA Science Inventory

    Epidemiological studies frequently use central site concentrations as surrogates of exposure to air pollutants. Variability in air pollutant infiltration due to differential air exchange rates (AERs) is potentially a major factor affecting the relationship between central site c...

  13. Development and Evaluation of a New Air Exchange Rate Algorithm for the Stochastic Human Exposure and Dose Simulation Model (ISES Presentation)

    EPA Science Inventory

    Previous exposure assessment panel studies have observed considerable seasonal, between-home and between-city variability in residential pollutant infiltration. This is likely a result of differences in home ventilation, or air exchange rates (AER). The Stochastic Human Exposure ...

  14. Investigation of the influence of groundwater advection on energy extraction rates for sustainable borehole heat exchanger operation

    NASA Astrophysics Data System (ADS)

    Schelenz, Sophie; Dietrich, Peter; Vienken, Thomas

    2016-04-01

    A sustainable thermal exploitation of the shallow subsurface requires a precise understanding of all relevant heat transport processes. Currently, planning practice of shallow geothermal systems (especially for systems < 30 kW) focuses on conductive heat transport as the main energy source while the impact of groundwater flow as the driver for advective heat transport is neglected or strongly simplified. The presented study proves that those simplifications of complex geological and hydrogeological subsurface characteristics are insufficient for a precise evaluation of site-specific energy extraction rates. Based on synthetic model scenarios with varying subsurface conditions (groundwater flow velocity and aquifer thickness) the impact of advection on induced long term temperature changes in 5 and 10 m distance of the borehole heat exchanger is presented. Extending known investigations, this study enhances the evaluation of shallow geothermal energy extraction rates by considering conductive and advective heat transport under varying aquifer thicknesses. Further, it evaluates the impact of advection on installation lengths of the borehole heat exchanger to optimize the initial financial investment. Finally, an evaluation approach is presented that classifies relevant heat transport processes according to their Péclet number to enable a first quantitative assessment of the subsurface energy regime and recommend further investigation and planning procedures.

  15. CO sub 2 enrichment of tomatoes: Relationship of foliar stress symptoms to starch concentrations and carbon exchange rates

    SciTech Connect

    Tripp, K.; Peet, M.; Pharr, D.M.; Willits, D. )

    1990-05-01

    CO{sub 2} enrichment of tomatoes results in a seasonally progressive downrolling, chlorosis and purpling of foliage, beginning with the older leaves, but eventually including the entire plant. This deformation has generally been attributed to excess starch. In a comparison of 2 cultivars given CO{sub 2} enrichment and treatments modifying source/sink ratios (fruit pruning, high night temperatures, decreased rooting volume), however, changes in deformation could not be related to changes in foliar starch concentrations. While CO{sub 2} enriched plants had higher foliar starch and greater foliar deformation, deformation increased over the season while starch decreased. Carbon exchange rates (CER) were low in lower canopy leaves, whether deformed or not. CO{sub 2} enrichment resulted in only slightly higher photosynthetic rates. Over all treatments and sampling data there was no relationship between foliar deformation and CER.

  16. Quantitative chemical exchange saturation transfer (qCEST) MRI - omega plot analysis of RF-spillover-corrected inverse CEST ratio asymmetry for simultaneous determination of labile proton ratio and exchange rate.

    PubMed

    Wu, Renhua; Xiao, Gang; Zhou, Iris Yuwen; Ran, Chongzhao; Sun, Phillip Zhe

    2015-03-01

    Chemical exchange saturation transfer (CEST) MRI is sensitive to labile proton concentration and exchange rate, thus allowing measurement of dilute CEST agent and microenvironmental properties. However, CEST measurement depends not only on the CEST agent properties but also on the experimental conditions. Quantitative CEST (qCEST) analysis has been proposed to address the limitation of the commonly used simplistic CEST-weighted calculation. Recent research has shown that the concomitant direct RF saturation (spillover) effect can be corrected using an inverse CEST ratio calculation. We postulated that a simplified qCEST analysis is feasible with omega plot analysis of the inverse CEST asymmetry calculation. Specifically, simulations showed that the numerically derived labile proton ratio and exchange rate were in good agreement with input values. In addition, the qCEST analysis was confirmed experimentally in a phantom with concurrent variation in CEST agent concentration and pH. Also, we demonstrated that the derived labile proton ratio increased linearly with creatine concentration (P < 0.01) while the pH-dependent exchange rate followed a dominantly base-catalyzed exchange relationship (P < 0.01). In summary, our study verified that a simplified qCEST analysis can simultaneously determine labile proton ratio and exchange rate in a relatively complex in vitro CEST system.

  17. Role of Exchange Protein Activated by cAMP 1 in Regulating Rates of Microtubule Formation in Cystic Fibrosis Epithelial Cells.

    PubMed

    Rymut, Sharon M; Ivy, Tracy; Corey, Deborah A; Cotton, Calvin U; Burgess, James D; Kelley, Thomas J

    2015-12-01

    The regulation of microtubule dynamics in cystic fibrosis (CF) epithelial cells and the consequences of reduced rates of microtubule polymerization on downstream CF cellular events, such as cholesterol accumulation, a marker of impaired intracellular transport, are explored here. It is identified that microtubules in both CF cell models and in primary CF nasal epithelial cells repolymerize at a slower rate compared with respective controls. Previous studies suggest a role for cAMP in modulating organelle transport in CF cells, implicating a role for exchange protein activated by cAMP (EPAC) 1, a regulator of microtubule elongation, as a potential mechanism. EPAC1 activity is reduced in CF cell models and in Cftr(-/-) mouse lung compared with respective non-CF controls. Stimulation of EPAC1 activity with the selective EPAC1 agonist, 8-cpt-2-O-Me-cAMP, stimulates microtubule repolymerization to wild-type rates in CF cells. EPAC1 activation also alleviates cholesterol accumulation in CF cells, suggesting a direct link between microtubule regulation and intracellular transport. To verify the relationship between transport and microtubule regulation, expression of the protein, tubulin polymerization-promoting protein, was knocked down in non-CF human tracheal (9/HTEo(-)) cells to mimic the microtubule dysregulation in CF cells. Transduced cells with short hairpin RNA targeting tubulin polymerization-promoting protein exhibit CF-like perinuclear cholesterol accumulation and other cellular manifestations of CF cells, thus supporting a role for microtubule regulation as a mechanism linking CFTR function to downstream cellular manifestation.

  18. Quantifying groundwater exchange rates in a beach barrier lagoon using a radioisotopic tracer and geophysical methods: Younger Lagoon, Santa Cruz, CA

    NASA Astrophysics Data System (ADS)

    Richardson, C. M.; Swarzenski, P. W.; Johnson, C.

    2013-12-01

    Coastal lagoons are highly productive systems with a strong dependence on the physico-chemical regime of their surrounding environment. Groundwater interactions with the nearshore environment can drive ecosystem stability and productivity. Lagoons with restricted surface connectivity interact with coastal waters via subsurface flow paths that follow natural hydraulic gradients, producing a dynamic freshwater-saltwater mixing zone with submarine groundwater discharge (SGD) regions that are tidally influenced. Recent studies demonstrate the importance of SGD in maintaining nearshore ecology through a number of processes, including enhanced chemical loadings, focused biogeochemical transformations, and complex water mixing scenarios (Slomp and Van Cappellen, 2004 and Taniguchi et al., 2002). Groundwater discharge to the coastal ocean is often slow, diffuse and site-specific. Traditional methods used to evaluate SGD fluxes operate at varying scales and typically result in over or underestimates of SGD. Novel monitoring and evaluation methods are required in order to better understand how coastal aquifer systems influence multi-scalar water and nutrient budgets. Recently developed methods to determine fluid exchange rates include the use of select U- and Th-series radionuclides, multi-channel resistivity imaging, as well as the integration of temperature data and 1-D analytical modeling. Groundwater fluxes were examined in a coastal lagoon system to characterize the physics of subsurface fluid transport evidenced by visible seepage faces at low tide. Fluid exchange rates were quantified to determine the spatial and temporal variability of groundwater movement using thermal time series, water level data, and a coupled radiotracer-geophysical method. Our investigation of subsurface characteristics and groundwater fluxes using both traditional and newly-developed methods indicated that seasonal water inputs and tidal controls on water table elevation significantly

  19. Heart rates and gas exchange in the Amazonian manatee (Trichechus inunguis) in relation to diving.

    PubMed

    Gallivan, G J; Kanwisher, J W; Best, R C

    1986-01-01

    Unrestrained Amazonian manatees (Trichechus inunguis) maintained a constant heart rate during diving and exhibited a slight tachycardia during breathing. 'Forcing' the manatees to dive caused a marked bradycardia. They exhibited a more pronounced tachycardia during breathing after 'forced' dives and hyperventilated during recovery dives. Manatees are capable of dives exceeding 10 min duration without having to resport to anaerobic metabolism, and even after 10 min dives recover within 3-4 short dives. The ability of manatees to make long dives, in spite of relatively poor O2 stores, is due to their low metabolic rate, while the rapid recovery is aided by their high CO2 stores which minimizes CO2 storage in the body. In manatees the changes in alveolar O2 and CO2 pressure (PAO2 and PACO2) in relation to dive time are slower and more variable than in other marine mammals. The lower rate of change is probably due to the manatees' reduced metabolic rate, while the greater variability is due to their breathing pattern, in which both ventilation and body gas stores influence alveolar gases.

  20. State-to-state quantum dynamics of O + O2 isotope exchange reactions reveals nonstatistical behavior at atmospheric conditions.

    PubMed

    Sun, Zhigang; Liu, Lan; Lin, Shi Ying; Schinke, Reinhard; Guo, Hua; Zhang, Dong H

    2010-01-12

    The O + O(2) exchange reaction is a prerequisite for the formation of ozone in Earth's atmosphere. We report here state-to-state differential and integral cross sections for several O + O(2) isotope-exchange reactions obtained by dynamically exact quantum scattering calculations at collision energies relevant to atmospheric conditions. These reactions are shown to be highly nonstatistical, evidenced by dominant forward scattering and deviation of the integral cross section from the statistical limit. Mechanistic analyses revealed that the nonstatistical channel is facilitated by short-lived osculating resonances. The theoretical results provided an in-depth interpretation of a recent molecular beam experiment of the exchange reaction and shed light on the initial step of ozone recombination.

  1. The role of dynamic surface water-groundwater exchange on streambed denitrification in a first-order, low-relief agricultural watershed

    USGS Publications Warehouse

    Rahimi Kazerooni, Mina N.; Essaid, Hedeff I.; Wilson, John T.

    2015-01-01

    The role of temporally varying surface water-groundwater (SW-GW) exchange on nitrate removal by streambed denitrification was examined along a reach of Leary Weber Ditch (LWD), Indiana, a small, first-order, low-relief agricultural watershed within the Upper Mississippi River basin, using data collected in 2004 and 2005. Stream stage, GW heads (H), and temperatures (T) were continuously monitored in streambed piezometers and stream bank wells for two transects across LWD accompanied by synoptic measurements of stream stage, H, T, and nitrate (NO3) concentrations along the reach. The H and T data were used to develop and calibrate vertical two-dimensional, models of streambed water flow and heat transport across and along the axis of the stream. Model-estimated SW-GW exchange varied seasonally and in response to high-streamflow events due to dynamic interactions between SW stage and GW H. Comparison of 2004 and 2005 conditions showed that small changes in precipitation amount and intensity, evapotranspiration, and/or nearby GW levels within a low-relief watershed can readily impact SW-GW interactions. The calibrated LWD flow models and observed stream and streambed NO3 concentrations were used to predict temporal variations in streambed NO3 removal in response to dynamic SW-GW exchange. NO3 removal rates underwent slow seasonal changes, but also underwent rapid changes in response to high-flow events. These findings suggest that increased temporal variability of SW-GW exchange in low-order, low-relief watersheds may be a factor contributing their more efficient removal of NO3.

  2. The role of dynamic surface water-groundwater exchange on streambed denitrification in a first-order, low-relief agricultural watershed

    NASA Astrophysics Data System (ADS)

    Rahimi, Mina; Essaid, Hedeff I.; Wilson, John T.

    2015-12-01

    The role of temporally varying surface water-groundwater (SW-GW) exchange on nitrate removal by streambed denitrification was examined along a reach of Leary Weber Ditch (LWD), Indiana, a small, first-order, low-relief agricultural watershed within the Upper Mississippi River basin, using data collected in 2004 and 2005. Stream stage, GW heads (H), and temperatures (T) were continuously monitored in streambed piezometers and stream bank wells for two transects across LWD accompanied by synoptic measurements of stream stage, H, T, and nitrate (NO3) concentrations along the reach. The H and T data were used to develop and calibrate vertical two-dimensional, models of streambed water flow and heat transport across and along the axis of the stream. Model-estimated SW-GW exchange varied seasonally and in response to high-streamflow events due to dynamic interactions between SW stage and GW H. Comparison of 2004 and 2005 conditions showed that small changes in precipitation amount and intensity, evapotranspiration, and/or nearby GW levels within a low-relief watershed can readily impact SW-GW interactions. The calibrated LWD flow models and observed stream and streambed NO3 concentrations were used to predict temporal variations in streambed NO3 removal in response to dynamic SW-GW exchange. NO3 removal rates underwent slow seasonal changes, but also underwent rapid changes in response to high-flow events. These findings suggest that increased temporal variability of SW-GW exchange in low-order, low-relief watersheds may be a factor contributing their more efficient removal of NO3.

  3. The rate of nitrite reduction in leaves as indicated by O₂ and CO₂ exchange during photosynthesis.

    PubMed

    Eichelmann, H; Oja, V; Peterson, R B; Laisk, A

    2011-03-01

    Light response (at 300 ppm CO(2) and 10-50 ppm O(2) in N(2)) and CO(2) response curves [at absorbed photon fluence rate (PAD) of 550 μmol m(-2) s(-1)] of O(2) evolution and CO(2) uptake were measured in tobacco (Nicotiana tabacum L.) leaves grown on either NO(3)(-) or NH(4)(+) as N source and in potato (Solanum tuberosum L.), sorghum (Sorghum bicolor L. Moench), and amaranth (Amaranthus cruentus L.) leaves grown on NH(4)NO(3). Photosynthetic O(2) evolution in excess of CO(2) uptake was measured with a stabilized zirconia O(2) electrode and an infrared CO(2) analyser, respectively, and the difference assumed to represent the rate of electron flow to acceptors alternative to CO(2), mainly NO(2)(-), SO(4)(2-), and oxaloacetate. In NO(3)(-)-grown tobacco, as well as in sorghum, amaranth, and young potato, the photosynthetic O(2)-CO(2) flux difference rapidly increased to about 1 μmol m(-2) s(-1) at very low PADs and the process was saturated at 50 μmol quanta m(-2) s(-1). At higher PADs the O(2)-CO(2) flux difference continued to increase proportionally with the photosynthetic rate to a maximum of about 2 μmol m(-2) s(-1). In NH(4)(+)-grown tobacco, as well as in potato during tuber filling, the low-PAD component of surplus O(2) evolution was virtually absent. The low-PAD phase was ascribed to photoreduction of NO(2)(-) which successfully competes with CO(2) reduction and saturates at a rate of about 1 μmol O(2) m(-2) s(-1) (9% of the maximum O(2) evolution rate). The high-PAD component of about 1 μmol O(2) m(-2) s(-1), superimposed on NO(2)(-) reduction, may represent oxaloacetate reduction. The roles of NO(2)(-), oxaloacetate, and O(2) reduction in the regulation of ATP/NADPH balance are discussed.

  4. Ligand binding and proton exchange dynamics in site-specific mutants of human myoglobin

    SciTech Connect

    Lambright, D.G.

    1992-01-01

    Site specific mutagenesis was used to make substitutions of four residues in the distal heme pocket of human myoglobin: Val68, His64, Lys45, and Asp60. Strongly diffracting crystals of the conservative mutation K45R in the met aquo form were grown in the trigonal space group P3[sub 2]21 and the X-ray crystal structure determined at 1.6 [angstrom] resolution. The overall structure is similar to that of sperm whale met aquo myoglobin. Several of the mutant proteins were characterized by 2-D NMR spectroscopy. The NMR data suggest the structural changes are localized to the region of the mutation. The dynamics of ligand binding to myoglobin mutants were studied by transient absorption spectroscopy following photolysis of the CO complexes. Transient absorption kinetics and spectra on the ns to ms timescale were measured in aqueous solution from 280 K to 310 K and in 75% glycerol: water from 250 K to 310 K. Two significant basis spectra were obtained from singular value decomposition of the matrix of time dependent spectra. The information was used to obtain approximations for the extent of ligand rebinding and the kinetics of conformational relaxation. Except for K45R, substitutions at Lys45 or Asp60 produce changes in the kinetics for ligand rebinding. Replacement of Lys45 with Arg increases the rate of ligand rebinding from the protein matrix by a factor of 2, but does not alter the rates for ligand escape or entry into the protein or the dynamics of the conformational relaxation. Substitutions at His64 and Val68 influence the kinetics of ligand rebinding and the dynamics of conformational relaxation. The results do not support the hypothesis that ligand migration between the heme pocket and solvent is determined solely by fluctuations of Arg45 and His64 between open and closed conformations of the heme pocket but can be rationalized if ligand diffusion through the protein matrix involves multiple competing pathways.

  5. Simplified quantification of labile proton concentration-weighted chemical exchange rate (kws) with RF saturation time dependent ratiometric analysis (QUESTRA) - Normalization of relaxation and RF irradiation spillover effects for improved quantitative chemical exchange saturation transfer (CEST) MRI

    PubMed Central

    Sun, Phillip Zhe

    2012-01-01

    Chemical exchange saturation transfer (CEST) MRI is an emerging imaging technique capable of detecting dilute proteins/peptides and microenvironmental properties, with promising in vivo applications. However, CEST MRI contrast is complex, varying not only with the labile proton concentration and exchange rate, but also with experimental conditions such as field strength and RF irradiation scheme. Furthermore, the optimal RF irradiation power depends on the exchange rate, which must be estimated in order to optimize the CEST MRI experiments. Although methods including numerical fitting with modified Bloch-McConnell equations, quantification of exchange rate with RF saturation time and power (QUEST and QUESP), have been proposed to address this relationship, they require multiple-parameter non-linear fitting and accurate relaxation measurement. Our work here extended the QUEST algorithm with ratiometric analysis (QUESTRA) that normalizes the magnetization transfer ratio (MTR) at labile and reference frequencies, which effectively eliminates the confounding relaxation and RF spillover effects. Specifically, the QUESTRA contrast approaches its steady state mono-exponentially at a rate determined by the reverse exchange rate (kws), with little dependence on bulk water T1, T2, RF power and chemical shift. The proposed algorithm was confirmed numerically, and validated experimentally using a tissue-like phantom of serially titrated pH compartments. PMID:21842497

  6. Kinetic bottlenecks to chemical exchange rates for deep-sea animals - Part 2: Carbon Dioxide

    NASA Astrophysics Data System (ADS)

    Hofmann, A. F.; Peltzer, E. T.; Brewer, P. G.

    2013-04-01

    Increased ocean acidification from fossil fuel CO2 invasion, from temperature-driven changes in respiration, and from possible leakage from sub-seabed geologic CO2 disposal has aroused concern over the impacts of elevated CO2 concentrations on marine life. Discussion of these impacts has so far focused only on changes in the oceanic bulk fluid properties (ΔpH, Δ[∑ CO2], etc.) as the critical variable and with a major focus on carbonate shell formation. Here we describe the rate problem for animals that must export CO2 at about the same rate at which O2 is consumed. We analyse the basic properties controlling CO2 export within the diffusive boundary layer around marine animals in an ocean changing in temperature (T) and CO2 concentration in order to compare the challenges posed by O2 uptake under stress with the equivalent problem of CO2 expulsion. The problem is more complex than that for a non-reactive gas, since with CO2 the influence of the seawater carbonate acid-base system needs to be considered. These reactions significantly facilitate CO2 efflux compared to O2 intake at equal temperature, pressure and fluid flow rate under typical oceanic concentrations. The effect of these reactions can be described by an enhancement factor, similar to that widely used for CO2 invasion at the sea surface. While organisms do need to actively regulate flow over their surface to thin the boundary layer to take up enough O2, this seems to be not necessary to facilitate CO2 efflux. Instead, the main impacts of rising oceanic CO2 will most likely be those associated with classical ocean acidification science. Regionally, as with O2, the combination of T, P and pH/pCO2 creates a zone of maximum CO2 stress at around 1000 m depth.

  7. Catecholaminergic Regulation of Learning Rate in a Dynamic Environment

    PubMed Central

    Jepma, Marieke; Nassar, Matthew R.; Rangel-Gomez, Mauricio; Meeter, Martijn; Nieuwenhuis, Sander

    2016-01-01

    Adaptive behavior in a changing world requires flexibly adapting one’s rate of learning to the rate of environmental change. Recent studies have examined the computational mechanisms by which various environmental factors determine the impact of new outcomes on existing beliefs (i.e., the ‘learning rate’). However, the brain mechanisms, and in particular the neuromodulators, involved in this process are still largely unknown. The brain-wide neurophysiological effects of the catecholamines norepinephrine and dopamine on stimulus-evoked cortical responses suggest that the catecholamine systems are well positioned to regulate learning about environmental change, but more direct evidence for a role of this system is scant. Here, we report evidence from a study employing pharmacology, scalp electrophysiology and computational modeling (N = 32) that suggests an important role for catecholamines in learning rate regulation. We found that the P3 component of the EEG—an electrophysiological index of outcome-evoked phasic catecholamine release in the cortex—predicted learning rate, and formally mediated the effect of prediction-error magnitude on learning rate. P3 amplitude also mediated the effects of two computational variables—capturing the unexpectedness of an outcome and the uncertainty of a preexisting belief—on learning rate. Furthermore, a pharmacological manipulation of catecholamine activity affected learning rate following unanticipated task changes, in a way that depended on participants’ baseline learning rate. Our findings provide converging evidence for a causal role of the human catecholamine systems in learning-rate regulation as a function of environmental change. PMID:27792728

  8. Fluence-dependent dynamics of the 5d6s exchange splitting in Gd metal after femtosecond laser excitation

    NASA Astrophysics Data System (ADS)

    Frietsch, Björn; Carley, Robert; Gleich, Markus; Teichmann, Martin; Bowlan, John; Weinelt, Martin

    2016-07-01

    We investigate the fluence-dependent dynamics of the exchange-split 5d6s valence bands of Gd metal after femtosecond, near-infrared (IR) laser excitation. Time- and angle-resolved photoelectron spectroscopy (tr-ARPES) with extreme ultraviolet (XUV) probe pulses is used to simultaneously map the transient binding energies of the minority and majority spin valence bands. The decay constant of the exchange splitting increases with fluence. This reflects the slower response of the occupied majority-spin component, which we attribute to Elliot–Yafet spin-flip scattering in accordance with the microscopic three-temperature model (M3TM). In contrast, the time constant of the partly unoccupied minority-spin band stays unaffected by a change in pump fluence. Here, we introduce as an alternative to superdiffusive spin transport exchange scattering, which is an ultrafast electronic mechanism explaining the observed dynamics. Exchange scattering can reduce the spin polarization in the partially unoccupied minority-spin band and thus its energetic position without effective demagnetization.

  9. Application of Multiplexed Replica Exchange Molecular Dynamics to the UNRES Force Field: Tests with α and α+β Proteins

    PubMed Central

    Czaplewski, Cezary; Kalinowski, Sebastian; Liwo, Adam; Scheraga, Harold A.

    2009-01-01

    The replica exchange (RE) method is increasingly used to improve sampling in molecular dynamics (MD) simulations of biomolecular systems. Recently, we implemented the united-residue UNRES force field for mesoscopic MD. Initial results from UNRES MD simulations show that we are able to simulate folding events that take place in a microsecond or even a millisecond time scale. To speed up the search further, we applied the multiplexing replica exchange molecular dynamics (MREMD) method. The multiplexed variant (MREMD) of the RE method, developed by Rhee and Pande, differs from the original RE method in that several trajectories are run at a given temperature. Each set of trajectories run at a different temperature constitutes a layer. Exchanges are attempted not only within a single layer but also between layers. The code has been parallelized and scales up to 4000 processors. We present a comparison of canonical MD, REMD, and MREMD simulations of protein folding with the UNRES force-field. We demonstrate that the multiplexed procedure increases the power of replica exchange MD considerably and convergence of the thermodynamic quantities is achieved much faster. PMID:20161452

  10. Evaluation of Instrumentation and Dynamic Thermal Ratings for Overhead Lines

    SciTech Connect

    Phillips, A.

    2013-01-31

    In 2010, a project was initiated through a partnership between the Department of Energy (DOE) and the New York Power Authority (NYPA) to evaluate EPRI's rating technology and instrumentation that can be used to monitor the thermal states of transmission lines and provide the required real-time data for real-time rating calculations. The project included the installation and maintenance of various instruments at three 230 kV line sites in northern New York. The instruments were monitored, and data collection and rating calculations were performed for about a three year period.

  11. Simultaneous experimental determination of labile proton fraction ratio and exchange rate with irradiation radio frequency power-dependent quantitative CEST MRI analysis.

    PubMed

    Sun, Phillip Zhe; Wang, Yu; Xiao, Gang; Wu, Renhua

    2013-01-01

    Chemical exchange saturation transfer (CEST) imaging is sensitive to dilute proteins/peptides and microenvironmental properties, and has been increasingly evaluated for molecular imaging and in vivo applications. However, the experimentally measured CEST effect depends on the CEST agent concentration, exchange rate and relaxation time. In addition, there may be non-negligible direct radio-frequency (RF) saturation effects, particularly severe for diamagnetic CEST (DIACEST) agents owing to their relatively small chemical shift difference from that of the bulk water resonance. As such, the commonly used asymmetry analysis only provides CEST-weighted information. Recently, it has been shown with numerical simulation that both labile proton concentration and exchange rate can be determined by evaluating the RF power dependence of DIACEST effect. To validate the simulation results, we prepared and imaged two CEST phantoms: a pH phantom of serially titrated pH at a fixed creatine concentration and a concentration phantom of serially varied creatine concentration titrated to the same pH, and solved the labile proton fraction ratio and exchange rate per-pixel. For the concentration phantom, we showed that the labile proton fraction ratio is proportional to the CEST agent concentration with negligible change in the exchange rate. Additionally, we found the exchange rate of the pH phantom is dominantly base-catalyzed with little difference in the labile proton fraction ratio. In summary, our study demonstrated quantitative DIACEST MRI, which remains promising to augment the conventional CEST-weighted MRI analysis.

  12. Simultaneous determination of labile proton fraction ratio and exchange rate with irradiation radio frequency (RF) power dependent quantitative CEST MRI analysis

    PubMed Central

    Sun, Phillip Zhe; Wang, Yu; Xiao, Gang; Wu, Renhua

    2014-01-01

    Chemical exchange saturation transfer (CEST) imaging is sensitive to dilute proteins/peptides and microenvironmental properties, and has been increasingly evaluated for molecular imaging and in vivo applications. However, the experimentally measured CEST effect depends on the CEST agent concentration, exchange rate and relaxation time. In addition, there may be non-negligible direct radio-frequency (RF) saturation effects, particularly severe for diamagnetic CEST (DIACEST) agents due to their relatively small chemical shift difference from that of the bulk water resonance. As such, the commonly used asymmetry analysis only provides CEST-weighted information. Recently, it has been shown with numerical simulation that both labile proton concentration and exchange rate can be determined by evaluating the RF power dependence of DIACEST effect. To validate the simulation results, we prepared and imaged two CEST phantoms: a pH phantom of serially titrated pH at a fixed creatine concentration and a concentration phantom of serially varied creatine concentration titrated to the same pH, and solved the labile proton fraction ratio and exchange rate per-pixel. For the concentration phantom, we showed that the labile proton fraction ratio is proportional to the CEST agent concentration with negligible change in the exchange rate. Additionally, we found the exchange rate of the pH phantom is dominantly base-catalyzed with little difference in the labile proton fraction ratio. In summary, our study demonstrated quantitative DIACEST MRI, which remains promising to augment the conventional CEST-weighted MRI analysis. PMID:23606428

  13. Firing rate of noisy integrate-and-fire neurons with synaptic current dynamics

    SciTech Connect

    Andrieux, David; Monnai, Takaaki

    2009-08-15

    We derive analytical formulas for the firing rate of integrate-and-fire neurons endowed with realistic synaptic dynamics. In particular, we include the possibility of multiple synaptic inputs as well as the effect of an absolute refractory period into the description. The latter affects the firing rate through its interaction with the synaptic dynamics.

  14. Reaction Engineering International and Pacific Northwest Laboratory staff exchange: Addressing computational fluid dynamics needs of the chemical process industry

    SciTech Connect

    Fort, J.A.

    1995-07-01

    Staff exchanges, such as the one described in this report, are intended to facilitate communications and collaboration among scientists and engineers at Department of Energy (DOE) laboratories, in US industry, and academia. Funding support for these exchanges is provided by the DOE, Office of Energy Research, Laboratory Technology Transfer Program. Funding levels for each exchange typically range from $20,000 to $40,000. The exchanges offer the opportunity for the laboratories to transfer technology and expertise to industry, gain a perspective to industry`s problems, and develop the basis for further cooperative efforts through Cooperative Research and Development Agreements (CRADAS) or other mechanisms. Information in this report on the staff exchange of the Pacific Northwest Laboratory (PNL) staff with Reaction Engineering International (REI) includes the significant accomplishments, significant problems, industry benefits realized, recommended follow-on work and potential benefit of that work. The objectives of this project were as follows: Work with REI to develop an understanding of the computational fluid dynamics (CFD) needs of the chemical process industry; assess the combined capabilities of the PNL and REI software analysis tools to address these needs; and establish a strategy for a future programmatically funded, joint effort to develop a new CFD tool for the chemical process industry.

  15. Improve Synergy Between Health Information Exchange and Electronic Health Records to Increase Rates of Continuously Insured Patients

    PubMed Central

    Gold, Rachel; Burdick, Tim; Angier, Heather; Wallace, Lorraine; Nelson, Christine; Likumahuwa-Ackman, Sonja; Sumic, Aleksandra; DeVoe, Jennifer E.

    2015-01-01

    Introduction: The Affordable Care Act increases health insurance options, yet many Americans may struggle to consistently maintain coverage. While health care providers have traditionally not been involved in providing insurance enrollment support to their patients, the ability for them to do so now exists. We propose that providers could capitalize on the expansion of electronic health records (EHRs) and the advances in health information exchanges (HIEs) to improve their patients’ insurance coverage rates and continuity. Evidence for Argument: We describe a project in which we are building strategies for linking, and thus improving synergy between, payer and EHR data. Through this effort, care teams will have access to new automated tools and increased EHR functionality designed to help them assist their patients in obtaining and maintaining health insurance coverage. Suggestion for the Future: The convergence of increasing EHR adoption, improving HIE functionality, and expanding insurance coverage options, creates new opportunities for clinics to help their patients obtain public health insurance. Harnessing this nascent ability to exchange information between payers and providers may improve synergies between HIE and EHRs, and thus support clinic-based efforts to keep patients continuously insured. PMID:26355818

  16. Transient secondary organic aerosol formation from limonene ozonolysis in indoor environments: impacts of air exchange rates and initial concentration ratios.

    PubMed

    Youssefi, Somayeh; Waring, Michael S

    2014-07-15

    Secondary organic aerosol (SOA) results from the oxidation of reactive organic gases (ROGs) and is an indoor particle source. The aerosol mass fraction (AMF), a.k.a. SOA yield, quantifies the SOA forming potential of ROGs and is the ratio of generated SOA to oxidized ROG. The AMF depends on the organic aerosol concentration, as well as the prevalence of later generation reactions. AMFs have been measured in unventilated chambers or steady-state flow through chambers. However, indoor settings have outdoor air exchange, and indoor SOA formation often occurs when ROGs are transiently emitted, for instance from emissions of cleaning products. Herein, we quantify "transient AMFs" from ozonolysis of pulse-emitted limonene in a ventilated chamber, for 18 experiments at low (0.28 h(-1)), moderate (0.53 h(-1)), and high (0.96 h(-1)) air exchange rates (AER) with varying initial ozone-limonene ratios. Transient AMFs increased with the amount of ROG reacted; AMFs also increased with decreasing AERs and increasing initial ozone-limonene ratios, which together likely promoted more ozone reactions with the remaining exocyclic bond of oxidized limonene products in the SOA phase. Knowing the AER and initial ozone-limonene ratio is crucial to predict indoor transient SOA behavior accurately.

  17. Biasing Potential Replica Exchange Multi-Site λ-Dynamics for Efficient Free Energy Calculations

    PubMed Central

    Armacost, Kira A.; Goh, Garrett B.; Brooks, Charles L.

    2016-01-01

    Traditional free energy calculation methods are well known for their drawbacks in scalability and speed in converging results particularly for calculations with large perturbations. In the present work, we report on the development of biasing potential replica exchange multi-site λ-dynamics (BP-REX MSλD), which is a free energy method that is capable of performing simultaneous alchemical free energy transformations, including perturbations between flexible moieties. BP-REX MSλD and the original MSλD are applied to a series of symmetrical 2,5-benzoquinone derivatives covering a diverse chemical space and range of conformational flexibility. Improved λ-space sampling is observed for the BP-REX MSλD simulations, yielding a 2–5-fold increase in the number of transitions between substituents compared to traditional MSλD. We also demonstrate the efficacy of varying the value of c, the parameter that controls the ruggedness of the landscape mediating the sampling of λ-states, based on the flexibility of the fragment. Finally, we developed a protocol for maximizing the transition frequency between fragments. This protocol reduces the “kinetic barrier” for alchemically transforming fragments by grouping and ordering based on volume. These findings are applied to a challenging test set involving a series of geldanamycin-based inhibitors of heat shock protein 90 (Hsp90). Even though the perturbations span volume changes by as large as 60 Å3, the values for the free energy change achieve an average unsigned error (AUE) of 1.5 kcal/mol relative to experimental Kd measurements with a reasonable correlation (R = 0.56). Our results suggest that the BP-REX MSλD algorithm is a highly efficient and scalable free energy method, which when utilized will enable routine calculations on the order of hundreds of compounds using only a few simulations. PMID:26579773

  18. Effect of the geometric phase on the dynamics of the hydrogen-exchange reaction.

    PubMed

    Juanes-Marcos, Juan Carlos; Althorpe, Stuart C; Wrede, Eckart

    2007-01-28

    A recent puzzle in nonadiabatic quantum dynamics is that geometric phase (GP) effects are present in the state-to-state opacity functions of the hydrogen-exchange reaction, but cancel out in the state-to-state integral cross sections (ICSs). Here the authors explain this result by using topology to separate the scattering amplitudes into contributions from Feynman paths that loop in opposite senses around the conical intersection. The clockwise-looping paths pass over one transition state (1-TS) and scatter into positive deflection angles; the counterclockwise-looping paths pass over two transition states (2-TS) and scatter into negative deflection angles. The interference between the 1-TS and 2-TS paths thus integrates to a very small value, which cancels the GP effects in the ICS. Quasiclassical trajectory (QCT) calculations reproduce the scattering of the 1-TS and 2-TS paths into positive and negative deflection angles and show that the 2-TS paths describe a direct insertion mechanism. The inserting atom follows a highly constrained "S-bend" path, which allows it to avoid both the other atoms and the conical intersection and forces the product diatom to scatter into high rotational states. By contrast, the quantum 2-TS paths scatter into a mainly statistical distribution of rotational states, so that the quantum 2-TS total ICS is roughly twice the QCT ICS at 2.3 eV total energy. This suggests that the S-bend constraint is relaxed by tunneling in the quantum system. These findings on H+H(2) suggest that similar cancellations or reductions in GP effects are likely in many other reactions.

  19. Dynamics of Inorganic Nutrients in Intertidal Sediments: Porewater, Exchangeable, and Intracellular Pools

    PubMed Central

    Garcia-Robledo, Emilio; Bohorquez, Julio; Corzo, Alfonso; Jimenez-Arias, Juan L.; Papaspyrou, Sokratis

    2016-01-01

    The study of inorganic nutrients dynamics in shallow sediments usually focuses on two main pools: porewater (PW) nutrients and exchangeable (EX) ammonium and phosphate. Recently, it has been found that microphytobenthos (MPB) and other microorganisms can accumulate large amounts of nutrients intracellularly (IC), highlighting the biogeochemical importance of this nutrient pool. Storing nutrients could support the growth of autotrophs when nutrients are not available, and could also provide alternative electron acceptors for dissimilatory processes such as nitrate reduction. Here, we studied the magnitude and relative importance of these three nutrient pools (PW, IC, and EX) and their relation to chlorophylls (used as a proxy for MPB abundance) and organic matter (OM) contents in an intertidal mudflat of Cadiz Bay (Spain). MPB was localized in the first 4 mm of the sediment and showed a clear seasonal pattern; highest chlorophylls content was found during autumn and lowest during spring-summer. The temporal and spatial distribution of nutrients pools and MPB were largely correlated. Ammonium was higher in the IC and EX fractions, representing on average 59 and 37% of the total ammonium pool, respectively. Similarly, phosphate in the IC and EX fractions accounted on average for 40 and 31% of the total phosphate pool, respectively. Nitrate in the PW was low, suggesting low nitrification activity and rapid consumption. Nitrate accumulated in the IC pool during periods of moderate MPB abundance, being up to 66% of the total nitrate pool, whereas it decreased when chlorophyll concentration peaked likely due to a high nitrogen demand. EX-Nitrate accounted for the largest fraction of total sediment nitrate, 66% on average. The distribution of EX-Nitrate was significantly correlated with chlorophyll and OM, which probably indicates a relation of this pool to an increased availability of sites for ionic adsorption. This EX-Nitrate pool could represent an alternative nitrate

  20. Dynamics of Inorganic Nutrients in Intertidal Sediments: Porewater, Exchangeable, and Intracellular Pools.

    PubMed

    Garcia-Robledo, Emilio; Bohorquez, Julio; Corzo, Alfonso; Jimenez-Arias, Juan L; Papaspyrou, Sokratis

    2016-01-01

    The study of inorganic nutrients dynamics in shallow sediments usually focuses on two main pools: porewater (PW) nutrients and exchangeable (EX) ammonium and phosphate. Recently, it has been found that microphytobenthos (MPB) and other microorganisms can accumulate large amounts of nutrients intracellularly (IC), highlighting the biogeochemical importance of this nutrient pool. Storing nutrients could support the growth of autotrophs when nutrients are not available, and could also provide alternative electron acceptors for dissimilatory processes such as nitrate reduction. Here, we studied the magnitude and relative importance of these three nutrient pools (PW, IC, and EX) and their relation to chlorophylls (used as a proxy for MPB abundance) and organic matter (OM) contents in an intertidal mudflat of Cadiz Bay (Spain). MPB was localized in the first 4 mm of the sediment and showed a clear seasonal pattern; highest chlorophylls content was found during autumn and lowest during spring-summer. The temporal and spatial distribution of nutrients pools and MPB were largely correlated. Ammonium was higher in the IC and EX fractions, representing on average 59 and 37% of the total ammonium pool, respectively. Similarly, phosphate in the IC and EX fractions accounted on average for 40 and 31% of the total phosphate pool, respectively. Nitrate in the PW was low, suggesting low nitrification activity and rapid consumption. Nitrate accumulated in the IC pool during periods of moderate MPB abundance, being up to 66% of the total nitrate pool, whereas it decreased when chlorophyll concentration peaked likely due to a high nitrogen demand. EX-Nitrate accounted for the largest fraction of total sediment nitrate, 66% on average. The distribution of EX-Nitrate was significantly correlated with chlorophyll and OM, which probably indicates a relation of this pool to an increased availability of sites for ionic adsorption. This EX-Nitrate pool could represent an alternative nitrate

  1. Dual-axis high-data-rate atom interferometer via cold ensemble exchange

    SciTech Connect

    Rakholia, Akash V.; McGuinness, Hayden J.; Biedermann, Grant W.

    2014-11-24

    We demonstrate a dual-axis accelerometer and gyroscope atom interferometer, which can form the building blocks of a six-axis inertial measurement unit. By recapturing the atoms after the interferometer sequence, we maintain a large atom number at high data rates of 50 to 100 measurements per second. Two cold ensembles are formed in trap zones located a few centimeters apart and are launched toward one another. During their ballistic trajectory, they are interrogated with a stimulated Raman sequence, detected, and recaptured in the opposing trap zone. As a result, we achieve sensitivities at μg/ √Hz and μrad/s/ √Hz levels, making this a compelling prospect for expanding the use of atom interferometer inertial sensors beyond benign laboratory environments.

  2. Dual-axis high-data-rate atom interferometer via cold ensemble exchange

    DOE PAGESBeta

    Rakholia, Akash V.; McGuinness, Hayden J.; Biedermann, Grant W.

    2014-11-24

    We demonstrate a dual-axis accelerometer and gyroscope atom interferometer, which can form the building blocks of a six-axis inertial measurement unit. By recapturing the atoms after the interferometer sequence, we maintain a large atom number at high data rates of 50 to 100 measurements per second. Two cold ensembles are formed in trap zones located a few centimeters apart and are launched toward one another. During their ballistic trajectory, they are interrogated with a stimulated Raman sequence, detected, and recaptured in the opposing trap zone. As a result, we achieve sensitivities at μg/ √Hz and μrad/s/ √Hz levels, making thismore » a compelling prospect for expanding the use of atom interferometer inertial sensors beyond benign laboratory environments.« less

  3. Structure and Dynamics of NBD1 from CFTR Characterized Using Crystallography and Hydrogen/Deuterium Exchange Mass Spectrometry

    SciTech Connect

    Lewis, H.A.; Wang, C.; Zhao, X.; Hamuro, Y.; Conners, K.; Kearins, M.C.; Lu, F.; Sauder, J.M.; Molnar, K.S.; Coales, S.J.; Maloney, P.C.; Guggino, W.B.; Wetmore, D.R.; Weber, P.C.; Hunt, J.F.

    2012-04-30

    The {Delta}F508 mutation in nucleotide-binding domain 1 (NBD1) of the cystic fibrosis transmembrane conductance regulator (CFTR) is the predominant cause of cystic fibrosis. Previous biophysical studies on human F508 and {Delta}F508 domains showed only local structural changes restricted to residues 509-511 and only minor differences in folding rate and stability. These results were remarkable because {Delta}F508 was widely assumed to perturb domain folding based on the fact that it prevents trafficking of CFTR out of the endoplasmic reticulum. However, the previously reported crystal structures did not come from matched F508 and {Delta}F508 constructs, and the {Delta}F508 structure contained additional mutations that were required to obtain sufficient protein solubility. In this article, we present additional biophysical studies of NBD1 designed to address these ambiguities. Mass spectral measurements of backbone amide {sup 1}H/{sup 2}H exchange rates in matched F508 and {Delta}F508 constructs reveal that {Delta}F508 increases backbone dynamics at residues 509-511 and the adjacent protein segments but not elsewhere in NBD1. These measurements also confirm a high level of flexibility in the protein segments exhibiting variable conformations in the crystal structures. We additionally present crystal structures of a broader set of human NBD1 constructs, including one harboring the native F508 residue and others harboring the {Delta}F508 mutation in the presence of fewer and different solubilizing mutations. The only consistent conformational difference is observed at residues 509-511. The side chain of residue V510 in this loop is mostly buried in all non-{Delta}F508 structures but completely solvent exposed in all {Delta}F508 structures. These results reinforce the importance of the perturbation {Delta}F508 causes in the surface topography of NBD1 in a region likely to mediate contact with the transmembrane domains of CFTR. However, they also suggest that increased

  4. Ozone dynamics and snow-atmosphere exchanges during ozone depletion events at Barrow, Alaska

    NASA Astrophysics Data System (ADS)

    Helmig, Detlev; Boylan, Patrick; Johnson, Bryan; Oltmans, Sam; Fairall, Chris; Staebler, Ralf; Weinheimer, Andrew; Orlando, John; Knapp, David J.; Montzka, Denise D.; Flocke, Frank; Frieß, Udo; Sihler, Holger; Shepson, Paul B.

    2012-10-01

    The behavior of lower atmospheric ozone and ozone exchanges at the snow surface were studied using a suite of platforms during the Ocean-Atmosphere-Sea Ice-Snow (OASIS) Spring 2009 experiment at an inland, coastal site east of Barrow, Alaska. A major objective was to investigate if and how much chemistry at the snow surface at the site contributes to springtime ozone depletion events (ODEs). Between March 8 and April 16, seven ODEs, with atmospheric ozone dropping below 1.0 ppbv, were observed. The depth of the ozone-depleted layer was variable, extending from the surface to ˜200-800 m. ODEs most commonly occurred during low wind speed conditions with flow coming from the Arctic Ocean. Two high-sensitivity ozone chemiluminescence instruments were used to accurately define the remaining sub-ppbv ozone levels during ODEs. These measurements showed variable residual ODE ozone levels ranging between 0.010 and 0.100 ppbv. During the most extended ODE, when ozone remained below 1.0 ppbv for over 78 h, these measurements showed a modest ozone recovery or production in the early afternoon hours, resulting in increases in the ozone mixing ratio of 0.100 to 0.800 ppbv. The comparison between high-sensitivity ozone measurements and BrO measured by longpath differential absorption spectroscopy (DOAS) during ODEs indicated that at low ozone levels formation of BrO is controlled by the amount of available ozone. Measurements of ozone in air drawn from below the snow surface showed depleted ozone in the snowpack, with levels consistently remaining <6 ppbv independent of above-surface ambient air concentrations. The snowpack was always a sink of ozone. Ozone deposition velocities determined from ozone surface flux measurements by eddy covariance were on the order of 0.01 cm s-1, which is of similar magnitude as ozone uptake rates found over snow at other polar sites that are not subjected to ODEs. The results from these multiple platform measurements unequivocally show that snow

  5. Neutralizing positive charges at the surface of a protein lowers its rate of amide hydrogen exchange without altering its structure or increasing its thermostability.

    PubMed

    Shaw, Bryan F; Arthanari, Haribabu; Narovlyansky, Max; Durazo, Armando; Frueh, Dominique P; Pollastri, Michael P; Lee, Andrew; Bilgicer, Basar; Gygi, Steven P; Wagner, Gerhard; Whitesides, George M

    2010-12-15

    This paper combines two techniques--mass spectrometry and protein charge ladders--to examine the relationship between the surface charge and hydrophobicity of a representative globular protein (bovine carbonic anhydrase II; BCA II) and its rate of amide hydrogen-deuterium (H/D) exchange. Mass spectrometric analysis indicated that the sequential acetylation of surface lysine-ε-NH3(+) groups--a type of modification that increases the net negative charge and hydrophobicity of the surface of BCA II without affecting its secondary or tertiary structure--resulted in a linear decrease in the aggregate rate of amide H/D exchange at pD 7.4, 15 °C. According to analysis with MS, the acetylation of each additional lysine generated between 1.4 and 0.9 additional hydrogens that are protected from H/D exchange during the 2 h exchange experiment at 15 °C, pD 7.4. NMR spectroscopy demonstrated that none of the hydrogen atoms which became protected upon acetylation were located on the side chain of the acetylated lysine residues (i.e., lys-ε-NHCOCH3) but were instead located on amide NHCO moieties in the backbone. The decrease in rate of exchange associated with acetylation paralleled a decrease in thermostability: the most slowly exchanging rungs of the charge ladder were the least thermostable (as measured by differential scanning calorimetry). This observation--that faster rates of exchange are associated with slower rates of denaturation--is contrary to the usual assumptions in protein chemistry. The fact that the rates of H/D exchange were similar for perbutyrated BCA II (e.g., [lys-ε-NHCO(CH2)2CH3]18) and peracetylated BCA II (e.g., [lys-ε-NHCOCH3]18) suggests that the electrostatic charge is more important than the hydrophobicity of surface groups in determining the rate of H/D exchange. These electrostatic effects on the kinetics of H/D exchange could complicate (or aid) the interpretation of experiments in which H/D exchange methods are used to probe the structural

  6. Dynamics of CO2-exchange and C-budgets due to soil erosion: Insights from a 4 years observation period

    NASA Astrophysics Data System (ADS)

    Hoffmann, Mathias; Albiac Borraz, Elisa; Garcia Alba, Juana; Augustin, Jürgen; Sommer, Michael

    2015-04-01

    Agriculture in the hummocky ground moraine landscape of NE-Germany is characterized by an increase in energy crop cultivation, like maize or sorghum. Both enhance lateral C fluxes by erosion and induce feedbacks on C dynamics of agroecosystems as a result of reduced wintertime plant cover and vigorous crop growth during summer. However, the actual impact of these phenomena on the CO2-sink/-source function of agricultural landscapes, is still not clear. Therefore, the interdisciplinary project "CarboZALF" was established in Dedelow/Prenzlau (NE-Germany) in 2009. Within the field experiment CarboZALF-D, CO2 fluxes for the soil-plant systems were monitored, covering typical landscape relevant soil states in respect to erosion and deposition, like Calcic Cutanic Luvisol and Endogleyic Colluvic Regosol. Automated chamber systems, each consisting of four transparent chambers (2.5 m height, basal area 2.25 m2), were placed along gradients at both measurement sites. Monitored CO2 fluxes were gap-filled on a high-temporal resolution by modelling ecosystem respiration (Reco), gross primary productivity (GPP) and net ecosystem exchange (NEE) based on parallel and continuous measurements of the CO2 exchange, soil and air temperatures as well as photosynthetic active radiation (PAR). Gap-filling was e.g. needed in case of chamber malfunctions and abrupt disturbances by farming practice. The monitored crop rotation was corn-winter wheat (2 a), sorghum-winter triticale and alfalfa (1.5 a). In our presentation we would like to show insights from a 4 years observation period, with prounounced differences between the eroded and the colluvial soil: The Endogleyic Colluvic Regosol showed higher flux rates for Reco, GPP and NEE compared to the Calcic Cutanic Luvisol. Site-specific NEE and C-balances were positively related to soil C-stocks as well as biomass production, and generated a minor C-sink in case of the Calcic Cutanic Luvisol and a highly variable C-source in case of the

  7. The dynamics of reductive sorption of oxygen by a granular bed of electron-ion exchangers with different copper dispersities

    NASA Astrophysics Data System (ADS)

    Konev, D. V.; Kravchenko, T. A.; Kalinichev, A. I.; Kipriyanova, E. S.

    2009-05-01

    The behavior of an immobile granular sorbent bed in one-component sorption in a column reactor is described in terms of the kinetic model of redox sorption taking into consideration the dispersity of metal particles, their radial distribution, peculiarities of chemical oxidation, and the relation of the overall rate of the process to the properties of the ion exchange matrix. The mathematical problem is formulated and solved numerically; the solution is analyzed theoretically in relation to the basic parameters of the sorption system. A satisfactory agreement is obtained between the experimental and calculated data on the reductive sorption of molecular oxygen from water on a copper-containing electron-ion exchanger.

  8. Scaling laws in the dynamics of crime growth rate

    NASA Astrophysics Data System (ADS)

    Alves, Luiz G. A.; Ribeiro, Haroldo V.; Mendes, Renio S.

    2013-06-01

    The increasing number of crimes in areas with large concentrations of people have made cities one of the main sources of violence. Understanding characteristics of how crime rate expands and its relations with the cities size goes beyond an academic question, being a central issue for contemporary society. Here, we characterize and analyze quantitative aspects of murders in the period from 1980 to 2009 in Brazilian cities. We find that the distribution of the annual, biannual and triannual logarithmic homicide growth rates exhibit the same functional form for distinct scales, that is, a scale invariant behavior. We also identify asymptotic power-law decay relations between the standard deviations of these three growth rates and the initial size. Further, we discuss similarities with complex organizations.

  9. Effects of dynamic aeroelasticity on handling qualities and pilot rating

    NASA Technical Reports Server (NTRS)

    Swaim, R. L.; Yen, W.-Y.

    1978-01-01

    Pilot performance parameters, such as pilot ratings, tracking errors, and pilot comments, were recorded and analyzed for a longitudinal pitch tracking task on a large, flexible aircraft. The tracking task was programmed on a fixed-base simulator with a CRT attitude director display of pitch angle command, pitch angle, and pitch angle error. Parametric variations in the undamped natural frequencies of the two lowest frequency symmetric elastic modes were made to induce varying degrees of rigid body and elastic mode interaction. The results indicate that such mode interaction can drastically affect the handling qualities and pilot ratings of the task.

  10. Effects of the turnover rate on the size distribution of firms: An application of the kinetic exchange models

    NASA Astrophysics Data System (ADS)

    Chakrabarti, Anindya S.

    2012-12-01

    We address the issue of the distribution of firm size. To this end we propose a model of firms in a closed, conserved economy populated with zero-intelligence agents who continuously move from one firm to another. We then analyze the size distribution and related statistics obtained from the model. There are three well known statistical features obtained from the panel study of the firms i.e., the power law in size (in terms of income and/or employment), the Laplace distribution in the growth rates and the slowly declining standard deviation of the growth rates conditional on the firm size. First, we show that the model generalizes the usual kinetic exchange models with binary interaction to interactions between an arbitrary number of agents. When the number of interacting agents is in the order of the system itself, it is possible to decouple the model. We provide exact results on the distributions which are not known yet for binary interactions. Our model easily reproduces the power law for the size distribution of firms (Zipf’s law). The fluctuations in the growth rate falls with increasing size following a power law (though the exponent does not match with the data). However, the distribution of the difference of the firm size in this model has Laplace distribution whereas the real data suggests that the difference of the log of sizes has the same distribution.

  11. Application of static and dynamic enclosures for determining dimethyl sulfide and carbonyl sulfide exchange in Sphagnum peatlands: Implications for the magnitude and direction of flux

    NASA Technical Reports Server (NTRS)

    De Mello, William Z.; Hines, Mark E.

    1994-01-01

    A static enclosure method was applied to determine the exchange of dimethyl sulfide (DMS) and carbonyl sulfide (OCS) between the surface of Sphagnum peatlands and the atmosphere. Measurements were performed concurrently with dynamic (flow through) enclosure measurements with sulfur-free air used as sweep gas. This latter technique has been used to acquire the majority of available data on the exchange of S gases between the atmosphere and the continental surfaces and has been criticized because it is thought to overestimate the true flux of gases by disrupting natural S gas gradients. DMS emission rates determined by both methods were not statistically different between 4 and greater than 400 nmol/sq m/h, indicating that previous data on emissions of at least DMS are probably valid. However, the increase in DMS in static enclosures was not linear, indicating the potential for a negative feedback of enlosure DMS concentrations on efflux. The dynamic enclosure method measured positive OCS flux rates (emission) at all sites, while data using static enclosures indicated that OCS was consumed from the atmosphere at these same sites at rates of 3.7 to 55 nmol/sq m/h. Measurements using both enclosure techniques at a site devoid of vegetation showed that peat was a source of both DMS and OCS. However, the rate of OCS efflux from decomposing peat was more than counterbalanced by OCS consumption by vegetation, including Sphagnum mosses, and net OCS uptake occurred at all sites. We propose that all wetlands are net sinks for OCS.

  12. Dynamic fitness landscapes: expansions for small mutation rates

    NASA Astrophysics Data System (ADS)

    Wilke, Claus O.; Ronnewinkel, Christopher

    2001-02-01

    We study the evolution of asexual microorganisms with small mutation rate in fluctuating environments, and develop techniques that allow us to expand the formal solution of the evolution equations to first order in the mutation rate. Our method can be applied to both discrete time and continuous time systems. While the behavior of continuous time systems is dominated by the average fitness landscape for small mutation rates, in discrete time systems it is instead the geometric mean fitness that determines the system's properties. In both cases, we find that in situations in which the arithmetic (resp. geometric) mean of the fitness landscape is degenerate, regions in which the fitness fluctuates around the mean value present a selective advantage over regions in which the fitness stays at the mean. This effect is caused by the vanishing genetic diffusion at low mutation rates. In the absence of strong diffusion, a population can stay close to a fluctuating peak when the peak's height is below average, and take advantage of the peak when its height is above average.

  13. A self-tuning model for inflation rate dynamics

    NASA Astrophysics Data System (ADS)

    Mamon, Rogemar; Duan, Zheng

    2010-09-01

    A regime-switching model is proposed to capture the structural changes in inflation dynamics. We apply a special version of the EM algorithm to find optimal parameter estimates of the model within the framework of a discrete-time finite state Markov chain that governs the switching of regimes from one state to another. The model is implemented to Canada's consumer price index (CPI) data series and its performance is assessed by comparing its one-step ahead predictions with the actual data. We found that, within the dataset studied, a two-state Markov-switching model is sufficient to capture the dynamics of Canadian CPI series. The model being proposed is adaptive as parameters are updated upon the arrival of a new set of information. A description of how to calculate the standard errors for parameter estimates using the Fisher information matrix is provided. We also determine the optimal number of states for the Markov chain within the dataset considered via the AIC analysis.

  14. Invariance of Firing Rate and Field Potential Dynamics to Stimulus Modulation Rate in Human Auditory Cortex

    PubMed Central

    Mukamel, Roy; Nir, Yuval; Harel, Michal; Arieli, Amos; Malach, Rafael; Fried, Itzhak

    2011-01-01

    The effect of stimulus modulation rate on the underlying neural activity in human auditory cortex is not clear. Human studies (using both invasive and noninvasive techniques) have demonstrated that at the population level, auditory cortex follows stimulus envelope. Here we examined the effect of stimulus modulation rate by using a rare opportunity to record both spiking activity and local field potentials (LFP) in auditory cortex of patients during repeated presentations of an audio-visual movie clip presented at normal, double, and quadruple speeds. Mean firing rate during evoked activity remained the same across speeds and the temporal response profile of firing rate modulations at increased stimulus speeds was a linearly scaled version of the response during slower speeds. Additionally, stimulus induced power modulation of local field potentials in the high gamma band (64–128 Hz) exhibited similar temporal scaling as the neuronal firing rate modulations. Our data confirm and extend previous studies in humans and anesthetized animals, supporting a model in which both firing rate, and high-gamma LFP power modulations in auditory cortex follow the temporal envelope of the stimulus across different modulation rates. PMID:20665720

  15. Predicting prey population dynamics from kill rate, predation rate and predator-prey ratios in three wolf-ungulate systems.

    PubMed

    Vucetich, John A; Hebblewhite, Mark; Smith, Douglas W; Peterson, Rolf O

    2011-11-01

    1. Predation rate (PR) and kill rate are both fundamental statistics for understanding predation. However, relatively little is known about how these statistics relate to one another and how they relate to prey population dynamics. We assess these relationships across three systems where wolf-prey dynamics have been observed for 41 years (Isle Royale), 19 years (Banff) and 12 years (Yellowstone). 2. To provide context for this empirical assessment, we developed theoretical predictions of the relationship between kill rate and PR under a broad range of predator-prey models including predator-dependent, ratio-dependent and Lotka-Volterra dynamics. 3. The theoretical predictions indicate that kill rate can be related to PR in a variety of diverse ways (e.g. positive, negative, unrelated) that depend on the nature of predator-prey dynamics (e.g. structure of the functional response). These simulations also suggested that the ratio of predator-to-prey is a good predictor of prey growth rate. That result motivated us to assess the empirical relationship between the ratio and prey growth rate for each of the three study sites. 4. The empirical relationships indicate that PR is not well predicted by kill rate, but is better predicted by the ratio of predator-to-prey. Kill rate is also a poor predictor of prey growth rate. However, PR and ratio of predator-to-prey each explained significant portions of variation in prey growth rate for two of the three study sites. 5. Our analyses offer two general insights. First, Isle Royale, Banff and Yellowstone are similar insomuch as they all include wolves preying on large ungulates. However, they also differ in species diversity of predator and prey communities, exploitation by humans and the role of dispersal. Even with the benefit of our analysis, it remains difficult to judge whether to be more impressed by the similarities or differences. This difficulty nicely illustrates a fundamental property of ecological

  16. Predicting prey population dynamics from kill rate, predation rate and predator-prey ratios in three wolf-ungulate systems.

    PubMed

    Vucetich, John A; Hebblewhite, Mark; Smith, Douglas W; Peterson, Rolf O

    2011-11-01

    1. Predation rate (PR) and kill rate are both fundamental statistics for understanding predation. However, relatively little is known about how these statistics relate to one another and how they relate to prey population dynamics. We assess these relationships across three systems where wolf-prey dynamics have been observed for 41 years (Isle Royale), 19 years (Banff) and 12 years (Yellowstone). 2. To provide context for this empirical assessment, we developed theoretical predictions of the relationship between kill rate and PR under a broad range of predator-prey models including predator-dependent, ratio-dependent and Lotka-Volterra dynamics. 3. The theoretical predictions indicate that kill rate can be related to PR in a variety of diverse ways (e.g. positive, negative, unrelated) that depend on the nature of predator-prey dynamics (e.g. structure of the functional response). These simulations also suggested that the ratio of predator-to-prey is a good predictor of prey growth rate. That result motivated us to assess the empirical relationship between the ratio and prey growth rate for each of the three study sites. 4. The empirical relationships indicate that PR is not well predicted by kill rate, but is better predicted by the ratio of predator-to-prey. Kill rate is also a poor predictor of prey growth rate. However, PR and ratio of predator-to-prey each explained significant portions of variation in prey growth rate for two of the three study sites. 5. Our analyses offer two general insights. First, Isle Royale, Banff and Yellowstone are similar insomuch as they all include wolves preying on large ungulates. However, they also differ in species diversity of predator and prey communities, exploitation by humans and the role of dispersal. Even with the benefit of our analysis, it remains difficult to judge whether to be more impressed by the similarities or differences. This difficulty nicely illustrates a fundamental property of ecological

  17. A CORBA-based object framework with patient identification translation and dynamic linking. Methods for exchanging patient data.

    PubMed

    Wang, C; Ohe, K

    1999-03-01

    Exchanging and integration of patient data across heterogeneous databases and institutional boundaries offers many problems. We focused on two issues: (1) how to identify identical patients between different systems and institutions while lacking universal patient identifiers; and (2) how to link patient data across heterogeneous databases and institutional boundaries. To solve these problems, we created a patient identification (ID) translation model and a dynamic linking method in the Common Object Request Broker Architecture (CORBA) environment. The algorithm for the patient ID translation is based on patient attribute matching plus computer-based human checking; the method for dynamic linking is temporal mapping. By implementing these methods into computer systems with help of the distributed object computing technology, we built a prototype of a CORBA-based object framework in which the patient ID translation and dynamic linking methods were embedded. Our experiments with a Web-based user interface using the object framework and dynamic linking-through the object framework were successful. These methods are important for exchanging and integrating patient data across heterogeneous databases and institutional boundaries.

  18. Dynamic NMR of Intramolecular Exchange Processes in EDTA Complexes of Sc[superscript 3+], Y[superscript 3+], and La[superscript 3+

    ERIC Educational Resources Information Center

    Ba, Yong; Han, Steven; Ni, Lily; Su, Tony; Garcia, Andres

    2006-01-01

    Dynamic NMR makes use of the effect of chemical exchanges on NMR spectra to study kinetics and thermodynamics. An advanced physical chemistry lab experiment was developed to study the intramolecular exchange processes of EDTA (the disodium salt of ethylenediaminetetraacetic acid) metal complexes. EDTA is an important chelating agent, used in…

  19. The CSG-2 Canadian strapdown gyroscope - Rate and dynamic tests

    NASA Astrophysics Data System (ADS)

    Gallop, L. D.; Vinnins, M.; Sinkiewicz, J. S.

    The development, general design, and performance characteristics of the Canadian Strapdown Gyroscope Model-2 (CSG-2), a two-degree-of-freedom dry tuned gyroscope, are reviewed. The manufacture of the gyro involves flexure mechanization, electric-discharge machining, and laser welding techniques, which lend themselves well to low-cost production. The instrument performance is highly repeatable, and reduction of thermal effects can be achieved either through changes in the torquer coil magnet material or through software compensation in systems applications. Static and rate test results qualify the CSG-2 gyroscope for inertial grade applications with thermal compensation.

  20. Enhancement of specific absorption rate by exchange coupling of the core-shell structure of magnetic nanoparticles for magnetic hyperthermia

    NASA Astrophysics Data System (ADS)

    Phadatare, M. R.; Meshram, J. V.; Gurav, K. V.; Hyeok Kim, Jin; Pawar, S. H.

    2016-03-01

    Conversion of electromagnetic energy into heat by nanoparticles (NPs) has the potential to be a powerful, non-invasive technique for biomedical applications such as magnetic fluid hyperthermia, drug release, disease treatment and remote control of single cell functions, but poor conversion efficiencies have hindered practical applications so far. In this paper, an attempt has been made to increase the efficiency of magnetic thermal induction by NPs. To increase the efficiency of magnetic thermal induction by NPs, one can take advantage of the exchange coupling between a magnetically hard core and magnetically soft shell to tune the magnetic properties of the NP and maximize the specific absorption rate, which is the gauge of conversion efficiency. In order to examine the tunability of magnetocrystalline anisotropy and its magnetic heating power, a representative magnetically hard material (CoFe2O4) has been coupled to a soft material (Ni0.5Zn0.5Fe2O4). The synthesized NPs show specific absorption rates that are of an order of magnitude larger than the conventional one.

  1. Nonlinear dynamical effects on reaction rates in thermally fluctuating environments.

    PubMed

    Kawai, Shinnosuke; Komatsuzaki, Tamiki

    2010-07-21

    A framework to calculate the rate constants of condensed phase chemical reactions of manybody systems is presented without relying on the concept of transition state. The theory is based on a framework we developed recently adopting a multidimensional underdamped Langevin equation in the region of a rank-one saddle. The theory provides a reaction coordinate expressed as an analytical nonlinear functional of the position coordinates and velocities of the system (solute), the friction constants, and the random force of the environment (solvent). Up to moderately high temperature, the sign of the reaction coordinate can determine the final destination of the reaction in a thermally fluctuating media, irrespective of what values the other (nonreactive) coordinates may take. In this paper, it is shown that the reaction probability is analytically derived as the probability of the reaction coordinate being positive, and that the integration with the Boltzmann distribution of the initial conditions leads to the exact reaction rate constant when the local equilibrium holds and the quantum effect is negligible. Because of analytical nature of the theory taking into account all nonlinear effects and their combination with fluctuation and dissipation, the theory naturally provides us with the firm mathematical foundation of the origin of the reactivity of the reaction in a fluctuating media.

  2. Nonlinear dynamical effects on reaction rates in thermally fluctuating environments.

    PubMed

    Kawai, Shinnosuke; Komatsuzaki, Tamiki

    2010-07-21

    A framework to calculate the rate constants of condensed phase chemical reactions of manybody systems is presented without relying on the concept of transition state. The theory is based on a framework we developed recently adopting a multidimensional underdamped Langevin equation in the region of a rank-one saddle. The theory provides a reaction coordinate expressed as an analytical nonlinear functional of the position coordinates and velocities of the system (solute), the friction constants, and the random force of the environment (solvent). Up to moderately high temperature, the sign of the reaction coordinate can determine the final destination of the reaction in a thermally fluctuating media, irrespective of what values the other (nonreactive) coordinates may take. In this paper, it is shown that the reaction probability is analytically derived as the probability of the reaction coordinate being positive, and that the integration with the Boltzmann distribution of the initial conditions leads to the exact reaction rate constant when the local equilibrium holds and the quantum effect is negligible. Because of analytical nature of the theory taking into account all nonlinear effects and their combination with fluctuation and dissipation, the theory naturally provides us with the firm mathematical foundation of the origin of the reactivity of the reaction in a fluctuating media. PMID:20544104

  3. Tuning towards dynamic freezing using a two-rate protocol

    NASA Astrophysics Data System (ADS)

    Kar, Satyaki; Mukherjee, Bhaskar; Sengupta, K.

    2016-08-01

    We study periodically driven closed quantum systems where two parameters of the system Hamiltonian are varied periodically in time with frequencies ω1 and ω2=r ω1 . We show that such drives may be used to tune towards dynamics-induced freezing where the wave function of the state of the system after a drive cycle at time T =2 π /ω1 has almost perfect overlap with the initial state. We locate regions in the (ω1,r ) plane where the freezing is near exact for a class of integrable models and a specific nonintegrable model. The integrable models that we study encompass Ising and XY models in d =1 , Kitaev model in d =2 , and Dirac fermions in graphene and atop a topological insulator surface, whereas the nonintegrable model studied involves the experimentally realized one-dimensional tilted Bose-Hubbard model in an optical lattice. In addition, we compute the relevant correlation functions of such driven systems and describe their characteristics in the region of the (ω1,r ) plane where the freezing is near exact. We supplement our numerical analysis with semianalytic results for integrable driven systems within adiabatic-impulse approximation and discuss experiments which may test our theory.

  4. Spin dynamics induced by ultrafast heating with ferromagnetic/antiferromagnetic interfacial exchange in perpendicularly magnetized hard/soft bilayers

    SciTech Connect

    Ma, Q. L. E-mail: mizukami@wpi-aimr.tohoku.ac.jp; Miyazaki, T.; Mizukami, S. E-mail: mizukami@wpi-aimr.tohoku.ac.jp; Iihama, S.; Zhang, X. M.

    2015-11-30

    The laser-induced spin dynamics of FeCo in perpendicularly magnetized L1{sub 0}-MnGa/FeCo bilayers with ferromagnetic and antiferromagnetic interfacial exchange coupling (IEC) are examined using the time-resolved magneto-optical Kerr effect. We found a precessional phase reversal of the FeCo layer as the IEC changes from ferromagnetic to antiferromagnetic. Moreover, a precession-suspension window was observed when the magnetic field was applied in a certain direction for the bilayer with ferromagnetic IEC. Our observations reveal that the spin dynamics modulation is strongly dependent on the IEC type within the Landau-Lifshitz-Gilbert depiction. The IEC dependence of the precessional phase and amplitude suggests the interesting method for magnetization dynamics modulation.

  5. Dynamics of self-rated health and selective mortality

    PubMed Central

    2011-01-01

    Self-rated health status (SRHS) is one of the most frequently used health measures in empirical health economics. This article analyzes the first seven waves of the Health and Retirement Study (HRS) and finds that (1) all available lags have decreasing but significant predictive power for current SRHS and (2) SRHS and future mortality are strongly related which leads to a specific selection problem known as survivorship bias. A parsimonious joint model with an autocorrelated latent health component in both the SRHS and the mortality equation is suggested. It is better able to capture the empirical facts than commonly used models including random effects and/or state dependence and better able to correct the survivorship bias than commonly used strategies such as inverse probability weighting. PMID:21423875

  6. Heart Rate Variability Dynamics for the Prognosis of Cardiovascular Risk

    PubMed Central

    Ramirez-Villegas, Juan F.; Lam-Espinosa, Eric; Ramirez-Moreno, David F.; Calvo-Echeverry, Paulo C.; Agredo-Rodriguez, Wilfredo

    2011-01-01

    Statistical, spectral, multi-resolution and non-linear methods were applied to heart rate variability (HRV) series linked with classification schemes for the prognosis of cardiovascular risk. A total of 90 HRV records were analyzed: 45 from healthy subjects and 45 from cardiovascular risk patients. A total of 52 features from all the analysis methods were evaluated using standard two-sample Kolmogorov-Smirnov test (KS-test). The results of the statistical procedure provided input to multi-layer perceptron (MLP) neural networks, radial basis function (RBF) neural networks and support vector machines (SVM) for data classification. These schemes showed high performances with both training and test sets and many combinations of features (with a maximum accuracy of 96.67%). Additionally, there was a strong consideration for breathing frequency as a relevant feature in the HRV analysis. PMID:21386966

  7. Dynamics of chest wall volume regulation during constant work rate exercise in patients with chronic obstructive pulmonary disease

    PubMed Central

    Takara, L.S.; Cunha, T.M.; Barbosa, P.; Rodrigues, M.K.; Oliveira, M.F.; Nery, L.E.; Neder, J.A.

    2012-01-01

    This study evaluated the dynamic behavior of total and compartmental chest wall volumes [(VCW) = rib cage (VRC) + abdomen (VAB)] as measured breath-by-breath by optoelectronic plethysmography during constant-load exercise in patients with stable chronic obstructive pulmonary disease. Thirty males (GOLD stages II-III) underwent a cardiopulmonary exercise test to the limit of tolerance (Tlim) at 75% of peak work rate on an electronically braked cycle ergometer. Exercise-induced dynamic hyperinflation was considered to be present when end-expiratory (EE) VCW increased in relation to resting values. There was a noticeable heterogeneity in the patterns of VCW regulation as EEVCW increased non-linearly in 17/30 “hyperinflators” and decreased in 13/30 “non-hyperinflators” (P < 0.05). EEVAB decreased slightly in 8 of the “hyperinflators”, thereby reducing and slowing the rate of increase in end-inspiratory (EI) VCW (P < 0.05). In contrast, decreases in EEVCW in the “non-hyperinflators” were due to the combination of stable EEVRC with marked reductions in EEVAB. These patients showed lower EIVCW and end-exercise dyspnea scores but longer Tlim than their counterparts (P < 0.05). Dyspnea increased and Tlim decreased non-linearly with a faster rate of increase in EIVCW regardless of the presence or absence of dynamic hyperinflation (P < 0.001). However, no significant between-group differences were observed in metabolic, pulmonary gas exchange and cardiovascular responses to exercise. Chest wall volumes are continuously regulated during exercise in order to postpone (or even avoid) their migration to higher operating volumes in patients with COPD, a dynamic process that is strongly dependent on the behavior of the abdominal compartment. PMID:23250012

  8. Exchange Rates and Fundamentals.

    ERIC Educational Resources Information Center

    Engel, Charles; West, Kenneth D.

    2005-01-01

    We show analytically that in a rational expectations present-value model, an asset price manifests near-random walk behavior if fundamentals are I (1) and the factor for discounting future fundamentals is near one. We argue that this result helps explain the well-known puzzle that fundamental variables such as relative money supplies, outputs,…

  9. [The conformational dynamic of the tetramer hemoglobin molecule as revealed by hydrogen exchange. II. Influence of the intersubunit contact splitting].

    PubMed

    Abaturov, L V; Molchanova, T P; Nosova, N G; Shliapnikov, S V; Faĭzulin, D A

    2006-01-01

    The rate of the H-D exchange of the peptide NH atoms of the isolated alpha and beta subunits of human Hb were studied at the pH range 5.5-9.0 and 20 degrees C by the IR spectroscopy. The factor retardation of the exchange rate of subunits -P in the range -10(2)-10(7). In comparison with tetramer Hb the probability of local fluctuations (1/P) is increased to a slightly greater extent for the monomeric alpha subunits then for the tetramer beta subunits. Unlike Hb oxygenation of subunits does not influence on the probability of the local fluctuations and subunits have no the pH-dependent change of the value 1/P observable for the ligand Hb. The possible mechanisms of the overall intensification of the local fluctuations upon the splitting of the Hb tetrameric contacts between subunits are discussed with the inviting of the structural crystallographic data.

  10. Investigation of mercury exchange between forest canopy vegetation and the atmosphere using a new dynamic chamber

    USGS Publications Warehouse

    Graydon, J.A.; St. Louis, V.L.; Lindberg, S.E.; Hintelmann, H.; Krabbenhoft, D.P.

    2006-01-01

    This paper presents the design of a dynamic chamber system that allows full transmission of PAR and UV radiation and permits enclosed intact foliage to maintain normal physiological function while Hg(0) flux rates are quantified in the field. Black spruce and jack pine foliage both emitted and absorbed Hg(0), exhibiting compensation points near atmospheric Hg(0) concentrations of ???2-3 ng m-3. Using enriched stable Hg isotope spikes, patterns of spike Hg(II) retention on foliage were investigated. Hg(0) evasion rates from foliage were simultaneously measured using the chamber to determine if the decline of foliar spike Hg(II) concentrations overtime could be explained by the photoreduction and re-emission of spike Hg to the atmosphere. This mass balance approach suggested that spike Hg(0) fluxes alone could not account for the measured decrease in spike Hg(II) on foliage following application, implying that either the chamber underestimates the true photoreduction of Hg(II) to Hg(0) on foliage, or other mechanisms of Hg(II) loss from foliage, such as cuticle weathering, are in effect. The radiation spectrum responsible for the photoreduction of newly deposited Hg(II) on foliage was also investigated. Our spike experiments suggest that some of the Hg(II) in wet deposition retained by the forest canopy may be rapidly photoreduced to Hg(0) and re-emitted back to the atmosphere, while another portion may be retained by foliage at the end of the growing season, with some being deposited in litterfall. This finding has implications for the estimation of Hg dry deposition based on throughfall and litterfall fluxes. ?? 2006 American Chemical Society.

  11. Effect of OPEC oil pricing on output, prices, and exchange rates in the United States and other industrialized countries

    SciTech Connect

    Fleisig, H.

    1981-01-01

    Following each major oil price increase, real gross national product (GNP) has fallen, unemployment and inflation have risen, and exchange rates have moved erratically. But how do oil price increases produce these effects. This paper discusses some of the macroeconomic consequences of too high and rising oil prices, and some of the policy options that might control these effects. It finds that the high and rising price of oil imports from the Organization of Petroleum Exporting Countries (OPEC) burdens the industrial oil-importing countries in two ways. First, because total expenditures on oil rise relative to income, the potential real standard of living in oil-importing countries falls. Together, the countries of the Organization for Economic Cooperation and Development (OECD), for example, may have paid as much as $150 billion more for oil in 1979 than they would have paid in a competitive oil market. Second, the rising oil price increases unemployment and inflation in ways that are difficult for policymakers in oil-importing countries to manage; on the one hand, the rising oil price produces general inflation, and on the other hand, it depresses domestic demand and employment. Policymakers attempt to control part of the inflation, at the cost of increasing unemployment. The total loss in output from the 1974 to 1975 recession, though part of it may have followed from factors unrelated to oil, was about $350 billion.

  12. Forecasting of high frequency foreign currency data using artificial neural networks. A study of intraday USD/DEM exchange rates

    SciTech Connect

    Lodhia, P.; Antonious, A.; Esat, I.

    1996-12-31

    There has been much recent interest in the application of artificial intelligence systems to real world problems. Substantial interest has been shown in their application to investment markets. Artificial Neural Networks are the most common technique here. This paper is concerned with the use of ANNs in forecasting exchange rates. Much research has been carried out in currency markets. However, many of the studies use end of day or average quotes for currencies as a basis for prediction. A growing school of thought propose that markets are non-random in the short-term and can be shown to follow patterns. This short-term time span can be described as being a period when the markets are inefficient at price adjustments. The use of intraday data is an ideal testing ground for ANNs based research. This paper aims to study the intraday forecasting of the US Dollar/German Deutschmark and to address the question of whether ANNs can make acceptable predictions. The problems of forecasting in such a complex environment will be addressed.

  13. Isobaric molecular dynamics version of the generalized replica exchange method (gREM): Liquid–vapor equilibrium

    SciTech Connect

    Malolepsza, Edyta; Secor, Maxim; Keyes, Tom

    2015-09-23

    A prescription for sampling isobaric generalized ensembles with molecular dynamics is presented and applied to the generalized replica exchange method (gREM), which was designed for simulating first-order phase transitions. The properties of the isobaric gREM ensemble are discussed and a study is presented of the liquid-vapor equilibrium of the guest molecules given for gas hydrate formation with the mW water model. As a result, phase diagrams, critical parameters, and a law of corresponding states are obtained.

  14. Isobaric Molecular Dynamics Version of the Generalized Replica Exchange Method (gREM): Liquid-Vapor Equilibrium.

    PubMed

    Małolepsza, Edyta; Secor, Maxim; Keyes, Tom

    2015-10-22

    A prescription for sampling isobaric generalized ensembles with molecular dynamics is presented and applied to the generalized replica exchange method (gREM), which was designed to simulate first-order phase transitions. The properties of the isobaric gREM ensemble are discussed, and a study is presented for the liquid-vapor equilibrium of the guest molecules given for gas hydrate formation with the mW water model. Phase diagrams, critical parameters, and a law of corresponding states are obtained. PMID:26398582

  15. A Complex-Valued Firing-Rate Model That Approximates the Dynamics of Spiking Networks

    PubMed Central

    Schaffer, Evan S.; Ostojic, Srdjan; Abbott, L. F.

    2013-01-01

    Firing-rate models provide an attractive approach for studying large neural networks because they can be simulated rapidly and are amenable to mathematical analysis. Traditional firing-rate models assume a simple form in which the dynamics are governed by a single time constant. These models fail to replicate certain dynamic features of populations of spiking neurons, especially those involving synchronization. We present a complex-valued firing-rate model derived from an eigenfunction expansion of the Fokker-Planck equation and apply it to the linear, quadratic and exponential integrate-and-fire models. Despite being almost as simple as a traditional firing-rate description, this model can reproduce firing-rate dynamics due to partial synchronization of the action potentials in a spiking model, and it successfully predicts the transition to spike synchronization in networks of coupled excitatory and inhibitory neurons. PMID:24204236

  16. Interactions among K+-Ca2+ Exchange, Sorption of m-Dinitrobenzene, and Smectite Quasicrystal Dynamics

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The fate of organic compounds in soils and sediments is influenced by sorption of the compounds on surfaces of soil materials. We investigated the interaction among sorption of an organic compound, cation exchange reactions, and both the size and swelling of smectite quasicrystals. Two reference sme...

  17. High-resolution determination of {sup 147}Pm in urine using dynamic ion-exchange chromatography

    SciTech Connect

    Elchuk, S.; Lucy, C.A.; Burns, K.I.

    1992-10-15

    Ion exchange preconcentration followed by HPLC purification prior to scintillation counting was used to measure the concentration of {sup 147}Pm in urine. the detection limit for this method was found to be 0.1 Bq (3 fg) of {sup 147}Pm in 500 ml of urine.

  18. Short Gamma-ray Bursts from Dynamically Assembled Compact Binaries in Globular Clusters: Pathways, Rates, Hydrodynamics, and Cosmological Setting

    NASA Astrophysics Data System (ADS)

    Lee, William H.; Ramirez-Ruiz, Enrico; van de Ven, Glenn

    2010-09-01

    We present a detailed assessment of the various dynamical pathways leading to the coalescence of compact objects in globular clusters (GCs) and Short Gamma-ray Burst (SGRB) production. We consider primordial binaries, dynamically formed binaries (through tidal two-body and three-body exchange interactions), and direct impacts of compact objects (WD/NS/BH). Here, we show that if the primordial binary fraction is small, close encounters dominate the production rate of coalescing compact systems. We find that the two dominant channels are the interaction of field neutron stars (NSs) with dynamically formed binaries and two-body encounters. Under such conditions, we estimate the redshift distribution and host galaxy demographics of SGRB progenitors, and find that GCs can provide a significant contribution to the overall observed rate. Regarding the newly identified channel of close stellar encounters involving WD/NS/BH, we have carried out precise modeling of the hydrodynamical evolution, giving us a detailed description of the resulting merged system. Our calculations show that there is in principle no problem in accounting for the global energy budget of a typical SGRB. The particulars of each encounter, however, are variable in several aspects and can lead to interesting diversity. First and most importantly, the characteristics of the encounter are highly dependent on the impact parameter. This is in contrast to the merger scenario, where the masses of the compact objects dictate a typical length and luminosity scale for SGRB activity. Second, the nature of the compact star itself can produce very different outcomes. Finally, the presence of tidal tails in which material will fall back onto the central object at a later time is a robust feature of the present set of calculations. The mass involved in these structures is considerably larger than for binary mergers. It is thus possible to account generically in this scenario for a prompt episode of energy release, as

  19. Investigation of hydrogen isotope exchange reaction rate in mixed gas (H{sub 2} and D{sub 2}) at pressure up to 200 MPa using Raman spectroscopy

    SciTech Connect

    Tikhonov, V.V.; Yukhimchuk, A.A.; Musyayev, R.K.; Gurkin, A.I.

    2015-03-15

    Raman spectroscopy is a relevant method for obtaining objective data on isotopic exchange rate in a gaseous mix of hydrogen isotopes, since it allows one to determine a gaseous mix composition in real time without sampling. We have developed a high-pressure fiber-optic probe to be used for obtaining protium Raman spectra under pressures up to 400 MPa and we have recorded spectral line broadening induced by molecule collisions starting from ∼ 40 MPa. Using this fiber-optic probe we have performed experiments to study isotopic exchange kinetics in a gaseous mix of hydrogen isotopes (protium-deuterium) at pressures up to 200 MPa. Preliminary results show that the dependence of the average isotopic exchange rate related to pressure take unexpected values at the very beginning of the time evolution. More work is required to understand this inconsistency.

  20. Membrane dynamics at the nuclear exchange junction during early mating (one to four hours) in the ciliate Tetrahymena thermophila.

    PubMed

    Cole, Eric S; Giddings, Thomas H; Ozzello, Courtney; Winey, Mark; O'Toole, Eileen; Orias, Judy; Hamilton, Eileen; Guerrier, Sabrice; Ballard, Anna; Aronstein, Tyler

    2015-02-01

    Using serial-section transmission electron microscopy and three-dimensional (3D) electron tomography, we characterized membrane dynamics that accompany the construction of a nuclear exchange junction between mating cells in the ciliate Tetrahymena thermophila. Our methods revealed a number of previously unknown features. (i) Membrane fusion is initiated by the extension of hundreds of 50-nm-diameter protrusions from the plasma membrane. These protrusions extend from both mating cells across the intercellular space to fuse with membrane of the mating partner. (ii) During this process, small membrane-bound vesicles or tubules are shed from the plasma membrane and into the extracellular space within the junction. The resultant vesicle-filled pockets within the extracellular space are referred to as junction lumens. (iii) As junction lumens fill with extracellular microvesicles and swell, the plasma membrane limiting these swellings undergoes another deformation, pinching off vesicle-filled vacuoles into the cytoplasm (reclamation). (iv) These structures (resembling multivesicular bodies) seem to associate with autophagosomes abundant near the exchange junction. We propose a model characterizing the membrane-remodeling events that establish cytoplasmic continuity between mating Tetrahymena cells. We also discuss the possible role of nonvesicular lipid transport in conditioning the exchange junction lipid environment. Finally, we raise the possibility of an intercellular signaling mechanism involving microvesicle shedding and uptake.

  1. Membrane Dynamics at the Nuclear Exchange Junction during Early Mating (One to Four Hours) in the Ciliate Tetrahymena thermophila

    PubMed Central

    Giddings, Thomas H.; Ozzello, Courtney; Winey, Mark; O'Toole, Eileen; Orias, Judy; Hamilton, Eileen; Guerrier, Sabrice; Ballard, Anna; Aronstein, Tyler

    2014-01-01

    Using serial-section transmission electron microscopy and three-dimensional (3D) electron tomography, we characterized membrane dynamics that accompany the construction of a nuclear exchange junction between mating cells in the ciliate Tetrahymena thermophila. Our methods revealed a number of previously unknown features. (i) Membrane fusion is initiated by the extension of hundreds of 50-nm-diameter protrusions from the plasma membrane. These protrusions extend from both mating cells across the intercellular space to fuse with membrane of the mating partner. (ii) During this process, small membrane-bound vesicles or tubules are shed from the plasma membrane and into the extracellular space within the junction. The resultant vesicle-filled pockets within the extracellular space are referred to as junction lumens. (iii) As junction lumens fill with extracellular microvesicles and swell, the plasma membrane limiting these swellings undergoes another deformation, pinching off vesicle-filled vacuoles into the cytoplasm (reclamation). (iv) These structures (resembling multivesicular bodies) seem to associate with autophagosomes abundant near the exchange junction. We propose a model characterizing the membrane-remodeling events that establish cytoplasmic continuity between mating Tetrahymena cells. We also discuss the possible role of nonvesicular lipid transport in conditioning the exchange junction lipid environment. Finally, we raise the possibility of an intercellular signaling mechanism involving microvesicle shedding and uptake. PMID:25107923

  2. Clinical impact of evaluation of cardiovascular control by novel methods of heart rate dynamics.

    PubMed

    Huikuri, Heikki V; Perkiömäki, Juha S; Maestri, Roberto; Pinna, Gian Domenico

    2009-04-13

    Heart rate variability (HRV) has been conventionally analysed with time- and frequency-domain methods, which measure the overall magnitude of RR interval fluctuations around its mean value or the magnitude of fluctuations in some predetermined frequencies. Analysis of heart rate dynamics by novel methods, such as heart rate turbulence after ventricular premature beats, deceleration capacity of heart rate and methods based on chaos theory and nonlinear system theory, have gained recent interest. Recent observational studies have suggested that some indices describing nonlinear heart rate dynamics, such as fractal scaling exponents, heart rate turbulence and deceleration capacity, may provide useful prognostic information in various clinical settings and their reproducibility may be better than that of traditional indices. For example, the short-term fractal scaling exponent measured by the detrended fluctuation analysis method has been shown to predict fatal cardiovascular events in various populations. Similarly, heart rate turbulence and deceleration capacity have performed better than traditional HRV measures in predicting mortality in post-infarction patients. Approximate entropy, a nonlinear index of heart rate dynamics, which describes the complexity of RR interval behaviour, has provided information on the vulnerability to atrial fibrillation. There are many other nonlinear indices which also give information on the characteristics of heart rate dynamics, but their clinical usefulness is not as well established. Although the concepts of nonlinear dynamics, fractal mathematics and complexity measures of heart rate behaviour, heart rate turbulence, deceleration capacity in relation to cardiovascular physiology or various cardiovascular events are still far away from clinical medicine, they are a fruitful area for research to expand our knowledge concerning the behaviour of cardiovascular oscillations in normal healthy conditions as well as in disease states.

  3. Modelling static and dynamic behaviour of proton exchange membrane fuel cells on the basis of electro-chemical description

    NASA Astrophysics Data System (ADS)

    Ceraolo, M.; Miulli, C.; Pozio, A.

    A simplified dynamical model of a fuel cell of the proton exchange membrane (PEM) type, based on physical-chemical knowledge of the phenomena occurring inside the cell has been developed by the authors. The model has been implemented in the MATLAB/SIMULINK environment. Lab tests have been carried out at ENEA's laboratories; and a good agreement has been found between tests and simulations, both in static and dynamic conditions. In a previous study [M. Ceraolo, R. Giglioli, C. Miulli, A. Pozio, in: Proceedings of the 18th International Electric Fuel Cell and Hybrid Vehicle Symposium (EVS18), Berlin, 20-24 October 2001, p. 306] the basic ideas of the model, as well as its experimental validation have been published. In the present paper, the full implementation of the model is reported in detail. Moreover, a procedure for evaluating all the needed numerical parameters is presented.

  4. Identifying Housing and Meteorological Conditions Influencing Residential Air Exchange Rates in the DEARS and RIOPA Studies: Development of Distributions for Human Exposure Modeling

    EPA Science Inventory

    Appropriate prediction of residential air exchange rate (AER) is important for estimating human exposures in the residential microenvironment, as AER drives the infiltration of outdoor-generated air pollutants indoors. AER differences among homes may result from a number of fact...

  5. Structure and water exchange dynamics of hydrated oxo halo ions in aqueous solution using QMCF MD simulation, large angle X-ray scattering and EXAFS.

    PubMed

    Eklund, Lars; Hofer, Tomas S; Persson, Ingmar

    2015-01-28

    Theoretical ab initio quantum mechanical charge field molecular dynamics (QMCF MD) has been applied in conjunction with experimental large angle X-ray scattering (LAXS) and EXAFS measurements to study structure and dynamics of the hydrated oxo chloro anions chlorite, ClO2(-), chlorate, ClO3(-), and perchlorate, ClO4(-). In addition, the structures of the hydrated hypochlorite, ClO(-), bromate, BrO3(-), iodate, IO3(-) and metaperiodate, IO4(-), ions have been determined in aqueous solution by means of LAXS. The structures of the bromate, metaperiodate, and orthoperiodate, H2IO6(3-), ions have been determined by EXAFS as solid sodium salts and in aqueous solution as well. The results show clearly that the only form of periodate present in aqueous solution is metaperiodate. The Cl-O bond distances in the hydrated oxo chloro anions as determined by LAXS and obtained in the QMCF MD simulations are in excellent agreement, being 0.01-0.02 Å longer than in solid anhydrous salts due to hydration through hydrogen bonding to water molecules. The oxo halo anions, all with unit negative charge, have low charge density making them typical structure breakers, thus the hydrogen bonds formed to the hydrating water molecules are weaker and more short-lived than those between water molecules in pure water. The water exchange mechanism of the oxo chloro anions resembles those of the oxo sulfur anions with a direct exchange at the oxygen atoms for perchlorate and sulfate. The water exchange rate for the perchlorate ion is significantly faster, τ0.5 = 1.4 ps, compared to the hydrated sulfate ion and pure water, τ0.5 = 2.6 and 1.7 ps, respectively. The angular radial distribution functions show that the chlorate and sulfite ions have a more complex water exchange mechanism. As the chlorite and chlorate ions are more weakly hydrated than the sulfite ion the spatial occupancy is less well-defined and it is not possible to follow any well-defined migration pattern as it is difficult to

  6. Structure and water exchange dynamics of hydrated oxo halo ions in aqueous solution using QMCF MD simulation, large angle X-ray scattering and EXAFS

    PubMed Central

    Eklund, Lars; Hofer, Tomas S.

    2014-01-01

    Theoretical ab initio quantum mechanical charge field molecular dynamics (QMCF MD) has been applied in conjunction with experimental large angle X-ray scattering (LAXS) and EXAFS measurements to study structure and dynamics of the hydrated oxo chloro anions chlorite, ClO2−, chlorate, ClO3−, and perchlorate, ClO4−. In addition, the structures of the hydrated hypochlorite, ClO−, bromate, BrO3−, iodate, IO3− and metaperiodate, IO4−, ions have been determined in aqueous solution by means of LAXS. The structures of the bromate, metaperiodate, and orthoperiodate, H2IO63−, ions have been determined by EXAFS as solid sodium salts and in aqueous solution as well. The results show clearly that the only form of periodate present in aqueous solution is metaperiodate. The Cl-O bond distances in the hydrated oxo chloro anions as determined by LAXS and obtained in the QMCF MD simulations are in excellent agreement, being 0.01–0.02 Å longer than in solid anhydrous salts due to hydration through hydrogen bonding to water molecules. The oxo halo anions, all with unit negative charge, have low charge density making them typical structure breakers, thus the hydrogen bonds formed to the hydrating water molecules are weaker and more short-lived than those between water molecules in pure water. The water exchange mechanism of the oxo chloro anions resembles those of the oxo sulfur anions with a direct exchange at the oxygen atoms for perchlorate and sulfate. The water exchange rate for the perchlorate ion is significantly faster, τ0.5=1.4 ps, compared to the hydrated sulfate ion and pure water, τ0.5=2.6 and 1.7 ps, respectively. The angular radial distribution functions show that the chlorate and sulfite ions have a more complex water exchange mechanism. As the chlorite and chlorate ions are more weakly hydrated than the sulfite ion the spatial occupancy is less well-defined and it is not possible to follow any well-defined migration pattern as it is difficult to

  7. Placing the Dynamics of Syringe Exchange Programs in the United States

    PubMed Central

    2007-01-01

    Drawing upon the broader health, social, and political geography literature this paper outlines a framework for considering place-based processes through which syringe exchange availability may be understood. It is argued that the geographic distribution of syringe exchange programs (SEPs) in the United States is linked to the social and political conditions of particular localities through three place characteristics: (1) structural constraints; (2) social and spatial distancing of injection drug users; and (3) localized action. Although SEPs remain a controversial issue and face ongoing obstacles from the government, law enforcement and local communities, they continue to operate through the efforts of grassroots organizations and local activists. Action on this issue occurs locally, and the characteristics of place-based factors will affect whether particular areas adopt SEPs. PMID:16797217

  8. Screened exchange dynamical mean-field theory and its relation to density functional theory: SrVO3 and SrTiO3

    NASA Astrophysics Data System (ADS)

    van Roekeghem, Ambroise; Biermann, Silke

    2014-12-01

    We present the first application of a recently proposed electronic-structure scheme to transition metal oxides: screened exchange dynamical mean-field theory includes non-local exchange beyond the local density approximation and dynamical correlations beyond standard dynamical mean-field theory. Our results for the spectral function of SrVO3 are in agreement with the available experimental data, including photoemission spectroscopy and thermodynamics. Finally, the 3d0 compound SrTiO3 serves as a test case to illustrate how the theory reduces to the band structure of standard electronic-structure techniques for weakly correlated compounds.

  9. Dynamic C and N stocks - key factors controlling the C gas exchange of maize in heterogenous peatland

    NASA Astrophysics Data System (ADS)

    Pohl, M.; Hoffmann, M.; Hagemann, U.; Giebels, M.; Albiac Borraz, E.; Sommer, M.; Augustin, J.

    2015-05-01

    The drainage and cultivation of fen peatlands create complex small-scale mosaics of soils with extremely variable soil organic carbon (SOC) stocks and groundwater levels (GWLs). To date, the significance of such sites as sources or sinks for greenhouse gases such as CO2 and CH4 is still unclear, especially if the sites are used for cropland. As individual control factors such as GWL fail to account for this complexity, holistic approaches combining gas fluxes with the underlying processes are required to understand the carbon (C) gas exchange of drained fens. It can be assumed that the stocks of SOC and N located above the variable GWL - defined as dynamic C and N stocks - play a key role in the regulation of the plant- and microbially mediated CO2 fluxes in these soils and, inversely, for CH4. To test this assumption, the present study analysed the C gas exchange (gross primary production - GPP; ecosystem respiration - Reco; net ecosystem exchange - NEE; CH4) of maize using manual chambers for 4 years. The study sites were located near Paulinenaue, Germany, where we selected three soil types representing the full gradient of GWL and SOC stocks (0-1 m) of the landscape: (a) Haplic Arenosol (AR; 8 kg C m-2); (b) Mollic Gleysol (GL; 38 kg C m-2); and (c) Hemic Histosol (HS; 87 kg C m-2). Daily GWL data were used to calculate dynamic SOC (SOCdyn) and N (Ndyn) stocks. Average annual NEE differed considerably among sites, ranging from 47 ± 30 g C m-2 yr-1 in AR to -305 ± 123 g C m-2 yr-1 in GL and -127 ± 212 g C m-2 yr-1 in HS. While static SOC and N stocks showed no significant effect on C fluxes, SOCdyn and Ndyn and their interaction with GWL strongly influenced the C gas exchange, particularly NEE and the GPP : Reco ratio. Moreover, based on nonlinear regression analysis, 86% of NEE variability was explained by GWL and SOCdyn. The observed high relevance of dynamic SOC and N stocks in the aerobic zone for plant and soil gas exchange likely originates from the

  10. Dynamic C and N stocks - key factors controlling the C gas exchange of maize in a heterogenous peatland

    NASA Astrophysics Data System (ADS)

    Pohl, M.; Hoffmann, M.; Hagemann, U.; Giebels, M.; Albiac Borraz, E.; Sommer, M.; Augustin, J.

    2014-11-01

    Drainage and cultivation of fen peatlands creates complex small-scale mosaics of soils with extremely variable soil organic carbon (SOC) stocks and groundwater-level (GWL). To date, it remains unclear if such sites are sources or sinks for greenhouse gases like CO2 and CH4, especially if used for cropland. As individual control factors like GWL fail to account for this complexity, holistic approaches combining gas fluxes with the underlying processes are required to understand the carbon (C) gas exchange of drained fens. It can be assumed that the stocks of SOC and N located above the variable GWL - defined as dynamic C and N stocks - play a key role in the regulation of plant- and microbially mediated C gas fluxes of these soils. To test this assumption, the present study analysed the C gas exchange (gross primary production - GPP, ecosystem respiration - Reco, net ecosystem exchange - NEE, CH4) of maize using manual chambers for four years. The study sites were located near Paulinenaue, Germany. Here we selected three soils, which represent the full gradient in pedogenesis, GWL and SOC stocks (0-1 m) of the fen peatland: (a) Haplic Arenosol (AR; 8 kg C m-2); (b) Mollic Gleysol (GL; 38 kg C m-2); and (c) Hemic Histosol (HS; 87 kg C m-2). Daily GWL data was used to calculate dynamic SOC (SOCdyn) and N (Ndyn) stocks. Average annual NEE differed considerably among sites, ranging from 47 ± 30 g C m-2 a-1 at AR to -305 ± 123 g C m-2 a-1 at GL and -127 ± 212 g C m-2 a-1 at HS. While static SOC and N stocks showed no significant effect on C fluxes, SOCdyn and Ndyn and their interaction with GWL strongly influenced the C gas exchange, particularly NEE and the GPP:Reco ratio. Moreover, based on nonlinear regression analysis, 86% of NEE variability was explained by GWL and SOCdyn. The observed high relevance of dynamic SOC and N stocks in the aerobic zone for plant and soil gas exchange likely originates from the effects of GWL-dependent N availability on C formation and

  11. Interactions among K+-Ca2+ exchange, sorption of m-dinitrobenzene, and smectite quasicrystal dynamics.

    PubMed

    Chatterjee, Ritushree; Laird, David A; Thompson, Michael L

    2008-12-15

    The fate of organic contaminants in soils and sediments is influenced by sorption of the compounds to surfaces of soil materials. We investigated the interaction among sorption of an organic compound, cation exchange reactions, and both the size and swelling of smectite quasicrystals. Two reference smectites that vary in location and amount of layer charge, SPV (a Wyoming bentonite) and SAz-1 were initially Ca- and K-saturated and then equilibrated with mixed 0.01 M KCl and 0.005 M CaCl2 salt solutions both with and without the presence of 200 mg L(-1) m-dinitrobenzene (m-DNB). In general, sorption of m-DNB increased with the amount of K+ in the system for both clays, and the SPV sorbed more m-DNB than the SAz-1. Sorption of m-DNB increased the preference of Ca-SPV for K+ relative to Ca2+ but had little effect on K+-Ca2+ selectivity for K-SPV. Selectivity for K+ relative to Ca2+ was slightly higher for both K-SAz-1 and Ca-SAz-1 in the presence of m-DNB than in its absence. Distinct hysteresis loops were observed for the K+-Ca2+ cation exchange reactions for both clays, and the legacy of having been initially Ca- or K-saturated influenced sorption of m-DNB by SPV but had little effect for SAz-1. Suspension X-ray diffraction was used to measure changes in d-spacing and the relative thickness of smectite quasicrystals during the cation exchange and m-DNB sorption reactions. The results suggest that interactions among cation exchange and organic sorption reactions are controlled byan inherently hysteretic complex feedback process that is regulated by changes in the size and extent of swelling of smectite quasicrystals. PMID:19174877

  12. Patchiness of ion-exchanged mica revealed by DNA binding dynamics at short length scales.

    PubMed

    Billingsley, D J; Lee, A J; Johansson, N A B; Walton, A; Stanger, L; Crampton, N; Bonass, W A; Thomson, N H

    2014-01-17

    The binding of double-stranded (ds) DNA to mica can be controlled through ion-exchanging the mica with divalent cations. Measurements of the end-to-end distance of linear DNA molecules discriminate whether the binding mechanism occurs through 2D surface equilibration or kinetic trapping. A range of linear dsDNA fragments have been used to investigate length dependences of binding. Mica, ion-exchanged with Ni(II) usually gives rise to kinetically trapped DNA molecules, however, short linear fragments (<800 bp) are seen to deviate from the expected behaviour. This indicates that ion-exchanged mica is heterogeneous, and contains patches or domains, separating different ionic species. These results correlate with imaging of dsDNA under aqueous buffer on Ni(II)-mica and indicate that binding domains are of the order of 100 nm in diameter. Shorter DNA fragments behave intermediate to the two extreme cases of 2D equilibration and kinetic trapping. Increasing the incubation time of Ni(II) on mica, from minutes to hours, brings the conformations of the shorter DNA fragments closer to the theoretical value for kinetic trapping, indicating that long timescale kinetics play a role in ion-exchange. X-ray photoelectron spectroscopy (XPS) was used to confirm that the relative abundance of Ni(II) ions on the mica surface increases with time. These findings can be used to enhance spatial control of binding of DNA to inorganic surfaces with a view to patterning high densities arrays.

  13. Dynamics of a network-based SIS epidemic model with nonmonotone incidence rate

    NASA Astrophysics Data System (ADS)

    Li, Chun-Hsien

    2015-06-01

    This paper studies the dynamics of a network-based SIS epidemic model with nonmonotone incidence rate. This type of nonlinear incidence can be used to describe the psychological effect of certain diseases spread in a contact network at high infective levels. We first find a threshold value for the transmission rate. This value completely determines the dynamics of the model and interestingly, the threshold is not dependent on the functional form of the nonlinear incidence rate. Furthermore, if the transmission rate is less than or equal to the threshold value, the disease will die out. Otherwise, it will be permanent. Numerical experiments are given to illustrate the theoretical results. We also consider the effect of the nonlinear incidence on the epidemic dynamics.

  14. Vaults are dynamically unconstrained cytoplasmic nanoparticles capable of half vault exchange.

    PubMed

    Yang, Jian; Kickhoefer, Valerie A; Ng, Benny C; Gopal, Ajaykumar; Bentolila, Laurent A; John, Scott; Tolbert, Sarah H; Rome, Leonard H

    2010-12-28

    Vaults are naturally occurring ribonucleoprotein particles with an enormous interior volume, large enough to encapsulate hundreds of proteins. They are highly conserved and are present in nearly all eukaryotic cells ranging from 10(4) to 10(7) particles per cell. Recombinant vaults can be produced in vitro and engineered to allow cell targeting and protein packaging. These nanometer-sized particles have many desirable characteristics that may give them advantages for use as drug delivery vehicles. Using photoactivatable green fluorescent protein (PAGFP) labeled vaults, we demonstrate that the particles rapidly diffuse throughout the cytoplasm following single pixel photoactivation in live cells. Their in vivo movement remained relatively unchanged despite exposure to a variety of cellular stresses, suggesting that vaults are largely unconstrained in the cytoplasm. Fluorescence resonance energy transfer (FRET) was observed from polyethylene glycol (PEG) fused hybrid cells that expressed either CFP or YFP labeled vaults, indicating that vaults can exchange major vault protein (MVP) subunits in vivo. Investigation into the mechanism of this exchange in vitro using recombinant vaults demonstrated that they were capable of rapidly separating at the particle waist and reassembling back into whole vaults, supporting a half vault exchange mechanism. This data suggests a means whereby vaults can functionally interact with their cellular environment and deliver materials packaged within their interior.

  15. Cation Exchange in Dynamic 3D Porous Magnets: Improvement of the Physical Properties.

    PubMed

    Grancha, Thais; Acosta, Alvaro; Cano, Joan; Ferrando-Soria, Jesús; Seoane, Beatriz; Gascon, Jorge; Pasán, Jorge; Armentano, Donatella; Pardo, Emilio

    2015-11-16

    We report two novel three-dimensional porous coordination polymers (PCPs) of formulas Li4{Mn4[Cu2(Me3mpba)2]3}·68H2O (2) and K4{Mn4[Cu2(Me3mpba)2]3}·69H2O (3) obtained-via alkali cation exchange in a single-crystal to single-crystal process-from the earlier reported anionic manganese(II)-copper(II) PCP of formula Na4{Mn4[Cu2(Me3mpba)2]3}·60H2O (1) [Me3mpba(4-) = N,N'-2,4,6-trimethyl-1,3-phenylenebis(oxamate)]. This postsynthetic process succeeds where the direct synthesis in solution from the corresponding building blocks fails and affords significantly more robust PCPs with enhanced magnetic properties [long-range 3D magnetic ordering temperatures for the dehydrated phases (1'-3') of 2.0 (1'), 12.0 (2'), and 20.0 K (3')]. Changes in the adsorptive properties upon postsynthetic exchange suggest that the nature, electrostatic properties, mobility, and location of the cations within the framework are crucial for the enhanced structural stability. Overall, these results further confirm the potential of postsynthetic methods (including cation exchange) to obtain PCPs with novel or enhanced physical properties while maintaining unaltered their open-framework structures. PMID:26492551

  16. Cation Exchange in Dynamic 3D Porous Magnets: Improvement of the Physical Properties.

    PubMed

    Grancha, Thais; Acosta, Alvaro; Cano, Joan; Ferrando-Soria, Jesús; Seoane, Beatriz; Gascon, Jorge; Pasán, Jorge; Armentano, Donatella; Pardo, Emilio

    2015-11-16

    We report two novel three-dimensional porous coordination polymers (PCPs) of formulas Li4{Mn4[Cu2(Me3mpba)2]3}·68H2O (2) and K4{Mn4[Cu2(Me3mpba)2]3}·69H2O (3) obtained-via alkali cation exchange in a single-crystal to single-crystal process-from the earlier reported anionic manganese(II)-copper(II) PCP of formula Na4{Mn4[Cu2(Me3mpba)2]3}·60H2O (1) [Me3mpba(4-) = N,N'-2,4,6-trimethyl-1,3-phenylenebis(oxamate)]. This postsynthetic process succeeds where the direct synthesis in solution from the corresponding building blocks fails and affords significantly more robust PCPs with enhanced magnetic properties [long-range 3D magnetic ordering temperatures for the dehydrated phases (1'-3') of 2.0 (1'), 12.0 (2'), and 20.0 K (3')]. Changes in the adsorptive properties upon postsynthetic exchange suggest that the nature, electrostatic properties, mobility, and location of the cations within the framework are crucial for the enhanced structural stability. Overall, these results further confirm the potential of postsynthetic methods (including cation exchange) to obtain PCPs with novel or enhanced physical properties while maintaining unaltered their open-framework structures.

  17. Gender- and age-related differences in heart rate dynamics: are women more complex than men?

    NASA Technical Reports Server (NTRS)

    Ryan, S. M.; Goldberger, A. L.; Pincus, S. M.; Mietus, J.; Lipsitz, L. A.

    1994-01-01

    OBJECTIVES. This study aimed to quantify the complex dynamics of beat-to-beat sinus rhythm heart rate fluctuations and to determine their differences as a function of gender and age. BACKGROUND. Recently, measures of heart rate variability and the nonlinear "complexity" of heart rate dynamics have been used as indicators of cardiovascular health. Because women have lower cardiovascular risk and greater longevity than men, we postulated that there are important gender-related differences in beat-to-beat heart rate dynamics. METHODS. We analyzed heart rate dynamics during 8-min segments of continuous electrocardiographic recording in healthy young (20 to 39 years old), middle-aged (40 to 64 years old) and elderly (65 to 90 years old) men (n = 40) and women (n = 27) while they performed spontaneous and metronomic (15 breaths/min) breathing. Relatively high (0.15 to 0.40 Hz) and low (0.01 to 0.15 Hz) frequency components of heart rate variability were computed using spectral analysis. The overall "complexity" of each heart rate time series was quantified by its approximate entropy, a measure of regularity derived from nonlinear dynamics ("chaos" theory). RESULTS. Mean heart rate did not differ between the age groups or genders. High frequency heart rate power and the high/low frequency power ratio decreased with age in both men and women (p < 0.05). The high/low frequency power ratio during spontaneous and metronomic breathing was greater in women than men (p < 0.05). Heart rate approximate entropy decreased with age and was higher in women than men (p < 0.05). CONCLUSIONS. High frequency heart rate spectral power (associated with parasympathetic activity) and the overall complexity of heart rate dynamics are higher in women than men. These complementary findings indicate the need to account for gender-as well as age-related differences in heart rate dynamics. Whether these gender differences are related to lower cardiovascular disease risk and greater longevity in

  18. Constant pH Replica Exchange Molecular Dynamics in Explicit Solvent Using Discrete Protonation States: Implementation, Testing, and Validation.

    PubMed

    Swails, Jason M; York, Darrin M; Roitberg, Adrian E

    2014-03-11

    By utilizing Graphics Processing Units, we show that constant pH molecular dynamics simulations (CpHMD) run in Generalized Born (GB) implicit solvent for long time scales can yield poor pKa predictions as a result of sampling unrealistic conformations. To address this shortcoming, we present a method for performing constant pH molecular dynamics simulations (CpHMD) in explicit solvent using a discrete protonation state model. The method involves standard molecular dynamics (MD) being propagated in explicit solvent followed by protonation state changes being attempted in GB implicit solvent at fixed intervals. Replica exchange along the pH-dimension (pH-REMD) helps to obtain acceptable titration behavior with the proposed method. We analyzed the effects of various parameters and settings on the titration behavior of CpHMD and pH-REMD in explicit solvent, including the size of the simulation unit cell and the length of the relaxation dynamics following protonation state changes. We tested the method with the amino acid model compounds, a small pentapeptide with two titratable sites, and hen egg white lysozyme (HEWL). The proposed method yields superior predicted pKa values for HEWL over hundreds of nanoseconds of simulation relative to corresponding predicted values from simulations run in implicit solvent.

  19. Sensitivity of high strain rate of structural elements in relation to dynamics properties of material

    NASA Astrophysics Data System (ADS)

    Kruszka, Leopold; Vorobiov, Iurii S.; Ovcharova, Nataliia Iu.

    2015-09-01

    Protective structures such as process chambers, protective boxes, facing elements of vehicles, personal protection equipment, motors cases etc. widely used in modern technology has been tested in the following project. Under the influence of impact loads, the three-dimensional dynamic stress-strain state with finite dynamic displacements and deformations has arised. The deformations occur in the elastic- plastic stage. In the analysis of the high-rate deformations, the dynamic properties of the materials, which are determined based on experimental data should be taken into account. The dynamic stress state of structural elements depends essentially on the dynamic properties of the materials used. The problem is solved using the finite element method, which takes into account the specifics of the process. Boundary conditions in the element nodes must satisfy the equality movement as well as derivatives. The formed function allows to describe continuous and smooth stress changes. The numerical analysis of the dynamic stress-strain state of structural elements under impact loads, takes into account different dynamic properties of the materials. A series of numerical calculations allows to reveal the features of high-rate deformation elements of protective structures and makes recommendations to improve their dynamic strength under different loading conditions.

  20. Reduced sensitivity to slow-rate dynamic auditory information in children with dyslexia.

    PubMed

    Poelmans, Hanne; Luts, Heleen; Vandermosten, Maaike; Boets, Bart; Ghesquière, Pol; Wouters, Jan

    2011-01-01

    The etiology of developmental dyslexia remains widely debated. An appealing theory postulates that the reading and spelling problems in individuals with dyslexia originate from reduced sensitivity to slow-rate dynamic auditory cues. This low-level auditory deficit is thought to provoke a cascade of effects, including inaccurate speech perception and eventually unspecified phoneme representations. The present study investigated sensitivity to frequency modulation and amplitude rise time, speech-in-noise perception and phonological awareness in 11-year-old children with dyslexia and a matched normal-reading control children. Group comparisons demonstrated that children with dyslexia were less sensitive than normal-reading children to slow-rate dynamic auditory processing, speech-in-noise perception, phonological awareness and literacy abilities. Correlations were found between slow-rate dynamic auditory processing and phonological awareness, and speech-in-noise perception and reading. Yet, no significant correlation between slow-rate dynamic auditory processing and speech-in-noise perception was obtained. Together, these results indicate that children with dyslexia have difficulties with slow-rate dynamic auditory processing and speech-in-noise perception and that these problems persist until sixth grade. PMID:21645986

  1. Mutagenesis in the switch IV of the helical domain of the human Gsalpha reduces its GDP/GTP exchange rate.

    PubMed

    Echeverría, V; Hinrichs, M V; Torrejón, M; Ropero, S; Martinez, J; Toro, M J; Olate, J

    2000-01-01

    The Galpha subunits of heterotrimeric G proteins are constituted by a conserved GTPase "Ras-like" domain (RasD) and by a unique alpha-helical domain (HD). Upon GTP binding, four regions, called switch I, II, III, and IV, have been identified as undergoing structural changes. Switch I, II, and III are located in RasD and switch IV in HD. All Galpha known functions, such as GTPase activity and receptor, effector, and Gbetagamma interaction sites have been found to be localized in RasD, but little is known about the role of HD and its switch IV region. Through the construction of chimeras between human and Xenopus Gsalpha we have previously identified a HD region, encompassing helices alphaA, alphaB, and alphaC, that was responsible for the observed functional differences in their capacity to activate adenylyl cyclase (Antonelli et al. [1994]: FEBS Lett 340:249-254). Since switch IV is located within this region and contains most of the nonconservative amino acid differences between both Gsalpha proteins, in the present work we constructed two human Gsalpha mutant proteins in which we have changed four and five switch IV residues for the ones present in the Xenopus protein. Mutants M15 (hGsalphaalphaS133N, M135P, P138K, P143S) and M17 (hGsalphaalphaS133N, M135P, V137Y, P138K, P143S) were expressed in Escherichia coli, purified, and characterized by their ability to bind GTPgammaS, dissociate GDP, hydrolyze GTP, and activate adenylyl cyclase. A decreased rate of GDP release, GTPgammaS binding, and GTP hydrolysis was observed for both mutants, M17 having considerably slower kinetics than M15 for all functions tested. Reconstituted adenylyl cyclase activity with both mutants showed normal activation in the presence of AlF(4)(-), but a decreased activation with GTPgammaS, which is consistent with the lower GDP dissociating rate they displayed. These data provide new evidence on the role that HD is playing in modulating the GDP/GTP exchange of the Gsalpha subunit. PMID

  2. The Dynamic Tensile Behavior of Railway Wheel Steel at High Strain Rates

    NASA Astrophysics Data System (ADS)

    Jing, Lin; Han, Liangliang; Zhao, Longmao; Zhang, Ying

    2016-10-01

    The dynamic tensile tests on D1 railway wheel steel at high strain rates were conducted using a split Hopkinson tensile bar (SHTB) apparatus, compared to quasi-static tests. Three different types of specimens, which were machined from three different positions (i.e., the rim, web and hub) of a railway wheel, were prepared and examined. The rim specimens were checked to have a higher yield stress and ultimate tensile strength than those web and hub specimens under both quasi-static and dynamic loadings, and the railway wheel steel was demonstrated to be strain rate dependent in dynamic tension. The dynamic tensile fracture surfaces of all the wheel steel specimens are cup-cone-shaped morphology on a macroscopic scale and with the quasi-ductile fracture features on the microscopic scale.

  3. Experimental Determination of Mechanisms and Rates of Fe-Mg Exchange Between Spinel Grains Mediated by a Fluid Phase

    NASA Astrophysics Data System (ADS)

    Mueller, T.; Dohmen, R.; Chakraborty, S.

    2008-12-01

    The overall mechanism and kinetics of mineral reactions results from a complex interaction of several processes such as surface reaction kinetics, volume diffusion and net transfer. In order to quantify the kinetics of reactions involving multiple phases in multicomponent systems, it is necessary to understand and characterize the nature and rates of each of these processes. Most laboratory experiments up to now have focused on kinetics of reactions where the reactants and products are in direct physical contact with each other. However, there is abundant textural evidence in rocks that reactions occurred between mineral grains that are physically separated from each other, frequently mediated by a fluid phase. We have devised an experimental setup to study the mechanism and kinetics of such reactions in the laboratory. Polished single crystals of two spinels (synthetic MgAl2O4 and a natural spinel with 44 mol% Hercynite component), 2mm on a side, were placed in a gold capsule (length: 2cm, diameter: 4mm) separated from each other by a 5mm long tube of Au or alumina. The capsule was welded shut after adding distilled water (80-100μl). Such capsules were annealed (2 Kbar, 700-750°C, up to 21 hours) in hydrothermal cold seal vessels. After annealing the crystals were cleaned in an ultrasonic bath in order to rinse them of possible quench products. The surfaces were examined optically and near surface chemistry was determined using Rutherford Backscattering Spectroscopy (RBS). We observe time dependent changes in the morphology as well as the chemistry of the crystals, as follows: After short times, the surface of the Mg spinel shows scattered etch pits while terraces form on the Fe spinel. After longer anneals, the etch pits disappear and the surface of the Mg spinels appear polished. Surface compositions are found to be different, depending on whether a Au or alumina separator was used in the experiments. The Fe rich spinel composition remains unchanged whereas

  4. Magnetization dynamics and damping due to electron-phonon scattering in a ferrimagnetic exchange model

    NASA Astrophysics Data System (ADS)

    Baral, Alexander; Vollmar, Svenja; Schneider, Hans Christian

    2014-07-01

    We present a microscopic calculation of magnetization damping for a magnetic "toy model." The magnetic system consists of itinerant carriers coupled antiferromagnetically to a dispersionless band of localized spins, and the magnetization damping is due to coupling of the itinerant carriers to a phonon bath in the presence of spin-orbit coupling. Using a mean-field approximation for the kinetic exchange model and assuming the spin-orbit coupling to be of the Rashba form, we derive Boltzmann scattering integrals for the distributions and spin conherences in the case of an antiferromagnetic exchange splitting, including a careful analysis of the connection between lifetime broadening and the magnetic gap. For incoherent scattering of itinerant carriers with the phonon bath, i.e., the Elliott-Yafet mechanism, we extract dephasing and magnetization times T1 and T2 from initial conditions corresponding to a tilt of the magnetization vector and draw a comparison to phenomenological equations such as the Landau-Lifshitz (LL) or the Gilbert damping. We also analyze magnetization precession and damping for this system including an anisotropy field and find a carrier mediated dephasing of the localized spin via the mean-field coupling.

  5. Erionite-Na upon heating: dehydration dynamics and exchangeable cations mobility.

    PubMed

    Ballirano, Paolo; Pacella, Alessandro

    2016-01-01

    Erionite is a fibrous zeolite significantly more tumorigenic than crocidolite asbestos upon inhalation. In recent years, several papers have been published aimed at characterizing from the crystal-chemical point of view erionite fibres. As their toxicity has been ascribed to Fe acquired within the human body, studies aimed at characterizing the iron topochemistry have also been published, suggesting a possible important role played by the ionic exchange properties and cations mobility of this zeolite on developing carcinogenicity. Here we report the analysis results of the thermal behaviour of erionite-Na, which has been found to deviate significantly from that of erionite-K. This result is in contrast with the current scientific view that differences in weighted ionic potential, Si/Al ratio and size of exchangeable cations result in significantly different thermal behaviours, all those parameters being nearly identical or very similar in both species. The different mobility of the extraframework cations observed in erionite samples with dissimilar chemistry is of particular interest within the frame of the hypothesis that their biological activity could depend, apart from surface interactions, also on bulk effects. PMID:26948139

  6. Erionite-Na upon heating: dehydration dynamics and exchangeable cations mobility

    NASA Astrophysics Data System (ADS)

    Ballirano, Paolo; Pacella, Alessandro

    2016-03-01

    Erionite is a fibrous zeolite significantly more tumorigenic than crocidolite asbestos upon inhalation. In recent years, several papers have been published aimed at characterizing from the crystal-chemical point of view erionite fibres. As their toxicity has been ascribed to Fe acquired within the human body, studies aimed at characterizing the iron topochemistry have also been published, suggesting a possible important role played by the ionic exchange properties and cations mobility of this zeolite on developing carcinogenicity. Here we report the analysis results of the thermal behaviour of erionite-Na, which has been found to deviate significantly from that of erionite-K. This result is in contrast with the current scientific view that differences in weighted ionic potential, Si/Al ratio and size of exchangeable cations result in significantly different thermal behaviours, all those parameters being nearly identical or very similar in both species. The different mobility of the extraframework cations observed in erionite samples with dissimilar chemistry is of particular interest within the frame of the hypothesis that their biological activity could depend, apart from surface interactions, also on bulk effects.

  7. Free energies and mechanisms of water exchange around Uranyl from first principles molecular dynamics

    SciTech Connect

    Atta-Fynn, Raymond; Bylaska, Eric J.; De Jong, Wibe A.

    2012-02-01

    From density functional theory (DFT) based ab initio (Car-Parrinello) metadynamics, we compute the activation energies and mechanisms of water exchange between the first and second hydration shells of aqueous Uranyl (UO{sub 2}{sup 2+}) using the primary hydration number of U as the reaction coordinate. The free energy and activation barrier of the water dissociation reaction [UO{sub 2}(OH{sub 2}){sub 5}]{sup 2+}(aq) {yields} [UO{sub 2}(OH{sub 2})4]{sup 2+}(aq) + H{sub 2}O are 0.7 kcal and 4.7 kcal/mol respectively. The free energy is in good agreement with previous theoretical (-2.7 to +1.2 kcal/mol) and experimental (0.5 to 2.2 kcal/mol) data. The associative reaction [UO{sub 2}(OH{sub 2}){sub 5}]{sup 2+}(aq) + H{sub 2}O {yields} [UO{sub 2}(OH{sub 2})6]{sup 2+}(aq) is short-lived with a free energy and activation barrier of +7.9 kcal/mol and +8.9 kca/mol respectively; it is therefore classified as associative-interchange. On the basis of the free energy differences and activation barriers, we predict that the dominant exchange mechanism between [UO{sub 2}(OH{sub 2}){sub 5}]{sup 2+}(aq) and bulk water is dissociative.

  8. Dynamics of the fully stripped ion-hydrogen atom charge exchange process in dense quantum plasmas

    SciTech Connect

    Zhang, Ling-yu; Wan, Jiang-feng; Zhao, Xiao-ying; Xiao, Guo-qing; Duan, Wen-shan; Qi, Xin; Yang, Lei

    2014-09-15

    The plasma screening effects of dense quantum plasmas on charge exchange processes of a fully stripped ion colliding with a hydrogen atom are studied by the classical trajectory Monte Carlo method. The inter-particle interactions are described by the exponential cosine-screened Coulomb potentials. It is found that in weak screening conditions, cross sections increase with the increase of the ionic charge Z. However, in strong screening conditions, the dependence of cross sections on the ionic charge is related to the incident particle energy. At high energies, cross sections show a linear increase with the increase of Z, whereas at low energies, cross sections for Z≥4 become approximately the same. The He{sup 2+} and C{sup 6+} impacting charge exchange cross sections in dense quantum plasmas are also compared with those in weakly coupled plasmas. The interactions are described by the static screened Coulomb potential. It is found that for both He{sup 2+} and C{sup 6+}, the oscillatory screening effects of dense quantum plasmas are almost negligible in weak screening conditions. However, in strong screening conditions, the oscillatory screening effects enhance the screening effects of dense quantum plasmas, and the enhancement becomes more and more significant with the increase of the screening parameter and the ionic charge.

  9. Gas-dynamics characteristics of wave energy exchanger as high-temperature preheater-compressor

    SciTech Connect

    Zubatov, N.

    1983-12-01

    In the magnetohydrodynamic (MHD) energy conversion and high-temperature steel production technological processes the air preheater is an essential component. It preheats the air used in fuel combustion, so that the flame temperature can reach the high levels required by the process. Many studies have indicated that air preheat temperature significantly affects MHD plant efficiency and blast-furnace performance. Combustion air preheating can be accomplished by either of two methods. One method (MHD power plant) utilizes the heat energy of the MHD generator exhaust gas directly. In this case, the preheater, classified as directly-fired, is located in the MHD generator exhaust gas stream as part of the bottoming plant. The alternate method of preheating the combustion air (blast-furnace systems) utilizes a separate heat source and fires the preheater with a clean fuel. This type of preheater is classified as indirectly-fired. The regenerative heat exchangers are used for both methods to achieve the high air preheat temperature required for combustion. Such heat exchangers operate on the principle of transferring heat through a separating medium that is heated for a time by a hot fluid, then cooled by a fluid of lower temperature. The preheater system requires several regenerators, arranged in parallel and with switchover valves, in order to deliver a continuous flow of preheated air.

  10. Price dynamics and market power in an agent-based power exchange

    NASA Astrophysics Data System (ADS)

    Cincotti, Silvano; Guerci, Eric; Raberto, Marco

    2005-05-01

    This paper presents an agent-based model of a power exchange. Supply of electric power is provided by competing generating companies, whereas demand is assumed to be inelastic with respect to price and is constant over time. The transmission network topology is assumed to be a fully connected graph and no transmission constraints are taken into account. The price formation process follows a common scheme for real power exchanges: a clearing house mechanism with uniform price, i.e., with price set equal across all matched buyer-seller pairs. A single class of generating companies is considered, characterized by linear cost function for each technology. Generating companies compete for the sale of electricity through repeated rounds of the uniform auction and determine their supply functions according to production costs. However, an individual reinforcement learning algorithm characterizes generating companies behaviors in order to attain the expected maximum possible profit in each auction round. The paper investigates how the market competitive equilibrium is affected by market microstructure and production costs.

  11. Effect of dynamic strain rate on micro-indentation properties of pure aluminum

    NASA Astrophysics Data System (ADS)

    Yamada, Hiroyuki; Hotta, Midori; Kami, Tsuyoshi; Ogasawara, Nagahisa; Chen, Xi

    2015-09-01

    Indentation is widely used to investigate the elastic and plastic properties of mechanical materials, which includes the strain rate sensitivity. The indentation exhibits an inhomogeneous strain distribution in contrast to compression and tensile tests with homogeneous deformation. Thus, the strain rate of the indentation may form the inhomogeneous distribution. Therefore, the effect of strain rate distribution of the indentation on pure aluminum with respect to the strain rate dependence of strength in order to clarify the effect of the strain rate on the indentation technique. First, the numerical simulation was established using the Cowper-Symonds equation as the dynamic constitutive equation. Secondary, the strain rate distribution was calculated from the equivalent plastic strain distribution. The strain rate distribution was quite different from the strain distribution, which showed that the strain rate at the crater rim was higher than that beneath the indenter. Finally, we try to perform the averaging of strain rate distribution in order to make an index of strain rate in the indentation. The average of strain rate distribution was calculated using the equivalent plastic strain above a boundary value that is the critical strain and the representative strain. There is correlation between the average strain rate and the loading curvature, which shows that the average strain rate can express as the representative of strain rate for the indentation technique.

  12. Ab initio calculation of transition state normal mode properties and rate constants for the H(T)+CH4(CD4) abstraction and exchange reactions

    NASA Astrophysics Data System (ADS)

    Schatz, George C.; Walch, Stephen P.; Wagner, Albert F.

    1980-11-01

    We present ab initio (GVB-POL-CI) calculations for enough of the region about the abstraction and exchange saddle points for H(T)+CH4(CD4) to perform a full normal mode analysis of the transition states. The resulting normal mode frequencies are compared to four other published surfaces: an ab initio UHF-SCF calculation by Carsky and Zahradnik, a semiempirical surface by Raff, and two semiempirical surfaces by Kurylo, Hollinden, and Timmons. Significant quantitative and qualitative differences exist between the POL-CI results and those of the other surfaces. Transition state theory rate constants and vibrationally adiabatic reaction threshold energies were computed for all surfaces and compared to available experimental values. For abstraction, the POL-CI rates are in good agreement with experimental rates and in better agreement than are the rates of any of the other surfaces. For exchange, uncertainties in the experimental values and in the importance of vibrationally nonadiabatic effects cloud the comparison of theory to experiment. Tentative conclusions are that the POL-CI barrier is too low by several kcal. Unless vibrationaly nonadiabatic effects are severe, the POL-CI surface is still in better agreement with experiment than are the other surfaces. The rates for a simple 3-atom transition state theory model (where CH3 is treated as an atom) are compared to the rates for the full 6-atom model. The kinetic energy coupling of reaction coordinate modes to methyl group modes is identified as being of primary importance in determining the accuracy of the 3-atom model for this system. Substantial coupling in abstraction, but not exchange, causes the model to fail for abstraction but succeed for exchange.

  13. The Seasonal Dynamics of Artificial Nest Predation Rates along Edges in a Mosaic Managed Reedbed.

    PubMed

    Malzer, Iain; Helm, Barbara

    2015-01-01

    Boundaries between different habitats can be responsible for changes in species interactions, including modified rates of encounter between predators and prey. Such 'edge effects' have been reported in nesting birds, where nest predation rates can be increased at habitat edges. The literature concerning edge effects on nest predation rates reveals a wide variation in results, even within single habitats, suggesting edge effects are not fixed, but dynamic throughout space and time. This study demonstrates the importance of considering dynamic mechanisms underlying edge effects and their relevance when undertaking habitat management. In reedbed habitats, management in the form of mosaic winter reed cutting can create extensive edges which change rapidly with reed regrowth during spring. We investigate the seasonal dynamics of reedbed edges using an artificial nest experiment based on the breeding biology of a reedbed specialist. We first demonstrate that nest predation decreases with increasing distance from the edge of cut reed blocks, suggesting edge effects have a pivotal role in this system. Using repeats throughout the breeding season we then confirm that nest predation rates are temporally dynamic and decline with the regrowth of reed. However, effects of edges on nest predation were consistent throughout the season. These results are of practical importance when considering appropriate habitat management, suggesting that reed cutting may heighten nest predation, especially before new growth matures. They also contribute directly to an overall understanding of the dynamic processes underlying edge effects and their potential role as drivers of time-dependent habitat use. PMID:26448338

  14. The Seasonal Dynamics of Artificial Nest Predation Rates along Edges in a Mosaic Managed Reedbed

    PubMed Central

    Malzer, Iain; Helm, Barbara

    2015-01-01

    Boundaries between different habitats can be responsible for changes in species interactions, including modified rates of encounter between predators and prey. Such ‘edge effects’ have been reported in nesting birds, where nest predation rates can be increased at habitat edges. The literature concerning edge effects on nest predation rates reveals a wide variation in results, even within single habitats, suggesting edge effects are not fixed, but dynamic throughout space and time. This study demonstrates the importance of considering dynamic mechanisms underlying edge effects and their relevance when undertaking habitat management. In reedbed habitats, management in the form of mosaic winter reed cutting can create extensive edges which change rapidly with reed regrowth during spring. We investigate the seasonal dynamics of reedbed edges using an artificial nest experiment based on the breeding biology of a reedbed specialist. We first demonstrate that nest predation decreases with increasing distance from the edge of cut reed blocks, suggesting edge effects have a pivotal role in this system. Using repeats throughout the breeding season we then confirm that nest predation rates are temporally dynamic and decline with the regrowth of reed. However, effects of edges on nest predation were consistent throughout the season. These results are of practical importance when considering appropriate habitat management, suggesting that reed cutting may heighten nest predation, especially before new growth matures. They also contribute directly to an overall understanding of the dynamic processes underlying edge effects and their potential role as drivers of time-dependent habitat use. PMID:26448338

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

    NASA Technical Reports Server (NTRS)

    Park, Michael A.; Green, Lawrence L.

    2000-01-01

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

  16. The Seasonal Dynamics of Artificial Nest Predation Rates along Edges in a Mosaic Managed Reedbed.

    PubMed

    Malzer, Iain; Helm, Barbara

    2015-01-01

    Boundaries between different habitats can be responsible for changes in species interactions, including modified rates of encounter between predators and prey. Such 'edge effects' have been reported in nesting birds, where nest predation rates can be increased at habitat edges. The literature concerning edge effects on nest predation rates reveals a wide variation in results, even within single habitats, suggesting edge effects are not fixed, but dynamic throughout space and time. This study demonstrates the importance of considering dynamic mechanisms underlying edge effects and their relevance when undertaking habitat management. In reedbed habitats, management in the form of mosaic winter reed cutting can create extensive edges which change rapidly with reed regrowth during spring. We investigate the seasonal dynamics of reedbed edges using an artificial nest experiment based on the breeding biology of a reedbed specialist. We first demonstrate that nest predation decreases with increasing distance from the edge of cut reed blocks, suggesting edge effects have a pivotal role in this system. Using repeats throughout the breeding season we then confirm that nest predation rates are temporally dynamic and decline with the regrowth of reed. However, effects of edges on nest predation were consistent throughout the season. These results are of practical importance when considering appropriate habitat management, suggesting that reed cutting may heighten nest predation, especially before new growth matures. They also contribute directly to an overall understanding of the dynamic processes underlying edge effects and their potential role as drivers of time-dependent habitat use.

  17. Resources, mortality, and disease ecology: Importance of positive feedbacks between host growth rate and pathogen dynamics

    PubMed Central

    Smith, Val H.; Holt, Robert D.; Smith, Marilyn S.; Niu, Yafen; Barfield, Michael

    2016-01-01

    Resource theory and metabolic scaling theory suggest that the dynamics of a pathogen within a host should strongly depend upon the rate of host cell metabolism. Once an infection occurs, key ecological interactions occur on or within the host organism that determine whether the pathogen dies out, persists as a chronic infection, or grows to densities that lead to host death. We hypothesize that, in general, conditions favoring rapid host growth rates should amplify the replication and proliferation of both fungal and viral pathogens. If a host population experiences an increase in mortality, to persist it must have a higher growth rate, per host, often reflecting greater resource availability per capita. We hypothesize that this could indirectly foster the pathogen, which also benefits from increased within-host resource turnover. We first bring together in a short review a number of key prior studies which illustrate resource effects on viral and fungal pathogen dynamics. We then report new results from a semi-continuous cell culture experiment with SHIV, demonstrating that higher mortality rates indeed can promote viral proliferation. We develop a simple model that illustrates dynamical consequences of these resource effects, including interesting effects such as alternative stable states and oscillatory dynamics. Our paper contributes to a growing body of literature at the interface of ecology and infectious disease epidemiology, emphasizing that host abundances alone do not drive community dynamics: the physiological state and resource content of infected hosts also strongly influence host-pathogen interactions. PMID:27642269

  18. Total dose effect on soft error rate for dynamic metal-oxide-semiconductor memory cells

    NASA Technical Reports Server (NTRS)

    Benumof, Reuben

    1989-01-01

    A simple model for the soft error rate for dynamic metal-oxide-semiconductor random access memories due to normal galactic radiation was devised and then used to calculate the rate of decrease of the single-event-upset rate with total radiation dose. The computation shows that the decrease in the soft error rate is less than 10 percent per day if the shielding is 0.5 g/sq cm and the spacecraft is in a geosynchronous orbit. The decrease is considerably less in a polar orbiting device.

  19. Beam dynamics simulations of the transverse-to-longitudinal emittance exchange proof-of-principle experiment at the Argonne Wakefield Accelerator

    SciTech Connect

    Rihaoui, M.; Gai, W.; Kim, K.-J.; Power, J. G.; Piot, P.; Sun, Y.-E.

    2009-01-22

    Transverse-to-longitudinal emittance exchange has promising applications in various advanced acceleration and light source concepts. A proof-of-principle experiment to demonstrate this phase space manipulation method is currently being planned at the Argonne Wakefield Accelerator. The experiment focuses on exchanging a low longitudinal emittance with a high transverse horizontal emittance and also incorporates room for possible parametric studies e.g. using an incoming flat beam with tunable horizontal emittance. In this paper, we present realistic start-to-end beam dynamics simulation of the scheme, explore the limitations of this phase space exchange.

  20. Beam dynamics simulations of the transverse-to-longitudinal emittance exchange proof-of-principle experiment at the Argonne Wakefield Accelerator.

    SciTech Connect

    Gao, F.; Gai, W.; Power, J. G.; Kim, K. J.; Sun, Y. E.; Piot, P.; Rihaoui, M.; High Energy Physics; Northern Illinois Univ.; FNAL

    2009-01-01

    Transverse-to-longitudinal emittance exchange has promising applications in various advanced acceleration and light source concepts. A proof-of-principle experiment to demonstrate this phase space manipulation method is currently being planned at the Argonne Wakefield Accelerator. The experiment focuses on exchanging a low longitudinal emittance with a high transverse horizontal emittance and also incorporates room for possible parametric studies e.g. using an incoming flat beam with tunable horizontal emittance. In this paper, we present realistic start-to-end beam dynamics simulation of the scheme, explore the limitations of this phase space exchange.

  1. Beam dynamics simulations of the transverse-to-longitudinal emittance exchange proof-of-principle experiment at the Argonne Wakefield Accelerator

    SciTech Connect

    Rihaoui, M.; Gai, W.; Kim, K.J.; Piot, Philippe; Power, John Gorham; Sun, Y.E.; /Fermilab

    2009-01-01

    Transverse-to-longitudinal emittance exchange has promising applications in various advanced acceleration and light source concepts. A proof-of-principle experiment to demonstrate this phase space manipulation method is currently being planned at the Argonne Wakefield Accelerator. The experiment focuses on exchanging a low longitudinal emittance with a high transverse horizontal emittance and also incorporates room for possible parametric studies e.g. using an incoming flat beam with tunable horizontal emittance. In this paper, we present realistic start-to-end beam dynamics simulation of the scheme, explore the limitations of this phase space exchange.

  2. Studies on Dynamic Damage Evolution for Pp/pa Polymer Blends Under High Strain Rates

    NASA Astrophysics Data System (ADS)

    Sun, Zi-Jian; Wang, Li-Li

    The dynamic damage evolution for PP/PA blends with different compatibilizers is studied in high strain rates from two different approaches, namely by determining the unloading elastic modulus of specimen experienced impact deformation and by combining the split Hopkinson pressure bar (SHPB) experimental technique with the back-propagation (BP) neural network. The results obtained by both approaches consistently show that a threshold strain ɛth exists for dynamic damage evolution, and both the damage evolution and ɛth are dependent on strain and strain rate. For non-linear visco-elastic materials, the damage evolution determined by the unloading elastic modulus provides an underestimation of real damage evolution.

  3. Injector Beam Dynamics for a High-Repetition Rate 4th-Generation Light Source

    SciTech Connect

    Papadopoulos, C. F.; Corlett, J.; Emma, P.; Filippetto, D.; Penn, G.; Qiang, J.; Reinsch, M.; Sannibale, F.; Steier, C.; Venturini, M.; Wells, R.

    2013-05-20

    We report on the beam dynamics studies and optimization methods for a high repetition rate (1 MHz) photoinjector based on a VHF normal conducting electron source. The simultaneous goals of beamcompression and reservation of 6-dimensional beam brightness have to be achieved in the injector, in order to accommodate a linac driven FEL light source. For this, a parallel, multiobjective optimization algorithm is used. We discuss the relative merits of different injector design points, as well as the constraints imposed on the beam dynamics by technical considerations such as the high repetition rate.

  4. Enhancing angular sampling rate of integral floating display using dynamically variable apertures.

    PubMed

    Hong, Jisoo; Yeom, Jiwoon; Lee, Byoungho

    2012-04-23

    Two novel methods are proposed which enhance the angular sampling rate of the integral floating display by adopting dynamically variable apertures in front of the lenslet array or the floating lens. Adopted dynamically variable apertures are opened sequentially in synchronization with proper elemental images to subdivide the angular sampling step by time-multiplexing method. Our proposed method can enhance the angular sampling rate, which is related to an expressible longitudinal range, without sacrificing other visual quality factors in tradeoff relationship. Especially, our proposed method with apertures on the floating lens provides two-dimensional/three-dimensional convertible feature to integral floating display system.

  5. Application of the electron nuclear dynamics method to hydrogen abstraction and exchange reactions of hydrogen + HOD and deuterium + ammonium ion

    NASA Astrophysics Data System (ADS)

    Coutinho Neto, Mauricio Domingues

    2001-07-01

    The field of quantum molecular dynamics have flourished in the last 20 years. Methods that propose the solution of the time dependent Schrodinger equation for a molecular reactive process abound in the literature. However the majority of these methods focus on solving the nuclear Schrodinger equation subject to a known electronic potential. The electron nuclear dynamics (END) method proposes a framework of a hierarchy of approximations to the Schrodinger equation based on the time dependent variational Principle (TDVP). A general approach is sought to solve the electronic and nuclear problem simultaneously without making use of the Born-Oppenheimer approximation. The purpose of this work is to apply the minimal END to areas where its unique qualities can give new insight into the relevant dynamics of a chemical or physical process. Minimal END is a method for direct non-adiabatic dynamics. It describes the electrons with a family of complex determinantal wave-functions in terms of non-orthogonal spin orbitals and treats the nuclei as classical particles. In the first two studies, we apply the END method to hydrogen abstraction and exchange reactions at hyper-thermal collision energies. We investigate the D2+ NH+3 reaction at collision energies ranging from 6 to 16 eV and the H + HOD reaction at a collision energy of 1.575 eV. Collision energies refer to center of mass energies. Emphasis is put on the details of the abstraction and exchange reaction mechanisms for ground state reactants. In a final application we use minimal END to study the interaction of a strong laser field with the diatomic molecules HF and LiH. Effects of the polarization of the electronic potential on the dynamics are investigated. Emphasis is also placed on the development of a general method for interpreting the final time dependent wave-function of the product fragments. The purpose is to analyze the final state wave-function in terms of charge transfer channels as well as individual

  6. Dependence of Dynamic Tensile Strength of Longyou Sandstone on Heat-Treatment Temperature and Loading Rate

    NASA Astrophysics Data System (ADS)

    Yao, Wei; Xu, Ying; Wang, Wei; Kanopolous, Patrick

    2016-10-01

    As a material for famous historical underground rock caverns, Longyou sandstone (LS) may fail under the combination of high loading rate and high temperature. The thermal damage induced by various heat-treatment temperatures (150, 250, 350, 450, 600 and 850 °C) is first characterized by X-ray Micro-computed tomography (CT) method. The damage variable derived from the average CT value for heat-treated LS specimen and reference specimen without heat treatment was used to quantify the thermal damage. The dynamic tensile strengths of these LS samples under different dynamic loading rates (ranging from 24 to 540 GPa/s) were then obtained using the split Hopkinson pressure bar (SHPB) system. The dynamic tensile strength of LS increases with the loading rate at a given heat-treatment temperature, and the tensile strength at the same loading rate decreases with the heat-treatment temperature except for 450 °C. Based on the experimental data, an empirical equation was established to relate the dynamic tensile strength of LS to the loading rate and the heat-treatment temperature.

  7. Long-term dynamics of production, respiration, and net CO2 exchange in two sagebrush-steppe ecosystems

    USGS Publications Warehouse

    Gilmanov, T.G.; Svejcar, T.J.; Johnson, D.A.; Angell, R.F.; Saliendra, Nicanor Z.; Wylie, B.K.

    2006-01-01

    We present a synthesis of long-term measurements of CO2 exchange in 2 US Intermountain West sagebrush-steppe ecosystems. The locations near Burns, Oregon (1995-2001), and Dubois, Idaho (1996-2001), are part of the AgriFlux Network of the Agricultural Research Service, United States Department of Agriculture. Measurements of net ecosystem CO2 exchange (F c) during the growing season were continuously recorded at flux towers using the Bowen ratio-energy balance technique. Data were partitioned into gross primary productivity (Pg) and ecosystem respiration (Re) using the light-response function method. Wintertime fluxes were measured during 1999/2000 and 2000/2001 and used to model fluxes in other winters. Comparison of daytime respiration derived from light-response analysis with nighttime tower measurements showed close correlation, with daytime respiration being on the average higher than nighttime respiration. Maxima of Pg and Re at Burns were both 20 g CO2?? m-2??d-1 in 1998. Maxima of Pg and R e at Dubois were 37 and 35 g CO2??m -2??d-1, respectively, in 1997. Mean annual gross primary production at Burns was 1 111 (range 475-1 715) g CO2?? m-2??y-1 about 30% lower than that at Dubois (1 602, range 963-2 162 g CO2??m-2??y-1). Across the years, both ecosystems were net sinks for atmospheric CO2 with a mean net ecosystem CO2 exchange of 82 g CO2?? m-2??y-1 at Burns and 253 g CO2?? m-2??y-1 at Dubois, but on a yearly basis either site could be a C sink or source, mostly depending on precipitation timing and amount. Total annual precipitation is not a good predictor of carbon sequestration across sites. Our results suggest that Fc should be partitioned into Pg and Re components to allow prediction of seasonal and yearly dynamics of CO2 fluxes.

  8. Static and dynamic strain energy release rates in toughened thermosetting composite laminates

    NASA Technical Reports Server (NTRS)

    Cairns, Douglas S.

    1992-01-01

    In this work, the static and dynamic fracture properties of several thermosetting resin based composite laminates are presented. Two classes of materials are explored. These are homogeneous, thermosetting resins and toughened, multi-phase, thermosetting resin systems. Multi-phase resin materials have shown enhancement over homogenous materials with respect to damage resistance. The development of new dynamic tests are presented for composite laminates based on Width Tapered Double Cantilevered Beam (WTDCB) for Mode 1 fracture and the End Notched Flexure (ENF) specimen. The WTDCB sample was loaded via a low inertia, pneumatic cylinder to produce rapid cross-head displacements. A high rate, piezo-electric load cell and an accelerometer were mounted on the specimen. A digital oscilloscope was used for data acquisition. Typical static and dynamic load versus displacement plots are presented. The ENF specimen was impacted in three point bending with an instrumented impact tower. Fracture initiation and propagation energies under static and dynamic conditions were determined analytically and experimentally. The test results for Mode 1 fracture are relatively insensitive to strain rate effects for the laminates tested in this study. The test results from Mode 2 fracture indicate that the toughened systems provide superior fracture initiation and higher resistance to propagation under dynamic conditions. While the static fracture properties of the homogeneous systems may be relatively high, the apparent Mode 2 dynamic critical strain energy release rate drops significantly. The results indicate that static Mode 2 fracture testing is inadequate for determining the fracture performance of composite structures subjected to conditions such as low velocity impact. A good correlation between the basic Mode 2 dynamic fracture properties and the performance is a combined material/structural Compression After Impact (CAI) test is found. These results underscore the importance of

  9. Selection on Network Dynamics Drives Differential Rates of Protein Domain Evolution

    PubMed Central

    Mannakee, Brian K.; Gutenkunst, Ryan N.

    2016-01-01

    The long-held principle that functionally important proteins evolve slowly has recently been challenged by studies in mice and yeast showing that the severity of a protein knockout only weakly predicts that protein’s rate of evolution. However, the relevance of these studies to evolutionary changes within proteins is unknown, because amino acid substitutions, unlike knockouts, often only slightly perturb protein activity. To quantify the phenotypic effect of small biochemical perturbations, we developed an approach to use computational systems biology models to measure the influence of individual reaction rate constants on network dynamics. We show that this dynamical influence is predictive of protein domain evolutionary rate within networks in vertebrates and yeast, even after controlling for expression level and breadth, network topology, and knockout effect. Thus, our results not only demonstrate the importance of protein domain function in determining evolutionary rate, but also the power of systems biology modeling to uncover unanticipated evolutionary forces. PMID:27380265

  10. Selection on Network Dynamics Drives Differential Rates of Protein Domain Evolution.

    PubMed

    Mannakee, Brian K; Gutenkunst, Ryan N

    2016-07-01

    The long-held principle that functionally important proteins evolve slowly has recently been challenged by studies in mice and yeast showing that the severity of a protein knockout only weakly predicts that protein's rate of evolution. However, the relevance of these studies to evolutionary changes within proteins is unknown, because amino acid substitutions, unlike knockouts, often only slightly perturb protein activity. To quantify the phenotypic effect of small biochemical perturbations, we developed an approach to use computational systems biology models to measure the influence of individual reaction rate constants on network dynamics. We show that this dynamical influence is predictive of protein domain evolutionary rate within networks in vertebrates and yeast, even after controlling for expression level and breadth, network topology, and knockout effect. Thus, our results not only demonstrate the importance of protein domain function in determining evolutionary rate, but also the power of systems biology modeling to uncover unanticipated evolutionary forces.

  11. An Autoethnographic Exchange: Exploring the Dynamics of Selves as Adult Learners and Adult Educators

    ERIC Educational Resources Information Center

    Plakhotnik, Maria S.; Delgado, Antonio; Seepersad, Rehana

    2015-01-01

    This article explores four former doctoral students' perceptions about their selves as adult learners and adult educators through the use of autoethnography and reflective dialogue. The dynamics between the two selves were explored to identify emerging themes and implications for practice in adult education. The duality of their roles as learners…

  12. Ratiometric analysis in hyperpolarized NMR (I): test of the two-site exchange model and the quantification of reaction rate constants.

    PubMed

    Li, Lin Z; Kadlececk, Stephen; Xu, He N; Daye, Dania; Pullinger, Benjamin; Profka, Harrilla; Chodosh, Lewis; Rizi, Rahim

    2013-10-01

    Conventional methods for the analysis of in vivo hyperpolarized (13) C NMR data from the lactate dehydrogenase (LDH) reaction usually make assumptions on the stability of rate constants and/or the validity of the two-site exchange model. In this study, we developed a framework to test the validity of the assumption of stable reaction rate constants and the two-site exchange model in vivo via ratiometric fitting of the time courses of the signal ratio L(t)/P(t). Our analysis provided evidence that the LDH enzymatic kinetics observed by hyperpolarized NMR are in near-equilibrium and satisfy the two-site exchange model for only a specific time window. In addition, we quantified both the forward and reverse exchange rate constants of the LDH reaction for the transgenic and mouse xenograft models of breast cancer using the ratio fitting method developed, which includes only two modeling parameters and is less sensitive to the influence of instrument settings/protocols, such as flip angles, degree of polarization and tracer dosage. We further compared the ratio fitting method with a conventional two-site exchange modeling method, i.e. the differential equation fitting method, using both the experimental and simulated hyperpolarized NMR data. The ratio fitting method appeared to fit better than the differential equation fitting method for the reverse rate constant on the mouse tumor data, with less relative errors on average, whereas the differential equation fitting method also resulted in a negative reverse rate constant for one tumor. The simulation results indicated that the accuracy of both methods depends on the width of the transport function, noise level and rate constant ratio; one method may be more accurate than the other based on the experimental/biological conditions aforementioned. We were able to categorize our tumor models into specific conditions of the computer simulation and to estimate the errors of rate quantification. We also discussed possible

  13. Constant pH Molecular Dynamics in Explicit Solvent with Enveloping Distribution Sampling and Hamiltonian Exchange

    PubMed Central

    2015-01-01

    We present a new computational approach for constant pH simulations in explicit solvent based on the combination of the enveloping distribution sampling (EDS) and Hamiltonian replica exchange (HREX) methods. Unlike constant pH methods based on variable and continuous charge models, our method is based on discrete protonation states. EDS generates a hybrid Hamiltonian of different protonation states. A smoothness parameter s is used to control the heights of energy barriers of the hybrid-state energy landscape. A small s value facilitates state transitions by lowering energy barriers. Replica exchange between EDS potentials with different s values allows us to readily obtain a thermodynamically accurate ensemble of multiple protonation states with frequent state transitions. The analysis is performed with an ensemble obtained from an EDS Hamiltonian without smoothing, s = ∞, which strictly follows the minimum energy surface of the end states. The accuracy and efficiency of this method is tested on aspartic acid, lysine, and glutamic acid, which have two protonation states, a histidine with three states, a four-residue peptide with four states, and snake cardiotoxin with eight states. The pKa values estimated with the EDS-HREX method agree well with the experimental pKa values. The mean absolute errors of small benchmark systems range from 0.03 to 0.17 pKa units, and those of three titratable groups of snake cardiotoxin range from 0.2 to 1.6 pKa units. This study demonstrates that EDS-HREX is a potent theoretical framework, which gives the correct description of multiple protonation states and good calculated pKa values. PMID:25061443

  14. Nonlinear systems dynamics in cardiovascular physiology: The heart rate delay map and lower body negative pressure

    NASA Technical Reports Server (NTRS)

    Hooker, John C.

    1990-01-01

    A preliminary study of the applicability of nonlinear dynamic systems analysis techniques to low body negative pressure (LBNP) studies. In particular, the applicability of the heart rate delay map is investigated. It is suggested that the heart rate delay map has potential as a supplemental tool in the assessment of subject performance in LBNP tests and possibly in the determination of susceptibility to cardiovascular deconditioning with spaceflight.

  15. Dynamics and energy exchanges between a linear oscillator and a nonlinear absorber with local and global potentials

    NASA Astrophysics Data System (ADS)

    Charlemagne, S.; Lamarque, C.-H.; Ture Savadkoohi, A.

    2016-08-01

    The dynamical behavior of a two degree-of-freedom system made up of a linear oscillator and a coupled nonlinear energy sink with nonlinear global and local potentials is studied. The nonlinear global potential of the energy sink performs direct interactions with the linear oscillator, while its local potential depends only on its own behavior during vibratory energy exchanges between two oscillators. A time multiple scale method around 1:1:1 resonance is used to detect slow invariant manifold of the system, its equilibrium and singular points. Detected equilibrium points permit us to predict periodic regime(s) while singular points can lead the system to strongly modulated responses characterized by persistent bifurcations. Several possible scenarios occurring during these strongly modulated regimes are highlighted. All analytical predictions are compared with those which are obtained by direct numerical integration of system equations.

  16. Structure, dynamics, and function of the hammerhead ribozyme in bulk water and at a clay mineral surface from replica exchange molecular dynamics.

    PubMed

    Swadling, Jacob B; Wright, David W; Suter, James L; Coveney, Peter V

    2015-03-01

    Compared with proteins, the relationship between structure, dynamics, and function of RNA enzymes (known as ribozymes) is far less well understood, despite the fact that ribozymes are found in many organisms and are often conceived as "molecular fossils" of the first self-replicating molecules to have arisen on Earth. To investigate how ribozymal function is governed by structure and dynamics, we study the full hammerhead ribozyme in bulk water and in an aqueous clay mineral environment by computer simulation using replica-exchange molecular dynamics. Through extensive sampling of the major conformational states of the hammerhead ribozyme, we are able to show that the hammerhead manifests a free-energy landscape reminiscent of that which is well known in proteins, exhibiting a "funnel" topology that guides the ribozyme into its globally most stable conformation. The active-site geometry is found to be closely correlated to the tertiary structure of the ribozyme, thereby reconciling conflicts between previously proposed mechanisms for the self-scission of the hammerhead. The conformational analysis also accounts for the differences reported experimentally in the catalytic activity of the hammerhead ribozyme, which is reduced when interacting with clay minerals as compared with bulk water.

  17. The permutation entropy rate equals the metric entropy rate for ergodic information sources and ergodic dynamical systems

    NASA Astrophysics Data System (ADS)

    Amigó, José M.; Kennel, Matthew B.; Kocarev, Ljupco

    2005-10-01

    Permutation entropy quantifies the diversity of possible orderings of the values a random or deterministic system can take, as Shannon entropy quantifies the diversity of values. We show that the metric and permutation entropy rates-measures of new disorder per new observed value-are equal for ergodic finite-alphabet information sources (discrete-time stationary stochastic processes). With this result, we then prove that the same holds for deterministic dynamical systems defined by ergodic maps on n-dimensional intervals. This result generalizes a previous one for piecewise monotone interval maps on the real line [C. Bandt, G. Keller, B. Pompe, Entropy of interval maps via permutations, Nonlinearity 15 (2002) 1595-1602.] at the expense of requiring ergodicity and using a definition of permutation entropy rate differing modestly in the order of two limits. The case of non-ergodic finite-alphabet sources is also studied and an inequality developed. Finally, the equality of permutation and metric entropy rates is extended to ergodic non-discrete information sources when entropy is replaced by differential entropy in the usual way.

  18. Molecular dynamics study of chemically engineered green fluorescent protein mutants: comparison of intramolecular fluorescence resonance energy transfer rate.

    PubMed

    Mitchell, Felicity L; Frank, Filipp; Marks, Gabriel E; Suzuki, Miho; Douglas, Kenneth T; Bryce, Richard A

    2009-04-01

    Because of its unusual spectroscopic properties, green fluorescent protein (GFP) has become a useful tool in molecular genetics, biochemistry and cell biology. Here, we computationally characterize the behavior of two GFP constructs, designed as bioprobes for enzymatic triggering using intramolecular fluorescence resonance energy transfer (FRET). These constructs differ in the location of an intramolecular FRET partner, an attached chemical chromophore (either near an N-terminal or C-terminal site). We apply the temperature replica exchange molecular dynamics method to the two flexible constructs in conjunction with a generalized Born implicit solvent model. The calculated rate of FRET was derived from the interchromophore distance, R, and orientational factor, kappa(2). In agreement with experiment, the construct with the C-terminally attached dye was predicted to have higher energy transfer rate than observed for the N-terminal construct. The molecular basis for this observation is discussed. In addition, we find that the orientational factor, kappa(2), deviates from the commonly assumed value, the implications of which are also considered.

  19. Influence of fluid dynamic conditions on enzymatic hydrolysis of lignocellulosic biomass: Effect of mass transfer rate.

    PubMed

    Wojtusik, Mateusz; Zurita, Mauricio; Villar, Juan C; Ladero, Miguel; Garcia-Ochoa, Felix

    2016-09-01

    The effect of fluid dynamic conditions on enzymatic hydrolysis of acid pretreated corn stover (PCS) has been assessed. Runs were performed in stirred tanks at several stirrer speed values, under typical conditions of temperature (50°C), pH (4.8) and solid charge (20% w/w). A complex mixture of cellulases, xylanases and mannanases was employed for PCS saccharification. At low stirring speeds (<150rpm), estimated mass transfer coefficients and rates, when compared to chemical hydrolysis rates, lead to results that clearly show low mass transfer rates, being this phenomenon the controlling step of the overall process rate. However, for stirrer speed from 300rpm upwards, the overall process rate is controlled by hydrolysis reactions. The ratio between mass transfer and overall chemical reaction rates changes with time depending on the conditions of each run.

  20. Computational modeling of dynamic mechanical properties of pure polycrystalline magnesium under high loading strain rates

    NASA Astrophysics Data System (ADS)

    Li, Qizhen

    2015-09-01

    Computational simulations were performed to investigate the dynamic mechanical behavior of pure polycrystalline magnesium under different high loading strain rates with the values of 800, 1000, 2000, and 3600 s-1. The Johnson-Cook model was utilized in the simulations based on finite element modeling. The results showed that the simulations provided well-matched predictions of the material behavior such as the strain rate-time history, the stress-strain curve, and the temperature increase. Under high loading strain rates, the tested material experienced linear strain hardening at the early stage of plastic deformation, increased strain hardening at the intermediate plastic deformation region, and decreased strain hardening at the region before fracture. The strain hardening rates for the studied high loading strain rate cases do not vary much with the change of strain rates.

  1. Influence of fluid dynamic conditions on enzymatic hydrolysis of lignocellulosic biomass: Effect of mass transfer rate.

    PubMed

    Wojtusik, Mateusz; Zurita, Mauricio; Villar, Juan C; Ladero, Miguel; Garcia-Ochoa, Felix

    2016-09-01

    The effect of fluid dynamic conditions on enzymatic hydrolysis of acid pretreated corn stover (PCS) has been assessed. Runs were performed in stirred tanks at several stirrer speed values, under typical conditions of temperature (50°C), pH (4.8) and solid charge (20% w/w). A complex mixture of cellulases, xylanases and mannanases was employed for PCS saccharification. At low stirring speeds (<150rpm), estimated mass transfer coefficients and rates, when compared to chemical hydrolysis rates, lead to results that clearly show low mass transfer rates, being this phenomenon the controlling step of the overall process rate. However, for stirrer speed from 300rpm upwards, the overall process rate is controlled by hydrolysis reactions. The ratio between mass transfer and overall chemical reaction rates changes with time depending on the conditions of each run. PMID:27233094

  2. Effects of Forest Succession on Exchangeable Cation Concentrations and Nitrogen Mineralization Rates in Soils Following Logging of Eastern Hemlock Forest, Whately, Massachusetts

    NASA Astrophysics Data System (ADS)

    Rhodes, A. L.; Sweezy, T.; Zukswert, J. M.; Dwyer, C. H.

    2012-12-01

    Ecological forest successions associated with invasive species and human disturbance may alter biogeochemical cycles within New England forests. Spread of the invasive insect hemlock woolly adelgid (Adelges tsugae) to eastern North America is causing mortality of the eastern hemlock (Tsuga canadensis), prompting salvage logging. Regrowth by deciduous hardwood trees is often observed. To evaluate whether changes in nutrient cycling could be altered by forest succession, we investigated exchangeable cation chemistry and nitrogen mineralization rates for soil in a mature, eastern hemlock forest and in a juvenile black birch (Betula lenta) forest in western MA. Eastern hemlock on this property was selectively logged 20 years ago, with black birch regrowth succeeding hemlock. We measured soil pH, exchangeable acidity (Al3+ and H+), exchangeable base cations (Ca2+, Mg2+, Na+, and K+), and nitrogen mineralization rates of organic and mineral horizons for 7 incubation periods between May 2011 - July 2012. We also measured the cation exchange capacity and nitrogen mineralization rates of soils from May - July 2012 (2 incubations) in a mature deciduous forest composed primarily of black birch. At each field site, 7 soil cores were collected. Soil horizons (organic and mineral) were separated and homogenized, and 3 replicates of each composite sample were analyzed for soil geochemistry. Organic soils within the juvenile black birch plot (BB) exhibit a low pH (4.3) similar to hemlock organic soils (HEM, pH=4.2). Surprisingly, exchangeable Al3+—the dominant cation in both plots—is significantly greater in organic soils at BB than at HEM (p<.001), and base saturation is less at BB (29%) than at HEM (46%, p<0.001) due to less Ca2+. There are no significant differences in the exchangeable cation chemistry of the mineral horizons at both sites, suggesting that the acidity difference of organic matter is not due to different soil mineralogy. In comparison, organic soil at the

  3. Iron isotope fractionation between aqueous Fe(II) and goethite revisited: New insights based on a multi-direction approach to equilibrium and isotopic exchange rate modification

    NASA Astrophysics Data System (ADS)

    Frierdich, Andrew J.; Beard, Brian L.; Reddy, Thiruchelvi R.; Scherer, Michelle M.; Johnson, Clark M.

    2014-08-01

    The Fe isotope compositions of naturally occurring Fe oxide minerals provide insights into biogeochemical processes that occur in modern and ancient environments. Key to understanding isotopic variations in such minerals is knowledge of the equilibrium Fe isotope fractionation factors between common minerals and aqueous Fe species. Because experimental measurements of isotopic fractionation may reflect a combination of kinetic and equilibrium fractionations during rapid dissolution and precipitation, even in experiments that employ the three-isotope method, assessment of the attainment of equilibrium is often difficult. Here, we re-examine Fe isotope exchange, via a 57Fe tracer, and natural mass-dependent fractionation, through changes in initial 56Fe/54Fe ratios, between aqueous Fe(II) (Fe(II)aq) and goethite. This approach uses the three-isotope method, but is distinct in its evaluation of kinetic isotope fractionation and the attainment of equilibrium by: (i) employing a multi-direction approach to equilibrium at 22 °C via reaction of three Fe(II)aq solutions that had different initial 56Fe/54Fe ratios, (ii) conducting isotopic exchange experiments at elevated temperature (50 °C), and (iii) modifying the rate of isotopic exchange through a combination of trace-element substitutions and particle coarsening to evaluate corresponding temporal changes in fractionation trajectories that may reflect changing instantaneous fractionation factors. We find that rapid isotopic exchange produces kinetic isotope effects between Fe(II)aq and goethite, which shifts the 56Fe/54Fe ratios of Fe(II)aq early in reactions toward that of goethite, indicating that the instantaneous Fe(II)aq-goethite fractionation factor under kinetic conditions is small. Importantly, however, this kinetic fractionation is “erased” with continued reaction, and this is evident by the congruence for multiple-exchange trajectories of distinct initial Fe(II)aq solutions toward the same final value

  4. Reduced Sensitivity to Slow-Rate Dynamic Auditory Information in Children with Dyslexia

    ERIC Educational Resources Information Center

    Poelmans, Hanne; Luts, Heleen; Vandermosten, Maaike; Boets, Bart; Ghesquiere, Pol; Wouters, Jan

    2011-01-01

    The etiology of developmental dyslexia remains widely debated. An appealing theory postulates that the reading and spelling problems in individuals with dyslexia originate from reduced sensitivity to slow-rate dynamic auditory cues. This low-level auditory deficit is thought to provoke a cascade of effects, including inaccurate speech perception…

  5. Selection Dynamics in Joint Matching to Rate and Magnitude of Reinforcement

    ERIC Educational Resources Information Center

    McDowell, J. J.; Popa, Andrei; Calvin, Nicholas T.

    2012-01-01

    Virtual organisms animated by a selectionist theory of behavior dynamics worked on concurrent random interval schedules where both the rate and magnitude of reinforcement were varied. The selectionist theory consists of a set of simple rules of selection, recombination, and mutation that act on a population of potential behaviors by means of a…

  6. Dynamics of Rate of Returns for Postgraduate Education in Taiwan: The Impact of Higher Education Expansion

    ERIC Educational Resources Information Center

    Yang, Chih-Hai; Lin, Chun-Hung A.; Lin, Chien-Ru

    2011-01-01

    This paper analyzes the dynamics of rate of returns for postgraduate education and the determinants of wage premiums for postgraduate labor, especially for the impact of higher education expansions, in terms of quantity and quality, since the late 1990s in Taiwan. Utilizing quasi-panel data over the 1990-2004 period and employing the double fixed…

  7. Optimal variable flip angle schemes for dynamic acquisition of exchanging hyperpolarized substrates

    NASA Astrophysics Data System (ADS)

    Xing, Yan; Reed, Galen D.; Pauly, John M.; Kerr, Adam B.; Larson, Peder E. Z.

    2013-09-01

    In metabolic MRI with hyperpolarized contrast agents, the signal levels vary over time due to T1 decay, T2 decay following RF excitations, and metabolic conversion. Efficient usage of the nonrenewable hyperpolarized magnetization requires specialized RF pulse schemes. In this work, we introduce two novel variable flip angle schemes for dynamic hyperpolarized MRI in which the flip angle is varied between excitations and between metabolites. These were optimized to distribute the magnetization relatively evenly throughout the acquisition by accounting for T1 decay, prior RF excitations, and metabolic conversion. Simulation results are presented to confirm the flip angle designs and evaluate the variability of signal dynamics across typical ranges of T1 and metabolic conversion. They were implemented using multiband spectral-spatial RF pulses to independently modulate the flip angle at various chemical shift frequencies. With these schemes we observed increased SNR of [1-13C]lactate generated from [1-13C]pyruvate, particularly at later time points. This will allow for improved characterization of tissue perfusion and metabolic profiles in dynamic hyperpolarized MRI.

  8. Dextran-grafted cation exchanger based on superporous agarose gel: adsorption isotherms, uptake kinetics and dynamic protein adsorption performance.

    PubMed

    Shi, Qing-Hong; Jia, Guo-Dong; Sun, Yan

    2010-07-30

    A novel chromatographic medium for high-capacity protein adsorption was fabricated by grafting dextran (40kDa) onto the pore surfaces of superporous agarose (SA) beads. The bead was denoted as D-SA. D-SA, SA and homogeneous agarose (HA) beads were modified with sulfopropyl (SP) group to prepare cation exchangers, and the adsorption and uptake of lysozyme on all three cation-exchange chromatographic beads (SP-HA, SP-SA and SP-D-SA) were investigated at salt concentrations of 6-50mmol/L. Static adsorption experiments showed that the adsorption capacity of SP-D-SA (2.24mmol/g) was 78% higher than that of SP-SA (1.26mmol/g) and 54% higher than that of SP-HA (1.45mmol/g) at a salt concentration of 6mmol/L. Moreover, salt concentration had less influence on the adsorption capacity and dissociation constant of SP-D-SA than it did on SP-HA, suggesting that dextran-grafted superporous bead is a more potent architecture for chromatographic beads. In the dynamic uptake of lysozyme to the three cation-exchange beads, the D(e)/D(0) (the ratio of effective pore diffusivity to free solution diffusivity) values of 1.6-2.0 were obtained in SA-D-SA, indicating that effective pore diffusivities of SP-D-SA were about two times higher than free solution diffusivity for lysozyme. At 6mmol/L NaCl, the D(e) value in SA-D-SA (22.0x10(-11)m(2)/s) was 14.4-fold greater than that in SP-HA. Due to the superior uptake kinetics in SA-D-SA, the highest dynamic binding capacity (DBC) and adsorption efficiency (the ratio of DBC to static adsorption capacity) was likewise found in SP-D-SA. It is thus confirmed that SP-D-SA has combined the advantages of superporous matrix structure and drafted ligand chemistry in mass transport and offers a new opportunity for the development of high-performance protein chromatography.

  9. Comparison of CO2 Dynamics and Air-Sea Exchange in Contrasting Tropical Reef Environments

    NASA Astrophysics Data System (ADS)

    Drupp, P. S.; De Carlo, E. H.; Mackenzie, F. T.; Shamberger, K. E.; Musielewicz, S. B.; Maenner-Jones, S.; Sabine, C. L.; Feely, R. A.

    2011-12-01

    Multiyear high temporal resolution CO2 records in three differing coral reef settings were obtained using buoys deployed in coastal waters of Oahu since June 2008. The buoys are located on the barrier reef of Kaneohe Bay and offshore of Honolulu, on the south shore of Oahu. Annualized CO2 air-sea fluxes at the three buoys ranged from +0.05 mol C/m2/yr offshore Honolulu on a fringing reef well mixed with the open ocean to -1.12 mol C/m2/yr on a barrier reef flat in Kaneohe Bay (positive values represent CO2 sinks from the atmosphere and negative values represent sources). These fluxes compare well to those estimated from previous studies in Kaneohe Bay as well as in other tropical reef environments. pCO2 measurements, made every 3 hours, at each location show strong temporal cycles on multiple time scales ranging from diel to seasonal at each buoy and an anticorrelation with pO2. These records, when combined with those of a prior buoy deployment in southern Kaneohe Bay and several synoptic studies, allow us to examine how the principal biological cycles of productivity/respiration and calcification/carbonate dissolution are influenced by changing water column properties, physical processes (e.g. residence time) and atmospheric conditions and how these processes ultimately impact the exchange of CO2 between the ocean and atmosphere on hourly to interannual cycles. The data clearly demonstrate the need for high frequency pCO2 data to characterize completely and accurately short-term local changes in the CO2-carbonic acid system parameters and how these changes overprint the longer scale process of ocean acidification as a result of invasion of CO2 into the ocean due to emissions of anthropogenic CO2 to the atmosphere. Since many coral reef ecosystems are still sources of CO2 to the atmosphere because of positive net ecosystem calcification, and in some instances net heterotrophy, such data are even more critical in terms of assessing future changes in the direction

  10. State Anxiety and Nonlinear Dynamics of Heart Rate Variability in Students

    PubMed Central

    Dimitriev, Aleksey D.

    2016-01-01

    Objectives Clinical and experimental research studies have demonstrated that the emotional experience of anxiety impairs heart rate variability (HRV) in humans. The present study investigated whether changes in state anxiety (SA) can also modulate nonlinear dynamics of heart rate. Methods A group of 96 students volunteered to participate in the study. For each student, two 5-minute recordings of beat intervals (RR) were performed: one during a rest period and one just before a university examination, which was assumed to be a real-life stressor. Nonlinear analysis of HRV was performed. The Spielberger’s State-Trait Anxiety Inventory was used to assess the level of SA. Results Before adjusting for heart rate, a Wilcoxon matched pairs test showed significant decreases in Poincaré plot measures, entropy, largest Lyapunov exponent (LLE), and pointwise correlation dimension (PD2), and an increase in the short-term fractal-like scaling exponent of detrended fluctuation analysis (α1) during the exam session, compared with the rest period. A Pearson analysis indicated significant negative correlations between the dynamics of SA and Poincaré plot axes ratio (SD1/SD2), and between changes in SA and changes in entropy measures. A strong negative correlation was found between the dynamics of SA and LLE. A significant positive correlation was found between the dynamics of SA and α1. The decreases in Poincaré plot measures (SD1, complex correlation measure), entropy measures, and LLE were still significant after adjusting for heart rate. Corrected α1 was increased during the exam session. As before, the dynamics of adjusted LLE was significantly correlated with the dynamics of SA. Conclusions The qualitative increase in SA during academic examination was related to the decrease in the complexity and size of the Poincaré plot through a reduction of both the interbeat interval and its variation. PMID:26807793

  11. Atomic hydrogen production rates for comet P/Halley from observations with Dynamics Explorer I

    NASA Technical Reports Server (NTRS)

    Craven, J. D.; Frank, L. A.

    1987-01-01

    Newly analyzed observations of the Dynamics Explorer I (DE1), launched on August 3, 1981, were used to determine the hydrogen production rate for Comet Halley at heliocentric distances, r, less than about 1.5 AU from measurements of the total Lyman-alpha flux at earth due to the cometary neutral hydrogen distribution. The production rates, determined as a function of r, were found to be consistent with in situ measurements from the Giotto and Vega spacecraft. The calculated rates are also consistent with remote observations using two sounding rockets and with the Pioneer-Venus and IUE spacecraft.

  12. Novel wireless sensor system for dynamic characterization of borehole heat exchangers.

    PubMed

    Martos, Julio; Montero, Álvaro; Torres, José; Soret, Jesús; Martínez, Guillermo; García-Olcina, Raimundo

    2011-01-01

    The design and field test of a novel sensor system based in autonomous wireless sensors to measure the temperature of the heat transfer fluid along a borehole heat exchanger (BHE) is presented. The system, by means of two special valves, inserts and extracts miniaturized wireless sensors inside the pipes of the borehole, which are carried by the thermal fluid. Each sensor is embedded in a small sphere of just 25 mm diameter and 8 gr weight, containing a transceiver, a microcontroller, a temperature sensor and a power supply. A wireless data processing unit transmits to the sensors the acquisition configuration before the measurements, and also downloads the temperature data measured by the sensor along its way through the BHE U-tube. This sensor system is intended to improve the conventional thermal response test (TRT) and it allows the collection of information about the thermal characteristics of the geological structure of subsurface and its influence in borehole thermal behaviour, which in turn, facilitates the implementation of TRTs in a more cost-effective and reliable way.

  13. Novel Wireless Sensor System for Dynamic Characterization of Borehole Heat Exchangers

    PubMed Central

    Martos, Julio; Montero, Álvaro; Torres, José; Soret, Jesús; Martínez, Guillermo; García-Olcina, Raimundo

    2011-01-01

    The design and field test of a novel sensor system based in autonomous wireless sensors to measure the temperature of the heat transfer fluid along a borehole heat exchanger (BHE) is presented. The system, by means of two specials valves, inserts and extracts miniaturized wireless sensors inside the pipes of the borehole, which are carried by the thermal fluid. Each sensor is embedded in a small sphere of just 25 mm diameter and 8 gr weight, containing a transceiver, a microcontroller, a temperature sensor and a power supply. A wireless data processing unit transmits to the sensors the acquisition configuration before the measurements, and also downloads the temperature data measured by the sensor along its way through the BHE U-tube. This sensor system is intended to improve the conventional thermal response test (TRT) and it allows the collection of information about the thermal characteristics of the geological structure of subsurface and its influence in borehole thermal behaviour, which in turn, facilitates the implementation of TRTs in a more cost-effective and reliable way. PMID:22164005

  14. Novel wireless sensor system for dynamic characterization of borehole heat exchangers.

    PubMed

    Martos, Julio; Montero, Álvaro; Torres, José; Soret, Jesús; Martínez, Guillermo; García-Olcina, Raimundo

    2011-01-01

    The design and field test of a novel sensor system based in autonomous wireless sensors to measure the temperature of the heat transfer fluid along a borehole heat exchanger (BHE) is presented. The system, by means of two special valves, inserts and extracts miniaturized wireless sensors inside the pipes of the borehole, which are carried by the thermal fluid. Each sensor is embedded in a small sphere of just 25 mm diameter and 8 gr weight, containing a transceiver, a microcontroller, a temperature sensor and a power supply. A wireless data processing unit transmits to the sensors the acquisition configuration before the measurements, and also downloads the temperature data measured by the sensor along its way through the BHE U-tube. This sensor system is intended to improve the conventional thermal response test (TRT) and it allows the collection of information about the thermal characteristics of the geological structure of subsurface and its influence in borehole thermal behaviour, which in turn, facilitates the implementation of TRTs in a more cost-effective and reliable way. PMID:22164005

  15. INVESTIGATION OF A DYNAMIC POWER LINE RATING CONCEPT FOR IMPROVED WIND ENERGY INTEGRATION OVER COMPLEX TERRAIN

    SciTech Connect

    Jake P. Gentle; Kurt S Myers; Tyler B Phillips; Inanc Senocak; Phil Anderson

    2014-08-01

    Dynamic Line Rating (DLR) is a smart grid technology that allows the rating of power line to be based on real-time conductor temperature dependent on local weather conditions. In current practice overhead power lines are generally given a conservative rating based on worst case weather conditions. Using historical weather data collected over a test bed area, we demonstrate there is often additional transmission capacity not being utilized with the current static rating practice. We investigate a new dynamic line rating methodology using computational fluid dynamics (CFD) to determine wind conditions along transmission lines at dense intervals. Simulated results are used to determine conductor temperature by calculating the transient thermal response of the conductor under variable environmental conditions. In calculating the conductor temperature, we use both a calculation with steady-state assumption and a transient calculation. Under low wind conditions, steady-state assumption predicts higher conductor temperatures that could lead to curtailments, whereas transient calculations produce conductor temperatures that are significantly lower, implying the availability of additional transmission capacity.

  16. Strain-rate-dependent model for the dynamic compression of elastoplastic spheres

    NASA Astrophysics Data System (ADS)

    Burgoyne, Hayden A.; Daraio, Chiara

    2014-03-01

    We present a force-displacement contact model for the compressive loading of elastoplastic spheres. This model builds from the well known Hertz contact law for elastic, quasistatic compression to incorporate a material's strain-rate-dependent plasticity in order to describe collisions between particles. In the quasistatic regime, finite-element analysis is used to derive an empirical function of the material properties. A Johnson-Cook strain rate dependence is then included into the model to study dynamic effects. We validate the model using split Hopkinson bar experiments and show that the model can accurately simulate the force-displacement response of strain-rate-dependent elastoplastic spheres during dynamic compression and unloading.

  17. Strain-rate-dependent model for the dynamic compression of elastoplastic spheres.

    PubMed

    Burgoyne, Hayden A; Daraio, Chiara

    2014-03-01

    We present a force-displacement contact model for the compressive loading of elastoplastic spheres. This model builds from the well known Hertz contact law for elastic, quasistatic compression to incorporate a material's strain-rate-dependent plasticity in order to describe collisions between particles. In the quasistatic regime, finite-element analysis is used to derive an empirical function of the material properties. A Johnson-Cook strain rate dependence is then included into the model to study dynamic effects. We validate the model using split Hopkinson bar experiments and show that the model can accurately simulate the force-displacement response of strain-rate-dependent elastoplastic spheres during dynamic compression and unloading. PMID:24730833

  18. Sodium sulfate impacts feeding, specific dynamic action, and growth rate in the freshwater bivalve Corbicula fluminea.

    PubMed

    Soucek, David John

    2007-08-01

    Sodium sulfate is a ubiquitous salt that reaches toxic concentrations due to mining and other industrial activities, yet is currently unregulated at the Federal level in the United States. Previous studies have documented reduced growth of clams downstream of sulfate-dominated effluents, altered bioenergetics in filter-feeding invertebrates, and interactions between sulfate and other toxicants. Therefore, the purpose of this study was to determine if sodium sulfate affects the bioenergetics of the filter-feeding, freshwater bivalve, Corbicula fluminea, and the mechanism by which the effects are elicited. In addition to measuring effects on feeding, respiration and growth rates, I evaluated the relative sensitivity of a green algae consumed by clams to determine if top-down or bottom-up effects might be exhibited under field conditions. This study demonstrated that sodium sulfate had no effect on basal metabolic rates, but significantly reduced the feeding, post-feeding metabolic, and growth rates of C. fluminea. The proposed mechanism for these impacts is that filtering rates are reduced upon exposure, resulting in reduced food consumption and therefore, preventing increased metabolic rates normally associated with post-feeding specific dynamic action (SDA). In the field, these effects may cause changes in whole stream respiration rates and organic matter dynamics, as well as alter uptake rates of other food-associated contaminants like selenium, the toxicity of which is known to be antagonized by sulfate, in filter-feeding bivalves.

  19. The orbital-based view on reaction dynamics: ligand exchange of Fe(CO)5 in solution

    NASA Astrophysics Data System (ADS)

    Föhlisch, Alexander

    2015-03-01

    Time resolved soft X-ray spectroscopy has proven recently, that it can beat the complexity of dynamics in materials and chemical processes by its high selectivity towards elemental, chemical, and magnetic properties. Changes in chemical bonding, in particular bond breaking and bond creation seem conceptually simple, but as a result of coherent wave packet motion it is difficult to catch the dynamic pathways in a multidimensional potential energy landscape. In this contribution we exploit the unique approach of femtosecond time resolved resonant inelastic X-ray scattering at LCLS to derive how ultrafast spin-crossover and ligation determines the pathways of ligand exchange of Ironpentacarbonyl (Fe(CO)5) in solution. As an outlook, it will be discussed, how non-linear X-ray processes can push time resolved soft X-ray spectroscopy in a new phase. In particular, stimulated Raman scattering and amplified spontaneous emission can overcome the weak scattering cross-sections of spontaneous processes, help to suppress sample damage and increase spectral resolution and excited state selectivity through the exploitation of Anti-Stokes Raman Scattering.

  20. Applications of hydrogen deuterium exchange (HDX) for the characterization of conformational dynamics in light-activated photoreceptors

    PubMed Central

    Lindner, Robert; Heintz, Udo; Winkler, Andreas

    2015-01-01

    Rational design of optogenetic tools is inherently linked to the understanding of photoreceptor function. Structural analysis of elements involved in signal integration in individual sensor domains provides an initial idea of their mode of operation, but understanding how local structural rearrangements eventually affect signal transmission to output domains requires inclusion of the effector regions in the characterization. However, the dynamic nature of these assemblies renders their structural analysis challenging and therefore a combination of high- and low-resolution techniques is required to appreciate functional aspects of photoreceptors. This review focuses on the potential of hydrogen-deuterium exchange coupled to mass spectrometry (HDX-MS) for complementing the structural characterization of photoreceptors. In this respect, the ability of HDX-MS to provide information on conformational dynamics and the possibility to address multiple functionally relevant states in solution render this methodology ideally suitable. We highlight recent examples demonstrating the potential of HDX-MS and discuss how these results can help to improve existing optogenetic systems or guide the design of novel optogenetic tools. PMID:26157802